WO2020218160A1

WO2020218160A1 - Water-absorbing resin particles, absorbent, and absorbent article

Info

Publication number: WO2020218160A1
Application number: PCT/JP2020/016747
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: JPWO2020218160A1

Abstract

Water-absorbing resin particles having a gel-layer internal strength, as determined by the following procedure, of 0.8-2.0 N. (1) Prepared is a jig comprising a disk part having front and back flat surfaces with a diameter of 2 cm and having a thickness of 5 mm and a rod part, an end of which has been connected to the center of a first surface of the disk part, which is one of the flat surfaces, the rod part having a circular cross-section with a diameter of 5 mm. Also prepared is a cylindrical vessel containing 176 g of physiological saline and having an inner bottom-surface diameter of 5.7 cm. The jig and the cylindrical vessel are disposed so that the height-direction axis of the cylindrical vessel passes through the center of the disk part. (2) The jig is immersed in the physiological saline so that the second surface of the disk part, which is the flat surface on the reverse side from the first surface, lies below 32 mm from the surface of the physiological saline, and 4.0 g of the water-absorbing resin particles are put into the cylindrical vessel in that state, thereby forming a swollen gel in which the jig has been partly embedded. (3) The jig is pushed down vertically at a speed of 10 cm/min, and a load imposed on the jig at the time when the jig has been pushed down by 6 mm is obtained as the gel-layer internal strength.

Description

Water-absorbent resin particles, absorbers and absorbent articles

The present invention relates to water-absorbent resin particles, absorbers and absorbent articles.

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

Absorbent articles can cause liquid pools during use. Since the liquid pool can cause discomfort when worn, an absorbent article having an improved liquid pool absorption time is desired.

One aspect of the present invention is to provide water-absorbent resin particles capable of obtaining an absorbent article having an improved liquid pool absorption time. 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 relates to water-absorbent resin particles having a gel layer internal strength of 0.8 to 2.0 N measured by the following procedure.
(1) One end is connected to the center of a disk portion having a thickness of 5 mm having a flat surface having a diameter of 2 cm on the front and back, and the first surface which is one flat surface of the disk portion, and the cross section has a diameter of 5 mm. A jig having a circular rod-shaped portion and a cylindrical container having a bottom inner diameter of 5.7 cm containing 176 g of physiological saline are prepared, and the central axis of the cylindrical container in the height direction is the disk portion. The jig and the cylindrical container are arranged so as to be located at the center of the.
(2) With the jig immersed in a position where the second surface of the disk portion, which is a flat surface opposite to the first surface, is 32 mm vertically downward from the water surface of the physiological saline solution. 4.0 g of water-absorbent resin particles are placed in the cylindrical container to form a swollen gel in which the jig is embedded.
(3) When the jig is pushed vertically downward by 6 mm at a speed of 10 cm / min, the load applied to the jig is obtained as the internal strength of the gel layer.

According to the above-mentioned water-absorbent resin particles, it is possible to obtain an absorbent article having an improved liquid pool absorption time.

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

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 improved liquid pool absorption time 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 the application of the water-absorbent resin particles, the absorber and the absorbent article to the adjustment of the liquid pool absorption time in the absorbent article.

It is sectional drawing which shows one Embodiment 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. It is a schematic diagram which shows an example of the measuring method of the internal strength of a gel layer. It is a graph which shows an example of the measurement result of the internal strength of a gel layer. It is a schematic diagram which shows an example of the measuring method of the liquid pool absorption time.

Hereinafter, some 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. “A or B” may include either A or B, or both. "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.

The internal strength of the gel layer measured by the following procedure of the water-absorbent resin particles according to one embodiment is 0.8 to 2.0 N.
(1) A disk portion having a thickness of 5 mm having a flat surface having a diameter of 2 cm on the front and back, and one end connected to the center of the first surface which is one flat surface of the disk portion, and having a cross section having a diameter of 5 mm. Prepare a jig having a circular rod-shaped portion and a cylindrical container having a bottom inner diameter of 5.7 cm containing 176 g of physiological saline, and the central axis of the cylindrical container in the height direction is at the center of the disk portion. Arrange the jig and the cylindrical container so that they are located.
(2) A cylindrical container in a state where the jig is immersed in a position where the second surface, which is a flat surface opposite to the first surface of the disk portion, is 32 mm vertically below the water surface of the physiological saline solution. 4.0 g of water-absorbent resin particles are put therein to form a swollen gel in which a jig is embedded.
(3) When the jig is pushed vertically downward by 6 mm at a speed of 10 cm / min, the load applied to the jig is obtained as the internal strength of the gel layer.

According to the water-absorbent resin particles in which the internal strength of the gel layer is within the above-mentioned range, it is possible to obtain an absorbent article having an improved liquid pool absorption time.

The internal strength of the gel layer is 0.8N or more, 0.9N or more, 1.0N or more, 1.1N or more, 1.2N or more, or 1.3N or more from the viewpoint of further improving the liquid pool absorption time. It may be 2.0N or less, 1.9N or less, 1.8N or less, 1.7N or less, 1.6N or less, or 1.5N or less. The internal strength of the gel layer may be, for example, 1.0 to 1.8 N or 1.2 to 1.6 N. When the internal strength of the gel layer is increased, gel blocking in the absorber is less likely to occur, and the liquid pool absorption time tends to be shorter. As the internal strength of the gel layer, the internal strength of the gel layer at room temperature (25 ± 2 ° C.) can be used.

The water-absorbent resin particles exhibiting a gel layer internal strength of 0.8 to 2.0 N are, for example, adjusting the cross-linking density inside and / or the surface layer of the water-absorbent resin particles (for example, forming a uniform cross-linked structure). ) Etc. can be obtained.

The gel layer internal strength measured by the above-mentioned procedures (1) to (3) can be specifically measured by the method described in Examples described later.

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 is 10 g / g or more, 15 g / g or more, 20 g / g or more, 25 g / g or more, 30 g / g or more, 32 g / g or more, or. It may be 34 g / g or more. The water-retaining amount of the physiological saline of the water-absorbent resin particles according to the present embodiment is 80 g / g or less, 70 g / g or less, 60 g / g or less, 55 g / g or less, 52 g / g or less, 50 g / g or less, 48 g / g. It may be g or less, 45 g / g or less, 42 g / g or less, or 40 g / g or less. The water-retaining amount of the physiological saline of the water-absorbent resin particles according to the present embodiment may be, for example, 10 to 80 g / g, 20 to 60 g / g, or 30 to 40 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 amount of water absorption of the physiological saline under a load of 4.14 kPa of the water-absorbent resin particles according to the present embodiment may be in the following range. The amount of water absorption is 2 mL / g or more, 5 mL / g or more, 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, or 25 mL / g. That may be the above. The water absorption amount may be 40 mL / g or less, 35 mL / g or less, 30 mL / g or less, 28 mL / g or less, 26 mL / g or less, or 24 mL / g or less. The water absorption amount may be, for example, 2 to 40 mL / g, 5 to 40 mL / g, 10 to 35 mL / g, 12 to 35 mL / g, or 15 to 30 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 may be, for example, 100 μm or more, 140 μm or more, 200 μm or more, 250 μm or more, 300 μm or more, 330 μm or more, or 350 μm or more. The medium particle size may be, for example, 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. The medium particle size may be, for example, 250-600 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 contain a polymer having a structural unit derived from the ethylenically unsaturated monomer, and the structural unit derived from the ethylenically unsaturated monomer can be contained. It can contain polymer particles containing the crosslinked polymer having. 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 may contain a polymer having at least one structural unit selected from the group consisting of structural units derived from (meth) acrylic acid and structural units derived from salts of (meth) acrylic acid. preferable.

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, and at least one selected from the group consisting of potassium persulfate, ammonium persulfate, and sodium persulfate is more preferable.

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 1 mol of ethylenically unsaturated monomer from the viewpoint that the water-soluble property is suppressed by appropriately cross-linking the obtained polymer and a sufficient amount of water absorption can be easily obtained. 30 mmol or less is preferable, 0.01 to 10 mmol is more preferable, 0.012 to 5 mmol is further preferable, 0.015 to 1 mmol is particularly preferable, 0.02 to 0.1 mmol is extremely preferable, and 0. 025 to 0.06 mmol is highly 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, the polymer particles (for example, the polymer particles containing a polymer having a structural unit derived from an ethylenically unsaturated monomer) are dried to remove water from the obtained hydrogel polymer. Is 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 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 adjust the internal strength of the gel layer to a suitable range while maintaining the water absorption characteristics such as the amount of water retained.

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. 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 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. 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 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. 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. 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. 1, 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 of adjusting the liquid pool absorption time in the absorbent article, and is a method of adjusting the liquid pool absorption time using the water-absorbent resin particles, the absorber or the absorbent article according to the present embodiment (for example). , A method for improving the absorption time of a pool) can be provided. The method for adjusting the liquid pool absorption time according to the present embodiment includes an adjustment step for adjusting the internal strength of the gel layer measured by the above-mentioned procedures (1) to (3) for the water-absorbent resin particles according to the present embodiment. .. In the adjusting step, the internal strength of the gel layer can be adjusted to each of the above ranges (for example, 0.8 to 2.0 N).

According to the present embodiment, the water-absorbent resin particles according to the present embodiment include a selection step of selecting the water-absorbent resin particles based on the internal strength of the gel layer measured by the above-mentioned procedures (1) to (3). A method for producing water-absorbent resin particles can be provided. In the selection step, the internal strength of the gel layer can be adjusted to each of the above ranges (for example, 0.8 to 2.0 N).

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

1. 1. Preparation 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 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. In the prepared separable flask, 293 g of n-heptane and 0.736 g of a dispersant (maleic anhydride-modified ethylene / propylene copolymer, manufactured by Mitsui Chemicals, Inc., high wax 1105A) were mixed. The dispersant was dissolved in n-heptane by heating the mixture in the separable flask to 80 ° C. while stirring with a stirrer. The formed solution was cooled to 50 ° C.

On the other hand, 92.0 g (1.03 mol) of an 80.5 mass% aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed in a beaker having an internal volume of 300 mL, and cooled from the outside by 20.9 mass. After adding 147.7 g of a% sodium hydroxide aqueous solution to neutralize 75 mol%, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HECAW-15F) as a thickener, water-soluble radical polymerization was started. 0.0648 g (0.272 mmol) of sodium hydroxide was added as an agent, and 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether was added as an internal cross-linking agent and dissolved to prepare an aqueous solution of the first stage.

Then, the aqueous solution prepared above was added to the separable flask, and after stirring for 10 minutes, sucrose stearic acid ester of HLB3 as a surfactant in 6.62 g of n-heptane (Mitsubishi Chemical Foods Co., Ltd., Ryo). A surfactant solution prepared by heating and dissolving 0.736 g of Tosugar ester S-370) was further added, and the inside of the system was sufficiently replaced with nitrogen while stirring at a stirring speed of 350 rpm. The first-stage polymerized slurry solution was obtained by immersing in a water bath at ° C. to raise the temperature and performing polymerization for 60 minutes.

On the other hand, 128.8 g (1.44 mol) of an 80.5 mass% acrylic acid aqueous solution as a water-soluble ethylenically unsaturated monomer was placed in another beaker having an internal volume of 500 mL, and 27 mass% while cooling from the outside. After 159.0 g of the aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol%, 0.0907 g (0.381 mmol) of sodium persulfate was used as the water-soluble radical polymerization initiator, and ethylene glycol di was used as the internal cross-linking agent. 0.0116 g (0.067 mmol) of glycidyl ether was added and dissolved to prepare a second-stage aqueous solution.

After cooling the inside of the separable flask system to 25 ° C. while stirring at a stirring speed of 650 rpm, the entire amount of the aqueous solution in the second stage is added to the polymerized slurry solution in the first stage. 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 hydrogel polymer.

0.589 g of a 45% by mass diethylenetriamine-5 sodium acetate aqueous solution was added to the hydrogel polymer after the second stage polymerization under stirring. Then, the flask was immersed in an oil bath set at 125 ° C., and 238.6 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface cross-linking agent, and the flask was kept at 83 ° C. for 2 hours.

Then, n-heptane was evaporated at 125 ° C. and dried to obtain polymer particles (dried product). The polymer particles are passed through a sieve having an opening of 850 μm, and 0.5% by mass of amorphous silica (Oriental Silicas Corporation, Toxile NP-S) with respect to the mass of the polymer particles is mixed with the polymer particles. , 226.4 g of water-absorbent resin particles containing amorphous silica were obtained. The medium particle size of the water-absorbent resin particles was 378 μm.

Example 2
231.2 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that the amount of water extracted by azeotropic distillation of n-heptane and water was changed to 257.2 g. The medium particle size of the water-absorbent resin particles was 359 μm.

Example 3
The rotation speed of the stirrer when obtaining the polymer slurry liquid of the first stage was changed to 425 rpm, the amount of water extracted by co-boiling distillation of n-heptane and water was changed to 271.0 g, and the polymer. 229.0 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 0.2% by mass of amorphous silica was mixed with the polymer particles with respect to the mass of the particles. The medium particle size of the water-absorbent resin particles was 360 μm.

Example 4
After changing the rotation speed of the stirrer to obtain the first-stage polymerized slurry liquid to 425 rpm and obtaining the hydrogel polymer, the inside of the separable flask system was cooled to 31 ° C., and then the second stage. The total amount of the aqueous solution of the eye was added to the polymerized slurry solution of the first stage, the amount of water extracted by co-boiling distillation of n-heptane and water was changed to 275.8 g, and the mass of the polymer particles. 232.0 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 0.2% by mass of amorphous silica was mixed with the polymer particles. The medium particle size of the water-absorbent resin particles was 148 μm.

Comparative Example 1
As the stirring blade, a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm was used. In the preparation of the aqueous liquid in the first stage, 2,2'-azobis (2'-azobis (2) as a water-soluble radical polymerization initiator -Amidinopropane) dihydrochloride 0.092 g (0.339 mmol), potassium persulfate 0.018 g (0.068 mmol), and ethylene glycol diglycidyl ether 0.0046 g (0.026 mmol) as an internal cross-linking agent. In addition, the rotation speed of the stirrer for obtaining the first-stage polymerized slurry liquid was changed to 550 rpm, and 2,2'-azobis (2-amidinopropane) dihydrochloride as a water-soluble radical polymerization initiator. Addition of 0.129 g (0.475 mmol) and 0.026 g (0.095 mmol) of potassium persulfate, changing the rotation speed of the stirrer for obtaining a hydrogel polymer to 1000 rpm, n -Except that the amount of water extracted by co-boiling distillation of heptane and water was 207.9 g, and 0.2% by mass of amorphous silica with respect to the mass of the polymer particles was mixed with the polymer particles. , 232.5 g of water-absorbent resin particles were obtained in the same manner as in Example 1. The medium particle size of the water-absorbent resin particles was 360 μm.

Comparative Example 2
As the stirring blade, a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm was used. In the preparation of the aqueous liquid in the first stage, 2,2'-azobis (2'-azobis (2) as a water-soluble radical polymerization initiator -Amidinopropane) dihydrochloride 0.092 g (0.339 mmol), potassium persulfate 0.018 g (0.068 mmol), and ethylene glycol diglycidyl ether 0.0046 g (0.026 mmol) as an internal cross-linking agent. In addition, the rotation speed of the stirrer when obtaining the polymerized slurry liquid in the first stage was changed to 550 rpm, and in the preparation of the aqueous liquid in the second stage, 2,2'as a water-soluble radical polymerization initiator. -Addition of 0.129 g (0.475 mmol) of azobis (2-amidinopropane) dihydrochloride and 0.026 g (0.095 mmol) of potassium persulfate, and a stirrer for obtaining a hydrogel polymer. The number of revolutions was changed to 1000 rpm, the amount of water extracted by co-boiling distillation of n-heptane and water was 216.7 g, and 0.2 mass% amorphous with respect to the mass of the polymer particles. 229.0 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 348 μm.

Comparative Example 3
As the stirring blade, a stirring blade having two stages of four inclined paddle blades having a blade diameter of 5 cm was used. In the preparation of the aqueous liquid in the first stage, the water-soluble radical polymerization initiator was used as the water-soluble radical polymerization initiator. , 2'-azobis (2-amidinopropane) dihydrochloride 0.092 g (0.339 mmol), and potassium persulfate 0.018 g (0.068 mmol), ethylene glycol diglycidyl ether 0.0046 g as internal cross-linking agent (0.026 mmol) was added, the rotation speed of the stirrer when obtaining the polymerized slurry liquid in the first stage was changed to 550 rpm, and water-soluble radical polymerization was carried out in the preparation of the aqueous liquid in the second stage. Addition of 0.129 g (0.475 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.026 g (0.095 mmol) of potassium persulfate as an initiator, and a hydrogel-like weight. The rotation speed of the stirrer for obtaining coalescence was changed to 1000 rpm, the amount of water extracted by co-boiling distillation of n-heptane and water was set to 232.0 g, and 0. 228.5 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 2% by mass of amorphous silica was mixed with the polymer particles. The medium particle size of the water-absorbent resin particles was 354 μm.

2. Evaluation <Saline water retention>
The water retention amount (room temperature, 25 ° C. ± 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 x length 200 mm) weighing 2.0 g of water-absorbent resin particles was placed in a 500 mL beaker. Pour 500 g of 0.9 mass% sodium chloride aqueous solution (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 ring, and let it stand for 30 minutes. The water-absorbent resin particles were swollen with. After 30 minutes, the cotton bag is 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 the cotton bag containing the swelling gel after dehydration. The mass Wa (g) of 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 amount of physiological saline water retained was calculated from the following formula.
Saline water retention (g / g) = [Wa-Wb] /2.0

<Amount of water absorption under load>
The water absorption amount (room temperature, 25 ° C. ± 2 ° C.) of the physiological saline under the load (pressurization) 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 (plexiglass)), 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

<Medium particle size>
50 g of water-absorbent resin particles were used for measuring the medium particle size. The measurement was performed in an environment with a temperature of 25 ± 2 ° C. and a humidity of 50 ± 10%.

From the top, JIS standard sieves have a mesh size of 850 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, a mesh size of 150 μm, and a sieve. Combined in the order of the saucer.

Water-absorbent resin particles were placed in the best combined sieve and classified according to JIS Z8815 (1994) using a low-tap shaker (manufactured by Iida Seisakusho Co., Ltd.). After classification, the mass of the water-absorbent resin 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 water-absorbent resin particles remaining on the sieve was plotted on a logarithmic probability paper by integrating the particle size distribution on the sieve in order from the one having the largest particle size. 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 defined as the medium particle size.

<Gel strength by card meter>
Weigh 49.0 g of physiological saline into a glass beaker with a capacity of 100 mL, put a magnetic stirrer bar (without a ring of 8 mmφ x 30 mm), and place it on a magnetic stirrer (manufactured by Koike Precision Instruments Mfg. Co., Ltd .: M-20G). Placed. Subsequently, the magnetic stirrer bar was adjusted to rotate at 600 rpm.

Next, 1.0 g of water-absorbent resin particles were put into a beaker being stirred, and stirring was continued until the rotating vortex disappeared and the liquid level became horizontal to prepare a gel. This gel was stored in a constant temperature and humidity chamber at 25 ° C. and 60% RH for 1 hour to prepare a measurement sample.

The gel strength (room temperature, temperature 25 ± 2 ° C.) of this measurement sample was measured using a card meter (manufactured by Ai Techno Engineering Co., Ltd .: Card Meter Mini ME-600). The conditions of the card meter are as follows.
・ Pressure sensitive shaft: 16 mmφ
・ Spring: for 400g ・ Load: 400g
・ Rise speed: 1 inch / 21 sec
・ Test mode: Viscous

<Internal strength of gel layer>
(Preparation for EZtest)
A small stirrer (product name: multi-stirrer MS-101 manufacturer: Sinix Co., Ltd.) was placed on the measuring table of EZtest (Shimadzu Corporation, product name: EZtest, model number: EZ-SX). Next, a container having a capacity of 200 mL (manufacturer: Hario product name: tall beaker 200 mL product number: TB-200 SCI) containing 176 g of physiological saline was placed on a small stirrer. The container is a cylindrical glass beaker with an inner diameter of 5.7 cm and a height of 11.1 cm. Next, a stirrer tip (length 40 mm, diameter 8 mm, no ring) was put into a container containing physiological saline. As the stirrer controller, "Product name: Multi-stirrer dedicated controller MC-303 Manufacturer: Sinix Co., Ltd." was used.

FIGS. 4 (A) and 4 (B) show a schematic view of the measuring device used for measuring the maximum gel resistance. 4 (A) and 4 (B) show measuring devices before and after swelling gel formation, respectively. As shown in FIGS. 4A and 4B, the jig 71 is attached to the load cell 70 of the EZtest. The jig 71 includes a disk portion 71b and a rod-shaped portion 71a. The disk portion 71b has a disk shape, has flat surfaces having a diameter of 2 cm on the front and back surfaces, and has a thickness of 5 mm. The rod-shaped portion 71a has a circular cross section with a diameter of 5 mm, and the rod-shaped portion 71a has a length of 5.5 cm. One end of the rod-shaped portion 71a is connected to the center of the first surface which is one flat surface of the disk portion 71b, and the other end of the rod-shaped portion 71a is connected to the load cell 70. The jig 71 is arranged so that the central axis in the height direction of the container is located at the center of the disk portion 71b of the jig 71.

The jig 71 was lowered so that the second surface (lower surface), which is a flat surface opposite to the first surface of the disk portion 71b of the jig 71, was brought into contact with the liquid surface. The contact between the lower surface of the disk portion 71b of the jig 71 and the liquid surface was visually confirmed. After that, the jig 71 was lowered by 32 mm from the contacted position, and that position was set as the measurement start position. By lowering by 32 mm, the distance d1 between the liquid level and the lower surface of the disc portion 71b of the jig 71 and the distance d2 between the lower surface of the disc portion 71b of the jig 71 and the stirrer tip 73 are reduced. It will be about 32 mm. As shown in FIG. 4 (A), at the measurement start position, 4.0 g of the water-absorbent resin particles were placed in the container with the jig 71 immersed in the physiological saline 72 under stirring at 600 rpm. 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 45-fold swollen gel. As shown in FIG. 4B, the jig 71 connected to the load cell 70 is embedded in the swelling gel 74.

(Measurement by EZtest)
The internal strength of the gel layer was measured by operating the jig attached to the EZtest by the software Trapezium X (manufacturing company: Shimadzu Corporation) for Shimadzu autograph. The measurement was performed in an environment with a temperature of 25 ± 2 ° C. and a humidity of 50 ± 10%.

Ten minutes after the stirring was stopped, the jig embedded in the swelling gel was pushed vertically downward (direction a shown in FIG. 4B) at a speed of 10 cm / min. The load applied to the jig when the jig was pushed in was measured as a test force. The test force was measured at room temperature (temperature 25 ± 2 ° C.). The internal strength of the gel layer was the test force observed when the jig reached a position of 6 mm after being pushed in. The jig was stopped when it reached the position where it was pushed in by 10 mm from the measurement start point. The test force is a value automatically detected by Trapezium X. FIG. 5 is a graph showing an example of the measurement test result of the internal strength of the gel layer. The horizontal axis in FIG. 5 is the vertical movement distance (displacement, unit: mm) of the jig, and the vertical axis is the test force (unit: N). As shown in FIG. 5, the test force increased as the jig moved in the vertical direction from the measurement start position. The test force when the displacement was 6 mm was obtained as the internal strength of the gel layer.

<Evaluation of absorbent articles>
(Liquid pool absorption time test)
(1) Preparation of artificial urine Sodium chloride, calcium chloride and magnesium sulfate were dissolved in ion-exchanged water at the following concentrations. A small amount of Blue No. 1 was added to the obtained solution to obtain artificial urine colored blue. The following concentrations are based on the total mass of artificial urine.
Artificial urine composition NaCl: 0.780% by mass
CaCl ₂ : 0.022% by mass
0054 ₄ : 0.038% by mass
Blue No. 1: 0.002% by mass

(2) Liquid pool absorption time test of absorbent article Using the device shown in FIG. 6, a liquid pool absorption time test of the absorbent article was performed in an environment of a temperature of 25 ± 2 ° C. and a humidity of 50 ± 10%. Roughly speaking, artificial urine is injected from vertically above the absorbent article for testing placed on the inclined plate in the measuring container made of acrylic resin with a liquid feed pump (DOSEIT P910 input diameter 0.5 cmφ manufactured by INTEGRA). It is a mechanism to evaluate the balance between the ability to absorb artificial urine before it flows down and the ability to suck up artificial urine that has not been completely absorbed and has accumulated at the bottom of the measuring container. Detailed specifications are shown below.

In the liquid pool absorption time test, an acrylic resin measuring container composed of a rectangular inclined plate having an inclined surface S ₀ inclined by 45 degrees with respect to a horizontal plane and a side plate 80 is used. The length of the inclined plate in the longitudinal direction (length of the long side) is 20 cm, the length of the inclined plate in the lateral direction (length of the short side) is 11 cm, and the short side is located on the horizontal plane. On the inclined surfaces S _0, the rectangular absorbent article 102 is placed. The absorbent article 102 is arranged with its lower short side located in the horizontal plane and its long side oriented in a direction inclined with respect to the horizontal plane. The inclined surface S ₀ was smooth, and no liquid was retained or absorbed on the plate.

The liquid pool absorption rate test of the absorbent article was carried out in the order of i), ii) and iii) below.
i) 4.2 g of water-absorbent resin particles and 3.9 g of crushed pulp were uniformly mixed by air papermaking to prepare a sheet-shaped absorber having a size of 10 cm × 15 cm. The absorber was placed on tissue paper (same size as the absorber and a basis weight of 16 g / m ² ), and tissue paper (same size as the absorber and a basis weight of 16 g / m ² ) was placed on the absorber. A load of 588 kPa was applied to the absorber sandwiched by the tissue paper for 30 seconds. A polyethylene-polypropylene air-through porous liquid permeable sheet having a basis weight of 22 g / m ² and having the same size as the absorber was placed on the sheet. Further, a polyethylene liquid permeable sheet having a size of 10 cm × 15 cm was attached to the surface opposite to the liquid permeable sheet to obtain an absorbent article for testing.
ii) The absorbent article for the test is made of acrylic resin so that the surface to which the liquid permeable sheet is attached is on the upper side and the longitudinal direction of the absorbent article is along the vertical direction (longitudinal direction of the inclined plate). It was attached to a 45-degree inclined surface in the measuring container.
iii) With a position 7.0 cm from the top of the sample as the input point, 40.0 mL of artificial urine adjusted to a liquid temperature of 25 ± 1 ° C. using a liquid feed pump 81 is 1 from a position 1 cm vertically above at a flow rate of 4 mL / sec. Infused every minute. After the injection of artificial urine, the time (seconds) until the artificial urine accumulated at the bottom of the measuring container without being completely absorbed was completely absorbed was measured and used as the pool absorption time (seconds) of the absorbent article. It is preferable that the liquid pool absorption time is short, and the number of injections until the absorption cannot be completed within 60 seconds was used as a criterion for judging superiority or inferiority.

According to Table 1, it is confirmed that adjusting the internal strength of the gel layer is effective in obtaining an absorbent article having an improved liquid pool absorption time.

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, 70 ... load cell, 71 ... Jig, 72 ... Physiological saline, 73 ... Stirrer tip, 74 ... Swelling gel, 80 ... Side plate, 81 ... Liquid feed pump, 100, 102 ... Absorbent article, 200 ... Stirring blade, 200a ... Shaft, 200b ... Flat plate Part, S ... slit, S ₀ ... inclined surface, Y ... measuring device.

Claims

Water-absorbent resin particles having a gel layer internal strength of 0.8 to 2.0 N measured by the following procedure.
(1) One end is connected to the center of a disk portion having a thickness of 5 mm having a flat surface having a diameter of 2 cm on the front and back, and the first surface which is one flat surface of the disk portion, and the cross section has a diameter of 5 mm. A jig having a circular rod-shaped portion and a cylindrical container having a bottom inner diameter of 5.7 cm containing 176 g of physiological saline are prepared, and the central axis of the cylindrical container in the height direction is the disk portion. The jig and the cylindrical container are arranged so as to be located at the center of the.
(2) With the jig immersed in a position where the second surface of the disk portion, which is a flat surface opposite to the first surface, is 32 mm vertically downward from the water surface of the physiological saline solution. 4.0 g of water-absorbent resin particles are placed in the cylindrical container to form a swollen gel in which the jig is embedded.
(3) When the jig is pushed vertically downward by 6 mm at a speed of 10 cm / min, the load applied to the jig is obtained as the internal strength of the gel layer.
The water-absorbent resin according to claim 1, which comprises a polymer having at least one structural unit selected from the group consisting of structural units derived from (meth) acrylic acid and structural units derived from salts of (meth) acrylic acid. particle.
An absorber containing the water-absorbent resin particles according to claim 1 or 2.
An absorbent article comprising the absorber according to claim 3.
The absorbent article according to claim 4, which is a diaper.