CN115279316B

CN115279316B - Absorbent sheet and absorbent article

Info

Publication number: CN115279316B
Application number: CN202180020584.7A
Authority: CN
Inventors: 田边友花
Original assignee: Sumitomo Seika Chemicals Co Ltd
Current assignee: Sumitomo Seika Chemicals Co Ltd
Priority date: 2020-03-18
Filing date: 2021-03-16
Publication date: 2024-03-05
Anticipated expiration: 2041-03-16
Also published as: KR20220156550A; JPWO2021187501A1; WO2021187501A1; CN115279316A

Abstract

The water-absorbent sheet according to one embodiment comprises an absorbent body comprising water-absorbent resin particles, wherein the water-absorbent resin particles have a 1 minute value of 15 to 40mL/g, a 5 minute value of 45 to 65mL/g, and a contact angle of 50 degrees or less, measured in the test performed in the following order of i) and ii), of the water-absorbent resin particles. i) Droplets corresponding to 0.01g of 0.9 mass% brine were dropped onto the surfaces of the water-absorbent resin particles at 25.+ -. 2 ℃ and the water-absorbent resin particles were brought into contact with the droplets. ii) after the droplet was brought into contact with the surface of the water-absorbent resin particle, the contact angle of the droplet was measured at a time after 0.1 seconds.

Description

Absorbent sheet and absorbent article

Technical Field

The present invention relates to a water-absorbent sheet and an absorbent article.

Background

Conventionally, an absorber containing water-absorbent resin particles has been used for an absorbent article for absorbing a liquid such as urine, which contains water as a main component. For example, patent document 1 discloses a method for producing water-absorbent resin particles having a particle diameter suitable for use in absorbent articles such as diapers, and patent document 2 discloses a method for using a hydrogel absorbent polymer having a specific saline flow transmissibility, absorption under pressure, and the like as an absorbent member effective for accommodating body fluids such as urine.

Technical literature of the prior art

Patent literature

Patent document 1: japanese patent laid-open No. 6-345819

Patent document 2: japanese patent laid-open No. 9-510889

Disclosure of Invention

Technical problem to be solved by the invention

In an absorbent article using a conventional absorbent body, there is a problem that a phenomenon (i.e., liquid flow (g)) in which liquid to be absorbed is not sufficiently absorbed by the absorbent body and an excessive amount of liquid flows on the surface of the absorbent body is likely to occur, and as a result, there is room for improvement in terms of leakage of the liquid to the outside of the absorbent article. That is, if the liquid supplied to the absorbent body does not sufficiently permeate into the absorbent body, there is a possibility that the residual liquid flows on the surface thereof and leaks to the outside of the absorbent body or the absorbent article. Therefore, the liquid needs to permeate into the absorber at a sufficient rate, and it is required to stably obtain a suitable permeation rate.

The purpose of the present invention is to provide a water-absorbing sheet and an absorbent article, which are provided with an absorber having an excellent liquid permeation rate and can suppress leakage of liquid.

Means for solving the technical problems

One aspect of the present invention relates to a water-absorbent sheet comprising an absorbent body comprising water-absorbent resin particles, wherein the water-absorbent resin particles have a 1 minute value of 15 to 40mL/g in the absence of a pressure DW, a 5 minute value of 45 to 65mL/g in the absence of a pressure DW, and a contact angle of 50 degrees or less as measured in a test performed in the following order of i) and ii),

i) Droplets corresponding to 0.01g of 0.9 mass% brine were dropped onto the surfaces of the water-absorbent resin particles at 25.+ -. 2 ℃ and the water-absorbent resin particles were brought into contact with the droplets.

ii) after the droplet was brought into contact with the surface of the water-absorbent resin particle, the contact angle of the droplet was measured at a time after 0.1 seconds.

Another aspect of the present invention relates to an absorbent article comprising the water-absorbent sheet.

Effects of the invention

According to the present invention, it is possible to provide a water-absorbent sheet and an absorbent article, which are provided with an absorber having an excellent liquid permeation rate and can suppress leakage of liquid.

Drawings

Fig. 1 is a schematic cross-sectional view showing an embodiment of a water-absorbent sheet.

Fig. 2 is a schematic plan view showing an example of a pattern of an adhesive (adhesive) formed on a core-wrap sheet.

Fig. 3 is a schematic cross-sectional view showing an embodiment of an absorbent article.

Fig. 4 is a plan view showing an example of a stirring blade (a flat blade having a slit in a flat plate portion).

FIG. 5 is a schematic view showing a measurement apparatus for non-pressurized DW of water-absorbent resin particles.

Fig. 6 is a schematic diagram showing a method of evaluating liquid leakage.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented by various modifications within the scope of the gist thereof.

In the present specification, "acrylic acid" and "methacrylic acid" are collectively referred to as "(meth) acrylic acid". The "acrylate" and "methacrylate" are likewise labeled as "(meth) acrylates". "(poly)" refers to both cases with and without the prefix "poly". In the same manner as described below, the upper limit value or the lower limit value of the numerical range in one stage can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range in another stage in the numerical range described in the present specification. In the numerical ranges described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the embodiment. "Water-soluble" means that it shows a solubility of 5% by mass or more in water at 25 ℃. The materials exemplified in the present specification may be used alone or in combination of 2 or more. The content of each component in the composition means the total amount of a plurality of substances present in the composition, unless otherwise specified, in the case where the plurality of substances corresponding to each component are present in the composition. The term "physiological saline" means a 0.9 mass% aqueous sodium chloride solution. "room temperature" means 25.+ -. 2 ℃.

[ Water absorbing sheet ]

The water-absorbent sheet according to one embodiment includes an absorber containing water-absorbent resin particles. The water-absorbent resin particles contained in the absorbent body have a 1-minute value of 15 to 40mL/g and a 5-minute value of 45 to 65mL/g. An absorber having an excellent liquid permeation rate can be obtained by the water-absorbent resin particles having a value of 1 minute without pressurization DW within the above range, and leakage from the absorbent article can be suppressed by the value of 5 minutes without pressurization DW within the above range.

The water-absorbent resin particles may have a value of 16 to 35mL/g, 16 to 30mL/g, or 16 to 25mL/g per 1 minute without pressurization DW from the viewpoint of further improving the liquid permeation rate. From the viewpoint of further suppressing leakage, the water-absorbent resin particles may have a value of 48 to 65mL/g, 50 to 63mL/g, or 51 to 60mL/g for 5 minutes without pressurization DW.

The water-absorbent resin particles may have a value of 34 to 50mL/g, 34 to 48mL/g, or 35 to 45mL/g in 2 minutes without pressurization DW from the viewpoint of further suppressing leakage. The 1 minute value, 2 minutes value, and 5 minutes value of the non-pressurized DW are values measured by the method described in examples described later.

The pressureless DW is the water absorption rate represented by the amount of absorption of physiological saline after a predetermined time elapses from the contact of the water-absorbent resin particles with physiological saline under no pressure. The unpressurized DW was represented by the absorption amount (mL) per 1g of the water-absorbent resin particles before absorption of the physiological saline. The 1 minute value, 2 minutes value and 5 minutes value of the non-pressurized DW refer to the absorption amounts after 1 minute, 2 minutes and 5 minutes, respectively, from the start of absorption of the physiological saline by the water-absorbent resin particles.

From the viewpoint of improving the liquid permeation rate, the water-absorbent resin particles according to the present embodiment have a contact angle of 50 degrees or less, as measured in the test performed in the following order of i) and ii).

From the viewpoint of further improving the liquid permeation rate, the contact angle of the water-absorbent resin particles may be 5 degrees or more and 50 degrees or less, 10 degrees or more and 49 degrees or less, or 15 degrees or more and 48 degrees or less. The contact angle is a value measured in accordance with JIS R3257 (1999) "wettability test method of substrate glass surface", and specifically, is measured by a method described in examples described later.

The water retention amount of the physiological saline of the water-absorbent resin particles may be, for example, 20g/g or more, 25g/g or more, 30g/g or more, 32g/g or more, 34g/g or more, 36g/g or more, or 38g/g or more, and 60g/g or less, 55g/g or less, 50g/g or less, 45g/g or less, or 42g/g or less. The water retention amount of physiological saline was measured by the method described in examples described later.

Examples of the shape of the water-absorbent resin particles include a substantially spherical shape, a crushed shape, a granular shape, and a shape formed by agglomerating primary particles having these shapes.

The water-absorbent resin particles according to the present embodiment may contain polymer particles and dry silica disposed on the surfaces of the polymer particles. For example, by mixing the polymer particles and the dry silica, the dry silica can be disposed on the surfaces of the polymer particles. By using such water-absorbent resin particles as an absorber, the liquid permeation rate can be increased, and leakage can be easily suppressed.

The dry silica is silica produced by a dry method, and examples thereof include fumed silica. Dry silica generally has active hydroxyl groups and thus is hydrophilic, but can also be rendered hydrophobic by surface treatment of the silica surface with alkylsilanes or the like. The dry silica preferably has hydrophilicity from the viewpoint of easy acquisition of excellent initial water absorption rate.

The dry silica uses secondary particles formed by collecting a plurality of primary particles, each of which is composed of nano-sized primary particles. In the dry silica, a plurality of secondary particles are associated with each other to form a secondary aggregate as an association of the secondary particles. In the dry silica and synthetic amorphous silica other than the dry silica (for example, wet silica produced by a wet method), for example, the shape of the agglomerate is different. In general, wet silica aggregates have a substantially spherical aggregate structure, whereas dry silica aggregates have a chain-like aggregate structure.

The specific surface area of the dry silica may be, for example, 50m ² Over/g, 75m ² Over/g, 100m ² Over/g, 125m ² Over/g, 150m ² Over/g, 170m ² Above/g or 200m ² The ratio of the total weight of the catalyst to the total weight of the catalyst is 1000m or more ² Per gram of less than 800m ² Less than/g and 600m ² Per gram of less than 400m ² Per gram or less than 350m ² And/g or less. The specific surface area of the dry silica may be, for example, 50 to 1000m ² /g、75～600m ² Per gram or 100-400 m ² And/g. The specific surface area of the silica can be determined by the BET specific surface area (N ₂ ) The method is used for measurement.

The bulk density of the dry silica may be, for example, 10 to 200g/L. From the viewpoint of easy acquisition of excellent water absorption properties, the bulk density of the dry silica is preferably 10g/L or more, 20g/L or more, 30g/L or more, or 40g/L or more, preferably 200g/L or less, 180g/L or less, 150g/L or less, 130g/L or less, 100g/L or less, 90g/L or less, or 80g/L or less. The bulk density of silica can be measured by using a pigment test method (JIS-K5101-12-1).

The average particle diameter (primary average particle diameter) of the primary particles of the dry silica is preferably 5nm or more, 7nm or more, 10nm or more, or 12nm or more, and preferably 500nm or less, 100nm or less, 50nm or less, 30nm or less, or 20nm or less, from the viewpoints of handleability and adhesion to the surface of the water-absorbent resin particles. More specifically, the primary average particle diameter of the dry silica is preferably 5nm to 500nm, more preferably 7nm to 50 nm. The average primary particle diameter of the silica can be measured by observation using a transmission electron microscope.

The average particle diameter of the secondary aggregation particles of the dry silica is preferably 1.0 μm or more, more preferably 10 μm or more, further preferably 20 μm or more, and is preferably 100 μm or less, more preferably 70 μm or less, further preferably 50 μm or less, from the viewpoint of easy availability of handleability and excellent water absorption characteristics. From the same viewpoint, more specifically, the average particle diameter of the secondary aggregation particles of the dry silica is preferably 1.0 μm or more and 100 μm or less, more preferably 10 μm or more and 70 μm or less. The average particle diameter of the secondary aggregated particles of silica can be measured by a dynamic light scattering method, a laser diffraction/scattering method, or a coulter counter method.

The water content of the dry silica may be, for example, 10 mass% or less, 5.0 mass% or less, 3.0 mass% or less, or 2.0 mass% or less. The lower limit of the water content of the dry silica may be, for example, 0.1 mass% or more. The dry silica may be fumed silica having a water content of 5 mass% or less. The water content of the dry silica can be measured by the pigment and extender pigment general test method ISO 787-2. The water content of the dry silica in the present specification is a water content based on the total mass of the dry silica and water in the dry silica.

Examples of the commercial products of the dry silica (hydrophilic dry silica) include "AEROSIL200", "AEROSIL300", "AEROSIL380", cabot Japan Corporation "CAB-O-SIL M-5", "CAB-O-SIL H-300", "CAB-O-SIL M-5", and "CAB-O-SIL M3KD" manufactured by NIPP ON AEROSIL CO., LTD. The dry silica may be used alone or in combination of 2 or more.

The proportion of the dry silica to the mass of the polymer particles may be 0.1 mass% or more, 0.2 mass% or more, 0.3 mass% or more, or 0.4 mass% or more, and may be 3.0 mass% or less, 2.0 mass% or less, 1.5 mass% or less, or 1.0 mass% or less. That is, from the viewpoint of adjusting the permeation rate of the liquid in the absorber, the proportion of the dry silica may be 0.1 mass% or more and 3.0 mass% or less, 0.2 mass% or more and 2.0 mass% or less, 0.3 mass% or more and 1.5 mass% or more and 1.0 mass% or less, based on the total mass of the polymer particles.

The polymer particles may be water-absorbent particles containing a polymer containing an ethylenically unsaturated monomer as a monomer unit. Examples of the ethylenically unsaturated monomer include water-soluble monomers such as (meth) acrylic acid and salts thereof, 2- (meth) acrylamide-2-methylpropanesulfonic acid and salts thereof, (meth) acrylamide, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-hydroxymethyl (meth) acrylamide, polyethylene glycol mono (meth) acrylate, N-diethylaminoethyl (meth) acrylate, N-diethylaminopropyl (meth) acrylate, and diethylaminopropyl (meth) acrylamide. The ethylenically unsaturated monomers may be used alone or in combination of 2 or more.

The proportion of the polymer containing an ethylenically unsaturated monomer as a monomer unit in the polymer particles may be 50 to 100 mass%, 60 to 100 mass%, 70 to 100 mass%, or 80 to 100 mass% based on the mass of the polymer particles. The polymer particles may be particles containing a (meth) acrylic polymer containing at least one of (meth) acrylic acid or a (meth) acrylic acid salt as a monomer unit. The total proportion of the monomer units derived from (meth) acrylic acid or (meth) acrylic acid salt in the (meth) acrylic polymer may be 90 to 100% by mass based on the mass of the polymer.

At least the polymer of the surface layer portion in the polymer particles may be crosslinked by reaction with a surface crosslinking agent. The surface crosslinking agent may be, for example, a compound having 2 or more functional groups (reactive functional groups) reactive with functional groups derived from an ethylenically unsaturated monomer.

Examples of the surface crosslinking agent include alkylene carbonate compounds such as ethylene carbonate; polyhydric alcohols such as ethylene glycol, propylene glycol, 1, 4-butanediol, trimethylolpropane, glycerol, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerol; polyglycidyl compounds such as (poly) ethylene glycol diglycidyl ether, (poly) glycerol triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and (poly) glycerol polyglycidyl ether; halogenated epoxy compounds such as epichlorohydrin, epibromohydrin, and α -methyl epichlorohydrin; compounds having 2 or more reactive functional groups, such as isocyanate compounds, e.g., 2, 4-toluene diisocyanate and hexamethylene diisocyanate; oxetane compounds such as 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, and 3-butyl-3-oxetaneethanol; oxazoline compounds such as 1, 2-ethylenebisoxazoline; hydroxyalkylamide compounds such as bis [ N, N-bis (. Beta. -hydroxyethyl) ] adipamide.

The surface cross-linking agent may comprise a polyglycidyl compound. The proportion of the polyglycidyl compound in the surface crosslinking agent may be 50 to 100 mass%, 60 to 100 mass%, 70 to 100 mass%, 80 to 100 mass% or 90 to 100 mass% based on the total mass of the surface crosslinking agent.

Inside the polymer particles, the polymer may also be internally crosslinked by self-crosslinking, crosslinking based on reaction with an internal crosslinking agent, or both. From the viewpoint of easy control of the water absorption characteristics, it is preferable to include at least a reaction based on an internal crosslinking agent.

The internal crosslinking agent may contain, for example, a compound having 2 or more polymerizable unsaturated groups, a compound having 2 or more reactive functional groups reactive with functional groups of an ethylenically unsaturated monomer, or 1 or 2 or more compounds containing a combination thereof.

Examples of the compound having 2 or more polymerizable unsaturated groups include di-or tri-meth-acrylates of polyhydric alcohols such as (poly) ethylene glycol, (poly) propylene glycol, trimethylolpropane, glycerol polyoxyethylene glycol, polyoxypropylene glycol and (poly) glycerol; unsaturated polyesters obtained by reacting the above-mentioned polyol with an unsaturated acid such as maleic acid or fumaric acid; bisacrylamides such as N, N' -methylenebis (meth) acrylamide; di-or tri (meth) acrylates obtained by reacting polyepoxides with (meth) acrylic acid; carbamoyl di (meth) acrylates obtained by reacting polyisocyanates such as toluene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth) acrylate; allylated starch; allylated cellulose; diallyl phthalate; n, N', N "-triallyl isocyanurate; divinylbenzene.

Examples of the compound having 2 or more reactive functional groups include glycidyl group-containing compounds such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether and (poly) glycerol diglycidyl ether; (Poly) ethylene glycol, (Poly) propylene glycol, (Poly) glycerol, pentaerythritol, ethylenediamine, polyethyleneimine, glycidyl (meth) acrylate.

The polymer particles may be post-polymerized crosslinked. For example, the post-polymerization crosslinking can be performed by adding a crosslinking agent to the polymer and heating.

Examples of the crosslinking agent for performing the post-polymerization crosslinking include: polyhydric alcohols such as ethylene glycol, propylene glycol, 1, 4-butanediol, trimethylolpropane, glycerol, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerol; a compound having 2 or more epoxy groups, such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerol diglycidyl ether; halogenated epoxy compounds such as epichlorohydrin, epibromohydrin and α -methyl epichlorohydrin; compounds having 2 or more isocyanate groups such as 2, 4-toluene diisocyanate and hexamethylene diisocyanate; oxazoline compounds such as 1, 2-vinylbisoxazoline; carbonate compounds such as ethylene carbonate; hydroxyalkylamide compounds such as bis [ N, N-bis (. Beta. -hydroxyethyl) ] adipamide. The crosslinking agent used for the post-polymerization crosslinking may be a polyglycidyl compound such as (poly) ethylene glycol diglycidyl ether, (poly) glycerol triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and polyglycidyl ether. These crosslinking agents may be used alone or in combination of 2 or more.

The post-polymerization crosslinking agent may comprise a polyglycidyl compound. The ratio of the polyglycidyl compound in the post-polymerization crosslinking agent may be 50 to 100 mass%, 60 to 100 mass%, 70 to 100 mass%, 80 to 100 mass% or 90 to 100 mass% based on the total mass of the post-polymerization crosslinking agent.

The addition period of the post-polymerization crosslinking may be any period after polymerization of the ethylenically unsaturated monomer used in the polymerization, and in the case of multi-stage polymerization, it is preferable to add the monomer after multi-stage polymerization. In addition, from the viewpoint of heat generation during and after polymerization, stagnation due to process delay, opening of a system when a crosslinking agent is added, and fluctuation of moisture due to addition of water or the like with the addition of the crosslinking agent, the crosslinking agent after polymerization is preferably added in a region of [ moisture content immediately after polymerization.+ -. 3% ] from the viewpoint of moisture content (content of water based on the mass of the aqueous gel polymer).

The median particle diameter of the polymer particles may be 130 to 800. Mu.m, 200 to 850. Mu.m, 250 to 700. Mu.m, 280 to 600. Mu.m, or 300 to 450. Mu.m. The polymer particles may have a desired particle size distribution at the time obtained by a production method described later, but the particle size distribution may be adjusted by performing an operation such as particle size adjustment using classification by a sieve.

The polymer particles may contain a certain amount of moisture in addition to the polymer of the ethylenically unsaturated monomer, and may further contain various additional components therein. Examples of the additional component include a gel stabilizer, a metal chelator, an antibacterial agent, and the like.

The water-absorbent resin particles can be produced, for example, by a method including a step of disposing dry silica on the surface of the polymer particles.

The polymer particles can be obtained, for example, by a method including a step of polymerizing a monomer containing an ethylenically unsaturated monomer. The polymerization method of the monomer can be selected from, for example, a reversed-phase suspension polymerization method, an aqueous solution polymerization method, a bulk polymerization method, and a precipitation polymerization method. By polymerizing an ethylenically unsaturated monomer in the presence of an internal crosslinking agent, polymer particles which are internally crosslinked by the crosslinking agent can be obtained. By polymerizing an ethylenically unsaturated monomer in the presence of inorganic particles such as silica, polymer particles containing inorganic particles inside can be obtained. Some or all of the ethylenically unsaturated monomers may form salts such as alkali metal salts.

In the case of the aqueous solution polymerization method, for example, the polymer particles can be obtained by a method comprising the steps of: polymerizing an ethylenically unsaturated monomer in an aqueous monomer solution containing the ethylenically unsaturated monomer and water to form an aqueous gel-like polymer comprising the polymer; the hydrogel polymer is dried. In the case of forming the hydrogel polymer in the form of a block, it may be coarsely crushed, and the coarsely crushed hydrogel polymer may be dried. The hydrogel polymer or a crude crushed product thereof may be crushed after drying, or the particles obtained by crushing may be classified. The polymer particles to be surface-crosslinked described later may be dried coarse particles, or may be particles obtained by further pulverizing the coarse particles. The polymer particles obtained by pulverizing the coarse pulverized material may be classified, and the particle size of the polymer particles may be adjusted as needed for surface crosslinking.

The concentration of the ethylenically unsaturated monomer in the aqueous monomer solution may be 20 mass% or more and the saturated concentration or less, 25 to 70 mass%, or 30 to 50 mass% based on the mass of the aqueous monomer solution.

The aqueous monomer solution may further contain a polymerization initiator. The polymerization initiator may be used alone, or 2 or more kinds may be used in combination. The polymerization initiator may be a photopolymerization initiator or a thermal radical polymerization initiator, or may be a water-soluble thermal radical polymerization initiator. The thermal radical polymerization initiator may be an azo compound, a peroxide, or a combination thereof. The amount of the polymerization initiator may be 0.00005 to 0.01 mole relative to 1 mole of the ethylenically unsaturated monomer.

As the azo-based compound, for example, examples thereof include 2,2' -azobis [2- (N-phenylamidino) propane ] dihydrochloride, 2' -azobis {2- [ N- (4-chlorophenyl) amidino ] propane } dihydrochloride, 2' -azobis {2- [ N- (4-hydroxyphenyl) amidino ] propane } dihydrochloride, and 2,2' -azobis [2- (N-benzamidine) propane ] dihydrochloride, 2' -azobis [2- (N-allylamidino) propane ] dihydrochloride, 2' -azobis (2-amidinopropane) dihydrochloride, 2' -azobis {2- [ N- (2-hydroxyethyl) amidino ] propane } dihydrochloride 2,2' -azobis [2- (5-methyl-2-imidazolin-2-yl) propane ] dihydrochloride, 2' -azobis [2- (4, 5,6, 7-tetrahydro-1H-1, 3-diaza-2-yl) propane ] dihydrochloride, 2' -azobis [2- (5-hydroxy-3, 4,5, 6-tetrahydropyrimidin-2-yl) propane ] dihydrochloride, 2' -azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl ] propane } dihydrochloride, 2,2 '-azobis (2-methylpropionamide) dihydrochloride, 2' -azobis [2- (2-imidazolin-2-yl) propane ] disulfate dihydrate, 2 '-azobis [ N- (2-carboxyethyl) -2-methylpropionamidine ] tetrahydrate, and 2,2' -azobis [ 2-methyl-N- (2-hydroxyethyl) propionamide ].

Examples of the peroxide include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; organic peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, and t-butyl peroxypivalate; hydrogen peroxide.

A polymerization initiator and a reducing agent can also be used in combination as a redox polymerization initiator. Examples of the reducing agent include sodium sulfite, sodium hydrogen sulfite, ferrous sulfate and L-ascorbic acid.

The aqueous monomer solution may further contain the above-mentioned internal crosslinking agent. The amount of the internal crosslinking agent may be 0 millimole or more, 0.001 millimole or more, 0.01 millimole or more, 0.015 millimole or more, or 0.020 millimole or more, and may be 2 millimole or less, 1 millimole or less, 0.5 millimole or less, or 0.1 millimole or less, relative to 1 mole of the ethylenically unsaturated monomer. The aqueous monomer solution may contain other additives such as chain transfer agent and thickener, if necessary.

The polymerization temperature varies depending on the polymerization initiator used, but may be, for example, 0 to 130℃or 10 to 110 ℃. The polymerization time may be 1 to 200 minutes or 5 to 100 minutes.

The water content of the hydrogel polymer formed by polymerization (the content of water based on the mass of the hydrogel polymer) may be 30 to 80 mass%, 40 to 75 mass%, or 50 to 70 mass%.

In the case of coarsely pulverizing the hydrogel polymer in the form of a block, the coarse particles obtained by coarse pulverization may be in the form of particles or may have a slender shape such as a particle-connected structure. The minimum width of the coarse product may be, for example, about 0.1 to 15mm or about 1.0 to 10 mm. The maximum width of the coarse crushed material can be about 0.1-200 mm or about 1.0-150 mm. Examples of the device for coarse crushing include a kneader (e.g., a pressure kneader, a double arm kneader, etc.), a meat chopper, a chopper, and a medicinal pulverizer (Pharma Mill). For the block-shaped hydrogel-like polymer, cutting may be performed before coarse crushing, if necessary.

The hydrogel polymer or its coarse particles are mainly dried for removing water. The drying method may be a general method such as natural drying, heat drying, or reduced pressure drying. The dried hydrogel polymer or a coarse product thereof is further pulverized, and the obtained particles are classified as needed, whereby polymer particles having a suitable particle diameter can be obtained. The pulverizing method is not particularly limited, and for example, a method using a roll mill (roll mill), a stamp mill, a jet mill, a high-speed rotary mill (hammer mill, pin mill, rotary mill, or the like), or a container-driven mill (rotary mill, vibration mill, planetary mill, or the like) can be applied. The classification method is not particularly limited, and for example, a method using a vibrating screen, a rotary shifter, a cylindrical stirring screen, a blast shifter, or a rotary vibrator can be applied.

In the case of the inverse suspension polymerization method, for example, the polymer particles can be obtained by a method comprising the steps of: polymerizing an ethylenically unsaturated monomer in a suspension containing a hydrocarbon dispersion medium, a monomer aqueous solution containing the ethylenically unsaturated monomer, a radical polymerization initiator, water, and the like, and a surfactant, which is dispersed in the hydrocarbon dispersion medium, thereby forming a particulate hydrogel-like polymer containing a polymer; and removing the hydrocarbon dispersion medium and water from the suspension.

The hydrocarbon dispersion medium may contain at least 1 compound selected from the group consisting of a chain aliphatic hydrocarbon having 6 to 8 carbon atoms and an alicyclic hydrocarbon having 6 to 8 carbon atoms. Examples of the hydrocarbon dispersion medium include chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2, 3-dimethylpentane, 3-ethylpentane, and n-octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1, 2-dimethylcyclopentane, cis-1, 3-dimethylcyclopentane and trans-1, 3-dimethylcyclopentane; aromatic hydrocarbons such as benzene, toluene and xylene. The hydrocarbon dispersion medium may be used alone or in combination of 2 or more. The amount of the hydrocarbon dispersion medium may be 30 to 1000 parts by mass, 40 to 500 parts by mass, or 50 to 300 parts by mass with respect to 100 parts by mass of the monomer aqueous solution containing the monomer.

The aqueous monomer solution in suspension for inverse suspension polymerization may further contain the above-mentioned internal crosslinking agent. The internal crosslinking agent is typically added to an aqueous monomer solution containing an ethylenically unsaturated monomer. The amount of the internal crosslinking agent may be 0 millimole or more, 0.001 millimole or more, 0.01 millimole or more, 0.015 millimole or more, or 0.020 millimole or more, and may be 2 millimole or less, 1 millimole or less, 0.5 millimole or less, or 0.1 millimole or less, relative to 1 mole of the ethylenically unsaturated monomer.

Suspensions used in reverse phase suspension polymerizations typically also contain surfactants. The surfactant may be a nonionic surfactant, an anionic surfactant, or the like. Examples of the nonionic surfactant include sorbitan fatty acid esters, (poly) glycerin fatty acid esters ("(poly)" means both cases with or without the linker term "poly"),. The same applies hereinafter), sucrose fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oils, polyoxyethylene hydrogenated castor oils, alkyl allyl formaldehyde condensation polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropylene alkyl ethers, polyethylene glycol fatty acid esters, and the like. Examples of the anionic surfactant include fatty acid salts, alkylbenzene sulfonates, alkylmethyl taurates, polyoxyethylene alkylphenyl ether sulfate salts, polyoxyethylene alkyl ether sulfonates, phosphate esters of polyoxyethylene alkyl ethers, phosphate esters of polyoxyethylene alkyl allyl ethers, and the like. The surfactant may be used alone or in combination of 2 or more. The amount of the surfactant may be 0.05 to 10 parts by mass, 0.08 to 5 parts by mass, or 0.1 to 3 parts by mass with respect to 100 parts by mass of the aqueous monomer solution.

The suspension used for the inverse suspension polymerization may further contain a polymer-based dispersing agent. Examples of the polymer-based dispersant include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified EPDM (ethylene-propylene-diene-terpolymer), maleic anhydride-modified polybutadiene, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, maleic anhydride-butadiene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ethylcellulose, ethylhydroxyethyl cellulose, and the like. The polymer-based dispersant may be used alone or in combination of 2 or more. The amount of the polymer-based dispersant may be 0.05 to 10 parts by mass, 0.08 to 5 parts by mass, or 0.1 to 3 parts by mass with respect to 100 parts by mass of the aqueous monomer solution.

The suspension for the reversed-phase suspension polymerization may contain other components such as a chain transfer agent and a thickener, as required. The polymerization temperature varies depending on the radical polymerization initiator used, but may be, for example, 20 to 150℃or 40 to 120 ℃. Typically, the reaction time is from 0.5 to 4 hours. The inverse suspension polymerization may be performed in a plurality of stages.

After the polymerization, the hydrocarbon dispersion medium and water are removed from the suspension containing the aqueous gel-like polymer and the hydrocarbon dispersion medium, whereby polymer particles can be obtained. For example, the hydrocarbon dispersion medium and water can be removed by azeotropic distillation, decantation, filtration, drying under reduced pressure, or a combination thereof. Some level of water, hydrocarbon dispersion medium, or both may remain in the polymer particles.

The method for producing the water-absorbent resin particles may further include the steps of: the polymer particles are surface crosslinked by heating a reaction mixture comprising the polymer particles and an aqueous solution of a surface crosslinking agent comprising water and a surface crosslinking agent.

The aqueous surface cross-linking agent solution contains water and a surface cross-linking agent dissolved in the water. The aqueous surface cross-linking agent solution may also contain a hydrophilic organic solvent. The organic solvent may be, for example, alcohols such as 2-propanol, ethanol, methanol, and propylene glycol. The ratio of water to the total amount of water and organic solvent may be not less than 100% by mass, or may be not less than 50% by mass, not less than 60% by mass, not less than 70% by mass, not less than 80% by mass, or not less than 90% by mass.

The polymer particles can be surface crosslinked by mixing the polymer particles with an aqueous solution of the surface crosslinking agent and, if necessary, heating the resulting reaction mixture while stirring. The heating temperature for surface crosslinking may be appropriately adjusted to perform surface crosslinking, and may be, for example, 70 to 300 ℃, 100 to 270 ℃, 120 to 250 ℃, 150 to 220 ℃, or 170 to 200 ℃. The reaction time for the surface crosslinking may be, for example, 1 to 200 minutes, 10 to 100 minutes, 20 to 80 minutes, 30 to 70 minutes, 40 to 60 minutes, or 5 to 100 minutes. The surface crosslinking step may be performed 2 times or more.

In the production of the water-absorbent resin particles, the surface crosslinking of the surface portion (surface and vicinity of the surface) of the hydrogel polymer may be performed using a crosslinking agent in the drying step (moisture removal step) or in the subsequent steps. By performing surface crosslinking, water absorption characteristics and the like can be easily controlled. The surface crosslinking may be performed at a time when the water-containing gel-like polymer has a specific water content. The surface crosslinking time may be at a time when the water content of the hydrogel polymer is 5 to 50 mass%, at a time when the water content is 10 to 40 mass%, or at a time when the water content is 15 to 35 mass%.

The water content (% by mass) of the hydrogel polymer was calculated by the following formula.

Water content= [ Ww/(ww+ws) ]×100

Ww: the amount of water content of the hydrogel polymer obtained by adding the amount of water content used as needed, such as a mixing coagulant, a surface cross-linking agent, etc., to the amount of water content discharged to the outside of the system in the drying step, which is subtracted from the amount of water content contained in the aqueous monomer solution before polymerization in the entire polymerization step.

Ws: the amount of the solid component is calculated based on the charged amounts of materials such as an ethylenically unsaturated monomer, a crosslinking agent, and an initiator constituting the hydrogel polymer.

If necessary, water and hydrocarbon dispersion medium are removed from the surface-crosslinked polymer particles. The surface cross-linked polymer particles may be further treated by drying, pulverizing, classifying or a combination thereof.

The method for producing the water-absorbent resin particles may include the steps of: after surface crosslinking, the dry silica is disposed.

The absorbent body according to the present embodiment contains the water-absorbent resin particles described above. The absorber may further contain a fibrous material, and may be, for example, a mixture containing water-absorbent resin particles and a fibrous material.

Fig. 1 is a cross-sectional view showing an example of a water-absorbent sheet. The water absorbent sheet 50 shown in fig. 1 has an absorber 10 and 2 core wrap sheets 20a, 20b. The core wrap sheets 20a, 20b are disposed on both sides of the absorbent body 10. In other words, the absorbent body 10 is disposed inside the core-wrap sheets 20a, 20b. The absorbent body 10 is held in shape by being sandwiched between 2 core-wrap sheets 20a, 20b. The core wrap 20a, 20b may be 2 sheets, or 1 sheet or 1 pouch folded.

The absorbent sheet 50 may also have an adhesive 21 between the core wrap sheet 20a and the absorbent body 10. Fig. 2 is a plan view showing an example of the pattern of the adhesive formed on the core wrap sheet. The adhesive 21 shown in fig. 2 is formed with a pattern composed of a plurality of linear portions arranged with a space therebetween on the core wrap sheet 20 a. However, the pattern of the adhesive 21 is not limited thereto. The adhesive 21 may be interposed not only between the core-wrap sheet 20a and the absorbent body 10 but also between the core-wrap sheet 20b and the absorbent body 10. The adhesive 21 is not particularly limited, and may be, for example, a hot melt adhesive.

The absorbent body 10 includes water-absorbent resin particles 10a and an optional fibrous layer 10b containing fibrous materials. The content of the water-absorbent resin particles in the absorber may be 80 to 100 mass%, 85 to 100 mass%, or 90 to 100 mass% based on the mass of the absorber 10.

From the viewpoint of easily obtaining sufficient water absorption performance, every 1m ² The content of the water-absorbent resin particles in the absorbent body 10 may be, for example, 30g or more, 50g or more, 70g or more, 80g or more, 90g or more, 100g or more, or 120g or more, and 1000g or less, 800g or less, 700g or less, 600g or less, 500g or less, 400g or 300g or less.

The thickness of the absorber 10 is not particularly limited, but may be, for example, 20mm or less, 15mm or less, 10mm or less, 5mm or less, 4mm or less, or 3mm or less, or may be 0.1mm or more, 0.2mm or more, or 0.3mm or more in a dry state. The mass per unit area of the absorbent body 10 may be 1000g/m ² Below, 800g/m ² Below or 600g/m ² Hereinafter, the concentration may be 100g/m ² The above.

In particular, in the case of forming a thin absorber, the content of the fiber layer in the absorber is preferably 0 to 10 mass%, more preferably 0 to 5 mass%, based on the mass of the absorber. That is, the content of the water-absorbent resin particles in the absorber is preferably 90 mass% or more, more preferably 95 mass% or more.

Examples of the fibrous material constituting the fibrous layer 10b include finely pulverized wood pulp, cotton linters, and rayon; cellulose fibers such as cellulose acetate; synthetic fibers such as polyamides, polyesters, and polyolefins. The fibrous material may be used alone or in combination of 2 or more kinds. As the fibrous material, hydrophilic fibers can be used.

In order to improve the shape retention of the absorbent body before and during use, the fibers may be bonded to each other by adding an adhesive binder to the fibers. Examples of the adhesive agent include heat-fusible synthetic fibers, heat-fusible adhesive agents, and adhesive emulsions. The adhesive may be used alone or in combination of 2 or more.

Examples of the heat-fusible synthetic fibers include all-melt adhesives such as polyethylene, polypropylene, and ethylene-propylene copolymers; and a non-full-melt adhesive composed of a side-by-side or core-sheath structure of polypropylene and polyethylene. In the above-mentioned non-all-melt adhesive, only the polyethylene portion can be thermally welded.

Examples of the hot melt adhesive include a mixture of a base polymer such as an ethylene-vinyl acetate copolymer, a styrene-isoprene-styrene block copolymer, a styrene-butadiene-styrene block copolymer, a styrene-ethylene-butylene-styrene block copolymer, a styrene-ethylene-propylene-styrene block copolymer, and amorphous polypropylene, with a tackifier, a plasticizer, and an antioxidant.

Examples of the adhesive emulsion include polymers of at least one monomer selected from the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene and vinyl acetate.

The absorbent body 10 (or the fibrous layer 10 b) may further contain a deodorant, an antibacterial agent, a perfume, or the like.

The core wrap sheets 20a, 20b may be, for example, nonwoven fabrics. The 2 core wrap sheets 20a, 20b may be the same or different nonwoven fabrics. The nonwoven fabric may be a nonwoven fabric (short fiber nonwoven fabric) composed of short fibers (i.e., filaments), or may be a nonwoven fabric (long fiber nonwoven fabric) composed of long fibers (i.e., filaments). The filaments are not limited thereto, but may have a fiber length of generally several hundred mm or less.

The core wrap sheets 20a, 20b may be heat-bonded nonwoven fabric, hot air nonwoven fabric, resin-bonded nonwoven fabric, spunbond nonwoven fabric, melt-blown nonwoven fabric, air-laid nonwoven fabric, spunlaced nonwoven fabric, point-bonded nonwoven fabric, or a laminate comprising 2 or more nonwoven fabrics selected from them.

The nonwoven fabric used as the core-wrap sheets 20a, 20b may be a nonwoven fabric formed of synthetic fibers, natural fibers, or a combination thereof. Examples of the synthetic fibers include fibers containing synthetic resins selected from the group consisting of polyolefins such as Polyethylene (PE) and polypropylene (PP), polyesters such as polyethylene terephthalate (PET), polypropylene terephthalate (PTT) and polyethylene naphthalate (PEN), polyamides such as nylon, and rayon. Examples of natural fibers include fibers including cotton, silk, hemp, and pulp (cellulose). The fibers forming the nonwoven fabric may be polyolefin fibers, polyester fibers, or a combination thereof. The core wrap sheets 20a, 20b may be tissue.

The water-absorbent sheet 50 can be obtained, for example, by the following method: the water-absorbent resin particles 10a or the mixture containing the water-absorbent resin particles 10a and the fibrous material is sandwiched between the core-wrap sheets 20a, 20b, and the resulting structure is pressurized while being heated as needed. If necessary, an adhesive 21 is disposed between the core-wrap sheets 20a, 20b and the water-absorbent resin particles 10a or a mixture containing them.

The water-absorbent sheet 50 may be provided as follows: the absorbent body 10 and the core wrap sheet are further provided on the surface of the core wrap sheet 20b opposite to the surface on which the absorbent body 10 is provided, and thus the absorbent body 10 is provided with two layers. Since the water-absorbent resin particles according to the present embodiment are particularly excellent in the leakage-suppressing property, they have high absorption performance even in a water-absorbent sheet having a single absorption layer, for example, and can suppress leakage of liquid.

From the viewpoint of easily obtaining sufficient water absorption performance, every 1m ² In the absorbent body 10, the content of the water-absorbent resin particles in the water-absorbent sheet 50 may be, for example, 30g or more, 50g or more, 70g or more, 80g or more, 90g or more, 100g or more, or 120g or more, and may be 1000g or less, 800g or less, 700g or less, 600g or less, 500g or less, 400g or less, or 300g or less.

The water-absorbent sheet according to the present embodiment may include 2 or more layers of the absorbent body. In this case, at least 1 layer is the absorber according to the present embodiment, so that the water absorption characteristics of the water-absorbent sheet can be improved. That is, the water-absorbent sheet according to the present embodiment can suppress leakage by having at least 1 layer of the absorber containing the water-absorbent resin particles having a 1 minute value of 15 to 40mL/g in the non-pressurized DW, a 5 minute value of 45 to 65mL/g in the non-pressurized DW, and a contact angle of 50 degrees or less. For example, in the case of a water-absorbent sheet having 2 or more layers of the absorbent material, the absorbent material may include the absorbent material including the water-absorbent resin particles according to the present embodiment and the absorbent material not including the water-absorbent resin particles according to the present embodiment, or may include a plurality of layers of the absorbent material including the water-absorbent resin particles according to the present embodiment.

The water-absorbent sheet according to the present embodiment is used for manufacturing various absorbent articles, for example.

[ absorbent article ]

The absorbent article according to the present embodiment includes the water-absorbent sheet according to the present embodiment. The absorbent article according to the present embodiment includes a core wrap sheet for maintaining the shape of the absorbent body; an outermost liquid-permeable sheet disposed on a side into which liquid to be absorbed permeates; an outermost liquid-impermeable sheet disposed on the side opposite to the side into which the liquid to be absorbed permeates. Examples of the absorbent article include diapers (e.g., paper diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat-absorbent pads, pet pads, parts for simple toilets, and animal waste disposal materials.

Fig. 3 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in fig. 3 includes a water-absorbent sheet 50, a liquid-permeable sheet 30, and a liquid-impermeable sheet 40. In other words, the water-absorbent sheet 50 is sandwiched between the liquid-permeable sheet 30 and the liquid-impermeable sheet 40.

The liquid-permeable sheet 30 is disposed at the position of the outermost layer on the side where the liquid to be absorbed permeates. The liquid-permeable sheet 30 is disposed outside the core-wrap sheet 20b in a state of being in contact with the core-wrap sheet 20 b. The liquid-impermeable sheet 40 is disposed at the position of the outermost layer on the opposite side of the liquid-permeable sheet 30 in the absorbent article 100. The liquid-impermeable sheet 40 is disposed outside the core-wrap sheet 20a in a state of being in contact with the core-wrap sheet 20 a. The liquid-permeable sheet 30 and the liquid-impermeable sheet 40 have main surfaces wider than the main surfaces of the water-absorbent sheet 50, and the outer edge portions of the liquid-permeable sheet 30 and the liquid-impermeable sheet 40 extend to the periphery of the absorbent body 10 and the core wrap sheets 20a, 20 b. However, the size relationship among the absorbent body 10, the core wrap sheets 20a, 20b, the liquid-permeable sheet 30, and the liquid-impermeable sheet 40 is not particularly limited, and may be appropriately adjusted according to the use of the absorbent article, etc.

The liquid-permeable sheet 30 may be a nonwoven fabric. The nonwoven fabric used as the liquid-permeable sheet 30 may have a suitable hydrophilicity from the viewpoint of the liquid-absorbing performance of the absorbent article. From this point of view, the liquid-permeable sheet 30 may be a nonwoven fabric having a hydrophilicity of 5 to 200 measured according to a measurement method based on pulp test method No.68 (2000) of pulp technology society. The hydrophilicity of the nonwoven fabric may be 10 to 150. For details of the pulp test method No.68, reference can be made, for example, to WO 2011/086843.

The nonwoven fabric having hydrophilicity may be, for example, a nonwoven fabric formed of fibers having a moderate degree of hydrophilicity such as rayon fibers, or a nonwoven fabric formed of fibers obtained by hydrophilizing hydrophobic chemical fibers such as polyolefin fibers and polyester fibers. Examples of the method for obtaining a nonwoven fabric comprising hydrophilized hydrophobic chemical fibers include a method for obtaining a nonwoven fabric by a spunbond method using chemical fibers in which a hydrophilizing agent is mixed with hydrophobic chemical fibers, a method for producing a spunbond nonwoven fabric from hydrophobic chemical fibers, a method for impregnating a spunbond nonwoven fabric obtained using hydrophobic chemical fibers with a hydrophilizing agent, and the like. As the hydrophilizing agent, anionic surfactants such as aliphatic sulfonate and higher alcohol sulfate, cationic surfactants such as quaternary ammonium salt, nonionic surfactants such as polyethylene glycol fatty acid ester, polyglycerin fatty acid ester and sorbitan fatty acid ester, silicone surfactants such as polyoxyalkylene modified silicone, and antifouling agents composed of polyester, polyamide, acrylic and urethane resins can be used.

The nonwoven fabric used as the liquid-permeable sheet 30 may have a weight per unit area (mass per unit area) of 5 to 200g/m from the viewpoint of being capable of imparting good liquid permeability, softness, strength and cushioning properties to the absorbent article and from the viewpoint of improving the liquid permeation rate of the absorbent article ² 、8～150g/m ² Or 10 to 100g/m ² . The thickness of the liquid-permeable sheet 30 may be 20 to 1400 μm, 50 to 1200 μm or 80 to 1000 μm.

The liquid-impermeable sheet 40 prevents the liquid absorbed into the absorbent body 10 from leaking out from the side of the liquid-impermeable sheet 40. The liquid-impermeable sheet 40 may be a resin sheet or a nonwoven fabric. The resin sheet may be a sheet made of a synthetic resin such as polyethylene, polypropylene, and polyvinyl chloride. The nonwoven fabric may be a spunbond/meltblown/spunbond (SMS) nonwoven fabric in which a water-resistant meltblown nonwoven fabric is sandwiched with a high strength spunbond nonwoven fabric. The liquid-impermeable sheet 40 may be a composite sheet of a resin sheet and a nonwoven fabric (e.g., spunbond nonwoven fabric, hydroentangled nonwoven fabric). The liquid-impermeable sheet 40 may have air permeability from the viewpoint of reducing the stuffiness during wearing and reducing the discomfort to the wearer. As the liquid-impermeable sheet 40 having air permeability, for example, a sheet of Low Density Polyethylene (LDPE) resin can be used.

From the viewpoint of ensuring softness without impairing the feeling of wearing the absorbent article, the liquid-impermeable sheet 40 may have a weight per unit area (mass per unit area) of 10 to 50g/m ² 。

The absorbent article 100 can be manufactured by a method including a step of disposing the water absorbent sheet 50 between the liquid-permeable sheet 30 and the liquid-impermeable sheet 40, for example. The laminate of the liquid-impermeable sheet 40, the water-absorbent sheet 50, and the liquid-permeable sheet 30 laminated in this order is pressurized as needed. Alternatively, the absorbent article 100 can also be obtained by the following method: the liquid-permeable sheet 30, the core-covering sheet 20b, the water-absorbent resin particles 10a, or a mixture containing the water-absorbent resin particles 10a and the fibrous material, the core-covering sheet 20a, and the liquid-impermeable sheet 40 are arranged in this order, and the resulting structure is pressurized while being heated as needed. In order to diffuse the liquid, a nonwoven fabric may be disposed between the liquid-permeable sheet 30 and the core wrap sheet 20 b.

Examples

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

1. Production of Water-absorbent resin particles

Production example 1

A round-bottom cylindrical type detachable flask having an inner diameter of 11cm and an inner volume of 2L and equipped with a reflux condenser, a dropping funnel, a nitrogen inlet pipe, and a stirrer was prepared. A stirring blade (flat blade) 200 of the general shape shown in fig. 4 is mounted on the stirrer. The stirring blade 200 includes a shaft 200a and a flat plate portion 200b. The flat plate portion 200b is welded to the shaft 200a and has a curved front end. The flat plate portion 200b has 4 slits S extending in the axial direction of the shaft 200 a. The 4 slits S are arranged in the width direction of the flat plate portion 200b, the width of the inner two slits S is 1cm, and the width of the outer two slits S is 0.5cm. The length of the flat plate portion 200b is about 10cm, and the width of the flat plate portion 200b is about 6cm. Next, 293g of n-heptane as a hydrocarbon dispersion medium was added to the separable flask, and 0.736g of a maleic anhydride-modified ethylene-propylene copolymer (manufactured by Mitsui Chemicals, inc., hi-WAX 1105A) as a polymer-based dispersant was added, thereby obtaining a mixture. After the dispersant was dissolved in n-heptane by heating to 80 ℃ while stirring the mixture with a stirrer, the mixture was cooled to 50 ℃.

Next, 92.0g (acrylic acid: 1.03 mol) of an aqueous 80.5% by mass acrylic acid solution as a water-soluble ethylenically unsaturated monomer was added to a beaker having an internal volume of 300 mL. Next, 147.7g of 20.9 mass% aqueous sodium hydroxide solution was added dropwise to the beaker while cooling from the outside, whereby 75 mol% neutralization was performed. Then, 0.092g (SUMITOMO SEIKA CHEMICALS co., ltd. Manufactured by HEC AW-15F) of hydroxyethylcellulose as a thickener, 0.0736g (0.272 mmol) of potassium persulfate as a water-soluble radical polymerization initiator, and 0.010g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added to dissolve them, thereby preparing an aqueous solution of stage 1.

Then, the aqueous solution of the stage 1 was added to the separable flask, and then stirred for 10 minutes. Then, a surfactant solution obtained by dissolving sucrose stearate (surfactant, manufactured by Mitsubishi-Chemical Foods Corporation, ryoto Sugar Ester S-370, HLB value: 3) 0.736g in n-heptane 6.62g was added to the separable flask. Then, the inside of the system was sufficiently replaced with nitrogen gas while stirring at a rotational speed of a stirrer of 350 rpm. Then, the flask was immersed in a water bath at 70℃to heat and perform polymerization for 60 minutes, thereby obtaining a stage 1 polymerization slurry.

Next, 128.8g (acrylic acid: 1.44 mol) of an aqueous 80.5 mass% acrylic acid solution as a water-soluble ethylenically unsaturated monomer was added to another beaker having an internal volume of 500 mL. Next, 159.0g of a 27 mass% aqueous sodium hydroxide solution was added dropwise to the beaker while cooling from the outside, whereby 75 mol% neutralization was performed. Then, 0.103g (0.381 mmol) of potassium persulfate as a water-soluble radical polymerization initiator and 0.0116g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and then dissolved, thereby preparing an aqueous solution of stage 2.

Next, the inside of the separable flask was cooled to 25 ℃ while stirring at 600rpm, and then the total amount of the aqueous liquid in the 2 nd stage was added to the polymerization slurry in the 1 st stage. Then, after the inside of the system was replaced with nitrogen gas for 30 minutes, the flask was immersed again in a water bath at 70℃and heated, and polymerization was carried out for 60 minutes, whereby a hydrogel polymer of stage 2 was obtained.

While stirring, 0.589g of 45 mass% pentasodium diethylenetriamine pentaacetate aqueous solution was added to the hydrogel polymer of stage 2. Then, the flask was immersed in an oil bath set at 125 ℃, and 255.3g of water was pumped out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, after adding 4.42g (ethylene glycol diglycidyl ether: 0.507 mmol) of a 2 mass% aqueous ethylene glycol diglycidyl ether solution as a surface cross-linking agent to the flask, the flask was kept at 83℃for 2 hours.

Then, polymer particles (dried product) were obtained by evaporating n-heptane and water at 125℃and drying until the evaporation from the inside of the system was hardly distilled off. After passing the polymer particles through a sieve having a pore diameter of 850. Mu.m, 0.5 mass% of dry silica (manufactured by Cabot Japan Corporation, M-5) was mixed with the polymer particles based on the total mass of the polymer particles, whereby 228.6g of water-absorbent resin particles a containing the dry silica was obtained.

Production example 2

In the preparation of the hydrogel polymer in the 2 nd stage, the temperature in the detachable flask was changed from 25 ℃ to 27 ℃; in the same manner as in production example 1 except that 248.0g of water was withdrawn outside the system by azeotropic distillation in the hydrogel polymer after the polymerization in the 2 nd stage, 231.5g of water-absorbent resin particles b were obtained.

Production example 3

In the same manner as in production example 1 except that dry silica was changed to wet silica (manufactured by Oriental Silicas Corporation, tokuseal NP-S), 230.1g of a water-absorbent resin particle comprising wet silica was obtained.

Production example 4

A water-absorbent resin particle d229.2g was obtained in the same manner as in production example 3, except that the amount of wet silica added was changed from 0.5 mass% to 0.1 mass% based on the total mass of the polymer particles.

Production example 5

A round-bottom cylindrical type detachable flask (baffle width: 7 mm) having a reflux condenser, a dropping funnel, a nitrogen inlet pipe, and a stirrer, an inner diameter of 11cm, and an inner volume of 2L, and having a side wall baffle at 4 places was prepared. As the stirrer, a stirrer having stirring blades having 4 inclined blades (blades surface-treated with a fluororesin) with 2 blade diameters of 5cm was used. Into the flask, 451.4g of n-heptane as a hydrocarbon dispersion medium was added, and 1.288g of sorbitan monolaurate (Nonion LP-20R, HLB value: 8.6,NOF CORPORATION. Manufactured) as a surfactant was added, whereby a mixture was obtained. After sorbitan monolaurate was dissolved in n-heptane by heating up to 50 ℃ while stirring the mixture at a rotation speed of a stirrer of 300rpm, the mixture was cooled to 40 ℃.

Next, 92.0g (acrylic acid: 1.03 mol) of an aqueous 80.5 mass% acrylic acid solution was placed in a 500mL Erlenmeyer flask. Next, 147.7g of 20.9 mass% aqueous sodium hydroxide solution was added dropwise while cooling with ice from the outside to neutralize acrylic acid, thereby obtaining an aqueous solution of partially neutralized acrylic acid. Next, an aqueous monomer solution was prepared by adding 0.1012g (0.374 mmol) of potassium persulfate as a water-soluble radical polymerization initiator to the aqueous solution of the acrylic acid partially neutralized product and then dissolving it.

After the aqueous monomer solution was added to the separable flask, the inside of the system was sufficiently replaced with nitrogen gas. Then, the mixture in the flask was stirred at a rotation speed of a stirrer of 700rpm, and after immersing the flask in a water bath of 70 ℃, the polymerization was terminated by holding for 60 minutes, thereby obtaining a hydrogel polymer.

Next, after adding a dispersion obtained by dispersing 0.092g of wet silica (Tokuseal NP-S) as a powdery inorganic coagulant in 100g of n-heptane to a polymerization liquid containing the produced aqueous gel-like polymer, n-heptane and a surfactant while stirring at a rotation speed of 1000 rpm. Then, the flask was immersed in an oil bath at 125℃to reflux n-heptane by azeotropic distillation of n-heptane and water, and 129.0g of water was withdrawn to the outside of the system. Then, after adding 4.14g (ethylene glycol diglycidyl ether: 0.475 mmol) of a 2 mass% aqueous ethylene glycol diglycidyl ether solution as a surface cross-linking agent to the flask, the flask was kept at 83℃for 2 hours.

Then, the water and n-heptane were evaporated at 120℃and dried until the evaporation from the inside of the system was hardly distilled off, thereby obtaining a dried product. The dried product was passed through a sieve having a pore diameter of 850. Mu.m, whereby 90.1g of water-absorbent resin particles e was obtained.

Production example 6

As the water-absorbent resin particles f, water-absorbent resin particles collected from an absorber of a child diaper "goo.n dry and comfortable air-permeable diaper L code" (purchased in 2019) of Daio Paper Corporation were used. Since the water-absorbent resin particles in the absorber are mixed with the pulp, the pulp is removed as much as possible by air injection.

Production example 7

In the preparation of the aqueous liquid in the stage 1, the water-soluble radical polymerization initiator used was changed to 0.092g (0.339 mmol) of 2,2' -azobis (2-amidinopropane) 2 hydrochloride and 0.018g (0.068 mmol) of potassium persulfate; in the preparation of the polymerization slurry in the stage 1, the rotation speed of the stirrer at the time of nitrogen substitution was changed to 425rpm; in the preparation of the aqueous liquid in the 2 nd stage, the water-soluble radical polymerization initiator used was changed to 0.129g (0.475 mmol) of 2,2' -azobis (2-amidinopropane) 2 hydrochloride and 0.026g (0.095 mmol) of potassium persulfate; in the hydrogel-like polymer after polymerization in stage 2, 253.3g of water was withdrawn outside the system by azeotropic distillation; in the same manner as in production example 1 except that the amount of dry silica added was changed to 0.8 mass% based on the total mass of the polymer particles, 223.5g of water-absorbent resin particles was obtained.

2. Evaluation of Water-absorbent resin particles

The following evaluations were performed on the water-absorbent resin particles a to g. The results are shown in Table 1.

< median particle diameter >)

The median particle diameter of the water-absorbent resin particles was measured by the following procedure. That is, a sieve having a pore diameter of 600 μm, a sieve having a pore diameter of 500 μm, a sieve having a pore diameter of 425 μm, a sieve having a pore diameter of 300 μm, a sieve having a pore diameter of 250 μm, a sieve having a pore diameter of 180 μm, a sieve having a pore diameter of 150 μm, and a tray were combined in this order from the top. The water-absorbent resin particles (50 g) were placed on the uppermost screen of the combination, and classified according to JIS Z8815 (1994) using a rotary (Ro-tap) vibrator (SIEVE FACTORY IIDA Co., ltd.). After classification, the mass of particles remaining on each sieve was calculated as a mass percentage with respect to the total amount and the particle size distribution was determined. Regarding the particle size distribution, by accumulating particles on a sieve in order of particle size from large to small, the relationship between the pore diameter of the sieve and the accumulated value of the mass percentage of particles remaining on the sieve is plotted on logarithmic probability paper. By connecting plotted points on the probability paper with a straight line, a particle diameter equivalent to 50 mass% of the cumulative mass percentage was obtained as a median particle diameter.

< Water retention volume >)

The water retention amount (room temperature) of the water-absorbent resin particles in physiological saline was measured as follows. First, a cotton bag (broad cotton cloth No. 60, 100mm across. Times.200 mm in longitudinal direction) weighing 2.0g of water-absorbent resin particles was placed in a beaker having an internal volume of 500 mL. 500g of a 0.9 mass% aqueous sodium chloride solution (physiological saline) was poured into the cotton bag containing the water-absorbent resin particles at a time so as not to cause caking, and the upper part of the cotton bag was then bound with a rubber band and allowed to stand for 30 minutes, whereby the water-absorbent resin particles were swollen. The cotton bag after 30 minutes was dehydrated for 1 minute by a dehydrator (manufactured by KOKUSAN Co.Ltd., product number: H-122) set to a centrifugal force of 167G, and the mass Wa [ G ] of the cotton bag containing the swollen gel after dehydration was measured. The same procedure was performed without adding the water-absorbent resin particles, and the empty mass Wb [ g ] of the cotton bag when wet was measured, and the water retention amount of the physiological saline of the water-absorbent resin particles was calculated from the following formula.

Water retention [ g/g ] = (Wa-Wb)/2.0

< non-pressurized DW >)

The non-pressurized DW of the water-absorbent resin particles was measured by using a measuring apparatus Z shown in fig. 5. The average value of the measured values at 3 points other than the lowest value and the highest value was obtained by performing 5 times of measurement on 1 kind of water-absorbent resin particles.

The measuring device Z includes a burette portion 71, a conduit 72, a flat measuring table 73, a nylon mesh 74, a stage 75, and a jig 76. The burette portion 71 has: a burette 71a with graduations; a rubber stopper 71b sealing the upper opening of the burette 71a; a cock 71c coupled to the front end of the lower part of the burette 71a; and an air introduction tube 71d and a cock 71e connected to the lower portion of the burette 71a. Burette portion 71 is secured with clamp 76. The measurement table 73 has a through hole 73a having a diameter of 2mm formed in a central portion thereof, and is supported by a stage 75 having a variable height. The through hole 73a of the measurement table 73 is connected to the tap 71c of the burette portion 71 via the conduit 72. The inner diameter of the conduit 72 is 6mm.

The measurement was performed at 25℃and 50.+ -. 10% humidity. First, the cock 71c and the cock 71e of the burette portion 71 are closed, and the physiological saline 77 adjusted to 25℃is put into the burette 71a from the opening in the upper portion of the burette 71a. After the opening of the burette 71a is sealed with the rubber stopper 71b, the cock 71c and the cock 71e are opened. The inside of the catheter 72 is filled with physiological saline 77 to prevent air bubbles from entering. The height of the measurement table 73 is adjusted so that the height of the water surface of the physiological saline 77 reaching the through hole 73a is the same as the height of the upper surface of the measurement table 73. At this time, it was confirmed that the same volume of air as the physiological saline sucked out of the through hole 73a was rapidly supplied from 71 d. After the adjustment, the height of the water surface of the physiological saline 77 in the burette 71a was read by the scale of the burette 71a, and the position was set to zero point (read value at 0 second).

A nylon mesh 74 (100 mm. Times.100 mm,250 mesh, thickness: about 50 μm) was laid in the vicinity of the through hole 73a in the measuring table 73, and a cylinder having an inner diameter of 30mm and a height of 20mm was placed in the center portion thereof. After 1.00g of the water-absorbent resin particles 78 were uniformly dispersed in the cylinder, the cylinder was carefully removed to obtain a sample in which the water-absorbent resin particles 78 were circularly dispersed in the center portion of the nylon mesh 74. Next, the nylon mesh 74 on which the water-absorbent resin particles 78 are placed is rapidly moved so that the center thereof becomes the position of the through hole 73a to start measurement, to such an extent that the water-absorbent resin particles 78 do not scatter. The time when the air bubbles were first introduced into the burette 71a from the air introduction tube 71d was designated as the time when water absorption was started (0 seconds).

The amount of decrease in physiological saline 77 (i.e., the amount of physiological saline 77 absorbed by the water-absorbent resin particles 78) in the burette 71a was sequentially read in 0.1mL units, and the amount Wc [ g ] of decrease in physiological saline 77 after 1 minute, 2 minutes, 5 minutes, and 10 minutes from the start of water absorption by the water-absorbent resin particles 78 was read. From Wc, the 1 minute value, 2 minutes value, 5 minutes value, and 10 minutes value of the non-pressurized DW were obtained by the following formulas. The unpressurized DW was a water absorption amount per 1.00g of the water-absorbent resin particles 78.

Non-pressurized DW value (mL/g) =wc/1.00

< contact Angle >

The contact angle was measured at a temperature of 25.+ -. 2 ℃ and a humidity of 50.+ -. 10%. A double-sided tape (for a concave-convex surface of a Scotch strong double-sided tape manufactured by 3M Japan Limited: 19 mm. Times.76 mm) was attached to a central portion of a slide Glass (manufactured by Matsunami Glass Ind. Ltd.: 26 mm. Times.76 mm), and a sample having an exposed adhesive surface was prepared. First, 1.0g of water-absorbent resin particles to be measured were uniformly dispersed on a double-sided tape attached to a slide glass. Then, the slide glass was turned over to remove the excessive water-absorbent resin particles, thereby preparing a sample for measurement. In this case, 0.2 to 0.3g of the water-absorbent resin particles are uniformly dispersed on the double-sided tape without any gap.

The microscope (KEYENCE CORPORATION, manufactured by VHX-5000) is composed of: a sample mounting table movable in the up-down direction; and a free angle observation stage provided with a mirror body fixing part capable of moving downwards to 90 degrees when the parallel time of the workbench is set to 0 degrees. As for the measurement of the contact angle, the following procedure was followed using the microscope, micropipette (Pipetman capacity 100-1000. Mu.L manufactured by Gilson, inc.), and pipette tip (Eppendorf ep T.I.P.S.Standard 50-1000. Mu.L) described above.

The microscope is adjusted so that the microscope body and the stage are horizontal, and a measurement sample is placed in the center of the stage. The tip of the pipette tip attached to the micropipette was set at a height of 7.+ -.1 mm above the vertical direction from the surface of the measurement sample. 1 drop (0.01 g) of 0.9 mass% saline weighed by a micropipette was added dropwise to a smooth surface of the sample, and a video of the liquid taken up by the surface of the sample was captured. An image of the time t=0.1 (seconds) after the extraction liquid reached the sample surface (this time was set to t=0 (seconds)), and the angle of a straight line connecting the left and right end points and the apex on the contact surface of the saline solution drop and the double-sided tape surface with respect to the double-sided tape surface was measured using the function of a microscope, and the angle was set to θ/2. The contact angle θ was obtained by multiplying this by 2. The measurement was repeated 5 times, and the average value was set as the contact angle of the water-absorbent resin particles. The reading method of the angle is in accordance with JIS R3257 (1999) "wettability test method of substrate glass surface".

TABLE 1

3. Production of water-absorbing sheet

As the upper sheet and the lower sheet, an air-laid nonwoven fabric cut into 12cm×32cm was prepared, and as the intermediate sheet, a hot air nonwoven fabric cut into 10cm×30cm was prepared.

Example 1

A hot-melt coater (Harry's Co., ltd., pump: marshal150, workbench: XA-DT, pot set temperature: 150 ℃, hose set temperature: 165 ℃, gun head set temperature: 170 ℃) was used on the upper sheet, and 0.1g of a hot-melt adhesive (Henkel Japan Ltd., ME-765E) was applied to the base material at 10 intervals of 10mm in the longitudinal direction as shown in FIG. 2. The coating pattern of the adhesive is spiral stripes. Then, 4.5g of the water-absorbent resin particles a were uniformly dispersed in the upper sheet except for the outer periphery 1cm at both ends in the width direction and the longitudinal direction.

After the hot air nonwoven fabric was placed on the surface on which the water-absorbent resin particles a were dispersed, the hot air nonwoven fabric was sandwiched between release papers from above and below, and then pressed and bonded at 110℃under 0.1MPa using a laminator (HASIMA CO., LTD., straight Linear Fussing Press, model HP-600 LFS) to remove the release papers, thereby obtaining a laminate in which an absorber (upper layer absorbent layer) composed of the air-laid nonwoven fabric, the hot melt adhesive, the water-absorbent resin particles a and the hot air nonwoven fabric were arranged in this order.

Subsequently, by the same procedure as described above, 0.1g of the hot-melt adhesive was applied to the lower sheet, and 4.5g of the water-absorbent resin particles a were uniformly dispersed in the air-laid nonwoven fabric. The laminate in which the hot air nonwoven fabric surface of the laminate and the both ends of the surface of the lower sheet on which the water-absorbent resin particles were dispersed were aligned was sandwiched from above and below by release paper, and the laminate was punched and bonded by using a laminator in the same manner as described above, and the release paper was removed, thereby producing a water-absorbent sheet. The obtained water-absorbent sheet was provided with an absorber (upper layer absorbent layer) composed of an air-laid nonwoven fabric, a hot-melt adhesive, and water-absorbent resin particles a, an absorber (lower layer absorbent layer) composed of a hot-air nonwoven fabric, and water-absorbent resin particles a, and an air-laid nonwoven fabric in this order.

Example 2

A water-absorbent sheet was produced in the same manner as in example 1, except that the water-absorbent resin particles a used in the upper and lower absorbent layers were changed to the water-absorbent resin particles b.

Example 3

A water-absorbent sheet was produced in the same manner as in example 1, except that the water-absorbent resin particles a used in the lower absorbent layer were changed to the water-absorbent resin particles d.

Example 4

By the same operation as in example 1, after the hot melt adhesive was applied to the lower sheet, the total of 9g of the water-absorbent resin particles a were uniformly dispersed in the upper sheet except for the outer peripheral 1cm range at both ends in the width direction and the length direction.

The hot melt adhesive was applied to the upper sheet by the same operation as described above. The surface of the upper sheet coated with the hot-melt adhesive was aligned with both ends of the surface of the lower sheet on which the water-absorbent resin particles were dispersed, and then sandwiched from above and below with release paper, and the release paper was removed by pressing and bonding in the same manner as in example 1, to thereby produce a water-absorbent sheet. The obtained water-absorbent sheet was provided with an absorbent layer composed of an air-laid nonwoven fabric, a hot-melt adhesive, water-absorbent resin particles a, a hot-melt adhesive, and an air-laid nonwoven fabric in this order.

Example 5

A water-absorbent sheet was produced in the same manner as in example 1, except that the water-absorbent resin particles a used in the upper and lower absorbent layers were changed to the water-absorbent resin particles g.

Comparative example 1

A water-absorbent sheet was produced in the same manner as in example 1, except that the water-absorbent resin particles a used in the upper and lower absorbent layers were changed to the water-absorbent resin particles c.

Comparative example 2

A water-absorbent sheet was produced in the same manner as in example 1, except that the water-absorbent resin particles a used in the upper and lower absorbent layers were changed to the water-absorbent resin particles e.

Comparative example 3

A water-absorbent sheet was obtained in the same manner as in example 1, except that the water-absorbent resin particles a used in the upper and lower absorbent layers were changed to the water-absorbent resin particles f.

Comparative example 4

A water-absorbent sheet was produced in the same manner as in example 3, except that the water-absorbent resin particles a used in the upper absorbent layer were changed to the water-absorbent resin particles c.

Comparative example 5

A water-absorbent sheet was produced in the same manner as in example 3, except that the water-absorbent resin particles a used in the upper absorbent layer were changed to the water-absorbent resin particles d.

Comparative example 6

A water-absorbent sheet was produced in the same manner as in comparative example 5, except that the water-absorbent resin particles a used in the upper absorbent layer were changed to the water-absorbent resin particles e.

Comparative example 7

A water-absorbent sheet was produced in the same manner as in example 3, except that the water-absorbent resin particles a used in the upper absorbent layer were changed to the water-absorbent resin particles f.

Comparative example 8

A water-absorbent sheet was produced in the same manner as in example 4, except that the water-absorbent resin particles a were changed to the water-absorbent resin particles c.

Comparative example 9

A water-absorbent sheet was produced in the same manner as in example 4, except that the water-absorbent resin particles a were changed to the water-absorbent resin particles e.

Comparative example 10

A water-absorbent sheet was produced in the same manner as in example 4, except that the water-absorbent resin particles a were changed to the water-absorbent resin particles f.

4. Evaluation of Water absorbing sheet

The following evaluation was performed on the water-absorbent sheet. The results are shown in Table 2.

(preparation of artificial urine)

By mixing 9865.75g of ion-exchanged water, 100.0g of sodium chloride (NaCl), calcium chloride dihydrate (CaCl) ₂ ·2H ₂ O) 3.0g, magnesium chloride hexahydrate (MgCl) ₂ ·6H ₂ O) 6.0g, and 1% by mass Triton X solution (Triton X-100/water mixture manufactured by FUJIFILM Wako Pure Chemical Corporation) 25.0g and edible blue No. 1 (coloring) 0.25g were used to prepare artificial urine.

< determination of permeation Rate >

An absorbent article was placed on a horizontal table in a room having a temperature of 25.+ -. 2 ℃. Next, a liquid-charging cylinder (cylinder having openings at both ends) having a capacity of 100mL and an inlet having an inner diameter of 3cm was placed in the center portion of the main surface of the absorbent article. Then, 80mL of the test solution of artificial urine adjusted to 25±1 ℃ in advance was put into the cylinder (supplied from the vertical direction) at one time. The absorption time from the start of the injection to the complete disappearance of the test liquid from the cylinder was measured using a stopwatch. This operation was further performed 2 times (3 times in total) at 30 minute intervals, and the total value of the absorption time was obtained as the permeation rate (seconds). The smaller the permeation rate, the more preferred.

< gradient absorption test >)

Fig. 6 is a schematic diagram showing a method of evaluating the leakage of the water-absorbent sheet. Will have a flat main face S ₁ A support plate 1 (here, an acrylic resin plate) having a length of 45cm is provided at a position opposite to the horizontal plane S ₀ Is fixed by the stand 81 in a state of being inclined by 45 + -2 degrees. The test water absorbing sheet 50 is attached to the main surface S of the fixed support plate 1 with its longitudinal direction oriented along the longitudinal direction of the support plate 1 ₁ And (3) upper part. Next, from a dropping funnel 82 disposed vertically above the water absorbing sheet 50, the test liquid 51 (artificial urine) was dropped to a position 13cm above the center of the absorber in the water absorbing sheet 50. 80mL of test solution was added dropwise at a rate of 8 mL/sec. Dropping funnel 82 The distance between the front end and the absorbent sheet 50 is 10.+ -.1 mm. The test solution was repeatedly added under the same conditions at 10 minute intervals from the start of the first test solution addition until leakage was observed. Further, the measurement was continued for the sample in which the leakage was observed for the first time, and the test solution was poured until the next leakage.

When the test liquid that is not absorbed by the water absorbing sheet 50 leaks from the lower portion of the support plate 1, the leaked test liquid is collected in the metal tray 84 disposed below the support plate 1. The weight (g) of the collected test liquid was measured by a balance 83, and the value was recorded as the leakage amount.

TABLE 2

The water absorbent sheet obtained in the examples has excellent liquid permeation rate and leakage resistance capable of not only suppressing initial leakage but also absorbing water many times.

Symbol description

1-supporting plate, 10-absorber, 10a, 78-water absorbent resin particles, 10 b-fiber layer, 20a, 20 b-core pack, 21-adhesive, 30-liquid-permeable sheet, 40-liquid-impermeable sheet, 50-water-absorbent sheet, 71-burette part, 71 a-burette, 71 b-rubber stopper, 71c,71 e-cock, 71 d-air introduction tube, 72-conduit, 73-measuring table, 74-nylon net, 73 a-through hole, 75-rack, 76-clamp, 77-physiological saline, 81-rack, 82-dropping funnel, 83-balance, 84-metal tray, 100-absorbent article, 200-stirring blade, 200 a-axis, 200 b-plate part, S-slit, Z-measuring device.

Claims

1. A water-absorbing sheet comprising an absorber containing water-absorbing resin particles,

the water-absorbent resin particles contain polymer particles and dry silica disposed on the surfaces of the polymer particles,

the water-absorbent resin particles have a 1-minute value of 15 to 40mL/g in the non-pressurized DW and a 5-minute value of 45 to 65mL/g in the non-pressurized DW,

the contact angle of the water-absorbent resin particles measured in the test performed in the following order of i) and ii) is 50 degrees or less,

i) Drops of 0.01g of 0.9 mass% brine are dropped onto the surfaces of the water-absorbent resin particles at 25.+ -. 2 ℃ and the water-absorbent resin particles are brought into contact with the drops,

ii) measuring the contact angle of the liquid droplet at a time after 0.1 seconds after the liquid droplet contacts the surface of the water-absorbent resin particles,

the pressureless DW is represented by the absorption amount per 1g of the water-absorbent resin particles before absorption of the physiological saline after a predetermined time elapses from the contact with the physiological saline under no pressure, and the 1 minute value and the 5 minute value of the pressureless DW refer to the absorption amount after 1 minute and 5 minutes, respectively, from the start of absorption of the physiological saline by the water-absorbent resin particles, and the unit of the absorption amount is mL.

2. The absorbent sheet according to claim 1, wherein,

the water-absorbent resin particles have a value of 34 to 50mL/g in 2 minutes without pressurization DW.

3. The absorbent sheet according to claim 1, wherein,

the dry silica has hydrophilicity.

4. The absorbent sheet according to any one of claims 1 to 3, wherein,

the water-absorbent resin particles are contained in an amount of 80 to 100% by mass based on the mass of the absorber.

5. An absorbent article provided with the water-absorbent sheet according to any one of claims 1 to 4.