Water-absorbing resin composition

Abstract

[Problem] To provide a novel water-absorbing resin composition capable of further improving reduction of urine smell as compared to the prior art, and of suppressing reappearance of a foul smell in a high temperature environment. [Solution] A water-absorbing resin composition containing a water-absorbing resin, a copper silicate, and a chelating agent.

Description

Water absorbent resin composition

[0001] The present invention relates to a water-absorbent resin composition.

[0002] Water-absorbent resins are widely used in sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads for the purpose of absorbing body fluids such as urine and blood, and are a major 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.

[0003] In recent years, a composition comprising an inorganic antibacterial agent in which an antibacterial metal such as silver, copper, or zinc is supported on an inorganic compound and a water-absorbent resin has been proposed as a composition for suppressing odor generation (see, for example, Patent Document 1). The inorganic antibacterial agent used in this composition has long-lasting antibacterial activity, and is therefore considered suitable for use in sanitary materials and the like.

[0004] International Publication No. 2006-046496

[0005] However, there was a problem that the bad odor that had been removed could return if the storage temperature was high. For example, if used diapers were thrown in the trash and stored in a hot environment such as summer, the bad odor would return.

[0006] Therefore, an object of the present invention is to provide a novel water-absorbing resin composition that can further improve the reduction of urine odor compared to conventional compositions and can also prevent the return of bad odor in high-temperature environments.

[0007] One aspect for achieving the above object is a water-absorbent resin composition containing a water-absorbent resin, a copper silicate, and a chelating agent.

[0008] According to the present invention, it is possible to provide a novel water-absorbing resin composition that can further improve the reduction of urine odor compared to conventional compositions and can also prevent the return of bad odor in high-temperature environments.

[0009] The present invention will now be described with reference to the best mode. Throughout this specification, singular expressions should be understood to include the plural concept unless otherwise specified. Therefore, singular articles (e.g., "a," "an," "the," etc. in English) should be understood to include the plural concept unless otherwise specified. Furthermore, unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20-25°C). "Mass" and "weight," "parts by mass" and "parts by weight," "%," "mass %," "wt %," "ppm by mass," and "ppm by weight" are all treated as having the same meaning. Furthermore, terms used in this specification should be understood to have the meaning commonly used in the relevant field unless otherwise specified. Therefore, unless otherwise defined, all technical and scientific 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 conflict, the present specification (including definitions) will prevail. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the claims. It should be understood that all combinations of the lower and upper limits disclosed in this specification are disclosed, that is, they may be grounds for amendment. It should be understood that all combinations of the embodiments are disclosed in this application, that is, they may be grounds for amendment.

[0010] One aspect for achieving the above object is a water-absorbent resin composition comprising a water-absorbent resin, a copper silicate, and a chelating agent. With this configuration, it is possible to provide a novel water-absorbent resin composition that further improves urine odor reduction compared to conventional compositions and can also suppress the recurrence of bad odors in high-temperature (e.g., 40°C) environments.

[0011] [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, and is generally in a powder form. Furthermore, "water-swellable" means that the absorbency under no load (CRC) as defined in EDANA WSP241.3(10) described below is 5 g / g or more, and "water-insoluble" means that the extractable content (Ext) as defined in EDANA WSP270.3(10) is 50 mass% or less.

[0012] The "water-absorbent resin" is preferably a hydrophilic cross-linked polymer (so-called internally cross-linked polymer) obtained by cross-linking polymerizing an unsaturated monomer having a carboxyl group, but the entire amount (100% by mass) does not need to be a cross-linked polymer.

[0013] In general, the term "water-absorbent resin" may refer to a "polymer crosslinked only internally (i.e., a polymer in which the crosslink density is substantially the same internally and on the surface)" or a "polymer crosslinked internally and on the surface (i.e., a polymer in which the crosslink density on the surface is relatively high compared to the crosslink density in the internally)." A polymer crosslinked only internally may be referred to as a "base polymer."

[0014] The "water-absorbent resin composition" in the present invention means a composition containing a water-absorbent resin, a copper silicate, a chelating agent, and optionally other components, but simply means a water-absorbent resin that is ready for shipment as a final product. Therefore, when a water-absorbent resin contains copper silicate, a chelating agent, and optionally 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."

[0015] [1-2] "EDANA", "WSP", "NWSP" "EDANA" is an abbreviation for European Disposables and Nonwovens Associations. Furthermore, "WSP" is an abbreviation for Worldwide Strategic Partners, and indicates a global standard measurement method for water-absorbent resins provided by EDANA. "NWSP" stands for "Non-Woven Standard Procedures-Edition 2015". 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).

[0016] [1-2-1] "CRC" (WSP241.3(10)) "CRC," which means absorption capacity under no load, is an abbreviation for Centrifuge Retention Capacity, and means absorption capacity under no load. Specifically, 0.2 g of a measurement object (for example, a water-absorbing agent or a water-absorbing resin) is placed in a nonwoven bag, and then immersed in a large excess of a 0.9% by mass aqueous solution of sodium chloride for 30 minutes to allow free swelling, and then dehydrated using a centrifuge (250 G) for 3 minutes, after which the absorption capacity (unit: g / g) is measured.

[0017] [1-2-2] "AAP" (NWSP 242.0.R2(15)) "AAP" meaning absorption capacity under pressure is an abbreviation for Absorption Against Pressure, and means the water absorption capacity ("water absorption capacity" is also referred to as "absorption capacity") of a measurement object (for example, a water-absorbing agent or a water-absorbing resin) under pressure. Specifically, AAP 0.3 psi (2.06 kPa) is obtained by subjecting 0.9 g of a measurement object (for example, a water-absorbing agent or a water-absorbing resin) to a large excess of a 0.9 mass % sodium chloride aqueous solution for 1 hour at 2.06 kPa (= 21 g / cm ２ This refers to the water absorption capacity (unit: g / g) after swelling under a load (=0.3 psi).

[0018] [2] Water-absorbent resin composition and method for producing the same A water-absorbent resin composition according to one embodiment of the present invention is a water-absorbent resin composition containing a water-absorbent resin, a copper silicate, and a chelating agent.

[0019] (Water-absorbent resin) In one embodiment of the present invention, the water-absorbent resin may be a polyacrylic acid (salt)-based water-absorbent resin, a polysulfonic acid (salt)-based water-absorbent resin, a maleic anhydride (salt)-based water-absorbent resin, a polyacrylamide-based water-absorbent resin, a polyvinyl alcohol-based water-absorbent resin, a polyethylene oxide-based water-absorbent resin, a polyaspartic acid (salt)-based water-absorbent resin, a polyglutamic acid (salt)-based water-absorbent resin, a polyalginic acid (salt)-based water-absorbent resin, a starch-based water-absorbent resin, or a cellulose-based water-absorbent resin. Of these, a polyacrylic acid (salt)-based water-absorbent resin is preferably used.

[0020] 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 having structural units derived from acrylic acid (salt) in the polymer and having a graft component as an optional component.

[0021] Specifically, the polyacrylic acid (salt)-based water-absorbing resin is a water-absorbing resin containing preferably 50 mol % to 100 mol %, more preferably 70 mol % to 100 mol %, still more preferably 90 mol % to 100 mol %, and particularly preferably substantially 100 mol % of acrylic acid (salt) relative to the total monomers involved in the polymerization reaction (excluding the internal crosslinking agent).

[0022] (Copper silicate) The copper silicate of the present invention has a structure in which copper ions and silicate anions in a copper salt are chemically bonded. It is not a mixture of copper salt and silicic acid simply mixed in a solid state, nor is it a substance in which copper is supported on copper-free silicic acid as a base material. In one embodiment of the present invention, the copper silicate contains oxygen atoms. In one embodiment of the present invention, the copper silicate contains sulfur atoms. This embodiment provides a more pronounced effect of suppressing malodors (particularly urine odors) and the effect of suppressing the recurrence of malodors in high-temperature environments. In one embodiment of the present invention, the copper silicate contains sodium atoms. In one embodiment of the present invention, the copper silicate contains aluminum atoms.

[0023] In one embodiment of the present invention, copper silicate can be obtained, for example, by mixing a precursor compound serving as a silicon source (e.g., silicate) with a precursor compound serving as a copper source (e.g., an inorganic copper salt or an organic copper salt) in water, and preferably adding an adjuster (e.g., sulfuric acid) that can adjust the solution to an acidic state. The amounts of the components mixed may be adjusted, for example, to achieve the following atomic ratio and mass ratio. The mixing temperature may be about room temperature (e.g., 10 to 40°C), or the mixture may be heated to a maximum of about 60°C. The mixing time may be, for example, about 1 minute to 3 days. The solid matter is filtered from the mixed solution, washed with ion-exchanged water, dried, and then the dried solid matter is pulverized to obtain powdered copper silicate.

[0024] In one embodiment of the present invention, the copper silicate comprises silicon atoms, copper atoms, sulfur atoms, oxygen atoms, and sodium atoms.

[0025] In one embodiment of the present invention, the atomic ratio of copper atoms to 100 silicon atoms in the copper silicate is 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. In one embodiment of the present invention, the atomic ratio of copper atoms to 100 silicon atoms in the copper silicate is 10 or less, 9 or less, 8 or less, 7 or less, or 6 or less.

[0026] In one embodiment of the present invention, the atomic ratio of sulfur atoms to 100 silicon atoms in the copper silicate is 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. In one embodiment of the present invention, the atomic ratio of sulfur atoms to 100 silicon atoms in the copper silicate is 10 or less, 9 or less, 8 or less, or 7 or less.

[0027] In one embodiment of the present invention, the atomic ratio of oxygen atoms to silicon atoms in the copper silicate is 200 or more, 250 or more, 300 or more, 350 or more, 400 or more, 450 or more, or 500 or more relative to 100 silicon atoms. In one embodiment of the present invention, the atomic ratio of oxygen atoms to silicon atoms in the copper silicate is 900 or less, 850 or less, 800 or less, 750 or less, 700 or less, 650 or less, or 600 or less relative to 100 silicon atoms.

[0028] In one embodiment of the present invention, the atomic ratio of sodium atoms to 100 silicon atoms in the copper silicate is 5 or more, 10 or more, 15 or more, or 20 or more. In one embodiment of the present invention, the atomic ratio of sodium atoms to 100 silicon atoms in the copper silicate is 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, or 25 or less.

[0029] In one embodiment of the present invention, the weight ratio of copper atoms in the copper silicate to 100 silicon atoms is 5 or more, 7 or more, 9 or more, or 10 or more. In one embodiment of the present invention, the weight ratio of copper atoms in the copper silicate to 100 silicon atoms is 20 or less, 18 or less, 16 or less, 14 or less, or 13 or less.

[0030] In one embodiment of the present invention, the weight ratio of sulfur atoms in the copper silicate to 100 silicon atoms is 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. In one embodiment of the present invention, the weight ratio of sulfur atoms in the copper silicate to 100 silicon atoms is 10 or less, 9 or less, 8 or less, or 7 or less.

[0031] In one embodiment of the present invention, the weight ratio of oxygen atoms in the copper silicate to 100 silicon atoms is 100 or more, 200 or more, 250 or more, or 300 or more. In one embodiment of the present invention, the weight ratio of oxygen atoms in the copper silicate to 100 silicon atoms is 600 or less, 550 or less, 500 or less, 450 or less, 400 or less, or 350 or less.

[0032] In one embodiment of the present invention, the weight ratio of sodium atoms in the copper silicate per 100 silicon atoms is 5 or more, 10 or more, 15 or more, or 17 or more. In one embodiment of the present invention, the weight ratio of sodium atoms in the copper silicate per 100 silicon atoms is 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, 25 or less, or 20 or less.

[0033] In one embodiment of the present invention, the copper silicate comprises silicon atoms, copper atoms, sulfur atoms, oxygen atoms, and aluminum atoms.

[0034] In one embodiment of the present invention, the atomic ratio of copper atoms to 100 silicon atoms in the copper silicate is 10 or more, 15 or more, 20 or more, 25 or more, 30 or more, or 35 or more. In one embodiment of the present invention, the atomic ratio of copper atoms to 100 silicon atoms in the copper silicate is 60 or less, 55 or less, 50 or less, 45 or less, or 40 or less.

[0035] In one embodiment of the present invention, the atomic ratio of sulfur atoms to 100 silicon atoms in the copper silicate is 0.01 or more, 0.05 or more, or 0.1 or more. In one embodiment of the present invention, the atomic ratio of sulfur atoms to 100 silicon atoms in the copper silicate is 2 or less, 1 or less, 0.8 or less, or 0.5 or less.

[0036] In one embodiment of the present invention, the atomic ratio of oxygen atoms to silicon atoms in the copper silicate is 400 or more, 450 or more, 500 or more, 550 or more, 600 or more, or 650 or more relative to 100 silicon atoms. In one embodiment of the present invention, the atomic ratio of oxygen atoms to silicon atoms in the copper silicate is 1100 or less, 1000 or less, 900 or less, 850 or less, 800 or less, or 750 or less relative to 100 silicon atoms.

[0037] In one embodiment of the present invention, the atomic ratio of aluminum atoms to 100 silicon atoms in the copper silicate is 0.01 or more, 0.05 or more, 0.1 or more, 0.5 or more, 1 or more, or 2 or more. In one embodiment of the present invention, the atomic ratio of aluminum atoms to 100 silicon atoms in the copper silicate is 10 or less, 7 or less, 5 or less, 3 or less, 2.5 or less, or 2 or less.

[0038] In one embodiment of the present invention, the weight ratio of copper atoms in the copper silicate to 100 silicon atoms is 40 or more, 50 or more, 60 or more, or 70 or more. In one embodiment of the present invention, the weight ratio of copper atoms in the copper silicate to 100 silicon atoms is 200 or less, 150 or less, or 100 or less.

[0039] In one embodiment of the present invention, the weight ratio of sulfur atoms in the copper silicate per 100 silicon atoms is 0.001 or more, 0.005 or more, 0.008 or more, or 0.01 or more. In one embodiment of the present invention, the weight ratio of sulfur atoms in the copper silicate per 100 silicon atoms is 5 or less, 3 or less, 1 or less, or 0.5 or less.

[0040] In one embodiment of the present invention, the weight ratio of oxygen atoms in the copper silicate to 100 silicon atoms is 150 or more, 200 or more, 250 or more, 300 or more, 350 or more, or 400 or more. In one embodiment of the present invention, the weight ratio of oxygen atoms in the copper silicate to 100 silicon atoms is 700 or less, 600 or less, 500 or less, or 450 or less.

[0041] In one embodiment of the present invention, the weight ratio of aluminum atoms in the copper silicate to 100 silicon atoms is 0.01 or more, 0.05 or more, 0.1 or more, 0.5 or more, 1 or more, or 2 or more. In one embodiment of the present invention, the weight ratio of aluminum atoms in the copper silicate to 100 silicon atoms is 10 or less, 7 or less, 5 or less, 3 or less, 2.5 or less, or 2 or less.

[0042] In this specification, the atomic ratio and weight ratio can be calculated by SEM-EDS analysis using a scanning electron microscope.

[0043] In one embodiment of the present invention, copper accounts for 50% by mass or more, 60% by mass or more, or 70% by mass or more of all polyvalent metal components contained in the copper silicate (upper limit: 100% by mass).

[0044] In one embodiment of the present invention, the copper silicate has an amorphous structure. This embodiment can improve the effect of suppressing malodors (particularly urine odors). Whether the copper silicate has an amorphous structure can be confirmed, for example, by X-ray crystal structure analysis.

[0045] In one embodiment of the present invention, the volume average particle size of the copper silicate is 0.1 to 100 μm, 0.5 to 50 μm, or 1 to 20 μm. The volume average particle size of the copper silicate can be measured using a laser diffraction particle size distribution analyzer.

[0046] In one embodiment of the present invention, the solubility of the copper silicate in ion-exchanged water at 25°C is 0.5 g / 100 mL-H ２ O or less, 0.3g / 100mL-H ２ 0 or less, or 0.1g / 100mL-H ２ 0 or less. By adopting such an embodiment, the copper silicate is prevented from penetrating into the water-absorbent resin, and the intended effect of the present invention can be efficiently achieved. For example, the solubility is determined by adding 0.1 g of the test substance to a 100 mL beaker, adding 20 g of ion-exchanged water at 20°C, and if insoluble matter is visually confirmed after 24 hours, the solubility is 0.5 g / 100 mL-H ２ Similarly, by changing the amount of water using the above method and visually checking for the presence or absence of insoluble matter, it is possible to easily determine whether the solubility is equal to or less than a predetermined value.

[0047] In one embodiment of the present invention, when the copper silicate contains zinc, the mass ratio of the zinc content to the silicon content in the copper silicate (zinc content / silicon content) is less than 50 / 50, less than 10 / 50, or less than 1 / 50.

[0048] In one embodiment of the present invention, the copper silicate does not contain zinc, zinc atoms.

[0049] In one embodiment of the present invention, the content of the copper silicate relative to the water absorbent resin is 0.01 to 10 mass%, 0.05 to 9 mass%, 0.1 to 8 mass%, 0.2 to 7 mass%, 0.3 to 6 mass%, 0.4 to 5 mass%, 0.5 to 4 mass%, 0.6 to 3 mass%, or 0.7 to 2 mass%.

[0050] (Chelating Agent) In one embodiment of the present invention, the chelating agent may be a compound having a chelating effect that captures metals. In one embodiment of the present invention, the chelating agent includes at least one compound selected from the group consisting of amino polycarboxylic acids, amino polyphosphates, and salts thereof.

[0051] The term "polyvalent" refers to the presence of multiple functional groups in one molecule, preferably 2 to 30, more preferably 3 to 20, even more preferably 4 to 10, and still more preferably 5 to 9 functional groups.

[0052] The molecular weight of the chelating agent is preferably 100 to 5,000, more preferably 150 to 1,000, from the viewpoint of its influence on polymerization and the physical properties of the resulting water-absorbing resin composition.

[0053] Specific examples of the amino polycarboxylic acid or salt thereof (amino polycarboxylic acid-based chelating agent) include iminodiacetic acid, hydroxyethyliminodiacetic acid, nitrilotriacetic acid, nitrilotripropionic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, trans-1,2-diaminocyclohexanetetraacetic acid, N,N-bis(2-hydroxyethyl)glycine, diaminopropanoltetraacetic acid, ethylenediamine2propionic acid, N-hydroxyethylethylenediaminetriacetic acid, glycol etherdiaminetetraacetic acid, diaminopropanetetraacetic acid, N,N'-bis(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid, 1,6-hexamethylenediamine-N,N,N',N'-tetraacetic acid, and salts thereof.

[0054] Specific examples of the amino polyphosphate or salts thereof (amino polyphosphate-based chelating agents) include ethylenediamine-N,N'-di(methylenephosphinic acid), ethylenediaminetetra(methylenephosphinic acid), cyclohexanediaminetetra(methylenephosphonic acid), ethylenediamine-N,N'-diacetic acid-N,N'-di(methylenephosphonic acid), ethylenediamine-N,N'-di(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), polymethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), and salts thereof.

[0055] Among these, from the viewpoint of suppressing malodors, amino polycarboxylic acid chelating agents having four or more (or five or more) carboxyl groups or amino polyphosphate chelating agents having four or more (or five or more) phosphonic acid groups are preferred. In one embodiment of the present invention, from the viewpoint of suppressing malodors, diethylenetriaminepentaacetic acid, nitrilotriacetic acid, triethylenetetraminehexaacetic acid, ethylenediaminetetra(methylenephosphonic acid), and salts thereof are more preferred.

[0056] In one embodiment of the present invention, salts of chelating agents include, but are not limited to, sodium.

[0057] In one embodiment of the present invention, the chelating agent may be a compound exemplified in US Pat. Nos. 6,599,989, 6,469,080, EP 2,163,302, and the like.

[0058] In one embodiment of the present invention, the content of the chelating agent relative to the water absorbent resin is 10 to 1000 ppm by mass, 20 to 800 ppm by mass, 30 to 600 ppm by mass, 40 to 500 ppm by mass, 50 to 300 ppm by mass, 60 to 200 ppm by mass, or 70 to 150 ppm by mass.

[0059] A preferred method for producing the water-absorbing resin composition will now be described. The method for producing the water-absorbing resin composition of one embodiment of the present invention is, of course, not limited to the following method.

[0060] [2-1] Step of Preparing Aqueous Monomer Solution This step is a step of preparing an aqueous monomer 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 relative to the total amount of monomers (excluding the internal crosslinking agent) used in the polymerization reaction being usually 50 mol % or more, preferably 70 mol % or more, and more preferably 90 mol % or more (upper limit: 100 mol %). Note that a slurry liquid of the monomer 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 describe an aqueous monomer solution.

[0061] (Acrylic Acid (Salt)) In an 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 may contain trace amounts of components such as a polymerization inhibitor and impurities. As the polymerization inhibitor, preferably, a methoxyphenol, more preferably a p-methoxyphenol, is used. From the viewpoint of the polymerizability of acrylic acid and the color tone of the water-absorbing agent, 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). As the impurities, in addition to organic compounds such as acetic acid, propionic acid, and furfural, the compounds described in U.S. Patent Application Publication No. 2008 / 0161512 are also contained in the acrylic acid used in an embodiment of the present invention.

[0062] Examples of the acrylic acid salt include salts obtained by neutralizing the above-mentioned acrylic acid with the following basic compounds (e.g., sodium acrylate). The acrylic acid salt may be a commercially available acrylic acid salt (e.g., sodium acrylate) or a salt obtained by neutralizing acrylic acid.

[0063] (Basic Compound) In an embodiment of the present invention, the basic compound refers to a compound exhibiting basicity, and specifically corresponds to 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 also 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.

[0064] Specific examples of the basic compound include carbonates and hydrogencarbonates of alkali metals, hydroxides of alkali metals, ammonia, organic amines, etc. Among them, a strongly basic compound is selected from the viewpoint of the water absorption performance of the water absorbent. Therefore, hydroxides of alkali metals such as sodium, potassium, and lithium are preferred, and sodium hydroxide is more preferred. Note that the basic compound is preferably in the form of an aqueous solution from the viewpoint of ease of handling.

[0065] (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 carried out before, during, or after polymerization, or may be carried out at multiple times or locations. Moreover, from the viewpoint of production efficiency of the water-absorbing agent, it is preferable to neutralize in a continuous manner.

[0066] In the present invention, when acrylic acid (salt) is used, 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-absorbing agent.

[0067] The range of the neutralization rate is applicable to any of the neutralization before, during, and after the polymerization, and also to the water-absorbing agent as a final product.

[0068] (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 acrylic acid (salt) as needed.

[0069] Specific examples of the other monomers include anionic unsaturated monomers and salts thereof, such as maleic acid (anhydride), 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 used is preferably 30 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less (lower limit: 0 mol %), based on the total amount of the monomers (excluding the internal crosslinking agent).

[0070] (Internal Crosslinking Agent) In a preferred production method, 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. At least one kind of internal crosslinking agent is selected from these internal crosslinking agents in consideration of reactivity, etc. Also, from the viewpoint of the water absorption performance of the water-absorbing agent, an internal crosslinking agent having two or more polymerizable unsaturated groups is preferably selected, an internal crosslinking agent having thermal decomposition properties at a drying temperature is more preferably selected, and an internal crosslinking agent having two or more polymerizable unsaturated groups having a (poly)alkylene glycol structure is further preferably selected.

[0071] Specific examples of the polymerizable unsaturated group include an allyl group and a (meth)acrylate group, and more preferably a (meth)acrylate group. 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.

[0072] 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 amount of monomers (excluding the internal crosslinking agent). By using an amount within this range, a water-absorbent resin or water-absorbing agent having the desired water-absorbing performance can be obtained. Furthermore, it is also preferable to consider adjusting the amount of the internal crosslinking agent in order to set the gel bulk density of the water-absorbent resin or water-absorbing agent within a predetermined range and to suppress an increase in water-soluble content and a decrease in absorbency due to a decrease in gel strength.

[0073] The internal cross-linking agent is preferably added in advance when preparing the aqueous monomer solution, in which case the cross-linking reaction is carried out simultaneously with the polymerization reaction. On the other hand, the polymerization reaction can be started without adding the internal cross-linking agent, and the internal cross-linking agent can be added during or after the polymerization reaction to carry out the cross-linking reaction. These methods can also be used in combination.

[0074] (Substances to be added to 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 of when the aqueous monomer solution is prepared, during the polymerization reaction and the cross-linking reaction, or after the polymerization reaction and the cross-linking reaction.

[0075] Specific examples of such substances include hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol (PVA), polyacrylic acid (salts), and crosslinked polyacrylic acid (salts); carbonates, azo compounds, various foam-generating blowing agents, 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.

[0076] 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 (for example, a starch-acrylic acid (salt) copolymer, a 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.

[0077] (Concentration of Monomer Component) 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, besides preparing the monomer as an aqueous solution, it is also possible to prepare a mixed solution of water and a hydrophilic solvent.

[0078] Moreover, the concentration of the total of the substances (components) (hereinafter also referred to as "monomer component") is preferably 10 mass % to 80 mass %, more preferably 20 mass % to 75 mass %, and even more preferably 30 mass % to 70 mass %, from the viewpoint of the physical properties of the water-absorbing agent. The concentration of the monomer component is calculated by the following formula (2).

[0079]

[0080] In the formula (2), the mass of the aqueous monomer solution does not include the mass of the graft component, the water-absorbent resin, or the hydrophobic organic solvent used in the reversed-phase suspension polymerization.

[0081] [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 internal crosslinking agent, which is obtained in the aqueous monomer solution preparation step, to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel").

[0082] (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 used in combination with a reducing agent that promotes the decomposition of these polymerization initiators. 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 polymerization initiator is selected from these polymerization initiators, taking into consideration factors such as the polymerization form. Furthermore, from the perspective of the handleability of the polymerization initiator and the physical properties of the water-absorbing agent, at least one of a peroxide and an azo compound is preferably selected as the polymerization initiator. Furthermore, when an oxidizing radical polymerization initiator is used, redox polymerization may be performed in combination with a reducing agent such as sodium sulfite, sodium bisulfite, ferrous sulfate, or L-ascorbic acid.

[0083] 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 amount of the monomers (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 amount of the monomers (excluding the internal crosslinking agent). By using an amount within this range, a water-absorbing agent having desired water absorption performance can be obtained.

[0084] 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. Alternatively, irradiation with active energy rays and the polymerization initiator may be used in combination.

[0085] (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 these, from the viewpoint of ease of polymerization control and the water absorption performance of the water-absorbing agent, aqueous solution polymerization or reversed-phase suspension polymerization is preferably selected, more preferably aqueous solution polymerization, and even more preferably continuous aqueous solution polymerization is selected. Reverse-phase suspension polymerization is described in International Publication Nos. 2007 / 004529 and 2012 / 023433. Furthermore, the continuous aqueous solution polymerization can produce water-absorbing agents with high productivity. Specific examples thereof include continuous belt polymerization described in U.S. Pat. Nos. 4,893,999, 6,906,159, 7,091,253, 7,741,400, 8,519,212, and JP-A-2005-36100, and continuous kneader polymerization described in U.S. Pat. No. 6,987,151.

[0086] In one embodiment of the aqueous solution polymerization, the temperature of the aqueous monomer solution at the start of polymerization is adjusted to 10°C or higher and lower than 30°C.

[0087] Preferred forms of the continuous aqueous solution polymerization include high-temperature initiation polymerization, high-concentration polymerization, and foam 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).

[0088] Although each of the above-mentioned polymerization modes can be carried out in an air atmosphere, 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) from the viewpoint of the color tone of the water-absorbing agent. 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 (= ppm)).

[0089] [2-3] Gel Crushing Step This step is a step of crushing 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 below.

[0090] The gel crushing refers to adjusting the hydrogel to a predetermined size using a gel crusher such as a kneader, a meat chopper, or a cutter mill.

[0091] With regard to the embodiments and operating conditions of gel pulverization, the contents described in International Publication No. 2011 / 126079 are preferably applied to the present invention. When the polymerization mode is kneader polymerization, the polymerization step and the gel pulverization step are carried out simultaneously. Furthermore, when a particulate hydrogel is obtained in the polymerization step, such as reversed-phase suspension polymerization, spray polymerization, or droplet polymerization, the gel pulverization step is considered to be carried out simultaneously with the polymerization step. Furthermore, by passing through the gel pulverization step in the present invention, an amorphously crushed water-absorbing resin or water-absorbing agent can be obtained.

[0092] [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.

[0093] Examples of the method for drying the hydrogel and / or particulate hydrogel include 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.

[0094] 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 of the water-absorbing resin or the water-absorbing agent and drying efficiency. Drying conditions other than the drying temperature, such as the hot air speed and drying time, may be appropriately set depending on 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 WO 2006 / 100300, WO 2011 / 025012, WO 2011 / 025013, WO 2011 / 111657, and the like are appropriately applied.

[0095] 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 resin or water-absorbing agent can be set within a desired range. Furthermore, the physical properties of the water-absorbent resin as an intermediate product can also be set within a desired range.

[0096] [2-5] Pulverization step, classification step This step is a step in which the dried polymer obtained through the drying step is pulverized (pulverization step) and adjusted to a particle size within a desired range (classification step) to obtain a water-absorbent resin powder (base polymer). By passing through the pulverization step after drying, it is possible to obtain an irregularly pulverized water-absorbent resin or water-absorbing agent. Pulverization may be performed two or more times as necessary.

[0097] Examples of the mill used in the milling step include high-speed rotary mills such as roll mills, hammer mills, screw mills, and pin mills, as well as vibration mills, knuckle mills, and cylindrical mixers. Among these, a roll mill is preferably selected from the viewpoint of milling efficiency. A plurality of these mills can also be used in combination.

[0098] Examples of a method for adjusting the particle size in the classification step 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 resin or water-absorbing agent is not limited to being performed in the pulverization step or the classification step, and can also be performed in a polymerization step (particularly, reverse phase suspension polymerization or droplet polymerization) or other steps (for example, a granulation step or a fine powder recovery step).

[0099] [2-6] Surface cross-linking step This step is a step of providing a portion with a higher cross-linking density on the surface layer of the base polymer obtained through the above-mentioned steps, and is configured to include a mixing step, a heat treatment step, and, if necessary, a cooling step, etc. In the surface cross-linking step, radical cross-linking, surface polymerization, a cross-linking reaction with a surface cross-linking agent, etc. occur on the surface of the base polymer, and a (surface-cross-linked) water absorbent resin is obtained.

[0100] [2-6-1] Mixing Step This step is a step of mixing a solution containing a surface crosslinking agent (hereinafter referred to as "surface crosslinking agent solution") with a base polymer in a mixer to obtain a humidified mixture.

[0101] (Surface Crosslinking Agent) In one embodiment of the present invention, a surface crosslinking agent is used during surface crosslinking. Specific examples of the surface crosslinking agent include the surface crosslinking agents described in U.S. Pat. No. 7,183,456. At least one type of surface crosslinking agent is selected from these surface crosslinking agents, taking into consideration reactivity and the like. Furthermore, from the viewpoints of the handleability of the surface crosslinking agent and the water absorption performance of the water-absorbing agent, it is preferable to select a surface crosslinking agent having two or more functional groups that react with a carboxyl group, and an organic compound that forms a covalent bond.

[0102] More specifically, examples of the surface cross-linking agent include 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 glycol, 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; poly 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 alkylene carbonate compounds such as 1,3-dioxopan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, and 1,3-dioxopan-2-one; polyglycidyl 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.Preferred surface cross-linking agents 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.

[0103] The amount of the surface crosslinking 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, still 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 crosslinking agent used within this range, an optimal crosslinked 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. Furthermore, adjusting the amount of the surface crosslinking agent according to the type is also effective in optimizing the gel bulk density of the water-absorbing resin or water-absorbing agent.

[0104] The surface crosslinking 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 parts by mass to 20 parts by mass, more preferably 0.3 parts by mass to 15 parts by mass, and even more preferably 0.5 parts by mass 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 crosslinking agent solution is improved, and the surface crosslinking agent can be uniformly mixed with the base polymer.

[0105] In addition, hydrophilic organic solvent can be used in combination with the water as needed to prepare the surface crosslinking agent solution.In this case, the amount of hydrophilic organic solvent used is preferably small so as not to cause 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 base polymer.However, from the viewpoint of carrying out appropriate surface crosslinking, a hydrophilic organic solvent may be added, 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 base polymer.

[0106] 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; and sulfoxides such as dimethyl sulfoxide.

[0107] (Mixing Method and 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 the solution is preferably sprayed or dropped onto the base polymer, more preferably sprayed and mixed.

[0108] [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.

[0109] 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 preferred in order to heat the entire humidified mixture uniformly. From this viewpoint, examples of the heat treatment device for the heat treatment include a paddle dryer, a multi-fin processor, and a tower dryer.

[0110] 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, the water absorption performance of the water-absorbing agent, and the like. The heating time is at least 5 minutes, 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 the water absorption performance of the resulting water-absorbing agent is improved.

[0111] [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, thereby quickly completing the surface cross-linking reaction.

[0112] [2-7] Step of adding chelating agent The water absorbent resin composition of one embodiment of the present invention contains a chelating agent. The chelating agent can be added to a monomer, a hydrogel, a dried polymer, a base polymer (water absorbent resin powder), or a surface-crosslinked water absorbent resin. In one embodiment of the present invention, the chelating agent is added after the polymerization step, after the gel crushing step, after the crushing step / classification step, or after the surface crosslinking step. In particular, it is preferable to add the chelating agent after the surface crosslinking step. The chelating agent may be added simultaneously with or sequentially to the copper silicate after the surface crosslinking step.

[0113] In one embodiment of the present invention, the amount of the chelating agent used is, in terms of active ingredient, 10 to 1000 ppm by mass, 20 to 800 ppm by mass, 30 to 600 ppm by mass, 40 to 500 ppm by mass, 50 to 300 ppm by mass, 60 to 200 ppm by mass, or 70 to 150 ppm by mass with respect to the water absorbent resin.

[0114] In one embodiment of the present invention, a heat treatment may be carried out after the addition of the chelating agent. The temperature for the heat treatment is preferably, for example, 45 to 75°C, 50 to 70°C, or 55 to 65°C. The time for the heat treatment may vary depending on the heating temperature, but is preferably, for example, about 5 to 60 minutes, 10 to 50 minutes, or 15 to 40 minutes. In one embodiment of the present invention, the above heat treatment may be carried out after the addition of the chelating agent, and then the copper silicate may be added.

[0115] [2-8] Step of Adding Copper Silicate The water-absorbent resin composition of one embodiment of the present invention contains copper silicate. The copper silicate can be added to a hydrogel, a dried polymer, a base polymer (water-absorbent resin powder), or a surface-crosslinked water-absorbent resin. In one embodiment of the present invention, the copper silicate is added after the polymerization step, after the gel-crushing step, after the crushing step / classification step, or after the surface-crosslinking step. It is particularly preferable to add the copper silicate after the surface-crosslinking step. By doing so, the abundance ratio of the copper silicate becomes higher on the surface of the water-absorbent resin than inside the water-absorbent resin. Therefore, in one embodiment of the present invention, a water-absorbent resin composition can be provided in which the abundance ratio of the copper silicate is higher on the surface of the water-absorbent resin than inside the water-absorbent resin.

[0116] In one embodiment of the present invention, the amount of copper silicate used is 0.01 to 10 mass%, 0.05 to 9 mass%, 0.1 to 8 mass%, 0.2 to 7 mass%, 0.3 to 6 mass%, 0.4 to 5 mass%, 0.5 to 4 mass%, 0.6 to 3 mass%, or 0.7 to 2 mass%, relative to the water absorbent resin.

[0117] In one embodiment of the present invention, no intentional heat treatment is performed after the copper silicate is added.

[0118] [2-9] Step of Adding a Coloring Inhibitor or a Urine Resistance Improver Generally, water-absorbent resins tend to be easily colored or deteriorated. Therefore, in the present invention, a coloring inhibitor or a urine resistance (weather resistance) improver selected from inorganic or organic reducing agents (particularly sulfur-based inorganic reducing agents) may be further added to prevent coloring or deterioration. The amount of these 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, based on 100 parts by mass of the water-absorbent resin, in terms of solid content. Such a preferred amount 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 coloring inhibitor or the urine resistance improver in the water-absorbent resin composition is each independently 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, based on 100 parts by mass of the water-absorbent resin. 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, particularly after surface crosslinking.

[0119] Examples of inorganic or organic reducing agents (particularly sulfur-based inorganic reducing agents) that can be used include sulfur-based reducing agents exemplified in U.S. Patent Application Publication No. 2010 / 0062252, particularly sulfites or hydrogen sulfites.

[0120] [2-10] Other Steps In the present invention, in addition to the steps described above, it is possible to carry out, as necessary, a granulation step, a sizing step, a fine powder removal step, a fine powder recovery step, a fine powder recycling step, a step of adding other additives, a step of removing iron, etc. Furthermore, the present invention may further include at least one step selected from a transportation step, a storage step, a packaging step, a keeping step, etc.

[0121] The sizing step includes a step of classifying and removing fine powder after the surface cross-linking step, and a step of classifying and pulverizing when the water absorbent resin aggregates and exceeds a desired size. The reusing step of the fine powder includes a step of adding the fine powder as it is or to a large hydrogel in a granulation step, which is a raw material, such as a hydrogel, in any step of a production step of a water absorbent resin.

[0122]

[0033] In addition, in the step of adding the coloring inhibitor or the 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 the urine resistance improver, or instead of the coloring inhibitor or the urine resistance improver. Furthermore, 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.

[0123] [3] Properties of the Water-Absorbent Resin Composition [3-1] Other Properties of the Water-Absorbent Resin Composition In one embodiment of the present invention, the water-absorbent resin composition preferably further has the following properties.

[0124] (3-1-1) Mass Average Particle Diameter (D50) In one embodiment of the present invention, the mass average particle diameter (D50) 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. As the range of the mass average particle diameter (D50), a range obtained by arbitrarily combining the above upper and lower limit values ​​is applied.

[0125] By setting the mass average particle diameter (D50) of the water-absorbent resin composition within the above range, in one embodiment of the present invention described later, it is possible to control the absorption capacity without load (CRC) and the absorption capacity under load (AAP) of the water-absorbent resin composition in a well-balanced manner. In other words, by setting it within the above range, it is possible to increase the absorption capacity without load (CRC) and the absorption capacity under load (AAP), and it is possible to suppress the particle coarseness of the water-absorbent resin, thereby improving the feel on the skin and the wearing comfort when used in absorbent articles such as disposable diapers and sanitary napkins.

[0126] (3-1-2) CRC (absorbency under no 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 a higher value is preferable, but from the viewpoint of 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, a typical 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 can be selected, such as 5 to 70 g / g, 20 to 50 g / g, or 24 to 45 g / g.

[0127] If the CRC is less than 5 g / g, the water absorption capacity of the water-absorbent resin composition is small, and the composition is not suitable for use as an absorbent material in absorbent articles such as disposable 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, and the composition is not suitable for use in high-absorption-rate disposable diapers. The CRC can be controlled by an internal crosslinking agent, a surface crosslinking agent, or the like.

[0128] (3-1-3) AAP (Water Absorption Capacity Under Pressure) In one embodiment of the present invention, the AAP (Water Absorption Capacity Under Pressure) of the water-absorbing 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, still more preferably 22 g / g or more, still more preferably 25 g / g or more, still more preferably 28 g / g or more, still more preferably 30 g / g or more. The upper limit is not particularly limited, but is preferably 40 g / g or less, 35 g / g or less, or 33 g / g or less.

[0129] If the AAP is less than 5 g / g, the absorbency will decrease when pressure is applied to the absorbent when actually used in a disposable diaper, etc., and the absorbent will not be suitable as an absorbent for absorbent articles such as disposable diapers, etc. The AAP can be controlled by the particle size, a surface cross-linking agent, etc.

[0130] [4] Uses of water-absorbent resin composition (absorbent body, absorbent layer) The water-absorbent resin composition according to the present invention is preferably used mainly as an absorbent body (absorbent layer) of absorbent articles such as disposable diapers and sanitary napkins, and more preferably 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, there is provided an absorbent body comprising the water-absorbent resin composition and hydrophilic fibers.

[0131] The absorbent refers to a water-absorbent resin composition formed into a sheet, fiber, or cylindrical shape, and is preferably formed into a sheet to form an absorbent layer. In addition to the water-absorbent 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 even 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-absorbent resin composition used is small, and for example, the deodorizing performance may not be sufficiently imparted to the entire diaper, which is not preferable.

[0132] When the absorbent body according to the present invention is produced from a water-absorbent resin composition and hydrophilic fibers, the production method is not particularly limited, but for example, a method can be mentioned in which the water-absorbent resin composition and the hydrophilic fibers are dry-mixed using a mixer or other mixer in a ratio that gives the above-mentioned core concentration, the resulting mixture is formed into a web by, for example, air papermaking, and then compression-molded as necessary to produce the absorbent body. Such an absorbent body has a density of 0.001 to 0.50 g / cc and a basis weight of 0.01 to 0.20 g / cm. ２ It is preferable that the compression molding is carried out in the range of 1000 to 15000.

[0133] [5] Absorbent Article The absorbent article according to the present invention includes the absorbent body (absorbent layer) and typically 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, there is provided an absorbent article including an absorbent body, a liquid-permeable top sheet, and a liquid-impermeable back sheet.

[0134] When the absorbent article is, for example, a disposable diaper, the disposable diaper is produced by sandwiching an absorbent body containing a water-absorbent resin composition between a liquid-permeable top sheet located on the side that comes into contact with the skin when worn and a liquid-impermeable back sheet located on the outside when worn. The disposable diaper is further provided with members known to those skilled in the art, such as adhesive tape, for fixing the disposable diaper after wearing.

[0135] The water-absorbent resin composition according to the present invention can be suitably used for not only the disposable diapers and sanitary napkins but also for pets and portable toilets.

[0136] The present invention encompasses the following aspects and configurations.

[0137] 1. A water-absorbent resin composition comprising a water-absorbent resin, a copper silicate, and a chelating agent.

[0138] 2. The water-absorbing resin composition according to 1., wherein the chelating agent comprises at least one compound selected from the group consisting of amino polycarboxylic acids, amino polyphosphates, and salts thereof.

[0139] 3. The water-absorbent resin composition according to 1. or 2., wherein the copper silicate is present at a higher ratio on the surface of the water-absorbent resin than inside the water-absorbent resin.

[0140] 4. The water-absorbing resin composition according to any one of 1. to 3., wherein the copper silicate has an amorphous structure.

[0141] 5. The solubility of the copper silicate in ion-exchanged water at 25°C is 0.5 g / 100 mL-H ２ 5. The water-absorbing resin composition according to any one of 1. to 4., wherein the water-absorbing resin composition has a viscosity of 0 or less.

[0142] 6. The water-absorbing resin composition according to any one of 1. to 5., wherein the copper silicate contains a sulfur atom.

[0143] 7. The water-absorbing resin composition according to any one of 1. to 6., wherein copper accounts for 50 mass % or more of all polyvalent metal components contained in the copper silicate.

[0144] 8. The water-absorbent resin composition according to any one of 1. to 7., wherein, when the copper silicate contains zinc, the mass ratio of the zinc content to the silicon content in the copper silicate is less than 50 / 50.

[0145] 9. An absorbent material comprising the water-absorbent resin composition according to any one of 1. to 8. above.

[0146] 10. An absorbent article comprising the absorbent body according to 9 above, a liquid-permeable top sheet, and a liquid-impermeable back sheet.

[0147] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention should not be construed as being limited to these examples and comparative examples. Examples obtained by appropriately combining the technical means disclosed in each example are also included within the scope of the present invention. The electrical equipment used in the examples and comparative examples, as well as for measuring the various physical properties of the water-absorbent resin and water-absorbent resin composition, uses a power supply of 200 V or 100 V / 60 Hz unless otherwise noted. The various physical properties of the water-absorbent resin and water-absorbent resin composition were measured under conditions of room temperature (20°C to 25°C) and a relative humidity of 50±5% RH unless otherwise noted. For convenience, "liter" may be expressed as "l" or "L," and "mass%" as "wt%."

[0148] [Production Example 1] A monomer aqueous solution was prepared by mixing 67.0 parts by mass of a 37% aqueous sodium acrylate solution, 10.2 parts by mass of acrylic acid, 0.084 parts by mass of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9), and 22.0 parts by mass of water. Nitrogen was blown into the monomer aqueous solution in a tray to reduce the dissolved oxygen content in the solution to 0.1 ppm or less. Subsequently, the temperature of the monomer aqueous solution was adjusted to 18°C ​​under a nitrogen atmosphere, and then 0.16 parts by mass of a 5% by mass aqueous sodium persulfate solution, 0.16 parts by mass of a 5% by mass aqueous 2,2'-azobis(2-amidinopropane) dihydrochloride solution, 0.15 parts by mass of a 0.5% by mass aqueous L-ascorbic acid solution, and 0.17 parts by mass of a 0.35% by mass aqueous hydrogen peroxide solution were added dropwise in this order with stirring. Polymerization initiated immediately after the addition of hydrogen peroxide. Stirring was then stopped, and the monomer temperature reached its peak temperature 10 minutes later. The peak temperature was 85°C. The tray was then immersed in a water bath at 80°C and aged for 10 minutes, and the resulting transparent cross-linked hydrogel polymer was crushed with a meat chopper. The crushed cross-linked hydrogel polymer (particulate hydrogel) was then spread on a 50-mesh wire netting (opening size: 300 µm) and dried with hot air at 180°C for 30 minutes to obtain a dried polymer.

[0149] The obtained dried polymer was pulverized in a pulverizer and classified into particles that passed through a 500 μm sieve and remained on a 105 μm sieve, to obtain a water-absorbent resin powder.

[0150]

[0122] 100 parts by mass of the obtained water absorbent resin powder was mixed with a surface crosslinking agent solution consisting of 0.05 part 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, and the mixture was heat-treated at 180°C for 40 minutes, thereby obtaining surface-crosslinked water absorbent resin particles.

[0151] [Example 1] 1.0 part by mass of a 1.0 mass% aqueous solution of diethylenetriaminepentaacetic acid trisodium was added to 100 parts by mass of the surface-crosslinked water-absorbent resin particles obtained in Production Example 1, and the mixture was heated at 60°C for 30 minutes. Thereafter, copper silicate (A) (volume average particle diameter: 7 µm, solubility in ion-exchanged water at 25°C: 0 g / 100 mL-H) satisfying the atomic ratio to Si and the weight ratio to Si shown in Table 1 below was added. ２ 1.0 part by mass of copper silicate (A) was added and mixed to obtain a mixture. Thereafter, the mixture was passed through a JIS standard sieve with an opening of 850 μm to obtain a water-absorbent resin composition (1). The measurement results of various physical properties of the obtained water-absorbent resin composition (1) are shown in Table 5. The copper silicate (A) has an amorphous structure.

[0152] The atomic ratio and weight ratio were measured by SEM-EDS analysis using a scanning electron microscope. Specifically, a JCM-6000 Neoscope tabletop scanning electron microscope (manufactured by JEOL Ltd.) was used to acquire images of the additive at a magnification of 1000x, and the atomic ratio and weight ratio of the constituent elements of the additive were analyzed by energy dispersive X-ray spectroscopy (EDS).

[0153] [Example 2] A water-absorbent resin composition (2) was obtained in the same manner as in Example 1, except that the 1.0 mass% aqueous solution of diethylenetriaminepentaacetic acid trisodium was changed to a 1.0 mass% aqueous solution of ethylenediaminetetra(methylenephosphonic acid) pentasodium. Measurement results of various physical properties of the water-absorbent resin composition (2) are shown in Table 5.

[0154] [Example 3] Copper silicate (A) was replaced with copper silicate (B) (volume average particle size: 3 μm, solubility in ion-exchanged water at 25°C: 0 g / 100 mL-H) whose atomic ratio to Si and weight ratio to Si are shown in the table below. ２A water-absorbent resin composition (3) was obtained in the same manner as in Example 1, except that copper silicate (B) was changed to copper silicate (B). The measurement results of various physical properties of the water-absorbent resin composition (3) are shown in Table 5. The copper silicate (B) has an amorphous structure.

[0155]

[0156] [Comparative Example 1] A comparative water-absorbent resin (1) was obtained in the same manner as in Example 1, except that 1.0 part by mass of the 1.0 mass% diethylenetriaminepentaacetic acid trisodium aqueous solution was changed to 1.0 part by mass of water and copper silicate (A) was not added. The measurement results of various physical property values ​​of the comparative water-absorbent resin (1) are shown in Table 5.

[0157] [Comparative Example 2] Except for not adding the copper silicate (A), a comparative water-absorbent resin composition (2) was obtained in the same manner as in Example 1. The measurement results of various physical properties of the comparative water-absorbent resin composition (2) are shown in Table 5.

[0158] [Comparative Example 3] Except for not adding a chelating agent, a comparative water-absorbent resin composition (3) was obtained in the same manner as in Example 1. The measurement results of various physical properties of the comparative water-absorbent resin composition (3) are shown in Table 5.

[0159] Comparative Example 4 Copper silicate (A) was replaced with a copper-free silicate (volume average particle size: 3.5 μm, solubility in ion-exchanged water at 25° C.: 0 g / 100 mL-H) that satisfied the atomic ratio to Si and weight ratio to Si shown in Table 2 below. ２ A comparative water-absorbing resin composition (4) was obtained in the same manner as in Example 1, except that the water-absorbing resin composition (4) was changed to the water-absorbing resin composition (4) in Example 1. The measurement results of various physical properties of the comparative water-absorbing resin composition (4) are shown in Table 5.

[0160]

[0161] Comparative Example 5 Copper silicate (A) was replaced with copper(II) gluconate (solubility in ion-exchanged water at 25°C is 30 g / 100 mL-H ２ A comparative water-absorbing resin composition (5) was obtained in the same manner as in Example 1, except that the water-absorbing resin composition (5) was changed to the water-absorbing resin composition (5) in Example 1. The measurement results of various physical properties of the comparative water-absorbing resin composition (5) are shown in Table 5.

[0162] [Comparative Example 6] Copper silicate (A) was mixed with copper chlorophyllin Na (solubility in ion-exchanged water at 25°C is 1 g / 100 mL-H ２ A comparative water-absorbing resin composition (6) was obtained in the same manner as in Example 1, except that the water-absorbing resin composition (6) was changed to the water-absorbing resin composition (6) in Example 1. The measurement results of various physical properties of the comparative water-absorbing resin composition (6) are shown in Table 5.

[0163] Comparative Example 7 A comparative water-absorbent resin composition (7) was obtained in the same manner as in Example 1, except that the copper silicate (A) was changed to a copper oxide-zinc oxide composite aluminosilicate (zeolite supporting copper and zinc) (trade name: Dashlight CZU, manufactured by Sinanen Zeomic Co., Ltd., average particle size = 4 µm) having an atomic number ratio to Si and a weight ratio to Si shown in the following Table 3. Table 5 shows the measurement results of various physical property values ​​of the comparative water-absorbent resin composition (7).

[0164]

[0165] [Evaluation of Water Absorbent Resin Composition] (a) Mass Average Particle Diameter (D50) The mass average particle diameter (D50) of a 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 having openings of 850 μm, 710 μm, 600 μm, 500 μm, 300 μm, 150 μm, and 45 μm in order from the top.

[0166] (b) Absorbency Capacity Against No Load (CRC) The CRC of the water-absorbent resin composition was measured in accordance with EDANA Method WSP241.3(10).

[0167] (c) Absorption capacity under load (AAP 0.3 psi) The AAP of the water-absorbent resin composition was measured in accordance with EDANA method NWSP 242.0. R2(15). The load was 0.3 psi (= 21 g / cm ２ = 2.06 kPa).

[0168] (d) Evaluation of Deodorizing Performance for Human Urine A simple absorbent was prepared by mixing 2.0 g of the water-absorbent resin (or water-absorbent resin composition) obtained in the above-described Examples or Comparative Examples with 4.0 g of pulverized wood pulp. The simple absorbent was placed in a 250 ml polypropylene cup with a lid, and 50 ml of human urine collected from multiple adults was poured into it. The human urine used was voided within 2 hours. The container was covered with a lid, and the simple absorbent was kept at 40°C. Three hours after absorption, the lid was opened, and 20 adult panelists smelled the odor from a position approximately 3 cm from the top of the cup to evaluate the deodorizing effect. The evaluation was based on the following evaluation criteria, with each person scoring on a 6-point scale, and the average of the scores was calculated.

[0169]

[0170] (e) Methyl mercaptan (MM) concentration 1. 5 g of a water-absorbing resin composition was placed in a mayonnaise bottle (manufactured by Nippon Yamamura Glass Co., Ltd., outer diameter 62 mm, height 109.2 mm, capacity 241.8 mL), and 25 g of a 0.9 mass % sodium chloride aqueous solution was added to swell the composition.

[0171] 2. The mayonnaise bottle was capped and placed in a paint shaker (No. 488 test disperser, manufactured by Toyo Seiki Seisakusho, Ltd.) The paint shaker was then shaken at 800 (cycles / min) for 1 minute and then stopped.

[0172] 3. 1 g of a 0.1% by mass aqueous solution of sodium methyl mercaptan (a commercially available 15% aqueous solution of the reagent diluted with a 0.9% by mass aqueous solution of sodium chloride) was further added to the mayonnaise bottle.

[0173] 4. The mayonnaise jar was capped and stored at 30°C for 1 hour, after which the lid was opened and the methyl mercaptan concentration in the air above the jar was measured using a detector tube.

[0174] (f) Methyl mercaptan (MM) concentration increase rate The same procedure as in 4. above was carried out, except that the storage temperature was changed to 40° C., and the methyl mercaptan (MM) concentration at 40° C. was measured. The MM concentration increase rate due to temperature increase was calculated according to the following formula.

[0175] MM concentration increase rate due to temperature increase [%]={(MM concentration at 40°C) / (MM concentration at 30°C)−1}×100.

[0176]

[0177] <Discussion> Comparative Example 1 is a blank test in which only the water-absorbent resin was used, and neither the urine odor nor the methyl mercaptan odor was suppressed.

[0178] A comparison of Comparative Examples 1 and 2 reveals that the effect of suppressing urine odor is not achieved simply by applying a chelating agent to a water-absorbent resin, and that it is only by applying a chelating agent and copper silicate in combination to a water-absorbent resin that it is possible to suppress not only urine odor but also methyl mercaptan odor, as shown in Examples 1 to 3. Also noteworthy is that the water-absorbent resin compositions of Examples 1 to 3 are able to suppress the reappearance of methyl mercaptan odor even when the storage environment changes to a high temperature.

[0179] As shown in Comparative Example 4, even when a silicate containing no copper is used in the water-absorbent resin, neither the urine odor nor the methyl mercaptan odor can be suppressed.

[0180] As shown in Comparative Examples 5 and 6, even when a water-soluble copper compound other than a silicate is applied to the water-absorbent resin, neither the urine odor nor the methyl mercaptan odor can be suppressed.

[0181] As shown in Comparative Example 7, when an inorganic antibacterial agent in which an antibacterial metal such as copper or zinc is supported on an inorganic compound is applied to a water-absorbent resin, the urine odor and methyl mercaptan odor can be suppressed to some extent, but if the storage environment changes to a high temperature, the once suppressed methyl mercaptan odor returns.

[0182] In this way, it can be seen that by applying a combination of copper silicate and a chelating agent to a water-absorbent resin, it is possible to further improve the reduction of urine odor compared to conventional methods, and also to obtain the effect of suppressing the recurrence of bad odor in high-temperature environments.

[0183] This application is based on Japanese Patent Application No. 2023-143714, filed on September 5, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A water-absorbent resin composition comprising a water-absorbent resin, a copper silicate, and a chelating agent.

2. The water-absorbent resin composition according to claim 1, wherein the chelating agent comprises at least one compound selected from the group consisting of amino polycarboxylic acids, amino polyphosphoric acids and salts thereof.

3. The water-absorbent resin composition according to claim 1 or 2, wherein the copper silicate is present in a greater proportion on the surface of the water-absorbent resin than inside the water-absorbent resin.

4. The water-absorbing resin composition according to any one of claims 1 to 3, wherein the copper silicate has an amorphous structure.

5. The solubility of the copper silicate in ion-exchanged water at 25°C is 0.5 g / 100 mL-H ２ The water-absorbing resin composition according to any one of claims 1 to 4, wherein the water-absorbing resin composition has a viscosity of 0 or less.

6. The water-absorbing resin composition according to any one of claims 1 to 5, wherein the copper silicate contains a sulfur atom.

7. The water-absorbent resin composition according to any one of claims 1 to 6, wherein copper accounts for 50 mass % or more of all polyvalent metal components contained in said copper silicate.

8. An absorbent comprising the water-absorbent resin composition according to any one of claims 1 to 7 and hydrophilic fibers.

9. An absorbent article comprising the absorbent body according to claim 8, a liquid-permeable top sheet, and a liquid-impermeable back sheet.

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