CN112566599B - Water-absorbing sheet and absorbent article comprising same - Google Patents

Water-absorbing sheet and absorbent article comprising same Download PDF

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Publication number
CN112566599B
CN112566599B CN201980053393.3A CN201980053393A CN112566599B CN 112566599 B CN112566599 B CN 112566599B CN 201980053393 A CN201980053393 A CN 201980053393A CN 112566599 B CN112566599 B CN 112566599B
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water
absorbing agent
particulate water
particulate
sheet
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CN112566599A (en
Inventor
野田由美
鸟井一司
植田裕子
北野贵洋
平内达史
堀本裕一朗
平冈隆一
池内博之
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Nippon Shokubai Co Ltd
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Nippon Shokubai Co Ltd
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    • 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
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
    • A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
    • A61L15/42—Use of materials characterised by their function or physical properties
    • A61L15/60—Liquid-swellable gel-forming materials, e.g. super-absorbents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • 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
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • 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
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L101/00—Compositions of unspecified macromolecular compounds
    • C08L101/12—Compositions of unspecified macromolecular compounds characterised by physical features, e.g. anisotropy, viscosity or electrical conductivity
    • C08L101/14—Compositions of unspecified macromolecular compounds characterised by physical features, e.g. anisotropy, viscosity or electrical conductivity the macromolecular compounds being water soluble or water swellable, e.g. aqueous gels

Abstract

The purpose of the present invention is to provide a novel water-absorbent sheet that can significantly reduce the amount of backflow even when the amount of liquid introduced increases as liquid is intermittently introduced multiple times (particularly 3 times or more) in a non-pressurized state. 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 first substrate is a water-permeable sheet on the side where a liquid to be absorbed is introduced, and the water-absorbent layer comprises: an intermediate sheet; a first particulate water-absorbing agent which is locally present on one surface side of the first base material which faces the second base material; and a second particulate water-absorbing agent which is locally present on a side of the second base material opposite to the first base material, wherein a transmittance of a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent with respect to the intermediate sheet is less than 60%, and a GPR of the second particulate water-absorbing agent is 45.0g/min or more.

Description

Water-absorbing sheet and absorbent article comprising same
Technical Field
The present invention relates to a water-absorbent sheet and an absorbent article including the same.
Background
water-Absorbent resins (SAP/Super Absorbent polymers) are water-swellable, water-insoluble polymer gelling agents and are used for sanitary materials such as paper diapers, sanitary napkins, and incontinence products for adults; soil water-retaining agents for agriculture, forestry and gardening, industrial water-stopping agents, and the like.
These absorbent articles are generally manufactured in a diaper manufacturing plant in the form of an absorbent body in which a water-absorbent resin and a fibrous material are mixed and molded for each absorbent article, and are processed into absorbent bodies of various shapes (for example, hourglass-shaped, fox-shaped, oval-shaped, and the like in a plan view) according to the purpose. These methods for producing an absorbent body can be processed into any shape by molding, and the amounts of fibers and water-absorbent resin can be easily adjusted for each absorbent article, and therefore, these methods are the mainstream of paper diapers today.
However, in recent years, in the production of paper diapers, paper diapers using the following absorbent bodies have been gradually produced: the absorbent material is obtained by cutting a long water-absorbent sheet obtained by fixing a water-absorbent resin between two sheets in a production process of a sanitary material (usually, the absorbent material is cut into a rectangular shape having a width of about 10cm and a length of 10 cm). A diaper manufacturer can simplify the manufacturing process of a diaper by purchasing or manufacturing a long continuous water-absorbent sheet, and can make the diaper thin because pulp is not used. The water-absorbent sheet is constituted by sandwiching or fixing water-absorbent resin particles between upper and lower sheets (particularly, nonwoven fabric sheets), and generally, after a long continuous sheet is produced, the long continuous sheet is cut into a rectangular shape having a width of about 10cm and a length of several 10cm, and incorporated into a disposable diaper (for example, patent document 1).
Unlike conventional sanitary materials (disposable diapers), disposable diapers based on water-absorbent sheets have a short history, and development of water-absorbent resins and parameter setting suitable for water-absorbent sheets have not been proposed in practice, and water-absorbent resins for conventional disposable diapers have been used as water-absorbent sheets as they are.
Documents of the prior art
Patent document
Patent document 1: international publication No. 2010-143635
Disclosure of Invention
The present inventors have found that: only the thin water-absorbent sheet as the main stream has a structure in which so-called "back flow" in which absorbed liquid is discharged occurs. And found that: this problem becomes obvious if the liquid is introduced intermittently a plurality of times (particularly 3 times or more) without pressurization and the amount of liquid introduced increases.
Accordingly, an object of the present invention is to provide a novel water-absorbent sheet capable of significantly reducing the amount of backflow even when the introduction environment of the liquid is such as described above.
The above problems are solved by the following water-absorbent sheet. The water-absorbing sheet comprises a first base material, a second base material, and a water-absorbing layer located between the first base material and the second base material, wherein the first base material is a water-permeable sheet located on a side where a liquid to be absorbed is introduced, and the water-absorbing layer comprises: an intermediate sheet; a first particulate water-absorbing agent which is locally present on one surface side of the first substrate which is opposed to the second substrate; and a second particulate water-absorbing agent which is locally present on a side of the second base material opposite to the first base material, wherein a transmittance of a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent with respect to the intermediate sheet is less than 60%, and a GPR of the second particulate water-absorbing agent is 45.0g/min or more.
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 diagram showing an apparatus for measuring GPR.
Fig. 3 is a plan view and a right side view showing a sample for evaluating a flow rate of a water-absorbent sheet produced in the example, which is wrapped with a liquid-impermeable sheet.
Fig. 4 is a top view and a front view of a liquid injection cartridge for evaluating a back flow rate.
FIG. 5 is a front view showing a state in which a liquid inlet cylinder is placed on a water-absorbent sheet used in an example of the present application.
FIG. 6 is a front view and a right side view showing a case where the water-absorbent sheet in FIG. 5 is poured with an aqueous sodium chloride solution from a liquid-pouring cylinder by using a funnel.
Fig. 7 is a schematic view showing an apparatus used for measuring the transmittance.
Detailed Description
The present invention will be described below while showing the best mode. The expression in the singular form should be understood to include the concept of the plural form thereof as well as the whole of the present specification unless specifically mentioned. Thus, reference to an article in the singular (e.g., "a," "an," "the," etc. in the case of english) should be construed as also including the plural concepts unless specifically mentioned otherwise. In addition, unless otherwise specified, terms used in the present specification should be understood to be used in the meaning generally used in the field. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. The present invention is not limited to the embodiments described below, and various modifications can be made within the scope of the claims.
[ 1. Definition of terms ]
[1-1. Water-absorbent sheet ]
The "water-absorbent sheet" in the present invention is a structure in which a water-absorbent resin (particulate water-absorbing agent) and an intermediate sheet are carried between 2 or more long substrates. In the water-absorbent sheet, an adhesive or a hot-melt adhesive may be used for bonding the substrate and at least one of the intermediate sheet and the particulate water-absorbing agent. The water-absorbent sheet may contain other components (fiber component, antibacterial agent, deodorant agent, etc.) in addition to the particulate water-absorbing agent. The water-absorbent sheet may contain other sheets in addition to the two substrates for sandwiching the particulate water-absorbing agent and the like.
Generally, the water-absorbent sheet is in the form of a continuous sheet or a roll formed by winding the continuous sheet. When the water-absorbent sheet is used, the continuous sheet is cut into an appropriate shape (such as a rectangle) and then used as an absorbent member of a disposable diaper or the like. On the other hand, in conventional disposable diapers having a high water absorbent resin concentration (for example, disposable diapers having an absorbent body made of pulp-free paper), an absorbent body formed separately is used for each disposable diaper. Therefore, such an absorbent body is different in technical properties from the water-absorbent sheet of the present invention.
[1-2. Water-absorbent resin ]
In the present specification, the term "water-absorbent resin" means: a polymer gelling agent having a water-swelling capacity (CRC) of not less than 5g/g as defined by ERT441.2-02 and a water-soluble component (Ext) of not more than 50% by mass as defined by ERT 470.2-02.
The water-absorbent resin is preferably a hydrophilic crosslinked polymer obtained by crosslinking and polymerizing an unsaturated monomer having a carboxyl group. The water-absorbent resin is in the form of a sheet, a fiber, a film, a particle, a gel, or the like. In one embodiment of the present invention, a particulate water-absorbent resin is used for the water-absorbent sheet.
In the present specification, the term "water-absorbent resin" is not limited to the embodiment in which only the total amount (100 mass%) of the water-absorbent resin is the same. It may be a water-absorbent resin composition containing additives and the like. In the present specification, the term "water-absorbent resin" is a concept including an intermediate in the production process of the water-absorbent resin. For example, a crosslinked hydrogel polymer after polymerization, a dried polymer after drying, a water-absorbent resin powder before surface crosslinking, and the like may be sometimes referred to as "water-absorbent resin".
As described above, in the present specification, the water-absorbent resin composition and the intermediate may be collectively referred to as "water-absorbent resin" in addition to the water-absorbent resin itself.
[1-3. Water-absorbing agent, particulate Water-absorbing agent ]
In the present specification, "water absorbing agent" means: an absorption gelling agent for absorbing an aqueous liquid (liquid) which comprises a water-absorbent resin as a main component. Here, the aqueous liquid (liquid) is not particularly limited as long as it contains water, not only water. The aqueous liquid absorbed by the water-absorbent sheet according to one embodiment of the present invention is urine, menstrual blood, sweat, or other body fluids.
In the present specification, the "particulate water-absorbing agent" refers to a particulate (powder) water-absorbing agent (corresponding to a particulate water-absorbing resin because the water-absorbing agent contains the water-absorbing resin as a main component). The concept of "particulate water-absorbing agent" includes any of a single particulate water-absorbing agent and an aggregate of a plurality of particulate water-absorbing agents. In the present specification, "granular" means having a granular form. Here, "particle" means a smaller divided body of matter, having a number
Figure GDA0002940849500000041
Size of several mm (reference "granule", mcGraw-H)The Committee for compilation of the ill science and technology terminology Dayu dictionary compiles McGraw-Hill science and technology terminology Dayu 3 rd edition, journal industry Press, 1996, p 1929). In the present specification, "particulate water-absorbing agent" may be abbreviated as "water-absorbing agent". In the water-absorbent sheet according to an embodiment of the present invention, the particulate water-absorbing agent preferably has a weight average particle diameter of 200 to 600 μm, more preferably 250 to 500 μm, and still more preferably 300 to 450 μm. In the water-absorbent sheet of the present invention, 95% or more of the entire particulate water-absorbing agent has a particle diameter of 850 μm or less, more preferably 98% or more of the entire particulate water-absorbing agent has a particle diameter of 850 μm or less, and still more preferably substantially 100% of the entire particulate water-absorbing agent has a particle diameter of 850 μm or less. In the examples of the present application, substantially 100% of the particulate water-absorbing agent as a whole has a particle diameter of 850 μm or less. In the present specification, the method of measuring the weight Average Particle size is calculated by the same method as that of "(3) Mass-Average Particle Diameter (D50) and logistic Standard development (σ ζ) of Particle Diameter Distribution" described in U.S. Pat. No. 7638570, based on the PSD obtained by the method of measuring "PSD" defined in ERT 420.2-02.
The particulate water-absorbing agent contains a water-absorbent resin as 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, even more preferably 90 to 100% by mass, and particularly preferably 95 to 100% by mass of a water-absorbent resin as a polymer. The remainder of the 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 about 95% by mass to about 99% by mass of the water-absorbent resin.
That is, the upper limit of the water-absorbent resin in the particulate water-absorbing agent is, for example, 100 mass%, 99 mass%, 97 mass%, 95 mass%, or 90 mass%. Also, it is preferable that: the water-absorbent resin composition contains 0 to 10 mass% of components, particularly water, additives (inorganic fine particles, polyvalent metal cations), and the like, in addition to the water-absorbent resin.
The particulate water-absorbing agent preferably has a water content of 0.2 to 30 mass%. As described above, the water-absorbent resin composition in which components such as water and additives are integrated with the water-absorbent resin and/or the water-absorbent resin composition in a mixed form is also included in the "particulate water-absorbing agent".
Examples of the water-absorbent resin which becomes the main component of the particulate water-absorbing agent include polyacrylic acid (salt) based resin, polysulfonic acid (salt) based resin, maleic anhydride (salt) based resin, polyacrylamide based resin, polyvinyl alcohol based resin, polyethylene oxide based resin, polyaspartic acid (salt) based resin, polyglutamic acid (salt) based resin, alginic acid (salt) based resin, starch based resin, and cellulose based resin. Among them, a polyacrylic acid (salt) based 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, "comprises 8230that" as the main component "means: the amount of the acrylic acid (salt) used in the polymerization of the polyacrylic acid (salt) is usually 50 to 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, and still more preferably substantially 100 mol% based on the whole monomers used in the polymerization (excluding the internal crosslinking agent).
[1-5.EDANA and ERT ]
"EDANA" is an abbreviation for European nonwoven industries (European Disposables and Nonwovens associates). "ERT" is an abbreviation of the method for measuring a water-absorbent resin (EDANA Recommended Test Methods) in the European standards (substantial world standards) established by EDANA. In the present specification, unless otherwise specified, the physical properties of the water-absorbent resin were measured in accordance with ERT 2002 edition.
[1-6. Other ]
In the present specification, "X to Y" indicating a range means "X or more and Y or less".
In the present specification, the unit "t (ton)" of mass means "Metric ton" unless otherwise noted. "ppm" means "mass ppm". "mass" and "weight", "mass part" and "part by weight", "mass%" and "wt%", and "mass ppm" and "weight ppm" are respectively regarded as the same meaning.
In the present specification, "acid (salt)" means "acid and/or salt thereof". "(meth) acrylic acid" means "acrylic acid and/or methacrylic acid".
In the present specification, the unit "liter" of volume is sometimes expressed as "L" or "L". Sometimes,% by mass is expressed as "wt%". When the measurement of a minor component was performed, the detection limit was expressed as n.d. (Non Detected) below.
[ 2. Water-absorbent sheet ]
The water-absorbent sheet of the present invention is a water-absorbent sheet comprising a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, wherein the first substrate is a water-permeable sheet located on a side where a liquid to be absorbed is introduced, and the water-absorbent layer comprises: an intermediate sheet; a first particulate water-absorbing agent which is locally present on one surface side of the first base material which faces the second base material; and a second particulate water-absorbing agent which is locally present on the side of the second substrate opposite to the first substrate, wherein the transmittance (also referred to simply as "transmittance" in the present specification) of a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent (also referred to as "water-absorbing agent mixture" in the present specification) with respect to the intermediate sheet, which is measured by the method described in the column of examples in the present specification, is less than 60%, and the GPR of the second particulate water-absorbing agent is 45.0g/min or more. With this configuration, even if the liquid is intermittently introduced a plurality of times (particularly 3 times or more) without pressurization and the amount of liquid introduced increases, the amount of reflux can be significantly reduced. In particular, with this configuration, very excellent results can be obtained in the measurement of the amount of reflux under specific conditions (also referred to as "specific reflux amount evaluation" in the present specification) in the examples of the present application. In other words, if the liquid is introduced intermittently and a plurality of times (particularly 3 times or more), the amount of the liquid becomes equal to or more than the set absorption amount and excessive "backflow" occurs in the case of the normal configuration. The inventors of the present invention found that: when the transmittance to the intermediate sheet is 60 mass% or more, the specific reflux amount evaluation is excellent. Hereinafter, the% by mass is simply referred to as "transmittance". The reason for this is that, in combination of the particulate water-absorbing agent and the intermediate sheet, which can achieve such a transmittance, the intermediate sheet easily captures the particulate water-absorbing agent present in the water-absorbent sheet. By causing the intermediate sheet to trap a large amount of the particulate water-absorbing agent, the particulate water-absorbing agent diffuses in the water-absorbent sheet, and the particulate water-absorbing agents present in the water-absorbent sheet are easily separated from each other by a gap. If the transmittance is less than 60%, the particulate water-absorbing agent present between the intermediate sheet and the substrate is less likely to be trapped by the intermediate sheet, the probability of the particulate water-absorbing agent being present between the intermediate sheet and the substrate increases, and the particulate water-absorbing agent is tightly present between the intermediate sheet and the substrate. In this way, a gel blocking phenomenon occurs between the particulate water-absorbing agents having absorbed water, and the liquid diffusibility is lowered, resulting in an excessive "amount of backflow". In other words, if the transmittance is 60% or more, the following technical effects are obtained: the particulate water-absorbing agent present between the intermediate sheet and the substrate is widely diffused into the intermediate sheet, whereby the particulate water-absorbing agents are easily separated from each other by a gap, and the performance of the particulate water-absorbing agent can be exhibited to the maximum, and the water-absorbable area can be utilized more widely even when the water-absorbing sheet is made. However, the present inventors have found that: even if the particulate water-absorbing agent has a transmittance of less than 60% with respect to the intermediate sheet, the "specific reflux amount evaluation" can be made excellent by locally making the particulate water-absorbing agent combined with the intermediate sheet into the first particulate water-absorbing agent and the second particulate water-absorbing agent, and making the GPR of the second particulate water-absorbing agent 45.0g/min or more. If the transmittance is less than 60%, the following technical effects are also obtained: the center sheet becomes soft and has a good texture, and is easily comfortable for the user to wear. The mechanism and the like described in the present specification do not limit the technical scope of the claims of the present application. Here, it is stated in advance that the water-absorbent sheet and the absorbent article designed to suppress the amount of return under ordinary conditions do not necessarily exhibit excellent results in the "evaluation of specific amount of return" in the present application. The water-absorbent sheet according to one embodiment of the present invention is suitable as an absorbent article (for example, a diaper) used in a time zone where an infant with a small bladder who starts to learn to walk moves back and forth in the daytime, for example, but the form of use is not limited thereto. As a method for achieving a transmittance of less than 60%, as described below, it is considered that: a method of controlling the fiber diameter (if the constituent member of the intermediate sheet is a fiber) or superposing a plurality of nonwoven fabrics (if the intermediate sheet is a nonwoven fabric) is suitable. In other words, the transmittance of less than 60% can be achieved by adjusting the properties of the members constituting the intermediate sheet, 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. If a person who intends to practice the present invention uses, for example, a through-air nonwoven fabric as the intermediate sheet, the transmittance can be adjusted by changing the heat treatment conditions, the fiber diameter, and the density of the through-air nonwoven fabric. Even in the case of using another kind of material as the intermediate sheet, the transmittance of less than 60% can be realized by appropriately changing the factors relating to the adjustment of the transmittance as described above.
Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description thereof is omitted. In addition, the dimensional ratio of the drawings is exaggerated for convenience of explanation and may be different from the actual ratio.
Fig. 1 is a schematic view showing a cross section of a water-absorbent sheet 40 according to an embodiment of the present invention. The first substrate 11 is located on the side where the liquid to be absorbed is introduced. That is, at least the first base material is disposed on the liquid discharge side (for example, the skin side in the case of a diaper). A water-absorbing layer 12 is disposed between a first substrate 11 and a second substrate 13. In fig. 1, the second base material 13 is only positioned on the side opposite to the side where the liquid to be absorbed is introduced through the water-absorbent layer 12, but the second base material 13 may be folded so as to wrap the first base material 11 by designing the area thereof to be larger than that of the first base material 11, for example. This can suppress the particulate water-absorbing agents 14a and 14b from falling off. The water-absorbent sheet 40 of fig. 1 has: an intermediate sheet 16; a first particulate water-absorbing agent 14a which is locally present on the first substrate 11 on the side of one surface thereof facing the second substrate; and a second particulate water-absorbing agent 14b locally present on the side of the second substrate 13 opposite to the first substrate. The water-absorbent-agent mixture in the intermediate sheet 16 has a transmittance of less than 60%, but is partially present as the particulate water-absorbing agent 14a and the particulate water-absorbing agent 14a, and the second particulate water-absorbing agent 14b has a GPR of 45.0g/min or more, and therefore, even if the particulate water-absorbing agent 14a and the particulate water-absorbing agent 14b are not present in the intermediate sheet 16 in large amounts, they are not present in the water-absorbent sheet but are diffused, the desired effects of the present invention are exhibited.
As described above, in the embodiment of fig. 1, the water-absorbent layer 12 has the particulate water-absorbing agent 14a fixed to the first substrate 11 and the particulate water-absorbing agent 14b fixed to the second substrate, and a part of the particulate water-absorbing agents 14a and 14b can be detached from the respective sheets. Therefore, the water-absorbent "layer" is not limited to a continuous body such as a sheet, and may be any form as long as it is present between the first substrate 11 and the second substrate 13 at a constant thickness. As a method for fixing the particulate water-absorbing agent to each substrate, for example, an adhesive may be used. A method for producing a water-absorbent sheet using an adhesive is described in detail in [ 3 ].
The water-absorbent sheet according to one embodiment of the present invention can be made thinner than an absorbent body used in a conventional absorbent article. When the water-absorbent sheet is used in a disposable diaper, the thickness 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, under 40% RH-50% RH. On the other hand, in view of the strength of the water-absorbent sheet and the diameter of the particulate water-absorbing agent, the lower limit of the thickness is 0.2mm or more, preferably 0.3mm or more, and more preferably 0.5mm or more. The thickness of the water-absorbent sheet used in the examples of the present application is 3mm to 5mm under the following conditions.
The thickness of the water-absorbent sheet was measured using a scale thickness gauge model (thickness measuring instrument) (model J-B, manufactured by Kawasaki corporation, measuring head, anvil, vertical phi 50 mm). The absorbent body was trisected along the longitudinal direction, and the measurement site was set to the central portion (point located at the intersection point of the diagonal lines from the end portions of the absorbent body). For example, in the case of a water-absorbent sheet having a length direction of 36cm and a width direction of 10cm, the measurement position is determined by three points, namely, a point (left) at a distance of 6cm from the left end in the length direction and 5cm from both ends in the width direction, a point (center) at a distance of 18cm from the left end in the length direction and 5cm from both ends in the width direction, and a point (right) at a distance of 30cm from the left end in the length direction and 5cm from both ends in the width direction, with respect to the length of 36cm in the length direction. The number of measurement points was measured 2 times for each part, and the total of the thickness measurement values was an average of 6 points. Specifically, a plate having a constant thickness is flatly attached to a lower measuring head of a thickness measuring instrument so that wrinkles and strain do not occur in a measuring portion of the water-absorbent sheet. Then, the upper measuring head of the thickness measuring instrument was brought close to a height position 2 to 3mm from the water-absorbent sheet, and then the hand was gradually released from the handle to measure the total thickness of the water-absorbent sheet and the plate. The thickness of the water-absorbent sheet is determined according to the formula T1= T2-T0 (T0: the thickness (mm) of the sheet, T1: the thickness (mm) of the water-absorbent sheet, T2: the thickness (mm) of the water-absorbent sheet and the sheet).
In order to further impart liquid permeability, diffusion properties, flexibility, and the like to the water-absorbent sheet, the surface of the water-absorbent sheet may be appropriately subjected to embossing. The embossed area may be the entire surface of the water-absorbent sheet or a part thereof. By providing the continuous embossed regions along the longitudinal direction of the water-absorbent sheet, the liquid can be easily diffused along the longitudinal direction. The particulate water-absorbing agent may be dispersed over the entire surface of the water-absorbent sheet, or a region where the particulate water-absorbing agent is not present may be partially provided. When the region where the particulate water-absorbing agent is not present is provided, it is preferably provided in a groove shape (stripe shape) along the longitudinal direction of the water-absorbent sheet. As described above, by providing the embossing region and/or the region where the particulate water-absorbing agent is not present continuously along the longitudinal direction, the region functions as a passage (liquid conveying passage) through which a large amount of liquid flows. The embossed region and/or the region where the particulate water-absorbing agent is not present may be provided linearly, may be provided in a curved shape, or may be provided in a wavy shape.
Hereinafter, each member constituting the water-absorbent sheet will be described in detail.
[2-1. First base material, second base material, and intermediate sheet ]
The first substrate is a water-permeable sheet positioned on the side where the liquid to be absorbed is introduced. The liquid to be absorbed is not limited to water, and may be urine, blood, sweat, feces, waste liquid, moisture, vapor, ice, a mixture of water and an organic solvent and/or an inorganic solvent, rainwater, groundwater, or the like, and is not particularly limited as long as water is contained. Preferred examples include urine, menstrual blood, sweat, and other body fluids.
The upper limit of the transmittance of the water-absorbent agent mixture in the water-absorbent sheet according to one embodiment of the present invention to the intermediate sheet is not particularly limited as long as it is less than 60%, and may be 59% or less, 57% or less, 55% or less, 53% or less, 51% or less, 49% or less, 47% or less, 45% or less, and 43% or less. The lower limit is preferably 10% or more, more preferably 20% or more, further preferably 30% or more, further preferably 35% or more, further preferably more than 40%, further preferably 42% or more, further preferably 44% or more, further preferably 46% or more, further preferably 48% or more, further preferably 50% or more. By having such a lower limit, the capturing ratio of the particulate water-absorbing agent is improved, and the desired effect of the present invention is easily exhibited.
The porosity of the water-absorbent agent mixture in the water-absorbent sheet according to one embodiment of the present invention to the intermediate sheet is preferably 80 to 99.9%, more preferably 85 to 99.9%, even more preferably 90 to 99.9%, particularly preferably 98.0 (or 98.1) to 99.9%, and most preferably 98.2 (98.3 or 98.4) to 99.5 (or 99.0)%. As described above, since the transmittance of less than 60% can be realized by the properties of the members constituting the intermediate sheet, 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, the void ratio and the transmittance do not have a direct relationship.
The first base material, the second base material, and the intermediate sheet used in the water-absorbent sheet according to one embodiment of the present invention are preferably nonwoven fabrics, respectively and independently. The material of the nonwoven fabric is not particularly limited, and polyolefin fibers (polyethylene (PE), polypropylene (PP), and the like), polyester fibers (polyethylene terephthalate (PET), 1, 3-trimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and the like), polyamide fibers (nylon, and the like), rayon fibers, pulp (cellulose) fibers, and the like are preferable from the viewpoint of liquid permeability, flexibility, and strength of the water-absorbent sheet. Further, nonwoven fabrics of other synthetic fibers, and nonwoven fabrics produced by mixing synthetic fibers with cotton, silk, hemp, pulp (cellulose) fibers, and the like are also preferable. The nonwoven fabric described above may be a nonwoven fabric including only 1 type of the above-described fibers, or a nonwoven fabric in which 2 or more types of the fibers are combined. The nonwoven fabric used for the first substrate and the second substrate is preferably produced by an air-laid method. Further, pulp (cellulose) fibers are preferable.
In the water-absorbent sheet according to one embodiment of the present invention, the nonwoven fabric used for the intermediate sheet is preferably a through-air nonwoven fabric. The nonwoven fabric used for the intermediate sheet is preferably bulky, and specifically, the thickness under no load is preferably 1.3mm or more, more preferably 1.5mm or more, further preferably 1.7mm or more, still more preferably 1.9mm or more, still more preferably 2.1mm or more, still more preferably 2.3mm or more, still more preferably 2.5mm or more, still more preferably 3mm or more, still more preferably 5mm or more, and still more preferably 7mm or more. The nonwoven fabric described above may contain a small amount of pulp fibers to such an extent that the thickness of the water-absorbent sheet is not increased. The upper limit of the thickness of the nonwoven fabric used for the intermediate sheet is not particularly limited, and the thickness under no load is preferably about 14mm or less, more preferably 13mm or less, further preferably 12mm or less, further preferably 11mm or less, and further preferably 10mm or less, for example.
In the water-absorbent sheet according to one embodiment of the present invention, the weight per unit area of the intermediate sheet is preferably 47g/m per 1 intermediate sheet 2 More preferably 50g/m or more 2 More preferably 55g/m 2 More than or equal to 61g/m, and more preferably 61g/m 2 More than or equal to 70g/m, and more preferably 70g/m 2 More than or equal to 80g/m, and more preferably 80g/m 2 More than or equal to, and more preferably 90g/m 2 More than or equal to, and more preferably 95g/m 2 As described above. The upper limit is not particularly limited, but is preferably 200g/m 2 Hereinafter, it is more preferably 150g/m 2 Hereinafter, it is more preferably 120g/m 2 The following.
In the water-absorbent sheet according to one embodiment of the present invention, the thickness of the intermediate sheet is thicker than the thickness of either the first base material or the second base material. More suitably, the thickness of the intermediate sheet is thicker than both the first and second substrates. This embodiment contributes to initial water retention of liquid absorption and leakage reduction, and the first base material and the second base material can be designed to be thin, so that the overall thickness of the water-absorbent sheet can be reduced. The ratio of the thickness of the intermediate sheet to the arithmetic mean of the thicknesses of the first base material and the second base material is preferably 1.5 to 100, more preferably 2 to 80, even more preferably 3 to 50, and even more preferably 3.2 to 15.
As described above, the nonwoven fabric used for the water-absorbent sheet according to one embodiment of the present invention is preferably a hydrophilic nonwoven fabric in order to improve water permeability, and the nonwoven fabric or the fibers as the nonwoven fabric material may be hydrophilized using a hydrophilizing agent (surfactant or the like).
Examples of the hydrophilizing agent include anionic surfactants (aliphatic sulfonates, higher alcohol sulfate salts, etc.), cationic surfactants (quaternary ammonium salts, etc.), nonionic surfactants (polyethylene glycol fatty acid esters, polyglycerol fatty acid esters, sorbitan fatty acid esters, etc.), silicone surfactants (polyoxyalkylene-modified silicones, etc.), detergents containing polyester, polyamide, acrylic, and urethane resins, and the like.
The water-absorbent sheet according to one embodiment of the present invention is a water-permeable sheet in which the first base material is located on the side where the liquid to be absorbed is introduced, but the second base material and the intermediate sheet are also preferably water-permeable sheets having water permeability, and may be the same type or different types from each other. The water permeability of the water-permeable sheet is preferably such that the water permeability coefficient (JIS A1218: 2009) is 1X 10 -5 cm/sec or more. The water permeability coefficient is more preferably 1X 10 -4 cm/sec or more, more preferably 1X 10 -3 cm/sec or more, more preferably 1X 10 -2 cm/sec or more, more preferably 1X 10 -1 cm/sec or more. The water-absorbent sheet according to one embodiment of the present invention is preferably a hydrophilic nonwoven fabric. The hydrophilic nonwoven fabric can effectively exhibit the desired effects of the present invention.
The thickness of the first base material and the second base material is preferably as thin as possible within the range of having strength as the water-absorbent sheet, and is appropriately selected from the range of 0.01 to 2mm, 0.02 to 1mm, 0.03 to 0.9mm, and 0.05 to 0.8mm, independently for each 1 base material. The basis weights of the first substrate and the second substrate are preferably 5 to 300g/m independently of each other per 1 substrate 2 More preferably 8 to 200g/m 2 More preferably 10 to 100g/m 2 More preferably 11 to 50g/m 2 。
[2-2. Water-absorbing layer ]
The water-absorbing layer in the water-absorbing sheet according to one embodiment of the present invention includes: an intermediate sheet; a first particulate water-absorbing agent which is locally present on one surface side of the first substrate which is opposed to the second substrate; and a second particulate water-absorbing agent locally present on a side of the second substrate opposite to the first substrate. The water-absorbent layer has an advantage that the first particulate water-absorbing agent and the second particulate water-absorbing agent can be easily localized on the first substrate and the second substrate more efficiently by providing the intermediate sheet. Further, the intermediate sheet is structured to form an air layer, which provides the following advantages: even if the water flows back from the water-absorbent sheet, the skin does not feel. The description of the intermediate sheet is as described above, and therefore, the description is omitted here. The local presence of the first particulate water-absorbing agent and the second particulate water-absorbing agent may be achieved by, for example, using an appropriate adhesive as described in [ 3 ].
(particulate Water-absorbing agent)
The water-absorbing layer in the water-absorbent sheet according to one embodiment of the present invention includes the first particulate water-absorbing agent and the second particulate water-absorbing agent. In the case of simply referring to the particulate water-absorbing agent unless otherwise stated, the term refers to a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent; or at least one of the first particulate water-absorbing agent and the second particulate water-absorbing agent. When the first particulate water-absorbing agent and/or the second particulate water-absorbing agent is a mixture of a plurality of particulate water-absorbing agents, the following description is a description of the physical properties of the mixture.
“CRC”(ERT441.2-02)
"CRC" is an abbreviation for centrifugal Retention Capacity, and refers to a 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 0.9 mass% aqueous sodium chloride solution in a large excess amount for 30 minutes to freely swell the water-absorbing agent, and then water was removed by a centrifugal separator (250G), thereby obtaining a water absorption capacity (unit: G/G).
The CRC of the second particulate water-absorbing agent in the water-absorbent sheet according to one embodiment of the present invention is preferably 30 to 50g/g, more preferably 31 to 45g/g, and still more preferably 32 to 42g/g. By doing so, excellent results are exhibited in the evaluation of the specific reflux amount.
The CRC of the first particulate water-absorbing agent in the water-absorbent sheet according to one embodiment of the present invention is preferably 30 to 50g/g, more preferably 31 to 48g/g, and still more preferably 32 to 45g/g. By doing so, excellent results are exhibited in the evaluation of the specific reflux amount.
The lower limit of CRC of the particulate water-absorbing agent in the water-absorbent sheet according to one embodiment of the present invention (CRC of the mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent) is preferably 30g/g or more, more preferably 32g/g or more, and still more preferably 33g/g or more. By doing so, excellent results are exhibited in the evaluation of the specific reflux amount. The upper limit is preferably 48g/g or less, more preferably 45g/g or less.
“AAP”(ERT442.2-02)
"AAP" is an abbreviation for adsorption age Pressure, and means a water Absorption capacity under Pressure of the particulate water absorbing agent. The method specifically comprises the following steps: the particulate water-absorbing agent was adjusted to 0.9g at 2.06kPa (21 g/cm) 2 0.3 psi) under a load, and the water absorption capacity after swelling for 1 hour in a significant excess of a 0.9 mass% aqueous sodium chloride solution (unit: g/g). In addition, ERT442.2-02 is expressed as Absorption Under Pressure (AUP), which is substantially the same.
The second particulate water-absorbing agent in the water-absorbent sheet according to an embodiment of the present invention preferably has aap2.1kpa in a range of 18 to 40g/g, more preferably 23 to 34g/g, and still more preferably 24 to 33g/g. By doing so, excellent results will be exhibited in the evaluation of the specific reflux amount.
The first particulate water-absorbing agent in the water-absorbent sheet according to an embodiment of the present invention preferably has aap2.1kpa of 18 to 40g/g, more preferably 23 to 36g/g, and still more preferably 24 to 34g/g. By doing so, excellent results are exhibited in the evaluation of the specific reflux amount.
"Water absorption time by Vortex flow (Vortex)"
The term "Vortex flow (Vortex)" in the present invention means a water absorption time obtained according to "test method of water absorption rate of super absorbent resin" described in JIS K7224-1996. The specific determination method comprises the following steps: to 1000 parts by weight of a 0.90 wt% aqueous sodium chloride solution prepared in advance, 0.02 part by weight of edible blue No. 1 as a food additive was added, and the liquid temperature was adjusted to 30 ℃.50 ml of a blue-colored 0.90% by weight aqueous sodium chloride solution was weighed into a 100ml beaker, and 2.00g of a particulate water-absorbing agent was charged while stirring at 600rpm with a cylindrical stirrer having a length of 40mm and a thickness of 8mm, and the water absorption time (sec) was measured. The end point was measured as the water absorption time (seconds) based on the standard described in "description of Water absorption Rate test method for super absorbent resin" in JIS K7224-1996, the time until the water-absorbing agent absorbed physiological saline and the stirring piece was covered with the test solution.
In the water-absorbent sheet according to an embodiment of the present invention, the second particulate water-absorbing agent preferably has a water absorption time as determined by the vortex method of not less than 10 seconds, more preferably not less than 20 seconds, still more preferably not less than 25 seconds, and still more preferably not less than 28 seconds. In the water-absorbent sheet according to an embodiment of the present invention, the upper limit of the water absorption time of the second particulate water-absorbing agent, which is determined by the vortex method, is not particularly limited, and may be, for example, 100 seconds or less, 80 seconds or less, or 60 seconds or less, from the viewpoint of preventing liquid leakage.
In the water-absorbent sheet according to an embodiment of the present invention, the first particulate water-absorbing agent preferably has a water absorption time as determined by the vortex method of not less than 10 seconds, more preferably not less than 20 seconds, still more preferably not less than 25 seconds, and still more preferably not less than 28 seconds. By significantly extending the water absorption time of the first particulate water-absorbing agent as determined by the vortex method, the diffusibility in the surface direction can be improved, the water absorption volume of the first particulate water-absorbing agent can be effectively utilized, and excellent results can be obtained in the evaluation of the specific reflux amount. In addition, the following technical effects are achieved: after the liquid to be absorbed is introduced from the first substrate side, it is easy to transport to the second particulate water-absorbing agent, and the second particulate water-absorbing agent can be effectively utilized. In the water-absorbent sheet according to an embodiment of the present invention, the upper limit of the water absorption time of the first particulate water-absorbing agent, which is determined by the vortex method, is not particularly limited, and may be, for example, 100 seconds or less, 80 seconds or less, or 60 seconds or less, from the viewpoint of preventing liquid leakage. The water absorption time determined by the vortex method can be controlled by the specific surface area of the water-absorbent resin particles, etc. When the specific surface area of the water-absorbent resin particles is large, the water absorption time tends to be short.
“GPR”
Gel Permeation Rate (GPR)
In the present specification, "liquid permeability" of the particulate water-absorbing agent means fluidity by liquid between swollen gel particles under load. As an index thereof, the Gel Permeation Rate (GPR) can be used. The Gel Permeation Rate (GPR) of the particulate water-absorbing agents (first particulate water-absorbing agent and second particulate water-absorbing agent) included in the water-absorbent sheet according to one embodiment of the present invention is measured by the following procedure with changing the measurement conditions in accordance with the Saline Flow Conductivity (SFC) test described in U.S. Pat. No. 5849405.
As an apparatus for measurement, an apparatus 400 shown in fig. 2 was used. The apparatus 400 is generally comprised of a container 410 and a canister 420. The container 410 is provided with a case 411 (inner diameter 6 cm), and a swollen gel 414 (product obtained by absorbing water in the particulate water-absorbing agent) and an introduction liquid 423 can be accommodated in the case 411. Further, by fitting the piston 412 to the cartridge 411, the pressure can be applied to the swollen gel 414. Metal meshes 413a and 413b (No. 400 stainless steel metal mesh, 38 μm mesh) are attached to the bottom surface of the case 411 and the bottom surface of the piston 412 so that the swollen gel 414 (and the particulate water-absorbing agent) cannot pass through. Here, a 0.90 wt% aqueous sodium chloride solution was used for the liquid 423. Liquid 423 is accumulated in tank 420. Liquid 423 is introduced into the cartridge 411 through an L-shaped tube 422 with a stopcock. Further, a glass tube 421 is inserted into the tank 420, and the inside of the glass tube 421 is filled with air. This allows the lower end of the glass tube 421 to be equal to the liquid level in the cartridge 411. That is, the liquid surface in the cartridge 411 can be kept constant while the liquid surface of the liquid 423 in the tank 420 is located above the lower end of the glass tube 421. In this measurement, the height difference between the lower liquid surface of the liquid 423 in the tank 420 (i.e., the lower end of the glass tube 421) and the bottom surface of the swollen gel 414 was set to 4cm. In other words, the liquid 423 having a predetermined hydrostatic pressure can be introduced into the cartridge 411 by the apparatus 400. Since the piston 412 is opened with the hole 415, the liquid 423 flows through the hole 415, further flows through the layer of the swollen gel 414, and flows out to the outside of the cartridge 411. The container 410 is placed on a stainless steel mesh 431 which does not prevent the passage of the liquid 423. Therefore, the liquid 423 flowing out of the cartridge 411 is finally collected in the trap container 432. The amount of the liquid 423 collected in the trap container 432 can be weighed by a top-loading scale 433.
Specific methods for measuring the Gel Permeation Rate (GPR) are shown below. The following operations were carried out at room temperature (20 to 25 ℃).
(1) The particulate water-absorbing agent (0.900 g) was uniformly charged into the cartridge 411.
(2) The particulate water-absorbing agent was allowed to absorb a liquid (0.00 to 0.90 mass% (0.9 mass% in the present application)) in an aqueous sodium chloride solution for 60 minutes without being pressurized, thereby preparing a swollen gel 414.
(3) A piston was placed on the swollen gel 414 so as to be in a pressurized state of 0.3psi (2.07 kPa).
(4) While maintaining the hydrostatic pressure at 3923dyne/cm 2 While introducing the liquid 423 into the cartridge 411, the layer of the swollen gel 414 is passed through.
(5) The amount of liquid 423 passed through the layer of swollen gel 414 was recorded at 5 second intervals for 3 minutes. That is, the flow rate of the liquid 423 passing through the layer of the swollen gel 414 was measured. The dish balance 433 and a computer (not shown) were used for the measurement.
(6) The flow rates 1 to 3 minutes after the start of the flow of the liquid 423 were averaged to calculate the Gel Permeation Rate (GPR) [ g/min ].
In the water-absorbent sheet according to an embodiment of the present invention, the first particulate water-absorbing agent has a GPR of more preferably 20g/min or more, more preferably 35g/min or more, still more preferably 45g/min or more, yet more preferably 50g/min or more, yet more preferably 55g/min or more, yet more preferably 75g/min or more, yet more preferably 95g/min or more, yet more preferably 118g/min or more, yet more preferably 150g/min or more, yet more preferably 160g/min or more, yet more preferably 165g/min or more, and yet more preferably 175g/min or more. In this embodiment, the liquid to be absorbed is easily transported to the second particulate water-absorbing agent after being introduced from the first substrate side, and the second particulate water-absorbing agent can be effectively used, and excellent results are exhibited in the evaluation of the specific reflux amount. In the water-absorbent sheet according to an embodiment of the present invention, the upper limit of GPR of the first particulate water-absorbing agent is not particularly limited, and is 500g/min or less, 400g/min or less, or 300g/min or less from the viewpoint of preventing leakage.
In the water-absorbent sheet according to an embodiment of the present invention, the GPR of the second particulate water-absorbing agent is 45g/min or more. In the present invention, since the intermediate sheet having a transmittance of less than 60% is used, if the GPR of the second particulate water-absorbing agent is less than 45g/min, the desired problem of the present invention cannot be solved. More specifically, the particulate water-absorbing agent can be distributed widely in the intermediate sheet and the liquid diffusibility can be improved as long as the transmittance is 60% or more, but if the transmittance is less than 60%, the liquid diffusibility by the intermediate sheet becomes insufficient. Thus, in the present invention, the second particulate water-absorbing agent takes on the diffusibility of the liquid. That is, after the liquid to be absorbed is introduced into the second particulate water-absorbing agent by the first particulate water-absorbing agent, the second particulate water-absorbing agent, which can have a so-called can-like action, appropriately diffuses the liquid to effectively utilize the water absorption area, and the second particulate water-absorbing agent absorbs the liquid without falling down, so that the desired object of the present invention can be solved even if the transmittance is less than 60%. In the water-absorbent sheet according to an embodiment of the present invention, the GPR of the second particulate water-absorbing agent may be 45g/min or more, preferably 46g/min or more, more preferably 47g/min or more, preferably 50g/min or more, further preferably 55g/min or more, further preferably 75g/min or more, further preferably 95g/min or more, further preferably 118g/min or more, more preferably 150g/min or more, more preferably 160g/min or more, further preferably 165g/min or more, and further preferably 175g/min or more. By having such a lower limit, gel blocking is suppressed, and the diffusibility is improved, so that liquid is easily absorbed by the absorbent body. In the water-absorbent sheet according to an embodiment of the present invention, the upper limit of GPR of the first particulate water-absorbing agent is not particularly limited, and is 500g/min or less, 400g/min or less, or 300g/min or less from the viewpoint of preventing leakage.
In the water-absorbent sheet according to one embodiment of the present invention, the GPR of the second particulate water-absorbing agent is 50g/min or more, the content of the first particulate water-absorbing agent in the water-absorbent sheet is 0.4 or less relative to the content of the second particulate water-absorbing agent, and the transmittance exceeds 40%. By adopting this embodiment, the desired effects of the present invention can be further enhanced. In the present embodiment, the GPR of the first particulate water-absorbing agent is 50g/min or more. By adopting this embodiment, the desired effects of the present invention can be further enhanced.
Degraded soluble component "
The upper limits of the deteriorated soluble component of the first particulate water-absorbing agent and the deteriorated soluble component of the second particulate water-absorbing agent in the water-absorbent sheet according to an embodiment of the present invention are not particularly limited, and each independently is preferably less than 50%, more preferably 25% or less, and further preferably 15% or less, from the viewpoint of leakage during long-term use. The lower limit is not particularly limited, and is, for example, about 1% or more, 3% or more, or 5% or more, from the viewpoint of liquid leakage during long-term use. The method for measuring the deteriorated soluble component is as follows.
L-ascorbic acid was added to a previously prepared physiological saline to a concentration of 0.05 mass% to prepare a deterioration test solution. Specifically, 0.50g of L-ascorbic acid was dissolved in 999.5g of physiological saline to prepare a deterioration test solution. 25ml of the deterioration test liquid was added to a glass beaker container having a capacity of 250ml, and 1.0g of the particulate water-absorbing agent was added thereto, thereby forming a swollen gel. The vessel was sealed with a lid, and the swollen gel was allowed to stand at 37 ℃ for 16 hours in an atmosphere (ETAC trademark, HISPEC series, HT320, 37 ℃ and scale of air speed variable device) of 37 ℃. After 16 hours, 175ml of physiological saline and a cylindrical stirrer having a length of 30mm and a thickness of 8mm were put in, and after deterioration, the mixture was stirred at 500rpm for 10 minutes to extract from the aqueous gel.
A measurement solution was prepared by weighing 20.0g of a filtrate obtained by filtering the extract with a filter paper (product name of ADVANTEC Toyo Co.) (JIS P3801, no.2, thickness of 0.26mm, and retained particle size of 5 μm), and further adding 30g of physiological saline.
The measurement method is as follows: the physiological saline was titrated with 0.1N NaOH aqueous solution to pH10, and thereafter, with 0.1N HCl aqueous solution to pH2.7, to obtain blank titration amounts ([ bNaOH ] ml, [ bHCl ] ml). The same titration procedure was also performed on the measurement solution to obtain the titration amounts ([ NaOH ] ml, [ HCl ] ml). For example, in the case of a known amount of the particulate water-absorbing agent composed of acrylic acid and its sodium salt, the soluble component in the particulate water-absorbing agent can be calculated by the following calculation formula based on the average molecular weight of the monomer and the titration amount obtained by the above operation:
deteriorated soluble component (% by mass) =0.1 × (average molecular weight) × 200 × 100 × ([ HCl ] - [ bHCl ])/1000/1.0/20.0
In the case of unknown amounts, the average molecular weight of the monomer was calculated using the neutralization rate obtained by titration.
Surface tension "
Surface tension is a parameter that expresses the work (free energy) required to increase the surface area of a solid or liquid per unit area. The surface tension referred to in this application means: surface tension of an aqueous solution obtained when the particulate water-absorbing agent was dispersed in a 0.90 mass% aqueous sodium chloride solution. The surface tension of the water absorbing agent is measured by the following procedure. That is, 50ml of physiological saline adjusted to 20 ℃ was put into a well-washed 100ml beaker, and the surface tension of the physiological saline was first measured using a surface tensiometer (K11 automatic surface tensiometer manufactured by KRUSS corporation). Then, 0.5g of a fluororesin rotor having a length of 25mm and sufficiently washed, and 0.5g of a particulate water-absorbing agent were put into a beaker containing physiological saline adjusted to 20 ℃ and subjected to surface tension measurement, and stirred at 500rpm for 4 minutes. After 4 minutes, the stirring was stopped, and after the hydrous particulate water-absorbing agent was 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 adopted, and the plate was cleaned with deionized water and heated and cleaned with a gas burner before each measurement. In the water-absorbent sheet according to one embodiment of the present invention, the surface tension of at least one of the first particulate water-absorbing agent and the second particulate water-absorbing agent is preferably 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 the following order. In the application of the particulate water-absorbing agent to the water-absorbing sheet, the influence of the surface tension is more likely to be exerted than in the conventional paper diaper, and the amount of the backflow in the paper diaper can be reduced by satisfying the above conditions with respect to the surface tension. In the water-absorbent sheet according to one embodiment of the present invention, the upper limit of the surface tension of at least one of the first particulate water-absorbing agent and the second particulate water-absorbing agent is not particularly limited, and is 73mN/m or less.
Particle shape "
In the water-absorbent sheet according to an embodiment of the present invention, at least one of the first particulate water-absorbing agent and the second particulate water-absorbing agent preferably includes particles in a randomly crushed shape as a particle shape. Here, the irregular crushed shape means crushed particles having an irregular shape. The irregular crushed shape can be easily fixed to the base material as compared with spherical particles obtained by reversed-phase suspension polymerization or gas-phase polymerization. The particulate water absorbing agent according to an embodiment of the present invention is preferably a pulverized product in aqueous solution polymerization. On the other hand, when the pulverization step is not performed, spherical particles or spherical particle granules obtained by, for example, reverse phase suspension polymerization or droplet polymerization such as spray polymerization of a polymerization monomer are not randomly crushed. In the embodiment of the present invention, if the particulate water-absorbing agent is irregularly crushed, the shape of the water-absorbing sheet can be more easily maintained than a water-absorbing agent having a high average circularity (for example, a spherical water-absorbing agent). In an embodiment of the present invention, the average circularity of at least one of the first particulate water-absorbing agent and the second particulate water-absorbing agent is preferably 0.70 or less, more preferably 0.60 or less, and still more preferably 0.55 or less.
The average circularity is calculated as follows. At least 100 particulate water-absorbing agents were randomly selected, and each particulate water-absorbing agent was photographed with an electron microscope (VE-9800, manufactured by keyence corporation) (magnification: 50 times), and an image of the particulate water-absorbing agent was obtained, and the circumference and the area of each particle were calculated using attached image analysis software. The circularity of each particle was obtained by the following formula, and the average value of the obtained values was calculated as the average circularity:
[ mathematical formula 1]
Circularity =4 × pi × area/(circumference) 2
The preferable order of the lower limit of the content of the particulate water-absorbing agent per unit volume of the water-absorbing sheet in the water-absorbing sheet according to one embodiment of the present invention is 50mg/cm 3 Above, 51mg/cm 3 Above, 52mg/cm 3 Above, 53mg/cm 3 Above, 54mg/cm 3 Above, 55mg/cm 3 Above, 57mg/cm 3 Above, 59mg/cm 3 Above, 60mg/cm 3 The above. In addition, the upper limit of the content of the particulate water-absorbing agent per unit volume of the water-absorbing sheet according to one embodiment of the present invention is not particularly limited, and is actually 600mg/cm 3 Hereinafter, it is preferably 500mg/cm 3 Hereinafter, more preferably 400mg/cm 3 Hereinafter, it is more preferably 300mg/cm 3 Hereinafter, more preferably 150mg/cm 3 The following. When the content of the particulate water-absorbing agent is in the above range, the water-absorbing sheet can exhibit the effects of the present invention with high efficiency. The content of the particulate water-absorbing agent per unit volume of the water-absorbing sheet used in the examples of the present application was 50mg/cm 3 The above.
The method for producing the particulate water-absorbing agent is not particularly limited as long as it is a method for producing a water-absorbing agent having desired physical properties, and the particulate water-absorbing agent can be suitably produced, for example, by referring to the publications described in examples.
In addition, the content weight of the first particulate water-absorbing agent in the water-absorbent sheet according to an embodiment of the present invention is preferably 1.0 or less, more preferably 0.5 or less, and still more preferably 0.4 or less, with respect to the content weight of the second particulate water-absorbing agent. When the content of the second particulate water-absorbing agent is equal to, preferably larger than, the content of the first particulate water-absorbing agent, it is considered that the second particulate water-absorbing agent having a function such as a so-called tank functions effectively, and the specific reflux amount evaluation is excellent.
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 first substrate is a water-permeable sheet located on a side where a liquid to be absorbed is introduced, and the water-absorbent layer comprises: an intermediate sheet; a first particulate water-absorbing agent which is locally present on one surface side of the first base material which faces the second base material; and a second particulate water-absorbing agent which is locally present on a side of the second substrate opposite to the first substrate, wherein a transmittance of a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent with respect to the intermediate sheet is less than 60%, a GPR of the second particulate water-absorbing agent is 45.0g/min or more, and a nonwoven fabric transmittance index (NPI) of the water-absorbing sheet is less than 60%. According to this embodiment, with this configuration, even if the liquid is intermittently introduced a plurality of times (particularly 3 times or more) in a state where the liquid is not pressurized and the amount of liquid introduced increases, the amount of backflow can be significantly reduced.
In one embodiment of the present invention, the upper limit of the nonwoven fabric transmission index (NPI) is not particularly limited, but is preferably 55 or less, and more preferably 50 or less. By having such a lower limit, the desired effects of the present invention can be exerted efficiently. In one embodiment of the present invention, the lower limit of the nonwoven fabric transmittance index (NPI) is not particularly limited, but is preferably 10 or more, more preferably 20 or more, and still more preferably 30 or more.
The nonwoven fabric transmittance index (NPI) described in the present specification is represented by the following formula:
[ mathematical formula 2]
-90-1.05×C-39.3×B+3.15×A-0.289×D-0.0472×(C-52.1)×(D-369)+3.62×(B-3.48)×(A-142)-0.0142×(A-142)×(D-369)
Here, A is a specific surface area (mm) of an intermediate sheet (e.g., nonwoven fabric) measured by X-ray CT -1 ) B is the thickness (mm) of the intermediate sheet (e.g., nonwoven fabric), and C is the basis weight (g/m) of the intermediate sheet (e.g., nonwoven fabric) 2 ) And D is an average particle diameter (μm) (D50) of the particulate water-absorbing agent.
Here, the specific surface area of the intermediate sheet is determined by analyzing an image captured by X-ray CT with analysis software as described below.
< imaging by X-ray CT >
The measurement was carried out on a sample (thickness was not changed) obtained by cutting the intermediate sheet into a square having a length of 10mm and a width of 10mm by using the MICRO FOCUS X-ray CT system instexIO SMX-100CT manufactured by Shimadzu corporation. The measurement conditions are as follows.
Image lateral dimension (pixel): 512
Image longitudinal dimension (pixel): 512
X-ray tube voltage (kV): 40
X-ray tube current (μ a): 50
English size (inch): 4.0
X-ray filter: is free of
SDD (distance of focus of X-ray source from X-ray detector) (mm): 500
SRD (distance between the focal point of the X-ray source and the rotation center of the measurement sample) (mm): 40
Scan mode 1: CBCT
Scan mode 2: conventional scanning
Scan angle: full scan
Number of views: 1200
Average number: 5
Smoothing: YZ
Layer thickness (mm): 0.012
Layer spacing (mm): 0.010
Division number: 50
BHC data: is free of
Clear mode: is provided with
FOV XY (maximum imaging area XY) (mm): 5.0
FOV Z (maximum capture area Z) (mm): 1.5
Three-dimensional pixel size (mm/voxel): 0.010.
< calculation of specific surface area >
The X-ray CT imaging data was analyzed by the following procedure using analysis software TRI/3D-PRT-LRG manufactured by Ratoc System Engineering.
1. Selecting particle measurement >3D particle > particle separation > giant particle separation from the menu. EV panels, BC panels, EVC panels, large particle separation panels are shown.
2. L-W is selected from the Binarize list of the EVC panel, and a circular measurement target region is selected by changing the L value. This process is applied to all layer images (selecting a measurement region having a cylindrical shape as a whole) by pressing "Execute". Press "ROI OK" of the macro-particle separation panel.
3. The fiber alone was selected by selecting L-W in the Binarize list of the EVC panel and setting the L value to 37580. Press "Execute". Select bD of BC panel, press "safekeeping".
4. A Labeling list is selected in the 3D list of the EVC panel, volume is selected, MAX is performed (displayed as 3dlabel count =1 by this operation).
5. Selecting particle measurement from menu > Void in 3D particle > post-separation measurement. The measurement panel is shown after separation. The inspection for edge particle removal was turned off, the inspection was performed in the surface area calculation of the measurement items, the Void calculation was selected, binary 5ch was selected with the calculation ROI designation, and the folder for storing data was selected by pressing "register OK". The calculation process is performed by pressing "execute latest registered data".
6. From the calculation results, the specific surface area was calculated by the following formula.
Specific surface area (mm) -1 ) = total particle surface area (mm) 2 ) V (total volume of granules (mm) 3 )
Although the calculation software is expressed as "particles" in terms of its configuration, the measurement result is actually a result of the measurement of the fiber, and there is no problem in the measurement/calculation.
[ 3. Method for producing Water-absorbent sheet ]
A method for producing a water-absorbent sheet according to an embodiment of the present invention includes at least one of the following steps: (1) A step of scattering the first particulate water-absorbing agent on the first base material; (2) A step of spraying the second particulate water-absorbing agent on the second base material; and (3) a step of scattering the first particulate water-absorbing agent and/or the second particulate water-absorbing agent in the intermediate sheet. As an example of a more specific production method, the following production methods (a) to (d) can be mentioned.
(a) The first particulate water-absorbing agent (and preferably the adhesive) is uniformly dispersed on the first substrate. An intermediate sheet is superposed thereon and crimped. Further, the second particulate water-absorbing agent (and preferably an adhesive) is uniformly dispersed on the surface of the intermediate sheet on the side not facing the first particulate water-absorbing agent. The intermediate sheet is superposed thereon and pressure-bonded (preferably under heating conditions in which the hot-melt adhesive melts or under a state in which the hot-melt adhesive melts).
(b) The second particulate water-absorbing agent is uniformly dispersed on the intermediate sheet. Further, an adhesive is spread on the second base material. The surface of the intermediate sheet on which the second particulate water-absorbing agent is dispersed and the surface of the second base material on which the adhesive is dispersed are pressure-bonded. Next, in the intermediate sheet after pressure bonding, the first particulate water-absorbing agent is uniformly dispersed on the surface opposite to the surface on which the second particulate water-absorbing agent is dispersed. Further, an adhesive is spread on the first base material. The surface of the intermediate sheet on which the first particulate water-absorbing agent is dispersed and the surface of the first base material on which the adhesive is dispersed are pressure-bonded. The pressure bonding is preferably performed under a heating condition that the hot melt adhesive is melted or in a state that the hot melt adhesive is melted.
(c) An adhesive is dispensed on the second substrate. Then, the second particulate water-absorbing agent is uniformly dispersed thereon. Subsequently, an intermediate sheet is placed thereon and pressure-bonded. Next, an adhesive was spread on the surface of the intermediate sheet not facing the second particulate water-absorbing agent. Then, the first particulate water-absorbing agent was uniformly dispersed thereon. Next, a first base material is placed thereon and pressure-bonded. The pressure bonding is preferably performed under a heating condition that the hot melt adhesive is melted or in a state that the hot melt adhesive is melted.
(d) An adhesive is dispensed on the second substrate. Then, the second particulate water-absorbing agent was uniformly dispersed thereon. Subsequently, an intermediate sheet is placed thereon and pressure-bonded. Next, the first particulate water-absorbing agent was uniformly dispersed on the surface of the intermediate sheet not facing the second particulate water-absorbing agent. Further, an adhesive is spread on the first base material. The surface of the intermediate sheet on which the first particulate water-absorbing agent is dispersed and the surface of the first base material on which the adhesive is dispersed are pressure-bonded. The pressure bonding is preferably performed under a heating condition that the hot melt adhesive is melted or in a state that the hot melt adhesive is melted.
As a step other than the above, embossing may be performed on the water-absorbent sheet for the purpose of improving the touch of the water-absorbent sheet and enhancing the liquid absorption performance. The embossing may be performed simultaneously when the first substrate and the second substrate are pressure-bonded, or may be performed after the sheet is produced.
In the method for producing a water-absorbent sheet according to one embodiment of the present invention, additives (deodorizing agent, fiber, antibacterial agent, gel stabilizer, and the like) may be appropriately added. The amount of the additive to be blended is preferably 0 to 50% by mass, and more preferably 0 to 10% by mass, based on the mass of the particulate water-absorbing agent. In the above production method, the particulate water-absorbing agent in which the additive is mixed in advance may be used, or the additive may be added in the middle of the production process.
The size of the produced water-absorbent sheet can be appropriately designed. Generally, the width is 3 to 10m and the length is 10 to 1000m (in the case of a continuous sheet or roll). The produced water-absorbent sheet is cut according to the purpose (size of the absorbent body to be used) and used.
In addition to the above examples, a method for producing a water-absorbent sheet is disclosed in, for example, the following patent documents: international publication nos. 2012/174026, 2013/078109, 2015/041784, 2011/117187, 2012/001117, 2012/024445, 2010/004894, 2010/004895, 2010/076857, 2010/373, 2010/113754, 082635, 2011/043256, 2011/086841, 2011/086842, 2011/086843 International publication Nos. 2011/086844, 2011/117997, 2011/118409, 2011/136087, 2012/043546, 2013/099634, 2013/099635, 2010-115406, 2002-345883, 6-315501, 6-190003, 6-190002, 6-190001, 2-252558, 2-252560, and 2-252561. The production methods of the water-absorbent sheets disclosed in these documents can be appropriately referred to.
In the water-absorbent sheet according to one embodiment of the present invention, as a method for fixing the substrates to each other or the substrate and the particulate water-absorbing agent, (i) an adhesive may be used and pressure-bonded as necessary; (ii) Various binders dissolved or dispersed in water, water-soluble polymers, or solvents; (iii) The substrates may also be heat sealed to each other at the melting point of the material of the substrates themselves. Preferably using an adhesive.
The adhesive used may be a solution type, but from the viewpoints of the complexity of removing the solvent, the problem of residual solvent, and the 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 separately used in the production process of the water-absorbent sheet. The form and melting point of the hot melt adhesive may be appropriately selected, and the hot melt adhesive may be in the form of granules, fibers, nets, films, or liquids that are melted by heating. The melting temperature or softening point of the hot-melt adhesive is 50 to 200 ℃, preferably 60 to 180 ℃. When the particulate adhesive is used, the particulate adhesive having a particle diameter of about 0.01 to 2 times, 0.02 to 1 times, or 0.05 to 0.5 times the average particle diameter of the particulate water-absorbing agent is used.
The following examples are given as a method of using a hot melt adhesive in the production of a water-absorbent sheet according to an embodiment of the present invention. The water-absorbent sheet can be produced by uniformly spreading a mixture of the particulate water-absorbing agent and the hot-melt adhesive on a base material (for example, nonwoven fabric), laminating the other base material, and then thermally pressing the laminated base material at a temperature near the melting temperature of the hot-melt adhesive.
The hot-melt adhesive used in the present invention may be suitably selected, and preferably 1 or more selected from ethylene-vinyl acetate copolymer adhesives, styrene elastomer adhesives, polyolefin adhesives, polyester adhesives, and the like may be suitably used.
Specifically, examples of the polyolefin adhesive include polyethylene, polypropylene, and atactic polypropylene, examples of the styrene 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), styrene-butadiene rubber (SBR), and copolymerized polyolefin, examples of the polyester adhesive include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and copolymerized polyester, 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.
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 includes an adhesive, the adhesive is preferably a hot-melt adhesive, and the amount (content) of the adhesive (e.g., hot-melt adhesive) is preferably more than 0 and 3.0 times or less, and more preferably 0.05 to 2.0 times the total mass of the first particulate water-absorbing agent and the second particulate water-absorbing agent. If the content of the adhesive (particularly, hot-melt adhesive) is too large, not only is it disadvantageous in terms of cost and quality of the water-absorbent sheet (increase in quality of the diaper), but also the particulate water-absorbing agent is subjected to swelling restriction, and the water absorption capacity of the water-absorbent sheet may be reduced.
[ 4. Absorbent article ]
An absorbent article according to an embodiment of the present invention has a structure in which the water-absorbent sheet described in [ 2] is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet. Accordingly, the present invention provides an absorbent article in which the water-absorbent sheet is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet, and the liquid-permeable sheet is positioned on the first base material side and the liquid-impermeable sheet is positioned on the second base material side. Specific examples of the absorbent article include disposable diapers, incontinence pads, sanitary napkins, pet sheets, food drip sheets, and cable water stoppers. By adopting the above-described configuration, an excellent result is obtained in the evaluation of the specific reflux amount.
As the liquid-permeable sheet and the liquid-impermeable sheet, sheets known in the art of absorbent articles can be used without particular limitation. Further, the absorbent article can be manufactured by a known method.
[ examples ]
The present invention will be described in more detail with reference to the following examples and comparative examples. The technical scope of the present invention is not limited to the following examples. In the following examples, unless otherwise specified, the operation was carried out under conditions of room temperature (25 ℃ C.)/relative humidity of 40 to 50% RH.
< production example >
Particulate water-absorbing agents (1) to (7) of polyacrylic acid (salt) resin were obtained by referring to production examples, and comparative examples described in the following patents and appropriately adjusting CRC by the amount of internal crosslinking agent. The physical properties of the obtained particulate water-absorbing agent are shown in table 1.
International publication No. 2014/034897
International publication No. 2017/170605
International publication No. 2016/204302
International publication No. 2014/054656
International publication No. 2015/152299
International publication No. 2018/062539
International publication No. 2012/043821.
[ production example of acrylic acid ]
Commercially available acrylic acid (acrylic acid dimer 2000ppm, acetic acid 500ppm, propionic acid 500ppm, p-methoxyphenol 200 ppm) was supplied to the bottom of a high boiling impurity separation column having a 50-stage baffleless perforated plate, and distilled with a reflux ratio of 1 to remove maleic acid, dimer (acrylic acid dimer) formed from acrylic acid, and the like, followed by further crystallization to obtain acrylic acid (acrylic acid dimer 20ppm, acetic acid 50ppm, propionic acid 50ppm, furfural 1ppm or less, protoanemonin 1ppm or less), and further, after distillation, p-methoxyphenol 50ppm was added.
[ preparation of aqueous sodium acrylate solution ]
1390g of the above acrylic acid was neutralized with 48% caustic soda at 20 to 40 ℃ to obtain a 100% neutralized aqueous solution of sodium acrylate at 37% concentration according to example 9 of U.S. Pat. No. 5,5210298.
< particulate Water-absorbing agent 1>
5.71g of polyethylene glycol diacrylate (average molar number of addition of ethylene oxide is 9) was dissolved in 5500g (monomer concentration: 33.0 mass%) of an aqueous solution of sodium acrylate having a neutralization degree of 73 mol%, which was obtained by mixing acrylic acid obtained in the above production example of acrylic acid, an aqueous solution of sodium acrylate obtained by the above production method of a sodium acrylate aqueous solution, and deionized water, to prepare a reaction solution. Then, the reaction solution was supplied to a reactor formed by capping a jacketed stainless double-arm type kneader having 2 sigma-type blades and an internal volume of 10L, and the system was replaced with nitrogen while maintaining the reaction solution at 30 ℃. Subsequently, 26.78g of a 10 mass% aqueous solution of sodium persulfate and 32.96g of a1 mass% aqueous solution of L-ascorbic acid were added while stirring the reaction mixture, and as a result, polymerization was started after about 1 minute. 40 minutes after the start of the polymerization, 184.3g of fine water-absorbent resin powder having a particle size of 150 μm or less was added thereto, and the resultant mixture was disintegrated by rotating the blade of the kneader at a high speed (130 rpm) for 10 minutes, and then the hydrogel polymer was taken out. The resulting hydrogel polymer is subdivided into particles of about 1 to 2 mm. The finely divided hydrogel polymer was spread on a 50-mesh (mesh size: 300 μm) metal gauze and dried with hot air at 175 ℃ for 65 minutes. Next, the dried product was pulverized by a roll mill, and further classified and mixed by a metal mesh having a mesh opening of 600 μm, thereby obtaining a water-absorbent resin (1-1) having an average particle diameter of 350 μm in a randomly crushed state.
100 parts by mass of the water-absorbent resin (1-1) thus obtained was mixed by spraying 3.83 parts by mass of an aqueous solution of a surface-crosslinking agent containing 0.03 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of 1, 4-butanediol, 0.5 parts by mass of propylene glycol, and 3.0 parts by mass of water. The above mixture was heat-treated at a heat medium temperature of 210 ℃ for 40 minutes using a paddle type mixing heat-treating machine to obtain a surface-crosslinked water-absorbent resin (1-2). 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (1-2) was mixed with 1.0 part by mass of water by spraying, cured at 60 ℃ for 1 hour in a closed vessel, and then passed through a sieve having a mesh opening of 710 μm to obtain a water-absorbent resin (1-3). A water-absorbent resin obtained by adding 0.3 part by mass of Aerosil200 (hydrophilic amorphous silica, manufactured by AEROSIL Co., ltd., japan) to and mixing with the water-absorbent resin (1-3) was used as the particulate water-absorbing agent (1).
< particulate Water-absorbing agent 2>
In 5500g (monomer concentration: 33.0 mass%) of an aqueous solution of sodium acrylate having a neutralization degree of 73 mol%, which was obtained by mixing acrylic acid obtained in the above production example of acrylic acid, an aqueous sodium acrylate solution obtained by the above production method of an aqueous sodium acrylate solution using the acrylic acid, and deionized water, 4.17g of polyethylene glycol diacrylate (average molar number of addition of ethylene oxide: 9) was dissolved to prepare a reaction solution. Then, the reaction solution was supplied to a reactor formed by capping a jacketed stainless double-arm kneader having 2 sigma-type blades and an internal volume of 10L, and the system was purged with nitrogen while maintaining the reaction solution at 30 ℃. Subsequently, 26.78g of a 10 mass% aqueous solution of sodium persulfate and 32.96g of a1 mass% aqueous solution of L-ascorbic acid were added while stirring the reaction mixture, and as a result, polymerization was started after about 1 minute. 40 minutes after the start of the polymerization, 181.5g of a fine water-absorbent resin powder having a particle size of 150 μm or less was added, and the gel was disintegrated by rotating the blade of the kneader at a high speed (130 rpm) for 10 minutes, and then the hydrogel polymer was taken out. The resulting hydrogel polymer is subdivided into particles of about 1 to 2 mm. The finely divided hydrogel polymer was spread on a 50-mesh (mesh size: 300 μm) metal gauze and dried with hot air at 175 ℃ for 65 minutes. Next, the dried product was pulverized by a roll mill, and further classified and mixed by a metal mesh having a mesh opening of 600 μm, thereby obtaining a water-absorbent resin (2-1) having an average particle diameter of 350 μm in a randomly pulverized state.
100 parts by mass of the water-absorbent resin (2-1) thus obtained was mixed with 3.83 parts by mass of an aqueous solution of a surface-crosslinking agent containing 0.03 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of 1, 4-butanediol, 0.5 parts by mass of propylene glycol, and 3.0 parts by mass of water by spraying. The mixture was subjected to heat treatment at a heat medium temperature of 195 ℃ for 40 minutes using a paddle type mixing heat treatment machine to obtain a surface-crosslinked water-absorbent resin (2-2). 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (2-2) was mixed with 1.0 part by mass of water by spraying, cured at 60 ℃ for 1 hour in a closed vessel, and then passed through a sieve having a mesh opening of 710 μm to obtain a water-absorbent resin (2-3). A water-absorbent resin obtained by adding and mixing 0.3 part by mass of Aerosil200 (hydrophilic amorphous silica, manufactured by AEROSIL Co., ltd., japan) to the water-absorbent resin (2-3) was used as the particulate water-absorbing agent (2).
[ removal of Water-absorbent resin from commercial Disposable diaper 1]
The water-absorbent resin was taken out from a commercially available disposable diaper (Moony Air Fit (L., lot No. 201512163072), manufactured by Unicharm Co., ltd., 2016, 5 months). At the time of taking out, only the water-absorbent resin is taken out so as not to be mixed with cotton pulp or the like. The water-absorbent resin taken out was in the form of particles obtained by granulating spherical particles. This water-absorbent resin was used as the particulate water-absorbing agent (T1). The physical properties of the particulate water-absorbing agent (T1) are shown in table 1.
[ example ]
[ example 1]
9.0g (dispersion amount: 225 g/m) was uniformly dispersed on the surface of a hot-air nonwoven fabric (1) (corresponding to an intermediate sheet) which was cut into a length of 10cm and a width of 40cm and had an olefin as a main component and a thickness of 8.3mm under no load 2 ) The particulate water-absorbing agent (1) (corresponding to the second particulate water-absorbing agent).
Then, a nonwoven fabric (B) having a length of 10cm and a width of 40cm (comprising pulp fibers as a main component and having a thickness of 0.7mm under no load) was cut into a sheet, and the sheet was produced by an air-laying method, corresponding to a second substrate, and having a basis weight of 42g/m 2 ) The surface of (2) was uniformly dispersed with 0.3 to 0.5g (dispersion amount: 7.5-12.5 g/m 2 ) An adhesive containing styrene-butadiene rubber (spray coating 77, manufactured by 3M JAPAN Co.).
Next, the surface of the nonwoven fabric (1) on which the particulate water-absorbing agent is dispersed and the surface of the nonwoven fabric (B) on which the adhesive is dispersed are superposed so as to face each other (so as to be in contact with each other), and pressure-bonded.
Then, 3.0g (dispersion amount: 75 g/m) of nonwoven fabric (1) was uniformly dispersed on the surface of the side not facing the particulate water-absorbing agent 2 ) Particulate water-absorbing agent (1) (corresponding to the first particulate water-absorbing agent).
Further, 0.3 to 0.5g of an adhesive (spray coating 77, manufactured by 3M JAPAN) containing styrene-butadiene rubber was uniformly dispersed thereon (dispersion amount: 7.5 to 12.5 g/M) 2 ) The nonwoven fabric (A) (containing pulp fibers as a main component). The thickness without load was 0.7mm. Is made by an air-laid method. Corresponding to the first substrate. Weight per unit area: 42g/m 2 ) The surface of the nonwoven fabric (1) on which the particulate water-absorbing agent is dispersed and the surface of the nonwoven fabric (a) on which the adhesive is dispersed are superposed so as to face each other (so as to be in contact with each other), and are pressed and bonded under pressure. In this manner, a water-absorbent sheet (1) was obtained.
[ example 2]
In example 1, as shown in table 2, a water-absorbent sheet (2) was obtained by using a nonwoven fabric (2) (a hot-air nonwoven fabric containing olefin as a main component) instead of the nonwoven fabric (1) and using the particulate water-absorbing agent (2) instead of the particulate water-absorbing agent (1) corresponding to the second particulate water-absorbing agent.
[ example 3]
In example 1, a water-absorbent sheet (3) was obtained using the particulate water-absorbing agent (2) in place of the particulate water-absorbing agent (1) corresponding to the first particulate water-absorbing agent.
[ example 4]
In example 3, 6.0g (dispersion amount: 150 g/m) of the particulate water-absorbing agent (1) was used 2 ) 6.0g of the particulate water-absorbing agent (2) (dispersion amount: 150g/m 2 ) To obtain a water-absorbent sheet (4).
Comparative example 1
In example 1, a comparative water-absorbent sheet (1) was obtained by using the particulate water-absorbing agent (T1) in place of the particulate water-absorbing agent (1) corresponding to the second particulate water-absorbing agent.
The absorbent body of the water-absorbent sheet thus obtained was evaluated (measurement of the amount of back-flow), and the results are shown in Table 3.
[ example 5]
In example 2, as shown in table 2, a water-absorbent sheet (5) was obtained by using a nonwoven fabric (1) in place of the nonwoven fabric (2).
[ example 6]
In example 1, 6.0g (dispersion amount: 150 g/m) of the particulate water-absorbing agent (1) was used 2 ) Particulate water-absorbing agent (2) 6.0g (dispersion amount: 150g/m 2 ) To obtain a water-absorbent sheet (6).
[ example 7]
In example 1, as shown in table 2, a water-absorbent sheet (7) was obtained by using a nonwoven fabric (2) instead of the nonwoven fabric (1).
[ method for evaluating absorbent sheet, etc. ]
< inverse flow volume >
As shown in FIG. 3, a water-absorbent sheet cut into a length of 10cm and a width of 40cm was wrapped with a liquid-impermeable sheet having a length of 14cm and a width of 40cm so that an opening portion was formed at the upper portion. The water-absorbent sheet wrapped with the liquid-impermeable sheet was placed on a flat surface, and a liquid-injecting cylinder (fig. 4) was placed on the flat surface in the center of the water-absorbent sheet as shown in fig. 5. In this state, a funnel capable of pouring a liquid at a flow rate of 7 ml/sec was used, and 80g of a 0.9 wt% aqueous sodium chloride solution at 23 ℃ was poured into the liquid pouring cylinder (fig. 6). After 10 minutes from the introduction of the liquid, 20 pieces of filter paper (model No.2, manufactured by ADVANTEC; circular filter paper having a diameter of 110 mm) having a weight measured in advance were placed on the center of the water-absorbent sheet, and a circular weight (1200 g) having a diameter of 100mm was further placed thereon and held for 1 minute. After 1 minute, the weight was removed and the first pour (g) was determined from the weight gain of the filter paper. After 1 minute from the removal of the weight, the same operation was repeated (10 minutes from the introduction of the liquid, the filter paper and the weight (1200 g) were placed and held for 1 minute, after 1 minute, the weight was removed, and the flow rate was measured, and the second and third flow rates (g) were measured. The smaller the third pouring amount (g), the more excellent the evaluation was. The amount of backflow of each water-absorbent sheet and each comparative water-absorbent sheet are shown in table 2.
< method for measuring the transmittance of particulate absorbent >
A nonwoven fabric (1) (corresponding to an intermediate sheet) cut into 80mm in diameter was placed on a JIS standard SIEVE (The IIDA TESTING SIEVE: JIS Z8801-1 (2000) having an inner diameter of 80mm) having a mesh opening of 850 μm or a SIEVE corresponding to The JIS standard SIEVE as shown in FIG. 7, and The periphery was fixed with an adhesive tape (The area through which The pellets were allowed to pass was at least 75mm in diameter or more). In this case, the nonwoven fabric (1) is provided in the screen so that the nonwoven fabric (1) in contact with the nonwoven fabric (A) (first base material) faces upward in the form of the water-absorbent sheet. As the nonwoven fabric (1), one which is taken out of the water-absorbent sheet by the method described later can be used. 10.0g of the particulate water-absorbing agent was put on the nonwoven fabric (1) in the sieve, and the resultant mixture was shaken for 5 minutes at room temperature (20 to 25 ℃ C.) and a relative humidity of 50% RH by using a rotary hammer type sieve shaker (ES-65 type sieve shaker available from Kabushiki Kaisha, ltd.; rotation speed: 230rpm, impact number: 130 rpm). As the particulate water-absorbing agent, a water-absorbing agent taken out from a water-absorbent sheet by a method described later can be used. After shaking, the mass (W (g)) of the particulate water-absorbing agent passing through the nonwoven fabric (1) and the JIS standard sieve 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.
[ mathematical formula 3]
The particulate absorbent has a transmittance (mass%) = { W/10.0 }. Times 100 \ 8230wherein the formula (i)
The transmittance of the nonwoven fabric (2) was measured in the same manner.
[ method for taking out nonwoven fabric used for particulate absorbent and intermediate sheet from water-absorbent sheet ]
The particulate absorbent and the intermediate sheet are taken out by peeling the upper nonwoven fabric (corresponding to the first base material) and the lower nonwoven fabric (corresponding to the second base material) from the water-absorbent sheet. The granular absorbent adhered to the nonwoven fabric and the intermediate sheet above and below are also completely removed. When the nonwoven fabrics above and below are peeled off, the water-absorbent sheet is cooled to sufficiently weaken the adhesiveness of the nonwoven fabrics and adhesives (hot melt adhesive, adhesive spray) to which the particulate water-absorbing agent is bonded, and then the nonwoven fabrics and the particulate water-absorbing agent are peeled off. By performing this step, the fibers of the intermediate sheet and the structural thickness can be taken out without changing, and the transmittance can be accurately measured. The method for cooling the water-absorbent sheet may be any of various means such as placing in a constant temperature bath at-10 ℃ or lower for a certain period of time, spraying cooling mist, and applying liquid nitrogen, and is not particularly limited as long as the means is performed under the conditions that the fibers, structure, and thickness of the intermediate sheet are not changed and the particulate water-absorbing agent contained in the water-absorbent sheet does not absorb moisture.
When the particulate water-absorbing agent taken out is hygroscopic, the water content may be adjusted to 10 mass% or less, preferably 5 ± 2 mass% by drying, and the above-mentioned transmittance and the respective physical properties defined in the present application may be measured. The drying conditions for adjusting the water content are not particularly limited as long as the water-absorbent resin (particulate water-absorbing agent) is not decomposed or modified, and drying under reduced pressure is preferable.
[ Table 1]
Figure GDA0002940849500000351
[ Table 2]
Weight per unit area (g/m) 2 ) Thickness (mm) Void ratio (%)
Nonwoven (1) 98.0 8.3 98.8
Nonwoven (2) 109.0 7.4 98.5
[ Table 3]
Figure GDA0002940849500000361
Description of the reference numerals
11. A first base material,
12. A water absorption layer,
13. A second base material,
14. Particulate water absorbent
14a first particulate Water-absorbing agent
14b second particulate Water-absorbing agent
16. An intermediate sheet,
40. A water-absorbing sheet,
400. The device,
410. A container,
411. A box,
412. A piston,
413a, 413b of expanded metal,
414. Swollen gels (gels obtained by causing a particulate water-absorbing agent to absorb water),
415. A hole,
420. A pot,
421. A glass tube,
422. An L-shaped tube with a cock glass tube,
423. Liquid, a,
431. A metal net made of stainless steel,
432. A collecting container,
433. And (4) a balance for loading on a dish.
The present application is based on Japanese patent application No. 2018-150124, no. 2018-150125, no. 2018-150129, which was filed on 8/9/2018, and No. 2018-185706, which is filed on 28/2018/9/2018, the disclosures of which are incorporated herein by reference in their entirety.

Claims (14)

1. A water-absorbent sheet having:
a first substrate;
a second substrate; and
a water-absorbing layer positioned between the first substrate and the second substrate,
the first substrate is a water-permeable sheet on the side where the liquid to be absorbed is introduced,
the water-absorbing layer has: an intermediate sheet; a first particulate water-absorbing agent locally present on one surface side of the first substrate opposite to the second substrate; and a second particulate water-absorbing agent locally present on a side of the second substrate opposite to the first substrate, a part of the first particulate water-absorbing agent and/or a part of the second particulate water-absorbing agent being detached from each substrate,
a transmittance of a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent to the intermediate sheet is 10% or more and less than 60%,
the GPR of the first particulate water-absorbing agent is 50g/min or more,
the GPR of the second particulate water-absorbing agent is 45.0g/min or more,
the method for determining GPR is as follows:
(1) 0.900g of a particulate water-absorbing agent was uniformly charged into the cartridge;
(2) Allowing the particulate water-absorbing agent to absorb a 0.90 mass% aqueous sodium chloride solution for 60 minutes without being pressurized to prepare a swollen gel;
(3) A piston was placed on the swollen gel to a pressurized state of 0.3 psi;
(4) While keeping the hydrostatic pressure at 3923dyne/cm 2 Introducing a liquid into the cartridge while introducing the liquid to allow the swollen gel layer to pass through;
(5) The amount of liquid passing through the swollen gel layer was recorded at 5 second intervals for 3 minutes, i.e., the flow rate of the liquid passing through the swollen gel layer was measured;
(6) The flow rates 1 to 3 minutes after the start of the liquid flow were averaged to calculate the gel permeation rate GPR,
the method for measuring the transmittance of the mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent to the intermediate sheet is as follows:
in a JIS standard sieve having a mesh opening of 850 μm, an intermediate sheet having a diameter of 80mm is provided so that the intermediate sheet in contact with a first base material in the form of a water-absorbent sheet faces upward, the area through which particles can pass is secured by a tape around the intermediate sheet to be at least 75mm in diameter, 10.0g of a particulate water-absorbing agent is put into the intermediate sheet in the sieve, the intermediate sheet is shaken for 5 minutes at room temperature and a relative humidity of 50 rh at 230rpm and 130rpm using a rotary hammer type sieve shaker, the mass W of the particulate water-absorbing agent passing through the intermediate sheet and the JIS standard sieve is measured, and the permeability of the particulate water-absorbing agent is calculated according to the following formula (1):
the transmittance of the particulate absorbent in mass% = { W/10.0} × 100, formula (1).
2. The water-absorbent sheet according to claim 1, wherein the intermediate sheet is a nonwoven fabric.
3. The water-absorbent sheet according to claim 1 or 2, wherein the thickness of the intermediate sheet is thicker than the thickness of either one of the first substrate and the second substrate.
4. The water-absorbent sheet according to claim 1 or 2, wherein the content of the mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent per unit volume of the water-absorbent sheet is 50mg/cm 3 The above.
5. The water-absorbent sheet according to claim 1 or 2, wherein a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent has a weight-average particle diameter of 200 to 600 μm.
6. The water-absorbent sheet according to claim 1 or 2, wherein a CRC of a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent is 33g/g or more.
7. The water-absorbent sheet according to claim 1 or 2, wherein the content of the first particulate water-absorbing agent relative to the content of the second particulate water-absorbing agent in the water-absorbent sheet is 0.4 or less.
8. The water-absorbent sheet according to claim 1 or 2, wherein the GPR of the second particulate water-absorbing agent is 50g/min or more, the content of the first particulate water-absorbing agent in the water-absorbent sheet is 0.4 or less relative to the content of the second particulate water-absorbing agent, and the transmittance exceeds 40%.
9. The water-absorbent sheet according to claim 1 or 2, wherein at least one of the first particulate water-absorbing agent and the second particulate water-absorbing agent has a surface tension of 65mN/m or more.
10. The water-absorbent sheet according to claim 1 or 2, wherein at least one of the first particulate water-absorbing agent and the second particulate water-absorbing agent has an average circularity of 0.70 or less.
11. The water-absorbent sheet according to claim 1 or 2, wherein at least one of the first particulate water-absorbing agent and the second particulate water-absorbing agent comprises a water-absorbing agent having a particle shape of irregular crushed shape.
12. The water-absorbent sheet according to claim 1 or 2, wherein the water-absorbent sheet comprises an adhesive,
the amount of the binder used is 0.05 to 2.0 times the total mass of the first particulate water-absorbing agent and the second particulate water-absorbing agent.
13. A water-absorbent sheet having:
a first substrate;
a second substrate; and
a water-absorbing layer positioned between the first substrate and the second substrate,
the first substrate is a water-permeable sheet on the side where a liquid to be absorbed is introduced, and the water-absorbing layer has: an intermediate sheet; a first particulate water-absorbing agent locally present on one surface side of the first substrate opposite to the second substrate; and a second particulate water-absorbing agent locally present on a side of the second substrate opposite to the first substrate, the particulate water-absorbing agent of a part of the first particulate water-absorbing agent and/or the second particulate water-absorbing agent having water absorbed therein being desorbed from each substrate,
wherein the GPR of the first particulate water-absorbing agent is 50g/min or more, the GPR of the second particulate water-absorbing agent is 45.0g/min or more, the nonwoven fabric transmittance index NPI of the water-absorbing sheet is 10% or more and less than 60%,
the GPR determination method comprises the following steps:
(1) 0.900g of a particulate water-absorbing agent was uniformly charged into the cartridge;
(2) Allowing the particulate water-absorbing agent to absorb a 0.90 mass% aqueous sodium chloride solution for 60 minutes without being pressurized to prepare a swollen gel;
(3) A piston was placed on the swollen gel to a pressurized state of 0.3 psi;
(4) While maintaining the hydrostatic pressure at 3923dyne/cm 2 Introducing a liquid into the cartridge while introducing the liquid to allow the swollen gel layer to pass through;
(5) The amount of liquid passing through the swollen gel layer was recorded at 5 second intervals for 3 minutes, i.e., the flow rate of the liquid passing through the swollen gel layer was measured;
(6) The flow rates 1 to 3 minutes after the start of the liquid flow were averaged to calculate the gel permeation rate GPR,
the nonwoven fabric transmission index NPI is represented by the formula:
-90-1.05×C-39.3×B+3.15×A-0.289×D-0.0472×(C-52.1)×(D-369)+3.62×(B-3.48)×(A-142)-0.0142×(A-142)×(D-369)
wherein A is the specific surface area of the intermediate sheet measured by X-ray CT in mm -1 B is the thickness of the middle sheet, and the unit is mm; c is the weight per unit area of the middle sheet in g/m 2 And D is an average particle diameter D50 of the particulate water-absorbing agent in unit μm.
14. An absorbent article comprising the water-absorbent sheet according to any one of claims 1 to 13 sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet, wherein the liquid-permeable sheet is positioned on the first substrate side and the liquid-impermeable sheet is positioned on the second substrate side.
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