KR20220156550A - Absorbent Sheets and Absorbent Articles - Google Patents

Abstract

An absorbent sheet according to one embodiment includes an absorbent body containing water absorbent polymer particles, and the water absorbent polymer particles have a 1-minute value of non-pressurized DW of 15 to 40 mL/g and a 5-minute value of non-pressurized DW of 45 to 65 mL/g. , and the contact angle of the water-absorbent resin particles, as measured by the test performed in the order of i) and ii) below, is 50 degrees or less.
i) At 25±2° C., droplets corresponding to 0.01 g of 0.9% by mass saline are dropped onto the surface of the water-absorbent resin particles, and the water-absorbent resin particles and the droplets are brought into contact with each other.
ii) The contact angle of the droplet at the point of time 0.1 second after the droplet contacts the surface of the water-absorbent resin particle is measured.

Description

Absorbent Sheets and Absorbent Articles

The present invention relates to an absorbent sheet and an absorbent article.

BACKGROUND OF THE INVENTION [0002] Conventionally, absorbent articles containing water-absorbent resin particles have been used for absorbent articles for absorbing a liquid containing water as a main component, such as urine. For example, in Patent Document 1, a method for producing water-absorbent resin particles having a particle diameter suitable for use in absorbent articles such as diapers is disclosed, and in Patent Document 2, an absorbent member effective for accommodating body fluids such as urine is specified. Methods of using hydrogel absorbent polymers having saline flow inducibility, performance under pressure, and the like are disclosed.

Japanese Unexamined Patent Publication No. 6-345819 Japanese Patent Publication No. 9-510889

In an absorbent article using a conventional absorbent article, the liquid to be absorbed is not sufficiently absorbed by the absorber, and a phenomenon (liquid flow) of excess liquid flowing on the surface of the absorber tends to occur, resulting in leakage of the liquid outside the absorbent article. There was room for improvement in terms of gender. That is, if the liquid supplied to the absorbent body does not sufficiently permeate the absorbent body, a problem may arise that the excess liquid leaks out of the absorbent body or absorbent article by flowing on the surface thereof. Therefore, it is necessary for the liquid to permeate into the absorber at a sufficient rate, and it is required that a suitable permeation rate be stably obtained.

An object of the present invention is to provide an absorbent sheet and an absorbent article that are provided with an absorbent body having an excellent liquid permeation rate and capable of suppressing liquid leakage.

One aspect of the present invention is an absorbent sheet having an absorbent body containing water absorbent polymer particles, wherein the water absorbent polymer particles have a 1-minute value of non-pressurized DW of 15 to 40 mL/g and a 5-minute value of non-pressurized DW of 45 to 65 mL/g. g, and the contact angle of the water-absorbent resin particles is 50 degrees or less, as measured by the test performed in the order of i) and ii) below.

i) At 25±2° C., droplets corresponding to 0.01 g of 0.9% by mass saline are dropped onto the surface of the water-absorbent resin particles, and the water-absorbent resin particles and the droplets are brought into contact with each other.

ii) The contact angle of the droplet at the point of time 0.1 second after the droplet contacts the surface of the water-absorbent resin particle is measured.

Another aspect of the present invention relates to an absorbent article comprising the absorbent sheet described above.

ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide an absorbent sheet and an absorbent article that are provided with an absorber having an excellent liquid permeation rate and capable of suppressing liquid leakage.

1 is a schematic cross-sectional view showing one embodiment of an absorbent sheet.
2 is a schematic plan view showing an example of an adhesive pattern formed on a core wrap sheet.
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 the flat plate portion).
5 is a schematic diagram showing a device for measuring non-pressurized DW of water absorbent resin particles.
6 is a schematic view showing a method for evaluating liquid leakage.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist.

In this specification, "acryl" and "methacryl" are combined and expressed as "(meth)acryl". "Acrylate" and "methacrylate" are similarly expressed as "(meth)acrylate". "(Poly)" shall mean both the case with the prefix "poly" and the case without it. In the same numerical ranges described step by step in the specification below, the upper or lower limit of the numerical range of a given step may be arbitrarily combined with the upper or lower limit of the numerical range of another step. In the numerical range described in this specification, the upper limit or lower limit of the numerical range may be replaced with the value shown in the examples. "Water solubility" means that which shows solubility of 5 mass % or more in water at 25 degreeC. The materials exemplified herein may be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified, when a plurality of substances corresponding to each component are present in the composition. "Physical saline solution" refers to a 0.9% by mass sodium chloride aqueous solution. “Room temperature” refers to 25±2°C.

[Absorption sheet]

A water absorbent sheet according to an embodiment includes an absorbent body containing water absorbent resin particles. The 1-minute value of non-pressurized DW of the water-absorbent resin particles contained in the absorber is 15 to 40 mL/g, and the 5-minute value of unpressurized DW is 45 to 65 mL/g. When the 1-minute value of the non-pressurized DW of the absorbent polymer particles is within the above range, an absorbent body having an excellent permeation rate of liquid can be obtained, and when the 5-minute value of the non-pressurized DW is within the above range, liquid leakage from the absorbent article is prevented. can be suppressed

From the viewpoint of further improving the permeation rate of the liquid, the 1-minute value of the non-pressurized DW of the water absorbent resin particles may be 16 to 35 mL/g, 16 to 30 mL/g, or 16 to 25 mL/g. From the viewpoint of further suppressing liquid leakage, the 5-minute value of the non-pressurized DW of the water absorbent resin particles may be 48 to 65 mL/g, 50 to 63 mL/g, or 51 to 60 mL/g.

From the viewpoint of further suppressing liquid leakage, the 2-minute value of the non-pressurized DW of the water absorbent resin particles may be 34 to 50 mL/g, 34 to 48 mL/g, or 35 to 45 mL/g. The 1-minute value, the 2-minute value, and the 5-minute value of unpressurized DW are values measured by the method described in the Examples described later.

The non-pressurized DW is an absorption rate indicated by the amount of physiological saline absorbed by the water-absorbent resin particles under no pressure until a predetermined time elapses after contact with the physiological saline solution. The non-pressurized DW is expressed as the water absorption amount (mL) per 1 g of water absorbent resin particles before absorption of physiological saline. The 1-minute value, 2-minute value, and 5-minute value of unpressurized DW mean the amount of absorption 1 minute, 2 minutes, and 5 minutes after the absorbent resin particles start to absorb physiological saline, respectively.

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

i) At 25±2° C., droplets corresponding to 0.01 g of 0.9% by mass saline are dropped onto the surface of the water-absorbent resin particles, and the water-absorbent resin particles and the droplets are brought into contact with each other.

ii) The contact angle of the droplet at the point of time 0.1 second after the droplet contacts the surface of the water-absorbent resin particle is measured.

From the viewpoint of further increasing the penetration rate of the liquid, 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 R 3257 (1999) "Test method for wettability of surface of base glass", and is specifically measured by the method described in Examples described later.

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

Examples of the shape of the water-absorbent resin particles include substantially spherical shape, crushed shape, granular shape, or a shape formed by aggregation of 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 surface of the polymer particles. For example, a dry silica can be arrange|positioned on the surface of a polymer particle by mixing a polymer particle and a dry silica. By using such water-absorbent resin particles for the absorbent body, the permeation rate of liquid is increased and leakage of liquid is easily suppressed.

Dry silica is silica manufactured by a dry process, and examples thereof include fumed silica. Fumed silica generally has an active hydroxyl group and therefore has hydrophilicity, but hydrophobicity can also be imparted by surface treatment of the silica surface with an alkylsilane or the like. From the standpoint of obtaining an excellent initial absorption rate, it is preferable that the fumed silica has hydrophilicity.

Dry silica takes the form of secondary particles formed by aggregating a plurality of primary particles with nanometer-sized primary particles as a structural unit. Further, in dry silica, a plurality of secondary particles are aggregated to form secondary aggregates, which are aggregates of secondary particles. In dry silica and synthetic amorphous silica other than dry silica (for example, wet silica produced by a wet method), the shape of the aggregate is different, for example. In general, wet silica aggregates are said to have a substantially spherical aggregate structure, whereas dry silica aggregates have a chain-shaped aggregate structure.

The specific surface area of the fumed silica is, for example, 50 m ² /g or more, 75 m ² /g or more, 100 m ² /g or more, 125 m ² /g or more, 150 m ² /g or more, 170 m ² /g or more, or 200 m ² /g or more, 1000 m ² /g or less, 800 m ² /g or less, 600 m ² /g or less, 400 m ² /g or less, or 350 m ² /g or less may be sufficient. The specific surface area of the dry silica may be, for example, 50 to 1000 m ² /g, 75 to 600 m ² /g, or 100 to 400 m ² /g. The specific surface area of silica can be measured by the BET specific surface area (N ₂ ) method.

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

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

The average particle diameter of the secondary aggregated particles of the fumed silica is preferably 1.0 μm or more, more preferably 10 μm or more, still more preferably 20 μm or more, from the viewpoint of easy handling and obtaining excellent water absorption characteristics. is 100 μm or less, more preferably 70 μm or less, and still more preferably 50 μm or less. From the same point of view, more specifically, the average particle diameter of the secondary aggregated 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 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 moisture content of the dry silica may be, for example, 10% by mass or less, 5.0% by mass or less, 3.0% by mass or less, or 2.0% by mass or less. The lower limit of the moisture content of the dry silica may be, for example, 0.1% by mass or more. The dry silica may be fumed silica having a water content of 5% by mass or less. The water content of dry silica can be measured according to the general test method ISO787-2 for pigments and extender pigments. The moisture content of the dry silica in this specification is the water content based on the total mass of the dry silica and the water in the dry silica.

Examples of commercially available dry silica (hydrophilic dry silica) include "Aerosil 200", "Aerosil 300", and "Aerosil 380" manufactured by Nippon Aerosil Co., Ltd., and "CAB-O-SIL M" manufactured by Cabot Japan Co., Ltd. -5", "CAB-O-SIL H-300", "CAB-O-SIL M-5", and "CAB-O-SIL M3KD". Dry silica may be used individually by 1 type, and may be used in combination of 2 or more types.

The ratio of the dry silica to the mass of the polymer particles may be 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, or 0.4% by mass or more, and 3.0% by mass or less, 2.0% by mass or less, 1.5% by mass or less, Or it may be 1.0 mass % or less. That is, the ratio of dry silica is 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 less, or 0.4 mass % or more and 1.0 mass % or less may be sufficient.

The polymer particles may be water absorbent particles containing a polymer containing an ethylenically unsaturated monomer as a monomer unit. The ethylenically unsaturated monomer may be a water-soluble monomer, and examples thereof include (meth)acrylic acid and its salts, 2-(meth)acrylamide-2-methylpropanesulfonic acid and its salts, (meth)acrylamide, N, N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, polyethylene glycol mono(meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate, and diethylaminopropyl (meth)acrylamide. An ethylenically unsaturated monomer may be used independently and may be used in combination of 2 or more type.

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

The polymer of at least a surface layer part among polymer particles may be crosslinked by reaction with a surface crosslinking agent. The surface crosslinking agent may be, for example, a compound having two or more functional groups (reactive functional groups) having reactivity with functional groups derived from ethylenically unsaturated monomers.

Examples of the surface crosslinking agent include alkylene carbonate compounds such as ethylene carbonate; polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; (Poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (Poly) Polyglycidyl compounds, such as glycerol polyglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; compounds having two or more reactive functional groups such as isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, oxetane compounds such as 3-butyl-3-oxetaneethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; and hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]adipamide.

The surface crosslinking agent may contain a polyglycidyl compound. The ratio of the polyglycidyl compound in the surface crosslinking agent is 50 to 100% by mass, 60 to 100% by mass, 70 to 100% by mass, 80 to 100% by mass, or 90 to 100% by mass based on the total mass of the surface crosslinking agent. It may be 100% by mass.

Also inside the polymer particles, the polymer may be internally crosslinked by self crosslinking, crosslinking by reaction with an internal crosslinking agent, or both of these. From the viewpoint of ease of control of absorption characteristics, it is preferable that at least a reaction by an internal crosslinking agent is included.

The internal crosslinking agent is, for example, one or two compounds including a compound having two or more polymerizable unsaturated groups, a compound having two or more reactive functional groups having reactivity with the functional group of an ethylenically unsaturated monomer, or a combination thereof. It may contain more than one species of compound.

Examples of the compound having two or more polymerizable unsaturated groups include (poly) ethylene glycol, (poly) propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and di- or tri-(meth)acrylic acid esters of polyols such as (poly)glycerin; unsaturated polyesters obtained by reacting the polyol with unsaturated acids such as maleic acid and fumaric acid; bisacrylamides such as N,N'-methylenebis(meth)acrylamide; di- or tri-(meth)acrylic acid esters obtained by reacting polyepoxide with (meth)acrylic acid; di(meth)acrylic acid carbyl esters obtained by reacting polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth)acrylate; allylated starch; allylated cellulose; diallylphthalate; N,N',N"-triallylisocyanurate; divinylbenzene.

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

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

As a crosslinking agent for crosslinking after polymerization, for example, ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene polyols such as glycol and polyglycerin; compounds having two or more epoxy groups such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; compounds having two or more isocyanate groups such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylene carbonate; and hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]adipamide. The crosslinking agent for crosslinking after polymerization is (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol Polyglycidyl compounds such as polyglycidyl ether and polyglycerol polyglycidyl ether may be used. These crosslinking agents may be used alone or in combination of two or more.

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

The timing of addition of crosslinking after polymerization may be after polymerization of the ethylenically unsaturated monomer used for polymerization, and in the case of multistage polymerization, it is preferably added after multistage polymerization. In addition, in consideration of heat generation during and after polymerization, retention due to delay in the process, opening of the system during addition of the crosslinking agent, and change in moisture due to addition of water due to the addition of the crosslinking agent, the crosslinking agent in the crosslinking after polymerization has a water content (function From the viewpoint of the water content based on the mass of the gel polymer), it is preferable to add in the range of [moisture content immediately after polymerization ± 3%].

The median particle diameter of the polymer particles may be 130 to 800 μm, 200 to 850 μm, 250 to 700 μm, 280 to 600 μm, or 300 to 450 μm. The polymer particles may have a desired particle size distribution at the time obtained by the manufacturing method described later, but may also adjust the particle size distribution by performing operations such as particle size adjustment using classification with a sieve.

In addition to the polymer of the ethylenically unsaturated monomer, the polymer particles may contain a certain amount of moisture, and may further contain various additional components therein. Examples of additional components include gel stabilizers, metal chelating agents, antibacterial agents, 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.

Polymer particles can be obtained, for example, by a method including a step of polymerizing a monomer containing an ethylenically unsaturated monomer. The monomer polymerization method may be selected from, for example, a reverse 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 internally crosslinked by the crosslinking agent may be obtained. Polymer particles containing inorganic particles inside may be obtained by polymerizing an ethylenically unsaturated monomer in the presence of inorganic particles such as silica. Some or all of the ethylenically unsaturated monomers may form salts such as alkali metal salts.

In the case of aqueous solution polymerization, for example, polymerizing an ethylenically unsaturated monomer in a monomer aqueous solution containing an ethylenically unsaturated monomer and water to form a hydrogel polymer containing the polymer, and drying the hydrogel polymer By the method to do, polymer particles can be obtained. When a blocky hydrogel polymer is formed, it may be coarsely ground and dried. The water-containing gel polymer or its crushed product may be pulverized after drying, or the particles obtained by pulverization may be classified. The polymer particles used for the surface crosslinking described later may be dried pulverized material or particles obtained by further pulverizing the pulverized material. After classifying the polymer particles obtained by pulverizing the pulverized material and adjusting the particle size of the polymer particles as necessary, you may use them for surface crosslinking.

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

The monomer aqueous solution may further contain a polymerization initiator. A polymerization initiator may be used independently or may be used in combination of 2 or more type. The polymerization initiator may be a photopolymerization initiator, a thermal radical polymerization initiator, or 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 mol with respect to 1 mol of the ethylenically unsaturated monomer.

As an azo compound, for example, 2,2'-azobis[2-(N-phenylamidino)propane] dihydrochloride, 2,2'-azobis{2-[N-(4-chlorophenyl) ) amidino] propane} dihydrochloride, 2,2'-azobis{2-[N-(4-hydroxyphenyl)amidino]propane} dihydrochloride, 2,2'-azobis[2-( N-benzylamidino) propane] dihydrochloride, 2,2'-azobis[2-(N-allylamidino)propane] dihydrochloride, 2,2'-azobis(2-amidinopropane) Dihydrochloride, 2,2'-Azobis{2-[N-(2-hydroxyethyl)amidino]propane} Dihydrochloride, 2,2'-Azobis[2-(5-methyl-2-imine Dazoline-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[2- (4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(5-hydroxy-3,4 ,5,6-tetrahydropyrimidin-2-yl)propane] dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl ]propane} dihydrochloride, 2,2'-azobis(2-methylpropionamide) dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] disulfate dihydrate, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate, and 2,2'-azobis[2-methyl-N-(2-hydroxy ethyl) propionamide].

Examples of the peroxide include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; Methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypival organic peroxides such as lattice; and hydrogen peroxide.

A combination of a polymerization initiator and a reducing agent may be used 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 aforementioned internal crosslinking agent. The amount of the internal crosslinking agent may be 0 millimoles or more, 0.001 millimoles or more, 0.01 millimoles or more, 0.015 millimoles or more, or 0.020 millimoles or more, and 2 millimoles or less, 1 millimoles or less, 0.5 millimoles or less, or 0.1 millimole or less may be sufficient. The monomer aqueous solution may further contain other additives such as a chain transfer agent and a thickener as needed.

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

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

In the case of coarse-grinding a bulky hydrogel polymer, the coarse-grained product obtained by coarse-graining may be in the form of particulates or may have a long, elongated shape in which particles are connected. The minimum width of the crushed material may be, for example, about 0.1 to 15 mm or about 1.0 to 10 mm. The maximum width of the crushed material may be about 0.1 to 200 mm or about 1.0 to 150 mm. Examples of equipment for crushing include a kneader (for example, a pressure type kneader, a twin arm type kneader, etc.), a meat chopper, a cutter mill, and a perm mill. If necessary, the bulky hydrogel polymer may be cut prior to crushing.

A water-containing gel polymer or a coarse product thereof is dried mainly to remove water. The drying method may be a general method such as natural drying, heat drying, or reduced pressure drying. Polymer particles having an appropriate particle size can be obtained by further pulverizing the dried hydrogel polymer or a coarse product thereof and classifying the obtained particles as necessary. The method of pulverization is not particularly limited, and examples thereof include a roller mill (roll mill), a stamp mill, a jet mill, a high-speed rotary mill (hammer mill, pin mill, rotor beater mill, etc.), or a vessel driven mill (rotary mill). , vibration mill, planetary mill, etc.) can be applied. The method of classification is not particularly limited either, and for example, a method using a vibrating sieve, a rotary sifter, a cylindrical stirring sieve, a blower sifter, or a low-tap shaker can be applied.

In the case of reverse phase suspension polymerization, for example, in a suspension containing a hydrocarbon dispersion medium, an aqueous monomer solution containing an ethylenically unsaturated monomer, a radical polymerization initiator, water, etc. dispersed in the hydrocarbon dispersion medium, and a surfactant, the ethylenically unsaturated Polymer particles can be obtained by a method comprising polymerizing a monomer, thereby forming a particulate hydrogel polymer containing a polymer, and removing a hydrocarbon dispersion medium and water from the suspension.

The hydrocarbon dispersion medium may contain at least one compound selected from the group consisting of chain aliphatic hydrocarbons of 6 to 8 carbon atoms and alicyclic hydrocarbons of 6 to 8 carbon atoms. Examples of the hydrocarbon dispersion medium include n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, n-octane, and the like. of chain aliphatic hydrocarbons; Cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethyl alicyclic hydrocarbons such as cyclopentane; Aromatic hydrocarbons, such as benzene, toluene, and xylene, are mentioned. A hydrocarbon dispersion medium may be used independently or may be used in combination of 2 or more types. 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 aqueous monomer solution containing the monomer.

The monomer aqueous solution in the suspension for reverse phase suspension polymerization may further contain the aforementioned internal crosslinking agent. The internal crosslinking agent is usually added to an aqueous monomer solution containing an ethylenically unsaturated monomer. The amount of the internal crosslinking agent may be 0 millimoles or more, 0.001 millimoles or more, 0.01 millimoles or more, 0.015 millimoles or more, or 0.020 millimoles or more, and 2 millimoles or less, 1 millimoles or less, 0.5 millimoles or less, or 0.1 millimole or less may be sufficient.

Suspension for reverse phase suspension polymerization usually further contains a surfactant. A nonionic surfactant, an anionic surfactant, etc. may be sufficient as surfactant. Examples of nonionic surfactants include sorbitan fatty acid esters and (poly)glycerin fatty acid esters ("(poly)" means both with and without the prefix "poly". The same applies hereafter.) , sucrose fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerine fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxy Ethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallylformaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropylalkyl ether, polyethylene glycol fatty acid ester, etc. can Examples of anionic surfactants include fatty acid salts, alkylbenzene sulfonates, alkylmethyl taurates, polyoxyethylene alkylphenyl ether sulfate ester salts, polyoxyethylene alkyl ether sulfonates, polyoxyethylene alkyl ether phosphoric acid esters, and phosphoric acid esters of polyoxyethylene alkyl allyl ethers. Surfactant may be used independently and may be used in combination of 2 or more type. 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 for reverse phase suspension polymerization may further contain a polymeric dispersant. Examples of the polymeric dispersant include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified EPDM (ethylene-propylene-diene-terpolymer), and maleic-acid-modified anhydride. Polybutadiene, maleic anhydride/ethylene copolymer, maleic anhydride/propylene copolymer, maleic anhydride/ethylene/propylene copolymer, maleic anhydride/butadiene copolymer, polyethylene, polypropylene, ethylene/propylene copolymer polymers, oxidized polyethylene, oxidized polypropylene, oxidized ethylene/propylene copolymers, ethylene/acrylic acid copolymers, ethyl cellulose, and ethyl hydroxyethyl cellulose. A polymer type dispersing agent may be used independently or may be used in combination of 2 or more type. The amount of the polymeric 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 based on 100 parts by mass of the aqueous monomer solution.

The suspension for reverse phase suspension polymerization may contain other components, such as a chain transfer agent and a thickener, as needed. The temperature of the polymerization reaction varies depending on the radical polymerization initiator used, but may be, for example, 20 to 150°C or 40 to 120°C. Reaction time is usually 0.5 to 4 hours. Reverse phase suspension polymerization may be divided into multiple times and performed.

After polymerization, polymer particles can be obtained by removing the hydrocarbon dispersion medium and water from the suspension containing the hydrogel polymer and the hydrocarbon dispersion medium. For example, the hydrocarbon dispersion medium and water can be removed by azeotropic distillation, decantation, filtration, vacuum drying, or a combination thereof. Water, a hydrocarbon dispersion medium, or both may remain to some extent in the polymer particles.

The method for producing the water-absorbent resin particles may further include a step of surface cross-linking the polymer particles by heating a reaction mixture containing a surface cross-linking agent aqueous solution containing polymer particles, water, and a surface cross-linking agent.

The surface cross-linking agent aqueous solution contains water and the surface cross-linking agent dissolved in water. The surface crosslinking agent aqueous solution may further contain a hydrophilic organic solvent. The organic solvent may be, for example, alcohol such as 2-propanol, ethanol, methanol, or propylene glycol. The ratio of water to the total amount of water and organic solvent is 100% by mass or less, and may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more.

The polymer particles can be surface crosslinked by mixing the polymer particles and the surface crosslinking agent aqueous solution and heating the formed reaction mixture while stirring as needed. The heating temperature for surface crosslinking may be appropriately adjusted so that surface crosslinking proceeds, and may be, for example, 70 to 300°C, 100 to 270°C, 120 to 250°C, 150 to 220°C, or 170 to 200°C. The reaction time of surface crosslinking may be 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, for example. You may perform the process of surface crosslinking twice or more.

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

The moisture content (mass %) of the hydrous gel polymer is calculated by the following formula.

Moisture content=[Ww/(Ww+Ws)]×100

Ww: A water-containing gel phase obtained by adding the amount of moisture used as necessary when mixing a flocculant, surface crosslinking agent, etc. to the amount of moisture contained in the monomer aqueous solution before polymerization in the entire polymerization process minus the amount of moisture discharged to the outside of the system by the drying step Moisture content of the polymer.

Ws: Solid content calculated from the input amount of materials such as ethylenically unsaturated monomers, crosslinking agents, and initiators constituting the hydrogel polymer.

From the polymer particles after surface crosslinking, water and a hydrocarbon dispersion medium are removed as needed. You may further process the polymer particle after surface crosslinking by drying, pulverization, classification, or a combination thereof.

The method for producing water-absorbent resin particles may include a step of disposing the dry silica after surface crosslinking.

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

1 is a cross-sectional view showing an example of an absorbent sheet. The absorbent sheet 50 shown in FIG. 1 has an absorbent body 10 and two core wrap sheets 20a and 20b. The core wrap sheets 20a and 20b are disposed on both sides of the absorber 10 . In other words, the absorber 10 is disposed inside the corewrap sheets 20a, 20b. The absorber 10 is shaped by being sandwiched between the two core wrap sheets 20a and 20b. The core wrap sheet 20a, 20b may be two sheets, a folded sheet, or a bag body.

The absorbent sheet 50 may further have an adhesive 21 interposed between the corewrap sheet 20a and the absorber 10. 2 is a plan view showing an example of an adhesive pattern formed on a core wrap sheet. The adhesive 21 shown in FIG. 2 forms a pattern composed of a plurality of linear parts arranged at intervals on the core wrap sheet 20a. However, the pattern of the adhesive 21 is not limited to this. The adhesive 21 may be interposed not only between the core wrap sheet 20a and the absorber 10, but also between the core wrap sheet 20b and the absorber 10. The adhesive 21 is not particularly limited, and may be, for example, a hot melt adhesive.

The absorbent body 10 has water absorbent resin particles 10a and a fibrous layer 10b optionally containing a fibrous material. The content of the water absorbent resin particles in the absorber may be 80 to 100% by mass, 85 to 100% by mass, or 90 to 100% by mass based on the mass of the absorber 10.

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

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

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

Examples of the fibrous material constituting the fibrous layer 10b include pulverized wood pulp, cotton, cotton linter, and rayon; cellulosic fibers such as cellulose acetate; and synthetic fibers such as polyamide, polyester, and polyolefin. A fibrous material may be used independently or may be used in combination of 2 or more types. As the fibrous material, hydrophilic fibers can be used.

In order to improve the shape retention before and during use of the absorber, the fibers may be bonded to each other by adding an adhesive binder to the fibrous material. Examples of the adhesive binder include heat-sealable synthetic fibers, hot-melt adhesives, and adhesive emulsions. An adhesive binder may be used independently or may be used in combination of 2 or more types.

Examples of heat-sealable synthetic fibers include pre-melting binders such as polyethylene, polypropylene, and ethylene-propylene copolymers; Non-melting type binders comprising a side-by-side or core-sheath structure of polypropylene and polyethylene are exemplified. In the non-melting type binder described above, only the polyethylene portion can be heat-sealed.

Examples of the hot melt adhesive include ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, and styrene-ethylene-butylene-styrene. and mixtures of base polymers such as block copolymers, styrene-ethylene-propylene-styrene block copolymers, and amorphous polypropylene with tackifiers, plasticizers, antioxidants, and the like.

As the adhesive emulsion, for example, at least one selected from the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene, and vinyl acetate Polymers of one type of monomers are exemplified.

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

The core wrap sheets 20a and 20b may be, for example, nonwoven fabric. The two core wrap sheets 20a and 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 (ie staples) or a nonwoven fabric composed of long fibers (ie filaments) (long fiber nonwoven fabric). The staple is not limited to this, but generally may have a fiber length of several hundred mm or less.

The core wrap sheet (20a, 20b) is a thermal bond nonwoven fabric, an air through nonwoven fabric, a resin bond nonwoven fabric, a spun bond nonwoven fabric, a melt blown nonwoven fabric, an airlaid nonwoven fabric, a spun lace nonwoven fabric, a point bond nonwoven fabric, or two or more types selected from these. A laminate made of nonwoven fabric may be used.

The nonwoven fabric used as the core wrap sheet 20a, 20b may be a nonwoven fabric formed by synthetic fibers, natural fibers, or a combination thereof. Examples of the synthetic fibers include polyolefins such as polyethylene (PE) and polypropylene (PP), polyesters such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT) and polyethylene naphthalate (PEN), and polyamides such as nylon. and fibers comprising synthetic resins selected from amides and rayons. Examples of natural fibers include fibers comprising cotton, silk, hemp, or pulp (cellulose). The fibers forming the nonwoven fabric may be polyolefin fibers, polyester fibers, or a combination thereof. The corewrap sheets 20a, 20b may be tissue paper.

The absorbent sheet 50 is, for example, sandwiched between the core wrap sheets 20a and 20b, the water absorbent resin particles (10a) or a mixture containing the water absorbent resin particles (10a) and the fibrous material, the formed structure It can be obtained by a method of pressurizing while heating as needed. If necessary, an adhesive 21 is disposed between the core wrap sheets 20a and 20b and the water absorbent resin particles 10a or a mixture containing the same.

The absorbent sheet 50 is formed by further providing the absorbent body 10 and the corewrap sheet on the opposite side of the corewrap sheet 20b to the side on which the absorber 10 is present, thereby forming the absorbent body 10 It is good also as a structure which has two layers. Since the water-absorbent resin particles according to the present embodiment are particularly excellent in suppression of leakage, for example, even in an absorbent sheet having a single absorbent layer, they have high water absorption performance and can suppress liquid leakage.

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

The absorbent sheet according to this embodiment may include two or more layers of the absorber described above. In this case, when at least one layer is the absorber according to the present embodiment, the absorbent sheet can improve its absorbent properties. That is, the absorbent sheet according to the present embodiment includes water-absorbent resin particles having a 1-minute value of non-pressurized DW of 15 to 40 mL/g, a 5-minute value of non-pressurized DW of 45 to 65 mL/g, and a contact angle of 50 degrees or less. Liquid leakage can be suppressed by having at least one absorber layer. For example, in the case of a water absorbent sheet having two or more layers of absorbent material, the absorbent material containing the water absorbent resin particles according to the present embodiment and the absorbent material not containing the water absorbent resin particles according to the present embodiment may be provided. You may have a plurality of layers of an absorber containing water-absorbent resin particles according to.

The absorbent sheet according to this embodiment is used, for example, to manufacture various absorbent articles.

[Absorbent article]

The absorbent article according to this embodiment includes the absorbent sheet according to this embodiment. The absorbent article according to the present embodiment includes a core wrap that shapes the absorber; a liquid-permeable sheet disposed on the outermost side of the liquid absorption target; A liquid impermeable sheet or the like disposed on the outermost side opposite to the side to which the liquid to be absorbed is penetrated. Examples of absorbent articles include diapers (for example, paper diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat-absorbent pads, pet sheets, simple toilet members, animal excrement treatment materials, and the like. can

3 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in FIG. 3 includes an absorbent sheet 50, a liquid permeable sheet 30, and a liquid impermeable sheet 40. In other words, the absorbent sheet 50 is sandwiched between the liquid-permeable sheet 30 and the liquid-impervious 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 enters. The liquid permeable sheet 30 is disposed outside the corewrap sheet 20b in a state in contact with the corewrap sheet 20b. The liquid impervious sheet 40 is disposed at the position of the outermost layer on the side opposite to 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 in contact with the core wrap sheet 20a. The liquid-permeable sheet 30 and the liquid-impervious sheet 40 have a main surface wider than that of the absorbent sheet 50, and the outer edges of the liquid-permeable sheet 30 and the liquid-impervious sheet 40 The portion extends around the absorber 10 and the corewrap sheets 20a, 20b. However, the size relationship of the absorber 10, the core wrap sheets 20a and 20b, the liquid-permeable sheet 30, and the liquid-impervious sheet 40 is not particularly limited, and is appropriately adjusted depending on the use of the absorbent article and the like. do.

The liquid-permeable sheet 30 may be a nonwoven fabric. The nonwoven fabric used as the liquid-permeable sheet 30 may have appropriate hydrophilicity from the viewpoint of the liquid absorption performance of the absorbent article. From that point of view, the liquid-permeable sheet 30 was tested according to Paper Pulp Test Method No. 4 by the Paper and Pulp Technology Association. 68 (2000) may be a nonwoven fabric having a hydrophilicity of 5 to 200 measured according to the measurement method. The hydrophilicity of the nonwoven fabric may be 10 to 150. Paper Pulp Test Method No. For details of 68, reference may be made to, for example, WO2011/086843.

The nonwoven fabric having hydrophilicity may be formed of fibers exhibiting appropriate hydrophilicity, such as rayon fibers, or those formed of fibers obtained by hydrophilizing hydrophilic chemical fibers such as polyolefin fibers and polyester fibers. It can be done. As a method of obtaining a nonwoven fabric comprising hydrophilic chemical fibers subjected to hydrophilic treatment, for example, a method of obtaining a nonwoven fabric by a spunbonding method using a mixture of hydrophilic chemical fibers and a hydrophilic agent, and a spunbonded nonwoven fabric with hydrophobic chemical fibers A method of entraining a hydrophilic agent when producing a fiber, a method of impregnating a spunbond nonwoven fabric obtained by using hydrophobic chemical fibers with a hydrophilic agent. Examples of the hydrophilic agent include anionic surfactants such as aliphatic sulfonates and higher alcohol sulfate ester salts, cationic surfactants such as quaternary ammonium salts, polyethylene glycol fatty acid esters, polyglycerol fatty acid esters, and sorbitan fatty acid esters. Silicone surfactants such as ionic surfactants and polyoxyalkylene-modified silicones, and stain release agents made of polyester, polyamide, acrylic, and urethane resins are used.

The weight per unit area (mass per unit area) of the nonwoven fabric used as the liquid-permeable sheet 30 is from the viewpoint of being able to impart good liquid permeability, flexibility, strength and cushioning properties to the absorbent article, and to increase the liquid permeation rate of the absorbent article quickly. From the viewpoint of doing, it may be 5 to 200 g/m ² , 8 to 150 g/m ² , or 10 to 100 g/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 impervious sheet 40 prevents the liquid absorbed by the absorber 10 from leaking out from the liquid impervious sheet 40 side. The liquid impervious sheet 40 may be a resin sheet or a nonwoven fabric. The resin sheet may be a sheet made of synthetic resin such as polyethylene, polypropylene, or polyvinyl chloride. The nonwoven fabric may be a spunbond/meltblown/spunbond (SMS) nonwoven fabric in which a water-resistant meltblown nonwoven fabric is sandwiched between high-strength spunbond nonwoven fabrics. The liquid impermeable sheet 40 may be a composite sheet of a resin sheet and a nonwoven fabric (eg, spunbond nonwoven fabric, spunlace nonwoven fabric). The liquid-impermeable sheet 40 may have air permeability from the viewpoint of reducing dampness during wearing and reducing 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 securing flexibility so as not to impair the comfort of the absorbent article, the weight per unit area (mass per unit area) of the liquid-impermeable sheet 40 may be 10 to 50 g/m ² .

The absorbent article 100 can be manufactured, for example, by a method including disposing the absorbent sheet 50 between the liquid-permeable sheet 30 and the liquid-impervious sheet 40. The laminated body of the liquid impervious sheet 40, the absorbent sheet 50 and the liquid permeable sheet 30 in this order is pressed as necessary. Alternatively, the liquid permeable sheet 30, the corewrap sheet 20b, the water absorbing resin particles 10a, or a mixture including the water absorbing resin particles 10a and the fibrous material, the corewrap sheet 20a, and the liquid The absorbent article 100 can also be obtained by a method in which the impervious sheet 40 is arranged in this order and the formed structure is pressed while heating as necessary. In addition, a nonwoven fabric may be placed between the liquid-permeable sheet 30 and the corewrap sheet 20b for the purpose of diffusing the liquid.

Example

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to these examples.

1. Fabrication of water-absorbent resin particles

(Production Example 1)

A round bottom cylindrical separable flask having an internal diameter of 11 cm and an internal volume of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet pipe, and a stirrer. The stirrer was equipped with a stirring blade (flat blade) 200 schematically shown in FIG. 4 . The stirring blade 200 includes a shaft 200a and a flat plate portion 200b. The flat plate part 200b has a curved tip while being welded to the shaft 200a. Four slits S extending along the axial direction of the shaft 200a are formed in the flat plate portion 200b. The four slits S are arranged in the width direction of the flat plate portion 200b, the inner two slits S have a width of 1 cm, and the outer two slits S have a width of 0.5 cm. The length of the flat plate part 200b is about 10 cm, and the width of the flat plate part 200 b is about 6 cm. Then, to the separable flask described above, 293 g of n-heptane was added as a hydrocarbon dispersion medium, and 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (Hiwax 1105A, manufactured by Mitsui Chemicals Co., Ltd.) was added as a polymer-based dispersant. By doing so, a mixture was obtained. After dissolving the dispersant in n-heptane by raising the temperature to 80°C while stirring the mixture with a stirrer, the mixture was cooled to 50°C.

Next, 92.0 g (acrylic acid: 1.03 mol) of an 80.5% by mass acrylic acid aqueous solution was added to a beaker having an internal volume of 300 mL as a water-soluble ethylenically unsaturated monomer. Then, 75 mol% of neutralization was performed by dripping 147.7 g of 20.9 mass % sodium hydroxide aqueous solution into a beaker, cooling from the exterior. Then, 0.092 g of hydroxyethyl cellulose (HEC AW-15F, manufactured by Sumitomo Seika Co., Ltd.) as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a water-soluble radical polymerization initiator, and ethylene glycol diglycidyl as an internal crosslinking agent A first stage aqueous solution was prepared by adding and dissolving 0.010 g (0.057 mmol) of ether.

And after adding the aqueous liquid of the above-mentioned 1st stage to the above-mentioned separable flask, it stirred for 10 minutes. Thereafter, a surfactant solution obtained by heating and dissolving 0.736 g of sucrose stearate (surfactant, manufactured by Mitsubishi Chemical Foods Co., Ltd., Lyoto Sugar Ester S-370, HLB value: 3) in 6.62 g of n-heptane was separated added to the flask. Then, the inside of the system was sufficiently substituted with nitrogen while stirring at the rotational speed of the stirrer at 350 rpm. Thereafter, the flask was immersed in a 70°C water bath to warm it, and polymerization was performed for 60 minutes to obtain a first-stage polymerization slurry liquid.

Next, 128.8 g (acrylic acid: 1.44 mol) of an 80.5% by mass acrylic acid aqueous solution was added as a water-soluble ethylenically unsaturated monomer to another beaker having an internal volume of 500 mL. Then, 75 mol% of neutralization was performed by dripping 159.0 g of 27 mass % sodium hydroxide aqueous solution into a beaker, cooling from the outside. After that, 0.103 g (0.381 mmol) of potassium persulfate as a water-soluble radical polymerization initiator and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added, followed by dissolution to prepare a second stage aqueous solution did.

Next, the inside of the above-described separable flask was cooled to 25° C. while stirring at a rotational speed of a stirrer of 600 rpm, and then the entire amount of the second stage aqueous liquid was added to the first stage polymerization slurry liquid. Subsequently, after purging the inside of the system with nitrogen for 30 minutes, the flask was again warmed by being immersed in a 70°C water bath, and a polymerization reaction was conducted for 60 minutes to obtain a second stage hydrogel polymer.

To the hydrogel polymer in the second stage, 0.589 g of a 45% by mass diethylenetriamine pentasodium pentacetic acid aqueous solution was added while stirring. Thereafter, the flask was immersed in an oil bath set at 125°C, and 255.3 g of water was taken out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, after adding 4.42 g (ethylene glycol diglycidyl ether: 0.507 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution as a surface crosslinking agent to the flask, the mixture was held at 83° C. for 2 hours did.

After that, n-heptane and water were evaporated at 125°C, and polymer particles (dried product) were obtained by drying until almost no evaporation from the inside of the system flowed out. After passing these polymer particles through a sieve with an opening size of 850 μm, 0.5% by mass of dry silica (manufactured by Cabot Japan Co., Ltd., M-5) based on the total mass of the polymer particles was mixed with the polymer particles, containing dry silica 228.6 g of water-absorbent resin particles a to be obtained.

(Production Example 2)

In the production of the hydrogel polymer in the second stage, the temperature in the separable flask was changed from 25°C to 27°C, and in the hydrogel polymer after polymerization in the second stage, 248.0 g of water was added by azeotropic distillation. 231.5 g of water-absorbent resin particles b were obtained in the same manner as in Production Example 1 except that they were taken out.

(Production Example 3)

230.1 g of water absorbent resin particles c containing wet silica were obtained in the same manner as in Production Example 1 except that the dry silica was changed to wet silica (Tokusil NP-S, manufactured by Oriental Silicas Corporation).

(Production Example 4)

229.2 g of water absorbent resin particles d were obtained in the same manner as in Production Example 3 except that the amount of wet silica added was changed from 0.5% by mass to 0.1% by mass based on the total mass of the polymer particles.

(Production Example 5)

A round-bottom cylindrical separable flask (baffle width: 7 mm) equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet pipe, and a stirrer, having an internal diameter of 11 cm and an internal volume of 2 L, and equipped with four side wall baffles was prepared. As the stirrer, one having a stirring blade having two stages of four inclined paddle blades (surface treated with fluorine resin) with a blade diameter of 5 cm was used. To the flask, 451.4 g of n-heptane was added as a hydrocarbon dispersion medium, and 1.288 g of sorbitan monolaurate (Nonion LP-20R, HLB value: 8.6, manufactured by Nichiyu Co., Ltd.) was added as a surfactant to obtain a mixture. . After dissolving sorbitan monolaurate in n-heptane by raising the temperature to 50°C while stirring the mixture at a rotation speed of a stirrer of 300 rpm, the mixture was cooled to 40°C.

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

After the monomer aqueous solution was added to the separable flask described above, the system was sufficiently substituted with nitrogen. Thereafter, the flask was immersed in a 70°C water bath while stirring the mixture in the flask at a rotational speed of a stirrer of 700 rpm, and then maintained for 60 minutes to complete polymerization, thereby obtaining a water-containing gel polymer.

Next, 0.092 g of wet silica (Tokusil NP-S) as a powdery inorganic coagulant was added in advance to the resulting polymerization solution containing the hydrous gel polymer, n-heptane and a surfactant while stirring at a rotation speed of a stirrer of 1000 rpm. - After adding the dispersion obtained by dispersing in 100 g of heptane, it was mixed for 10 minutes. Thereafter, the flask was immersed in a 125°C oil bath, and 129.0 g of water was taken out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, after adding 4.14 g (ethylene glycol diglycidyl ether: 0.475 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution as a surface crosslinking agent to the flask, the mixture was held at 83° C. for 2 hours did.

Thereafter, water and n-heptane were evaporated at 120°C and dried until almost no evaporation from the inside of the system flowed out to obtain a dried product. By passing the dried product through a sieve having an opening size of 850 μm, 90.1 g of water-absorbent resin particles e were obtained.

(Production Example 6)

Water-absorbent resin particles collected from the absorber of Daio Paper Co., Ltd.'s children's diaper "Goo.N Soft Breathable Pants Type L Size" (purchased in 2019) were used as water-absorbent resin particles f. Since the water absorbent resin particles in the absorber were mixed with the pulp, the pulp was removed as much as possible by air blowing.

(Production Example 7)

In the preparation of the first-stage aqueous solution, the water-soluble radical polymerization initiator used was 0.092 g (0.339 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.018 g (0.068 mmol) of potassium persulfate ), in the preparation of the polymerization slurry liquid in the first stage, the rotation speed of the stirrer at the time of nitrogen substitution was changed to 425 rpm, in the preparation of the aqueous solution in the second stage, a water-soluble radical polymerization initiator used to 0.129 g (0.475 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.026 g (0.095 mmol) of potassium persulfate, in the hydrous gel polymer after polymerization in the second stage , 253.3 g of water was removed from the system by azeotropic distillation, and the addition amount of dry silica was changed to 0.8% by mass based on the total mass of the polymer particles. In the same manner as in Production Example 1, water absorbent resin particles g 223.5 g was obtained.

2. Evaluation of water absorbent resin particles

The water-absorbent resin particles a to g were evaluated as follows. The results are shown in Table 1.

<median particle size>

The median particle size of the water absorbent resin particles was measured according to the following procedure. That is, JIS standard sieve from above, sieve with eye size 600 μm, sieve with eye size 500 μm, sieve with eye size 425 μm, sieve with eye size 300 μm, sieve with eye size 250 μm, sieve with eye size 180 μm, sieve with eye size 150 μm , and , and were combined in the order of the saucer. 50 g of water-absorbent resin particles were placed in the uppermost sieve of the combination, and classified according to JIS Z 8815 (1994) using a rotary tap shaker (manufactured by Iida Seisakusho Co., Ltd.). After classification, the mass of the particles remaining on each sieve was calculated as a mass percentage with respect to the total amount to obtain a particle size distribution. Regarding this particle size distribution, the relationship between the integrated value of the size of the eyes of the sieve and the mass percentage of the particles remaining on the sieve was plotted on a logarithmic probability paper by integrating over the sieve in order from the particle size to the largest. By connecting the plots on the probability paper with a straight line, a particle size corresponding to 50% by mass of the cumulative mass percentage was obtained as a median particle size.

<reservation amount>

The water retention amount (room temperature) of the physiological saline solution of the water absorbent resin particles was measured in the following procedure. First, a cotton bag (cotton broad No. 60, width 100 mm × length 200 mm) weighing 2.0 g of water absorbent resin particles was placed in a beaker with an internal volume of 500 mL. After injecting 500 g of 0.9% by mass aqueous sodium chloride solution (physiological saline) into a cotton bag containing water absorbent resin particles at once so as not to form lumps, the upper part of the cotton bag was tied with a rubber band and allowed to stand for 30 minutes to swell the water absorbent resin particles. . After 30 minutes, the cotton bag was dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set at a centrifugal force of 167 G, and the mass Wa [g] of the bag containing the swollen gel after dehydration was measured did. The same operation was performed without adding the water absorbent resin particles, the empty mass Wb [g] of the cotton bag when wet was measured, and the water retention amount of the physiological saline solution of the water absorbent resin particles was calculated from the following formula.

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

<Unpressurized DW>

The non-pressurized DW of the water absorbent resin particles was measured using a measuring device Z shown in FIG. 5 . The measurement was performed 5 times for one type of water-absorbent resin particle, and the average value of three measured values excluding the lowest and highest values was obtained.

The measuring device Z has a burette part 71, a conduit 72, a flat measuring table 73, a nylon mesh 74, a mount 75, and a clamp 76. The burette unit 71 includes a burette 71a with scales written thereon, a rubber stopper 71b that seals the opening at the top of the burette 71a, and a cock 71c connected to the lower end of the burette 71a. ), and an air inlet pipe 71d and a cock 71e connected to the lower portion of the burette 71a. The burette part 71 is fixed with a clamp 76. The measuring stand 73 has a through hole 73a with a diameter of 2 mm formed in its central portion, and is supported by a stand 75 having a variable height. The through hole 73a of the measuring table 73 and the cock 71c of the buret part 71 are connected by a conduit 72. The inner diameter of conduit 72 is 6 mm.

The measurement was performed under an environment of a temperature of 25°C and a humidity of 50±10%. First, the cock 71c and cock 71e of the burette part 71 were closed, and physiological saline 77 adjusted to 25° C. was introduced into the burette 71a from the upper opening of the burette 71a. After sealing the opening of the burette 71a with the rubber stopper 71b, the cock 71c and the cock 71e were opened. The inside of the conduit 72 was filled with physiological saline solution 77 to prevent air bubbles from entering. The height of the measuring table 73 was adjusted so that the height of the water surface of the physiological saline solution 77 reaching the through hole 73a was equal to the height of the upper surface of the measuring table 73. At this time, it was confirmed that the same volume of air as the physiological saline solution sucked out from the through hole 73a was rapidly supplied from the 71d. After the adjustment, the height of the water surface of the physiological saline solution 77 in the burette 71a was read on the scale of the burette 71a, and the position was taken as the zero point (reading value at 0 second).

A nylon mesh 74 (100 mm × 100 mm, 250 mesh, thickness: about 50 μm) was spread near the through hole 73 a on the measuring table 73, and a cylinder with an inner diameter of 30 mm and a height of 20 mm was placed in the center thereof. After uniformly spreading 1.00 g of water absorbing resin particles 78 on the cylinder, the cylinder was carefully removed to obtain a sample in which the water absorbing resin particles 78 were dispersed in the center of the nylon mesh 74 in a circular shape. Subsequently, the nylon mesh 74 on which the water absorbing resin particles 78 were placed was moved so fast that the water absorbing resin particles 78 did not scatter so that the center thereof was at the position of the through hole 73a, and measurement was started. . The time when air bubbles were first introduced into the burette 71a from the air inlet pipe 71d was set as the start of absorption (0 second).

The reduced amount of physiological saline 77 in the burette 71a (that is, the amount of physiological saline 77 absorbed by the water absorbent polymer particles 78) is sequentially read in units of 0.1 mL, and the water absorbent resin particles 78 absorb water. The weight loss Wc [g] of physiological saline (77) at 1 minute, 2 minutes, 5 minutes and 10 minutes calculated from the start was read. From Wc, the 1-minute value, 2-minute value, 5-minute value, and 10-minute value of unpressurized DW were obtained by the following formula. The unpressurized DW is the water absorption amount per 1.00 g of the water absorbent resin particles 78.

Unpressurized DW value [mL/g]=Wc/1.00

<contact angle>

The measurement of the contact angle was performed under an environment of a temperature of 25±2° C. and a humidity of 50±10%. A double-sided tape (3M Japan strong double-sided tape for uneven surfaces: 19 mm × 76 mm) was affixed to the center of a slide glass (manufactured by Matsunami Glass Kogyo: 26 mm × 76 mm) to prepare an exposed adhesive surface. First, 1.0 g of water-absorbent resin particles to be measured were uniformly spread on a double-sided tape attached to a slide glass. Thereafter, the slide glass was turned over to remove excess water-absorbent resin particles to prepare a sample for measurement. At this time, 0.2 to 0.3 g of water-absorbent resin particles were evenly spread on the double-sided tape without gaps.

The microscope (manufactured by Keyence: VHX-5000) has a stage for placing samples that is movable in the vertical direction, and a scope fixing section that is movable up to 90 degrees downward when parallel to the stage is set to 0 degrees. Consists of an observation stand. The contact angle was measured in the following procedure using the above-mentioned microscope, micropipette (GILSON Pipetman capacity 100-1000 μL), and pipette tip (Eppendorf ep T.I.P.S. Standard 50-1000 μL).

The scope part of the microscope was adjusted to be level with the stage part, and the sample for measurement was placed in the center of the stage part. The front end of the pipette tip attached to the micropipette was placed at a height of 7 ± 1 mm vertically from the surface of the measurement sample. One drop (0.01 g) of 0.9% by mass saline solution weighed with a micropipette was added dropwise to a place with a smooth surface of the sample, and a video was taken until the liquid was absorbed on the surface of the measurement sample. An image was taken at the time of t = 0.1 (seconds) after the liquid landed on the sample surface (the time point was t = 0 (seconds)), and the left and right demerits of the contact surface between the saline droplet and the double-sided tape surface The angle with respect to the double-sided tape surface of the straight line connecting the (端点) and the vertex was measured using the function of a microscope, and the angle was set as θ/2. By doubling this, the contact angle θ was obtained. The measurement was repeated 5 times, and the average value was taken as the contact angle of the water-absorbent resin particles. The method for reading the angle is based on JIS R 3257 (1999) "Method for testing wettability of substrate glass surface".

3. Fabrication of absorbent sheet

As the top sheet and the bottom sheet, air-laid nonwoven fabric cut to 12 cm x 32 cm was prepared, and as the middle sheet, an air-laid nonwoven fabric cut to 10 cm x 30 cm was prepared.

(Example 1)

With a hot melt coater (Hariz Co., Ltd., pump: Marshal 150, table: XA-DT, tank set temperature: 150 °C, hose set temperature: 165 °C, gun head set temperature: 170 °C) on the top sheet, 0.1 g of Ten hot-melt adhesives (ME-765E, manufactured by Henkel Japan Co., Ltd.) were applied to the base material along the lengthwise direction, at intervals of 10 mm as shown in FIG. 2 . The application pattern of the adhesive was a spiral stripe. Thereafter, 4.5 g of the water-absorbent resin particles a were uniformly spread on portions excluding the outer circumference of 1 cm at both ends in the short and long longitudinal directions of the top sheet.

After placing the air-through nonwoven fabric on the surface where the water absorbent resin particles a are sprayed, hold it from the top and bottom with release paper, and use a laminating machine (Hashima Corporation, Straight Linear Fussing Press, model HP-600LFS) at 110°C and 0.1 MPa. Pressed and bonded under conditions, the release paper was removed, and a laminate was obtained in which an air-laid nonwoven fabric, a hot melt adhesive, an absorbent body composed of water absorbing resin particles a (upper absorbent layer), and an air through nonwoven fabric were arranged in this order.

Next, 0.1 g of hot melt adhesive was applied to the lower sheet in the same manner as above, and 4.5 g of water-absorbent resin particles a were uniformly spread on the airlaid nonwoven fabric. Holding the air-through nonwoven fabric surface of the laminate and the surface sprayed with the water absorbent resin particles of the lower sheet from the top and bottom of the laminate with both ends aligned, and pressing them together using a laminating machine in the same operation as above, The release paper was removed to prepare an absorbent sheet. The obtained absorbent sheet includes an air-laid nonwoven fabric, a hot melt adhesive, an absorber made of water absorbing resin particles a (upper absorbent layer), an air-through nonwoven fabric, an absorber made of water absorbent resin particles a (lower absorbent layer), a hot melt adhesive, and an air-laid nonwoven fabric in this order. are placed

(Example 2)

An 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 water-absorbent resin particles b.

(Example 3)

An absorbent sheet was produced in the same manner as in Example 1 except that the water absorbent resin particles a used for the lower absorbent layer were changed to the water absorbent resin particles d.

(Example 4)

After the hot melt was applied to the lower sheet in the same manner as in Example 1, 9 g of the total amount of water-absorbent resin particles a was uniformly spread on both ends of the upper sheet in the short and long directions except for the outer circumference of 1 cm.

A hot melt adhesive was applied to the top sheet in the same manner as above. After aligning both ends of the upper sheet coated with hot melt adhesive and the lower sheet coated with water absorbent resin particles, hold them from top to bottom with release paper, press them together in the same operation as in Example 1, and remove the release paper. , fabricated an absorbent sheet. In the obtained absorbent sheet, an air-laid nonwoven fabric, a hot melt adhesive, an absorbent layer made of water-absorbent resin particles a, a hot melt adhesive, and an air-laid nonwoven fabric are arranged in this order.

(Example 5)

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

(Comparative Example 1)

A water absorbent sheet was prepared in the same manner as in Example 1 except that water absorbent resin particles a used for the upper and lower absorbent layers were changed to water absorbent resin particles c.

(Comparative Example 2)

An 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 water-absorbent resin particles e.

(Comparative Example 3)

An 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 water-absorbent resin particles f.

(Comparative Example 4)

An absorbent sheet was produced in the same manner as in Example 3, except that the water absorbent resin particle a used for the upper absorbent layer was changed to the water absorbent resin particle c.

(Comparative Example 5)

An absorbent sheet was produced in the same manner as in Example 3, except that the water absorbent resin particles a used for 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 water absorbent resin particles a used for the upper absorbent layer were changed to water absorbent resin particles e.

(Comparative Example 7)

An absorbent sheet was produced in the same manner as in Example 3, except that the water absorbent resin particles a used for 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 for changing water absorbent resin particle a to water absorbent resin particle c.

(Comparative Example 9)

A water absorbent sheet was produced in the same manner as in Example 4 except for changing the water absorbent resin particle a to the water absorbent resin particle e.

(Comparative Example 10)

A water absorbent sheet was produced in the same manner as in Example 4 except for changing water absorbent resin particle a to water absorbent resin particle f.

4. Evaluation of absorbent sheet

About the absorbent sheet, the following evaluation was performed. The results are shown in Table 2.

(preparation of artificial urine)

9865.75 g of ion-exchanged water, 100.0 g of sodium chloride (NaCl), 3.0 g of calcium chloride dihydrate (CaCl ₂ 2H ₂ O), 6.0 g of magnesium chloride hexahydrate (MgCl ₂ 6H ₂ O), 1% by mass Triton X solution Artificial urine was prepared by mixing 25.0 g (a mixture of Triton X-100 and water manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 0.25 g of Edible Blue No. 1 (for coloring).

<Measurement of penetration rate>

In a room at a temperature of 25±2° C., the absorbent article was placed on a horizontal platform. Next, a liquid input cylinder (both ends of which are open) having a capacity of 100 mL and having an inlet with an inner diameter of 3 cm was placed in the center of the main surface of the absorbent article. Subsequently, a test solution of 80 mL of artificial urine previously adjusted to 25 ± 1 ° C. was put into the cylinder at once (supplied from the vertical direction). Using a stopwatch, the absorption time from the start of injection until the test solution completely disappeared from the cylinder was measured. This operation was repeated twice (three times in total) at intervals of 30 minutes, and the total value of the absorption time was obtained as the permeation rate (seconds). It is preferable that the permeation rate be smaller.

<Gradient absorption test>

Fig. 6 is a schematic view showing a method for evaluating the leak property of an absorbent sheet. A support plate 1 (here, an acrylic resin plate) having a length of 45 cm having a flat main surface S ₁ was fixed by a mount 81 in a state inclined at 45 ± 2 degrees with respect to the horizontal surface S ₀ . On the main surface S ₁ of the fixed support plate 1, the absorbent sheet 50 for testing was affixed in a direction along the longitudinal direction of the support plate 1 in its longitudinal direction. Subsequently, the test liquid 51 (artificial urine) was dripped from the dropping funnel 82 disposed vertically above the absorbent sheet 50 toward a position 13 cm above the center of the absorbent body in the absorbent sheet 50. A test solution of 80 mL per time was added dropwise at a rate of 8 mL/sec. The distance between the tip of the dropping funnel 82 and the absorbent sheet 50 was 10 ± 1 mm. At 10-minute intervals from the start of the first test solution injection, the test solution was repeatedly injected under the same conditions, and the test solution was injected until leakage was observed. In addition, for those in which leakage was observed at the first time, the measurement was then continued, and the test solution was injected until leakage next time.

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

The absorbent sheets obtained in Examples had excellent liquid permeation rates, were able to suppress liquid leakage in the initial stage, and had leakage resistance capable of absorbing multiple times.

One… support plate
10... absorber
10a, 78... absorbent resin particles
10b... fiber layer
20a, 20b... core wrap sheet
21... glue
30... liquid permeable sheet
40... liquid impervious sheet
50... absorbent sheet
71... buret part
71a... burette
71b... rubber stopper
71c, 71e... cock
71d... air inlet pipe
72... conduit
73... measuring table
74... nylon mesh
73a... through hole
75... trestle
76... clamp
77... saline solution
81... trestle
82... dropping funnel
83... balance
84... metal tray
100... absorbent article
200... stirring wing
200a... axis
200b... reputation department
S... slit
Z... measuring device

Claims (6)

An absorbent sheet having an absorbent body containing absorbent resin particles, comprising:
The 1-minute value of non-pressurized DW of the water absorbent polymer particles is 15 to 40 mL/g, and the 5-minute value of non-pressurized DW is 45 to 65 mL/g,
The absorbent sheet, wherein the water-absorbent resin particles have a contact angle of 50 degrees or less, as measured by tests performed in the order of i) and ii) below.
i) At 25±2° C., a droplet equivalent to 0.01 g of 0.9% by mass saline solution is dropped onto the surface of the water-absorbent resin particle, and the water-absorbent resin particle and the droplet are brought into contact.
ii) The contact angle of the droplet at the point of time 0.1 second after the droplet contacts the surface of the water-absorbent resin particle is measured. The method of claim 1,
The absorbent sheet wherein the 2-minute value of the non-pressurized DW of the water absorbent polymer particles is 34 to 50 mL/g. According to claim 1 or claim 2,
The water absorbent sheet wherein the water absorbent resin particles contain polymer particles and dry silica disposed on the surface of the polymer particles. The method of claim 3,
The absorbent sheet, wherein the fumed silica has hydrophilicity. The method according to any one of claims 1 to 4,
The absorbent sheet wherein the content of the water absorbent resin particles is 80 to 100% by mass based on the mass of the absorbent body. An absorbent article comprising the absorbent sheet according to any one of claims 1 to 5.

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