JP2015178099A - Water-absorbing resin particle, method of producing water-absorbing resin particle and absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-absorbing resin particle with high gel strength while maintaining water absorption ability to electrolyte aqueous solution.SOLUTION: A water-absorbing resin particle comprises a core particle comprising water-absorbing resin comprising a hydroxy group and an anionic functional group, and a crosslinked product layer formed by surface cross-linking of the surface of the core particle with a surface crosslinking agent under a basic condition and disposed in at least part of the surface of the core particle.

Description

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

  The water-absorbent resin absorbs several tens to several hundred times as much water as its own weight. As the water-absorbing resin, a crosslinked polyacrylic acid is mainly used, and is widely used in sanitary products such as paper diapers and sanitary products, civil engineering, food, and agriculture. In general, it is known that a water-absorbing resin has a low gel strength in a structure having a high water-absorbing property. Therefore, the gel strength is increased by using a method such as cross-linking the surface. For example, when an aqueous solution containing polyvalent metal ions such as calcium ions is absorbed into the surface layer of the crosslinked polyacrylic acid, the carboxyl groups in the crosslinked polyacrylic acid and the polyvalent metal ions are ion-bonded to absorb water. Attempts have been made to increase the gel strength of conductive resins (see, for example, Patent Documents 1 and 2). In addition, methods for increasing the gel strength by adding a crosslinking agent that reacts with a carboxyl group contained in a crosslinked polyacrylic acid have been studied (for example, see Patent Documents 3 and 4). On the other hand, a method of increasing the gel strength by coating the surface of a crosslinked polyacrylic acid with a polyfunctional monomer having ethylene glycols and a glycidyl group and crosslinking the surface is also studied (for example, see Patent Document 5).

  On the other hand, polysaccharides such as carboxymethyl cellulose (for example, see Patent Document 6), carboxyethyl cellulose (for example, see Patent Document 7), guar gum, carrageenan, etc. (for example, Patent Document) 8)) is being studied.

JP 2005-263858 A JP 2001-224959 A Japanese Patent No. 3913867 Japanese Patent No. 3598141 Japanese Patent No. 3389130 International Publication No. 2012/147255 JP 2010-18670 A JP 2003-154262 A

  When the methods disclosed in Patent Documents 1 to 4 are used, since the carboxyl group involved in water absorption is used for the crosslinking reaction, there is a problem that water absorption is reduced. In the method disclosed in Patent Document 5, the carboxyl group is not consumed in the cross-linking reaction, but the water-absorbing property of the polyacrylic acid cross-linked product is lowered because one cross-linked layer is present on the surface of the water-absorbing resin.

  The polysaccharides and the like disclosed in Patent Documents 6 to 8 have high water absorption with respect to the aqueous electrolyte solution, but have a problem in gel strength. In addition, since polysaccharides have a small amount of anionic functional groups that contribute to water absorption per unit mass, there is a concern that the decrease in water absorption will increase when a conventional surface crosslinking method for crosslinking carboxyl groups is applied. Therefore, there is a demand for a water-absorbing resin having high gel strength while maintaining water absorption.

  The present invention has been made in view of the above circumstances, and provides water-absorbent resin particles having high gel strength and an absorbent body using the same while maintaining water absorbency with respect to an aqueous electrolyte solution. Furthermore, the present invention provides a method for producing water-absorbing resin particles having high gel strength while maintaining water absorption with respect to an aqueous electrolyte solution.

  As a result of intensive studies, the inventors of the present invention have obtained a core particle containing a water-absorbing resin having an anionic functional group such as a carboxyl group and a hydroxyl group. By cross-linking using a surface cross-linking agent, it was found that water-absorbing resin particles having surface cross-linking with high gel strength can be obtained while maintaining water absorption with respect to the aqueous electrolyte solution, and the present invention has been completed.

  That is, the present invention provides a surface-crosslinked water-absorbent resin particle having a high gel strength while maintaining water absorbency with respect to an aqueous electrolyte solution, an absorbent body using the same, and a method for producing the water-absorbent resin particle. About things.

<1> core particles containing a water-absorbent resin having a hydroxyl group and an anionic functional group;
A cross-linked product layer formed by surface cross-linking with a surface cross-linking agent under a basic condition under a basic condition, and disposed on at least a part of the surface of the core particle;
Water-absorbent resin particles having
<2> The water absorbent resin particle according to <1>, wherein the anionic functional group includes a carboxyl group.
<3> The water absorbent resin particle according to <1> or <2>, wherein the core particle is an internal cross-linked product of the water absorbent resin.
<4> The water absorbent resin particle according to any one of <1> to <3>, wherein the water absorbent resin contains a polysaccharide.
<5> The water-absorbent resin particles according to <4>, wherein the polysaccharide includes a cellulose derivative.
<6> The water-absorbent resin particle according to <5>, wherein the cellulose derivative contains carboxymethylcellulose.
<7> The water absorbent resin particle according to any one of <1> to <6>, wherein the surface cross-linking agent includes a polyvalent epoxy compound.
<8> The water-absorbent resin particle according to <7>, wherein the polyvalent epoxy compound contains ethylene glycol diglycidyl ether.
<9> A method for producing water-absorbing resin particles, comprising a step of bringing the surface of a core particle containing a water-absorbing resin having a hydroxyl group and an anionic functional group into contact with a surface crosslinking agent under basic conditions.
<10> The method for producing water absorbent resin particles according to <9>, wherein the anionic functional group contains a carboxyl group.
<11> The method for producing water absorbent resin particles according to <9> or <10>, wherein the core particle is an internal cross-linked product of the water absorbent resin.
<12> The method for producing water absorbent resin particles according to any one of <9> to <11>, wherein the water absorbent resin contains a polysaccharide.
<13> The method for producing water absorbent resin particles according to <12>, wherein the polysaccharide includes a cellulose derivative.
<14> The method for producing water-absorbent resin particles according to <13>, wherein the cellulose derivative contains carboxymethylcellulose.
<15> The method for producing water-absorbent resin particles according to any one of <9> to <14>, wherein the surface cross-linking agent includes a polyvalent epoxy compound.
<16> The method for producing water-absorbent resin particles according to <15>, wherein the polyvalent epoxy compound contains ethylene glycol diglycidyl ether.
<17> The method for producing water absorbent resin particles according to any one of <9> to <16>, wherein the contacting step is performed by a spraying method, a dropping method, or a solution method.
<18> An absorber comprising the water-absorbent resin particles according to any one of <1> to <8>.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the water absorbing resin particle with high gel strength, and an absorber using the same, maintaining the water absorption with respect to electrolyte aqueous solution. Furthermore, according to the present invention, it is possible to provide a method for producing water-absorbing resin particles having high gel strength while maintaining water absorption with respect to the aqueous electrolyte solution.

  In the present specification, a numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively. Further, in the present specification, the content of each component in the composition is the total amount of the plurality of substances present in the composition unless there is a specific notice when there are a plurality of substances corresponding to each component in the composition. Means.

  The present invention relates to a core particle containing a water-absorbing resin containing an anionic functional group such as a carboxyl group and a hydroxyl group, and by crosslinking a hydroxyl group having a low contribution to water absorption using a surface cross-linking agent. The surface-crosslinked water-absorbent resin particles having high gel strength, an absorbent body using the same, and a method for producing the water-absorbent resin particles are provided.

<Water-absorbent resin particles and production method thereof>
The water-absorbent resin particles of the present invention are formed by surface-crosslinking a core particle containing a water-absorbent resin having a hydroxyl group and an anionic functional group with a surface crosslinking agent under a basic condition using a surface crosslinking agent, And a crosslinked product layer disposed on at least a part of the surface of the core particle.

In the present invention, the water-absorbing resin refers to a cross-linked resin that can absorb water several to several hundred times its own weight.
The water absorbent resin according to the present invention may be a water absorbent resin having an anionic functional group such as a carboxyl group and a hydroxyl group.
The anionic functional group is not particularly limited as long as the effect of the present invention is achieved. Specific examples include a carboxyl group, a sulfonic acid group, a phosphoric acid group, and a cyano group. From the viewpoint of safety, a carboxyl group is preferable. The resin may have only one kind of anionic group or two or more kinds. The proportion of the carboxyl group in the anionic functional group is preferably 50 mol% or more, more preferably 80 mol% or more, and further preferably 100 mol%.
In the present invention, a water-absorbent resin synthesized from a monomer having an anionic functional group and a monomer having a hydroxyl group or a group which can be changed to a hydroxyl group by hydrolysis, a polymer containing both an anionic functional group and a functional group of a hydroxyl group. Crosslinked water-absorbing resins, water-absorbing resins cross-linked by mixing a polymer having an anionic functional group and a polymer having a hydroxyl group can be used. These resins may be used alone or in combination.

  When the water-absorbing resin according to the present invention is synthesized by polymerizing monomers, a monomer having an anionic functional group, a monomer having a hydroxyl group, and a monomer capable of changing the functional group to a hydroxyl group by hydrolysis after polymerization of vinyl acetate or the like The water-absorbent resin according to the present invention is obtained by reacting at least one of them. Examples of the monomer having an anionic functional group include anionic unsaturated monomers such as acrylic acid, methacrylic acid, maleic acid, vinyl sulfonic acid, and styrene sulfonic acid, and salts thereof. Examples of the monomer having a functional group that can be changed to a hydroxyl group by hydrolysis or the like include a specific functional group-containing unsaturated monomer such as vinyl acetate. Examples of the monomer having a hydroxyl group include hydroxyl group-containing acrylate monomers such as 4-hydroxybutyl acrylate and 1,4-cyclohexanedimethanol monoacrylate. One or more of these monomers may be mixed and used, and a polymer having an anionic functional group may be synthesized from one or more types of monomers having an anionic functional group. A polymer having a hydroxyl group may be synthesized from at least one of a monomer having a functional group and a monomer having a hydroxyl group, and these polymers may be mixed and used.

Examples of the water absorbent resin having an anionic functional group and a hydroxyl group include polysaccharides and synthetic polymers. Examples of the polysaccharide include, but are not limited to, polysaccharides, polysaccharide derivatives and alkali metal salts such as sodium salts and potassium salts thereof.
Examples of the polysaccharide include cellulose nitrate, cellulose sulfate, cellulose acetate, carboxymethyl cellulose, carboxyethyl cellulose, chondroitin sulfate, oxidized starch, phosphorylated starch, carrageenan, xanthan gum, alginic acid, hyaluronic acid and the like. Alkali metal salts such as sodium salts and potassium salts are also included. As the polysaccharide, carboxymethyl cellulose and alkali metal salts thereof are particularly preferable.
As the synthetic polymer, an anionic polymer and a hydroxyl group-containing polymer can be used. As the anionic polymer, a polymer having an anionic functional group such as polyacrylic acid, polystyrene sulfonic acid, and polyvinyl sulfonic acid can be used. Examples of the hydroxyl group-containing polymer include polyvinyl alcohol and polyethylene glycol. Copolymers of these anionic polymers and hydroxyl group-containing polymers, resins obtained by crosslinking a mixture of an anionic polymer and a hydroxyl group-containing polymer, and the like are listed as water-absorbing resins containing an anionic functional group and a hydroxyl group. In addition to these resins, polymers containing other functional groups may be included. These polymers can be used either in a crosslinked state or in an uncrosslinked state. The following hydroxyl group-containing polymers can be used by mixing with anionic functional group-containing polysaccharides, synthetic polymers and the like. Examples of the hydroxyl group-containing polymer include polysaccharides and synthetic polymers. Specific examples of the hydroxyl group-containing polymer are as described above. Polysaccharides include cellulose, methylcellulose, ethylcellulose, hydroxymethylcellulose, cationized cellulose, hydroxyethylcellulose, hydroxypropylcellulose, ethylhydroxycellulose, hydroxypropylmethylcellulose, gum arabic, guar gum, locust bean gum, pectin, tragacanth, corn starch, starch Acetylated starch, dextrin, gelatin, casein, agar and the like.
In the present invention, it is preferable that a polysaccharide is contained as the water-absorbing resin. When the polysaccharide is contained as the water absorbent resin, the proportion of the polysaccharide in the water absorbent resin is preferably 50% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass. In the present invention, it is preferable to include a cellulose derivative as the polysaccharide for the reason of maintaining the water absorption of the aqueous electrolyte solution. When a cellulose derivative is included as the water absorbent resin, the proportion of the cellulose derivative in the water absorbent resin is preferably 50% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. In the present invention, it is preferable to include carboxymethyl cellulose as the cellulose derivative for reasons of safety to the living body. When carboxymethyl cellulose is included as the water absorbent resin, the proportion of carboxymethyl cellulose in the water absorbent resin is preferably 50% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more.

  As a ratio of the functional group amount contained in the water absorbent resin, the ratio of the anionic functional group to the hydroxyl group is, for example, in the range of 0.1 mol% to 99 mol%, and preferably 1 mol% to 70 mol%. 5 mol%-50 mol% are more preferable. When the ratio of the anionic functional group is 0.1 mol% or more, the water absorbing property of the water absorbing resin can be sufficiently maintained. If it is 99 mol% or less, the amount of hydroxyl groups used for surface crosslinking is sufficient, and surface crosslinking can be applied.

  When the water-absorbent resin of the present invention contains carboxymethylcellulose, the weight average molecular weight of carboxymethylcellulose is preferably 1000 or more, more preferably 10,000 or more, and even more preferably 100,000 or more. The weight average molecular weight is preferably 10 million or less, more preferably 5 million or less, and further preferably 4 million or less. If the weight average molecular weight is 1000 or more, sufficient water absorption performance can be secured, and if it is 10 million or less, it is easy to knead during synthesis. The degree of polymerization of the glucose ring is preferably 50 to 2000, more preferably 200 to 1000, and even more preferably 300 to 600. The substitution degree of the carboxyl group is preferably from 0.1 to 2.8, more preferably from 0.3 to 1.4, and even more preferably from 0.5 to 1.1. When the degree of substitution is 0.1 or more, the water absorption of the water absorbent resin can be sufficiently maintained. When the degree of substitution is 2.8 or less, the amount of hydroxyl groups that can be used for crosslinking is sufficient, and surface crosslinking can be applied. In addition, a substitution degree shows the average number by which the hydroxyl group was substituted by the carboxyl group with respect to one glucose ring.

In the present invention, it is preferable from the viewpoint of improving the gel strength that the core particle is an internal cross-linked product of a water absorbent resin. The cross-linking here (hereinafter also referred to as internal cross-linking) does not include “surface cross-linking” that further cross-links the surface of the internally cross-linked resin particles.
Although it does not specifically limit as a crosslinking agent at the time of performing internal bridge | crosslinking of a water absorbing resin, The polyhydric epoxy compound, polyhydric aldehyde compound, polyhydric carboxylic acid compound, polyhydric isocyanate compound, polyhydric compound which has 2 or more functional groups. Examples include vinyl compounds, polyvalent acrylate compounds, polyvalent methacrylate compounds, and polyvalent halogen compounds. Substances having two or more kinds of different functional groups in one molecule such as epichlorohydrin and glycidyl methacrylate can also be used.
Examples of the cross-linking agent include polyvalent epoxy compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether, as well as many such as glutaraldehyde, glyoxal, and terephthalaldehyde. Polyhydric carboxylic acid such as polyhydric aldehyde compound, malic acid, citric acid, tartaric acid, polyacrylic acid, maleic acid, succinic acid, polyisocyanate compound such as diphenylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, divinyl sulfone, etc. Polyvalent vinyl compounds, polyvalent acrylate compounds such as polyethylene glycol diacrylate, poly Polyvalent methacrylate compounds such Chi glycol dimethacrylate, haloepoxy compounds such as epichlorohydrin, but like polyvalent halogen compound is not limited thereto. In particular, ethylene glycol diglycidyl ether is preferred.

  As a method of internal cross-linking of the water-absorbent resin, in the case of cross-linking at the time of polymer synthesis from a monomer, a polyvalent vinyl compound, a polyvalent acrylate compound, a polyvalent methacrylate compound, etc. are used by radical polymerization or the like. It can be crosslinked during polymerization. When the polysaccharide, one kind or two or more kinds of polymers are crosslinked, various crosslinking methods can be applied using a crosslinking agent capable of crosslinking at least one of an anionic functional group and a hydroxyl group. For example, an alkoxide in a polymer may be reacted with a crosslinking agent such as a polyvalent epoxy compound, a polyvalent acrylate compound, a polyvalent vinyl compound, a polyvalent methacrylate compound, a haloepoxy compound, or a polyvalent halogen compound under basic conditions. it can.

  The water absorption ratio of the water absorbent resin is preferably 40 g / g or more with respect to 1 g of the water absorbent resin. If the water absorption ratio is 40 g / g or more, the amount of water-absorbing resin used can be suppressed, which is preferable. 50 g / g or more is more preferable, and 60 g / g or more is more preferable. There is no particular upper limit for the water absorption capacity, but 3000 g / g or less is preferable in order to prevent the strength of the gel from being lowered and the handleability during water absorption to be deteriorated.

  The water retention ratio of the water absorbent resin is preferably 40 g / g or more with respect to 1 g of the water absorbent resin. If the water absorption ratio is 40 g / g or more, the amount of water-absorbing resin used can be suppressed, which is preferable. 50 g / g or more is more preferable, and 60 g / g or more is more preferable. There is no particular upper limit of the water retention ratio, but 3000 g / g or less is preferable in order to prevent the gel strength from being lowered and the handleability during water absorption to deteriorate.

  In the present invention, the shape of the core particles is not particularly limited, and can be selected according to the type and use of the water absorbent resin. For example, spherical shape, scale shape, fibrous shape, crushed shape, granular shape, rod shape, needle shape, plate shape and the like can be mentioned, and spherical shape or crushed shape is preferable from the viewpoint of particle strength.

  The size of the core particles is not particularly limited, and can be selected according to the type and use of the water absorbent resin. From the viewpoint of handleability, the average particle diameter is preferably 150 μm to 1000 μm. When the average particle size is 150 μm or more, the powder tends to be less scattered during use, and when it is 1000 μm or less, the water absorption tends to be maintained at a high level. The average particle diameter is more preferably 200 μm to 800 μm, and further preferably 250 μm to 700 μm. The average particle diameter of the core particles can be measured by a dry particle size distribution meter.

  The core particles may be composed only of the water-absorbent resin or may contain other components as necessary. Examples of such components include clay, surfactant, deodorant, blood coagulant, blood coagulation inhibitor, and antibacterial agent.

The method for producing the core particles is not particularly limited, and can be selected from commonly used methods. For example, it can be produced by a method described in International Publication No. 2012/147255, Japanese Patent Application Laid-Open No. 2012-012462, and the like.
Alternatively, the core particles may be obtained by pulverizing and classifying the internally cross-linked water-absorbent resin after internal cross-linking of the water-absorbent resin.

The method for producing water-absorbent resin particles of the present invention includes a step of bringing the surface of a core particle containing a water-absorbent resin having a hydroxyl group and an anionic functional group into contact with a surface cross-linking agent under basic conditions. By passing through the manufacturing method of the water-absorbent resin particles of the present invention, in the water-absorbent resin particles of the present invention, a crosslinked product layer is disposed on at least a part of the surface of the core particles.
In the step of bringing the surface of the core particle and the surface cross-linking agent into contact with each other under a basic condition (that is, a method of surface cross-linking treatment), a solution containing the surface cross-linking agent is used, and the surface of the core particle containing the water-absorbent resin is applied Method of spraying (spraying method), method of cross-linking core particles containing a water-absorbing resin in a solution containing a surface cross-linking agent (solution method), method of dropping a solution onto the core particles containing a water-absorbing resin and cross-linking (dropping method) ) Etc. are applicable. Further, the basic aqueous solution and the surface cross-linking agent can be used separately. For example, a method in which a basic aqueous solution is preliminarily absorbed in core particles containing a water absorbent resin, and a solution containing a crosslinking agent is brought into contact with the core particles containing a water absorbent resin. For example, a method of surface cross-linking the core particles after synthesis of the water-absorbent resin can be used. In the present invention, the contacting step is preferably performed by a spray method, a dropping method or a solution method.

The surface cross-linking agent can be used as long as it is a cross-linking agent that reacts with a hydroxyl group, and is not particularly limited. However, a polyvalent epoxy compound, a polyvalent aldehyde compound, a polyvalent carboxylic acid compound, a polyvalent isocyanate compound, a polyvalent vinyl compound, a polyvalent vinyl compound, Examples thereof include compounds having two or more functional groups in one molecule such as a polyvalent acrylate compound, a polyvalent methacrylate compound, and a polyvalent halogen compound. Compounds having different functional groups such as epichlorohydrin and glycidyl methacrylate can also be used.
Examples of the surface cross-linking agent include polyhydric epoxy compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether, glutaraldehyde, glyoxal, and terephthalaldehyde. Multivalent aldehyde compounds, polyvalent carboxylic acids such as malic acid, citric acid, tartaric acid, polyacrylic acid, maleic acid and succinic acid, polyvalent isocyanate compounds such as diphenylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate and isophorone diisocyanate, divinyl sulfone Polyvalent vinyl compounds such as polyethylene glycol diacrylate, polyvalent acrylate compounds such as Polyvalent methacrylate compounds such triethylene glycol dimethacrylate, haloepoxy compounds such as epichlorohydrin, but like polyvalent halogen compound is not limited thereto.

  The cross-linked product layer is disposed on at least a part of the surface of the core particle by cross-linking the surface of the core particle containing the water-absorbent resin with a surface cross-linking agent in a basic environment. Thereby, the surface of the core particle containing a water absorbing resin can be surface-crosslinked, maintaining the water absorption with respect to aqueous electrolyte solution. As a basic aqueous solution used for forming a basic environment, an aqueous solution containing a basic reagent such as sodium hydroxide, potassium hydroxide, ammonia or the like can be used. The basic aqueous solution can be used as long as it has a pH of 8 or more, and a pH of 10 or more is preferable for improving the reaction time. An arbitrary organic solvent may be contained in the basic aqueous solution.

In the case of surface crosslinking under basic conditions, examples of the surface crosslinking agent include polyvalent epoxy compounds, polyvalent vinyl compounds, polyvalent acrylate compounds, polyvalent methacrylate compounds, haloepoxy compounds such as epichlorohydrin, and polyvalent halogen compounds. However, it is not limited to these. Moreover, the functional group which a surface crosslinking agent has may be the same kind of functional group, or a different kind of functional group.
Among these, it is preferable that a polyvalent epoxy compound is included as a surface crosslinking agent. When a polyvalent epoxy compound is included as the surface crosslinking agent, the proportion of the polyvalent epoxy compound in the surface crosslinking agent is preferably 50% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. More preferably, the polyvalent epoxy compound contains ethylene glycol diglycidyl ether. When ethylene glycol diglycidyl ether is included as the surface crosslinking agent, the proportion of ethylene glycol diglycidyl ether in the surface crosslinking agent is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more.

  The surface cross-linking agent can be used as it is, but can also be used by dissolving in an arbitrary organic solvent. As the organic solvent, a hydrophilic organic solvent can be used. For example, alcohol compounds such as methanol, ethanol, isopropanol, n-propanol, and butanol, ketone compounds such as acetone and methyl ethyl ketone, dimethyl sulfoxide, and the like can be used, but not limited thereto.

  When the core particles containing a water-absorbing resin are cross-linked using an isocyanate compound as a surface cross-linking agent, the surface cross-linking agent is applied to the surface of the core particles containing the water-absorbing resin by spraying, dropping or the like. be able to. When an isocyanate compound is used as the surface crosslinking agent, hexamethylene diisocyanate is preferable. Further, the isocyanate compound as the surface cross-linking agent may be used as it is, or may be used after being dissolved in an arbitrary organic solvent.

  The amount of the surface cross-linking agent can be 0.001% by mass to 50% by mass with respect to the amount of the core particles containing the water absorbent resin. 0.01 mass%-20 mass% are preferable, and 0.1 mass%-10 mass% are more preferable. When the amount is 0.001% by mass or more, sufficient surface crosslinking is obtained, and when the amount is 50% by mass or less, a decrease in water absorption due to excessive progress of surface crosslinking is suppressed.

  The gel strength of the water-absorbent resin particles of the present invention is preferably 2.5N or more, and more preferably 3.0N or more. If it is 2.5 N or more, a decrease in water absorption due to deformation of the water absorbent resin particles at the time of load is suppressed. Although the upper limit of the gel strength is not particularly provided, when the gel strength is increased, the water absorption may be lowered.

  In the present embodiment, the water absorption magnification, water retention magnification, and gel strength of the water absorbent resin particles are measured as follows.

(Water absorption ratio)
The water absorption ratio of the water absorbent resin particles is measured according to JIS K7223-1996. About 0.5 g of water-absorbent resin particles (A) are put in a nylon 255 mesh bag having a size of 20 cm × 10 cm and immersed in a container containing 2 L of artificial urine for 1 hour. Thereafter, the bag is taken out from the container and suspended in the air for 15 minutes, and then the mass (B) is measured. The same bag without water-absorbing resin particles as described above is immersed in a container containing artificial urine for 1 hour, and the mass (C) after suspending in the air for 15 minutes is also measured. From the mass of the water absorbent resin particles (A), the mass of the bag containing the water absorbent resin particles after absorption of the artificial urine (B), and the mass of the bag only (C), the water absorption magnification is determined by the following formula (1).
The composition of the artificial urine is a solution in which 200 g of urea, 80 g of sodium chloride, 8 g of magnesium sulfate heptahydrate, and 6 g of calcium chloride dihydrate are dissolved in 10 L of ion exchange water.
Artificial urine water absorption [g / g] = (B−A−C) / A (1)

(Water retention ratio)
The nylon bag containing the water-absorbent resin particles after measuring the water absorption rate according to JIS K7223-1996 is placed in a wide-mouthed bottle (manufactured by Techjam Corporation), and the bottom of the nylon bag is wide-mouthed. Close the lid to hold the bag with the lid so that it is 1/3 from the bottom of the bottle. Centrifuge at 1000 rpm (min ⁻¹ ) for 90 seconds in a centrifuge (trade name: SUPREMA 23 (“SUPREMA” is a registered trademark)) manufactured by Tommy Seiko Co., Ltd.). The nylon bag containing the water-absorbent resin particles is taken out and the mass (D) is measured so as not to touch the water accumulated at the bottom of the wide-mouth bottle. Only a nylon bag containing no water-absorbent resin particles is centrifuged in the same manner, and the mass (C ′) is measured. The water retention magnification is obtained from the following formula (2). From the mass (D) of the nylon bag containing the water-absorbent resin particles after centrifugation, the mass (C ′) of only the nylon bag after centrifugation and the mass (A) of the water-absorbent resin particles, the following formula (2) Obtain the water retention magnification. The composition of the artificial urine is the same as that used for measuring the water absorption magnification.
Artificial urine water retention ratio [g / g] = (D-A-C ') / A (2)

(Gel strength)
20 g of artificial urine is absorbed in 1.0 g of water-absorbent resin particles to obtain a gel strength measurement sample. The sample was packed in a plastic container having an inner diameter of 2.7 cm and an inner height of 3.4 cm, and a gel strength measuring device (manufactured by Yamaden Co., Ltd., tabletop physical property measuring instrument, product name: TPU-2CL) was used to measure the diameter 2 Measure the strength when pushed in 1 cm at a descending speed of 1 mm / sec with a 5 cm plunger. The peak strength at this time is defined as gel strength.

<Absorber>
The absorber of the present invention includes the water absorbent resin particles of the present invention. For details and preferred embodiments of each component of the water-absorbent resin particles contained in the absorbent body of the present invention, reference can be made to the description given above for the water-absorbent resin particles.

  The absorbent body of the present invention may contain other components in addition to the water absorbent resin particles. Examples of other components include cellulose fiber, synthetic resin fiber, deodorant, antibacterial agent, blood coagulant, and blood anticoagulant. In the absorbent body of the present invention, the water-absorbent resin particles of the present invention may be used alone or in combination of two or more, or water-absorbent resin particles other than the water-absorbent resin particles of the present invention may be used in combination. .

  The use of the absorbent body of the present invention is not particularly limited, and examples thereof include sanitary products such as disposable diapers and sanitary products, pet products, civil engineering materials, food materials, agricultural materials, and the like.

  Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the following examples.

(Production Example 1)
28.4 g of carboxymethylcellulose (manufactured by Wako Pure Chemical Industries, Ltd., sodium carboxymethylcellulose, weight average molecular weight 1 million, polymerization degree 750, substitution degree 0.75) was dissolved in 255 mL of 1.5 M aqueous sodium hydroxide solution. To this aqueous solution, 5.23 g of ethylene glycol diglycidyl ether was added and mixed with stirring at 30 ° C. for 2 hours. Thereafter, the mixture was allowed to stand at 60 ° C. for 6 hours to be heated and gelled. This gel was pulverized to an appropriate size. The crushed gel was immersed in 500 mL of methanol for 3 hours to remove the methanol. This operation was repeated twice. Then, it was made to dry at 50 degreeC with the vacuum dryer for 3 hours. This was further pulverized to obtain water-absorbent resin powder (core particles) as particles that passed through a sieve having an opening of 300 μm and not passed through a sieve having an opening of 150 μm.

Example 1
To 2.5 g of dimethyl sulfoxide, 0.45 g of 5M sodium hydroxide aqueous solution and 0.66 g of ethylene glycol diglycidyl ether were added. To this solution, 5 g of the water-absorbent resin powder obtained in Production Example 1 was added and stirred at 60 ° C. for 2 hours. Thereafter, the water absorbent resin powder was taken out and washed with 2.5 g of methanol. Thereafter, it was dried at 30 ° C. under reduced pressure for 3 hours to obtain surface-crosslinked water-absorbent resin particles. Table 1 shows the water absorption capacity, water retention capacity, and gel strength of the water-absorbent resin particles.

(Example 2)
To 0.58 g of dimethyl sulfoxide, 0.10 g of 5 M aqueous sodium hydroxide solution and 0.30 g of ethylene glycol diglycidyl ether were added. While stirring 5 g of the water-absorbent resin powder obtained in Production Example 1 with a spoon, this solution was added dropwise so that the powder was uniformly coated. Then, it heated at 80 degreeC for 2 hours. The water absorbent resin powder was washed with 2.5 g of methanol and dried at 30 ° C. under reduced pressure for 3 hours to obtain surface-crosslinked water absorbent resin particles. Table 1 shows the water absorption capacity, water retention capacity, and gel strength of the water-absorbent resin particles.

(Example 3)
To 3.2 g of ethanol, 0.58 g of 5M aqueous sodium hydroxide solution and 0.20 g of ethylene glycol diglycidyl ether were added. To this solution, 4 g of the water absorbent resin powder obtained in Production Example 1 was added while stirring with a stirrer. Then, it heated at 54 degreeC for 1 hour. The water absorbent resin powder was washed with 2.5 g of methanol and dried under reduced pressure conditions at 30 ° C. for 3 hours to obtain surface-crosslinked water absorbent resin particles. Table 1 shows the water absorption capacity, water retention capacity, and gel strength of the water-absorbent resin particles.

(Comparative Example 1)
A surface cross-linking solution was prepared by adding 6.25 g of methanol, 1.13 g of water and 4 mg of ethylene glycol diglycidyl ether. While stirring the water-absorbent resin powder produced in Production Example 1, 5 g of the surface cross-linking liquid was added dropwise and heated at 100 ° C. for 1 hour. Thereafter, it was rinsed with 20 g of methanol, and dried under reduced pressure at 30 ° C. for 3 hours to obtain surface-crosslinked water-absorbent resin particles. Table 1 shows the water absorption capacity, water retention capacity, and gel strength of the water-absorbent resin particles.

  As is clear from the results shown in Table 1, in Examples 1 to 3, in which the core particles containing the water-absorbent resin were surface-crosslinked with a surface cross-linking agent under basic conditions, the gel strength was maintained while maintaining the water-absorbency. Was able to improve. On the other hand, in Comparative Example 1 in which surface crosslinking was not performed under basic conditions, the water absorption was greatly reduced.

Claims (18)

Core particles containing a water-absorbent resin having a hydroxyl group and an anionic functional group;
A cross-linked product layer formed by surface cross-linking with a surface cross-linking agent under a basic condition under a basic condition, and disposed on at least a part of the surface of the core particle;
Water-absorbent resin particles having   The water-absorbent resin particle according to claim 1, wherein the anionic functional group contains a carboxyl group.   The water absorbent resin particle according to claim 1 or 2, wherein the core particle is an internal cross-linked product of the water absorbent resin.   The water absorbent resin particle according to any one of claims 1 to 3, wherein the water absorbent resin contains a polysaccharide.   The water-absorbent resin particles according to claim 4, wherein the polysaccharide contains a cellulose derivative.   The water-absorbent resin particles according to claim 5, wherein the cellulose derivative contains carboxymethyl cellulose.   The water-absorbent resin particles according to any one of claims 1 to 6, wherein the surface crosslinking agent contains a polyvalent epoxy compound.   The water-absorbent resin particles according to claim 7, wherein the polyvalent epoxy compound contains ethylene glycol diglycidyl ether.   A method for producing water-absorbing resin particles, comprising a step of bringing a surface of a core particle containing a water-absorbing resin having a hydroxyl group and an anionic functional group into contact with a surface cross-linking agent under basic conditions.   The method for producing water-absorbent resin particles according to claim 9, wherein the anionic functional group contains a carboxyl group.   The method for producing water-absorbent resin particles according to claim 9 or 10, wherein the core particle is an internal cross-linked product of the water-absorbent resin.   The method for producing water-absorbent resin particles according to any one of claims 9 to 11, wherein the water-absorbent resin contains a polysaccharide.   The method for producing water-absorbent resin particles according to claim 12, wherein the polysaccharide contains a cellulose derivative.   The method for producing water-absorbent resin particles according to claim 13, wherein the cellulose derivative contains carboxymethyl cellulose.   The method for producing water-absorbent resin particles according to any one of claims 9 to 14, wherein the surface crosslinking agent contains a polyvalent epoxy compound.   The method for producing water-absorbent resin particles according to claim 15, wherein the polyvalent epoxy compound contains ethylene glycol diglycidyl ether.   The method for producing water-absorbent resin particles according to any one of claims 9 to 16, wherein the contacting step is performed by a spraying method, a dropping method, or a solution method.   The absorber containing the water absorbing resin particle of any one of Claims 1-8.