CN117257553A - Water-absorbing sheet and absorbent article comprising same - Google Patents
Water-absorbing sheet and absorbent article comprising same Download PDFInfo
- Publication number
- CN117257553A CN117257553A CN202311262915.5A CN202311262915A CN117257553A CN 117257553 A CN117257553 A CN 117257553A CN 202311262915 A CN202311262915 A CN 202311262915A CN 117257553 A CN117257553 A CN 117257553A
- Authority
- CN
- China
- Prior art keywords
- water
- substrate
- absorbing agent
- sheet
- particulate water
- 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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Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- 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
- A61F13/535—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 inhomogeneous in the plane of the pad, e.g. core absorbent layers being of different sizes
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
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-
- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- 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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- B01J20/28—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
-
- 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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- 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
- 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
- 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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- 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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- 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
Abstract
The present invention relates to a water-absorbent sheet and an absorbent article comprising the same. Provided is a novel water-absorbing sheet which can significantly reduce the discharge of liquid from the water-absorbing sheet caused by reverse flow even when liquid is intermittently introduced a plurality of times (in particular, 3 times or more). A water-absorbing sheet comprising a first substrate, a second substrate, and a water-absorbing layer between the first substrate and the second substrate, wherein the water-absorbing layer contains a particulate water-absorbing agent, the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid, and the ratio of the thickness (mm) of the first substrate to the 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.
Description
The present application is a divisional application of chinese patent application having a filing date of 2020, 11/30, a filing number of 202080082864.6, and an invention name of "water-absorbent sheet and absorbent article comprising the same".
Technical Field
The present invention relates to a water-absorbent sheet and an absorbent article comprising the same.
Background
The water-absorbent resin (SAP/Super Absorbent polymer) is a water-swellable, water-insoluble, high-molecular gelling agent, and is used for sanitary materials such as paper diapers, sanitary napkins, adult-oriented incontinence products, and the like; soil water-retaining agent for agriculture, forestry and gardening, industrial water-stopping agent and the like.
These absorbent articles are generally manufactured in a diaper manufacturing factory in the form of an absorbent body obtained by mixing a water-absorbent resin with a fibrous material and molding each absorbent article, and are manufactured into various shapes (for example, hourglass type, fox type, elliptical type, etc. in plan view) according to the purpose. In these absorbent body manufacturing methods, since the absorbent body can be molded separately and processed into an arbitrary shape, the amounts of the fibers and the water-absorbent resin can be easily adjusted for each absorbent article, and thus, the present-day paper diapers have become the mainstream.
In recent years, however, in the production of disposable diapers, the production of disposable diapers has been started with an absorbent article obtained by cutting a long water-absorbent sheet obtained by fixing a water-absorbent resin between two sheets in a sanitary material production process (referred to as a water-absorbent sheet, which is usually cut into a rectangular shape having a width of about 10cm and a length of 10 cm). The paper diaper manufacturer can simplify the process of manufacturing the paper diaper by purchasing or manufacturing the long continuous water-absorbing sheet, and can reduce the paper diaper by not using pulp. The water-absorbent sheet is constituted by sandwiching and fixing water-absorbent resin particles between upper and lower sheets (particularly, nonwoven fabric sheets), and is usually produced by cutting a long continuous sheet after the long continuous sheet is produced, and then the long continuous sheet is formed into a rectangular shape having a width of about 10cm and a length of 10cm, and incorporated into a paper diaper (for example, international publication No. 2010/143635).
Unlike conventional sanitary materials (disposable diapers), the history of disposable diapers based on water-absorbent sheets is still short, and development of water-absorbent resins suitable for water-absorbent sheets and parameter development have not been substantially performed in practical cases, and conventional water-absorbent resins for disposable diapers have been used directly for water-absorbent sheets.
Disclosure of Invention
Problems to be solved by the invention
The inventors found that: as long as the water-absorbent sheet mainly made of a thin material is structurally liable to generate absorbed liquid, the water-absorbent sheet is pressed and discharged in the direction of introduction of the absorbed liquid, so-called "backflow". "reverse flow" is also known as Re-wet. And found that: if the liquid is intermittently introduced a plurality of times (in particular, 3 times or more) and the liquid introduction amount becomes large, the problem of occurrence of backflow becomes remarkable. When the back flow occurs, the skin in contact with the water-absorbing sheet is exposed to a high moisture content by contact with the liquid in the back flow. Therefore, not only the user may feel uncomfortable, but also the skin in contact with the water-absorbent sheet may be prone to inflammation.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a novel water-absorbing sheet capable of remarkably reducing discharge of a liquid from the water-absorbing sheet due to backflow even if the liquid is intermittently introduced a plurality of times (in particular, 3 times or more).
Solution for solving the problem
The present inventors have conducted intensive studies to solve the above problems. The result shows that: the above-described problems can be solved by a water-absorbent sheet comprising 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 contains a particulate water-absorbing agent, the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid, and the ratio of the thickness (mm) of the first substrate to the 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.
In another aspect of the present invention, there is provided a water-absorbing sheet comprising a first substrate, a second substrate, and a water-absorbing layer between the first substrate and the second substrate, wherein the water-absorbing layer contains a particulate water-absorbing agent, the water-absorbing 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, according to another aspect of the present invention, there is provided a water-absorbing sheet comprising a first substrate, a second substrate, and a water-absorbing layer between the first substrate and the second substrate, wherein the water-absorbing layer contains a particulate water-absorbing agent, the water-absorbing 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 (thickness (mm) of the first substrate/thickness (mm) of the second substrate) is 1.5 or more and less than 14.
Another aspect of the present invention provides a water-absorbing sheet comprising a first substrate, a second substrate, a water-absorbing layer between the first substrate and the second substrate, and a cover sheet disposed on the surface of the first substrate, wherein the water-absorbing layer contains a particulate water-absorbing agent, the surface of the cover sheet forms a liquid-absorbing surface that directly absorbs liquid, and the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm)/thickness of the second substrate (mm)) 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 view showing a cross section of a water-absorbent sheet according to another embodiment of the present invention.
FIG. 5 is a schematic view illustrating a method for measuring the transmittance of the nonwoven fabric with respect to the particulate water absorbing agent.
Fig. 6 is a plan view and a right side view showing a sample for evaluating a specific amount of backflow, and is a view showing a case where the water-absorbent sheet produced in the example is wrapped with a liquid-impermeable sheet.
Fig. 7 is a plan view and a front view of the liquid injection cylinder for evaluating a specific amount of reflux.
Fig. 8 is a front view showing a case where a liquid injection tube is placed on the water-absorbing sheet used in the examples of the present application in the specific reflux amount evaluation.
Fig. 9 is a front view showing a case where an aqueous sodium chloride solution was poured into the water-absorbent sheet from the liquid injection tube using a funnel in the specific reflux amount evaluation.
Fig. 10 is a schematic view showing an apparatus for evaluating the leakage amount in the plane direction.
Fig. 11 is a schematic diagram illustrating a method for measuring the fuzzing area ratio of a nonwoven fabric.
Fig. 12 is a plan view and a front view of the liquid injection tube for evaluating the specific return amount of pressurization.
FIG. 13 is a front view showing a case where a liquid injection tube is placed on a water-absorbing sheet used in the examples of the present application in the evaluation of the specific return amount under pressure.
FIG. 14 is a front view showing a case where an aqueous sodium chloride solution was poured from a liquid injection tube into a water-absorbent sheet using a funnel in the evaluation of the specific return amount under pressure.
FIG. 15 is a schematic view showing a cross section of a water-absorbing sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbing sheet produced in the example.
FIG. 16 is a schematic view showing a cross section of a water-absorbing sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbing sheet produced in the example.
Fig. 17 is a schematic diagram illustrating a method for measuring elongation of a nonwoven fabric.
FIG. 18 is a schematic view showing a cross section of a water-absorbent sheet according to the 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-absorbing sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbing sheet produced in the example.
FIG. 21 is a schematic view showing a cross section of a water-absorbing sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbing sheet produced in the example.
Fig. 22 is a schematic diagram illustrating a method for measuring elongation of a nonwoven fabric.
FIG. 23 is a schematic view illustrating a method for measuring the transmittance of the nonwoven fabric with respect to the particulate water absorbing agent.
Fig. 24 is a plan view and a right side view showing a sample for evaluating a specific amount of backflow, and is a view showing a case where the water-absorbent sheet produced in the example is wrapped with a liquid-impermeable sheet.
Fig. 25 is a plan view and a front view of the liquid injection cylinder for evaluating a specific amount of backflow.
Fig. 26 is a front view showing a case where a liquid injection tube is placed on the water-absorbing sheet used in the examples of the present application in the specific reflux amount evaluation.
Fig. 27 is a front view showing a case where an aqueous sodium chloride solution was poured into a water-absorbing sheet from a liquid injection tube using a funnel in the evaluation of a specific reflux amount.
Detailed Description
The present invention will be described below while showing the best mode. For the purposes of this specification as a whole, singular forms shall be understood to include the plural concepts thereof, unless specifically mentioned otherwise. Thus, unless specifically mentioned otherwise, it is to be understood that singular forms (e.g., "a," "an," "the," etc. in the case of English) also include plural forms of the concepts thereof. Further, unless specifically mentioned otherwise, the terms used in the present specification should be construed as being used in accordance with the meanings commonly used in the art. Accordingly, unless otherwise defined, all technical and scientific terms used in this specification 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 following embodiments, and various modifications can be made within the scope of the claims.
[ first invention ]
The first invention will be described. The water-absorbent sheet of the first 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 contains a particulate water-absorbing agent, the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid, and the ratio of the thickness (mm) of the first substrate to the 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.
[ 1. Definition of terms ]
[1-1 Water-absorbent sheet ]
The term "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 water-absorbing sheet, an adhesive may be used for bonding the substrates to each other and/or bonding the substrate to the particulate water-absorbing agent, or a hot-melt adhesive may be used. The water-absorbing sheet may contain other components (fibrous component, antibacterial agent, deodorant, etc.) in addition to the particulate water-absorbing agent. There are water-absorbing sheets comprising other sheets in addition to 2 sheets of a base material sandwiching a particulate water-absorbing agent or the like. In the present embodiment, there may be water-absorbing sheets including other sheets in addition to the 2 sheets of base material sandwiching the particulate water-absorbing agent or the like, as long as the solution of the object of the invention of the present application is not hindered. A water-absorbing sheet obtained by sandwiching a particulate water-absorbing agent or the like with 2 sheets of a base material is a preferred embodiment.
In general, the water-absorbent sheet is 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 (rectangle or the like) and then incorporated into an absorbent article (paper diaper, sanitary napkin, incontinence pad or the like) for use. An absorbent article such as a disposable diaper (disposable diaper), a sanitary napkin, and an incontinence pad includes: an absorber for absorbing and retaining body fluids such as urine and menstrual blood discharged from the body, a soft liquid-permeable front sheet disposed on the side contacting the body, and a liquid-impermeable back sheet disposed on the side opposite to the side contacting the body. The water-absorbent sheet can be used as the aforementioned absorber. Conventional disposable diapers are absorbent articles which are molded for each disposable diaper and which have a shape suitable for buttocks. Therefore, such an absorber is technically different from the water-absorbent sheet of the present invention.
[1-2 Water-absorbent resin ]
In the present specification, "water-absorbent resin" means: a polymer gel having a water swelling property (CRC) of 5g/g or more as defined by ERT441.2-02 and a water-soluble component (Ext) of 50 mass% or less as defined by ERT 470.2-02.
The water-absorbent resin is preferably a hydrophilic crosslinked polymer obtained by crosslinking polymerization of an unsaturated monomer having a carboxyl group. The shape of the water-absorbent resin is a sheet, a fiber, a film, a particle, a gel, or the like. The water-absorbent sheet according to one embodiment of the present invention uses a particulate water-absorbent resin.
In the present specification, the term "water-absorbent resin" is not limited to the total amount (100 mass%) but is merely a mode of the water-absorbent resin. The water-absorbent resin composition may contain additives and the like as long as the CRC and Ext described above are satisfied. In the present specification, the term "water-absorbent resin" means a concept including intermediates 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 are sometimes also referred to as "water-absorbent resins".
As described above, in this specification, the water-absorbent resin composition and the intermediate are sometimes 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) comprising 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. The water-absorbent sheet according to one embodiment of the present invention absorbs water-based liquids such as urine, menstrual blood, sweat, and other body fluids.
In the present specification, the "particulate water absorbing agent" refers to a particulate (powdery) water absorbing agent (the water absorbing agent contains a water absorbing resin as a main component and thus corresponds to the particulate water absorbing resin). The concept of "particulate water absorbing agent" includes any one of a particulate water absorbing agent of a single particle and an aggregate of a plurality of particulate water absorbing agents. In the present specification, "particulate" means having a form of particles. Herein, "particles" refer to smaller segments of matter,is described (refer to "granule", mcGraw-Hill science and technology dictionary, 3 rd edition of McGraw-Hill science and technology dictionary, journal industry Press, 1996, page 1929). In the present invention, the form of the water absorbing agent is not limited to the particulate water absorbing agent. In the present specification, the present invention is described taking the particulate water absorbing agent as an example, but the "particulate water absorbing agent" may be replaced with the "water absorbing agent". In the present specification, the term "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. Mu.m. Here, if the weight average particle diameter of the particulate water absorbing agent is less than 200 μm, there is a concern that the handleability may be lowered. Further, if the weight average particle diameter of the particulate water absorbing agent exceeds 600. Mu.m, the texture of the water absorbing sheet may be lowered. 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. Mu.m, more preferably 300 to 450. Mu.m. In the water-absorbent sheet of the present invention, the particle diameter is preferably 95% by mass or more and 850 μm or less of the entire particulate water-absorbing agent, more preferably 98% by mass or more and 850 μm or less of the entire particulate water-absorbing agent, and still more preferably 850 μm or less of the entire particulate water-absorbing agent. In the examples of the present application, the particle diameter of 850 μm or less was set to substantially 100% by mass of the whole particulate water absorbing agent. In this specification, the method for measuring the weight average particle diameter is calculated from the PSD obtained by the method for measuring the "PSD" specified in ERT420.2-02 by the same method as "(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution" described in U.S. Pat. No. 7638570.
The particulate water absorbing agent contains a water absorbent resin in the form of a polymer (or, 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% by mass, preferably 70 to 100% by mass, more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, particularly preferably 95 to 100% by mass of the water absorbing 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% by mass of the water absorbing 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%. And, it is preferable that: in addition to the water-absorbent resin, 0 to 10 mass% of components, in particular, water, additives (inorganic particles, polyvalent metal cations) and the like are contained.
The particulate water absorbing agent preferably has a water content of 0.2 to 30% by mass. As described above, a 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 as the main component of the particulate water-absorbing agent include polyacrylic acid (salt) resins, polysulfonic acid (salt) resins, maleic anhydride (salt) resins, polyacrylamide resins, polyvinyl alcohol resins, polyethylene oxide resins, polyaspartic acid (salt) resins, polyglutamic acid (salt) resins, alginic acid (salt) resins, starch resins, and cellulose resins. 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 polymerizing the polyacrylic acid (salt) is usually 50 to 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably substantially 100 mol% based on the whole of the monomers used for polymerization (excluding the internal crosslinking agent).
[1-5.EDANA and ERT ]
"EDANA" is a shorthand for European nonwoven industry Congress (European Disposables and Nonwovens Associations). "ERT" is an abbreviation for the method (EDANA Recommended Test Methods) for measuring water-absorbent resins according to the European standard (essentially the world standard) 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. Others ]
In the present specification, "X to Y" in the expression range means "X or more and Y or less".
In the present specification, unless otherwise noted, the unit "t (ton)" of mass means "Metric ton". "ppm" refers to "mass ppm". "mass" and "weight", "parts by mass" and "parts by weight", "percent by mass" and "percent by weight", and "ppm by mass" and "ppm by weight", respectively, are to be regarded as the same meaning.
In the present specification, "-acid (salt)" means "-acid and/or salt thereof. "(meth) acrylic" means "acrylic and/or methacrylic".
In this specification, the unit "liter" of volume is sometimes expressed as "L" or "L". "mass%" is sometimes expressed as "wt%". When the trace component is measured, the detection limit is expressed as n.d. (Non Detected) or less.
[ 2. Water-absorbing sheet ]
The water-absorbing sheet of the present invention comprises a first substrate, a second substrate, and a water-absorbing layer located between the first substrate and the second substrate, wherein the water-absorbing layer contains a particulate water-absorbing agent, the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid, and the ratio of the thickness (mm) of the first substrate to the 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.
With this configuration, even when the liquid is intermittently introduced a plurality of times (in particular, 3 times or more) and the liquid introduction amount becomes large, the discharge of the liquid from the water-absorbing 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 substrate forming the liquid-absorbing surface that directly absorbs liquid is 1.5 or more and less than 14 relative to the thickness (mm) of the second substrate. That is, the first substrate is significantly thicker than the second substrate. A liquid-absorbing surface that directly absorbs liquid is formed on a surface of the first substrate that is significantly thicker than the second substrate. In this specification, "directly" does not include a method of sequentially absorbing liquid permeated from another substrate or the like. In the present specification, the case where a cover sheet described later is disposed on the surface of the first substrate includes a case where a liquid-absorbing surface that directly absorbs liquid is formed on the surface of the first substrate.
In another aspect of the present invention, the surface of the first substrate is a liquid-absorbing surface that directly absorbs the liquid, and therefore, the water-absorbing layer is not disposed on the first substrate. Thus, the water-absorbent sheet according to one embodiment of the present invention is a water-absorbent sheet comprising 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 contains a particulate water-absorbing agent, and wherein the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm)/thickness of the second substrate (mm)) is 1.5 or more and less than 14. In this embodiment, even if a part of the particulate water absorbing agent contained in the water absorbing layer penetrates the first substrate and moves on the first substrate to expose a part of the particulate water absorbing agent, the water absorbing layer is not considered to be disposed. The cause of this movement is assumed to be, for example, vibration generated when the water-absorbing 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 found that: in conventional water-absorbent sheets (for example, water-absorbent sheets in which the thicknesses of the first substrate and the second substrate are the same in order to produce a thin water-absorbent sheet), the amount of backflow is significantly large in the measurement of backflow under specific conditions (also referred to as "specific backflow amount evaluation" in the present specification) in the examples of the present application. In other words, if the liquid is intermittently introduced a plurality of times (in particular, 3 times or more), the liquid amount becomes equal to or more than the set absorption amount and an excessive "backflow" occurs in the normal configuration. In contrast, in the present invention, by increasing the distance between the liquid suction surface of the first substrate and the water-absorbing layer by a significant thickness of the first substrate on the liquid introduction side compared to the second substrate, the liquid introduced from the liquid suction surface is not retained on the liquid suction surface (and the introduced liquid is not retained locally), and the liquid can be effectively fed into the water-absorbing layer of the lower layer that performs the water-absorbing function. Specifically, this is considered to be because: when the liquid passes through the first substrate, the liquid has high diffusibility in the planar direction, and the diffused liquid (for example, urine) can be widely and omnidirectionally transferred (moved) to the entire surface of the water-absorbing layer. That is, when the absorbed liquid reaches the water-absorbing layer, the liquid has already spread in the plane direction, and therefore, even if a large amount of liquid is introduced into the water-absorbing layer, the water-absorbing layer absorbs the liquid that spreads in the plane direction rather than locally. Thus, the liquid can be sufficiently absorbed and held in the water absorbing layer. It is also considered that the first base material is imparted with a liquid-diffusing function of the hydrophilic pulp contained in the conventional absorber. Further, since the first base material is significantly thicker when the liquid is once absorbed by the water absorbing layer, the liquid absorbed by the water absorbing layer can be significantly reduced from flowing back to the liquid absorbing surface of the first base material, and thus the liquid flowing back can be prevented from rising to (contacting) the skin. On the other hand, even if the second substrate is significantly thickened as compared with the first substrate, the desired effect of the present invention cannot be obtained. The reason for this is not clear, in other words, it can be said that it is an unexpected effect to those skilled in the art.
In the water-absorbing sheet, the water absorbing function of the water-absorbing layer is mainly carried by the water-absorbing agent. In particular, the function of the water absorbing agent is more important in a water absorbing sheet having a structure different from that of a conventional absorbent article in which pulp is present in the water absorbing layer. Particularly in the present invention, since the first substrate is significantly thicker, it is difficult for the liquid once introduced into the water absorbing agent to flow back to the liquid suction surface of the first substrate. Here, in addition to the reverse flow, there is also leakage in the face direction (lateral leakage), which means: and a phenomenon in which the liquid which is not absorbed instantaneously after reaching the water-absorbing layer leaks out from the water-absorbing sheet in the plane direction. The invention presents the following constitution: by utilizing the advantage that the particulate water absorbing agent is formed in a sheet (layer) shape, the liquid diffusion in the surface direction of the water absorbing layer is utilized to the maximum extent, thereby suppressing the backflow to the first substrate and suppressing the leakage (lateral leakage) from the surface direction of the water absorbing sheet. Specifically, in the present invention, since the first substrate is significantly thicker than the second substrate, the liquid is highly diffusible in the planar direction when passing through the first substrate, and the absorption rate is significantly high, in other words, the particulate water absorbing agent that performs the function of a tank absorbs the diffused liquid (for example, urine) widely and omnidirectionally in the planar direction. That is, when the absorbed liquid reaches the water-absorbing layer, the liquid has already spread in the plane direction, and therefore, even if a large amount of liquid is introduced into the water-absorbing layer, the water-absorbing layer absorbs the liquid that spreads in the plane direction rather than locally. Thus, the liquid can be sufficiently absorbed and held in the water absorbing layer, and leakage from the water absorbing sheet in the face direction is remarkably low. Further, even if the liquid that the water absorbing layer fails to absorb is to flow backward, the first base material is significantly thicker than the second base material, so that the liquid can be prevented from rising to the skin. Therefore, the "specific reflux amount evaluation" can be made excellent, and leakage in the plane direction can be suppressed. Incidentally, the water-absorbent sheet or the absorbent article designed to suppress the amount of backflow under normal conditions does not necessarily exhibit excellent results in the "specific backflow amount evaluation" of 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 in which an infant whose bladder is small, for example, to begin learning to walk, moves back and forth during the daytime or the like, 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.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and duplicate descriptions are omitted. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from actual ratios.
First, the structure of the water-absorbing sheet will be described with reference to fig. 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 other embodiments of the present invention.
In fig. 1, arrows indicate directions in which absorbed liquid is introduced. The first substrate 11 is positioned on the side where the liquid to be absorbed (sucked liquid) is introduced with respect to the water-absorbing layer 12. That is, the first base material 11 is disposed on the liquid discharge side (for example, the skin side in the paper diaper). Thereby, the first substrate 11 forms a liquid-absorbing surface that directly absorbs liquid. A water absorbing layer 12 is disposed between the first substrate 11 and the second substrate 13.
In FIG. 1, water-absorbing layer 12 includes particulate water-absorbing agent 14. In the mode of FIG. 1, water absorbing layer 12 shows a state in which particulate water absorbing agent 14 is present between first substrate 11 and second substrate 13. Water-absorbing layer 12 includes particulate water-absorbing agent 14 in contact with (or fixed to) first substrate 11 and particulate water-absorbing agent 14 in contact with (or fixed to) second substrate 13. A part of particulate water absorbing agent 14 may not contact each of substrates 11 and 13 (or may not be fixed, and may be released from each of substrates 11 and 13). Therefore, the water-absorbing "layer" does not mean a continuous body such as a sheet, and may be any one as long as it exists between the first substrate 11 and the second substrate 13 with a constant thickness. In the case where particulate water absorbing agent 14 is fixed to each of substrates 11 and 13, an adhesive may be used, for example. The method for producing the water-absorbent sheet using the adhesive is described in detail in [ 3 ].
Within first substrate 11, particulate water absorbing agent 14 may be present. As particulate water absorbing agent 14 in first substrate 11, for example, particulate water absorbing agent 14 in contact with (or fixed to) first substrate 11, or particulate water absorbing agent 14 in contact with (or fixed to) second substrate 13 may be detached and trapped in particulate water absorbing agent 14 in first substrate 11. When particulate water absorbing agent 14 is present in the first base material, the content ratio of particulate water absorbing agent 14 in first base material 11 is preferably 5% or more, more preferably 10% or more, still more preferably 20% or more, and still more preferably 30% or more, with respect to particulate water absorbing agent 14 contained in the entire water absorbing sheet 10. The upper limit is not particularly limited, but the preferable order is 90% or less, 70% or less, and 50% or less. In the present specification, the content ratio of particulate water absorbing agent 14 in first substrate 11 to particulate water absorbing agent 14 contained in the entire water absorbing sheet 10 is calculated by the method of the example described later.
The water-absorbent sheet 10 has a cover sheet 16. The wrapping sheet 16 has the following purpose: the purpose of holding the shape of the water-absorbing sheet 10, which is a structure in which the particulate water-absorbing agent 14 is supported between the first substrate 11 and the second substrate 13; so that particulate water-absorbing agent 14 supported between first substrate 11 and second substrate 13 does not fall off (fall off) from the absorber (water-absorbing sheet 10); when particulate water absorbing agent 14 is transferred to the outer surface (liquid absorbing surface that directly absorbs liquid) of first substrate 11 through first substrate 11, particulate water absorbing agent 14 is not brought into direct contact with the skin. 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 transfer to the outer surface (liquid-absorbing surface that directly absorbs liquid) of the first substrate 11 by surface treatment of the first substrate 11, and the like. As a method of maintaining the effect of the present application without causing particulate water absorbing agent 14 to fall off from water-absorbing sheet 10, it is preferable to have coated sheet 16.
The cover sheet 16 is disposed on the first base material 11, and is folded so as to cover the entirety of the water-absorbing layer 12 and the second base material 13. Thus, the cover sheet 16 covers the entirety of the first substrate 11, the water absorbing layer 12, and the second substrate 13. With this structure, the particulate water absorbing agent 14 can be prevented from falling off the water absorbing sheet 10. The cover sheet 16 does not necessarily cover the entirety of the first substrate 11, the water absorbing layer 12, and the second substrate 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 side surface of the second base material 13 opposite to the liquid-absorbent surface (i.e., the surface on which the water-absorbent layer 12 is disposed). That is, with respect to 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, one end of the cover sheet 16 overlaps the other end of the cover sheet 16. In this case, the cover sheet 16 covers the entire or a part of the surface of the first substrate 11 opposite to the surface on which the water absorbing layer 12 is provided, the side surface of the water absorbing layer 12, and the side surface of the second substrate 13.
Here, with respect to 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, one end of the cover sheet 16 is separated from the other end of the cover sheet 16. For example, in fig. 2, the cover sheet 16 is disposed on the first base material 11, is folded so as to cover the side surface of the water-absorbing layer 12 and the side surface of the second base material 13, and is disposed at a distance from one end of the cover sheet 16 to the other end of the cover sheet 16 on the surface of the second base material 13 opposite to the liquid-absorbing surface that directly absorbs liquid (i.e., the surface on which the water-absorbing layer 12 is disposed). In this case, the cover sheet 16 covers the liquid suction 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 according to the present invention, the coating sheet 16 is not necessarily required to be constituted, but the water-absorbent sheet 10 according to the present invention is provided with the coating sheet 16 in such a constitution, 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 one embodiment of the present invention preferably has the cover sheet 16 disposed at least on the surface of the first substrate 11. In the present specification, the first substrate 11 forms a liquid-absorbing surface that directly absorbs liquid in the case of having the cover sheet 16 as described above, but in the case of forming a liquid-absorbing surface that directly absorbs liquid in the water-absorbing sheet 10 having the cover sheet 16, for example, the cover sheet 16 may be replaced with the following description: a water-absorbing sheet comprising a first substrate, a second substrate, a water-absorbing layer between the first substrate and the second substrate, and a coating sheet disposed on the surface of the first substrate, wherein the water-absorbing layer contains a particulate water-absorbing agent, the surface of the coating sheet forms a liquid-absorbing surface that directly absorbs liquid, and the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm)/thickness of the second substrate (mm)) is 1.5 or more and less than 14.
As a method of 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 is preferably in direct contact with particulate water absorbing agent 14 in water absorbing layer 12 or in contact with an adhesive, and/or second substrate 13 is preferably in direct contact with particulate water absorbing agent 14 in water absorbing layer 12 or in contact with an adhesive. As described above, the water-absorbent sheet of the present invention has a simple structure substantially containing only the following substances: the present invention relates to a particulate water absorbing agent comprising 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 at least one of the first substrate and the second substrate, and a coating sheet for coating a part or all of them as needed (the case where additives and the like described in the present specification, which may be contained in the particulate water absorbing agent, are not excluded). More preferably, the composition is a simple composition comprising only the following substances: the particulate water absorbing agent is formed by 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 coating sheet for coating all of them. That is, the water-absorbent sheet of the present invention can effectively reduce the specific amount of backflow despite its simple structure.
In the present invention, the ratio of the thickness (mm) of the first substrate to the 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. If 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 suction surface of the first substrate and the water suction layer and the second substrate may not be sufficiently ensured, and the liquid temporarily reaching the water suction layer and the second substrate may flow back. In the case where the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate is 14 or more, the liquid absorbing surface of the first substrate 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 substrate leaks in the plane direction before reaching the water absorbing layer.
The lower limit of the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate is preferably 1.7 or more, more preferably 2.5 or more, still more preferably 3.2 or more, still more 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 substrate to the thickness (mm) of the second substrate is preferably 12 or less, more preferably 10 or less, further preferably 9 or less, and still further 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 backflow 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 substrate to the thickness (mm) of the second substrate 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 substrate to the thickness (mm) of the second substrate 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 substrate can have a low-density and fluffy form, and can be thinned as compared with an absorbent article used in a conventional type of absorbent article. When the water-absorbent sheet is used in a paper diaper, the thickness thereof is, for example, 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 at 40% RH to 50% RH. On the other hand, in view of the strength of the water-absorbing 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 examples of the present application was 2 to 5mm.
The thicknesses of the first substrate, the second substrate, the cover sheet, and the water-absorbing sheet in the present application were measured using a scale thickness gauge (thickness measuring instrument) (model: J-B, measuring head: 50mm in the up-down direction of anvil, manufactured by Kawasaki Co., ltd.). The number of measurement points was measured 2 times for each part at 5 selected positions in the sheet to be measured, and the measurement value was an average value of 5 total positions. In measuring the thickness, the thickness was measured by gradually removing the hand from the grip so as to prevent the pressure from being applied to the sheet as much as possible. Specifically, the sheet to be measured is flatly attached to a plate having a constant thickness so as not to cause wrinkles or deformations in the measurement site of the sheet, and the plate is set on the lower measurement head of the thickness measuring device. Next, the upper measuring head of the thickness measuring instrument was moved closer to a height position of 2 to 3mm from the sheet to be measured, and then the hand was gradually moved away from the handle, whereby the total thickness of the sheet and the plate to be measured was measured. The thickness of the sheet to be measured is determined by the formula t1=t2 to T0 (T0: thickness of plate (mm), T1: thickness of sheet to be measured (mm), T2: thickness of sheet to be measured and plate (mm)).
Here, the content of the particulate water absorbing agent contained in the water absorbing sheet is preferably 50 to 400g/m 2 More preferably 100 to 350g/m 2 More preferably 125 to 250g/m 2 。
In the surface of the first substrate on the water absorbing layer side (the surface on which the particulate water absorbing agent is disposed), the ratio of the region containing 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%, still more preferably more than 90% in terms of area. The upper limit of the ratio of the region containing the particulate water absorbing agent in the water absorbing layer-side surface of the first substrate is not particularly limited, but is 99.5% or less in terms of area from the practical point of view. By setting the particulate water absorbing agent in such a range, the particulate water absorbing agent is disposed in good balance, and the effect of reducing the amount of reflux is further exhibited. The ratio of the region containing the particulate water absorbing agent in the water absorbing layer side surface of the first substrate is the same as the ratio of the region containing the particulate water absorbing agent in the water absorbing layer side surface (surface on which the particulate water absorbing agent is disposed) of the second substrate.
Here, the ratio of the region containing the particulate water absorbing agent in the water absorbing layer-side surface of the first substrate may be controlled by adjusting the scattering region of the particulate water absorbing agent at the time of manufacturing the water absorbing sheet.
Further, the ratio of the region containing the particulate water absorbing agent in the water absorbing layer side surface of the first substrate can be calculated by taking an image of and analyzing the cross section of the produced water absorbing sheet by an X-ray CT apparatus (insexio SMX-100 CT). Specifically, by taking a cross section of the water-absorbing sheet, the interface between the first substrate or the second substrate and the water-absorbing layer is classified into a region where the particulate water-absorbing agent is present and a region where the particulate water-absorbing agent is not present, and the ratio of the regions is calculated by summing up the respective regions. The ratio of the region containing the particulate water absorbing agent was calculated by photographing 3 or more cross sections of the water absorbing sheet in the width direction, the ratio of the region containing the particulate water absorbing agent obtained from each cross section was averaged, and the value obtained therefrom was regarded as "ratio of the region containing the particulate water absorbing agent".
In order to impart liquid permeability, diffusibility, softness, and the like to the water-absorbent sheet, the surface of the water-absorbent sheet (the surface of the first substrate or the surface of a coating sheet described later) may be appropriately embossed. The region to be embossed may be the entire surface of the water-absorbent sheet or may be a part of the surface. By providing a continuous embossed region along the longitudinal direction of the water-absorbent sheet, the liquid can be easily spread along the longitudinal direction. For example, by providing an embossing region continuously along the longitudinal direction, the region functions as a passage (liquid carrying passage) for circulating a large amount of liquid. The embossed area may be provided in a straight line, may be provided in a curved line, or may be provided in a wavy line.
The particulate water absorbing agent may be dispersed over the entire surface of the water absorbing sheet, or a region where the particulate water absorbing agent is not present may be provided locally. That is, in the water-absorbing layer between the first substrate and the second substrate, the particulate water-absorbing agent may be dispersed over the entire surface of the water-absorbing layer, or a region where the particulate water-absorbing agent is not present may be provided in a part of the water-absorbing 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. As a means for providing the region where the particulate water absorbing agent is not present in the part of the water absorbing layer, the region containing the particulate water absorbing agent in the water absorbing layer between the first substrate and the second substrate is disposed in a state in which the region is disposed with a gap substantially containing no particulate water absorbing agent therebetween. When the region where the particulate water absorbing agent is not present is provided in a part of the water absorbing 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 absorbing sheet. In this way, by continuously providing the region where the particulate water absorbing agent is not present along the longitudinal direction, the region functions as a passage (liquid transport passage) for circulating a large amount of liquid. The region where the particulate water absorbing agent is not present may be provided in a straight line, may be provided in a curved line, or may be provided in a wavy line.
In the case where the region where the particulate water absorbing agent is not present is provided in a part of the water absorbing layer, the first substrate preferably has stretchability, and the elongation of the first substrate is more preferably 10% or more. In one embodiment, in the water-absorbing sheet of the present invention, in the water-absorbing layer between the first substrate and the second substrate, the region containing the particulate water-absorbing agent is disposed with a gap substantially free of the particulate water-absorbing agent therebetween, 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 is dispersed in a region where the particulate water absorbing agent is not present in a local portion of the first substrate or the second substrate. Thus, the particulate water absorbing agent is disposed with a gap substantially free of the particulate water absorbing agent interposed therebetween.
In the conventional structure of the water-absorbent sheet, the water-absorbent resin particles that have absorbed liquid may swell, thereby weakening the fixation of the water-absorbent resin particles to the upper and lower sheets, and the water-absorbent resin particles may move in the sheet. Thus, the water-absorbent resin particles are unevenly distributed in the sheet, and the shape of the water-absorbent sheet collapses. In this case, the liquid absorbency of the water absorbent sheet varies, and causes leakage. The water-absorbent resin particles may sometimes fall off from the inside to the outside of the sheet.
In one embodiment of the water-absorbing sheet of the present invention, the first substrate has an elongation of 10% or more, and when the region where the particulate water-absorbing agent is not present is provided in a part of the water-absorbing layer, the specific reflux amount can be effectively reduced, and the shape of the sheet (the sheet has a high shape retention) can be maintained even after absorbing the liquid.
Hereinafter, a description will be given of a manner in which, in the water absorbing layer between the first substrate and the second substrate, the region containing the particulate water absorbing agent is disposed with a gap substantially free of the particulate water absorbing agent therebetween, and the elongation of the first substrate is 10% or more, with reference to fig. 3. 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 modes ((a) to (c)) of the water-absorbent sheet 10. In fig. 3 (a) to (c), arrows indicate directions in which the absorbed liquid is introduced. The first substrate 11 is positioned on the side where the liquid to be absorbed (sucked liquid) is introduced with respect to the water-absorbing layer 12. That is, the first base material 11 is disposed on the liquid discharge side (for example, on the skin side in a paper diaper). A water absorbing layer 12 is disposed between the first substrate 11 and the second substrate 13.
In fig. 3 (a) to (c), water-absorbing layer 12 contains particulate water-absorbing agent 14. In the modes (a) to (c) of fig. 3, a state is shown in which particulate water absorbing agent 14 is present between first substrate 11 and second substrate 13 in water absorbing layer 12. A portion of particulate water absorbing agent 14 may be detached from each of substrates 11, 13. Particulate water absorbing agent 14 (a region including particulate water absorbing agent 14) is disposed across gap 15 substantially free of particulate water absorbing agent 14. Therefore, the water-absorbent "layer" does not mean a continuous body such as a sheet, and may be any one as long as it exists between the first substrate 11 and the second substrate 13 with a constant thickness and length. For example, the water-absorbing layer 12 may intermittently exist with a certain thickness and length between the first substrate 11 and the second substrate 13. When particulate water absorbing agent 14 is fixed to substrate 11 and/or substrate 13, an adhesive may be used, for example. The method for producing the water-absorbent sheet using the adhesive is described in detail in [ 3 ].
Here, in fig. 3 (a), the gap 15 is formed between the first substrate 11 and the second substrate 13, but the embodiment of fig. 3 (b) and 3 (c) is also included as the gap 15 in the present invention. In (b) of FIG. 3, the region containing particulate water absorbing agent 14 is partitioned by the contact of first substrate 11 with second substrate 13. The first substrate and the second substrate are in contact with each other, but maintain the liquid passage, and thus they are regarded as gaps. Further, since the water-absorbent layer 12 is partitioned by 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, the water-absorbent layer 12 intermittently exists in this embodiment. In fig. 3 (c), the end portion of the water-absorbing sheet 10 is closed by the first substrate 11 and the second substrate 13 by overlapping the end portion of the first substrate 11 and the end portion of the second substrate 13. In this case, too, the first base material 11 (the first base material 11 and the second base material 13, as the case may be) enters the end portion of the water-absorbent layer 12, and the water-absorbent layer 12 is not present at the end portion of the water-absorbent 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 mentioned: such as particulate water-absorbing agent 14 in contact with (or fixed to) first substrate 11; particulate water-absorbing agent 14 in contact with (or fixed to) second substrate 13 is detached and trapped in particulate water-absorbing agent 14 in first substrate 11. When particulate water absorbing agent 14 is present in first substrate 11, the content ratio of particulate water absorbing agent 14 in first substrate 11 is preferably 5% or more, more preferably 10% or more, still more preferably 20% or more, and still more preferably 30% or more, with respect to particulate water absorbing agent 14 contained in the entire water absorbing sheet 10. The upper limit is not particularly limited, but the preferable order is 90% or less, 70% or less, and 50% or less. In the present specification, the content ratio of particulate water absorbing agent 14 in first substrate 11 to particulate water absorbing agent 14 contained in the entire water absorbing sheet 10 is calculated by the method of the example described later.
Since particulate water absorbing agent 14 is not dispersed and disposed in the region of gap 15, the region of gap 15 does not substantially contain particulate water absorbing agent 14. Additives and the like other than particulate water absorbing agent 14 may be contained in the region of 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 by contact with an adhesive. Since first substrate 11 has stretchability, when a region including particulate water absorbing agent 14 is present on second substrate 13, first substrate 11 stretches and contracts following the region including particulate water absorbing agent 14. Accordingly, first substrate 11 has a shape such that it covers the region containing particulate water absorbing agent 14 in the region containing particulate water absorbing agent 14, and has a shape such that it is recessed toward second substrate 13 after being along the upper side surface of the region containing particulate water absorbing agent 14 in gap 15.
In the water-absorbent sheet of the present invention, the ratio (Lb/La) of the thickness (Lb) to the thickness (La) of the gap 15 from the liquid-absorbing surface of the first substrate 11 to the surface of the second substrate 13 on the water-absorbing layer 12 side is preferably 1.05 or less, the thickness (Lb) being the thickness from the liquid-absorbing surface of the first substrate 11 to the surface of the second substrate 13 on the water-absorbing layer 12 side in the region containing the particulate water-absorbing agent 14. First substrate 11 has stretchability, and therefore, the portion of first substrate 11 in contact with particulate water absorbing agent 14 takes on a shape (i.e., follows and stretches) that follows the shape of the region containing particulate water absorbing agent 14 (i.e., the shape of particulate water absorbing agent 14 on the side in contact with first substrate 11 in particulate water absorbing agent 14 in contact with the first substrate). Accordingly, first substrate 11 is capable of adhering to particulate water absorbing agent 14 (the region including particulate water absorbing agent 14), and thereby, first substrate 11 and particulate water absorbing agent 14 (the region including particulate water absorbing agent 14) are in an integrated state. 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 containing particulate water absorbing agent 14 is highly conformal. Thus, even after swelling of particulate water absorbing agent 14, the maintenance of gap 15 is high, and the reverse flow can be further reduced. Lb/La is usually 1 or more.
In the water-absorbing 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 continuously provided along one direction of the liquid suction surface of the first substrate 11. The shape of the continuous gaps 15 may be, for example, linear, curved, or wavy, and the gaps 15 are preferably arranged in parallel in a linear shape. Therefore, in the water-absorbing sheet 10, the region containing the particulate water-absorbing agent 14 and the gap 15 have a shape extending in one direction (the plane direction perpendicular to the liquid absorption direction) of the liquid absorption surface of the first substrate 11, and are preferably arranged side by side. That is, the region containing particulate water absorbing agent 14 is in a state of being arranged in a stripe shape (vertical bar shape). Accordingly, since gaps 15 are also formed in the shape of a vertical bar, gaps 15 are easily maintained even when particulate water absorbing agent 14 swells, and as a result, 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-suction surface of the first substrate 11, that is, any one of the longitudinal direction, the width direction, or the direction inclined with respect to these directions in the liquid-suction surface of the first substrate 11. From the viewpoint of balancing the action of gap 15 with the action of particulate water absorbing agent 14, in water absorbing sheet 10, the region containing particulate water absorbing agent 14 and gap 15 preferably have a shape extending along the longitudinal direction in the liquid absorbing surface of first substrate 11, and are arranged side by side.
In the surface of first substrate 11 on the water-absorbing layer 12 side (the surface where particulate water absorbing agent 14 is disposed), the ratio of the region containing particulate water absorbing agent 14 is preferably 90% or less, more preferably 80% or less, and still more preferably 75% or less in terms of area. Further, the ratio of the region containing particulate water absorbing agent 14 in the surface of the water absorbing layer 12 side of the first substrate 11 is preferably 10% or more, more preferably 20% or more, by area. By setting particulate water absorbing agent 14 in such a range, the balance between the action of gap 15 and the action of particulate water absorbing agent 14 becomes appropriate, and the effect of reducing the amount of reflux is further exhibited. 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 is the same as the ratio of the region containing particulate water absorbing agent 14 in the surface of second substrate 13 on the water absorbing layer 12 side (the surface where particulate water absorbing agent 14 is disposed).
The water-absorbent sheet 10 has a cover sheet 16. The wrapping sheet 16 has the following purpose: the purpose of holding the shape of the water-absorbing sheet 10, which is a structure in which the particulate water-absorbing agent 14 is supported between the first substrate 11 and the second substrate 13; so that particulate water-absorbing agent 14 supported between first substrate 11 and second substrate 13 does not fall off (fall off) from the absorber (water-absorbing sheet 10); when particulate water absorbing agent 14 is transferred to the outer surface (surface in direct contact with liquid) of first substrate 11 through first substrate 11, particulate water absorbing agent 14 is not brought into direct contact with the skin. Without the cover sheet 16, there are, for example, the following methods: a method of sealing (closing) by bonding the respective substrates 11, 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 of maintaining the effect of the present application without causing particulate water absorbing agent 14 to fall off from water-absorbing sheet 10, it is preferable to have coated sheet 16. The constitution of the wrapping sheet 16 is already described in fig. 1 and 2, and thus the description thereof is omitted.
Therefore, the water-absorbent sheet 10 of the present invention preferably has the cover sheet 16 disposed at least on the surface of the first substrate 11 (i.e., on the liquid suction surface of the first substrate 11). In the present specification, the first substrate 11 forms a liquid-absorbing surface that directly absorbs liquid in the case of having the cover sheet 16 as described above, but in the case of a water-absorbing sheet having the cover sheet 16, for example, the cover sheet 16 forms a liquid-absorbing surface that directly absorbs liquid, the following can be used in the other words: a water-absorbing sheet comprising a first substrate, a second substrate, a water-absorbing layer between the first substrate and the second substrate, and a coating sheet disposed on the surface of the first substrate, wherein the water-absorbing layer comprises a particulate water-absorbing agent, the region comprising the particulate water-absorbing agent is disposed with a gap substantially free of the particulate water-absorbing agent interposed therebetween, the surface of the coating sheet forms a liquid-absorbing surface that directly absorbs liquid, the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm)/thickness of the second substrate (mm)) is 1.5 or more and less than 14, and the elongation of the first substrate is 10% or more.
In the water-absorbent sheet 10 of the present invention, the first substrate 11 is preferably in direct contact with the particulate water-absorbing agent 14 in the water-absorbent layer 12 or in contact with an adhesive, and/or the second substrate 13 is preferably in direct contact with the particulate water-absorbing agent 14 in the water-absorbent layer 12 or in contact with an adhesive. As described above, the water-absorbent sheet of the present invention has a simple structure substantially containing only the following substances: the present invention relates to a particulate water absorbing agent comprising 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 at least one of the first substrate and the second substrate, and a coating sheet for coating a part or all of them as needed (the case where additives and the like described in the present specification, which may be contained in the particulate water absorbing agent, are not excluded). More preferably, the composition is a simple composition comprising only the following substances: the present invention provides a particulate water absorbing agent comprising 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 coating sheet for coating all of these. That is, the water-absorbent sheet of the present invention can effectively reduce the specific amount of backflow despite its simple structure.
In the present invention, the elongation of the first substrate is 10% or more, preferably 15% or more, more preferably 17% or more, still more preferably 20% or more, and still more preferably 22% or more. The upper limit of the elongation of the first base material is not particularly limited, but is preferably 60% or less. By setting the elongation of the first base material to such a range, the first base material is likely to follow the shape of the particulate water absorbing agent, and as a result, the shape retention of the water absorbing sheet is further improved, and the pouring rate can be further reduced. The elongation of the first substrate was measured by the method described in examples below. In the present specification, the "elongation of the nonwoven fabric (first substrate)" is a value when the elongation is measured in the direction of maximum elongation. The elongation of the first substrate may be controlled by bulk density, weight per unit area, material, grid structure, manufacturing process conditions, and the like.
In the present invention, the direction of extension of the first base material is not particularly limited as long as it is any direction parallel to the surface direction of the first base material other than the thickness direction. For example, if the water-absorbent sheet is a rectangular water-absorbent sheet, the sheet may be elongated in any one of the directions of all angles such as the long-side direction, the short-side direction, and the diagonal direction of the sheet plane, with the elongation in the above range. The same applies to square, oval, and round water-absorbing sheets. Preferably a substrate that can be elongated (isotropically) from all directions.
In the present invention, in order to further impart liquid permeability, diffusibility, softness, and the like to the water-absorbent sheet 10, the surface of the first substrate 11 may be subjected to a roughening process. That is, in one embodiment of the present invention, the surface of the first substrate 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 roughened. In the present specification, "fuzzing" refers to a state in which fibers on the surface are fuzzed.
In one embodiment of the water-absorbing sheet of the present invention, when the surface of the first substrate on the water-absorbing layer side is roughened, the specific amount of reflux can be effectively reduced, and the particulate water-absorbing agent can be effectively prevented from falling off from the water-absorbing sheet after the water-absorbing sheet temporarily absorbs the liquid.
The method in which the surface of the first substrate 11 on the water absorbing layer 12 side is roughened will be described. Fig. 4 shows a water-absorbent sheet having a first substrate 11 with a surface on the water-absorbent layer 12 side having been roughened. As shown in fig. 4, the first base material 11 is subjected to fiber fluffing on the water-absorbent layer 12 side surface facing the water-absorbent layer 12. A part of the fluffed fibers of first substrate 11 exceeds particulate water absorbing agent 14 and is brought into contact with and bonded to second substrate 13 coated with an adhesive. Accordingly, even after particulate water absorbing agent 14 absorbs water and swells, first substrate 11 and second substrate 13 can continue to adhere via the fluffed fibers of first substrate 11, and thereby particulate water absorbing agent 14 between first substrate 11 and second substrate 13 can be held. Thus, the first substrate 11 and the second substrate 13 are bonded to each other, so that the particulate water absorbing agent 14 is retained even after the water absorbing sheet 10 absorbs water, and the gel fall-off rate can be reduced.
In one embodiment, the surface of first substrate 11 on the water absorbing layer 12 side is roughened, and the first substrate does not support 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 absorbing layer 12. In this case, particulate water absorbing agent 14 is fixed to second base material 13 by an adhesive. Thus, in one embodiment, first substrate 11 is preferably in direct contact with particulate water absorbing agent 14 in water absorbing layer 12, and second substrate 13 is preferably in contact with particulate water absorbing agent 14 in water absorbing layer 12 via an adhesive.
The reason why the surface of the first substrate 11 on the water absorbing layer 12 side is preferably roughened and the first substrate does not support the particulate water absorbing agent 14 with an adhesive is not clear, but the effect is confirmed by a specific amount of return in examples. That is, the specific amount of backflow is preferably smaller in the case where the adhesive is not applied to the raised surface on the water absorbing layer 12 side of the first substrate 11 and the particulate water absorbing agent 14 is not carried by the first substrate, than in the case where the adhesive is applied to the raised surface on the water absorbing layer 12 side of the first substrate 11 and the particulate water absorbing agent 14 is carried by the first substrate by the adhesive.
Here, the adhesive to be applied to the surface of the second substrate 13 on the water absorbing layer 12 side, that is, the adhesive on the second substrate 13 is preferably a hot melt adhesive. By making the adhesive a hot melt adhesive, the adhesion between the fluffed fibers of the first substrate 11 and the second substrate 13 becomes good, and the water-absorbing sheet 10 continues to adhere to the first substrate 11 and the second substrate 13 after absorbing water, thereby retaining the particulate water-absorbing agent 14 between the first substrate 11 and the second substrate 13.
The water-absorbent sheet 10 has a cover sheet 16. In the water-absorbent sheet 10 according to the present invention, the coating sheet 16 is not necessarily configured, but the first substrate 11 and the coating sheet 16 having the surface on the water-absorbent layer 12 side thereof raised are provided in the water-absorbent sheet 10, so that the particulate water-absorbing agent 14 can be effectively prevented from falling off the water-absorbent sheet 10. The cover sheet 16 is formed as described above and is therefore omitted.
Therefore, the water-absorbent sheet 10 of the present invention preferably has the cover sheet 16 disposed at least on the surface of the first substrate 11 (i.e., on the liquid suction surface of the first substrate 11). In the present specification, the first substrate 11 forms a liquid-absorbing surface that directly absorbs liquid even when the cover sheet 16 is provided as described above, but in the case where the cover sheet 16 forms a liquid-absorbing surface that directly absorbs liquid in a water-absorbing sheet provided with the cover sheet 16, for example, the following can be used in the other words: a water-absorbing sheet comprising a first substrate, a second substrate, a water-absorbing layer between the first substrate and the second substrate, and a coating sheet disposed on the surface of the first substrate, wherein the water-absorbing layer contains a particulate water-absorbing agent, the surface of the coating sheet forms a liquid-absorbing surface that directly absorbs liquid, the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm)/thickness of the second substrate (mm)) is 1.5 or more and less than 14, and the surface of the first substrate 11 on which the water-absorbing layer 12 is disposed (surface on the water-absorbing layer 12 side) is roughened.
In the water-absorbent sheet 10 of the present invention, the first substrate 11 is preferably in direct contact with the particulate water-absorbing agent 14 in the water-absorbent layer 12 or via an adhesive, more preferably in direct contact. And/or, second substrate 13 is preferably contacted with particulate water absorbing agent 14 in water absorbing layer 12 directly or with an adhesive, more preferably with an adhesive. As described above, the water-absorbent sheet of the present invention has a simple structure substantially containing only the following substances: the present invention relates to a particulate water absorbing agent comprising 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 at least one of the first substrate and the second substrate, and a coating sheet for coating a part or all of them as needed (the case where additives and the like described in the present specification, which may be contained in the particulate water absorbing agent, are not excluded). More preferably, the composition is a simple composition comprising only the following substances: the particulate water absorbing agent is formed by 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 coating sheet for coating all of them. That is, the water-absorbent sheet of the present invention can effectively reduce the specific amount of backflow despite its simple structure.
In the water-absorbent sheet 10 having the first substrate 11 whose surface on the water-absorbent layer 12 side has been roughened, the particulate water-absorbing agent 14 can be effectively prevented from falling off from the water-absorbent sheet 10, and therefore, the content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 10 can be set to 200g/m 2 . Therefore, in the water-absorbent sheet 10 having the first substrate 11 whose surface on the water-absorbent layer 12 side has been roughened, the content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 10 is preferably 200g/m 2 The above, in turn, is preferably 230g/m 2 Above, 250g/m 2 Above, 270g/m 2 Above, 280g/m 2 Above, 300g/m 2 The above. The upper limit of the content of particulate water-absorbing agent 14 contained in water-absorbing sheet 10 at this time is not particularly limited, but is preferably 360g/m from the viewpoint of retaining water-absorbing agent 14 2 Hereinafter, more preferably 350g/m 2 Hereinafter, 325g/m is more preferable 2 The following is given.
In addition, in the water-absorbent sheet 10 having the first substrate 11 whose surface on the water-absorbent layer 12 side has been roughened, the particulate water-absorbing agent 14 can be effectively suppressed from falling off from the water-absorbent sheet 10, and therefore, the amount of the adhesive (preferably, the hot-melt adhesive) can be reduced. Therefore, in the water-absorbent sheet 10 having the first substrate 11 whose surface on the water-absorbent layer 12 side has been roughened, the content of the adhesive dispersed on the second substrate 13 is preferably 1 to 50g/m 2 More preferably 5 to 50g/m 2 More preferably 10 to 45g/m 2 Particularly preferably 15 to 30g/m 2 Most preferably 15 to 25g/m 2 。
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 surface of the first substrate on the water absorbing layer side is roughened, the roughened fibers of the first substrate are entangled with the particulate water absorbing agent, and the particulate water absorbing agent is held by the first substrate, the amount of the adhesive agent relative to the particulate water absorbing agent can be reduced. This further exerts an effect of reducing the specific amount of backflow.
In the water-absorbent sheet, when the surface of the first substrate on the water-absorbent layer side is roughened, the fuzzing area ratio in the fuzzing area measurement test of the roughened surface is preferably 5% or more. The fuzzing area ratio of the fuzzed surface of the first substrate is preferably 5% or more, 7% or more, or 10% or more in this order. The upper limit of the fuzzing area ratio of the fuzzed surface of the first substrate is not particularly limited, but is preferably 30% or less, more preferably 28% or less, and further preferably 25% or less from the viewpoint of restricting the swelling of the particulate water absorbing agent. In the present specification, the fuzzing area ratio in the fuzzing area measurement test was calculated by the method described in examples described below.
In one embodiment of the water-absorbing sheet of the present invention, when the surface of the first substrate on the water-absorbing layer side is roughened, the particulate water-absorbing agent can be effectively prevented from falling off from the water-absorbing sheet, as well as the specific amount of reflux. For example, the falling-off rate of the particulate water absorbing agent calculated in the examples of the present invention is preferably 10 mass% or less, more preferably 5 mass% or less, and further preferably 3 mass% or less. This effect is effectively exhibited by the surface of the first substrate on the water absorbing layer side being fluffed.
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 substrate ]
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 it contains water. Urine, menstrual blood, sweat, and other body fluids are preferably mentioned.
The first base material is a water-permeable sheet and is located on the liquid-absorbing side, whereby the effect of the present invention, that is, the performance (flow-down amount, leakage in the surface direction, etc.) of the water-absorbent sheet can be fully exhibited. Regarding the water permeability in the water permeable sheet, the water permeability coefficient (JIS A1218:2009) is preferably 1X 10 -5 cm/sec or more. The water permeability coefficient is more preferably 1×10 -4 cm/sec or more, more preferably 1X 10 -3 cm/sec or more, particularly preferably 1X 10 -2 cm/sec or more, most preferably 1X 10 -1 cm/sec or more. The first substrate used in the examples of the present application has a water permeability coefficient of 1×10 -5 cm/sec or more.
In the present invention, the bulk density of the first substrate is preferably 0.1g/cm 3 Hereinafter, more preferably 0.08g/cm 3 Hereinafter, it is more preferably 0.05g/cm 3 The following is given. The bulk density of the first substrate is preferably 0.001g/cm 3 The above is more preferable0.005g/cm 3 The above is more preferably 0.01g/cm 3 The above. In the present specification, bulk density refers to a mass per unit volume, and is not a density obtained by compressing a substrate under high pressure (when voids are eliminated), but is a density obtained from a volume of the substrate including a void volume. The first substrate had a bulk density of 0.1g/cm 3 Hereinafter, the first substrate is light. Fluffy refers to a low bulk density and is significantly thicker. In the present invention, by making the first base material fluffy, the liquid to be absorbed in contact with the liquid suction surface of the first base material rapidly flows into the water-absorbing layer as the lower layer and the second base material, and the liquid retained in the liquid suction surface of the first base material can be reduced. Further, when the absorbed liquid reaches the water-absorbing layer, the liquid spreads in the plane direction, and therefore, even if a large amount of liquid is introduced into the water-absorbing layer, the water-absorbing layer absorbs the liquid that spreads in the plane direction rather than locally. That is, the fluffy first substrate has low water absorption, high hydraulic permeability, and high liquid diffusivity. This can reduce the amount of pouring out of the water-absorbing sheet. The moisture of the liquid suction 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 3 The following is given. 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 substrate is preferably 3 to 80g/m 2 More preferably 5 to 70g/m 2 More preferably 10 to 60g/m 2 . When the weight per unit area of the first substrate is in such a range, the pouring rate can be further reduced, and the particulate water absorbing agent can be easily introduced into the first substrate, and as a result, the shape retention of the water absorbing 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 to such a range, the distance between the liquid suction surface of the first base material and the water suction layer and the second base material can be sufficiently ensured, and the backflow of the liquid that reaches the water suction layer and the second base material temporarily can be significantly reduced, and the leakage in the surface direction can be reduced.
The thickness, bulk density, and weight per unit area of the first substrate can be controlled by the material constituting the first substrate, the method of producing the first substrate, and the like, and the thickness and bulk density of the first substrate can be 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, further preferably 70% by mass or more, 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, but is preferably 97 mass% or less. By setting the transmittance of the particulate water absorbing agent to such a range for the first substrate, the particulate water absorbing agent is likely to enter the first substrate on the side of the first substrate which contacts 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 a ratio of the particulate water absorbing agent that transmits through the first substrate, and the particulate water absorbing agent present on the first substrate is obtained from the weight of the particulate water absorbing agent that has passed through the first substrate when the particulate water absorbing agent is screened under predetermined conditions described later, and specifically, is a value calculated by the method described in examples described later. Here, in the case where the first substrate is a nonwoven fabric, the transmittance of 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 a hot air nonwoven fabric is used as the first substrate as described later, the transmittance can be adjusted by changing the heat treatment conditions, fiber diameter, and density of the hot air nonwoven fabric.
In one embodiment, the surface of the first substrate on the water absorbing layer side is fluffed.
"Material constituting substrate"
Examples of the material constituting the first substrate include paper (toilet paper, for example, face tissues, toilet papers, and towel papers), mesh, nonwoven fabric, woven fabric, and film. Among them, from the viewpoint of water permeability, a nonwoven fabric is preferably used as at least the first base material.
The nonwoven fabric to be used is not particularly limited, and examples thereof include nonwoven fabrics formed of polyolefin fibers such as Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyester fibers such as 1, 3-propanediol terephthalate (PTT) and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers, from the viewpoints of liquid permeability, flexibility, and strength when a water-absorbent sheet is produced; nonwoven fabrics made from blends of cotton, silk, hemp, pulp (cellulose) fibers, and the like.
As a material of the nonwoven fabric that can be used as the first base material, rayon fibers, polyolefin fibers, polyester fibers, pulp fibers, fibers obtained by mixing them, and the like are preferable, and polyolefin fibers are more preferable. These fibers may be hydrophilized.
The nonwoven fabric that can be used as the first 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 spun-bonding method, or a hydroentanglement method, and is preferably a nonwoven fabric obtained by a hot air method or an air-laid method, and is preferably a nonwoven fabric obtained by a hot air method (hot air nonwoven fabric).
The hot air method means: and processing to blow hot air to the heat-fusible composite fibers such as PE/PP and PE/PET, to increase the air quantity contained between the fibers, to increase the volume and to reduce the density. In addition, the air-laid method is a method of producing a nonwoven fabric by uniformly dispersing air-borne air and sucking the air-borne air onto a metal mesh, and the air is used for dispersing pulp fibers, so that the volume can be increased and the density can be reduced. By making the first substrate a hot air nonwoven fabric, the liquid to be absorbed can be easily and quickly introduced into the first substrate after contacting the liquid suction surface of the first substrate. That is, by using the hot air nonwoven fabric as the first base material, the first base material having low water absorption capacity and high water permeability can be produced, and the flow-back amount in the water-absorbing sheet can be significantly reduced.
[2-2. Second substrate ]
The second base material is a water-permeable sheet and is located on the opposite side to the liquid-absorbing side, whereby the effect of the present invention, that is, the performance (flow-down amount, leakage in the surface direction, etc.) of the water-absorbent sheet can be fully exhibited. Regarding the water permeability in the water permeable sheet, the water permeability coefficient (JIS A1218:2009) is preferably 1X 10 -5 cm/sec or more. The water permeability coefficient is more preferably 1×10 -4 cm/sec or more, more preferably 1X 10 -3 cm/sec or more, particularly preferably 1X 10 -2 cm/sec or more, most preferably 1X 10 -1 cm/sec or more.
The thickness of the second substrate 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 substrate 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, for example, 40% RH to 50% RH.
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 substrate and the second substrate to the above-described ranges, the desired effects of the present invention can be effectively achieved. Furthermore, according to an embodiment 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 more preferably: 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 particularly preferable is: the thickness of the first base material is 1.4mm to 2mm, and the thickness of the second base material is 0.3mm to 0.5 mm.
In the present invention, the bulk density of the second substrate is preferably 1g/cm 3 Hereinafter, more preferably 0.5g/cm 3 Hereinafter, it is more preferably 0.3g/cm 3 The following is given. The bulk density of the second substrate is preferably 0.05g/cm 3 The above is more preferably 0.07g/cm 3 The above is more preferably 0.08g/cm 3 The above. By setting the bulk density of the second substrate to such a range, the liquid introduced into the second substrate can be easily held, and the backflow can be reduced.
In the present invention, the weight per unit area of the second substrate is preferably 5 to 100g/m 2 More preferably 10 to 70g/m 2 More preferably 15 to 65g/m 2 。
The thickness, bulk density, and weight per unit area of the second substrate are controlled by the material constituting the second substrate, the method of producing the second substrate, and the like, and the thickness and bulk density of the second substrate are determined based on the balance thereof.
The void ratio of the first substrate, the second substrate, and the cover sheet (e.g., nonwoven fabric) can be measured by the following equation. Basis weight A (g/m) used in substrate (or coated sheet) 2 ) Thickness B (mm) of the substrate (or clad sheet), density C (g/cm) of the raw material (e.g., polyolefin) used in the substrate (or clad sheet) 3 )
Void ratio of substrate (or sheet) =100- { (a/10000)/(B/10) }/c×100
The liquid diffusion area of the second substrate is preferably 1000mm 2 The above is more preferably 3000mm 2 The above is more preferably 6000mm 2 The above is particularly preferably 7000mm 2 The above. The upper limit of the liquid diffusion area of the second substrate is not particularly limited, and is preferably 10,000mm, for example 2 The following is given. When the liquid diffusion area of the second substrate is within the above range, the absorbed liquid can be in the plane direction in the second substrate when reaching the second substrateAnd fully spread. Thus, even if a large amount of liquid having passed through the water-absorbing layer is introduced into the second base material, the second base material absorbs the liquid that spreads in the plane direction rather than locally. Thus, the second substrate can sufficiently absorb and hold the liquid, the amount of backflow in the water-absorbent sheet can be significantly reduced, and leakage in the plane direction can be significantly reduced.
Here, the liquid diffusion area means: the area in the plane direction in which the liquid diffuses when the liquid contacts with the substrate (for example, nonwoven fabric) and/or when the liquid passes through the substrate in a direction perpendicular to the plane direction of the substrate is a value calculated by the method described in examples described later. The larger the liquid diffusion area of the substrate, the higher the liquid diffusivity of the substrate in the plane direction.
"Material constituting substrate"
The material constituting the second base material 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 fibers, polyolefin fibers, polyester fibers, pulp fibers, and fibers obtained by mixing them are preferable, and polyolefin fibers are more preferable.
The nonwoven fabric that can be used 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 spunbonding method, or a hydroentangled method, and preferably a nonwoven fabric obtained by an air-laid method (air-laid nonwoven fabric) or a nonwoven fabric obtained by a hydroentangled method (hydroentangled nonwoven fabric). The hydroentanglement method is a method of interlacing fibers by high-pressure water flow, and is a method of not using an adhesive. By making the second substrate of an air-laid nonwoven fabric or a spunlaced nonwoven fabric, the amount of backflow in the water-absorbent sheet can be significantly reduced, and leakage in the plane direction can be significantly reduced.
[2-3 Water-absorbing layer ]
The water absorbing layer in the water absorbing 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 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 specified, the following description refers 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 agent contained in the water absorbing layer is mixed. Further, regarding the physical properties of the particulate water absorbing agent, it is possible to take out only the particulate water absorbing agent from the water absorbing sheet to measure the physical properties so as not to mix cotton pulp or the like.
"surface tension"
The surface tension means: the parameters of the work (free energy) required to increase the surface area of the solid or liquid are expressed in terms of the unit area. The surface tension referred to in this application means: surface tension of an aqueous solution when the particulate water absorbing agent is dispersed in a 0.90 mass% aqueous solution of sodium chloride. The surface tension of the water absorbing agent was measured by the following procedure. Specifically, 50ml of physiological saline adjusted to 20℃was put into a sufficiently cleaned 100ml beaker, and the surface tension of the physiological saline was measured by a surface tensiometer (KRUSS Co., ltd. K11 automatic surface tensiometer). Subsequently, 0.5g of a 25mm long fluororesin rotor and a particulate water absorbing agent, which had been sufficiently cleaned, were put into a beaker containing physiological saline adjusted to 20℃and measured for surface tension, and stirred at 500rpm for 4 minutes. After 4 minutes, stirring was stopped, and after the aqueous particulate water absorbing agent had settled, the same operation was performed again to measure the surface tension of the supernatant liquid. In the present invention, a plate method using a platinum plate was used, and the plate was sufficiently washed with deionized water before each measurement, and was heated and washed with a gas burner.
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 the particulate water absorbing agent is applied to the water absorbing sheet, the influence of the surface tension is more likely to occur than in conventional paper diapers, and by making the surface tension satisfy the above conditions, the amount of backflow in the water absorbing sheet can be reduced, and leakage in the plane direction can be reduced.
In the water-absorbing 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 practically 73mN/m or less.
In the water-absorbent sheet according to one embodiment of the present invention, the CRC (water absorption capacity without load) of the particulate water-absorbing agent is preferably 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 making the CRC of the particulate water absorbing agent satisfy the above condition, the pouring amount in the water absorbing sheet can be reduced. The CRC of the particulate water absorbing agent is abbreviated as Centrifuge Retention Capacity (centrifuge retention capacity) defined by ERT441.2-02, and refers to the water absorption capacity (sometimes referred to as "water absorption capacity") of the particulate water absorbing agent under no pressure. 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 significantly excessive 0.9 mass% aqueous sodium chloride solution for 30 minutes to freely swell the bag, and thereafter, the water absorption capacity (unit: G/G) was increased by removing water by a centrifuge (250G).
In the water-absorbent sheet according to one embodiment of the present invention, the AAP (absorption capacity under pressure) of the particulate water-absorbing agent is preferably 25g/g or more, more preferably 28g/g or more, particularly preferably 30g/g or more, and most preferably 33g/g or more in order of less than or equal to the AAP (absorption capacity under pressure) of the particulate water-absorbing agent, from the viewpoint of improving the performance (reducing the backflow amount) of the water-absorbent sheet. The AAP of the particulate water absorbing agent refers to the abbreviation Absorption Against Pressure specified by ERT442.2-02, and refers to the absorption capacity under pressure of the particulate water absorbing agent. The method specifically comprises the following steps: the particulate water-absorbing agent was brought to a pressure of 0.9g at 2.06kPa (21 g/cm 2 0.3 psi) in a significant excess of 0.9 mass% aqueous sodium chloride solution for 1 hour (unit: g/g). Note that Absorption Under Pressure (AUP) is expressed in ERT442.2-02, and is substantially the same.
In the water-absorbent sheet according to one embodiment of the present invention, the particulate water-absorbing agent is preferably 25 to 50g/g, more preferably 30 to 45g/g, and particularly preferably 30 to 40g/g in order of 5 minutes or less (immersion holding capacity 5 minutes value) of DRC from the viewpoint of improving the performance (reduction in specific backflow amount) of the water-absorbent sheet. The term "DRC 5 min" as used herein means the water absorption capacity under no pressure for 5 minutes, and the larger the value of DRC5min, the faster the absorption rate. In the detailed description of DRC5min of the water absorbing agent, the descriptions of the sections "0151" to "0152", the sections "0328" and the sections "0484" to "0487" (including those of fig. 1) in the specification of U.S. patent application publication No. 2019/011411 are incorporated herein by reference.
In the water-absorbent sheet according to one 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, still more preferably 70g/min or more, still more preferably 100g/min or more, and particularly preferably 150/min or more, from the viewpoint of shortening the water absorption time in the pressurization specific reflux amount evaluation described later, that is, the effect of improving the water absorption rate is excellent. That is, when the GPR of the particulate water absorbing agent is 20g/min or more, the water absorbing time can be shortened in the specific return amount under pressure evaluation, and thus the water absorbing rate is improved. Thus, the user's uncomfortable feeling can be reduced. The surface of the first substrate on the water-absorbing layer side is roughened, and such an effect is effectively exhibited. 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 abbreviated as Gel Permeation Rate (gel permeation rate) and means a flow rate (unit: g/min) at which a liquid passes between particles of a swollen gel when the particulate water absorbing agent swells under a load. In the detailed description of the method for measuring GPR, the descriptions in the "0237" to "0239" sections (including fig. 5) of the specification of international publication No. 2019/074094 are incorporated by reference into the present specification.
"particle shape"
In the water-absorbing sheet according to one embodiment of the present invention, the particulate water-absorbing agent is not limited in particle shape, and may be, for example, a spherical particulate water-absorbing agent (and granulated product thereof). In a preferred embodiment, the particulate water absorbing agent is preferably irregularly crushed. Here, the irregular crushed shape refers to crushed particles whose shape is not fixed. This is because: the irregular crushed shape can be easily fixed to the substrate as compared with spherical particles obtained by inverse 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, in the case where the pulverization step is not performed, spherical particles or granules of spherical particles obtained by, for example, reversed-phase suspension polymerization, spray polymerization of a monomer and droplet polymerization such as polymerization are not irregularly pulverized. In the embodiment of the present invention, if the particulate water absorbing agent is irregularly crushed, the shape of the water absorbing sheet is more easily maintained than a water absorbing agent having a high average roundness (for example, a spherical water absorbing agent). In the embodiment of the present invention, the average roundness 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 calculation method of the average roundness is as follows. More than 100 particulate water-absorbing agents were randomly selected, each particulate water-absorbing agent was photographed with an electron microscope (VE-9800, manufactured by ken corporation) (magnification: 50 times), an image of the particulate water-absorbing agent was obtained, and the circumference and area of each particle were calculated using attached image analysis software. The roundness of each particle was obtained by the following equation, and the average value of the obtained values was calculated as the average roundness.
[ mathematics 1]
Roundness=4×pi×area/(circumference) 2
Particle size "
The particle diameter of the particulate water absorbing agent (or the particulate water absorbing resin particles) according to one embodiment of the present invention may be 150 to 600 μm, which is a weight average particle diameter obtained by the measurement method of "PSD" specified in ERT 420.2-02.
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 it can be suitably produced by referring to, for example, the publication of the examples.
[ 2-4. Coating sheet ]
In the water-absorbent sheet according to one embodiment of the present invention, it is preferable that the water-absorbent sheet has a coating sheet disposed on at least the surface of the first substrate. The cover sheet may be disposed on the surface of the first base material, and the cover sheet is more preferably disposed so as to cover the side surface of the first base material and the side surface of the water-absorbing layer, and further preferably to cover the side surface of the first base material, the side surface of the water-absorbing layer, and the side surface of the second base material, and to cover a part or the whole of the surface of the second base material opposite to the side where the liquid to be absorbed is introduced.
In a preferred embodiment of the present invention, the water-absorbent sheet is provided with a cover sheet, which is a water-permeable sheet and is located at least on the surface (liquid-absorbent side) of the first substrate.
The thickness of the coated 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 coated sheet 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 40% RH to 50% RH, for example.
In the present invention, the bulk density of the coated sheet is preferably 1g/cm 3 Hereinafter, more preferably 0.5g/cm 3 Hereinafter, it is more preferably 0.3g/cm 3 The following is given. The bulk density of the coated sheet is preferably 0.1g/cm 3 The above is more preferably 0.12g/cm 3 The above is more preferably 0.13g/cm 3 The above.
In the present invention, the unit area weight of the coated sheet is preferably 5 to 100g/m 2 More preferably 5 to 70g/m 2 More preferably 10 to 65g/m 2 。
The thickness, bulk density, and weight per unit area of the clad sheet can be controlled by the material constituting the clad sheet, the method of producing the clad sheet, and the like, and the thickness and bulk density of the clad sheet can be determined based on the balance of these materials.
"Material constituting 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 face tissue, toilet paper, and towel paper), mesh, nonwoven fabric, woven fabric, and film.
The nonwoven fabric to be used is not particularly limited, and examples thereof include nonwoven fabrics formed of polyolefin fibers such as Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyester fibers such as 1, 3-propanediol terephthalate (PTT) and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers, from the viewpoints of liquid permeability, flexibility, and strength when a water-absorbent sheet is produced; nonwoven fabrics made from blends of cotton, silk, hemp, pulp (cellulose) fibers, and the like.
The nonwoven fabric usable as the cover sheet is preferably a rayon fiber, a polyolefin fiber, a polyester fiber, a pulp fiber, a fiber obtained by mixing them, or the like, and more preferably a polyolefin fiber. These fibers may be hydrophilized.
The nonwoven fabric usable 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 hydroentangled method, or the like, and preferably a nonwoven fabric obtained by a spunbond method (spunbond nonwoven fabric). As in the case of seating a child wearing an absorbent article such as a disposable diaper, the water-absorbent sheet is preferably a water-repellent cover sheet, for example, a spunbond nonwoven fabric, in order not to allow urine absorbed by the water-absorbent sheet to leak out of the sheet (so-called backflow does not occur) in a state where the water-absorbent sheet is loaded with a load (in a pressurized state). The method for producing a spunbond nonwoven fabric is a method in which continuous long fibers obtained by melting/spinning a raw material resin are directly gathered 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 substrate, the method for producing the second substrate, and the method for producing the coated sheet are different. By appropriately changing the manufacturing method of each member constituting the water-absorbing sheet in this way, the desired effect of the present invention can be effectively exhibited. According to one embodiment of the present invention, the first substrate is a hot air nonwoven fabric, the second substrate is an air-laid nonwoven fabric or a spun-laced nonwoven fabric, and the cover sheet is a spunbonded nonwoven fabric, which are nonwoven fabrics different from each other. In this way, the desired effects of the present invention can be effectively exhibited.
[ 3 ] method for producing Water-absorbent sheet ]
The method for producing a water-absorbing sheet according to one embodiment of the present invention includes at least one of (1) a step of dispersing a particulate water-absorbing agent on a first substrate and (2) a step of dispersing 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) are given.
When the first substrate has a roughened surface, one surface of the first substrate may be roughened in advance before the production methods (a) to (d).
The method of raising the surface of the first substrate on the water-absorbing side is not particularly limited, and known methods may be used, and examples thereof include methods using needles, fruits of thistle (raised grass), and brushes (bristles). Industrially, the first substrate may be fluffed by a method of rotating a roller around which a card clothing or a thistle fruit is wound, and advancing the clothing thereon to scrape out fibers from spun yarn on the surface of the clothing.
For example, as a method using a brush, a nonwoven fabric was left standing 60cm on a horizontal plane, and a weight of 10kg larger than the width of the nonwoven fabric was carried on each of the two ends in the winding length direction, and the nonwoven fabric was fixed. The brush was inserted vertically at a point 10cm from the end in the winding longitudinal direction of the nonwoven fabric. The brush was inserted with its hair tips (the tips of the hairs) into contact with the horizontal surface so that the long sides of the brush became the width direction of the nonwoven fabric, and then the brush was horizontally moved 40cm with respect to the winding length direction. The brush and the weight are removed from the nonwoven fabric, and the nonwoven fabric having the surface on which the brush moves is cut, whereby a fluffed nonwoven fabric can be obtained.
The conditions for obtaining a nonwoven fabric having been raised are preferably, for example, the following conditions.
Bristles
Trade name: 25mm x 0.1m sealing brush (PBT/blue), manufacturer: ESCO Co Ltd
Hair length: 25mm, wool diameter: 0.2mm
Brush length: 100mm, brush width: 5mm, material: PBT (polybutylene terephthalate)
Speed of movement of the brush: 16 m/min=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 overlapped and pressure-bonded. The pressure bonding is preferably thermal pressure bonding around the melting temperature of the adhesive.
(b) After the adhesive is uniformly dispersed on the second substrate, the particulate water absorbing agent is uniformly dispersed. The first base material is overlapped with the surface of the second base material on which the particulate water absorbing agent is dispersed, and heat-press-bonding is performed.
(c) The particulate water absorbing agent is spread on the second substrate, preferably, the binder is spread so as to pass through the heating furnace, and is fixed to such an extent that the particulate water absorbing agent does not escape. The first base material is overlapped with the surface of the second base material on which the particulate water absorbing agent is dispersed, and heat-press-bonding is performed.
(d) After the adhesive is melt-coated on the second substrate, the particulate water absorbing agent is uniformly dispersed to form a layer. The first substrate is overlapped with the surface of the second substrate on which the particulate water absorbing agent is dispersed, and pressure bonding is performed using a roller press or the like.
Among these methods, the method (d) is preferable from the viewpoint of uniformly applying the adhesive. The water-absorbing sheet may be produced by using the methods (a) to (d) in combination.
When the region where the particulate water absorbing agent is not present is provided in the water absorbing layer, the particulate water absorbing agent may be dispersed in a striped pattern in the above-described methods (a) to (d). Specifically, the particulate water absorbing agent may be spread on the adhesive spread in a stripe pattern on the substrate (for example, the first substrate), and the other substrate may be overlapped on the surface of the substrate on which the particulate water absorbing agent is spread, and the adhesive may be spread in a stripe pattern on the substrate (for example, the second substrate) opposite to the substrate on which the particulate water absorbing agent is spread in a stripe pattern (for example, the first substrate), and the two substrates may be overlapped so that the surface on which the particulate water absorbing agent is spread and the surface on which the adhesive is spread are aligned, and the two substrates may be heat-pressed. Specifically, the following methods (a ') to (d') can be used.
(a') on the first substrate, dispersing the particulate water-absorbing agent 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 overlapped and pressure-bonded. The pressure bonding is preferably thermal pressure bonding around the melting temperature of the adhesive.
(b') dispersing the particulate water absorbing agent uniformly after dispersing the adhesive in a stripe shape on the second substrate. The first base material is overlapped with the surface of the second base material on which the particulate water absorbing agent is dispersed, and heat-press-bonding is performed.
(c') on the second substrate, the particulate water absorbing agent is spread in a stripe shape, and the adhesive is preferably uniformly spread so as to pass through the heating furnace, so as to be fixed to such an extent that the particulate water absorbing agent does not escape. The first base material is overlapped with the surface of the second base material on which the particulate water absorbing agent is dispersed, and heat-press-bonding is performed.
(d') after the adhesive is melt-coated on the second substrate, dispersing the particulate water absorbing agent in stripes to form a layer. The first substrate is overlapped with the surface of the second substrate on which the particulate water absorbing agent is dispersed, and pressure bonding is performed using a roller press or the like.
Here, in the present invention, the method of dispersing the particulate water absorbing agent in a stripe shape is not particularly limited, and may be dispersed in a stripe shape by using, for example, a hollowed-out cardboard. Specifically, a board having the same dimensions as the water-absorbent sheet and hollowed out in a vertical stripe pattern arranged in a certain width and length was used as the hollowed-out cardboard. The hollowed-out cardboard is carried on a substrate to be dispersed with the particulate water absorbing agent, and the particulate water absorbing agent is dispersed in the portion of the hole that has been hollowed out. After the particulate water absorbing agent is dispersed, when the hollow paperboard is removed, the particulate water absorbing agent is dispersed in a striped state on the substrate.
Further, the particulate water absorbing agent can be spread in a stripe shape on the substrate by applying the adhesive to the substrate by screen printing or the like, spreading the particulate water absorbing agent on the substrate, and then, dusting the particulate water absorbing agent on the substrate without contact with the adhesive.
As shown in fig. 1 to 4, the method of providing the water-absorbent sheet with the cover sheet includes (3) a step of covering the first substrate, the water-absorbent layer, and the second substrate with the cover sheet disposed on the first substrate. For example, the sheet obtained by the above-described step (a) or (b) and having the first substrate, the water-absorbing layer and the second substrate in pressure-bonding is carried on the cover sheet with the first substrate facing downward, the 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 folded, the adhesive surface of the second substrate is wrapped so as to be in contact with the cover sheet, and the cover sheet is turned upside down, and then pressure-bonding is performed, whereby the water-absorbing sheet having the cover sheet can be obtained.
As a step other than the above, the water-absorbent sheet may be embossed for the purpose of improving the touch feeling of the water-absorbent sheet and improving the liquid-absorbing performance. The embossing process may be performed simultaneously when the first substrate and the second substrate are pressure bonded, or may be performed after the sheet is manufactured. Further, the wrapping sheet may be embossed.
In the method for producing a water-absorbent sheet according to one embodiment of the present invention, additives (deodorant, fiber, antibacterial agent, gel stabilizer, etc.) may be appropriately blended. The blending amount of the additive is preferably 0 to 50% by mass, more preferably 1 to 10% by mass, relative to 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 during the production process.
The dimensions of the produced water-absorbent sheet can be appropriately designed. Typically, the transverse width is 3 to 10m and the length is 10m to 1000m (in the state of a continuous sheet or roll). The produced water-absorbent sheet is used by cutting according to the purpose (the size of the absorber used).
In addition to the above examples, the following patent documents, for example, disclose a method for producing a water-absorbent sheet: international publication No. 2012/174026, international publication No. 2013/078109, international publication No. 2015/047784, 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. 2010/082573, international publication No. 2010/113754, international publication No. 2010/143635, international publication No. 2011/04 315501, 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. 2010/136087, international publication No. 2013/043546, international publication No. 2013/0934, international publication No. 2013/11335, japanese laid-open patent application No. 2002-open No. wo-flat top-open No. 2012, japanese patent application No. 2012-open No. 37,5835, japanese patent application No. 2002-open No. 37-open No. 37,360, japanese patent application No. 37-open No. 2002-open No. japanese-open patent application No. 1-open No. wo 35, japanese-open No. 2002-open No. jp-open No. wo 35, no. 2002-japanese-open patent application No. jp-open No. from japanese-open 2, no. top-open 2, no. from any 2. The method for producing the water-absorbent sheet 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 base materials to each other or to the particulate water-absorbing agent, the base materials may be (i) pressure-bonded, may be (ii) dissolved or dispersed in water, a water-soluble polymer or a solvent, may be (iii) heat-sealed at the melting point of the base materials themselves, or may be (iv) fixed with an adhesive. The base materials or the base material and the particulate water absorbing agent are preferably (iv) fixed with an adhesive.
The adhesive used may be a solution type, but from the viewpoint of time and effort for removing the solvent, the problem of residual solvent, and the problem of productivity, a hot melt adhesive having high productivity and no problem of residual solvent is preferable. 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 used separately in the process of producing the water absorbing sheet. The form and melting point of the hot-melt adhesive may be appropriately selected, and may be in the form of particles, fibers, meshes, films, or a liquid state in which the hot-melt adhesive is melted by heating. From the viewpoint of uniformly applying the adhesive, it is preferable to disperse the melted hot-melt adhesive.
In a preferred embodiment, when the surface of the first substrate on the water absorbing layer side is roughened, the hot melt adhesive is dispersed in the second substrate. The water-absorbing sheet can be produced by superposing the first substrate on which the particulate water-absorbing agent is dispersed and the second substrate on which the hot-melt adhesive is dispersed so that the surface on which the particulate water-absorbing agent is dispersed and the surface on which the hot-melt adhesive is dispersed are aligned, and performing pressure bonding.
As the hot melt adhesive used in the present invention, it is appropriately selected, and preferable is: more than 1 selected from ethylene-vinyl acetate copolymer adhesives, styrene-based elastomer adhesives, polyolefin-based adhesives, polyester-based adhesives, and the like can be suitably used.
Specifically, examples of the polyolefin-based adhesive include polyethylene, polypropylene, and atactic polypropylene, examples of the styrene-based elastomer adhesive include styrene-isoprene block copolymer (SIS), styrene-butadiene block copolymer (SBS), styrene-isobutylene block copolymer (SIBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), and other styrene block copolymers, copolyolefin, and the like, examples of the polyester-based adhesive include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and copolyester, and examples of the ethylene-vinyl acetate copolymer adhesive include ethylene-vinyl acetate copolymer (EVA) adhesive, ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), and the like.
Examples of the commercial products of the HOT melt adhesive include Jaourmelt3889U (manufactured by JAOUR HOT MELT ADHESIVE Co., ltd., main component: styrene block copolymer, hydrocarbon resin, white mineral oil), MOESCOMELT TN-640Z (manufactured by MOESCO Co., ltd.), MOESCOMELT TN-781Z (manufactured by MOESCO Co., ltd.), MOESCOMELT TN-262Z (manufactured by MOESCO Co., ltd.), 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, 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, relative to the mass of the particulate water-absorbing agent. If the content of the binder (particularly, the hot-melt binder) is too large, not only the cost and the quality of the water-absorbing sheet (the quality of the diaper increases) become disadvantageous, but also the particulate water-absorbing agent may be limited by swelling and the water-absorbing ability of the water-absorbing sheet may be lowered.
[ 4. Absorbent article ]
An absorbent article according to one 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 constituted by sandwiching the water-absorbent sheet of the present invention between a liquid-permeable sheet and a liquid-impermeable sheet, the liquid-permeable sheet being located on the first base material side, and the liquid-impermeable sheet being located on the second base material side. Specific examples of the absorbent article include paper diapers, incontinence pads, sanitary napkins, pet sheets, drip sheets for foods, and water-stops for cables.
As the liquid-permeable sheet and the liquid-impermeable sheet, sheets known in the technical field 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, unless otherwise specified, the operation was performed under conditions of room temperature (25 ℃) and relative humidity of 40 to 50% RH.
Example A
< production example >
Production example 1
The particulate water absorbing agents (1) to (3) of the polyacrylic acid (salt) resin were obtained by appropriately adjusting the CRC according to the amount of the internal crosslinking agent, with reference to production examples, and comparative examples described in the following patents. 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 ]
Acrylic acid (acrylic acid dimer 2000ppm, acetic acid 500ppm, propionic acid 500ppm, p-methoxyphenol 200 ppm) which is commercially available was supplied to the bottom of a high boiling impurity separation column having 50 stages of baffle-free porous plates, distilled with a reflux ratio of 1, and after removing maleic acid, a dimer formed from acrylic acid (acrylic acid dimer), and the like, further crystallization was performed to obtain acrylic acid (acrylic acid dimer 20ppm, acetic acid 50ppm, propionic acid 50ppm, furfural 1ppm or less, protoanemonin 1ppm or less), and after the distillation, p-methoxyphenol 50ppm was added.
[ preparation of aqueous sodium acrylate solution ]
According to example 9 of U.S. Pat. No. 5210298, 1390g of the above-mentioned acrylic acid was neutralized with 48% caustic soda at 20 to 40℃to obtain a 100% neutralized aqueous sodium acrylate solution having a concentration of 37%.
< 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 production example of acrylic acid, an aqueous sodium acrylate solution obtained by the production method of the aqueous sodium acrylate solution using the acrylic acid, and deionized water, 4.11g of polyethylene glycol diacrylate (average addition mole number of ethylene oxide: 9) was dissolved to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by capping a jacketed stainless steel double arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ℃. Then, 28.66g of a 10% by mass aqueous solution of sodium persulfate and 35.28g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and as a result, polymerization was started after about 1 minute. After 40 minutes from the start of polymerization, the hydrogel polymer was taken out. The resulting hydrogel-like polymer is finely divided 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 size of 600. Mu.m, whereby an irregularly pulverized water-absorbent resin (1-1) having an average particle diameter of 350 μm was obtained.
To 100 parts by mass of the water-absorbent resin (1-1) thus obtained, 4.03 parts by mass of an aqueous surface cross-linking 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 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 sprayed and mixed, and the mixture was cured at 60℃for 1 hour in a closed container, and then the resultant was passed through a sieve having a mesh size of 710. Mu.m, to obtain a water-absorbent resin (1-3). A particulate water-absorbing agent (1) was obtained by adding 0.3 parts by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL Co., ltd., japan) to water-absorbent resin (1-3) and mixing the resultant mixture.
< particulate Water absorbing agent (2) >)
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 production example of acrylic acid, an aqueous sodium acrylate solution obtained by the production method of the aqueous sodium acrylate solution using the acrylic acid, and deionized water, 5.01g of polyethylene glycol diacrylate (average addition mole number of ethylene oxide: 9) was dissolved to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by capping a jacketed stainless steel double arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen gas 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 solution, and as a result, polymerization was started after about 1 minute. After 40 minutes from the start of polymerization, the hydrogel polymer was taken out. The resulting hydrogel-like polymer is finely divided 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 size of 600. Mu.m, whereby an irregularly pulverized water-absorbent resin (2-1) having an average particle diameter of 350 μm was obtained.
To 100 parts by mass of the water-absorbent resin (2-1) thus obtained, 4.03 parts by mass of an aqueous surface cross-linking 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 treatment machine to obtain a surface-crosslinked water-absorbent resin (2-2). 3.0 parts by mass of water was sprayed and mixed to 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (2-2), and the mixture was cured at 60℃for 1 hour in a closed container, and then the resultant was passed through a sieve having a mesh size of 710. Mu.m, to obtain a water-absorbent resin (2-3). A particulate water-absorbing agent (2) was obtained by adding 0.3 parts by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL Co., ltd., japan) to water-absorbent resin (2-3) and mixing the resultant mixture.
< particulate Water absorbing agent (3) >)
In 5500g (monomer concentration: 38.0 mass%) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing acrylic acid obtained in the production example of acrylic acid, an aqueous sodium acrylate solution obtained by the production method of the aqueous sodium acrylate solution using the acrylic acid, and deionized water, 3.77g of polyethylene glycol diacrylate (average addition mole number of ethylene oxide: 9) was dissolved to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by capping a jacketed stainless steel double arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ℃. Subsequently, 30.68g of a 10% by mass aqueous solution of sodium persulfate and 37.76g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and as a result, polymerization was started after about 1 minute. After 40 minutes from the start of polymerization, the hydrogel polymer was taken out. The resulting hydrogel-like polymer is finely divided 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 by a metal mesh having a mesh size of 600. Mu.m, whereby an irregularly pulverized water-absorbent resin (3-1) having an average particle diameter of 350. Mu.m was obtained.
To 100 parts by mass of the water-absorbent resin (3-1) thus obtained, 3.83 parts by mass of an aqueous surface cross-linking agent solution comprising 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 was spray-mixed. The above mixture was heat-treated 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 sprayed and mixed, and the mixture was cured in a closed container at 60℃for 1 hour, and then passed through a sieve having a mesh size of 710. Mu.m, to obtain a water-absorbent resin (3-3). A particulate water-absorbing agent (3) was obtained by adding 0.3 parts by mass of Aerosil200 (hydrophilic amorphous silica, manufactured by AEROSIL Co., ltd., japan) to water-absorbing resin (3-3) and mixing the resultant mixture.
[ extraction of Water-absorbent resin from commercially available paper diaper ]
< particulate Water absorbing agent (4) >)
The water-absorbent resin was taken out of commercially available disposable diapers (product of UniCharm, inc. (L. Batch: 201512163072)), and only the water-absorbent resin was taken out of the diapers so as not to mix with cotton pulp or the like during the taking out, and the water-absorbent resin was in the form of particles obtained by granulating spherical particles, and the water-absorbent resin was used as the particulate water-absorbing agent (4).
[ method for 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 particles) according to one embodiment of the present invention is a weight average particle diameter obtained by the measurement method of "PSD" specified in ERT 420.2-02. The weight average particle diameters of the particulate water absorbing agents are shown in Table 1.
< CRC (Water absorption Rate without pressure) (ERT 441.2-02) >)
After 0.2G (weight before water absorption) of the particulate water absorbing agent was put into a nonwoven fabric bag, the bag was immersed in a significantly excessive 0.9 mass% aqueous sodium chloride solution for 30 minutes to allow free swelling, and after that, the weight after water absorption of the particulate water absorbing agent was measured after water removal by a centrifuge (250G). The water absorption capacity (unit: g/g) was determined by "(weight of particulate water absorbing agent after water absorption-weight of particulate water absorbing agent before water absorption)/(weight of particulate water absorbing agent before water absorption) ×100". The CRC of each particulate water absorbing agent is shown in Table 1.
< surface tension >
In the present invention, the surface tension means the surface tension of an aqueous solution when the particulate water absorbing agent is dispersed in 0.90 mass% aqueous sodium chloride solution.
50ml of physiological saline adjusted to 20℃was poured into a sufficiently cleaned 100ml beaker, and the surface tension of the physiological saline was measured by a surface tensiometer (KRUSS Co., ltd. K11 automatic surface tensiometer). In the present invention, a plate method using a platinum plate was used, and the plate was sufficiently washed with deionized water before each measurement, and was heated and washed with a gas burner.
Subsequently, 0.5g of a 25mm long fluororesin rotor and a particulate water absorbing agent, which had been sufficiently cleaned, were put into a beaker containing physiological saline adjusted to 20℃and measured for surface tension, and stirred at 500rpm for 4 minutes. After 4 minutes, stirring was stopped, and after the aqueous particulate water absorbing agent had settled, the same operation was performed again to measure the surface tension of the supernatant liquid. The surface tension (unit: mN/m) of the particulate water absorbing agent was determined from the surface tension of the supernatant liquid when the particulate water absorbing agent was dispersed in physiological saline. The surface tension of each particulate water absorbing agent is shown in table 1.
[ examples ]
Example 1
Nonwoven fabric E (pulp fiber as a main component, 0.4mm thick, produced by air-laid method, corresponding to the second substrate, weight per unit area: 47 g/m) 2 ) Uniformly spread (spread amount: 12.5 to 17.5g/m 2 ) After 0.5 to 0.7g of an adhesive (spray 77, 3m japan company) containing styrene-butadiene rubber, 9.0g of the particulate water absorbing agent (1) was uniformly dispersed on the adhesive dispersing surface (dispersion amount: 225g/m 2 )。
Next, a heated air nonwoven fabric A (corresponding to the first substrate: weight per unit area: 41 g/m) having an olefin as a main component and a thickness of 1.4mm was cut into 10cm in the longitudinal direction and 40cm in the transverse direction 2 ) The surface of the nonwoven fabric E on which the particulate water absorbing agent is dispersed is pressure-bonded to obtain an intermediate sheet X.
Next, a spunbonded nonwoven fabric (corresponding to a cover sheet, weight per unit area: 13 g/m) having an olefin as a main component and a thickness of 0.1mm, cut into 24cm in the longitudinal direction and 40cm in the transverse direction, was laid 2 Bulk density 0.13g/cm 3 ) As a result, the nonwoven fabric a side of the intermediate sheet X is placed in contact with the spunbond nonwoven fabric.
Subsequently, after 0.1 to 0.2g of an adhesive (spray 77, 3M JAPAN company) containing styrene-butadiene rubber was uniformly spread on the surface (upper surface) of the nonwoven fabric E side of the intermediate sheet X, the excess portion of the spunbond nonwoven fabric was folded, and the nonwoven fabric E side of the intermediate sheet X (surface of the nonwoven fabric E side of the intermediate sheet X) was wrapped so as to be in contact with the spunbond nonwoven fabric, turned upside down, and then pressed and bonded under pressure to obtain a water-absorbent sheet (1).
Example 2
A spunbonded nonwoven fabric (corresponding to a cover sheet) having an olefin as a main component and a thickness of 0.1mm, which was cut into 24cm in the longitudinal direction and 40cm in the transverse direction, was laid in advance, and a hot air nonwoven fabric A (corresponding to a first base material) having an olefin as a main component and a thickness of 1.4mm, which was cut into 10cm in the longitudinal direction and 40cm in the transverse direction, 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 (pulp fiber as a main component, 0.4mm in thickness, produced by an air-laid method) was cut into a nonwoven fabric E having a longitudinal direction of 10cm and a transverse direction of 40cm, and the nonwoven fabric E was obtained by an air-laid method, and was equivalent to a second substrate, and the weight per unit area was 47g/m 2 ) Uniformly dispersed (dispersion amount: 12.5 to 17.5g/m 2 ) 0.5 to 0.7g of an adhesive (spray 77, 3M JAPAN Co.) 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 overlapped (contact) and pressed together, and then uniformly dispersed (dispersion amount: 2.5 to 5.0 g/m) on the nonwoven fabric E 2 ) 0.1 to 0.2g of an adhesive (spray 77, 3M JAPAN Co.) containing styrene-butadiene rubber was used to obtain an intermediate sheet Y.
Then, the extra portion of the spunbonded nonwoven fabric located at the lowermost layer was folded, and the nonwoven fabric E of the intermediate sheet Y (the surface of the nonwoven fabric E side of the intermediate sheet Y) was wrapped so as to be in contact with the spunbonded nonwoven fabric, and turned upside down, and then, was subjected to pressure bonding to obtain a water-absorbent sheet (2).
Example 3
A water-absorbing sheet (3) was obtained in the same manner as in example 2, except that the particulate water-absorbing agent (2) was used in place of the particulate water-absorbing agent (1).
Example 4
A water-absorbing 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-absorbing sheet (5) was obtained in the same manner as in example 2, except that the particulate water-absorbing agent (4) was used in place of the particulate water-absorbing agent (1).
Example 6
A hot-air nonwoven fabric B having a thickness of 2.0mm (weight per unit area: 43g/m was used 2 ) A water-absorbent sheet (6) was obtained in the same manner as in example 2, except that the hot-air nonwoven fabric a was replaced.
Example 7
A hot-air nonwoven fabric C (weight per unit area: 37 g/m) having a thickness of 1.5mm was used 2 ) A water-absorbent sheet (7) was obtained in the same manner as in example 2, except that the hot-air 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 used 2 ) A water-absorbent sheet (8) was obtained in the same manner as in example 2, except that the hot-air nonwoven fabric a was replaced.
Example 9
The spun-laced nonwoven F (composed of PET resin and pulp, thickness: 0.4mm, weight per unit area: 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.
Example 10
A hot-air nonwoven fabric G (weight per unit area: 20G/m) having a thickness of 0.7mm was used 2 ) 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 heated air nonwoven fabric A having an olefin as a main component and having a thickness of 1.4mm, which had been cut into 10cm in the longitudinal direction and 40cm in the transverse direction, was carried, 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 A 2 )。
Next, a nonwoven fabric E (pulp fiber was used as the nonwoven fabric E cut into a length of 10cm and a width of 40cmA main component. The thickness was 0.4mm. Fabricated by air-laying. Corresponds to the second substrate. Weight per unit area: 47g/m 2 ) Uniformly dispersed (dispersion amount: 12.5 to 17.5g/m 2 ) 0.5 to 0.7g of an adhesive (spray 77, 3M JAPAN Co.) containing styrene-butadiene rubber. Thereafter, the surface of the nonwoven fabric a on which the particulate water absorbing agent is dispersed is overlapped with the surface of the nonwoven fabric E on which the adhesive is dispersed (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 )。
Next, the nonwoven fabric E (the same nonwoven fabric (thickness: 0.4 mm) as the nonwoven fabric E used above; corresponding to the first base material) cut into 10cm in the longitudinal direction and 40cm in the transverse direction was uniformly spread (spread amount: 12.5 to 17.5 g/m) 2 ) 0.5 to 0.7g of an adhesive (spray 77, 3M JAPAN Co.) 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 overlapped (contacted) and pressed and bonded under pressure to obtain an intermediate sheet Z.
Finally, on the nonwoven fabric E of the intermediate sheet Z (the nonwoven fabric side on which the particulate water absorbing agent is first dispersed), the particulate water absorbing agent is uniformly dispersed (dispersion amount: 2.5 to 5.0g/m 2 ) After 0.1 to 0.2g of an adhesive (spray 77, 3M JAPAN Co.) containing styrene-butadiene rubber, the resultant was wrapped with a spun-bonded nonwoven fabric having an olefin as a main component and a thickness of 0.1mm, which was cut into 24cm in the longitudinal direction and 40cm in the transverse direction, and pressure-bonded, thereby obtaining a water-absorbent sheet (11).
In comparative example 1, the particulate water absorbing agent corresponding to the nonwoven fabric E of the first substrate had a transmittance of 0.3 mass%, and the particulate water absorbing agent was contained in a proportion of 0%. In the water-absorbent sheet obtained in comparative example 1, the "thickness of the first substrate/thickness of the second substrate" was 1.
Comparative example 2
The olefin is cut into a length of 24cm and a width of 40cm in advance and is used as a main component and has a thicknessA spunbonded nonwoven fabric (corresponding to a cover sheet) of 0.1mm, on which a heated air nonwoven fabric A (corresponding to a first base material) having an olefin as a main component and a thickness of 1.4mm cut into a length of 10cm and a width of 40cm was carried, was uniformly spread (spread amount: 225 g/m) 2 ) 9.0g of the particulate water-absorbing agent (1).
Next, the nonwoven fabric A (corresponding to the second base material, hereinafter referred to as "nonwoven fabric A2" for convenience) was uniformly spread (spread amount: 12.5 to 17.5 g/m) on the surface of the hot air nonwoven fabric A (corresponding to the second base material, hereinafter referred to as "nonwoven fabric A2") cut into a thickness of 1.4mm in the longitudinal direction of 10cm and in the transverse direction of 40cm 2 ) 0.5 to 0.7g of an adhesive (spray 77, 3M JAPAN Co.) containing styrene-butadiene rubber. Thereafter, the adhesive-dispersed surface of the nonwoven fabric A2 is overlapped with the particulate water absorbing agent-dispersed surface of the nonwoven fabric A in a manner (contact manner), and the resultant is pressed and bonded, and then uniformly dispersed (dispersion amount: 2.5 to 5.0 g/m) on the nonwoven fabric A2 2 ) 0.1 to 0.2g of an adhesive (spray 77, 3M JAPAN Co.) containing styrene-butadiene rubber was used to obtain an intermediate piece Z2.
Then, the extra portion of the spunbonded nonwoven fabric located at the lowermost layer is folded, the intermediate sheet Z2 is wrapped so as to be in contact with the spunbonded nonwoven fabric, and the intermediate sheet Z2 is turned upside down, and then the water-absorbent sheet (12) is obtained by press-bonding.
Comparative example 3
A spunbonded nonwoven fabric (corresponding to a cover sheet) having an olefin as a main component and a thickness of 0.1mm cut into 24cm in the longitudinal direction and 40cm in the transverse direction was laid in advance, and a hot air nonwoven fabric A (corresponding to a first base material) having an olefin as a main component and a thickness of 1.4mm cut into 10cm in the longitudinal direction and 40cm in the transverse direction was carried 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 surplus portion of the spunbonded nonwoven fabric located at the lowermost layer is folded, the surface of the nonwoven fabric on which the particulate water absorbing agent (1) is spread is wrapped so as to contact the spunbonded nonwoven fabric, and the sheet is turned upside down, and then pressed and bonded to obtain a water absorbing sheet (13). The spun-bonded nonwoven fabric having the particulate water absorbing agent (1) dispersed therein was uniformly dispersed with 0.5 to 0.7g of an adhesive (spray 77, 3M JAPAN company) containing styrene-butadiene rubber only in a portion thereof in contact with the surface of the nonwoven fabric, and then wrapped.
Comparative example 4
The spun-laced nonwoven F (composed of PET resin and pulp, thickness: 0.4mm, weight per unit area: 45 g/m) 2 ) A water-absorbent sheet (14) was obtained in the same manner as in example 2, except that the hot-air nonwoven fabric A was replaced.
In comparative example 4, the particulate water absorbing agent corresponding to the nonwoven fabric F of the first substrate had a transmittance of 1 mass% and the particulate water absorbing agent had a content of 0%. In the water-absorbent sheet obtained in comparative example 4, the "thickness of the first substrate/thickness of the second substrate" was 1.
The nonwoven fabrics a to G used in this example were all water permeable sheets.
[ method for measuring physical Properties of nonwoven Fabric ]
The thickness, bulk density, liquid diffusion area, and transmittance of the particulate water absorbing agent to the nonwoven fabrics a to F used in examples 1 to 10 and comparative examples 1 to 4 were measured in the following manner.
< measurement of nonwoven Fabric thickness >
The measurement was performed using a dial gauge (dial thickness gauge) large size (thickness gauge) (model J-B, measuring head, anvil, up-down, 50mm, manufactured by Kawasaki Co., ltd.). The number of measurement points was 5 times at different positions, and the measurement value was set as an average value at 5. In measuring the thickness, the hand is slowly removed from the handle in order to apply as little pressure as possible to the nonwoven fabric, and the thickness is 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 transverse direction was measured. The length of the nonwoven fabric in the machine direction and the cross direction and the thickness measured by < thickness measurement > are multiplied, respectively, the volume of the nonwoven fabric is calculated, and the bulk density is 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 >
A sieve of 30cm in diameter obtained using a mesh of 2mm in mesh and a wire diameter of 0.9mm was placed on a plane, and a nonwoven fabric (second base material) cut into 10cm squares was placed. A syringe needle having a diameter of 0.50mm was mounted in a 1ml syringe, and 1.00g of physiological saline containing 20ppm of blue No. 1 reagent was measured, and physiological saline of the syringe was injected vertically 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 passing through the nonwoven fabric and the mesh does not contact the mesh. If the nonwoven fabric absorbs physiological saline and the liquid is finished to diffuse, the diffusion area of the physiological saline is measured.
< transmittance of particulate Water absorbing agent to nonwoven Fabric >
In a JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80mm; JIS Z8801-1 (2000)) having a mesh opening 32 of 850 μm or a sieve 31 corresponding to The JIS standard sieve, a nonwoven fabric (first base material 11) cut to a diameter of 80mm was provided as shown in FIG. 5, and The periphery was fixed with an adhesive tape 33 (an area through which particles could pass was ensured to be at least 75mm in diameter). As the nonwoven fabric (first base material 11), a nonwoven fabric taken out of the water-absorbent sheet by a method described later can be used. Particulate water-absorbing agent 14 (weight average particle diameter: 367. Mu.m, particle size distribution: 850 μm to 600. Mu.m, 6.1%, 600 μm to 500. Mu.m, 14.5%, 500 μm to 300. Mu.m, 50%, 300 μm to 150. Mu.m, 27.6%, 150 μm to 45 μm, 1.9%, 45 μm or less, 0.1%) was put on a nonwoven fabric (first substrate 11) in a sieve 31 (arrow direction in FIG. 5), and 10.0g was used, and the mixture was oscillated for 5 minutes at room temperature (20 to 25 ℃) and relative humidity of 50% RH using a rotary hammer sieve (ES-65 type sieve manufactured by Kagaku Kogyo Co., ltd., rotational speed: 230rpm, impact number: 130 rpm). After shaking, the mass (W (g)) of particulate water-absorbing agent 14 (that is, particulate water-absorbing agent 14 present in a portion 31a below mesh 32 of screen 31) passing through mesh 32 of screen 31 corresponding to the above-mentioned JIS standard screen and the nonwoven fabric (first substrate 11) was measured, and the transmittance of the particulate water-absorbing agent was calculated according to the following formula (i). The measurement was performed 3 times, and the average value was calculated. In table 1, the transmittance (mass%) of the particulate water absorbing agent is shown as "transmittance (mass%)".
[ math figure 2]
Transmittance (mass%) of particulate water absorbing agent = { W/10.0} ×100 … (i)
< method of 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 absorbing 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 taken out entirely. When the nonwoven fabrics above and below are peeled off, the water-absorbent sheet is cooled, and the adhesive properties of the adhesive (hot melt adhesive, adhesive cement paste) for attaching the nonwoven fabric and the particulate water absorbing agent are sufficiently weakened, and then the nonwoven fabrics are peeled off. By performing this step, the nonwoven fabric can be taken out without changing the fiber and the structure thickness of the nonwoven fabric, and the transmittance can be accurately measured. The method of cooling the water-absorbing sheet is not particularly limited as long as the fiber, structure and thickness of the nonwoven fabric are not changed and the particulate water-absorbing agent contained in the water-absorbing sheet is not absorbed by moisture, as long as the cooling method is carried out by leaving the water-absorbing sheet in a constant temperature bath at-10 ℃ or lower for a predetermined period of time, blowing a cooling spray, applying liquid nitrogen, and the like.
When the particulate water absorbing agent to be taken out absorbs moisture, the moisture content may be adjusted to 10 mass% or less, preferably to 5±2 mass% by drying, for example, and the above-mentioned transmittance and physical 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 and modification of the water-absorbent resin (particulate water-absorbent agent) do not occur, and drying under reduced pressure is preferable.
< measurement of the content ratio of particulate Water absorbing agent in upper nonwoven Fabric (corresponding to first substrate)
The sample (thickness was not changed) obtained by cutting the upper nonwoven fabric into a square having a longitudinal direction of 10mm and a transverse direction of 10mm was measured by using a MICRO FOCUS X-ray CT system inspeXio SMX-100CT manufactured by Shimadzu corporation. The measurement conditions are as follows.
[ X-ray CT-based imaging ]
Image lateral dimension (pixel): 512
Image vertical dimension (pixel): 512
X-ray tube voltage (kV): 50
X-ray tube current (μa): 40
English size (inch): 4.0
An X-ray filter: without any means for
SDD (distance of focus of X-ray source from X-ray detector) (mm): 700
SRD (distance of focal spot of X-ray source from rotation center of measurement sample) (mm): 550
Scan mode 1: CBCT
Scan pattern 2: routine scanning
Scanning angle: full scan
Number of fields of view: 2400
Average number: 5
Smoothing: YZ
Slice thickness (mm): 0.166
BHC data: without any means for
Fine mode: has the following components
FOV XY (maximum imaging area XY) (mm): 50.3
FOV Z (maximum shot region Z) (mm): 40.0.
next, the X-ray CT imaging data was analyzed by the following procedure using analysis software Win ROOF manufactured by san francisco corporation.
(1) Win ROOF is turned on, and the image (Jpeg) to be analyzed stored in the X-ray CT is selected.
(2) On the screen, clicking (selecting) is performed according to the procedures of binary processing, automatic binarization, modality method, threshold (appropriate adjustment) and operation.
(3) The polygonal ROI was selected to enclose 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 absorbing sheet was calculated in the same manner as in (3).
Based on the calculation result, the content (%) of the particulate water absorbing agent in the first substrate is calculated by the following formula.
The content ratio (%) of the particulate water absorbing agent in the first substrate=the particulate water absorbing agent area (I) in the first substrate/the particulate water absorbing agent total area (II) ×100
That is, the content ratio of the particulate water absorbing agent in the first substrate is expressed as an area% of the particulate water absorbing agent relative to the total area. The particulate water absorbing agent may be regarded as not being present because it is less than a few% if any on the surface of the first substrate on the side where the liquid to be absorbed is introduced.
[ method for evaluating Water-absorbent sheet ]
< reverse flow amount (evaluation of specific reverse flow amount) >)
As shown in fig. 6, the water-absorbent sheet 10 having a longitudinal direction of 10cm and a transverse direction of 40cm was wrapped with the liquid-impermeable sheet 21 having a longitudinal direction of 14cm and a transverse direction of 40cm so that an opening was formed in the upper portion. The water-absorbent sheet 10 wrapped with the liquid-impermeable sheet 21 was placed on a flat surface, and a liquid-injecting tube 41 (fig. 7) was placed at the center of the water-absorbent sheet 10 thereon as shown in fig. 8. In this state, 80g of a 23℃0.9 wt% aqueous sodium chloride solution was poured into the liquid pouring tube 41 using a funnel 42 capable of pouring a liquid at a flow rate of 7 ml/sec (FIG. 9). In this case, the liquid is poured into the water-absorbent sheet 10 exposed from the liquid-impermeable sheet 21. After 10 minutes from the time of liquid introduction, 20 pieces of filter paper 43 (model No.2, manufactured by ADVANTEC Co., ltd.; circular filter paper having a diameter of 110 mm) having a weight measured in advance were placed in the center of the water-absorbent sheet 10, and a weight 44 (1200 g) having a diameter of 100mm and a circular shape was further placed and held for 1 minute. After 1 minute, the weight 44 was removed, and the first pouring amount (g) was measured based on the weight gain of the filter paper 43. After 1 minute from the removal of the weight 44, the same operation was repeated (liquid was poured → after 10 minutes of pouring, the filter paper 43 and the weight 44 (1200 g) were carried, and the mixture was kept for 1 minute → after 1 minute, the weight was removed, and the pouring amount was measured, and the second pouring amount (g) and the third pouring amount (g) were measured. The total of the measured first to third pouring flows is shown in table 1.
< leakage amount (Tilt evaluation) >)
The amount of leakage was measured using the apparatus shown in fig. 10.
The following mechanism is taken as an outline: a commercially available laboratory apparatus stand 60 and a tube 61 were used to tilt and fix an acrylic plate 63, and then physiological saline was poured into a water absorbing sheet fixed to the plate from vertically above with a funnel, and the leakage amount was measured. The detailed specifications are shown below.
The length of the acrylic plate 63 in the inclined surface direction was 400mm, and was fixed by the stand 60 so that the angle with respect to the horizontal was 20 °. The acrylic plate 63 has a width of 200mm and a thickness of 3mm. The surface of the acrylic plate 63 is smooth, and therefore, the liquid does not remain on or be absorbed by the plate. The funnel 64 is fixed to the upper vertical side of the inclined acryl plate 63 using the stand 60. Funnel 64 used was a funnel into which liquid was poured at 7 mL/sec.
A metal tray 65 was provided below the acrylic plate 63, and the test liquid, which had all flowed down in the form of a leak, was received, and the mass thereof was recorded with an accuracy of 0.1 g.
The leak test in tilting using this device was performed as follows. 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 the acryl plate 63.
A stamp was marked on a portion 1.5cm downward from the upper end of the water-absorbent sheet, and the inlet of the funnel was fixed so that the distance from the vertically upper side of the stamp became 15.+ -.2 mm.
To the dropping funnel 64, 20mL of physiological saline was added at a time. The test liquid was not absorbed by the water absorbing sheet 66, but flowed on the inclined acrylic plate 63, and the amount of the liquid contained in the metal tray 65 was measured as the first leakage amount (mL) in the plane direction, and after 10 minutes, 20mL of physiological saline was similarly charged, and after the second leakage amount was measured, and after 10 minutes, 20mL of physiological saline was similarly charged, and the third leakage amount was measured. The leak amounts in the table are the total of the first to third leak 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 backflow amount than the water-absorbent sheets of comparative examples 1 to 4, and the leakage occurring from the water-absorbent sheets was also significantly reduced.
On the other hand, in comparative examples 1, 2 and 4, in which the thickness ratio of the first substrate to the second substrate was 1, which exhibited a multilayer structure, the amount of backflow was significantly increased.
Example 11
A spun-bonded nonwoven fabric (corresponding to a cover sheet) having polyolefin fibers as a main component and a thickness of 0.1mm, which was cut into 24cm in the longitudinal direction and 40cm in the transverse direction, was laid in advance, and a fluffed hot-air nonwoven fabric A (corresponding to a first base material) having polyolefin fibers as a main component and a thickness of 1.4mm, which was cut into 10cm in the longitudinal direction and 40cm in the transverse direction, was placed on the center, and 9.0g (a dispersion amount: 225 g/m) of a particulate water absorbing agent (2) was uniformly dispersed on the fluffed surface of the nonwoven fabric A 2 ). The fuzzing treatment of the nonwoven fabric a was performed according to the method described below.
Next, a nonwoven fabric E (pulp fiber as a main component, 0.4mm in thickness, produced by an air-laid method) was cut into a nonwoven fabric E having a longitudinal direction of 10cm and a transverse direction of 40cm, and the nonwoven fabric E was obtained by an air-laid method, and was equivalent to a second substrate, and the weight per unit area was 47g/m 2 ) Uniformly spread and heated to 135 ℃ to prepare a liquid HOT melt adhesive (JaourMelt 3889U, manufactured by jaourhot MELT ADHESIVE company, main component: styrene block copolymer, hydrocarbon resin, white mineral oil) 0.8g (dispersion: 20.0g/m 2 ). 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 overlapped (contacted) and pressed and bonded under pressure to obtain an intermediate sheet Y.
On the surface of the nonwoven fabric E of the intermediate sheet Y, 0.3g (dispersion amount: 7.5 g/m) of a liquid HOT melt adhesive (Jaourmelt 3889U, manufactured by JAOUR HOT MELT ADHESIVE Co., ltd., main component: styrene block copolymer, hydrocarbon resin, white mineral oil) was dispersed and heated to 135 DEG C 2 ). Then, the excess portion of the spun-bonded nonwoven fabric was folded, the surface of the nonwoven fabric E of the intermediate sheet Y was wrapped so as to be in contact with the spun-bonded nonwoven fabric, and the spun-bonded nonwoven fabric was turned upside down, and then the water-absorbent sheet (21) was obtained by press-bonding.
Example 12
The dispersion amount of the particulate water-absorbing agent was set to 12.0g (dispersion amount: 300 g/m) 2 ) A water-absorbent sheet (22) was obtained in the same manner as in example 11.
Example 13
A water-absorbent sheet (23) was obtained in the same manner as in example 12, except that the nonwoven fabric A which had not been subjected to the fluffing treatment was used instead of the nonwoven fabric A which had been subjected to the fluffing treatment.
Example 14
The adhesive to be applied to the nonwoven fabric E was set to 0.8g (applied amount: 20.0 g/M) of an adhesive containing styrene-butadiene rubber (spray 77, 3M JAPAN Co.) 2 ) A water-absorbent sheet (24) was obtained in the same manner as in example 11.
Example 15
A water-absorbing 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 (38 mass% monomer concentration) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing acrylic acid obtained in the production example of acrylic acid, an aqueous sodium acrylate solution obtained by the production method of the aqueous sodium acrylate solution using the acrylic acid, and deionized water, 5.03g of polyethylene glycol diacrylate (average addition mole number of ethylene oxide: 9) was dissolved to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by capping a jacketed stainless steel double arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ℃. Subsequently, 30.68g of a 10% by mass aqueous solution of sodium persulfate and 37.76g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and as a result, polymerization was started after about 1 minute. After 40 minutes from the start of polymerization, the hydrogel polymer was taken out. The resulting hydrogel-like polymer is finely divided 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 by a metal mesh having a mesh size of 600. Mu.m, whereby an irregularly pulverized water-absorbent resin (5-1) having an average particle diameter of 380. Mu.m was obtained.
To 100 parts by mass of the water-absorbent resin (5-1) thus obtained, 3.83 parts by mass of an aqueous surface cross-linking 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 was spray-mixed. The above mixture was heat-treated 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 sprayed and mixed, and the mixture was cured at 60℃for 1 hour in a closed container, and then the cured product was passed through a sieve having a mesh size of 710. Mu.m, to obtain a water-absorbent resin (5-3). A particulate water-absorbing agent (5) was obtained by adding 0.3 parts by mass of Aerosil200 (hydrophilic amorphous silica, manufactured by AEROSIL Co., ltd., japan) to water-absorbent resin (5-3) and mixing the resultant mixture.
Example 16
A water-absorbing 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 production example of acrylic acid, an aqueous sodium acrylate solution obtained by the production method of the aqueous sodium acrylate solution using the acrylic acid, and deionized water, 4.11g of polyethylene glycol diacrylate (average addition mole number of ethylene oxide: 9) was dissolved to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by capping a jacketed stainless steel double arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ℃. Then, 28.66g of a 10% by mass aqueous solution of sodium persulfate and 35.28g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and as a result, polymerization was started after about 1 minute.
After 40 minutes from the start of polymerization, 181.5g of fine powder of water-absorbent resin having a particle size of 150 μm or less was added, and the gel was broken by high-speed rotation (130 rpm) of a kneader plate for 10 minutes, followed by removal of the water-containing gel-like polymer. The resulting hydrogel-like polymer is finely divided 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 by a metal mesh having a mesh size of 600. Mu.m, whereby an irregularly pulverized water-absorbent resin (6-1) having an average particle diameter of 350. Mu.m was obtained.
To 100 parts by mass of the water-absorbent resin (6-1) thus obtained, 4.03 parts by mass of an aqueous surface cross-linking 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 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 sprayed and mixed, and the mixture was cured at 60℃for 1 hour in a closed container, and then the cured product was passed through a sieve having a mesh size of 710. Mu.m, to obtain a water-absorbent resin (6-3). A particulate water-absorbing agent (6) was obtained by adding 0.3 parts by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL Co., ltd., japan) to water-absorbent resin (6-3) and mixing the resultant mixture.
Example 17
A water-absorbing 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) >)
An aqueous monomer solution (a') was prepared by charging a polypropylene vessel having a capacity of 2 liters with 351.7g of acrylic acid, 0.860g of polyethylene glycol diacrylate (molecular weight: 523) as an internal crosslinking agent (0.034 mol% based on a carboxyl group-containing unsaturated monomer), 2.15g of 1.0 wt% aqueous solution of trisodium diethylenetriamine pentaacetate (dtpa·3na), 149.0g of 48.5 wt% aqueous solution of sodium hydroxide, and 336.2g of deionized water (ion-exchanged water), and mixing them.
Subsequently, the aqueous monomer solution (a') is cooled while stirring. At the time when the liquid temperature reached 40.0 ℃, 144.8g of 48.5 wt% aqueous sodium hydroxide solution adjusted to 40 ℃ was added and mixed, thereby producing a monomer aqueous solution (a). At this time, the temperature of the aqueous monomer solution (a) was raised to 78.2℃by the neutralization heat in the second stage immediately after the production. Immediately after the start of mixing of the 48.5 wt% aqueous sodium hydroxide solution, the precipitate was observed, but gradually dissolved to form a transparent homogeneous solution.
Then, after adding 15.49g of 4.0 wt% sodium persulfate aqueous solution to the above-mentioned monomer aqueous solution (a) in a stirred state, the mixture was immediately poured into a stainless steel pan (vat) container (340X 340mm bottom, 25mm height, inner surface: coated with Teflon (registered trademark)) in an atmosphere-open system. The time from the start of the neutralization in the second stage to the injection of the aqueous monomer solution (a) into the bottom plate type container heated to a surface temperature of 40℃by using a heating plate (NEO HOTPLATE HI-1000/Kagaku Kogyo Co., ltd.) was set to 55 seconds.
After 60 seconds from the injection of the aqueous monomer solution (a) into the tray vessel, the polymerization reaction was started. In this polymerization reaction, the reaction proceeds by expanding and foaming in all directions while generating steam, and then, the reaction product is contracted to a size slightly larger than that of the tray-type container. After 3 minutes from the start of the polymerization reaction, the hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel") was taken out (7-1). The series of operations was performed in an atmosphere-open system.
The aqueous gel (7-1) obtained by the polymerization reaction was cut into short strips, and fed into a screw extruder to be gel-pulverized, thereby obtaining a granular aqueous gel (7-2). The screw extruder had a perforated plate with a diameter of 100mm, a hole diameter of 11.0mm, a number of holes of 40, an aperture ratio of 62.5% and a thickness of 10mm at the tip end portion, and an outer diameter of the screw shaft of 86mm.
The gel pulverization is performed by simultaneously supplying the short aqueous gel (7-1) and the steam from different supply ports, respectively, in a state where the rotation speed of the screw shaft of the screw extruder is 130 rpm. The amount of the aqueous gel (7-1) supplied was 4640 g/min, and the amount of the steam supplied was 83 g/min.
The particulate aqueous gel (7-2) was spread on a 50-mesh metal mesh, dried with hot air at 190℃for 30 minutes, and the dried product was crushed by a roll mill (WML roll crusher/Kogyo Co., ltd.) and was further sieved with a JIS sieve having meshes of 850 μm, 600 μm, 500 μm, 300 μm and 150 μm, followed by blending, whereby an irregularly crushed precursor water-absorbent resin (A) having a weight average particle diameter (D50) of 305 μm and a logarithmic standard deviation (σζ) of particle size distribution of 0.35 was obtained. The Centrifuge Retention Capacity (CRC) of the precursor water-absorbent resin (A) was 48.4 (g/g).
A surface cross-linking agent solution formed of 0.03 part 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 so that the CRC of the resulting water-absorbent resin (1) became 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 diethylenetriamine pentaacetic acid (DTPA.3Na) was uniformly mixed with respect to 100 parts by weight of the water-absorbent resin. After drying at 60℃for 1 hour, it was passed through a JIS standard sieve having a mesh opening size of 850. Mu.m, and 0.3 parts by weight of silica (trade name: REOLOSIL QS-20, manufactured by TOKUYAMA) was mixed. For mixing, 30g of a water-absorbent resin was put into a mayonnaise bottle having a capacity of 225mL together with silica, and mixed by shaking of TURBULA SHAKER MIXER T F type (manufactured by Shinmaru Enterprises Co.) for 60 minutes to obtain water-absorbent resin particles (7).
Example 18
A spun-bonded nonwoven fabric (corresponding to a cover sheet) having polyolefin fibers as a main component and having a thickness of 0.1mm, which was cut into 24cm in the longitudinal direction and 40cm in the transverse direction, was laid in advance, and a fluffed HOT-air nonwoven fabric A (corresponding to a first base material) having polyolefin fibers as a main component and having a thickness of 1.4mm, which was cut into 10cm in the longitudinal direction and 40cm in the transverse direction, was placed in the center thereof, and the fluffed surface of the nonwoven fabric A was uniformly dispersed and heated to 135℃to prepare 0.8g (dispersion amount: 20.0 g/m) of a liquid HOT-melt adhesive (Jaourmelt 3889U, manufactured by JAOUR HOT MELT ADHESIVE Co., main component: styrene block copolymer, hydrocarbon resin, white mineral oil) 2 ) Thereafter, 12.0g (dispersion amount: 300g/m 2 )。
Next, a nonwoven fabric E (pulp fiber as a main component, 0.4mm in thickness, produced by an air-laid method) was cut into a nonwoven fabric E having a longitudinal direction of 10cm and a transverse direction of 40cm, and the nonwoven fabric was obtained by an air-laid method, and the nonwoven fabric was equivalent to a second substrate, and the weight per unit area was 47g/m 2 ) The intermediate sheet Y is obtained by overlapping the surface of the nonwoven fabric a on which the binder and the particulate water absorbing agent are dispersed in a manner (contact manner) and pressing the overlapping surfaces under pressure.
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 (Jaourmelt 3889U, manufactured by JAOUR HOT MELT ADHESIVE Co., ltd., main component: styrene block copolymer, hydrocarbon resin, white mineral oil) 2 ). Then, the excess portion of the spun-bonded nonwoven fabric was folded, wrapped so that the surface of the nonwoven fabric E of the intermediate sheet Y was in contact with the spun-bonded nonwoven fabric, turned upside down, and then pressed and bonded under pressure to obtain water-absorbing propertyA sheet (28).
< fluffing treatment >
The nonwoven fabric was placed on a horizontal table having a smooth surface, and a weight of 10kg was carried on both ends of the nonwoven fabric in the longitudinal direction, and the nonwoven fabric was fixed. The brush (length: 100mm, hair length: 25mm, brush material: polybutylene terephthalate resin, brush diameter: 0.2 mm) was held from above perpendicularly to the long axis of the nonwoven fabric, lowered vertically downward toward the surface of the nonwoven fabric, and was inserted while directly pressing the nonwoven fabric with the tip of the brush until it contacted the table top. 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 in the portion where the brush was moved was cut to obtain a fluffed nonwoven fabric.
< method for measuring area ratio of fluffing >
The nonwoven fabric subjected to the napping 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)). Then, the nonwoven fabric was lifted vertically upward by about 10cm to keep the plastic sheet horizontal. Both ends of the long axis of the nonwoven fabric to be suspended were held from below by clamps having a weight of 70g and a nip of 10cm or more (see fig. 11 (b)). Photographs of the upper surface of the nonwoven fabric stretched on the plastic sheet were taken from a direction perpendicular to the short axis of the nonwoven fabric (taken from the arrow direction of fig. 11 (b)).
The photographed picture is read into image analysis software windorof (ver.6.1), and "monochrome image processing" is performed by the "image processing" tag. Thereafter, as shown in fig. 11 (c), the range of the raised fibers (the range of 5mm upward from the nonwoven fabric surface) is selected by the rectangular ROI, and "automatic binarization" is selected from the "binarization" labels, so that only the raised fibers can be selected, and the threshold value is adjusted. The "area ratio" of "total area number" was selected from the "measurement" labels and run to calculate the fuzzing area ratio of the nonwoven fabric.
< evaluation of specific return flow under pressure >
As shown in fig. 6, the water-absorbent sheet 10 having a longitudinal direction of 10cm and a transverse direction of 40cm was wrapped with the liquid-impermeable sheet 21 having a longitudinal direction of 14cm and a transverse direction of 40cm so that an opening was formed in the upper portion. The water-absorbent sheet 10 wrapped with the liquid-impermeable sheet 21 was placed on a flat surface, and a liquid-feeding tube 45 (a plastic tube having an inner diameter of 26mm, an outer diameter of 30mm, a length of 150mm, and a weight of 34g, and a liquid-feeding tube having a weight of 30mm, an outer diameter of 60mm, a length of 62mm, and a weight of 1030g, respectively, were attached thereto, and FIG. 12) was placed in the center of the water-absorbent sheet 10 as shown in FIG. 13. In this state, 80g (fig. 14) of an aqueous solution containing 0.9 wt% sodium chloride and 0.002 wt% edible blue No. 1 (tokyo chemical industry company) at 23 ℃ was charged into the liquid charging tube 45 using a funnel 42 capable of charging liquid at a flow rate of 7 ml/sec. The time from the instant of pouring the aqueous solution to the time when the entire aqueous solution in the liquid pouring cylinder 45 is absorbed by the water-absorbing sheet 10 is measured. In this case, the liquid is poured into the water-absorbent sheet 10 exposed from the liquid-impermeable sheet 21. After 10 minutes from the time of liquid introduction, 20 pieces of filter paper 43 (model No.2, manufactured by ADVANTEC Co., ltd.; circular filter paper having a diameter of 110 mm) having a weight measured in advance were placed in the center of the water-absorbent sheet 10, and a circular weight 44 (1200 g) having a diameter of 100mm was further placed, and the mixture was kept for 1 minute. After 1 minute, the weight 44 was removed, and the first pouring amount (g) was measured based on the weight gain of the filter paper 43. The same operation (liquid input→measurement of the water absorption time of the liquid→10 minutes after the input, carrying of the filter paper 43 and the weight 44 (1200 g), and holding for 1 minute→1 minute after the removal of the weight, measurement of the pouring amount) was repeated 1 minute after the removal of the weight 44, and the second pouring amount (g) and the third pouring amount (g) were measured. The total of the measured water absorption time and the first to third pouring amounts is shown in Table 1.
< shedding 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 water-absorbent sheet 40cm×10cm, the whole of the surface and the side surface on the second substrate side and the surface 1cm from the outer periphery toward the inner side among the surfaces on the first substrate side were covered with a plastic sheet and fixed with an adhesive tape. 300ml of physiological saline (0.9% aqueous sodium chloride solution) was uniformly poured into the surface of the water-absorbent sheet covered with the plastic sheet. After 10 minutes from 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 Dai Kagaku Co., ltd.). Two posts of an electromagnetic sieving machine (manufactured by Retsch Co., ltd., AS 200) were respectively fitted with sleeves (ASS ONE, sleeve with 360 DEG rotation of claws), 1 SUS tube (diameter 13mm, inner diameter 10mm, length 290 mm) was fixed in parallel to the ground by each sleeve, and a large-sized clip (150 mm of a nip) fitted to the SUS tube was used to clamp the water-absorbing sheet together with the plastic bag, and the sheet was vibrated for 1 minute with a vibration width of 3 mm. The water-absorbing sheet was removed from the large-sized clamp of the electromagnetic sieve machine together with the plastic bag, and the weight of the particulate water-absorbing agent that had fallen out of the water-absorbing 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 physiological saline was 300g.
Abscission rate of particulate water absorbing agent (%) =abscission of particulate water absorbing agent (g)/(weight of water absorbing sheet (g) +weight of physiological saline (g)) ×100.
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 layer of a laminate of a first substrate is laminated on a second substrate and a two-layer system in which 2 layers of a laminate of a first substrate are laminated on a second substrate are disclosed. In both the single-layer system and the two-layer system, the first substrate having a liquid suction surface that directly absorbs 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 a liquid-absorbing surface that directly absorbs liquid in the two-layer system is an intermediate substrate, referred to herein as an "intermediate nonwoven fabric".
< production example >
Production example 1
The particulate water absorbing agents (1) and (2) of the polyacrylic acid (salt) resin were obtained by appropriately adjusting the CRC according to the amount of the internal crosslinking agent, taking as reference the production examples, examples and comparative examples described in the following patents. 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 ]
Acrylic acid (acrylic acid dimer 2000ppm, acetic acid 500ppm, propionic acid 500ppm, p-methoxyphenol 200 ppm) which is commercially available was supplied to the bottom of a high boiling impurity separation column having 50 stages of baffle-free porous plates, distilled with a reflux ratio of 1, and after removing maleic acid, a dimer formed from acrylic acid (acrylic acid dimer), and the like, further crystallization was performed to obtain acrylic acid (acrylic acid dimer 20ppm, acetic acid 50ppm, propionic acid 50ppm, furfural 1ppm or less, protoanemonin 1ppm or less), and after the distillation, p-methoxyphenol 50ppm was added.
[ preparation of aqueous sodium acrylate solution ]
According to example 9 of U.S. Pat. No. 5210298, 1390g of the above-mentioned acrylic acid was neutralized with 48% caustic soda at 20 to 40℃to obtain a 100% neutralized aqueous sodium acrylate solution having a concentration of 37%.
< 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 production example of acrylic acid, an aqueous sodium acrylate solution obtained by the production method of the aqueous sodium acrylate solution using the acrylic acid, and deionized water, 4.00g of polyethylene glycol diacrylate (average addition mole number of ethylene oxide: 9) was dissolved to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by capping a jacketed stainless steel double arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ℃. Then, 28.66g of a 10% by mass aqueous solution of sodium persulfate and 35.28g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and as a result, polymerization was started after about 1 minute. After 40 minutes from the start of polymerization, 181.5g of fine powder of water-absorbent resin having a particle size of 150 μm or less was added, and the gel was broken by high-speed rotation (130 rpm) of a kneader plate for 10 minutes, followed by removal of the water-containing gel-like polymer. The resulting hydrogel-like polymer is finely divided 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 by a metal mesh having a mesh size of 600. Mu.m, whereby an irregularly pulverized water-absorbent resin (1-1) having an average particle diameter of 350. Mu.m was obtained. To 100 parts by mass of the water-absorbent resin (1-1) thus obtained, 4.03 parts by mass of an aqueous surface cross-linking 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 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 sprayed and mixed, and the mixture was cured at 60℃for 1 hour in a closed container, and then the cured product was passed through a sieve having a mesh size of 710. Mu.m, to obtain a water-absorbent resin (1-3). A particulate water-absorbing agent (1) was obtained by adding 0.3 parts by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL Co., ltd., japan) to water-absorbent resin (1-3) and mixing the resultant mixture.
[ method for 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 particles) according to one embodiment of the present invention is a weight average particle diameter obtained by the measurement method of "PSD" specified in ERT 420.2-02. The weight average particle diameters of the particulate water absorbing agents are shown in Table 3.
< CRC (Water absorption Rate without pressure) (ERT 441.2-02) >)
After 0.2G (weight before water absorption) of the particulate water absorbing agent was put into a nonwoven fabric bag, the bag was immersed in a significantly excessive 0.9 mass% aqueous sodium chloride solution for 30 minutes to allow free swelling, and after that, the weight after water absorption of the particulate water absorbing agent was measured after water removal by a centrifuge (250G). The water absorption capacity (unit: g/g) was determined by "(weight of particulate water absorbing agent after water absorption-weight of particulate water absorbing agent before water absorption)/(weight of particulate water absorbing agent 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 means the surface tension of an aqueous solution when the particulate water absorbing agent is dispersed in 0.90 mass% aqueous sodium chloride solution.
50ml of physiological saline adjusted to 20℃was poured into a sufficiently cleaned 100ml beaker, and the surface tension of the physiological saline was measured by a surface tensiometer (KRUSS Co., ltd. K11 automatic surface tensiometer). In the present invention, a plate method using a platinum plate was used, and the plate was sufficiently washed with deionized water before each measurement, and was heated and washed with a gas burner.
Subsequently, 0.5g of a 25mm long fluororesin rotor and a particulate water absorbing agent, which were sufficiently washed, were put into a beaker containing physiological saline after surface tension measurement adjusted to 20℃and stirred at 500rpm for 4 minutes. After 4 minutes, stirring was stopped, and after the aqueous particulate water absorbing agent had settled, the same operation was performed again to measure the surface tension of the supernatant liquid. The surface tension (unit: mN/m) of the particulate water absorbing agent was determined from the surface tension of the supernatant liquid when the particulate water absorbing agent was dispersed in physiological saline. The surface tension of each particulate water absorbing agent is shown in tables 4 and 6.
[ examples ]
< preparation of hollowed-out cardboard >
The hollow-out cardboard sheets 1 to 6 were prepared for dispersing the particulate water absorbing agent in a stripe pattern on the nonwoven fabric. In the hollow-out cardboard sheets 1 to 6, openings were formed in the portions of the paper having a longitudinal direction of 14cm and a transverse direction of 44cm at which the regions where the particulate water absorbing agent was present were formed, so as to linearly form the regions where the particulate water absorbing agent was present and the regions where the particulate water absorbing agent was not present along the longitudinal direction. In the hollow-out cardboard sheets 1 to 6, the outer periphery thereof was set as a frame, and the paper was not cut (that is, the hollow-out cardboard sheet was perforated by hollowing out the portions of the region where the particulate water absorbing agent was present in order from the end in the width direction in the region other than the frame). The shapes (S-1) to (S-6) formed by the cut-out paper sheets 1 to 6 will be described with reference to fig. 15 (a) to 15 (c) and fig. 16 (a) to 16 (c). Fig. 15 (a) to 15 (c) and fig. 16 (a) to 16 (c) are schematic cross-sectional views of a single-layer type water-absorbing sheet cut in the width direction. In the shapes (S-1) to (S-6), the region containing 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 absorbing sheet. Accordingly, the ratio of the area of "particulate water absorbing agent 14" to the area of "gap 15" shown below may be from either one of the left and right sides in the width direction.
Fig. 15 (a) is a (S-1) shape formed by using the hollowed-out cardboard 1. In the shape of (S-1), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 15mm, gap 15:25mm, particulate water absorbing agent 14:20mm, gap 15:25mm, particulate water absorbing agent 14:15 mm).
Fig. 15 (b) is a (S-2) shape formed by using the hollowed-out cardboard 2. In the shape of (S-2), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 20mm, gap 15:20mm, particulate water absorbing agent 14:20mm, gap 15:20mm, particulate water absorbing agent 14:20 mm).
Fig. 15 (c) is a (S-3) shape formed by using the hollowed-out cardboard 3. In the shape of (S-3), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order in the width direction: 10mm, gap 15:35mm, particulate water absorbing agent 14:10mm, gap 15:35mm, particulate water absorbing agent 14:10 mm).
Fig. 16 (a) is a (S-4) shape formed by using the hollowed-out cardboard 4. In the shape of (S-4), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 25mm, gap 15:10mm, particulate water absorbing agent 14:30mm, gap 15:10mm, particulate water absorbing agent 14:25 mm).
Fig. 16 (b) is a (S-5) shape formed by using the hollowed-out cardboard 5. In the shape of (S-5), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 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 14:17.5 mm).
Fig. 16 (c) is a (S-6) shape formed by using the hollowed-out cardboard 6. In the shape of (S-6), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 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 14:10 mm).
Example 1
A hollow paperboard 1 (see fig. 15 (a)) was placed on a nonwoven fabric a (produced by a hot air method, having an olefin as a main component and a thickness of 1.4mm, corresponding to the intermediate nonwoven fabric) cut into 10cm in the longitudinal direction and 40cm in the transverse direction. The hollow paperboard 1 has 3 rectangular holes, and the position of the nonwoven fabric a under the hollow paperboard 1 is adjusted so that the nonwoven fabric a can be seen from the holes to the maximum. Calculating the area of each hole of the hollowed-out paperboard 1 relative to the whole Ratio of total area of the partial holes, the particulate water-absorbing agent (1) was 4.5g (dispersion amount: 112.5g/m 2 ) The nonwoven fabric a, which can be seen from each hole, was uniformly dispersed by being distributed and measured in terms of the area ratio of each hole. In the case where a part of the particulate water absorbing agent (1) is scattered on the hollowed-out cardboard, the hollowed-out cardboard 1 is inclined toward the nonwoven 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 hollowed-out cardboard 1. Thereafter, the hollow paperboard 1 is removed from the nonwoven a.
Unlike the nonwoven fabric a, the nonwoven fabric a cut into 10cm in the longitudinal direction and 40cm in the transverse direction (the same nonwoven fabric (thickness: 1.4 mm) as the nonwoven fabric a, hereinafter referred to as nonwoven fabric A2, which corresponds to the first base material (upper nonwoven fabric)), was uniformly spread with an adhesive (spray 77, 3M JAPAN company) containing styrene-butadiene rubber in an amount of 0.7 to 0.9g (spread amount: 17.5 to 21.5 g/M), and then, the surface of the nonwoven fabric a on which the particulate water absorbing agent (1) was spread was overlapped (in a contact manner) with the surface of the nonwoven fabric A2 on which the adhesive was spread, and was pressure-bonded.
On the surface of the nonwoven fabric a on the side not facing the particulate water absorbing agent (1), the hollow-out cardboard 1 is placed (see fig. 15 (a)). The position is adjusted in such a way that the nonwoven a under the hollow paperboard 1 can be seen to the maximum from the 3 rectangular holes of the hollow paperboard 1. The ratio of the area of each hole to the total area of all holes of the hollowed-out cardboard 1 was calculated, 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 dispersed. In the case where a part of the particulate water absorbing agent (1) is scattered on the hollowed-out cardboard, the hollowed-out cardboard 1 is inclined toward the nonwoven 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 hollowed-out cardboard 1. Thereafter, the hollow paperboard 1 is removed from the nonwoven a.
Nonwoven fabric E (produced by air-laid method, pulp fiber as main component, thickness of 0.4mm, weight per unit area of 47 g/m) 10cm in longitudinal direction and 40cm in transverse direction 2 . Corresponding to the second base material (lower nonwoven fabric)), uniformly dispersing 0.7-0.9 g of the adhesiveThe intermediate sheet X is obtained by overlapping (in contact with) the surface of the nonwoven fabric a on which the particulate water absorbing agent (1) is dispersed and the surface of the nonwoven fabric E on which the adhesive is dispersed so as to be aligned, and pressing the overlapping surfaces under pressure.
Finally, the intermediate sheet X was cut into a nonwoven fabric F (produced by a spunbonding method) having a length of 24cm and a width of 40cm, and the nonwoven fabric was produced by using an olefin as a main component, and had a thickness of 0.1mm and a basis weight of 13g/m 2 . Bulk density: 0.15g/cm 3 . Corresponding to the wrapping sheet) to obtain the water-absorbent sheet (1).
Example 2
A nonwoven fabric F (corresponding to a wrapping sheet) cut into 24cm in the vertical direction and 40cm in the horizontal direction was laid in advance, a nonwoven fabric a (corresponding to a first base material) cut into 10cm in the vertical direction and 40cm in the horizontal direction was placed thereon, and a hollow paperboard 1 was placed on the surface of the nonwoven fabric a (see fig. 15 (a)). The position is adjusted in such a way that the nonwoven a under the hollow paperboard 1 can be seen to the maximum from the 3 rectangular holes of the hollow paperboard 1. The ratio of the area of each hole to the total area of all holes of the hollowed-out cardboard 1 was calculated, and 9.0g (dispersion amount: 225 g/m) of the particulate water absorbing agent (1) 2 ) The nonwoven fabric a, which can be seen from each hole, was uniformly dispersed by being distributed and measured in terms of the area ratio of each hole. In the case where a part of the particulate water absorbing agent (1) is scattered on the hollowed-out cardboard, the hollowed-out cardboard 1 is inclined toward the nonwoven 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 hollowed-out cardboard 1. Thereafter, the hollow paperboard 1 is removed from the nonwoven a.
After 0.7 to 0.9g (dispersion amount: 17.5 to 21.5 g/M) of an adhesive containing styrene-butadiene rubber (spray 77, 3M JAPAN Co.) was uniformly dispersed on a nonwoven fabric E (corresponding to the second base material) having a longitudinal direction of 10cm and a transverse direction of 40cm, the surface of the nonwoven fabric A on which the particulate water absorbing agent (1) was dispersed was overlapped with the surface of the nonwoven fabric E on which the adhesive was dispersed in a butt joint manner (in a contact manner), and press-bonding was performed, to obtain an intermediate sheet Y.
Finally, the intermediate sheet Y is wrapped with the nonwoven fabric F and pressure-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 hot-air nonwoven fabric G having a thickness of 0.7mm was used instead of the hot-air nonwoven fabric a.
Example 4
A water-absorbing sheet (4) was obtained in the same manner as in example 2, except that the hollow-out cardboard 2 (see fig. 15 (b)) was used instead of the hollow-out cardboard 1.
Example 5
A water-absorbing sheet (5) was obtained in the same manner as in example 2, except that the hollow-out cardboard 3 (see fig. 15 (c)) was used instead of the hollow-out cardboard 1.
Example 6
A water-absorbing sheet (6) was obtained in the same manner as in example 2, except that the cardboard sheet 4 (see fig. 16 (a)) was used instead of the cardboard sheet 1.
Example 7
A water-absorbing sheet (7) was obtained in the same manner as in example 2, except that the hollow-out cardboard 5 (see fig. 16 (b)) was used instead of the hollow-out cardboard 1.
Example 8
A water-absorbing sheet (8) was obtained in the same manner as in example 2, except that the hollow-out cardboard 6 (see fig. 16 (c)) was used instead of the hollow-out cardboard 1.
Example 9
A water-absorbing sheet (9) was obtained in the same manner as in example 2, except that a nonwoven fabric B (produced by a hot air method; olefin was used as a main component, and the thickness was 2.0 mm.) was used instead of the nonwoven fabric a.
Example 10
A water-absorbing sheet (10) was obtained in the same manner as in example 2, except that a nonwoven fabric C (produced by a hot air method; olefin was used as a main component, and the thickness was 1.5 mm.) was used instead of the nonwoven fabric a.
Comparative example 1
4.5g of the particulate water-absorbing agent (1) was uniformly dispersed on the nonwoven fabric A cut into 10cm in the longitudinal direction and 40cm in the transverse direction.
After 0.7 to 0.9g (dispersion amount: 17.5 to 21.5 g/M) of an adhesive containing styrene-butadiene rubber (spray 77, 3M JAPAN Co.) was uniformly dispersed on a nonwoven fabric E (corresponding to the first substrate) having a longitudinal direction of 10cm and a transverse direction of 40cm, the surface of the nonwoven fabric A on which the particulate water absorbing agent (1) was dispersed was overlapped (in contact) with the surface of the nonwoven fabric E on which the adhesive was dispersed, and then pressure-bonded.
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.
The intermediate sheet Z was obtained by uniformly dispersing 0.7 to 0.9g of the adhesive on a nonwoven fabric E (hereinafter referred to as a nonwoven fabric E2, which corresponds to a second substrate) having a longitudinal direction of 10cm and a transverse direction of 40cm, respectively, and then overlapping (in contact) the surface of the nonwoven fabric a on which the particulate water absorbing agent (1) was dispersed and the surface of the nonwoven fabric E2 on which the adhesive was dispersed so as to be aligned. Finally, the intermediate sheet Z is wrapped with a nonwoven fabric F and pressure-bonded, thereby obtaining a water-absorbent sheet (11).
Comparative example 2
A water-absorbing sheet (12) was obtained in the same manner as in example 1, except that the particulate water-absorbing agent (1) was uniformly dispersed throughout the entire surface of the nonwoven fabric A without using the hollow-out cardboard (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 A2. 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 this example were all water permeable sheets.
[ method for measuring physical Properties of nonwoven Fabric ]
The elongation, thickness, bulk density, liquid diffusion area, and transmittance of the particulate water absorbing agent to the nonwoven fabrics a to C, E and G used in example 1, examples 2 to 10, and comparative examples 1 to 4 were measured in the following manner.
[ method of measuring elongation ]
The nonwoven fabric for measuring 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 of the present example used for the water-absorbent sheet, the dimensions of 100mm in the longitudinal direction (short side) and 400mm in the transverse direction (long side), the longitudinal direction (short side) and the transverse direction (long side) were taken as the width direction and the winding length direction of the nonwoven fabric roll, respectively. As shown in fig. 17 (a), reference lines were drawn parallel to the short sides of the cut nonwoven fabric at positions 5mm away from both ends of the nonwoven fabric for measuring elongation. Each clip is sandwiched by a double clip (double clip) so as to overlap with the reference line (fig. 17 (b)). The double-layer cloth gripper uses a clip with a claw length of more than 30 mm. The 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 110g. And holding the double-layer cloth clip without the heavy object at room temperature, lifting the heavy object attached to the other double-layer cloth clip, floating the heavy object in the air, and maintaining the non-woven fabric in an elongated state due to the weight of the double-layer cloth clip and the heavy object for 20 seconds. Next, the length of the nonwoven fabric in the longitudinal direction was measured while floating in the air (fig. 17 (c)). The ratio was determined as the elongation by using the following equation, based on the length of the long side after floating in the air and the length of the long side before floating in the air, which was 100 mm.
[ math 3]
< measurement of nonwoven Fabric thickness >
The measurement was performed using a dial gauge (thickness gauge) (model J-B, model J, measuring head, anvil up-down 50mm, manufactured by Kawasaki Co., ltd.). The number of measurement points was 5 times at different positions, and the measurement value was set as an average value at 5. In measuring the thickness, the hand is slowly removed from the handle in order to apply as little pressure as possible to the nonwoven fabric, and the thickness is 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 transverse direction was measured. The length of the nonwoven fabric in the machine direction and the cross direction and the thickness measured by < thickness measurement > are multiplied, respectively, the volume of the nonwoven fabric is calculated, and the bulk density is 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 >
A sieve of 30cm in diameter obtained using a mesh of 2mm in mesh and a wire diameter of 0.9mm was placed on a plane, and a nonwoven fabric (second base material) cut into 10cm squares was placed. A syringe needle having a diameter of 0.50mm was mounted in a 1ml syringe, and 1.00g of physiological saline containing 20ppm of blue No. 1 reagent was measured, and physiological saline of the syringe was injected vertically 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 passing through the nonwoven fabric and the mesh does not contact the mesh. If the nonwoven fabric absorbs physiological saline and the liquid is finished to diffuse, the diffusion area of the physiological saline is measured.
< transmittance of particulate Water absorbing agent to nonwoven Fabric >
In a JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80mm; JIS Z8801-1 (2000)) having a mesh opening 32 of 850 μm or a sieve 31 corresponding to The JIS standard sieve, a nonwoven fabric (first base material 11) cut to a diameter of 80mm was provided as shown in FIG. 5, and The periphery was fixed with an adhesive tape 33 (an area through which particles could pass was ensured to be at least 75mm in diameter). As the nonwoven fabric (first base material 11), a nonwoven fabric taken out of the water-absorbent sheet by a method described later can be used. Particulate water-absorbing agent 14 (weight average particle diameter: 367. Mu.m, particle size distribution: 850 μm to 600. Mu.m, 6.1%, 600 μm to 500. Mu.m, 14.5%, 500 μm to 300. Mu.m, 50%, 300 μm to 150. Mu.m, 27.6%, 150 μm to 45 μm, 1.9%, 45 μm or less, 0.1%) was put on a nonwoven fabric (first substrate 11) in a sieve 31 (arrow direction in FIG. 5), and 10.0g was used, and the mixture was oscillated for 5 minutes at room temperature (20 to 25 ℃) and relative humidity of 50% RH using a rotary hammer sieve (ES-65 type sieve manufactured by Kagaku Kogyo Co., ltd., rotational speed: 230rpm, impact number: 130 rpm). After shaking, the mass (W (g)) of particulate water-absorbing agent 14 after passing through the nonwoven fabric (first substrate 11) and mesh 32 of screen 31 corresponding to the above-mentioned JIS standard sieve (i.e., particulate water-absorbing agent 14 present in portion 31a below mesh 32 of screen 31) was measured, and the transmittance of particulate water-absorbing agent 14 was calculated according to the following formula (i). The average value was calculated by performing 2 measurements.
[ mathematics 4]
Transmittance (mass%) of particulate water absorbing agent = { W/10.0} ×100 … (i)
The particulate water absorbing agent used for measuring the transmittance is a particulate water absorbing agent comprising 90% by weight 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. Thus, the transmittance of the particulate water absorbing agent calculated in this example to the first substrate also corresponds to the transmittance of the particular particulate water absorbing agent to the first substrate.
< method of 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 absorbing 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 agent attached to the upper and lower nonwoven fabrics and the intermediate nonwoven fabric was also taken out entirely. When the nonwoven fabrics above and below are peeled off, the water-absorbent sheet is cooled, and the adhesive properties of the adhesive (hot melt adhesive, adhesive cement paste) for attaching the nonwoven fabric and the particulate water absorbing agent are sufficiently weakened, and then the nonwoven fabrics are peeled off. By performing this step, the nonwoven fabric can be taken out without changing the fiber and the structure thickness of the nonwoven fabric, and the transmittance can be accurately measured. The method of cooling the water-absorbing sheet is not particularly limited as long as the fiber, structure and thickness of the nonwoven fabric are not changed and the particulate water-absorbing agent contained in the water-absorbing sheet is not absorbed by moisture, as long as the cooling method is carried out by leaving the water-absorbing sheet in a constant temperature bath at-10 ℃ or lower for a predetermined period of time, blowing a cooling spray, applying liquid nitrogen, and the like.
When the particulate water absorbing agent to be taken out absorbs moisture, the moisture content may be adjusted to 10 mass% or less, preferably to 5±2 mass% by drying, for example, and the above-mentioned transmittance and physical 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 and modification of the water-absorbent resin (particulate water-absorbent agent) do not occur, and drying under reduced pressure is preferable.
< determination of the content ratio of particulate Water absorbing agent in upper nonwoven Fabric >
The sample (thickness was not changed) obtained by cutting the upper nonwoven fabric into a square having a longitudinal direction of 10mm and a transverse direction of 10mm was measured by using a MICRO FOCUS X-ray CT system inspeXio SMX-100CT manufactured by Shimadzu corporation. The measurement conditions are as follows.
[ X-ray CT-based imaging ]
Image lateral dimension (pixel): 512
Image vertical dimension (pixel): 512
X-ray tube voltage (kV): 50
X-ray tube current (μa): 40
English size (inch): 4.0
An X-ray filter: without any means for
SDD (distance of focus of X-ray source from X-ray detector) (mm): 700
SRD (distance of focal spot of X-ray source from rotation center of measurement sample) (mm): 550
Scan mode 1: CBCT
Scan pattern 2: routine scanning
Scanning angle: full scan
Number of fields of view: 2400
Average number: 5
Smoothing: YZ
Slice thickness (mm): 0.166
BHC data: without any means for
Fine mode: has the following components
FOV XY (maximum imaging area XY) (mm): 50.3
FOV Z (maximum shot region Z) (mm): 40.0.
next, the X-ray CT imaging data was analyzed by the following procedure using analysis software Win ROOF manufactured by san francisco corporation.
(1) Win ROOF is turned on, and the image (Jpeg) to be analyzed stored in the X-ray CT is selected.
(2) On the screen, clicking (selecting) is performed according to the procedures of binary processing, automatic binarization, modality method, threshold (appropriate adjustment) and operation.
(3) The polygonal ROI was selected to enclose 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 absorbing sheet was calculated in the same manner as in (3).
Based on the calculation result, the content (%) of the particulate water absorbing agent in the first substrate is calculated by the following formula.
The content ratio (%) of the particulate water absorbing agent in the first substrate=the particulate water absorbing agent area (I) in the first substrate/the particulate water absorbing agent total area (II) ×100
That is, the content ratio of the particulate water absorbing agent in the first substrate is expressed as an area% of the particulate water absorbing agent relative to the total area. The particulate water absorbing agent may be regarded as not being present because it is present in less than a few% on the liquid absorbing surface of the first substrate (the surface on the side where the liquid to be absorbed by the upper nonwoven fabric is introduced) directly absorbing the liquid. In the following examples, the content of the particulate water absorbing agent in the first substrate was 5% or more with respect to the particulate water absorbing agent contained in the entire water absorbing sheet.
[ method for evaluating Water-absorbent sheet ]
< reverse flow amount (evaluation of specific reverse flow amount) >)
As shown in fig. 6, the water-absorbent sheet 10 having a longitudinal direction of 10cm and a transverse direction of 40cm was wrapped with the liquid-impermeable sheet 21 having a longitudinal direction of 14cm and a transverse direction of 40cm so that an opening was formed in the upper portion. The water-absorbent sheet 10 wrapped with the liquid-impermeable sheet 21 was placed on a flat surface, and a liquid-injecting tube 41 (fig. 7) was placed at the center of the water-absorbent sheet 10 thereon as shown in fig. 8. In this state, 80g of a 23℃0.9 wt% aqueous sodium chloride solution was poured into the liquid pouring tube 41 using a funnel 42 capable of pouring a liquid at a flow rate of 7 ml/sec (FIG. 9). In this case, the liquid is poured into the sheet 22 with respect to the water-absorbent sheet 10 exposed from the liquid-impermeable sheet 21. After 10 minutes from the time of liquid introduction, 20 sheets of filter paper 43 (model No.2, manufactured by ADVANTEC Co., ltd.; circular filter paper having a diameter of 110 mm) having a weight measured in advance were placed in the center of the sheet 22, that is, in the center of the water-absorbent sheet 10, and further, a weight 44 (1200 g) having a diameter of 100mm and a circular shape was placed and held for 1 minute. After 1 minute, the weight 44 was removed, and the first pouring amount (g) was measured based on the weight gain of the filter paper 43. After 1 minute from the removal of the weight 44, the same operation was repeated (liquid was poured → after 10 minutes of pouring, the filter paper 43 and the weight 44 (1200 g) were carried, and the mixture was kept for 1 minute → after 1 minute, the weight was removed, and the pouring amount was measured, and the second pouring amount (g) and the third pouring amount (g) were measured. The total of the measured first to third pouring flows is shown in tables 4 and 6.
< method of calculating thickness ratio (Lb/La) >)
La is a thickness from the liquid suction surface of the upper nonwoven fabric (liquid suction 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 suction surface of the upper nonwoven fabric (liquid suction surface of the first substrate) to the surface of the lower nonwoven fabric (second substrate) on the water-absorbing layer side in the region containing the particulate water absorbing agent.
[ measurement of thickness of Water-absorbent sheet by X-ray CT ]
In the X-ray CT-based image capturing, both ends of a water-absorbing sheet cut into 180mm long were fixed with an adhesive tape to a plastic plate having a longitudinal direction of 350mm, a transverse direction of 100mm and a thickness of 3mm, and the plastic plate was placed on an inner plate of an X-ray apparatus (manufactured by Shimadzu corporation, inspeXio SMX-100 CT) perpendicularly to the thickness direction, and the center of the water-absorbing sheet was measured under the following conditions, whereby the image capturing was performed.
The using device comprises: inspeXio SMX-100CT (manufactured by Shimadzu corporation)
X-ray tube voltage (kV): 80
X-ray tube current (μa): 40
English size (inch): 4.0
An X-ray filter: without any means for
SOD(mm)：700
SRD(mm)：550
Number of fields of view: 2400
Average number: 5X 1
Slice thickness (mm): 0.166
CT mode 1: CBCT
CT mode 2: conventional operation
Scanning angle: full scan
BHC data: without any means for
Center adjustment: has the following components
Fine mode: has the following components
FOV(XY)(mm)：50.3
FOV(Z)(mm)：20.0
Voxel size (mm/voxel): 0.098
A sectional view was obtained in which the captured stereoscopic image was divided into 203 parts in the longitudinal direction, 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 suction surface of the upper nonwoven fabric to the surface of the lower nonwoven fabric on the water-absorbing layer side in the gap under the upper nonwoven fabric, and Lb is the thickness from the liquid suction surface of the upper nonwoven fabric to the surface of the lower nonwoven fabric on the water-absorbing layer side in the region under the upper nonwoven fabric containing the particulate water absorbing agent.
< evaluation of shape retention >
After the water-absorbing sheet was evaluated for the < amount of backflow >, the center of the water-absorbing sheet was cut in the width direction, and the region (i.e., the gap) containing no particulate water-absorbing agent was visually checked. At this time, the presence of the substance in the gap was confirmed and evaluated according to the following evaluation criteria.
Evaluation criterion
And (2) the following steps: the regions containing the particulate water absorbing agent are separated by gaps
(i.e., there is no member in the gap or there is a base material having a water-absorbing layer mainly in the gap (i.e., upper nonwoven fabric and lower nonwoven fabric in the case of the single-layer mode; upper nonwoven fabric, middle nonwoven fabric and lower nonwoven fabric in the case of the two-layer mode))
X: the space is present in a small proportion, and the regions containing the particulate water-absorbing agent in parallel are connected to each other (not separated by the space)
(that is, the particulate water absorbing agent enters into the region regarded as the gap, or the presence ratio of the base material having the water absorbing layer becomes smaller).
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 results of evaluation of physical properties of the substrates used in the respective water-absorbent sheets, and the results of evaluation of the water-absorbent sheets. In tables 3 to 6, SAP means particulate water absorbing agent. The SAP placement area (%) in tables 3 and 5 means: in the upper nonwoven fabric surface direction, the ratio of the area of the region containing the particulate water absorbing agent to the total area of the substrate provided with the particulate water absorbing agent, the region (%) where the SAP is not provided means: in the face direction of the upper nonwoven fabric, the ratio of the area of the region (i.e., the gap) free of the particulate water absorbing agent to the total area of the substrate on which the particulate water absorbing agent is disposed. Here, the substrate provided with the particulate water absorbing agent means: a substrate in which a particulate water absorbing agent is dispersed. In this example, the upper nonwoven fabric, the intermediate nonwoven fabric, and the lower nonwoven fabric were the same size.
TABLE 3
TABLE 4
TABLE 5
TABLE 6
From the above results, the water-absorbent sheets of examples 2 to 10 were high in shape retention and significantly less in backflow compared with the water-absorbent sheets of comparative examples 1 to 4. The method can confirm that: in the single-layer type and two-layer type water absorbent sheets, the use of the stretchable upper nonwoven fabric provides gaps in the water absorbent layer, and thus the flow-down rate can be reduced, and the shape retention is high.
In the present embodiment, the two-layer system tends to have a larger amount of backflow than the single-layer system. It may also be one of the reasons that the amount of the particulate water absorbing agent of the two-layer type relative to the upper layer 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 of the single-layer type relative to the upper layer 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 reverse flow rate between the single-layer system and the two-layer system is difficult to be generalized.
The present application is based on japanese patent application nos. 2019-215887 and 2019-215888, both filed on 11-month 28, the disclosures of which are incorporated herein by reference in their entirety.
Description of the reference numerals
10. Water-absorbing sheet
11. A first base material,
12. A water-absorbing layer,
13. A second base material,
14. A particulate water absorbing agent,
15. A gap(s),
16. A wrapping sheet,
21. A liquid impermeable sheet,
31. A sieve(s),
31a part under the screen,
32. Mesh openings,
33. Adhesive tape,
41. A liquid injection cylinder,
42. A funnel(s),
60. A stand table,
61. A pipe(s),
63. Acrylic plate,
64. A funnel(s),
65. A metal tray.
[ second invention ]
Next, a description is given of a second invention. The water-absorbent sheet of the second aspect of the 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 contains a particulate water-absorbing agent, the region containing the particulate water-absorbing agent is disposed with a gap substantially free of the particulate water-absorbing agent interposed therebetween, the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid, and the first substrate has an elongation of 10% or more.
[ File name ] Specification
[ invention ] Water-absorbing sheet and absorbent article comprising same
Technical Field
The present invention relates to a water-absorbent sheet and an absorbent article comprising the same.
Background
The water-absorbent resin (SAP/Super Absorbent polymer) is a water-swellable, water-insoluble, high-molecular gelling agent, and is used for sanitary materials such as paper diapers, sanitary napkins, adult-oriented incontinence products, and the like; soil water-retaining agent for agriculture, forestry and gardening, industrial water-stopping agent and the like.
These absorbent articles are generally manufactured in a diaper manufacturing factory in the form of an absorbent body obtained by mixing a water-absorbent resin with a fibrous material and molding each absorbent article, and are manufactured into various shapes (for example, hourglass type, fox type, elliptical type, etc. in plan view) according to the purpose. In these absorbent body manufacturing methods, since the absorbent body can be molded separately and processed into an arbitrary shape, the amounts of the fibers and the water-absorbent resin can be easily adjusted for each absorbent article, and thus, the present-day paper diapers have become the mainstream.
In recent years, however, in the production of disposable diapers, the production of disposable diapers has been started with an absorbent article obtained by cutting a long water-absorbent sheet obtained by fixing a water-absorbent resin between two sheets in a sanitary material production process (referred to as a water-absorbent sheet, which is usually cut into a rectangular shape having a width of about 10cm and a length of 10 cm). The paper diaper manufacturer can simplify the process of manufacturing the paper diaper by purchasing or manufacturing the long continuous water-absorbing sheet, and can reduce the paper diaper by not using pulp. The water-absorbent sheet is constituted by sandwiching and fixing water-absorbent resin particles between upper and lower sheets (particularly, nonwoven fabric sheets), and is usually produced by cutting a long continuous sheet after the long continuous sheet is produced, and then the long continuous sheet is formed into a rectangular shape having a width of about 10cm and a length of 10cm, and incorporated into a paper diaper (for example, international publication No. 2010/143635).
Unlike conventional sanitary materials (disposable diapers), the history of disposable diapers based on water-absorbent sheets is still short, and development of water-absorbent resins suitable for water-absorbent sheets and parameter development have not been substantially performed in practical cases, and conventional water-absorbent resins for disposable diapers have been used directly for water-absorbent sheets.
Disclosure of Invention
Problems to be solved by the invention
The inventors found that: if the water-absorbent sheet is a thin main stream, the absorbed liquid is likely to be caused to flow in a so-called "reverse flow" in which the absorbed liquid is discharged in the direction of introduction by applying pressure to the water-absorbent sheet. "reverse flow" is also known as Re-wet. And found that: if the liquid is intermittently introduced a plurality of times (in particular, 3 times or more) and the liquid introduction amount becomes large, the problem of occurrence of backflow becomes remarkable. When the back flow occurs, the skin in contact with the water-absorbing sheet is exposed to a high moisture content by contact with the liquid in the back flow. Therefore, not only the user may feel uncomfortable, but also the skin in contact with the water-absorbent sheet may be prone to inflammation.
In addition, in such a conventional water-absorbent sheet structure, the absorbed water-absorbent resin particles swell, and therefore, the fixation of the water-absorbent resin particles to the upper and lower sheets becomes weak, and the water-absorbent resin particles may move in the sheets. Thus, the water-absorbent resin particles are biased in the sheet, and the shape of the water-absorbent sheet collapses. In this case, the liquid absorbency of the water absorbent sheet varies, and causes leakage. The water-absorbent resin particles may sometimes fall off from the inside to the outside of the sheet.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a novel water-absorbent sheet which can significantly reduce the discharge of liquid from the water-absorbent sheet due to backflow even when liquid is intermittently introduced a plurality of times (in particular, 3 times or more), and which maintains the sheet shape (the sheet has a high shape retention) even after liquid is absorbed.
Solution for solving the problem
The present inventors have conducted intensive studies to solve the above problems. The result shows that: the above-described problems can be solved by a water-absorbent sheet comprising 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 contains a particulate water-absorbing agent, regions containing the particulate water-absorbing agent are arranged with gaps substantially free of the particulate water-absorbing agent therebetween, the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid, and the first substrate has an elongation of 10% or more.
In another aspect of the present invention, the water-absorbent sheet is formed by stacking only a laminate, in which the first base material is stacked on the water-absorbent layer, on the second base material in the water-absorbent sheet.
Further, according to another aspect of the present invention, there is provided a water-absorbent sheet comprising a laminate in which the first base material is laminated on the water-absorbent layer, and a constituent body in which an intermediate base material is laminated on the water-absorbent layer, laminated 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 the 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-absorbing sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbing sheet produced in the example.
FIG. 21 is a schematic view showing a cross section of a water-absorbing sheet for explaining the form of the particulate water-absorbing agent and the gaps in the water-absorbing sheet produced in the example.
Fig. 22 is a schematic diagram illustrating a method for measuring elongation of a nonwoven fabric.
FIG. 23 is a schematic view illustrating a method for measuring the transmittance of the nonwoven fabric with respect to the particulate water absorbing agent.
Fig. 24 is a plan view and a right side view showing a sample for evaluating the pouring amount, and is a view showing a state in which the water-absorbent sheet produced in the example is wrapped with the liquid-impermeable sheet.
Fig. 25 is a plan view and a front view of the liquid injection tube for evaluating the pouring amount.
FIG. 26 is a front view showing a case where a liquid injection tube is placed on a water-absorbing sheet used in the examples of the present application.
FIG. 27 is a front view showing a case where an aqueous sodium chloride solution is 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. For the purposes of this specification as a whole, singular forms shall be understood to include the plural concepts thereof, unless specifically mentioned otherwise. Thus, unless specifically mentioned otherwise, it is to be understood that singular forms (e.g., "a," "an," "the," etc. in the case of English) also include plural forms of the concepts thereof. Further, unless specifically mentioned otherwise, the terms used in the present specification should be construed as being used in accordance with the meanings commonly used in the art. Accordingly, unless otherwise defined, all technical and scientific terms used in this specification 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 following embodiments, 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 ] in the first invention are equally applicable to the second invention. Therefore, these definitions are omitted here, but are incorporated by reference into the second invention.
[ 2. Water-absorbing sheet ]
The water-absorbing sheet of the present invention comprises a first substrate, a second substrate, and a water-absorbing layer located between the first substrate and the second substrate, wherein the water-absorbing layer contains a particulate water-absorbing agent, the region containing the particulate water-absorbing agent is disposed with a gap substantially free of the particulate water-absorbing agent interposed therebetween, the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid, and the first substrate has an elongation of 10% or more.
With this configuration, even when the liquid is intermittently introduced a plurality of times (in particular, 3 times or more) and the liquid introduction amount becomes large, the discharge of the liquid from the water-absorbing sheet due to the reverse flow can be significantly reduced, and the shape retention after the liquid absorption is high. In the water-absorbent sheet of the present invention, the elongation of the first substrate forming the liquid-absorbing surface that directly absorbs liquid is 10% or more. That is, the first base material has stretchability. A liquid-absorbing surface that directly absorbs liquid is formed on the surface of the stretchable first substrate. Here, in the present specification, "liquid suction surface" means: the surface of the substrate on the side where the liquid is absorbed, i.e., the surface on the side where the liquid is to be introduced. In the present specification, "directly" does not include a method of sequentially absorbing liquid permeated from another substrate or the like. In the present specification, when a cover sheet to be described later is disposed on the surface of the first substrate, the mode of forming a liquid-absorbing surface that directly absorbs liquid on the surface of the first substrate is included.
In the first aspect of the present invention, the surface of the first substrate is a liquid-absorbing surface that directly absorbs liquid, and therefore, the water-absorbing layer is not disposed on the first substrate. Accordingly, in one embodiment of the present invention, the water-absorbent sheet is a water-absorbent sheet comprising 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 contains a particulate water-absorbing agent, the water-absorbent layer is not disposed on the first substrate, a region containing the particulate water-absorbing agent is disposed with a gap substantially free of the particulate water-absorbing agent interposed therebetween, 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 penetrates the first substrate and moves on the first substrate to expose a part, the water absorbing layer is not considered to be disposed. The cause of this movement is assumed to be, for example, vibration generated when the water-absorbing 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 found that: in the conventional water-absorbent sheet (for example, a water-absorbent sheet described in japanese patent application laid-open No. 105380752, a water-absorbent sheet in which a guide groove (corresponding to a gap) is provided in a water-absorbent layer between a first substrate and a second substrate), the shape retention property is poor even if the pouring rate can be reduced in the measurement of the backflow under specific conditions (also referred to as "specific backflow amount evaluation" in the present specification) in the examples of the present application.
Here, when there is introduction of the liquid, the gap existing between the regions including the particulate water absorbing agent may function as a liquid passage when the liquid is introduced from the first substrate to the water absorbing layer. That is, since the liquid passage is provided, the liquid introduced from the liquid suction surface is not retained on the liquid suction surface (and the introduced liquid is not retained locally), and the liquid can be efficiently fed into the water-absorbing layer of the lower layer that performs the water-absorbing function. Specifically, a liquid (for example, urine) passing through the first substrate is introduced into the entire surface of the water-absorbent layer and the gaps. The liquid introduced into the gap is not a particulate water-absorbing agent that impedes the passage of the liquid relative to the region containing the particulate water-absorbing agent, and absorption by the particulate water-absorbing agent is also retarded, and therefore diffusion is easy. As a result of the liquid diffusing, the liquid absorbing amount of the particulate water absorbing agent at the portion where the liquid is introduced is prevented from becoming larger, and the liquid absorbing amount of the particulate water absorbing agent at the portion away from the liquid introducing portion becomes smaller, so that the liquid absorbing amount is prevented from becoming smaller. Therefore, the following actions can be prevented: the particulate water absorbing agent has a function of increasing the amount of backflow, at a site where the particulate water absorbing agent is saturated and swelled, in other words, at a site where the particulate water absorbing agent cannot absorb liquid. Thus, it can be considered that: as a result, the reverse flow rate can be reduced.
However, for example, when the particulate water absorbing agent absorbs a liquid and swells, the volume of the region containing the particulate water absorbing agent increases, and therefore, the swollen particulate water absorbing agent intrudes into the region regarded as a gap, and the gap decreases. In this case, it can be considered that: if the liquid is intermittently introduced a plurality of times, the liquid absorbing capacity gradually decreases due to the decrease in the gap. When the liquid is discharged from the water absorbing 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 be saturated and swelled, so that the amount of the liquid flowing back to the liquid absorbing surface of the first substrate gradually increases gradually. This causes the liquid that flows back to rise to the skin (contact with the skin), and thus gives a sense of discomfort.
In the conventional structure of a water-absorbing sheet having a gap in a water-absorbing layer (for example, a water-absorbing sheet described in japanese patent application laid-open No. 105380752), the particulate water-absorbing agent may be less fixed to the first substrate and/or the second substrate due to swelling of the particulate water-absorbing agent, and the particulate water-absorbing agent may be moved in the water-absorbing layer. Thus, the particulate water absorbing agent is biased in the water absorbing layer, and the shape of the water absorbing sheet collapses (shape retention is lowered).
In contrast, it can be considered that: the water-absorbing sheet of the present invention can buffer the volume increase of the region containing the particulate water-absorbing agent by imparting stretchability to the first substrate. That is, in the case where the particulate water absorbing agent is swollen, the first substrate is elongated according to the swelling, and therefore, the decrease in the gap can be suppressed, and thus, the shape of the gap can be maintained. Thus, even if the liquid is intermittently introduced a plurality of times, the liquid diffusing ability is not reduced, and the pouring rate can be reduced. Further, since the swelling of the particulate water absorbing agent is buffered by expanding and contracting the first base material, 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 expands due to the swelling of the particulate water absorbing agent to follow the shape of the swollen particulate water absorbing agent. Thereby, the first substrate and the particulate water absorbing agent become entangled with each other, 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 particulate water-absorbing agent from the region containing the particulate water-absorbing agent in the water-absorbing layer, and can maintain the shape of the water-absorbent sheet, and thus has high shape retention. In the embodiment of the present invention, the effect of reducing the backflow of the single-layer type water-absorbent sheet is greater in the multi-layer type (two-layer type) water-absorbent sheet and the single-layer type water-absorbent sheet. The water-absorbent sheet of the multi-layer system (two-layer system) is formed by stacking a laminate having a first substrate and a water-absorbent layer and a constituent body having an intermediate substrate and a water-absorbent layer, and a laminate having only 1 layer of the laminate having the first substrate and a water-absorbent layer, on the second substrate, on the water-absorbent layer (the water-absorbent layer is located on the second substrate side). The reason for this is not clear, in other words, it can be said that it is an unexpected effect to those skilled in the art.
In the water-absorbing sheet, the water absorbing function in the water-absorbing layer is mainly carried by the water absorbing agent (particulate water absorbing agent). In particular, the role of the water absorbing agent is becoming more important in the water absorbing sheet that is different from the conventional absorbent article in which pulp is present in the water absorbing layer. 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 absorbing layer can be maintained, and the liquid temporarily introduced into the water absorbing agent is less likely to flow back to the liquid absorbing surface of the first base material. Thus, the shape of the water-absorbent sheet can be maintained (i.e., the shape retention is high), and the "specific reflux amount evaluation" can be made excellent. Incidentally, the water-absorbent sheet or the absorbent article designed to suppress the amount of backflow under normal conditions does not necessarily exhibit excellent results in the "specific backflow amount evaluation" of 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 in which an infant whose bladder is small, for example, to begin learning to walk, moves back and forth during the daytime or the like, 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.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and duplicate descriptions are omitted. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from actual ratios.
The water-absorbent sheet according to the first embodiment of the present invention is formed by stacking only a laminate in which a first base material is stacked on a water-absorbent layer, on a second base material. That is, in the first embodiment, the water-absorbing layer is sandwiched between the first substrate and the second substrate. The first embodiment will be described with reference to fig. 18.
Fig. 18 is a schematic view showing a cross section of the water-absorbent sheet 10 according to the 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 directions in which the liquid to be absorbed is introduced. The first substrate 11 is positioned on the side where the liquid to be absorbed (sucked liquid) is introduced with respect to the water-absorbing layer 12. That is, the first base material is disposed on the liquid discharge side (for example, the skin side in the paper diaper). A water-absorbing layer 12 is disposed between the first substrate 11 and the second substrate 13. That is, the laminate 18 having the first base material 11 laminated on the water absorbing layer 12 is laminated on the second base material 13.
In (a) to (c) of fig. 18, water-absorbing layer 12 contains particulate water-absorbing agent 14. In the modes (a) to (c) of fig. 18, a state is shown in which particulate water absorbing agent 14 is present between first substrate 11 and second substrate 13 in water absorbing layer 12. A portion of particulate water absorbing agent 14 may be detached from each of substrates 11, 13. Particulate water absorbing agent 14 (a region including particulate water absorbing agent 14) is disposed across gap 15 substantially free of particulate water absorbing agent 14. Therefore, the water-absorbent "layer" does not mean a continuous body such as a sheet, and may be any one as long as it exists between the first substrate 11 and the second substrate 13 with a constant thickness and length. For example, the water-absorbing layer 12 may intermittently exist with a certain thickness and length between the first substrate 11 and the second substrate 13. When particulate water absorbing agent 14 is fixed to substrate 11 and/or substrate 13, an adhesive may be used, for example. The method for producing the water-absorbent sheet using the adhesive is described in detail in [ 3 ].
Here, in fig. 18 (a), the gap 15 is formed between the first substrate 11 and the second substrate 13, but the gap 15 in the present invention also includes the embodiments of fig. 18 (b) and 18 (c). In (b) of fig. 18, the region containing particulate water absorbing agent 14 is partitioned by the contact of first substrate 11 with second substrate 13. The first substrate and the second substrate are in contact with each other, but maintain the liquid passage, and thus they are regarded as gaps. Further, since the water-absorbent layer 12 is partitioned by 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, the water-absorbent layer 12 intermittently exists in this embodiment. In fig. 18 (c), the end portion of the water-absorbing sheet 10 is closed by the first substrate 11 and the second substrate 13 by overlapping the end portion of the first substrate 11 and the end portion of the second substrate 13. In this case, too, the first base material 11 (the first base material 11 and the second base material 13, as the case may be) enters the end portion of the water-absorbent layer 12, and the water-absorbent layer 12 is not present at the end portion of the water-absorbent layer 12. The manner of the water-absorbing layer 12 and the gap 15 is also applicable to the second embodiment described later.
Within first substrate 11, particulate water absorbing agent 14 may be present. As particulate water absorbing agent 14 in first substrate 11, for example, particulate water absorbing agent 14 in contact with (or fixed to) first substrate 11, or particulate water absorbing agent 14 in contact with (or fixed to) second substrate 13 may be detached and trapped in particulate water absorbing agent 14 in first substrate 11. When particulate water absorbing agent 14 is present in first substrate 11, the content ratio of particulate water absorbing agent 14 in first substrate 11 is preferably 5% or more, more preferably 10% or more, still more preferably 20% or more, and still more preferably 30% or more, with respect to particulate water absorbing agent 14 contained in the entire water absorbing sheet 10. The upper limit is not particularly limited, but the preferable order is 90% or less, 70% or less, and 50% or less. In the present specification, the content ratio of particulate water absorbing agent 14 in first substrate 11 to particulate water absorbing agent 14 contained in the entire water absorbing sheet 10 is calculated by the method of the example described later.
Since particulate water absorbing agent 14 is not dispersed and disposed in the region of gap 15, the region of gap 15 does not substantially contain particulate water absorbing agent 14. Additives and the like other than particulate water absorbing agent 14 may be contained in the region of 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 by contact with an adhesive. Since first substrate 11 has stretchability, when a region including particulate water absorbing agent 14 is present on second substrate 13, first substrate 11 stretches and contracts following the region including particulate water absorbing agent 14. Accordingly, first substrate 11 has a shape such that it covers the region containing particulate water absorbing agent 14 in the region containing particulate water absorbing agent 14, and has a shape such that it is recessed toward second substrate 13 after being along the upper side surface of the region containing particulate water absorbing agent 14 in 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 substrate 11 to the surface on the water-absorbing layer side of the second substrate 13 in the region including the particulate water-absorbing agent 14 to the thickness (La) from the liquid-absorbing surface of the first substrate 11 to the surface on the water-absorbing layer 12 side of the second substrate in the gap 15 is preferably 1.05 or less. First substrate 11 has stretchability, and therefore, the portion of first substrate 11 in contact with particulate water absorbing agent 14 takes on a shape (i.e., follows and stretches) that follows the shape of the region containing particulate water absorbing agent 14 (i.e., the shape of particulate water absorbing agent 14 on the side in contact with first substrate 11 in particulate water absorbing agent 14 in contact with the first substrate). Accordingly, first substrate 11 is capable of adhering to particulate water absorbing agent 14 (the region including particulate water absorbing agent 14), and thereby, first substrate 11 and particulate water absorbing agent 14 (the region including particulate water absorbing agent 14) are in an integrated state. 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 containing particulate water absorbing agent 14 is highly conformal. Thus, even after swelling of particulate water absorbing agent 14, the maintenance of gap 15 is high, and the reverse flow can be further reduced. Lb/La is usually 1 or more.
In the water-absorbing 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 continuously provided along one direction of the liquid suction surface of the first substrate 11. The shape of the continuous gaps 15 may be, for example, linear, curved, or wavy, and the gaps 15 are preferably arranged in parallel in a linear shape. Therefore, in the water-absorbing sheet 10, the region containing the particulate water-absorbing agent 14 and the gap 15 have a shape extending in one direction (the plane direction perpendicular to the liquid absorption direction) of the liquid absorption surface of the first substrate 11, and are preferably arranged side by side. That is, the region containing particulate water absorbing agent 14 is in a state of being arranged in a stripe shape (vertical bar shape). Accordingly, since gaps 15 are also formed in the shape of a vertical bar, gaps 15 are easily maintained even when particulate water absorbing agent 14 swells, and as a result, 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-suction surface of the first substrate 11, that is, any one of the longitudinal direction, the width direction, or the direction inclined with respect to these directions in the liquid-suction surface of the first substrate 11. From the viewpoint of balancing the action of gap 15 with the action of particulate water absorbing agent 14, in water absorbing sheet 10, the region containing particulate water absorbing agent 14 and gap 15 preferably have a shape extending along the longitudinal direction in the liquid absorbing surface of first substrate 11, and are arranged side by side.
In the surface of first substrate 11 on the water-absorbing layer 12 side (the surface where particulate water absorbing agent 14 is disposed), the ratio of the region containing particulate water absorbing agent 14 (hereinafter also referred to as "the ratio of the region where particulate water absorbing agent 14 is present") is preferably 90% or less, more preferably 80% or less, still more preferably 75% or less by area. Further, the ratio of the region containing particulate water absorbing agent 14 in the surface of the water absorbing layer 12 side of the first substrate 11 is preferably 10% or more, more preferably 20% or more, by area. By setting particulate water absorbing agent 14 in such a range, the balance between the action of gap 15 and the action of particulate water absorbing agent 14 becomes appropriate, and the effect of reducing the amount of reflux is further exhibited. 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 is the same as the ratio of the region containing particulate water absorbing agent 14 in the surface of second substrate 13 on the water absorbing layer 12 side (the surface where particulate water absorbing agent 14 is disposed).
Here, the ratio of the region containing particulate water absorbing agent 14 in the surface of the water absorbing layer 12 side of the first substrate 11 may be controlled by adjusting the scattering region of the particulate water absorbing agent 14 at the time of manufacturing the water absorbing sheet 10.
Further, for example, the ratio of the region including particulate water absorbing agent 14 in the surface of first substrate 11 on the water absorbing layer 12 side can be calculated by taking an image of the cross section obtained by cutting produced water absorbing sheet 10 by an X-ray CT apparatus (insexio SMX-100 CT) and analyzing the same. Specifically, the cross section of water-absorbing sheet 10 is taken, the interface between first substrate 11 or second substrate 13 and water-absorbing layer 12 is classified into a region where particulate water-absorbing agent 14 is present and a region where particulate water-absorbing agent 14 is not present, and the ratio of the regions can be calculated by summing up the respective regions and calculating the ratio of the regions including particulate water-absorbing agent 14. The ratio of the region containing particulate water absorbing agent 14 was calculated by taking 3 or more images of the cross section in the short side direction of water absorbing sheet 10, and the ratio of the region containing particulate water absorbing agent 14 obtained from each cross section was averaged, and the average value was regarded as "the ratio of the region containing particulate water absorbing agent 14".
The content of particulate water-absorbing agent 14 contained in water-absorbent sheet 10 is preferably 200 to 360g/m 2 More preferably 250 to 350g/m 2 Further preferably 300 to 325g/m 2 。
The water-absorbent sheet 10 has a cover sheet 16. The wrapping sheet 16 has the following purpose: the purpose of holding the shape of the water-absorbing sheet 10, which is a structure in which the particulate water-absorbing agent 14 is supported between the first substrate 11 and the second substrate 13; so that particulate water-absorbing agent 14 supported between first substrate 11 and second substrate 13 does not fall off (fall off) from the absorber (water-absorbing sheet 10); when particulate water absorbing agent 14 is transferred to the outer surface (surface in direct contact with liquid) of first substrate 11 through first substrate 11, particulate water absorbing agent 14 is not brought into direct contact with the skin. Without the cover sheet 16, there are, for example, the following methods: a method of sealing (closing) by bonding the respective substrates 11, 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 of maintaining the effect of the present application without causing particulate water absorbing agent 14 to fall off from water-absorbing sheet 10, it is preferable to have coated sheet 16.
The cover sheet 16 is disposed on the first base material 11, and is folded so as to cover the entirety of the water-absorbing layer 12 and the second base material 13. Thus, the cover sheet 16 covers the entirety of the first substrate 11, the water absorbing layer 12, and the second substrate 13. With this structure, the particulate water absorbing agent 14 can be prevented from falling off the water absorbing sheet 10. The cover sheet 16 does not necessarily cover the entirety of the first substrate 11, the water absorbing layer 12, and the second substrate 13. For example, the cover sheet 16 may be disposed on the first base material 11, folded so as to include the side surface of the water-absorbing layer 12 and the side surface of the second base material 13, and folded toward the side surface of the second base material 13 opposite to the liquid-absorbing surface (i.e., the surface on which the water-absorbing layer 12 is disposed). That is, with respect to 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, one end of the cover sheet 16 overlaps the other end of the cover sheet 16. In this case, the cover sheet 16 covers the side surfaces of the first substrate 11, the water absorbing layer 12, and the second substrate 13, and covers the whole or a part of the surface of the second substrate 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, folded so as to cover 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 may be disposed separately from the other end of the cover sheet 16 on the surface of the second base material 13 opposite to the absorption surface (i.e., the surface on which the water-absorbing layer 12 is disposed). In this case, the cover sheet 16 covers the liquid suction surface and 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-absorbing sheet according to the present invention, the coating sheet 16 is not necessarily required to be constituted, and the water-absorbing sheet 10 according to the present invention is provided with the coating sheet 16 in such a constitution, whereby the particulate water-absorbing agent 14 can be prevented from falling off from the water-absorbing 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 substrate 11 (i.e., on the suction surface of the first substrate 11). In the present specification, the first substrate 11 forms a liquid-absorbing surface that directly absorbs liquid in the case of having the cover sheet 16 as described above, but in the case of the water-absorbent sheet 10 having the cover sheet 16, for example, the cover sheet 16 forms a liquid-absorbing surface that directly absorbs liquid, the following can be used in the other words: a water-absorbing sheet comprising a first substrate, a second substrate, a water-absorbing layer between the first substrate and the second substrate, and a coating sheet disposed on the surface of the first substrate, wherein the water-absorbing layer contains a particulate water-absorbing agent, the region containing the particulate water-absorbing agent is disposed with a gap substantially free of the particulate water-absorbing agent interposed therebetween, the surface of the coating sheet forms a liquid-absorbing surface that directly absorbs liquid, and the elongation of the first substrate is 10% or more.
As a method of 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 the particulate water-absorbing agent 14 in the water-absorbent layer 12 or in contact with an adhesive, and/or the second substrate 13 is preferably in direct contact with the particulate water-absorbing agent 14 in the water-absorbent layer 12 or in contact with an adhesive. As described above, the water-absorbent sheet of the present invention has a simple structure substantially containing only the following substances: the present invention relates to a particulate water absorbing agent comprising 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 at least one of the first substrate and the second substrate, and a coating sheet for coating a part or all of them as needed (the case where additives and the like described in the present specification, which may be contained in the particulate water absorbing agent, are not excluded). More preferably, the composition is a simple composition comprising only the following substances: the present invention provides a particulate water absorbing agent comprising 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 coating sheet for coating all of these. That is, the water-absorbent sheet of the present invention can effectively reduce the specific amount of backflow despite its simple structure.
The water-absorbent sheet according to the second embodiment of the present invention is formed by laminating a laminate in which a first substrate is laminated on a water-absorbent layer a and a constituent in which an intermediate substrate is laminated on a water-absorbent layer B, on a second substrate (the water-absorbent layer is positioned on the second substrate side). In the following, a second embodiment will be described with reference to fig. 19, and in the second embodiment, the technical features that can be applied to the same configuration as the first embodiment will be omitted. FIG. 19 is a schematic view showing a cross section 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 the first substrate 11a, the water-absorbent layer 12a (water-absorbent layer a), the intermediate substrate 11B, and the water-absorbent layer 12B (water-absorbent layer B) on the second substrate 13 in this order from the direction in which the liquid to be absorbed is introduced (the arrow direction in fig. 19). Specifically, the water-absorbent sheet 20 is formed by stacking a laminate 18a and a constituent body 18b on the second substrate 13, wherein the laminate 18a has the first substrate 11a stacked on the water-absorbent layer 12a, and the constituent body 18b has the intermediate substrate 11b stacked on the water-absorbent layer 12b, and wherein the water-absorbent layers 12a, 12b are stacked on the second substrate 13 so as to be located on the second substrate 13 side. Hereinafter, particulate water absorbing agent 14 in laminate 18a is referred to as particulate water absorbing agent 14a, gap 15 is referred to as gap 15a, particulate water absorbing agent 14 in constituent 18b is referred to as particulate water absorbing agent 14b, and gap 15 is referred to as gap 15b. The first substrate 11a in the second embodiment is the same as the first substrate 11 in the first embodiment, and therefore may be abbreviated as the first substrate 11. In addition, with respect to particulate water absorbing agent 14a and gap 15a in the second embodiment, it is also sometimes simply referred to as particulate water absorbing agent 14 and gap 15.
Water-absorbing layers 12a and 12b are each composed of particulate water absorbing agents 14a and 14b, as in the first embodiment. Specifically, water-absorbing 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-absorbing 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 water absorbing layers 12a and 12b, regions containing particulate water absorbing agents 14a and 14b are arranged to be separated by gaps 15a and 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 a part of the second substrate 13 are preferably the same as those of the water-absorbent sheet 10 described in the first embodiment. That is, the region including particulate water absorbing agent 14a, 14b and gaps 15a, 15b preferably have a shape elongated in one direction of the liquid suction surface of the first substrate, and are arranged in parallel.
In fig. 19, the region including particulate water absorbing agent 14a in laminate 18a and the region including particulate water absorbing agent 14b in structure 18b are arranged in the same thickness and width so as to overlap each other in the plane direction of first substrate 11a (that is, in the same position in the direction perpendicular to the liquid absorption plane of first substrate 11 a), but the positional relationship, the relationship of thickness and width is not limited thereto. For example, the region of laminate 18a containing particulate water absorbing agent 14a and the region of construct 18b containing particulate water absorbing agent 14b may be offset so as not to overlap in the planar direction. Further, the region containing particulate water absorbing agent 14a in laminate 18a may be wider or narrower in width, or thicker or thinner than the region containing particulate water absorbing agent 14b in constituent 18 b.
Particulate water absorbing agents 14a, 14b may be present in first substrate 11a and intermediate substrate 11 b. For example, particulate water-absorbing agent 14a may be present in first substrate 11a, particulate water-absorbing agent 14a may be present in intermediate substrate 11b on the liquid-absorbing surface side of intermediate substrate 11b, and particulate water-absorbing agent 14b may be present on the second substrate 13 side of intermediate substrate 11 b.
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 gap 15 of the first embodiment may be replaced with the first substrate 11a, the water-absorbent layer 12b, the particulate water-absorbing agent 14a, and the gap 15a of the laminate 18a disposed on the liquid introducing side, respectively, with respect to the following technical features;
(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 substrate 11 to the surface of the second substrate 13 on the water-absorbing layer 12 side in the region containing the particulate water absorbing agent 14 to a thickness (La) from the liquid-absorbing surface of the first substrate 11 to the surface of the second substrate 13 on the water-absorbing layer 12 side in the gap 15.
In the two-layer system (2), the region including particulate water absorbing agents 14a and 14b of laminate 18a and structure 18b may be formed so as not to overlap gaps 15a and 15b in the surface direction of first substrate 11 a. In this case, "among the gaps 15" to be the La-basis "means the gaps 15a close to the liquid-absorbing surface of the first substrate 11a (i.e., in the laminate 11 a), and" among the regions containing the particulate water absorbing agent 14 "to be the Lb-basis" the region containing the particulate water absorbing agent 14 "means the region containing the particulate water absorbing agent 14a close to the liquid-absorbing surface of the first substrate 11a (i.e., in the laminate 11 a).
That is, in the water-absorbing 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 relative to the particulate water-absorbing agent 14 contained in the entire water-absorbing 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) to the thickness (La) of the gap 15a from the liquid suction surface of the first substrate 11a to the surface of the second substrate 13 on the water-absorbing layer 12b side in the region including the particulate water-absorbing agent 14a is preferably 1.05 or less. In water-absorbent sheet 20, the preferable ranges of water-absorbent sheet 10 described in the first embodiment can be similarly applied to the content ratio of particulate water-absorbing agent 14a and Lb/La in first substrate 11 a.
The water-absorbent sheet 20 has a cover sheet 16. The wrapping sheet 16 is disposed on the first base material 11a, and is folded so as to wrap the entire laminate 18a, the constituent body 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 cover sheet 16 disposed at least on the surface of the first substrate 11a (i.e., the liquid-absorbing surface of the first substrate).
In the present specification, the following may be used interchangeably: a water-absorbing sheet comprising a first substrate, an intermediate substrate, a second substrate, a water-absorbing layer, and a coating sheet, wherein a laminate having the first substrate laminated on the water-absorbing layer and a structure having the intermediate substrate laminated on the water-absorbing layer, wherein the water-absorbing layer is positioned on the second substrate side, the coating sheet is disposed on the surface of the first substrate, the water-absorbing layer contains a particulate water-absorbing agent, a region containing the particulate water-absorbing agent is disposed across a gap substantially free of the particulate water-absorbing agent, the surface of the coating sheet forms a liquid-absorbing surface that directly absorbs liquid, and the elongation of the first substrate 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 the particulate water-absorbing agent 14a in the water-absorbent layer 12a or by means of an adhesive, it is preferable that the intermediate substrate 11b is in direct contact with the particulate water-absorbing agent 14b in the water-absorbent layer 12b or by means of an adhesive, and/or it is preferable that the second substrate 13 is in direct contact with the particulate water-absorbing agent 14b in the water-absorbent layer 12b or by means of an adhesive.
In the water-absorbent sheet 20 according to the second embodiment, the ratio of the region containing particulate water absorbing agent 14a in the surface of the first substrate 11a on the water-absorbing layer 12a side (the surface where particulate water absorbing agent 14a is disposed) and the ratio of the region containing particulate water absorbing agent 14b in the water-absorbing layer 12b side (the surface where 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 in terms of area. Further, the ratio of the region containing particulate water absorbing agent 14a in the surface on the water absorbing layer 12a side of the first substrate 11a and the ratio of the region containing particulate water absorbing agent 14b in the water absorbing layer 12b side of the intermediate substrate 11b are preferably 10% or more, more preferably 20% or more in terms of area. By providing particulate water absorbing agents 14a and 14b in such a range, the balance between the action of gaps 15a and 15b and the action of particulate water absorbing agents 14a and 14b becomes appropriate, and the effect of reducing the amount of reflux is further exhibited. The ratio of the region containing particulate water absorbing agent 14a in the water absorbing layer 12a side surface of first substrate 11a is the same as the ratio of the region containing particulate water absorbing agent 14a in the water absorbing layer 12a side surface of intermediate substrate 11b (the surface where particulate water absorbing agent 14a is disposed), and the ratio of the region containing particulate water absorbing agent 14b in the water absorbing layer 12b of intermediate substrate 11b is the same as the ratio of the region containing particulate water absorbing agent 14b in the water absorbing layer 12b of second substrate 13 (the surface where particulate water absorbing agent 14b is disposed).
In water-absorbing sheet 20, the ratio of the areas where particulate water-absorbing agents 14a and 14b are present in first substrate 11 or second substrate 13 can be calculated in the same manner as in water-absorbing sheet 10.
Here, the content of particulate water absorbing agent 14 contained in water-absorbent sheet 20 is preferably 200 to 360g/m 2 More preferably 210 to 350g/m 2 Further preferably 225 to 325g/m 2 . In water-absorbing sheet 20, the total amount of particulate water-absorbing agents 14a and 12b present in water-absorbing layers 12a and 12b may be adjusted so as to fall within the above range, and it is preferable that: the particulate water absorbing agent 14a, 12b is preferably present in the water absorbing layers 12a, 12b in an amount of 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, the first base material 11 may have a fluffy shape (a shape having a low bulk density and a significantly thick shape) according to one embodiment, but may be thinner than an absorber used in conventional type of absorbent articles. When the water-absorbent sheets 10 and 20 are used in a paper 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 at 40% RH to 50% RH, for example. On the other hand, in view of the strength of the water-absorbing sheets 10, 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, still more preferably 0.5mm or more. The thickness of the water-absorbent sheets 10, 20 used in the examples of the present application was 2 to 5mm.
The thicknesses of the first substrate 11, the intermediate substrate 11B, the second substrate 13, the cover sheet 16, and the water-absorbing sheets 10 and 20 in the present application were measured using a dial thickness gauge (thickness gauge) (model: J-B, manufactured by Kawasaki Co., ltd., measuring head: 50mm in the top and bottom directions). The number of measurement points was measured 2 times for each part at 5 selected positions in the sheet to be measured, and the measurement value was an average value of 5 total positions. In measuring the thickness, the thickness was measured by gradually removing the hand from the grip so as to prevent the pressure from being applied to the sheet as much as possible. Specifically, the sheet to be measured is flatly attached to a plate having a constant thickness so as not to cause wrinkles or deformations in the measurement site of the sheet, and the plate is set on the lower measurement head of the thickness measuring device. Next, the upper measuring head of the thickness measuring instrument was moved closer to a height position of 2 to 3mm from the sheet to be measured, and then the hand was gradually moved away from the handle, whereby the total thickness of the sheet and the plate to be measured was measured. The thickness of the sheet to be measured is determined by the formula t1=t2 to T0 (T0: thickness of plate (mm), T1: thickness of sheet to be measured (mm), T2: thickness of sheet to be measured and plate (mm)).
In order to impart liquid permeability, diffusibility, softness, and the like to the water-absorbent sheets 10, 20, embossing may be appropriately performed on the surfaces of the water-absorbent sheets 10, 20 (the liquid-absorbing surface of the first substrate 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 of the surface. By providing the continuous embossed regions along the longitudinal direction of the water-absorbent sheets 10, 20, the liquid can be easily spread along the longitudinal direction. In the water-absorbing sheets 10, 20, the water-absorbing layer 12 has gaps 15 in which the particulate water-absorbing agent 14 is not present. As described above, by providing the embossing area continuously along the longitudinal direction in addition to the gap 15, the area functions as a liquid passage (liquid conveyance passage) for circulating a large amount of liquid. The embossing area may be provided in a straight line, a curved line, or a wavy line.
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 substrate ]
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 it contains water. Urine, menstrual blood, sweat, and other body fluids are preferably mentioned.
The first base material is a water-permeable sheet and is located on the liquid-absorbing side, whereby the effect of the present invention, that is, the performance (flow-down amount, leakage in the surface direction, etc.) of the water-absorbent sheet can be fully exhibited. Regarding the water permeability in the water permeable sheet, the water permeability coefficient (JIS A1218:2009) is preferably 1X 10 -5 cm/sec or more. The water permeability coefficient is more preferably 1×10 -4 cm/sec or more, more preferably 1X 10 -3 cm/sec or more, particularly preferably 1X 10 -2 cm/sec or more, most preferably 1X 10 -1 cm/sec or more. The first substrate used in the examples of the present application has a water permeability coefficient of 1×10 -5 cm/sec or more.
In the present invention, the elongation of the first substrate is 10% or more, preferably 15% or more, more preferably 17% or more, still more preferably 20% or more, and still more preferably 22% or more. The upper limit of the elongation of the first base material is not particularly limited, but is preferably 60% or less. By setting the elongation of the first base material to such a range, the first base material is likely to follow the shape of the particulate water absorbing agent, and as a result, the shape retention of the water absorbing sheet is further improved, and the pouring rate can be further reduced. The elongation of the first substrate was measured by the method described in examples below. In the present specification, the "elongation of the nonwoven fabric (first substrate)" is a value when the elongation is measured in the direction of the most elongation. The elongation of the first substrate may be controlled by bulk density, weight per unit area, material, grid structure, manufacturing process conditions, and the like.
In the present invention, the direction of extension of the first base material is not particularly limited as long as it is any direction parallel to the surface direction of the first base material other than the thickness direction. For example, if the water-absorbent sheet is a rectangular water-absorbent sheet, the sheet may be elongated in any one of the directions of all angles such as the long-side direction, the short-side direction, and the diagonal direction of the sheet plane, with the elongation in the above range. The same applies to square, oval, and round water-absorbing sheets. Preferably a substrate that can be elongated (isotropically) from all directions.
In the present invention, the weight per unit area of the first substrate is preferably 3 to 80g/m 2 More preferably 5 to 70g/m 2 More preferably 10 to 60g/m 2 . When the weight per unit area of the first substrate is in such a range, the particulate water absorbing agent is easily introduced into the first substrate, and as a result, the shape retention of the water absorbing sheet is further improved, and the pouring rate can be further reduced.
In the present invention, the bulk density of the first substrate is preferably 0.1g/cm 3 Hereinafter, more preferably 0.08g/cm 3 Hereinafter, it is more preferably 0.05g/cm 3 The following is given. The bulk density of the first substrate is preferably 0.001g/cm 3 The above is more preferably 0.005g/cm 3 The above is more preferably 0.01g/cm 3 The above. In the present specification, bulk density refers to a mass per unit volume, and is not a density obtained by compressing a substrate under high pressure (when voids are eliminated), but is a density obtained from a volume of the substrate including a void volume. The first substrate had a bulk density of 0.1g/cm 3 Hereinafter, the first substrate is light. Fluffy refers to a low bulk density and is significantly thicker. In the present invention, the particulate water absorbing agent is easily incorporated into the first base material by making the first base material fluffy, and as a result, the shape retention of the water absorbing sheet is further improved, and the pouring rate can be further reduced. In the present invention, the following effects can be expected by making the first substrate fluffy. That is, since the first substrate is fluffy, the liquid to be absorbed in contact with the liquid suction surface of the first substrate rapidly flows into the water-absorbing layer as the lower layer and the second substrate, and the liquid retained in the liquid suction surface of the first substrate can be reduced. Further, when the absorbed liquid reaches the water-absorbing layer, the liquid spreads in the plane direction, and therefore, even if a large amount of liquid is introduced into the water-absorbing layer, the water-absorbing layer absorbs the liquid that spreads in the plane direction rather than locally. That is, the fluffy first substrate has low water absorption, high hydraulic permeability, and high liquid diffusivity. Thereby, suction can be reduced Pouring amount in the aqueous sheet. The moisture of the liquid suction 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 3 The following is given. 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 to such a range, the distance between the liquid suction surface of the first base material and the water-suction layer and the second base material can be sufficiently ensured, and the occurrence of backflow of the liquid having reached the water-suction 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 of producing the first substrate, and the like, and the thickness and bulk density of the first substrate can be 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 further preferably 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 transmittance of the particulate water absorbing agent to such a range for the first substrate, the particulate water absorbing agent is likely to enter the first substrate on the side of the first substrate which contacts 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 a ratio of the particulate water absorbing agent that transmits through the first substrate, and as shown in fig. 23, the particulate water absorbing agent present on the first substrate is obtained 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, a value calculated by the method described in examples described later. In the case where a plurality of water-absorbing layers are present as in the second embodiment, the particulate water-absorbing agent used for the transmittance uses the entirety of the particulate water-absorbing agent contained 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 may be adjusted to a desired range by appropriately adjusting the properties of the member constituting the first substrate, the surface state thereof, the complexity of the mesh structure, the fiber diameter, the fusion state between fibers, the weight per unit area, the thickness, and the like. For example, if a hot air nonwoven fabric is used as the first substrate as described later, the transmittance can be adjusted by changing the heat treatment conditions, fiber diameter, and density of the hot air nonwoven fabric.
"Material constituting substrate"
Examples of the material constituting the first substrate include paper (toilet paper, for example, face tissues, toilet papers, and towel papers), mesh, nonwoven fabric, woven fabric, and film. Among them, from the viewpoint of water permeability, a nonwoven fabric is preferably used as at least the first base material.
The nonwoven fabric to be used is not particularly limited, and examples thereof include nonwoven fabrics formed of polyolefin fibers such as Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyester fibers such as 1, 3-propanediol terephthalate (PTT) and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers, from the viewpoints of liquid permeability, flexibility, and strength when a water-absorbent sheet is produced; nonwoven fabrics made from blends of cotton, silk, hemp, pulp (cellulose) fibers, and the like.
As a material of the nonwoven fabric that can be used as the first base material, rayon fibers, polyolefin fibers, polyester fibers, pulp fibers, fibers obtained by mixing them, and the like are preferable, and polyolefin fibers are more preferable. These fibers may be hydrophilized.
The nonwoven fabric that can be used as the first 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 spun-bonding method, or a hydroentanglement method, and is preferably a nonwoven fabric obtained by a hot air method or an air-laid method, and is preferably a nonwoven fabric obtained by a hot air method (hot air nonwoven fabric).
The hot air method means: and processing to blow hot air to the heat-fusible composite fibers such as PE/PP and PE/PET, to increase the air quantity contained between the fibers, to increase the volume and to reduce the density. In addition, the air-laid method is a method of producing a nonwoven fabric by uniformly dispersing air-borne air and sucking the air-borne air onto a metal mesh, and the air is used for dispersing pulp fibers, so that the volume can be increased and the density can be reduced. By making the first substrate a hot air nonwoven fabric, the liquid to be absorbed can be easily and quickly introduced into the first substrate after contacting the liquid suction surface of the first substrate. That is, by using the hot air nonwoven fabric as the first base material, the first base material having low water absorption capacity and high water permeability can be produced, and the flow-back amount in the water-absorbing sheet can be significantly reduced.
[2-1-1. Intermediate substrate ]
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 substrate is the same as the range described in the first substrate column. The water permeability coefficient of the intermediate substrate (intermediate nonwoven fabric) used in the examples of the present application was 1×10 -5 cm/sec or more.
The elongation of the intermediate substrate is preferably 10% or more, 15% or more, 17% or more, 20% or more, or 22% or more. The upper limit of the elongation of the intermediate substrate is not particularly limited, but is preferably 60% or less. By setting the elongation of the intermediate base material to such a range, the intermediate base material easily follows the shape of the particulate water absorbing agent, and as a result, the shape retention of the water absorbing sheet is further improved, and the pouring rate can be further reduced.
The weight per unit area, bulk density, thickness, transmittance of the particulate water absorbing agent, and appropriate ranges of transmittance of the specific particulate water absorbing agent are the same as those described in the first substrate column.
The material constituting the intermediate substrate is the same as that described in the first substrate column.
[2-2. Second substrate ]
The second base material is a water-permeable sheet and is located on the opposite side to the liquid-absorbing side, whereby the effect of the present invention, that is, the performance (flow-down amount, leakage in the surface direction, etc.) of the water-absorbent sheet can be fully exhibited. Regarding the water permeability in the water permeable sheet, the water permeability coefficient (JIS A1218:2009) is preferably 1X 10 -5 cm/sec or more. The water permeability coefficient is more preferably 1×10 -4 cm/sec or more, more preferably 1X 10 -3 cm/sec or more, particularly preferably 1X 10 -2 cm/sec or more, most preferably 1X 10 -1 cm/sec or more.
The thickness of the second substrate 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 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 an 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 0.9mm. By adjusting the thicknesses of the first substrate and the second substrate to the above-described ranges, the desired effects of the present invention can be effectively achieved. Furthermore, according to an embodiment 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 more preferably: 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 particularly preferable is: the thickness of the first base material is 0.7mm to 2mm, and the thickness of the second base material is 0.3mm to 0.5 mm.
In the present invention, the bulk density of the second substrate is preferably 1g/cm 3 Hereinafter, more preferably 0.5g/cm 3 Hereinafter, it is more preferably 0.3g/cm 3 The following is given. The bulk density of the second substrate is preferably 0.05g/cm 3 The above is more preferably 0.07g/cm 3 The above is more preferably 0.08g/cm 3 The above. By setting the bulk density of the second substrate to such a range, the liquid introduced into the second substrate can be easily held, and the backflow can be reduced.
In the present invention, the weight per unit area of the second substrate is preferably 5 to 100g/m 2 More preferably 10 to 70g/m 2 More preferably 15 to 65g/m 2 。
The thickness, bulk density, and weight per unit area of the second substrate are controlled by the material constituting the second substrate, the method of producing the second substrate, and the like, and the thickness and bulk density of the second substrate are determined based on the balance thereof.
The void ratio of the first substrate, the second substrate, and the cover sheet (e.g., nonwoven fabric) can be measured by the following equation. Basis weight A (g/m) used in substrate (or coated sheet) 2 ) Thickness B (mm) of the substrate (or clad sheet), density C (g/cm) of the raw material (e.g., polyolefin) used in the substrate (or clad sheet) 3 )
Void ratio of substrate (or sheet) =100- { (a/10000)/(B/10) }/c×100
The liquid diffusion area of the second substrate is preferably 1000mm 2 The above is more preferably 3000mm 2 The above is more preferably 6000mm 2 The above is particularly preferably 7000mm 2 The above. The upper limit of the liquid diffusion area of the second substrate is not particularly limited, and is preferably 10,000mm, for example 2 The following is given. When the liquid diffusion area of the second substrate is within the above range, the absorbed liquid can sufficiently diffuse in the second substrate in the planar direction when reaching the second substrate. Thus, even if a large amount of liquid having passed through the water-absorbing layer is introduced into the second base material, the second base material absorbs in the planar directionLiquid that spreads upward rather than locally. Thus, the liquid can be sufficiently absorbed and held in the second substrate, and the pouring amount in the water-absorbent sheet can be significantly reduced.
Here, the liquid diffusion area means: the area in the plane direction in which the liquid diffuses when the liquid contacts with the substrate (for example, nonwoven fabric) and/or when the liquid passes through the substrate in a direction perpendicular to the plane direction of the substrate is a value calculated by the method described in examples described later. The larger the liquid diffusion area of the substrate, the higher the liquid diffusivity of the substrate in the plane direction.
"Material constituting substrate"
The material constituting the second base material 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 fibers, polyolefin fibers, polyester fibers, pulp fibers, and fibers obtained by mixing them are preferable, and polyolefin fibers are more preferable.
The nonwoven fabric that can be used 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 spunbonding method, or a hydroentangled method, and preferably a nonwoven fabric obtained by an air-laid method (air-laid nonwoven fabric) or a nonwoven fabric obtained by a hydroentangled method (hydroentangled nonwoven fabric). The hydroentanglement method is a method of interlacing fibers by high-pressure water flow, and is a method of not using an adhesive. By making the second substrate of an air-laid nonwoven fabric or a spunlaced nonwoven fabric, the amount of backflow in the water-absorbent sheet can be significantly reduced, and leakage in the plane direction can be significantly reduced.
[2-3 Water-absorbing layer ]
The water absorbing layer in the water absorbing 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 nonwoven fabric is present in the water-absorbent layer. In the case where a plurality of water-absorbing layers are present as in the second embodiment, the water-absorbing layers may have the same composition or may have 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 specified, the following description refers 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 agent contained in the water absorbing layer is mixed. Further, regarding the physical properties of the particulate water absorbing agent, it is possible to take out only the particulate water absorbing agent from the water absorbing sheet to measure the physical properties so as not to mix cotton pulp or the like.
"surface tension"
The surface tension means: the parameters of the work (free energy) required to increase the surface area of the solid or liquid are expressed in terms of the unit area. The surface tension referred to in this application means: surface tension of an aqueous solution when the particulate water absorbing agent is dispersed in a 0.90 mass% aqueous solution of sodium chloride. The surface tension of the water absorbing agent was measured by the following procedure. Specifically, 50ml of physiological saline adjusted to 20℃was put into a sufficiently cleaned 100ml beaker, and the surface tension of the physiological saline was measured by a surface tensiometer (KRUSS Co., ltd. K11 automatic surface tensiometer). Subsequently, 0.5g of a 25mm long fluororesin rotor and a particulate water absorbing agent, which had been sufficiently cleaned, were put into a beaker containing physiological saline adjusted to 20℃and measured for surface tension, and stirred at 500rpm for 4 minutes. After 4 minutes, stirring was stopped, and after the aqueous particulate water absorbing agent had settled, the same operation was performed again to measure the surface tension of the supernatant liquid. In the present invention, a plate method using a platinum plate was used, and the plate was sufficiently washed with deionized water before each measurement, and was heated and washed with a gas burner.
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 the particulate water absorbing agent is applied to the water absorbing sheet, the influence of the surface tension is more likely to occur than in conventional paper diapers, and the pouring rate in the water absorbing sheet can be reduced by making the surface tension satisfy the above conditions.
In the water-absorbing 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 practically 73mN/m or less.
In the water-absorbent sheet according to one embodiment of the present invention, the CRC (water absorption capacity without load) of the particulate water-absorbing agent is preferably 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 making the CRC of the particulate water absorbing agent satisfy the above condition, the pouring amount in the water absorbing sheet can be reduced. The CRC of the particulate water absorbing agent is abbreviated as Centrifuge Retention Capacity (centrifuge retention capacity) defined by ERT441.2-02, and refers to the water absorption capacity (sometimes referred to as "water absorption capacity") of the particulate water absorbing agent under no pressure. 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 significantly excessive 0.9 mass% aqueous sodium chloride solution for 30 minutes to freely swell the bag, and thereafter, the water absorption capacity (unit: G/G) was increased by removing water by a centrifuge (250G).
"particle shape"
In the water-absorbing sheet according to one embodiment of the present invention, the particulate water-absorbing agent is not limited in particle shape, and may be, for example, a spherical particulate water-absorbing agent (and granulated product thereof). In a preferred embodiment, the particulate water absorbing agent is preferably irregularly crushed. Here, the irregular crushed shape refers to crushed particles whose shape is not fixed. This is because: the irregular crushed shape can be easily fixed to the substrate as compared with spherical particles obtained by inverse 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, in the case where the pulverization step is not performed, spherical particles or granules of spherical particles obtained by, for example, reversed-phase suspension polymerization, spray polymerization of a monomer and droplet polymerization such as polymerization are not irregularly pulverized. In the embodiment of the present invention, if the particulate water absorbing agent is irregularly crushed, the shape of the water absorbing sheet is more easily maintained than a water absorbing agent having a high average roundness (for example, a spherical water absorbing agent). In the embodiment of the present invention, the average roundness 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 calculation method of the average roundness is as follows. More than 100 particulate water-absorbing agents were randomly selected, each particulate water-absorbing agent was photographed with an electron microscope (VE-9800, manufactured by ken corporation) (magnification: 50 times), an image of the particulate water-absorbing agent was obtained, and the circumference and area of each particle were calculated using attached image analysis software. The roundness of each particle was obtained by the following equation, and the average value of the obtained values was calculated as the average roundness.
[ math 5]
Roundness=4×pi×area/(circumference) 2
Particle size "
The particle diameter of the particulate water absorbing agent (or the particulate water absorbing resin particles) according to one embodiment of the present invention may be 150 to 600 μm, which is a weight average particle diameter obtained by the measurement method of "PSD" specified in ERT 420.2-02. In the present invention, the weight average particle diameter is a value calculated by the method described in 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 it can be suitably produced by referring to, for example, the publication of the examples.
[ 2-4. Coating sheet ]
In the water-absorbent sheet according to one embodiment of the present invention, it is preferable that the water-absorbent sheet has a coating sheet disposed on at least the surface of the first substrate. The cover sheet may be disposed on the surface of the first base material, and the cover sheet is more preferably disposed so as to cover the side surface of the first base material and the side surface of the water-absorbing layer, and further preferably to cover the side surface of the first base material, the side surface of the water-absorbing layer, and the side surface of the second base material, and to cover a part or the whole of the surface of the second base material opposite to the side where the liquid to be absorbed is introduced.
In a preferred embodiment of the present invention, the water-absorbent sheet is provided with a cover sheet, which is a water-permeable sheet and is located at least on the surface (liquid-absorbent side) of the first substrate.
The thickness of the coated 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 coated sheet 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 40% RH to 50% RH, for example.
In the present invention, the bulk density of the coated sheet is preferably 1g/cm 3 Hereinafter, more preferably 0.5g/cm 3 Hereinafter, it is more preferably 0.3g/cm 3 The following is given. The bulk density of the coated sheet is preferably 0.1g/cm 3 The above is more preferably 0.12g/cm 3 The above is more preferably 0.13g/cm 3 The above.
In the present invention, the unit area weight of the coated sheet is preferably 5 to 100g/m 2 More preferably 5 to 70g/m 2 More preferably 10 to 65g/m 2 。
The thickness, bulk density, and weight per unit area of the clad sheet can be controlled by the material constituting the clad sheet, the method of producing the clad sheet, and the like, and the thickness and bulk density of the clad sheet can be determined based on the balance of these materials.
"Material constituting 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 face tissue, toilet paper, and towel paper), mesh, nonwoven fabric, woven fabric, and film.
The nonwoven fabric to be used is not particularly limited, and examples thereof include nonwoven fabrics formed of polyolefin fibers such as Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyester fibers such as 1, 3-propanediol terephthalate (PTT) and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers, from the viewpoints of liquid permeability, flexibility, and strength when a water-absorbent sheet is produced; nonwoven fabrics made from blends of cotton, silk, hemp, pulp (cellulose) fibers, and the like.
The nonwoven fabric usable as the cover sheet is preferably a rayon fiber, a polyolefin fiber, a polyester fiber, a pulp fiber, a fiber obtained by mixing them, or the like, and more preferably a polyolefin fiber. These fibers may be hydrophilized.
The nonwoven fabric usable 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 hydroentangled method, or the like, and preferably a nonwoven fabric obtained by a spunbond method (spunbond nonwoven fabric). As in the case of seating a child wearing an absorbent article such as a disposable diaper, the water-absorbent sheet is preferably a water-repellent cover sheet, for example, a spunbond nonwoven fabric, in order not to allow urine absorbed by the water-absorbent sheet to leak out of the sheet (so-called backflow does not occur) in a state where the water-absorbent sheet is loaded with a load (in a pressurized state). The method for producing a spunbond nonwoven fabric is a method in which continuous long fibers obtained by melting/spinning a raw material resin are directly collected and formed into 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 substrate, the method for producing the second substrate, and the method for producing the coated sheet are different. By appropriately changing the manufacturing method of each member constituting the water-absorbing sheet in this way, the desired effect of the present invention can be effectively exhibited. According to one embodiment of the present invention, the first substrate is a hot air nonwoven fabric, the second substrate is an air-laid nonwoven fabric or a spun-laced nonwoven fabric, and the cover sheet is a spunbonded nonwoven fabric, which are nonwoven fabrics different from each other. In this way, the desired effects of the present invention can be effectively exhibited.
[ 3 ] method for producing Water-absorbent sheet ]
The method for producing a water-absorbing sheet according to the first and second embodiments of the present invention includes: (1) At least one of a step of dispersing the particulate water absorbing agent on the first substrate and (2) a step of dispersing the particulate water absorbing agent on the second substrate. As a more specific example of the production method, the following production methods (a) to (d) are given as examples of the water-absorbent sheet according to the first embodiment. The water-absorbent sheet according to the second embodiment includes the following production methods (e) to (h).
(a) On the first substrate, the particulate water absorbing agent is dispersed 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 overlapped and pressure-bonded. The pressure bonding is preferably thermal pressure bonding around the melting temperature of the adhesive.
(b) The particulate water absorbing agent is uniformly dispersed on the second substrate after the adhesive is dispersed in a stripe shape. The first base material is overlapped with the surface of the second base material on which the particulate water absorbing agent is dispersed, and heat-press-bonding is performed.
(c) On the second substrate, the particulate water absorbing agent is spread in a stripe shape, and the adhesive is preferably uniformly spread so as to pass through the heating furnace, so that it is fixed to such an extent that the particulate water absorbing agent does not escape. The first base material is overlapped with the surface of the second base material on which the particulate water absorbing agent is dispersed, and heat-press-bonding is performed.
(d) After the adhesive is melt-coated on the second substrate, the particulate water absorbing agent is spread in a stripe shape to form a layer. The first substrate is overlapped with the surface of the second substrate on which the particulate water absorbing agent is dispersed, and pressure bonding is performed using a roller press or the like.
(e) On the first substrate (or intermediate substrate), the particulate water-absorbing agent is dispersed 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 and the surface of the intermediate base material (or the first base material) on which the adhesive is dispersed are overlapped so as to be aligned, and pressure-bonded to each other, thereby obtaining a bonded body of the first base material and the intermediate base material. The particulate water absorbing agent is spread in a stripe shape on an intermediate substrate of a joined body of the first substrate and the intermediate substrate. The adhesive is uniformly spread on the second substrate. The surface of the bonded body of the first base material and the intermediate base material, on which the particulate water absorbing agent is dispersed, is overlapped with the surface of the second base material, on which the adhesive is dispersed, in a butt joint manner, and is pressure-bonded. The pressure bonding is preferably thermal pressure bonding around the melting temperature of the adhesive.
(f) After the adhesive is uniformly spread on the second substrate, the particulate water absorbing agent is spread in a stripe shape. The intermediate base material is superimposed on the surface of the second base material on which the particulate water absorbing agent is dispersed, and the resultant is subjected to thermocompression bonding to obtain a bonded body of the intermediate base material and the second base material. The particulate water absorbing agent is spread in a stripe shape on the intermediate substrate of the joined body of the intermediate substrate and the second substrate. The adhesive is uniformly spread on the first substrate. The surface of the bonded body of the intermediate substrate and the second substrate on which the particulate water absorbing agent is dispersed is overlapped with the surface of the first substrate on which the adhesive is dispersed, and is pressure-bonded.
(g) On the second substrate, the particulate water absorbing agent is spread in a stripe shape, and preferably, the adhesive is uniformly spread so as to pass through the heating furnace, so as to be fixed to such an extent that the particulate water absorbing agent does not escape. The first substrate is overlapped with the surface of the second substrate on which the particulate water absorbing agent is dispersed, and the resultant is subjected to thermocompression bonding to obtain a bonded body of the intermediate substrate and the second substrate. The particulate water absorbing agent is spread in a stripe shape on the intermediate substrate of the joined body of the intermediate substrate and the second substrate, and the adhesive is preferably uniformly spread so as to pass through the heating furnace, so as to be fixed to such an extent that the particulate water absorbing agent does not escape. The first base material is overlapped on the surface of the joint body of the intermediate base material and the second base material on which the particulate water absorbing agent is dispersed, and the heat and pressure bonding is performed.
(h) After the adhesive is melt-coated on the second substrate, the particulate water absorbing agent is spread in a stripe shape to form a layer. The intermediate base material is superimposed on the surface of the second base material on which the particulate water absorbing agent is dispersed, and pressure bonding is performed by using a roll or the like to obtain a bonded body of the intermediate base material and the second base material. After the adhesive is applied by melt-coating to the first substrate of the joined body of the intermediate substrate and the second substrate, the particulate water absorbing agent is spread in a stripe shape to form a layer. The first substrate is superimposed on the surface of the joined body of the intermediate substrate and the second substrate on which the particulate water absorbing agent is dispersed, and pressure bonding is performed by using 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-absorbing sheet may be produced by using the methods (a) to (d) in the first embodiment and the methods (e) to (h) in the second embodiment in combination.
Here, in the present invention, the method of dispersing the particulate water absorbing agent in a stripe shape is not particularly limited, and may be dispersed in a stripe shape by using, for example, a hollowed-out cardboard. Specifically, a board having the same dimensions as the water-absorbent sheet and hollowed out in a vertical stripe pattern arranged in a certain width and length was used as the hollowed-out cardboard. The hollowed-out cardboard is carried on a substrate to be dispersed with the particulate water absorbing agent, and the particulate water absorbing agent is dispersed in the portion of the hole that has been hollowed out. After the particulate water absorbing agent is dispersed, when the hollow paperboard is removed, the particulate water absorbing agent is dispersed in a striped state on the substrate.
Further, the particulate water absorbing agent can be spread in a stripe shape on the substrate by applying the adhesive to the substrate by screen printing or the like, spreading the particulate water absorbing agent on the substrate, and then, dusting the particulate water absorbing agent on the substrate without contact with the adhesive.
As shown in fig. 18 and 19, the mode in which the water-absorbent sheet includes a cover sheet includes (3) a step of covering the first substrate, the water-absorbent layer, and the second substrate with the cover sheet disposed on the first substrate or a step of covering the first substrate, the water-absorbent layer, the intermediate substrate, the water-absorbent layer, and the second substrate with the cover sheet disposed on the first substrate. For example, a sheet obtained by pressing the first base material, the water-absorbing layer, and the second base material obtained through the steps (a), (b), or (e), or (f), or a sheet obtained by pressing the first base material, the water-absorbing layer, the intermediate base material, the water-absorbing layer, and the second base material is placed on the coated sheet with the first base material facing downward, an adhesive is spread on the second base material (the surface on the side not pressed with the water-absorbing layer) as the upper surface, and the excess portion of the coated sheet exposed from the first base material is folded and wrapped so that the adhesive surface of the second base material contacts the coated sheet, and the coated sheet is turned upside down, and then pressed and pressed, whereby a water-absorbing sheet having the coated sheet can be obtained.
As a step other than the above, the water-absorbent sheet may be embossed for the purpose of improving the touch feeling of the water-absorbent sheet and improving the liquid-absorbing performance. The embossing process may be performed simultaneously when the first substrate and the second substrate are pressure bonded, or may be performed after the sheet is manufactured. Further, the wrapping sheet may be embossed.
In the method for producing a water-absorbent sheet according to one embodiment of the present invention, additives (deodorant, fiber, antibacterial agent, gel stabilizer, etc.) may be appropriately blended. The blending amount of the additive is preferably 0 to 50% by mass, more preferably 1 to 10% by mass, relative to 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 during the production process.
The dimensions of the produced water-absorbent sheet can be appropriately designed. Typically, the transverse width is 3 to 10m and the length is 10m to 1000m (in the state of a continuous sheet or roll). The produced water-absorbent sheet is used by cutting according to the purpose (the size of the absorber used).
In addition to the above examples, the following patent documents, for example, disclose a method for producing a water-absorbent sheet: international publication No. 2012/174026, international publication No. 2013/078109, international publication No. 2015/047784, 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. 2010/082573, international publication No. 2010/113754, international publication No. 2010/143635, international publication No. 2011/04 315501, 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. 2010/136087, international publication No. 2013/043546, international publication No. 2013/0934, international publication No. 2013/11335, japanese laid-open patent application No. 2002-open No. wo-flat top-open No. 2012, japanese patent application No. 2012-open No. 37,5835, japanese patent application No. 2002-open No. 37-open No. 37,360, japanese patent application No. 37-open No. 2002-open No. japanese-open patent application No. 1-open No. wo 35, japanese-open No. 2002-open No. jp-open No. wo 35, no. 2002-japanese-open patent application No. jp-open No. from japanese-open 2, no. top-open 2, no. from any 2. The method for producing the water-absorbent sheet 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 base materials to each other or to the particulate water-absorbing agent, the base materials may be (i) pressure-bonded, may be (ii) dissolved or dispersed in water, a water-soluble polymer or a solvent, may be (iii) heat-sealed at the melting point of the base materials themselves, or may be (iv) fixed with an adhesive. The base materials or the base material and the particulate water absorbing agent are preferably (iv) fixed with an adhesive.
The adhesive used may be a solution type, but from the viewpoint of time and effort for removing the solvent, the problem of residual solvent, and the problem of productivity, a hot melt adhesive having high productivity and no problem of residual solvent is preferable. 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 used separately in the process of producing the water absorbing sheet. The form and melting point of the hot-melt adhesive may be appropriately selected, and may be in the form of particles, fibers, meshes, films, or a liquid state in which the hot-melt adhesive is melted by 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 is used in which the particle diameter is about 0.01 to 2 times, 0.02 to 1 times, and 0.05 to 0.5 times the average particle diameter of the particulate water absorbing agent.
When a hot-melt adhesive is used in the production of the water-absorbent sheet according to one embodiment of the present invention, the water-absorbent sheet can be produced by uniformly dispersing a mixture of the particulate water-absorbing agent and the hot-melt adhesive on a substrate (for example, a nonwoven fabric), further laminating another 1 substrate, and then performing heat-press bonding in the vicinity of the melting temperature of the hot-melt adhesive.
As the hot melt adhesive used in the present invention, it is appropriately selected, and preferable is: more than 1 selected from ethylene-vinyl acetate copolymer adhesives, styrene-based elastomer adhesives, polyolefin-based adhesives, polyester-based adhesives, and the like can be suitably used.
Specifically, examples of the polyolefin-based adhesive include polyethylene, polypropylene, and atactic polypropylene, examples of the styrene-based elastomer adhesive include styrene-isoprene block copolymer (SIS), styrene-butadiene block copolymer (SBS), styrene-isobutylene block copolymer (SIBS), and styrene-ethylene-butylene-styrene block copolymer (SEBS), and the like, and examples of the copolymer polyolefin include polyester-based adhesive include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and a copolymer polyester, and examples of the ethylene-vinyl acetate copolymer adhesive include ethylene-vinyl acetate copolymer (EVA) adhesive, ethylene-ethyl acrylate copolymer (EEA), and ethylene-butyl acrylate copolymer (EBA).
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, 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, relative to the mass of the particulate water-absorbing agent. If the content of the binder (particularly, the hot-melt binder) is too large, not only the cost and the quality of the water-absorbing sheet (the quality of the diaper increases) become disadvantageous, but also the particulate water-absorbing agent may be limited by swelling and the water-absorbing ability of the water-absorbing sheet may be lowered.
[ 4. Absorbent article ]
An absorbent article according to one 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 constituted by sandwiching the water-absorbent sheet of the present invention between a liquid-permeable sheet and a liquid-impermeable sheet, the liquid-permeable sheet being located on the first base material side, and the liquid-impermeable sheet being located on the second base material side. Specific examples of the absorbent article include paper diapers, incontinence pads, sanitary napkins, pet sheets, drip sheets for foods, and water-stops for cables.
As the liquid-permeable sheet and the liquid-impermeable sheet, sheets known in the technical field 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, unless otherwise specified, the operation was performed under conditions of room temperature (25 ℃) and relative humidity of 40 to 50% RH.
In the following examples, a single-layer system in which only 1 layer of a laminate of a first substrate is laminated on a second substrate and a two-layer system in which 2 layers of a laminate of a first substrate are laminated on a second substrate are disclosed. In both the single-layer system and the two-layer system, the first substrate having a liquid suction surface that directly absorbs 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 a liquid-absorbing surface that directly absorbs liquid in the two-layer system is an intermediate substrate, referred to herein as an "intermediate nonwoven fabric".
< production example >
Production example 1
The particulate water absorbing agents (1) and (2) of the polyacrylic acid (salt) resin were obtained by appropriately adjusting the CRC according to the amount of the internal crosslinking agent, taking as reference the production examples, examples and comparative examples described in the following patents. 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 ]
Acrylic acid (acrylic acid dimer 2000ppm, acetic acid 500ppm, propionic acid 500ppm, p-methoxyphenol 200 ppm) which is commercially available was supplied to the bottom of a high boiling impurity separation column having 50 stages of baffle-free porous plates, distilled with a reflux ratio of 1, and after removing maleic acid, a dimer formed from acrylic acid (acrylic acid dimer), and the like, further crystallization was performed to obtain acrylic acid (acrylic acid dimer 20ppm, acetic acid 50ppm, propionic acid 50ppm, furfural 1ppm or less, protoanemonin 1ppm or less), and after the distillation, p-methoxyphenol 50ppm was added.
[ preparation of aqueous sodium acrylate solution ]
According to example 9 of U.S. Pat. No. 5210298, 1390g of the above-mentioned acrylic acid was neutralized with 48% caustic soda at 20 to 40℃to obtain a 100% neutralized aqueous sodium acrylate solution having a concentration of 37%.
< 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 production example of acrylic acid, an aqueous sodium acrylate solution obtained by the production method of the aqueous sodium acrylate solution using the acrylic acid, and deionized water, 4.00g of polyethylene glycol diacrylate (average addition mole number of ethylene oxide: 9) was dissolved to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by capping a jacketed stainless steel double arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ℃. Then, 28.66g of a 10% by mass aqueous solution of sodium persulfate and 35.28g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and as a result, polymerization was started after about 1 minute. After 40 minutes from the start of polymerization, 181.5g of fine powder of water-absorbent resin having a particle size of 150 μm or less was added, and the gel was broken by high-speed rotation (130 rpm) of a kneader plate for 10 minutes, followed by removal of the water-containing gel-like polymer. The resulting hydrogel-like polymer is finely divided 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 by a metal mesh having a mesh size of 600. Mu.m, whereby an irregularly pulverized water-absorbent resin (1-1) having an average particle diameter of 350. Mu.m was obtained. To 100 parts by mass of the water-absorbent resin (1-1) thus obtained, 4.03 parts by mass of an aqueous surface cross-linking 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 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 sprayed and mixed, and the mixture was cured at 60℃for 1 hour in a closed container, and then the cured product was passed through a sieve having a mesh size of 710. Mu.m, to obtain a water-absorbent resin (1-3). A particulate water-absorbing agent (1) was obtained by adding 0.3 parts by mass of Aerosil90G (hydrophilic amorphous silica, manufactured by AEROSIL Co., ltd., japan) to water-absorbent resin (1-3) and mixing the resultant mixture.
[ method for 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 particles) according to one embodiment of the present invention is a weight average particle diameter obtained by the measurement method of "PSD" specified in ERT 420.2-02. The weight average particle diameters of the particulate water absorbing agents are shown in tables 8 and 10.
< CRC (Water absorption Rate without pressure) (ERT 441.2-02) >)
After 0.2G (weight before water absorption) of the particulate water absorbing agent was put into a nonwoven fabric bag, the bag was immersed in a significantly excessive 0.9 mass% aqueous sodium chloride solution for 30 minutes to allow free swelling, and after that, the weight after water absorption of the particulate water absorbing agent was measured after water removal by a centrifuge (250G). The water absorption capacity (unit: g/g) was determined by "(weight of particulate water absorbing agent after water absorption-weight of particulate water absorbing agent before water absorption)/(weight of particulate water absorbing agent before water absorption) ×100". The CRC of each particulate water absorbing agent is shown in tables 8 and 10.
< surface tension >
In the present invention, the surface tension means the surface tension of an aqueous solution when the particulate water absorbing agent is dispersed in 0.90 mass% aqueous sodium chloride solution.
50ml of physiological saline adjusted to 20℃was poured into a sufficiently cleaned 100ml beaker, and the surface tension of the physiological saline was measured by a surface tensiometer (KRUSS Co., ltd. K11 automatic surface tensiometer). In the present invention, a plate method using a platinum plate was used, and the plate was sufficiently washed with deionized water before each measurement, and was heated and washed with a gas burner.
Subsequently, 0.5g of a 25mm long fluororesin rotor and a particulate water absorbing agent, which were sufficiently washed, were put into a beaker containing physiological saline after surface tension measurement adjusted to 20℃and stirred at 500rpm for 4 minutes. After 4 minutes, stirring was stopped, and after the aqueous particulate water absorbing agent had settled, the same operation was performed again to measure the surface tension of the supernatant liquid. The surface tension (unit: mN/m) of the particulate water absorbing agent was determined from the surface tension of the supernatant liquid when the particulate water absorbing agent was dispersed in physiological saline. The surface tension of each particulate water absorbing agent is shown in tables 8 and 10.
[ examples ]
< preparation of hollowed-out cardboard >
The hollow-out cardboard sheets 1 to 6 were prepared for dispersing the particulate water absorbing agent in a stripe pattern on the nonwoven fabric. In the hollow-out cardboard sheets 1 to 6, openings were formed in the portions of the paper having a longitudinal direction of 14cm and a transverse direction of 44cm at which the regions where the particulate water absorbing agent was present were formed, so as to linearly form the regions where the particulate water absorbing agent was present and the regions where the particulate water absorbing agent was not present along the longitudinal direction. In the hollow-out cardboard sheets 1 to 6, the outer periphery thereof was set as a frame, and the paper was not cut (that is, the hollow-out cardboard sheet was perforated by hollowing out the portions of the region where the particulate water absorbing agent was present in order from the end in the width direction in the region other than the frame). The shapes (S-1) to (S-6) formed by using the cut-out paper sheets 1 to 6 will be described with reference to fig. 20 (a) to 20 (c) and fig. 21 (a) to 21 (c). Fig. 20 (a) to 20 (c) and fig. 21 (a) to 21 (c) are schematic cross-sectional views of a single-layer type water-absorbent sheet cut in the width direction. In the shapes (S-1) to (S-6), the region containing 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 absorbing sheet. Accordingly, the ratio of the area of "particulate water absorbing agent 14" to the area of "gap 15" shown below may be from either one of the left and right sides in the width direction.
Fig. 20 (a) is a (S-1) shape formed by using the hollowed-out cardboard 1. In the shape of (S-1), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 15mm, gap 15:25mm, particulate water absorbing agent 14:20mm, gap 15:25mm, particulate water absorbing agent 14:15 mm).
Fig. 20 (b) is a (S-2) shape formed by using the hollowed-out cardboard 2. In the shape of (S-2), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 20mm, gap 15:20mm, particulate water absorbing agent 14:20mm, gap 15:20mm, particulate water absorbing agent 14:20 mm).
Fig. 20 (c) is a (S-3) shape formed by using the hollowed-out cardboard 3. In the shape of (S-3), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order in the width direction: 10mm, gap 15:35mm, particulate water absorbing agent 14:10mm, gap 15:35mm, particulate water absorbing agent 14:10 mm).
Fig. 21 (a) is a (S-4) shape formed by using the hollowed-out cardboard 4. In the shape of (S-4), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 25mm, gap 15:10mm, particulate water absorbing agent 14:30mm, gap 15:10mm, particulate water absorbing agent 14:25 mm).
Fig. 21 (b) is a (S-5) shape formed by using the hollowed-out cardboard 5. In the shape of (S-5), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 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 14:17.5 mm).
Fig. 21 (c) is a (S-6) shape formed by using the hollowed-out cardboard 6. In the shape of (S-6), between first substrate 11 and second substrate 13, "particulate water absorbing agent 14" is formed in this order along the width direction: 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 14:10 mm).
Example 1
A hollow paperboard 1 (see fig. 20 (a)) was placed on a nonwoven fabric a (produced by a hot air method, having an olefin as a main component and a thickness of 1.4mm, corresponding to the intermediate nonwoven fabric) cut into 10cm in the longitudinal direction and 40cm in the transverse direction. The hollow paperboard 1 has 3 rectangular holes, and the position of the nonwoven fabric a under the hollow paperboard 1 is adjusted so that the nonwoven fabric a can be seen from the holes to the maximum. The ratio of the area of each hole to the total area of all holes of the hollowed-out cardboard 1 was calculated, and 4.5g (spread amount: 112.5 g/m) of the particulate water absorbing agent (1) 2 ) The nonwoven fabric a, which can be seen from each hole, was uniformly dispersed by being distributed and measured in terms of the area ratio of each hole. In the case where a part of the particulate water absorbing agent (1) is scattered on the hollowed-out cardboard, the hollowed-out cardboard 1 is inclined toward the nonwoven 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 hollowed-out cardboard 1. Thereafter, the hollow paperboard 1 is removed from the nonwoven a.
Unlike the nonwoven fabric a, the nonwoven fabric a cut into 10cm in the longitudinal direction and 40cm in the transverse direction (the same nonwoven fabric (thickness: 1.4 mm) as the nonwoven fabric a, hereinafter referred to as nonwoven fabric A2, which corresponds to the first base material (upper nonwoven fabric)), was uniformly spread with an adhesive (spray 77, 3M JAPAN company) containing styrene-butadiene rubber in an amount of 0.7 to 0.9g (spread amount: 17.5 to 21.5 g/M), and then, the surface of the nonwoven fabric a on which the particulate water absorbing agent (1) was spread was overlapped (in a contact manner) with the surface of the nonwoven fabric A2 on which the adhesive was spread, and was pressure-bonded.
On the surface of the nonwoven fabric a on the side not facing the particulate water absorbing agent (1), the hollow-out cardboard 1 is placed (see fig. 20 (a)). The position is adjusted in such a way that the nonwoven a under the hollow paperboard 1 can be seen to the maximum from the 3 rectangular holes of the hollow paperboard 1. The ratio of the area of each hole to the total area of all holes of the hollowed-out cardboard 1 was calculated, 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 dispersed. In the case where a part of the particulate water absorbing agent (1) is scattered on the hollowed-out cardboard, the hollowed-out cardboard 1 is inclined toward the nonwoven 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 hollowed-out cardboard 1. Thereafter, the hollow paperboard 1 is removed from the nonwoven a.
Nonwoven fabric E (produced by air-laid method, pulp fiber as main component, thickness of 0.4mm, weight per unit area of 47 g/m) 10cm in longitudinal direction and 40cm in transverse direction 2 . Corresponding to the second base material (lower nonwoven fabric)), 0.7 to 0.9g of the adhesive is uniformly dispersed, and then the intermediate sheet X is obtained by superposing (in contact with) the surface of the nonwoven fabric a on which the particulate water absorbing agent (1) is dispersed and the surface of the nonwoven fabric E on which the adhesive is dispersed so as to be in butt joint, and pressing and bonding the resultant sheet.
Finally, the intermediate sheet X was cut into a nonwoven fabric F (produced by a spunbonding method) having a length of 24cm and a width of 40cm, and the nonwoven fabric was produced by using an olefin as a main component, and had a thickness of 0.1mm and a basis weight of 13g/m 2 . Bulk density: 0.15g/cm 3 . Corresponding to the wrapping sheet) to obtain the water-absorbent sheet (1).
Example 2
A nonwoven fabric F (corresponding to a wrapping sheet) cut into 24cm in the vertical direction and 40cm in the horizontal direction was laid in advance, a nonwoven fabric a (corresponding to a first base material) cut into 10cm in the vertical direction and 40cm in the horizontal direction was placed thereon, and a hollow paperboard 1 was placed on the surface of the nonwoven fabric a (see fig. 20 (a)). The position is adjusted in such a way that the nonwoven a under the hollow paperboard 1 can be seen to the maximum from the 3 rectangular holes of the hollow paperboard 1. The ratio of the area of each hole to the total area of all holes of the hollowed-out cardboard 1 was calculated, and 9.0g (dispersion amount: 225 g/m) of the particulate water absorbing agent (1) 2 ) The nonwoven fabric a, which can be seen from each hole, was uniformly dispersed by being distributed and measured in terms of the area ratio of each hole. In the case where a part of the particulate water absorbing agent (1) is scattered on the hollowed-out cardboard, the hollowed-out cardboard 1 is inclined toward the nonwoven 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 hollowed-out cardboard 1. Thereafter, the hollow paperboard 1 is removed from the nonwoven a.
After 0.7 to 0.9g (dispersion amount: 17.5 to 21.5 g/M) of an adhesive containing styrene-butadiene rubber (spray 77, 3M JAPAN Co.) was uniformly dispersed on a nonwoven fabric E (corresponding to the second base material) having a longitudinal direction of 10cm and a transverse direction of 40cm, the surface of the nonwoven fabric A on which the particulate water absorbing agent (1) was dispersed was overlapped with the surface of the nonwoven fabric E on which the adhesive was dispersed in a butt joint manner (in a contact manner), and press-bonding was performed, to obtain an intermediate sheet Y.
Finally, the intermediate sheet Y is wrapped with the nonwoven fabric F and pressure-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 hot-air nonwoven fabric G having a thickness of 0.7mm was used instead of the hot-air nonwoven fabric a.
Example 4
A water-absorbing sheet (4) was obtained in the same manner as in example 2, except that the hollow-out cardboard 2 (see fig. 20 (b)) was used instead of the hollow-out cardboard 1.
Example 5
A water-absorbing sheet (5) was obtained in the same manner as in example 2, except that the hollow-out cardboard 3 (see fig. 20 (c)) was used instead of the hollow-out cardboard 1.
Example 6
A water-absorbing sheet (6) was obtained in the same manner as in example 2, except that the hollow-out cardboard 4 (see fig. 21 (a)) was used instead of the hollow-out cardboard 1.
Example 7
A water-absorbing sheet (7) was obtained in the same manner as in example 2, except that the hollow-out cardboard 5 (see fig. 21 (b)) was used instead of the hollow-out cardboard 1.
Example 8
A water-absorbing sheet (8) was obtained in the same manner as in example 2, except that the hollow-out cardboard 6 (see fig. 21 (c)) was used instead of the hollow-out cardboard 1.
Example 9
A water-absorbing sheet (9) was obtained in the same manner as in example 2, except that a nonwoven fabric B (produced by a hot air method; olefin was used as a main component, and the thickness was 2.0 mm.) was used instead of the nonwoven fabric a.
Example 10
A water-absorbing sheet (10) was obtained in the same manner as in example 2, except that a nonwoven fabric C (produced by a hot air method; olefin was used as a main component, and the thickness was 1.5 mm.) was used instead of the nonwoven fabric a.
Comparative example 1
4.5g of the particulate water-absorbing agent (1) was uniformly dispersed on the nonwoven fabric A cut into 10cm in the longitudinal direction and 40cm in the transverse direction.
After 0.7 to 0.9g (dispersion amount: 17.5 to 21.5 g/M) of an adhesive containing styrene-butadiene rubber (spray 77, 3M JAPAN Co.) was uniformly dispersed on a nonwoven fabric E (corresponding to the first substrate) having a longitudinal direction of 10cm and a transverse direction of 40cm, the surface of the nonwoven fabric A on which the particulate water absorbing agent (1) was dispersed was overlapped (in contact) with the surface of the nonwoven fabric E on which the adhesive was dispersed, and then pressure-bonded.
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.
The intermediate sheet Z was obtained by uniformly dispersing 0.7 to 0.9g of the adhesive on a nonwoven fabric E (hereinafter referred to as a nonwoven fabric E2, which corresponds to a second substrate) having a longitudinal direction of 10cm and a transverse direction of 40cm, respectively, and then overlapping (in contact) the surface of the nonwoven fabric a on which the particulate water absorbing agent (1) was dispersed and the surface of the nonwoven fabric E2 on which the adhesive was dispersed so as to be aligned. Finally, the intermediate sheet Z is wrapped with a nonwoven fabric F and pressure-bonded, thereby obtaining a water-absorbent sheet (11).
Comparative example 2
A water-absorbing sheet (12) was obtained in the same manner as in example 1, except that the particulate water-absorbing agent (1) was uniformly dispersed throughout the entire surface of the nonwoven fabric A without using the hollow-out cardboard (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 A2. 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 this example were all water permeable sheets.
[ method for measuring physical Properties of nonwoven Fabric ]
The elongation, thickness, bulk density, liquid diffusion area, and transmittance of the particulate water absorbing agent to the nonwoven fabrics a to C, E and G used in examples 1 to 10 and comparative examples 1 to 4 were measured in the following manner.
[ method of measuring elongation ]
The nonwoven fabric for measuring 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 of the present example used for the water-absorbent sheet, the dimensions of 100mm in the longitudinal direction (short side) and 400mm in the transverse direction (long side), the longitudinal direction (short side) and the transverse direction (long side) were taken as the width direction and the winding length direction of the nonwoven fabric roll, respectively. As shown in fig. 22 (a), reference lines were drawn parallel to the short sides of the cut nonwoven fabric at positions 5mm away from the ends of the nonwoven fabric for measuring elongation. Each clip is sandwiched by a double-layered clip so as to overlap with the reference line (fig. 22 (b)). The double-layer cloth gripper uses a clip with a claw length of more than 30 mm. The 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 110g. And holding the double-layer cloth clip without the heavy object at room temperature, lifting the heavy object attached to the other double-layer cloth clip, floating the heavy object in the air, and maintaining the non-woven fabric in an elongated state due to the weight of the double-layer cloth clip and the heavy object for 20 seconds. Next, the length of the nonwoven fabric in the longitudinal direction was measured while floating in the air (fig. 22 (c)). The ratio was determined as the elongation by using the following equation, based on the length of the long side after floating in the air and the length of the long side before floating in the air, which was 100 mm.
[ math figure 6]
< measurement of nonwoven Fabric thickness >
The measurement was performed using a dial gauge (thickness gauge) (model J-B, model J, measuring head, anvil up-down 50mm, manufactured by Kawasaki Co., ltd.). The number of measurement points was 5 times at different positions, and the measurement value was set as an average value at 5. In measuring the thickness, the hand is slowly removed from the handle in order to apply as little pressure as possible to the nonwoven fabric, and the thickness is 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 transverse direction was measured. The length of the nonwoven fabric in the machine direction and the cross direction and the thickness measured by < thickness measurement > are multiplied, respectively, the volume of the nonwoven fabric is calculated, and the bulk density is 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 >
A screen having a diameter of 30cm obtained by using a net having a mesh of 2mm and a wire of 0.9mm was placed on a flat surface, and a nonwoven fabric (second base material) cut into 10cm squares was placed. A syringe needle having a diameter of 0.50mm was mounted in a 1ml syringe, and 1.00g of physiological saline containing 20ppm of blue No. 1 reagent was measured, and physiological saline of the syringe was injected vertically 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 passing through the nonwoven fabric and the mesh does not contact the mesh. If the nonwoven fabric absorbs physiological saline and the liquid is finished to diffuse, the diffusion area of the physiological saline is measured.
< transmittance of particulate Water absorbing agent to nonwoven Fabric >
In a JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80mm; JIS Z8801-1 (2000)) having a mesh opening 32 of 850 μm or a sieve 31 corresponding to The JIS standard sieve, a nonwoven fabric (first base material 11) cut to a diameter of 80mm was provided as shown in FIG. 23, and The periphery was fixed with an adhesive tape 33 (an area through which particles could pass was ensured to be at least 75mm in diameter). As the nonwoven fabric (first base material 11), a nonwoven fabric taken out of the water-absorbent sheet by a method described later can be used. Particulate water-absorbing agent 14 (weight average particle diameter: 367. Mu.m, particle size distribution: 850 μm to 600. Mu.m, 6.1%, 600 μm to 500. Mu.m, 14.5%, 500 μm to 300. Mu.m, 50%, 300 μm to 150. Mu.m, 27.6%, 150 μm to 45 μm, 1.9%, 45 μm or less, 0.1%) was put on a nonwoven fabric (first substrate 11) in a sieve 31 (arrow direction in FIG. 23), and 10.0g was used, and the mixture was oscillated for 5 minutes at room temperature (20 to 25 ℃) and relative humidity of 50% RH using a rotary hammer sieve (ES-65 type sieve manufactured by Kagaku Kogyo Co., ltd., rotational speed: 230rpm, impact number: 130 rpm). After shaking, the mass (W (g)) of particulate water-absorbing agent 14 after passing through the nonwoven fabric (first substrate 11) and mesh 32 of screen 31 corresponding to the above-mentioned JIS standard sieve (i.e., particulate water-absorbing agent 14 present in portion 31a below mesh 32 of screen 31) was measured, and the transmittance of particulate water-absorbing agent 14 was calculated according to the following formula (i). The average value was calculated by performing 2 measurements.
[ math 7]
Transmittance (mass%) of particulate water absorbing agent = { W/10.0} ×100 … (i)
The particulate water absorbing agent used for measuring the transmittance is a particulate water absorbing agent comprising 90% by weight 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. Thus, the transmittance of the particulate water absorbing agent calculated in this example to the first substrate also corresponds to the transmittance of the particular particulate water absorbing agent to the first substrate.
[ method for evaluating Water-absorbent sheet ]
< method of 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 absorbing 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 agent attached to the upper and lower nonwoven fabrics and the intermediate nonwoven fabric was also taken out entirely. When the nonwoven fabrics above and below are peeled off, the water-absorbent sheet is cooled, and the adhesive properties of the adhesive (hot melt adhesive, adhesive cement paste) for attaching the nonwoven fabric and the particulate water absorbing agent are sufficiently weakened, and then the nonwoven fabrics are peeled off. By performing this step, the nonwoven fabric can be taken out without changing the fiber and the structure thickness of the nonwoven fabric, and the transmittance can be accurately measured. The method of cooling the water-absorbing sheet is not particularly limited as long as the fiber, structure and thickness of the nonwoven fabric are not changed and the particulate water-absorbing agent contained in the water-absorbing sheet is not absorbed by moisture, as long as the cooling method is carried out by leaving the water-absorbing sheet in a constant temperature bath at-10 ℃ or lower for a predetermined period of time, blowing a cooling spray, applying liquid nitrogen, and the like.
When the particulate water absorbing agent to be taken out absorbs moisture, the moisture content may be adjusted to 10 mass% or less, preferably to 5±2 mass% by drying, for example, and the above-mentioned transmittance and physical 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 and modification of the water-absorbent resin (particulate water-absorbent agent) do not occur, and drying under reduced pressure is preferable.
< determination of the content ratio of particulate Water absorbing agent in upper nonwoven Fabric >
The sample (thickness was not changed) obtained by cutting the upper nonwoven fabric into a square having a longitudinal direction of 10mm and a transverse direction of 10mm was measured by using a MICRO FOCUS X-ray CT system inspeXio SMX-100CT manufactured by Shimadzu corporation. The measurement conditions are as follows.
[ X-ray CT-based imaging ]
Image lateral dimension (pixel): 512
Image vertical dimension (pixel): 512
X-ray tube voltage (kV): 50
X-ray tube current (μa): 40
English size (inch): 4.0
An X-ray filter: without any means for
SDD (distance of focus of X-ray source from X-ray detector) (mm): 700
SRD (distance of focal spot of X-ray source from rotation center of measurement sample) (mm): 550
Scan mode 1: CBCT
Scan pattern 2: routine scanning
Scanning angle: full scan
Number of fields of view: 2400
Average number: 5
Smoothing: YZ
Slice thickness (mm): 0.166
BHC data: without any means for
Fine mode: has the following components
FOV XY (maximum imaging area XY) (mm): 50.3
FOV Z (maximum shot region Z) (mm): 40.0.
next, the X-ray CT imaging data was analyzed by the following procedure using analysis software Win ROOF manufactured by san francisco corporation.
(1) Win ROOF is turned on, and the image (Jpeg) to be analyzed stored in the X-ray CT is selected.
(2) On the screen, clicking (selecting) is performed according to the procedures of binary processing, automatic binarization, modality method, threshold (appropriate adjustment) and operation.
(3) The polygonal ROI was selected to enclose 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 obtained water absorbing sheet was calculated in the same manner as in (3).
Based on the calculation result, the content (%) of the particulate water absorbing agent in the first substrate is calculated by the following formula.
The content ratio (%) of the particulate water absorbing agent in the first substrate=the particulate water absorbing agent area (I) in the first substrate/the particulate water absorbing agent total area (II) ×100
That is, the content ratio of the particulate water absorbing agent in the first substrate is expressed as an area% of the particulate water absorbing agent relative to the total area. The particulate water absorbing agent may be regarded as not being present because it is present in less than a few% on the liquid absorbing surface of the first substrate (the surface on the side where the liquid to be absorbed by the upper nonwoven fabric is introduced) directly absorbing the liquid. In the following examples, the content of the particulate water absorbing agent in the first substrate was 5% or more with respect to the particulate water absorbing agent contained in the entire water absorbing sheet.
[ method for evaluating Water-absorbent sheet ]
< reverse flow amount (evaluation of specific reverse flow amount) >)
As shown in fig. 24, the water-absorbent sheet 10 having a longitudinal direction of 10cm and a transverse direction of 40cm was wrapped with the liquid-impermeable sheet 21 having a longitudinal direction of 14cm and a transverse direction of 40cm so that an opening was formed in the upper portion. The water-absorbent sheet 10 wrapped with the liquid-impermeable sheet 21 was placed on a flat surface, and a liquid-injecting tube 41 (fig. 25) was placed at the center of the water-absorbent sheet 10 thereon 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 pouring tube 41 using a funnel 42 capable of pouring a liquid at a flow rate of 7 ml/sec (FIG. 27). In this case, the liquid is poured into the sheet 22 with respect to the water-absorbent sheet 10 exposed from the liquid-impermeable sheet 21. After 10 minutes from the time of liquid introduction, 20 sheets of filter paper 43 (model No.2, manufactured by ADVANTEC Co., ltd.; circular filter paper having a diameter of 110 mm) having a weight measured in advance were placed in the center of the sheet 22, that is, in the center of the water-absorbent sheet 10, and further, a weight 44 (1200 g) having a diameter of 100mm and a circular shape was placed and held for 1 minute. After 1 minute, the weight 44 was removed, and the first pouring amount (g) was measured based on the weight gain of the filter paper 43. After 1 minute from the removal of the weight 44, the same operation was repeated (liquid was poured → after 10 minutes of pouring, the filter paper 43 and the weight 44 (1200 g) were carried, and the mixture was kept for 1 minute → after 1 minute, the weight was removed, and the pouring amount was measured, and the second pouring amount (g) and the third pouring amount (g) were measured. The total of the measured first to third pouring flows is shown in tables 8 and 10.
< method of calculating thickness ratio (Lb/La) >)
La is a thickness from the liquid suction surface of the upper nonwoven fabric (liquid suction 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 suction surface of the upper nonwoven fabric (liquid suction surface of the first substrate) to the surface of the lower nonwoven fabric (second substrate) on the water-absorbing layer side in the region containing the particulate water absorbing agent.
[ measurement of thickness of Water-absorbent sheet by X-ray CT ]
In the X-ray CT-based image capturing, both ends of a water-absorbing sheet cut into 180mm long were fixed with rubber tapes to a plastic plate having a longitudinal direction of 350mm, a transverse direction of 100mm and a thickness of 3mm, and the plastic plate was placed on an inner plate of an X-ray apparatus (manufactured by Shimadzu corporation, inspeXio SMX-100 CT) perpendicularly to the thickness direction, and the center of the water-absorbing sheet was measured under the following conditions, whereby the image capturing was performed.
The using device comprises: inspeXio SMX-100CT (manufactured by Shimadzu corporation)
X-ray tube voltage (kV): 80
X-ray tube current (μa): 40
English size (inch): 4.0
An X-ray filter: without any means for
SOD(mm)：700
SRD(mm)：550
Number of fields of view: 2400
Average number: 5X 1
Slice thickness (mm): 0.166
CT mode 1: CBCT
CT mode 2: conventional operation
Scanning angle: full scan
BHC data: without any means for
Center adjustment: has the following components
Fine mode: has the following components
FOV(XY)(mm)：50.3
FOV(Z)(mm)：20.0
Voxel size (mm/voxel): 0.098
A sectional view was obtained in which the captured stereoscopic image was divided into 203 parts in the longitudinal direction, 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 suction surface of the upper nonwoven fabric to the surface of the lower nonwoven fabric on the water-absorbing layer side in the gap under the upper nonwoven fabric, and Lb is the thickness from the liquid suction surface of the upper nonwoven fabric to the surface of the lower nonwoven fabric on the water-absorbing layer side in the region under the upper nonwoven fabric containing the particulate water absorbing agent.
< evaluation of shape retention >
After the water-absorbing sheet was evaluated for the < amount of backflow >, the center of the water-absorbing sheet was cut in the width direction, and the region (i.e., the gap) containing no particulate water-absorbing agent was visually checked. At this time, the presence of the substance in the gap was confirmed and evaluated according to the following evaluation criteria.
Evaluation criterion
And (2) the following steps: the regions containing the particulate water absorbing agent are separated by gaps
(i.e., there is no member in the gap or there is a base material having a water-absorbing layer mainly in the gap (i.e., upper nonwoven fabric and lower nonwoven fabric in the case of the single-layer mode; upper nonwoven fabric, middle nonwoven fabric and lower nonwoven fabric in the case of the two-layer mode))
X: the space is present in a small proportion, and the regions containing the particulate water-absorbing agent in parallel are connected to each other (not separated by the space)
(that is, the particulate water-absorbing agent enters into the region regarded as the gap, or the existing proportion of the base material having the water-absorbing layer becomes smaller)
The following tables 7 to 10 show the structures of the water-absorbent sheets produced in examples 1 to 10 and comparative examples 1 to 4, the results of evaluation of physical properties of the substrates used in the respective water-absorbent sheets, and the results of evaluation of the water-absorbent sheets. In tables 7 to 10, SAP refers to particulate water absorbing agents. The SAP placement area (%) in tables 7 and 9 means: in the upper nonwoven fabric surface direction, the ratio of the area of the region containing the particulate water absorbing agent to the total area of the substrate provided with the particulate water absorbing agent, the region (%) where the SAP is not provided means: in the face direction of the upper nonwoven fabric, the ratio of the area of the region (i.e., the gap) free of the particulate water absorbing agent to the total area of the substrate on which the particulate water absorbing agent is disposed. Here, the substrate provided with the particulate water absorbing agent means: a substrate in which a particulate water absorbing agent is dispersed. In this example, the upper nonwoven fabric, the intermediate nonwoven fabric, and the lower nonwoven fabric were the same size.
TABLE 7
TABLE 8
TABLE 9
TABLE 10
From the above results, the water-absorbent sheets of examples 1 to 10 were high in shape retention and significantly less in backflow compared with the water-absorbent sheets of comparative examples 1 to 4. The method can confirm that: in the single-layer type and two-layer type water absorbent sheets, the use of the stretchable upper nonwoven fabric provides gaps in the water absorbent layer, and thus the flow-down rate can be reduced, and the shape retention is high.
In the present embodiment, the two-layer system tends to have a larger amount of backflow than the single-layer system. It may also be one of the reasons that the amount of the particulate water absorbing agent of the two-layer type relative to the upper layer 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 of the single-layer type relative to the upper layer 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 reverse flow rate between the single-layer system and the two-layer system is difficult to be generalized.
The present application is based on japanese patent application nos. 2019-215887 and 2019-215888, both filed on 11-month 28, the disclosures of which are incorporated herein by reference in their entirety.
Industrial applicability
10. Water-absorbing sheet
11. 11a first substrate,
11b intermediate substrate,
12. 12a, 12b water-absorbing layer,
13. A second base material,
14. 14a, 14b particulate water-absorbing agent,
15. 15a, 15b gap
16. A wrapping sheet,
18. 18a laminate,
18b structure,
20. A water-absorbing sheet,
21. A liquid-impermeable sheet,
31. A sieve(s),
31a part under the screen, 32 meshes,
33. Adhesive tape
41. A liquid injection cylinder,
42. A funnel(s),
43. Filter paper
44. A weight body,
45. A liquid injection cylinder,
60. A stand table,
61. A pipe(s),
63. Acrylic plate,
64. A funnel(s),
65. A metal tray.
Claims (15)
1. A water-absorbent sheet having a first substrate, a second substrate, and a water-absorbent layer between the first substrate and the second substrate,
the water absorbing layer contains a particulate water absorbing agent, a region containing the particulate water absorbing agent is disposed across a gap substantially free of the particulate water absorbing agent,
the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid,
The first substrate has an elongation of 10% or more.
2. The water-absorbent sheet according to claim 1, wherein the first substrate has a weight per unit area of 10 to 60g/m 2 。
3. The water-absorbent sheet according to claim 1 or 2, wherein the first substrate has a bulk density of 0.1g/cm 3 The following is given.
4. The water-absorbent sheet according to any one of claims 1 to 3, wherein the first substrate is a hot air nonwoven fabric.
5. The water-absorbent sheet according to any one of claims 1 to 4, which is formed by laminating a laminate comprising the first substrate and the water-absorbent layer a and a constituent body comprising the intermediate substrate and the water-absorbent layer B, on the second substrate.
6. The water-absorbent sheet according to any one of claims 1 to 5, which is formed by laminating only a laminate comprising the first substrate and the second substrate on the water-absorbent layer.
7. The water-absorbent sheet according to claim 6, wherein a ratio (Lb/La) of a thickness (Lb) to a thickness (La) of a thickness from the liquid-absorbing surface of the first substrate to the water-absorbing layer-side surface of the second substrate in a region containing the particulate water absorbing agent is 1.05 or less, and the thickness (La) is a thickness from the liquid-absorbing surface of the first substrate to the water-absorbing layer-side surface of the second substrate in the gap.
8. The water-absorbent sheet according to any one of claims 1 to 7, wherein the second substrate is a spunlaced nonwoven fabric.
9. The water-absorbent sheet according to any one of claims 1 to 8, wherein the first substrate contains the particulate water-absorbing agent, and the content of the particulate water-absorbing agent in the first substrate is 5% or more relative to the particulate water-absorbing agent contained in the entire water-absorbent sheet.
10. The water-absorbent sheet according to any one of claims 1 to 9, wherein the particulate water-absorbing agent has a transmittance of 40 mass% or more to the first substrate.
11. The water-absorbing sheet according to any one of claims 1 to 10, wherein the region containing the particulate water-absorbing agent and the gap have a shape extending in one direction of the liquid suction surface of the first substrate, and are arranged side by side.
12. The water-absorbent sheet according to any one of claims 1 to 11, which has a coated sheet disposed at least on a surface of the first substrate.
13. The water-absorbent sheet according to any one of claims 1 to 12, wherein the particulate water-absorbing agent has a CRC of 30g/g or more.
14. The water-absorbent sheet according to any one of claims 1 to 13, wherein the water-absorbent sheet comprises an adhesive,
The amount of the binder to be used is 0.05 to 2.0 times the mass of the particulate water absorbing agent.
15. An absorbent article comprising the water-absorbent sheet according to any one of claims 1 to 14 sandwiched 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.
Applications Claiming Priority (6)
| 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 |
| CN202080082864.6A CN114746058A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202080082864.6A Division CN114746058A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
Publications (1)
| Publication Number | Publication Date |
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| CN117257553A true CN117257553A (en) | 2023-12-22 |
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| CN202311262915.5A Pending CN117257553A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
| CN202080082864.6A Pending CN114746058A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
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| CN202080082864.6A Pending CN114746058A (en) | 2019-11-28 | 2020-11-30 | Water-absorbing sheet and absorbent article comprising same |
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| Country | Link |
|---|---|
| JP (2) | JP7410175B2 (en) |
| CN (2) | CN117257553A (en) |
| WO (1) | WO2021107159A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPS544309B2 (en) * | 1971-05-28 | 1979-03-05 | ||
| JPS59903Y2 (en) * | 1977-08-26 | 1984-01-11 | 日本合成化学工業株式会社 | Physiological absorption material |
| JP2001105520A (en) * | 1999-01-22 | 2001-04-17 | Mitsui Chemicals Inc | Moisture permeable composite nonwoven fabric |
| JP3737328B2 (en) * | 2000-01-21 | 2006-01-18 | 花王株式会社 | Absorption sheet |
| JP5417133B2 (en) * | 2009-06-17 | 2014-02-12 | 花王株式会社 | Absorbent articles |
| US20130018349A1 (en) * | 2010-03-25 | 2013-01-17 | Sumitomo Seika Chemicals Co., Ltd. | Water-absorbent sheet structure |
| PL2550946T3 (en) * | 2010-03-25 | 2015-03-31 | Sumitomo Seika Chemicals | Water-absorbing sheet structure |
| JP5868110B2 (en) * | 2010-10-18 | 2016-02-24 | 花王株式会社 | Absorbent articles |
| US9566198B2 (en) * | 2013-03-15 | 2017-02-14 | Dsg Technology Holdings Ltd. | Method of making an absorbent composite and absorbent articles employing the same |
| JP2017530753A (en) * | 2014-09-12 | 2017-10-19 | ザ プロクター アンド ギャンブル カンパニー | Process for producing an absorbent article comprising a topsheet / trapping layer laminate |
| EP3586957B1 (en) * | 2017-02-22 | 2022-03-30 | Nippon Shokubai Co., Ltd. | Absorbent article comprising water-absorbing sheet |
| 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 |
| RU2748668C1 (en) * | 2017-12-29 | 2021-05-28 | Као Корпорейшн | Absorber and absorbent product |
| JP7096688B2 (en) | 2018-03-28 | 2022-07-06 | 大王製紙株式会社 | Absorbent article |
| CN111971011B (en) * | 2018-04-13 | 2022-05-31 | 株式会社日本触媒 | Water-absorbing sheet, method for producing water-absorbing sheet, and absorbent article |
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