JP7488910B2 - Water-absorbent resin composition - Google Patents

Description

The present invention relates to a water-absorbent resin composition.

Water-absorbent resins are widely used in sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads to absorb body fluids such as urine and blood, and are the main constituent material of these sanitary materials. In recent years, with the increasing demand for disposable diapers for adults due to the aging of society, there has been an increasing demand for water-absorbent resins to be endowed with deodorizing properties, in particular excellent deodorizing properties against the bad odors caused by urine.

Various methods have been proposed to impart deodorizing properties to absorbent resins. For example, methods of mixing peroxo compounds, heavy metals (zeolite powder), and porous polymers into absorbents are known (Patent Documents 1, 2, and 3, respectively). In addition, a composition containing an absorbent resin and a hydrophobic porous polymer has been proposed to control odors that may arise from body fluids such as urine or blood (Patent Document 4).

JP 2015-168824 A JP 2001-505237 A JP 2017-140332 A International Publication No. 2005/120594

In recent years, there has been an increasing demand for water-absorbent resins with excellent deodorizing performance, and there is a need for better deodorizing technology, especially for the bad odor caused by urine.

Therefore, the present invention aims to provide a novel water-absorbing resin composition that has better deodorizing ability than conventional compositions.

One embodiment for achieving the above object is a water-absorbent resin composition comprising a water-absorbent resin and at least one of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle, and having a span value represented by the following formula 1 of 1.10 or less.

In the above formula (1),
D(90%) is the particle size (unit: μm) at which the cumulative particle size distribution from the minimum diameter is 90%.
D(10%) is the particle size (unit: μm) at which the cumulative particle size distribution from the minimum diameter is 10%.
D(50%) is the particle size (unit: μm) at which the cumulative amount from the minimum size is 50% in the cumulative particle size distribution of particle sizes, where D(90%), D(10%), and D(50%) are cumulative values on a mass basis.

According to the present application, it is possible to provide a novel water-absorbent resin composition that has superior deodorizing ability compared to water-absorbent resin compositions that use conventional deodorizers.

The present invention will be described below while showing the best mode. Throughout this specification, singular expressions should be understood to include the concept of the plural form, unless otherwise specified. Therefore, singular articles (for example, in the case of English, "a", "an", "the", etc.) should be understood to include the concept of the plural form, unless otherwise specified. In addition, it should be understood that the terms used in this specification are used in the sense commonly used in the field, unless otherwise specified. Therefore, unless otherwise defined, all technical terms and scientific and technical terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this invention belongs. In the event of a conflict, this specification (including definitions) shall prevail. The present invention is not limited to the following embodiments, and can be modified in various ways within the scope of the claims. In addition, it should be understood that all combinations of the lower limit and upper limit values disclosed in this specification are disclosed. In other words, it should be understood that they can be the basis for amendment. In addition, it should be understood that all combinations of the embodiments are disclosed in this application. In other words, it should be understood that they can be the basis for amendment.

One aspect for achieving the above object is a water-absorbent resin composition comprising a water-absorbent resin and at least one component selected from the group consisting of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle, and having a span value represented by the following formula 1 of 1.10 or less.

In the above formula (1),
D(90%) is the particle size (unit: μm) at which the cumulative particle size distribution from the minimum diameter is 90%.
D(10%) is the particle size (unit: μm) at which the cumulative particle size distribution from the minimum diameter is 10%.
D(50%) is the particle size (unit: μm) at which the cumulative amount from the minimum size is 50% in the cumulative particle size distribution of particle sizes, where D(90%), D(10%), and D(50%) are cumulative values on a mass basis.

This configuration makes it possible to provide a new water-absorbent resin composition that has superior deodorizing capabilities compared to water-absorbent resin compositions that use conventional deodorizers.

[1] Definition of Terms [1-1] Water-absorbent resin, base polymer, water-absorbent resin composition In the present invention, the term "water-absorbent resin" refers to a water-swellable, water-insoluble polymer gelling agent, which is generally in a powder form. In addition, "water-swellable" refers to a water-absorbency capacity without load (CRC) of 5 g/g or more as specified in EDANA WSP241.3(10) described later, and "water-insoluble" refers to a soluble content (Ext) of 50 mass% or less as specified in WSP270.3(10).

The "water-absorbent resin" is preferably a hydrophilic cross-linked polymer (so-called internally cross-linked polymer) obtained by cross-linking polymerization of unsaturated monomers having carboxyl groups, but the entire amount (100% by mass) does not have to be a cross-linked polymer.

In addition, the term "water-absorbent resin" generally refers to either a "polymer that is cross-linked only internally (i.e., a polymer in which the cross-linking density inside and on the surface is substantially the same)" or a "polymer that is cross-linked both internally and on the surface (i.e., a polymer in which the cross-linking density on the surface is relatively high compared to the cross-linking density inside)." In this specification, however, we will use different terms, and a polymer that is cross-linked only internally will be referred to as a "base polymer," and a polymer that is cross-linked both internally and on the surface will be referred to as a "water-absorbent resin."

In the present invention, the term "water-absorbent resin composition" refers to a composition that contains a water-absorbent resin and at least one of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle, and optionally contains other components, but in simple terms, it refers to a water-absorbent resin that is ready for shipment as a final product. Therefore, when the "water-absorbent resin" contains at least one of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle, and optionally contains other additives, it becomes a "water-absorbent resin composition." In this specification, the water-absorbent resin composition may be simply referred to as a water-absorbing agent.

[1-2] "EDANA" and "WSP"
"EDANA" is an abbreviation for European Disposables and Nonwovens Associations. "WSP" is an abbreviation for Worldwide Strategic Partners, and indicates a global standard measurement method for water-absorbent resins provided by EDANA. In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured in accordance with the original WSP (revised in 2010/publicly known document).

[1-2-1] "CRC" (WSP241.3(10))
"CRC" meaning the absorbency without pressure is an abbreviation of Centrifuge Retention Capacity, and means the absorbency of the water absorbent or water absorbent resin without pressure. Specifically, it is the absorbency (unit: g/g) after 0.2 g of the water absorbent or water absorbent resin is placed in a nonwoven bag, immersed in a large excess of 0.9 mass% sodium chloride aqueous solution for 30 minutes to allow the water absorbent resin to freely swell, and then dehydrated for 3 minutes using a centrifuge (250G).

[1-2-2] "AAP" (WSP242.3(10))
"AAP" is an abbreviation for Absorption Against Pressure, and means the absorbency under pressure of a water-absorbing agent or water-absorbing resin. Specifically, it means the absorbency (unit: g/g) after 0.9 g of the water-absorbing agent or water-absorbing resin is swollen under a load of 4.83 kPa (0.7 psi) for 1 hour in a large excess of a 0.9% by mass aqueous sodium chloride solution.

[2] Water-absorbent resin composition and manufacturing method thereof The water-absorbent resin composition in an embodiment of the present invention contains a water-absorbent resin and at least one component selected from the group consisting of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle, and has a span value represented by formula 1 of 1.10 or less.

Examples of absorbent resins include polyacrylic acid (salt)-based absorbent resins, polysulfonic acid (salt)-based absorbent resins, maleic anhydride (salt)-based absorbent resins, polyacrylamide-based absorbent resins, polyvinyl alcohol-based absorbent resins, polyethylene oxide-based absorbent resins, polyaspartic acid (salt)-based absorbent resins, polyglutamic acid (salt)-based absorbent resins, polyalginic acid (salt)-based absorbent resins, starch-based absorbent resins, and cellulose-based absorbent resins. Of these, polyacrylic acid (salt)-based absorbent resins are preferably used.

In the embodiment of the present invention, the term "polyacrylic acid (salt)-based water-absorbent resin" refers to a water-absorbent resin made from acrylic acid and/or its salt (hereinafter referred to as "acrylic acid (salt)"). In other words, the polyacrylic acid (salt)-based water-absorbent resin is a water-absorbent resin that has structural units derived from acrylic acid (salt) in the polymer and has a graft component as an optional component.

Specifically, polyacrylic acid (salt)-based water-absorbing resins are water-absorbing resins that contain preferably 50 mol% to 100 mol%, more preferably 70 mol% to 100 mol%, even more preferably 90 mol% to 100 mol%, and particularly preferably essentially 100 mol% acrylic acid (salt) relative to the total monomers involved in the polymerization reaction (excluding the internal crosslinking agent).

Next, a preferred method for producing the water-absorbent resin composition will be described in detail. Of course, the method is not limited to the following method.

[2-1] Preparation of Monomer Aqueous Solution This step is a step of preparing a monomer aqueous solution containing a monomer containing acrylic acid (salt) as a main component and at least one type of internal crosslinking agent. The "main component" refers to the amount (content) of acrylic acid (salt) used with respect to the entire monomers (excluding the internal crosslinking agent) to be subjected to the polymerization reaction, which is usually 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more (upper limit is 100 mol%). Note that a monomer slurry liquid can also be used within a range that does not affect the water absorption performance of the water absorbing agent obtained as a final product, but for convenience, the present specification will explain the monomer aqueous solution.

(Acrylic acid (salt))
In the embodiment of the present invention, from the viewpoint of the physical properties and productivity of the water absorbing agent, it is preferable to use a known acrylic acid (salt) as a monomer (also referred to as a polymerizable monomer). Known acrylic acid contains a small amount of components such as a polymerization inhibitor and impurities. As the polymerization inhibitor, preferably, methoxyphenols, more preferably p-methoxyphenols, are used. The content (concentration) of the polymerization inhibitor in the acrylic acid is preferably 200 ppm (mass basis) or less, more preferably 10 ppm (mass basis) to 160 ppm (mass basis), and even more preferably 20 ppm (mass basis) to 100 ppm (mass basis) from the viewpoint of the polymerizability of the acrylic acid and the color tone of the water absorbing agent. As the impurities, in addition to organic compounds such as acetic acid, propionic acid, and furfural, each compound described in U.S. Patent Application Publication No. 2008/0161512 is also contained in the acrylic acid used in the embodiment of the present invention.

Further, examples of the acrylic acid salt include salts obtained by neutralizing the above-mentioned acrylic acid with the following basic compounds. The acrylic acid salt may be a commercially available acrylic acid salt (e.g., sodium acrylate) or a salt obtained by neutralizing acrylic acid.

(Basic Compound)
The basic compound in the embodiment of the present invention refers to a compound exhibiting basicity, specifically, sodium hydroxide, etc. Note that commercially available sodium hydroxide contains heavy metals such as zinc, lead, and iron on the order of ppm (by mass), and strictly speaking, can be expressed as a composition, but in the present invention, such a composition is also treated as being included in the category of a basic compound.

Specific examples of the basic compound include carbonates and hydrogen carbonates of alkali metals, hydroxides of alkali metals, ammonia, organic amines, etc. Among them, from the viewpoint of the water absorption performance of the water absorbent, a strongly basic compound is selected. Therefore, hydroxides of alkali metals such as sodium, potassium, and lithium are preferred, and sodium hydroxide is more preferred. From the viewpoint of handling, the basic compound is preferably made into an aqueous solution.

(Neutralization)
When a salt obtained by neutralizing acrylic acid is used as the acrylic acid salt, the timing of neutralization is not particularly limited, and the neutralization may be performed before, during, or after polymerization, and may be performed at multiple times or locations. In addition, from the viewpoint of production efficiency of the water absorbing agent, it is preferable to neutralize in a continuous manner.

When acrylic acid (salt) is used in the present invention, the neutralization rate is preferably 10 mol% to 90 mol%, more preferably 40 mol% to 85 mol%, even more preferably 50 mol% to 80 mol%, and particularly preferably 60 mol% to 78 mol%, based on the acid groups of the monomer. By setting the neutralization rate within this range, it is possible to suppress a decrease in the water absorption performance of the water absorbent.

The above-mentioned range of neutralization rate applies to the neutralization before, during, and after the polymerization. It also applies to the water-absorbing agent as a final product.

(Other monomers)
In the present invention, monomers other than the above-mentioned acrylic acid (salt) (hereinafter referred to as "other monomers") can be used in combination with the acrylic acid (salt) as necessary.

Specific examples of the other monomers include anionic unsaturated monomers and salts thereof, such as (anhydrous) maleic acid, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, 2-(meth)acryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, and 2-hydroxyethyl (meth)acryloyl phosphate; mercaptan group-containing unsaturated monomers; phenolic hydroxyl group-containing unsaturated monomers; amide group-containing unsaturated monomers, such as (meth)acrylamide, N-ethyl (meth)acrylamide, and N,N-dimethyl (meth)acrylamide; and amino group-containing unsaturated monomers, such as N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, and N,N-dimethylaminopropyl (meth)acrylamide. The other monomers include water-soluble or hydrophobic unsaturated monomers. When the other monomers are used, the amount of the other monomers is preferably 30 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less, based on the total amount of the monomers (excluding the internal crosslinking agent).

(Internal Crosslinking Agent)
In a preferred method of preparation, an internal crosslinking agent is used. Specific examples of the internal crosslinking agent include N,N'-methylenebis(meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkane, (poly)ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl (meth)acrylate. Among these internal crosslinking agents, at least one type of internal crosslinking agent is selected in consideration of reactivity, etc. Also, from the viewpoint of the water absorbing performance of the water absorbing agent, preferably an internal crosslinking agent having two or more polymerizable unsaturated groups, more preferably an internal crosslinking agent having thermal decomposition at a drying temperature, and further preferably an internal crosslinking agent having two or more polymerizable unsaturated groups having a (poly)alkylene glycol structure is selected.

Specific examples of the polymerizable unsaturated group include allyl groups and (meth)acrylate groups, and more preferably (meth)acrylate groups. Specific examples of the (poly)alkylene glycol structure include polyethylene glycol. The number of alkylene glycol units (hereinafter sometimes referred to as n) is preferably 1 to 100, more preferably 6 to 50, even more preferably 6 to 20, and most preferably 6 to 10.

The amount of the internal crosslinking agent used is preferably 0.0001 mol% to 10 mol%, more preferably 0.001 mol% to 5 mol%, and even more preferably 0.01 mol% to 1 mol%, based on the total monomer (excluding the internal crosslinking agent). By using an amount within this range, a water absorbent with the desired water absorption performance can be obtained. It is also preferable to consider adjusting the amount of internal crosslinking agent in order to set the gel bulk density of the water absorbent resin or water absorbent within a specified range and suppress an increase in water-soluble content and a decrease in absorption capacity due to a decrease in gel strength.

It is preferable to add the internal crosslinking agent in advance when preparing the aqueous monomer solution. In this case, the crosslinking reaction is carried out simultaneously with the polymerization reaction. On the other hand, the polymerization reaction can be started without adding an internal crosslinking agent, and the internal crosslinking agent can be added during or after the polymerization reaction to carry out the crosslinking reaction. These methods can also be used in combination.

(Substances added to the aqueous monomer solution)
In an embodiment of the present invention, from the viewpoint of improving the physical properties of the water-absorbing agent, the following substances can be added to the aqueous monomer solution at one or more points during the preparation of the aqueous monomer solution, during the polymerization reaction and the crosslinking reaction, or after the polymerization reaction and the crosslinking reaction.

Specific examples of the substance include hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol (PVA), polyacrylic acid (salt), and crosslinked polyacrylic acid (salt); carbonates, azo compounds, foaming agents that generate various bubbles, surfactants, chelating agents, and chain transfer agents. The amount of the hydrophilic polymer added is preferably 50% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less (the lower limit is 0% by mass) relative to the aqueous monomer solution. The amount of the compound added is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less (the lower limit is 0% by mass) relative to the aqueous monomer solution.

When a water-soluble resin or a water-absorbent resin is used as the hydrophilic polymer, a graft polymer or a water-absorbent resin composition (e.g., starch-acrylic acid (salt) copolymer, PVA-acrylic acid (salt) copolymer, etc.) is obtained. These graft polymers or water-absorbent resin compositions are also included in the category of the polyacrylic acid (salt)-based water-absorbent resin according to the present invention.

(Monomer component concentration)
The above-mentioned substances (components) are selected according to the purpose, and if necessary, the amounts of each are specified so as to satisfy the above-mentioned ranges, and then mixed together to prepare an aqueous monomer solution. In the present invention, the monomer can be prepared not only as an aqueous solution, but also as a mixed solution of water and a hydrophilic solvent.

From the viewpoint of the physical properties of the water-absorbing agent, the concentration of the total of the substances (components) (hereinafter also referred to as "monomer component") is preferably 10% by mass to 80% by mass, more preferably 20% by mass to 75% by mass, and even more preferably 30% by mass to 70% by mass. The concentration of the monomer component is calculated from the following formula (2).

In addition, in the above formula (2), (the mass of the monomer aqueous solution) does not include the mass of the graft component, the water-absorbent resin, or the hydrophobic organic solvent in the reverse phase suspension polymerization.

[2-2] Polymerization step This step is a step of polymerizing the aqueous monomer solution containing acrylic acid (salt) as a main component and at least one type of internal crosslinking agent obtained in the aqueous monomer solution preparation step to obtain a hydrous gel-like crosslinked polymer (hereinafter referred to as "hydrous gel").

(Polymerization initiator)
In one embodiment of the present invention, a polymerization initiator is used during polymerization. Examples of the polymerization initiator include a thermally decomposable polymerization initiator, a photodecomposable polymerization initiator, or a redox-based polymerization initiator that is used in combination with a reducing agent that promotes the decomposition of the polymerization initiator. Specific examples of the polymerization initiator include radical polymerization initiators such as sodium persulfate, potassium persulfate, ammonium persulfate, t-butyl hydroperoxide, hydrogen peroxide, and 2,2'-azobis(2-amidinopropane) dihydrochloride. At least one type of polymerization initiator is selected from these polymerization initiators, taking into consideration the polymerization form and the like. In addition, from the viewpoint of the handling of the polymerization initiator and the physical properties of the water absorbing agent, the polymerization initiator is preferably a peroxide or an azo compound, more preferably a peroxide, and even more preferably a persulfate. In addition, when an oxidizing radical polymerization initiator is used, redox polymerization may be performed in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid.

The amount of the polymerization initiator used is preferably 0.001 mol% to 1 mol%, more preferably 0.001 mol% to 0.5 mol%, and even more preferably 0.01 mol% to 0.1 mol%, based on the total monomer (excluding the internal crosslinking agent). The amount of the reducing agent used is preferably 0.0001 mol% to 0.02 mol%, more preferably 0.0005 mol% to 0.015 mol%, based on the total monomer (excluding the internal crosslinking agent). By using an amount within this range, a water absorbent having the desired water absorption performance can be obtained.

In one embodiment of the present invention, the polymerization reaction may be initiated by irradiation with thermal energy or active energy rays such as radiation, electron beams, or ultraviolet rays. Irradiation with active energy rays may also be used in combination with the polymerization initiator.

(Polymerization form)
Examples of polymerization forms applicable to the present invention include aqueous solution polymerization, reversed-phase suspension polymerization, spray polymerization, droplet polymerization, bulk polymerization, and precipitation polymerization. Among them, from the viewpoint of ease of polymerization control and water absorption performance of the water absorbing agent, preferably aqueous solution polymerization or reversed-phase suspension polymerization, more preferably aqueous solution polymerization, and even more preferably continuous aqueous solution polymerization is selected. Reverse-phase suspension polymerization is described in International Publication No. 2007/004529, International Publication No. 2012/023433, and the like. In addition, the continuous aqueous solution polymerization can produce the water absorbing agent with high productivity, and specific examples thereof include continuous belt polymerization described in U.S. Pat. No. 4,893,999, U.S. Pat. No. 6,906,159, U.S. Pat. No. 7,091,253, U.S. Pat. No. 7,741,400, U.S. Pat. No. 8,519,212, JP-A-2005-36100, and continuous kneader polymerization described in U.S. Pat. No. 6,987,151, and the like.

Preferred forms of the continuous aqueous solution polymerization include high-temperature initiation polymerization, high-concentration polymerization, and foaming polymerization. High-temperature initiation polymerization is a polymerization form in which the temperature of the aqueous monomer solution at the start of polymerization is preferably 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, and particularly preferably 50°C or higher (the upper limit is the boiling point of the aqueous monomer solution). High-concentration polymerization is a polymerization form in which the monomer concentration at the start of polymerization is preferably 30% by mass or higher, more preferably 35% by mass or higher, even more preferably 40% by mass or higher, and particularly preferably 45% by mass or higher (the upper limit is the saturated concentration of the aqueous monomer solution).

Although each of the above-mentioned polymerization forms can be carried out in an air atmosphere, from the viewpoint of the color tone of the water absorbent, it is preferable to carry out the polymerization in an inert gas atmosphere such as nitrogen or argon (oxygen concentration is 1% by volume or less). It is also preferable to sufficiently replace the dissolved oxygen in the aqueous monomer solution with an inert gas (dissolved oxygen amount is less than 1 mg/L).

By forming a foamed (also called porous) hydrogel, water-absorbent resin, or water-absorbing agent through foaming polymerization, the water absorption rate of the water-absorbing agent can be improved, and the water-absorbing agent can be easily fixed in absorbent articles. The foamed shape can be confirmed by looking at holes (e.g. holes with a diameter of 1 to 100 μm) on the particle surface using an electron microscope. The number of holes is preferably one or more per water-absorbing agent, or even 1 to 10,000 or 10 to 1,000, and can be controlled by the foaming polymerization.

The foaming polymerization is a preferred technique for increasing the BET specific surface area of the water-absorbing resins and water-absorbing agents described below.

[2-3] Gel Crushing Step This step is a step of pulverizing the hydrogel obtained in the polymerization step to obtain a particulate hydrogel (hereinafter also referred to as "particulate hydrogel"). Note that this step is referred to as "gel crushing" to distinguish it from the "crushing" in the crushing step described later.

The gel crushing refers to adjusting the hydrogel to a specified size using a gel crusher such as a kneader, meat chopper, or cutter mill.

Regarding the embodiment and operating conditions of gel crushing, the contents described in the pamphlet of International Publication No. 2011/126079 are preferably applied to the present invention. When the polymerization form is kneader polymerization, the polymerization process and the gel crushing process are carried out simultaneously. When a particulate hydrogel is obtained in the polymerization process, such as in reversed-phase suspension polymerization, spray polymerization, or droplet polymerization, the gel crushing process is considered to be carried out simultaneously with the polymerization process. In addition, by passing through the gel crushing process in the present invention, an amorphous crushed water-absorbing resin or water-absorbing agent can be obtained.

The gel pulverized by the gel crushing process is generally preferably in the range of 0.1 to 10 mm. If the gel is finer than 0.1 mm, the resulting water-absorbent resin may have poor physical properties. If it is larger than 10 mm, it may be difficult to dry. The mass average particle diameter (D50) of the particulate hydrous gel is preferably 500 μm to 2000 μm, more preferably 550 μm to 1500 μm, and even more preferably 600 μm to 1000 μm.

In order to increase the specific surface area of the water-absorbing resin or water-absorbing agent described later, it is preferable to use the gel crushing method described in International Publication No. 2011/126079. The gel crushing technique may also be combined with the foaming polymerization described above.

The mass average particle diameter (D50) of the particulate hydrogel is measured by the method described in International Publication No. WO 2011/126079.

[2-4] Drying step This step is a step of drying the hydrogel and/or particulate hydrogel obtained in the polymerization step and/or gel crushing step to a desired resin solid content to obtain a dried polymer. The resin solid content is determined from the loss on drying (the change in mass when 1 g of the water-absorbent resin is heated at 180°C for 3 hours), and is preferably 80% by mass or more, more preferably 85% to 99% by mass, even more preferably 90% to 98% by mass, and particularly preferably 92% to 97% by mass.

Methods for drying the hydrous gel and/or particulate hydrous gel include, for example, heat drying, hot air drying, reduced pressure drying, fluidized bed drying, infrared drying, microwave drying, drum dryer drying, drying by azeotropic dehydration with a hydrophobic organic solvent, high humidity drying using high-temperature water vapor, etc. Among these, from the viewpoint of drying efficiency, hot air drying is preferred, and band drying in which hot air drying is performed on a ventilated belt is more preferred.

The drying temperature (hot air temperature) in the hot air drying is preferably 120°C to 250°C, more preferably 140°C to 200°C, from the viewpoint of the color tone and drying efficiency of the water-absorbent resin. The drying conditions other than the drying temperature, such as the hot air speed and drying time, may be appropriately set according to the water content and total mass of the particulate hydrogel to be dried and the target resin solid content. When band drying is performed, the conditions described in International Publication Nos. 2006/100300, 2011/025012, 2011/025013, 2011/111657, etc. are appropriately applied.

The drying time is preferably 10 minutes to 2 hours, more preferably 20 minutes to 150 minutes, and even more preferably 30 minutes to 100 minutes. By setting the drying temperature and drying time within the ranges, the physical properties of the obtained water absorbent can be set within the desired range. Furthermore, the physical properties of the water absorbent resin as an intermediate product can also be set within the desired range.

[2-5] Crushing step, classification step This step is a step of pulverizing (crushing step) the dried polymer obtained through the drying step, and adjusting the particle size to a desired range (classification step) to obtain a base polymer (water-absorbent resin before surface crosslinking). By passing through the pulverizing step after drying, an amorphous pulverized water-absorbent resin or water-absorbing agent can be obtained. Crushing may be performed two or more times as necessary. By appropriately adjusting the conditions in the pulverizing step and classification step, a base polymer (water-absorbent resin before surface crosslinking) satisfying a desired span value can be obtained, and thus a water-absorbent resin composition satisfying a desired span value can be obtained.

Examples of the crushing machine used in the crushing step include high-speed rotary crushers such as roll mills, hammer mills, screw mills, and pin mills, as well as vibration mills, knuckle-type crushers, and cylindrical mixers. Among these, a roll mill is preferably selected from the viewpoint of crushing efficiency. In addition, a plurality of these crushers can be used in combination.

Methods for adjusting the particle size in the classification process include sieve classification using a JIS standard sieve (JIS Z8801-1 (2000)) and air flow classification. Among these, sieve classification is preferably selected from the viewpoint of classification efficiency. Note that the adjustment of the particle size of the water absorbent is not limited to being performed in the grinding process or classification process, but can also be performed in the polymerization process (especially reverse phase suspension polymerization or droplet polymerization, etc.) or other processes (for example, the granulation process or fine powder recovery process).

In one embodiment of the present invention, the mass average particle diameter (D50) of the base polymer is 300 to 600 μm. In another embodiment of the present invention, the proportion of particles of the base polymer less than 150 μm is 5% by mass or less. The lower limit of the proportion of particles less than 150 μm is 0% by mass. The mass average particle diameter (D50) of the base polymer is preferably 300 to 500 μm, and more preferably 300 to 450 μm. The proportion of particles of the base polymer less than 150 μm is more preferably 4% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2% by mass or less.

In one embodiment of the present invention, the span value is 1.10 or less. If it exceeds 1.10, the intended effect of the present invention cannot be achieved. According to an embodiment of the present invention, it is preferably adjusted to be 0.40 or more, more preferably adjusted to be 0.40 to 1.10, even more preferably adjusted to be 0.45 to 1.05, and even more preferably adjusted to be 0.50 to 1.00.

The above-mentioned span value in one embodiment of the present invention can be applied not only to the water absorbent resin after surface cross-linking, but also to the water absorbent (particulate water absorbent) as a final product. Therefore, it is preferable to perform a surface cross-linking treatment (surface cross-linking step) so as to maintain the span value adjusted by the base polymer, and it is more preferable to adjust the span value to a specific value by providing an appropriate sizing step after the surface cross-linking step.

In one embodiment of the present invention, the mass average particle diameter (D50) of the base polymer can be applied not only to the water absorbent resin after surface crosslinking, but also to the water absorbent (particulate water absorbent) as a final product. Therefore, it is preferable to maintain the mass average particle diameter (D50) adjusted by the base polymer. Therefore, the mass average particle diameter (D50) of the water absorbent resin composition is preferably 300 to 600 μm, more preferably 300 to 500 μm, and even more preferably 300 to 450 μm.

[2-6] Surface cross-linking step This step is a step for providing a portion with a higher cross-linking density on the surface layer of the base polymer obtained through each step described above, and is configured to include a mixing step, a heat treatment step, and a cooling step as necessary. In the surface cross-linking step, radical cross-linking, surface polymerization, a cross-linking reaction with a surface cross-linking agent, and the like occur on the surface of the base polymer, and a surface-cross-linked water absorbent resin is obtained.

[2-6-1] Mixing Step This step is a step of mixing a solution containing a surface crosslinking agent (hereinafter, referred to as a "surface crosslinking agent solution") with a base polymer in a mixer to obtain a humidified mixture.

(Surface Cross-Linking Agent)
In one embodiment of the present invention, a surface cross-linking agent is used during surface cross-linking. Specific examples of the surface cross-linking agent include those described in U.S. Pat. No. 7,183,456. At least one type of surface cross-linking agent is selected from these surface cross-linking agents, taking into consideration reactivity and the like. In addition, from the viewpoints of the handling of the surface cross-linking agent and the water absorption performance of the water absorbing agent, it is preferable to select an organic compound that is a surface cross-linking agent having two or more functional groups that react with a carboxyl group and that forms a covalent bond.

More specifically, the surface cross-linking agent may be ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,4-pentanediol, 1,3-pentanediol, 1,2-pentanediol, 2,3-pentanediol, 2,4-pentanediol, dipropylene glycol, polypropylene polyhydric alcohol compounds such as ethylene glycol, glycerin, polyglycerin, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 1,3-hexanediol, 1,2-hexanediol, 2,3-hexanediol, 2,4-hexanediol, diethanolamine, and triethanolamine; polyhydric amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyallylamine, and polyethyleneimine; haloepoxy compounds; Condensates of divalent amine compounds and haloepoxy compounds, oxazoline compounds such as 1,2-ethylenebisoxazoline, oxazolidinone compounds, 1,3-dioxolan-2-one (ethylene carbonate), 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, Examples of the surface crosslinking agent include alkylene carbonate compounds such as 4,6-dimethyl-1,3-dioxan-2-one, 1,3-dioxopan-2-one, polyhydric glycidyl compounds such as ethylene glycol diglycidyl ether, polyethylene diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidol, oxetane compounds, and vinyl ether compounds. Examples of the surface crosslinking agent include polyhydric alcohol compounds such as propylene glycol and 1,3-propanediol, alkylene carbonate compounds such as ethylene carbonate, polyhydric glycidyl compounds such as ethylene glycol diglycidyl ether, and polyhydric amines such as diethylenetriamine.

The amount of the surface cross-linking agent used (the total amount when multiple types are used) is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, even more preferably 0.01 to 2 parts by mass, even more preferably 0.1 to 1.8 parts by mass, and even more preferably 0.5 to 1.5 parts by mass, relative to 100 parts by mass of the base polymer. By setting the amount of the surface cross-linking agent used within this range, an optimal cross-linked structure can be formed in the surface layer of the base polymer, and a water-absorbing resin or water-absorbing agent with high physical properties can be obtained. In addition, adjusting the amount of the surface cross-linking agent according to the type is also effective in optimizing the gel bulk density of the water-absorbing resin or water-absorbing agent.

The surface cross-linking agent is preferably added to the base polymer in the form of an aqueous solution. In this case, the amount of water used is preferably 0.1 to 20 parts by mass, more preferably 0.3 to 15 parts by mass, and even more preferably 0.5 to 10 parts by mass, relative to 100 parts by mass of the base polymer. By setting the amount of water used within this range, the handleability of the surface cross-linking agent solution is improved, and the surface cross-linking agent can be evenly mixed with the base polymer.

In addition, a hydrophilic organic solvent can be used in combination with the water as necessary to prepare the surface crosslinking agent solution. In this case, the amount of the hydrophilic organic solvent used is preferably small so as not to cause an unpleasant odor, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less, relative to 100 parts by mass of the base polymer. However, from the viewpoint of performing moderate surface crosslinking, it is preferable to add a hydrophilic organic solvent, and the amount added is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the base polymer.

Specific examples of the hydrophilic organic solvent include lower alcohols (e.g., having 1 to 3 carbon atoms) such as methyl alcohol and isopropyl alcohol; ketones such as acetone; ethers such as dioxane; amides such as N,N-dimethylformamide; sulfoxides such as dimethyl sulfoxide, etc.

(Mixing method, mixing conditions)
The base polymer and the surface crosslinking agent solution are mixed by a method in which a surface crosslinking agent solution is prepared in advance and then mixed with the base polymer by preferably spraying or dropping the solution onto the base polymer, more preferably by spraying.

[2-6-2] Heat Treatment Step This step is a step in which heat is applied to the humidified mixture obtained in the mixing step to cause a crosslinking reaction on the surface of the base polymer.

The heat treatment of the humidified mixture may be performed by heating the humidified mixture in a stationary state or in a fluidized state using a power such as stirring, but heating under stirring is preferable in that the entire humidified mixture can be heated evenly. From this viewpoint, examples of heat treatment equipment that performs the heat treatment include a paddle dryer, a multi-fin processor, and a tower dryer.

The heating temperature in this step is preferably 150°C to 250°C, more preferably 170°C to 250°C, and even more preferably 180°C to 230°C, from the viewpoints of the type and amount of the surface cross-linking agent and the water absorption performance of the water absorbent. The heating time is at least 5 minutes, and preferably at least 7 minutes. The upper limit is preferably 150 minutes or less, more preferably 120 minutes or less, and even more preferably 100 minutes or less. Controlling the heating temperature and heating time within the above ranges is preferable because it improves the water absorption performance of the obtained water absorbent.

[2-6-3] Cooling step This step is an optional step that is provided as necessary after the heat treatment step. This step is a step of forcibly cooling the high-temperature water absorbent resin that has been subjected to the heat treatment step to a predetermined temperature, and quickly completing the surface cross-linking reaction.

[2-7] Addition of at least one component of hydrophobic porous polymer adsorbent and resin having nitrogen-containing heterocycle This step is a step of adding at least one component of hydrophobic porous polymer adsorbent and resin having nitrogen-containing heterocycle. In other words, in one embodiment of the present invention, the water-absorbent resin composition contains at least one component of hydrophobic porous polymer adsorbent and resin having nitrogen-containing heterocycle. By having such a configuration, it has a better deodorizing ability than a water-absorbent resin composition using a conventional deodorant. The mechanism of having a better deodorizing ability will be explained below. However, such a mechanism is speculation, and the technical scope of the present invention is not limited by such a mechanism.

The substances that are thought to cause urine odor are primarily basic compounds such as ammonia and amines, which are produced by the decomposition of urea and amino acids, and hydrophobic compounds of medium molecular size, such as phenols.

Conventional water-absorbent resins, particularly polyacrylic acid (salt)-based water-absorbent resins suitable for use in sanitary materials, have the ability to adsorb the above-mentioned basic compounds because they have acid groups, but the deodorizing effect of the swollen gel that actually absorbed urine was insufficient (Comparative Example 1). In addition, because the resin is hydrophilic, its deodorizing effect on hydrophobic compounds of medium molecular size is thought to be weaker than that on the above-mentioned basic compounds.

On the other hand, as described above, in the present invention, the water-absorbent resin composition contains at least one component of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle.

This (water-insoluble) hydrophobic porous polymer adsorbent is believed to be effective in adsorbing hydrophobic compounds of medium molecular size and exerting a deodorizing effect. More specifically, it is believed that the hydrophobic porous polymer adsorbent efficiently adsorbs hydrophobic compounds of medium molecular size (e.g., phenol, cresol, phenylacetic acid), etc., and has the effect of reducing urine odor. However, as described below, the mechanism by which a hydrophobic porous polymer adsorbent does not have better deodorizing ability unless the span value is adjusted to a specific value or less is unknown.

As described above, in one embodiment of the present invention, the water-absorbent resin composition contains a resin having a nitrogen-containing heterocycle. Here, the nitrogen-containing heterocycle is typically basic like ammonia, and therefore is not considered to have high adsorption performance for basic substances derived from urine. However, it was a surprising result that the addition of such a basic resin having a nitrogen-containing heterocycle gave a better deodorizing ability. The mechanism that brings about such a result is unknown, and in other words, it can be said that this is an invention with an inventive step that cannot be predicted even by those skilled in the art. Furthermore, in one embodiment of the present invention, the water-absorbent resin composition contains both a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle. By including both of the above compounds, a synergistic effect of further deodorizing effect can be expected.

In one embodiment of the present invention, the amount of at least one of the hydrophobic porous polymer adsorbent and the resin having a nitrogen-containing heterocycle (the total amount when used in combination; the amount added in terms of solid content in the case of a water dispersion or an aqueous solution) is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 8 parts by mass, even more preferably 0.15 to 5 parts by mass, and particularly preferably 0.2 to 3 parts by mass, relative to 100 parts by mass of the water absorbent resin, from the viewpoint of the urine odor suppression effect. Such a preferred amount is consistent with the preferred content in the water absorbent resin composition, unless a treatment (e.g., heating at a high temperature) that opens the nitrogen-containing heterocycle is performed. That is, according to one embodiment of the present invention, in the water absorbent resin composition, the content of at least one of the hydrophobic porous polymer adsorbent and the resin having a nitrogen-containing heterocycle (when used in combination, the total content thereof; in the form of a water dispersion or an aqueous solution, the amount added in terms of solid content) is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 8 parts by mass, further preferably 0.15 to 5 parts by mass, and particularly preferably 0.2 to 3 parts by mass, relative to 100 parts by mass of the water absorbent resin.

(Hydrophobic Porous Polymer Adsorbent)
In one embodiment of the invention, the hydrophobic porous polymeric adsorbent is a hydrophobic porous polymeric adsorbent that is not naturally occurring (i.e., a synthetic adsorbent).

In one embodiment of the present invention, there is no particular limitation on the method of mixing the surface-crosslinked water-absorbent resin with the hydrophobic porous polymer adsorbent. For example, the hydrophobic porous polymer adsorbent may be added to the base polymer before surface-crosslinking, and then the base polymer may be surface-crosslinked. However, in order to enhance the deodorizing effect of the hydrophobic porous polymer adsorbent, it is preferable to add the hydrophobic porous polymer adsorbent to the surface-crosslinked water-absorbent resin. In that sense, it is better not to add the hydrophobic porous polymer adsorbent in the surface-crosslinking step.

In one embodiment of the present invention, the hydrophobic porous polymer adsorbent is a polymer that is hydrophobic and has an average pore diameter of 20 to 1200 Å. It is believed that this embodiment can efficiently adsorb substances that cause urine odor, such as phenol, cresol, and phenylacetic acid.

In this specification, the term "hydrophobic polymer" in the context of a hydrophobic porous polymer adsorbent refers to a polymer that has low affinity for water, and for example, when the static contact angle with water is measured, the contact angle is 90° or more.

In one embodiment of the present invention, the hydrophobic porous polymer adsorbent is preferably a porous polymer obtained by copolymerizing hydrophobic non-crosslinkable monomers, crosslinkable monomers, etc., from the viewpoint of having a hydrophobic composition. Examples of hydrophobic non-crosslinkable monomers include monovinyl aromatic monomers such as styrene, methylstyrene, vinylnaphthalene, vinylpyridine, phenyl(meth)acrylate, and benzyl(meth)acrylate; vinyl carboxylate monomers such as vinyl acetate and vinyl propionate; and (meth)acrylic acid aliphatic esters such as ethyl(meth)acrylate and propyl(meth)acrylate.

In contrast, inorganic adsorbents such as zeolite, which are commonly known as adsorbents, are highly polar and have small average pore diameters of less than 20 Å, so they have insufficient adsorption capacity for odor-causing substances and, as a result, insufficient deodorizing properties.

Examples of hydrophobic crosslinkable monomers include aromatic monomers having two or more vinyl groups, such as divinylbenzene, divinyltoluene, and divinylnaphthalene; di(meth)acrylates such as ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate; and polyhydric alcohol esters of (meth)acrylic acid, such as trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, and pentaerythritol tetrakis(meth)acrylate.

In one embodiment of the present invention, the average pore diameter of the hydrophobic porous polymer adsorbent in the water absorbent resin composition is preferably 20 to 1200 Å, more preferably 50 to 1000 Å, even more preferably 60 to 950 Å, even more preferably 70 to 800 Å, even more preferably 80 to 750 Å, and even more preferably 90 to 730 Å, from the viewpoint of reducing urine odor. It is believed that by setting the average pore diameter in such a range, it is possible to efficiently adsorb substances causing urine odor such as phenol, cresol, and phenylacetic acid. In addition, according to an embodiment of the present invention, the average pore diameter of the hydrophobic porous polymer adsorbent in the water absorbent resin composition may be more than 100 Å, for example, 150 Å or more, 200 Å or more, or 250 Å or more. According to an embodiment of the present invention, the average pore diameter of the hydrophobic porous polymer adsorbent in the water absorbent resin composition may be more than 100 Å and 900 Å or less. In this way, the hydrophobic porous polymer adsorbent of the embodiment of the present invention is relatively hydrophobic, and the pore size may be a size ranging from tens to hundreds of Å.

The average pore diameter of the hydrophobic porous polymer adsorbent can be determined as follows:

[BET specific surface area]
The sample is vacuum-dried at 180°C for 2 hours, and then the amount of nitrogen gas adsorption at the boiling point of liquid nitrogen (-195.8°C) is measured at multiple points using a high-precision gas/vapor adsorption measuring device (BELSORP-max/BEL Japan Co., Ltd.) while gradually increasing the relative pressure in the range of 0.02 to 1.00, to create a nitrogen adsorption isotherm for the sample. Next, the results at relative pressures of 0.02 to 1.00 are BET plotted to determine the BET specific surface area per weight ( ^m2 /g) (S).

[Average pore diameter]
The sample is vacuum-dried at 180°C for 2 hours, and then the amount of nitrogen gas adsorption at the boiling point of liquid nitrogen (-195.8°C) is measured at multiple points using a high-precision gas/vapor adsorption measuring device (BELSORP-max/BEL Japan Co., Ltd.) while gradually increasing the relative pressure in the range of 0.02 to 1.00, to prepare a nitrogen adsorption isotherm for the sample. From this nitrogen adsorption isotherm, the pore volume (mL/g) (V) of the sample is determined, and the average pore diameter (D) of the polymolecular mass is calculated from the following formula:

D = 4 x V/S x ¹⁰⁴
(V: pore volume (mL/g), S: BET specific surface area (m ² /g))
In one embodiment of the present invention, the BET specific surface area of the hydrophobic porous polymer adsorbent in the water absorbent resin composition is preferably 20 to 2000 m ² /g from the viewpoint of reducing urine odor, and more preferably 50 to 2000 m ² /g, 70 to 1200 m ² /g, 80 to 1000 m ² /g, 90 to 900 m ² /g, and 100 to 850 m ² /g.

In one embodiment of the present invention, the average particle diameter of the hydrophobic porous polymer adsorbent in the water-absorbent resin composition is preferably 1 to 2000 μm, more preferably 10 to 1500 μm, even more preferably 50 to 1000 μm, and even more preferably 60 to 800 μm, from the viewpoint of mixability with the water-absorbent resin. The average particle diameter of the hydrophobic porous polymer adsorbent is determined by taking an image at a magnification of 50 to 500 times using a scanning electron microscope (Keyence Corporation; VF-9800), randomly selecting 20 points from the captured image as samples using image analysis software, and measuring the particle diameter.

In addition, in one embodiment of the present invention, the amount of hydrophobic porous polymer adsorbent added is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 8 parts by mass, even more preferably 0.15 to 5 parts by mass, and particularly preferably 0.2 to 3 parts by mass, relative to 100 parts by mass of the water-absorbent resin, from the viewpoint of the urine odor suppression effect. 0.3 parts by mass or more, 0.4 parts by mass or more, 0.5 parts by mass or more, more than 0.5 parts by mass, or 0.7 parts by mass or more are also preferred. Such a preferred amount to be added corresponds to the preferred content in the water-absorbent resin composition.

That is, according to one embodiment of the present invention, the content of the hydrophobic porous polymer adsorbent in the water absorbent resin composition is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 8 parts by mass, even more preferably 0.15 to 5 parts by mass, and particularly preferably 0.2 to 3 parts by mass, and is preferably 0.3 parts by mass or more, 0.4 parts by mass or more, 0.5 parts by mass or more, more than 0.5 parts by mass, or 0.7 parts by mass or more. If the content is less than the preferred amount, the urine odor suppression effect may not be sufficiently obtained. Also, if the content is more than the preferred amount, the water absorption capacity of the water absorbent resin may decrease.

In one embodiment of the present invention, specific examples of hydrophobic porous polymer adsorbents include styrene-based and methacrylic acid ester-based synthetic adsorbents such as the Chromalite AD series, Chromalite PCG series, and Purosorb PAD series manufactured by Purolite Co., Ltd.; styrene-based or (meth)acrylic synthetic adsorbents such as the Diaion HP series and Diaion HP2MGL manufactured by Mitsubishi Chemical Corporation; styrene-based or (meth)acrylic synthetic adsorbents such as the Amberlite XAD series and Amberlite FPX series manufactured by Organo Corporation; and porous polymers having phenyl groups as described in JP 2017-140332 A, etc.

In one embodiment of the present invention, the hydrophobic porous polymer adsorbents may be used alone or in combination of two or more.

<Total specific surface area per gram of water-absorbent resin>
The total specific surface area of the hydrophobic porous polymer adsorbent per 1 g of water absorbent resin means the total specific surface area of the hydrophobic porous polymer adsorbent added per unit amount of water absorbent resin, and can be calculated by the following formula.

The total specific surface area per 1 g of the water-absorbent resin is preferably ^0.2 m2 or more, more preferably 0.3 ^m2 or more, and even more preferably 0.4 ^m2 or more, from the viewpoint of suppressing urine odor. There is no particular upper limit, but from the viewpoint of economic efficiency, for example, ¹⁰⁰ m2 or less is preferable. Of course, such a preferable total specific surface area per 1 g of the water-absorbent resin coincides with the preferable total specific surface area in the water-absorbent resin composition. That is, according to one embodiment of the present invention, in the water absorbent resin composition, the total specific surface area per 1 g of the water absorbent resin is preferably 0.2 m ² or more, more preferably 0.3 m ² or more, and even more preferably 0.4 m ² or more, from the viewpoint of suppressing urine odor, and is 1.0 m ² or more, 1.5 m ² or more, 2.0 m ² or more, more than 2.5 m 2, more than 3.0 m ² , more than 3.5 m ² , 4.0 m ² or more, 4.2 m ² or more, 4.5 m ² or more, 5.0 m ² or more, 5.5 m ² or more, or 6.0 m ² or more. There is no particular limit as to the upper limit, but from the viewpoint of economic efficiency, for example, 100 m ² or less is preferable, and it may be 50 m ² or less, 40 m ² or less, 30 m ^{2 or} less, 20 m ² or less, or 10 m ² or less.

The hydrophobic porous polymer adsorbent may be prepared by purchasing a commercially available product.

(Resin having nitrogen-containing heterocycle)
In one embodiment of the present invention, the water-absorbent resin composition contains a resin having a nitrogen-containing heterocycle. The substances causing urine odor are considered to be basic compounds such as ammonia and amines generated by decomposition of urea and amino acids. Conventional water-absorbent resins, particularly polyacrylic acid (salt)-based water-absorbent resins suitable for use in sanitary materials, have an adsorption performance for the above-mentioned basic compounds because they have acid groups, but the deodorizing effect of the swollen gel that has actually absorbed urine is insufficient. Here, the nitrogen-containing heterocycle is typically basic like ammonia, and therefore is considered not to have a high adsorption performance for basic substances derived from urine. However, it was a surprising result that the addition of such a resin having a basic nitrogen-containing heterocycle provided a better deodorizing ability.

In one embodiment of the present invention, in order to enhance the deodorizing effect of the resin having a nitrogen-containing heterocycle, it is preferable to add the resin having a nitrogen-containing heterocycle to the surface-crosslinked water-absorbent resin as a method of mixing the water-absorbent resin with the resin having a nitrogen-containing heterocycle. If the resin having a nitrogen-containing heterocycle is mixed with the base polymer before surface crosslinking, the base polymer and the resin having a nitrogen-containing heterocycle may undergo a crosslinking reaction due to the subsequent heat treatment during surface crosslinking, and the deodorizing effect may be lost. More specifically, for example, if an oxazoline group-containing polymer is used as the resin having a nitrogen-containing heterocycle, the oxazoline ring is opened by the heat during crosslinking. Then, the residue interacts with the functional group of the structural unit constituting the water-absorbent resin and a crosslinking reaction occurs. Therefore, the specific functional group (nitrogen-containing heterocycle) that is thought to be necessary for expressing the deodorizing effect disappears, and the deodorizing effect may be lost. In other words, examples in which a compound having an oxazoline group or the like is used as a crosslinking agent for the water-absorbent resin are conventionally known, but in such an example, a crosslinking reaction occurs and the nitrogen-containing heterocycle disappears, so that the deodorizing effect of the present application cannot be obtained. In this sense, it is better not to add the resin having a nitrogen-containing heterocycle in the surface cross-linking step. Therefore, according to one embodiment of the present invention, in the manufacturing method of the water absorbent resin composition, after the resin having a nitrogen-containing heterocycle functioning as a cross-linking agent is added, it is preferable not to carry out a heating step at a high temperature. Therefore, even if a heating step is carried out, the temperature is less than 100°C, 90°C or less, 80°C or less, 70°C or less, or 65°C or less.

According to one embodiment of the present invention, the resin having a nitrogen-containing heterocycle is a water-insoluble or water-dispersible polymer having a LogP of 1.5 or more. In other words, the resin having a nitrogen-containing heterocycle is added to the water-absorbent resin in the form of a water dispersion. According to one embodiment of the present invention, the resin having a nitrogen-containing heterocycle is added to the water-absorbent resin in a form that is not dispersed in any dispersing medium, that is, in a dry form.

In this application, LogP refers to the n-octanol/water partition coefficient (Log10Pow), which may be determined in accordance with OECD Test Guideline (OECD Council Decision "C(81)30 Final Annex 1") 107 or Japanese Industrial Standard Z7260-107 (2000) "Measurement of partition coefficient (1-octanol/water) - Shake flask method", but in principle, the value determined by the following calculation method is used in the present invention.

The values of VMLogP(i) and MSLogP(i) below are calculated at 25°C using ACD/LogP DB Release 100 Product Version 10.01 manufactured by Advanced Chemistry Development. Unless otherwise specified, LogP is a so-called common logarithm value with base 10.

First, the LogP (VMLogP(i): i is the same as above) of the virtual monomer unit (Virtual Monomer) in which a methyl group is added to the polymerization reaction site of each monomer (i) (i is a sequential number starting from 1 to identify each monomer) is calculated.

Virtual monomer units are based on the repeating structure in the polymer and may not match the monomers actually used in the production of the polymer. Specifically, they are defined as follows:

When the monomer is a polymerizable unsaturated monomer, the polymerization reaction site is C=C, and two methyl groups are introduced into the unsaturated bond.

When the monomer is a ring-opening polymerizable monomer, two methyl groups are introduced into a ring-opening unit of a ring structure (for example, an epoxy group in the case of ethylene oxide).

When the monomer is a condensation polymerizable monomer, a methyl group is introduced into the condensation polymerizable unit (e.g., ester, ether, amide).

In addition, when the monomer has a repeating unit of a cellulose skeleton, methyl groups can be introduced into each polyether unit as a condensation polymerization unit. In addition, in the case of a polymeric unsaturated monomer, such as a polyalkylene oxide having an unsaturated group (e.g., monoacrylate of methoxypolyethylene glycol), two methyl groups can be introduced into an unsaturated bond (e.g., C=C of acrylic acid), and at the same time, the polymer unit in the monomer (e.g., polyethylene oxide) can be decomposed to introduce methyl groups, and the condensation polymerization unit (e.g., COOH of acrylic acid) can also be methylated.

For example, in the case of polyethylene, a polymer formed by polymerization of unsaturated monomers, monomer (1) is ethylene, and VMLogP(1) is the LogP of n-butane. In the case of a styrene-butadiene copolymer, monomer (1) is styrene and monomer (2) is butadiene, VMLogP(1) is the LogP of 2-phenylbutane, and VMLogP(2) is the LogP of 3-hexene. In the case of 100% saponified polyvinyl alcohol, VMLogP(1) is the LogP of 3-butanol.

In addition, in the case of polyethylene glycol, a polymer obtained by polymerization of ring-opening polymerizable monomers, monomer (1) is ethylene oxide, and VMLogP(1) is the LogP of methyl-n-propyl ether.

In addition, in the case of polyaspartic acid, a polymer formed by polymerization of condensation polymerizable monomers, monomer (2) is aspartic acid, and VMLogP (1) is the LogP of N-methyl-methylaspartic acid ester.

Next, VMLogP(i) is corrected by the molar ratio (Mol Ratio) (MR(i): i is the same as above) of each monomer constituting the polymer for which LogP is to be calculated (VMLogP(i) x MR(i)). Note that MR(j) of monomer (j) that does not constitute the polymer is 0, and MR(i) is 1 if it is a homopolymer.

Finally, LogP is calculated by adding up the above correction values for all monomers (Equation 1 below).

(In formula 1, VMLogP(i) is a calculated value of the "n-octanol-water partition coefficient" at 25°C of a virtual monomer unit (VM) in which both ends of a polymer repeating unit (i) are methylated, and MR(i) is the "molar ratio (MR)" of the repeating unit (i).)
Examples of the Log P include acrylic acid homopolymer having a value of 1.12 and styrene homopolymer having a value of 4.09.

Such a resin having a nitrogen-containing heterocycle, which is a water-insoluble or water-dispersible polymer with a LogP of 1.5 or more, does not easily penetrate into the water-absorbent resin when used. Therefore, the interaction between the functional group (particularly the carboxyl group) of the constituent unit of the water-absorbent resin and the functional group (nitrogen-containing heterocycle) effective for deodorization inside the water-absorbent resin can be suppressed as much as possible. Therefore, the functional group (i.e., the nitrogen-containing heterocycle) effective for deodorization can remain near the surface of the water-absorbent resin, and a high adsorption effect can be exhibited against the substance causing the urine odor. Here, in this specification, "water-insoluble" means that the mass (solubility) dissolved in ion-exchanged water at 25°C is 1 g or less (1 mass% or less). In addition, "dissolved" means a state in which floating matter or precipitate cannot be visually confirmed when light is irradiated. From the viewpoint of deodorizing effect, the LogP of the resin having a nitrogen-containing heterocycle is preferably 1.5 or more, more preferably 2.0 or more, and even more preferably 3.0 or more. The upper limit of LogP is, for example, less than 4.09. A water-insoluble or water-dispersible polymer with LogP of 1.5 or more means that the resin having a nitrogen-containing heterocycle is particulate. Thus, according to one embodiment of the present invention, in the water-absorbent resin composition, the average particle size of the resin having a nitrogen-containing heterocycle is preferably 10 to 250,000 nm, more preferably 30 to 600 nm, and even more preferably 50 to 300 nm. Here, the average particle size of the resin having a nitrogen-containing heterocycle can be measured by an appropriate method according to the characteristics of the resin. If the particles are contained in an aqueous dispersion, the average particle size (volume average particle size) can be measured using a particle size distribution measuring instrument ("NICOMP Model 380" manufactured by Particle Sizing Systems) using a dynamic light scattering method. In the case of powder particles, the average particle size (volume average particle size) can be calculated by measuring 50 particles using a tabletop scanning electron microscope (JEOL's "JCM-6000").

In one embodiment of the present invention, the amount of the resin having a nitrogen-containing heterocycle is preferably 0.01 to 30 parts by mass, more preferably 0.05 to 10 parts by mass, even more preferably 0.1 to 5 parts by mass, and even more preferably 0.2 to 3 parts by mass, relative to 100 parts by mass of the water-absorbent resin, from the viewpoint of the urine odor suppression effect, and is particularly preferably 0.3 parts by mass or more, more than 0.3 parts by mass, more than 0.5 parts by mass, more than 1.0 parts by mass, more than 1.5 parts by mass, or 2.0 parts by mass or more. Such a preferred amount is consistent with the preferred content in the water-absorbent resin composition, unless a treatment (e.g., heating at a high temperature) that opens the nitrogen-containing heterocycle is performed. That is, according to one embodiment of the present invention, in the water absorbent resin composition, the content of the resin having a nitrogen-containing heterocycle is preferably 0.01 to 30 parts by mass, more preferably 0.05 to 10 parts by mass, further preferably 0.1 to 5 parts by mass, particularly preferably 0.2 to 3 parts by mass, and particularly preferably 0.3 parts by mass or more, more than 0.3 parts by mass, more than 0.5 parts by mass, 1.0 parts by mass or more, more than 1.0 parts by mass, 1.5 parts by mass or more, or 2.0 parts by mass or more.

In the present invention, a specific structure, a nitrogen-containing heterocycle, contributes to the urine odor reducing effect.

Therefore, it is necessary not only to add the resin having a nitrogen-containing heterocycle in the above-mentioned preferred amount, but also to avoid the above-mentioned ring-opening and crosslinking reaction of the nitrogen-containing heterocycle caused by heating and to leave a necessary amount of the nitrogen-containing heterocycle to exert the effect. Here, the content of the nitrogen-containing heterocycle present in the water-absorbent resin composition of the present invention is defined by an index called "abundance of nitrogen-containing heterocycle". The abundance of nitrogen-containing heterocycle means the ratio of the peak height derived from the nitrogen-containing heterocycle to the peak height derived from the water-absorbent resin detected by FT-IR measurement of the water-absorbent resin composition. The abundance of the nitrogen-containing heterocycle is measured by measuring the height of a peak derived from the nitrogen-containing heterocycle detected at 1600 to 1700 cm ⁻¹ and the height of a peak derived from a C═O bond of a carboxylate of the water absorbent resin composition detected at 1500 to 1600 cm ⁻¹ using FT-IR (Nicolet iS50 manufactured by Thermo Fisher Scientific) under conditions of a diamond ATR method, a wave number range of 4000 to 650 cm ⁻¹ , a scan count of 64, and a resolution of 4 cm ⁻¹ in an environment of 25° C., and calculating the abundance of the nitrogen-containing heterocycle from the measured value obtained after baseline correction according to the following formula.

Abundance of nitrogen-containing heterocycles (%) = h1/h2 x 100
h1: peak height derived from a nitrogen-containing heterocycle of the water-absorbent resin composition. h2: peak height derived from a C═O bond of a carboxylate of the water-absorbent resin composition.

The abundance level is calculated by measuring five times for the same sample and taking the arithmetic mean of the three values excluding the maximum and minimum values.

In one embodiment of the present invention, the abundance of the nitrogen-containing heterocycle is preferably 3.0% or more, 4.0% or more, 5.0% or more, 6.0% or more, 7.0% or more, 8.0% or more, 10.0% or more, 12.0% or more, 13.0% or more, 14.0% or more, 15.0% or more, 20.0% or more, 30.0% or more, 40.0% or more, or 42.0% or more. If the abundance of the nitrogen-containing heterocycle is less than 3.0%, the odor caused by urine may not be sufficiently reduced. In one embodiment of the present invention, the abundance of the nitrogen-containing heterocycle is 200% or less, or 150% or less. If the abundance of the nitrogen-containing heterocycle exceeds 200%, adverse effects such as a decrease in the absorption capacity of the water-absorbent resin composition or a decrease in the water absorption rate due to excessive hydrophobicity may occur. Therefore, in one embodiment of the present invention, there is provided a water-absorbent resin composition comprising a water-absorbent resin and at least one component selected from the group consisting of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle, and having the span value of 1.10 or less, and in the case where the water-absorbent resin composition comprises a resin having a nitrogen-containing heterocycle, the abundance of the nitrogen-containing heterocycle is 3.0% or more.

In one embodiment of the present invention, the water-absorbent resin in the water-absorbent resin composition for which the abundance of nitrogen-containing heterocycles is calculated is a polyacrylic acid (salt)-based water-absorbent resin.

According to one embodiment of the present invention, it is preferable that the nitrogen-containing heterocycle has at least one heteroatom, and more preferably two or more. This embodiment allows the intended effect of the present invention to be more efficiently achieved. According to one embodiment of the present invention, it is preferable that the nitrogen-containing heterocycle has three or less heteroatoms. This embodiment allows the intended effect of the present invention to be more efficiently achieved. The nitrogen-containing heterocycle is not limited to containing only nitrogen atoms, and is not limited to containing oxygen atoms or sulfur atoms.

According to one embodiment of the present invention, examples of the nitrogen-containing heterocycle include 6-membered nitrogen-containing heterocycles such as pyridine ring, pyrazine ring, triazine ring, pyrimidine ring, and pyridazine ring, 5-membered nitrogen-containing heterocycles such as imidazole ring, oxazole ring, thiazole ring, oxadiazole ring, thiadiazole ring, triazole ring, pyrazole ring, and oxazoline ring, and condensed nitrogen-containing heterocycles such as quinoline ring, quinoxaline ring, naphthyridine ring, benzimidazole ring, benzothiazole ring, and benzoxazole ring. By adopting such an embodiment, the intended effect of the present invention can be more efficiently achieved.

Among these, in order to more efficiently achieve the intended effects of the present invention, an oxazoline ring, a triazine ring, and a pyridine ring are preferred, with an oxazoline ring and a triazine ring being more preferred.

Therefore, according to one embodiment of the present invention, the resin having a nitrogen-containing heterocycle is a polymer having an oxazoline group (oxazoline group-containing polymer). In such an oxazoline group-containing polymer, the amount of oxazoline groups (the number of oxazoline groups per 1 g of the oxazoline group-containing polymer) is preferably 0.1 mmol/g to 10 mmol/g, and more preferably 0.5 mmol/g to 8 mmol/g.

According to one embodiment of the present invention, the oxazoline group-containing polymer has structural units derived from an oxazoline group-containing monomer.

According to one embodiment of the present invention, the oxazoline group-containing polymer has structural units derived from an oxazoline group-containing monomer and structural units derived from a monomer other than the oxazoline group-containing monomer.

As the oxazoline group-containing monomer, any suitable monomer may be used as long as it has an ethylenically unsaturated hydrocarbon group and an oxazoline group. Examples of such oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 5-methyl-2-vinyl-2-oxazoline, 4,4-dimethyl-2-vinyl-2-oxazoline, 4,4-dimethyl-2-vinyl-5,5-dihydro-4H-1,3-oxazoline, 2-isopropenyl-2-oxazoline, and 4,4-dimethyl-2-isopropenyl-2-oxazoline, and preferably 2-isopropenyl-2-oxazoline and 4,4-dimethyl-2-isopropenyl-2-oxazoline.

Any suitable monomer may be used as the other monomer, so long as it does not have an oxazoline group. Examples of such other monomers include N-vinyl lactam monomers such as N-vinylpyrrolidone; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso-nonyl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate; N-substituted or unsubstituted (meth)acrylamides such as (meth)acrylamide, N-monomethyl (meth)acrylamide, N-monoethyl (meth)acrylamide, and N,N-dimethyl (meth)acrylamide; styrene, α-methylstyrene, diphenyl ether, and the like. Examples of the monomer include vinyl aryl monomers such as vinyl benzene, vinyl toluene, indene, vinyl naphthalene, phenylmaleimide, and vinyl aniline; alkenes such as ethylene, propylene, butadiene, isobutylene, and octene; vinyl carboxylates such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; vinyl ethylene carbonate and derivatives thereof; unsaturated amines such as N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylamide, vinyl pyridine, vinyl imidazole, and salts or quaternized products thereof; and vinyl cyanide monomers such as acrylonitrile and methacrylonitrile. Among these, preferred are (meth)acrylic acid esters, vinyl aryl monomers, and vinyl cyanide monomers, and more preferred are (meth)acrylic acid esters.

In the oxazoline group-containing polymer, the proportion of structural units derived from oxazoline group-containing monomers relative to 100 mol% of all structural units is preferably 15 mol% to 95 mol%, more preferably 20 mol% to 95 mol%, more preferably 30 mol% to 90 mol%, and even more preferably 40 mol% to 85 mol%.

According to one embodiment of the present invention, the resin having a nitrogen-containing heterocycle is an amino resin. Examples of the amino resin include a condensate of an amino compound and formaldehyde. Examples of the amino compound include urea, thiourea, and polyfunctional amino compounds. Among them, polyfunctional amino compounds are preferably used, and as described above, polyfunctional amino compounds having a triazine ring structure are more preferably used. Examples of polyfunctional amino compounds having a triazine ring structure include melamine; amino compounds represented by general formula (1); guanamine compounds such as benzoguanamine, cyclohexanecarboguanamine, cyclohexenecarboguanamine, acetoguanamine, norbornenecarboguanamine, and spiroguanamine; and the like. Among these, melamine and benzoguanamine are preferred. Only one type of amino compound may be used, or two or more types may be used.

In the general formula (1), R ¹ may be the same or different and represents a hydrogen atom or an alkyl group which may have a substituent, and at least one of R ¹ is an alkyl group which may have a substituent. In the general formula (1), R ¹ is preferably a hydrogen atom or a hydroxyalkyl group.

When the amino resin particles are formed only from an amino resin, the resin can be obtained by reacting the amino compound with formaldehyde by any suitable method (addition condensation reaction). Examples of methods for producing resins formed from amino resins include those described in JP-A-2000-256432, JP-A-2002-293854, JP-A-2002-293855, JP-A-2002-293856, JP-A-2002-293857, JP-A-2003-55422, JP-A-2003-82049, JP-A-2003-138023, JP-A-2003-147039, JP-A-2003-171432, JP-A-2003-176330, JP-A-2005-97575, JP-A-2007-186716, and JP-A-2008-101040. Specifically, for example, the above-mentioned amino compound (preferably a polyfunctional amino compound) and formaldehyde are subjected to an addition condensation reaction in a preferably basic aqueous medium to generate a condensate oligomer, and then an acid catalyst such as dodecylbenzenesulfonic acid or sulfuric acid is mixed into the aqueous medium in which the condensate oligomer is dissolved or dispersed, and cured to produce resin particles formed from an amino resin having a crosslinked structure. Both the step of generating the condensate oligomer and the step of forming the amino resin particles having a crosslinked structure are preferably carried out under a heated state at a temperature of 50°C to 100°C.

According to one embodiment of the present invention, the resin having a nitrogen-containing heterocycle is a melamine-formaldehyde condensate and contains the following structural units:

According to one embodiment of the present invention, the resin having a nitrogen-containing heterocycle is a polymer having a pyridine ring as a repeating structural unit. Specific examples include polymers made from 2-vinylpyridine or 4-vinylpyridine, polymers of methylated quaternary salts of these, and 4-aminopyridine-branched polystyrene.

According to one embodiment of the present invention, the weight average molecular weight of the resin having a nitrogen-containing heterocycle is preferably 5,000 or more, more preferably 10,000 or more. The upper limit is determined appropriately, but is usually 10 million or less, and preferably 1 million or less. The weight average molecular weight of the resin having a nitrogen-containing heterocycle is measured by GPC.

According to one embodiment of the present invention, one or more types of resins having nitrogen-containing heterocycles may be used in combination.

In addition, resins having nitrogen-containing heterocycles may be prepared by purchasing commercially available products.

According to one embodiment of the present invention, the water-absorbent resin composition contains a binder that binds the water-absorbent resin and the components. The technical significance of this is as follows: in the water-absorbent resin composition, different materials are present: the water-absorbent resin; and at least one of the components of the hydrophobic porous polymer adsorbent and the resin having a nitrogen-containing heterocycle. When different materials are present, they tend to segregate from each other. If segregation occurs, a stable deodorizing effect may not be obtained. In one embodiment of the present invention, the inclusion of the binder binds the water-absorbent resin and at least one of the components of the hydrophobic porous polymer adsorbent and the resin having a nitrogen-containing heterocycle, so that they are evenly distributed in the water-absorbent resin composition, and a stable deodorizing effect is obtained.

According to one embodiment of the present invention, the binder is a polyol. Polyol refers to a compound having two or more hydroxyl groups, such as propylene glycol, ethylene glycol, tetramethylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, and glycerin.

According to one embodiment of the present invention, the binder may be included in a surface cross-linking agent used for surface cross-linking of the water-absorbent resin (base polymer).

According to one embodiment of the present invention, at least one of the surface cross-linking agents may also function as a binder. Also, according to one embodiment of the present invention, the binder is a surface cross-linking agent remaining on the surface of the surface-cross-linked water-absorbent resin. In other words, the binder may be a surface cross-linking agent remaining on the surface of the water-absorbent resin after the surface cross-linking treatment.

According to one embodiment of the present invention, the amount of binder contained in the water absorbent resin composition is preferably 0.1 to 10% by mass, more preferably 0.2 to 7% by mass, and even more preferably 0.3 to 5% by mass. If the amount of binder is less than the preferred amount, the deodorizing effect may not be sufficiently stabilized. If the amount of binder is more than the preferred amount, the water absorption capacity of the water absorbent resin may decrease. The amount of binder contained in the water absorbent resin composition may be measured, for example, by extracting with saline solution or the like and measuring with a measuring device such as HPLC.

In one embodiment of the present invention, there is no particular limitation on the method of adding the binder to the water-absorbent resin composition. As described above, the binder may be added during the surface treatment, or the binder may be mixed with the water-absorbent resin after the surface treatment.

In one embodiment of the present invention, the molecular weight of the binder is preferably 40 to 800, more preferably 50 to 300, and even more preferably 60 to 200. The molecular weight of the binder can be appropriately measured using a gas chromatograph mass spectrometer (GC-MS), a liquid chromatograph mass spectrometer (LC-MS), gel permeation chromatography (GPC), or the like.

In one embodiment of the present invention, when mixing a water-absorbent resin (e.g., surface-crosslinked) with at least one of the components of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle, it is preferable to apply sufficient torque to uniformly and reliably mix the water-absorbent resin with at least one of the components of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle.

Suitable devices for use in the mixing include, for example, an agitator mixer, a cylindrical mixer, a double-walled conical mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a flow type rotary disk mixer, an airflow type mixer, a double-arm kneader, an internal mixer, a grinding kneader, a rotary mixer, and a screw extruder. When using an agitator mixer, the rotation speed is preferably 5 rpm to 10,000 rpm, and more preferably 10 rpm to 2,000 rpm.

[2-8] Addition step of chelating agent The present inventors also confirmed that the deodorizing effect is remarkably enhanced by the synergistic effect of adding a chelating agent. Therefore, in one embodiment of the present invention, the water-absorbent resin composition contains a chelating agent. The amount of the chelating agent used is preferably 0 to 3 parts by mass, more preferably 0.001 to 1 part by mass, and particularly preferably 0.05 to 0.5 parts by mass, relative to 100 parts by mass of the water-absorbent resin. Such a preferred amount is consistent with the preferred content in the water-absorbent resin composition. That is, according to one embodiment of the present invention, the content of the chelating agent in the water-absorbent resin composition is preferably 0 to 3 parts by mass, more preferably 0.001 to 1 part by mass, and particularly preferably 0.05 to 0.5 parts by mass, relative to 100 parts by mass of the water-absorbent resin. These are added to a monomer, a hydrous gel, a dried polymer, a powder, or the like, and the addition step is appropriately determined after the polymerization step, but it is preferable to add after polymerization, further after drying, and particularly after surface crosslinking.

Chelating agents that can be used include those exemplified in U.S. Pat. Nos. 6,599,989 and 6,469,080, and European Patent No. 2,163,302, in particular non-polymeric chelating agents, as well as organophosphorus chelating agents, and aminocarboxylic acid chelating agents such as diethylenetriaminepentaacetic acid or a salt thereof, and ethylenediaminetetraacetic acid or a salt thereof.

[2-9] Step of adding coloring inhibitor or urine resistance improver Generally, since water absorbent resins tend to be easily colored or deteriorated, in the present invention, in order to prevent coloring or deterioration, it is preferable to further include a coloring inhibitor or a urine resistance (weather resistance) improver selected from α-hydroxycarboxylic acids (particularly lactic acid or a salt thereof), inorganic or organic reducing agents (particularly sulfur-based inorganic reducing agents). The amount of these used is preferably 0 to 3 parts by mass, more preferably 0.001 to 1 parts by mass, and particularly preferably 0.05 to 0.5 parts by mass, based on 100 parts by mass of the water absorbent resin. Such a preferred amount of use corresponds to the preferred content in the water absorbent resin composition. That is, according to one embodiment of the present invention, in the water absorbent resin composition, the content of the coloring inhibitor or the urine resistance improver is preferably 0 to 3 parts by mass, more preferably 0.001 to 1 parts by mass, and particularly preferably 0.05 to 0.5 parts by mass, based on 100 parts by mass of the water absorbent resin, independently of each other. These are added to a monomer, a hydrogel, a dried polymer, a powder, or the like, and the addition step is appropriately determined after the polymerization step. Among these, since the reducing agent is consumed in the polymerization, it is preferable to add it after polymerization, further after drying, and particularly after surface crosslinking.

Examples of α-hydroxycarboxylic acids include malic acid, succinic acid, lactic acid, and salts thereof (particularly monovalent salts) as exemplified in U.S. Patent Application Publication No. 2009/0312183. Examples of inorganic or organic reducing agents (particularly sulfur-based inorganic reducing agents) that can be used include sulfur-based reducing agents, particularly sulfites and hydrogen sulfites, as exemplified in U.S. Patent Application Publication No. 2010/0062252.

[2-10] Antibacterial Agent Addition Step In the present invention, the water absorbent resin composition may further contain an antibacterial agent. The bad odor caused by urine is generated by the proliferation of microorganisms and the like over time, and the putrid odor and irritating odor generated by the decomposition of organic matter in urine increases over time. By further containing an antibacterial agent, not only the initial urine odor can be suppressed, but also the urine odor after a medium to long period of time can be suppressed by suppressing the proliferation of microorganisms and the like over time.

The procedure for mixing the water-absorbent resin and the antibacterial agent is not particularly limited. For example, the antibacterial agent may be added to the base polymer before it is surface-crosslinked, and then the base polymer may be surface-crosslinked. However, in order to enhance the deodorizing effect of the antibacterial agent, it is preferable to add the antibacterial agent to the surface-crosslinked water-absorbent resin.

An antibacterial agent is an agent that has the effect of suppressing the growth of bacteria such as Staphylococcus aureus, Escherichia coli, and ammonia-producing bacteria. Antibacterial agents can be broadly divided into inorganic antibacterial agents that contain antibacterial metals such as Ag, Cu, and Zn as active ingredients supported on an inorganic carrier or as salts or complexes of organic compounds, and organic antibacterial agents that do not contain antibacterial metals. In the embodiment of the present invention, any inorganic or organic antibacterial agent that has the effect of suppressing the growth of microorganisms over time can be preferably used. Among them, organic antibacterial agents are more preferable in that they can eliminate concerns about the adverse effects of antibacterial metals on the human body.

Specific examples of inorganic antibacterial agents include silicate-based agents in which antibacterial metals are supported on silicates such as zeolite, silica gel, calcium silicate, and clay minerals; phosphate-based agents in which antibacterial metals are supported on phosphates such as zirconium phosphate, calcium phosphate, aluminum phosphate, and hydroxyapatite; simple metals such as antibacterial metal nanoparticles; antibacterial metal compounds such as antibacterial metal halides and oxides; and antibacterial metal salts or complexes of organic compounds, polymers, etc.

Therefore, in one embodiment of the present invention, an inorganic antibacterial agent (an antibacterial metal (e.g., Ag) supported on a silicate (e.g., zeolite)) is not included in the water absorbent resin composition, or if it is included, the content is preferably less than 10 ppm by mass, 9 ppm by mass or less, 7 ppm by mass or less, or 5 ppm by mass or less.

Specific examples of organic antibacterial agents include alcohol compounds such as 2-bromo-2-nitro-1,3-propanediol and N-(2-hydroxypropyl)-aminomethanol; phenol compounds such as 3-methyl-4-isopropylphenol (isopropylmethylphenol), 2-isopropyl-5-methylphenol, o-phenylphenol, sodium o-phenylphenol, chloroxylenol (4-chloro-3,5-dimethylphenol), p-chloro-m-cresol, tribromophenol, and 4-chloro-2-phenylphenol; ester compounds such as fatty acid monoglycerides, p-hydroxybenzoic acid esters, and sucrose fatty acid esters; and 2,4,4'-trichloro-2'-hydroxydiphenyl ether. ether-based compounds; nitrile-based compounds such as 2,4,5,6-tetrachloroisophthalonitrile and 1,2-dibromo-2,4-dicyanobutane; halogen-based antibacterial agents such as chlorinated isocyanuric acid, α-chloronaphthalene, and polyvinylpyrrolidone iodine; pyridine-quinoline-based antibacterial agents such as (2-pyridylthio-1-oxide) and 2.3.5.6-tetrachloro-4(methylsulfonyl)pyridine; triazine-based compounds such as hexahydro-1,3,5-tris(2-hydroxyethyl)-S-triazine; isothiazolone-based compounds such as 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, and 1,2-benzothiazolone. imidazole-thiazole compounds such as 2-(4-thiocyanomethylthio)benzimidazole, 2-(4'-thiazolyl)benzimidazole, and 2-methoxycarbonylaminobenzimidazole; anilide compounds such as 3,4,4-trichlorocarbanilide and 3-trifluoromethyl-4,4'-dichlorocarbanilide; biguanide compounds such as polyhexamethylene biguanidine hydrochloride, polyhexamethylene biguanidine gluconate, chlorhexidine hydrochloride, and chlorhexidine gluconate; disulfide compounds such as bis(dimethylthiocarbamoyl)disulfide; carbohydrate compounds such as polyglucosamine, chitosan, and aminoglycoside ST-7; tropolone antibacterial agents such as hinokitiol; alkylbenzyl Examples of the antibacterial agent include quaternary ammonium salt compounds such as dimethylammonium salts (benzalkonium chloride, etc.), alkyldimethylammonium chloride, didecyldimethylammonium chloride, didecyldimethylammonium gluconate, cetyldimethylbenzylammonium chloride, octadecylamine acetate, 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride, poly[polymethylene(dimethyliminio)chloride], poly[oxyethylene(dimethyliminio)ethylene(dimethyliminio)ethylenedichloride], and amphoteric and anionic surfactant compounds such as alkyldi(aminoethyl)glycine, alkylbetaine, and aliphatic monoglyceride. Among these, from the viewpoint of providing a stable antibacterial property to the water absorbent resin composition, antibacterial agents that are water-soluble or water-dispersible are particularly preferably used, and among these, phenolic compounds, quaternary ammonium salt compounds, biguanide compounds, and amphoteric and anionic surfactant compounds are preferably used.

In an embodiment of the present invention, the amount of the antibacterial agent added to the water absorbent resin is preferably 0.001 to 5 mass%, more preferably 0.01 to 4 mass%, even more preferably 0.03 to 3 mass%, and particularly preferably 0.05 to 2 mass%, from the viewpoint of the effect of suppressing the generation of putrid odors and irritating odors.

[2-11] Other Steps In the present invention, in addition to the above-mentioned steps, a granulation step, a sizing step, a fine powder removal step, a fine powder recovery step, a fine powder reuse step, a step of adding other additives, an iron removal step, etc. may be carried out as necessary. In addition, at least one step selected from a transportation step, a storage step, a packaging step, a keeping step, etc. may be further included.

The granulation process includes a process of classifying and removing fine powder after the surface cross-linking process, and a process of classifying and pulverizing the water-absorbent resin when the resin aggregates and exceeds a desired size. The fine powder recycling process includes a process of adding the fine powder as it is or to the water-containing gel, which is a raw material, in any step of the water-absorbent resin manufacturing process, after making the fine powder into a large hydrous gel in a granulation process.

In addition, in the step of adding the coloring inhibitor or urine resistance improver, in order to impart various functions to the water absorbent, one or more other additives selected from an oxidizing agent, an organic powder such as a metal soap, pulp, a thermoplastic fiber, etc. can be added together with the coloring inhibitor or urine resistance improver, or instead of the coloring inhibitor or urine resistance improver. These other additives can be mixed simultaneously with or separately from the surface crosslinking agent. That is, the water absorbent resin composition of the present invention can also contain such other additives.

In one embodiment of the present invention, the water-absorbent resin composition may not contain a material having the function of polymerizing a phenolic compound.

In one embodiment of the present invention, the water-absorbent resin composition may not contain natural deodorant components (particularly, plant components).

[3] Characteristics of the water-absorbent resin composition [3-1] Span value In one embodiment of the present invention, the water-absorbent resin composition has a span value of 1.10 or less. If the span value exceeds 1.10, the desired effect of the present invention cannot be achieved. According to an embodiment of the present invention, the span value is 0.40 or more. According to such an embodiment, the desired effect of the present invention can be efficiently achieved. According to an embodiment of the present invention, the span value is preferably 0.40 to 1.10, more preferably 0.45 to 1.05, and even more preferably 0.50 to 1.00. The mechanism by which the desired deodorizing effect is obtained by adjusting the span value to a specific value or less and combining it with at least one of the hydrophobic porous polymer adsorbent and the resin having a nitrogen-containing heterocycle is not clear, and the configuration, which at first glance seems completely unrelated to deodorizing properties, was a surprising result that contributed to solving the problem.

[3-2] Other Properties of the Water-Absorbent Resin Composition In one embodiment of the present invention, the water-absorbent resin preferably further has the following properties.

(3-2-1) Mass average particle diameter D (50%)
In one embodiment of the present invention, the mass average particle diameter D(50%) of the water absorbent resin composition is preferably 300 μm or more, more preferably 305 μm or more, even more preferably 310 μm or more, and particularly preferably 315 μm or more. Also, it is preferably 600 μm or less, more preferably 550 μm or less, even more preferably 500 μm or less, and particularly preferably 450 μm or less. The range of the mass average particle diameter D(50%) is any combination of the above upper and lower limits.

By setting the mass average particle diameter D (50%) of the water-absorbent resin within the above range, the absorbency without load (CRC) and absorbency under load (AAP) of the water-absorbent composition can be controlled in a well-balanced manner in one embodiment of the present invention described later. In other words, by setting the mass average particle diameter D (50%) within the above range, the absorbency without load (CRC) and absorbency under load (AAP) can be increased, and the coarseness of the particles of the water-absorbent resin can be suppressed, thereby improving the feel on the skin and the fit when used in absorbent articles such as disposable diapers and sanitary napkins.

(3-2-2) CRC (absorbency without load)
In one embodiment of the present invention, the CRC (centrifuge retention capacity) of the water absorbent resin composition is usually 5 g/g or more, preferably 20 g/g or more, more preferably 24 g/g or more, and even more preferably 30 g/g or more. The upper limit is not particularly limited and the higher the value, the more preferable it is. However, from the viewpoint of the balance with other physical properties, it is preferably 70 g/g or less, more preferably 50 g/g or less, and even more preferably 45 g/g or less. Therefore, the representative range of the CRC (centrifuge retention capacity) can be appropriately selected within the range of the above-mentioned upper and lower limits. For example, any range such as 5 to 70 g/g, 20 to 50 g/g, or 24 to 45 g/g can be selected.

If the CRC is less than 5 g/g, the absorbency of the water-absorbing resin composition is low and the composition is not suitable for use as an absorbent for absorbent articles such as paper diapers. If the CRC is more than 70 g/g, the rate at which the composition absorbs body fluids such as urine and blood decreases, making the composition unsuitable for use in paper diapers with high water absorption rates. The CRC can be controlled by an internal crosslinking agent, a surface crosslinking agent, or the like.

(3-2-3) AAP (water absorption capacity under pressure)
In one embodiment of the present invention, the AAP (absorption capacity under pressure) of the water absorbent resin composition is preferably 5 g/g or more, more preferably 8 g/g or more, even more preferably 10 g/g or more, still more preferably 12 g/g or more, preferably 14 g/g or more, still more preferably 18 g/g or more, and still more preferably 22 g/g or more. The upper limit is not particularly limited, but is preferably 30 g/g or less.

If the AAP is less than 5 g/g, the absorbency decreases when pressure is applied to the absorbent when it is actually used in disposable diapers, etc., and the absorbent is not suitable for use as an absorbent in absorbent articles such as disposable diapers. The AAP can be controlled by particle size, surface cross-linking agents, etc.

(3-2-4) Contact angle In one embodiment of the present invention, the contact angle of the water absorbent resin composition is preferably 35° or more, more preferably 40° or more, further preferably 45° or more, and even more preferably 50° or more, 54° or more, 55° or more, 56° or more, or even more preferably more than 100°.

When the contact angle has such a lower limit, the absorption of urine, etc. by the absorbent resin slows down. This improves the diffusibility of urine, etc. when applied to an absorbent body or absorbent article. This increases the area that comes into contact with the absorbent resin, etc., and allows for the effective use of the deodorant area. Furthermore, it is expected that urine backflow will be reduced.

In one embodiment of the present invention, the contact angle of the water-absorbent resin composition is preferably 120° or less, and more preferably 110° or less. By having such an upper limit, the absorption of urine, etc. by the water-absorbent resin is not excessively slowed down, so that leakage of urine, etc. can be prevented when applied to an absorbent body or absorbent article.

(Combination of Particularly Preferred Embodiments)
Although any combination of the embodiments (configurations) described in the present invention is considered to be disclosed (i.e., subject to legal amendment), specifically preferred embodiments or combinations thereof are described.

In one embodiment of the present invention, the hydrophobic porous polymer adsorbent is a styrene-based adsorbent.

In one embodiment of the present invention, the resin having a nitrogen-containing heterocycle is a water-insoluble or water-dispersible polymer having a LogP of 1.5 or more.

In one embodiment of the present invention, the amount of the resin having a nitrogen-containing heterocycle added is more than 0.3 parts by mass, more than 0.5 parts by mass, more than 1.0 parts by mass, 1.5 parts by mass or more, or 2.0 parts by mass or more per 100 parts by mass of the absorbent resin.

According to one embodiment of the present invention, the nitrogen-containing heterocycle contains two heteroatoms.

In one embodiment of the present invention, the resin having a nitrogen-containing heterocycle is a water-insoluble or water-dispersible polymer having a LogP of 1.5 or more, and the amount of the resin having a nitrogen-containing heterocycle added is more than 0.3 parts by mass, more than 0.5 parts by mass, more than 1.0 parts by mass, 1.5 parts by mass or more, or 2.0 parts by mass or more, relative to 100 parts by mass of the water absorbent resin. Furthermore, the nitrogen-containing heterocycle contains two heteroatoms.

In one embodiment of the present invention, the water-absorbent resin composition includes a binder that binds the water-absorbent resin with at least one of the components of the hydrophobic porous polymer adsorbent and the resin having a nitrogen-containing heterocycle.

In one embodiment of the present invention, the water-absorbent resin composition contains a chelating agent.

In one embodiment of the present invention, the contact angle of the water-absorbent resin composition is 50° or more, 55° or more, or greater than 100°.

According to one embodiment of the present invention, the total specific surface area of the hydrophobic porous polymer adsorbent per gram of water absorbent resin is greater than 2.5 ^m2 , greater than 3.0 ^m2 , or greater than 3.5 ^m2 .

In one embodiment of the present invention, the abundance of nitrogen-containing heterocycles is 7.0% or more, 14.0% or more, or 42.0% or more.

[4] Uses of the water-absorbing resin composition (absorbent material, absorbent layer)
The water-absorbent resin composition according to the present invention is preferably used as an absorbent body (absorbent layer) of absorbent articles such as disposable diapers and sanitary napkins, and more preferably used as an absorbent body (absorbent layer) of absorbent articles in which a large amount is used per absorbent article. Thus, in one embodiment of the present invention, an absorbent body is provided that includes the water-absorbent resin composition and hydrophilic fibers.

The absorbent refers to a particulate water-absorbing agent formed into a sheet, fiber, or cylinder, and is preferably formed into a sheet to form an absorbent layer. In addition to the water-absorbing resin composition of the present invention, absorbent materials such as pulp fibers, adhesives, nonwoven fabrics, etc. can also be used in combination for molding. In this case, the amount of water-absorbing agent in the absorbent (absorbent layer) (hereinafter referred to as "core concentration") is preferably in the range of 20 to 100% by mass, more preferably in the range of 30 to 90% by mass, and more preferably in the range of 40 to 80% by mass. If the core concentration is less than 20% by mass, the amount of the water-absorbing resin composition used is small, and for example, the deodorizing performance may not be sufficiently imparted to the entire diaper, which is not preferable.

When the absorbent according to the present invention is produced from the water-absorbent resin composition and the hydrophilic fibers, the production method is not particularly limited, but for example, the water-absorbent resin composition and the hydrophilic fibers are dry-mixed using a mixer or other mixer at a ratio that results in the above-mentioned core concentration, and the resulting mixture is formed into a web shape by, for example, air papermaking, and then compression molded as necessary. Such an absorbent is preferably compression molded to have a density in the range of 0.001 to 0.50 g/cc and a basis weight in the range of 0.01 to 0.20 g/ ^cm2 .

[5] Absorbent article The absorbent article according to the present invention includes the absorbent body (absorbent layer) and usually includes a liquid-permeable top sheet and a liquid-impermeable back sheet. Examples of absorbent articles include disposable diapers and sanitary napkins. Thus, in one embodiment of the present invention, an absorbent article is provided that includes an absorbent body, a liquid-permeable top sheet, and a liquid-impermeable back sheet.

When the absorbent article is, for example, a disposable diaper, in one embodiment of the present invention, the disposable diaper is produced by sandwiching an absorbent body containing a water-absorbing agent between a liquid-permeable top sheet that is located on the side that comes into contact with the skin when worn, and a liquid-impermeable back sheet that is located on the outside when worn. The disposable diaper is further provided with members known to those skilled in the art, such as an adhesive tape for fixing the disposable diaper after wearing.

The absorbent article of the present invention contains a specific water-absorbent resin composition, and therefore aims to be a novel water-absorbent resin composition that has better deodorizing capabilities than conventional compositions.

The water-absorbent resin composition according to the present invention can be suitably used not only for the disposable diapers and sanitary napkins, but also for applications such as pet urine absorbents and urine gelling agents for portable toilets. More specifically, the present invention relates to a water-absorbent resin composition, absorbent body, and absorbent article that exhibit excellent deodorizing performance, particularly excellent deodorizing performance against malodors caused by urine, when used in sanitary materials such as paper diapers and incontinence pads.

The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples and comparative examples, and examples obtained by appropriately combining the technical means disclosed in each example are also included in the scope of the present invention. Unless otherwise noted, the electrical equipment used in the examples and comparative examples, as well as for measuring the various physical properties of the water absorbent, uses a power source of 200V or 100V/60Hz. Unless otherwise noted, the various physical properties of the water absorbent were measured under conditions of room temperature (20°C to 25°C) and a relative humidity of 50±5% RH. For convenience, "liter" may be expressed as "l" or "L," and "mass %" as "wt%."

[Physical Properties of Water-Absorbent Resin Composition]
Hereinafter, methods for measuring various physical properties of the water-absorbing resin composition according to the present invention will be described.

(a) Span Value The span value of the water absorbent resin composition was determined in accordance with the particle size analysis method of EDANA method WSP220.2 by using sieves with openings of 850 μm, 710 μm, 600 μm, 500 μm, 300 μm, 150 μm, and 45 μm in order from the top, and by the following formula.

D(90%) is the particle size at which the cumulative particle size distribution from the minimum diameter is 90% (unit: μm)
D(10%) is the particle size (unit: μm) at which the cumulative particle size distribution from the minimum diameter is 10%.
D(50%) is the particle size at which the cumulative particle size distribution from the minimum diameter is 50% (unit: μm)
Here, D(90%), D(10%), and D(50%) are cumulative values based on mass.

As mentioned above, the span value can be set to the desired span value by appropriately combining grinding, classification, granulation, etc.

(b) Mass average particle diameter D (50%)
The mass average particle diameter D (50%) of the water absorbent resin composition was measured in accordance with the particle size analysis method of EDANA method WSP220.2 by using a combination of sieves with openings of 850 μm, 710 μm, 600 μm, 500 μm, 300 μm, 150 μm, and 45 μm in order from the top.

(c) Absorption capacity without load (CRC)
The CRC of the water-absorbent resin and the water-absorbent resin composition was measured in accordance with EDANA method WSP241.3(10).

(d) Absorption Capacity Under Pressure (AAP)
The AAP of the water-absorbent resin and the water-absorbent resin composition was measured in accordance with EDANA method WSP242.3(10), except that the load condition was changed to 4.83 kPa.

(e) Deodorizing performance (deodorizing test)
50 ml of human urine collected from multiple adults was added to a 250 ml polypropylene cup with a lid, and 2.0 g of the water-absorbing resin (or water-absorbing resin composition) obtained in the Examples or Comparative Examples described below was added thereto to form a swollen gel. Human urine was used within 2 hours after excretion. The container was covered with a lid, and the swollen gel was kept at 37°C. The lid was opened after a predetermined time from liquid absorption, and a panel of four or more adults smelled the odor at a position about 3 cm from the top of the cup to judge the deodorizing effect. The judgment was made by each person scoring on a 6-point scale using the following judgment criteria, and the average was calculated.

(f) Contact angle A double-sided adhesive tape was applied onto a SUS plate, a water-absorbent resin composition was spread thereon, and the water-absorbent resin composition that did not adhere to the double-sided tape was scraped off to prepare a sample plate whose surface was covered with the water-absorbent resin composition. The contact angle when 0.90% by mass physiological saline was brought into contact with the sample plate was measured by a drop method using a contact angle meter (FACE CA-X type, manufactured by Kyowa Interface Science Co., Ltd.) under conditions of 20°C and 60% RH. The contact angle 1 second after a drop of 0.90% by mass physiological saline was dropped onto the sample plate was measured five times for one sample, and the average value was calculated to be the contact angle of the water-absorbent resin composition.

[Production Example 1]
A reaction liquid was prepared by dissolving 8.7 parts by mass of polyethylene glycol diacrylate (n=8) as an internal crosslinking agent in 5,500 parts by mass of a 33% by mass aqueous solution of sodium acrylate (neutralization rate: 75 mol%) as a monomer component.

Next, the reaction liquid was degassed for 30 minutes under a nitrogen gas atmosphere. The reaction liquid was then fed into a reactor equipped with a jacketed stainless steel twin bowl kneader with a capacity of 10 L and two sigma-type blades and a lid, and the atmosphere in the reactor was replaced with nitrogen gas while the reaction liquid was kept at 30°C. Next, 2.4 parts by mass of sodium persulfate and 0.12 parts by mass of L-ascorbic acid were each added as aqueous solutions while stirring the reaction liquid, and polymerization began approximately 1 minute later. The peak temperature reached approximately 80°C in approximately 20 minutes after the start of polymerization, and stirring was continued thereafter, and a particulate hydrogel polymer was taken out 60 minutes after the start of polymerization.

The mass average particle diameter (D50) of the particulate hydrogel polymer was measured by the method described in International Publication WO 2011/126079 and was found to be approximately 1,800 μm.

The obtained hydrous gel polymer was spread on a wire mesh with 300 μm openings and dried with hot air at 150°C for 90 minutes.

The dried material was then pulverized using a roll mill, and further classified and mixed using a JIS standard sieve with an opening of 600 μm to obtain an irregularly crushed resin (base polymer) (1). The obtained base polymer (1) had a mass average particle diameter D (50%) of 328 μm, a particle ratio of more than 850 μm of 0.0 mass%, a particle ratio of 710 μm or more and less than 850 μm of 0.0 mass%, a particle ratio of 600 μm or more and less than 710 μm of 1.4 mass%, a particle ratio of 500 μm or more and less than 600 μm of 6.1 mass%, a particle ratio of 300 μm or more and less than 500 μm of 54.9 mass%, a particle ratio of 150 μm or more and less than 300 μm of 35.4 mass%, a particle ratio of 45 μm or more and less than 150 μm of 2.1 mass%, and a particle ratio of less than 45 μm of 0.1 mass%.

Next, 100 parts by mass of the base polymer (1) was mixed with a surface crosslinking agent consisting of 0.05 parts by mass of ethylene glycol diglycidyl ether, 1 part by mass of propylene glycol, 3 parts by mass of water, and 1 part by mass of isopropyl alcohol in a stirring mixer. The mixture was then heat-treated at 210°C for 50 minutes to perform surface crosslinking.

Next, 3.0 parts by mass of a 1.0% by mass aqueous solution of diethylenetriaminepentaacetic acid trisodium was added and mixed, and the mixture was further heated at 60°C for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain water-absorbent resin (1).

[Production Example 2]
The base polymer (1) obtained in Production Example 1 was further pulverized using a roll mill, classified using a sieve with an opening of 150 μm, and mixed to obtain a base polymer (2). The obtained base polymer (2) had a mass average particle diameter D (50%) of 330 μm, a particle ratio of more than 850 μm of 0.0 mass%, a particle ratio of 710 μm or more and less than 850 μm of 0.0 mass%, a particle ratio of 600 μm or more and less than 710 μm of 0.7 mass%, a particle ratio of 500 μm or more and less than 600 μm of 4.7 mass%, a particle ratio of 300 μm or more and less than 500 μm of 59.2 mass%, a particle ratio of 150 μm or more and less than 300 μm of 33.1 mass%, a particle ratio of 45 μm or more and less than 150 μm of 2.2 mass%, and a particle ratio of less than 45 μm of 0.1 mass%.

Next, 100 parts by mass of the base polymer (2) was mixed with a surface crosslinking agent consisting of 0.05 parts by mass of ethylene glycol diglycidyl ether, 1 part by mass of propylene glycol, 3 parts by mass of water, and 1 part by mass of isopropyl alcohol in a stirring mixer. The mixture was then heat-treated at 210°C for 50 minutes to perform surface crosslinking.

Next, 3.0 parts by mass of a 1.0% by mass aqueous solution of diethylenetriamine pentaacetate trisodium was added and mixed, and the mixture was further heated at 60°C for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin (2).

[Production Example 3]
The water-absorbent resin (2) obtained in Production Example 2 was further classified using sieves with openings of 500 μm and 150 μm, and the resulting mixture was mixed to obtain a water-absorbent resin (3).

The obtained water absorbent resin (3) had a mass average particle diameter D (50%) of 324 μm, a particle ratio exceeding 850 μm of 0.0 mass%, a particle ratio of 710 μm or more and less than 850 μm of 0.0 mass%, a particle ratio of 600 μm or more and less than 710 μm of 0.0 mass%, a particle ratio of 500 μm or more and less than 600 μm of 0.1 mass%, a particle ratio of 300 μm or more and less than 500 μm of 70.5 mass%, a particle ratio of 150 μm or more and less than 300 μm of 29.4 mass%, a particle ratio of 45 μm or more and less than 150 μm of 0.0 mass%, and a particle ratio of less than 45 μm of 0.0 mass%.

[Production Example 4]
In Production Example 1, the dried product was pulverized using a roll mill, and then classified using a sieve with an opening of 850 μm, followed by compounding to obtain a base polymer (4).

The obtained base polymer (4) had a mass average particle diameter D (50%) of 361 μm, a particle ratio of more than 850 μm of 0.0 mass%, a particle ratio of 710 μm or more and less than 850 μm of 0.8 mass%, a particle ratio of 600 μm or more and less than 710 μm of 12.4 mass%, a particle ratio of 500 μm or more and less than 600 μm of 14.8 mass%, a particle ratio of 300 μm or more and less than 500 μm of 34.9 mass%, a particle ratio of 150 μm or more and less than 300 μm of 29.3 mass%, a particle ratio of 45 μm or more and less than 150 μm of 7.5 mass%, and a particle ratio of less than 45 μm of 0.3 mass%. Next, 100 parts by mass of the base polymer (4) was mixed with a surface crosslinking agent consisting of 0.05 parts by mass of ethylene glycol diglycidyl ether, 1 part by mass of propylene glycol, 3 parts by mass of water, and 1 part by mass of isopropyl alcohol in a stirring mixer. Thereafter, the mixture was heat-treated at 210° C. for 50 minutes to carry out surface cross-linking.
Next, 3.0 parts by mass of a 1.0% by mass aqueous solution of trisodium diethylenetriaminepentaacetate was added and mixed, and the mixture was further heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water absorbent resin (4).

[Production Example 5]
100 parts by mass of the base polymer (1) obtained in Production Example 1 was mixed with 0.05 parts by mass of ethylene glycol diglycidyl ether, 3 parts by mass of water, and a surface crosslinking agent consisting of 2 parts by mass of isopropyl alcohol in a stirring mixer. The mixture was then heat-treated at 210°C for 50 minutes to perform surface crosslinking. Next, 3.0 parts by mass of a 1.0% by mass diethylenetriamine pentaacetic acid trisodium aqueous solution was added and mixed, and the mixture was further heated at 60°C for 30 minutes. The mixture was then crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin (5).

[Production Example 6]
100 parts by mass of the base polymer (1) obtained in Production Example 1 was mixed with a surface crosslinking agent consisting of 0.05 parts by mass of ethylene glycol diglycidyl ether, 1 part by mass of propylene glycol, 3 parts by mass of water, and 1 part by mass of isopropyl alcohol in a stirring mixer. The mixture was then heat-treated at 210°C for 50 minutes to perform surface crosslinking. The mixture was then crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin (6).

[Example 1]
0.1 parts by mass (solid content equivalent) of Chromalite PCG600M (Purolite Co., Ltd., styrene-based synthetic adsorbent, average particle size 70 μm, specific surface area 700 m ² /g, average pore diameter 100 Å) was added and mixed with 100 parts by mass of the water-absorbing resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (1). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.92% by mass.

[Example 2]
0.5 parts by mass (solid content equivalent) of Chromalite PCG600M was added and mixed with 100 parts by mass of the water-absorbing resin (1) obtained in Production Example 1, and the mixture was heated at 60°C for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (2). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.93% by mass.

[Example 3]
1.0 part by mass (solid content equivalent) of Chromalite PCG600M was added and mixed with 100 parts by mass of the water-absorbing resin (1) obtained in Production Example 1, and the mixture was heated at 60°C for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (3). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.96% by mass.

[Example 4] (without binder)
A water absorbent resin composition (4) was obtained in the same manner as in Example 3, except that the water absorbent resin (5) obtained in Production Example 5 was used. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1.

[Example 5] (No chelating agent)
A water absorbent resin composition (5) was obtained in the same manner as in Example 3, except that the water absorbent resin (6) obtained in Production Example 6 was used. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of the binder contained in the water absorbent resin composition was 0.95% by mass.

[Example 6]
0.5 parts by mass (solid content equivalent) of Purosorb PAD600FM (Purolite Co., Ltd., styrene-based synthetic adsorbent, average particle size 210 μm, specific surface area 830 m ² /g, average pore diameter 630 Å) was added and mixed with 100 parts by mass of the water-absorbing resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (6). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.94% by mass.

[Example 7]
0.5 parts by mass (solid content equivalent) of Purosorb PAD600 (Purolite Co., Ltd., styrene-based synthetic adsorbent, average particle size 460 μm, specific surface area 830 m ² /g, average pore diameter 630 Å) was added and mixed with 100 parts by mass of the water-absorbing resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (7). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.93% by mass.

[Example 8]
0.5 parts by mass (solid content equivalent) of Purosorb PAD610 (Purolite Co., Ltd., acrylic synthetic adsorbent, average particle size 460 μm, specific surface area 490 m ² /g, average pore diameter 700 Å) was added and mixed with 100 parts by mass of the water-absorbing resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (8). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.96% by mass.

[Example 9]
0.5 parts by mass (solid content equivalent) of Diaion 20HP (manufactured by Mitsubishi Chemical Corporation, styrene-based synthetic adsorbent, average particle size 390 μm, specific surface area 590 m ² /g, average pore diameter 290 Å) was added and mixed with 100 parts by mass of the water-absorbing resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (9). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.94% by mass.

[Example 10]
0.5 parts by mass (solid content equivalent) of Diaion HP2MG (manufactured by Mitsubishi Chemical Corporation, acrylic synthetic adsorbent, average particle size 600 μm, specific surface area 570 m ² /g, average pore diameter 240 Å) was added and mixed with 100 parts by mass of the water-absorbing resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (10). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.95% by mass.

[Example 11]
0.5 parts by mass (solid content equivalent) of Purosorb PAD300 (Purolite Co., Ltd., acrylic synthetic adsorbent, average particle size 450 μm, specific surface area 90 m ² /g, average pore diameter 280 Å) was added and mixed with 100 parts by mass of the water-absorbing resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (11). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.93% by mass.

[Example 12]
0.5 parts by mass (solid content equivalent) of Chromalite PCG600M was added and mixed with 100 parts by mass of the water-absorbing resin (2) obtained in Production Example 2, and the mixture was heated at 60°C for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (12). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.96% by mass.

[Example 13]
0.5 parts by mass (solid content equivalent) of Chromalite PCG600M was added and mixed with 100 parts by mass of the water-absorbing resin (3) obtained in Production Example 3, and the mixture was heated at 60°C for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (13). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1. The amount of binder contained in the water-absorbing resin composition was 0.94% by mass.

[Example 14]
0.75 parts by mass (0.3 parts by mass in terms of solid content) of 40% by mass of water-dispersible emulsion A (styrene/butyl acrylate/2-isopropenyl-2-oxazoline/divinylbenzene=58.1/21.8/20.0/0.1% by mass, LogP=3.29, average particle size: 80 nm) was added and mixed with 100 parts by mass of the water-absorbent resin (1) obtained in Production Example 1, and the mixture was heated at 60 ° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin composition (14). The cumulative particle size and span value, the deodorization test results, the CRC and AAP measurement results are shown in Table 2. The amount of binder contained in the water-absorbent resin composition was 0.96% by mass.

[Example 15]
A water-absorbent resin composition (15) was obtained in the same manner as in Example 14, except that the amount of the water-dispersible emulsion A was changed to 2.5 parts by mass (1 part by mass in terms of solid content). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2. The amount of the binder contained in the water-absorbent resin composition was 0.94% by mass.

[Example 16]
A water-absorbent resin composition (16) was obtained in the same manner as in Example 14, except that the amount of the water-dispersible emulsion A was changed to 7.5 parts by mass (3 parts by mass in terms of solid content). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2. The amount of the binder contained in the water-absorbent resin composition was 0.96% by mass.

[Example 17]
0.3 parts by mass of Eposter S (manufactured by Nippon Shokubai Co., Ltd., triazine group-containing polymer, average particle size 0.2 μm, solubility in ion-exchanged water at 25° C. is 0% by mass) was added and mixed with 100 parts by mass of the water-absorbent resin (1) obtained in Production Example 1, and then passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin composition (17). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2. The amount of binder contained in the water-absorbent resin composition was 0.93% by mass.

[Example 18]
A water absorbent resin composition (18) was obtained in the same manner as in Example 17, except that Eposter S (manufactured by Nippon Shokubai Co., Ltd., triazine group-containing polymer, average particle size 0.2 μm, solubility in ion-exchanged water at 25° C. is 0 mass%) was changed to 1 part by mass. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2. The amount of the binder contained in the water absorbent resin composition was 0.94 mass%.

[Example 19]
A water absorbent resin composition (19) was obtained in the same manner as in Example 17, except that Eposter S (manufactured by Nippon Shokubai Co., Ltd., triazine group-containing polymer, average particle size 0.2 μm, solubility in ion-exchanged water at 25° C. is 0 mass%) was changed to 3 parts by mass. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2. The amount of the binder contained in the water absorbent resin composition was 0.95 mass%.

[Example 20]
100 parts by mass of the water absorbent resin (1) obtained in Production Example 1 was mixed with 1 part by mass (solid content equivalent) of poly4-vinylpyridine (Strem Chemicals, Inc., pyridine group-containing polymer, 250 μm or less), and then passed through a JIS standard sieve with an opening of 850 μm to obtain a water absorbent resin composition (20). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2. The amount of the binder contained in the water absorbent resin composition was 0.96% by mass.

[Example 21] (No chelating agent)
2.5 parts by mass (1 part by mass in terms of solid content) of water-dispersible emulsion A was added and mixed with 100 parts by mass of the water-absorbent resin (6) obtained in Production Example 6, and the mixture was heated at 60°C for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin composition (21). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2. The amount of binder contained in the water-absorbent resin composition was 0.94% by mass.

[Example 22] (No binder)
100 parts by mass of the water-absorbing resin (5) obtained in Production Example 5 was mixed with 1 part by mass of Eposter S (manufactured by Nippon Shokubai Co., Ltd., triazine group-containing polymer, average particle size 0.2 μm, solubility in ion-exchanged water at 25° C. is 0% by mass), and then passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbing resin composition (22). The cumulative particle size and span value, deodorization test results, CRC, and AAP measurement results are shown in Table 2.

[Example 23]
0.75 parts by mass (0.3 parts by mass in terms of solid content) of water-dispersible emulsion A was added and mixed with 100 parts by mass of the water-absorbent resin (1) obtained in Production Example 1, and then 0.5 parts by mass (solid content equivalent) of Chromalite PCG600M was added and mixed, and the mixture was heated at 60 ° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin composition (23). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 3. The amount of binder contained in the water-absorbent resin composition was 0.94% by mass.

[Comparative Example 1]
The water absorbent resin (1) obtained in Production Example 1 was used as it was as a comparative water absorbent resin composition (1). The cumulative particle size and span value, the cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Tables 1 and 2.

[Comparative Example 2]
0.5 parts by mass (solid content equivalent) of Chromalite PCG600M was added and mixed with 100 parts by mass of the water absorbent resin (4) obtained in Production Example 4, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a comparative water absorbent resin composition (2). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1.

[Comparative Example 3]
1.0 part by mass (solid content equivalent) of Eposter MX020W (styrene-acrylic fine particles, average particle diameter 0.02 μm, theoretical specific surface area 333 m ² /g, manufactured by Nippon Shokubai Co., Ltd.), which is a fine particle having no pore structure, was added and mixed with 100 parts by mass of the water absorbent resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a comparative water absorbent resin composition (3). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1.

[Comparative Example 4]
1.0 part by mass (solid content equivalent) of HSZ-500KOA (L-type zeolite, manufactured by Tosoh Corporation, SiO ₂ /Al ₂ O ₃ =6.1 (mol/mol), average particle size 3 μm, specific surface area 290 m ² /g, average pore diameter 8 Å) was added and mixed with 100 parts by mass of the water absorbent resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a comparative water absorbent resin composition (4). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1.

[Comparative Example 5]
0.5 parts by mass (solid content equivalent) of potassium peroxymonosulfate (manufactured by Aldrich, product name OXONE) was added and mixed with 100 parts by mass of the water absorbent resin (1) obtained in Production Example 1, and the mixture was heated at 60° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a comparative water absorbent resin composition (5). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 1.

[Comparative Example 6]
3.3 parts by mass (1 part by mass in terms of solid content) of an aqueous solution of 30% by mass of Epomin P-1000 (manufactured by Nippon Shokubai Co., Ltd., water-soluble polyethyleneimine (nitrogen-containing non-heterocyclic resin)) was added and mixed with 100 parts by mass of the water absorbent resin (1) obtained in Production Example 1, and the mixture was heated at 60°C for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a comparative water absorbent resin composition (6). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 7]
A comparative water-absorbent resin composition (7) was obtained in the same manner as in Example 14, except that the heating temperature after the addition and mixing of the water-dispersible emulsion A was changed to 150°C.

[Example 24]
4 parts by mass (1 part by mass in terms of solid content) of 25% by mass of water-soluble polymer B (2-isopropenyl-2-oxazoline / ethyl acrylate / methyl methacrylate / methoxypolyethylene glycol acrylate (n = 9) = 50 / 22 / 3 / 25% by mass, weight average molecular weight = about 40,000, Log P = 1.07) was added and mixed with 100 parts by mass of the water-absorbent resin (1) obtained in Production Example 1, and the mixture was heated at 60 ° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin composition (24). The deodorization test results, CRC and AAP measurement results are shown in Table 2. The amount of binder contained in the water-absorbent resin composition was 0.95% by mass.

[Production Example 7]
A solution (A) was prepared by adding 10% by weight polyethylene glycol diacrylate (weight average molecular weight: 523) aqueous solution (3.92 g) as an internal crosslinking agent and 20% by weight disodium ethylenediaminetetraacetate aqueous solution (0.66 g) as a chelating agent to acrylic acid (216.2 g), and a solution (B) was prepared by diluting 48.5% by weight sodium hydroxide aqueous solution (180.6 g) with deionized water (209.8 g) adjusted to 50 ° C. in a polypropylene container with a capacity of 1.5 L and an inner diameter of 80 mm. The solution (C) was prepared by adding and mixing the solution (B) while stirring the solution (A) using a magnetic stirrer.

Thereafter, stirring of the above solution (C) was continued, and when the temperature of solution (C) reached 95°C (=polymerization initiation temperature), a 10% by mass aqueous solution of sodium persulfate (3.6 g) was added to solution (C) as a polymerization initiator and stirred for approximately 3 seconds to obtain a monomer aqueous solution (7).

Next, the monomer aqueous solution (7) was poured into a bat-shaped container in an open-air system. The bat-shaped container had a bottom size of 250 mm x 250 mm, a top size of 640 mm x 640 mm, a height of 50 mm, a trapezoidal central cross section, and a Teflon (trademark) sheet attached to the inner surface. The bat-shaped container was placed on a hot plate heated to 100°C and preheated. After the monomer aqueous solution (7) was poured into the bat-shaped container, the polymerization reaction started about 5 seconds later. The polymerization reaction proceeded while the monomer aqueous solution (7) expanded and foamed in all directions while generating steam, and then the resulting hydrogel (7) shrunk to a size slightly larger than the bottom of the bat-shaped container, and ended. The polymerization reaction (expansion and contraction) ended within about 1 minute, but the hydrogel (7) was maintained in the bat-shaped container for 2 minutes after that. The polymerization reaction yielded a hydrogel (7) containing air bubbles.

Next, the hydrous gel (7) obtained by the above polymerization reaction was divided into 16 equal parts, and then the gel was crushed using a tabletop meat chopper with a perforated plate (MEAT-CHOPPER TYPE: 12VR-400KSOX, manufactured by Iizuka Kogyo Co., Ltd.) while simultaneously adding the hydrous gel and adding 25 parts by mass of a 0.2% by mass aqueous solution of sodium hydrogen sulfite at 25°C to the hydrous gel per 100 parts by mass (265 g) of the solid content of the hydrous gel, thereby obtaining a particulate hydrous gel (7).

Next, 450 g of the particulate hydrogel (7) was spread on a wire mesh with an opening of 300 μm (50 mesh) and dried at 180° C. for 30 minutes in a static dryer (ventilated batch dryer 71-S6 (manufactured by Satake Chemical Machinery Co., Ltd.)) to obtain a particulate dried polymer (7).

Next, the dried polymer (7) was put into a roll mill (WML type roll mill, manufactured by Inokuchi Giken Co., Ltd.) and pulverized, and then the particles passing through a JIS standard sieve with a mesh size of 150 μm were classified to obtain a fine powder of water-absorbent resin (7).

Next, 300 g of the fine powdered water-absorbent resin (7) was placed in a 5 L mortar mixer (manufactured by Nishinippon Shikenki Seisakusho) kept warm in a water bath at 80°C, and while rotating the stirring blades of the mortar mixer at high speed of 60 Hz/100 V, 300 g of a 0.05 mass% aqueous hydrogen peroxide solution as an aqueous liquid for granulation was heated to 80°C and then added all at once. Within 10 seconds after addition, the fine powdered water-absorbent resin (7) and water were mixed to form granules, and the granulated gel (7) was obtained by removing the granules 1 minute after addition.

[Production Example 8]
Polymerization and gel crushing were repeated under the same conditions as in Production Example 7 to obtain a particulate hydrogel (8).

Next, 360 g of the particulate hydrogel (8) and 90 g of the granulated gel (7) obtained in Production Example 7 were combined and spread on a wire mesh with an opening of 300 μm (50 mesh), and dried at 180° C. for 30 minutes in a static dryer (ventilated batch dryer 71-S6 (manufactured by Satake Chemical Machinery Co., Ltd.)) to obtain a particulate dried polymer (7).

Next, the dried polymer (8) was put into a roll mill (WML type roll grinder, manufactured by Inokuchi Giken Co., Ltd.) and crushed, and then classified by a Rotap type sieve classifier using two types of JIS standard sieves with mesh sizes of 850 μm and 150 μm to obtain an irregularly crushed water absorbent resin (8).

Next, a surface cross-linking agent solution (8) consisting of ethylene glycol diglycidyl ether (product name: Denacol EX-810, Nagase Chemtex Corporation, 0.025 parts by mass), propylene glycol (1.35 parts by mass), and deionized water (3.15 parts by mass) was added to the irregularly crushed water absorbent resin (8) (100 parts by mass) and mixed with a spatula until uniform, thereby obtaining a humidified mixture (8). Next, the humidified mixture (8) was uniformly placed in a stainless steel container and heat-treated at 180°C for 40 minutes, obtaining a surface-cross-linked water absorbent resin (8).

Next, 2.0 parts by mass of a 2.5% by mass aqueous solution of sodium hydrogen sulfite was added and mixed, and the mixture was further heated at 60°C for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin (8).

[Production Example 9]
A granulated gel (9) was obtained in the same manner as in Production Example 7, except that the amount of 20 mass% disodium ethylenediaminetetraacetate aqueous solution added in the polymerization was 2.64 g, the aqueous sodium hydrogensulfite solution added in the gel crushing was deionized water, and the concentration of the aqueous hydrogen peroxide solution added in the fine powder granulation was 0.1 mass%.

[Production Example 10]
In Production Example 8, except that the amount of 20 mass% disodium ethylenediaminetetraacetate aqueous solution added in polymerization was 2.64 g, the aqueous sodium hydrogensulfite solution added in gel crushing was deionized water, the granulated gel to be combined with the particulate hydrous gel was the granulated gel (9) obtained in Production Example 9, and the concentration of the aqueous sodium hydrogensulfite solution added after surface crosslinking was 5.0 mass%, a water absorbent resin (10) was obtained in the same manner as in Production Example 8.

[Production Example 11]
A granulated gel (11) was obtained in the same manner as in Production Example 9, except that the chelating agent added in the polymerization was a 20% by mass aqueous solution of trisodium diethylenetriaminepentaacetate.

[Production Example 12]
In Production Example 10, a chelating agent added in polymerization was a 20 mass% aqueous solution of trisodium diethylenetriaminepentaacetate, a granulated gel to be combined with a particulate hydrogel was the granulated gel (11) obtained in Production Example 11, and a concentration of an aqueous solution of sodium hydrogen sulfite to be added after surface crosslinking was 7.5 mass%, except that a water absorbent resin (12) was obtained in the same manner as in Production Example 10.

[Production Example 13]
A granulated gel (13) was obtained in the same manner as in Production Example 11, except that the amount of 20% by mass disodium ethylenediaminetetraacetate aqueous solution added in the polymerization was 1.32 g, and the 0.1% by mass hydrogen peroxide aqueous solution added in the fine powder granulation was changed to a 0.2% by mass sodium hydrogen sulfite aqueous solution.

[Production Example 14]
A water absorbent resin (14) was obtained in the same manner as in Production Example 12, except that in Production Example 12, the amount of 20 mass% disodium ethylenediaminetetraacetate aqueous solution added in the polymerization was 1.32 g, the granulated gel to be combined with the particulate hydrogel was the granulated gel (13) obtained in Production Example 13, and the concentration of the sodium hydrogensulfite aqueous solution added after surface crosslinking was 5.0 mass%.

[Production Example 15]
A granulated gel (15) was obtained in the same manner as in Production Example 13, except that the concentration of the disodium ethylenediaminetetraacetate aqueous solution added in the polymerization was 1.0 mass%, and the aqueous sodium hydrogensulfite solution added in the fine powder granulation was an aqueous sodium sulfite solution.

[Production Example 16]
In Production Example 14, except that the concentration of the disodium ethylenediaminetetraacetate aqueous solution added in the polymerization was 1.0 mass%, the granulated gel to be combined with the particulate hydrogel was the granulated gel (15) obtained in Production Example 15, and the sodium hydrogensulfite aqueous solution to be added after the surface crosslinking was an aqueous sodium sulfite solution, a water absorbent resin (16) was obtained in the same manner as in Production Example 14.

[Production Example 17]
In Production Example 7, the amount of 10 mass% polyethylene glycol diacrylate (weight average molecular weight: 523) aqueous solution added in the polymerization was 2.04 g, the amount of 20 mass% disodium ethylenediaminetetraacetate aqueous solution was 3.97 g, and the amount of deionized water was 246.3 g, the concentration of the sodium hydrogensulfite aqueous solution added in the gel crushing was 1.0 mass%, and the concentration of the hydrogen peroxide aqueous solution added in the fine powder granulation was 0.3 mass%, except that a granulated gel (17) was obtained in the same manner as in Production Example 7.

[Production Example 18]
In Production Example 8, the amount of 10 mass% polyethylene glycol diacrylate (weight average molecular weight: 523) aqueous solution added in the polymerization was 2.04 g, the amount of 20 mass% disodium ethylenediaminetetraacetate aqueous solution was 3.97 g, and the amount of deionized water was 246.3 g, the concentration of the sodium hydrogensulfite aqueous solution added in the gel crushing was 1.0 mass%, and the granulated gel to be combined with the particulate hydrous gel was the granulated gel (17) obtained in Production Example 17. Except for this, a water absorbent resin (18) was obtained in the same manner as in Production Example 8.

[Production Example 19]
A granulated gel (19) was obtained in the same manner as in Production Example 17, except that in Production Example 17, the amount of 20 mass% disodium ethylenediaminetetraacetate aqueous solution added in the polymerization was 1.32 g, the concentration of the sodium hydrogensulfite aqueous solution added in the gel crushing was 1.2 mass%, and the concentration of the hydrogen peroxide aqueous solution added in the fine powder granulation was 0.2 mass%.

[Production Example 20]
In Production Example 18, except that the amount of 20 mass% disodium ethylenediaminetetraacetate aqueous solution added in polymerization was 1.32 g, the concentration of the sodium hydrogensulfite aqueous solution added in gel crushing was 1.2 mass%, the granulated gel to be combined with the particulate hydrogel was the granulated gel (19) obtained in Production Example 19, and the sodium hydrogensulfite aqueous solution added after surface crosslinking was deionized water, a water absorbent resin (20) was obtained in the same manner as in Production Example 18.

[Production Example 21]
A granulated gel (21) was obtained in the same manner as in Production Example 17, except that the chelating agent added in the polymerization was 0.66 g of a 20 mass % aqueous solution of pentasodium ethylenediaminetetramethylenephosphonate.

[Production Example 22]
A water absorbent resin (22) was obtained in the same manner as in Production Example 18, except that in Production Example 18, the chelating agent added in the polymerization was 0.66 g of a 20 mass% aqueous solution of pentasodium ethylenediaminetetramethylenephosphonic acid, and the granulated gel to be combined with the particulate hydrogel was the granulated gel (21) obtained in Production Example 21.

[Production Example 23]
A granulated gel (23) was obtained in the same manner as in Production Example 21, except that in Production Example 21, the amount of 20 mass% pentasodium ethylenediaminetetramethylenephosphonate aqueous solution added in the polymerization was 3.97 g, the concentration of the aqueous sodium hydrogensulfite solution added in the gel crushing was 0.8 mass%, and the 0.3 mass% aqueous hydrogen peroxide solution added in the fine powder granulation was changed to a 0.2 mass% aqueous sodium hydrogensulfite solution.

[Production Example 24]
In Production Example 22, except that the amount of 20 mass% pentasodium ethylenediaminetetramethylenephosphonic acid aqueous solution added in polymerization was 3.97 g, the concentration of the aqueous sodium hydrogensulfite solution added in gel crushing was 0.8 mass%, the granulated gel to be combined with the particulate hydrous gel was the granulated gel (23) obtained in Production Example 23, and the concentration of the aqueous sodium hydrogensulfite solution added after surface crosslinking was 1.25 mass%, a water absorbent resin (24) was obtained in the same manner as in Production Example 22.

[Production Example 25]
A granulated gel (25) was obtained in the same manner as in Production Example 23, except that in Production Example 23, the amount of 20 mass% pentasodium ethylenediaminetetramethylenephosphonate aqueous solution added in the polymerization was 1.32 g, the aqueous sodium hydrogensulfite solution added in the gel crushing was an aqueous sodium sulfite solution, and the aqueous sodium hydrogensulfite solution added in the fine powder granulation was an aqueous sodium sulfite solution.

[Production Example 26]
In Production Example 24, except that the amount of 20 mass% pentasodium ethylenediaminetetramethylenephosphonate aqueous solution added in polymerization was 1.32 g, the aqueous sodium hydrogensulfite solution added in gel crushing was an aqueous sodium sulfite solution, the granulated gel combined with the particulate hydrogel was the granulated gel (25) obtained in Production Example 25, and the aqueous sodium hydrogensulfite solution added after surface crosslinking was an aqueous sodium sulfite solution, a water absorbent resin (26) was obtained in the same manner as in Production Example 24.

[Production Example 27]
A water-absorbent resin (27) was obtained in the same manner as in Production Example 8, except that the dried polymer (8) was pulverized twice with a roll mill.

[Production Example 28]
In Production Example 27, after pulverization, the product was classified using two types of JIS standard sieves having openings of 850 μm and 106 μm with a Rotap type sieve classifier in the same manner as in Production Example 27, except that a water absorbent resin (28) was obtained.

[Example 25]
1.25 parts by mass (0.5 parts by mass in terms of solid content) of 40% by mass of water-dispersible emulsion A (styrene / butyl acrylate / 2-isopropenyl-2-oxazoline / divinylbenzene = 58.1 / 21.8 / 20.0 / 0.1 mass%, Log P = 3.29, average particle size: 80 nm) was added and mixed with 100 parts by mass of the water-absorbent resin (8) obtained in Production Example 8, and the mixture was further heated at 60 ° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin composition (25). The cumulative particle size and span value, deodorization test results, CRC, and AAP measurement results are shown in Table 2.

[Example 26]
A water absorbent resin composition (26) was obtained in the same manner as in Example 25, except that the water absorbent resin (8) in Example 25 was changed to the water absorbent resin (10) obtained in Production Example 10. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Example 27]
A water absorbent resin composition (27) was obtained in the same manner as in Example 25, except that the water absorbent resin (8) in Example 25 was changed to the water absorbent resin (12) obtained in Production Example 12. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Example 28]
A water absorbent resin composition (28) was obtained in the same manner as in Example 25, except that the water absorbent resin (8) was changed to 100 parts by mass of the water absorbent resin (14) obtained in Production Example 14. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Example 29]
A water absorbent resin composition (29) was obtained in the same manner as in Example 25, except that the water absorbent resin (8) in Example 25 was changed to the water absorbent resin (16) obtained in Production Example 16. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Example 30]
2 parts by mass (0.5 parts by mass in terms of solid content) of 25% by mass of water-soluble polymer B (2-isopropenyl-2-oxazoline / ethyl acrylate / methyl methacrylate / methoxypolyethylene glycol acrylate (n = 9) = 50 / 22 / 3 / 25% by mass, weight average molecular weight = about 40,000, Log P = 1.07) was added and mixed with 100 parts by mass of the water-absorbent resin (18) obtained in Production Example 18, and the mixture was heated at 60 ° C. for 30 minutes. Thereafter, the mixture was crushed and passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin composition (30). The cumulative particle size and span value, deodorization test results, CRC, and AAP measurement results are shown in Table 2.

[Example 31]
A water absorbent resin composition (31) was obtained in the same manner as in Example 30, except that the water absorbent resin (18) in Example 30 was changed to the water absorbent resin (20) obtained in Production Example 20. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Example 32]
A water absorbent resin composition (32) was obtained in the same manner as in Example 30, except that the water absorbent resin (18) in Example 30 was changed to the water absorbent resin (22) obtained in Production Example 22. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Example 33]
A water absorbent resin composition (33) was obtained in the same manner as in Example 30, except that the water absorbent resin (18) in Example 30 was changed to the water absorbent resin (24) obtained in Production Example 24. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Example 34]
A water absorbent resin composition (34) was obtained in the same manner as in Example 30, except that the water absorbent resin (18) in Example 30 was changed to the water absorbent resin (26) obtained in Production Example 26. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Example 35]
A water absorbent resin composition (35) was obtained in the same manner as in Example 30, except that the water absorbent resin (18) in Example 30 was changed to the water absorbent resin (27) obtained in Production Example 27. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Example 36]
A water absorbent resin composition (36) was obtained in the same manner as in Example 14, except that the water absorbent resin (1) in Example 14 was changed to the water absorbent resin (27) obtained in Production Example 27. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 8]
The water-absorbent resin (8) obtained in Production Example 8 was used as it was as a comparative water-absorbent resin composition (8). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 9]
The water absorbent resin (10) obtained in Production Example 10 was used as it was as a comparative water absorbent resin composition (9). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 10]
The water absorbent resin (12) obtained in Production Example 12 was used as it was as a comparative water absorbent resin composition (10). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 11]
The water absorbent resin (14) obtained in Production Example 14 was used as it was as a comparative water absorbent resin composition (11). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 12]
The water absorbent resin (16) obtained in Production Example 16 was used as it was as a comparative water absorbent resin composition (12). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 13]
The water absorbent resin (18) obtained in Production Example 18 was used as it was as a comparative water absorbent resin composition (13). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 14]
The water absorbent resin (20) obtained in Production Example 20 was used as it was as a comparative water absorbent resin composition (14). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 15]
The water absorbent resin (22) obtained in Production Example 22 was used as it was as a comparative water absorbent resin composition (15). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 16]
The water absorbent resin (24) obtained in Production Example 24 was used as it was as a comparative water absorbent resin composition (16). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 17]
The water absorbent resin (26) obtained in Production Example 26 was used as it was as a comparative water absorbent resin composition (17). The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 18]
A comparative water absorbent resin composition (18) was obtained in the same manner as in Example 30, except that the water absorbent resin (18) in Example 30 was changed to the water absorbent resin (28) obtained in Production Example 28. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

[Comparative Example 19]
A comparative water absorbent resin composition (19) was obtained in the same manner as in Example 14, except that the water absorbent resin (1) in Example 14 was changed to the water absorbent resin (28) obtained in Production Example 28. The cumulative particle size and span value, the deodorization test results, and the CRC and AAP measurement results are shown in Table 2.

<Considerations>
The following considerations are made from the results shown in Table 1. Note that a deodorization test result of 3.00 or more means that the desired effect of the present application is not being obtained, and a deodorization test result of less than 3.00 means that the desired effect of the present application is being obtained.

Comparing Comparative Examples 1, 8 to 17 with the Examples, it can be seen that the water-absorbent resin composition containing at least one of the components of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle significantly reduced the intensity level of urine odor in the deodorization test, and has a high urine odor suppression effect. In particular, comparing Example 1 with Example 23, it can be seen that the urine odor suppression effect is further improved by using a hydrophobic porous polymer adsorbent in combination with a resin having a nitrogen-containing heterocycle.

On the other hand, when comparing Comparative Examples 2, 18, and 19 with the Examples, it can be seen that even if the composition contains at least one of the components of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle, if the span value is outside the range of the present invention, the urine odor suppression effect obtained is significantly reduced.

In addition, from Comparative Examples 3 and 4, when microparticles without a pore structure or zeolite, an inorganic porous adsorbent, are used instead of the hydrophobic porous polymer, a sufficient deodorizing effect cannot be obtained even though the total specific surface area of the adsorbent is about the same as in the Examples. This shows that the adsorbent needs to be a hydrophobic porous polymer with a pore structure.

Furthermore, Comparative Example 5 shows that even when potassium peroxomonosulfate, which is said to bind with odor-causing substances such as ammonia, trimethylamine, and dimethyl disulfide and exhibit a deodorizing effect, is used instead of the hydrophobic porous polymer adsorbent, a sufficient deodorizing effect cannot be obtained.

Furthermore, Comparative Example 6 shows that when a resin that contains nitrogen but is not a heterocyclic compound is used, the urine odor suppression effect is not obtained.

Furthermore, Comparative Example 7 shows that when a resin having a nitrogen-containing heterocycle is added to a water-absorbent resin and then heated at a temperature expected during surface treatment, the urine odor suppression effect is not obtained.

Therefore, in order to solve the problem of the present invention, it is important that the composition "contains a water-absorbent resin and at least one of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle, and has a span value that is less than or equal to a specific value."

This application is based on Japanese Patent Application No. 2020-176572, filed on October 21, 2020, the disclosure of which is hereby incorporated by reference in its entirety.

Claims (14)

The present invention relates to a water-absorbent resin, and at least one of a hydrophobic porous polymer adsorbent and a resin having a nitrogen-containing heterocycle,
the nitrogen-containing heterocycle is selected from a pyridine ring, a pyrazine ring, a triazine ring, a pyrimidine ring, a pyridazine ring, an imidazole ring, an oxazole ring, an oxadiazole ring, a triazole ring, a pyrazole ring, or an oxazoline ring;
A water-absorbent resin composition having a span value represented by the following formula 1 of 1.10 or less.

D(90%) is the particle size at which the cumulative particle size distribution from the minimum diameter is 90% (unit: μm)
D(10%) is the particle size (unit: μm) at which the cumulative particle size distribution from the minimum diameter is 10%.
D(50%) is the particle size at which the cumulative particle size distribution from the minimum diameter is 50% (unit: μm)
Here, D(90%), D(10%), and D(50%) are cumulative values based on mass. 2. The water-absorbing resin composition according to claim 1 , wherein the resin having a nitrogen-containing heterocycle is a water-insoluble or water-dispersible polymer having a LogP of 1.5 or more as defined by the following formula 1:

(In formula 1, VMLogP(i) is the calculated value of the "n-octanol-water partition coefficient" at 25°C of a virtual monomer unit (VM) in which both ends of a polymer repeating unit (i) are methylated, and MR(i) is the "molar ratio (Mol Ratio (MR))" of the repeating unit (i).) 3. The water-absorbing resin composition according to claim 2 , wherein the average particle diameter of the resin having a nitrogen-containing heterocycle is 50 to 250,000 nm. The water-absorbing resin composition according to any one of claims 1 to 3 , wherein the hydrophobic porous polymer adsorbent is a porous polymer containing a constitutional unit derived from a hydrophobic monomer and having an average pore diameter of 50 to 1000 Å. The water-absorbing resin composition according to any one of claims 1 to 4 , wherein the specific surface area of the hydrophobic porous polymer adsorbent is 20 to 2000 m ² /g. The water-absorbing resin composition according to any one of claims 1 to 5 , wherein the content of the resin having a nitrogen-containing heterocycle is 0.01 to 30 parts by mass based on 100 parts by mass of the water-absorbing resin. The water-absorbent resin composition according to any one of claims 1 to 5 , wherein the content of said hydrophobic porous polymer adsorbent is 0.05 to 10 parts by mass relative to 100 parts by mass of said water-absorbent resin. The water-absorbing resin composition according to any one of claims 1 to 7 , which has a contact angle of 35° or more. The water-absorbing resin composition according to any one of claims 1 to 8 , further comprising a binder that binds the water-absorbing resin and the component. The water-absorbing resin composition according to claim 9 , wherein the binder is a polyol. The water-absorbing resin composition according to any one of claims 1 to 10 , further comprising a chelating agent. The water absorbent resin composition according to any one of claims 1 to 11 , wherein the water absorbent resin has a water absorption capacity under pressure (AAP 4.83 kPa) of 5 g/g or more. An absorbent comprising the water-absorbent resin composition according to any one of claims 1 to 12 . An absorbent article comprising the absorbent body according to claim 13 , a liquid-permeable top sheet, and a liquid-impermeable back sheet.