WO2020218162A1

WO2020218162A1 - Water-absorbent resin particles and production method thereof, absorbent body, and absorbent article

Info

Publication number: WO2020218162A1
Application number: PCT/JP2020/016750
Authority: WO
Inventors: 河原　徹
Original assignee: 住友精化株式会社
Priority date: 2019-04-23
Filing date: 2020-04-16
Publication date: 2020-10-29
Also published as: JPWO2020218162A1; JP7143513B2

Abstract

These water-absorbent resin particles 10a have a gel repulsive force disappearance distance of 3.5-6.0 mm which is measured in the order of (1)-(4) below. (1) Gel that has swollen to 30 times the size of said water-absorbent resin particles is prepared in a recessed part of a container having the recessed part opened toward an upper side in the vertical direction. (2) The flat surface of a jig having the flat surface is brought into contact with the surface of the gel from the upper side in the vertical direction. (3) The operation to vertically push the jig against the gel by 6.0 mm and pull the jig back from the gel by 6.0 mm is repeated three times, and in each of the three times pull-back operations in the repeated operations, a moving distance in which the load applied to the jig disappears is obtained. (4) The average value of the total three moving distances obtained in step (3) is obtained as a gel repulsive force disappearance distance.

Description

Water-absorbent resin particles and their manufacturing methods, absorbers, and absorbent articles

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

Conventionally, an absorber containing water-absorbent resin particles has been used as an absorbent article for absorbing a liquid (for example, urine) containing water as a main component. For example, Patent Document 1 below discloses water-absorbent resin particles having a particle size that are suitably used for absorbent articles such as diapers. Further, Patent Document 2 describes a method of using a hydrogel-absorbing polymer having specific saline flow inducibility, pressure-lowering performance, etc. as an effective absorbent member for accommodating a body fluid such as urine. It is disclosed.

Japanese Unexamined Patent Publication No. 06-345819 Special Table No. 09-510889

If the liquid provided for the absorbent article does not sufficiently permeate the absorbent article, the excess liquid may flow on the surface of the absorbent article and leak to the outside of the absorbent article. Therefore, it is required that the liquid permeates the absorbent article at an excellent permeation rate.

One aspect of the present invention is to provide water-absorbent resin particles capable of obtaining an absorbent article having an excellent permeation rate and a method for producing the same. Another aspect of the present invention is to provide an absorber and an absorbent article using the water-absorbent resin particles.

One aspect of the present invention provides water-absorbent resin particles having a gel repulsive force disappearance distance of 3.5 to 6.0 mm measured by the following procedures (1) to (4).
(1) A gel that swells 30 times as much as the water-absorbent resin particles is prepared in the recess of a container having a recess that opens upward in the vertical direction.
(2) The flat surface of the jig having a flat surface is brought into contact with the surface of the gel from above in the vertical direction.
(3) After pushing the jig 6.0 mm into the gel in the vertical direction, the operation of pulling the jig back from the gel by 6.0 mm is repeated three times, and in each of the three pulling operations in the repeated operation. Obtain a moving distance at which the load applied to the jig disappears.
(4) The average value of a total of three moving distances obtained in the step (3) is obtained as the gel repulsive force disappearance distance.

According to the above-mentioned water-absorbent resin particles, an absorbent article having an excellent permeation rate can be obtained.

Another aspect of the present invention provides an absorber containing the above-mentioned water-absorbent resin particles.

Another aspect of the present invention provides an absorbent article comprising the absorber described above.

Another aspect of the present invention provides a method for producing water-absorbent resin particles, which comprises a step of selecting water-absorbent resin particles based on the gel repulsive force disappearance distance measured by the following procedures (1) to (4). To do.
(1) A gel that swells 30 times as much as the water-absorbent resin particles is prepared in the recess of a container having a recess that opens upward in the vertical direction.
(2) The flat surface of the jig having a flat surface is brought into contact with the surface of the gel from above in the vertical direction.
(3) After pushing the jig 6.0 mm into the gel in the vertical direction, the operation of pulling the jig back from the gel by 6.0 mm is repeated three times, and in each of the three pulling operations in the repeated operation. Obtain a moving distance at which the load applied to the jig disappears.
(4) The average value of a total of three moving distances obtained in the step (3) is obtained as the gel repulsive force disappearance distance.

According to the above-mentioned method for producing water-absorbent resin particles, it is possible to obtain water-absorbent resin particles capable of obtaining an absorbent article having an excellent permeation rate.

According to one aspect of the present invention, it is possible to provide water-absorbent resin particles capable of obtaining an absorbent article having an excellent permeation rate and a method for producing the same. Further, according to another aspect of the present invention, it is possible to provide an absorber and an absorbent article using the water-absorbent resin particles. According to another aspect of the present invention, it is possible to provide application of resin particles, absorbers and absorbent articles to absorbents. According to another aspect of the present invention, it is possible to provide application of resin particles, absorbers and absorbent articles to the adjustment of permeation rate in absorbent articles.

It is a drawing which shows the transition of the load applied to the jig. It is sectional drawing 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 the schematic which shows the measuring apparatus of the water absorption amount under the load of the water-absorbing resin particle.

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

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.

In the water-absorbent resin particles according to the present embodiment, the gel repulsive force disappearance distance measured by the following procedures (1) to (4) is 3.5 to 6.0 mm.
(1) A gel that swells 30 times as much as the water-absorbent resin particles is prepared in the recess of a container having a recess that opens upward in the vertical direction.
(2) The flat surface of the jig having a flat surface is brought into contact with the surface of the gel from above in the vertical direction.
(3) After pushing the jig 6.0 mm into the gel in the vertical direction, the operation of pulling the jig back from the gel by 6.0 mm is repeated three times, and in each of the three pulling operations in the repeated operation. Obtain a moving distance at which the load applied to the jig disappears.
(4) The average value of a total of three moving distances obtained in the step (3) is obtained as the gel repulsive force disappearance distance.

The 30-fold swollen gel used in step (1) in the gel repulsive force disappearance test can be obtained by mixing 1 part by mass of water-absorbent resin particles and 29 parts by mass of physiological saline. In the step (1), the container has a bottomed recess, and the container is arranged so that the opening direction of the recess is located on the upper side in the vertical direction. The container has, for example, a flat bottom surface. In the container, the side wall forming the recess may have a shape that does not interfere with the operation of each subsequent step, and for example, the side wall does not come into contact with the jig and the side wall. The cross section of the recess perpendicular to the opening direction is, for example, circular. Glass can be used as the material of the container.

In step (2), a jig having a flat surface and capable of transmitting the load applied when it comes into contact with the gel to the detector can be used. The shape of the flat surface may be circular, for example, and the diameter of the circular flat surface may be 4.9 cm. The jig includes, for example, a flat plate portion having a flat surface in contact with the gel. The height of the flat plate portion may be 1 mm or more, and may exceed 1 mm. The step (3) may be performed after the jig is brought into contact with the surface of the gel in the step (2) and then the jig is pulled away from the gel.

In step (3), the operation of pushing the jig 6.0 mm into the gel in the vertical direction and then pulling the jig back 6.0 mm from the gel is repeated three times, and in each of the three pulling back operations of the repeated operation, the jig is used. A total of three moving distances are obtained in which the load applied to the jig disappears. In step (3), in each of the three pull-back operations, the time point at which the load applied to the jig disappears is specified, and the jig is pushed from the state where the jig is pushed into the gel by 6.0 mm until the load disappears. Get the travel distance of. In the step (3), for example, a vertical load applied to the jig can be obtained as the gel repulsive force. As the time when the load disappears, the time when the perceived load becomes 0N can be adopted. The scanning speed of the jig in the step (3) may be, for example, 10 mm / min. Then, in the step (4), the average value of the total three moving distances obtained in the step (3) is obtained as the gel repulsive force disappearance distance.

FIG. 1 is a drawing showing a transition of the load applied to the jig in the step (3). By pushing the jig 6.0 mm into the gel in step (3), the load increases as the displacement on the left side changes from zero to 6.0 mm on the right side as shown by arrow A, and then the jig is removed from the gel. By pulling back 0 mm, the load decreases as the displacement changes from 6.0 mm to 0 mm as shown by arrow B. Then, in the step (3), in each of the three pull-back operations, the time point at which the load applied to the jig disappears is specified, and the jig is pushed into the gel by 6.0 mm until the load disappears. Obtain the moving distance of the jig. For example, the distance C in FIG. 1 indicates the moving distance in the third pull-back operation.

The gel repulsive force disappearance distance is preferably 3.6 mm or more, 3.7 mm or more, or 3.8 mm or more from the viewpoint of easily obtaining an excellent permeation rate in an absorbent article. The gel repulsive force disappearance distance is preferably 5.5 mm or less, 5.0 mm or less, 4.5 mm or less, 4.2 mm or less, 4.1 mm or less, or 4.0 mm or less. As the gel repulsive force disappearance distance, the gel repulsive force disappearance distance at room temperature (25 ± 2 ° C.) can be used.

The water-absorbent resin particles according to the present embodiment may be any water-absorbent resin particles as long as they can retain water, and the liquid to be absorbed may contain water. The water-absorbent resin particles according to the present embodiment have excellent absorbency of body fluids such as urine, sweat, and blood (for example, menstrual blood). The water-absorbent resin particles according to the present embodiment can be used as a constituent component of the absorber according to the present embodiment.

The water retention amount of the physiological saline of the water-absorbent resin particles according to the present embodiment (water retention amount under no pressurization) is preferably in the following range. The amount of water retained is preferably 10 g / g or more, 15 g / g or more, 20 g / g or more, 25 g / g or more, or 30 g / g or more from the viewpoint of easily obtaining an excellent permeation rate in the absorbent article. The amount of water retained is 80 g / g or less, 70 g / g or less, 60 g / g or less, 55 g / g or less, 50 g / g or less, 48 g / g or less, 45 g / g or less from the viewpoint of easily obtaining an excellent permeation rate in an absorbent article. It is preferably g or less, 42 g / g or less, 40 g / g or less, or 38 g / g or less. From these viewpoints, the water retention amount is preferably 10 to 80 g / g. As the water retention amount, the water retention amount at room temperature (25 ± 2 ° C.) can be used. The amount of water retained can be measured by the method described in Examples described later.

The water absorption amount of the physiological saline under a load of 4.14 kPa of the water-absorbent resin particles according to the present embodiment is preferably in the following range. The amount of water absorption is 10 mL / g or more, 12 mL / g or more, 15 mL / g or more, 18 mL / g or more, 20 mL / g or more, 22 mL / g or more, 25 mL / g from the viewpoint of easily obtaining an excellent permeation rate in an absorbent article. It is preferably g or more, or 26 mL / g or more. The amount of water absorption is preferably 40 mL / g or less, 35 mL / g or less, 30 mL / g or less, or 28 mL / g or less from the viewpoint of easily suppressing excessive swelling in the absorbent article. From these viewpoints, the water absorption amount is preferably 10 to 40 mL / g. As the water absorption amount, the water absorption amount at room temperature (25 ± 2 ° C.) can be used. The amount of water absorption can be measured by the method described in Examples described later.

Examples of the shape of the water-absorbent resin particles according to the present embodiment include substantially spherical, crushed, and granular shapes. Further, the water-absorbent resin particles according to the present embodiment may be in a form in which fine particles (primary particles) are aggregated (secondary particles) in addition to a form in which each is composed of a single particle. The medium particle size of the water-absorbent resin particles (water-absorbent resin particles before water absorption) according to the present embodiment is preferably in the following range. The medium particle size is 250 μm or more, 280 μm or more, 300 μm or more, 310 μm or more, 320 μm or more, 330 μm or more, 340 μm or more, 350 μm or more, from the viewpoint of avoiding gel blocking and easily maintaining a good permeation rate of the absorbent article. Alternatively, 360 μm or more is preferable. The medium particle size is preferably 600 μm or less, 550 μm or less, 500 μm or less, 450 μm or less, 400 μm or less, or 380 μm or less from the viewpoint of easily keeping the tactile sensation of the absorbent article soft. From these viewpoints, the medium particle size is preferably 250 to 600 μm. The water-absorbent resin particles according to the present embodiment may have a desired particle size distribution at the time of being obtained by the production method described later, but the particle size distribution can be obtained by performing an operation such as particle size adjustment using classification with a sieve. May be adjusted.

The water-absorbent resin particles according to the present embodiment are, for example, crosslinked polymers (derived from ethylenically unsaturated monomers) obtained by polymerizing a monomer containing an ethylenically unsaturated monomer as polymer particles. A crosslinked polymer having a structural unit to be used) can be included. That is, the water-absorbent resin particles according to the present embodiment can have a structural unit derived from an ethylenically unsaturated monomer, and are a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer. It can contain polymer particles containing. As the ethylenically unsaturated monomer, a water-soluble ethylenically unsaturated monomer can be used. Examples of the polymerization method include a reverse phase suspension polymerization method, an aqueous solution polymerization method, a bulk polymerization method, and a precipitation polymerization method. Among these, the reverse phase suspension polymerization method or the aqueous solution polymerization method is preferable from the viewpoint of ensuring good water absorption characteristics (water retention amount, etc.) of the obtained water-absorbent resin particles and easy control of the polymerization reaction. In the following, a reverse phase suspension polymerization method will be described as an example as a method for polymerizing an ethylenically unsaturated monomer.

The ethylenically unsaturated monomer is preferably water-soluble, for example, (meth) acrylic acid and a salt thereof, 2- (meth) acrylamide-2-methylpropanesulfonic acid and a salt thereof, (meth) acrylamide, N. , N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-diethylamino Examples thereof include propyl (meth) acrylate and diethylaminopropyl (meth) acrylamide. When the ethylenically unsaturated monomer has an amino group, the amino group may be quaternized. The ethylenically unsaturated monomer may be used alone or in combination of two or more. Functional groups such as the carboxyl group and amino group of the above-mentioned monomers can function as functional groups capable of cross-linking in the surface cross-linking step described later.

Among these, from the viewpoint of industrial availability, the ethylenically unsaturated monomer is selected from the group consisting of (meth) acrylic acid and its salts, acrylamide, methacrylamide, and N, N-dimethylacrylamide. It is preferable to contain at least one compound selected, and more preferably to contain at least one compound selected from the group consisting of (meth) acrylic acid and salts thereof, and acrylamide. From the viewpoint of further enhancing the water absorption characteristics (water retention amount and the like), the ethylenically unsaturated monomer further preferably contains at least one compound selected from the group consisting of (meth) acrylic acid and salts thereof. That is, the water-absorbent resin particles preferably have a structural unit derived from at least one selected from the group consisting of (meth) acrylic acid and salts thereof.

As the monomer for obtaining the water-absorbent resin particles, a monomer other than the above-mentioned ethylenically unsaturated monomer may be used. Such a monomer can be used, for example, by being mixed with an aqueous solution containing the above-mentioned ethylenically unsaturated monomer. The amount of the ethylenically unsaturated monomer used should be the total amount of the monomer (the total amount of the monomer for obtaining the water-absorbent resin particles. For example, the total amount of the monomer giving the structural unit of the crosslinked polymer. The same shall apply hereinafter). On the other hand, it is preferably 70 to 100 mol%. Above all, the ratio of (meth) acrylic acid and a salt thereof is more preferably 70 to 100 mol% with respect to the total amount of the monomers. "Ratio of (meth) acrylic acid and its salt" means the ratio of the total amount of (meth) acrylic acid and its salt.

According to the present embodiment, as an example of the water-absorbent resin particles, the water-absorbent resin particles containing a crosslinked polymer having a structural unit derived from the ethylenically unsaturated monomer and the above-mentioned ethylenically unsaturated monomer. However, it contains at least one compound selected from the group consisting of (meth) acrylic acid and a salt thereof, and the ratio of the (meth) acrylic acid and a salt thereof is the total amount of the monomer for obtaining the water-absorbent resin particles. (For example, 70 to 100 mol% of the total amount of the monomers giving the structural unit of the crosslinked polymer) can be provided.

The ethylenically unsaturated monomer is usually preferably used as an aqueous solution. The concentration of the ethylenically unsaturated monomer in the aqueous solution containing the ethylenically unsaturated monomer (hereinafter, simply referred to as “monomer aqueous solution”) is preferably 20% by mass or more and preferably 25 to 70% by mass. More preferably, 30 to 55% by mass is further preferable. Examples of the water used in the aqueous solution include tap water, distilled water, ion-exchanged water and the like.

When the ethylenically unsaturated monomer has an acid group, the monomer aqueous solution may be used by neutralizing the acid group with an alkaline neutralizer. The degree of neutralization of the ethylenically unsaturated monomer by the alkaline neutralizing agent increases the osmotic pressure of the obtained water-absorbent resin particles and further enhances the water absorption characteristics (water retention amount, etc.). It is preferably 10 to 100 mol%, more preferably 50 to 90 mol%, and even more preferably 60 to 80 mol% of the acidic group in the weight. Examples of the alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide and potassium carbonate; ammonia and the like. The alkaline neutralizer may be used alone or in combination of two or more. The alkaline neutralizer may be used in the form of an aqueous solution to simplify the neutralization operation. Neutralization of the acid group of the ethylenically unsaturated monomer can be performed, for example, by adding an aqueous solution of sodium hydroxide, potassium hydroxide or the like to the above-mentioned monomer aqueous solution and mixing them.

In the reverse phase suspension polymerization method, the monomer aqueous solution is dispersed in a hydrocarbon dispersion medium in the presence of a surfactant, and the ethylenically unsaturated monomer is polymerized using a radical polymerization initiator or the like. Can be done. As the radical polymerization initiator, a water-soluble radical polymerization initiator can be used.

Examples of the surfactant include nonionic surfactants and anionic surfactants. Nonionic surfactants include sorbitan fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, and polyoxyethylene. Alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, Examples thereof include polyethylene glycol fatty acid ester. Anionic surfactants include fatty acid salts, alkylbenzene sulfonates, alkylmethyl taurates, polyoxyethylene alkylphenyl ether sulfates, polyoxyethylene alkyl ether sulfonates, and polyoxyethylene alkyl ether phosphates. , Phosphate ester of polyoxyethylene alkyl allyl ether and the like. The surfactant may be used alone or in combination of two or more.

From the viewpoint that the W / O type reverse phase suspension is in a good state, water-absorbent resin particles having a suitable particle size can be easily obtained, and industrially available, the surfactant is a sorbitan fatty acid ester. It preferably contains at least one compound selected from the group consisting of polyglycerin fatty acid esters and sucrose fatty acid esters. From the viewpoint that an appropriate particle size distribution of the water-absorbent resin particles can be easily obtained, and from the viewpoint that the water-absorbing characteristics (water retention amount, etc.) of the water-absorbent resin particles and the performance of the absorbent article using the same can be easily improved, the surfactant is used. , Sucrose fatty acid ester is preferably contained, and sucrose stearic acid ester is more preferable.

The amount of the surfactant used is preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of the aqueous monomer solution from the viewpoint of obtaining a sufficient effect on the amount used and economically. .08 to 5 parts by mass is more preferable, and 0.1 to 3 parts by mass is further preferable.

In reverse phase suspension polymerization, a polymer-based dispersant may be used in combination with the above-mentioned surfactant. Examples of the polymer dispersant include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride-modified EPDM (ethylene / propylene / diene / terpolymer), and maleic anhydride. Modified polybutadiene, maleic anhydride / ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, maleic anhydride / butadiene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer Examples thereof include coalescence, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymer, ethylene / acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose and the like. The polymer-based dispersant may be used alone or in combination of two or more. As the polymer-based dispersant, from the viewpoint of excellent dispersion stability of the monomer, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, and maleic anhydride / ethylene copolymer weight. Combined, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene / propylene copolymer At least one selected from the group consisting of coalescing is preferable.

The amount of the polymer-based dispersant used is preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of the monomer aqueous solution from the viewpoint of obtaining a sufficient effect on the amount used and from the viewpoint of economic efficiency. , 0.08 to 5 parts by mass is more preferable, and 0.1 to 3 parts by mass is further preferable.

The hydrocarbon dispersion medium may contain at least one compound selected from the group consisting of chain aliphatic hydrocarbons having 6 to 8 carbon atoms and alicyclic hydrocarbons having 6 to 8 carbon atoms. As the hydrocarbon dispersion medium, a chain aliphatic hydrocarbon such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, n-octane; cyclohexane , Methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentane and other alicyclic hydrocarbons; benzene, Examples include aromatic hydrocarbons such as toluene and xylene. The hydrocarbon dispersion medium may be used alone or in combination of two or more.

The hydrocarbon dispersion medium may contain at least one selected from the group consisting of n-heptane and cyclohexane from the viewpoint of being industrially easily available and having stable quality. From the same viewpoint, as the mixture of the above-mentioned hydrocarbon dispersion medium, for example, commercially available ExxonHeptane (manufactured by ExxonMobil: containing 75 to 85% of n-heptane and isomeric hydrocarbons) is used. You may.

The amount of the hydrocarbon dispersion medium used is preferably 30 to 1000 parts by mass and 40 to 500 parts by mass with respect to 100 parts by mass of the monomer aqueous solution from the viewpoint of appropriately removing the heat of polymerization and easily controlling the polymerization temperature. Is more preferable, and 50 to 400 parts by mass is further preferable. When the amount of the hydrocarbon dispersion medium used is 30 parts by mass or more, the polymerization temperature tends to be easily controlled. When the amount of the hydrocarbon dispersion medium used is 1000 parts by mass or less, the productivity of polymerization tends to be improved, which is economical.

The radical polymerization initiator is preferably water-soluble, and is, for example, a persulfate such as potassium persulfate, ammonium persulfate, sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t. -Peroxides such as butyl cumylperoxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, hydrogen peroxide; 2,2'-azobis (2-amidinopropane) ) 2 hydrochloride, 2,2'-azobis [2- (N-phenylamidino) propane] 2 hydrochloride, 2,2'-azobis [2- (N-allylamidino) propane] 2 hydrochloride, 2,2 '-Azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} Dihydrochloride, 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2'-azobis [2-methyl-N- (2-Hydroxyethyl) -propionamide], azo compounds such as 4,4'-azobis (4-cyanovaleric acid) and the like can be mentioned. The radical polymerization initiator may be used alone or in combination of two or more. Examples of the radical polymerization initiator include potassium persulfate, ammonium persulfate, sodium persulfate, 2,2'-azobis (2-amidinopropane) dihydrochloride, and 2,2'-azobis [2- (2-imidazolin-2-). Il) Propane] dihydrochloride and at least one selected from the group consisting of 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propan} 2 hydrochloride. Is preferable. By using sodium persulfate, it is easy to increase the gel repulsive force disappearance distance and adjust it to a suitable range while maintaining water absorption characteristics such as water retention.

The amount of the radical polymerization initiator used may be 0.05 to 10 mmol per 1 mol of the ethylenically unsaturated monomer. When the amount of the radical polymerization initiator used is 0.05 mmol or more, the polymerization reaction does not require a long time and is efficient. When the amount of the radical polymerization initiator used is 10 mmol or less, it is easy to suppress the occurrence of a rapid polymerization reaction.

The above-mentioned radical polymerization initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, and L-ascorbic acid.

At the time of the polymerization reaction, the monomer aqueous solution used for the polymerization may contain a chain transfer agent. Examples of the chain transfer agent include hypophosphates, thiols, thiolic acids, secondary alcohols, amines and the like.

In order to control the particle size of the water-absorbent resin particles, the monomer aqueous solution used for polymerization may contain a thickener. Examples of the thickener include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide and the like. If the stirring speed at the time of polymerization is the same, the higher the viscosity of the aqueous monomer solution, the larger the medium particle size of the obtained particles tends to be.

Cross-linking by self-cross-linking may occur during polymerization, but cross-linking may be performed by using an internal cross-linking agent. When an internal cross-linking agent is used, it is easy to control the water absorption characteristics (water retention amount, etc.) of the water-absorbent resin particles. The internal cross-linking agent is usually added to the reaction solution during the polymerization reaction. Examples of the internal cross-linking agent include di or tri (meth) acrylic acid esters of polyols such as ethylene glycol, propylene glycol, trimethylpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; Unsaturated polyesters obtained by reacting polyols with unsaturated acids (maleic acid, fumaric acid, etc.); bis (meth) acrylamides such as N, N'-methylenebis (meth) acrylamide; polyepoxides and (meth) Di or tri (meth) acrylic acid esters obtained by reacting with acrylic acid; di (meth) obtained by reacting polyisocyanate (tolylene diisocyanate, hexamethylene diisocyanate, etc.) with hydroxyethyl (meth) acrylate. ) Acrylic acid carbamil esters; compounds having two or more polymerizable unsaturated groups such as allylated starch, allylated cellulose, diallyl phthalate, N, N', N "-triallyl isocyanurate, divinylbenzene; Poly such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, polyglycerol polyglycidyl ether, etc. Glycidyl compound; haloepoxy compound such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; 2 reactive functional groups such as isocyanate compound (2,4-tolylene diisocyanate, hexamethylene diisocyanate, etc.) Examples thereof include compounds having more than one. The internal cross-linking agent may be used alone or in combination of two or more. As the internal cross-linking agent, a polyglycidyl compound is preferable, and a diglycidyl ether compound is used. Is more preferable, and at least one selected from the group consisting of (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether is further preferable.

The amount of the internal cross-linking agent used is from the viewpoint that an excellent permeation rate can be easily obtained in the absorbent article, and the water-soluble property is suppressed by appropriately cross-linking the obtained polymer, so that a sufficient water absorption amount can be obtained. From the viewpoint of ease, 30 mmol or less is preferable, 0.01 to 10 mmol is more preferable, 0.012 to 5 mmol is further preferable, and 0.015 to 1 mmol is particularly preferable, per 1 mol of the ethylenically unsaturated monomer. , 0.02 to 0.1 mmol is very preferred, and 0.025 to 0.06 mmol is very preferred.

An ethylenically unsaturated monomer, a radical polymerization initiator, a surfactant, a polymer-based dispersant, a hydrocarbon dispersion medium, etc. (if necessary, an internal cross-linking agent) are mixed and heated under stirring to obtain oil. Reversed phase suspension polymerization can be performed in a medium water system.

When performing reverse phase suspension polymerization, a monomer aqueous solution containing an ethylenically unsaturated monomer is used as a hydrocarbon dispersion medium in the presence of a surfactant (more polymer-based dispersant if necessary). Disperse. At this time, before the start of the polymerization reaction, the timing of adding the surfactant, the polymer-based dispersant, etc. may be either before or after the addition of the monomer aqueous solution.

Among them, from the viewpoint of easily reducing the amount of the hydrocarbon dispersion medium remaining in the obtained water-absorbent resin, the surfactant is prepared after the monomer aqueous solution is dispersed in the hydrocarbon dispersion medium in which the polymer-based dispersant is dispersed. It is preferable to carry out the polymerization after further dispersing the above.

Reverse phase suspension polymerization can be carried out in one stage or in multiple stages of two or more stages. Reversed phase suspension polymerization is preferably carried out in 2 to 3 steps from the viewpoint of increasing productivity.

When reverse phase suspension polymerization is carried out in two or more stages, the reaction mixture obtained in the first step polymerization reaction after the first step reverse phase suspension polymerization is subjected to an ethylenically unsaturated single amount. The body may be added and mixed, and the reverse phase suspension polymerization of the second and subsequent steps may be carried out in the same manner as in the first step. In the reverse phase suspension polymerization in each stage of the second and subsequent stages, in addition to the ethylenically unsaturated monomer, the above-mentioned radical polymerization initiator and / or internal cross-linking agent is used in the reverse phase of each stage of the second and subsequent stages. Based on the amount of ethylenically unsaturated monomer added during suspension polymerization, reverse phase suspension polymerization is carried out by adding within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer. Is preferable. An internal cross-linking agent may be used in the reverse phase suspension polymerization in each of the second and subsequent stages, if necessary. When an internal cross-linking agent is used, it is added within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer based on the amount of the ethylenically unsaturated monomer provided in each stage, and the suspension is reversed. It is preferable to carry out turbid polymerization.

The temperature of the polymerization reaction varies depending on the radical polymerization initiator used, but by advancing the polymerization rapidly and shortening the polymerization time, the efficiency is improved and the heat of polymerization is easily removed to carry out the reaction smoothly. From the viewpoint, 20 to 150 ° C. is preferable, and 40 to 120 ° C. is more preferable. The reaction time is usually 0.5-4 hours. The completion of the polymerization reaction can be confirmed, for example, by stopping the temperature rise in the reaction system. As a result, the polymer of the ethylenically unsaturated monomer is usually obtained in the state of a hydrogel.

After polymerization, cross-linking may be performed by adding a cross-linking agent to the obtained hydrogel polymer and heating it. By performing cross-linking after the polymerization, the degree of cross-linking of the hydrogel polymer can be increased and the water absorption characteristics (water retention amount, etc.) can be further improved.

Examples of the post-polymerization 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 diglycidyl ether. Compounds having two or more epoxy groups, such as (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepicrolhydrin; 2,4- Compounds having two or more isocyanate groups such as tolylene diisocyanate and hexamethylene diisocyanate; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylenecarbonate; bis [N, N-di (β-hydroxy) Ethyl)] Hydroxyalkylamide compounds such as adipamide can be mentioned. Among these, polyglycidyl compounds such as (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and polyglycerol polyglycidyl ether are preferable. .. The cross-linking agent may be used alone or in combination of two or more.

The amount of the cross-linking agent after polymerization is set per 1 mol of ethylenically unsaturated monomer from the viewpoint that suitable water absorption characteristics (water retention amount, etc.) can be easily obtained by appropriately cross-linking the obtained hydrogel-like polymer. , 30 mmol or less, more preferably 10 mmol or less, further preferably 0.01 to 5 mmol, particularly preferably 0.012 to 1 mmol, extremely preferably 0.015 to 0.1 mmol, 0.02 to 0.02 to 0.05 mmol is highly preferred.

The timing of adding the cross-linking agent after polymerization may be after the polymerization of the ethylenically unsaturated monomer used for polymerization, and in the case of multi-stage polymerization, it is preferable to add it after multi-stage polymerization. The post-polymerization cross-linking agent contains water in consideration of heat generation during and after polymerization, retention due to process delay, opening of the system when the cross-linking agent is added, and fluctuation of water content due to addition of water accompanying the addition of the cross-linking agent. From the viewpoint of rate (described later), it is preferable to add in the region of [moisture content immediately after polymerization ± 3% by mass].

Subsequently, by carrying out drying to remove water from the obtained hydrogel-like polymer, polymer particles (for example, polymer particles having a structural unit derived from an ethylenically unsaturated monomer) can be obtained. As a drying method, for example, (a) a hydrogel-like polymer is dispersed in a hydrocarbon dispersion medium, and co-boiling distillation is performed by heating from the outside, and the hydrocarbon dispersion medium is refluxed to remove water. Examples thereof include (b) a method of taking out the hydrogel polymer by decantation and drying under reduced pressure, and (c) a method of filtering the hydrogel polymer with a filter and drying under reduced pressure. Above all, it is preferable to use the method (a) because of the simplicity in the manufacturing process.

The particle size of the water-absorbent resin particles can be adjusted by adjusting the rotation speed of the stirrer during the polymerization reaction, or by adding a flocculant into the system after the polymerization reaction or in the early stage of drying. By adding a flocculant, the particle size of the obtained water-absorbent resin particles can be increased. As the flocculant, an inorganic flocculant can be used. Examples of the inorganic flocculant (for example, powdered inorganic flocculant) include silica, zeolite, bentonite, aluminum oxide, talc, titanium dioxide, kaolin, clay, hydrotalcite and the like. From the viewpoint of excellent aggregating effect, the aggregating agent is preferably at least one selected from the group consisting of silica, aluminum oxide, talc and kaolin.

In the reverse phase suspension polymerization, as a method of adding the flocculant, the flocculant is previously dispersed in a hydrocarbon dispersion medium or water of the same type as that used in the polymerization, and then the hydrogel polymer is mixed under stirring. A method of mixing in a hydrocarbon dispersion medium containing the mixture is preferable.

The amount of the flocculant added is preferably 0.001 to 1 part by mass, more preferably 0.005 to 0.5 part by mass, based on 100 parts by mass of the ethylenically unsaturated monomer used for the polymerization. 01 to 0.2 parts by mass is more preferable. When the amount of the flocculant added is within the above range, water-absorbent resin particles having the desired particle size distribution can be easily obtained.

In the production of water-absorbent resin particles, surface cross-linking of the surface portion (surface and vicinity of the surface) of the hydrogel polymer is performed using a surface cross-linking agent in the drying step (moisture removing step) or subsequent steps. Is preferable. By performing surface cross-linking, it is easy to control the gel repulsive force disappearance distance and water absorption characteristics (water retention amount, etc.) of the water-absorbent resin particles. The surface cross-linking is preferably performed at a timing when the hydrogel polymer has a specific water content. The time of surface cross-linking is preferably when the water content of the hydrogel polymer is 5 to 50% by mass, more preferably 10 to 40% by mass, and even more preferably 15 to 35% by mass. The water content (mass%) of the hydrogel polymer is calculated by the following formula.
Moisture content = [Ww / (Ww + Ws)] x 100
Ww: Necessary when mixing a flocculant, a surface cross-linking agent, etc. to the amount obtained by subtracting the amount of water discharged to the outside of the system by the drying step from the amount of water contained in the monomer aqueous solution before polymerization in the entire polymerization step The amount of water in the hydrogel polymer to which the amount of water used is added.
Ws: A solid content calculated from the amount of materials such as an ethylenically unsaturated monomer, a cross-linking agent, and an initiator that constitute a hydrogel polymer.

Examples of the surface cross-linking agent include compounds having two or more reactive functional groups. Surface cross-linking agents include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; (poly) ethylene glycol diglycidyl ether. , (Poly) Glycerin diglycidyl ether, (Poly) Glycerin triglycidyl ether, Trimethylol propantriglycidyl ether (Poly) propylene glycol Polyglycidyl ether, (Poly) Oxetane Polyglycidyl ether and other polyglycidyl compounds; Epichlorohydrin, Haloepoxy compounds such as epibromhydrin and α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylenediisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol , 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol and other oxetane compounds; 1,2-ethylenebisoxazoline and the like. Examples thereof include oxazoline compounds; carbonate compounds such as ethylene carbonate; hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide. The surface cross-linking agent may be used alone or in combination of two or more. As the surface cross-linking agent, a polyglycidyl compound is preferable, and (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and polyglycerol are used. At least one selected from the group consisting of polyglycidyl ether is more preferable.

The amount of the surface cross-linking agent used is preferably 0.01 to 20 mmol with respect to 1 mol of the ethylenically unsaturated monomer used for polymerization from the viewpoint that suitable water absorption characteristics (water retention amount, etc.) can be easily obtained. 0.05 to 10 mmol is more preferable, 0.1 to 5 mmol is further preferable, 0.15 to 1 mmol is particularly preferable, and 0.2 to 0.5 mmol is extremely preferable.

After surface cross-linking, polymer particles which are surface-cross-linked dried products can be obtained by distilling off water and a hydrocarbon dispersion medium by a known method, drying under heating and reduced pressure, and the like.

The polymerization reaction can be carried out using various stirrers having stirring blades. As the stirring blade, a flat plate blade, a lattice blade, a paddle blade, a propeller blade, an anchor blade, a turbine blade, a Faudler blade, a ribbon blade, a full zone blade, a max blend blade 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. The flat plate portion may have a slit or the like. When a flat plate blade is used as the stirring blade, it is easy to uniformly carry out the cross-linking reaction in the polymer particles, and it is easy to reduce the gel repulsive force disappearance distance and adjust it to a suitable range while maintaining the water absorption characteristics such as the amount of water retention. ..

In addition to the polymer particles, the water-absorbent resin particles according to the present embodiment include, for example, a gel stabilizer and a metal chelating agent (ethylenediaminetetraacetic acid and its salt, diethylenetriamine-5 acetic acid and its salt, for example, diethylenetriamine-5 sodium acetate and the like). , Additional components such as fluidity improver (lubricant) can be further included. Additional components may be located inside the polymer particles, on the surface of the polymer particles, or both.

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.

When the water-absorbent resin particles contain inorganic particles arranged on the surface of the polymer particles, the content of the inorganic particles may be in the following range based on the total mass of the polymer particles. The content of the inorganic particles may be 0.05% by mass or more, 0.1% by mass or more, 0.15% by mass or more, or 0.2% by mass or more. The content of the inorganic particles may be 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, or 0.5% by mass or less.

The inorganic particles here usually have a minute size as compared with the size of the 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.

The absorber according to this embodiment contains the water-absorbent resin particles according to this embodiment. The absorber according to the present embodiment may contain a fibrous substance, for example, a mixture containing water-absorbent resin particles and the fibrous substance. The structure of the absorber may be, for example, a structure 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 a configuration or another configuration.

Examples of the fibrous material include finely pulverized wood pulp; cotton; cotton linter; rayon; cellulosic fibers such as cellulose acetate; synthetic fibers such as polyamide, polyester and polyolefin; and a mixture of these fibers. The average fiber length of the fibrous material is usually 0.1 to 10 mm, and may be 0.5 to 5 mm. The fibrous material may be used alone or in combination of two or more. As the fibrous material, hydrophilic fibers can be used.

In order to enhance the shape 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, and adhesive emulsions. The adhesive binder may be used alone or in combination of two or more.

Examples of the heat-bondable synthetic fiber include a total fusion type binder such as polyethylene, polypropylene, and an ethylene-propylene copolymer; 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 can be heat-sealed.

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

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

The absorber according to the present embodiment may contain an inorganic powder (for example, amorphous silica), a deodorant, an antibacterial agent, a pigment, a dye, a fragrance, an adhesive and the like. When the water-absorbent resin particles contain inorganic particles, the absorber may contain an inorganic powder in addition to the inorganic particles in the water-absorbent resin particles.

The shape of the absorber according to the present embodiment may be, for example, a sheet shape. The thickness of the absorber (for example, the thickness of the sheet-shaped absorber) may be 0.1 to 20 mm or 0.3 to 15 mm.

The content of the water-absorbent resin particles in the absorber is 2 to 100% by mass, 10 to 80% by mass, or 20 to 20 to 100% by mass with respect to the total of the water-absorbent resin particles and the fibrous material from the viewpoint of easily obtaining sufficient absorption characteristics. It may be 60% by mass.

The content of the water-absorbent resin particles in the absorber is preferably 100 to 1000 g, more preferably 150 to 800 g, and even more preferably 200 to 700 g per 1 m ^{2 of} the absorber from the viewpoint of easily obtaining sufficient absorption characteristics. The content of the fibrous substance in the absorber is preferably 50 to 800 g, more preferably 100 to 600 g, and even more preferably 150 to 500 g per 1 m ^{2 of} the absorber from the viewpoint of easily obtaining sufficient absorption characteristics.

The absorbent article according to the present embodiment includes an absorber according to the present embodiment. Other constituent members of the absorbent article according to the present embodiment include a core wrap that retains the shape of the absorber and prevents the constituent members of the absorber from falling off or flowing; on the outermost side on the side where the liquid to be absorbed enters. Liquid permeable sheet to be arranged; Examples thereof include a liquid permeable sheet arranged on the outermost side opposite to the side where the liquid to be absorbed enters. Absorbent articles include diapers (for example, paper diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat pads, pet sheets, simple toilet materials, animal excrement treatment materials, and the like. ..

FIG. 2 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in FIG. 2 includes an absorbent body 10, core wraps 20a and 20b, a liquid permeable sheet 30, and a liquid permeable sheet 40. In the absorbent article 100, the liquid permeable sheet 40, the core wrap 20b, the absorbent body 10, the core wrap 20a, and the liquid permeable sheet 30 are laminated in this order. In FIG. 2, 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 according to the present embodiment 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. 2) 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. 2) in contact with the absorber 10. The absorber 10 is arranged between the core wrap 20a and the core wrap 20b. Examples of the core wraps 20a and 20b include tissues, non-woven fabrics, woven fabrics, synthetic resin films having liquid permeation holes, net-like sheets having a mesh, and the like. The core wrap 20a and the core wrap 20b have, for example, a main surface having the same size as the absorber 10.

The liquid permeable sheet 30 is arranged on the outermost side on the side where the liquid to be absorbed enters. The liquid permeable sheet 30 is arranged on the core wrap 20a in contact with the core wrap 20a. Examples of the liquid permeable sheet 30 include non-woven fabrics made of synthetic resins such as polyethylene, polypropylene, polyester and polyamide, and porous sheets. The liquid permeable sheet 40 is arranged on the outermost side of the absorbent article 100 on the opposite side of the liquid permeable sheet 30. The liquid permeable sheet 40 is arranged under the core wrap 20b in contact with the core wrap 20b. Examples of the liquid impermeable sheet 40 include a sheet made of a synthetic resin such as polyethylene, polypropylene, and polyvinyl chloride, and a sheet made of a composite material of these synthetic resins and a non-woven fabric. The liquid permeable sheet 30 and the liquid permeable sheet 40 have, for example, a main surface wider than the main surface of the absorber 10, and the outer edges of the liquid permeable sheet 30 and the liquid permeable sheet 40 are It extends around the absorber 10 and the core wraps 20a, 20b.

The magnitude relationship between the absorbent body 10, the core wraps 20a and 20b, the liquid permeable sheet 30, and the liquid permeable 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. 2, the absorber may be wrapped by a plurality of core wraps, and the absorber is wrapped by one core wrap. It may be.

The absorber may be adhered to the top sheet. When the absorber is sandwiched or covered by the core wrap, it is preferable that at least the core wrap and the top sheet are adhered, and the core wrap and the top sheet are adhered and the core wrap and the absorber are adhered to each other. Is more preferable. As a method of adhering the absorber, a hot melt adhesive is applied to the top sheet at predetermined intervals in a striped shape, a spiral shape, etc. in the width direction and adhered; starch, carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, etc. Examples thereof include a method of adhering using a water-soluble binder such as a water-soluble polymer. Further, when the absorber contains heat-sealing synthetic fibers, a method of adhering by heat-sealing of the heat-sealing synthetic fibers may be adopted.

According to the present embodiment, it is possible to provide a liquid absorbing method using the water-absorbent resin particles, the absorbent body or the absorbent article according to the present embodiment. The liquid absorbing method according to the present embodiment includes a step of bringing the liquid to be absorbed into contact with the water-absorbent resin particles, the absorber or the absorbent article according to the present embodiment.

According to the present embodiment, it is a method for adjusting the permeation rate (permeation rate of a liquid) in an absorbent article, and is a method for adjusting the permeation rate using the water-absorbent resin particles, an absorber or the absorbent article according to the present embodiment. (For example, an improvement method) can be provided. The method for adjusting the permeation rate according to the present embodiment includes an adjustment step for adjusting the gel repulsive force disappearance distance measured by the above-mentioned procedures (1) to (4) for the water-absorbent resin particles according to the present embodiment. In the adjusting step, the gel repulsive force disappearance distance can be adjusted to each of the above ranges (for example, 3.5 to 6.0 mm).

According to the present embodiment, the water-absorbent resin particles according to the present embodiment are provided with a selection step of selecting the water-absorbent resin particles based on the gel repulsive force disappearance distance measured by the above-mentioned procedures (1) to (4). , A method for producing water-absorbent resin particles can be provided. In the selection step, the gel repulsive force disappearance distance can be adjusted to each of the above ranges (for example, 3.5 to 6.0 mm).

According to the present embodiment, it is possible to provide a method for producing an absorber using the water-absorbent resin particles obtained by the above-mentioned method for producing water-absorbent resin particles. The method for producing an absorber according to the present embodiment includes a particle manufacturing step for obtaining water-absorbent resin particles by the above-mentioned method for producing water-absorbent resin particles. The method for producing an absorber according to the present embodiment may include a step of mixing the water-absorbent resin particles and the fibrous material after the particle manufacturing step. According to the present embodiment, it is possible to provide a method for producing an absorbent article using the absorber obtained by the above-mentioned method for producing an absorber. The method for producing an absorbent article according to the present embodiment includes an absorber manufacturing step for obtaining an absorber by the above-mentioned method for manufacturing an absorber. The method for producing an absorbent article according to the present embodiment may include a step of obtaining an absorbent article by using the absorber and other constituent members of the absorbent article after the absorbent body manufacturing step. For example, an absorbent article is obtained by laminating the absorber and other constituent members of the absorbent article with each other.

Hereinafter, the content of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[1. Manufacture of water-absorbent resin particles]
(Example 1)
A round-bottomed cylindrical separable flask having an inner diameter of 11 cm and an internal volume of 2 L equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer was prepared. The stirrer was equipped with a stirrer blade (flat blade) 200 whose outline is 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. Subsequently, 293 g of n-heptane was added as a hydrocarbon dispersion medium to the above-mentioned separable flask, and a maleic anhydride-modified ethylene-propylene copolymer (manufactured by Mitsui Chemicals Co., Ltd., High Wax 1105A) was added as a polymer-based dispersant. A mixture was obtained by adding 0.736 g. The dispersant was dissolved in n-heptane by heating the mixture to 80 ° C. with stirring with a stirrer, and then the mixture was cooled to 50 ° C.

Next, 92.0 g (acrylic acid: 1.03 mol) of an 80.5 mass% acrylic acid aqueous solution was added as a water-soluble ethylenically unsaturated monomer to a beaker having an internal volume of 300 mL. Subsequently, while cooling from the outside, 147.7 g of a 20.9 mass% sodium hydroxide aqueous solution was added dropwise into the beaker to neutralize 75 mol%. Then, 0.092 g of hydroxylethyl cellulose (manufactured by Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener and 0.092 g of 2,2'-azobis (2-amidinopropane) dihydrochloride as a water-soluble radical polymerization initiator. (0.339 mmol), 0.0162 g (0.068 mmol) of sodium persulfate, and 0.0046 g (0.026 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent are added and dissolved to dissolve the first step. An aqueous solution was prepared.

Then, the above-mentioned first-stage aqueous solution was added to the above-mentioned separable flask while stirring at a stirring speed of 425 rpm, and then the mixture was stirred for 10 minutes. Then, it was obtained by heating and dissolving 0.736 g of sucrose stearic acid ester (surfactant, manufactured by Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370, HLB value: 3) in 6.62 g of n-heptane. The detergent solution was added to the separable flask. Then, the inside of the system was sufficiently replaced with nitrogen while stirring at a stirring speed of 425 rpm. Then, the flask was immersed in a water bath at 70 ° C. to raise the temperature, and polymerization was carried out for 60 minutes to obtain a first-stage polymerization slurry solution.

Next, 128.8 g (acrylic acid: 1.44 mol) of an 80.5 mass% acrylic acid aqueous solution was added as a water-soluble ethylenically unsaturated monomer to another beaker having an internal volume of 500 mL. Subsequently, while cooling from the outside, 159.0 g of a 27 mass% sodium hydroxide aqueous solution was added dropwise into the beaker to neutralize 75 mol%. Then, as a water-soluble radical polymerization initiator, 0.129 g (0.475 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.0226 g (0.095 mmol) of sodium persulfate, an internal cross-linking agent. To prepare a second-stage aqueous solution, 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether was added and then dissolved.

Next, the inside of the separable flask described above was cooled to 25 ° C. while stirring at a rotation speed of 650 rpm of the stirrer, and then the entire amount of the aqueous solution of the second stage described above was added to the polymerized slurry solution of the first stage described above. Was added to. Subsequently, after replacing the inside of the system with nitrogen for 30 minutes, the flask was again immersed in a water bath at 70 ° C. to raise the temperature, and the polymerization reaction was carried out for 60 minutes to obtain a second-stage hydrogel polymer. It was.

0.589 g of a 45% by mass diethylenetriamine-5 sodium acetate aqueous solution was added to the above-mentioned second-stage hydrogel polymer under stirring. Then, the temperature of the reaction solution was raised in an oil bath at 125 ° C., and 233.7 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (ethylene glycol diglycidyl ether: 0.507 mmol 0.507 mmol) of 2% by mass of an ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface cross-linking agent, and the mixture was held at 83 ° C. for 2 hours.

Then, n-heptane was evaporated at 125 ° C. and dried to obtain polymer particles (dried product). After passing the polymer particles through a sieve having an opening of 850 μm, 0.2% by mass of amorphous silica (Tokuseal NP-S manufactured by Oriental Silicas Corporation) is weighted based on the total mass of the polymer particles. By mixing with the coalesced particles, 228.2 g of water-absorbent resin particles containing amorphous silica were obtained. The medium particle size of the water-absorbent resin particles was 355 μm.

(Example 2)
In the hydrogel polymer after the second stage polymerization, 225.8 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 216.7 g of water was extracted from the system by azeotropic distillation. Obtained. The medium particle size of the water-absorbent resin particles was 372 μm.

(Example 3)
In the preparation of the first-stage aqueous solution, 0.092 g (0.339 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.0162 g of sodium persulfate were used as water-soluble radical polymerization initiators. Instead of (0.068 mmol), 0.0648 g (0.272 mmol) of potassium persulfate is used, and the amount of the internal cross-linking agent used is 0.0046 g (0.026 mmol) to 0.010 g (0.057 mmol). ), The rotation speed of the stirrer was changed to 350 rpm in the preparation of the polymerized slurry liquid in the first stage, and as a water-soluble radical polymerization initiator in the preparation of the aqueous liquid in the second stage, 2, 0.0907 g (0.381 mmol) of sodium persulfate instead of 0.129 g (0.475 mmol) of 2'-azobis (2-amidinopropane) dihydrochloride and 0.0226 g (0.095 mmol) of sodium persulfate 238.6 g of water was extracted from the system by co-boiling distillation in the hydrogel polymer after the second stage polymerization, and 0.2 with respect to the mass of the polymer particles. 226.4 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 0.5% by mass of amorphous silica was mixed with the polymer particles instead of% by mass of amorphous silica. The medium particle size of the water-absorbent resin particles was 378 μm.

(Example 4)
In the hydrogel polymer after the second stage polymerization, 230.0 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 207.4 g of water was extracted from the system by azeotropic distillation. Obtained. The medium particle size of the water-absorbent resin particles was 360 μm.

(Comparative Example 1)
When dissolving the maleic anhydride-modified ethylene-propylene copolymer, a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm was used as the stirrer instead of the flat plate blade, the first stage. In the preparation of the aqueous solution of 2,2'-azobis (2-amidinopropane) dihydrochloride 0.092 g (0.339 mmol) and sodium persulfate 0.0162 g (0.068) as a water-soluble radical polymerization initiator. 0.0736 g (0.272 mmol) of potassium persulfate was used instead of (mmol), and the amount of the internal cross-linking agent used was changed from 0.0046 g (0.026 mmol) to 0.010 g (0.057 mmol). That, the rotation speed of the stirrer was changed to 550 rpm in the preparation of the polymerized slurry liquid in the first stage, and 2,2'-azobis as a water-soluble radical polymerization initiator in the preparation of the aqueous liquid in the second stage. 0.103 g (0.381 mmol) of potassium persulfate was used in place of 0.129 g (0.475 mmol) of the (2-amidinopropane) dihydrochloride and 0.0226 g (0.095 mmol) of sodium persulfate. The rotation speed of the stirrer when adding the entire amount of the aqueous liquid in the second stage to the polymerized slurry liquid in the first stage was changed to 1000 rpm, and in the hydrogel polymer after the polymerization in the second stage. 248.4 g of water was extracted from the system by co-boiling distillation, and 0.5 mass% amorphous instead of 0.2 mass% amorphous silica with respect to the mass of the polymer particles. 226.0 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that silica was mixed with the polymer particles. The medium particle size of the water-absorbent resin particles was 372 μm.

(Comparative Example 2)
In the hydrogel polymer after the second stage polymerization, 257.7 g of water was extracted from the system by co-boiling distillation, and 0.5% by mass of amorphous was amorphous with respect to the mass of the polymer particles. 228.0 g of water-absorbent resin particles were obtained in the same manner as in Comparative Example 1 except that 0.2% by mass of amorphous silica was mixed with the polymer particles in place of the quality silica. The medium particle size of the water-absorbent resin particles was 352 μm.

(Comparative Example 3)
In the hydrogel polymer after the second stage polymerization, 228.4 g of water-absorbent resin particles were obtained in the same manner as in Comparative Example 1, except that 273.6 g of water was extracted from the system by azeotropic distillation. Obtained. The medium particle size of the water-absorbent resin particles was 345 μm.

[2. Evaluation methods]
<Medium particle size>
The above-mentioned medium particle diameter of the water-absorbent resin particles was measured by the following procedure in an environment of a temperature of 25 ± 2 ° C. and a humidity of 50 ± 10%. That is, from the top, the JIS standard sieve has a mesh size of 600 μm, a mesh size of 500 μm, a mesh size of 425 μm, a mesh size of 300 μm, a mesh size of 250 μm, a mesh size of 180 μm, and a mesh size of 150 μm. , And the saucer in that order. 50 g of water-absorbent resin 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 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.

<Water retention>
The water retention amount (room temperature, 25 ± 2 ° C.) of the physiological saline of the water-absorbent resin particles was measured by the following procedure. First, a cotton bag (Membroad No. 60, width 100 mm × length 200 mm) weighing 2.0 g of water-absorbent resin particles was placed in a beaker having an internal volume of 500 mL. After pouring 500 g of physiological saline into a cotton bag containing water-absorbent resin particles at a time so that mamaco cannot be formed, tie the upper part of the cotton bag with a rubber band and let it stand for 30 minutes to swell the water-absorbent resin particles. I let you. After 30 minutes, the cotton bag was dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set to have a centrifugal force of 167 G, and then contained a swelling gel after dehydration. The mass Wa [g] of the cotton bag was measured. The same operation was performed without adding the water-absorbent resin particles, the empty mass Wb [g] of the cotton bag when wet was measured, and the water retention amount of the physiological saline of the water-absorbent resin particles was calculated from the following formula. The results are shown in Table 1.
Water retention [g / g] = (Wa-Wb) /2.0

<Amount of water absorption under load>
The amount of water absorption (room temperature, 25 ° C. ± 2 ° C.) of the physiological saline under the load of the water-absorbent resin particles was measured using the measuring device Y shown in FIG. The measuring device Y is composed of a burette unit 61, a conduit 62, a measuring table 63, and a measuring unit 64 placed on the measuring table 63. The burette portion 61 has a burette 61a extending in the vertical direction, a rubber stopper 61b arranged at the upper end of the burette 61a, a cock 61c arranged at the lower end of the burette 61a, and one end extending into the burette 61a in the vicinity of the cock 61c. It has an air introduction pipe 61d and a cock 61e arranged on the other end side of the air introduction pipe 61d. The conduit 62 is attached between the burette portion 61 and the measuring table 63. The inner diameter of the conduit 62 is 6 mm. A hole having a diameter of 2 mm is formed in the central portion of the measuring table 63, and the conduit 62 is connected to the hole. The measuring unit 64 has a cylinder 64a (made of acrylic resin), a nylon mesh 64b adhered to the bottom of the cylinder 64a, and a weight 64c. The inner diameter of the cylinder 64a is 20 mm. The opening of the nylon mesh 64b is 75 μm (200 mesh). Then, at the time of measurement, the water-absorbent resin particles 65 to be measured are uniformly sprinkled on the nylon mesh 64b. The diameter of the weight 64c is 19 mm, and the mass of the weight 64c is 119.6 g. The weight 64c is placed on the water-absorbent resin particles 65, and a load of 4.14 kPa can be applied to the water-absorbent resin particles 65.

After 0.100 g of the water-absorbent resin particles 65 were placed in the cylinder 64a of the measuring device Y, the weight 64c was placed and the measurement was started. Since the same volume of air as the physiological saline absorbed by the water-absorbent resin particles 65 is quickly and smoothly supplied to the inside of the burette 61a from the air introduction pipe, the water level of the physiological saline inside the burette 61a is reduced. However, the amount of physiological saline absorbed by the water-absorbent resin particles 65 is obtained. The scale of the burette 61a is engraved from the top to the bottom in increments of 0 mL to 0.5 mL, and the scale Va of the burette 61a before the start of water absorption and the burette 61a 60 minutes after the start of water absorption are used as the water level of the physiological saline. The scale Vb of the above was read, and the amount of water absorption under load was calculated from the following formula. The results are shown in Table 1.
Water absorption under load [mL / g] = (Vb-Va) /0.1

<Gel repulsive force disappearance distance>
(Preparation of swelling gel)
10 g of water-absorbent resin particles were put into a cylindrical container (inner diameter: 11.3 cm, height: 5.7 cm, material: glass) containing 290 g of physiological saline at room temperature (25 ° C.) under stirring at 600 rpm. A stirrer tip (length: 40 mm, diameter: 8 mm, no ring) was used for stirring. The surface of the saline solution is located at a height of 2.8 cm from the bottom surface without stirring. After confirming that the water-absorbent resin particles had swollen and the vortices on the liquid surface had converged, stirring was stopped. Then, it was allowed to stand for 10 minutes to obtain a 30-fold swollen gel.

(Measurement of gel repulsive force disappearance distance)
EZtest (manufactured by Shimadzu Corporation, product name: EZtest, model number: EZ-SX) is used to measure the gel repulsive force disappearance distance. The jig provided in EZtest can be attached to the load cell of EZtest, and the position of the jig in the vertical direction can be adjusted using the software Trapezium X (manufactured by Shimadzu Corporation) for Shimadzu autograph. The load cell senses the response of the load applied to the jig when the jig is brought into contact with the surface of the gel with respect to the 30-fold swollen gel placed on the measuring table, and the load is used as the test force on the measurement screen. Displayed above. The jig includes a disk portion and a rod-shaped portion. The disk portion is in the shape of a disk having flat surfaces on the front and back surfaces, having a diameter of 4.9 cm and a thickness of 1.2 cm. The length of the rod-shaped portion is 14 cm. One end of the rod-shaped portion is connected to the center of the flat surface of the disk portion, and the other end of the rod-shaped portion is connected to the load cell. The position of the container is adjusted so that the central axis in the height direction of the container is located at the center of the disk portion. The clearance between the jig and the inner wall of the container is 3.2 cm.

The measurement was performed in an environment with a temperature of 25 ± 2 ° C and a humidity of 50 ± 10%. In the measuring machine adjusted as described above, the above-mentioned container containing the 30-fold swollen gel was placed on the measuring table. Next, the jig was lowered until the load cell connected to the jig sensed a test force of 0.01 N, and the jig and the gel surface were brought into contact with each other. Next, the jig was placed at the measurement start position by raising the jig by 0.05 mm.

Subsequently, the jig was pushed into the gel by 6.0 mm at a speed of 10 mm / min, and then the jig was pulled back from the gel by 6.0 mm at a speed of 10 mm / min. Then, in the pulling operation, the time point at which the load applied to the jig disappears is specified, and the moving distance of the jig from the state where the jig is pushed into the gel by 6.0 mm until the load disappears (first point). The distance traveled) was obtained. As the time point when the load disappears, the time point when the perceived load becomes 0N was adopted. As the distance at which the jig was raised until the load became 0 N, a value automatically detected by Trapezium X was used.

Next, the operation of pushing the jig 6.0 mm into the gel at a speed of 10 mm / min and then pulling the jig back 6.0 mm from the gel at a speed of 10 mm / min is repeated twice more, and in each of the pulling back operations, the jig The moving distances (moving distances of the second and third points) at which the load applied to the jig disappears were obtained.

Then, the average value of these three moving distances was obtained as the gel repulsive force disappearance distance (25 ° C.). The results are shown in Table 1.

<Evaluation of absorbent articles>
[Making absorbent articles]
Using an airflow type mixer (Padformer manufactured by Otec Co., Ltd.), 10 g of water-absorbent resin particles and 6.8 g of crushed pulp are uniformly mixed by air papermaking to form a sheet having a size of 40 cm x 12 cm. An absorber was prepared. Next, with two sheets of tissue paper having a basis weight of 16 g / m ² having the same size as the sheet-shaped absorber sandwiching the upper and lower sides of the absorber, a load of 196 kPa is applied to the whole for 30 seconds and pressed. Obtained a laminate. Further, an absorbent article was prepared by arranging an air-through type porous liquid permeable sheet made of polyethylene-polypropylene having a basis weight of 22 g / m ² having the same size as the absorber on the upper surface of the laminate.

[Measurement of penetration rate]
The absorbent article was placed on a horizontal table in an environment of a temperature of 25 ± 2 ° C. and a humidity of 50 ± 10%. Next, a liquid injection cylinder (cylinder with both ends open) having a capacity of 100 mL and having an inner diameter of 3 cm was placed in the center of the main surface of the absorbent article. Subsequently, 80 mL of physiological saline, which had been previously colored with a small amount of Blue No. 1 and adjusted to 25 ± 1 ° C., was charged into the cylinder at one time (supplied from the vertical direction). Using a stopwatch, the absorption time from the start of injection until the saline solution completely disappeared from the cylinder was measured. This operation was performed twice more at intervals of 30 minutes (three times in total), and the total value of the absorption time was obtained as the permeation rate [seconds]. The faster the penetration rate, the better. The results are shown in Table 1.

According to Table 1, it is confirmed that adjusting the gel repulsive force disappearance distance is effective in obtaining an absorbent article having an excellent permeation rate.

10 ... Absorbent, 10a, 65 ... Water-absorbent resin particles, 10b ... Fiber layer, 20a, 20b ... Core wrap, 30 ... Liquid permeable sheet, 40 ... Liquid permeable sheet, 61 ... Burette part, 61a ... Burette, 61b ... rubber stopper, 61c ... cock, 61d ... air introduction pipe, 61e ... cock, 62 ... conduit, 63 ... measuring table, 64 ... measuring unit, 64a ... cylinder, 64b ... nylon mesh, 64c ... weight, 100 ... absorbent article , 200 ... Stirring blade, 200a ... Shaft, 200b ... Flat plate, S ... Slit, Y ... Measuring device.

Claims

Water-absorbent resin particles having a gel repulsive force disappearance distance of 3.5 to 6.0 mm measured by the following procedures (1) to (4).
(1) A gel that swells 30 times as much as the water-absorbent resin particles is prepared in the recess of a container having a recess that opens upward in the vertical direction.
(2) The flat surface of the jig having a flat surface is brought into contact with the surface of the gel from above in the vertical direction.
(3) After pushing the jig 6.0 mm into the gel in the vertical direction, the operation of pulling the jig back from the gel by 6.0 mm is repeated three times, and in each of the three pulling operations in the repeated operation. Obtain a moving distance at which the load applied to the jig disappears.
(4) The average value of a total of three moving distances obtained in the step (3) is obtained as the gel repulsive force disappearance distance.
The water-absorbent resin particle according to claim 1, wherein the water absorption amount of the physiological saline under a load of 4.14 kPa is 22 mL / g or more.
The water-absorbent resin particle according to claim 1 or 2, which has a structural unit derived from at least one selected from the group consisting of (meth) acrylic acid and a salt thereof.
An absorber containing the water-absorbent resin particles according to any one of claims 1 to 3.
An absorbent article comprising the absorber according to claim 4.
The absorbent article according to claim 5, which is a diaper.
A method for producing water-absorbent resin particles, comprising a step of selecting water-absorbent resin particles based on the gel repulsive force disappearance distance measured by the following procedures (1) to (4).
(1) A gel that swells 30 times as much as the water-absorbent resin particles is prepared in the recess of a container having a recess that opens upward in the vertical direction.
(2) The flat surface of the jig having a flat surface is brought into contact with the surface of the gel from above in the vertical direction.
(3) After pushing the jig 6.0 mm into the gel in the vertical direction, the operation of pulling the jig back from the gel by 6.0 mm is repeated three times, and in each of the three pulling operations in the repeated operation. Obtain a moving distance at which the load applied to the jig disappears.
(4) The average value of a total of three moving distances obtained in the step (3) is obtained as the gel repulsive force disappearance distance.