JP6681495B1 - Water-absorbent resin particles, absorber and absorbent article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an absorbent article capable of suitably diffusing a liquid in a plane direction of an absorbent body when absorbing the liquid, and water-absorbent resin particles and the absorbent body which give the absorbent article. An absorbent article 100 includes an absorbent body 10, the absorbent body 10 contains water-absorbent resin particles 10a, and the water-absorbent resin particles 10a are measured by the following procedures (1) to (6). The swelling height is 10 mm or less. (1) A container having a recess having a bottom area of 50 cm 2 is arranged with the recess opened in the vertical direction. (2) Place 1.00 g of water-absorbent resin particles in the recess. (3) A nonwoven fabric is arranged on the water absorbent resin particles in the recess. (4) A weight having a mass of 90 g is arranged on the non-woven fabric. (5) Supplying saline into the recess. (6) The moving distance in the vertical direction of the weight when 300 seconds have elapsed from the start of swelling of the water absorbent resin particles is measured as the swelling height. [Selection diagram] Figure 1

Description

  The present invention relates to water absorbent resin particles, an absorbent body and an absorbent article.

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

Japanese Patent Laid-Open No. 06-345819 Japanese Patent Publication No. 09-510889

  When the absorbent article absorbs liquid, if the solution does not diffuse sufficiently and stays only near the liquid absorbing site (liquid infiltrating site), excess liquid flows on the surface of the absorbent product, etc. A problem such as leakage to the outside may occur. Therefore, for absorbent articles, it is required that the liquid diffuses favorably when it absorbs liquid, and in particular, when absorbing liquid, liquid absorbs in the plane direction of the absorbent body (direction perpendicular to the thickness direction). Is required to diffuse appropriately.

  An object of one aspect of the present invention is to provide a water-absorbent resin particle and an absorbent body that provide an absorbent article that allows the liquid to suitably diffuse in the plane direction of the absorbent body when absorbing the liquid. Another object of another aspect of the present invention is to provide an absorbent article in which the liquid can be suitably diffused when absorbing the liquid.

  The present inventor can suppress the vertical swelling of the water-absorbent resin particles when the water-absorbent resin particles absorb the liquid, and the liquid can be suitably diffused in the plane direction of the absorber when the water-absorbent resin particles are absorbed. It has been found to be effective in obtaining articles.

One aspect of the present invention provides water-absorbent resin particles having a swelling height of 10 mm or less measured by the following procedures (1) to (6).
(1) A container having a recess having a bottom area of 50 cm ² is arranged with the recess opening in the vertical direction.
(2) Place 1.00 g of water-absorbent resin particles in the recess.
(3) A nonwoven fabric is arranged on the water absorbent resin particles in the recess.
(4) A weight having a mass of 90 g is arranged on the non-woven fabric.
(5) Supplying saline into the recess.
(6) The moving distance in the vertical direction of the weight when 300 seconds have elapsed from the start of swelling of the water absorbent resin particles is measured as the swelling height.

  With the above water-absorbent resin particles, it is possible to obtain an absorbent article in which the liquid can suitably diffuse in the plane direction of the absorber when absorbing the liquid.

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

  Another aspect of the present invention provides an absorbent article including the absorbent body described above.

  Advantageous Effects of Invention According to one aspect of the present invention, it is possible to provide a water-absorbent resin particle and an absorbent body that provide an absorbent article that can suitably diffuse the liquid in the plane direction of the absorbent body when absorbing the liquid. Further, according to another aspect of the present invention, it is possible to provide an absorbent article in which the liquid can suitably diffuse in the plane direction of the absorber when absorbing the liquid. According to another aspect of the present invention, it is possible to provide application of the resin particles, the absorbent body, and the absorbent article to the liquid absorption.

It is sectional drawing which shows an example of an absorbent article. It is a schematic diagram showing a measuring device of swelling height. It is a schematic diagram showing a measuring device of water absorption under load of water-absorbent resin particles.

  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 the present specification, “acrylic” and “methacrylic” are collectively referred to as “(meth) acrylic”. "Acrylate" and "methacrylate" are also referred to as "(meth) acrylate". In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value of the numerical range of a certain stage can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range of another stage. In the numerical ranges described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples. “Water-soluble” means exhibiting a solubility of 5% by mass or more in water at 25 ° C. The materials exemplified in this specification may be used alone or in combination of two or more kinds. The content of each component in the composition means the total amount of the plurality of substances present in the composition, unless there is a plurality of substances corresponding to each component in the composition, unless otherwise specified. The "physiological saline" refers to a 0.9 mass% sodium chloride aqueous solution.

In the water absorbent resin particles according to the present embodiment, the swelling height (gel swelling height) measured by the following procedures (1) to (6) is 10 mm or less.
(1) A container having a recess having a bottom area of 50 cm ² is arranged with the recess opening in the vertical direction.
(2) Place 1.00 g of water-absorbent resin particles in the recess.
(3) A nonwoven fabric is arranged on the water absorbent resin particles in the recess.
(4) A weight having a mass of 90 g is arranged on the non-woven fabric.
(5) Supplying saline into the recess.
(6) The moving distance in the vertical direction of the weight when 300 seconds have elapsed from the start of swelling of the water absorbent resin particles is measured as the swelling height.

  According to the water-absorbent resin particles according to the present embodiment, when the liquid is absorbed, the liquid can be suitably diffused in the plane direction of the absorber (the direction perpendicular to the thickness direction, the direction parallel to the liquid absorption surface). A sex article can be obtained. According to the water-absorbent resin particles according to the present embodiment, while having suitable water absorption characteristics (water retention amount, water absorption rate, water absorption amount under load, etc.), when the liquid is absorbed, the liquid is absorbed in the plane direction of the absorber. An absorbent article that can be suitably diffused can be obtained.

  When the water-absorbent resin particles swell as they absorb liquid, the absorber and the absorbent article may expand in the thickness direction (direction perpendicular to the liquid-absorbing surface). If it expands too much in the thickness direction, it may be misunderstood by the user, his / her guardian, or caregiver that the liquid has sufficiently absorbed and cannot be used further. In addition, in a wearing article such as a diaper, it is possible to suppress liquid leakage by arranging a liquid absorbing member (for example, gather) from the liquid absorbing position in the plane direction of the absorbent body, but conventionally it is sufficiently sufficient against expansion in the thickness direction. No measures have been taken. On the other hand, according to the water-absorbent resin particles according to the present embodiment, while suppressing the expansion in the thickness direction of the absorbent body and the absorbent article, when the liquid is absorbed, the liquid can be preferably diffused in the plane direction of the absorbent body. A sex article can be obtained.

  The swelling height is preferably 9.5 mm or less, 9.2 mm or less, 9.0 mm or less, 8.8 mm or less, or 8.6 mm or less from the viewpoint of easily obtaining an absorbent article in which a liquid can be suitably diffused. The swelling height may be 8.5 mm or less, or 8.4 mm or less. The swelling height may be 1 mm or more, 3 mm or more, 5 mm or more, 7 mm or more, or 8 mm or more.

In step (1) in the swelling height test, the container has a bottomed recess, and the container is arranged such that the opening direction of the recess is positioned in the vertical direction. The container has, for example, a bottom surface that is a flat surface. In the container, the side wall forming the recess extends, for example, in the opening direction of the recess. In a cross section perpendicular to the opening direction of the recess, the recess has, for example, a circular shape. As the recess having a circular cross section, for example, a recess having an inner diameter of 80 mm and a bottom area of 50.24 cm ² can be used.

  In the step (2), water absorbent resin particles can be arranged on the bottom surface of the recess. In the step (2), the water absorbent resin particles can be uniformly arranged on the bottom surface of the recess.

As the nonwoven fabric in the step (3), a liquid permeable nonwoven fabric having a basis weight of 12 g / m ² can be used. In the step (3), the nonwoven fabric can be brought into contact with the water absorbent resin particles in the recess of the container. The size of the non-woven fabric is not particularly limited, and it is sufficient that the weight in the step (4) and the water-absorbent resin particles do not come into direct contact by using the non-woven fabric.

  The weight in step (4) can move in the vertical direction in the container without resistance and may have a flat surface. The weight may be perforated with a plurality of holes through which liquid may pass. In the step (4), the flat surface of the weight can be brought into contact with the nonwoven fabric. In the step (4), for example, the weight is gently placed on the nonwoven fabric so that a load other than the load due to the mass of the weight is not applied to the water-absorbent resin particles. The weight may be a single member or may be composed of a plurality of members. The weight has, for example, a flat plate portion having a flat surface and a convex portion extending from the flat plate portion.

  The amount of physiological saline used in the step (5) can be adjusted so that the water-absorbent resin particles are sufficiently immersed in the physiological saline. The amount of physiological saline used is, for example, 20 to 200 g.

  As the start of swelling of the water absorbent resin particles in the step (6), the time when the water absorbent resin particles swell and the weight starts moving can be used. By using the moving distance when 300 seconds have passed from the start of swelling, the water-absorbent resin particles that give an absorbent article in which the liquid can be suitably diffused can be easily selected.

  The water-absorbent resin particles according to the present embodiment need only be able to retain water, and the liquid to be absorbed can contain water. The water-absorbent resin particles according to the present embodiment are excellent in absorbability of body fluids such as urine, sweat, 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 capacity of the physiological saline of the water absorbent resin particles according to the present embodiment is preferably within the following range. From the viewpoint of easily increasing the absorption capacity of the absorbent article, the water retention amount is 20 g / g or more, 30 g / g or more, 34 g / g or more, 35 g / g or more, 40 g / g or more, 45 g / g or more, or 50 g / g. It is preferably g or more. From the viewpoint of easily suppressing excessive swelling in the absorbent article, the water retention amount is 80 g / g or less, 75 g / g or less, 70 g / g or less, 65 g / g or less, 60 g / g or less, or 55 g / g or less. preferable. From these viewpoints, the water retention amount is preferably 20 to 80 g / g, more preferably 30 to 55 g / g. As the water retention amount, the water retention amount at 25 ° C. can be used. The water retention amount can be measured by the method described in Examples below.

  The water absorption amount of the physiological saline solution under the load of the water absorbent resin particles according to the present embodiment is preferably within the following range. The water absorption amount 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, 24 mL / g or more, from the viewpoint of easily obtaining an absorbent article in which the liquid can suitably diffuse. Alternatively, 28 mL / g or more is preferable. The water absorption amount is preferably 40 mL / g or less, 35 mL / g or less, or 30 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 amount of absorbed physiological saline under load, the amount of absorbed water (25 ° C.) at a load of 4.14 kPa can be used. The water absorption amount can be measured by the method described in Examples below.

The water absorption rate of the physiological saline of the water absorbent resin particles according to the present embodiment is preferably within the following range. The water absorption rate is preferably 60 seconds or less, 57 seconds or less, or 55 seconds or less from the viewpoint that the liquid is easily absorbed by the absorbent article. The water absorption rate is 20 seconds or more, 25 seconds or more, 30 seconds or more, 33 seconds or more, 35 seconds or more, 40 seconds or more, or 45 from the viewpoint of easily preventing gel blocking that occurs when the liquid stays in a narrow area. Seconds or more are preferable. From these viewpoints, the water absorption rate is preferably 20 to 60 seconds. As the water absorption rate, the water absorption rate at 25 ° C. can be used. The water absorption rate can be measured according to the Vortex method (Japanese Industrial Standard JIS K 7224 (1996)). Specifically, 2.0 ± 0.002 g of the water-absorbent resin particles was added to 50 ± 0.1 g of physiological saline that was stirred at 600 rpm (rpm = min ⁻¹ ) and after addition of the water-absorbent resin particles, The water absorption speed can be obtained as the time [sec] until the vortex disappears and the liquid surface becomes flat.

  Examples of the shape of the water absorbent resin particles according to the present embodiment include a substantially spherical shape, a crushed shape, and a granular shape. The median particle diameter of the water absorbent resin particles according to the present embodiment may be 250 to 850 μm, 300 to 700 μm, or 300 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 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 can include, as polymer particles, for example, a cross-linked polymer obtained by polymerizing a monomer containing an ethylenically unsaturated monomer. That is, the water absorbent resin particles according to the present embodiment can have a structural unit derived from an ethylenically unsaturated monomer. A water-soluble ethylenically unsaturated monomer can be used as the ethylenically unsaturated monomer. Examples of the polymerization method include a reverse phase suspension polymerization method, an aqueous solution polymerization method, a bulk polymerization method, a precipitation polymerization method and the like. Among these, the reverse phase suspension polymerization method or the aqueous solution polymerization method is preferable from the viewpoints of ensuring good water absorbing properties of the water-absorbent resin particles to be obtained and controlling the polymerization reaction easily. In the following, the reverse phase suspension polymerization method will be described as an example of the method for polymerizing the ethylenically unsaturated monomer.

  The ethylenically unsaturated monomer is preferably water-soluble, and examples thereof include (meth) acrylic acid and salts thereof, 2- (meth) acrylamide-2-methylpropanesulfonic acid and salts 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 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 kinds. A functional group such as a carboxyl group and an amino group of the above-mentioned monomer can function as a functional group capable of being crosslinked in the surface crosslinking step described later.

  Among these, the ethylenically unsaturated monomer is selected from the group consisting of (meth) acrylic acid and its salts, acrylamide, methacrylamide, and N, N-dimethylacrylamide from the viewpoint of being industrially easily available. It is preferable to contain at least one compound selected, and it is more preferable 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 capacity, etc.), the ethylenically unsaturated monomer more 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 by being mixed with an aqueous solution containing the above-mentioned ethylenically unsaturated monomer. The amount of the ethylenically unsaturated monomer used is preferably 70 to 100 mol% based on the total amount of the monomers. Above all, the proportion of (meth) acrylic acid and its salt is more preferably 70 to 100 mol% with respect to the total amount of the monomers.

  Usually, the ethylenically unsaturated monomer is 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 the saturated concentration or less, and 25 to 70% by mass is preferable. More preferably, 30 to 55 mass% is still more preferable. Examples of 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 aqueous monomer solution may be used after neutralizing the acid group with an alkaline neutralizing agent. The degree of neutralization of the ethylenically unsaturated monomer with the alkaline neutralizing agent is determined from the viewpoint of increasing the osmotic pressure of the water-absorbent resin particles to be obtained and further improving the water absorption characteristics (water retention capacity, etc.). It is preferably 10 to 100 mol%, more preferably 50 to 90 mol%, and further preferably 60 to 80 mol% of the acidic group in the monomer. Examples of the alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium hydroxide and potassium carbonate; ammonia and the like. The alkaline neutralizing agent may be used alone or in combination of two or more kinds. The alkaline neutralizing agent may be used in the form of an aqueous solution in order to simplify the neutralizing operation. The acid group of the ethylenically unsaturated monomer can be neutralized by, for example, dropping an aqueous solution of sodium hydroxide, potassium hydroxide or the like into the above-mentioned aqueous monomer solution and mixing them.

  In the reverse phase suspension polymerization method, an aqueous monomer 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. You can A water-soluble radical polymerization initiator can be used as the radical polymerization initiator.

  Examples of the surfactant include nonionic surfactants and anionic surfactants. As the nonionic surfactant, sorbitan fatty acid ester and (poly) glycerin fatty acid ester (“(poly)” means both with and without the prefix “poly”. The same applies hereinafter. ), Sucrose fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene castor Oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyene Alkyl ethers, and polyethylene glycol fatty acid ester. Examples of anionic surfactants include fatty acid salts, alkylbenzene sulfonates, alkylmethyl taurates, polyoxyethylene alkylphenyl ether sulfates, polyoxyethylene alkyl ether sulfonates, and polyoxyethylene alkyl ether phosphates. , Phosphoric acid ester of polyoxyethylene alkyl allyl ether, and the like. The surfactant may be used alone or in combination of two or more kinds.

  The surfactant is a sorbitan fatty acid ester, from the viewpoint that the W / O type reversed phase suspension is in a good state, water-absorbent resin particles having a suitable particle size are easily obtained, and industrially easily available. It is preferable to contain at least one compound selected from the group consisting of polyglycerin fatty acid ester and sucrose fatty acid ester. From the viewpoint of easily obtaining an appropriate particle size distribution of the water absorbent resin particles, and from the viewpoint of easily improving the water absorbing properties of the water absorbent resin particles and the performance of the absorbent article using the same, the surfactant is a sucrose fatty acid ester. Is preferred, and sucrose stearate is more preferred.

  The amount of the surfactant used is preferably 0.05 to 10 parts by mass, based on 100 parts by mass of the aqueous monomer solution, from the viewpoint that the effect on the amount used is sufficiently obtained and from the economical viewpoint. 0.08 to 5 parts by mass is more preferable, and 0.1 to 3 parts by mass is still more preferable.

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

  The amount of the polymeric dispersant 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 that the effect on the amount used can be sufficiently obtained and from the economical viewpoint. , 0.08 to 5 parts by mass is more preferable, and 0.1 to 3 parts by mass is still more 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, chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane and n-octane; cyclohexane Alicyclic hydrocarbons such as methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentane; benzene; Examples thereof include aromatic hydrocarbons such as toluene and xylene. The hydrocarbon dispersion medium may be used alone or in combination of two or more kinds.

  The hydrocarbon dispersion medium may contain at least one selected from the group consisting of n-heptane and cyclohexane from the viewpoint of industrial availability and stable quality. From the same viewpoint, as the mixture of the above-mentioned hydrocarbon dispersion media, for example, commercially available exol heptane (manufactured by Exxon Mobil: n-heptane and 75-85% of isomer hydrocarbons) is used. May be.

  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 aqueous monomer 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, control of the polymerization temperature tends to be easy. 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 examples thereof include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t. -Butyl cumyl peroxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, peroxides such as hydrogen peroxide; 2,2'-azobis (2-amidinopropane ) Dihydrochloride, 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride, 2,2'-azobis [2- (N-allylamidino) propane] dihydrochloride, 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], 4,4′-azobis (4-cyanovaleric acid) and the like. The radical polymerization initiator may be used alone or in combination of two or more kinds. As the radical polymerization initiator, potassium persulfate, ammonium persulfate, sodium persulfate, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2- (2-imidazoline-2- At least one selected from the group consisting of yl) propane] dihydrochloride and 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride Is preferred.

  The amount of the radical polymerization initiator used may be 0.05 to 10 mmol based on 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 prevent a rapid polymerization reaction from occurring.

  The above radical polymerization initiator can 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.

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

  The aqueous monomer solution used for polymerization may contain a thickening agent in order to control the particle size of the water absorbent resin particles. 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 during polymerization is the same, the higher the viscosity of the aqueous monomer solution, the larger the median particle size of the particles obtained.

  Although crosslinking by self-crosslinking occurs during the polymerization, the crosslinking may be performed by using an internal crosslinking agent. When the internal cross-linking agent is used, it is easy to control the water absorption characteristics (swelling height, 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, trimethylolpropane, 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 ) Carbamyl acid esters; Compounds having two or more polymerizable unsaturated groups such as allylated starch, allylated cellulose, diallyl phthalate, N, N ', N "-triallyl isocyanurate, and divinylbenzene; ) Polyglycidyl such as 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 Compounds; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; isocyanate compounds (2,4-tolylene diisocyanate, hexamethylene diisocyanate, etc.) Examples thereof include compounds having two or more reactive functional groups, etc. The internal cross-linking agents may be used alone or in combination of two or more. A compound is preferable, a diglycidyl ether compound 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 such that it is easy to obtain an absorbent article in which the liquid can suitably diffuse, and the water-soluble property is suppressed by the resulting polymer being appropriately cross-linked, and a sufficient water absorption amount is obtained. From the viewpoint of easily obtaining, it is preferably 30 mmol or less, more preferably 0.01 to 10 mmol, still more preferably 0.012 to 5 mmol, and 0.015 to 1 mmol per 1 mol of the ethylenically unsaturated monomer. Particularly preferred is 0.02 to 0.1 millimole and very preferred is 0.02 to 0.05 millimole.

  An ethylenically unsaturated monomer, a radical polymerization initiator, a surfactant, a polymer-based dispersant, a hydrocarbon dispersion medium, etc. (and optionally an internal cross-linking agent) are mixed under heating in a mixed state, and oil is added. Reverse phase suspension polymerization can be performed in a medium water system.

  When carrying out reverse-phase suspension polymerization, an aqueous monomer solution containing an ethylenically unsaturated monomer is used as a hydrocarbon dispersion medium in the presence of a surfactant (and a polymer dispersant if necessary). Disperse. At this time, the surfactant, the polymeric dispersant, etc. may be added before or after the polymerization reaction is started, either before or after the addition of the aqueous monomer solution.

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

  The reverse phase suspension polymerization can be carried out in one stage or in multiple stages of two or more stages. The reverse phase suspension polymerization is preferably carried out in 2 to 3 stages from the viewpoint of improving productivity.

  When performing reverse phase suspension polymerization in multiple stages of two or more stages, after performing the first stage reverse phase suspension polymerization, the reaction mixture obtained in the first stage polymerization reaction is mixed with an ethylenically unsaturated monomer. The body may be added and mixed, and the reverse phase suspension polymerization of the second and subsequent stages may be carried out in the same manner as in the first stage. In the reverse phase suspension polymerization in each of the second and subsequent stages, in addition to the ethylenically unsaturated monomer, the radical polymerization initiator and / or the internal crosslinking agent described above are used in the reverse phase in each of the second and subsequent stages. Based on the amount of the 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 ethylenically unsaturated monomer. It is preferable. In the reverse phase suspension polymerization in the second and subsequent stages, an internal crosslinking agent may be used if necessary. When an internal cross-linking agent is used, it is added in an amount within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer based on the amount of ethylenically unsaturated monomer to be supplied to each stage, and the reverse phase suspension is added. It is preferable to carry out turbid polymerization.

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

  After the polymerization, a cross-linking agent may be added to the obtained hydrous gel polymer after the polymerization, and the cross-linking may be performed by heating. By carrying out crosslinking after the polymerization, the degree of crosslinking of the hydrogel polymer can be increased and the water absorption properties (swelling height, water retention amount, etc.) can be further improved.

  Post-polymerization crosslinking agents include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, polyglycerin; (poly) ethylene glycol diglycidyl ether. Compounds having two or more epoxy groups, such as (poly) propylene glycol diglycidyl ether and (poly) glycerin diglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; 2,4- Compounds having two or more isocyanate groups such as tolylene diisocyanate and hexamethylene diisocyanate; oxazoline compounds such as 1,2-ethylenebisoxazoline; ethylene car Carbonate compounds such as sulfonates; bis [N, N-di (beta-hydroxyethyl)] hydroxyalkylamide compound such Ajipuamido the like. 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 crosslinking agent may be used alone or in combination of two or more kinds.

  The amount of the post-polymerization crosslinking agent is preferably 30 mmol or less, and more preferably 10 mmol or less, per 1 mol of the ethylenically unsaturated monomer from the viewpoint of easily obtaining suitable water absorption characteristics (swelling height, water retention amount, etc.). Preferably, 0.01 to 5 millimole is more preferable, 0.012 to 1 millimole is particularly preferable, 0.015 to 0.1 millimole is extremely preferable, and 0.02 to 0.05 millimole is very preferable.

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

  Subsequently, the obtained hydrous gel polymer is dried to remove water to obtain polymer particles (for example, polymer particles having a structural unit derived from an ethylenically unsaturated monomer). As a drying method, for example, (a) the hydrogel polymer is dispersed in a hydrocarbon dispersion medium, and azeotropic distillation is performed by externally heating the mixture to reflux the hydrocarbon dispersion medium to remove water. Examples thereof include a method, (b) a method of taking out the hydrous gel polymer by decantation and drying under reduced pressure, and a method (c) of filtering the hydrous gel polymer by a filter and drying under reduced pressure. Above all, it is preferable to use the method (a) because it is easy 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 coagulant into the system after the polymerization reaction or at the beginning of the drying. By adding the aggregating agent, the particle diameter of the resulting water absorbent resin particles can be increased. An inorganic coagulant can be used as the coagulant. Examples of the inorganic coagulant (for example, powdery inorganic coagulant) 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 a flocculant, after preliminarily dispersing the flocculant in a hydrocarbon dispersion medium or water of the same kind as that used in the polymerization, under stirring, to give a hydrogel polymer. The method of mixing in the hydrocarbon dispersion medium containing is preferable.

  The addition amount of the aggregating agent is preferably 0.001 to 1 part by mass, more preferably 0.005 to 0.5 part by mass, and even more preferably 0.001 part by mass with respect to 100 parts by mass of the ethylenically unsaturated monomer used for the polymerization. More preferably, it is from 01 to 0.2 parts by mass. When the amount of the aggregating agent added is within the above range, water-absorbent resin particles having a desired particle size distribution can be easily obtained.

In the production of the water-absorbent resin particles, in the drying step (water removal step) or in subsequent steps, 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. Is preferred. By carrying out surface cross-linking, it is easy to control the water absorption characteristics (swelling height, water retention amount, etc.) of the water absorbent resin particles. The surface cross-linking is preferably carried out at the timing when the hydrogel polymer has a specific water content. The time of surface cross-linking is preferably a time point when the water content of the hydrogel polymer is 5 to 50% by mass, more preferably 10 to 40% by mass, and further preferably 15 to 35% by mass. The water content (mass%) of the water-containing gel polymer is calculated by the following formula.
Moisture content = [Ww / (Ww + Ws)] × 100
Ww: Required when mixing the coagulant, surface cross-linking agent, etc. to the amount obtained by subtracting the amount of water discharged to the outside of the system in the drying process from the amount of water contained in the aqueous monomer solution before the polymerization in the entire polymerization process The water content of the hydrogel polymer including the water content used according to the above.
Ws: Solid content calculated from the charged amounts of materials such as an ethylenically unsaturated monomer, a cross-linking agent, and an initiator that compose the hydrogel polymer.

  Examples of the surface cross-linking agent include compounds having two or more reactive functional groups. As the surface cross-linking agent, polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol and polyglycerin; (poly) ethylene glycol diglycidyl ether Polyglycidyl compounds such as (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, trimethylolpropane triglycidyl ether (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether; epichlorohydrin, Haloepoxy compounds such as epibromhydrin and α-methylepichlorohydrin; 2,4-tolylene diisocyanate, hexamethylene diisocyanate Isocyanate compound; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, 3 -Oxetane compounds such as butyl-3-oxetane ethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylene carbonate; hydroxyalkyl such as bis [N, N-di (β-hydroxyethyl)] adipamide Examples thereof include amide compounds. The surface cross-linking agent may be used alone or in combination of two or more kinds. The surface cross-linking agent is preferably a polyglycidyl compound, such as (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and polyglycerol. At least one selected from the group consisting of polyglycidyl ether is more preferable.

  The amount of the surface cross-linking agent used is 0.01 to 20 with respect to 1 mol of the ethylenically unsaturated monomer used for the polymerization, from the viewpoint that suitable water absorption characteristics (swelling height, water retention amount, etc.) are easily obtained. Millimol is preferred, 0.05-10 mmol is more preferred, 0.1-5 mmol is even more preferred, 0.15-1 mmol is particularly preferred, and 0.2-0.5 mmol is highly preferred.

  After the surface cross-linking, water and the hydrocarbon dispersion medium are distilled off by a known method to obtain polymer particles which are surface cross-linked dry products.

  As described above, the polymer particles contained in the water-absorbent resin particles can be obtained by using the internal cross-linking agent used during the polymerization of the monomer, and the internal cross-linking agent and the monomer are used after the polymerization of the monomer. An external cross-linking agent (a post-polymerization cross-linking agent used after the polymerization of the monomer, and a surface cross-linking agent used in the drying step after the polymerization of the monomer or the subsequent steps) can be used. The ratio of the amount of the external cross-linking agent used to the internal cross-linking agent (external cross-linking agent / internal cross-linking agent) is preferably 5 to 100 from the viewpoint that suitable water absorption characteristics (swelling height, water retention amount, etc.) are easily obtained. -80 are more preferable, 15-50 are still more preferable, and 15-30 are especially preferable. The water absorbent resin particles may include polymer particles that are a reaction product using an internal crosslinking agent, and may include polymer particles that are a reaction product using an internal crosslinking agent and an external crosslinking agent. The ratio of the amount of the external crosslinking agent used to the internal crosslinking agent in the polymer particles is preferably within the above range.

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

  The water absorbent resin particles may include a plurality of inorganic particles arranged on the surface of the polymer particles. For example, the inorganic particles can be arranged on the surface of the polymer particles by mixing the polymer particles and the inorganic particles. The inorganic particles may be silica particles such as amorphous silica.

  When the water absorbent resin particles include the 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, 0.5% by mass or less, or 0.3% by mass or less.

  The inorganic particles here usually have a fine 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 diameter can be measured by the pore electrical resistance method or the laser diffraction / scattering method depending on the characteristics of the particles.

  The absorber according to the present embodiment contains the water absorbent resin particles according to the present embodiment. The absorber according to the present embodiment may contain a fibrous substance, and is, for example, a mixture containing water-absorbent resin particles and a fibrous substance. The structure of the absorbent body may be, for example, a structure in which the water-absorbent resin particles and the fibrous substance are uniformly mixed, and the water-absorbent resin particles are sandwiched between the fibrous substances formed into a sheet or layer. It may be a configuration or another configuration.

  Examples of the fibrous material include finely pulverized wood pulp; cotton; cotton linters; rayon; cellulosic fibers such as cellulose acetate; synthetic fibers such as polyamide, polyester and polyolefin; and a mixture of these fibers. The fibrous material may be used alone or in combination of two or more kinds. Hydrophilic fibers can be used as the fibrous material.

  The fibers may be bonded to each other by adding an adhesive binder to the fibrous material in order to improve the shape retention of the absorbent body before and during use. Examples of the adhesive binder include heat-fusible synthetic fibers, hot melt adhesives and adhesive emulsions. The adhesive binder may be used alone or in combination of two or more kinds.

  Examples of the heat-fusible synthetic fiber include a total fusion type binder such as polyethylene, polypropylene and an ethylene-propylene copolymer; and a non-total fusion type binder having a side-by-side or core-sheath structure of polypropylene and polyethylene. In the above non-total melting type binder, only the polyethylene portion can be heat-sealed.

  Examples of hot melt adhesives include ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, 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 a polymer 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 separately from 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 absorbent body (for example, the thickness of the sheet-shaped absorbent body) 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% by mass based on the total amount of the water-absorbent resin particles and the fibrous substance, from the viewpoint of easily obtaining sufficient water-absorbing performance. It may be 60% by weight.

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

  The absorbent article according to the present embodiment includes the absorbent body according to the present embodiment. The absorbent article according to the present embodiment is a core wrap that retains the shape of the absorbent body and prevents the constituent members of the absorbent body from falling off or flowing; Sheet: A liquid-impermeable sheet or the like arranged on the outermost side on the side opposite to the side where the liquid to be sucked enters. Examples of absorbent articles include diapers (eg, paper diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat pads, pet sheets, simple toilet parts, animal excrement disposal materials, etc. ..

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

  The absorber 10 includes the water-absorbent resin particles 10a according to the present embodiment and the 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 surface side of the absorbent body 10 (the upper side of the absorbent body 10 in FIG. 1) while being in contact with the absorbent body 10. The core wrap 20b is arranged on the other surface side of the absorbent body 10 (below the absorbent body 10 in FIG. 1) while being in contact with the absorbent body 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 while being in contact with the core wrap 20a. Examples of the liquid permeable sheet 30 include a nonwoven fabric made of a synthetic resin such as polyethylene, polypropylene, polyester, polyamide, and a porous sheet. The liquid impermeable sheet 40 is arranged on the outermost side of the absorbent article 100 on the side opposite to the liquid permeable sheet 30. The liquid impermeable sheet 40 is arranged below the core wrap 20b while being 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, a sheet made of a composite material of these synthetic resins and a non-woven fabric, and the like. The liquid permeable sheet 30 and the liquid impermeable sheet 40 have, for example, a main surface wider than the main surface of the absorber 10, and the outer edge portions of the liquid permeable sheet 30 and the liquid impermeable sheet 40 are It extends around the absorber 10 and the core wraps 20a, 20b.

  The size relationship among the absorbent body 10, the core wraps 20a and 20b, the liquid permeable sheet 30, and the liquid impermeable sheet 40 is not particularly limited, and is appropriately adjusted according to the application of the absorbent article and the like. The method of retaining the shape of the absorbent core 10 using the core wraps 20a and 20b is not particularly limited, and the absorbent core may be wrapped with a plurality of core wraps as shown in FIG. 1, and the absorbent core may be wrapped with one core wrap. But it's okay.

  The absorber may be adhered to the topsheet. When the absorbent body is sandwiched or covered by the core wrap, it is preferable that at least the core wrap and the top sheet are bonded together, and the core wrap and the top sheet are bonded together and the core wrap and the absorbent body are bonded together. Is more preferable. As a method for adhering the absorbent body, a method in which a hot-melt adhesive is applied to the top sheet at predetermined intervals in the width direction in a stripe shape, a spiral shape or the like and adhered; starch, carboxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, etc. Examples of the method include bonding using a water-soluble binder such as the water-soluble polymer described above. Further, when the absorbent body contains the heat-fusible synthetic fiber, a method of adhering the heat-fusible synthetic fiber by heat fusion may be adopted.

  According to the present embodiment, it is possible to provide a liquid absorbing method using the water absorbent resin particles, the absorber or the absorbent article according to the present embodiment. The liquid absorbing method according to the present embodiment includes a step of bringing a 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, a method of improving the diffusion distance of the liquid in the plane direction of the absorbent body in the absorbent article, using the water-absorbent resin particles, the absorbent body or the absorbent article according to the present embodiment, diffusion A method of improving the distance can be provided. According to the present embodiment, it is possible to provide a method for suppressing the expansion of the water-absorbent resin particles in the vertical direction using the water-absorbent resin particles having the swelling height of 10 mm or less. According to this embodiment, it is possible to provide a method for producing water-absorbent resin particles, which includes a selection step of selecting water-absorbent resin particles based on the above-described swelling height. In the selection step, for example, the water absorbent resin particles are selected based on whether the swelling height is 10 mm or less.

  Hereinafter, the contents 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.

<Production of water absorbent resin particles>
(Example 1)
A round-bottomed cylindrical separable flask having an inner diameter of 11 cm and an inner volume of 2 L equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirrer (stirring blade having two inclined paddle blades with a blade diameter of 5 cm in two stages). Prepared. To this flask, 293 g of n-heptane was added as a hydrocarbon dispersion medium, and 0.736 g of a maleic anhydride-modified ethylene / propylene copolymer (Mitsui Chemicals, Inc., Hiwax 1105A) was added as a polymeric dispersant. This gave a mixture. After heating the mixture to 80 ° C. with stirring to dissolve the dispersant, the mixture was cooled to 50 ° C.

  Next, to a beaker having an internal volume of 300 mL, 92.0 g (acrylic acid: 1.03 mol) of an aqueous 80.5 mass% acrylic acid solution was added as a water-soluble ethylenically unsaturated monomer. Subsequently, while being cooled from the outside, 147.7 g of a 20.9 mass% aqueous sodium hydroxide solution was dropped into the beaker to neutralize 75 mol% of acrylic acid. After that, 0.092 g of hydroxyethyl cellulose (HEC AW-15F, manufactured by Sumitomo Seika Chemicals Ltd.) as a thickener, and 0.092 g of 2,2′-azobis (2-amidinopropane) dihydrochloride as a water-soluble radical polymerization initiator. (0.339 mmol) and 0.018 g (0.068 mmol) of potassium persulfate, and 0.005 g (0.029 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent, and then dissolved to add the first step. An aqueous solution of was prepared.

  Then, the above-mentioned first-stage aqueous liquid was added to the above separable flask while stirring at a rotation speed of the stirrer of 550 rpm, followed by stirring for 10 minutes. Then, it was obtained by heating and dissolving 0.736 g of sucrose stearate (surfactant, manufactured by Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370, HLB value: 3) in 6.62 g of n-heptane. The surfactant solution was added to the separable flask. Then, the system was sufficiently replaced with nitrogen while stirring at a rotation speed of the stirrer of 550 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 liquid.

  Next, 128.8 g (acrylic acid: 1.43 mol) of an 80.5 mass% acrylic acid aqueous solution as a water-soluble ethylenically unsaturated monomer was added 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 dropped into the beaker to neutralize 75 mol% of acrylic acid. Then, after adding 2,29'-azobis (2-amidinopropane) dihydrochloride 0.129 g (0.475 mmol) and potassium persulfate 0.026 g (0.095 mmol) as a water-soluble radical polymerization initiator, A second-stage aqueous liquid was prepared by dissolving.

  Next, after the inside of the separable flask described above was cooled to 25 ° C. while stirring at a rotation speed of the stirrer of 1000 rpm, the total amount of the above-mentioned second-stage aqueous liquid was added to the above-mentioned first-stage polymerized slurry liquid. Was added to. Then, after the system was replaced with nitrogen for 30 minutes, the flask was again immersed in a 70 ° C. water bath to raise the temperature, and a polymerization reaction was carried out for 60 minutes. After that, 0.580 g of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether (ethylene glycol diglycidyl ether: 0.067 mmol) was added as a post-polymerization crosslinking agent to obtain a second stage hydrogel polymer. .

  0.265 g of a 45% by mass aqueous solution of diethylenetriaminepentaacetic acid 5 sodium salt was added to the above-mentioned second stage hydrogel polymer under stirring. Then, the flask was immersed in an oil bath set at 125 ° C., and 223.7 g of water was extracted out of the system while refluxing the n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g of a 2% by mass ethylene glycol diglycidyl ether aqueous solution (ethylene glycol diglycidyl ether: 0.507 mmol) was added to the flask as a surface cross-linking agent, and the mixture was kept at 83 ° C. for 2 hours.

  Then, n-heptane was evaporated at 125 ° C. and dried to obtain polymer particles (dry product). After passing the polymer particles through a sieve with an opening of 850 μm, 0.2% by mass of amorphous silica (TOKUSIL NP-S, manufactured by Oriental Silicas Corporation) was added based on the total mass of the polymer particles. By mixing with the coalesced particles, 229.6 g of water-absorbent resin particles containing amorphous silica was obtained. The median particle diameter of the water absorbent resin particles was 346 μm. In Example 1, the molar ratio of the amount of the external crosslinking agent to the amount of the internal crosslinking agent used was 19.8.

(Example 2)
230.6 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 231.7 g of water was extracted from the second-stage hydrogel polymer by azeotropic distillation. The median particle diameter of the water absorbent resin particles was 361 μm.

(Example 3)
231.1 g of water-absorbent resin particles was obtained in the same manner as in Example 1 except that 234.2 g of water was extracted from the second-stage hydrogel polymer by azeotropic distillation. The median particle diameter of the water absorbent resin particles was 355 μm.

(Comparative Example 1)
In the preparation of the first-stage aqueous liquid, 0.0736 g (0.272 mmol) of potassium persulfate was used as a water-soluble radical polymerization initiator, and 2,2′-azobis (2-amidinopropane) dihydrochloride was added. No addition, 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether was used as an internal crosslinking agent; potassium persulfate was used as a water-soluble radical polymerization initiator in the preparation of the second-stage aqueous liquid. 0.090 g (0.334 mmol) was used and 2,2'-azobis (2-amidinopropane) dihydrochloride was not added, and 0.012 g (0.069 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent. ) Was used; in the preparation of the hydrogel polymer, a crosslinking reaction was performed after the polymerization reaction was performed for 60 minutes. Without addition, 0.265 g of a 45% by mass aqueous solution of 5% sodium diethylenetriaminepentaacetate was added; in the hydrogel polymer after the second stage polymerization, 247.9 g of water was removed from the system by azeotropic distillation. Extracted: 231.0 g of water-absorbent resin particles was obtained in the same manner as in Example 1 except that 0.5% by mass of the amorphous silica was mixed with the polymer particles. It was The median particle diameter of the water absorbent resin particles was 355 μm. In Comparative Example 1, the molar ratio of the amount of the external crosslinking agent to the amount of the internal crosslinking agent used was 4.0.

(Comparative example 2)
In the hydrogel polymer after the second-stage polymerization, 256.1 g of water was extracted out of the system by azeotropic distillation, and 0.1% by mass of amorphous particles was used with respect to the mass of the polymer particles. 230.8 g of water-absorbent resin particles was obtained in the same manner as in Comparative Example 1 except that high quality silica was mixed with polymer particles. The median particle diameter of the water absorbent resin particles was 349 μm.

(Comparative example 3)
In the hydrogel polymer after the second-stage polymerization, 278.9 g of water was extracted out of the system by azeotropic distillation, and 0.2% by mass of the amorphous polymer was used with respect to the mass of the polymer particles. 230.8 g of water-absorbent resin particles was obtained in the same manner as in Comparative Example 1 except that high quality silica was mixed with polymer particles. The median particle diameter of the water absorbent resin particles was 347 μm.

(Comparative example 4)
Inner diameter 11 cm, equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer (stirring blade having two inclined paddle blades with a blade diameter of 5 cm (two surface-treated with fluororesin)) A 2 L round bottom cylindrical separable flask with side wall baffles (baffle width: 7 mm) was prepared. Into this flask, 451.4 g of n-heptane was placed as a hydrocarbon dispersion medium, and 0.984 g of sorbitan monolaurate (NOF Corporation, Nonion LP-20R, HLB value: 8.6) was added as a surfactant. This gave a mixture. The sorbitan monolaurate was dissolved in n-heptane by raising the temperature to 50 ° C. while stirring this mixture at a rotation speed of a stirrer of 300 rpm, and then the internal temperature was cooled to 40 ° C.

  Next, 92.0 g (acrylic acid: 1.03 mol) of an 80.5 mass% acrylic acid aqueous solution was added to an Erlenmeyer flask having an internal volume of 500 mL. Subsequently, while cooling with ice from the outside, 147.7 g of a 20.9 mass% sodium hydroxide aqueous solution was dropped into the Erlenmeyer flask to neutralize 75 mol% of acrylic acid. Then, 0.101 g (0.374 mmol) of potassium persulfate was added as a radical polymerization initiator to the aqueous solution of partially neutralized acrylic acid, and then dissolved to prepare an aqueous monomer solution.

After the above monomer aqueous solution was added to the above separable flask, the inside of the system was sufficiently replaced with nitrogen. Then, the flask was immersed in a water bath at 70 ° C. while stirring at a rotation speed of a stirrer of 700 rpm, and then held for 60 minutes to obtain a hydrogel polymer.
did.

  Then, while stirring at a rotation speed of a stirrer of 1000 rpm, amorphous silica (powdered inorganic coagulant, Oriental Silicas Corporation) was added to the polymer solution containing the above-mentioned hydrogel polymer, n-heptane and a surfactant. Tokusil NP-S) (0.092 g, manufactured by Co., Ltd.) was previously dispersed in 100 g of n-heptane, and the resulting mixture was mixed for 10 minutes to obtain a reaction solution. Then, the flask containing the reaction solution was immersed in an oil bath at 125 ° C., and 112 g of water was extracted out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.97 g of a 10% by mass ethylene glycol diglycidyl ether aqueous solution (ethylene glycol diglycidyl ether: 2.85 mmol) was added as a post-polymerization crosslinking agent, and the mixture was kept at an internal temperature of 80 ± 2 ° C. for 2 hours.

  After that, water and n-heptane were evaporated, and the product was dried until almost no evaporation product from the system was distilled. Then, the flask was once removed from the oil bath, and 13.8 g of water was sprayed at a flow rate of 0.3 g per second. After that, polymer particles (dry product) were obtained by maintaining the system at 80 ° C. for 30 minutes while blowing nitrogen at a flow rate of 200 mL per minute. The polymer particles were passed through a sieve with an opening of 850 μm to obtain 90.5 g of water-absorbent resin particles. The median particle diameter of the water absorbent resin particles was 356 μm.

(Comparative example 5)
Inner diameter 11 cm, equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer (stirring blade having two inclined paddle blades with a blade diameter of 5 cm (two surface-treated with fluororesin)) A 2 L round bottom cylindrical separable flask with side wall baffles (baffle width: 7 mm) was prepared. To this flask, 451 g of n-heptane was placed as a hydrocarbon dispersion medium, and 0.984 g of sorbitan monolaurate (NOF Corporation, Nonion LP-20R, HLB value: 8.6) was added as a surfactant. A mixture was obtained. The sorbitan monolaurate was dissolved in n-heptane by raising the temperature to 50 ° C. while stirring this mixture at a rotation speed of a stirrer of 300 rpm, and then the internal temperature was cooled to 40 ° C.

  Next, 92.0 g (acrylic acid: 1.03 mol) of an 80.5 mass% acrylic acid aqueous solution was added to an Erlenmeyer flask having an internal volume of 500 mL. Subsequently, while cooling with ice from the outside, 147.7 g of a 20.9 mass% sodium hydroxide aqueous solution was dropped into the Erlenmeyer flask to neutralize 75 mol% of acrylic acid. Then, 0.101 g (0.374 mmol) of potassium persulfate was added as a radical polymerization initiator to the aqueous solution of partially neutralized acrylic acid, and then dissolved to prepare an aqueous monomer solution.

  After the above monomer aqueous solution was added to the above separable flask, the inside of the system was sufficiently replaced with nitrogen. Then, the reaction solution was obtained by immersing the flask in a water bath at 70 ° C. while stirring at a rotation speed of a stirrer of 700 rpm, and holding it for 60 minutes.

  Then, the flask containing the reaction solution was immersed in an oil bath at 125 ° C., and 129 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, after adding 4.14 g (ethylene glycol diglycidyl ether: 0.48 mmol) of a 2 mass% ethylene glycol diglycidyl ether aqueous solution as a surface cross-linking agent, the mixture was kept at an internal temperature of 80 ± 2 ° C. for 2 hours.

  Then, n-heptane was evaporated at 125 ° C. and dried to obtain polymer particles (dry product). The polymer particles were passed through a sieve with an opening of 850 μm to obtain 90.0 g of water-absorbent resin particles. The median particle diameter of the water absorbent resin particles was 180 μm.

<Measurement of medium particle size>
The above-mentioned median particle diameter of the water absorbent resin particles was measured by the following procedure. That is, from the top of the JIS standard sieve, a sieve having an opening of 600 μm, a sieve having an opening of 500 μm, a sieve having an opening of 425 μm, a sieve having an opening of 300 μm, a sieve having an opening of 250 μm, a sieve having an opening of 180 μm, a sieve having an opening of 150 μm. , And a saucer in this order. 50 g of the water-absorbent resin particles were put into the combined uppermost sieve and shaken for 10 minutes using a low-tap shaker for classification. After the classification, the mass of the particles remaining on each sieve was calculated as a mass percentage with respect to the total amount to determine the particle size distribution. With respect to this particle size distribution, the relationship between the mesh opening 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 over the sieve in order from the largest particle diameter. By connecting the plots on the probability paper with a straight line, the particle size corresponding to the cumulative mass percentage of 50 mass% was obtained as the median particle size.

<Measurement of swelling height>
The swelling height was measured using the measuring device X shown in FIG. The measuring device X shown in FIG. 2 includes a moving distance measuring device 51, a concave circular cup (height 45 mm, outer diameter 90 mm, concave portion depth 40 mm, concave portion inner diameter 80 mm) 52, and a plastic convex circular piston ( The outer diameter is 79 mm) 53. The convex circular piston 53 has a flat plate portion having a flat surface and a convex portion extending from the flat plate portion. In the flat plate portion of the convex circular piston 53, 60 through holes 53a having a diameter of 2 mm and penetrating the flat plate portion are evenly formed. The measuring device X has a sensor (lower part of the moving distance measuring device 51, manufactured by Keyence Corporation, IL-100) capable of measuring the displacement of the distance by the laser light L in units of 0.01 mm. The displacement of the distance includes an amplifier unit (Keyence Co., Ltd., IL-1000), a channel unit (Keyence Co., Ltd., NR-TH08), and a data logger (Keyence Co., NR). -500) and then using data analysis software (WAVE LOGGER manufactured by Keyence Corporation). A predetermined amount of water-absorbent resin particles 54 can be uniformly dispersed in the concave circular cup 52. A non-woven fabric 55 (a liquid-permeable non-woven fabric having a basis weight of 12 g / m ² ) can be placed on the water-absorbent resin particles 54 in the concave portion of the concave circular cup 52. The convex circular piston 53 can uniformly apply a load of 90 g to the water absorbent resin particles 54 via the nonwoven fabric 55.

  The measurement was performed in an environment of a temperature of 25 ° C. and a humidity of 60 ± 10%. After 1.0 g of the water-absorbent resin particles 54 was uniformly dispersed on the entire bottom surface of the concave circular cup 52 in the recess, a nonwoven fabric 55 was placed on the water-absorbent resin particles 54. Next, after gently placing the convex circular piston 53 on the non-woven fabric 55, the laser light L of the sensor of the movement distance measuring device 51 is positioned at the center of the tip of the convex portion of the convex circular piston 53. It was adjusted. With the load of 90 g applied to the water-absorbent resin particles 54 by the convex circular piston 53, physiological saline (20 g) adjusted in advance to 25 ° C. is passed through the through hole 53 a of the convex circular piston 53 to form the concave circular cup 52. Water absorption starts (0 second) when it is sensed that the water absorbent resin particles 54 have swollen and pushed up the convex circular piston 53 (automatic measurement starts when 0.5 mm displacement is observed). The distance at which the water-absorbent resin particles 54 swelled and the convex circular piston 53 was pushed up (the displacement difference of the convex circular piston 53 in the direction perpendicular to the bottom surface of the concave portion of the concave circular cup 52) was measured. The water level of the physiological saline is checked every 3 seconds from the start of the physiological saline injection, and the saline is intermittently maintained so as to maintain the water surface near the height of the flat surface of the flat plate portion of the convex circular piston 53. Water injection was continued. The moving distance of the convex circular piston 53 after 5 minutes (300 seconds) from the start of water absorption was obtained as the swelling height [mm].

<Water retention amount of water-absorbent resin particles>
The water retention capacity of physiological saline of the water-absorbent resin particles (room temperature, 25 ° C ± 2 ° C) was measured by the following procedure. First, a cotton bag (Membroad No. 60, width 100 mm x length 200 mm) in which 2.0 g of water-absorbent resin particles was weighed was placed in a beaker having an internal volume of 500 mL. After pouring 500 g of 0.9 mass% sodium chloride aqueous solution (physiological saline solution) into the cotton bag containing the water-absorbent resin particles at once so as not to make Mako, tie the upper part of the cotton bag with a rubber band and let stand for 30 minutes. The water absorbent resin particles were swollen by placing them. The cotton bag after 30 minutes 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 the swollen gel after dehydration was included. 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 capacity 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

<Water absorption rate of water-absorbent resin particles>
The water absorption rate of the physiological saline solution of the water absorbent resin particles was measured by the following procedure based on the Vortex method. First, 50 ± 0.1 g of 0.9 mass% sodium chloride aqueous solution (physiological saline) adjusted to a temperature of 25 ± 0.2 ° C. in a constant temperature water tank was weighed into a beaker having an internal volume of 100 mL. Next, a magnetic stirrer bar (8 mmφ × 30 mm, no ring) was used to stir at a rotation speed of 600 rpm to generate a vortex. 2.0 ± 0.002 g of water-absorbent resin particles were added at once to the aqueous sodium chloride solution. The time [seconds] from the addition of the water-absorbent resin particles to the time when the vortex on the liquid surface converges was measured, and the time was obtained as the water-absorption rate of the water-absorbent resin particles. The results are shown in Table 1.

<Water absorption amount of water-absorbent resin particles under load>
The water absorption amount (room temperature, 25 ° C. ± 2 ° C.) of the physiological saline solution under load (under pressure) 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 part 61, a conduit 62, a measuring table 63, and a measuring part 64 placed on the measuring table 63. The buret part 61 has a burette 61a extending in the vertical direction, a rubber plug 61b arranged at the upper end of the buret 61a, a cock 61c arranged at the lower end of the buret 61a, and one end extending into the buret 61a near the cock 61c. It has an air introducing pipe 61d and a cock 61e arranged on the other end side of the air introducing 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 center of the measuring table 63, and the conduit 62 is connected to the hole. The measuring section 64 has a cylinder 64a (made of acrylic resin (Plexiglas)), 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 evenly spread on the nylon mesh 64b. The weight 64c has a diameter of 19 mm, and the weight 64c has a mass of 120 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 putting 0.100 g of the water-absorbent resin particles 65 into 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 solution absorbed by the water-absorbent resin particles 65 is rapidly and smoothly supplied into the buret 61a from the air introduction pipe, the amount of the physiological saline solution inside the buret 61a is reduced. Is the amount of physiological saline absorbed by the water-absorbent resin particles 65. The scale of the buret 61a is engraved from 0 mL to 0.5 mL in a downward direction from the top, and the burette 61a 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 physiological saline level. The scale Vb 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 pressure [mL / g] = (Vb-Va) /0.1

<Evaluation of absorber performance>
(Preparation of test solution)
In a container having an internal volume of 10 L, 60 g of sodium chloride, 1.8 g of calcium chloride dihydrate, 3.6 g of magnesium chloride hexahydrate and an appropriate amount of distilled water were put and then completely dissolved. Next, after adding 0.02 g of polyoxyethylene nonylphenyl ether, the mass of the entire aqueous solution was adjusted to 6000 g by adding distilled water. Then, a test solution (artificial urine) was obtained by coloring with a small amount of Blue No. 1.

(Preparation of absorbent article)
A sheet-shaped absorber having a size of 40 cm × 12 cm was obtained by uniformly mixing 10 g of the water-absorbent resin particles and 10 g of crushed pulp by air-papermaking using an air flow type mixing device (pad former manufactured by Autech Co., Ltd.). Was produced. Next, after arranging the absorber on the core wrap (tissue paper) having the same size as the absorber and having a basis weight of 16 g / m ² , the basis weight 16 g having the same size as the absorber is provided on the upper surface of the absorber. / M ² core wrap (tissue paper) was placed. A laminated body was obtained by applying a load of 196 kPa to the absorbent body sandwiched by the core wraps for 30 seconds. Further, an air-through type porous liquid permeable sheet made of polyethylene-polypropylene having a basis weight of 22 g / m ² and having the same size as the absorber is arranged on the upper surface of the laminate, and polyethylene having the same size and the same basis weight. An absorbent article was produced by arranging a liquid-impermeable sheet made from the product on the lower surface of the laminate.

(Evaluation of diffusion length and permeation rate)
In a room at a temperature of 25 ± 2 ° C., a measuring instrument equipped with a liquid charging cylinder having an opening with an inner diameter of 3 cm was placed at the center of an absorbent article placed on a horizontal table. Next, 50 mL of the test solution adjusted to 25 ± 1 ° C. was charged into the cylinder at one time (supplied from the vertical direction), and the stopwatch was started. The absorption time from the start of feeding until the test liquid was completely absorbed by the absorber was measured. This operation was repeated twice at 30-minute intervals (three times in total), and the total value of the absorption time was obtained as the permeation rate (unit: second). A shorter permeation rate is preferred. Further, 120 minutes after the start of the first injection of the test liquid, the spread dimension in the longitudinal direction (the plane direction of the absorber in the absorbent article) of the absorbent article in which the test liquid has penetrated (passes through the central portion of the absorbent article, Moreover, the distance (diffusion distance) between both ends of the diffusion region of the test liquid (unit: cm) was measured. The diffusion length was measured in units of 0.5 cm. The results are shown in Table 1.

  According to Table 1, it is confirmed that by reducing the swelling height, it is possible to obtain an absorbent article in which the liquid can suitably diffuse in the plane direction of the absorbent body when absorbing the liquid.

10 ... Absorber, 10a, 54, 65 ... Water absorbent resin particles, 10b ... Fiber layer, 20a, 20b ... Core wrap, 30 ... Liquid permeable sheet, 40 ... Liquid impermeable sheet, 51 ... Moving distance measuring device, 52 ... concave circular cup, 53 ... convex circular piston, 53a ... through hole, 55 ... non-woven fabric, 61 ... burette part, 61a ... burette, 61b ... rubber stopper, 61c ... cock, 61d ... air introducing pipe, 61e ... cock, 62 ... Conduit, 63 ... Measuring stand, 64 ... Measuring part, 64a ... Cylinder, 64b ... Nylon mesh, 64c ... Weight, 100 ... Absorbent article, L ... Laser light, X, Y ... Measuring device.

Claims (4)

A water-absorbent resin particle containing a cross-linked polymer having a structural unit derived from an ethylenically unsaturated monomer,
The ethylenically unsaturated monomer contains at least one compound selected from the group consisting of (meth) acrylic acid and salts thereof,
The ratio of the (meth) acrylic acid and its salt is 70 to 100 mol% with respect to the total amount of monomers for obtaining the water-absorbent resin particles,
The water retention capacity of physiological saline is 30 to 80 g / g,
Has a medium particle size of 250 to 850 μm,
Water-absorbent resin particles having a swelling height of 10 mm or less measured by the following procedures (1) to (6).
(1) A container having a recess having a bottom area of 50 cm ² is arranged with the recess opening in the vertical direction.
(2) Place 1.00 g of water-absorbent resin particles in the recess.
(3) A nonwoven fabric is arranged on the water absorbent resin particles in the recess.
(4) A weight having a mass of 90 g is arranged on the non-woven fabric.
(5) Supplying saline into the recess.
(6) The moving distance in the vertical direction of the weight when 300 seconds have elapsed from the start of swelling of the water absorbent resin particles is measured as the swelling height. An absorbent body containing the water absorbent resin particles according to claim 1 . An absorbent article comprising the absorbent body according to claim 2 . The absorbent article according to claim 3 , which is a diaper.

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