CN114746058A - Water-absorbing sheet and absorbent article comprising same - Google Patents
Water-absorbing sheet and absorbent article comprising same Download PDFInfo
- Publication number
- CN114746058A CN114746058A CN202080082864.6A CN202080082864A CN114746058A CN 114746058 A CN114746058 A CN 114746058A CN 202080082864 A CN202080082864 A CN 202080082864A CN 114746058 A CN114746058 A CN 114746058A
- Authority
- CN
- China
- Prior art keywords
- water
- absorbing agent
- base material
- absorbent
- substrate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
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- A61F13/00—Bandages or dressings; Absorbent pads
- A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
- A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
- B01J20/26—Synthetic macromolecular compounds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
- B01J20/26—Synthetic macromolecular compounds
- B01J20/261—Synthetic macromolecular compounds obtained by reactions only involving carbon to carbon unsaturated bonds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
-
- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
- B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
- B01J20/28016—Particle form
-
- D—TEXTILES; PAPER
- D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
- D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
- D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
- D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
- D04H1/44—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling
- D04H1/46—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling by needling or like operations to cause entanglement of fibres
- D04H1/492—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling by needling or like operations to cause entanglement of fibres by fluid jet
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- D—TEXTILES; PAPER
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- D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
- D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
- D04H1/54—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
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- A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
- A61F2013/530131—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium being made in fibre but being not pulp
- A61F2013/530226—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium being made in fibre but being not pulp with polymeric fibres
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- A—HUMAN NECESSITIES
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- A61F13/00—Bandages or dressings; Absorbent pads
- A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
- A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
- A61F2013/530131—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium being made in fibre but being not pulp
- A61F2013/530379—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium being made in fibre but being not pulp comprising mixtures of fibres
- A61F2013/530386—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium being made in fibre but being not pulp comprising mixtures of fibres with pulp and polymeric
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- A—HUMAN NECESSITIES
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- A61F13/00—Bandages or dressings; Absorbent pads
- A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
- A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
- A61F2013/530481—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having superabsorbent materials, i.e. highly absorbent polymer gel materials
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- A—HUMAN NECESSITIES
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- A61F13/00—Bandages or dressings; Absorbent pads
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- A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
- A61F2013/530481—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having superabsorbent materials, i.e. highly absorbent polymer gel materials
- A61F2013/530489—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having superabsorbent materials, i.e. highly absorbent polymer gel materials being randomly mixed in with other material
- A61F2013/530496—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having superabsorbent materials, i.e. highly absorbent polymer gel materials being randomly mixed in with other material being fixed to fibres
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- A—HUMAN NECESSITIES
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- A61F13/00—Bandages or dressings; Absorbent pads
- A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
- A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
- A61F2013/530868—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium characterized by the liquid distribution or transport means other than wicking layer
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- A—HUMAN NECESSITIES
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- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F13/00—Bandages or dressings; Absorbent pads
- A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
- A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
- A61F13/534—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having an inhomogeneous composition through the thickness of the pad
- A61F2013/53445—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having an inhomogeneous composition through the thickness of the pad from several sheets
Landscapes
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Chemistry (AREA)
- Analytical Chemistry (AREA)
- Heart & Thoracic Surgery (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Life Sciences & Earth Sciences (AREA)
- Vascular Medicine (AREA)
- Biomedical Technology (AREA)
- Epidemiology (AREA)
- Textile Engineering (AREA)
- Mechanical Engineering (AREA)
- Absorbent Articles And Supports Therefor (AREA)
- Laminated Bodies (AREA)
Abstract
Provided is a novel water-absorbent sheet which can significantly reduce the discharge of liquid from the water-absorbent sheet due to a reverse flow even when the liquid is introduced intermittently and repeatedly (particularly, 3 or more times). A water-absorbent sheet comprising a first base material, a second base material, and a water-absorbent layer located between the first base material and the second base material, wherein the water-absorbent layer comprises a particulate water-absorbing agent, the surface of the first base material forms a liquid-absorbing surface that directly absorbs liquid, and the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14.
Description
Technical Field
The present invention relates to a water-absorbent sheet and an absorbent article including the same.
Background
water-Absorbent resins (SAP/Super Absorbent polymer) are water-swellable, water-insoluble polymeric gelling agents and are used in sanitary materials such as disposable diapers, sanitary napkins, incontinence products for adults, and the like; soil water-retaining agents for agriculture, forestry and gardening, industrial water-stopping agents and the like.
These absorbent articles are generally manufactured in a diaper manufacturing plant in the form of an absorbent body obtained by mixing a water-absorbent resin with a fibrous material and molding the mixture for each absorbent article, and are processed into absorbent bodies of various shapes (for example, hourglass-shaped, fox-shaped, oval-shaped, and the like in plan view) according to the purpose. These methods for producing an absorbent body can be processed into an arbitrary shape by molding, and the amounts of fibers and water-absorbent resin can be easily adjusted for each absorbent article, and therefore, these methods are the mainstream of paper diapers today.
In recent years, however, in the production of paper diapers, paper diapers using an absorbent body obtained by cutting a long water-absorbent sheet (referred to as a water-absorbent sheet, which is generally cut into a rectangle having a width of about 10cm and a length of several 10 cm) in which a water-absorbent resin is fixed between two sheets in a production process of a sanitary material have been gradually produced. A diaper manufacturer can simplify the manufacturing process of a diaper by purchasing or manufacturing a long continuous water-absorbent sheet, and can reduce the size of the diaper by not using pulp. The water-absorbent sheet has a structure in which water-absorbent resin particles are sandwiched and fixed between upper and lower sheets (particularly nonwoven fabric sheets), and is generally incorporated into a disposable diaper (for example, international publication No. 2010/143635) by cutting a long continuous sheet after the production of the long continuous sheet to form a rectangle having a width of about 10cm and a length of 10 cm.
Unlike conventional sanitary materials (disposable diapers), disposable diapers based on water-absorbent sheets have a short history, and development and parameter development of water-absorbent resins suitable for water-absorbent sheets have not been made in practice, and conventional water-absorbent resins for disposable diapers have been used as water-absorbent sheets as they are.
Disclosure of Invention
Problems to be solved by the invention
The present inventors have found that: as long as the water-absorbent sheet, which is mainly thin, is structured to easily absorb a liquid, a so-called "reverse flow" is generated in which the water-absorbent sheet is pressed to discharge the liquid in the direction of introduction of the absorbed liquid. The "retrograde flow" is also known as Re-wet. And found that: if the liquid is intermittently introduced a plurality of times (particularly 3 times or more) and the amount of liquid introduced increases, the problem of occurrence of reverse flow becomes obvious. When a reverse flow occurs, the skin contacting the water-absorbent sheet is exposed to a high humidity state due to contact with the liquid in the reverse flow. Therefore, not only the user feels uncomfortable, but also the skin in contact with the water-absorbent sheet is likely to be inflamed.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a novel water-absorbent sheet capable of significantly reducing the discharge of liquid from the water-absorbent sheet due to a reverse flow even if the liquid is introduced intermittently and repeatedly (particularly, 3 times or more).
Means for solving the problems
The present inventors have made extensive studies to solve the above problems. As a result, they found that: the above object can be achieved by a water-absorbent sheet comprising a first base material, a second base material, and a water-absorbent layer located between the first base material and the second base material, wherein the water-absorbent layer comprises a particulate water-absorbing agent, a liquid-absorbing surface for directly absorbing a liquid is formed on the surface of the first base material, and the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14.
In another aspect of the present invention, there is provided a water-absorbent sheet comprising a first substrate, a second substrate, and a water-absorbent layer disposed between the first substrate and the second substrate, wherein the water-absorbent layer comprises a particulate water-absorbing agent, the water-absorbent layer is not disposed on the first substrate, and a ratio of a thickness (mm) of the first substrate to a thickness (mm) of the second substrate (thickness (mm) of the first substrate/thickness (mm) of the second substrate) is 1.5 or more and less than 14.
Further, a water-absorbent sheet according to another aspect of the present invention comprises a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, wherein the water-absorbent layer comprises a particulate water-absorbing agent, the water-absorbent layer is not disposed on the first substrate, the thickness of the first substrate is 0.7mm or more and 5mm or less, and the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate (the thickness (mm) of the first substrate/the thickness (mm) of the second substrate) is 1.5 or more and less than 14.
The water-absorbent sheet according to another aspect of the present invention comprises a first base material, a second base material, a water-absorbent layer disposed between the first base material and the second base material, and a cover sheet disposed on a surface of the first base material, wherein the water-absorbent layer comprises a particulate water-absorbing agent, a surface of the cover sheet forms a liquid-absorbing surface for directly absorbing liquid, and a ratio of a thickness of the first base material to a thickness of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14.
Drawings
Fig. 1 is a schematic view showing a cross section of a water-absorbent sheet according to an embodiment of the present invention.
Fig. 2 is a schematic view showing a cross section of a water-absorbent sheet according to another embodiment of the present invention.
Fig. 3 is a schematic view showing a cross section of a water-absorbent sheet according to another embodiment of the present invention.
Fig. 4 is a schematic cross-sectional view of a water-absorbent sheet according to another embodiment of the present invention.
Fig. 5 is a schematic diagram illustrating a method for measuring the transmittance of the particulate water-absorbing agent to the nonwoven fabric.
Fig. 6 is a plan view and a right side view showing a sample for evaluating a specific amount of reflux, and is a view showing a case where the water-absorbent sheet manufactured in the example was wrapped with a liquid-impermeable sheet.
Fig. 7 is a plan view and a front view of a liquid injection cartridge for evaluating a specific back flow amount.
Fig. 8 is a front view showing a state in which a liquid inlet tube was placed on a water absorbing sheet used in examples of the present application in the evaluation of a specific reflux amount.
Fig. 9 is a front view showing a case where an aqueous sodium chloride solution was poured from a liquid injection cylinder into a water-absorbent sheet using a funnel in the evaluation of the specific reflux amount.
Fig. 10 is a schematic diagram showing an apparatus for evaluating the amount of leakage in the plane direction.
Fig. 11 is a schematic diagram illustrating a method for measuring the fluffing area ratio of the nonwoven fabric.
Fig. 12 is a plan view and a front view of a liquid injection cartridge for evaluating a pressurized specific reflux amount.
FIG. 13 is a front view showing a state in which a liquid injection tube was placed on a water-absorbent sheet used in examples of the present application in evaluation of a specific amount of reflux by pressurization.
FIG. 14 is a front view showing a case where an aqueous sodium chloride solution was poured from a liquid injection cylinder into a water-absorbent sheet using a funnel in evaluation of a specific amount of reflux under pressure.
FIG. 15 is a schematic sectional view of a water-absorbent sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbent sheet produced in examples.
FIG. 16 is a schematic sectional view of a water-absorbent sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbent sheet produced in the examples.
Fig. 17 is a schematic view illustrating a method of measuring the elongation of the nonwoven fabric.
Fig. 18 is a schematic view showing a cross section of a water-absorbent sheet according to a first embodiment of the present invention.
Fig. 19 is a schematic view showing a cross section of a water-absorbent sheet according to a second embodiment of the present invention.
FIG. 20 is a schematic sectional view of a water-absorbent sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbent sheet produced in the examples.
Fig. 21 is a schematic view showing a cross section of a water-absorbent sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbent sheet produced in example.
Fig. 22 is a schematic diagram illustrating a method for measuring the elongation of the nonwoven fabric.
Fig. 23 is a schematic diagram illustrating a method for measuring the transmittance of the particulate water-absorbing agent to a nonwoven fabric.
Fig. 24 is a plan view and a right side view showing a sample for evaluating a specific amount of reflux, and is a view showing a case where the water-absorbent sheet produced in the example was wrapped with a liquid-impermeable sheet.
Fig. 25 is a plan view and a front view of a liquid injection cartridge for evaluating a specific backflow amount.
FIG. 26 is a front view showing a state in which a liquid inlet tube was placed on a water-absorbent sheet used in an example of the present application in the evaluation of a specific reflux amount.
Fig. 27 is a front view showing a case where an aqueous sodium chloride solution was poured from a liquid injection cylinder into a water-absorbent sheet using a funnel in the evaluation of a specific reflux amount.
Detailed Description
The present invention will be described below with reference to the best mode. The expression in the singular form should be understood to include the concept of the plural form thereof as well as the whole of the present specification unless specifically mentioned. Thus, unless specifically mentioned otherwise, it is to be understood that the singular forms of articles (e.g., "a," "an," "the," etc. in the english case) also include the plural forms of concepts. In addition, unless otherwise specified, terms used in the present specification should be understood to be used in the meaning generally used in the art. Accordingly, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. The present invention is not limited to the embodiments described below, and various modifications can be made within the scope of the claims.
[ first invention ]
The first invention will be explained. The water-absorbent sheet of the first aspect of the invention comprises a first base material, a second base material, and a water-absorbent layer disposed between the first base material and the second base material, wherein the water-absorbent layer comprises a particulate water-absorbing agent, the surface of the first base material forms a liquid-absorbing surface for directly absorbing liquid, and the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14.
[ 1. definition of terms ]
[1-1. Water-absorbent sheet ]
The "water-absorbent sheet" in the present invention refers to a structure in which a water-absorbent resin (particulate water-absorbing agent) is supported between 2 or more long substrates. In the above water-absorbent sheet, an adhesive may be used for bonding the substrates to each other and/or for bonding the substrate to the particulate water-absorbing agent, or a hot-melt adhesive may be used. The water-absorbent sheet may contain other components (fiber component, antimicrobial agent, deodorant agent, etc.) in addition to the particulate water-absorbing agent. There are water-absorbent sheets comprising other sheets in addition to 2 sheets of base materials sandwiching the particulate water-absorbing agent and the like. In the present embodiment, as long as the solution of the problem of the present invention is not hindered, there may be a water-absorbent sheet including other sheets in addition to 2 sheets of the base material sandwiching the particulate water-absorbing agent or the like. A water-absorbent sheet in which a particulate water-absorbing agent or the like is sandwiched between 2 substrates is a preferred embodiment.
Generally, the water-absorbent sheet is in the form of a continuous sheet or a roll formed by winding the continuous sheet. When the water-absorbent sheet is used, the continuous sheet is cut into an appropriate shape (such as a rectangle), and then incorporated into an absorbent article (such as a disposable diaper, a sanitary napkin, or an incontinence pad) for use. Absorbent articles such as disposable diapers (disposable diapers), sanitary napkins, and incontinence pads include: an absorbent body that absorbs and retains body fluids such as urine and menstrual blood excreted from the body, a flexible liquid-permeable front sheet disposed on the side that contacts the body, and a liquid-impermeable back sheet disposed on the side opposite to the side that contacts the body. The water-absorbent sheet can be used as the aforementioned absorbent body. A conventional paper diaper is an absorbent article which is formed for each paper diaper and has a shape suitable for the buttocks. Therefore, such an absorbent body is different in technical properties from the water-absorbent sheet of the present invention.
[1-2. Water-absorbent resin ]
In the present specification, the term "water-absorbent resin" means: a high-molecular gelling agent having a water-swelling capacity (CRC) of 5g/g or more as defined in ERT441.2-02 and a water-soluble component (Ext) of 50 mass% or less as defined in ERT 470.2-02.
The water-absorbent resin is preferably a hydrophilic crosslinked polymer obtained by crosslinking and polymerizing an unsaturated monomer having a carboxyl group. The water-absorbent resin is in the form of a sheet, a fiber, a film, a granule, a gel, or the like. In one embodiment of the present invention, a particulate water-absorbent resin is used for the water-absorbent sheet.
In the present specification, the term "water-absorbent resin" is not limited to the embodiment in which the total amount (100 mass%) is only the water-absorbent resin. The water-absorbent resin composition may contain additives as long as the CRC and Ext are satisfied. In the present specification, the term "water-absorbent resin" refers to a concept including an intermediate in a process for producing a water-absorbent resin. For example, a crosslinked hydrogel polymer after polymerization, a dried polymer after drying, a water-absorbent resin powder before surface crosslinking, and the like may be sometimes referred to as "water-absorbent resin".
As described above, in the present specification, the water-absorbent resin composition and the intermediate may be collectively referred to as "water-absorbent resin" in addition to the water-absorbent resin itself.
[1-3. Water-absorbing agent, particulate Water-absorbing agent ]
In the present specification, "water absorbing agent" means: an absorbent gelling agent for absorbing an aqueous liquid (liquid) which comprises a water-absorbent resin as a main component. Here, the aqueous liquid (liquid) is not particularly limited as long as it is a liquid containing water, in addition to water. The water-absorbent sheet according to one embodiment of the present invention absorbs aqueous liquids such as urine, menstrual blood, sweat, and other body fluids.
In the present specification, the "particulate water-absorbing agent" refers to a particulate (powder-like) water-absorbing agent (which corresponds to a particulate water-absorbing resin because the water-absorbing agent contains the water-absorbing resin as a main component). The concept of "particulate water-absorbing agent" includes any of a single particulate water-absorbing agent and an aggregate of a plurality of particulate water-absorbing agents. In the present specification, "granular" means having a granular form. Here, "particle" means a small divided body of a substance, having a number
Several mm in size (cf. particles, compiled by the Committee for compilation of the term McGraw-Hill science and technology, Dacron dictionary 3 rd edition, journal industry press, 1996, p.1929). In the present invention, the form of the water-absorbing agent is not limited to the particulate water-absorbing agent. In this specification, the present invention will be described by taking a particulate water-absorbing agent as an example, but the "particulate water-absorbing agent" may be replaced with a "water-absorbing agent". In the present specification, "particulate water-absorbing agent" may be abbreviated as "water-absorbing agent".
In the water-absorbent sheet of the present invention, the particulate water-absorbing agent has a weight-average particle diameter of 200 to 600 μm. Here, if the weight average particle diameter of the particulate water-absorbing agent is less than 200 μm, handling properties may be reduced. Further, if the weight average particle diameter of the particulate water-absorbing agent exceeds 600 μm, the texture of the water-absorbent sheet may be reduced. In the water-absorbent sheet according to one embodiment of the present invention, the particulate water-absorbing agent preferably has a weight average particle diameter of 250 to 500 μm, more preferably 300 to 450 μm. In the water-absorbent sheet of the present invention, it is preferable that 95% by mass or more of the entire particulate water-absorbing agent has a particle diameter of 850 μm or less, more preferably 98% by mass or more of the entire particulate water-absorbing agent has a particle diameter of 850 μm or less, and still more preferably substantially 100% by mass or more of the entire particulate water-absorbing agent has a particle diameter of 850 μm or less. In the examples of the present application, substantially 100 mass% of the entire particulate water-absorbing agent was a particle diameter of 850 μm or less. In the present specification, the weight Average Particle size is measured by the same method as that described in U.S. Pat. No. 7638570, namely "(3) Mass-Average Particle Diameter (D50) and Log arithmic Standard development (σ ζ) of Particle Diameter Distribution", based on the PSD obtained by the method of measuring "PSD" defined in ERT 420.2-02.
The particulate water-absorbing agent contains a water-absorbent resin in a polymer form (also referred to as particulate water-absorbent resin, water-absorbent resin particles) as a main component. The particulate water-absorbing agent contains 60 to 100 mass%, preferably 70 to 100 mass%, more preferably 80 to 100 mass%, even more preferably 90 to 100 mass%, and particularly preferably 95 to 100 mass% of a water-absorbent resin in the form of a polymer. The balance of the above particulate water absorbing agent may optionally contain water, additives (inorganic fine particles, polyvalent metal cations, etc.), and the like. The particulate water-absorbing agent used in the examples of the present application contains 80 to 100 mass% of a water-absorbent resin.
That is, the upper limit of the water-absorbent resin in the particulate water-absorbing agent is, for example, 100 mass%, 99 mass%, 97 mass%, 95 mass%, 90 mass%. Also, it is preferable that: the water-absorbing resin composition contains 0 to 10 mass% of components, particularly water, additives (inorganic fine particles, polyvalent metal cations), and the like, in addition to the water-absorbing resin.
The particulate water absorbing agent preferably has a water content of 0.2 to 30 mass%. As described above, the water-absorbent resin composition in which components such as water and additives are integrated and/or mixed with the water-absorbent resin is also included in the "particulate water-absorbing agent".
Examples of the water-absorbent resin which becomes the main component of the particulate water-absorbing agent include polyacrylic acid (salt) based resin, polysulfonic acid (salt) based resin, maleic anhydride (salt) based resin, polyacrylamide based resin, polyvinyl alcohol based resin, polyethylene oxide based resin, polyaspartic acid (salt) based resin, polyglutamic acid (salt) based resin, polymalic acid (salt) based resin, starch based resin, and cellulose based resin. Among them, a polyacrylic acid (salt) resin is preferably used as the water-absorbent resin.
[1-4. polyacrylic acid (salt) ]
In the present specification, "polyacrylic acid (salt)" means polyacrylic acid and/or a salt thereof. The polyacrylic acid (salt) is a polymer containing a repeating unit of acrylic acid and/or a salt thereof (hereinafter referred to as "acrylic acid (salt)") as a main component and further containing a graft component as an optional component. The polyacrylic acid (salt) is obtained by polymerization of acrylic acid (salt), hydrolysis of polyacrylamide, polyacrylonitrile, or the like. The polyacrylic acid (salt) is preferably obtained by polymerization of acrylic acid (salt).
Here, "containing … as a main component" means: the amount of the acrylic acid (salt) used in the polymerization of the polyacrylic acid (salt) is usually 50 to 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, and still more preferably substantially 100 mol% based on the whole monomers used in the polymerization (excluding the internal crosslinking agent).
[1-5.EDANA and ERT ]
"EDANA" is short for European Disposablees and nonwoven associates. "ERT" is an abbreviation of EDANA Recommended Test Methods for measuring a water-absorbent resin in the Europe standards (substantial world standards) established by EDANA. In the present specification, unless otherwise specified, the physical properties of the water-absorbent resin were measured in accordance with ERT of 2002 edition.
[1-6. other ]
In the present specification, "X to Y" indicating a range means "X or more and Y or less".
In the present specification, the unit "t (ton)" of mass means "Metric ton" unless otherwise noted. "ppm" means "mass ppm". "mass" and "weight", "mass part" and "part by weight", "mass%" and "wt%", and "mass ppm" and "weight ppm" are respectively regarded as the same meaning.
In the present specification, "acid (salt)" means "acid and/or salt thereof". "(meth) acrylic acid" means "acrylic acid and/or methacrylic acid".
In the present specification, the unit "liter" of volume is sometimes expressed as "L" or "L". Sometimes,% by mass is expressed as "wt%". When the measurement of a minor component was performed, the detection limit was expressed as n.d. (Non Detected) below.
[ 2. Water-absorbent sheet ]
The water-absorbent sheet of the present invention is a water-absorbent sheet comprising a first base material, a second base material, and a water-absorbent layer located between the first base material and the second base material, wherein the water-absorbent layer contains a particulate water-absorbing agent, the surface of the first base material forms a liquid-absorbing surface that directly absorbs liquid, and the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14.
With this configuration, even if the liquid is introduced intermittently and a large amount of liquid is introduced (particularly 3 or more times), the discharge of the liquid from the water-absorbent sheet due to the reverse flow can be significantly reduced. In the water-absorbent sheet of the present invention, the thickness (mm) of the first base material forming the liquid-absorbing surface for directly absorbing liquid is 1.5 or more and less than 14 relative to the thickness (mm) of the second base material. That is, the first substrate is significantly thicker than the second substrate. A liquid absorbing surface for directly absorbing liquid is formed on the surface of the first base material which is significantly thicker than the second base material. In the present specification, "directly" does not include a mode of sequentially absorbing liquids permeated from other base materials or the like. In the present specification, the case where a cover sheet described later is disposed on the surface of the first base material includes a mode in which a liquid-absorbing surface for directly absorbing liquid is formed on the surface of the first base material.
In another embodiment of the present invention, the surface of the first base material is a liquid-absorbing surface that directly absorbs the liquid, and therefore, the water-absorbing layer is not disposed on the first base material. Accordingly, an embodiment of the present invention provides a water-absorbent sheet comprising a first substrate, a second substrate, and a water-absorbent layer disposed between the first substrate and the second substrate, wherein the water-absorbent layer comprises a particulate water-absorbing agent, the water-absorbent layer is not disposed on the first substrate, and a ratio of a thickness of the first substrate to a thickness of the second substrate (thickness (mm) of the first substrate/thickness (mm) of the second substrate) is 1.5 or more and less than 14. In this embodiment, the particulate water-absorbing agent contained in the water-absorbing layer is not regarded as being disposed as a water-absorbing layer even if a part thereof passes through the first base material and moves on the first base material to expose a part thereof. The reason for this movement is assumed to be, for example, vibration generated when the water-absorbent sheet is transported or conveyed as a final product. The case where the particulate water-absorbing agent is intentionally dispersed or disposed on the first substrate does not fall within the scope of the present embodiment.
The inventors of the present invention found that: in the conventional water-absorbent sheet (for example, a water-absorbent sheet in which the first base and the second base have the same thickness in order to form a thin water-absorbent sheet), the backflow amount is significantly large in the measurement of the backflow amount under the specific conditions in the examples of the present application (also referred to as "specific backflow amount evaluation" in the present specification). In other words, if the liquid is introduced intermittently and a plurality of times (particularly, 3 times or more), the amount of the liquid becomes equal to or more than the set absorption amount and an excessive amount of "backflow" occurs in the case of the normal configuration. In contrast, in the present invention, by making the first base material on the liquid introduction side significantly thicker than the second base material, the distance between the liquid suction surface and the water-absorbent layer of the first base material can be made longer, and thus the liquid introduced from the liquid suction surface can be efficiently sent to the water-absorbent layer of the lower layer that performs the water-absorbing function without being retained on the liquid suction surface (and further without being retained locally). Specifically, this is considered to be because: when the liquid passes through the first base material, the liquid has high diffusibility in the in-plane direction, and the diffused liquid (e.g., urine) can be transferred (moved) to the entire surface of the water-absorbent layer in a wide range and all directions. That is, when the absorbed liquid reaches the water-absorbent layer, the liquid is already spread in the plane direction, and therefore, even if a large amount of liquid is introduced into the water-absorbent layer, the water-absorbent layer absorbs the liquid spreading in the plane direction rather than spreading locally. Thus, the liquid can be sufficiently absorbed and retained in the water-absorbent layer. It is also considered that the first base material is imparted with the liquid diffusibility function of the hydrophilic pulp contained in the conventional absorbent body. Further, when the liquid is absorbed by the water-absorbent layer, the first base material is significantly thick, and therefore, the liquid absorbed by the water-absorbent layer can be significantly reduced from flowing backward and flowing backward to the liquid-absorbing surface of the first base material, and the liquid flowing backward can be prevented from rising to (coming into contact with) the skin. On the other hand, even if the second substrate is significantly thickened compared to the first substrate, the desired effects of the present invention cannot be obtained. The reason for this is not clear, in other words, it can be said that this is an effect unexpected to those skilled in the art.
In the water-absorbent sheet, the water-absorbing function of the water-absorbent layer is mainly exerted by the water-absorbing agent. In particular, in a water-absorbent sheet having a structure different from that of a conventional absorbent article in which pulp exists in a water-absorbent layer, the role of the water-absorbing agent is more important. In particular, in the present invention, since the first base material is significantly thick, it is difficult for the liquid once introduced into the water-absorbing agent to flow back to the liquid-absorbing surface of the first base material. Here, in addition to the reverse flow, there is a leakage in the plane direction (lateral leakage) which means: and a phenomenon that the liquid which is not instantaneously absorbed and cleaned after reaching the water-absorbent layer leaks out from the water-absorbent sheet in the surface direction. The present invention presents the following constitution: by utilizing the advantage that the particulate water-absorbing agent is formed in a sheet (layer) shape, liquid diffusion in the surface direction of the water-absorbing layer is utilized to the maximum extent, and backflow to the first substrate is suppressed and leakage (lateral leakage) from the surface direction of the water-absorbing sheet is suppressed. Specifically, in the present invention, since the first base material is significantly thicker than the second base material, the particulate water-absorbing agent, which has a high liquid diffusibility in the planar direction when the liquid passes through the first base material, and a significantly high absorption rate, in other words, which performs a function like a can, absorbs the diffused liquid (e.g., urine) widely and omnidirectionally in the planar direction. That is, when the absorbed liquid reaches the water-absorbent layer, the liquid is already spread in the plane direction, and therefore, even if a large amount of liquid is introduced into the water-absorbent layer, the water-absorbent layer absorbs the liquid spreading in the plane direction rather than spreading locally. Therefore, the water-absorbent layer can sufficiently absorb and hold the liquid, and the leakage from the surface direction of the water-absorbent sheet is remarkably low. Further, even if the liquid that cannot be absorbed by the water-absorbing layer is to flow back, the first base material is significantly thicker than the second base material, and thus the liquid can be prevented from rising to the skin. Therefore, the "specific reflux amount evaluation" can be made excellent, and the leakage in the plane direction can be suppressed. Incidentally, the water-absorbent sheet or the absorbent article designed to suppress the amount of flow backward under normal conditions does not necessarily exhibit excellent results in the "evaluation of specific amount of flow backward" in the present application. The water-absorbent sheet according to one embodiment of the present invention is suitable as an absorbent article (for example, a diaper) used in a time zone where an infant who has started to learn to walk and has a small bladder moves back and forth in the daytime, for example, but the use mode is not limited thereto. The mechanism and the like described in the present specification do not limit the technical scope of the claims of the present application.
Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description thereof is omitted. In addition, the dimensional ratio in the drawings is exaggerated for convenience of explanation and may be different from the actual ratio.
First, the structure of the water-absorbent sheet will be described with reference to FIGS. 1 to 4. Fig. 1 is a schematic view showing a cross section of a water-absorbent sheet 10 according to an embodiment of the present invention. Fig. 2 to 4 are schematic views showing cross sections of the water-absorbent sheet 10 according to another embodiment of the present invention.
In fig. 1, arrows indicate the direction in which the absorbed liquid is introduced. The first substrate 11 is located on the side where the liquid to be absorbed (absorbed liquid) is introduced with respect to the water-absorbent layer 12. That is, the first base material 11 is disposed on the liquid discharge side (for example, the skin side in a diaper). Thereby, the first base material 11 forms a liquid-absorbing surface directly absorbing the liquid. A water-absorbing layer 12 is disposed between the first substrate 11 and the second substrate 13.
In fig. 1, water-absorbent layer 12 contains particulate water-absorbing agent 14. In the embodiment of fig. 1, the water-absorbent layer 12 shows a state where the particulate water-absorbing agent 14 is present between the first substrate 11 and the second substrate 13. Water-absorbent layer 12 includes particulate water-absorbing agent 14 contacting (or fixed to) first substrate 11 and particulate water-absorbing agent 14 contacting (or fixed to) second substrate 13. A part of particulate water-absorbing agent 14 may not contact each of substrates 11, 13 (or may not be fixed and may be detached from each of substrates 11, 13). Therefore, the water-absorbent "layer" does not mean a continuous body such as a sheet, and may be any as long as it is present between the first substrate 11 and the second substrate 13 with a constant thickness. When the particulate water-absorbing agent 14 is fixed to the respective substrates 11 and 13, an adhesive may be used, for example. The method for producing a water-absorbent sheet using an adhesive is described in detail in [ 3 ].
Within first substrate 11, particulate water-absorbing agent 14 may be present. Particulate water-absorbing agent 14 in first substrate 11 may be, for example, particulate water-absorbing agent 14 that is in contact with (or fixed to) first substrate 11, or particulate water-absorbing agent 14 that is in contact with (or fixed to) second substrate 13, is detached and trapped in first substrate 11. When the particulate water-absorbing agent 14 is present in the first substrate, the content of the particulate water-absorbing agent 14 in the first substrate 11 is preferably 5% or more, more preferably 10% or more, further preferably 20% or more, and still further preferably 30% or more, with respect to the particulate water-absorbing agent 14 contained in the entire water-absorbent sheet 10. The upper limit is not particularly limited, and the preferable order is 90% or less, 70% or less, and 50% or less. In this specification, the content ratio of the particulate water-absorbing agent 14 in the first substrate 11 to the particulate water-absorbing agent 14 included in the entire water-absorbent sheet 10 is calculated by the method of the example described later.
The water-absorbent sheet 10 has a cover sheet 16. The cover sheet 16 has the following purpose: the object of maintaining the shape of the water-absorbent sheet 10, which is a structure in which the particulate water-absorbing agent 14 is carried between the first substrate 11 and the second substrate 13; the purpose is to prevent the particulate water-absorbing agent 14 carried between the first base material 11 and the second base material 13 from falling (falling) off from the absorbent body (water-absorbent sheet 10); the particulate water-absorbing agent 14 is not brought into direct contact with the skin when the particulate water-absorbing agent 14 passes through the first substrate 11 and migrates to the outer surface of the first substrate 11 (the liquid-absorbing surface where liquid is directly absorbed). Without the cover sheet 16, there are, for example, the following methods: a method of sealing (closing) by bonding the substrates 11, 13 to each other; a method of suppressing the migration to the outer surface of the first substrate 11 (the liquid absorption surface that directly absorbs liquid) by surface treatment of the first substrate 11, and the like. As a method for preventing particulate water-absorbing agent 14 from falling off water-absorbing sheet 10 while maintaining the effects of the present application, it is preferable to include cover sheet 16.
The cover sheet 16 is disposed on the first base material 11 and folded so as to cover the entire water-absorbent layer 12 and the second base material 13. Thus, the cover sheet 16 covers the entirety of the first base material 11, the water-absorbent layer 12, and the second base material 13. With such a configuration, it is possible to suppress the particulate water-absorbing agent 14 from falling off from the water-absorbent sheet 10. The cover sheet 16 does not necessarily cover the entirety of the first base material 11, the water-absorbing layer 12, and the second base material 13. For example, the cover sheet 16 may be disposed on the first base material 11, folded so as to cover the side surface of the water-absorbent layer 12 and the side surface of the second base material 13, and folded toward the surface of the second base material 13 opposite to the surface on which the water-absorbent layer 12 is disposed (i.e., the surface on which the water-absorbent layer 12 is provided). That is, with respect to the cover sheet 16, one end of the cover sheet 16 overlaps the other end of the cover sheet 16 on the surface of the second base 13 opposite to the surface on which the water-absorbing layer 12 is provided. In this case, the cover sheet 16 covers the liquid-absorbing surface and the side surface of the first base material 11, the side surface of the water-absorbing layer 12, and the side surface of the second base material 13, and covers the whole or a part of the surface of the second base material 13 opposite to the surface on which the water-absorbing layer 12 is provided.
Here, in the cover sheet 16, one end of the cover sheet 16 is separated from the other end of the cover sheet 16 on the surface of the second base material 13 opposite to the surface on which the water-absorbing layer 12 is provided. For example, in fig. 2, the cover sheet 16 is disposed on the first base material 11, is folded so as to wrap the side surface of the water-absorbent layer 12 and the side surface of the second base material 13, and is disposed so that one end of the cover sheet 16 is spaced apart from the other end of the cover sheet 16 on the surface of the second base material 13 opposite to the surface on which the liquid is directly absorbed (i.e., the surface on which the water-absorbent layer 12 is provided). In this case, the cover sheet 16 covers the liquid-absorbing surface and the side surface of the first base material 11, the side surface of the water-absorbing layer 12, and the side surface of the second base material 13, and covers a part of the surface of the second base material 13 opposite to the surface on which the water-absorbing layer 12 is provided.
In the water-absorbent sheet 10 of the present invention, the covering sheet 16 is not essential, but the water-absorbent sheet 10 of the present invention is provided with the covering sheet 16 in such a configuration, so that the particulate water-absorbing agent 14 can be prevented from falling off from the water-absorbent sheet 10.
Therefore, the water-absorbent sheet 10 according to one embodiment of the present invention preferably has a cover sheet 16 disposed at least on the surface of the first base material 11. In the present description, the first base material 11 also forms the liquid-absorbing surface that directly absorbs liquid in the case where the cover sheet 16 is provided as described above, but for example, in the case where the cover sheet 16 forms the liquid-absorbing surface that directly absorbs liquid in the water-absorbent sheet 10 having the cover sheet 16, the following can be said to be the case: a water-absorbent sheet comprising a first base material, a second base material, a water-absorbent layer located between the first base material and the second base material, and a cover sheet disposed on the surface of the first base material, wherein the water-absorbent layer contains a particulate water-absorbing agent, the surface of the cover sheet forms a liquid-absorbing surface for directly absorbing liquid, and the ratio of the thickness of the first base material to the thickness of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14.
As a method for fixing the cover sheet 16 to the respective substrates 11 and 13, for example, an adhesive may be used.
In the present invention, first substrate 11 and particulate water-absorbing agent 14 in water-absorbing layer 12 are preferably in direct contact or contact via an adhesive, and/or second substrate 13 and particulate water-absorbing agent 14 in water-absorbing layer 12 are preferably in direct contact or contact via an adhesive. As described above, the water-absorbent sheet of the present invention has a simple structure substantially containing only the following substances: the particulate water-absorbing agent may be composed of a first base material, a second base material, a particulate water-absorbing agent sandwiched between the first base material and the second base material, an adhesive for fixing the particulate water-absorbing agent to at least one of the first base material and the second base material, and a wrapping sheet for wrapping a part or all of them as necessary (the case where the particulate water-absorbing agent includes the additives described in the present specification and the like which may be included in the particulate water-absorbing agent is not excluded). More preferably, the present invention is a simple configuration including only the following components: the particulate water-absorbing agent-containing sheet includes a first substrate, a second substrate, a particulate water-absorbing agent sandwiched between the first substrate and the second substrate, an adhesive for fixing the particulate water-absorbing agent to the second substrate between the particulate water-absorbing agent and the second substrate, and a cover sheet for covering all of them. That is, the water-absorbent sheet of the present invention can effectively reduce the specific amount of reflux despite its simple configuration.
In the present invention, the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14. When the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate is less than 1.5, the distance between the liquid-absorbing surface of the first substrate and the water-absorbing layer and the second substrate is not sufficiently ensured, and there is a possibility that the liquid once having reached the water-absorbing layer and the second substrate flows back. In addition, when the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material is 14 or more, the liquid-absorbing surface of the first base material is separated from the water-absorbing layer, and therefore, there is a possibility that the liquid absorbed from the liquid-absorbing surface of the first base material leaks in the surface direction before reaching the water-absorbing layer.
The lower limit of the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material is preferably 1.7 or more, more preferably 2.5 or more, further preferably 3.2 or more, further preferably 3.4 or more, particularly preferably 3.5 or more, and most preferably 3.6 or more. The upper limit of the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material is preferably 12 or less, more preferably 10 or less, still more preferably 9 or less, and still more preferably 8 or less. By setting the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material in such a range, the reverse flow can be significantly reduced.
In the water-absorbent sheet according to one embodiment of the present invention, the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material is 1.5 or more and less than 14. In the water-absorbent sheet according to one embodiment of the present invention, the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material is preferably 1.7 or more and less than 14, more preferably 3 or more and 12 or less, and still more preferably 3.4 or more and 10 or less.
In the water-absorbent sheet according to one embodiment of the present invention, the first base material can have a low-density and bulky form, and can be made thinner than an absorbent body used in a conventional absorbent article. When the water-absorbent sheet is used in a disposable diaper, the thickness is preferably 15mm or less, more preferably 10mm or less, still more preferably 7mm or less, particularly preferably 5mm or less, and most preferably 4mm or less, for example, at 40% RH to 50% RH. On the other hand, in view of the strength of the water-absorbent sheet and the diameter of the particulate water-absorbing agent, the lower limit of the thickness is preferably 0.2mm or more, more preferably 0.3mm or more, and still more preferably 0.5mm or more. The thickness of the water-absorbent sheet used in the examples of the present application is 2 to 5 mm.
In the present application, the thicknesses of the first base material, the second base material, the cover sheet, and the water-absorbent sheet were measured using a caliper gauge (model No. J-B, manufactured by Kawasaki, Ltd.) with a gauge head of 50mm diameter up and down an anvil. The number of measurement points was determined by selecting 5 sites from different sites in the slice to be measured, measuring each site 2 times, and setting the measurement value as an average value of 5 sites in total. In the measurement of the thickness, the hand is slowly moved away from the handle so as not to apply pressure to the sheet to be measured as much as possible, and the thickness is measured. As a specific procedure, a sheet to be measured is flatly stuck to a plate having a constant thickness so as not to cause wrinkles or strain in a measurement portion of the sheet, and the plate is set on a lower measurement head of a thickness measurement instrument. Then, the upper measuring head of the thickness measuring instrument is moved close to a height position of 2 to 3mm from the sheet to be measured, and then the hand is slowly moved away from the handle to measure the total thickness of the sheet to be measured and the plate. The thickness of the sheet to be measured is determined by the formula T1 ═ T2-T0 (T0: thickness (mm) of the sheet, T1: thickness (mm) of the sheet to be measured, and T2: thickness (mm) of the sheet to be measured and the sheet to be measured).
Here, the content of the particulate water-absorbing agent contained in the water-absorbent sheet is preferably 50 to 400g/m2More preferably 100 to 350g/m2More preferably 125 to 250g/m2。
In the surface on the water-absorbing layer side of the first substrate (the surface on which the particulate water-absorbing agent is disposed), the ratio of the region including the particulate water-absorbing agent (hereinafter also referred to as "the ratio of the region where the particulate water-absorbing agent 14 is present") is preferably more than 75%, more preferably more than 80%, and still more preferably more than 90% by area. The upper limit of the ratio of the region containing the particulate water-absorbing agent on the surface of the first base material on the water-absorbing layer side is not particularly limited, and is 99.5% or less in terms of area in a practical viewpoint. By providing the particulate water-absorbing agent in such a range, the particulate water-absorbing agent is disposed in a good balance, and the effect of reducing the amount of backflow is further exhibited. The ratio of the region containing the particulate water-absorbing agent on the surface on the water-absorbing layer side of the first substrate is the same as the ratio of the region containing the particulate water-absorbing agent on the surface on the water-absorbing layer side of the second substrate (the surface on which the particulate water-absorbing agent is disposed).
Here, the ratio of the region containing the particulate water-absorbing agent in the surface on the water-absorbing layer side of the first substrate can be controlled by adjusting the scattering region of the particulate water-absorbing agent at the time of manufacturing the water-absorbing sheet.
Further, by imaging and analyzing the cross section of the produced water-absorbent sheet with an X-ray CT apparatus (instexio SMX-100CT), the ratio of the region including the particulate water-absorbing agent in the surface of the first base material on the water-absorbing layer side can be calculated. Specifically, the ratio of the regions containing the particulate water-absorbing agent can be calculated by imaging the cross section of the water-absorbent sheet, classifying the interface between the first substrate or the second substrate and the water-absorbent layer into a region where the particulate water-absorbing agent is present and a region where the particulate water-absorbing agent is not present, summing the regions, and calculating the ratio. Note that, the ratio of the region including the particulate water-absorbing agent was calculated by taking 3 or more images of a cross section of the water-absorbing sheet in the width direction, and the ratio of the region including the particulate water-absorbing agent obtained from each cross section was averaged, and the value obtained thereby was defined as "the ratio of the region including the particulate water-absorbing agent".
In order to further impart liquid permeability, diffusion properties, flexibility, and the like to the water-absorbent sheet, the surface of the water-absorbent sheet (the surface of the first base material or the surface of a cover sheet described later) may be appropriately subjected to embossing. The embossed region may be the entire surface of the water-absorbent sheet or a part thereof. By providing the continuous embossed regions along the longitudinal direction of the water-absorbent sheet, the liquid can be easily diffused along the longitudinal direction. For example, by providing an embossed region continuously along the longitudinal direction, the region functions as a passage (liquid conveying passage) through which a large amount of liquid flows. The embossing region may be linear, curved, or wavy.
The particulate water-absorbing agent may be spread over the entire surface of the water-absorbent sheet, or a region where the particulate water-absorbing agent is not present may be provided locally. That is, in the water-absorbent layer between the first substrate and the second substrate, the particulate water-absorbing agent may be spread over the entire surface of the water-absorbent layer, or a region where the particulate water-absorbing agent is not present may be provided in a part of the water-absorbent layer.
Here, a description will be given of a mode in which a region where the particulate water-absorbing agent is not present is provided in a part of the water-absorbing layer between the first substrate and the second substrate. In the case where the particulate water-absorbing agent is not present in the water-absorbent layer, the particulate water-absorbing agent-containing region is disposed between the first substrate and the second substrate with a gap substantially not containing the particulate water-absorbing agent interposed therebetween. When the region where the particulate water-absorbing agent is not present is provided in a part of the water-absorbent layer, the region where the particulate water-absorbing agent is not present is preferably provided in a groove shape (stripe shape) along the longitudinal direction of the water-absorbent sheet. In this manner, by providing a region where the particulate water-absorbing agent is not present continuously along the longitudinal direction, the region functions as a passage (liquid carrying passage) through which a large amount of liquid flows. The region where the particulate water-absorbing agent is not present may be provided linearly, may be provided in a curved shape, or may be provided in a wavy shape.
In the case where a region where the particulate water-absorbing agent is not present is provided in a part of the water-absorbent layer, the first substrate preferably has elasticity, and the elongation of the first substrate is more preferably 10% or more. In one embodiment, in the water-absorbent sheet of the present invention, the region containing the particulate water-absorbing agent in the water-absorbent layer between the first substrate and the second substrate is disposed with a gap substantially not containing the particulate water-absorbing agent, and the elongation of the first substrate is 10% or more. For example, the particulate water-absorbing agent is not dispersed over the entire surface of the first substrate or the second substrate, but the particulate water-absorbing agent is dispersed in a region where the particulate water-absorbing agent is not present in a partial region of the first substrate or the second substrate. Thus, the particulate water-absorbing agent is disposed with a gap substantially not containing the particulate water-absorbing agent.
In the conventional water-absorbent sheet, the water-absorbent resin particles that have absorbed liquid swell and are thus less fixed to the upper and lower sheets, and the water-absorbent resin particles may move in the sheet. In this way, the water-absorbent resin particles are unevenly distributed in the sheet, and the shape of the water-absorbent sheet is collapsed. In this case, the water-absorbent sheet has a variation in liquid absorbency, which causes leakage. In some cases, the water-absorbent resin particles may fall from the inside of the sheet to the outside.
In one embodiment of the water-absorbent sheet of the present invention, when the elongation of the first substrate is 10% or more and a region where the particulate water-absorbing agent is not present is provided in a part of the water-absorbent layer, the specific amount of return flow can be effectively reduced, and the shape of the sheet can be maintained even after liquid absorption (the shape retention of the sheet is high).
Hereinafter, with reference to fig. 3, a mode in which a region containing the particulate water-absorbing agent is disposed with a gap substantially not containing the particulate water-absorbing agent interposed therebetween in the water-absorbent layer between the first substrate and the second substrate, and the elongation of the first substrate is 10% or more will be described. Fig. 3 is a schematic view showing a cross section of a water-absorbent sheet 10 according to another embodiment of the present invention. Fig. 3 shows 3 embodiments ((a) to (c)) of the water-absorbent sheet 10. In fig. 3 (a) to (c), arrows indicate the direction in which the absorbed liquid is introduced. The first substrate 11 is located on the side where the liquid to be absorbed (absorbed liquid) is introduced with respect to the water-absorbent layer 12. That is, the first base material 11 is disposed on the liquid discharge side (for example, on the skin side in a diaper). A water-absorbing layer 12 is disposed between the first substrate 11 and the second substrate 13.
In fig. 3 (a) to (c), the water-absorbent layer 12 contains the particulate water-absorbing agent 14. In the embodiments (a) to (c) of fig. 3, the water-absorbing layer 12 is shown in a state where the particulate water-absorbing agent 14 is present between the first substrate 11 and the second substrate 13. A part of particulate water-absorbing agent 14 may be detached from each of substrates 11, 13. The particulate water-absorbing agent 14 (region including the particulate water-absorbing agent 14) is disposed with a gap 15 substantially not including the particulate water-absorbing agent 14 interposed therebetween. Therefore, the water-absorbent "layer" does not mean a continuous body such as a sheet, and may be any as long as it is present between the first base material 11 and the second base material 13 with a constant thickness and length. For example, the water-absorbent layer 12 may be intermittently present between the first substrate 11 and the second substrate 13 with a certain thickness and length. When the particulate water-absorbing agent 14 is fixed to the substrate 11 and/or the substrate 13, an adhesive may be used, for example. A method for producing a water-absorbent sheet using an adhesive is described in detail in [ 3 ].
Here, although the gap 15 is formed between the first base material 11 and the second base material 13 in fig. 3 (a), the gap 15 in the present invention includes the embodiments of fig. 3 (b) and 3 (c). In fig. 3 (b), the regions containing particulate water-absorbing agent 14 are separated by the contact of first substrate 11 with second substrate 13. The first substrate and the second substrate are in contact, but maintain a liquid passage, and thus are viewed as a gap. Further, the water-absorbent layer 12 is separated due to the first base material 11 (the first base material 11 and the second base material 13 as the case may be) entering the water-absorbent layer 12, and therefore, in this mode, the water-absorbent layer 12 exists intermittently. In fig. 3 (c), the end of the water-absorbent sheet 10 is closed by the first base material 11 and the second base material 13 by overlapping the end of the first base material 11 with the end of the second base material 13. In this case, the first base material 11 (the first base material 11 and the second base material 13 in some cases) enters the end of the water-absorbing layer 12, and the water-absorbing layer 12 is not present at the end of the water-absorbing layer 12.
Within first substrate 11, particulate water-absorbing agent 14 may be present. As particulate water-absorbing agent 14 in first substrate 11, there may be: for example, particulate water-absorbing agent 14 contacting (or fixed to) first substrate 11; particulate water-absorbing agent 14 that has contacted (or fixed to) second substrate 13 is detached and captured into particulate water-absorbing agent 14 in first substrate 11. When the particulate water-absorbing agent 14 is present in the first substrate 11, the content of the particulate water-absorbing agent 14 in the first substrate 11 is preferably 5% or more, more preferably 10% or more, further preferably 20% or more, and still further preferably 30% or more, with respect to the particulate water-absorbing agent 14 contained in the entire water-absorbent sheet 10. The upper limit is not particularly limited, and the order is preferably 90% or less, 70% or less, and 50% or less. In this specification, the content ratio of the particulate water-absorbing agent 14 in the first substrate 11 to the particulate water-absorbing agent 14 contained in the entire water-absorbent sheet 10 is calculated by the method of the example described later.
Since the particulate water-absorbing agent 14 is not scattered and disposed in the region of the gap 15, the region of the gap 15 does not substantially contain the particulate water-absorbing agent 14. Additives and the like other than particulate water-absorbing agent 14 may be contained in the region of this gap 15. For example, the gap 15 may be formed by the first substrate 11 being in direct contact with the second substrate 13 or being in contact with an adhesive. Since the first substrate 11 has stretchability, when a region including the particulate water-absorbing agent 14 is present on the second substrate 13, the first substrate 11 stretches and contracts following the region including the particulate water-absorbing agent 14. Therefore, the first substrate 11 has a shape covering the region including the particulate water-absorbing agent 14 in the region including the particulate water-absorbing agent 14, and has a shape recessed toward the second substrate 13 along the upper side of the region including the particulate water-absorbing agent 14 in the gap 15.
In the water-absorbent sheet of the present invention, the ratio (Lb/La) of the thickness (Lb) from the liquid-absorbing surface of the first base material 11 to the surface of the second base material 13 on the water-absorbing layer 12 side in the region including the particulate water-absorbing agent 14 to the thickness (La) from the liquid-absorbing surface of the first base material 11 to the surface of the second base material 13 on the water-absorbing layer 12 side in the gap 15 is preferably 1.05 or less. The first substrate 11 has stretchability, and therefore, the portion of the first substrate 11 that is in contact with the particulate water-absorbing agent 14 takes on a shape that follows (i.e., follows and stretches) the shape of the region containing the particulate water-absorbing agent 14 (i.e., the shape of the particulate water-absorbing agent 14 on the side that is in contact with the first substrate 11, of the particulate water-absorbing agent 14 that is in contact with the first substrate). Therefore, the first substrate 11 can be in close contact with the particulate water-absorbing agent 14 (the region including the particulate water-absorbing agent 14), and thus the first substrate 11 and the particulate water-absorbing agent 14 (the region including the particulate water-absorbing agent 14) are integrated. In this case, since the difference between the thickness of La and the thickness of Lb is small, Lb/La is 1.05 or less. In this case, the shape of the region including the particulate water-absorbing agent 14 has high shape retention. Therefore, even after the particulate water-absorbing agent 14 swells, the gap 15 can be maintained highly, and backflow can be further reduced. In general, Lb/La is 1 or more.
In the water-absorbent sheet 10, the gap 15 is formed by providing a region where the particulate water-absorbing agent 14 is not present on a part of the second substrate 13. The gaps 15 (i.e., regions where the particulate water-absorbing agent 14 is not present) can further function as liquid passages by being provided continuously along one direction in the liquid-absorbing surface of the first base material 11. The shape of the continuously provided gaps 15 may be, for example, a linear shape, a curved shape, or a wavy shape, and it is preferable that the gaps 15 be provided in a linear shape. Therefore, in the water-absorbent sheet 10, the region including the particulate water-absorbing agent 14 and the gap 15 have a shape extending along one direction (a plane direction perpendicular to the liquid absorption direction) of the liquid-absorbing surface of the first base material 11, and are preferably arranged in parallel. That is, the region containing the particulate water-absorbing agent 14 is arranged in a stripe shape (vertical stripe shape). This also forms the gap 15 into a vertical stripe shape, and therefore, even when the particulate water-absorbing agent 14 swells, the gap 15 is easily maintained, and as a result, the backflow can be further reduced. Here, the "one direction" may be any direction other than the thickness direction, which is parallel to the surface direction in the liquid-absorbing surface of the first base material 11, that is, any of the longitudinal direction, the width direction, or the direction inclined with respect to these directions in the liquid-absorbing surface of the first base material 11. From the viewpoint of balancing the function of the gap 15 and the function of the particulate water-absorbing agent 14, in the water-absorbent sheet 10, the region including the particulate water-absorbing agent 14 and the gap 15 preferably have a shape extending along the longitudinal direction of the liquid-absorbing surface of the first base material 11 and are arranged in parallel.
The ratio of the region including the particulate water-absorbing agent 14 in the surface of the first substrate 11 on the water-absorbing layer 12 side (the surface on which the particulate water-absorbing agent 14 is disposed) is preferably 90% or less, more preferably 80% or less, and still more preferably 75% or less by area. The ratio of the region including the particulate water-absorbing agent 14 in the surface of the first substrate 11 on the water-absorbent layer 12 side is preferably 10% or more, and more preferably 20% or more, by area. By providing the particulate water-absorbing agent 14 in such a range, the balance between the action of the gap 15 and the action of the particulate water-absorbing agent 14 becomes appropriate, and the effect of reducing the amount of backflow is further exerted. The ratio of the region including the particulate water-absorbing agent 14 on the surface of the first substrate 11 on the water-absorbing layer 12 side is the same as the ratio of the region including the particulate water-absorbing agent 14 on the surface of the second substrate 13 on the water-absorbing layer 12 side (the surface on which the particulate water-absorbing agent 14 is disposed).
The water-absorbent sheet 10 has a cover sheet 16. The cover sheet 16 has the following purpose: the object of maintaining the shape of the water-absorbent sheet 10, which is a structure in which the particulate water-absorbing agent 14 is carried between the first substrate 11 and the second substrate 13; the purpose is to prevent particulate water-absorbing agent 14 carried between first base material 11 and second base material 13 from falling (falling) off from the absorbent body (water-absorbent sheet 10); the particulate water-absorbing agent 14 is not brought into direct contact with the skin when the particulate water-absorbing agent 14 is transferred to the outer surface (surface directly contacting the liquid) of the first substrate 11 through the first substrate 11. Without the cover sheet 16, there are, for example, the following methods: a method of sealing (closing) by bonding the respective substrates 11 and 13 to each other; a method of suppressing transfer to the outer surface of the first substrate 11 by surface treatment of the first substrate 11, and the like. As a method for preventing the particulate water-absorbing agent 14 from falling off the water-absorbent sheet 10 while maintaining the effects of the present application, it is preferable to have a covering sheet 16. The configuration of the cover sheet 16 is already described with reference to fig. 1 and 2, and therefore, the description thereof is omitted.
Therefore, the water-absorbent sheet 10 of the present invention preferably has the coating sheet 16 disposed at least on the surface of the first substrate 11 (i.e., on the surface of the first substrate 11 on which the liquid is sucked). In the present description, the first base material 11 also forms the liquid-absorbing surface that directly absorbs liquid when the cover sheet 16 is provided as described above, but for example, in the case where the cover sheet 16 forms the liquid-absorbing surface that directly absorbs liquid in the water-absorbing sheet having the cover sheet 16, the following can be said to be the case: a water-absorbent sheet comprising a first base material, a second base material, a water-absorbent layer located between the first base material and the second base material, and a cover sheet disposed on the surface of the first base material, wherein the water-absorbent layer comprises a particulate water-absorbing agent, a region containing the particulate water-absorbing agent is disposed with a gap substantially not containing the particulate water-absorbing agent interposed therebetween, the surface of the cover sheet forms a liquid-absorbing surface that directly absorbs liquid, the ratio of the thickness of the first base material to the thickness of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14, and the elongation of the first base material is 10% or more.
In the water-absorbent sheet 10 of the present invention, the first substrate 11 is preferably in direct contact with or in contact with the particulate water-absorbing agent 14 in the water-absorbent layer 12 via an adhesive, and/or the second substrate 13 is preferably in direct contact with or in contact with the particulate water-absorbing agent 14 in the water-absorbent layer 12 via an adhesive. As described above, the water-absorbent sheet of the present invention has a simple structure substantially containing only the following substances: the particulate water-absorbing agent may be composed of a first base material, a second base material, a particulate water-absorbing agent sandwiched between the first base material and the second base material, an adhesive for fixing the particulate water-absorbing agent to at least one of the first base material and the second base material, and a wrapping sheet for wrapping a part or all of them as necessary (the case where the particulate water-absorbing agent includes the additives described in the present specification and the like which may be included in the particulate water-absorbing agent is not excluded). More preferably, the present invention is a simple configuration including only the following components: the particulate water-absorbing agent-containing sheet includes a first base material, a second base material, a particulate water-absorbing agent sandwiched between the first base material and the second base material, an adhesive for fixing the particulate water-absorbing agent to the second base material between the particulate water-absorbing agent and the second base material, and a cover sheet for covering all of them. That is, the water-absorbent sheet of the present invention can effectively reduce the specific amount of reflux despite its simple configuration.
In the present invention, the elongation of the first base material is 10% or more, preferably 15% or more, more preferably 17% or more, further preferably 20% or more, and further preferably 22% or more. The upper limit of the elongation of the first base material is not particularly limited, and is preferably 60% or less. When the elongation of the first base material is in such a range, the first base material easily follows the shape of the particulate water-absorbing agent, and as a result, the shape retention property of the water-absorbent sheet is further improved, and the amount of flow-back can be further reduced. The elongation of the first base material is measured by the method described in the examples described below. In the present specification, the "elongation of the nonwoven fabric (first base material)" is a value obtained by measuring the elongation in the direction of maximum elongation. The elongation of the first base material can be controlled by the volume density, the weight per unit area, the material, the lattice structure, the production process conditions, and the like.
In the present invention, the direction of elongation of the first base material is not particularly limited as long as the first base material is elongated in any direction parallel to the plane direction of the first base material, except the thickness direction. For example, in the case of a rectangular water-absorbent sheet, any direction having an angle such as a long-side direction, a short-side direction, a diagonal direction, or the like in the plane of the sheet may be elongated with an elongation in the above-described range. The same applies to the case of a square, oval, or circular water-absorbent sheet. Preferably a substrate that is capable of (isotropically) elongating from all directions.
In the present invention, the surface of the first base material 11 may be subjected to a raising process in order to further impart liquid permeability, liquid diffusibility, flexibility, and the like to the water-absorbent sheet 10. That is, in one embodiment of the present invention, the surface of the first base material 11 opposite to the liquid-absorbing surface that directly absorbs liquid, that is, the surface on which the water-absorbing layer 12 is provided (the surface on the water-absorbing layer 12 side) is raised. In the present specification, "fluffing" refers to a state where fibers on the surface are fluffed.
In one embodiment of the water-absorbent sheet of the present invention, when the surface of the first substrate on the water-absorbent layer side has fluff, the specific reflux amount can be effectively reduced, and the particulate water-absorbing agent can be effectively prevented from falling off from the water-absorbent sheet after the water-absorbent sheet has absorbed a liquid once.
Here, a mode in which the surface of the first base material 11 on the water-absorbing layer 12 side is raised will be described. Fig. 4 shows a water-absorbent sheet having a first substrate 11 with a raised surface on the water-absorbent layer 12 side. As shown in fig. 4, the first base material 11 has fiber fluff on the surface facing the water-absorbent layer 12 on the water-absorbent layer 12 side. A part of the raised fibers of the first substrate 11 exceeds the particulate water-absorbing agent 14 and comes into contact with and adheres to the second substrate 13 coated with the adhesive. Therefore, even after the particulate water-absorbing agent 14 swells by absorbing water, the first substrate 11 and the second substrate 13 can be continuously bonded to each other via the raised fibers of the first substrate 11, and thereby the particulate water-absorbing agent 14 can be held between the first substrate 11 and the second substrate 13. Therefore, by bonding the first substrate 11 and the second substrate 13, the particulate water-absorbing agent 14 is retained even after the water-absorbent sheet 10 absorbs water, and the gel-shedding rate can be reduced.
In one embodiment, the surface of the first substrate 11 on the water-absorbent layer 12 side is fluffed, and the first substrate does not carry the particulate water-absorbing agent 14 with an adhesive. That is, first substrate 11 is in direct contact with particulate water-absorbing agent 14 in water-absorbent layer 12. In this case, particulate water-absorbing agent 14 is fixed to second base material 13 by the adhesive. Thus, in one embodiment, first substrate 11 and particulate water-absorbing agent 14 in water-absorbing layer 12 are preferably in direct contact, and second substrate 13 and particulate water-absorbing agent 14 in water-absorbing layer 12 are preferably in contact via an adhesive.
The reason why the surface of the first substrate 11 on the water-absorbing layer 12 side is preferably fluffed and the first substrate carries the particulate water-absorbing agent 14 without using an adhesive is not specifically described in detail, but the effect thereof is verified by specifying the amount of the reflux in the examples. That is, as compared with the mode in which the adhesive is applied to the napped surface on the water-absorbing layer 12 side of the first base material 11 and the first base material carries the particulate water-absorbing agent 14 with the adhesive, the specific amount of backflow is preferably reduced in the mode in which the adhesive is not applied to the napped surface on the water-absorbing layer 12 side of the first base material 11 and the first base material carries the particulate water-absorbing agent 14 without the adhesive.
Here, the adhesive to be applied to the surface of the second base material 13 on the water-absorbing layer 12 side, that is, the adhesive on the second base material 13 is preferably a hot-melt adhesive. By using the hot-melt adhesive as the adhesive, the adhesion between the raised fibers of the first substrate 11 and the second substrate 13 becomes good, and the water-absorbent sheet 10 is bonded continuously to the first substrate 11 and the second substrate 13 even after absorbing water, whereby the particulate water-absorbing agent 14 is held between the first substrate 11 and the second substrate 13.
The water-absorbent sheet 10 has a covering sheet 16. In the water-absorbent sheet 10 according to the present invention, the covering sheet 16 is not essential, but the first base material 11 and the covering sheet 16 having raised surfaces on the water-absorbent layer 12 side are provided in the water-absorbent sheet 10, whereby the particulate water-absorbing agent 14 can be effectively prevented from falling off from the water-absorbent sheet 10. The cover sheet 16 is omitted because of the above-described structure.
Therefore, the water-absorbent sheet 10 of the present invention preferably has the coating sheet 16 disposed at least on the surface of the first substrate 11 (i.e., on the surface of the first substrate 11 on which the liquid is sucked). In the present specification, the first base material 11 also forms the liquid-absorbing surface that directly absorbs liquid in the case where the cover sheet 16 is provided as described above, but for example, in the case where the cover sheet 16 forms the liquid-absorbing surface that directly absorbs liquid in the water-absorbing sheet having the cover sheet 16, the following can be said to be replaced: a water-absorbent sheet comprising a first base material, a second base material, a water-absorbent layer positioned between the first base material and the second base material, and a cover sheet disposed on the surface of the first base material, wherein the water-absorbent layer comprises a particulate water-absorbing agent, the surface of the cover sheet forms a liquid-absorbing surface that directly absorbs liquid, the ratio of the thickness of the first base material to the thickness of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14, and the surface of the first base material 11 on which the water-absorbent layer 12 is provided (surface on the water-absorbent layer 12 side) has raised.
In the water-absorbent sheet 10 of the present invention, the first substrate 11 and the particulate water-absorbing agent 14 in the water-absorbent layer 12 are preferably in direct contact or in contact via an adhesive, and more preferably in direct contact. And/or, second substrate 13 and particulate water-absorbing agent 14 in water-absorbing layer 12 are preferably in direct contact or in contact via an adhesive, more preferably in contact via an adhesive. As described above, the water-absorbent sheet of the present invention has a simple structure substantially containing only: the particulate water-absorbing agent may be composed of a first base material, a second base material, a particulate water-absorbing agent sandwiched between the first base material and the second base material, an adhesive for fixing the particulate water-absorbing agent to at least one of the first base material and the second base material, and a wrapping sheet for wrapping a part or all of them as necessary (the case where the particulate water-absorbing agent includes the additives described in the present specification and the like which may be included in the particulate water-absorbing agent is not excluded). More preferably, the composition is a simple composition containing only the following substances: the particulate water-absorbing agent-containing sheet includes a first substrate, a second substrate, a particulate water-absorbing agent sandwiched between the first substrate and the second substrate, an adhesive for fixing the particulate water-absorbing agent to the second substrate between the particulate water-absorbing agent and the second substrate, and a cover sheet for covering all of them. That is, the water-absorbent sheet of the present invention can effectively reduce the specific amount of reflux despite its simple configuration.
In the water-absorbent sheet 10 having the first substrate 11 whose surface on the water-absorbing layer 12 side has been raised, since the particulate water-absorbing agent 14 can be effectively prevented from falling off from the water-absorbent sheet 10, the content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 10 can be set to 200g/m2. Therefore, in the water-absorbent sheet 10 having the first substrate 11 whose surface on the water-absorbent layer 12 side has been raised, the content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 10 is preferably 200g/m2The above sequence is preferably 230g/m2Above, 250g/m2Above 270g/m2Above, 280g/m2Above, 300g/m2As described above. The upper limit of the content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 10 in this case is not particularly limited, but is preferably 360g/m from the viewpoint of retaining the water-absorbing agent 142Hereinafter, more preferably 350g/m2Hereinafter, more preferably 325g/m2The following.
Further, in the water-absorbent sheet 10 having the first substrate 11 whose surface on the water-absorbent layer 12 side has been raised, since the particulate water-absorbing agent 14 can be effectively prevented from falling off from the water-absorbent sheet 10, the amount of the adhesive (preferably, a hot-melt adhesive) can be reduced. Therefore, in the water-absorbent sheet 10 having the first base material 11 whose surface on the water-absorbent layer 12 side has been raised, the content of the adhesive scattered on the second base material 13 is preferably 1 to 50g/m 2More preferably 5 to 50g/m2More preferably 10 to 45g/m2Particularly preferably 15 to 30g/m2Most preferably 15 to 25g/m2。
In one embodiment, the mass ratio of the particulate water-absorbing agent to the binder is preferably 80:20 to 99:1, more preferably 85:15 to 98:2, still more preferably 90:10 to 98:2, particularly preferably 91:9 to 97:3, and most preferably 92:8 to 96: 4. Since the fluffing occurs on the surface of the first base material on the water-absorbent layer side, the fluffed fibers of the first base material are entangled with the particulate water-absorbing agent, and the particulate water-absorbing agent is held by the first base material, the amount of the adhesive to the particulate water-absorbing agent can be reduced. This further exerts an effect of reducing the specific reflux amount.
In the water-absorbent sheet, when the surface of the first base material on the water-absorbent layer side has fluff, the fluff area ratio in the measurement test of the fluff area of the fluff surface is preferably 5% or more. The raising area ratio of the raised surface of the first base material is preferably 5% or more, 7% or more, and 10% or more in this order. The upper limit of the raised area ratio of the raised surface of the first substrate is not particularly limited, and is preferably 30% or less, more preferably 28% or less, and even more preferably 25% or less, from the viewpoint of limiting swelling of the particulate water-absorbing agent. In the present specification, the percentage of raised area in the raised area measurement test is calculated by the method described in the examples below.
In one embodiment of the water-absorbent sheet of the present invention, when the surface of the first base material on the water-absorbent layer side has fluff, the specific reflux amount can be effectively reduced, and the particulate water-absorbing agent can be effectively prevented from falling off from the water-absorbent sheet. For example, the falling-off rate of the particulate water-absorbing agent calculated in the examples of the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, and further preferably 3% by mass or less. This effect is effectively exhibited by the occurrence of fuzzing on the surface of the first base material on the water-absorbent layer side.
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims.
Hereinafter, each member constituting the water-absorbent sheet will be described in detail.
[2-1. first base Material ]
The first substrate is a water-permeable sheet located on the side where the liquid to be absorbed is introduced. The liquid to be absorbed is not limited to water, and may be urine, blood, sweat, feces, waste liquid, moisture, vapor, ice, a mixture of water and an organic solvent and/or an inorganic solvent, rainwater, groundwater, or the like, and is not particularly limited as long as water is contained. Preferred examples include urine, menstrual blood, sweat, and other body fluids.
The first base material is a water-permeable sheet and is positioned on the liquid-absorbing side, whereby the effects of the present invention, that is, the performance (such as a reverse flow rate and a leakage in the surface direction) of the water-absorbent sheet can be sufficiently exhibited. Regarding the water permeability of the water permeable sheet, the water permeability coefficient (JIS A1218:2009) is preferably 1X 10-5cm/sec or more. The water permeability coefficient is more preferably 1X 10-4cm/sec or more, more preferably 1X 10-3cm/sec or more, particularly preferably 1X 10-2cm/sec or more, most preferably 1X 10-1cm/sec or more. The first substrate used in the examples of the present application had a water permeability of 1X 10-5cm/sec or more.
In the present invention, the bulk density of the first substrate is preferably 0.1g/cm3Hereinafter, more preferably 0.08g/cm3Hereinafter, more preferably 0.05g/cm3The following. The bulk density of the first substrate is preferably 0.001g/cm3Above, more preferably 0.005g/cm3Above, more preferably 0.01g/cm3The above. In the present specification, the bulk density is a mass per unit volume, and is not a density when the substrate is compressed at a high pressure (when voids are eliminated), but a density obtained from the volume of the substrate including the volume of voids. The bulk density of the first substrate was 0.1g/cm3The following means that the first substrate is light. Fluffy means low bulk density and significantly thick. In the present invention, by making the first base material bulky, the liquid to be absorbed which is in contact with the liquid-absorbing surface of the first base material flows into the water-absorbing layer and the second base material as the lower layer quickly, and the liquid retained in the liquid-absorbing surface of the first base material can be reduced. Further, since the liquid spreads in the planar direction when the absorbed liquid reaches the water-absorbent layer, even if a large amount of liquid is introduced into the water-absorbent layer, the water-absorbent layer absorbs the liquid that spreads in the planar direction rather than spreading locally. That is, the bulky first base material has a low water absorption capacity, a high liquid permeability, and a high liquid diffusibility. This can reduce the amount of flow backward through the water-absorbent sheet. The moisture of the liquid-absorbing surface of the first base material can be suppressed, and the discomfort to the skin can be reduced. The bulk density of the first substrate is preferably 0.1g/cm 3The following. In the present specification, the bulk density is a value calculated in examples described later.
In the present invention, the weight per unit area of the first base material is preferably 3 to 80g/m2More preferably 5 to 70g/m2More preferably 10 to 60g/m2. When the weight per unit area of the first substrate is in such a range, the amount of flow-back can be further reduced, and the particulate water-absorbing agent can be easily taken into the first substrate, and as a result, the shape retention of the water-absorbent sheet can be further improved.
The thickness of the first base material is preferably 0.7mm or more, more preferably 1.0mm or more, still more preferably 1.2mm or more, particularly preferably 1.3mm or more, and most preferably 1.4mm or more at 40% RH to 50% RH, for example. The upper limit of the thickness of the first base material is preferably 5mm or less, more preferably 4mm or less, still more preferably 3mm or less, particularly preferably 2.5mm or less, and most preferably 2mm or less, at 40% RH to 50% RH, for example. By setting the thickness of the first base material within such a range, the distance between the liquid-absorbing surface of the first base material and the water-absorbing layer and the second base material can be sufficiently ensured, occurrence of reverse flow of liquid once reaching the water-absorbing layer and the second base material can be remarkably reduced, and leakage in the plane direction can be reduced.
The thickness, bulk density, and weight per unit area of the first base material can be controlled by the material constituting the first base material, the method for producing the first base material, and the like, and the thickness and bulk density of the first base material are determined based on the balance between them.
The permeability of the particulate water-absorbing agent of the first substrate (the permeability of the particulate water-absorbing agent to the first substrate) is preferably 40% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more and 70% by mass or more in the order of preference, particularly preferably 80% by mass or more, and most preferably 90% by mass or more. The upper limit of the transmittance is not particularly limited, and is preferably 97 mass% or less. When the permeability of the particulate water-absorbing agent to the first substrate is in such a range, the particulate water-absorbing agent is likely to enter the first substrate on the side of the first substrate in contact with the water-absorbing layer. Thus, the particulate water-absorbing agent can absorb the moisture contained in the first base material, and the backflow is further reduced. In the present specification, the transmittance of the particulate water-absorbing agent to the first substrate is the ratio of the particulate water-absorbing agent that has passed through the first substrate, and the particulate water-absorbing agent present on the first substrate is determined from the weight of the particulate water-absorbing agent that has passed through the first substrate when screening is performed under the predetermined conditions described later, specifically, is a value calculated by the method described in the examples described later. Here, in the case where the first base material is a nonwoven fabric, the transmittance of the first base material can be adjusted to a desired range by appropriately adjusting the properties of the members constituting the first base material, the surface state thereof, the complexity of the lattice structure, the fiber diameter, the fusion state between fibers, the weight per unit area, the thickness, and the like. For example, if the first base material uses an air-through nonwoven fabric as described later, the transmittance can be adjusted by changing the heat treatment conditions, the fiber diameter, and the density of the air-through nonwoven fabric.
In one embodiment, the first base material has fluff on the surface on the water-absorbent layer side.
Material for forming substrate "
Examples of the material constituting the first substrate include paper (toilet paper, such as facial tissue, toilet paper, and towel paper), a web, a nonwoven fabric, a woven fabric, and a film. Among them, from the viewpoint of water permeability, a nonwoven fabric is preferably used as at least the first substrate.
The nonwoven fabric to be used is not particularly limited, and from the viewpoints of liquid permeability, flexibility, and strength in the case of forming a water-absorbent sheet, there may be mentioned nonwoven fabrics formed of polyolefin fibers such as Polyethylene (PE) and polypropylene (PP), polyester fibers such as polyethylene terephthalate (PET), 1, 3-trimethylene terephthalate (PTT) and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers; and non-woven fabrics made of a mixture of cotton, silk, hemp, pulp (cellulose) fibers, and the like.
The material of the nonwoven fabric that can be used as the first base material is preferably rayon fiber, polyolefin fiber, polyester fiber, pulp fiber, or a mixture thereof, and more preferably polyolefin fiber. These fibers may be subjected to a hydrophilization treatment.
The nonwoven fabric usable as the first substrate is not particularly limited, and may be a nonwoven fabric obtained by any method such as a through-air method, an air-laid method, a spunbond method, a spunlace method, or the like, preferably a nonwoven fabric obtained by a through-air method or an air-laid method, and preferably a nonwoven fabric obtained by a through-air method (through-air nonwoven fabric).
The hot air method means: the heat-fusible composite fibers such as PE/PP and PE/PET are heat-fused by blowing hot air, and the amount of air contained between the fibers is increased to increase the volume and reduce the density. In addition, the air-laid method is a method of producing a nonwoven fabric by uniformly dispersing the nonwoven fabric by being carried on an air stream and sucking the nonwoven fabric on a metal mesh, and since air is used for dispersing pulp fibers, the volume can be increased and the density can be reduced. By using the first base material as the hot air nonwoven fabric, the liquid to be absorbed can be easily and quickly introduced into the first base material after contacting the liquid-absorbing surface of the first base material. That is, by using the air-through nonwoven fabric as the first base material, the first base material having low water absorption and high liquid permeability can be produced, and the amount of back flow in the water-absorbent sheet can be significantly reduced.
[2-2. second base Material ]
The second base material is a water-permeable sheet and is positioned on the side opposite to the liquid-absorbing side, whereby the effects of the present invention, that is, the performance (such as the amount of flow reversing and leakage in the plane direction) of the water-absorbent sheet can be sufficiently exhibited. Regarding the water permeability of the water permeable sheet, the water permeability coefficient (JIS A1218: 2009) is preferably 1X 10-5cm/sec or more. The water permeability coefficient is more preferably 1X 10-4cm/sec or more, more preferably 1X 10-3cm/sec or more, particularly preferably 1X 10-2cm/sec or more, most preferably 1X 10-1cm/sec or more.
The thickness of the second base material is preferably 0.05mm or more, more preferably 0.08mm or more, still more preferably 0.1mm or more, particularly preferably 0.2mm or more, and most preferably 0.3mm or more at 40% RH to 50% RH, for example. The thickness of the second base material is preferably 0.9mm or less, more preferably 0.8mm or less, still more preferably 0.7mm or less, particularly preferably 0.6mm or less, and most preferably 0.5mm or less at 40% RH to 50% RH, for example.
Here, according to an embodiment of the present invention, the thickness of the first base material is 0.7mm or more and 5mm or less, and the thickness of the second base material is 0.05mm or more and 0.9mm or less. By adjusting the thicknesses of the first base material and the second base material to the above ranges, the desired effects of the present invention can be effectively achieved. Further, according to an aspect of the present invention, it is preferable that: the thickness of the first base material is 1.0mm or more and 4mm or less, and the thickness of the second base material is 0.08mm or more and 0.8mm or less, more preferably: the thickness of the first base material is 1.2mm or more and 3mm or less, and the thickness of the second base material is 0.1mm or more and 0.7mm or less, and it is more preferable that: the thickness of the first base material is 1.3mm or more and 2.5mm or less, and the thickness of the second base material is 0.2mm or more and 0.6mm or less, and it is particularly preferable that: the first base material has a thickness of 1.4mm or more and 2mm or less, and the second base material has a thickness of 0.3mm or more and 0.5mm or less.
In the present invention, the bulk density of the second substrate is preferably 1g/cm3Hereinafter, more preferably 0.5g/cm3Hereinafter, more preferably 0.3g/cm3The following. The bulk density of the second substrate is preferably 0.05g/cm3Above, more preferably 0.07g/cm3The above is more preferably 0.08g/cm3As described above. By setting the bulk density of the second base material to such a range, the liquid introduced into the second base material can be easily held, and the backflow can be reduced.
In the present invention, the second base material preferably has a weight per unit area of 5 to 100g/m2More preferably 10 to 70g/m2More preferably 15 to 65g/m2。
The thickness, bulk density, and basis weight of the second substrate are controlled by the material constituting the second substrate, the method for producing the second substrate, and the like, and the thickness and bulk density of the second substrate are determined based on the balance between these.
The void ratio of the first base material, the second base material, and the cover sheet (for example, nonwoven fabric) can be measured by the following formula. Weight per unit area A (g/m) used for base material (or cover sheet)2) Thickness B (mm) of base material (or coating sheet), density C (g/cm) of raw material (e.g., polyolefin) used in base material (or coating sheet)3)
The porosity (%) of the substrate (or sheet) is 100- { (a/10000)/(B/10) }/C × 100
The liquid diffusion area of the second substrate is preferably 1000mm2Above, more preferably 3000mm2Above, more preferably 6000mm2Above, 7000mm is particularly preferable2The above. The upper limit of the liquid spreading area of the second substrate is not particularly limited, and is preferably 10,000mm, for example2The following. When the liquid diffusion area of the second substrate is in the above range, the second substrate is suckedWhen the collected liquid reaches the second base material, the liquid can be sufficiently diffused in the planar direction in the second base material. Thus, even if a large amount of liquid having passed through the water-absorbent layer is introduced into the second base material, the second base material absorbs the liquid spreading in the planar direction rather than spreading locally. Therefore, the liquid can be sufficiently absorbed and held in the second base material, the amount of reverse flow in the water-absorbent sheet can be significantly reduced, and the leakage in the plane direction can be significantly reduced.
Here, the liquid spreading area means: the area in the plane direction in which the liquid diffuses when the liquid contacts the substrate (for example, nonwoven fabric) and/or when the liquid passes through the substrate in the direction perpendicular to the plane direction of the substrate is a value calculated by the method described in the examples below. The larger the liquid diffusion area of the substrate, the higher the liquid diffusibility of the substrate in the planar direction.
Material for forming substrate "
The material constituting the second substrate is preferably a nonwoven fabric. As the material of the nonwoven fabric, the same material as the first base material can be used, and for example, rayon fiber, polyolefin fiber, polyester fiber, pulp fiber, and a fiber obtained by mixing these fibers are preferable, and polyolefin fiber is more preferable.
The nonwoven fabric usable as the second substrate is not particularly limited, and may be a nonwoven fabric obtained by any method such as a hot air method, an air-laid method, a spunbond method, a spunlace method, and the like, and is preferably a nonwoven fabric obtained by an air-laid method (air-laid nonwoven fabric) or a nonwoven fabric obtained by a spunlace method (spunlace nonwoven fabric). The hydroentangling method is a method of interlacing fibers with a high-pressure water stream, and is a method of not using an adhesive. By using the air-laid nonwoven fabric or the spunlace nonwoven fabric as the second base material, the amount of backflow in the water-absorbent sheet can be significantly reduced, and the leakage in the plane direction can be significantly reduced.
[2-3. Water-absorbing layer ]
The water-absorbing layer in the water-absorbent sheet according to one embodiment of the present invention has a particulate water-absorbing agent. In the water-absorbent sheet according to one embodiment of the present invention, it is preferable that no other substrate such as a nonwoven fabric is present in the water-absorbent layer.
(particulate Water-absorbing agent)
The water-absorbing layer contains a particulate water-absorbing agent. When the water-absorbing agent is a mixture of a plurality of particulate water-absorbing agents unless otherwise stated, the following description is about the physical properties of the mixture. That is, the physical properties of the particulate water-absorbing agent are physical properties when all the particulate water-absorbing agents contained in the water-absorbing layer are mixed. Further, with respect to the physical properties of the particulate water-absorbing agent, only the particulate water-absorbing agent may be taken out from the water-absorbing sheet so as not to be mixed with cotton pulp or the like, and the physical properties may be measured.
Surface tension "
The surface tension refers to: the parameters of the work (free energy) required to increase the surface area of a solid or liquid are expressed in terms of per unit area. The surface tension referred to in this application means: surface tension of an aqueous solution when the particulate water-absorbing agent was dispersed in a 0.90 mass% aqueous sodium chloride solution. The surface tension of the water absorbing agent is measured by the following procedure. That is, 50ml of physiological saline adjusted to 20 ℃ was put into a well-washed 100ml beaker, and the surface tension of the physiological saline was first measured using a surface tension meter (K11 Autotensiometer manufactured by KRUSS). Then, a sufficiently cleaned 25mm long fluororesin rotor and 0.5g of the particulate water-absorbing agent were put into a beaker containing physiological saline adjusted to 20 ℃ and subjected to surface tension measurement, and stirred at 500rpm for 4 minutes. After 4 minutes, the stirring was stopped, and after the water-containing particulate water-absorbing agent had settled, the same operation was again performed to measure the surface tension of the supernatant liquid. In the present invention, a plate method using a platinum plate was adopted, and the plate was sufficiently washed with deionized water and heated and washed with a gas burner before each measurement.
In the water-absorbent sheet according to one embodiment of the present invention, the surface tension of the particulate water-absorbing agent is preferably 60mN/m or more, 65mN/m or more, 66mN/m or more, 67mN/m or more, 69mN/m or more, 70mN/m or more, 71mN/m or more, and most preferably 72mN/m or more in this order. When a particulate water-absorbing agent is applied to a water-absorbing sheet, the influence of surface tension is more likely to be exhibited than in a conventional paper diaper, and the surface tension satisfies the above condition, whereby the amount of flow backward in the water-absorbing sheet can be reduced, and leakage in the plane direction can be reduced.
In the water-absorbent sheet according to one embodiment of the present invention, the upper limit of the surface tension of the particulate water-absorbing agent is not particularly limited, and is actually 73mN/m or less.
In the water-absorbent sheet according to one embodiment of the present invention, the particulate water-absorbing agent preferably has a CRC (water absorption capacity without load) of 30g/g or more, 32g/g or more, 33g/g or more, 34g/g or more, and most preferably 35g/g or more in this order. When CRC of the particulate water-absorbing agent satisfies the above condition, the amount of flow backward in the water-absorbent sheet can be reduced. CRC of the particulate water-absorbing agent is abbreviated as "Centrifuge Retention Capacity" defined in ERT441.2-02, and is referred to as "water absorption Capacity" in some cases. The method specifically comprises the following steps: after 0.2G of the particulate water-absorbing agent was put into a nonwoven fabric bag, the bag was immersed in a 0.9 mass% aqueous sodium chloride solution in a large excess amount for 30 minutes to freely swell the water-absorbing agent, and then the water content was removed by a centrifugal separator (250G), thereby obtaining a water absorption capacity (unit: G/G).
In the water-absorbent sheet according to one embodiment of the present invention, from the viewpoint of improving the performance of the water-absorbent sheet (reducing the amount of reflux), the particulate water-absorbing agent preferably has an AAP (absorbency under pressure) of 25g/g or more, more preferably 28g/g or more, particularly preferably 30g/g or more, and most preferably 33g/g or more in this order. The AAP of the particulate water-absorbing agent is an abbreviation of Absorption Against Pressure defined by ERT442.2-02, and is a water Absorption capacity under Pressure of the particulate water-absorbing agent. The method specifically comprises the following steps: the particulate water-absorbing agent was adjusted to 0.9g at 2.06kPa (21 g/cm)20.3psi) under a load, and the water absorption capacity after swelling for 1 hour in a significant excess of 0.9 mass% aqueous sodium chloride solution (unit: g/g). In addition, ERT442.2-02 is expressed as Absorption Under Pressure (AUP), which is substantially the same.
In the water-absorbent sheet according to one embodiment of the present invention, from the viewpoint of improving the performance of the water-absorbent sheet (reducing the specific reflux amount), the particulate water-absorbing agent preferably has a DRC (5 min immersion retention capacity) of 25 to 50g/g, more preferably 30 to 45g/g, and particularly preferably 30 to 40g/g in this order. The DRC5min of the particulate water-absorbing agent means a water absorption capacity without load at 5 minutes, and the larger the DRC5min value, the faster the absorption rate. In detail, with respect to the DRC5min of the water-absorbing agent, the descriptions of the paragraphs "0151" to "0152", the paragraphs "0328" and the paragraphs "0484" to "0487" (including that of fig. 1) in the specification of U.S. patent application publication No. 2019/0111411 are incorporated herein by reference.
In the water-absorbent sheet according to an embodiment of the present invention, the GPR of the particulate water-absorbing agent is preferably 20g/min or more, more preferably 50g/min or more, further preferably 70g/min or more, further preferably 100g/min or more, and particularly preferably 150/min or more, from the viewpoint of excellent effect of shortening the water absorption time in the evaluation of the specific amount of reflux under pressure described later, that is, the effect of increasing the water absorption rate. That is, when the GPR of the particulate water-absorbing agent is 20g/min or more, the water absorption time can be shortened in the evaluation of the specific amount of reflux under pressure, and therefore, the water absorption rate is improved. This reduces the discomfort felt by the user. Such an effect is effectively exhibited by the occurrence of fuzzing on the surface of the first base material on the water-absorbent layer side. The upper limit of the GPR of the particulate water-absorbing agent is not particularly limited, but is preferably 1000g/min or less. The GPR of the particulate water-absorbing agent is an abbreviation for Gel Permeation Rate, and refers to a flow Rate (unit: g/min) at which liquid passes between particles of the swollen Gel when the particulate water-absorbing agent is swollen under a load. The details of the method for measuring GPR are incorporated herein by reference into the sections "0237" to "0239" (including FIG. 5) of the International publication No. 2019/074094.
Particle shape "
In the water-absorbent sheet according to one embodiment of the present invention, the particulate water-absorbing agent may have, for example, a spherical particulate water-absorbing agent (and its granulated product) without limitation to the particle shape. In a preferred embodiment, the particulate water-absorbing agent is preferably irregularly crushed. Here, the irregularly-crushed shape means a crushed particle having an unfixed shape. This is because: the irregularly-crushed shape can be easily fixed to the base material as compared with spherical particles obtained by reversed-phase suspension polymerization or gas-phase polymerization. The particulate water absorbing agent according to an embodiment of the present invention is preferably a pulverized product in aqueous solution polymerization. On the other hand, when the pulverization step is not performed, spherical particles or granules of spherical particles obtained by reverse phase suspension polymerization, droplet polymerization such as spray polymerization of a monomer and polymerization are not irregularly crushed. In the embodiment of the present invention, if the particulate water-absorbing agent has an irregularly crushed shape, the shape of the water-absorbing sheet can be more easily maintained than a water-absorbing agent having a high average circularity (for example, a spherical water-absorbing agent). In the embodiment of the present invention, the average circularity of the particulate water-absorbing agent is preferably 0.70 or less, more preferably 0.60 or less, and still more preferably 0.55 or less.
The average circularity is calculated as follows. At least 100 particulate water-absorbing agents were randomly selected, and each particulate water-absorbing agent was photographed by an electron microscope (VE-9800, manufactured by keyence corporation) (magnification: 50 times), and an image of the particulate water-absorbing agent was obtained, and the perimeter and the area of each particle were calculated by using attached image analysis software. The circularity of each particle was obtained by the following equation, and the average value of the obtained values was calculated as an average circularity.
[ mathematical formula 1]
Particle size "
The particle diameter of the particulate water-absorbing agent (or particulate water-absorbent resin, water-absorbent resin particles) according to one embodiment of the present invention is a weight average particle diameter obtained by a method of measuring "PSD" defined in ERT420.2-02, and may be 150 to 600 μm.
The method for producing the particulate water-absorbing agent is not particularly limited as long as it is a method for producing a water-absorbing agent having desired physical properties, and the particulate water-absorbing agent can be suitably produced, for example, with reference to the publications described in examples.
[ 2-4. clad sheet ]
The water-absorbent sheet according to one embodiment of the present invention preferably has a covering sheet disposed on at least a surface of the first base material. The cover sheet may be disposed on the surface of the first base material, and more preferably, the cover sheet is disposed so as to cover the side surface of the first base material and the side surface of the water-absorbent layer, and further preferably covers the side surface of the first base material, the side surface of the water-absorbent layer, and the side surface of the second base material, and covers a part or the whole of the surface of the second base material opposite to the side of introduction of the liquid to be absorbed.
In a preferred embodiment of the present invention, the water-absorbent sheet comprises a cover sheet, and the cover sheet is a water-permeable sheet and is located at least on the surface (liquid-absorbing side) of the first substrate.
The thickness of the cover sheet is preferably 0.001mm or more, more preferably 0.005mm or more, still more preferably 0.01mm or more, particularly preferably 0.1mm or more, and most preferably 0.2mm or more at 40% RH to 50% RH, for example. The thickness of the cover sheet is, for example, preferably less than 0.9mm, more preferably 0.8mm or less, still more preferably 0.7mm or less, particularly preferably 0.6mm or less, and most preferably 0.5mm or less at 40% RH to 50% RH.
In the present invention, the volume density of the cover sheet is preferably 1g/cm3Hereinafter, more preferably 0.5g/cm3Hereinafter, more preferably 0.3g/cm3The following. The volume density of the wrapping sheet is preferably 0.1g/cm3Above, more preferably 0.12g/cm3Above, more preferably 0.13g/cm3The above.
In the present invention, the weight per unit area of the coated sheet is preferably 5 to 100g/m2More preferably 5 to 70g/m2More preferably 10 to 65g/m2。
The thickness, bulk density, and weight per unit area of the wrapping sheet can be controlled by the material constituting the wrapping sheet, the manufacturing method of the wrapping sheet, and the thickness and bulk density of the wrapping sheet are determined based on the balance between these.
Material for forming wrapping sheet "
The material constituting the cover sheet is not particularly limited as long as the purpose of providing the cover sheet is achieved, and examples thereof include paper (toilet paper, such as facial tissue, toilet tissue, and towel paper), a net, a nonwoven fabric, a woven fabric, and a film.
The nonwoven fabric to be used is not particularly limited, and from the viewpoint of liquid permeability, flexibility, and strength when made into a water-absorbent sheet, there may be mentioned a nonwoven fabric formed of polyolefin fibers such as Polyethylene (PE) and polypropylene (PP), polyester fibers such as polyethylene terephthalate (PET), 1, 3-trimethylene terephthalate (PTT) and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers; and non-woven fabrics made of a mixture of cotton, silk, hemp, pulp (cellulose) fibers, and the like.
The material of the nonwoven fabric that can be used as the cover sheet is preferably rayon fiber, polyolefin fiber, polyester fiber, pulp fiber, or a mixture thereof, and more preferably polyolefin fiber. These fibers may be subjected to a hydrophilization treatment.
The nonwoven fabric that can be used as the cover sheet is not particularly limited, and may be a nonwoven fabric obtained by any method such as a hot air method, an air-laid method, a spunbond method, a spunlace method, or the like, and is preferably a nonwoven fabric obtained by a spunbond method (spunbond nonwoven fabric). In order to prevent urine absorbed by the water-absorbent sheet from seeping out of the sheet (so-called back flow) when the water-absorbent sheet is under load (in a pressurized state), as in the case where an infant wearing an absorbent article such as a disposable diaper is seated on the seat, a water-repellent cover sheet is preferred, and a spunbond nonwoven fabric is preferred, for example. The method for producing a spunbond nonwoven fabric is a method in which continuous long fibers obtained by melting and spinning a raw material resin are directly aggregated to form a fleece (fleece). Examples of the raw material resin include polyethylene, polypropylene, and polylactic acid.
According to one embodiment of the present invention, the method for producing the first base material, the method for producing the second base material, and the method for producing the cover sheet are different. By appropriately changing the production method of each member constituting the water-absorbent sheet in this way, the desired effects of the present invention can be effectively exhibited. According to one embodiment of the present invention, the first base material is a hot air nonwoven fabric, the second base material is an air-laid nonwoven fabric or a spunlace nonwoven fabric, and the cover sheet is a spunbond nonwoven fabric, which are different nonwoven fabrics. In this manner, the desired effects of the present invention can be effectively exhibited.
[ 3. method for producing Water-absorbent sheet ]
A method for producing a water-absorbent sheet according to an embodiment of the present invention includes at least one of (1) a step of spreading a particulate water-absorbing agent on a first substrate and (2) a step of spreading a particulate water-absorbing agent on a second substrate. As a more specific example of the production method, the following production methods (a) to (d) can be mentioned.
When the first base material has a raised surface, the first base material may be raised on one surface thereof in advance before the production methods (a) to (d).
The method for raising the water-absorbing side surface of the first base material is not particularly limited, and known methods can be used, and examples thereof include a method using needles, thistle fruits (teasels), and brushes (bristles). Industrially, the first base material can be fluffed by rotating a roller around which a card clothing or thistle fruit is wound, and advancing the cloth thereon to scrape fibers from the spun yarn on the surface of the cloth.
For example, as a method using a brush, a nonwoven fabric is left standing by 60cm on a horizontal plane, and a weight of 10kg, which is larger than the width of the nonwoven fabric, is loaded on each of both ends in the winding length direction, to fix the nonwoven fabric. The brush was inserted perpendicularly to a point 10cm from the end of the nonwoven fabric in the take-up length direction. The brush was inserted until the brush tip (tip of the bristle) was in contact with the horizontal plane so that the long side of the brush was in the width direction of the nonwoven fabric, and then the brush was moved horizontally by 40cm with respect to the winding length direction. The brush and the weight are removed from the nonwoven fabric, and the nonwoven fabric on the surface on which the brush is moved is cut, whereby a fluffed nonwoven fabric can be obtained.
The conditions for obtaining the napped nonwoven fabric are preferably, for example, the following conditions.
Bristles
Trade name: 25mm by 0.1m sealing brush (PBT/blue), manufacturer: ESCO Co Ltd
Hair length: 25mm, diameter of hair: 0.2mm
Brush length: 100mm, brush width: 5mm, material quality: PBT (polybutylene terephthalate)
Moving speed of brush: the value of 16m/min is 0.27 m/s.
(a) The particulate water-absorbing agent is uniformly dispersed on the first substrate. The adhesive is uniformly spread on the second substrate. The surface of the first base material on which the particulate water-absorbing agent is dispersed and the surface of the second base material on which the adhesive is dispersed are superposed and pressure-bonded so as to be aligned. The pressure bonding is preferably a heat pressure bonding at a temperature near the melting temperature of the adhesive.
(b) After the adhesive is uniformly spread on the second base material, the particulate water-absorbing agent is uniformly spread. The first base material was superposed on the surface of the second base material on which the particulate water-absorbing agent was dispersed, and was heated and pressure-bonded.
(c) The particulate water-absorbing agent, preferably an adhesive, is dispersed on the second substrate so as to pass through the heating furnace and be fixed to such an extent that the particulate water-absorbing agent does not escape. The first base material was superposed on the surface of the second base material on which the particulate water-absorbing agent was dispersed, and was heated and pressure-bonded.
(d) The adhesive is melt-coated on the second substrate, and then the particulate water-absorbing agent is uniformly dispersed to form a layer. The first base material is superposed on the surface of the second base material on which the particulate water-absorbing agent is dispersed, and is pressed by a roller press or the like.
Among these methods, the method (d) is preferable from the viewpoint of uniform application of the adhesive. The water-absorbent sheet may be produced by using the methods (a) to (d) in combination.
When a region where the particulate water-absorbing agent is not present is provided in the water-absorbent layer, the particulate water-absorbing agent may be dispersed in a stripe pattern in the above-described methods (a) to (d). Specifically, the particulate water-absorbing agent may be sprayed onto a substrate (e.g., a first substrate) onto which a strip-shaped adhesive agent is sprayed, and another substrate may be placed on the surface of the substrate on which the particulate water-absorbing agent is sprayed and heated and pressed, or the adhesive agent may be sprayed onto a substrate (e.g., a second substrate) facing the substrate (e.g., the first substrate) on which the strip-shaped adhesive agent is sprayed, and the two substrates may be placed on each other so that the surface on which the particulate water-absorbing agent is sprayed and the surface on which the adhesive agent is sprayed face each other, and heated and pressed. That is, the following production methods (a ') to (d') can be exemplified.
(a') the particulate water-absorbing agent is scattered in a stripe pattern on the first base material. The adhesive is uniformly spread on the second substrate. The surface of the first base material on which the particulate water-absorbing agent is dispersed and the surface of the second base material on which the adhesive is dispersed are superposed and pressure-bonded so as to be aligned. The pressure bonding is preferably heat pressure bonding at a temperature near the melting temperature of the adhesive.
(b') spreading the adhesive in a stripe pattern on the second substrate, and then uniformly spreading the particulate water-absorbing agent. The first base material was superposed on the surface of the second base material on which the particulate water-absorbing agent was dispersed, and was heated and pressure-bonded.
(c') the particulate water-absorbing agent is dispersed in a stripe pattern on the second substrate, and preferably, the adhesive is uniformly dispersed and passed through the heating furnace to be fixed to such an extent that the particulate water-absorbing agent does not escape. The first base material was superposed on the surface of the second base material on which the particulate water-absorbing agent was dispersed, and was heated and pressure-bonded.
(d') after melt-coating the adhesive on the second substrate, spreading the particulate water-absorbing agent in a stripe pattern to form a layer. The first base material is superposed on the surface of the second base material on which the particulate water-absorbing agent is dispersed, and is pressed by pressing with a roller or the like.
Here, in the present invention, the method for scattering the particulate water-absorbing agent in a stripe shape is not particularly limited, and the scattering in a stripe shape can be performed by using, for example, a stencil paper sheet. Specifically, a board having the same size as the water-absorbent sheet and hollowed out in a vertical stripe pattern arranged at a constant width and length was used as the hollowed-out cardboard. The stencil sheet is carried on a substrate on which the particulate water-absorbing agent is to be spread, and the particulate water-absorbing agent is spread to the portion of the holes which have been hollowed out. After the particulate water-absorbing agent is dispersed, when the stencil paper sheet is removed, the particulate water-absorbing agent is dispersed in a stripe-like state on the base material.
Further, the particulate water-absorbing agent can be spread in a stripe pattern on the base material by coating the base material with an adhesive in a vertical stripe pattern by screen printing or the like, and then spraying the particulate water-absorbing agent on the base material, followed by scraping off the particulate water-absorbing agent on the base material, which is not in contact with the adhesive.
As shown in fig. 1 to 4, the embodiment in which the water-absorbent sheet includes a covering sheet includes (3) a step of covering the first base material, the water-absorbent layer, and the second base material with the covering sheet disposed on the first base material. For example, a sheet obtained by pressure-bonding the first base material, the water absorbing layer, and the second base material through the above-described step (a) or (b) is placed on the cover sheet with the first base material facing downward, an adhesive is spread on the second base material (the surface on the side not pressure-bonded with the water absorbing layer) as the upper surface, the excess portion of the cover sheet exposed from the first base material is bent, the cover sheet is wrapped with the adhesive surface of the second base material in contact therewith, the cover sheet is turned upside down, and then pressure-bonding is performed, whereby a water absorbing sheet having the cover sheet can be obtained.
As a step other than the above, the water-absorbent sheet may be subjected to embossing for the purpose of improving the touch of the water-absorbent sheet and enhancing the liquid absorption performance. The embossing may be performed simultaneously with the pressure bonding of the first substrate and the second substrate, or may be performed after the sheet is produced. In addition, embossing may be performed on the cover sheet.
In the method for producing a water-absorbent sheet according to one embodiment of the present invention, additives (deodorizing agent, fiber, antibacterial agent, gel stabilizer, and the like) may be appropriately added. The amount of the additive is preferably 0 to 50% by mass, more preferably 1 to 10% by mass, based on the mass of the particulate water-absorbing agent. In the above-mentioned production method, the particulate water-absorbing agent in which the additive is mixed in advance may be used, or the additive may be added in the course of the production process.
The size of the produced water-absorbent sheet can be appropriately designed. Usually, the width in the transverse direction is 3 to 10m, and the length is 10 to 1000m (in the state of a continuous sheet or roll). The produced water-absorbent sheet is cut according to the purpose (size of the absorbent body to be used) and used.
In addition to the above examples, for example, the following patent documents also disclose a method for producing a water-absorbent sheet: international publication No. 2012/174026, International publication No. 2013/078109, International publication No. 2015/041784, International publication No. 2011/117187, International publication No. 2012/001117, International publication No. 2012/024445, International publication No. 2010/004894, International publication No. 2010/004895, International publication No. 2010/076857, International publication No. 2010/082373, International publication No. 2010/113754, International publication No. 2010/143635, International publication No. 2011/043256, International publication No. 2011/086841, International publication No. 2011/086842, International publication No. 2011/086843, International publication No. 2011/086844, International publication No. 2011/117997, International publication No. 2011/118409, International publication No. 2011/136087, International publication No. 2012/043546, International publication No. 2013/099634, International publication No. 2013/099635, Japanese patent application laid-open Nos. 2010-115406, 2002-345883, 6-315501, 6-190003, 6-190002, 6-190001, 2-252558, 2-252560 and 2-252561. The production methods of the water-absorbent sheets disclosed in these documents can be appropriately referred to.
In the water-absorbent sheet according to one embodiment of the present invention, as a method for fixing the substrates to each other or the substrate and the particulate water-absorbing agent, (i) pressure bonding, or (ii) various binders dissolved or dispersed in water, a water-soluble polymer, or a solvent, or (iii) heat sealing the substrates to each other at a melting point of the material of the substrates themselves, or (iv) fixing using an adhesive may be employed. The substrate and each other or the substrate and the particulate water-absorbing agent are preferably (iv) fixed using an adhesive.
The adhesive used may be a solution type, but from the viewpoint of the time and effort required for removing the solvent, the problem of the residual solvent, and the problem of productivity, a hot melt adhesive having high productivity and no problem of the residual solvent is preferred. In the present invention, the hot-melt adhesive may be contained in advance on the surface of the substrate or the particulate water-absorbing agent, or may be separately used in the production process of the water-absorbent sheet. The form and melting point of the hot melt adhesive may be appropriately selected, and the hot melt adhesive may be in the form of particles, fibers, nets, films, or liquids that melt upon heating. From the viewpoint of uniform application of the adhesive, it is preferable to spread the molten hot-melt adhesive.
In a preferred embodiment, when the surface of the first base material on the water-absorbing layer side has raised, the hot-melt adhesive is spread on the second base material. The water-absorbent sheet can be produced by superposing the first base material on which the particulate water-absorbing agent is dispersed and the second base material on which the hot-melt adhesive is dispersed so that the surfaces on which the particulate water-absorbing agent is dispersed and the hot-melt adhesive are aligned, and pressure-bonding the substrates.
The hot melt adhesive used in the present invention may be appropriately selected, and is preferably: at least 1 kind selected from ethylene-vinyl acetate copolymer adhesives, styrene elastomer adhesives, polyolefin adhesives, polyester adhesives and the like can be suitably used.
Specifically, examples of the polyolefin adhesive include polyethylene, polypropylene and atactic polypropylene, examples of the styrene elastomer adhesive include styrene block copolymers such as styrene-isoprene block copolymer (SIS), styrene-butadiene block copolymer (SBS), styrene-isobutylene block copolymer (SIBS) and styrene-ethylene-butylene-styrene block copolymer (SEBS), and copolymerized polyolefins, examples of the polyester adhesive include polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and copolymerized polyesters, and examples of the ethylene-vinyl acetate copolymer adhesive include ethylene-vinyl acetate copolymer (EVA) adhesive, ethylene-ethyl acrylate copolymer (EEA), and the like, Ethylene-butyl acrylate copolymer (EBA) and the like.
Examples of commercially available HOT-melt adhesives include JaourMelt3889U (manufactured by JAOUR HOT MELT ADHESIVE, main component: styrene block copolymer, hydrocarbon resin, white mineral oil), MORESCOMELT TN-640Z (manufactured by MORESCO), MORESCOMELT TN-781Z (manufactured by MORESCO), and MORESCOMELT TN-262Z (manufactured by MORESCO).
In the water-absorbent sheet and/or the method for producing the same according to one embodiment of the present invention, the water-absorbent sheet preferably contains an adhesive, the adhesive is preferably a hot-melt adhesive, and the amount (content) of the adhesive (e.g., hot-melt adhesive) is preferably 3.0 times or less, more preferably 0.01 to 2.5 times, and still more preferably 0.05 to 2.0 times the mass of the particulate water-absorbing agent. If the content of the adhesive (particularly, hot-melt adhesive) is too large, not only is it disadvantageous in terms of cost and quality of the water-absorbent sheet (increase in quality of the diaper), but the particulate water-absorbing agent may be restricted from swelling and the water-absorbing capacity of the water-absorbent sheet may be lowered.
[ 4. absorbent article ]
An absorbent article according to an embodiment of the present invention has a structure in which the water-absorbent sheet described in [ 2 ] is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet. Here, the liquid-permeable sheet is located on the first base material side, and the liquid-impermeable sheet is located on the second base material side. That is, the absorbent article according to one embodiment of the present invention is configured by sandwiching the water-absorbent sheet according to the present invention between a liquid-permeable sheet and a liquid-impermeable sheet, wherein the liquid-permeable sheet is positioned on the first base material side and the liquid-impermeable sheet is positioned on the second base material side. Specific examples of the absorbent article include disposable diapers, incontinence pads, sanitary napkins, pet sheets, drip sheets for foods, and water stoppers for cables.
As the liquid-permeable sheet and the liquid-impermeable sheet, sheets known in the art of absorbent articles can be used without particular limitation. Further, the absorbent article can be manufactured by a known method.
Examples
The present invention will be described in more detail with reference to the following examples and comparative examples. The technical scope of the present invention is not limited to the following examples. In the following examples, the operation was carried out under the conditions of room temperature (25 ℃ C.)/relative humidity of 40 to 50% RH unless otherwise specified.
[ example A ]
< production example >
Production example 1
Particulate water-absorbing agents (1) to (3) of a polyacrylic acid (salt) resin were obtained by referring to production examples, and comparative examples described in the following patents and appropriately adjusting CRC in accordance with the amount of internal crosslinking agent. The physical properties of the obtained particulate water-absorbing agent are shown in table 1.
International publication No. 2014/034897
International publication No. 2017/170605
International publication No. 2016/204302
International publication No. 2014/054656
International publication No. 2015/152299
International publication No. 2018/062539
International publication No. 2012/043821.
[ production example of acrylic acid ]
Commercially available acrylic acid (acrylic acid dimer 2000ppm, acetic acid 500ppm, propionic acid 500ppm, p-methoxyphenol 200ppm) was supplied to the bottom of a high boiling impurity separation column having a 50-stage baffleless perforated plate, and distilled with a reflux ratio of 1 to remove maleic acid, dimer (acrylic acid dimer) formed from acrylic acid, and the like, followed by further crystallization to obtain acrylic acid (acrylic acid dimer 20ppm, acetic acid 50ppm, propionic acid 50ppm, furfural 1ppm or less, protoanemonin 1ppm or less), and further, after distillation, p-methoxyphenol 50ppm was added.
[ preparation of aqueous solution of sodium acrylate ]
1390g of the acrylic acid was neutralized with 48% caustic soda at 20 to 40 ℃ in example 9 of U.S. Pat. No. 5210298 to obtain a 100% neutralized aqueous solution of sodium acrylate at 37% concentration.
< particulate Water-absorbing agent (1) >
In 5500g (monomer concentration: 36.0 mass%) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing acrylic acid obtained in the above production example of acrylic acid, an aqueous solution of sodium acrylate obtained by the above production method of an aqueous solution of sodium acrylate using the acrylic acid, and deionized water, 4.11g of polyethylene glycol diacrylate (average molar number of addition of ethylene oxide: 9) was dissolved to prepare a reaction solution. Then, the reaction solution was supplied to a reactor formed by capping a jacketed stainless double-arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen while maintaining the reaction solution at 30 ℃. Subsequently, 28.66g of a 10 mass% aqueous solution of sodium persulfate and 35.28g of a 1 mass% aqueous solution of L-ascorbic acid were added while stirring the reaction mixture, and as a result, polymerization started after about 1 minute. After 40 minutes from the start of the polymerization, the hydrogel polymer was taken out. The resulting hydrogel-like polymer is subdivided into particles of about 2 to 4 mm. The finely divided hydrogel polymer was spread on a 50-mesh (mesh size: 300 μm) metal mesh, and dried with hot air at 175 ℃ for 65 minutes. Next, the dried product was pulverized by a roll mill, and further classified and mixed by a metal mesh having a mesh opening of 600. mu.m, thereby obtaining a water-absorbent resin (1-1) having an average particle diameter of 350 μm in a irregularly pulverized state.
To 100 parts by mass of the water-absorbent resin (1-1) thus obtained, 4.03 parts by mass of an aqueous surface-crosslinking agent solution composed of 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 parts by mass of propylene glycol, and 3.0 parts by mass of water was sprayed and mixed. The above mixture was subjected to heat treatment at a heat medium temperature of 100 ℃ for 40 minutes using a paddle type mixing heat treatment machine to obtain a surface-crosslinked water-absorbent resin (1-2). To 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (1-2), 3.0 parts by mass of water was mixed by spraying, and the mixture was cured at 60 ℃ for 1 hour in a closed vessel, and then passed through a sieve having a mesh size of 710 μm to obtain a water-absorbent resin (1-3). A water-absorbent resin obtained by adding and mixing 0.3 part by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL Co., Ltd., Japan) to the water-absorbent resin (1-3) was used as the particulate water-absorbing agent (1).
< particulate Water-absorbing agent (2) >
5.01g of polyethylene glycol diacrylate (average molar number of addition of ethylene oxide: 9) was dissolved in 5500g (monomer concentration: 36.0 mass%) of an aqueous solution of sodium acrylate having a neutralization degree of 75 mol%, which was obtained by mixing acrylic acid obtained in the above production example of acrylic acid, an aqueous solution of sodium acrylate obtained by the above production method of an aqueous solution of sodium acrylate using the acrylic acid, and deionized water, to prepare a reaction solution. Then, the reaction solution was supplied to a reactor formed by capping a jacketed stainless double-arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen while maintaining the reaction solution at 30 ℃. Subsequently, 29.07g of a 10 mass% aqueous solution of sodium persulfate and 35.78g of a 1 mass% aqueous solution of L-ascorbic acid were added while stirring the reaction mixture, and as a result, polymerization started after about 1 minute. After 40 minutes from the start of the polymerization, the hydrogel polymer was taken out. The resulting hydrogel-like polymer is subdivided into particles of about 2 to 4 mm. The finely divided hydrogel polymer was spread on a 50-mesh (mesh size: 300 μm) metal mesh, and dried with hot air at 175 ℃ for 65 minutes. Next, the dried product was pulverized by a roll mill, and further classified and mixed by a metal mesh having a mesh opening of 600. mu.m, thereby obtaining a water-absorbent resin (2-1) having an average particle diameter of 350 μm in a irregularly pulverized state.
To 100 parts by mass of the water-absorbent resin (2-1) thus obtained, 4.03 parts by mass of an aqueous surface-crosslinking agent solution composed of 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 part by mass of propylene glycol, and 3.0 parts by mass of water was spray-mixed. The above mixture was heat-treated at a heat medium temperature of 100 ℃ for 40 minutes using a paddle type mixing heat-treating machine to give a surface-crosslinked water-absorbent resin (2-2). To 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (2-2), 3.0 parts by mass of water was mixed by spraying, and the mixture was cured at 60 ℃ for 1 hour in a closed vessel, and then passed through a sieve having a mesh size of 710 μm to obtain a water-absorbent resin (2-3). A water-absorbent resin obtained by adding 0.3 part by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL Co., Ltd., Japan) to water-absorbent resin (2-3) and mixing was used as particulate water-absorbing agent (2).
< particulate Water-absorbing agent (3) >
To 5500g (monomer concentration: 38.0 mass%) of an aqueous solution of sodium acrylate having a neutralization degree of 75 mol% obtained by mixing acrylic acid obtained in the above production example of acrylic acid, an aqueous solution of sodium acrylate obtained by the above production method of an aqueous solution of sodium acrylate using the acrylic acid, and deionized water was dissolved 3.77g of polyethylene glycol diacrylate (average molar number of addition of ethylene oxide: 9) to prepare a reaction solution. Then, the reaction solution was supplied to a reactor formed by capping a jacketed stainless double-arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen while maintaining the reaction solution at 30 ℃. Then, 30.68g of a 10 mass% aqueous solution of sodium persulfate and 37.76g of a 1 mass% aqueous solution of L-ascorbic acid were added to the reaction mixture while stirring the reaction mixture, and as a result, polymerization was started after about 1 minute. After 40 minutes from the start of the polymerization, the hydrogel polymer was taken out. The resulting hydrogel-like polymer is subdivided into particles of about 2 to 4 mm. The finely divided hydrogel polymer was spread on a 50-mesh (mesh size: 300 μm) metal mesh, and dried with hot air at 175 ℃ for 65 minutes. Next, the dried product was pulverized by a roll mill, and further classified and blended with a metal mesh having a mesh opening of 600. mu.m, thereby obtaining a water-absorbent resin (3-1) having an average particle diameter of 350. mu.m in a random pulverized state.
To 100 parts by mass of the water-absorbent resin (3-1) thus obtained, 3.83 parts by mass of an aqueous solution of a surface-crosslinking agent comprising 0.03 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of 1, 4-butanediol, 0.5 parts by mass of propylene glycol, and 3.0 parts by mass of water were spray-mixed. The mixture was subjected to heat treatment at a heat medium temperature of 195 ℃ for 40 minutes using a paddle type mixing heat treatment machine to obtain a surface-crosslinked water-absorbent resin (3-2). To 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (3-2), 1.0 part by mass of water was mixed by spraying, and the mixture was cured at 60 ℃ for 1 hour in a closed vessel, and then passed through a sieve having a mesh size of 710 μm to obtain a water-absorbent resin (3-3). A water-absorbent resin obtained by adding 0.3 part by mass of Aerosil200 (hydrophilic amorphous silica, manufactured by AEROSIL Co., Ltd., Japan) to water-absorbent resin (3-3) and mixing was used as particulate water-absorbing agent (3).
[ Water-absorbent resin taken out of commercially available paper diaper ]
< particulate Water-absorbing agent (4) >
A water-absorbent resin was taken out from a commercially available disposable diaper (Moony Air Fit ((L., lot No.: 201512163072), manufactured by Unicharm, available in 2016, 5 months), and only the water-absorbent resin was taken out so as not to be mixed with cotton pulp or the like at the time of taking out, and the water-absorbent resin taken out was in a particle shape obtained by granulating spherical particles, and this water-absorbent resin was used as the particulate water-absorbing agent (4).
[ method of measuring physical Properties of particulate Water-absorbing agent ]
< weight average particle size >
The particle diameter of the particulate water-absorbing agent (or the particulate water-absorbent resin, water-absorbent resin particles) according to one embodiment of the present invention is a weight average particle diameter obtained by a method of measuring "PSD" specified in ERT 420.2-02. The weight average particle diameter of each particulate water-absorbing agent is shown in table 1.
< CRC (Water absorption Capacity without load) (ERT441.2-02) >
After 0.2G (pre-water absorption weight) of the particulate water-absorbing agent was put into a nonwoven fabric bag, the bag was immersed in a 0.9 mass% aqueous sodium chloride solution in a large excess amount for 30 minutes to allow the water-absorbing agent to freely swell, and after removing water by a centrifugal separator (250G), the post-water absorption weight of the particulate water-absorbing agent was measured. The water absorption capacity (unit: g/g) is determined by "(weight after water absorption of particulate water-absorbing agent weight before water absorption)/(particulate water-absorbing agent weight before water absorption) × 100". CRC of each particulate water-absorbing agent is shown in table 1.
< surface tension >
In the present invention, the surface tension refers to the surface tension of an aqueous solution when the particulate water-absorbing agent is dispersed in a 0.90 mass% aqueous sodium chloride solution.
50ml of physiological saline adjusted to 20 ℃ was put into a well-washed 100ml beaker, and the surface tension of the physiological saline was measured using a surface tension meter (K11 Autotensiometer manufactured by KRUSS Co.). In the present invention, a plate method using a platinum plate was adopted, and the plate was sufficiently washed with deionized water and heated and washed with a gas burner before each measurement.
Then, a sufficiently cleaned 25mm long fluororesin rotor and 0.5g of the particulate water-absorbing agent were put into a beaker containing physiological saline adjusted to 20 ℃ and subjected to surface tension measurement, and stirred at 500rpm for 4 minutes. After 4 minutes, the stirring was stopped, and after the water-containing particulate water-absorbing agent had settled, the same operation was again performed to measure the surface tension of the supernatant liquid. Here, the surface tension (unit: mN/m) of the particulate water-absorbing agent is determined from the surface tension of a supernatant liquid when the particulate water-absorbing agent is dispersed in physiological saline. The surface tension of each particulate water-absorbing agent is shown in table 1.
[ example ]
[ example 1]
A nonwoven fabric E having a longitudinal length of 10cm and a transverse length of 40cm (comprising pulp fibers as a main component and having a thickness of 0.4 mm. produced by an air-laying method) was formed corresponding to the second substrate and had a basis weight of 47g/m2) The upper uniform dispersion (dispersion amount: 12.5 to 17.5g/m2) After 0.5 to 0.7g of an adhesive (spray 77, manufactured by 3 mjaan corporation) containing styrene-butadiene rubber, 9.0g of the particulate water-absorbing agent (1) (dispersion amount: 225g/m2)。
Then, a hot-air nonwoven fabric A (corresponding to the first base material; basis weight: 41 g/m) having a thickness of 1.4mm and comprising olefin as a main component, cut into a length of 10cm and a width of 40cm 2) The sheet is placed on the surface of the nonwoven fabric E on which the particulate water-absorbing agent is dispersed, and is pressed under pressure to obtain an intermediate sheet X.
Then, a spun-bonded nonwoven fabric (equivalent to a covering sheet, basis weight: 13 g/m) having a thickness of 0.1mm and comprising olefin as a main component, cut into a length of 24cm and a width of 40cm was laid2And a bulk density of 0.13g/cm3) As a result, the nonwoven fabric a side of the intermediate sheet X is placed in contact with the spunbond nonwoven fabric.
Next, 0.1 to 0.2g of an adhesive (spray glue 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber was uniformly spread on the nonwoven fabric E side surface (upper surface) of the intermediate body sheet X, and then the excess portion of the spunbond nonwoven fabric was folded, wrapped in such a manner that the nonwoven fabric E of the intermediate body sheet X (nonwoven fabric E side surface of the intermediate body sheet X) was in contact with the spunbond nonwoven fabric, turned upside down, and then pressure-bonded to obtain a water-absorbent sheet (1).
[ example 2]
A spun-bonded nonwoven fabric (corresponding to a covering sheet) cut to have a length of 24cm and a width of 40cm and containing olefin as a main component and having a thickness of 0.1mm was laid in advance, a hot-air nonwoven fabric A (corresponding to a first base material) cut to have a length of 10cm and a width of 40cm and containing olefin as a main component and having a thickness of 1.4mm was placed thereon, and 9.0g (dispersion amount: 225 g/m) of the particulate water-absorbing agent (1) was uniformly dispersed on the surface of the nonwoven fabric A 2)。
Next, a nonwoven fabric E (comprising pulp fibers as a main component and having a thickness of 0.4mm, produced by an air-laying method) cut into a length of 10cm and a width of 40cm was produced, which corresponded to a second base material and had a basis weight of 47g/m2) On the surface of (b), uniformly spread (spread amount: 12.5 to 17.5g/m2)0.5 to 0.7g of an adhesive (spray coating 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber. Thereafter, the surface of the nonwoven fabric A on which the particulate water-absorbing agent is dispersed and the surface of the nonwoven fabric E on which the adhesive is dispersed are superposed so as to be aligned (in contact), pressed and pressure-bonded, and then uniformly dispersed on the nonwoven fabric E (dispersion amount: 2.5 to 5.0 g/m)2) An adhesive (spray glue 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber 0.1-0.2 g to obtain an intermediate sheet Y.
Then, the excess portion of the spunbond nonwoven fabric positioned at the lowermost layer is folded, wrapped so that the nonwoven fabric E of the intermediate body panel Y (the surface of the intermediate body panel Y on the nonwoven fabric E side) comes into contact with the spunbond nonwoven fabric, turned upside down, and then pressed and bonded to obtain the water-absorbent sheet (2).
[ example 3]
A water-absorbent sheet (3) was obtained in the same manner as in example 2, except that the particulate water-absorbing agent (2) was used instead of the particulate water-absorbing agent (1).
[ example 4]
A water-absorbent sheet (4) was obtained in the same manner as in example 2, except that the particulate water-absorbing agent (3) was used instead of the particulate water-absorbing agent (1).
[ example 5]
A water-absorbent sheet (5) was obtained in the same manner as in example 2, except that the particulate water-absorbing agent (4) was used instead of the particulate water-absorbing agent (1).
[ example 6]
A hot air nonwoven fabric B having a thickness of 2.0mm (basis weight: 43 g/m) was used2) A water-absorbent sheet (6) was obtained in the same manner as in example 2, except that the air-through nonwoven fabric a was replaced.
[ example 7]
A hot air nonwoven fabric C having a thickness of 1.5mm (basis weight: 37 g/m) was used2) A water-absorbent sheet (7) was obtained in the same manner as in example 2, except that the air-through nonwoven fabric a was replaced.
[ example 8]
A hot air nonwoven fabric D (weight per unit area: 45 g/m) having a thickness of 1.5mm was used2) A water-absorbent sheet (8) was obtained in the same manner as in example 2, except that the air-through nonwoven fabric a was replaced.
[ example 9]
Using a spunlace nonwoven fabric F (made of PET resin and pulp, thickness: 0.4mm, basis weight: 45 g/m)2) A water-absorbent sheet (9) was obtained in the same manner as in example 2, except that the nonwoven fabric E was replaced with the other nonwoven fabric E.
[ example 10]
A hot air nonwoven fabric G having a thickness of 0.7mm (weight per unit area: 20G/m) was used2) A water-absorbent sheet (10) was obtained in the same manner as in example 2, except that the nonwoven fabric a was replaced.
Comparative example 1
A hot air nonwoven fabric A of 1.4mm thickness containing olefin as a main component and cut into 10cm in the longitudinal direction and 40cm in the transverse direction was supported, and 4.5g (dispersion amount: 112.5 g/m) of the particulate water-absorbing agent (1) was uniformly dispersed on the surface of the nonwoven fabric A2)。
Next, a nonwoven fabric E (comprising pulp fibers as a main component and having a thickness of 0.4mm, produced by an air-laying method) cut into a length of 10cm and a width of 40cm was produced, which corresponded to a second base material and had a basis weight of 47g/m2) On the surface of (b), uniformly spread (spread amount: 12.5 to 17.5g/m2)0.5 to 0.7g of an adhesive (spray coating 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber. Thereafter, the particulate water-absorbing agent-dispersed surface of the nonwoven fabric a and the adhesive-dispersed surface of the nonwoven fabric E were superposed so as to be aligned (in contact), and pressure-bonded.
Next, 4.5g (dispersion amount: 112.5 g/m) of the particulate water-absorbing agent (1) was uniformly dispersed on the surface of the nonwoven fabric A on the side not facing the particulate water-absorbing agent (1)2)。
Then, a nonwoven fabric E (the same nonwoven fabric (thickness: 0.4mm) as the nonwoven fabric E used above, corresponding to the first base material) cut into a length of 10cm and a width of 40cm was uniformly spread (spread amount: 12.5 to 17.5 g/m) 2) Comprises styrene butadiene rubber (spray glue 77, manufactured by 3M JAPAN) 0.5-0.7 g. Thereafter, the surface of the nonwoven fabric a on which the particulate water-absorbing agent is dispersed and the surface of the nonwoven fabric E on which the adhesive is dispersed are superposed so as to be aligned (in contact), and pressure-bonded, thereby obtaining an intermediate sheet Z.
Finally, the nonwoven fabric E of the intermediate sheet Z (nonwoven fabric side on which the particulate water-absorbing agent was first dispersed) was uniformly dispersed (dispersion amount: 2.5 to 5.0 g/m)2)0.1 to 0.2g of an adhesive containing styrene-butadiene rubber (spray glue 77, manufactured by 3M JAPAN Co., Ltd.) was wrapped with a spun-bonded nonwoven fabric cut into 24cm in the longitudinal direction and 40cm in the transverse direction, containing olefin as a main component, and having a thickness of 0.1mm, and pressure-bonded to obtain a water-absorbent sheet (11).
In comparative example 1, the nonwoven fabric E corresponding to the first substrate had a transmittance of 0.3 mass% of the particulate water-absorbing agent, and the particulate water-absorbing agent content was 0%. In addition, in the water-absorbent sheet obtained in comparative example 1, "thickness of first base material/thickness of second base material" was 1.
Comparative example 2
A spun-bonded nonwoven fabric (corresponding to a covering sheet) cut into a length of 24cm and a width of 40cm and having an olefin as a main component and a thickness of 0.1mm was laid in advance, a hot-air nonwoven fabric A (corresponding to a first base material) cut into a length of 10cm and a width of 40cm and having an olefin as a main component and a thickness of 1.4mm was placed thereon, and the nonwoven fabric A was uniformly spread on the surface thereof (spread amount: 225 g/m) 2) Particulate Water-absorbing agent (1)9.0 g.
Then, a hot air nonwoven fabric A (corresponding to a second base material, hereinafter, the nonwoven fabric A will be referred to as "nonwoven fabric A2" for convenience) having a thickness of 1.4mm and cut into a length of 10cm and a width of 40cm was uniformly spread (spread amount: 12.5 to 17.5 g/m)2)0.5 to 0.7g of an adhesive (spray coating 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber. Then, the adhesive-dispersed surface of the nonwoven fabric A2 was superimposed on the particulate water-absorbing agent-dispersed surface of the nonwoven fabric A in such a manner that the adhesive-dispersed surfaces were aligned (in contact) with each other, and after pressure bonding, the adhesive-dispersed surface was further uniformly dispersed on the nonwoven fabric A2 (dispersion amount: 2.5 to 5.0 g/m)2) An adhesive (spray glue 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber 0.1-0.2 g to obtain an intermediate sheet Z2.
Then, the excess portion of the spunbonded nonwoven fabric positioned at the lowermost layer was folded, wrapped in such a manner that the intermediate sheet Z2 was in contact with the spunbonded nonwoven fabric, turned upside down, and then pressure-bonded to obtain a water-absorbent sheet (12).
Comparative example 3
A spun-bonded nonwoven fabric (corresponding to a covering sheet) cut to have a length of 24cm and a width of 40cm and having an olefin as a main component and a thickness of 0.1mm was laid in advance, a hot-air nonwoven fabric A (corresponding to a first base material) cut to have a length of 10cm and a width of 40cm and having an olefin as a main component and a thickness of 1.4mm was laid thereon, and 9.0g (dispersion amount: 225 g/m) of the particulate water-absorbing agent (1) was uniformly dispersed on the surface of the nonwoven fabric A 2)。
Then, the excess portion of the spunbond nonwoven fabric located at the lowermost layer was folded, wrapped in such a manner that the nonwoven fabric surface on which the particulate water-absorbing agent (1) was dispersed was in contact with the spunbond nonwoven fabric, turned upside down, and then pressure-bonded to obtain a water-absorbent sheet (13). The spun-bonded nonwoven fabric was wrapped with 0.5 to 0.7g of an adhesive containing styrene-butadiene rubber (spray glue 77, manufactured by 3M JAPAN) uniformly spread only on the part of the spun-bonded nonwoven fabric in contact with the surface of the nonwoven fabric on which the particulate water-absorbing agent (1) was spread.
Comparative example 4
A spunlace nonwoven fabric F (made of PET resin and pulp, thickness: 0.4mm, basis weight: 45 g/m) was used2) A water-absorbent sheet (14) was obtained in the same manner as in example 2, except that the nonwoven fabric a was replaced with the hot-air nonwoven fabric a.
In comparative example 4, the nonwoven fabric F corresponding to the first substrate had a transmittance of 1 mass% of the particulate water-absorbing agent, and the particulate water-absorbing agent content was 0%. In addition, in the water-absorbent sheet obtained in comparative example 4, "thickness of first base material/thickness of second base material" was 1.
The nonwoven fabrics a to G used in the present example were all water-permeable sheets.
[ method of measuring physical Properties of nonwoven Fabric ]
The thickness, bulk density, liquid diffusion area, and permeability of the particulate water-absorbing agent to the nonwoven fabrics used in examples 1 to 10 and comparative examples 1 to 4 were measured by the following methods.
< measurement of thickness of nonwoven Fabric >
The measurement was carried out using a dial thickness gauge (dial thickness gauge) large-size (thickness measuring instrument) (model J-B, manufactured by Kawasaki, Ltd., measuring head, anvil, vertical diameter 50 mm). The number of measurement points was measured 5 times at different sites, and the measured values were averaged at 5 sites. In order to measure the thickness, the hand was slowly removed from the handle so as not to apply pressure to the nonwoven fabric as much as possible, and the thickness was measured.
< method for calculating bulk Density of nonwoven Fabric >
The weight of the nonwoven fabric cut into a size of 10cm or more in the machine direction and 40cm or more in the cross direction was measured. The longitudinal and transverse lengths of the nonwoven fabric and the thickness measured by < thickness measurement > were multiplied, respectively, to calculate the volume of the nonwoven fabric, and the bulk density was calculated by dividing the weight of the nonwoven fabric by the volume of the nonwoven fabric.
< method for measuring liquid diffusion area of nonwoven Fabric >
A30 cm-diameter sieve obtained using a net having a mesh opening of 2mm and a wire diameter of 0.9mm was placed on a flat surface, and a nonwoven fabric (second base material) cut into a 10cm square was placed thereon. A syringe having a bore diameter of 0.50mm was attached to a 1ml syringe, 1.00g of physiological saline containing 20ppm of blue reagent No. 1 was measured, and the physiological saline of the syringe was vertically injected into the center of the nonwoven fabric on the screen. At this time, the mesh of the screen is sufficiently spaced from the plane so that the physiological saline passed through the nonwoven fabric and the mesh does not contact the mesh. When the nonwoven fabric absorbed physiological saline and the liquid was completely diffused, the diffusion area of physiological saline was measured.
< permeability of particulate Water-absorbing agent to nonwoven Fabric >
A non-woven fabric (first base material 11) cut to a diameter of 80mm as shown in FIG. 5 was placed on a JIS standard sieve (The IIDA TESTING SIEVE: 80mm in inner diameter; JIS Z8801-1(2000)) having a mesh opening 32 of 850 μm mesh or a sieve 31 corresponding to The JIS standard sieve, and The periphery was fixed with an adhesive tape 33 (The area through which The pellets were allowed to pass was at least 75mm in diameter). As the nonwoven fabric (first substrate 11), a nonwoven fabric taken out of the water-absorbent sheet by a method described later can be used. 10.0g of particulate water-absorbing agent 14 (weight-average particle diameter: 367 μm, particle size distribution: 6.1% for 850 to 600 μm, 14.5% for 600 to 500 μm, 50% for 500 to 300 μm, 27.6% for 300 to 150 μm, 1.9% for 150 to 45 μm, and 0.1% for 45 μm or less) was put into a nonwoven fabric (first substrate 11) in a sieve 31 (arrow direction in FIG. 5), and the resultant mixture was shaken at room temperature (20 to 25 ℃ C.) and a relative humidity of 50% RH for 5 minutes by using a rotary hammer type shaker (ES-65 type shaker manufactured by Kabushiki Kaisha, rotational speed: 230rpm, impact number: 130 rpm). After the shaking, the mass (w (g)) of particulate water-absorbing agent 14 (i.e., particulate water-absorbing agent 14 present in portion 31a below mesh 32 of screen 31) after passing through mesh 32 of screen 31 of the nonwoven fabric (first substrate 11) and the JIS standard screen was measured, and the permeability of the particulate water-absorbing agent was calculated according to the following formula (i). Note that, 3 measurements were performed, and the average value was calculated. In table 1, the transmittance (mass%) of the particulate water-absorbing agent is shown as "transmittance (mass%)".
[ mathematical formula 2]
The particulate water-absorbing agent has a permeability (mass%) { W/10.0} × 100 … formula (i)
< method for removing particulate Water-absorbing agent from Water-absorbing sheet >
The particulate water-absorbing agent is taken out by peeling the upper nonwoven fabric and the lower nonwoven fabric from the water-absorbent sheet (when the intermediate sheet is included, the intermediate sheet and the particulate water-absorbing agent are taken out). The particulate water-absorbing agent attached to the upper and lower nonwoven fabrics and the intermediate sheet was also entirely removed. When the upper and lower nonwoven fabrics are peeled off, the water-absorbing sheet is cooled to sufficiently weaken the adhesiveness of the adhesive (hot melt adhesive, spray adhesive) to which the nonwoven fabric or the particulate water-absorbing agent is attached, and then peeled off. By performing this step, the fibers of the nonwoven fabric and the structural thickness can be taken out without changing, and the transmittance can be accurately measured. The method of cooling the water-absorbent sheet may be any of various means such as leaving the sheet in a constant temperature bath at-10 ℃ or lower for a certain period of time, spraying cooling mist, and applying liquid nitrogen, and is not particularly limited as long as the cooling is performed under conditions such that the fibers, structure, and thickness of the nonwoven fabric are not changed and the particulate water-absorbent agent contained in the water-absorbent sheet does not absorb moisture.
When the particulate water-absorbing agent taken out is hygroscopic, the water content may be adjusted to 10 mass% or less, preferably 5 ± 2 mass% by drying, and the above-mentioned transmittance and the respective physical properties defined in the present application may be measured. The drying conditions for adjusting the water content are not particularly limited as long as decomposition or modification of the water-absorbent resin (particulate water-absorbing agent) does not occur, and drying under reduced pressure is preferable.
< measurement of the content ratio of particulate water-absorbing agent in the upper nonwoven Fabric (corresponding to the first base Material) >
The measurement was carried out on a sample (thickness was not changed) obtained by cutting the upper nonwoven fabric into a square having a length of 10mm and a width of 10mm by using the inch Xio SMX-100CT system of MICRO FOCUS X-ray CT system manufactured by Shimadzu corporation. The measurement conditions are as follows.
[ imaging based on X-ray CT ]
Image lateral dimension (pixel): 512
Image longitudinal dimension (pixel): 512
X-ray tube voltage (kV): 50
X-ray tube current (μ a): 40
English size (inch): 4.0
An X-ray filter: is free of
SDD (distance of focus of X-ray source from X-ray detector) (mm): 700
SRD (distance between focal point of X-ray source and rotation center of measurement sample) (mm): 550
Scanning mode 1: CBCT
Scanning mode 2: conventional scanning
Scanning angle: full scan
Number of visual fields: 2400
Average number: 5
Smoothing: YZ
Slice thickness (mm): 0.166
BHC data: is free of
Fine mode: is provided with
FOV XY (maximum imaging area XY) (mm): 50.3
FOV Z (maximum capture area Z) (mm): 40.0.
next, the X-ray CT imaging data was analyzed using an analysis software Win ROOF manufactured by mitsubishi corporation according to the following procedure.
(1) The Win ROOF is opened and the image to be analyzed (Jpeg) stored in the X-ray CT is selected.
(2) On the screen, the click (selection) is performed in accordance with the flow of the binarization process, the automatic binarization, the modal method, the threshold value (appropriate adjustment), and the operation.
(3) The polygonal ROI was selected to surround the particulate water-absorbing agent in the first substrate (upper nonwoven fabric), and the area of the particulate water-absorbing agent was calculated.
(4) The total area of the particulate water-absorbing agent in the water-absorbent sheet was calculated in the same manner as in (3).
From the calculation result, the content ratio (%) of the particulate water-absorbing agent in the first base material is calculated by the following formula.
The content ratio (%) of the particulate water-absorbing agent in the first base material is ═ particulate water-absorbing agent area (I)/particulate water-absorbing agent total area (II) × 100 in the first base material
That is, the content ratio of the particulate water-absorbing agent in the first base material is expressed by area% of the particulate water-absorbing agent with respect to the total area. The particulate water-absorbing agent is not present on the surface of the first base material on the side where the liquid to be absorbed is introduced, because it is less than several% if present.
[ evaluation method of Water-absorbing sheet ]
< amount of flow reversal (evaluation of specific amount of flow reversal) >
As shown in FIG. 6, a water-absorbent sheet 10 having a length of 10cm and a width of 40cm was wrapped with a liquid-impermeable sheet 21 having a length of 14cm and a width of 40cm so that an opening portion was formed at the upper portion. The water-absorbent sheet 10 wrapped with the liquid-impermeable sheet 21 is placed on a flat surface, and a liquid injection cylinder 41 (fig. 7) is placed on the flat surface at the center of the water-absorbent sheet 10 as shown in fig. 8. In this state, 80g of a 0.9 wt% aqueous sodium chloride solution at 23 ℃ was poured into the liquid injection cylinder 41 using a funnel 42 capable of pouring a liquid at a flow rate of 7 ml/sec (fig. 9). In this case, a liquid is introduced into the water-absorbent sheet 10 exposed from the liquid-impermeable sheet 21. After 10 minutes from the introduction of the liquid, 20 pieces of filter paper 43 (model No.2, manufactured by ADVANTEC; circular filter paper having a diameter of 110 mm) having a weight measured in advance were placed on the center of the water-absorbent sheet 10, and a circular weight 44(1200g) having a diameter of 100mm was placed thereon and held for 1 minute. After 1 minute, the weight 44 was removed and the first pour (g) was determined from the weight gain of the filter paper 43. After 1 minute from the removal of the weight 44, the same operation was repeated (liquid addition → filter paper 43 and weight 44(1200g) were carried 10 minutes after addition, hold 1 minute → removal of the weight, and measurement of the flow rate), and the second and third flow rates (g, g) were measured. The total of the first to third measured flow rates is shown in table 1.
< leakage amount (Tilt evaluation) >
The amount of leakage was measured using the apparatus shown in FIG. 10.
The outline is as follows: a mechanism for measuring the leakage amount by inclining and fixing an acrylic plate 63 using a commercially available stand 60 for a laboratory device and a tube 61, and then pouring a physiological saline solution into a water-absorbent sheet fixed to the plate from the vertical direction by a funnel. The detailed specifications are shown below.
The acrylic plate 63 has a length of 400mm in the direction of the inclined surface and is fixed by the mount 60 so as to form an angle of 20 ° with respect to the horizontal. The acrylic plate 63 has a width of 200mm and a thickness of 3 mm. The acrylic plate 63 has a smooth surface, and therefore, liquid does not stay on or be absorbed by the plate. The funnel 64 is fixed vertically above the inclined acrylic plate 63 using the mount 60. Funnel 64 used a funnel that dropped the liquid at 7 mL/sec.
A metal tray 65 was provided below the acrylic plate 63, and received all of the test liquid flowing down in the form of leakage, and the mass thereof was recorded with an accuracy of 0.1 g.
The leak test in the tilt using this apparatus was performed in the following manner. As shown in fig. 10, the back surface of the water-absorbent sheet 10 cut into a size of 100mm in length and 100mm in width was stuck to an acrylic plate 63.
A mark is marked on a part of the water absorbing sheet which faces downwards by 1.5cm from the upper end, and the feeding port of the funnel is fixed in a manner that the distance from the vertical upper part of the mark reaches 15 +/-2 mm.
20mL of physiological saline was put into the dropping funnel 64 at one time. The test solution was flowed on the inclined acrylic plate 63 without being absorbed by the water-absorbent sheet 66, and the amount of the liquid contained in the metal tray 65 was measured, and as a first leakage amount (mL) in the plane direction, after 10 minutes, 20mL of physiological saline was similarly introduced, and after measuring a second leakage amount, further after 10 minutes, 20mL of physiological saline was similarly introduced, and a third leakage amount was measured. The leakage amounts in the table are the total values of the first to third leakage amounts.
Table 1 shows the structures and evaluation results of the water-absorbent sheets of examples 1 to 10 and comparative examples 1 to 4.
[ Table 1]
From the above results, the water-absorbent sheets of examples 1 to 10 were significantly less in the amount of backflow and significantly reduced in the leakage from the water-absorbent sheets, as compared with the water-absorbent sheets of comparative examples 1 to 4.
On the other hand, in comparative example 1 in which the multilayer structure was exhibited, and comparative examples 2 and 4 in which the thickness ratio of the first base material to the second base material was 1, the amount of reverse flow was significantly increased.
[ example 11]
A spun-bonded nonwoven fabric (corresponding to a covering sheet) cut to have a longitudinal length of 24cm and a transverse length of 40cm and having a polyolefin fiber as a main component and a thickness of 0.1mm was laid in advance, a fluffed hot-air nonwoven fabric A (corresponding to a first base material) cut to have a longitudinal length of 10cm and a transverse length of 40cm and having a polyolefin fiber as a main component and a thickness of 1.4mm was placed at the center of the spun-bonded nonwoven fabric A, and 9.0g (scattering amount: 225 g/m) of the particulate water-absorbing agent (2) was uniformly scattered on the fluffed surface of the nonwoven fabric A2). The raising treatment of the nonwoven fabric a was performed by the method described below.
Then, a nonwoven fabric E (comprising pulp fibers as a main component and having a thickness of 0.4mm, produced by an air-laid method and corresponding to a second base material) having a longitudinal length of 10cm and a transverse length of 40cm was cut into a sheet-like nonwoven fabric E corresponding to a weight per unit area of 47g/m2) The surface (c) was uniformly dispersed and heated to 135 ℃ to prepare a liquid HOT-melt adhesive (JaourMelt3889U, JAOUR HOT MELT ADHESIVE, main component: styrene block copolymer, hydrocarbon resin, white mineral oil) 0.8g (dispersion amount: 20.0g/m2). Thereafter, the particulate water-absorbing agent-dispersed surface of the nonwoven fabric a was bonded to the adhesive-dispersed surface of the nonwoven fabric E The intermediate sheet Y is obtained by stacking (contact method) and pressure-bonding.
A HOT melt adhesive (JaourMelt3889U, manufactured by JAOUR HOT MELT ADHESIVE, main component: styrene block copolymer, hydrocarbon resin, white mineral oil) heated to 135 ℃ and made liquid was spread on the surface of the nonwoven fabric E of the intermediate sheet Y in an amount of 0.3g (spreading amount: 7.5 g/m)2). Then, the excess portion of the spunbond nonwoven fabric was folded, wrapped so that the surface of the nonwoven fabric E of the intermediate sheet Y was in contact with the spunbond nonwoven fabric, turned upside down, and then pressure-bonded to obtain a water-absorbent sheet (21).
[ example 12]
The dispersion amount of the particulate water-absorbing agent was set to 12.0g (dispersion amount: 300 g/m)2) Except for this, a water-absorbent sheet (22) was obtained in the same manner as in example 1.
[ example 13]
A water-absorbent sheet (23) was obtained in the same manner as in example 2, except that the non-woven fabric a without the fluff treatment was used instead of the non-woven fabric a with the fluff treatment.
[ example 14]
The adhesive to be applied to the nonwoven fabric E was 0.8g (application amount: 20.0 g/M) of an adhesive containing styrene-butadiene rubber (spray coating 77, manufactured by 3M JAPAN Co., Ltd.) 2) Except for this, a water-absorbent sheet (24) was obtained in the same manner as in example 1.
[ example 15]
A water-absorbent sheet (25) was obtained in the same manner as in example 12, except that the particulate water-absorbing agent (5) obtained by the following production method was used.
< particulate Water-absorbing agent (5) >
In 5500g (monomer concentration: 38% by mass) of an aqueous solution of sodium acrylate having a neutralization degree of 75 mol% obtained by mixing acrylic acid obtained in the above production example of acrylic acid, an aqueous solution of sodium acrylate obtained by the above production method of an aqueous solution of sodium acrylate using the acrylic acid, and deionized water, 5.03g of polyethylene glycol diacrylate (average molar number of addition of ethylene oxide: 9) was dissolved to prepare a reaction solution. Then, the reaction solution was supplied to a reactor formed by capping a jacketed stainless double-arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen while maintaining the reaction solution at 30 ℃. Then, 30.68g of a 10 mass% aqueous solution of sodium persulfate and 37.76g of a 1 mass% aqueous solution of L-ascorbic acid were added to the reaction mixture while stirring the reaction mixture, and as a result, polymerization was started after about 1 minute. After 40 minutes from the start of the polymerization, the hydrogel polymer was taken out. The resulting hydrogel-like polymer is subdivided into particles of about 2 to 4 mm. The finely divided hydrogel polymer was spread on a 50-mesh (mesh size: 300 μm) metal mesh, and dried with hot air at 175 ℃ for 65 minutes. Next, the dried product was pulverized by a roll mill, and further classified and blended with a metal mesh having a mesh opening size of 600 μm, thereby obtaining a water-absorbent resin (5-1) having an average particle size of 380. mu.m in a irregularly pulverized state.
To 100 parts by mass of the water-absorbent resin (5-1) thus obtained, 3.83 parts by mass of an aqueous surface-crosslinking agent solution composed of 0.03 part by mass of ethylene glycol diglycidyl ether, 0.3 part by mass of 1, 4-butanediol, 0.5 part by mass of propylene glycol, and 3.0 parts by mass of water were spray-mixed. The above mixture was subjected to heat treatment at a heat medium temperature of 210 ℃ for 40 minutes using a paddle type mixing heat treatment machine to obtain a surface-crosslinked water-absorbent resin (5-2). To 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (5-2), 1.0 part by mass of water was mixed by spraying, and the mixture was cured at 60 ℃ for 1 hour in a closed vessel, and then passed through a sieve having a mesh opening of 710 μm to obtain a water-absorbent resin (5-3). A water-absorbent resin obtained by adding 0.3 part by mass of Aerosil200 (hydrophilic amorphous silica, manufactured by AEROSIL Co., Ltd., Japan) to water-absorbent resin (5-3) and mixing was used as particulate water-absorbing agent (5).
[ example 16]
A water-absorbent sheet (26) was obtained in the same manner as in example 12, except that the particulate water-absorbing agent (6) obtained by the following production method was used.
< particulate Water-absorbing agent (6) >
In 5500g (monomer concentration: 36.0 mass%) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing acrylic acid obtained in the above production example of acrylic acid, an aqueous solution of sodium acrylate obtained by the above production method of an aqueous solution of sodium acrylate using the acrylic acid, and deionized water, 4.11g of polyethylene glycol diacrylate (average molar number of addition of ethylene oxide: 9) was dissolved to prepare a reaction solution. Then, the reaction solution was supplied to a reactor formed by capping a jacketed stainless double-arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen while maintaining the reaction solution at 30 ℃. Subsequently, 28.66g of a 10 mass% aqueous solution of sodium persulfate and 35.28g of a 1 mass% aqueous solution of L-ascorbic acid were added while stirring the reaction mixture, and as a result, polymerization started after about 1 minute.
After 40 minutes from the start of the polymerization, 181.5g of a fine powder of a water-absorbent resin having a particle size of 150 μm or less was added thereto, and gel disintegration was carried out for 10 minutes by high-speed rotation (130rpm) using a plate of a kneader, and then the hydrogel polymer was taken out. The obtained hydrogel-like polymer is subdivided into particles of about 1 to 2 mm. The finely divided hydrogel polymer was spread on a 50-mesh (mesh size: 300 μm) metal gauze, and dried with hot air at 175 ℃ for 65 minutes. Next, the dried product was pulverized by a roll mill, and further classified and blended with a metal mesh having a mesh opening size of 600 μm, thereby obtaining a water-absorbent resin (6-1) having an average particle size of 350 μm in a irregularly pulverized state.
To 100 parts by mass of the water-absorbent resin (6-1) thus obtained, 4.03 parts by mass of an aqueous surface-crosslinking agent solution composed of 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 part by mass of propylene glycol, and 3.0 parts by mass of water was spray-mixed. The above mixture was subjected to heat treatment at a heat medium temperature of 100 ℃ for 40 minutes using a paddle type mixing heat treatment machine to obtain a surface-crosslinked water-absorbent resin (6-2). To 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (6-2), 3.0 parts by mass of water was mixed by spraying, and the mixture was cured at 60 ℃ for 1 hour in a closed vessel, and then passed through a sieve having a mesh opening of 710 μm to obtain a water-absorbent resin (6-3). A water-absorbent resin obtained by adding 0.3 part by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL, Japan) to water-absorbent resin (6-3) and mixing was used as particulate water-absorbing agent (6).
[ example 17]
A water-absorbent sheet (27) was obtained in the same manner as in example 12, except that the particulate water-absorbing agent (7) obtained by the following production method was used.
< particulate Water-absorbing agent (7) >
Into a 2-liter polypropylene container, 351.7g of acrylic acid, 0.860g (molecular weight: 523) of polyethylene glycol diacrylate as an internal crosslinking agent (0.034 mol% based on the carboxyl group-containing unsaturated monomer), 2.15g of a 1.0 wt% aqueous solution of trisodium diethylenetriaminepentaacetate (dtpa.3na), 149.0g of a 48.5 wt% aqueous solution of sodium hydroxide, and 336.2g of deionized water (ion-exchanged water) were put and mixed to prepare an aqueous monomer solution (a').
Subsequently, the aqueous monomer solution (a') was cooled while being stirred. When the liquid temperature reached 40.0 ℃, 144.8g of a 48.5 wt% aqueous sodium hydroxide solution adjusted to 40 ℃ was added and mixed to prepare an aqueous monomer solution (a). At this time, the temperature of the aqueous monomer solution (a) was increased to 78.2 ℃ by the heat of neutralization in the second stage immediately after the production. Immediately after the 48.5 wt% aqueous solution of sodium hydroxide was mixed, the precipitate was observed, but the precipitate was gradually dissolved to form a transparent homogeneous solution.
Then, 15.49g of a 4.0 wt% aqueous sodium persulfate solution was added to the stirred aqueous monomer solution (a), and immediately thereafter, the mixture was poured into an vat-type stainless steel pan container (bottom 340X 340mm, height 25mm, inner surface: coated with Teflon (registered trademark)) in an open-air system. The time from the start of the second-stage neutralization to the injection of the aqueous monomer solution (a) into the tray-type container heated to a surface temperature of 40 ℃ using a hot plate (NEO HOTPLATE HI-1000, Kyoho Co., Ltd.) was 55 seconds.
After 60 seconds from the injection of the aqueous monomer solution (a) into the bottom-pan type vessel, the polymerization reaction was started. In this polymerization reaction, water vapor is generated while the reaction proceeds in a four-sided expanding and foaming manner, and then the reaction product shrinks to a size slightly larger than that of the bottom-tray container. After 3 minutes had elapsed since the start of the polymerization reaction, the crosslinked hydrogel polymer (hereinafter referred to as "hydrogel") was taken out (7-1). It should be noted that this series of operations is performed in an open-air system.
The hydrous gel (7-1) obtained by the above polymerization reaction was cut into short strips, and the cut strips were fed to a screw extruder to pulverize the gel, thereby obtaining a granular hydrous gel (7-2). The screw extruder was equipped with a perforated plate having a diameter of 100mm, a hole diameter of 11.0mm, a number of holes of 40, an opening ratio of 62.5% and a thickness of 10mm at the tip end, and the outer diameter of the screw shaft was 86 mm.
The gel pulverization is carried out by simultaneously supplying the water-containing gel (7-1) in the form of short strands and water vapor from different supply ports, respectively, while setting the rotation speed of the screw shaft of the screw extruder at 130 rpm. The amount of the water-containing gel (7-1) supplied was 4640g per minute, and the amount of the water vapor supplied was 83g per minute.
This particulate water-containing gel (7-2) was spread on a 50-mesh wire gauze, hot-air dried at 190 ℃ for 30 minutes, and the dried product was pulverized with a roll mill (WML type roll pulverizer/Kokoku corporation, Limited Co., Ltd.), further sieved with a JIS sieve having mesh openings of 850. mu.m, 600. mu.m, 500. mu.m, 300. mu.m and 150. mu.m, and then blended, thereby obtaining a precursor water-absorbent resin (A) having a weight-average particle diameter (D50) of 305. mu.m and a logarithmic standard deviation (σ ζ) of particle size distribution of 0.35 in an irregularly pulverized form. The retention capacity (CRC) of the precursor water-absorbent resin (A) in a centrifuge was 48.4 (g/g).
A surface cross-linking agent solution comprising 0.03 parts by weight of ethylene glycol diglycidyl ether, 1.5 parts by weight of propylene glycol and 3.5 parts by weight of deionized water was uniformly mixed with respect to 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 100 ℃ for about 30 minutes to obtain a CRC of the resulting water-absorbent resin (1) of about 35[ g/g ]. Thereafter, the mixture was cooled, and an aqueous solution of 1 part by weight of deionized water and 0.05 part by weight of trisodium diethylenetriaminepentaacetate (DTPA · 3Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60 ℃ for 1 hour, the resultant was passed through a JIS standard sieve having a mesh opening size of 850. mu.m, and 0.3 part by weight of silica (trade name: REOLOSIL QS-20, manufactured by TOKUYAMA) was mixed. For the mixing, 30g of the water-absorbent resin was charged into a mayonnaise bottle having a capacity of 225mL together with silica, and mixed for 60 minutes by shaking of TURBULA SHAKER MIXER T2F model (manufactured by Shinmau Enterprises), to obtain water-absorbent resin particles (7).
[ example 18]
A spun-bonded nonwoven fabric (corresponding to a covering sheet) cut to have a length of 24cm and a width of 40cm and having a polyolefin fiber as a main component and a thickness of 0.1mm was laid in advance, a fluffed HOT-air nonwoven fabric A (corresponding to a first base material) cut to have a length of 10cm and a width of 40cm and having a polyolefin fiber as a main component and a thickness of 1.4mm was placed at the center of the spun-bonded nonwoven fabric A, and a HOT-melt adhesive (JaourMelt3889U, manufactured by JAOUR HOT MELT ADHESIVE, a main component of which is a styrene block copolymer, a hydrocarbon resin, and a white mineral oil) was uniformly spread and heated to 135 ℃ on the fluffed surface of the nonwoven fabric A to form a liquid (dispersion amount: 20.0 g/m)2) Thereafter, 12.0g (dispersion amount: 300g/m2)。
Next, a nonwoven fabric E (comprising pulp fibers as a main component and having a thickness of 0.4mm, produced by an air-laying method) cut into a length of 10cm and a width of 40cm was used as a second base material, and the basis weight was 47g/m2) The nonwoven fabric a was superposed on the adhesive-dispersed and particulate water-absorbing agent in a face-to-face manner (contact manner), and pressure-bonded to obtain an intermediate sheet Y.
The surface of the nonwoven fabric E of the intermediate sheet Y was uniformly coated with 0.3g (dispersion amount: 7.5 g/m) of a liquid HOT-melt adhesive (JaourMelt3889U, JAOUR HOT MELT ADHESIVE, main component: styrene block copolymer, hydrocarbon resin, white mineral oil) heated to 135 ℃ to obtain a liquid adhesive2). Then, the excess portion of the spunbond nonwoven fabric is folded, and the surface of the nonwoven fabric E of the intermediate sheet Y is brought into contact with the spunbond nonwoven fabricThe sheet is wrapped, turned upside down, and then pressed under pressure to obtain a water-absorbent sheet (28).
< fuzzing treatment >
The nonwoven fabric was placed on a horizontal table having a smooth surface, and a 10kg weight was placed on both ends of the nonwoven fabric in the long axis direction to fix the nonwoven fabric. The brush (length: 100mm, hair length: 25mm, brush material: polybutylene terephthalate resin, brush diameter: 0.2mm) was held from above perpendicularly to the major axis of the nonwoven fabric, lowered vertically downward toward the surface of the nonwoven fabric, and inserted until the nonwoven fabric was contacted with the table top while being directly pressed by the tip of the brush. Thereafter, the brush is horizontally moved to a desired length without applying a load to the nonwoven fabric in the longitudinal direction. The brush and the weight were removed, and the nonwoven fabric of the portion where the brush was moved was cut to obtain a fluffed nonwoven fabric.
< method of measuring area ratio of fuzz >
The nonwoven fabric subjected to the raising treatment was cut into a size of 20cm × 10cm, and a smooth plastic plate having a width of 3cm was inserted perpendicularly to the long axis of the nonwoven fabric into the lower side of the nonwoven fabric (see fig. 11 (a)). Subsequently, the nonwoven fabric was lifted vertically upward by about 10cm to keep the plastic plate horizontal. Both ends of the long axis of the suspended nonwoven fabric were held from below by a clip having a weight of 70g and a nip of 10cm or more (see fig. 11 (b)). A photograph of the upper surface of the nonwoven fabric stretched on the plastic plate was taken from a direction perpendicular to the minor axis of the nonwoven fabric (taken from the direction of the arrow in fig. 11 (b)).
The taken photograph was read into the image analysis software winrofof (ver.6.1), and the "monochrome image processing" was performed by the "image processing" tag. Thereafter, as shown in fig. 11 (c), a raised area (an area 5mm upward from the nonwoven fabric surface) is selected by the rectangular ROI, and "automatic binarization" is selected from the "binarization processing" label, so that only raised fibers can be selected, and the threshold value is adjusted. The "area ratio" of "total area/number of pieces" was selected from the "measurement" label and run, and the raising area ratio of the nonwoven fabric was calculated.
< evaluation of specific amount of reflux under pressure >
As shown in FIG. 6, a water-absorbent sheet 10 having a length of 10cm and a width of 40cm was wrapped with a liquid-impermeable sheet 21 having a length of 14cm and a width of 40cm so that an opening portion was formed at the upper portion. A water-absorbent sheet 10 wrapped with a liquid-impermeable sheet 21 was placed on a flat surface, and a liquid-feeding cylinder 45 (a liquid-feeding cylinder in which weights of 30mm in inner diameter, 60mm in outer diameter, 62mm in length, and 1030g in weight were attached to a plastic cylinder of 26mm in inner diameter, 30mm in outer diameter, 150mm in length, and 34g in weight, FIG. 12) was placed on the flat surface at the center of the water-absorbent sheet 10, as shown in FIG. 13. In this state, 80g of an aqueous solution containing 0.9 wt% of sodium chloride and 0.002 wt% of edible blue No. 1 (tokyo chemical industry co.) was poured into a liquid pouring cylinder 45 at 23 ℃ using a funnel 42 capable of pouring a liquid at a flow rate of 7 ml/sec (fig. 14). The time from the moment of putting the aqueous solution into the cylinder 45 until all the aqueous solution in the cylinder was absorbed by the water-absorbent sheet 10 was measured. In this case, a liquid is injected into the water-absorbent sheet 10 exposed from the liquid-impermeable sheet 21. After 10 minutes from the introduction of the liquid, 20 pieces of filter paper 43 (model No.2, manufactured by ADVANTEC, Inc.; circular filter paper with a diameter of 110 mm) having a weight measured in advance were placed on the center of the water-absorbent sheet 10, and a circular weight 44(1200g) with a diameter of 100mm was placed thereon and held for 1 minute. After 1 minute, the weight 44 was removed and the first pour (g) was determined from the weight gain of the filter paper 43. After 1 minute from the removal of the weight 44, the same operation was repeated (liquid input → measurement of the water absorption time of the liquid → 10 minutes after the input, the filter paper 43 and the weight 44(1200g) were placed, and the holding time was maintained for 1 minute → 1 minute after the holding time → removal of the weight, and the flow rate was measured), and the second flow rate (g) and the third flow rate (g) were measured. The total of the measured water absorption time and the first to third flow rates is shown in table 1.
< falling-off Rate of particulate Water-absorbing agent >
The falling-off rate of the particulate water-absorbing agent was calculated as follows. After measuring the weight of the 40cm × 10cm water-absorbent sheet, the entire second substrate side surface and the entire side surface, and the surface of the first substrate side surface up to 1cm from the outer periphery toward the inner side were covered with a plastic sheet and fixed with an adhesive tape. 300ml of physiological saline (0.9% sodium chloride aqueous solution) was uniformly poured onto the surface of the water-absorbent sheet covered with the plastic sheet. After 10 minutes of the injection of the physiological saline, the plastic sheet covering the water-absorbent sheet was removed, and the water-absorbent sheet was put into a plastic bag (OK bag No.18, 53 cm. times.38 cm, manufactured by Dacang industries, Ltd.). Sleeves (ASS ONE, sleeve with claw 360 degree rotation type) were attached to two columns of an electromagnetic shaker (AS 200 manufactured by Retsch Corp.), 1 SUS tube (diameter 13mm, inner diameter 10mm, length 290mm) was fixed parallel to the ground by each sleeve, a water-absorbent sheet was clamped together with a plastic bag by a large-sized clamp (clamping opening 150mm) attached to the SUS tube, and the SUS tube was vibrated for 1 minute with a vibration width of 3 mm. The water-absorbent sheet was removed together with the plastic bag from the large-size gripper of the electromagnetic shaker, and the weight of the particulate water-absorbing agent falling from the water-absorbent sheet into the plastic bag was measured. The falling-off rate of the particulate water-absorbing agent was measured by the following formula. In the following formula, the weight of the physiological saline was 300 g.
The dropping rate (%) of the particulate water-absorbing agent is (g)/(weight of water-absorbing sheet (g) + weight of physiological saline (g)) x 100 of dropped particulate water-absorbing agent.
Table 2 shows the structures and evaluation results of the water-absorbent sheets of examples 11 to 18.
[ Table 2]
[ example B ]
In the following examples, a single-layer system in which only 1 laminate of the first substrate is laminated on the water-absorbing layer (region including the particulate water-absorbing agent) and a two-layer system in which 2 laminates of the first substrate are laminated on the water-absorbing layer (region including the particulate water-absorbing agent) and a second substrate are disclosed. In both the single-layer system and the two-layer system, the first substrate having a liquid absorption surface for directly absorbing liquid is referred to as "upper nonwoven fabric", and the second substrate is referred to as "lower nonwoven fabric". The substrate other than the first substrate having the liquid absorption surface directly absorbing the liquid in the two-layer system is an intermediate substrate, and is referred to herein as an "intermediate nonwoven fabric".
< production example >
Production example 1
Particulate water-absorbing agents (1) and (2) of polyacrylic acid (salt) resin were obtained by referring to production examples, and comparative examples described in the following patents and appropriately adjusting CRC in accordance with the amount of internal crosslinking agent. The physical properties of the obtained particulate water-absorbing agent are shown in table 3.
International publication No. 2014/034897
International publication No. 2017/170605
International publication No. 2016/204302
International publication No. 2014/054656
International publication No. 2015/152299
International publication No. 2018/062539
International publication No. 2012/043821.
[ production example of acrylic acid ]
Commercially available acrylic acid (acrylic acid dimer 2000ppm, acetic acid 500ppm, propionic acid 500ppm, p-methoxyphenol 200ppm) was supplied to the bottom of a high boiling impurity separation column having a 50-stage baffleless perforated plate, and distilled with a reflux ratio of 1 to remove maleic acid, dimer (acrylic acid dimer) formed from acrylic acid, and the like, followed by further crystallization to obtain acrylic acid (acrylic acid dimer 20ppm, acetic acid 50ppm, propionic acid 50ppm, furfural 1ppm or less, protoanemonin 1ppm or less), and further, after distillation, p-methoxyphenol 50ppm was added.
[ preparation of aqueous solution of sodium acrylate ]
1390g of the acrylic acid was neutralized with 48% caustic soda at 20 to 40 ℃ in example 9 of U.S. Pat. No. 5210298 to obtain a 100% neutralized aqueous solution of sodium acrylate at 37% concentration.
< particulate Water-absorbing agent (1) >
In 5500g (monomer concentration: 35.5 mass%) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing acrylic acid obtained in the above production example of acrylic acid, an aqueous solution of sodium acrylate obtained by the above production method of an aqueous solution of sodium acrylate using the acrylic acid, and deionized water, 4.00g of polyethylene glycol diacrylate (average molar number of addition of ethylene oxide: 9) was dissolved to prepare a reaction solution. Then, the reaction solution was supplied to a reactor formed by capping a jacketed stainless double-arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen while maintaining the reaction solution at 30 ℃. Subsequently, 28.66g of a 10 mass% aqueous solution of sodium persulfate and 35.28g of a 1 mass% aqueous solution of L-ascorbic acid were added while stirring the reaction mixture, and as a result, polymerization started after about 1 minute. 40 minutes after the start of the polymerization, 181.5g of a fine water-absorbent resin powder having a particle size of 150 μm or less was added thereto, and gel disintegration was carried out for 10 minutes by high-speed rotation (130rpm) using a plate of a kneader, and then the hydrogel polymer was taken out. The obtained hydrogel-like polymer is subdivided into particles of about 1 to 2 mm.
The finely divided hydrogel polymer was spread on a 50-mesh (mesh size: 300 μm) metal gauze, and dried with hot air at 175 ℃ for 65 minutes. Next, the dried product was pulverized by a roll mill, and further classified and blended with a metal mesh having a mesh opening of 600. mu.m, thereby obtaining a water-absorbent resin (1-1) having an average particle diameter of 350. mu.m in a random pulverized state. To 100 parts by mass of the water-absorbent resin (1-1) thus obtained, 4.03 parts by mass of an aqueous solution of a surface-crosslinking agent comprising 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 part by mass of propylene glycol, and 3.0 parts by mass of water was spray-mixed. The above mixture was subjected to heat treatment at a heat medium temperature of 100 ℃ for 40 minutes using a paddle type mixing heat treatment machine to obtain a surface-crosslinked water-absorbent resin (1-2). To 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (1-2), 3.0 parts by mass of water was mixed by spraying, and the mixture was cured at 60 ℃ for 1 hour in a closed vessel, and then passed through a sieve having a mesh opening of 710 μm to obtain a water-absorbent resin (1-3). A water-absorbent resin obtained by adding and mixing 0.3 part by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL Co., Ltd., Japan) to the water-absorbent resin (1-3) was used as the particulate water-absorbing agent (1).
[ method of measuring physical Properties of particulate Water-absorbing agent ]
< weight average particle diameter >
The particle diameter of the particulate water-absorbing agent (or the particulate water-absorbent resin, water-absorbent resin particles) according to one embodiment of the present invention is a weight average particle diameter obtained by a method of measuring "PSD" specified in ERT 420.2-02. The weight average particle diameter of each particulate water-absorbing agent is shown in table 3.
< CRC (Water absorption Capacity without load) (ERT441.2-02) >
After 0.2G (pre-water absorption weight) of the particulate water-absorbing agent was put into a nonwoven fabric bag, the bag was immersed in a 0.9 mass% aqueous sodium chloride solution in a large excess amount for 30 minutes to allow the water-absorbing agent to freely swell, and after removing water by a centrifugal separator (250G), the post-water absorption weight of the particulate water-absorbing agent was measured. The water absorption capacity (unit: g/g) is determined by "(weight after water absorption of particulate water-absorbing agent weight before water absorption)/(particulate water-absorbing agent weight before water absorption) × 100". The CRC of each particulate water-absorbing agent is shown in tables 4 and 6.
< surface tension >
In the present invention, the surface tension refers to the surface tension of an aqueous solution when the particulate water-absorbing agent is dispersed in a 0.90 mass% aqueous sodium chloride solution.
50ml of physiological saline adjusted to 20 ℃ was put into a well-washed 100ml beaker, and the surface tension of the physiological saline was measured using a surface tension meter (K11 Autotensiometer manufactured by KRUSS Co.). In the present invention, a plate method using a platinum plate was adopted, and the plate was sufficiently washed with deionized water and heated and washed with a gas burner before each measurement.
Then, a sufficiently cleaned 25mm long fluororesin rotor and 0.5g of the particulate water-absorbing agent were put into a beaker containing the physiological saline after the surface tension measurement adjusted to 20 ℃ and stirred at 500rpm for 4 minutes. After 4 minutes, the stirring was stopped, and after the water-containing particulate water-absorbing agent had settled, the same operation was again performed to measure the surface tension of the supernatant liquid. Here, the surface tension (unit: mN/m) of the particulate water-absorbing agent is determined from the surface tension of a supernatant liquid when the particulate water-absorbing agent is dispersed in physiological saline. The surface tensions of the particulate water-absorbing agents are shown in tables 4 and 6.
[ examples ]
< preparation of hollow paperboard >
Hollow-out paper boards 1 to 6 are prepared for spreading a particulate water absorbing agent in a stripe pattern on a nonwoven fabric. The stencil paper sheets 1 to 6 were perforated in a portion where a region where the particulate water-absorbing agent was present, in a paper sheet having a longitudinal length of 14cm and a transverse length of 44cm, so that the region where the particulate water-absorbing agent was present and the region where the particulate water-absorbing agent was not present were linearly formed along the longitudinal direction. In the stencil sheets 1 to 6, the outer periphery thereof was set to 2cm, and the paper was not cut (that is, the stencil sheet was formed by hollowing out a portion of a region where the particulate water absorbing agent was present in the region other than the frame in the width direction in order from the end portion to create a hole). The shapes (S-1) to (S-6) formed by the stencil paper sheets 1 to 6 will be described with reference to FIG. 15 (a) to FIG. 15 (c) and FIG. 16 (a) to FIG. 16 (c). Fig. 15 (a) to 15 (c) and fig. 16 (a) to 16 (c) are schematic cross-sectional views of a single-layer water-absorbent sheet cut in the width direction. In the shapes (S-1) to (S-6), the region including the particulate water-absorbing agent 14 and the gap 15 are formed so as to be bilaterally symmetrical with respect to the widthwise central portion of the water-absorbent sheet. Therefore, the region ratio of the "particulate water-absorbing agent 14" and the "gap 15" shown below may be from either the left or right along the width direction.
Fig. 15 (a) shows a (S-1) shape formed by the stencil sheet 1. (S-1) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 15mm, gap 15: 25mm, particulate water-absorbing agent 14: 20mm, gap 15: 25mm, particulate water-absorbing agent 14: 15mm ".
Fig. 15 (b) shows a (S-2) shape formed by the stencil sheet 2. (S-2) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 20mm, gap 15: 20mm, particulate water-absorbing agent 14: 20mm, gap 15: 20mm, particulate water-absorbing agent 14: 20mm ".
Fig. 15 (c) shows a (S-3) shape formed by the stencil paper 3. (S-3) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 10mm, gap 15: 35mm, particulate water-absorbing agent 14: 10mm, gap 15: 35mm, particulate water-absorbing agent 14: 10mm ".
Fig. 16 (a) shows a (S-4) shape formed by the stencil sheet 4. (S-4) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 25mm, gap 15: 10mm, particulate water-absorbing agent 14: 30mm, gap 15: 10mm, particulate water-absorbing agent 14: 25mm ".
Fig. 16 (b) shows a (S-5) shape formed by the hollow cardboard 5. (S-5) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 17.5mm, gap 15: 10mm, particulate water-absorbing agent 14: 17.5mm, gap 15: 10mm, particulate water-absorbing agent 14: 17.5mm, gap 15: 10mm, particulate water-absorbing agent 14: 17.5mm ".
Fig. 16 (c) shows a (S-6) shape formed by the stencil sheet 6. (S-6) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm ".
[ example 1]
The stencil paper sheet 1 was placed on a nonwoven fabric a (produced by a hot air method) cut to a length of 10cm and a width of 40cm, which had olefin as a main component and a thickness of 1.4mm and corresponded to an intermediate nonwoven fabric (see fig. 15 (a)). The hollow board 1 has 3 rectangular holes to make the bottom of the hollow board 1 be seen from the holes to the maximum The position of the nonwoven fabric A is adjusted. Calculating the ratio of the area of each hole to the total area of all holes of the stencil paper sheet 1, 4.5g (dispersion amount: 112.5 g/m) of the particulate water-absorbing agent (1) was added2) The nonwoven fabric a, which can be seen from each hole, was uniformly spread by dividing and measuring the area ratio of each hole. Under the condition that a part of the particulate water-absorbing agent (1) is scattered on the hollow-out paper board, the hollow-out paper board 1 is inclined towards the non-woven fabric A on which the particulate water-absorbing agent (1) is scattered, so that the particulate water-absorbing agent falls into the holes of the hollow-out paper board 1. Thereafter, the stencil sheet 1 is removed from the nonwoven fabric a.
Unlike the nonwoven fabric a, a nonwoven fabric a cut to have a vertical length of 10cm and a horizontal length of 40cm (the same nonwoven fabric (thickness of 1.4mm) as the nonwoven fabric a, hereinafter referred to as a nonwoven fabric a2, corresponding to a first base material (upper nonwoven fabric)) was uniformly spread with 0.7 to 0.9g (spread amount: 17.5 to 21.5g/M) of an adhesive containing styrene-butadiene rubber (spray glue 77, manufactured by 3M JAPAN), and then the surface of the nonwoven fabric a on which the particulate water absorbent (1) was spread was overlapped with the surface of the nonwoven fabric a2 on which the adhesive was spread (in contact therewith) and pressure-bonded thereto.
A stencil paper sheet 1 was placed on the surface of the nonwoven fabric a on the side not facing the particulate water-absorbing agent (1) (see fig. 15 (a)). The position is adjusted so that the nonwoven fabric a under the stencil sheet 1 can be seen from the 3 rectangular holes of the stencil sheet 1 to the maximum. The ratio of the area of each hole of the stencil paper sheet 1 to the total area of all the holes was calculated, and 4.5g of the particulate water-absorbing agent (1) was distributed and measured in accordance with the area ratio of each hole, and the nonwoven fabric a which could be seen from each hole was uniformly spread. Under the condition that a part of the particulate water-absorbing agent (1) is scattered on the hollow-out paper board, the hollow-out paper board 1 is inclined towards the non-woven fabric A on which the particulate water-absorbing agent (1) is scattered, so that the particulate water-absorbing agent falls into the holes of the hollow-out paper board 1. Thereafter, the stencil sheet 1 is removed from the nonwoven fabric a.
Nonwoven fabric E having a machine direction of 10cm and a cross direction of 40cm (produced by air-laid method, containing pulp fibers as a main component, having a thickness of 0.4mm, and having a basis weight of 47 g/m)2. Corresponding to the second substrate (lower nonwoven fabric)), 0.7 to 0.9g of the adhesive was uniformly spread, and then the surface of the nonwoven fabric a on which the particulate water-absorbing agent (1) was spread was overlapped (in contact with) so that the surface of the nonwoven fabric E on which the adhesive was spread was aligned, and pressure-bonded, thereby obtaining an intermediate sheet X.
Finally, the intermediate sheet X was cut into a nonwoven fabric F (produced by a spunbond method) having a length of 24cm and a width of 40cm, and having a thickness of 0.1mm and a basis weight of 13g/m, with olefin as a main component2. Bulk density: 0.15g/cm3. Corresponding to a wrapping sheet) to obtain a water-absorbent sheet (1).
[ example 2]
A nonwoven fabric F cut into a length of 24cm and a width of 40cm (corresponding to a covering sheet) was laid in advance, a nonwoven fabric a cut into a length of 10cm and a width of 40cm (corresponding to a first base material) was placed thereon, and a cut-out cardboard 1 was placed on the surface of the nonwoven fabric a (see fig. 15 (a)). The position of the nonwoven fabric A under the stencil sheet 1 can be adjusted so as to be maximally visible through the 3 rectangular holes of the stencil sheet 1. The ratio of the area of each hole to the total area of all holes of the stencil paper sheet 1 was calculated, and 9.0g (dispersion amount: 225 g/m) of the particulate water-absorbing agent (1) was added2) The nonwoven fabric a, which can be seen from each hole, was uniformly spread by dividing and measuring the area ratio of each hole. When a part of the particulate water absorbing agent (1) is scattered on the hollow-out paper board, the hollow-out paper board 1 is inclined toward the nonwoven fabric a on which the particulate water absorbing agent (1) is scattered, and the particulate water absorbing agent falls into the holes of the hollow-out paper board 1. Thereafter, the stencil sheet 1 is removed from the nonwoven fabric a.
0.7 to 0.9g (dispersion amount: 17.5 to 21.5g/M) of an adhesive (spray glue 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber was uniformly dispersed on a nonwoven fabric E (corresponding to a second base material) having a vertical length of 10cm and a horizontal length of 40cm, and then the surface of the nonwoven fabric A on which the particulate water-absorbing agent (1) was dispersed was superposed on the surface of the nonwoven fabric E on which the adhesive was dispersed (in contact therewith) and pressure-bonded to obtain an intermediate sheet Y.
Finally, the intermediate sheet Y is wrapped with the nonwoven fabric F and pressure-bonded to obtain a water-absorbent sheet (2).
[ example 3]
A water-absorbent sheet (3) was obtained in the same manner as in example 2, except that a 0.7mm thick through-air nonwoven fabric G was used in place of the through-air nonwoven fabric A.
[ example 4]
A water-absorbent sheet (4) was obtained in the same manner as in example 2, except that a stencil sheet 2 (see fig. 15 (b)) was used instead of the stencil sheet 1.
[ example 5]
A water-absorbent sheet (5) was obtained in the same manner as in example 2, except that a stencil sheet 3 (see fig. 15 (c)) was used instead of the stencil sheet 1.
[ example 6]
A water-absorbent sheet (6) was obtained in the same manner as in example 2, except that a stencil sheet 4 (see fig. 16 (a)) was used instead of the stencil sheet 1.
[ example 7]
A water-absorbent sheet (7) was obtained in the same manner as in example 2, except that a hollow-out paper sheet 5 (see fig. 16 (b)) was used instead of the hollow-out paper sheet 1.
[ example 8]
A water-absorbent sheet (8) was obtained in the same manner as in example 2, except that a hollow cardboard 6 (see fig. 16 (c)) was used instead of the hollow cardboard 1.
[ example 9]
A water-absorbent sheet (9) was obtained in the same manner as in example 2, except that a nonwoven fabric B (produced by a hot air method, containing olefin as a main component and having a thickness of 2.0 mm) was used in place of the nonwoven fabric a.
[ example 10]
A water-absorbent sheet (10) was obtained in the same manner as in example 2, except that a nonwoven fabric C (produced by a hot air method, containing olefin as a main component and having a thickness of 1.5 mm) was used in place of the nonwoven fabric a.
Comparative example 1
4.5g of the particulate water-absorbing agent (1) was uniformly spread on the nonwoven fabric A cut into a length of 10cm and a width of 40 cm.
0.7 to 0.9g (dispersion amount: 17.5 to 21.5g/M) of an adhesive (spray glue 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber was uniformly dispersed on a nonwoven fabric E (corresponding to a first base material) having a vertical length of 10cm and a horizontal length of 40cm, and then the surface of the nonwoven fabric A on which the particulate water-absorbing agent (1) was dispersed was superposed (in contact) so as to be in contact with the surface of the nonwoven fabric E on which the adhesive was dispersed, and pressure-bonding was performed.
On the surface of the nonwoven fabric A on the side not opposed to the particulate water-absorbing agent (1), 4.5g of the particulate water-absorbing agent (1) was uniformly dispersed.
After 0.7 to 0.9g of the adhesive was uniformly spread on a nonwoven fabric E having a length of 10cm and a width of 40cm (hereinafter referred to as a nonwoven fabric E2 corresponding to a second base material) separately from the nonwoven fabric E, the nonwoven fabric a and the particulate water-absorbing agent (1) were superposed on each other so that the surfaces thereof were in contact with each other and the adhesive-spread surface of the nonwoven fabric E2 was pressed and bonded together under pressure to obtain an intermediate sheet Z. Finally, the intermediate sheet Z was wrapped with a nonwoven fabric F and pressure-bonded, thereby obtaining a water-absorbent sheet (11).
Comparative example 2
A water-absorbent sheet (12) was obtained in the same manner as in example 1, except that the particulate water-absorbing agent (1) was uniformly dispersed on the entire surface of the nonwoven fabric a without using the stencil paper sheet 1.
Comparative example 3
A water-absorbent sheet (13) was obtained in the same manner as in example 1, except that the nonwoven fabric E was used instead of the nonwoven fabric a 2. As the intermediate nonwoven fabric, nonwoven fabric a was used.
Comparative example 4
A water-absorbent sheet (14) was obtained in the same manner as in example 2, except that the nonwoven fabric E was used instead of the nonwoven fabric a.
The nonwoven fabrics a to C, G used in the present example were all water-permeable sheets.
[ method of measuring physical Properties of nonwoven Fabric ]
The elongation, thickness, bulk density, liquid diffusion area and permeability of the nonwoven fabrics a to C, E and G used in examples 1, 2 to 10 and comparative examples 1 to 4 were measured by the following methods.
[ method for measuring elongation ]
The nonwoven fabric for measuring the elongation was cut into a rectangle having a long side of 100mm and a short side of 30 mm. In this case, the long side is the width direction of the nonwoven fabric roll, and the short side is the winding length direction of the nonwoven fabric roll. In the nonwoven fabric having the dimensions of 100mm in the longitudinal direction (short side) and 400mm in the transverse direction (long side) used for the water-absorbent sheet in this example, the longitudinal direction (short side) was defined as the width direction of the nonwoven fabric roll, and the transverse direction (long side) was defined as the winding length direction of the nonwoven fabric roll. As shown in fig. 17 (a), reference lines were drawn parallel to the short sides at positions 5mm from both ends of the cut nonwoven fabric for measuring the elongation. Each clip was clipped with a double clip (fig. 17 (b)) so as to overlap the reference line. The double-layer clip uses a clip with the length of the claw being more than 30 mm. And (3) a weight is installed on one double-layer cloth clip, and the total weight of the double-layer cloth clip with the weight and the weight is set to be 110 g. And (3) holding the double-layer cloth clip without the weight under the room temperature atmosphere, lifting the weight attached to the other double-layer cloth clip to enable the weight to float in the air, and maintaining the non-woven fabric in the state of elongation due to the weight of the double-layer cloth clip and the weight for 20 seconds. Next, the length of the nonwoven fabric in the longitudinal direction was measured while being kept floating in the air ((c) of fig. 17). From the length of the long side after floating in the air and the length of the long side before floating in the air of 100mm, the elongation is determined as a ratio by using the following equation, with respect to how much the length after floating in the air is elongated.
[ mathematical formula 3]
< measurement of thickness of nonwoven Fabric >
The measurement was carried out using a dial type thickness gauge (thickness measuring instrument) (model J-B, manufactured by Kawasaki, Ltd., measuring head: 50mm in vertical direction of anvil). The number of measurement points was measured 5 times at different sites, and the measured values were averaged at 5 sites. In order to measure the thickness, the hand was slowly removed from the handle so as not to apply pressure to the nonwoven fabric as much as possible, and the thickness was measured.
< method for calculating bulk Density of nonwoven Fabric >
The weight of the nonwoven fabric cut into a size of 10cm or more in the machine direction and 40cm or more in the cross direction was measured. The longitudinal and transverse lengths of the nonwoven fabric and the thickness measured by < thickness measurement > were multiplied, respectively, to calculate the volume of the nonwoven fabric, and the bulk density was calculated by dividing the weight of the nonwoven fabric by the volume of the nonwoven fabric.
< method for measuring liquid diffusion area of nonwoven Fabric >
A30 cm-diameter sieve obtained using a net having a mesh opening of 2mm and a wire diameter of 0.9mm was placed on a flat surface, and a nonwoven fabric (second base material) cut into a 10cm square was placed thereon. A syringe having a bore diameter of 0.50mm was attached to a 1ml syringe, 1.00g of physiological saline containing 20ppm of blue reagent No. 1 was measured, and the physiological saline of the syringe was vertically injected into the center of the nonwoven fabric on the screen. At this time, the mesh of the screen is sufficiently spaced from the plane so that the physiological saline passed through the nonwoven fabric and the mesh does not contact the mesh. When the nonwoven fabric absorbed physiological saline and the liquid was completely diffused, the diffusion area of physiological saline was measured.
< permeability of particulate Water-absorbing agent to nonwoven Fabric >
A non-woven fabric (first base material 11) cut to a diameter of 80mm as shown in FIG. 5 was placed on a JIS standard sieve (The IIDA TESTING SIEVE: 80mm in inner diameter; JIS Z8801-1(2000)) having a mesh opening 32 of 850 μm mesh or a sieve 31 corresponding to The JIS standard sieve, and The periphery was fixed with an adhesive tape 33 (The area through which The pellets were allowed to pass was at least 75mm in diameter). As the nonwoven fabric (first substrate 11), a nonwoven fabric taken out of the water-absorbent sheet by a method described later can be used. 10.0g of particulate water-absorbing agent 14 (weight-average particle diameter: 367 μm, particle size distribution: 6.1% for 850 to 600 μm, 14.5% for 600 to 500 μm, 50% for 500 to 300 μm, 27.6% for 300 to 150 μm, 1.9% for 150 to 45 μm, and 0.1% for 45 μm or less) was put into a nonwoven fabric (first substrate 11) in a sieve 31 (arrow direction in FIG. 5), and the resultant mixture was shaken at room temperature (20 to 25 ℃ C.) and a relative humidity of 50% RH for 5 minutes by using a rotary hammer type shaker (ES-65 type shaker manufactured by Kabushiki Kaisha, rotational speed: 230rpm, impact number: 130 rpm). After shaking, the mass (w (g)) of particulate water-absorbing agent 14 (i.e., particulate water-absorbing agent 14 in portion 31a existing below mesh 32 of screen 31) after passing through mesh 32 of screen 31 of the nonwoven fabric (first substrate 11) and the JIS standard screen was measured, and the transmittance of particulate water-absorbing agent 14 was calculated according to the following formula (i). Note that 2 measurements were performed, and the average value was calculated.
[ mathematical formula 4]
The particulate water-absorbing agent has a permeability (mass%) { W/10.0} × 100 … formula (i)
The particulate water-absorbing agent used for measuring the transmittance is a particulate water-absorbing agent containing 90 wt% or more of a particulate water-absorbing agent having a weight-average particle diameter of 300 to 450 μm and a particle size distribution of 850 to 150 μm. Therefore, the calculated permeability of the particulate water-absorbing agent to the first substrate in this example also corresponds to the permeability of the specific particulate water-absorbing agent to the first substrate.
< method for removing particulate Water-absorbing agent from Water-absorbing sheet >
The particulate water-absorbing agent is taken out by peeling the upper nonwoven fabric and the lower nonwoven fabric from the water-absorbent sheet (when the intermediate nonwoven fabric is included, the intermediate nonwoven fabric and the particulate water-absorbing agent are taken out). The particulate water-absorbing agents attached to the upper and lower nonwoven fabrics and the intermediate nonwoven fabric were also all taken out. When the upper and lower nonwoven fabrics are peeled off, the water-absorbing sheet is cooled to sufficiently weaken the adhesiveness of the adhesive (hot melt adhesive, spray adhesive) to which the nonwoven fabric or the particulate water-absorbing agent is attached, and then peeled off. By performing this step, the fibers of the nonwoven fabric and the structural thickness can be taken out without changing, and the transmittance can be accurately measured. The method of cooling the water-absorbent sheet may be any of various means such as leaving the sheet in a constant temperature bath at-10 ℃ or lower for a certain period of time, spraying cooling mist, and applying liquid nitrogen, and is not particularly limited as long as the cooling is performed under conditions such that the fibers, structure, and thickness of the nonwoven fabric are not changed and the particulate water-absorbent agent contained in the water-absorbent sheet does not absorb moisture.
When the particulate water-absorbing agent taken out is hygroscopic, the water content may be adjusted to 10 mass% or less, preferably 5 ± 2 mass% by drying, and the above-mentioned transmittance and the respective physical properties defined in the present application may be measured. The drying conditions for adjusting the water content are not particularly limited as long as decomposition or modification of the water-absorbent resin (particulate water-absorbing agent) does not occur, and drying under reduced pressure is preferable.
< measurement of particulate Water-absorbing agent content in Upper nonwoven Fabric >
The measurement was carried out on a sample (thickness was not changed) obtained by cutting the upper nonwoven fabric into a square having a length of 10mm and a width of 10mm by using the inch Xio SMX-100CT system of MICRO FOCUS X-ray CT system manufactured by Shimadzu corporation. The measurement conditions are as follows.
[ imaging based on X-ray CT ]
Image lateral dimension (pixel): 512
Image longitudinal dimension (pixel): 512
X-ray tube voltage (kV): 50
X-ray tube current (μ a): 40
English size (inch): 4.0
An X-ray filter: is free of
SDD (distance of focus of X-ray source from X-ray detector) (mm): 700
SRD (distance between focal point of X-ray source and rotation center of measurement sample) (mm): 550
Scanning mode 1: CBCT
Scanning mode 2: conventional scanning
Scanning angle: full scan
Number of visual fields: 2400
Average number: 5
Smoothing: YZ
Slice thickness (mm): 0.166
BHC data: is free of
Fine mode: is provided with
FOV XY (maximum imaging area XY) (mm): 50.3
FOV Z (maximum capture area Z) (mm): 40.0.
next, the X-ray CT imaging data was analyzed using an analysis software Win ROOF manufactured by mitsubishi corporation according to the following procedure.
(1) The Win ROOF is opened and the image to be analyzed (Jpeg) stored in the X-ray CT is selected.
(2) On the screen, the click (selection) is performed in accordance with the flow of the binarization process, the automatic binarization, the modal method, the threshold value (appropriate adjustment), and the operation.
(3) The polygonal ROI was selected to surround the particulate water-absorbing agent in the first substrate (upper nonwoven fabric), and the area of the particulate water-absorbing agent was calculated.
(4) The total area of the particulate water-absorbing agent in the water-absorbent sheet was calculated in the same manner as in (3).
From the calculation result, the content ratio (%) of the particulate water-absorbing agent in the first base material was calculated by the following formula.
The content ratio (%) of the particulate water-absorbing agent in the first base material is ═ particulate water-absorbing agent area (I)/particulate water-absorbing agent total area (II) × 100 in the first base material
That is, the content ratio of the particulate water-absorbing agent in the first base material is expressed by area% of the particulate water-absorbing agent with respect to the total area. The particulate water-absorbing agent is not present on the liquid-absorbing surface of the first base material (the surface on which the liquid to be absorbed by the upper nonwoven fabric is introduced) because it is present at less than several% even if it is. In the following examples, the content of the particulate water-absorbing agent in the first substrate was 5% or more of the particulate water-absorbing agent contained in the entire water-absorbing sheet.
[ evaluation method of Water-absorbing sheet ]
< reverse flow rate (specific Return flow rate evaluation) >
As shown in FIG. 6, a water-absorbent sheet 10 having a vertical dimension of 10cm and a horizontal dimension of 40cm was wrapped with a liquid-impermeable sheet 21 having a vertical dimension of 14cm and a horizontal dimension of 40cm so that an opening portion was formed at the upper portion. The water-absorbent sheet 10 wrapped with the liquid-impermeable sheet 21 is placed on a flat surface, and a liquid-injecting cylinder 41 (fig. 7) is placed thereon at the center of the water-absorbent sheet 10 as shown in fig. 8. In this state, 80g of a 0.9 wt% aqueous sodium chloride solution at 23 ℃ was poured into the liquid injection cylinder 41 using a funnel 42 capable of pouring a liquid at a flow rate of 7 ml/sec (fig. 9). In this case, a liquid is put into the water-absorbent sheet 10 exposed from the liquid-impermeable sheet 21 in the sheet 22. After 10 minutes from the introduction of the liquid, 20 pieces of filter paper 43 (model No.2, manufactured by ADVANTEC; circular filter paper having a diameter of 110 mm) having a weight measured in advance were placed at the center of the sheet 22, that is, at the center of the water-absorbent sheet 10, and a circular weight 44(1200g) having a diameter of 100mm was placed thereon and held for 1 minute. After 1 minute, the weight 44 was removed and the first pour (g) was determined from the weight gain of the filter paper 43. After 1 minute from the removal of the weight 44, the same operation was repeated (liquid addition → filter paper 43 and weight 44(1200g) were carried 10 minutes after addition, hold 1 minute → removal of the weight, and measurement of the flow rate), and the second and third flow rates (g, g) were measured. The total of the first to third measured flow rates is shown in tables 4 and 6.
< method for calculating thickness ratio (Lb/La) >
La is a thickness from the liquid-absorbing surface of the upper nonwoven fabric (liquid-absorbing surface of the first base material) to the surface of the lower nonwoven fabric (second base material) on the water-absorbing layer side in the gap, and Lb is a thickness from the liquid-absorbing surface of the upper nonwoven fabric (liquid-absorbing surface of the first base material) to the surface of the lower nonwoven fabric (second base material) on the water-absorbing layer side in the region including the particulate water-absorbing agent.
[ measurement of thickness of Water-absorbent sheet based on X-ray CT ]
In the imaging of the water-absorbent sheet by X-ray CT, both ends of the water-absorbent sheet cut into 180mm long pieces were fixed to a plastic plate having a length of 350mm, a width of 100mm and a thickness of 3mm by tapes, the plastic plate was set on an inner plate of an X-ray apparatus (instex SMX-100CT, manufactured by shimadzu corporation) so as to be perpendicular to the thickness direction, and the center of the water-absorbent sheet was measured under the following conditions, thereby performing the imaging.
The using device comprises: instexio SMX-100CT (manufactured by Shimadzu corporation)
X-ray tube voltage (kV): 80
X-ray tube current (μ a): 40
English size (inch): 4.0
An X-ray filter: is free of
SOD(mm)：700
SRD(mm)：550
Number of visual fields: 2400
Average number: 5X 1
Slice thickness (mm): 0.166
CT mode 1: CBCT
CT mode 2: general operation
Scanning angle: full scan
BHC data: is free of
Center adjustment: is provided with
Fine mode: is provided with
FOV(XY)(mm)：50.3
FOV(Z)(mm)：20.0
Voxel size (mm/voxel): 0.098
A cross-sectional view obtained by dividing the three-dimensional image obtained by photographing into 203 pieces in the longitudinal direction was obtained, and the thickness of the water-absorbing sheet was measured from the images of the 50 th, 100 th and 150 th sheets. When the thickness is measured, La is the thickness from the liquid-absorbing surface of the upper nonwoven fabric to the surface of the lower nonwoven fabric on the water-absorbing layer side in the gap below the upper nonwoven fabric, and Lb is the thickness from the liquid-absorbing surface of the upper nonwoven fabric to the surface of the lower nonwoven fabric on the water-absorbing layer side in the region containing the particulate water-absorbing agent below the upper nonwoven fabric.
< evaluation of shape Retention >
After the water-absorbent sheet was evaluated for < backflow amount >, the center of the water-absorbent sheet was cut along the width direction, and regions (i.e., gaps) not containing the particulate water-absorbing agent were visually confirmed. At this time, the presence of the substance in the gap was confirmed, and the evaluation was performed according to the following evaluation criteria.
Evaluation criteria
Good: the regions containing the particulate water-absorbing agent are separated by gaps
(i.e., no member is present in the gap or a substrate having a water-absorbing layer is mainly present in the gap (i.e., an upper nonwoven fabric and a lower nonwoven fabric in the case of a single-layer system; an upper nonwoven fabric, an intermediate nonwoven fabric, and a lower nonwoven fabric in the case of a two-layer system))
X: the ratio of the gaps existing is small, and the regions containing the particulate water-absorbing agent arranged in parallel are connected to each other (not separated by the gaps)
(that is, the particulate water-absorbing agent enters a region regarded as a gap, or the proportion of the substrate having the water-absorbing layer present becomes small).
Tables 3 to 6 below show the structures of the water-absorbent sheets produced in examples 1 to 10 and comparative examples 1 to 4, the evaluation results of the physical properties of the substrates used in the respective water-absorbent sheets, and the evaluation results of the water-absorbent sheets. In tables 3 to 6, SAP means a particulate water absorbing agent. In addition, SAP arrangement region (%) in tables 3 and 5 means: the ratio of the area of the region containing the particulate water-absorbing agent to the total area of the base material on which the particulate water-absorbing agent is disposed in the plane direction of the upper nonwoven fabric, and the region (%) in which the SAP is not disposed means: the ratio of the area of the region not containing the particulate water-absorbing agent (i.e., the gap) to the total area of the substrate on which the particulate water-absorbing agent is disposed, in the plane direction of the upper nonwoven fabric. Here, the substrate provided with the particulate water-absorbing agent means: a substrate in which the particulate water-absorbing agent is dispersed. In this embodiment, the upper nonwoven fabric, the middle nonwoven fabric, and the lower nonwoven fabric have the same size.
[ Table 3]
[ Table 4]
[ Table 5]
[ Table 6]
From the above results, the water-absorbent sheets of examples 2 to 10 had higher shape retention property and significantly less amount of reverse flow than the water-absorbent sheets of comparative examples 1 to 4. It can be confirmed that: in the water-absorbent sheets of the single-layer system and the two-layer system, by using the stretchable upper nonwoven fabric and providing the gaps in the water-absorbent layer, the amount of flow backward can be reduced, and the shape retention property is high.
In addition, in the present embodiment, the two-layer system tends to increase the amount of backflow as compared with the single-layer system. It may be one of the reasons that the amount of the particulate water-absorbing agent in the two-layer system with respect to the upper nonwoven fabric (i.e., the amount of the particulate water-absorbing agent located between the upper nonwoven fabric and the intermediate nonwoven fabric) is smaller than the amount of the particulate water-absorbing agent in the single-layer system with respect to the upper nonwoven fabric (i.e., the amount of the particulate water-absorbing agent located between the upper nonwoven fabric and the lower nonwoven fabric). Therefore, it is considered that the difference in the effect of reducing the flow rate between the single-layer system and the two-layer system is difficult to be summarized.
It should be noted that the present application is based on japanese patent application No. 2019-215887 applied on 11/28/2019 and japanese patent application No. 2019-215888 applied on 11/28/2019, the disclosures of which are incorporated by reference in their entirety.
Description of the reference numerals
10 Water-absorbent sheet
11 a first base material,
12 a water absorption layer,
13 a second substrate,
14 a particulate water-absorbing agent,
15 gaps are formed,
16 wrapping sheets,
21 a liquid-impermeable sheet,
31 mesh sieve,
31a part below the screen,
32 meshes of,
33 adhesive tape,
41 liquid injection cylinder,
42 funnel, a,
60 stand, a,
61 tubes,
63 acrylic plates,
64 funnels,
65 metal pallet.
[ second invention ]
Next, a second invention will be explained. The water-absorbent sheet according to a second aspect of the present invention comprises a first base material, a second base material, and a water-absorbent layer disposed between the first base material and the second base material, wherein the water-absorbent layer contains a particulate water-absorbing agent, the region containing the particulate water-absorbing agent is disposed with a space substantially not containing the particulate water-absorbing agent interposed therebetween, a liquid-absorbing surface for directly absorbing liquid is formed on the surface of the first base material, and the elongation of the first base material is 10% or more.
[ filename ] description
[ title ] Water-absorbing sheet and absorbent article including same
Technical Field
The present invention relates to a water-absorbent sheet and an absorbent article including the same.
Background
water-Absorbent resins (SAP/Super Absorbent polymer) are water-swellable, water-insoluble polymer gelling agents and are used for sanitary materials such as paper diapers, sanitary napkins, incontinence products for adults, and the like; soil water-retaining agents for agriculture, forestry and gardening, industrial water-stopping agents and the like.
These absorbent articles are generally manufactured in a diaper manufacturing plant in the form of an absorbent body obtained by mixing a water-absorbent resin with a fibrous material and molding the mixture for each absorbent article, and are processed into absorbent bodies of various shapes (for example, hourglass-shaped, fox-shaped, oval-shaped, and the like in plan view) according to the purpose. These methods for producing an absorbent body can be processed into an arbitrary shape by molding, and the amounts of fibers and water-absorbent resin can be easily adjusted for each absorbent article, and therefore, these methods are the mainstream of paper diapers today.
In recent years, however, in the production of disposable diapers, disposable diapers using an absorbent material obtained by cutting a long water-absorbent sheet in which a water-absorbent resin is fixed between two sheets in a production process of a sanitary material (referred to as a water-absorbent sheet, which is generally cut into a rectangular shape having a width of about 10cm and a length of several 10 cm) have been gradually produced. By purchasing or manufacturing a long continuous water-absorbing sheet, a diaper manufacturer can simplify the manufacturing process of the diaper, and can reduce the size of the diaper by not using pulp. The water-absorbent sheet has a structure in which water-absorbent resin particles are sandwiched and fixed between upper and lower sheets (particularly nonwoven fabric sheets), and is generally incorporated into a disposable diaper (for example, international publication No. 2010/143635) by cutting a long continuous sheet after the production of the long continuous sheet to form a rectangle having a width of about 10cm and a length of 10 cm.
Unlike conventional sanitary materials (disposable diapers), disposable diapers based on water-absorbent sheets have a short history, and development and parameter development of water-absorbent resins suitable for water-absorbent sheets have not been practically performed, and conventional water-absorbent resins for disposable diapers have been used as they are for water-absorbent sheets.
Disclosure of Invention
Problems to be solved by the invention
The present inventors have found that: in the case of a water-absorbent sheet having a thin main stream, the absorbed liquid is likely to occur in the structure, and the pressure is applied to the water-absorbent sheet, thereby discharging the absorbed liquid in the introduction direction of the absorbed liquid, so-called "reverse flow". The "retrograde flow" is also known as Re-wet. And found that: if the liquid is intermittently introduced a plurality of times (particularly 3 times or more) and the amount of liquid introduced increases, the problem of occurrence of reverse flow becomes remarkable. When a reverse flow occurs, the skin contacting the water-absorbent sheet is exposed to a high humidity state due to contact with the liquid in the reverse flow. Therefore, not only the user feels uncomfortable, but also the skin in contact with the water-absorbent sheet is likely to be inflamed.
In addition, in the conventional water-absorbent sheet, the water-absorbent resin particles absorbed are swollen, and therefore, the fixation of the water-absorbent resin particles to the upper and lower sheets is weakened, and the water-absorbent resin particles may move in the sheet. In this way, the water-absorbent resin particles are unevenly distributed in the sheet, and the shape of the water-absorbent sheet is collapsed. In this case, the water-absorbent sheet has a variation in liquid absorbency, which causes leakage. In some cases, the water-absorbent resin particles may fall out from the inside to the outside of the sheet.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a novel water-absorbent sheet which can remarkably reduce the discharge of liquid from the water-absorbent sheet due to a reverse flow even if the liquid is introduced intermittently and a plurality of times (particularly, 3 or more times), and which can maintain a sheet shape (high shape retention property of the sheet) even after the liquid is absorbed.
Means for solving the problems
The present inventors have made extensive studies to solve the above problems. As a result, they found that: the above object can be achieved by a water-absorbent sheet comprising a first base material, a second base material, and a water-absorbent layer located between the first base material and the second base material, wherein the water-absorbent layer comprises a particulate water-absorbing agent, a region containing the particulate water-absorbing agent is disposed with a gap substantially not containing the particulate water-absorbing agent interposed therebetween, a liquid-absorbing surface for directly absorbing liquid is formed on the surface of the first base material, and the elongation of the first base material is 10% or more.
In another aspect of the present invention, the water-absorbent sheet is obtained by laminating only a laminate in which the first substrate is laminated on the water-absorbent layer, on the second substrate in the water-absorbent sheet.
In another aspect of the present invention, the water-absorbent sheet is obtained by laminating a laminate in which the first base material is laminated on the water-absorbent layer and a structure in which an intermediate base material is laminated on the water-absorbent layer, on the second base material in the water-absorbent sheet.
Drawings
Fig. 18 is a schematic view showing a cross section of a water-absorbent sheet according to a first embodiment of the present invention.
Fig. 19 is a schematic view showing a cross section of a water-absorbent sheet according to a second embodiment of the present invention.
FIG. 20 is a schematic view showing a cross section of a water-absorbent sheet for explaining the particulate water-absorbing agent and the form of the gaps in the water-absorbent sheet produced in examples.
FIG. 21 is a schematic view showing a cross section of a water-absorbent sheet for explaining the particulate water-absorbing agent and the form of the gaps in the water-absorbent sheet produced in examples.
Fig. 22 is a schematic diagram illustrating a method for measuring the elongation of the nonwoven fabric.
Fig. 23 is a schematic view for explaining a method of measuring the permeability of the particulate water-absorbing agent to the nonwoven fabric.
Fig. 24 is a plan view and a right side view showing a sample for evaluating a flow-back amount, and is a view showing a state in which a water-absorbent sheet produced in example was wrapped with a liquid-impermeable sheet.
Fig. 25 is a plan view and a front view of a liquid injection cylinder for evaluating a back flow rate.
FIG. 26 is a front view showing a state in which a liquid inlet tube is placed on a water-absorbent sheet used in an example of the present application.
FIG. 27 is a front view showing a case where an aqueous sodium chloride solution was poured into a water-absorbent sheet from a liquid-pouring cylinder using a funnel.
Detailed Description
The present invention will be described below while showing the best mode. The expression in the singular form should be understood to include the concept of the plural form thereof as well as the whole of the present specification unless specifically mentioned. Thus, unless specifically mentioned otherwise, it is to be understood that the singular forms of articles (e.g., "a," "an," "the," etc. in the english case) also include the plural forms of concepts. In addition, unless otherwise specified, terms used in the present specification should be understood to be used in the meaning generally used in the art. Accordingly, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. The present invention is not limited to the embodiments described below, and various modifications can be made within the scope of the claims.
[ 1. definition of terms ]
The definitions of [1-1. water-absorbent sheet ], [1-2. water-absorbent resin ], [1-3. water-absorbing agent, particulate water-absorbing agent ], [1-4. polyacrylic acid (salt) ], [1-5.EDANA and ERT ], [1-6. other ] in the first invention can be similarly applied to the second invention. Therefore, these definitions are omitted herein, but are incorporated by reference into the second invention.
[ 2. Water-absorbent sheet ]
The water-absorbent sheet of the present invention is a water-absorbent sheet comprising a first base material, a second base material, and a water-absorbent layer located between the first base material and the second base material, wherein the water-absorbent layer comprises a particulate water-absorbing agent, a region containing the particulate water-absorbing agent is disposed with a gap substantially not containing the particulate water-absorbing agent, a liquid-absorbing surface for directly absorbing liquid is formed on the surface of the first base material, and the elongation of the first base material is 10% or more.
With this configuration, even if the liquid is introduced intermittently and a large amount of liquid is introduced (particularly, 3 times or more), the discharge of the liquid from the water-absorbent sheet due to the reverse flow can be significantly reduced, and the shape retention after liquid absorption is high. In the water-absorbent sheet of the present invention, the first base material forming the liquid-absorbing surface for directly absorbing liquid has an elongation of 10% or more. That is, the first base material has stretchability. A liquid-absorbing surface for directly absorbing liquid is formed on the surface of the stretchable first base material. Here, in the present specification, the "liquid absorption surface" means: the surface of the substrate on the side where the liquid is absorbed, that is, the surface on the side where the liquid is introduced. In the present specification, "directly" does not include a mode of sequentially absorbing liquids permeated from other substrates and the like. In the present specification, when a cover sheet described later is disposed on the surface of the first base material, the present specification includes a mode in which a liquid-absorbing surface for directly absorbing liquid is formed on the surface of the first base material.
In the first aspect of the present invention, since the surface of the first base material is a liquid-absorbing surface that directly absorbs liquid, the water-absorbing layer is not disposed on the first base material. Accordingly, an absorbent sheet according to one embodiment of the present invention is an absorbent sheet comprising a first substrate, a second substrate, and an absorbent layer located between the first substrate and the second substrate, wherein the absorbent layer comprises a particulate water-absorbing agent, the absorbent layer is not disposed on the first substrate, a region containing the particulate water-absorbing agent is disposed with a gap substantially not containing the particulate water-absorbing agent, and the elongation of the first substrate is 10% or more. In this embodiment, even if a part of the particulate water-absorbing agent contained in the water-absorbing layer passes through the first base material and moves on the first base material to expose a part, the water-absorbing layer is not regarded as being disposed. The reason for this movement is assumed to be, for example, vibration generated when the water-absorbent sheet is transported or conveyed as a final product. The case where the particulate water-absorbing agent is intentionally dispersed or disposed on the first base material does not fall within the scope of the present embodiment.
The present inventors have found that: in the conventional water-absorbent sheet (for example, a water-absorbent sheet in which guide grooves (corresponding to gaps) are provided in a water-absorbing layer located between a first substrate and a second substrate, as in the water-absorbent sheet described in japanese patent application laid-open No. 105380752), even when the amount of backflow can be reduced in the measurement of the amount of backflow under specific conditions in the examples of the present application (also referred to as "specific backflow amount evaluation" in the present specification), the shape retention property is poor.
Here, when liquid is introduced, the gap existing between the regions including the particulate water-absorbing agent functions as a liquid passage when liquid is introduced from the first base material to the water-absorbent layer. That is, the presence of the liquid passage enables the liquid introduced from the liquid absorbing surface to be efficiently sent to the water absorbing layer in the lower layer that performs the water absorbing function without being retained on the liquid absorbing surface (and further, without being locally retained by the introduced liquid). Specifically, the liquid (e.g., urine) passing through the first base material is introduced into the entire surface and gaps of the water-absorbent layer. The liquid introduced into the gap does not interfere with the particulate water-absorbing agent in the region including the particulate water-absorbing agent, and the liquid is easily diffused because the absorption by the particulate water-absorbing agent is also reduced. As a result of the liquid diffusion, the liquid absorption amount of the particulate water-absorbing agent at the portion where the liquid is introduced is prevented from being varied such that the liquid absorption amount of the particulate water-absorbing agent at the portion distant from the liquid introduction portion is increased and the liquid absorption amount is reduced. Therefore, the following effects can be prevented: the particulate water-absorbing agent has an effect of causing a site of saturated swelling, in other words, a site of non-absorption of liquid, and an increase in the amount of backflow. It can thus be considered that: as a result, the reverse flow rate can be reduced.
However, for example, when the particulate water-absorbing agent absorbs liquid and swells, the volume of the region including the particulate water-absorbing agent increases, and therefore, the swollen particulate water-absorbing agent enters a region regarded as a gap, and the gap decreases. In this case, it can be considered that: when the liquid is intermittently introduced a plurality of times, the liquid absorption capacity gradually decreases due to the decrease in the gap. Further, when the liquid is discharged from the water-absorbent layer, the liquid is less likely to pass through the gaps as the gaps decrease, and a part of the particulate water-absorbing agent is likely to swell to saturation, so that the amount of the liquid flowing back to the liquid-absorbing surface of the first base material gradually increases. This causes the backflow of liquid to rise to (come into contact with) the skin, thereby causing discomfort.
In addition, in the conventional water-absorbent sheet having a gap in the water-absorbent layer (for example, the water-absorbent sheet disclosed in japanese patent application laid-open No. 105380752), the particulate water-absorbing agent is less fixed to the first base material and/or the second base material due to swelling of the particulate water-absorbing agent, and the particulate water-absorbing agent may move in the water-absorbent layer. In this way, the particulate water-absorbing agent tends to be unevenly distributed in the water-absorbing layer, and the shape of the water-absorbing sheet is collapsed (shape retention property is lowered).
In contrast, it can be considered that: the water-absorbent sheet of the present invention can absorb an increase in volume of the region containing the particulate water-absorbing agent by imparting stretchability to the first substrate. That is, when the particulate water-absorbing agent swells, the first base material is stretched by the swelling, and therefore, the reduction of the gap can be suppressed, and the shape of the gap can be maintained. Thus, even if the liquid is intermittently introduced a plurality of times, the diffusing capacity of the liquid is not reduced, and the pouring amount can be reduced. Further, since swelling of the particulate water-absorbing agent is buffered by causing the first base material to expand and contract, the fixation of the particulate water-absorbing agent to the first base material and/or the second base material is not weakened. Specifically, the first substrate in contact with the particulate water-absorbing agent is elongated to follow the shape of the swollen particulate water-absorbing agent due to swelling of the particulate water-absorbing agent. Thereby, the first substrate and the particulate water-absorbing agent become intertwined, and the particulate water-absorbing agent is more firmly held between the first substrate and the second substrate. Therefore, the water-absorbent sheet of the present invention can suppress the movement of the region containing the particulate water-absorbing agent in the self-absorbent layer of the particulate water-absorbing agent, and can maintain the shape of the water-absorbent sheet, and therefore has high shape retention. In the embodiment of the present invention, the effect of reducing the backflow of the single-layer water-absorbent sheet is greater in the multi-layer water-absorbent sheet (two-layer water-absorbent sheet) and the single-layer water-absorbent sheet. The multilayer type (two-layer type) water-absorbent sheet is obtained by laminating a laminate in which a first substrate is laminated on a water-absorbing layer and a structure in which an intermediate substrate is laminated on the water-absorbing layer, on a second substrate (with the water-absorbing layer on the second substrate side), and the single-layer type water-absorbent sheet is obtained by laminating only 1 layer of the laminate in which the first substrate is laminated on the water-absorbing layer. The reason for this is not clear, in other words, it can be said that this is an effect unexpected to those skilled in the art.
In the water-absorbent sheet, the water-absorbing function in the water-absorbing layer is mainly carried by the water-absorbing agent (particulate water-absorbing agent). In particular, in a water-absorbent sheet having a structure different from that of a conventional absorbent article in which pulp exists in the water-absorbent layer, the role of the water-absorbing agent becomes more important. In particular, in the present invention, since the first base material has stretchability, the shape of the gap provided between the regions including the particulate water-absorbing agent in the water-absorbent layer can be maintained, and it is difficult for the liquid once introduced into the water-absorbing agent to flow back to the liquid-absorbing surface of the first base material. Therefore, the shape of the water-absorbent sheet can be maintained (i.e., the shape retention property is high), and the "specific reflux amount evaluation" can be made excellent. Incidentally, a water-absorbent sheet or an absorbent article designed to suppress the amount of reflux under normal conditions does not necessarily exhibit excellent results in the "evaluation of specific amount of reflux" in the present application. The water-absorbent sheet according to one embodiment of the present invention is suitable as an absorbent article (e.g., diaper) used in a time zone where an infant who starts learning to walk and has a small bladder moves around during the day, for example, but the use mode is not limited thereto. The mechanism and the like described in the present specification do not limit the technical scope of the claims of the present application.
Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description thereof is omitted. In addition, the dimensional ratio of the drawings is exaggerated for convenience of explanation and may be different from the actual ratio.
The water-absorbent sheet according to the first embodiment of the present invention is obtained by laminating only a laminate in which a first substrate is laminated on a water-absorbent layer on a second substrate. That is, in the first embodiment, the water-absorbing layer is sandwiched between the first base material and the second base material. The first embodiment will be described with reference to fig. 18.
Fig. 18 is a schematic view showing a cross section of a water-absorbent sheet 10 according to a first embodiment of the present invention. Fig. 18 shows 3 modes ((a) to (c)) of the water-absorbent sheet 10. In fig. 18 (a) to (c), arrows indicate the direction in which the liquid to be absorbed is introduced. The first substrate 11 is located on the side where the liquid to be absorbed (absorbed liquid) is introduced with respect to the water-absorbent layer 12. That is, the first base material is disposed on the liquid discharge side (for example, the skin side in a diaper). A water-absorbing layer 12 is disposed between a first substrate 11 and a second substrate 13. That is, the laminated body 18 in which the first base material 11 is laminated on the water-absorbent layer 12 is laminated on the second base material 13.
In fig. 18 (a) to (c), water-absorbing layer 12 contains particulate water-absorbing agent 14. In the embodiments (a) to (c) of fig. 18, the water-absorbing layer 12 is shown in a state where the particulate water-absorbing agent 14 is present between the first substrate 11 and the second substrate 13. A part of the particulate water-absorbing agent 14 may be detached from each of the substrates 11, 13. The particulate water-absorbing agent 14 (region including the particulate water-absorbing agent 14) is disposed with a gap 15 substantially not including the particulate water-absorbing agent 14 interposed therebetween. Therefore, the water-absorbent "layer" does not mean a continuous body such as a sheet, and may be any as long as it is present between the first base material 11 and the second base material 13 with a constant thickness and length. For example, the water-absorbent layer 12 may be intermittently present between the first substrate 11 and the second substrate 13 with a certain thickness and length. When the particulate water-absorbing agent 14 is fixed to the substrate 11 and/or the substrate 13, an adhesive may be used, for example. A method for producing a water-absorbent sheet using an adhesive is described in detail in [ 3 ].
Here, although the gap 15 is formed between the first base material 11 and the second base material 13 in fig. 18 (a), the gap 15 in the present invention includes the embodiments of fig. 18 (b) and 18 (c). In fig. 18 (b), the regions containing particulate water-absorbing agent 14 are separated by the contact of first substrate 11 with second substrate 13. The first substrate and the second substrate are in contact, but maintain a liquid passage, and thus are viewed as a gap. Further, the water-absorbent layer 12 is separated due to the first base material 11 (the first base material 11 and the second base material 13 as the case may be) entering the water-absorbent layer 12, and therefore, in this mode, the water-absorbent layer 12 exists intermittently. In fig. 18 (c), the end of the water-absorbent sheet 10 is closed by the first base material 11 and the second base material 13 by overlapping the end of the first base material 11 with the end of the second base material 13. In this case, the first base material 11 (the first base material 11 and the second base material 13 in some cases) enters the end of the water-absorbing layer 12, and the water-absorbing layer 12 is not present at the end of the water-absorbing layer 12. The embodiments of the water-absorbing layer 12 and the gap 15 can be similarly applied to the second embodiment described later.
Within first substrate 11, particulate water-absorbing agent 14 may be present. Particulate water-absorbing agent 14 in first substrate 11 may be, for example, particulate water-absorbing agent 14 that is in contact with (or fixed to) first substrate 11, or particulate water-absorbing agent 14 that is in contact with (or fixed to) second substrate 13, is detached and trapped in first substrate 11. When the particulate water-absorbing agent 14 is present in the first substrate 11, the content of the particulate water-absorbing agent 14 in the first substrate 11 is preferably 5% or more, more preferably 10% or more, further preferably 20% or more, and still further preferably 30% or more, with respect to the particulate water-absorbing agent 14 contained in the entire water-absorbent sheet 10. The upper limit is not particularly limited, and the order is preferably 90% or less, 70% or less, and 50% or less. In this specification, the content ratio of the particulate water-absorbing agent 14 in the first substrate 11 to the particulate water-absorbing agent 14 contained in the entire water-absorbent sheet 10 is calculated by the method of the example described later.
Since the particulate water-absorbing agent 14 is not scattered and arranged in the region of the gap 15, the region of the gap 15 does not substantially contain the particulate water-absorbing agent 14. Additives and the like other than particulate water-absorbing agent 14 may be contained in the region of this gap 15. For example, the gap 15 may be formed by the first substrate 11 being in direct contact with the second substrate 13 or being in contact with an adhesive. Since the first substrate 11 has stretchability, when a region including the particulate water-absorbing agent 14 is present on the second substrate 13, the first substrate 11 stretches and contracts following the region including the particulate water-absorbing agent 14. Therefore, the first substrate 11 has a shape covering the region including the particulate water-absorbing agent 14 in the region including the particulate water-absorbing agent 14, and has a shape recessed toward the second substrate 13 along the upper side of the region including the particulate water-absorbing agent 14 in the gap 15.
In the water-absorbent sheet according to the first embodiment of the present invention, the ratio (Lb/La) of the thickness (Lb) from the liquid-absorbing surface of the first base material 11 to the surface of the second base material 13 on the water-absorbing layer side in the region including the particulate water-absorbing agent 14 to the thickness (La) from the liquid-absorbing surface of the first base material 11 to the surface of the second base material on the water-absorbing layer 12 side in the gap 15 is preferably 1.05 or less. The first substrate 11 has stretchability, and therefore, the portion of the first substrate 11 that is in contact with the particulate water-absorbing agent 14 takes on a shape that follows (i.e., follows and stretches) the shape of the region containing the particulate water-absorbing agent 14 (i.e., the shape of the particulate water-absorbing agent 14 on the side that is in contact with the first substrate 11, of the particulate water-absorbing agent 14 that is in contact with the first substrate). Therefore, the first substrate 11 can be in close contact with the particulate water-absorbing agent 14 (the region including the particulate water-absorbing agent 14), and thus the first substrate 11 and the particulate water-absorbing agent 14 (the region including the particulate water-absorbing agent 14) are integrated. In this case, since the difference between the thickness of La and the thickness of Lb is small, Lb/La is 1.05 or less. In this case, the shape of the region including the particulate water-absorbing agent 14 has high shape retention. Therefore, even after the particulate water-absorbing agent 14 swells, the gap 15 can be maintained highly, and backflow can be further reduced. In general, Lb/La is 1 or more.
In the water-absorbent sheet 10, the gap 15 is formed by providing a region where the particulate water-absorbing agent 14 is not present on a part of the second substrate 13. The gap 15 (i.e., the region where the particulate water-absorbing agent 14 is not present) can further function as a liquid passage by being provided continuously along one direction of the liquid-absorbing surface of the first base material 11. The shape of the continuous gap 15 may be, for example, a straight line, a curved line, or a wavy line, and it is preferable that the gaps 15 be arranged in parallel in a straight line. Therefore, in the water-absorbent sheet 10, the region including the particulate water-absorbing agent 14 and the gap 15 have a shape extending along one direction (a plane direction perpendicular to the liquid absorption direction) of the liquid-absorbing surface of the first base material 11, and are preferably arranged in parallel. That is, the region containing the particulate water-absorbing agent 14 is in a state of being arranged in a stripe shape (vertical stripe shape). Thus, the gap 15 is also formed in a vertical stripe shape, and therefore, even when the particulate water-absorbing agent 14 swells, the gap 15 is easily maintained, and as a result, the backflow can be further reduced. Here, the "one direction" may be any direction other than the thickness direction, which is parallel to the surface direction in the liquid-absorbing surface of the first base material 11, that is, any of the longitudinal direction, the width direction, or the direction inclined with respect to these directions in the liquid-absorbing surface of the first base material 11. From the viewpoint of balancing the function of the gap 15 and the function of the particulate water-absorbing agent 14, in the water-absorbent sheet 10, the region including the particulate water-absorbing agent 14 and the gap 15 preferably have a shape extending along the longitudinal direction of the liquid-absorbing surface of the first base material 11 and are arranged in parallel.
In the surface of the first substrate 11 on the water-absorbing layer 12 side (the surface on which the particulate water-absorbing agent 14 is disposed), the ratio of the region including the particulate water-absorbing agent 14 (hereinafter also referred to as "the ratio of the region where the particulate water-absorbing agent 14 is present") is preferably 90% or less, more preferably 80% or less, and still more preferably 75% or less in terms of area. The ratio of the region including the particulate water-absorbing agent 14 in the surface of the first substrate 11 on the water-absorbent layer 12 side is preferably 10% or more, and more preferably 20% or more, by area. By providing the particulate water-absorbing agent 14 in such a range, the balance between the action of the gap 15 and the action of the particulate water-absorbing agent 14 becomes appropriate, and the effect of reducing the amount of backflow is further exerted. The ratio of the region including the particulate water-absorbing agent 14 on the surface of the first substrate 11 on the water-absorbing layer 12 side is the same as the ratio of the region including the particulate water-absorbing agent 14 on the surface of the second substrate 13 on the water-absorbing layer 12 side (the surface on which the particulate water-absorbing agent 14 is disposed).
Here, the ratio of the region containing particulate water-absorbing agent 14 in the surface of first substrate 11 on the water-absorbing layer 12 side can be controlled by adjusting the scattering region of particulate water-absorbing agent 14 at the time of manufacturing water-absorbing sheet 10.
Further, the ratio of the region including the particulate water-absorbing agent 14 in the surface of the first base material 11 on the water-absorbing layer 12 side can be calculated by imaging and analyzing the cross section obtained by cutting the produced water-absorbing sheet 10 with, for example, an X-ray CT apparatus (instexio SMX-100 CT). Specifically, the ratio of the region including the particulate water-absorbing agent 14 can be calculated by imaging the cross section of the water-absorbent sheet 10, classifying the interface between the first substrate 11 or the second substrate 13 and the water-absorbent layer 12 into a region where the particulate water-absorbing agent 14 is present and a region where the particulate water-absorbing agent 14 is not present, summing the regions, and calculating the ratio thereof. Note that the ratio of the region including the particulate water-absorbing agent 14 was calculated by taking 3 or more images of a cross section of the water-absorbent sheet 10 in the short side direction, and the ratio of the region including the particulate water-absorbing agent 14 obtained from each cross section was averaged, and the average value was defined as "the ratio of the region including the particulate water-absorbing agent 14".
The content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 10 is preferably 200 to 360g/m2More preferably 250 to 350g/m2More preferably 300 to 325g/m2。
The water-absorbent sheet 10 has a cover sheet 16. The cover sheet 16 has the following purpose: the object of maintaining the shape of the water-absorbent sheet 10, which is a structure in which the particulate water-absorbing agent 14 is carried between the first substrate 11 and the second substrate 13; the purpose is to prevent the particulate water-absorbing agent 14 carried between the first base material 11 and the second base material 13 from falling (falling) off the absorbent body (water-absorbing sheet 10); the particulate water-absorbing agent 14 is not brought into direct contact with the skin when the particulate water-absorbing agent 14 is transferred to the outer surface (surface directly contacting the liquid) of the first substrate 11 through the first substrate 11. Without the cover sheet 16, there are, for example, the following methods: a method of sealing (closing) by bonding the respective substrates 11 and 13 to each other; a method of suppressing transfer to the outer surface of the first substrate 11 by surface treatment of the first substrate 11, and the like. As a method for preventing the particulate water-absorbing agent 14 from falling off the water-absorbent sheet 10 while maintaining the effects of the present application, it is preferable to have a covering sheet 16.
The cover sheet 16 is disposed on the first base material 11 and folded so as to cover the entire water-absorbent layer 12 and the second base material 13. Thus, the cover sheet 16 covers the entirety of the first base material 11, the water-absorbent layer 12, and the second base material 13. With such a configuration, it is possible to suppress the particulate water-absorbing agent 14 from falling off from the water-absorbent sheet 10. The cover sheet 16 does not necessarily cover the entire first base material 11, the water-absorbing layer 12, and the second base material 13. For example, the cover sheet 16 may be disposed on the first base material 11, folded so as to include a side surface of the water-absorbing layer 12 and a side surface of the second base material 13, and folded toward a surface of the second base material 13 opposite to the surface on which the water-absorbing layer 12 is provided (i.e., the surface on which the water-absorbing layer 12 is provided). That is, with respect to the cover sheet 16, one end of the cover sheet 16 overlaps the other end of the cover sheet 16 on the surface of the second base 13 opposite to the surface on which the water-absorbing layer 12 is provided. In this case, the cover sheet 16 covers the side surfaces of the first base material 11, the water-absorbing layer 12, and the second base material 13, and covers the entire surface or a part of the surface of the second base material 13 opposite to the surface on which the water-absorbing layer 12 is provided. For example, the cover sheet 16 may be disposed on the first base material 11, bent so as to wrap the side surface of the water-absorbing layer 12 and the side surface of the second base material 13, and one end of the cover sheet 16 and the other end of the cover sheet 16 may be disposed separately on the surface of the second base material 13 opposite to the absorbing surface (i.e., the surface on which the water-absorbing layer 12 is provided). In this case, the cover sheet 16 covers the liquid-absorbing surface and the side surface of the first base material 11, the side surface of the water-absorbing layer 12, and the side surface of the second base material 13, and covers a part of the surface of the second base material 13 opposite to the surface on which the water-absorbing layer 12 is provided. In the water-absorbent sheet according to the present invention, the covering sheet 16 is not essential, and the water-absorbent sheet 10 according to the present invention is provided with the covering sheet 16 in such a configuration, whereby the particulate water-absorbing agent 14 can be prevented from falling off from the water-absorbent sheet 10.
Therefore, the water-absorbent sheet 10 according to the first embodiment of the present invention preferably has the cover sheet 16 disposed at least on the surface of the first base material 11 (i.e., on the surface of the first base material 11 on the liquid-absorbing surface). In the present description, the first base material 11 also forms the liquid-absorbing surface that directly absorbs liquid when the cover sheet 16 is provided as described above, but for example, in the case where the cover sheet 16 forms the liquid-absorbing surface that directly absorbs liquid in the water-absorbent sheet 10 having the cover sheet 16, the following can be said to be the case: a water-absorbent sheet comprising a first base material, a second base material, a water-absorbent layer disposed between the first base material and the second base material, and a cover sheet disposed on the surface of the first base material, wherein the water-absorbent layer comprises a particulate water-absorbing agent, a region containing the particulate water-absorbing agent is disposed with a gap substantially not containing the particulate water-absorbing agent interposed therebetween, the surface of the cover sheet forms a liquid-absorbing surface for directly absorbing liquid, and the elongation of the first base material is 10% or more.
As a method for fixing the cover sheet 16 to the respective substrates 11 and 13, for example, an adhesive may be used.
In the water-absorbent sheet 10 according to the first embodiment of the present invention, the first substrate 11 is preferably in direct contact with or in contact with the particulate water-absorbing agent 14 in the water-absorbent layer 12 via an adhesive, and/or the second substrate 13 is preferably in direct contact with or in contact with the particulate water-absorbing agent 14 in the water-absorbent layer 12 via an adhesive. As described above, the water-absorbent sheet of the present invention has a simple structure substantially containing only the following substances: the particulate water-absorbing agent may be composed of a first base material, a second base material, a particulate water-absorbing agent sandwiched between the first base material and the second base material, an adhesive for fixing the particulate water-absorbing agent to at least one of the first base material and the second base material, and a wrapping sheet for wrapping a part or all of them as necessary (the case where the particulate water-absorbing agent includes the additives described in the present specification and the like which may be included in the particulate water-absorbing agent is not excluded). More preferably, the present invention is a simple configuration including only the following components: the particulate water-absorbing agent-containing sheet includes a first base material, a second base material, a particulate water-absorbing agent sandwiched between the first base material and the second base material, an adhesive for fixing the particulate water-absorbing agent to the second base material between the particulate water-absorbing agent and the second base material, and a cover sheet for covering all of them. That is, the water-absorbent sheet of the present invention can effectively reduce the specific amount of reflux despite its simple configuration.
A water-absorbent sheet according to a second embodiment of the present invention is obtained by laminating a laminate in which a first substrate is laminated on a water-absorbent layer a and a structure in which an intermediate substrate is laminated on a water-absorbent layer B (with the water-absorbent layer on the second substrate side). Hereinafter, a second embodiment will be described with reference to fig. 19, and technical features that can be applied to the second embodiment are omitted. Fig. 19 is a schematic cross-sectional view of a water-absorbent sheet 20 according to a second embodiment of the present invention.
As shown in fig. 19, the water-absorbent sheet 20 is formed by stacking a first base material 11a, a water-absorbent layer 12a (water-absorbent layer a), an intermediate base material 11B, and a water-absorbent layer 12B (water-absorbent layer B) on a second base material 13 in this order from the introduction direction of the liquid to be absorbed (the direction of the arrow in fig. 19). That is, the water-absorbent sheet 20 is formed by laminating a laminate 18a in which the first base material 11a is laminated on the water-absorbent layer 12a and a structure 18b in which the intermediate base material 11b is laminated on the water-absorbent layer 12b on the second base material 13 such that the water- absorbent layers 12a and 12b are positioned on the second base material 13 side, on the second base material 13. Hereinafter, the particulate water-absorbing agent 14 in the laminate 18a is referred to as particulate water-absorbing agent 14a, the gap 15 is referred to as gap 15a, the particulate water-absorbing agent 14 in the construct 18b is referred to as particulate water-absorbing agent 14b, and the gap 15 is referred to as gap 15 b. The first base material 11a in the second embodiment is the same as the first base material 11 in the first embodiment, and therefore, may be abbreviated as the first base material 11. Further, particulate water-absorbing agent 14a and gap 15a in the second embodiment may also be simply referred to as particulate water-absorbing agent 14 and gap 15.
The water-absorbing layers 12a, 12b are composed of particulate water-absorbing agents 14a, 14b, respectively, as in the first embodiment. Specifically, water-absorbent layer 12a is composed of particulate water-absorbing agent 14a fixed to first substrate 11a and particulate water-absorbing agent 14a fixed to intermediate substrate 11b, and water-absorbent layer 12b is composed of particulate water-absorbing agent 14b fixed to intermediate substrate 11b and particulate water-absorbing agent 14b fixed to second substrate 13. In the water- absorbent layers 12a, 12b, regions including the particulate water-absorbing agents 14a, 14b are disposed so as to be separated by gaps 15a, 15b, respectively.
In the water-absorbent sheet 20, the gaps 15a, 15b (regions where the particulate water-absorbing agent 14 is not present) provided in the intermediate substrate 11b and in a portion of the second substrate 13 are preferably in the same manner as in the water-absorbent sheet 10 according to the first embodiment. That is, the regions including the particulate water-absorbing agents 14a, 14b and the gaps 15a, 15b are preferably elongated in one direction along the liquid-absorbing surface of the first base material, and are arranged in parallel.
In fig. 19, the region containing the particulate water-absorbing agent 14a in the laminate 18a and the region containing the particulate water-absorbing agent 14b in the construct 18b are arranged to have the same thickness and width so as to overlap in the plane direction of the first base material 11a (i.e., so as to be at the same position in the first base material 11a in the direction perpendicular to the liquid-absorbing surface), but the positional relationship, and the relationship between the thickness and the width are not limited thereto. For example, the region containing the particulate water-absorbing agent 14a in the layered body 18a and the region containing the particulate water-absorbing agent 14b in the construct 18b may be arranged at a position so as not to overlap in the plane direction. Further, the region containing the particulate water-absorbing agent 14a in the layered body 18a may be wider or narrower in width, or thicker or thinner, than the region containing the particulate water-absorbing agent 14b in the constituent body 18 b.
Particulate water-absorbing agents 14a, 14b may be present in the first base material 11a and the intermediate base material 11 b. For example, particulate water-absorbing agent 14a may be present in first base material 11a, particulate water-absorbing agent 14a may be present in intermediate base material 11b on the surface of the liquid-absorbing surface side of intermediate base material 11b, and particulate water-absorbing agent 14b may be present on the surface of intermediate base material 11b on the second base material 13 side.
In the water-absorbent sheet 20 according to the second embodiment of the present invention, the first substrate 11, the water-absorbent layer 12, the particulate water-absorbing agent 14, and the gaps 15 of the first embodiment may be referred to as a first substrate 11a, a water-absorbent layer 12b, a particulate water-absorbing agent 14a, and gaps 15a of the laminate 18a disposed on the liquid introduction side;
(1) content ratio of particulate water-absorbing agent 14 in first substrate 11
(2) A ratio (Lb/La) of a thickness (Lb) from the liquid-absorbing surface of the first base material 11 to the surface of the second base material 13 on the water-absorbing layer 12 side in a region including the particulate water-absorbing agent 14 to a thickness (La) from the liquid-absorbing surface of the first base material 11 to the surface of the second base material 13 on the water-absorbing layer 12 side in the gap 15.
In the two-layer system (2), the regions including the particulate water-absorbing agents 14a and 14b of the layered body 18a and the constituent 18b and the gaps 15a and 15b may be formed so as not to overlap in the surface direction of the first substrate 11 a. In this case, "gap 15" in "gap 15" to be the La reference means gap 15a close to the liquid-absorbing surface of the first base material 11a (i.e., in the laminated body 11 a), and "a region including the particulate water-absorbing agent 14" in "a region including the particulate water-absorbing agent 14" to be the Lb reference means a region including the particulate water-absorbing agent 14a close to the liquid-absorbing surface of the first base material 11a (i.e., in the laminated body 11 a).
That is, in the water-absorbent sheet 20 according to the second embodiment of the present invention, when the particulate water-absorbing agent 14 is present in the first substrate 11a, the content ratio of the particulate water-absorbing agent 14 in the first substrate 11a is preferably 5% or more with respect to the particulate water-absorbing agent 14 contained in the entire water-absorbent sheet 20.
In the water-absorbent sheet 20 according to the second embodiment of the present invention, the ratio (Lb/La) of the thickness (Lb) from the liquid-absorbing surface of the first base material 11a to the surface of the second base material 13 on the water-absorbing layer 12b side in the region including the particulate water-absorbing agent 14a to the thickness (La) from the liquid-absorbing surface of the first base material 11a to the surface of the second base material 13 on the water-absorbing layer 12b side is preferably 1.05 or less. In the water-absorbent sheet 20, the preferable ranges of the water-absorbent sheet 10 described in the first embodiment can be similarly applied to the content ratio Lb/La of the particulate water-absorbing agent 14a in the first substrate 11 a.
The water-absorbent sheet 20 has a covering sheet 16. The cover sheet 16 is disposed on the first base material 11a, and is folded so as to cover the entire laminated body 18a, the structure 18b, and the second base material 13. Therefore, the water-absorbent sheet 20 according to the second embodiment of the present invention preferably has the covering sheet 16 disposed at least on the surface of the first base material 11a (i.e., the liquid-suction surface of the first base material).
In the present specification, the following can be said to be replaced: a water-absorbent sheet comprising a first base material, an intermediate base material, a second base material, a water-absorbent layer, and a cover sheet, wherein a laminate in which the first base material is laminated on the water-absorbent layer and the intermediate base material is laminated on the water-absorbent layer, and a structure are laminated on the second base material, wherein the water-absorbent layer is positioned on the second base material side, the cover sheet is disposed on the surface of the first base material, the water-absorbent layer contains a particulate water-absorbing agent, a region containing the particulate water-absorbing agent is disposed with a gap substantially not containing the particulate water-absorbing agent interposed therebetween, the surface of the cover sheet forms a liquid-absorbing surface that directly absorbs liquid, and the elongation of the first base material is 10% or more.
In the water-absorbent sheet 20 according to the second embodiment of the present invention, it is preferable that the first substrate 11a is in direct contact with or in contact with the particulate water-absorbing agent 14a in the water-absorbent layer 12a via an adhesive, it is preferable that the intermediate substrate 11b is in direct contact with or in contact with the particulate water-absorbing agent 14b in the water-absorbent layer 12b via an adhesive, and/or it is preferable that the second substrate 13 is in direct contact with or in contact with the particulate water-absorbing agent 14b in the water-absorbent layer 12b via an adhesive.
In the water-absorbent sheet 20 according to the second embodiment, the ratio of the region including the particulate water-absorbing agent 14a on the surface of the first substrate 11a on the water-absorbent layer 12a side (surface on which the particulate water-absorbing agent 14a is disposed) and the ratio of the region including the particulate water-absorbing agent 14b on the water-absorbent layer 12b side (surface on which the particulate water-absorbing agent 14b is disposed) of the intermediate substrate 11b are preferably 90% or less, more preferably 80% or less, and still more preferably 75% or less by area. The ratio of the region including the particulate water-absorbing agent 14a in the surface of the first substrate 11a on the water-absorbing layer 12a side and the ratio of the region including the particulate water-absorbing agent 14b in the water-absorbing layer 12b side of the intermediate substrate 11b are preferably 10% or more, and more preferably 20% or more in terms of area. By providing particulate water-absorbing agents 14a, 14b in such a range, the balance between the action of gaps 15a, 15b and the action of particulate water-absorbing agents 14a, 14b becomes appropriate, and the effect of reducing the amount of backflow is further exerted. The ratio of the region including the particulate water-absorbing agent 14a in the surface on the water-absorbing layer 12a side of the first substrate 11a is the same as the ratio of the region including the particulate water-absorbing agent 14a in the surface on the water-absorbing layer 12a side of the intermediate substrate 11b (the surface on which the particulate water-absorbing agent 14a is disposed), and the ratio of the region including the particulate water-absorbing agent 14b in the water-absorbing layer 12b of the intermediate substrate 11b is the same as the ratio of the region including the particulate water-absorbing agent 14b in the water-absorbing layer 12b of the second substrate 13 (the surface on which the particulate water-absorbing agent 14b is disposed).
In the water-absorbent sheet 20, the ratio of the existing region of the particulate water-absorbing agents 14a and 14b in the first substrate 11 or the second substrate 13 can be calculated in the same manner as in the water-absorbent sheet 10.
Here, the content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 20 is preferably 200 to 360g/m2More preferably 210 to 350g/m2More preferably 225 to 325g/m2. In the water-absorbent sheet 20, the total amount of the particulate water-absorbing agents 14a and 12b present in the water-absorbing layers 12a and 12b may be adjusted so as to fall within the above range, and it is preferable that: the amount of the particulate water-absorbing agents 14a, 12b present in the water-absorbing layers 12a, 12b is preferably 2:1 to 1:2, more preferably 1.5:1 to 1: 1.5.
In the water- absorbent sheets 10 and 20 according to the first and second embodiments of the present invention, according to one embodiment, the first base material 11 can be in a bulky form (a form in which the bulk density is low and the thickness is remarkably large), but can be made thinner than an absorbent body used in a conventional absorbent article. When the water- absorbent sheets 10 and 20 are used in a disposable diaper, the thickness thereof is preferably 15mm or less, more preferably 10mm or less, still more preferably 7mm or less, particularly preferably 5mm or less, and most preferably 4mm or less, for example, at 40% RH to 50% RH. On the other hand, in view of the strength of the water- absorbent sheets 10 and 20 and the diameter of the particulate water-absorbing agent 14, the lower limit of the thickness is preferably 0.2mm or more, more preferably 0.3mm or more, and still more preferably 0.5mm or more. The water- absorbent sheets 10 and 20 used in the examples of the present application have a thickness of 2 to 5 mm.
In the present application, the thicknesses of the first base material 11, the intermediate base material 11B, the second base material 13, the cover sheet 16, and the water- absorbent sheets 10 and 20 were measured by using a dial thickness gauge (thickness measuring instrument) (model No. J-B, manufactured by Kawasaki, Ltd., measuring head: anvil, vertical phi 50 mm). The number of measurement points was determined by selecting 5 sites from different sites in the slice to be measured, measuring each site 2 times, and setting the measurement value as an average value of 5 sites in total. In the measurement of the thickness, the hand is slowly moved away from the handle so as not to apply pressure to the sheet to be measured as much as possible, and the thickness is measured. As a specific procedure, a sheet to be measured is flatly stuck to a plate having a constant thickness so as not to cause wrinkles or strain in a measurement portion of the sheet, and the plate is set on a lower measurement head of a thickness measurement instrument. Then, the upper measuring head of the thickness measuring instrument is moved close to a height position of 2 to 3mm from the sheet to be measured, and then the hand is slowly moved away from the handle to measure the total thickness of the sheet to be measured and the plate. The thickness of the sheet to be measured is determined by the formula T1 ═ T2-T0 (T0: thickness (mm) of the sheet, T1: thickness (mm) of the sheet to be measured, and T2: thickness (mm) of the sheet to be measured and the sheet to be measured).
In order to impart further liquid permeability, liquid diffusibility, flexibility, and the like to the water- absorbent sheets 10, 20, embossing processing may be appropriately performed on the surfaces of the water-absorbent sheets 10, 20 (the liquid-absorbing surface of the first base material 11 that directly absorbs liquid or the surface of the cover sheet 16). The embossed region may be the entire surface of the water- absorbent sheets 10 and 20, or may be a part thereof. By providing the continuous embossed regions along the longitudinal direction of the water- absorbent sheets 10 and 20, the liquid can be easily diffused along the longitudinal direction. In the water- absorbent sheets 10, 20, the water-absorbent layer 12 has gaps 15 where the particulate water-absorbing agent 14 is not present. In this manner, by providing the embossing regions continuously along the longitudinal direction in addition to the gap 15, the regions function as a liquid passage (liquid transfer passage) through which a large amount of liquid flows. The embossing area may be linear, curved, or wavy.
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims.
Hereinafter, each member constituting the water-absorbent sheet will be described in detail.
[2-1. first base Material ]
The first substrate is a water-permeable sheet located on the side where the liquid to be absorbed is introduced. The liquid to be absorbed is not limited to water, and may be urine, blood, sweat, feces, waste liquid, moisture, vapor, ice, a mixture of water and an organic solvent and/or an inorganic solvent, rainwater, groundwater, or the like, and is not particularly limited as long as water is contained. Preferred examples include urine, menstrual blood, sweat, and other body fluids.
The first base material is a water-permeable sheet and is positioned on the liquid-absorbing side, whereby the effects of the present invention, that is, the performance (such as a reverse flow rate and a leakage in the plane direction) of the water-absorbent sheet can be sufficiently exhibited. Regarding the water permeability of the water permeable sheet, the water permeability coefficient (JIS A1218:2009) is preferably 1X 10-5cm/sec or more. The water permeability coefficient is more preferably 1X 10-4cm/sec or more, more preferably 1X 10-3cm/sec or more, particularly preferably 1X 10-2cm/sec or more, most preferably 1X 10-1cm/sec or more. The first substrate used in the examples of the present application had a water permeability of 1X 10-5cm/sec or more.
In the present invention, the elongation of the first base material is 10% or more, preferably 15% or more, more preferably 17% or more, further preferably 20% or more, and further preferably 22% or more. The upper limit of the elongation of the first base material is not particularly limited, and is preferably 60% or less. When the elongation of the first base material is in such a range, the first base material easily follows the shape of the particulate water-absorbing agent, and as a result, the shape retention property of the water-absorbent sheet is further improved, and the amount of flow-back can be further reduced. The elongation of the first base material is measured by the method described in the examples described below. In the present specification, the "elongation of the nonwoven fabric (first base material)" is a value obtained by measuring the elongation in the most elongated direction. The elongation of the first base material can be controlled by the volume density, the weight per unit area, the material, the lattice structure, the production process conditions, and the like.
In the present invention, the direction of elongation of the first base material is not particularly limited as long as the first base material is elongated in any direction parallel to the plane direction of the first base material, except the thickness direction. For example, in the case of a rectangular water-absorbent sheet, any direction having an angle such as a long-side direction, a short-side direction, a diagonal direction, or the like in the plane of the sheet may be elongated with an elongation in the above-described range. The same applies to the case of a square, oval, or circular water-absorbent sheet. Preferably a substrate that is capable of (isotropically) elongating from all directions.
In the present invention, the weight per unit area of the first base material is preferably 3 to 80g/m2More preferably 5 to 70g/m2More preferably 10 to 60g/m2. When the weight per unit area of the first substrate is in such a range, the particulate water-absorbing agent is easily incorporated into the first substrate, and as a result, the shape retention property of the water-absorbing sheet is further improved, and the amount of flow-back can be further reduced.
In the present invention, the bulk density of the first substrate is preferably 0.1g/cm3Hereinafter, more preferably 0.08g/cm3Hereinafter, more preferably 0.05g/cm3The following. The bulk density of the first substrate is preferably 0.001g/cm 3More preferably 0.005g/cm or more3The concentration is more preferably 0.01g/cm3As described above. In the present specification, the bulk density is a mass per unit volume, and is not a density when the substrate is compressed at high pressure (when voids are eliminated), but a density determined from the volume of the substrate including the void volume. The first substrate has a bulk density of 0.1g/cm3The following means that the first substrate is light. Fluffy means low bulk density and significantly thick. In the present invention, the particulate water-absorbing agent is easily taken into the first base material by making the first base material bulky, and as a result, the shape retention of the water-absorbing sheet is further improved, and the flow rate can be further reduced. In the present invention, the first base material is bulky, and the following effects can be expected. That is, since the first base material is bulky, the liquid to be absorbed which is in contact with the liquid-absorbing surface of the first base material flows into the water-absorbing layer and the second base material as the lower layer quickly, and the liquid retained in the liquid-absorbing surface of the first base material can be reduced. Further, since the liquid spreads in the planar direction when the absorbed liquid reaches the water-absorbent layer, even if a large amount of liquid is introduced into the water-absorbent layer, the water-absorbent layer absorbs the liquid that spreads in the planar direction rather than spreading locally. I.e. fluffy The first substrate (2) has a low water absorption capacity, a high liquid permeability, and a high liquid diffusibility. This can reduce the amount of backflow in the water-absorbent sheet. The moisture of the liquid absorbing surface of the first base material can be suppressed, and the discomfort caused to the skin can be reduced. The bulk density of the first substrate is preferably 0.1g/cm3The following. In the present specification, the bulk density is a value calculated in examples described later.
The thickness of the first base material is preferably 0.3mm or more, more preferably 0.4mm or more, still more preferably 0.5mm or more, particularly preferably 0.6mm or more, and most preferably 0.7mm or more at 40% RH to 50% RH, for example. The thickness of the first base material is preferably 5mm or less, more preferably 4mm or less, still more preferably 3mm or less, particularly preferably 2.5mm or less, and most preferably 2mm or less at 40% RH to 50% RH, for example. By setting the thickness of the first base material within such a range, the distance between the liquid-absorbing surface of the first base material and the water-absorbing layer and the second base material can be sufficiently secured, and occurrence of reverse flow of the liquid that has reached the water-absorbing layer and the second base material can be significantly reduced.
The thickness and bulk density of the first substrate can be controlled by the material constituting the first substrate, the method for producing the first substrate, and the like, and the thickness and bulk density of the first substrate are determined based on the balance thereof.
The transmittance of the particulate water-absorbing agent of the first substrate (the transmittance of the particulate water-absorbing agent to the first substrate) is preferably 40% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, and 70% by mass or more, particularly preferably 80% by mass, and most preferably 90% by mass or more. The upper limit of the transmittance is not particularly limited, but is preferably 99 mass% or less. By setting the permeability of the particulate water-absorbing agent to the first substrate in such a range, the particulate water-absorbing agent is easily taken into the first substrate on the side of the first substrate in contact with the water-absorbing layer. Thereby, the particulate water-absorbing agent can absorb the moisture contained in the first base material, and the backflow is further reduced. In the present specification, the transmittance of the particulate water-absorbing agent to the first substrate is a ratio of the particulate water-absorbing agent that has passed through the first substrate, and as shown in fig. 23, the particulate water-absorbing agent present on the first substrate is determined from the weight of the particulate water-absorbing agent that has passed through the first substrate when screening is performed under predetermined conditions described later, specifically, is a value calculated by the method described in the examples described later. In addition, when a plurality of water-absorbing layers are present as in the second embodiment, the particulate water-absorbing agent used for the transmittance is the entire particulate water-absorbing agent included in each water-absorbing layer. Here, in the case where the first substrate is a nonwoven fabric, the transmittance of the particulate water-absorbing agent to the first substrate can be adjusted to a desired range by appropriately adjusting the properties of the members constituting the first substrate, the surface state thereof, the complexity of the lattice structure, the fiber diameter, the fusion state between fibers, the weight per unit area, the thickness, and the like. For example, if the first base material uses an air-through nonwoven fabric as described later, the transmittance can be adjusted by changing the heat treatment conditions, the fiber diameter, and the density of the air-through nonwoven fabric.
Material for forming substrate "
Examples of the material constituting the first substrate include paper (toilet paper, such as facial tissue, toilet paper, and towel paper), a web, a nonwoven fabric, a woven fabric, and a film. Among them, from the viewpoint of water permeability, a nonwoven fabric is preferably used as at least the first substrate.
The nonwoven fabric to be used is not particularly limited, and from the viewpoints of liquid permeability, flexibility, and strength in the case of forming a water-absorbent sheet, there may be mentioned nonwoven fabrics formed of polyolefin fibers such as Polyethylene (PE) and polypropylene (PP), polyester fibers such as polyethylene terephthalate (PET), 1, 3-trimethylene terephthalate (PTT) and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers; and nonwoven fabrics made of a mixture of cotton, silk, hemp, pulp (cellulose) fibers, and the like.
The material of the nonwoven fabric usable as the first substrate is preferably rayon fiber, polyolefin fiber, polyester fiber, pulp fiber, or a mixture thereof, and more preferably polyolefin fiber. These fibers may be subjected to a hydrophilization treatment.
The nonwoven fabric usable as the first substrate is not particularly limited, and may be a nonwoven fabric obtained by any method such as a through-air method, an air-laid method, a spunbond method, a spunlace method, or the like, preferably a nonwoven fabric obtained by a through-air method or an air-laid method, and preferably a nonwoven fabric obtained by a through-air method (through-air nonwoven fabric).
The hot air method means: the heat-fusible composite fibers such as PE/PP and PE/PET are heat-fused by blowing hot air, and the amount of air contained between the fibers is increased to increase the volume and reduce the density. In addition, the air-laid method is a method of producing a nonwoven fabric by uniformly dispersing the nonwoven fabric by being carried on an air stream and sucking the nonwoven fabric on a metal mesh, and since air is used for dispersing pulp fibers, the volume can be increased and the density can be reduced. By using the first base material as the hot air nonwoven fabric, the liquid to be absorbed can be easily and quickly introduced into the first base material after contacting the liquid-absorbing surface of the first base material. That is, by using the air-through nonwoven fabric as the first base material, the first base material having low water absorption capacity and high liquid permeability can be obtained, and the amount of flow backward in the water-absorbent sheet can be significantly reduced.
[2-1-1. intermediate base Material ]
The intermediate substrate is any substrate disposed between the first substrate and the second substrate, and is a water-permeable sheet.
The suitable range of the water permeability coefficient of the intermediate base material is the same as the range described in the column of the first base material. The intermediate substrate (intermediate nonwoven fabric) used in the examples of the present application had a water permeability coefficient of 1X 10 -5cm/sec or more.
The elongation of the intermediate base material is preferably 10% or more, 15% or more, 17% or more, 20% or more, and 22% or more in this order. The upper limit of the elongation of the intermediate base material is not particularly limited, and is preferably 60% or less. When the elongation of the intermediate substrate is in such a range, the intermediate substrate easily follows the shape of the particulate water-absorbing agent, and as a result, the shape retention property of the water-absorbent sheet is further improved, and the amount of flow-back can be further reduced.
Suitable ranges for the weight per unit area, the bulk density, the thickness of the intermediate substrate, the transmittance of the particulate water-absorbing agent, and the transmittance of the specific particulate water-absorbing agent are the same as those described in the first substrate section.
Further, the material constituting the intermediate base material is also the same as that described in the column of the first base material.
[2-2. second base Material ]
The second base material is a water-permeable sheet and is positioned on the side opposite to the liquid-absorbing side, whereby the effects of the present invention, that is, the performance (such as the amount of flow reversing and leakage in the plane direction) of the water-absorbent sheet can be sufficiently exhibited. Regarding the water permeability of the water permeable sheet, the water permeability coefficient (JIS A1218: 2009) is preferably 1X 10-5cm/sec or more. The water permeability coefficient is more preferably 1X 10 -4cm/sec or more, more preferably 1X 10-3cm/sec or more, particularly preferably 1X 10-2cm/sec or more, most preferably 1X 10-1cm/sec or more.
The thickness of the second base material is preferably 0.05mm or more, more preferably 0.08mm or more, still more preferably 0.1mm or more, particularly preferably 0.2mm or more, and most preferably 0.3mm or more at, for example, 40% RH to 50% RH. The thickness of the second substrate is preferably less than 0.9mm, more preferably 0.8mm or less, still more preferably 0.7mm or less, particularly preferably 0.6mm or less, and most preferably 0.5mm or less at, for example, 40% RH to 50% RH.
Here, according to one embodiment of the present invention, the thickness of the first base material is 0.3mm or more and 5mm or less, and the thickness of the second base material is 0.05mm or more and less than 0.9 mm. By adjusting the thicknesses of the first base material and the second base material to the above ranges, the desired effects of the present invention can be effectively achieved. Further, according to an aspect of the present invention, it is preferable that: the thickness of the first base material is 0.4mm or more and 4mm or less, and the thickness of the second base material is 0.08mm or more and 0.8mm or less, more preferably: the thickness of the first base material is 0.5mm or more and 3mm or less, and the thickness of the second base material is 0.1mm or more and 0.7mm or less, and it is more preferable that: the thickness of the first base material is 0.6mm or more and 2.5mm or less, and the thickness of the second base material is 0.2mm or more and 0.6mm or less, and it is particularly preferable that: the first base material has a thickness of 0.7mm or more and 2mm or less, and the second base material has a thickness of 0.3mm or more and 0.5mm or less.
In the present invention, the bulk density of the second substrate is preferably 1g/cm3Hereinafter, more preferably 0.5g/cm3Hereinafter, more preferably 0.3g/cm3The following. The bulk density of the second substrate is preferably 0.05g/cm3Above, more preferably 0.07g/cm3Above, more preferably 0.08g/cm3The above. By setting the bulk density of the second base material in such a range, the liquid introduced into the second base material can be easily held, and the reverse flow can be reduced.
In the present invention, the second base material preferably has a weight per unit area of 5 to 100g/m2More preferably 10 to 70g/m2More preferably 15 to 65g/m2。
The thickness, bulk density, and weight per unit area of the second base material are controlled by the material constituting the second base material, the manufacturing method of the second base material, and the like, and the thickness and bulk density of the second base material are determined based on the balance thereof.
The void ratio of the first base material, the second base material, and the cover sheet (for example, nonwoven fabric) can be measured by the following formula. Weight per unit area A (g/m) used in base material (or cover sheet)2) Thickness B (mm) of base material (or coating sheet), density C (g/cm) of raw material (e.g., polyolefin) used in base material (or coating sheet)3)
The porosity (%) of the substrate (or sheet) is 100- { (a/10000)/(B/10) }/C × 100
The liquid diffusion area of the second substrate is preferably 1000mm2Above, more preferably 3000mm2Above, more preferably 6000mm2Above, 7000mm is particularly preferable2As described above. The upper limit of the liquid spreading area of the second substrate is not particularly limited, and is preferably 10,000mm, for example2The following. When the liquid diffusion area of the second base material is in the above range, the liquid can be sufficiently diffused in the planar direction in the second base material when the absorbed liquid reaches the second base material. Thereby, even ifWhen a large amount of liquid having passed through the water-absorbent layer is introduced into the second substrate, the second substrate also absorbs the liquid spreading in the planar direction rather than spreading locally. Therefore, the liquid can be sufficiently absorbed and held in the second base material, and the flow rate of the water-absorbent sheet can be significantly reduced.
Here, the liquid spreading area means: the area in the plane direction in which the liquid diffuses when the liquid contacts the substrate (for example, nonwoven fabric) and/or when the liquid passes through the substrate in the direction perpendicular to the plane direction of the substrate is a value calculated by the method described in the examples below. The larger the liquid diffusion area of the substrate, the higher the liquid diffusibility of the substrate in the planar direction.
Material for forming substrate "
The material constituting the second substrate is preferably a nonwoven fabric. As the material of the nonwoven fabric, the same material as the first base material can be used, and for example, rayon fiber, polyolefin fiber, polyester fiber, pulp fiber, and a fiber obtained by mixing these fibers are preferable, and polyolefin fiber is more preferable.
The nonwoven fabric usable as the second substrate is not particularly limited, and may be a nonwoven fabric obtained by any method such as a hot air method, an air-laid method, a spunbond method, a spunlace method, and the like, and is preferably a nonwoven fabric obtained by an air-laid method (air-laid nonwoven fabric) or a nonwoven fabric obtained by a spunlace method (spunlace nonwoven fabric). The hydroentangling method is a method of interlacing fibers with a high-pressure water stream, and is a method of not using an adhesive. By using the air-laid nonwoven fabric or the spunlace nonwoven fabric as the second base material, the amount of backflow in the water-absorbent sheet can be significantly reduced, and the leakage in the plane direction can be significantly reduced.
[2-3. Water-absorbing layer ]
The water-absorbing layer in the water-absorbent sheet according to one embodiment of the present invention has a particulate water-absorbing agent. In the water-absorbent sheet according to one embodiment of the present invention, it is preferable that no other substrate such as a nonwoven fabric is present in the water-absorbent layer. When a plurality of water-absorbing layers are present as in the second embodiment, the water-absorbing layers may have the same composition or different compositions.
(particulate Water-absorbing agent)
The water-absorbing layer contains a particulate water-absorbing agent. When the water-absorbing agent is a mixture of a plurality of particulate water-absorbing agents unless otherwise stated, the following description is related to the physical properties of the mixture. That is, the physical properties of the particulate water-absorbing agent are physical properties when all the particulate water-absorbing agents contained in the water-absorbent layer are mixed. Further, with respect to the physical properties of the particulate water-absorbing agent, only the particulate water-absorbing agent may be taken out from the water-absorbing sheet so as not to be mixed with cotton pulp or the like, and the physical properties may be measured.
Surface tension "
The surface tension means: the parameters of the work (free energy) required to increase the surface area of a solid or liquid are expressed in terms of per unit area. The surface tension referred to in this application means: surface tension of an aqueous solution when the particulate water-absorbing agent was dispersed in a 0.90 mass% aqueous sodium chloride solution. The surface tension of the water absorbing agent is measured by the following procedure. That is, 50ml of physiological saline adjusted to 20 ℃ was put into a well-washed 100ml beaker, and the surface tension of the physiological saline was first measured using a surface tension meter (K11 Autotensiometer manufactured by KRUSS). Then, a sufficiently cleaned 25mm long fluororesin rotor and 0.5g of the particulate water-absorbing agent were put into a beaker containing physiological saline adjusted to 20 ℃ and subjected to surface tension measurement, and stirred at 500rpm for 4 minutes. After 4 minutes, the stirring was stopped, and after the water-containing particulate water-absorbing agent had settled, the same operation was again performed to measure the surface tension of the supernatant liquid. In the present invention, a plate method using a platinum plate was adopted, and the plate was sufficiently washed with deionized water and heated and washed with a gas burner before each measurement.
In the water-absorbent sheet according to one embodiment of the present invention, the surface tension of the particulate water-absorbing agent is preferably 60mN/m or more, 65mN/m or more, 66mN/m or more, 67mN/m or more, 69mN/m or more, 70mN/m or more, 71mN/m or more, and most preferably 72mN/m or more, in this order. When a particulate water-absorbing agent is applied to a water-absorbing sheet, the influence of surface tension is more likely to be exhibited than in a conventional paper diaper, and the amount of flow backward in the water-absorbing sheet can be reduced by satisfying the above conditions with respect to surface tension.
In the water-absorbent sheet according to one embodiment of the present invention, the upper limit of the surface tension of the particulate water-absorbing agent is not particularly limited, and is actually 73mN/m or less.
In the water-absorbent sheet according to one embodiment of the present invention, the particulate water-absorbing agent preferably has a CRC (water absorption capacity without load) of 30g/g or more, 32g/g or more, 33g/g or more, 34g/g or more, and most preferably 35g/g or more in this order. By allowing the CRC of the particulate water-absorbing agent to satisfy the above conditions, the amount of backflow in the water-absorbing sheet can be reduced. CRC of the particulate water-absorbing agent is abbreviated as "Centrifuge Retention Capacity" defined in ERT441.2-02, and is referred to as "water absorption Capacity" in some cases. Specifically, the method comprises the following steps: after 0.2G of the particulate water-absorbing agent was put into a nonwoven fabric bag, the bag was immersed in a 0.9 mass% aqueous sodium chloride solution in a large excess amount for 30 minutes to freely swell the water-absorbing agent, and then the water content was removed by a centrifugal separator (250G), thereby obtaining a water absorption capacity (unit: G/G).
Particle shape "
In the water-absorbent sheet according to one embodiment of the present invention, the particulate water-absorbing agent may have, for example, a spherical particulate water-absorbing agent (and a granulated substance thereof) without limitation to the particle shape thereof. In a preferred embodiment, the particulate water-absorbing agent is preferably irregularly crushed. Here, the irregularly-crushed shape means a crushed particle having an unfixed shape. This is because: the irregularly-crushed shape can be easily fixed to the base material as compared with spherical particles obtained by reversed-phase suspension polymerization or gas-phase polymerization. The particulate water absorbing agent according to an embodiment of the present invention is preferably a pulverized product in aqueous solution polymerization. On the other hand, when the pulverization step is not performed, spherical particles or granules of spherical particles obtained by reverse phase suspension polymerization, droplet polymerization such as spray polymerization of a monomer and polymerization are not irregularly crushed. In the embodiment of the present invention, if the particulate water-absorbing agent has an irregularly crushed shape, the shape of the water-absorbing sheet can be more easily maintained than a water-absorbing agent having a high average circularity (for example, a spherical water-absorbing agent). In the embodiment of the present invention, the average circularity of the particulate water-absorbing agent is preferably 0.70 or less, more preferably 0.60 or less, and still more preferably 0.55 or less.
The average circularity is calculated as follows. At least 100 particulate water-absorbing agents were randomly selected, and each particulate water-absorbing agent was photographed by an electron microscope (VE-9800, manufactured by keyence corporation) (magnification: 50 times), and an image of the particulate water-absorbing agent was obtained, and the perimeter and the area of each particle were calculated by using attached image analysis software. The circularity of each particle was obtained by the following equation, and the average value of the obtained values was calculated as an average circularity.
[ math figure 5]
Particle size "
The particle diameter of the particulate water-absorbing agent (or the particulate water-absorbent resin, water-absorbent resin particles) according to one embodiment of the present invention is a weight average particle diameter obtained by a method of measuring "PSD" defined in ERT420.2-02, and may be 150 to 600. mu.m. In the present invention, the weight average particle diameter is a value calculated by the method described in the examples described below.
The method for producing the particulate water-absorbing agent is not particularly limited as long as it is a method for producing a water-absorbing agent having desired physical properties, and the particulate water-absorbing agent can be suitably produced, for example, with reference to the publications described in examples.
[ 2-4. clad sheet ]
The water-absorbent sheet according to one embodiment of the present invention preferably has a covering sheet disposed at least on the surface of the first base material. The cover sheet may be disposed on the surface of the first base material, and more preferably, the cover sheet is disposed so as to cover the side surface of the first base material and the side surface of the water-absorbent layer, and further preferably covers the side surface of the first base material, the side surface of the water-absorbent layer, and the side surface of the second base material, and covers a part or the whole of the surface of the second base material on the side opposite to the side where the liquid to be absorbed is introduced.
In a preferred embodiment of the present invention, the water-absorbent sheet includes a covering sheet, and the covering sheet is a water-permeable sheet and is positioned at least on the surface (liquid-absorbing side) of the first substrate.
The thickness of the cover sheet is preferably 0.001mm or more, more preferably 0.005mm or more, still more preferably 0.01mm or more, particularly preferably 0.1mm or more, and most preferably 0.2mm or more at 40% RH to 50% RH, for example. The thickness of the cover sheet is, for example, preferably less than 0.9mm, more preferably 0.8mm or less, still more preferably 0.7mm or less, particularly preferably 0.6mm or less, and most preferably 0.5mm or less at 40% RH to 50% RH.
In the present invention, the volume density of the coating sheet is preferably 1g/cm3Hereinafter, more preferably 0.5g/cm3Hereinafter, more preferably 0.3g/cm3The following. The volume density of the wrapping sheet is preferably 0.1g/cm3Above, more preferably 0.12g/cm3Above, more preferably 0.13g/cm3The above.
In the present invention, the weight per unit area of the coated sheet is preferably 5 to 100g/m2More preferably 5 to 70g/m2More preferably 10 to 65g/m2。
The thickness, bulk density, and weight per unit area of the wrapping sheet can be controlled by the material constituting the wrapping sheet, the manufacturing method of the wrapping sheet, and the thickness and bulk density of the wrapping sheet are determined based on the balance between these.
Material for forming wrapping sheet "
The material constituting the cover sheet is not particularly limited as long as the purpose of providing the cover sheet is achieved, and examples thereof include paper (toilet paper, such as facial tissue, toilet tissue, and towel paper), a net, a nonwoven fabric, a woven fabric, and a film.
The nonwoven fabric to be used is not particularly limited, and from the viewpoint of liquid permeability, flexibility, and strength when made into a water-absorbent sheet, there may be mentioned a nonwoven fabric formed of polyolefin fibers such as Polyethylene (PE) and polypropylene (PP), polyester fibers such as polyethylene terephthalate (PET), 1, 3-trimethylene terephthalate (PTT) and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers; and non-woven fabrics made of a mixture of cotton, silk, hemp, pulp (cellulose) fibers, and the like.
The material of the nonwoven fabric that can be used as the cover sheet is preferably rayon fiber, polyolefin fiber, polyester fiber, pulp fiber, or a mixture thereof, and more preferably polyolefin fiber. These fibers may be subjected to a hydrophilization treatment.
The nonwoven fabric that can be used as the cover sheet is not particularly limited, and may be a nonwoven fabric obtained by any method such as a hot air method, an air-laid method, a spunbond method, a spunlace method, or the like, and is preferably a nonwoven fabric obtained by a spunbond method (spunbond nonwoven fabric). In order to prevent urine absorbed by the water-absorbent sheet from seeping out of the sheet (so-called back flow) when the water-absorbent sheet is under load (in a pressurized state), as in the case where an infant wearing an absorbent article such as a disposable diaper is seated on the seat, a water-repellent cover sheet is preferred, and a spunbond nonwoven fabric is preferred, for example. The method for producing a spunbond nonwoven fabric is a method in which continuous long fibers obtained by melting and spinning a raw material resin are directly collected to form a fleece (fleece). Examples of the raw material resin include polyethylene, polypropylene, and polylactic acid.
According to one embodiment of the present invention, a method for manufacturing the first base material, a method for manufacturing the second base material, and a method for manufacturing the cover sheet are different. By appropriately changing the production method of each member constituting the water-absorbent sheet in this way, the desired effects of the present invention can be effectively exhibited. According to one embodiment of the present invention, the first base material is a hot air nonwoven fabric, the second base material is an air-laid nonwoven fabric or a spunlace nonwoven fabric, and the cover sheet is a spun-bonded nonwoven fabric, which are different nonwoven fabrics from each other. In this manner, the desired effects of the present invention can be effectively exhibited.
[ 3. method for producing Water-absorbent sheet ]
The method for producing a water-absorbent sheet according to the first and second embodiments of the present invention includes: (1) at least one of (1) the step of spreading the particulate water-absorbing agent on the first substrate and (2) the step of spreading the particulate water-absorbing agent on the second substrate. As an example of a more specific production method, the following production methods (a) to (d) can be cited for the water-absorbent sheet according to the first embodiment. The following production methods (e) to (h) can be mentioned as examples of the water-absorbent sheet according to the second embodiment.
(a) On the first base material, the particulate water-absorbing agent is scattered in a stripe shape. The adhesive is uniformly spread on the second substrate. The surface of the first base material on which the particulate water-absorbing agent is dispersed and the surface of the second base material on which the adhesive is dispersed are superposed and pressure-bonded so as to be aligned. The pressure bonding is preferably a heat pressure bonding at a temperature near the melting temperature of the adhesive.
(b) After the adhesive is spread in a stripe pattern on the second base material, the particulate water-absorbing agent is uniformly spread. The first base material was superposed on the surface of the second base material on which the particulate water-absorbing agent was dispersed, and was heated and pressure-bonded.
(c) The particulate water-absorbing agent is spread in stripe form on the second substrate, and preferably, the adhesive is uniformly spread and passed through a heating furnace to be fixed to such an extent that the particulate water-absorbing agent does not escape. The first base material was superposed on the surface of the second base material on which the particulate water-absorbing agent was dispersed, and was heated and pressure-bonded.
(d) After the adhesive is melt-coated on the second substrate, the particulate water-absorbing agent is spread in a stripe pattern to form a layer. The first base material is superposed on the surface of the second base material on which the particulate water-absorbing agent is dispersed, and is pressed by pressing with a roller or the like.
(e) On the first base material (or the intermediate base material), the particulate water-absorbing agent is scattered in a stripe shape. The adhesive is uniformly spread on the intermediate substrate (or the first substrate). The surface of the first base material (or the intermediate base material) on which the particulate water-absorbing agent is dispersed is superposed on the surface of the intermediate base material (or the first base material) on which the adhesive is dispersed, and the resultant is pressure-bonded to obtain a bonded body of the first base material and the intermediate base material. The particulate water-absorbing agent is scattered in a stripe pattern on the intermediate substrate of the assembly of the first substrate and the intermediate substrate. The adhesive is uniformly spread on the second substrate. The surface of the joined body of the first base material and the intermediate base material on which the particulate water-absorbing agent is dispersed and the surface of the second base material on which the adhesive is dispersed are superposed so as to be aligned with each other, and pressure-bonded. The pressure bonding is preferably a heat pressure bonding at a temperature near the melting temperature of the adhesive.
(f) After the adhesive was uniformly spread on the second base material, the particulate water-absorbing agent was spread in a stripe shape. The intermediate base material was superposed on the surface of the second base material on which the particulate water-absorbing agent was dispersed, and was heated and pressure-bonded to obtain a joined body of the intermediate base material and the second base material. The particulate water-absorbing agent is scattered in a stripe pattern on the intermediate base material of the assembly of the intermediate base material and the second base material. The adhesive is uniformly spread on the first base material. The surface of the joined body of the intermediate base material and the second base material on which the particulate water-absorbing agent is dispersed is superposed on the surface of the first base material on which the adhesive is dispersed, and pressure-bonded thereto.
(g) On the second base material, the particulate water-absorbing agent is scattered in a stripe shape, and preferably, the adhesive is uniformly scattered and passed through a heating furnace to be fixed to such an extent that the particulate water-absorbing agent does not escape. The first base material was superposed on the surface of the second base material on which the particulate water-absorbing agent was dispersed, and was heated and pressure-bonded to obtain a joined body of the intermediate base material and the second base material. The particulate water-absorbing agent is dispersed in a stripe shape on the intermediate substrate of the assembly of the intermediate substrate and the second substrate, and preferably, the adhesive is uniformly dispersed and passed through a heating furnace to be fixed to such an extent that the particulate water-absorbing agent does not escape. The first base material was superposed on the surface of the joined body of the intermediate base material and the second base material on which the particulate water-absorbing agent was dispersed, and was subjected to thermocompression bonding.
(h) After the adhesive is melt-coated on the second substrate, the particulate water-absorbing agent is spread in a stripe pattern to form a layer. The intermediate base material is superposed on the surface of the second base material on which the particulate water-absorbing agent is dispersed, and pressure-bonded using a roller press or the like, to obtain a joined body of the intermediate base material and the second base material. After the adhesive was melt-coated on the first base material of the assembly of the intermediate base material and the second base material, the particulate water-absorbing agent was scattered in a stripe pattern to form a layer. The first base material is superposed on the surface of the joined body of the intermediate base material and the second base material on which the particulate water-absorbing agent is dispersed, and is pressed by pressing with a roller or the like.
Among these methods, from the viewpoint of simplicity and high production efficiency of the production method, the methods (a) and (b) are preferable in the first embodiment, and the methods (e) and (f) are preferable in the second embodiment. The water-absorbent sheet may be produced by combining the methods (a) to (d) in the first embodiment and the methods (e) to (h) in the second embodiment.
Here, in the present invention, the method for scattering the particulate water-absorbing agent in a stripe shape is not particularly limited, and the scattering in a stripe shape can be performed by using, for example, a stencil paper sheet. Specifically, a board having the same size as the water-absorbent sheet and hollowed out in a vertical stripe pattern arranged at a constant width and length was used as the hollowed-out cardboard. The stencil sheet is carried on a substrate on which the particulate water-absorbing agent is to be spread, and the particulate water-absorbing agent is spread to the portion of the holes which have been hollowed out. After the particulate water-absorbing agent is dispersed, when the stencil paper sheet is removed, the particulate water-absorbing agent is dispersed in a stripe-like state on the base material.
Further, the particulate water-absorbing agent may be spread in stripes on the base material by coating the adhesive in stripes on the base material by screen printing or the like, and then scattering the particulate water-absorbing agent on the base material without contacting the adhesive.
As shown in fig. 18 and 19, the embodiment in which the water-absorbent sheet includes the cover sheet includes (3) a step of covering the first base material, the water-absorbent layer, and the second base material with the cover sheet disposed on the first base material or covering the first base material, the water-absorbent layer, the intermediate base material, the water-absorbent layer, and the second base material with the cover sheet disposed on the first base material. For example, a sheet obtained by pressure-bonding the first substrate, the water-absorbing layer, and the second substrate or a sheet obtained by pressure-bonding the first substrate, the water-absorbing layer, the intermediate substrate, the water-absorbing layer, and the second substrate obtained through the step (a) or (b) or (e) or (f) described above is placed on the cover sheet with the first substrate facing downward, an adhesive is spread on the second substrate (the surface on the side not pressure-bonded with the water-absorbing layer) as the upper surface, the excess portion of the cover sheet exposed from the first substrate is bent, the cover sheet is wrapped in such a manner that the adhesive surface of the second substrate comes into contact with the cover sheet, and the cover sheet is turned upside down and then pressure-bonded, whereby the water-absorbing sheet provided with the cover sheet can be obtained.
As a step other than the above, the water-absorbent sheet may be subjected to embossing for the purpose of improving the touch of the water-absorbent sheet and enhancing the liquid absorption performance. The embossing may be performed simultaneously with the pressure bonding of the first substrate and the second substrate, or may be performed after the sheet is produced. In addition, embossing may be performed on the cover sheet.
In the method for producing a water-absorbent sheet according to one embodiment of the present invention, additives (deodorizing agent, fiber, antibacterial agent, gel stabilizer, and the like) may be appropriately added. The amount of the additive is preferably 0 to 50% by mass, more preferably 1 to 10% by mass, based on the mass of the particulate water-absorbing agent. In the above-mentioned production method, the particulate water-absorbing agent in which the additive is mixed in advance may be used, or the additive may be added in the course of the production process.
The size of the produced water-absorbent sheet can be appropriately designed. Usually, the width in the transverse direction is 3 to 10m, and the length is 10 to 1000m (in the state of a continuous sheet or roll). The produced water-absorbent sheet is cut according to the purpose (size of the absorbent body to be used) and used.
In addition to the above examples, for example, the following patent documents also disclose a method for producing a water-absorbent sheet: international publication No. 2012/174026, International publication No. 2013/078109, International publication No. 2015/041784, International publication No. 2011/117187, International publication No. 2012/001117, International publication No. 2012/024445, International publication No. 2010/004894, International publication No. 2010/004895, International publication No. 2010/076857, International publication No. 2010/082373, International publication No. 2010/113754, International publication No. 2010/143635, International publication No. 2011/043256, International publication No. 2011/086841, International publication No. 2011/086842, International publication No. 2011/086843, International publication No. 2011/086844, International publication No. 2011/117997, International publication No. 2011/118409, International publication No. 2011/136087, International publication No. 2012/043546, International publication No. 2013/099634, International publication No. 2013/099635, Japanese patent application laid-open Nos. 2010-115406, 2002-345883, 6-315501, 6-190003, 6-190002, 6-190001, 2-252558, 2-252560 and 2-252561. The production methods of the water-absorbent sheets disclosed in these documents can be appropriately referred to.
In the water-absorbent sheet according to one embodiment of the present invention, as a method for fixing the substrates to each other or the substrate and the particulate water-absorbing agent, (i) pressure bonding, or (ii) various binders dissolved or dispersed in water, a water-soluble polymer, or a solvent, or (iii) heat sealing the substrates to each other at a melting point of the material of the substrates themselves, or (iv) fixing using an adhesive may be employed. The substrate and each other or the substrate and the particulate water-absorbing agent are preferably (iv) fixed using an adhesive.
The adhesive used may be a solution type, but from the viewpoint of the time and effort required for removing the solvent, the problem of the residual solvent, and the problem of productivity, a hot melt adhesive having high productivity and no problem of the residual solvent is preferred. In the present invention, the hot-melt adhesive may be contained in advance on the surface of the substrate or the particulate water-absorbing agent, or may be separately used in the production process of the water-absorbent sheet. The form and melting point of the hot melt adhesive may be appropriately selected, and the hot melt adhesive may be in the form of particles, fibers, nets, films, or liquids that melt upon heating. The melting temperature or softening point of the hot melt adhesive is preferably 50 to 200 ℃ and 60 to 180 ℃. When the particulate adhesive is used, the particulate adhesive having a particle diameter of about 0.01 to 2 times, 0.02 to 1 times, or 0.05 to 0.5 times the average particle diameter of the particulate water absorbing agent is used.
When a hot-melt adhesive is used in the production of a water-absorbent sheet according to an embodiment of the present invention, a mixture of a particulate water-absorbing agent and a hot-melt adhesive is uniformly dispersed on a base material (for example, a nonwoven fabric), and another 1 sheet of the base material is laminated and then heated and pressure bonded in the vicinity of the melting temperature of the hot-melt adhesive, whereby a water-absorbent sheet can be produced.
The hot melt adhesive used in the present invention may be appropriately selected, and is preferably: at least 1 kind selected from ethylene-vinyl acetate copolymer adhesives, styrene elastomer adhesives, polyolefin adhesives, polyester adhesives and the like can be suitably used.
Specifically, examples of the polyolefin-based adhesive include polyethylene, polypropylene and atactic polypropylene, and examples of the styrene-based elastomer adhesive include styrene-based elastomer adhesives, examples thereof include styrene-isoprene block copolymers (SIS), styrene-butadiene block copolymers (SBS), styrene-isobutylene block copolymers (SIBS), styrene-ethylene-butylene-styrene block copolymers (SEBS), and the like, copolymerized polyolefins, and the like, as polyester-based adhesives, examples thereof include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and copolyester, and as the ethylene-vinyl acetate copolymer adhesive, examples thereof include ethylene-vinyl acetate copolymer (EVA) adhesives, ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), and the like.
In the water-absorbent sheet and/or the method for producing the same according to one embodiment of the present invention, the water-absorbent sheet preferably contains an adhesive, the adhesive is preferably a hot-melt adhesive, and the amount (content) of the adhesive (e.g., hot-melt adhesive) is preferably 3.0 times or less, more preferably 0.01 to 2.5 times, and still more preferably 0.05 to 2.0 times the mass of the particulate water-absorbing agent. If the content of the adhesive (particularly, hot melt adhesive) is too large, it is disadvantageous not only in terms of cost and quality of the water-absorbent sheet (increase in quality of diaper), but also the particulate water-absorbing agent is restricted from swelling and the water-absorbing capacity of the water-absorbent sheet may be lowered.
[ 4. absorbent article ]
An absorbent article according to an embodiment of the present invention has a structure in which the water-absorbent sheet described in [ 2 ] is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet. Here, the liquid-permeable sheet is located on the first base material side, and the liquid-impermeable sheet is located on the second base material side. That is, the absorbent article according to one embodiment of the present invention is configured by sandwiching the water-absorbent sheet according to the present invention between a liquid-permeable sheet and a liquid-impermeable sheet, wherein the liquid-permeable sheet is positioned on the first base material side and the liquid-impermeable sheet is positioned on the second base material side. Specific examples of the absorbent article include disposable diapers, incontinence pads, sanitary napkins, pet sheets, drip sheets for foods, and water stoppers for cables.
As the liquid-permeable sheet and the liquid-impermeable sheet, sheets known in the art of absorbent articles can be used without particular limitation. Further, the absorbent article can be manufactured by a known method.
Examples
The present invention will be described in more detail with reference to the following examples and comparative examples. The technical scope of the present invention is not limited to the following examples. In the following examples, the operation was carried out under the conditions of room temperature (25 ℃ C.)/relative humidity of 40 to 50% RH unless otherwise specified.
In the following examples, a single-layer system in which only 1 laminate of the first substrate is laminated on the water-absorbing layer (region including the particulate water-absorbing agent) and a two-layer system in which 2 laminates of the first substrate are laminated on the water-absorbing layer (region including the particulate water-absorbing agent) and a second substrate are disclosed. In both the single-layer system and the two-layer system, the first substrate having a liquid absorption surface for directly absorbing liquid is referred to as "upper nonwoven fabric", and the second substrate is referred to as "lower nonwoven fabric". The substrate other than the first substrate having the liquid absorption surface directly absorbing the liquid in the two-layer system is an intermediate substrate, and is referred to herein as an "intermediate nonwoven fabric".
< production example >
Production example 1
Particulate water-absorbing agents (1) and (2) of polyacrylic acid (salt) resin were obtained by appropriately adjusting CRC in accordance with the amount of internal crosslinking agent with reference to production examples, and comparative examples described in the following patents. The physical properties of the obtained particulate water-absorbing agent are shown in tables 7 and 9.
International publication No. 2014/034897
International publication No. 2017/170605
International publication No. 2016/204302
International publication No. 2014/054656
International publication No. 2015/152299
International publication No. 2018/062539
International publication No. 2012/043821.
[ production example of acrylic acid ]
Commercially available acrylic acid (acrylic acid dimer 2000ppm, acetic acid 500ppm, propionic acid 500ppm, p-methoxyphenol 200ppm) was supplied to the bottom of a high boiling impurity separation column having a 50-stage baffleless perforated plate, and distilled with a reflux ratio of 1 to remove maleic acid, dimer (acrylic acid dimer) formed from acrylic acid, and the like, followed by further crystallization to obtain acrylic acid (acrylic acid dimer 20ppm, acetic acid 50ppm, propionic acid 50ppm, furfural 1ppm or less, protoanemonin 1ppm or less), and further, after distillation, p-methoxyphenol 50ppm was added.
[ preparation of aqueous solution of sodium acrylate ]
1390g of the acrylic acid was neutralized with 48% caustic soda at 20 to 40 ℃ in example 9 of U.S. Pat. No. 5210298 to obtain a 100% neutralized aqueous solution of sodium acrylate at 37% concentration.
< particulate Water-absorbing agent (1) >
In 5500g (monomer concentration: 35.5 mass%) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing acrylic acid obtained in the above production example of acrylic acid, an aqueous solution of sodium acrylate obtained by the above production method of an aqueous solution of sodium acrylate using the acrylic acid, and deionized water, 4.00g of polyethylene glycol diacrylate (average molar number of addition of ethylene oxide: 9) was dissolved to prepare a reaction solution. Then, the reaction solution was supplied to a reactor formed by capping a jacketed stainless double-arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen while maintaining the reaction solution at 30 ℃. Subsequently, 28.66g of a 10 mass% aqueous solution of sodium persulfate and 35.28g of a 1 mass% aqueous solution of L-ascorbic acid were added while stirring the reaction mixture, and as a result, polymerization started after about 1 minute. 40 minutes after the start of the polymerization, 181.5g of a fine water-absorbent resin powder having a particle size of 150 μm or less was added thereto, and gel disintegration was carried out for 10 minutes by high-speed rotation (130rpm) using a plate of a kneader, and then the hydrogel polymer was taken out. The obtained hydrogel-like polymer is subdivided into particles of about 1 to 2 mm.
The finely divided hydrogel polymer was spread on a 50-mesh (mesh size: 300 μm) metal mesh, and dried with hot air at 175 ℃ for 65 minutes. Next, the dried product was pulverized by a roll mill, and further classified and blended with a metal mesh having a mesh opening of 600. mu.m, thereby obtaining a water-absorbent resin (1-1) having an average particle diameter of 350. mu.m in a random pulverized state. To 100 parts by mass of the water-absorbent resin (1-1) thus obtained, 4.03 parts by mass of an aqueous solution of a surface-crosslinking agent comprising 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 part by mass of propylene glycol, and 3.0 parts by mass of water was spray-mixed. The above mixture was heat-treated at a heat medium temperature of 100 ℃ for 40 minutes using a paddle type mixing heat-treating machine to obtain a surface-crosslinked water-absorbent resin (1-2). To 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (1-2), 3.0 parts by mass of water was mixed by spraying, and the mixture was cured at 60 ℃ for 1 hour in a closed vessel, and then passed through a sieve having a mesh opening of 710 μm to obtain a water-absorbent resin (1-3). A water-absorbent resin obtained by adding 0.3 part by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL, Japan) to the water-absorbent resin (1-3) and mixing was used as the particulate water-absorbing agent (1).
[ method of measuring physical Properties of particulate Water-absorbing agent ]
< weight average particle diameter >
The particle diameter of the particulate water-absorbing agent (or the particulate water-absorbent resin, water-absorbent resin particles) according to one embodiment of the present invention is a weight average particle diameter obtained by a method of measuring "PSD" specified in ERT 420.2-02. The weight average particle diameter of each particulate water-absorbing agent is shown in tables 8 and 10.
< CRC (Water absorption Capacity without load) (ERT441.2-02) >
After 0.2G (pre-water absorption weight) of the particulate water-absorbing agent was put into a nonwoven fabric bag, the bag was immersed in a 0.9 mass% aqueous sodium chloride solution in a large excess amount for 30 minutes to allow the water-absorbing agent to freely swell, and after removing water by a centrifugal separator (250G), the post-water absorption weight of the particulate water-absorbing agent was measured. The water absorption capacity (unit: g/g) is determined by "(weight after water absorption of particulate water-absorbing agent weight before water absorption)/(particulate water-absorbing agent weight before water absorption) × 100". CRC of each particulate water-absorbing agent is shown in tables 8 and 10.
< surface tension >
In the present invention, the surface tension refers to the surface tension of an aqueous solution when the particulate water-absorbing agent is dispersed in a 0.90 mass% aqueous sodium chloride solution.
50ml of physiological saline adjusted to 20 ℃ was put into a well-washed 100ml beaker, and the surface tension of the physiological saline was measured using a surface tension meter (K11 Autotensiometer manufactured by KRUSS Co.). In the present invention, a plate method using a platinum plate was used, and the plate was sufficiently washed with deionized water and heated and washed with a gas burner before each measurement.
Then, a sufficiently cleaned 25mm long fluororesin rotor and 0.5g of the particulate water-absorbing agent were put into a beaker containing the physiological saline after the surface tension measurement adjusted to 20 ℃ and stirred at 500rpm for 4 minutes. After 4 minutes, the stirring was stopped, and after the water-containing particulate water-absorbing agent had settled, the same operation was again performed to measure the surface tension of the supernatant liquid. Here, the surface tension (unit: mN/m) of the particulate water-absorbing agent is determined from the surface tension of a supernatant liquid when the particulate water-absorbing agent is dispersed in physiological saline. The surface tensions of the particulate water-absorbing agents are shown in tables 8 and 10.
[ example ]
< preparation of hollow paperboard >
Hollow-out paper boards 1 to 6 are prepared for spreading a particulate water absorbing agent in a stripe pattern on a nonwoven fabric. The stencil paper sheets 1 to 6 were perforated in a portion where a region where the particulate water-absorbing agent was present, in a paper sheet having a longitudinal length of 14cm and a transverse length of 44cm, so that the region where the particulate water-absorbing agent was present and the region where the particulate water-absorbing agent was not present were linearly formed along the longitudinal direction. In the stencil sheets 1 to 6, the outer periphery thereof was set to 2cm, and the paper was not cut (that is, the stencil sheet was formed by hollowing out a portion of a region where the particulate water absorbing agent was present in the region other than the frame in the width direction in order from the end portion to create a hole). The shapes (S-1) to (S-6) formed by the stencil paper sheets 1 to 6 will be described with reference to FIGS. 20 (a) to 20 (c) and 21 (a) to 21 (c). Fig. 20 (a) to 20 (c) and 21 (a) to 21 (c) are schematic cross-sectional views of a single-layer water-absorbent sheet cut in the width direction. In the shapes (S-1) to (S-6), the region including the particulate water-absorbing agent 14 and the gap 15 are formed so as to be bilaterally symmetrical with respect to the widthwise central portion of the water-absorbent sheet. Therefore, the region ratio of the "particulate water-absorbing agent 14" and the "gap 15" shown below may be from either the left or right along the width direction.
Fig. 20 (a) shows a (S-1) shape formed by the stencil sheet 1. (S-1) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 15mm, gap 15: 25mm, particulate water-absorbing agent 14: 20mm, gap 15: 25mm, particulate water-absorbing agent 14: 15mm ".
Fig. 20 (b) shows a (S-2) shape formed by the stencil sheet 2. (S-2) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 20mm, gap 15: 20mm, particulate water-absorbing agent 14: 20mm, gap 15: 20mm, particulate water-absorbing agent 14: 20mm ".
Fig. 20 (c) shows a (S-3) shape formed by the stencil paper 3. (S-3) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 10mm, gap 15: 35mm, particulate water-absorbing agent 14: 10mm, gap 15: 35mm, particulate water-absorbing agent 14: 10mm ".
Fig. 21 (a) shows a (S-4) shape formed by the stencil sheet 4. (S-4) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 25mm, gap 15: 10mm, particulate water-absorbing agent 14: 30mm, gap 15: 10mm, particulate water-absorbing agent 14: 25mm ".
Fig. 21 (b) shows a (S-5) shape formed by the hollow cardboard 5. (S-5) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 17.5mm, gap 15: 10mm, particulate water-absorbing agent 14: 17.5mm, gap 15: 10mm, particulate water-absorbing agent 14: 17.5mm, gap 15: 10mm, particulate water-absorbing agent 14: 17.5mm ".
Fig. 21 (c) shows a (S-6) shape formed by the stencil sheet 6. (S-6) shape, between the first substrate 11 and the second substrate 13, the "particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm, gap 15: 5mm, particulate water-absorbing agent 14: 10mm ".
[ example 1]
The stencil paper sheet 1 was placed on a nonwoven fabric a (produced by a hot air method) cut to a length of 10cm and a width of 40cm, which had olefin as a main component and a thickness of 1.4mm and corresponded to an intermediate nonwoven fabric (see fig. 20 (a)). The stencil paper sheet 1 has 3 rectangular holes, and the position thereof is adjusted so that the nonwoven fabric a under the stencil paper sheet 1 can be seen from the holes to the maximum. Calculating the ratio of the area of each hole to the total area of all holes of the stencil paper sheet 1, 4.5g (dispersion amount: 112.5 g/m) of the particulate water-absorbing agent (1) was added 2) The nonwoven fabric a, which can be seen from each hole, was uniformly spread by dividing and measuring the area ratio of each hole. Under the condition that a part of the particulate water-absorbing agent (1) is scattered on the hollow-out paper board, the hollow-out paper board 1 is inclined towards the non-woven fabric A on which the particulate water-absorbing agent (1) is scattered, so that the particulate water-absorbing agent falls into the holes of the hollow-out paper board 1. Thereafter, the stencil sheet 1 is removed from the nonwoven fabric a.
Unlike the nonwoven fabric a, a nonwoven fabric a cut to a length of 10cm and a width of 40cm (the same nonwoven fabric (thickness: 1.4mm) as the nonwoven fabric a, hereinafter referred to as a nonwoven fabric a2 corresponding to a first base material (upper nonwoven fabric)) was uniformly spread with 0.7 to 0.9g (spread amount: 17.5 to 21.5g/M) of an adhesive containing styrene-butadiene rubber (spray glue 77, manufactured by 3M JAPAN corporation), and then the nonwoven fabric a with the particulate water-absorbing agent (1) spread thereon was overlapped (in contact) with the adhesive-spread surface of the nonwoven fabric a2 so as to be in face-up with the adhesive-spread surface, and pressure-bonded thereto.
A perforated paper sheet 1 was placed on the surface of the nonwoven fabric a on the side not facing the particulate water-absorbing agent (1) (see fig. 20 (a)). The position is adjusted so that the nonwoven fabric a under the stencil sheet 1 can be seen from the 3 rectangular holes of the stencil sheet 1 to the maximum. The ratio of the area of each hole of the stencil paper sheet 1 to the total area of all the holes was calculated, and 4.5g of the particulate water-absorbing agent (1) was distributed and measured in accordance with the area ratio of each hole, and the nonwoven fabric a which could be seen from each hole was uniformly spread. Under the condition that a part of the particulate water-absorbing agent (1) is scattered on the hollow-out paper board, the hollow-out paper board 1 is inclined towards the non-woven fabric A on which the particulate water-absorbing agent (1) is scattered, so that the particulate water-absorbing agent falls into the holes of the hollow-out paper board 1. Thereafter, the stencil sheet 1 is removed from the nonwoven fabric a.
Nonwoven fabric E having a machine direction of 10cm and a cross direction of 40cm (produced by air-laid method, containing pulp fibers as a main component, having a thickness of 0.4mm, and having a basis weight of 47 g/m)2. Corresponding to the second substrate (lower nonwoven fabric)), 0.7 to 0.9g of the adhesive was uniformly spread, and then the surface of the nonwoven fabric a on which the particulate water-absorbing agent (1) was spread was overlapped (in contact with) so that the surface of the nonwoven fabric E on which the adhesive was spread was aligned, and pressure-bonded, thereby obtaining an intermediate sheet X.
Finally, the intermediate sheet X was cut into a nonwoven fabric F (produced by a spunbond method) having a length of 24cm and a width of 40cm, and having a thickness of 0.1mm and a basis weight of 13g/m, with olefin as a main component2. Bulk density: 0.15g/cm3. Equivalent to a clad sheet) is performedWrapping to obtain the water-absorbent sheet (1).
[ example 2]
A nonwoven fabric F cut into a length of 24cm and a width of 40cm (corresponding to a covering sheet) was laid in advance, a nonwoven fabric a cut into a length of 10cm and a width of 40cm (corresponding to a first base material) was placed thereon, and a cut-out cardboard 1 was placed on the surface of the nonwoven fabric a (see fig. 20 (a)). The position of the nonwoven fabric A under the stencil sheet 1 can be adjusted so as to be maximally visible through the 3 rectangular holes of the stencil sheet 1. The ratio of the area of each hole to the total area of all holes of the stencil paper sheet 1 was calculated, and 9.0g (dispersion amount: 225 g/m) of the particulate water-absorbing agent (1) was added 2) The nonwoven fabric a, which can be seen from each hole, was uniformly spread by dividing and measuring the area ratio of each hole. Under the condition that a part of the particulate water-absorbing agent (1) is scattered on the hollow-out paper board, the hollow-out paper board 1 is inclined toward the non-woven fabric A on which the particulate water-absorbing agent (1) is scattered, so that the particulate water-absorbing agent falls into the holes of the hollow-out paper board 1. Thereafter, the stencil sheet 1 is removed from the nonwoven fabric a.
0.7 to 0.9g (dispersion amount: 17.5 to 21.5g/M) of an adhesive (spray glue 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber was uniformly dispersed on a nonwoven fabric E (corresponding to a second base material) having a vertical length of 10cm and a horizontal length of 40cm, and then the surface of the nonwoven fabric A on which the particulate water-absorbing agent (1) was dispersed was superposed on the surface of the nonwoven fabric E on which the adhesive was dispersed (in contact therewith) and pressure-bonded to obtain an intermediate sheet Y.
Finally, the intermediate sheet Y is wrapped with the nonwoven fabric F and pressure-bonded, thereby obtaining a water-absorbent sheet (2).
[ example 3]
A water-absorbent sheet (3) was obtained in the same manner as in example 2, except that a 0.7mm thick through-air nonwoven fabric G was used in place of the through-air nonwoven fabric A.
[ example 4]
A water-absorbent sheet (4) was obtained in the same manner as in example 2, except that a stencil sheet 2 (see fig. 20 (b)) was used instead of the stencil sheet 1.
[ example 5]
A water-absorbent sheet (5) was obtained in the same manner as in example 2, except that a hollow cardboard 3 (see fig. 20 (c)) was used instead of the hollow cardboard 1.
[ example 6]
A water-absorbent sheet (6) was obtained in the same manner as in example 2, except that a hollow cardboard 4 (see fig. 21 (a)) was used instead of the hollow cardboard 1.
[ example 7]
A water-absorbent sheet (7) was obtained in the same manner as in example 2, except that a stencil sheet 5 (see fig. 21 (b)) was used instead of the stencil sheet 1.
[ example 8]
A water-absorbent sheet (8) was obtained in the same manner as in example 2, except that a stencil sheet 6 (see fig. 21 (c)) was used instead of the stencil sheet 1.
[ example 9]
A water-absorbent sheet (9) was obtained in the same manner as in example 2, except that a nonwoven fabric B (produced by a hot air method, containing olefin as a main component and having a thickness of 2.0 mm) was used in place of the nonwoven fabric a.
[ example 10]
A water-absorbent sheet (10) was obtained in the same manner as in example 2, except that a nonwoven fabric C (produced by a hot air method, containing olefin as a main component and having a thickness of 1.5 mm) was used in place of the nonwoven fabric a.
Comparative example 1
4.5g of the particulate water-absorbing agent (1) was uniformly spread on the nonwoven fabric A cut into a length of 10cm and a width of 40 cm.
0.7 to 0.9g (dispersion amount: 17.5 to 21.5g/M) of an adhesive (spray glue 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber was uniformly dispersed on a nonwoven fabric E (corresponding to a first base material) having a vertical length of 10cm and a horizontal length of 40cm, and then the surface of the nonwoven fabric A on which the particulate water-absorbing agent (1) was dispersed was superposed (in contact) so as to be in contact with the surface of the nonwoven fabric E on which the adhesive was dispersed, and pressure-bonding was performed.
On the surface of the nonwoven fabric A on the side not opposed to the particulate water-absorbing agent (1), 4.5g of the particulate water-absorbing agent (1) was uniformly scattered.
After 0.7 to 0.9g of the adhesive was uniformly spread on a nonwoven fabric E having a length of 10cm and a width of 40cm (hereinafter referred to as a nonwoven fabric E2 corresponding to a second base material) separately from the nonwoven fabric E, the nonwoven fabric a and the particulate water-absorbing agent (1) were superposed on each other so that the surfaces thereof were in contact with each other and the adhesive-spread surface of the nonwoven fabric E2 was pressed and bonded together under pressure to obtain an intermediate sheet Z. Finally, the intermediate sheet Z was wrapped with a nonwoven fabric F and pressure-bonded, thereby obtaining a water-absorbent sheet (11).
Comparative example 2
A water-absorbent sheet (12) was obtained in the same manner as in example 1, except that the particulate water-absorbing agent (1) was uniformly dispersed on the entire surface of the nonwoven fabric a without using the stencil paper sheet 1.
Comparative example 3
A water-absorbent sheet (13) was obtained in the same manner as in example 1, except that the nonwoven fabric E was used instead of the nonwoven fabric a 2. As the intermediate nonwoven fabric, nonwoven fabric a was used.
Comparative example 4
A water-absorbent sheet (14) was obtained in the same manner as in example 2, except that the nonwoven fabric E was used instead of the nonwoven fabric a.
The nonwoven fabrics a to C, G used in the present example were all water-permeable sheets.
[ method of measuring physical Properties of nonwoven Fabric ]
The elongation, thickness, bulk density, liquid diffusion area and permeability of the nonwoven fabrics a to C, E and G used in examples 1 to 10 and comparative examples 1 to 4 were measured by the following methods.
[ method of measuring elongation ]
The nonwoven fabric for measuring the elongation was cut into a rectangle having a long side of 100mm and a short side of 30 mm. In this case, the long side is the width direction of the nonwoven fabric roll, and the short side is the winding length direction of the nonwoven fabric roll. In the nonwoven fabric having the dimensions of 100mm in the longitudinal direction (short side) and 400mm in the transverse direction (long side) used for the water-absorbent sheet in this example, the longitudinal direction (short side) was defined as the width direction of the nonwoven fabric roll, and the transverse direction (long side) was defined as the winding length direction of the nonwoven fabric roll. As shown in fig. 22 (a), reference lines were drawn parallel to the short sides at positions 5mm from both ends of the cut nonwoven fabric for measuring the elongation. Each clip was clamped by a double-layered clip so as to overlap the reference line ((b) of fig. 22). The double-layer clip uses a clip with the length of the claw being more than 30 mm. And (3) a weight is installed on one double-layer cloth clip, and the total weight of the double-layer cloth clip with the weight and the weight is set to be 110 g. And (3) holding the double-layer cloth clip without the weight under the room temperature atmosphere, lifting the weight attached to the other double-layer cloth clip to enable the weight to float in the air, and maintaining the non-woven fabric in the state of elongation due to the weight of the double-layer cloth clip and the weight for 20 seconds. Next, the length of the nonwoven fabric in the longitudinal direction was measured while being kept floating in the air (fig. 22 (c)). From the length of the long side after floating in the air and the length of the long side before floating in the air of 100mm, the elongation is determined as a ratio by using the following equation, with respect to how much the length after floating in the air is elongated.
[ mathematical formula 6]
< measurement of thickness of nonwoven Fabric >
The measurement was carried out using a dial type thickness gauge (thickness measuring instrument) (model J-B, manufactured by Kawasaki, Ltd., measuring head, anvil, and vertical diameter 50 mm). The number of measurement points was measured 5 times at different sites, and the measured values were averaged at 5 sites. In order to measure the thickness, the hand was slowly removed from the handle so as not to apply pressure to the nonwoven fabric as much as possible, and the thickness was measured.
< method for calculating bulk Density of nonwoven Fabric >
The weight of the nonwoven fabric cut into a size of 10cm or more in the machine direction and 40cm or more in the cross direction was measured. The longitudinal and transverse lengths of the nonwoven fabric and the thickness measured by < thickness measurement > were multiplied, respectively, to calculate the volume of the nonwoven fabric, and the bulk density was calculated by dividing the weight of the nonwoven fabric by the volume of the nonwoven fabric.
< method for measuring liquid diffusion area of nonwoven Fabric >
A30 cm-diameter sieve obtained using a net having a mesh opening of 2mm and a thread shape of 0.9mm was placed on a flat surface, and a nonwoven fabric (second base material) cut into a 10cm square was placed thereon. A syringe having a diameter of 0.50mm was attached to a 1ml syringe, 1.00g of physiological saline containing 20ppm of blue No. 1 reagent was measured, and the physiological saline of the syringe was vertically injected into the center of the nonwoven fabric on the sieve. At this time, the mesh of the screen is sufficiently spaced from the plane so that the physiological saline passed through the nonwoven fabric and the mesh does not contact the mesh. When the nonwoven fabric absorbed physiological saline and the liquid was completely diffused, the diffusion area of physiological saline was measured.
< permeability of particulate Water-absorbing agent to nonwoven Fabric >
A JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80 mm; JIS Z8801-1(2000)) having a mesh opening 32 of 850 μm or a sieve 31 corresponding to The JIS standard sieve was provided with a nonwoven fabric (first base material 11) cut to a diameter of 80mm as shown in FIG. 23, and The periphery was fixed with an adhesive tape 33 (The area through which The pellets were allowed to pass was at least 75mm in diameter). As the nonwoven fabric (first substrate 11), a nonwoven fabric taken out of the water-absorbent sheet by a method described later can be used. 10.0g of a particulate water-absorbing agent 14 (weight-average particle diameter: 367 μm, particle size distribution: 6.1% for 850 to 600 μm, 14.5% for 600 to 500 μm, 50% for 500 to 300 μm, 27.6% for 300 to 150 μm, 1.9% for 150 to 45 μm, and 0.1% for 45 μm or less) was put into a nonwoven fabric (first substrate 11) in a sieve 31 (arrow direction in FIG. 23), and the resultant mixture was shaken for 5 minutes at room temperature (20 to 25 ℃ C.) and a relative humidity of 50% RH by using a rotary hammer type shaker (ES-65 type shaker manufactured by Kakko Kagaku Co., Ltd.; rotation speed: 230rpm, impact number: 130 rpm). After shaking, the mass (w (g)) of particulate water-absorbing agent 14 (i.e., particulate water-absorbing agent 14 in portion 31a existing below mesh 32 of screen 31) after passing through mesh 32 of screen 31 of the nonwoven fabric (first substrate 11) and the JIS standard screen was measured, and the transmittance of particulate water-absorbing agent 14 was calculated according to the following formula (i). Note that 2 measurements were performed, and the average value was calculated.
[ math figure 7]
The particulate water-absorbing agent has a permeability (mass%) { W/10.0} × 100 … formula (i)
The particulate water-absorbing agent used for measuring the transmittance is a particulate water-absorbing agent containing 90 wt% or more of a particulate water-absorbing agent having a weight-average particle diameter of 300 to 450 μm and a particle size distribution of 850 to 150 μm. Therefore, the calculated permeability of the particulate water-absorbing agent to the first substrate in this example also corresponds to the permeability of the specific particulate water-absorbing agent to the first substrate.
[ evaluation method of Water-absorbing sheet ]
< method for removing particulate Water-absorbing agent from Water-absorbing sheet >
The particulate water-absorbing agent is taken out by peeling the upper nonwoven fabric and the lower nonwoven fabric from the water-absorbent sheet (when the intermediate nonwoven fabric is included, the intermediate nonwoven fabric and the particulate water-absorbing agent are taken out). The particulate water-absorbing agents attached to the upper and lower nonwoven fabrics and the intermediate nonwoven fabric were also all taken out. When the upper and lower nonwoven fabrics are peeled off, the water-absorbing sheet is cooled to sufficiently weaken the adhesiveness of the adhesive (hot melt adhesive, spray adhesive) to which the nonwoven fabric or the particulate water-absorbing agent is attached, and then peeled off. By performing this step, the fibers of the nonwoven fabric and the structural thickness can be taken out without changing, and the transmittance can be accurately measured. The method of cooling the water-absorbent sheet may be any of various means such as leaving the sheet in a constant temperature bath at-10 ℃ or lower for a certain period of time, spraying cooling mist, and applying liquid nitrogen, and is not particularly limited as long as the cooling is performed under conditions such that the fibers, structure, and thickness of the nonwoven fabric are not changed and the particulate water-absorbent agent contained in the water-absorbent sheet does not absorb moisture.
When the particulate water-absorbing agent taken out has absorbed moisture, the moisture content may be adjusted to 10 mass% or less, preferably 5 ± 2 mass%, for example, by drying, and the above-mentioned transmittance and the respective properties specified in the present application may be measured. The drying conditions for adjusting the water content are not particularly limited as long as decomposition or modification of the water-absorbent resin (particulate water-absorbing agent) does not occur, and drying under reduced pressure is preferable.
< measurement of content ratio of particulate Water-absorbing agent in Upper nonwoven Fabric >
The measurement was carried out on a sample (thickness was not changed) obtained by cutting the upper nonwoven fabric into a square having a length of 10mm and a width of 10mm by using the inch Xio SMX-100CT system of MICRO FOCUS X-ray CT system manufactured by Shimadzu corporation. The measurement conditions are as follows.
[ imaging based on X-ray CT ]
Image lateral dimension (pixel): 512
Image longitudinal dimension (pixel): 512
X-ray tube voltage (kV): 50
X-ray tube current (μ a): 40
English size (inch): 4.0
An X-ray filter: is free of
SDD (distance of focus of X-ray source from X-ray detector) (mm): 700
SRD (distance between focal point of X-ray source and rotation center of measurement sample) (mm): 550
Scanning mode 1: CBCT
Scanning mode 2: conventional scanning
Scanning angle: full scan
Number of visual fields: 2400
Average number: 5
Smoothing: YZ
Slice thickness (mm): 0.166
BHC data: is free of
Fine mode: is provided with
FOV XY (maximum shooting area XY) (mm): 50.3
FOV Z (maximum capture area Z) (mm): 40.0.
next, the X-ray CT imaging data was analyzed using an analysis software Win ROOF manufactured by mitsubishi corporation according to the following procedure.
(1) The Win ROOF is opened and the image to be analyzed (Jpeg) stored in the X-ray CT is selected.
(2) On the screen, the click (selection) is performed in accordance with the flow of the binarization process, the automatic binarization, the modal method, the threshold value (appropriate adjustment), and the operation.
(3) The polygonal ROI was selected to surround the particulate water-absorbing agent in the first substrate (upper nonwoven fabric), and the area of the particulate water-absorbing agent was calculated.
(4) The total area of the particulate water-absorbing agent in the water-absorbent sheet thus obtained was calculated in the same manner as in (3).
From the calculation result, the content ratio (%) of the particulate water-absorbing agent in the first base material was calculated by the following formula.
The content ratio (%) of the particulate water-absorbing agent in the first base material is ═ particulate water-absorbing agent area (I)/particulate water-absorbing agent total area (II) × 100 in the first base material
That is, the content ratio of the particulate water-absorbing agent in the first substrate is expressed by an area% of the particulate water-absorbing agent with respect to the total area. The particulate water-absorbing agent is not present on the liquid-absorbing surface of the first base material (the surface on which the liquid to be absorbed by the upper nonwoven fabric is introduced) because it is present at less than several% even if it is. In the following examples, the content of the particulate water-absorbing agent in the first substrate was 5% or more of the particulate water-absorbing agent contained in the entire water-absorbing sheet.
[ evaluation method of Water-absorbing sheet ]
< amount of flow reversal (evaluation of specific amount of flow reversal) >
As shown in FIG. 24, a water-absorbent sheet 10 having a vertical length of 10cm and a horizontal length of 40cm was wrapped with a liquid-impermeable sheet 21 having a vertical length of 14cm and a horizontal length of 40cm so that an opening portion was formed at the upper portion. The water-absorbent sheet 10 wrapped with the liquid-impermeable sheet 21 is placed on a flat surface, and a liquid injection cylinder 41 (fig. 25) is placed on the flat surface at the center of the water-absorbent sheet 10 as shown in fig. 26. In this state, 80g of a 0.9 wt% aqueous sodium chloride solution at 23 ℃ was poured into the liquid injection cylinder 41 using a funnel 42 capable of pouring a liquid at a flow rate of 7 ml/sec (fig. 27). In this case, a liquid is put into the water-absorbent sheet 10 exposed from the liquid-impermeable sheet 21 in the sheet 22. After 10 minutes from the introduction of the liquid, 20 pieces of filter paper 43 (model No.2, manufactured by ADVANTEC; circular filter paper having a diameter of 110 mm) having a weight measured in advance were placed at the center of the sheet 22, that is, at the center of the water-absorbent sheet 10, and a circular weight 44(1200g) having a diameter of 100mm was placed thereon and held for 1 minute. After 1 minute, the weight 44 was removed and the first pour (g) was determined from the weight gain of the filter paper 43. After 1 minute from the removal of the weight 44, the same operation was repeated (liquid addition → filter paper 43 and weight 44(1200g) were carried 10 minutes after addition, hold 1 minute → removal of the weight, and measurement of the flow rate), and the second and third flow rates (g, g) were measured. The total of the first to third measured flow rates is shown in tables 8 and 10.
< method for calculating thickness ratio (Lb/La) >
La is a thickness from the liquid-absorbing surface of the upper nonwoven fabric (liquid-absorbing surface of the first substrate) to the surface of the lower nonwoven fabric (second substrate) on the water-absorbing layer side in the gap, and Lb is a thickness from the liquid-absorbing surface of the upper nonwoven fabric (liquid-absorbing surface of the first substrate) to the surface of the lower nonwoven fabric (second substrate) on the water-absorbing layer side in the region including the particulate water absorbing agent.
[ measurement of thickness of Water-absorbent sheet based on X-ray CT ]
In the imaging of the water-absorbent sheet by X-ray CT, both ends of the water-absorbent sheet cut to 180mm length were fixed to a plastic plate having a length of 350mm, a width of 100mm and a thickness of 3mm by rubber tapes, the plastic plate was set on an internal plate of an X-ray apparatus (instex SMX-100CT manufactured by shimadzu corporation) so as to be perpendicular to the thickness direction, and the center of the water-absorbent sheet was measured under the following conditions, thereby performing the imaging.
The using device comprises: instexio SMX-100CT (manufactured by Shimadzu)
X-ray tube voltage (kV): 80
X-ray tube current (μ a): 40
English size (inch): 4.0
An X-ray filter: is composed of
SOD(mm)：700
SRD(mm)：550
Number of visual fields: 2400
Average number: 5X 1
Slice thickness (mm): 0.166
CT mode 1: CBCT
CT mode 2: general operation
Scanning angle: full scan
BHC data: is composed of
Center adjustment: is provided with
Fine mode: is provided with
FOV(XY)(mm)：50.3
FOV(Z)(mm)：20.0
Voxel size (mm/voxel): 0.098
A cross-sectional view obtained by dividing the three-dimensional image obtained by photographing into 203 pieces in the longitudinal direction was obtained, and the thickness of the water-absorbing sheet was measured from the images of the 50 th, 100 th and 150 th sheets. When the thickness is measured, La is the thickness from the liquid-absorbing surface of the upper nonwoven fabric to the surface of the lower nonwoven fabric on the water-absorbing layer side in the gap below the upper nonwoven fabric, and Lb is the thickness from the liquid-absorbing surface of the upper nonwoven fabric to the surface of the lower nonwoven fabric on the water-absorbing layer side in the region containing the particulate water-absorbing agent below the upper nonwoven fabric.
< evaluation of shape Retention >
After the water-absorbent sheet was evaluated for < backflow amount >, the center of the water-absorbent sheet was cut along the width direction, and regions (i.e., gaps) not containing the particulate water-absorbing agent were visually confirmed. At this time, the presence of the substance in the gap was confirmed, and the evaluation was performed according to the following evaluation criteria.
Evaluation criteria
Good: the regions containing the particulate water-absorbing agent are separated by gaps
(i.e., no member is present in the gap or a substrate having a water-absorbing layer is mainly present in the gap (i.e., an upper nonwoven fabric and a lower nonwoven fabric in the case of a single-layer system; an upper nonwoven fabric, an intermediate nonwoven fabric, and a lower nonwoven fabric in the case of a two-layer system))
X: the ratio of the gaps existing is small, and the regions containing the particulate water-absorbing agent arranged in parallel are connected to each other (not separated by the gaps)
(that is, the particulate water-absorbing agent enters a region regarded as a gap, or the proportion of the substrate having the water-absorbing layer is reduced)
Tables 7 to 10 below show the structures of the water-absorbent sheets produced in examples 1 to 10 and comparative examples 1 to 4, the evaluation results of the physical properties of the substrates used in the respective water-absorbent sheets, and the evaluation results of the water-absorbent sheets. In tables 7 to 10, SAP means a particulate water absorbing agent. In addition, SAP arrangement region (%) in tables 7 and 9 means: the ratio of the area of the region containing the particulate water-absorbing agent to the total area of the base material on which the particulate water-absorbing agent is disposed in the plane direction of the upper nonwoven fabric, and the region (%) in which the SAP is not disposed means: the ratio of the area of the region not containing the particulate water-absorbing agent (i.e., the gap) to the total area of the substrate on which the particulate water-absorbing agent is disposed in the plane direction of the upper nonwoven fabric. Here, the substrate provided with the particulate water-absorbing agent means: a substrate in which the particulate water-absorbing agent is dispersed. In this embodiment, the upper nonwoven fabric, the middle nonwoven fabric, and the lower nonwoven fabric have the same size.
[ Table 7]
[ Table 8]
[ Table 9]
[ Table 10]
From the above results, the water-absorbent sheets of examples 1 to 10 had higher shape retention property and significantly less amount of reverse flow than the water-absorbent sheets of comparative examples 1 to 4. It can be confirmed that: in the water-absorbent sheets of the single-layer system and the two-layer system, by using the stretchable upper nonwoven fabric and providing the gaps in the water-absorbent layer, the amount of flow backward can be reduced, and the shape retention property is high.
In addition, in the present embodiment, the two-layer system tends to increase the amount of backflow as compared with the single-layer system. It may be one of the reasons that the amount of the particulate water-absorbing agent in the two-layer system with respect to the upper nonwoven fabric (i.e., the amount of the particulate water-absorbing agent located between the upper nonwoven fabric and the intermediate nonwoven fabric) is smaller than the amount of the particulate water-absorbing agent in the single-layer system with respect to the upper nonwoven fabric (i.e., the amount of the particulate water-absorbing agent located between the upper nonwoven fabric and the lower nonwoven fabric). Therefore, it is considered that the difference in the effect of reducing the flow rate between the single-layer system and the two-layer system is difficult to be summarized.
It should be noted that the present application is based on japanese patent application No. 2019-215887 applied on 11/28/2019 and japanese patent application No. 2019-215888 applied on 11/28/2019, the disclosures of which are incorporated by reference in their entirety.
Industrial applicability
10 Water-absorbent sheet
11. 11a first substrate,
11b an intermediate substrate,
12. 12a and 12b water-absorbing layers,
13 a second substrate,
14. 14a, 14b particulate water-absorbing agent,
15. 15a, 15b gap
16 wrapping sheets,
18. 18a laminated body,
18b construct,
20 a water-absorbent sheet,
21 a liquid-impermeable sheet,
31 mesh sieve,
31a part below the screen,
32 meshes of,
33 adhesive tape
41 liquid injection cylinder,
42 funnel, a,
43 Filter paper
44 weight, a weight,
45 liquid injection cylinder,
60 stand, a,
61 tubes,
63 acrylic plates,
64 funnels,
65 metal pallet.
Claims (43)
1. A water-absorbent sheet comprising a first base material, a second base material, and a water-absorbent layer located between the first base material and the second base material,
the water-absorbing layer contains a particulate water-absorbing agent,
the surface of the first base material forms a liquid absorbing surface for directly absorbing liquid,
the ratio of the thickness (mm) of the first base material to the thickness (mm) of the second base material (thickness (mm) of the first base material/thickness (mm) of the second base material) is 1.5 or more and less than 14.
2. The water-absorbent sheet according to claim 1, wherein the bulk density of the first substrate is 0.1g/cm3The following.
3. The water-absorbent sheet according to claim 1 or 2, wherein the first substrate is a hot air nonwoven fabric.
4. The water-absorbent sheet according to any one of claims 1 to 3, which comprises a coating sheet disposed on at least a surface of the first substrate.
5. The water-absorbent sheet according to any one of claims 1 to 4, wherein the first substrate contains the particulate water-absorbing agent,
the content ratio of the particulate water-absorbing agent in the first substrate is 5% or more of the particulate water-absorbing agent contained in the entire water-absorbing sheet.
6. The water-absorbent sheet according to any one of claims 1 to 5, wherein the liquid diffusion area of the second substrate is 6000mm2The above.
7. The water-absorbent sheet according to any one of claims 1 to 5, wherein the liquid diffusion area of the second substrate is 7000mm2The above.
8. The water-absorbent sheet according to any one of claims 1 to 7, wherein the second substrate is a spunlace nonwoven fabric.
9. The water-absorbent sheet according to any one of claims 1 to 8, wherein the first substrate has a thickness of 0.7mm or more and 5mm or less.
10. The water-absorbent sheet according to any one of claims 1 to 9, wherein the thickness of the second substrate is 0.05 to 0.9 mm.
11. The water-absorbent sheet according to any one of claims 1 to 10, wherein the particulate water-absorbing agent has a transmittance of 40 mass% or more with respect to the first substrate.
12. The water-absorbent sheet according to any one of claims 1 to 11, wherein the particulate water-absorbing agent has a CRC of 30g/g or more.
13. The water-absorbent sheet according to any one of claims 1 to 11, wherein the particulate water-absorbing agent has a CRC of 33g/g or more.
14. The water-absorbent sheet according to any one of claims 1 to 11, wherein the particulate water-absorbing agent has a CRC of 35g/g or more.
15. The water-absorbent sheet according to any one of claims 1 to 14, wherein the particulate water-absorbing agent has an AAP of 25g/g or more.
16. The water-absorbent sheet according to any one of claims 1 to 15, wherein the surface tension of the particulate water-absorbing agent is 60mN/m or more.
17. The water-absorbent sheet according to any one of claims 1 to 16, wherein the water-absorbent sheet comprises an adhesive,
the amount of the adhesive used is 0.05 to 2.0 times the mass of the particulate water-absorbing agent.
18. The water-absorbent sheet according to any one of claims 1 to 17, wherein a region containing the particulate water-absorbing agent in the water-absorbent layer is disposed with a gap substantially not containing the particulate water-absorbing agent interposed therebetween,
the first base material has an elongation of 10% or more.
19. The water-absorbent sheet according to any one of claims 1 to 18, wherein the first substrate has a weight per unit area of 10 to 60g/m2。
20. The water absorbent sheet according to claim 18 or 19, wherein a ratio (Lb/La) of a thickness (Lb) to a thickness (La) is 1.05 or less, the thickness (Lb) being a thickness from the liquid absorption surface of the first base material to a surface of the second base material on the water absorption layer side in a region including the particulate water absorbing agent, the thickness (La) being a thickness from the liquid absorption surface of the first base material to a surface of the second base material on the water absorption layer side in the gap.
21. The water-absorbent sheet according to any one of claims 18 to 20, wherein the region containing the particulate water-absorbing agent and the gap have a shape extending in one direction of the liquid-absorbing surface of the first substrate, and are arranged in parallel.
22. The water-absorbent sheet according to any one of claims 1 to 17, wherein the surface of the first substrate on the water-absorbent layer side is fluffed.
23. The water-absorbent sheet according to claim 22, wherein a raised area percentage of the raised surface in a raised area measurement test is 5% or more.
24. The water-absorbent sheet according to claim 22 or 23, wherein the first substrate carries the particulate water-absorbing agent without an adhesive.
25. The water-absorbent sheet according to any one of claims 22 to 24, wherein the particulate water-absorbing agent is contained in an amount of 200g/m2As described above.
26. The water-absorbent sheet according to any one of claims 22 to 25, wherein the adhesive on the second substrate is a hot-melt adhesive.
27. The water-absorbent sheet according to any one of claims 22 to 26, wherein the GPR of the particulate water-absorbing agent is 20g/min or more.
28. An absorbent article comprising the water-absorbent sheet according to any one of claims 1 to 27 sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet, wherein the liquid-permeable sheet is located on the first base material side and the liquid-impermeable sheet is located on the second base material side.
29. A water-absorbent sheet comprising a first base material, a second base material, and a water-absorbent layer located between the first base material and the second base material,
the water-absorbing layer contains a particulate water-absorbing agent, and a region containing the particulate water-absorbing agent is disposed with a gap substantially not containing the particulate water-absorbing agent interposed therebetween,
The surface of the first base material forms a liquid absorbing surface for directly absorbing liquid,
the first base material has an elongation of 10% or more.
30. The water-absorbent sheet according to claim 29, wherein the first substrate has a weight per unit area of 10 to 60g/m2。
31. The water-absorbent sheet according to claim 29 or 30, wherein the first substrate has a bulk density of 0.1g/cm3The following.
32. The water-absorbent sheet according to any one of claims 29 to 31, wherein the first substrate is a through-air nonwoven fabric.
33. The water-absorbent sheet according to any one of claims 29 to 32, wherein a laminate in which the first substrate is laminated on the water-absorbent layer a and a structure in which an intermediate substrate is laminated on the water-absorbent layer B are laminated on the second substrate are laminated.
34. The water-absorbent sheet according to any one of claims 29 to 33, wherein only a laminate in which the first substrate is laminated on the water-absorbent layer is laminated on the second substrate.
35. The water-absorbent sheet according to claim 34, wherein a ratio (Lb/La) of a thickness (Lb) to a thickness (La) of 1.05 or less, the thickness (Lb) being a thickness from the liquid-absorbing surface of the first base material to a surface of the second base material on the water-absorbing layer side in a region including the particulate water-absorbing agent, and the thickness (La) being a thickness from the liquid-absorbing surface of the first base material to a surface of the second base material on the water-absorbing layer side in the gap.
36. The water absorbent sheet according to any one of claims 29 to 35, wherein the second substrate is a spunlace nonwoven.
37. The water-absorbent sheet according to any one of claims 29 to 36, wherein the first substrate contains the particulate water-absorbing agent, and a content ratio of the particulate water-absorbing agent in the first substrate is 5% or more of the particulate water-absorbing agent contained in the entire water-absorbent sheet.
38. The water-absorbent sheet according to any one of claims 29 to 37, wherein the particulate water-absorbing agent has a transmittance of 40 mass% or more with respect to the first substrate.
39. The water-absorbent sheet according to any one of claims 29 to 38, wherein the region containing the particulate water-absorbing agent and the gap have a shape extending in one direction of the liquid-absorbing surface of the first substrate, and are arranged in parallel.
40. The water-absorbent sheet according to any one of claims 29 to 39, which comprises a coating sheet disposed on at least a surface of the first substrate.
41. The water-absorbent sheet according to any one of claims 29 to 40, wherein the particulate water-absorbing agent has a CRC of 30g/g or more.
42. The water-absorbent sheet according to any one of claims 29 to 41, wherein the water-absorbent sheet comprises an adhesive,
The amount of the adhesive is 0.05 to 2.0 times the mass of the particulate water absorbent.
43. An absorbent article comprising the water-absorbent sheet according to any one of claims 29 to 42 sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet, wherein the liquid-permeable sheet is located on the first base material side and the liquid-impermeable sheet is located on the second base material side.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311262915.5A CN117257553A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2019215888 | 2019-11-28 | ||
| JP2019215887 | 2019-11-28 | ||
| JP2019-215887 | 2019-11-28 | ||
| JP2019-215888 | 2019-11-28 | ||
| PCT/JP2020/044517 WO2021107159A1 (en) | 2019-11-28 | 2020-11-30 | Water-absorbent sheet and absorbent article including same |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202311262915.5A Division CN117257553A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN114746058A true CN114746058A (en) | 2022-07-12 |
Family
ID=76130603
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202080082864.6A Pending CN114746058A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
| CN202311262915.5A Pending CN117257553A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
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| CN202311262915.5A Pending CN117257553A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
Country Status (4)
| Country | Link |
|---|---|
| JP (2) | JP7410175B2 (en) |
| CN (2) | CN114746058A (en) |
| WO (1) | WO2021107159A1 (en) |
| ZA (1) | ZA202205800B (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117942226A (en) * | 2022-10-27 | 2024-04-30 | 尤妮佳股份有限公司 | Absorbent article |
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| CN102395344A (en) * | 2009-06-17 | 2012-03-28 | 花王株式会社 | Absorbent article |
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| JP2001105520A (en) * | 1999-01-22 | 2001-04-17 | Mitsui Chemicals Inc | Moisture permeable composite nonwoven fabric |
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| WO2016040091A1 (en) | 2014-09-12 | 2016-03-17 | The Procter & Gamble Company | Process for making an absorbent article comprising a topsheet/acquisition layer laminate |
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| JP6932887B2 (en) | 2017-06-20 | 2021-09-08 | 日本製紙クレシア株式会社 | Absorbent article for light incontinence |
| JP2019042005A (en) | 2017-08-31 | 2019-03-22 | 日本製紙クレシア株式会社 | High-absorbent sheet and absorbent article with the same |
| WO2019130591A1 (en) | 2017-12-29 | 2019-07-04 | 花王株式会社 | Absorber and absorbent article |
| JP7096688B2 (en) | 2018-03-28 | 2022-07-06 | 大王製紙株式会社 | Absorbent article |
| WO2019198821A1 (en) | 2018-04-13 | 2019-10-17 | 株式会社日本触媒 | Water absorbent sheet, water absorbent sheet production method, and absorbent article |
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2020
- 2020-11-30 CN CN202080082864.6A patent/CN114746058A/en active Pending
- 2020-11-30 CN CN202311262915.5A patent/CN117257553A/en active Pending
- 2020-11-30 WO PCT/JP2020/044517 patent/WO2021107159A1/en active Application Filing
- 2020-11-30 JP JP2021561588A patent/JP7410175B2/en active Active
-
2022
- 2022-05-25 ZA ZA2022/05800A patent/ZA202205800B/en unknown
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2023
- 2023-12-21 JP JP2023215752A patent/JP2024026458A/en active Pending
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| CN102395344A (en) * | 2009-06-17 | 2012-03-28 | 花王株式会社 | Absorbent article |
| WO2011117997A1 (en) * | 2010-03-25 | 2011-09-29 | 住友精化株式会社 | Water-absorbing sheet structure |
| US20130018349A1 (en) * | 2010-03-25 | 2013-01-17 | Sumitomo Seika Chemicals Co., Ltd. | Water-absorbent sheet structure |
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Also Published As
| Publication number | Publication date |
|---|---|
| WO2021107159A1 (en) | 2021-06-03 |
| ZA202205800B (en) | 2023-11-29 |
| JP2024026458A (en) | 2024-02-28 |
| CN117257553A (en) | 2023-12-22 |
| JPWO2021107159A1 (en) | 2021-06-03 |
| JP7410175B2 (en) | 2024-01-09 |
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