WO2021187525A1

WO2021187525A1 - Production methods for water absorbent resin particles, absorbent body, and absorbent article

Info

Publication number: WO2021187525A1
Application number: PCT/JP2021/010817
Authority: WO
Inventors: 崇志居藤
Original assignee: 住友精化株式会社
Priority date: 2020-03-18
Filing date: 2021-03-17
Publication date: 2021-09-23
Also published as: JPWO2021187525A1

Abstract

Disclosed is a production method for water absorbent resin particles including polymer particles, said production method involving: polymerizing monomers including ethylenically unsaturated monomers to obtain a water-containing polymer gel; grinding the water-containing polymer gel to obtain a particle group containing a fine powder having a particle size of less than 180 μm; granulating the particle group to obtain a granulated particle group that includes granulated particles; and further grinding the granulated particle group to obtain polymer particles. The granulated particle group prior to further grinding includes at least 70 mass% granulated particles that would not traverse a JIS-standard sieve that has an aperture of 850 µm.

Description

Method for manufacturing water-absorbent resin particles, absorbers and absorbent articles

The present invention relates to a method for producing water-absorbent resin particles, an absorber and an absorbent article.

Absorbents are used for absorbent articles for absorbing water-based liquids such as urine. The composition of the absorber generally includes water-absorbent resin particles and fibrous material.

In the production of water-absorbent resin particles, a step of pulverizing the block-shaped polymer obtained by polymerization into particles is performed. Small particles such as particles having a particle size of less than 180 μm generated by pulverization are used by increasing the particle size by granulation (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-54151

The water-absorbent resin particles used for the absorber are generally finer than the fibrous material, and the water-absorbent resin particles may move between the fibrous material. If the position of the water-absorbent resin particles changes in the absorber, the absorption performance of the absorber becomes non-uniform, and there is a possibility that sufficient performance cannot be exhibited. In addition, the non-uniform absorption performance of the absorber may affect the decrease in the strength of the absorber after absorbing a liquid such as urine. Therefore, it is desirable that the water-absorbent resin particles are well entangled with the fibrous material used for the absorber and have high retention with respect to the fibrous material.

An object of the present invention is to provide water-absorbent resin particles having high retention on fibrous substances.

The method for producing water-absorbent resin particles containing the polymer particles of the present invention is to polymerize a monomer containing an ethylenically unsaturated monomer to obtain a hydrogel polymer, and to obtain the hydrogel polymer. Particles are obtained to obtain a particle group containing fine particles having a particle diameter of less than 180 μm, the particle group is granulated to obtain a granulated particle group containing granulated particles, and the granulated particle group is atomized again. The abundance of the granulated particles that do not pass through the JIS standard sieve having a mesh size of 850 μm is 70% by mass or more in the granulated particle group before repartitioning, which includes obtaining polymer particles.

In the above method, it is preferable that the abundance rate of the granulated particles that do not pass through the JIS standard sieve having a mesh size of 31.5 mm is 5% by mass or more in the granulated particle group before repartitioning.

The above method may further include subjecting the polymer particles to surface cross-linking to obtain water-absorbent resin particles.

The present invention also provides a method for producing an absorber, which comprises obtaining water-absorbent resin particles by the above method and obtaining an absorber containing the water-absorbent resin particles and a fibrous substance.

The present invention also provides a method for producing an absorbent article, which comprises obtaining an absorber by the above method and arranging the absorber between a liquid permeable sheet and a liquid permeable sheet.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide water-absorbent resin particles having high retention to fibrous substances.

It is a schematic cross-sectional view which shows an example of an absorbent article. It is a top view which shows the outline shape of the stirring blade used in an Example. It is a schematic diagram which shows the measuring apparatus of the absorption magnification under pressure of a water-absorbing resin particle. It is the schematic which shows the measuring method of the water absorption resin particle retention rate.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

In this specification, "acrylic" and "methacryl" are collectively referred to as "(meth) acrylic". Similarly, "acrylate" and "methacrylate" are also referred to as "(meth) acrylate". "(Poly)" shall mean both with and without the "poly" prefix. In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range of one step can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range of another step. In the numerical range 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 examples. "Water-soluble" means that it exhibits a solubility in water of 5% by mass or more at 25 ° C. The materials exemplified in the present specification 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 when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. "Saline" refers to a 0.9% by mass sodium chloride aqueous solution. The particles that pass through the sieve of the opening X mean that the particles have a size that allows them to pass through the sieve of the opening X, and a step of actually passing the particles through the sieve of the opening X is required. It is not something to do.

The method for producing water-absorbent resin particles containing polymer particles according to the present embodiment is to polymerize a monomer containing an ethylenically unsaturated monomer to obtain a hydrogel polymer, and to obtain the hydrogel polymer. The polymer is granulated to obtain a particle group containing fine particles having a particle diameter of less than 180 μm, the particle group is granulated to obtain a granulated particle group containing granulated particles, and the granulated particle group is regenerated. Includes, to obtain polymer particles by particle formation. Hereinafter, each step will be described in detail.

[polymerization]
First, a monomer containing an ethylenically unsaturated monomer is polymerized to obtain a hydrogel polymer. The hydrogel-like polymer may be a crosslinked polymer formed by polymerization of a monomer containing an ethylenically unsaturated monomer, which contains water and becomes a gel. The water-absorbent resin particles obtained by the production method according to the present embodiment can contain a crosslinked polymer formed by polymerizing a monomer containing an ethylenically unsaturated monomer. The crosslinked polymer has a monomeric unit derived from an ethylenically unsaturated monomer. That is, the water-absorbent resin particles according to the present embodiment can have a structural unit derived from an ethylenically unsaturated monomer.

Polymerization can be carried out by, for example, an aqueous solution polymerization method. Hereinafter, the polymerization of the monomer by the aqueous solution polymerization method will be described.

The ethylenically unsaturated monomer is preferably water-soluble. Examples of the ethylenically unsaturated monomer include α, β-unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, maleic anhydride and fumaric acid, and carboxylic acid-based monomers such as salts thereof; (meth). ) Nonionic monomers such as acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate; N, N- Amino group-containing unsaturated monomers such as diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylamide and quaternized products thereof; vinyl sulfonic acid, styrene sulfonic acid, 2 Examples thereof include sulfonic acid-based monomers such as- (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid and salts thereof. As the ethylenically unsaturated monomer, one type may be used alone, or two or more types may be used in combination.

The ethylenically unsaturated monomer preferably contains at least one selected from the group consisting of (meth) acrylic acid and salts thereof, (meth) acrylamide, and N, N-dimethylacrylamide, and is preferably (meth) acrylic acid. It is more preferable to contain at least one selected from and salts thereof. Further, (meth) acrylic acid and a salt thereof may be copolymerized with another ethylenically unsaturated monomer. In this case, 70 to 100 mol% of the above (meth) acrylic acid and a salt thereof are preferably used, more preferably 80 to 100 mol%, and 90 to 90 to 100 mol% of the total amount of the ethylenically unsaturated monomer. It is more preferable to use 100 mol%. The ethylenically unsaturated monomer preferably contains at least one of acrylic acid and a salt thereof.

When the ethylenically unsaturated monomer has an acid group such as (meth) acrylic acid and 2- (meth) acrylamide-2-methylpropanesulfonic acid, the acid group is an alkaline neutralizer in advance if necessary. Can be used as neutralized by. Examples of such an alkaline neutralizer include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide and potassium carbonate; ammonia and the like. These alkaline neutralizers may be used in the form of an aqueous solution in order to simplify the neutralization operation. One type of alkaline neutralizer may be used alone, or two or more types may be used in combination. The acid group may be neutralized before the polymerization of the ethylenically unsaturated monomer as a raw material, or during or after the polymerization.

The degree of neutralization of the ethylenically unsaturated monomer by the alkaline neutralizer enhances the water absorption performance by increasing the osmotic pressure of the obtained water-absorbent resin particles, and is safe due to the presence of the excess alkaline neutralizer. From the viewpoint of preventing problems such as, usually, it is preferably 10 to 100 mol%, more preferably 30 to 90 mol%, further preferably 40 to 85 mol%, and 50. It is even more preferably ~ 80 mol%. Here, the degree of neutralization is the degree of neutralization for all the acid groups of the ethylenically unsaturated monomer.

The ethylenically unsaturated monomer is usually preferably used in the state of an aqueous solution. The concentration of the ethylenically unsaturated monomer in the aqueous solution containing the ethylenically unsaturated monomer (hereinafter, simply referred to as "monomeric aqueous solution") may be 20% by mass or more and the saturation concentration or less, and is 25 to 70% by mass. %, More preferably 30 to 50% by mass.

The amount of the ethylenically unsaturated monomer used is the total amount of the monomers (the total amount of the monomers for obtaining the water-absorbent resin particles. For example, the total amount of the monomers giving the structural unit of the crosslinked polymer. The same shall apply hereinafter). It may be 70 to 100 mol%, 80 to 100 mol%, 90 to 100 mol%, 95 to 100 mol%, or 100 mol%. Among them, the ratio of (meth) acrylic acid and its salt may be 70 to 100 mol% with respect to the total amount of the monomer, 80 to 100 mol%, 90 to 100 mol%, 95 to 100 mol%, or It may be 100 mol%. "Ratio of (meth) acrylic acid and its salt" means the ratio of the total amount of (meth) acrylic acid and its salt.

The water-absorbent resin particles are, for example, water-absorbent resin particles containing a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer, and the ethylenically unsaturated monomer is composed of (meth) acrylic acid and It contains at least one compound selected from the group consisting of the salts, and the ratio of (meth) acrylic acid and its salts is 70 to 100 mol% with respect to the total amount of monomers for obtaining water-absorbent resin particles. It may be a thing.

The monomer aqueous solution may contain a polymerization initiator. The polymerization of the monomer contained in the aqueous monomer solution is started by adding a polymerization initiator to the aqueous monomer solution and, if necessary, heating, irradiating with light or the like. Examples of the polymerization initiator include a photopolymerization initiator and a radical polymerization initiator, and among them, a water-soluble radical polymerization initiator is preferably used. The polymerization initiator may be, for example, an azo compound, a peroxide or the like.

Examples of the azo compound include 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride and 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-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2 -(2-Imidazoline-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (4,5,6,7-tetrahydro-1H-1,3-diazepine-2-yl) propane] Dihydrochloride, 2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidine-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) -Imidazoline-2-yl) propane] disulfate dihydrate, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropion amidine] tetrahydrate, 2,2'-azobis Examples thereof include azo compounds such as [2-methyl-N- (2-hydroxyethyl) propionamide]. From the viewpoint that water-absorbent resin particles having good water-absorbing performance can be easily obtained, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxy) Ethyl) -2-imidazolin-2-yl] propane} dihydrochloride and 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropion amidine] tetrahydrate are preferred. One of these azo compounds may be used alone, or two or more thereof may be used in combination.

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-butyl cumyl peroxide, t. -Organic peroxides such as butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate; peroxides such as hydrogen peroxide can be mentioned. Among these peroxides, potassium persulfate, ammonium persulfate, sodium persulfate or hydrogen peroxide is preferably used from the viewpoint of obtaining water-absorbent resin particles having good water absorption performance, and potassium persulfate and persulfate are preferable. It is more preferable to use ammonium sulfate or sodium persulfate. One of these peroxides may be used alone, or two or more thereof may be used in combination.

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

The total amount of the polymerization initiator used is preferably 0.001 to 1 mol with respect to 100 mol of the ethylenically unsaturated monomer used for the polymerization from the viewpoint of avoiding a rapid polymerization reaction and shortening the polymerization reaction time. , 0.005 to 0.5 mol, more preferably 0.008 to 0.3 mol, even more preferably 0.01 to 0.2 mol.

The monomer aqueous solution preferably contains an internal cross-linking agent. By including the internal cross-linking agent, the obtained cross-linked polymer can have cross-linking by the internal cross-linking agent in addition to self-cross-linking by the polymerization reaction as its internal cross-linking structure. As the internal cross-linking agent, for example, a compound having two or more polymerizable unsaturated groups is used, and preferably, a compound having two polymerizable unsaturated groups is used. For example, di or tri (meth) acrylic acid esters of polyols such as (poly) ethylene glycol, (poly) propylene glycol, trimethylpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and (poly) glycerin; Unsaturated polyesters obtained by reacting the above polyol with unsaturated acids such as maleic acid and fumaric acid; bisacrylamides such as N, N'-methylenebis (meth) acrylamide; polyepoxide and (meth) acrylic acid. Di or tri (meth) acrylic acid esters obtained by reaction; carbamil di (meth) acrylic acid obtained by reacting polyisocyanate such as tolylene diisocyanate or hexamethylene diisocyanate with hydroxyethyl (meth) acrylic acid. Esters; allylicated starch; allylated cellulose; diallyl phthalate; N, N', N "-triallyl isocyanurate; divinylbenzene and the like.

Further, in addition to the compound having two or more polymerizable unsaturated groups, a compound having two or more reactive functional groups can be used as an internal cross-linking agent. For example, glycidyl group-containing compounds such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether; (poly) ethylene glycol, (poly) propylene glycol, (poly). Examples thereof include glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl (meth) acrylate. Among these, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether are preferable from the viewpoint of excellent reactivity at low temperature. These internal cross-linking agents may be used alone or in combination of two or more.

When an internal cross-linking agent is used, the amount used is 0.0001 mol with respect to 100 mol of the ethylenically unsaturated monomer in order to sufficiently enhance the water absorption performance such as the water absorption capacity of the obtained water-absorbent resin particles. The above is preferable, 0.001 mol or more is more preferable, 0.003 mol or more is further preferable, and 0.01 mol or more is further preferable.

The addition of the internal cross-linking agent insolubilizes the cross-linked polymer and brings about a suitable water absorption capacity, but an increase in the amount of the internal cross-linking agent added leads to a decrease in the water absorption capacity of the obtained water-absorbent resin particles. Therefore, the amount of the internal cross-linking agent is preferably, for example, 0.50 mol or less, more preferably 0.25 mol or less, and further preferably 0. It is 10 mol or less.

The monomer aqueous solution may contain additives such as a chain transfer agent and a thickener, if necessary. Examples of the chain transfer agent include thiols, thiol acids, secondary alcohols, hypophosphorous acid, phosphorous acid and the like. Examples of the thickener include carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polyethylene glycol, polyacrylic acid, neutralized polyacrylic acid, polyacrylamide and the like. One of these may be used alone, or two or more thereof may be used in combination. A solvent other than water, such as a water-soluble organic solvent, may be appropriately added to the monomer aqueous solution.

The polymerization method is, for example, a static polymerization method in which the monomer aqueous solution is polymerized without stirring (for example, a static state), or a stirring polymerization method in which the monomer aqueous solution is polymerized while being stirred in the reaction apparatus. It's okay. It is preferable to obtain a hydrogel-like polymer by aqueous solution static polymerization, which is a static polymerization method. In the static polymerization method, when the polymerization is completed, a single block-shaped hydrogel-like polymer occupying substantially the same volume as the monomer aqueous solution existing in the reaction vessel can be obtained.

The form of production may be batch, semi-continuous, continuous, etc. For example, in the aqueous solution static continuous polymerization, a polymerization reaction can be carried out while continuously supplying a monomer aqueous solution to a belt conveyor-shaped continuous polymerization apparatus to obtain a hydrogel having a continuous shape such as a band shape. ..

The polymerization temperature varies depending on the polymerization initiator used, but is preferably 0 to 130 ° C., more preferably 10 to 110 ° C. from the viewpoint of increasing the productivity by rapidly advancing the polymerization and shortening the polymerization time. The polymerization time is appropriately set according to the type and amount of the polymerization initiator used, the reaction temperature, and the like, but is preferably 1 to 200 minutes, more preferably 5 to 100 minutes.

The water content of the block-shaped water-containing gel-like polymer obtained by polymerizing the monomers is preferably 30 to 80% by mass, more preferably 40 to 75% by mass, from the viewpoint that the coarse crushing step can be easily carried out. 50 to 70% by mass is more preferable. The water content of the water-containing gel-like polymer is adjusted by operations such as the water content of the monomer aqueous solution, drying after polymerization, and humidification. The water content of the hydrogel polymer is the content of water in the total mass of the hydrogel polymer in% by mass.

[Particle]
Next, the hydrogel polymer is atomized to obtain a particle group containing fine particles having a particle size of less than 180 μm. In the particle formation step, it is sufficient that a group of particles containing fine particles having a particle diameter of less than 180 μm is finally obtained. A step of obtaining a particle group and a step of further crushing the coarsely crushed product to obtain a particle group may be included. The particle swarming step may include the step of drying the hydrogel polymer, the crude product and / or the particle group. The coarsely crushed product is preferably subjected to crushing after undergoing a drying step. The particle swarming step may further include a step of classifying the particle group obtained by pulverization. The particle group obtained by the particle swarming step may consist only of fine particles having a particle size of less than 180 μm. Hereinafter, each step in the particle formation step will be described in detail.

(Rough crushing)
The particleization step can include a step of coarsely crushing the hydrogel polymer to obtain a coarsely crushed product. The crude product obtained by coarsely crushing the hydrogel-like polymer may be in the form of a hydrogel. The coarsely crushed product may be in the form of particles, or may have an elongated shape in which particles are connected. The size of the minimum side of the coarsely crushed product may be, for example, about 0.1 to 15 mm, preferably about 1.0 to 10 mm. The size of the maximum side of the coarsely crushed product may be about 0.1 to 200 mm, preferably about 1.0 to 150 mm.

As the coarse crushing device, for example, a kneader (for example, a pressurized kneader, a double-armed kneader, etc.), a meat chopper, a cutter mill, a pharma mill, or the like can be used. Of these, a double-armed kneader, a meat chopper, and a cutter mill are more preferable. The crushing device may be of the same type as the crushing device described later. In the rough crushing step, the hydrogel polymer may be cut into a size of, for example, about 5 cm square using a cutting machine. After cutting the hydrogel polymer with a cutting machine, it may be further coarsely crushed using a crushing device. When the above-mentioned polymerization step is carried out by stirring polymerization with an apparatus such as a kneader, the polymerization step and the coarse crushing step may be carried out substantially at the same time.

(Dry)
The particleization step can include the step of drying the hydrogel polymer, the coarsely crushed product and / or the pulverized product. These dried products can be obtained by removing the solvent containing water in the hydrogel polymer, coarsely crushed product or crushed product by heating and / or blowing air. Drying is preferably carried out after the hydrogel polymer is roughly crushed and before crushing. That is, the particle-forming step preferably includes a step of drying the hydrogel-like coarse crushed product to obtain a dry crushed product.

The drying method may be natural drying, heat drying, vacuum drying or the like. The drying may be performed under normal pressure or reduced pressure, for example, and may be performed under an air flow such as nitrogen in order to improve the drying efficiency. For drying, a plurality of methods may be used in combination. When the drying is carried out at normal pressure, the drying temperature is preferably 70 to 250 ° C, more preferably 80 to 200 ° C. The drying step is carried out until the water content of the coarsely crushed product is 20% by mass or less, preferably 10% by mass or less, and more preferably 5% by mass or less. The drying temperature may be 120 ° C. or higher, 150 ° C. or higher, or 180 ° C. or higher.

(Crushing)
The particleization step can include a step of crushing a hydrogel polymer, a coarsely crushed product and / or a dried product thereof. By pulverizing the hydrogel polymer, coarsely crushed product and / or dried product thereof, a particle group containing fine powder can be obtained. The pulverization is preferably carried out after coarse crushing and drying. That is, the particle swarming step preferably includes a step of pulverizing the dried coarse crushed product to obtain a particle group containing fine powder.

For crushing, for example, roller mill (roll mill), stamp mill, jet mill, high-speed rotary crusher (hammer mill, pin mill, rotor beater mill, etc.), container-driven mill (rotary mill, vibration mill, planetary mill, etc.), etc. Crusher can be used. Preferably, a high speed rotary grinder is used. The crusher may have an opening on the outlet side, such as a perforated plate, a screen, or a grid, for controlling the maximum particle size of the crushed particles. The shape of the opening may be polygonal, circular, or the like, and the maximum diameter of the opening may be 0.1 to 5 mm, 0.3 to 3.0 mm, or 0.5 to 1.5 mm.

Grinding may be performed so that at least a part of the particle group becomes fine powder having a particle size of less than 180 μm. In the pulverization, for example, while pulverizing for the main purpose of obtaining polymer particles having a particle size of less than 850 μm and having an appropriate particle size that can be used without granulation, some fine particles having a particle size of less than 180 μm are generated. It can be done in such a way.

The abundance of fine particles having a particle size of less than 180 μm in the total amount of the particle group obtained by the particle swarming step may be, for example, 1 to 100% by mass, preferably 30 to 60% by mass. The particle size of less than 180 μm means that the particle size can pass through a JIS standard sieve having a mesh size of 180 μm.

The particle group obtained by the particle formation step may include particles having a particle diameter of 180 μm or more and less than 850 μm (particles that pass through a JIS standard sieve having a mesh size of 850 μm and do not pass through a JIS standard sieve having a mesh size of 180 μm). , Particles having a particle diameter of 250 μm or more and less than 850 μm (particles that pass through a JIS standard sieve having a mesh size of 850 μm and do not pass through a JIS standard sieve having a mesh size of 250 μm) may be included.

(Classification)
The particle swarming step may further include a step of classifying a group of particles containing fine particles having a particle size of less than 180 μm obtained by grinding. Classification refers to an operation of dividing a certain particle group into two or more particle groups having different particle size distributions according to the particle size. By classification, a particle group consisting of only fine particles having a particle size of less than 180 μm may be separated, or the abundance of fine particles having a particle size of less than 180 μm in the particle group may be increased. If necessary, a part of the classified particles may be pulverized again, or the pulverization step and the classification step may be repeated.

A known classification method can be used for the classification of the particle group, and for example, screen classification, wind power classification, or the like may be used. Screen classification is a method of classifying particles on a screen into particles that pass through the mesh of the screen and particles that do not pass through the screen by vibrating the screen. Wind power classification is a method of classifying particles using the flow of air. As the classification method, it is preferable to use screen classification. Examples of the screen classification include a vibrating sieve, a rotary shifter, a cylindrical stirring sieve, a blower shifter, a low-tap type shaker, an electric vibration type shaker, and the like.

[Granulation]
Next, a group of particles containing fine particles having a particle size of less than 180 μm is granulated to obtain a group of granulated particles containing the granulated particles. Granulation is performed so that the abundance of granulated particles that do not pass through the JIS standard sieve having a mesh size of 850 μm is 70% by mass or more in the obtained granulated particle group. In the present specification, granulation means agglomerating particles to obtain particles having a larger particle size than the original particles.

According to the production method according to the present embodiment, the fibers are granulated so that the abundance of the granulated particles that do not pass through the JIS standard sieve having an opening of 850 μm in the granulated particle group is 70% by mass or more. It is possible to obtain water-absorbent resin particles having high retention on the material. The reason why such an effect is obtained is not clear, but the present inventor speculates as follows. However, the present invention is not limited to the following mechanism. In the production method according to the present embodiment, when granulating fine powder, granulation is performed by sufficiently kneading granulated particles having a large particle size to a certain ratio or more. The fact that more granulated particles with a large particle size can be obtained means that the degree of kneading is higher. It is considered that the particles that have undergone such a granulation step have a more complicated shape, such that the particles obtained by re-granulation after that have more fine voids inside and have a plurality of protrusions. It is considered that the water-absorbent resin particles containing the polymer particles having such a shape are more likely to be entangled with the fibrous material, and the retention property to the fibrous material is enhanced.

In the particle group to be subjected to granulation, the abundance of fine powder having a particle diameter of less than 180 μm is 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more. It may be 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more or 98% by mass or more, 100% by mass, 98% by mass or less, 95% by mass or less, 90% by mass or less, 80% by mass. % Or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, or 30% by mass or less.

Granulation can be performed, for example, by mixing a group of particles and water. Water may be used as an aqueous solution containing components such as water-soluble polymerizable monomers such as water-soluble salts and ethylenically unsaturated monomers, cross-linking agents and hydrophilic organic solvents. As the cross-linking agent, for example, the above-mentioned internal cross-linking agent or the later-described surface cross-linking agent can be used. The proportion of water in the aqueous liquid may be, for example, 90 to 100% by mass. As a method of mixing the particle group and water, for example, water may be dropped little by little, the whole amount may be added at once, sprayed, or mixed in the state of steam.

The mixed amount of water is preferably 55 parts by mass or more, and more preferably 60 parts by mass or more with respect to 100 parts by mass of the particle group. When the mixing amount of water is 55 parts by mass or more, the particle group and water can be mixed more uniformly. The mixing amount of water is preferably 115 parts by mass or less, and more preferably 105 parts by mass or less with respect to 100 parts by mass of the particle group. When the mixing amount of water is 115 parts by mass or less, the subsequent drying can be performed more efficiently.

The temperature at the time of mixing may be, for example, 40 to 150 ° C, preferably 60 to 100 ° C. The temperature at the time of mixing may be 80 to 95 ° C. Granulation is preferably carried out by mixing water that has been preheated to a mixing temperature with a group of particles. From the viewpoint of more uniform granulation, it is preferable that the granulation is carried out by putting all the preheated water into the pre-stirred particle group in the mixing container at one time.

From the viewpoint of further increasing the particle size of the obtained granulated particles and making the mixing more uniform, the mixing time of the particle group and water is such that the entire amount of the particle group and water used for mixing is put into the same mixing container. After that, it is preferably 10 to 100 seconds, and more preferably 15 to 90 seconds.

Mixing of the particle group and water can be performed using, for example, various stirrers having stirring blades. As the stirring blade, flat plate blades, lattice blades, paddle blades, propeller blades, anchor blades, turbine blades, Faudler blades, ribbon blades, full zone blades, Maxblend blades and the like can be used. The flat plate blade has a shaft (stirring shaft) and a flat plate portion (stirring portion) arranged around the shaft. Further, the flat plate portion may have a slit or the like. When a flat plate blade is used as the stirring blade, granulation can be performed more uniformly, and a group of granulated particles having a relatively large size tends to be easily obtained. Examples of the stirring type mixer include a mortar mixer, a continuous kneader, a ladyge mixer and the like.

From the viewpoint of setting the particle size distribution of the obtained granulated particles in a more preferable range, the mixing conditions of the particle group and water are as follows, for example, the mixing amount of water is 55 to 115 parts by mass with respect to 100 parts by mass of the particle group, and the mixing temperature. The mixing time may be 40 to 150 ° C., and the mixing time may be 10 to 100 seconds after the entire amount of the particle group and water is put into the same container, and the mixing amount of water is 60 to 100 parts by mass with respect to 100 parts by mass of the particle group. It may be a combination of 105 parts by mass, a mixing temperature of 60 to 100 ° C., and a mixing time of 15 to 90 seconds after the entire amount of the particle group and water is put into the same container. The mixing conditions of the particle group and water may be set so that the ratio of the granulated particles having a predetermined particle size in the obtained granulated particle group is a certain value or more. The particles may be confirmed with the naked eye during or after mixing, and if necessary, further mixing may be performed by heating, adding water, adding particle groups, or the like.

[Measurement of particle size distribution of granulated particles]
The particle size distribution of the granulated particle group can be measured after the granulation step. For the measurement of the particle size distribution of the granulated particle group, it is preferable to use the granulated particle group obtained by granulation as it is without drying. The particle size distribution can be measured using all or part of the granulated particle group obtained by granulation. The amount of the granulated particle group used for measuring the particle size distribution may be, for example, 30 g or more or 100 g or more, and may be 30 to 100 g.

The particle size distribution of the granulated particle group is measured by classifying the granulated particle group using a JIS standard sieve with each opening. For classification, for example, using an electromagnetic vibration type sieve shaker Octagon 200 (manufactured by endcotts) in which the vibration intensity is set to 7, a JIS standard sieve and a saucer having a predetermined opening into which measurement samples are placed are placed in the vertical direction. This can be done by vibrating for 10 minutes to shake the particles.

In the granulated particle group obtained by granulation, the abundance rate of the granulated particles that do not pass through the JIS standard sieve having an opening of 850 μm is 70% by mass or more, preferably 75% by mass or more, and 77% by mass or more. It may be 80% by mass or more, 85% by mass or more, or 88% by mass or more. In the granulated particle group, the abundance rate of the granulated particles that do not pass through the JIS standard sieve having an opening of 850 μm may be, for example, 100% by mass, 98% by mass or less, 95% by mass or less, 90% by mass or less, 88% by mass. % Or less, 85% by mass or less, or 80% by mass or less.

In the granulated particle group obtained by granulation, the abundance rate of the granulated particles that do not pass through the JIS standard sieve having a mesh size of 9.5 mm may be, for example, 55% by mass or more, preferably 60% by mass or more. .. The abundance rate may be 70% by mass or more, 80% by mass or more, or 85% by mass or more. In the granulated particle group, the abundance rate of the granulated particles that do not pass through the JIS standard sieve having a mesh size of 9.5 mm may be, for example, 100% by mass, 98% by mass or less, 95% by mass or less, 93% by mass or less. It may be 90% by mass or less, 88% by mass or less, 85% by mass or less, 80% by mass or less, 75% by mass or less, or 70% by mass or less.

In the granulated particle group obtained by granulation, the abundance rate of the granulated particles that do not pass through the JIS standard sieve having a mesh size of 31.5 mm may be, for example, 5% by mass or more, and 10% by mass or more or 15% by mass or more. Is preferable. The abundance rate is 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more. It may be 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, or 90% by mass or more.

In the granulated particle group obtained by granulation, the abundance rate of the granulated particles that do not pass through the JIS standard sieve having a mesh size of 31.5 mm may be, for example, 100% by mass, 98% by mass or less, 95% by mass or less. 93% by mass or less, 90% by mass or less, 85% by mass or less, 80% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, It may be 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, or 25% by mass or less.

The granulated particles used for measuring the particle size distribution may be returned to the manufacturing process of the water-absorbent resin particles and used continuously in the production of the water-absorbent resin particles. When only a part of the granulated particle group obtained by granulation is used for measuring the particle size distribution, the granulated particles used for measuring the particle size distribution need not be used for producing the water-absorbent resin particles.

[Reparticle]
Next, the granulated particle group obtained by granulation is re-granulated to obtain polymer particles. Polymer particles having a desired particle size can be obtained by re-granulating the particles whose particle size has been increased by granulation.

In the repartitioning step, it is sufficient that polymer particles having a desired particle size are finally obtained. , The step of further crushing the granulated coarse crushed product to obtain the granulated crushed product (polymer particles) may be included. The re-granulation step may include a step of drying the granulated particles, the granulated coarse crushed product, or the pulverized granulated product. The granulated coarse crushed product is preferably subjected to pulverization after undergoing a drying step. The repartitioning step may further include a step of classifying the granulated pulverized product obtained by pulverization.

The re-granulation step can include a step of coarsely crushing the granulated particles to obtain a granulated coarse crushed product. The granulated coarse crushed product may be in the form of a hydrogel. The size of the minimum side of the granulated coarse crushed product may be, for example, about 0.1 to 15 mm, preferably about 1.0 to 10 mm. The coarse crushing may be performed only on granulated particles having a large size, such as those having a minimum side size of more than 5 mm or more than 10 mm. The coarsening apparatus used in the repartitioning may be the same as that used for the coarsening in the above-mentioned particleization step.

The re-granulation step can include a step of drying the granulated particles, the granulated coarse crushed product, or the pulverized granulated product. By drying, a granulated dried product can be obtained. Drying in the repartitioning step is preferably performed on the granulated coarse crushed product. That is, the drying step in the repartitioning step is preferably performed after coarse crushing. The drying temperature may be 120 ° C. or higher, 150 ° C. or higher, or 180 ° C. or higher. When the drying is carried out at normal pressure, the drying temperature is preferably 70 to 250 ° C, more preferably 80 to 200 ° C. The drying is preferably carried out until the water content of the finally obtained polymer particles is 10% by mass or less, and more preferably 5% by mass or less. As the drying method, the same method as the drying in the above-mentioned particleization step can be applied.

The re-granulation step can include a step of crushing granulated particles, granulated coarse crushed products and / or dried products thereof. In the repartitioning step, pulverization is preferably performed after coarse pulverization and drying. The repartitioning step preferably includes a step of drying the granulated coarse crushed product and then pulverizing it to obtain polymer particles. The pulverizer used for pulverization in the repartitioning step may be the same as that used for pulverization in the above-mentioned particleization step.

According to the method for producing water-absorbent resin particles according to the present embodiment, the particle size distribution of the polymer particles obtained by repartitioning tends to be more suitable. Specifically, in the polymer particles obtained by repartitioning, the yield of particles having a particle size of 180 μm or more and less than 850 μm can be improved, and the generation rate of fine particles having a particle size of less than 180 μm can be suppressed. .. A high yield of polymer particles having a particle size of 180 μm or more and less than 850 μm indicates that the granulation strength is higher.

The repartitioning step may include a step of further classifying the polymer particles after crushing. The method for classifying the particles after re-particle formation may be the same as the classification method shown in the above-mentioned particle-forming step, and it is preferable to use screen classification.

When fine powder having a particle size of less than 180 μm is obtained again by re-granulation, the particle size may be increased to a desired particle size by performing granulation again. In the granulation performed after the re-granulation, it is not necessary to obtain granulated particles having a large particle size as in the first granulation described above, and the final required particle size (for example, the particle size is 180 μm or more and less than 850 μm). Granulation may be performed until the range) is reached. The steps of reparticle formation and granulation may be repeated a plurality of times.

[Surface cross-linking]
The method for producing water-absorbent resin particles according to the present embodiment may include a step of surface cross-linking of polymer particles. The surface cross-linking can be performed, for example, by adding a cross-linking agent (surface cross-linking agent) for performing the surface cross-linking to the polymer particles and reacting them. The surface cross-linking agent may be added at any timing after pulverization in the repartitioning step, and may be performed before or after drying in the reparticlening step, or before or after classification. good. When the classification is performed after pulverization in the reparticle step, the addition of the surface cross-linking agent is preferably performed after the drying and classification in the reparticle step. By adding a surface cross-linking agent and performing the surface cross-linking treatment, the cross-linking density in the vicinity of the surface of the polymer particles is increased, so that the water absorption performance of the obtained water-absorbent resin particles can be improved.

The surface cross-linking agent can be added, for example, by adding a surface cross-linking agent solution or by spraying the surface cross-linking agent solution. From the viewpoint of uniformly dispersing the surface cross-linking agent, the surface cross-linking agent is preferably added as a surface cross-linking agent solution by dissolving the surface cross-linking agent in a solvent such as water and / or alcohol. Further, the surface cross-linking step may be carried out once or divided into a plurality of times of two or more times.

The surface cross-linking agent may contain, for example, two or more functional groups (reactive functional groups) having reactivity with a functional group derived from an ethylenically unsaturated monomer. Examples of the surface cross-linking agent include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; (poly) ethylene glycol di. Polyglycidyl compounds such as glycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether; epichlorohydrin, epibromhydrin, α- Haloepoxy compounds such as methyl epichlorohydrin; 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- Oxetane compounds such as oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol; 1,2-ethylenebisoxazoline Oxazoline compounds such as; carbonate compounds such as ethylene carbonate; hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide and the like. Among these, (poly) ethylene glycol diglycidyl ether, (poly) ethylene glycol triglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (poly) ) Polyglycidyl compounds such as glycerol polyglycidyl ether and / or polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, polyoxyethylene glycol and polyoxypropylene glycol are preferable, and polyglycidyl compounds are preferable. More preferred. These surface cross-linking agents may be used alone or in combination of two or more. For example, a polyglycidyl compound and polyols may be used in combination.

The amount of the surface cross-linking agent added is usually based on 100 mol of the total amount of the ethylenically unsaturated monomer used for the polymerization from the viewpoint of appropriately increasing the cross-linking density near the surface of the water-absorbent resin particles (polymer particles). , Preferably 0.0001 to 4.0 mol, more preferably 0.001 to 2.0 mol.

The surface cross-linking step is preferably carried out in the presence of water in the range of 1 to 200 parts by mass with respect to 100 parts by mass of the ethylenically unsaturated monomer. The amount of water can be adjusted by appropriately using a water-soluble organic solvent such as water and / or alcohol. By adjusting the amount of water in the surface cross-linking step, the water-absorbent resin particles (polymer particles) can be more preferably cross-linked in the vicinity of the particle surface.

The treatment temperature of the surface cross-linking agent is appropriately set according to the surface cross-linking agent used, and may be 20 to 250 ° C. The treatment time with the surface cross-linking agent may be 1 to 200 minutes or 5 to 100 minutes.

Surface cross-linking may be performed only once or at multiple timings. The surface cross-linking may be carried out after the pulverization step and before the pulverization in addition to the execution after the pulverization step or after the pulverization step.

[Water-absorbent resin particles]
The water-absorbent resin particles obtained by the production method according to the present embodiment include the above-mentioned polymer particles. The water-absorbent resin particles may be composed of only polymer particles, for example, a gel stabilizer, a metal chelating agent (ethylenediamine tetraacetic acid and a salt thereof, diethylenetriamine-5 acetic acid and a salt thereof, for example, diethylenetriamine-5 sodium acetate and the like, etc. ), An additional component such as a fluidity improver (lubricant) may be further contained. Additional components may be placed inside, on the surface, or both of the polymer particles.

The water-absorbent resin particles may contain a plurality of inorganic particles arranged on the surface of the polymer particles. For example, by mixing the polymer particles and the inorganic particles, the inorganic particles can be arranged on the surface of the polymer particles. The inorganic particles may be silica particles such as amorphous silica. Inorganic particles usually have a small size as compared with the size of polymer particles. For example, the average particle size of the inorganic particles may be 0.1 to 50 μm, 0.5 to 30 μm, or 1 to 20 μm. The average particle size can be measured by the pore electric resistance method or the laser diffraction / scattering method depending on the characteristics of the particles.

When the water-absorbent resin particles include inorganic particles arranged on the surface, the content of the inorganic particles is 0.05 parts by mass or more and 0.1 parts by mass or more based on 100 parts by mass of the total mass of the polymer particles. , 0.15 parts by mass or more or 0.2 parts by mass or more, 5.0 parts by mass or less, 3.0 parts by mass or less, 1.0 parts by mass or less, 0.5 parts by mass or less or 0.3 It may be less than or equal to a mass part.

The shape of the water-absorbent resin particles obtained by the production method according to the present embodiment may be, for example, a crushed shape, an amorphous shape, an amorphous crushed shape, or a shape formed by aggregating these particles. The medium particle size of the water-absorbent resin particles may be 130 to 800 μm, 200 to 850 μm, 250 to 700 μm, 300 to 600 μm, or 300 to 450 μm.

The CRC (centrifuge retention capacity, Centrifuge Retention Capacity) of the water-absorbent resin particles obtained by the production method according to the present embodiment is, for example, 25 g / g or more, 28 g / g or more, 30 g / g or more, or 32 g / g or more. It may be 40 g / g or less, 38 g / g or less, 36 g / g or less, 34 g / g or less, or 33 g / g or less. CRC is measured by the method described in Examples described later with reference to the EDANA method (NWSP 241.0.R2 (15), page.769-778).

The absorption ratio (AAP, Absorption Against Pressure) of the water-absorbent resin particles obtained by the production method according to the present embodiment under 2.07 kPa (0.3 psi) pressurization is, for example, 18 g / g or more, 20 g / g or more, or It may be 22 g / g or more, 30 g / g or less, 28 g / g or less, 26 g / g or less, or 24 g / g or less. The absorption ratio of the water-absorbent resin particles under 2.07 kPa pressurization is measured by the method described in Examples described later.

The water absorption rate of the water-absorbent resin particles obtained by the production method according to the present embodiment by Vortex is, for example, 30 seconds or more, 32 seconds or more, 34 seconds or more, 36 seconds or more, 38 seconds, 40 seconds or more, 42 seconds or more. , 44 seconds or more, 46 seconds or more, or 48 seconds or more, and may be 90 seconds or less, 80 seconds or less, 70 seconds or less, 60 seconds or less, 55 seconds or less, 50 seconds or less, or 40 seconds or less. The water absorption rate by the Vortex method is measured in accordance with (Japanese Industrial Standard JIS K 7224 (1996)). Specifically, in a 100 mL beaker with a flat bottom surface, 2.0 ± 0.002 g of water-absorbent resin particles were added to 50 ± 0.1 g of physiological saline stirred at ^{600 rpm (rpm = min -1).} The water absorption rate can be obtained as the time [seconds] from the addition of the water-absorbent resin particles to the disappearance of the vortex and the flattening of the liquid surface.

The water-absorbent resin particles obtained by the production method according to the present embodiment are excellent in absorption of body fluids such as urine and blood. For example, sanitary products such as disposable diapers, sanitary napkins and tampons, pet sheets, dogs or cats. It can be applied to fields such as animal excrement treatment materials such as toilet formulations.

The water-absorbent resin particles can be suitably used for the absorber. The water-absorbent resin particles obtained by the production method according to the present embodiment are excellent in entanglement with the fibrous material and have high retention with respect to the fibrous material, and are therefore suitable for an absorber containing the fibrous material. The absorber containing the water-absorbent resin particles and the fibrous material obtained by the production method according to the present embodiment has excellent shape retention and is more likely to exhibit water absorption performance. The method for producing an absorber according to the present embodiment includes, for example, obtaining water-absorbent resin particles by the above-mentioned method and obtaining an absorber containing water-absorbent resin particles and a fibrous substance.

The method for producing the absorber may include, for example, mixing the water-absorbent resin particles and the fibrous material, forming a mixture of the water-absorbent resin particles and the fibrous material in a sheet shape, and the like. good. The water-absorbent resin particles and the fibrous material can be mixed, for example, by air papermaking.

The content of the water-absorbent resin particles in the absorber is 100 to 1000 g (that is, 100 to 1000 g / m) per square meter of the absorber from the viewpoint of obtaining sufficient liquid absorption performance when the absorber is used for an absorbent article. ² ) is preferable, more preferably 150 to 800 g / m ² , and even more preferably 200 to 700 g / m ² . From the viewpoint of exhibiting sufficient liquid absorption performance as an absorbent article, the content ^{is preferably 100 g / m 2} or more. From the viewpoint of suppressing the occurrence of the gel blocking phenomenon, the content ^{is preferably 1000 g / m 2} or less.

The mass ratio of the water-absorbent resin particles in the absorber may be 2% to 100%, preferably 10% to 80%, and 20% to 70% with respect to the total of the water-absorbent resin particles and the fibrous material. More preferably. The structure of the absorber may be, for example, a form in which the water-absorbent resin particles and the fibrous material are uniformly mixed, and the water-absorbent resin particles are sandwiched between the fibrous material formed in a sheet or layer. It may be in a form or in any other form. The absorber may have a structure that does not contain fibrous substances, or may be composed of, for example, only water-absorbent resin particles.

Examples of the fibrous material include finely pulverized wood pulp, cotton, cotton linter, rayon, cellulosic fibers such as cellulose acetate, and synthetic fibers such as polyamide, polyester, and polyolefin. Further, the fibrous material may be a mixture of the above-mentioned fibers. As the fibrous material, a non-woven fabric such as air-through or air-laid is preferable from the viewpoint of being excellent in retention with water-absorbent resin particles obtained by the production method according to the present embodiment.

In order to further enhance the morphological retention before and during use of the absorber, the fibers may be adhered to each other by adding an adhesive binder to the fibrous material. Examples of the adhesive binder include heat-sealing synthetic fibers, hot melt adhesives, adhesive emulsions, and the like.

Examples of the heat-bondable synthetic fiber include a total fusion type binder such as polyethylene, polypropylene, and an ethylene-propylene copolymer, and a non-total fusion type binder having a side-by-side or core-sheath structure of polypropylene and polyethylene. In the above-mentioned non-total fusion type binder, only the polyethylene portion is heat-sealed. Examples of hot melt adhesives include ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, and styrene-ethylene-propylene-styrene block copolymer. , A compounding of a base polymer such as amorphous polypropylene and a tackifier, a plasticizer, an antioxidant and the like.

Adhesive emulsions include, for example, 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. Be done. These adhesive binders may be used alone or in combination of two or more.

The absorber may further contain additives such as inorganic particles (for example, amorphous silica), deodorants, pigments, dyes, antibacterial agents, fragrances, and adhesives. These additives can impart various functions to the absorber. When the water-absorbent resin particles contain inorganic particles, the absorber may contain inorganic particles in addition to the inorganic particles in the water-absorbent resin particles. Examples of the inorganic particles include silicon dioxide, zeolite, kaolin, clay and the like.

The shape of the absorber is not particularly limited, and may be, for example, a sheet shape. The thickness of the absorber (for example, the thickness of the sheet-shaped absorber) may be, for example, 0.1 to 20 mm and 0.3 to 15 mm.

The above absorber can be suitably used for an absorbent article. The method for producing an absorbent article according to the present embodiment includes, for example, arranging an absorber between a liquid permeable sheet and a liquid permeable sheet. The absorber used in the absorbent article may be one having water-absorbent resin particles, may be composed of only water-absorbent resin particles, or may contain fibrous substances in addition to the water-absorbent resin particles. It may be.

Since the water-absorbent resin particles obtained by the production method according to the present embodiment have excellent retention to fibrous substances, the absorbent article is fibrous at a position where it comes into contact with the water-absorbent resin particles as a constitution of, for example, a liquid permeable sheet. When a substance is contained, the water-absorbent resin particles are likely to be entangled with the fibrous substance. Therefore, the absorbent article is more likely to maintain its shape and more easily exhibit water absorption performance.

The absorbent article may include an absorber, a liquid permeable sheet and a liquid permeable sheet. The liquid permeable sheet (liquid permeable top sheet) is arranged on the outermost side on the side where the liquid to be absorbed enters. The liquid impermeable sheet (liquid impermeable back sheet) is arranged on the outermost side opposite to the side on which the liquid to be absorbed enters. The absorbent article may further include a core wrap. The core wrap retains the shape of the absorber.

Examples of absorbent articles include diapers (for example, paper diapers), toilet training pants, incontinence pads, sanitary products (sanitary napkins, tampons, etc.), sweat pads, pet sheets, toilet materials, animal excrement treatment materials, and the like. ..

FIG. 1 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in FIG. 1 includes an absorbent body 10, core wraps 20a and 20b, a liquid permeable top sheet 30, and a liquid permeable back sheet 40. In the absorbent article 100, the liquid permeable back sheet 40, the core wrap 20b, the absorbent body 10, the core wrap 20a, and the liquid permeable top sheet 30 are laminated in this order. In FIG. 1, there is a portion shown so that there is a gap between the members, but the members may be in close contact with each other without the gap.

The absorber 10 has a water-absorbent resin particle 10a and a fiber layer 10b containing a fibrous material. The water-absorbent resin particles 10a are dispersed in the fiber layer 10b.

The core wrap 20a is arranged on one side of the absorber 10 (upper side of the absorber 10 in FIG. 1) in contact with the absorber 10. The core wrap 20b is arranged on the other side of the absorber 10 (lower side of the absorber 10 in FIG. 1) in contact with the absorber 10. The absorber 10 is arranged between the core wrap 20a and the core wrap 20b.

The core wrap 20a and the core wrap 20b have, for example, a main surface having the same size as the absorber 10. By using the core wrap, it is possible to maintain the shape retention of the absorber and prevent the water-absorbent resin particles and the like constituting the absorber from falling off and flowing. Examples of the core wrap include non-woven fabrics, woven fabrics, tissues, synthetic resin films having liquid permeation holes, net-like sheets having a mesh, and the like, and from the viewpoint of economy, a tissue made by wet-molding crushed pulp is preferable. Used.

The liquid permeable top sheet 30 is arranged on the outermost side on the side where the liquid to be absorbed enters. The liquid permeable top sheet 30 is arranged on the core wrap 20a in contact with the core wrap 20a. The liquid permeable back sheet 40 is arranged on the outermost side of the absorbent article 100 on the opposite side of the liquid permeable top sheet 30. The liquid impermeable back sheet 40 is arranged under the core wrap 20b in contact with the core wrap 20b. The liquid permeable top sheet 30 and the liquid permeable back sheet 40 have, for example, a main surface wider than the main surface of the absorber 10, and the liquid permeable top sheet 30 and the liquid permeable back sheet 40 have. The outer edge extends around the absorber 10 and the core wraps 20a, 20b.

Examples of the liquid permeable top sheet 30 include non-woven fabrics and porous sheets. Examples of the non-woven fabric include thermal-bonded non-woven fabric, air-through non-woven fabric, resin-bonded non-woven fabric, spunbond non-woven fabric, melt-blow non-woven fabric, spunbond / melt-blow / spunbond non-woven fabric, air-laid non-woven fabric, spunlace non-woven fabric, point-bond non-woven fabric and the like. Of these, thermal bond non-woven fabrics, air-through non-woven fabrics, spunbond non-woven fabrics, and spunbond / melt blow / spunbond non-woven fabrics are preferably used.

As a constituent material of the liquid permeable top sheet 30, a resin or fiber known in the art can be used, and polyethylene (from the viewpoint of liquid permeability, flexibility and strength when used in an absorbent article, polyethylene ( Polyester such as PE), polypropylene (PP), polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polyester such as polyethylene naphthalate (PEN), polyamide such as nylon, rayon, and other synthetic resins or fibers. Examples include cotton, silk, linen and pulp (cellulose) fibers. As the constituent material, synthetic fibers are preferably used from the viewpoint of increasing the strength of the liquid permeable top sheet 30, and among them, polyolefin and polyester are preferable. These materials may be used alone or in combination of two or more kinds of materials.

It is desirable that the non-woven fabric used for the liquid permeable top sheet 30 has appropriate hydrophilicity from the viewpoint of improving the liquid absorption performance of the absorbent article. From this point of view, it is preferable that the hydrophilicity when measured according to the "hydrophilicity of the non-woven fabric" described in International Publication No. 2011/086843 (based on the pulp and paper test method No. 68 (2000)) is 5 to 200. Those of 10 to 150 are more preferable. As the non-woven fabric having such hydrophilicity, among the above-mentioned non-woven fabrics, those in which the material itself exhibits appropriate hydrophilicity such as rayon fiber may be used, and hydrophobic chemistry such as polyolefin fiber and polyester fiber may be used. A fiber may be used which has been hydrophilized by a known method to impart an appropriate degree of hydrophilicity.

Examples of the method for hydrophilizing chemical fibers include a method of obtaining a non-woven fabric by a spunbond method obtained by mixing a hydrophobic chemical fiber with a hydrophilic agent in a spunbonded non-woven fabric, and a spunbonded non-woven fabric using hydrophobic chemical fibers. Examples thereof include a method of accommodating a hydrophilic agent when producing the above, a method of impregnating the spunbonded non-woven fabric with a hydrophobic chemical fiber, and then impregnating the hydrophilic agent. Hydrophilic agents include anionic surfactants such as aliphatic sulfonates and higher alcohol sulfates, cationic surfactants such as quaternary ammonium salts, polyethylene glycol fatty acid esters, polyglycerin fatty acid esters, and sorbitan fatty acids. Nonionic surfactants such as esters, silicone-based surfactants such as polyoxyalkylene-modified silicones, and stain-releasing agents made of polyester-based, polyamide-based, acrylic-based, and urethane-based resins are used.

The non-woven fabric used for the liquid permeable top sheet 30 is appropriately bulky from the viewpoint of imparting good liquid permeability, flexibility, strength and cushioning property to the absorbent article and increasing the liquid penetration rate of the absorbent article. It is preferably high and has a large amount of grain. The basis weight of the non-woven fabric is preferably 5 to 200 g / m ² , more preferably 8 to 150 g / m ² , and even more preferably 10 to 100 g / m ² . The thickness of the non-woven fabric is preferably 20 to 1400 μm, more preferably 50 to 1200 μm, and even more preferably 80 to 1000 μm.

The liquid impermeable back sheet 40 prevents the liquid absorbed by the absorber 10 from leaking from the back sheet 40 side to the outside. The liquid impermeable back sheet 40 is made of a liquid impermeable film mainly composed of a polyolefin resin such as polyethylene (PE) and polypropylene (PP), a breathable resin film, and a non-woven fabric such as spunbond or spunlace. A composite film to which the above resin films are bonded, a spunbond / melt blow / spunbond (SMS) non-woven fabric in which a water-resistant melt-blown non-woven fabric is sandwiched between high-strength spun-bonded non-woven fabrics can be used. From the viewpoint of ensuring flexibility so as not to impair the wearing feeling of the absorbent article, the back sheet 40 should use a resin film having ^{a basis weight of 10 to 50 g / m 2 mainly made of low density polyethylene (LDPE) resin.} Can be done. In addition, when a breathable material is used, the stuffiness at the time of wearing is reduced, and the discomfort given to the wearer can be reduced.

The magnitude relationship between the absorbent body 10, the core wraps 20a and 20b, the liquid permeable top sheet 30, and the liquid permeable back sheet 40 is not particularly limited, and is appropriately adjusted according to the use of the absorbent article and the like. Further, the method of retaining the shape of the absorber 10 by using the core wraps 20a and 20b is not particularly limited, and as shown in FIG. 1, the absorber may be sandwiched by a plurality of core wraps, and the absorber may be sandwiched by one core wrap. May be coated.

The absorber 10 may be adhered to the liquid permeable top sheet 30. By adhering the absorbent body 10 and the liquid permeable top sheet 30, the liquid is guided to the absorbent body more smoothly, so that it is easy to obtain an excellent absorbent article by preventing liquid leakage. When the absorber 10 is sandwiched or covered by the core wrap, it is preferable that at least the core wrap and the liquid permeable top sheet 30 are adhered to each other, and it is more preferable that the core wrap and the absorber 10 are adhered to each other. Examples of the bonding method include a method of applying a hot melt adhesive to the liquid permeable top sheet 30 at predetermined intervals in the width direction in a vertical stripe shape, a spiral shape, or the like, and bonding starch or carboxymethyl cellulose. , Polyvinyl alcohol, polyvinylpyrrolidone, and other methods of bonding using a water-soluble binder selected from water-soluble polymers. When the absorber 10 contains a heat-sealing synthetic fiber, a method of adhering by heat-sealing may be adopted.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples.

Manufacturing example 1
[polymerization]
509.71 g (7.07 mol) of 100% acrylic acid was placed in a round bottom cylindrical separable flask having an inner diameter of 11 cm and an internal volume of 2 L equipped with a stirrer. After adding 436.47 g of ion-exchanged water into the flask while stirring this acrylic acid, 444.68 g of 48% by mass sodium hydroxide was added dropwise under an ice bath to give a monomer concentration of 45.1 mass. Acrylic acid partial neutralization solution (neutralization rate 75.4 mol%) 1390.86 g was prepared. The preparation of this acrylic acid partial neutralizing solution was repeated to obtain a required amount.

To 2781.72 g of the acrylic acid partial neutralizing solution prepared above, 406.89 g of ion-exchanged water and 2.90 g of polyethylene glycol diacrylate (n = 9) (Nippon Oil Co., Ltd., Blemmer ADE-400A) are added to the reaction solution. (Aqueous monomer solution) was obtained. Next, this reaction solution was replaced with nitrogen gas for 30 minutes in a nitrogen gas atmosphere. Next, a stainless steel double-armed kneader with a jacket having two sigma-shaped blades with an openable and closable lid equipped with a thermometer and a nitrogen blowing tube was prepared. The above reaction solution was supplied to the kneader, and the system was replaced with nitrogen gas while keeping the reaction solution at 30 ° C. Subsequently, while stirring the reaction solution, 92.63 g (7.780 mmol) of a 2.0 mass% sodium persulfate aqueous solution and 15.85 g of a 0.5 mass% L-ascorbic acid aqueous solution were added. After 1 minute, the temperature began to rise and polymerization started. After 6 minutes, the maximum temperature during the polymerization was 93 ° C., and then stirring was continued while maintaining the jacket temperature at 60 ° C., and 60 minutes after the start of the polymerization, the produced hydrogel-like polymer was taken out. The obtained hydrogel-like polymer was sequentially charged into a meat chopper 12VR-750SDX manufactured by Kiren Royal Co., Ltd. and subdivided (coarse) to obtain a hydrogel-like coarsely crushed product. The diameter of the hole in the plate located at the outlet of the meat chopper was 6.4 mm.

[Dry]
The hydrogel-like coarsely crushed product was spread on a wire mesh having a mesh size of 0.8 cm × 0.8 cm and dried with hot air at 160 ° C. for 60 minutes to obtain a coarsely crushed and dried product.

[Crushing]
Next, the coarsely crushed dried product was crushed using a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 12000 rpm) to obtain a particle group (A) containing amorphous crushed fine powder.

[Classification]
The particle group (A) was classified using a JIS standard sieve having a mesh size of 850 μm, a JIS standard sieve having a mesh size of 250 μm, and a JIS standard sieve having a mesh size of 180 μm. By classification, the fraction passed through a JIS standard sieve with a mesh size of 850 μm and did not pass through a JIS standard sieve with a mesh size of 250 μm, and passed through a water-absorbent resin particle (A1) and a JIS standard sieve with a mesh size of 180 μm. A fraction (a1) was obtained.

<Comparative example 1>
A surface cross-linking agent solution consisting of 0.0783 g of ethylene carbonate, 0.125 g of propylene glycol, and 0.5 g of ion-exchanged water is mixed with 25 g of water-absorbent resin particles (A1) after classification at 25 ° C. for 35 minutes to form a mixture. Got Then, the mixture was heat-treated at 200 ° C. for 35 minutes to obtain surface-crosslinked water-absorbent resin particles (A2).

The surface-crosslinked water-absorbent resin particles (A2) were classified with a JIS standard sieve having an opening of 850 μm and a JIS standard sieve having an opening of 250 μm. By classification, water-absorbent resin particles (A3) were obtained, which were fractions that passed through a JIS standard sieve having a mesh size of 850 μm and did not pass through a JIS standard sieve having a mesh size of 250 μm.

By mixing 0.075 g of silicon dioxide (product name Aerosil 200, manufactured by Nippon Aerosil) with 25 g of water-absorbent resin particles (A3), water-absorbent resin particles (A4) were obtained as Comparative Example 1. For mixing, 25 g of water-absorbent resin particles are placed in a mayonnaise bottle having a capacity of 225 ml together with silicon dioxide, and shaken for 3 minutes under the condition of 750 (cycle / min (CPM)) using a paint shaker (manufactured by Toyo Seiki Seisakusho). It was carried out by stirring sufficiently. The CRC of the water-absorbent resin particles (A4) was 34 g / g, and the medium particle size was 467 μm.

<Example 1>
[Granulation]
40 g of the fine powder (a1) was placed in a round-bottomed cylindrical separable flask having an inner diameter of 11 cm and an internal volume of 2 L (the 2 L container was kept warm in a bath at 80 ° C.) equipped with a stirrer. The stirrer was equipped with a stirrer 200 as a stirrer, which is generally shown in FIG. 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 tip. The flat plate portion 200b is formed with four slits S extending along the axial direction of the shaft 200a. The four slits S are arranged in the width direction of the flat plate portion 200b, the width of the two inner slits S is 1 cm, and the width of the two outer slits S is 0.5 cm. The length of the flat plate portion 200b is about 10 cm, and the width of the flat plate portion 200b is about 6 cm.

While rotating the stirring blade of the stirrer at 284 rpm, 40 g of ion-exchanged water heated to 90 ° C. was put into the flask at one time. Granulated particles were obtained by stirring the fine powder and water in the flask for 90 seconds. The total amount of the obtained contents (granulated particle group) was taken out from the flask, and the particle size distribution of the granulated particle group described later was measured using the total amount.

[Reparticle]
After measuring the particle size distribution, the granulated particles exceeding 10 mm were cut (coarsely crushed) to a size of 3 to 10 mm. The entire amount of the granulated particles including the cut particles was dried with hot air at 150 ° C. for 60 minutes to obtain a coarsely crushed dried product of the granulated particles. Next, the coarsely crushed and dried product was pulverized using a centrifugal pulverizer (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm) to obtain water-absorbent resin particles (B1) that had undergone granulation and re-pulverization. The water-absorbent resin particles (B1) were classified with a JIS standard sieve having an opening of 850 μm and a JIS standard sieve having an opening of 180 μm. By classification, water-absorbent resin particles (B2) were obtained, which were fractions that passed through a JIS standard sieve having a mesh size of 850 μm and did not pass through a JIS standard sieve having a mesh size of 180 μm. At this stage, the particle yield after granulation and crushing described later was measured.

[Surface cross-linking]
A surface cross-linking agent solution consisting of 0.0783 g of ethylene carbonate, 0.125 g of propylene glycol, and 0.5 g of ion-exchanged water was mixed with 25 g of water-absorbent resin particles (B2) at 25 ° C. for 35 minutes to obtain a mixture. .. Then, the mixture was heat-treated at 200 ° C. for 35 minutes to obtain surface-crosslinked water-absorbent resin particles (B3).

The surface-crosslinked water-absorbent resin particles (B3) were classified with a JIS standard sieve having an opening of 850 μm and a JIS standard sieve having an opening of 250 μm. By classification, water-absorbent resin particles (B4) were obtained, which were fractions that passed through a JIS standard sieve having a mesh size of 850 μm and did not pass through a JIS standard sieve having a mesh size of 250 μm.

Water-absorbent resin particles (B5) were obtained as Example 1 by mixing 0.075 g of silicon dioxide (product name Aerosil 200, manufactured by Nippon Aerosil) with 25 g of water-absorbent resin particles (B4). For mixing, 25 g of water-absorbent resin particles are placed in a mayonnaise bottle having a capacity of 225 ml together with silicon dioxide, and shaken for 3 minutes under the condition of 750 (cycle / min (CPM)) using a paint shaker (manufactured by Toyo Seiki Seisakusho). It was carried out by stirring sufficiently. The CRC of the water-absorbent resin particles (B5) was 31 g / g, and the medium particle size was 419 μm.

<Example 2>
In the granulation step, the same procedure as in Example 1 was carried out except that the stirring time in the round-bottomed cylindrical separable flask having an internal volume of 2 L was changed to 15 seconds. ) Was obtained. The CRC of the water-absorbent resin particles (B6) was 30 g / g, and the medium particle size was 467 μm.

<Example 3>
In the granulation step, the same procedure as in Example 1 was carried out except that the amount of ion-exchanged water heated to 90 ° C. was changed to 25 g, and water-absorbent resin particles (B7) were obtained as Example 3. The CRC of the water-absorbent resin particles (B7) was 32 g / g, and the medium particle size was 446 μm.

<Comparative example 2>
In the granulation step, the same procedure as in Example 1 was carried out except that the amount of ion-exchanged water heated to 90 ° C. was changed to 20 g, and water-absorbent resin particles (B8) were obtained as Comparative Example 2. The CRC of the water-absorbent resin particles (B8) was 32 g / g, and the medium particle size was 428 μm.

<Comparative example 3>
In the granulation step, the same procedure as in Example 1 was carried out except that the amount of ion-exchanged water heated to 90 ° C. was changed to 10 g, and water-absorbent resin particles (B9) were obtained as Comparative Example 3. The CRC of the water-absorbent resin particles (B9) was 31 g / g, and the medium particle size was 444 μm.

<Measurement of particle size distribution of granulated particles>
A sample of the entire amount of the granulated particle group obtained by granulation or an arbitrary amount (about 30 g to 100 g) was used as a sample for measuring the particle size distribution of the granulated particle group. Sieves with JIS standard meshes of 106 mm, 53 mm, 31.5 mm, 9.5 mm, 2.8 mm, 850 μm, and 180 μm, and a saucer are placed in this order from the top, and the measurement sample is placed on a sieve with a mesh size of 106 mm. I put it in. Using an electromagnetic vibration type sieve shaker Octagon 200 (manufactured by endcotts) with a vibration intensity set to 7, the sieve and saucer are vibrated in the vertical direction for 10 minutes, and the measurement sample is shaken for 10 minutes. Was classified.

Based on the total amount of granulated particles remaining on each sieve and the amount of sample used for measurement, the abundance of granulated particles of 31.5 mm or more and 850 μm or more from the formulas (1), (2) and (3) The abundance of granulated particles and the abundance of granulated particles of 9.5 mm or more were calculated, respectively. The results are shown in Table 1. The measurement sample was returned to the original production process after the measurement and continued to be used in the production of the water-absorbent resin particles.
Formula (1): "% of granulated particles abundance of 31.5 mm or more" = (total amount of granulated particles remaining on each sieve having a mesh size of 106 mm, 53 mm, and 31.5 mm) / (subject to measurement) Sample amount)
Formula (2): "% of granulated particles abundance of 850 μm or more" = (total of granulated particles remaining on each sieve having a mesh size of 106 mm, 53 mm, 31.5 mm, 9.5 mm, 2.8 mm, and 850 μm) Amount) / (Amount of sample used for measurement)
Formula (3): "% of granulated particles abundance of 9.5 mm or more" = (total amount of granulated particles remaining on each sieve having a mesh size of 106 mm, 53 mm, 31.5 mm, and 9.5 mm) / ( Sample amount used for measurement)

<Particle yield after granulation and crushing>
After granulation, drying and re-grinding, and before surface cross-linking, the particles were recovered and classified using JIS standard sieves with openings of 180 μm and 850 μm. Among all the collected particles, the mass ratio of the particles that passed through the sieve with a mesh size of 850 μm and did not pass through the sieve with a mesh size of 180 μm was calculated, and the yield of the particles having a particle diameter of 180 μm or more and less than 850 μm was obtained. The results are shown in Table 1. It is preferable that the higher the yield of particles having a particle size of 180 μm or more and less than 850 μm after granulation and re-grinding, the higher the granulation strength.

<Medium particle size>
The medium particle size of the water-absorbent resin particles was measured by the following procedure. From the top of the JIS standard sieve, a sieve with a mesh size of 600 μm, a sieve with a mesh size of 500 μm, a sieve with a mesh size of 425 μm, a sieve with a mesh size of 300 μm, a sieve with a mesh size of 250 μm, a sieve with a mesh size of 180 μm, a sieve with a mesh size of 150 μm and a saucer. Combined in the order of. 50 g of particles were placed in the best combined sieve and classified according to JIS Z 8815 (1994) using a low-tap shaker (manufactured by Iida Seisakusho Co., Ltd.). After the classification, the mass of the particles remaining on each sieve was calculated as a mass percentage with respect to the total amount, and the particle size distribution was obtained. The relationship between the mesh size of the sieve and the integrated value of the mass percentage of the particles remaining on the sieve was plotted on a logarithmic probability paper by integrating on the sieve in order from the one having the largest particle size with respect to this particle size distribution. By connecting the plots on the probability paper with a straight line, the particle size corresponding to the cumulative mass percentage of 50% by mass was obtained as the medium particle size.

<CRC>
The CRC was measured by the following procedure with reference to the EDANA method (NWSP 241.0.R2 (15), page.769-778). The measurement was carried out in an environment where the temperature was 25 ° C. ± 2 ° C. and the humidity was 50% ± 10%.

A non-woven fabric with a size of 60 mm x 170 mm (product name: Heat Pack MWA-18, manufactured by Nippon Paper Papylia Co., Ltd.) was folded in half in the longitudinal direction to adjust the size to 60 mm x 85 mm. A 60 mm × 85 mm non-woven fabric bag was produced by crimping the non-woven fabrics to each other on both sides extending in the longitudinal direction with a heat seal (a crimped portion having a width of 5 mm was formed on both sides along the longitudinal direction). 0.2 g of the particles to be measured were precisely weighed and contained inside the non-woven fabric bag. Then, the non-woven fabric bag was closed by crimping the remaining one side extending in the lateral direction with a heat seal.

The entire non-woven fabric bag was completely moistened by floating the non-woven fabric bag on 1000 g of physiological saline contained in a stainless steel vat (240 mm × 320 mm × 45 mm) without folding the non-woven fabric bag. One minute after the non-woven fabric bag was put into the physiological saline solution, the non-woven fabric bag was immersed in the physiological saline solution with a spatula to obtain a non-woven fabric bag containing the gel.

Thirty minutes after the non-woven fabric bag was put into the physiological saline solution (a total of 1 minute of floating time and 29 minutes of immersion time), the non-woven fabric bag was taken out from the physiological saline solution. Then, the non-woven fabric bag was put in a centrifuge (manufactured by Kokusan Co., Ltd., model number: H-122). After the centrifugal force in the centrifuge reached 250 G, the non-woven fabric bag was dehydrated for 3 minutes. After dehydration, the mass Ma of the non-woven fabric bag containing the mass of the gel was weighed. The non-woven fabric bag was subjected to the same operation as described above without accommodating the particles to be measured, and the mass Mb of the non-woven fabric bag was measured. The CRC was calculated based on the following formula. Mc is a scaled value of 0.2 g of the mass of the particles used in the measurement.
CRC [g / g] = {(Ma-Mb) -Mc} / Mc

(Absorption ratio under pressure (AAP))
The absorption ratio (AAP) under pressure of 2.07 kPa (0.3 psi) was measured using the measuring device 110 shown in FIG. The measurement was carried out in an environment where the temperature was 25 ° C. ± 2 ° C. and the humidity was 50% ± 10%. First, a weight 112 (cross section: circular) adjusted to a pressure of 2.07 kPa, a plastic cylinder 114 with an inner diameter of 60 mm, and a 400 mesh (opening 38 μm) arranged at one end (bottom surface) of the cylinder 114. The measuring device 110 provided with the wire mesh 116 of the above was prepared. The weight 112 includes a disc portion 112a, a rod-shaped portion 112b extending from the center of the disc portion 112a in a direction perpendicular to the disc portion 112a, and a cylindrical portion 112c having a through hole inserted into the rod-shaped portion 112b in the center. have. The disk portion 112a of the weight 112 has a diameter substantially equal to the inner diameter of the cylinder 114 so that it can be moved in the longitudinal direction of the cylinder 114 inside the cylinder 114. The diameter of the cylindrical portion 112c is smaller than the diameter of the disc portion 112a. One end of the cylinder 114 is open but shielded by a wire mesh 116, and the other end of the cylinder 114 is open so that the weight 112 can be inserted. Inside the cylinder 114, 0.90 g of particles 120 to be measured were uniformly sprayed on the wire mesh 116. Then, after the weight 112 is inserted into the cylinder 114 and the weight 112 is placed on the measurement target particle 120, the total mass of the measuring device 110 (the total mass of the measuring device 110 and the measurement target particle 120 before liquid absorption). Wa [g] was measured.

After placing a glass filter 140 (ISO4793 P-250) with a diameter of 90 mm and a thickness of 7 mm in the center of the bottom surface of the recess of the stainless petri dish 130 with a diameter of 150 mm, 0 so that the water surface is at the same height as the upper surface of the glass filter 140. A 90% by mass aqueous sodium chloride solution (25 ° C ± 2 ° C) was added. A sheet of filter paper 150 (ADVANTEC Toyo Co., Ltd., product name: (No. 3), thickness 0.23 mm, reserved particle diameter 5 μm) with a diameter of 90 mm is placed on the glass filter 140 so that the entire surface is wet and the surface is completely wet. , Excess liquid was removed. Then, the above-mentioned measuring device 110 was placed on the filter paper 150, and the liquid was absorbed by the particles 120 to be measured under a load. After 1 hour, the measuring device 110 was lifted, and the total mass of the measuring device 110 (total mass of the measuring device 110 and the particles 120 to be measured after absorbing the liquid) Wb [g] was measured.

From Wa and Wb, the absorption ratio (AAP) [g / g] under 2.07 kPa pressurization was calculated based on the following formula. The results are shown in Table 2.
AAP [g / g] = (Wb [g] -Wa [g]) /0.90 [g]

<Vortex water absorption rate>
The water absorption rate of the physiological saline of the water-absorbent resin particles was measured by the following procedure based on the Vortex method. The measurement was carried out in an environment where the temperature was 25 ° C. ± 2 ° C. and the humidity was 50% ± 10%.
First, 50 ± 0.1 g of a 0.9 mass% sodium chloride aqueous solution (physiological saline) adjusted to a temperature of 25 ± 0.2 ° C. in a constant temperature water tank was weighed in a beaker having an internal volume of 100 mL. Next, a vortex was generated by stirring at a rotation speed of 600 rpm using a magnetic stirrer bar (8 mmφ × 30 mm, without ring). 2.0 ± 0.002 g of water-absorbent resin particles were added to the aqueous sodium chloride solution at one time. The time [seconds] from the addition of the water-absorbent resin particles to the time when the vortex on the liquid surface converged was measured, and the time was obtained as the water absorption rate of the water-absorbent resin particles. The results are shown in Table 2.

<Water-absorbent resin particle retention rate>
The water-absorbent resin particle retention rate was measured by the following method. The measurement was carried out in an environment where the temperature was 25 ° C. ± 2 ° C. and the humidity was 50% ± 10%. Roughly speaking, after the acrylic plate is tilted and fixed using a commercially available pedestal for experimental equipment, the water-absorbent resin particles are charged vertically above the non-woven fabric placed on the plate, and the total amount of the charged resin particles is increased. The amount of water-absorbent resin particles held on the non-woven fabric without falling from the non-woven fabric, that is, the retention rate was evaluated. A more detailed measurement method is shown below.

The retention rate was measured by the method outlined in FIG. _{An acrylic inclined plate S 0} having a length of 55 cm in the inclined surface direction was fixed so as to form an angle of 35 ± 2 ° with respect to the horizontal. As the non-woven fabric 77, an air-through non-woven fabric porous liquid permeable sheet made of polyethylene-polypropylene having a basis weight of 22 g / m ^{2 cut into 12 × 40 cm was used.} The non-woven fabric 77 was attached on _{the inclined plate S 0} so that the longitudinal direction of the non-woven fabric 77 was parallel to the inclined direction of the _{inclined plate S 0 with} the surface (back surface) that normally contacts the absorber in the absorbent article as the upper side. A stainless steel bat 79 having a size of 28.5 mm × 22.0 mm was placed below the lower end of the non-woven fabric 77 to receive the water-absorbent resin particles dropped from the non-woven fabric 77.

The water-absorbent resin particle charging device shown in FIG. 4 includes a funnel 71, a damper 73, and a cylinder 75. The funnel 71 has a supply port for supplying water-absorbent resin particles (upper end opening; diameter (inner diameter): 91 mm) and a discharge port for discharging water-absorbent resin particles (lower end opening. Diameter (inner diameter): 8 mm). It has a tapered shape that narrows from the supply port to the discharge port. The inclination angle of the side wall of the funnel 71 is 20 ° with respect to the axial direction of the funnel 71. The length from the supply port to the discharge port in the funnel 71 is 114 mm. The axially perpendicular cross section of the funnel 71 including the supply port and the discharge port is circular. The constituent material of the funnel 71 is stainless steel. The funnel 71 is fixed by gripping the outer peripheral portion on the supply port side with a support ring.

The damper 73 is a member having a length of 47 mm and a width of 15 mm. The damper 73 is arranged at the discharge port of the funnel 71, and opens and closes the discharge port of the funnel 71. The cylinder 75 is a member having a length of 35 mm and an inner diameter of 20 mm. The cylinder 75 is arranged on the discharge port side of the funnel 71 so that the portion on the discharge port side of the funnel 71 is located inside.

First, using a spirit level, it was confirmed that the upper end surface of the funnel 71 was installed horizontally. Next, with the discharge port closed by the damper 73, 5.00 g of the water-absorbent resin particles to be measured were housed in the funnel 71. The position of 300mm in the inclination direction parallel to the direction of the inclined plate S ₀ from the lower end of the nonwoven fabric 77 and a closing point, was placed a damper 73 (outlet) vertically above 30mm of the charged points. The discharge port was opened by quickly pulling out the damper 73, and the water-absorbent resin particles were dropped onto the non-woven fabric 77. The weight of the water-absorbent resin particles that fell on the lower vat 79 without staying on the non-woven fabric 77 was measured. From the following formula (4), the retention rate of the water-absorbent resin particles when tilted at 35 ° was calculated. The results are shown in Table 2.
Formula (4): Water-absorbent resin particle retention rate [%] = (5.00 [g] -amount of dropped water-absorbent resin particles [g]) / 5.00 [g]

The water-absorbent resin particles obtained in the examples had a high retention rate with respect to the non-woven fabric. On the other hand, the water-absorbent resin particles of Comparative Example 1 which had not undergone the steps of particle formation, granulation, and reparticle formation had a low retention rate with respect to the non-woven fabric. Further, the water-absorbent resin particles of Comparative Examples 2 and 3 in which the degree of granulation was low and the proportion of granulated particles having a large particle size was low, although they had undergone the steps of granulation, granulation and re-granulation, were also retained in the non-woven fabric. The rate was low.

10 ... Absorbent, 10a ... Water-absorbent resin particles, 10b ... Fiber layer, 20a, 20b ... Core wrap, 30 ... Liquid permeable top sheet, 40 ... Liquid permeable back sheet, 71 ... Rohto, 73 ... Damper, 75, 114 ... Cylinder, 77 ... Non-woven fabric, 79 ... Vat, 100 ... Absorbent article, 110 ... Measuring device, 112 ... Weight, 112a ... Disc, 112b ... Rod, 112c ... Column, 116 ... Wire mesh, 120 ... Measurement Target particles, 130 ... Stainless petri dish, 140 ... Glass filter, 150 ... Filter paper, 200 ... Stirring blade, 200a ... Shaft, 200b ... Flat plate, S ... Slit, S ₀ ... Inclined plate.

Claims

Polymerizing a monomer containing an ethylenically unsaturated monomer to obtain a hydrogel polymer,
To obtain a particle group containing fine particles having a particle size of less than 180 μm by granulating the hydrogel polymer.
To obtain a granulated particle group containing granulated particles by granulating the particle group,
Including that the granulated particle group is reparticleted to obtain polymer particles.
A method for producing water-absorbent resin particles containing polymer particles, wherein the abundance of the granulated particles that do not pass through a JIS standard sieve having an opening of 850 μm is 70% by mass or more in the granulated particle group before reparticle formation.
The method according to claim 1, wherein the abundance rate of the granulated particles that do not pass through the JIS standard sieve having a mesh size of 31.5 mm is 5% by mass or more in the granulated particle group before re-particle formation.
The method according to claim 1 or 2, further comprising subjecting the polymer particles to surface cross-linking to obtain water-absorbent resin particles.
Obtaining water-absorbent resin particles by the method according to any one of claims 1 to 3,
A method for producing an absorber, which comprises obtaining an absorber containing the water-absorbent resin particles and a fibrous substance.
Obtaining an absorber by the method according to claim 4
A method for producing an absorbent article, comprising arranging the absorber between a liquid permeable sheet and a liquid permeable sheet.