Water-absorbent resin composition

Abstract

[Problem] The present invention addresses the problem of providing a novel water-absorbent resin composition which can further improve the reduction of urine odor compared to conventional water-absorbent resin compositions and which can suppress the regeneration of malodor in a high-temperature environment. [Solution] The present invention is a water-absorbent resin composition containing a water-absorbent resin, a copper silicate, and a chelating agent.

Description

Technical Field

[0001] This invention relates to a water-absorbing resin composition. Background Technology

[0002] Absorbent polymers (APIs) are widely used in hygiene materials such as diapers, sanitary napkins, and incontinence pads to absorb urine, blood, and other bodily fluids, and are a major component of these materials. In recent years, with the aging population leading to increased demand for adult diapers, the requirements for imparting deodorizing properties to APIs have been continuously increasing.

[0003] In recent years, compositions comprising an inorganic antibacterial agent and a water-absorbing resin have been proposed as odor-suppressing compositions. The inorganic antibacterial agent is formed by loading antibacterial metals such as silver, copper, and zinc onto an inorganic compound (see, for example, Patent Document 1). The inorganic antibacterial agent used in this composition possesses long-lasting antibacterial activity and is therefore considered suitable for use in sanitary materials, etc.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2006 / 046496 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] However, there is a problem that the odor that was temporarily eliminated can reappear in high-temperature environments. For example, if used diapers are thrown into the trash and stored in high-temperature environments such as summer, the odor will return.

[0009] Therefore, the objective of this invention is to provide a novel absorbent resin composition that, compared to conventional compositions, further improves the reduction of urine odor and also inhibits the re-generation of odor in high-temperature environments.

[0010] Solution for solving the problem

[0011] One solution for achieving the above objective is a water-absorbing resin composition comprising a water-absorbing resin, a copper silicate, and a chelating agent.

[0012] Invention Effects

[0013] According to the present invention, a novel absorbent resin composition is provided that, compared with the past, can further improve the reduction of urine odor and also inhibit the regeneration of odor in high-temperature environments. Detailed Implementation

[0014] Hereinafter, the present invention will be described with reference to the preferred mode. For the purposes of this specification as a whole, unless otherwise specified, the singular form should be understood to include the concept of its plural form. Therefore, unless otherwise specified, articles in the singular form (e.g., "a," "an," "the," etc. in English) should be understood to include the concept of its plural form. Furthermore, unless otherwise specified, measurements of operation and physical properties are performed at room temperature (20°C to 25°C). "mass" and "weight," "parts by mass" and "parts by weight," "%" and "mass%" and "weight%," "mass ppm" and "weight ppm" are considered synonymous. Furthermore, unless otherwise specified, the terminology used in this specification should be understood to be used according to its common meaning in the art. Therefore, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as conventionally understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, this specification (including definitions) shall prevail. The present invention is not limited to the embodiments described below, and various modifications may be made within the scope of the claims. Furthermore, all lower and upper limit values ​​disclosed in this specification should be understood as representing all possible combinations. That is, they should be understood as grounds for modification. Additionally, it should be understood that this application discloses all combinations of embodiments. That is, they should be understood as grounds for modification.

[0015] One solution for achieving the above objective is a water-absorbing resin composition comprising a water-absorbing resin, a copper silicate, and a chelating agent. According to this composition, a novel water-absorbing resin composition can be provided that further improves the reduction of urine odor compared to conventional compositions, and can also inhibit the re-generation of odor in high-temperature environments (e.g., 40°C).

[0016] [1] Definition of terminology

[0017] [1-1] Water-absorbing resin, base polymer, water-absorbing resin composition

[0018] In this invention, "water-absorbing resin" refers to a water-swellable and water-insoluble polymer gelling agent, generally in powder form. In addition, "water-swellable" means that the unpressurized absorption ratio (CRC) is 5 g / g or more as specified in EDANA WSP241.3 (10) below, and "water-insoluble" means that the soluble component (Ext) is 50% by mass or less as specified in EDANA WSP270.3 (10).

[0019] The "hygroscopic resin" is preferably a hydrophilic crosslinked polymer (so-called internal crosslinked polymer) formed by crosslinking and polymerizing unsaturated monomers with carboxyl groups, but it is not necessary for all of its amount (100% by mass) to be a crosslinked polymer.

[0020] In addition, generally speaking, "hygroscopic resin" sometimes refers to "a polymer that is cross-linked only internally (i.e., a polymer in which the cross-linking density is substantially the same internally and on the surface)" 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 relative to the cross-linking density internally)". Sometimes, polymers that are cross-linked only internally are referred to as "base polymers".

[0021] In this invention, "water-absorbing resin composition" refers to a composition containing water-absorbing resin, copper silicate, and chelating agent, and other components as needed. In short, it refers to a water-absorbing resin in a state suitable for shipment as a final product. Therefore, if the water-absorbing resin contains copper silicate, chelating agent, and other additives as needed, it becomes a "water-absorbing resin composition." It should be noted that in this specification, the water-absorbing resin composition is sometimes simply referred to as "water-absorbing agent."

[0022] [1-2] "EDANA", "WSP", "NWSP"

[0023] "EDANA" is the abbreviation for the European Disposables and Nonwovens Association. "WSP" stands for Worldwide Strategic Partners, indicating that EDANA provides the world standard testing method for absorbent polymers. "NWSP" stands for "Non-Woven Standard Procedures - Edition 2015". In this invention, unless otherwise specified, the physical properties of absorbent polymers are determined according to the original WSP (2010 revision / publicly available literature).

[0024] [1-2-1]"CRC" (WSP241.3(10))

[0025] "CRC" stands for Centrifuge Retention Capacity, which refers to the absorption rate under no pressure. Specifically, it is the absorption rate (unit: g / g) obtained by placing 0.2 grams of the test object (e.g., absorbent or water-absorbing resin) in a nonwoven bag, then immersing it in a large excess of 0.9% sodium chloride aqueous solution for 30 minutes to allow it to swell freely, and then dehydrating it in a centrifuge (250G) for 3 minutes.

[0026] [1-2-2]"AAP" (NWSP 242.0.R2(15))

[0027] "AAP" stands for Absorption Against Pressure, referring to the percentage of water absorbed by a test substance (e.g., a water-absorbing agent or superabsorbent resin) under pressure (the "water absorption ratio" is also called "absorption rate"). Specifically, AAP 0.3 psi (2.06 kPa) means that 0.9 g of the test substance (e.g., a water-absorbing agent or superabsorbent resin) at 2.06 kPa (= 21 g / cm³) is absorbed under pressure. 2 =0.3psi) water absorption ratio (in g / g) after swelling for 1 hour in a large excess of 0.9% by mass sodium chloride aqueous solution.

[0028] [2] Water-absorbing resin composition and its manufacturing method

[0029] One embodiment of the present invention comprises a water-absorbing resin composition containing a water-absorbing resin, a copper silicate, and a chelating agent.

[0030] (Water-absorbing resin)

[0031] In one embodiment of the present invention, the water-absorbing resin may include: polyacrylic acid (salt) based water-absorbing resin, polysulfonic acid (salt) based water-absorbing resin, maleic anhydride (salt) based water-absorbing resin, polyacrylamide based water-absorbing resin, polyvinyl alcohol based water-absorbing resin, polyethylene oxide based water-absorbing resin, polyaspartic acid (salt) based water-absorbing resin, polyglutamic acid (salt) based water-absorbing resin, polyalginic acid (salt) based water-absorbing resin, starch based water-absorbing resin, and cellulose based water-absorbing resin. Polyacrylic acid (salt) based water-absorbing resin is preferred.

[0032] In the embodiments of the present invention, "polyacrylic acid (salt) based water-absorbing resin" refers to a water-absorbing resin made from acrylic acid and / or its salts (hereinafter referred to as "acrylic acid (salt)"). That is, a polyacrylic acid (salt) based water-absorbing resin is a water-absorbing resin in which the polymer has structural units derived from acrylic acid (salt) and has grafted components as arbitrary components.

[0033] Specifically, a 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%, even more preferably 90 mol% to 100 mol%, and particularly preferably substantially 100 mol% of acrylic acid (salt) relative to all monomers involved in the polymerization reaction (excluding internal crosslinking agents).

[0034] (Copper silicate)

[0035] The copper silicate of the present invention is a structure in which copper ions in a copper salt are chemically bonded to silicate anions. It is not merely a mixture of copper salt and silicic acid in a solid state, nor is it a substance that supports copper using copper-free silicic acid as a substrate. 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. With this embodiment, the effect of suppressing odors (especially urine odor) and the effect of suppressing the re-generation of odors under high-temperature environments become more significant. 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.

[0036] In one embodiment of the invention, copper silicate can be obtained, for example, by mixing a precursor compound (e.g., silicate) that will become a silicon source with a precursor compound (e.g., an inorganic salt of copper, an organic salt of copper) in water, preferably with an acidifying agent (e.g., sulfuric acid). Regarding the mixing amount, it is sufficient, for example, to adjust to the following atomic number ratio and mass ratio. The mixing temperature can be around room temperature (e.g., 10°C to 40°C), or it can be heated to an upper limit of around 60°C. The mixing time can be, for example, from 1 minute to about 3 days. The solids are filtered from the mixture, washed with deionized water, dried, and then the dried solids are pulverized to obtain powdered copper silicate.

[0037] In one embodiment of the present invention, the copper silicate contains silicon atoms, copper atoms, sulfur atoms, oxygen atoms and sodium atoms.

[0038] In one embodiment of the present invention, the ratio of the number of copper atoms in the copper silicate to the number of silicon atoms 100 is 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. In another embodiment of the present invention, the ratio of the number of copper atoms in the copper silicate to the number of silicon atoms 100 is 10 or less, 9 or less, 8 or less, 7 or less, or 6 or less.

[0039] In one embodiment of the present invention, the ratio of sulfur atoms in the copper silicate to silicon atoms 100 is 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. In another embodiment of the present invention, the ratio of sulfur atoms in the copper silicate to silicon atoms 100 is 10 or less, 9 or less, 8 or less, or 7 or less.

[0040] In one embodiment of the present invention, the ratio of oxygen atoms in the copper silicate to silicon atoms 100 is 200 or more, 250 or more, 300 or more, 350 or more, 400 or more, 450 or more, or 500 or more. In another embodiment of the present invention, the ratio of oxygen atoms in the copper silicate to silicon atoms 100 is 900 or less, 850 or less, 800 or less, 750 or less, 700 or less, 650 or less, or 600 or less.

[0041] In one embodiment of the present invention, the ratio of sodium atoms in the copper silicate to silicon atoms 100 is 5 or more, 10 or more, 15 or more, or 20 or more. In another embodiment of the present invention, the ratio of sodium atoms in the copper silicate to silicon atoms 100 is 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, or 25 or less.

[0042] In one embodiment of the present invention, the weight ratio of copper atoms in the copper silicate is 5 or more, 7 or more, 9 or more, or 10 or more relative to silicon atoms 100. In another embodiment of the present invention, the weight ratio of copper atoms in the copper silicate is 20 or less, 18 or less, 16 or less, 14 or less, or 13 or less relative to silicon atoms 100.

[0043] In one embodiment of the present invention, the weight ratio of sulfur atoms in the copper silicate is 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more relative to silicon atoms 100. In another embodiment of the present invention, the weight ratio of sulfur atoms in the copper silicate is 10 or less, 9 or less, 8 or less, or 7 or less relative to silicon atoms 100.

[0044] In one embodiment of the present invention, the weight ratio of oxygen atoms in the copper silicate is 100 or more, 200 or more, 250 or more, or 300 or more relative to silicon atoms 100. In another embodiment of the present invention, the weight ratio of oxygen atoms in the copper silicate is 600 or less, 550 or less, 500 or less, 450 or less, 400 or less, or 350 or less relative to silicon atoms 100.

[0045] In one embodiment of the present invention, the weight ratio of sodium atoms in the copper silicate is 5 or more, 10 or more, 15 or more, or 17 or more relative to silicon atoms 100. In another embodiment of the present invention, the weight ratio of sodium atoms in the copper silicate is 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, 25 or less, or 20 or less relative to silicon atoms 100.

[0046] In one embodiment of the present invention, the copper silicate contains silicon atoms, copper atoms, sulfur atoms, oxygen atoms and aluminum atoms.

[0047] In one embodiment of the present invention, the ratio of the number of copper atoms in the copper silicate to the number of silicon atoms 100 is 10 or more, 15 or more, 20 or more, 25 or more, 30 or more, or 35 or more. In another embodiment of the present invention, the ratio of the number of copper atoms in the copper silicate to the number of silicon atoms 100 is 60 or less, 55 or less, 50 or less, 45 or less, or 40 or less.

[0048] In one embodiment of the present invention, the ratio of sulfur atoms in the copper silicate to silicon atoms 100 is 0.01 or more, 0.05 or more, or 0.1 or more. In another embodiment of the present invention, the ratio of sulfur atoms in the copper silicate to silicon atoms 100 is 2 or less, 1 or less, 0.8 or less, or 0.5 or less.

[0049] In one embodiment of the present invention, the ratio of oxygen atoms in the copper silicate to silicon atoms 100 is 400 or more, 450 or more, 500 or more, 550 or more, 600 or more, or 650 or more. In another embodiment of the present invention, the ratio of oxygen atoms in the copper silicate to silicon atoms 100 is 1100 or less, 1000 or less, 900 or less, 850 or less, 800 or less, or 750 or less.

[0050] In one embodiment of the present invention, the ratio of aluminum atoms in the copper silicate to silicon atoms 100 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 another embodiment of the present invention, the ratio of aluminum atoms in the copper silicate to silicon atoms 100 is 10 or less, 7 or less, 5 or less, 3 or less, 2.5 or less, or 2 or less.

[0051] In one embodiment of the present invention, the weight ratio of copper atoms in the copper silicate is 40 or more, 50 or more, 60 or more, or 70 or more relative to silicon atoms 100. In another embodiment of the present invention, the weight ratio of copper atoms in the copper silicate is 200 or less, 150 or less, or 100 or less relative to silicon atoms 100.

[0052] In one embodiment of the present invention, the weight ratio of sulfur atoms in the copper silicate relative to silicon atoms 100 is 0.001 or more, 0.005 or more, 0.008 or more, or 0.01 or more. In another embodiment of the present invention, the weight ratio of sulfur atoms in the copper silicate relative to silicon atoms 100 is 5 or less, 3 or less, 1 or less, or 0.5 or less.

[0053] In one embodiment of the present invention, the weight ratio of oxygen atoms in the copper silicate relative to silicon atoms 100 is 150 or more, 200 or more, 250 or more, 300 or more, 350 or more, or 400 or more. In another embodiment of the present invention, the weight ratio of oxygen atoms in the copper silicate relative to silicon atoms 100 is 700 or less, 600 or less, 500 or less, or 450 or less.

[0054] In one embodiment of the present invention, the weight ratio of aluminum atoms in the copper silicate relative to silicon atoms 100 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 another embodiment of the present invention, the weight ratio of aluminum atoms in the copper silicate relative to silicon atoms 100 is 10 or less, 7 or less, 5 or less, 3 or less, 2.5 or less, or 2 or less.

[0055] It should be noted that the atomic ratio and weight ratio in this specification can be calculated by using SEM-EDS (Scanning Electron Microscope-Energy Dispersive System) analysis with a scanning electron microscope.

[0056] In one embodiment of the present invention, copper accounts for 50% or more, 60% or more, or 70% or more (up to 100% by mass) of all the polyvalent metal components contained in the copper silicate.

[0057] In one embodiment of the invention, the copper silicate is composed of an amorphous structure. This embodiment improves the effect of suppressing odors (especially urine odor). Whether it is an amorphous structure can be confirmed by methods such as X-ray crystal structure analysis.

[0058] In one embodiment of the present invention, the volume average particle size of the copper silicate is 0.1 μm to 100 μm, 0.5 μm to 50 μm, or 1 μm to 20 μm. The volume average particle size of the copper silicate can be determined using a laser diffraction particle size distribution measuring device.

[0059] In one embodiment of the present invention, the solubility of copper silicate in ion-exchanged water at 25°C is less than 0.5 g / 100 mL H₂O, less than 0.3 g / 100 mL H₂O, or less than 0.1 g / 100 mL H₂O. This embodiment suppresses the penetration of copper silicate into the absorbent resin, thereby efficiently achieving the desired effect of the present invention. Regarding solubility, for example, 0.1 g of the test substance is placed in a 100 mL beaker, and 20 g of ion-exchanged water at 20°C is added. If insoluble matter is visually confirmed after 24 hours, the solubility can be confirmed to be less than 0.5 g / 100 mL H₂O. Similarly, by changing the amount of water using the above method and visually confirming the presence or absence of insoluble matter, it is easy to determine whether the solubility is below or above a specified value.

[0060] In one embodiment of the present invention, when the copper silicate contains zinc, the mass ratio of zinc content to silicon content in the copper silicate (zinc content / silicon content) is less than 50 / 50, less than 10 / 50, or less than 1 / 50.

[0061] In one embodiment of the present invention, the copper silicate does not contain zinc or zinc atoms.

[0062] In one embodiment of the present invention, the content of copper silicate relative to the water-absorbing resin is 0.01% to 10% by mass, 0.05% to 9% by mass, 0.1% to 8% by mass, 0.2% to 7% by mass, 0.3% to 6% by mass, 0.4% to 5% by mass, 0.5% to 4% by mass, 0.6% to 3% by mass, or 0.7% to 2% by mass.

[0063] (chelating agent)

[0064] In one embodiment of the invention, the chelating agent may be a compound having a chelating effect that captures metals. In one embodiment of the invention, the chelating agent contains at least one compound selected from the group consisting of aminopolycarboxylic acids, aminopolyphosphates, and their salts.

[0065] It should be noted that the above-mentioned "multi-functionality" refers to having multiple functional groups within one molecule, preferably 2 to 30, more preferably 3 to 20, further preferably 4 to 10, and even more preferably 5 to 9 functional groups.

[0066] From the viewpoint of the effect on polymerization and the physical properties of the resulting water-absorbing resin composition, the molecular weight of the chelating agent is preferably 100 to 5000, more preferably 150 to 1000.

[0067] Examples of amino polycarboxylic acids or their salts (amino polycarboxylic acid chelating agents) include: iminodiacetic acid, hydroxyethyliminodiacetic acid, hypozinotriacetic acid, hypozinotripropionic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, trans-1,2-diaminocyclohexanetetraacetic acid, N,N-bis(2-hydroxyethyl)glycine, diaminopropanoltetraacetic acid, ethylenediaminedipropionic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol ether diaminetetraacetic acid, diaminopropanetetraacetic acid, N,N'-bis(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid, 1,6-hexamethylenediamine-N,N,N',N'-tetraacetic acid and their salts.

[0068] Examples of amino polyphosphoric acids or their salts (amino polyphosphoric acid chelating agents) include: ethylenediamine-N,N'-di(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), cyclohexanediaminetetra(methylenephosphonic acid), ethylenediamine-N,N'-diacetic acid-N,N'-di(methylenephosphonic acid), ethylenediamine-N,N'-di(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), poly(methylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), and their salts.

[0069] From the viewpoint of suppressing malodor, amino polycarboxylic acid chelating agents having four or more (or five or more) carboxyl groups or amino polyphosphoric acid 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 malodor, diethylenetriaminepentaacetic acid, hypozoxytriacetic acid, triethylenetetraminehexaacetic acid, ethylenediaminetetra(methylenephosphonic acid), and their salts are further preferred.

[0070] In one embodiment of the present invention, the salt used as a chelating agent may include sodium, but is not limited thereto.

[0071] In one embodiment of the present invention, the chelating agent may be a compound exemplified in U.S. Patent No. 6,599,989, U.S. Patent No. 6,469,080, European Patent No. 2,163,302, etc.

[0072] In one embodiment of the invention, the content of the chelating agent relative to the water-absorbing resin is 10 ppm to 1000 ppm, 20 ppm to 800 ppm, 30 ppm to 600 ppm, 40 ppm to 500 ppm, 50 ppm to 300 ppm, 60 ppm to 200 ppm, or 70 ppm to 150 ppm.

[0073] The preferred method for manufacturing the water-absorbing resin composition will be described below. However, the method for manufacturing the water-absorbing resin composition according to one aspect of the present invention is not limited to the method described below.

[0074] [2-1] Preparation process of monomer aqueous solution

[0075] This step involves preparing an aqueous monomer solution containing a monomer comprising acrylic acid (salt) as the main component and at least one internal crosslinking agent. The term "main component" refers to the amount (content) of acrylic acid (salt) relative to all monomers supplied to the polymerization reaction (excluding the internal crosslinking agent), typically 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more (up to a maximum of 100 mol%). It should be noted that a monomer slurry can also be used within a range that does not affect the water-absorbing properties of the absorbent obtained as the final product; however, for convenience, this specification describes the aqueous monomer solution.

[0076] (Acrylic acid (salt))

[0077] In embodiments of the present invention, from the viewpoint of the physical properties and yield of the absorbent, it is preferable to use known acrylic acid (salt) as a monomer (also called a polymerizable monomer). Known acrylic acid may contain trace amounts of polymerization inhibitors, impurities, etc. As the polymerization inhibitor, methoxyphenols are preferred, and p-methoxyphenols are more preferred. From the viewpoint of the polymerizability of acrylic acid and the color of the absorbent, 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 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 included in the acrylic acid used in embodiments of the present invention.

[0078] Additionally, examples of acrylates include salts obtained by neutralizing acrylic acid with a basic compound (e.g., sodium acrylate). These acrylates can be commercially available acrylates (e.g., sodium acrylate) or salts obtained by neutralizing acrylic acid.

[0079] (Alkaline compounds)

[0080] In the embodiments of this invention, alkaline compounds refer to compounds that exhibit alkalinity; specifically, sodium hydroxide and the like fall into this category. It should be noted that commercially available sodium hydroxide, at the ppm (mass standard) level, contains heavy metals such as zinc, lead, and iron, and strictly speaking, can also be described as a composition. However, in this invention, such compositions are also considered to be included within the scope of alkaline compounds.

[0081] Specific examples of the alkaline compound include alkali metal carbonates, bicarbonates, alkali metal hydroxides, ammonia, and organic amines. From the viewpoint of the absorbent properties of the desiccant, a strongly alkaline compound is selected. Therefore, hydroxides of alkali metals such as sodium, potassium, and lithium are preferred, and sodium hydroxide is more preferred. It should be noted that, from an operational point of view, this alkaline compound is preferably prepared as an aqueous solution.

[0082] (Neutralization)

[0083] When using the salt obtained by neutralizing acrylic acid as the acrylate, the timing of neutralization is not particularly limited; it can be performed at any time before polymerization, during polymerization, or after polymerization, or at multiple times or locations. Furthermore, from the viewpoint of desiccant production efficiency, continuous neutralization is preferred.

[0084] When acrylic acid (salt) is used in this invention, the neutralization rate relative to the acid groups of the monomer is preferably 10 mol% to 90 mol%, more preferably 40 mol% to 85 mol%, further preferably 50 mol% to 80 mol%, and particularly preferably 60 mol% to 78 mol%. By setting the neutralization rate within this range, the reduction in the water absorption performance of the water-absorbing agent can be suppressed.

[0085] It should be noted that the range of neutralization rates applies to any of the above-mentioned neutralization processes before, during, and after polymerization. Furthermore, this also applies to the desiccant used as the final product.

[0086] (Other monomers)

[0087] In this invention, monomers other than the above-mentioned acrylic acid (salt) (hereinafter referred to as "other monomers") may be used in combination with acrylic acid (salt) as needed.

[0088] Other monomers mentioned include: maleic acid (anhydride), itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluenesulfonic acid, vinyl toluenesulfonic acid, styrene sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, 2-(meth)acryloyl ethanesulfonic acid, 2-(meth)acryloyl propanesulfonic acid, 2-hydroxyethyl(meth)acryloyl phosphate, and other anionic unsaturated monomers and their salts; unsaturated monomers containing thiol groups; unsaturated monomers containing phenolic hydroxyl groups; unsaturated monomers containing amide groups, such as (meth)acrylamide, N-ethyl(meth)acrylamide, and N,N-dimethyl(meth)acrylamide; and unsaturated monomers containing amino groups, such as N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, and N,N-dimethylaminopropyl(meth)acrylamide. Additionally, these other monomers include water-soluble or hydrophobic unsaturated monomers. When using this other monomer, its amount relative to all monomers (excluding the internal crosslinking agent) is preferably 30 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less (lower limit: 0 mol%).

[0089] (Internal cross-linking agent)

[0090] In the preferred manufacturing method, an internal crosslinking agent is used. Specific examples of such internal crosslinking agents include: N,N'-methylenebis(meth)acrylamide, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate, glycerol 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, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerol, pentaerythritol, ethylenediamine, polyethyleneimine, glycidyl methacrylate, etc. Considering reactivity and other factors, at least one internal crosslinking agent can be selected from these internal crosslinking agents. Furthermore, from the viewpoint of the water-absorbing properties of the absorbent, it is preferable to select an internal crosslinking agent having two or more polymerizable unsaturated groups; more preferably, an internal crosslinking agent that exhibits thermal decomposition at drying temperatures; and even more preferably, an internal crosslinking agent containing two or more polymerizable unsaturated groups having a (poly)alkylene glycol structure.

[0091] Examples of polymerizable unsaturated groups include allyl, (meth)acrylate, and more preferably (meth)acrylate. Additionally, examples of the (poly)alkylene glycol structure include polyethylene glycol. It should be noted that 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.

[0092] The amount of the internal crosslinking agent relative to all monomers (excluding the internal crosslinking agent) 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%. By setting the amount within this range, a water-absorbing resin or water-absorbing agent with the desired water-absorbing properties can be obtained. In addition, it is also preferable to adjust the amount of the internal crosslinking agent so that the gel bulk density of the water-absorbing resin or water-absorbing agent is within a specified range, thereby suppressing the increase of water-soluble components and the decrease of absorption rate that accompany the decrease in gel strength.

[0093] The internal crosslinking agent is preferably added in advance when preparing the monomer aqueous solution, in which case the crosslinking reaction occurs simultaneously with the polymerization reaction. Alternatively, the polymerization reaction can be initiated without adding the internal crosslinking agent, and the internal crosslinking agent can be added during or after the polymerization reaction to carry out the crosslinking reaction. Furthermore, these methods can be used in combination.

[0094] (Substances added to the monomer aqueous solution)

[0095] In embodiments of the present invention, from the viewpoint of improving the physical properties of the water-absorbing agent, the following substances may be added to the monomer aqueous solution at any of the following points: during the preparation of the monomer aqueous solution, during the polymerization and crosslinking reactions, or after the polymerization and crosslinking reactions.

[0096] Specific examples of such substances include: hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol (PVA), polyacrylic acid (salt), and cross-linked polyacrylic acid (salt); compounds such as carbonates, azo compounds, foaming agents that generate various bubbles, surfactants, chelating agents, and chain transfer agents. The amount of the hydrophilic polymer added relative to the monomer aqueous solution is preferably 50% by mass or less, more preferably 20% by mass or less, further preferably 10% by mass or less, and particularly preferably 5% by mass or less (lower limit: 0% by mass). Furthermore, the amount of the compound added relative to the monomer aqueous solution is preferably 5% by mass or less, more preferably 1% by mass or less, and further preferably 0.5% by mass or less (lower limit: 0% by mass).

[0097] If a water-soluble resin or a water-absorbing resin is used as the hydrophilic polymer, a grafted polymer or water-absorbing resin composition (e.g., starch-acrylate (salt) copolymer, PVA-acrylate (salt) copolymer, etc.) can be obtained. These grafted polymer or water-absorbing resin compositions are also included in the scope of the polyacrylate (salt)-based water-absorbing resins of the present invention.

[0098] (Concentration of monomeric components)

[0099] Depending on the purpose, various of the above-mentioned substances (components) are selected, and their respective amounts are specified and mixed together as needed to satisfy the stated range, thereby preparing a monomer aqueous solution. It should be noted that, in this invention, in addition to preparing the monomer into an aqueous solution, a mixed solution of water and a hydrophilic solvent can also be prepared.

[0100] Furthermore, from the viewpoint of the physical properties of the absorbent, the total concentration of each substance (component) (hereinafter also referred to as "monomer component") is preferably 10% to 80% by mass, more preferably 20% to 75% by mass, and even more preferably 30% to 70% by mass. The concentration of the monomer component is calculated by the following formula (2).

[0101] [Mathematical Expression 1]

[0102]

[0103] It should be noted that in the above formula (2), (mass of monomer aqueous solution) does not include the mass of grafted components or water-absorbing resins, or the mass of hydrophobic organic solvents in reverse suspension polymerization.

[0104] [2-2] Polymerization process

[0105] This process involves polymerizing the aqueous solution of the monomer obtained in the preparation process of the monomer aqueous solution, which contains a monomer with acrylic acid (salt) as the main component and at least one internal crosslinking agent, to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel").

[0106] (Polymerization initiator)

[0107] In one embodiment of the present invention, a polymerization initiator is used during polymerization. Examples of such polymerization initiators include thermally decomposable polymerization initiators, photodecomposable polymerization initiators, or redox polymerization initiators that also incorporate a reducing agent that promotes the decomposition of these polymerization initiators. Specific examples of such polymerization initiators include free radical polymerization initiators such as sodium persulfate, potassium persulfate, ammonium persulfate, tert-butyl hydroperoxide, hydrogen peroxide, and 2,2'-azobis(2-amidinylpropane) dihydrochloride. At least one polymerization initiator can be selected from these initiators, taking into account the polymerization method, etc. Furthermore, from the viewpoint of operability of the polymerization initiator and the physical properties of the desiccant, at least one of peroxides and azo compounds is preferably selected as the polymerization initiator. Additionally, when using an oxidizing free radical polymerization initiator, redox polymerization can be carried out using reducing agents such as sodium sulfite, sodium bisulfite, ferrous sulfate, and L-ascorbic acid, for example.

[0108] The amount of the polymerization initiator relative to all monomers (excluding the internal crosslinking agent) 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%. Furthermore, the amount of the reducing agent relative to all monomers (excluding the internal crosslinking agent) is preferably 0.0001 mol% to 0.02 mol%, more preferably 0.0005 mol% to 0.015 mol%. By setting the amount within this range, a water-absorbing agent with the desired water-absorbing properties can be obtained.

[0109] Alternatively, in one embodiment of the present invention, the polymerization reaction can also be initiated by heat energy or by irradiation with active energy rays such as radiation, electron beams, or ultraviolet rays. Alternatively, irradiation with active energy rays and the polymerization initiator can be combined.

[0110] (Aggregation method)

[0111] Examples of polymerization methods applicable to this invention include aqueous solution polymerization, reverse suspension polymerization, spray polymerization, droplet polymerization, bulk polymerization, and precipitation polymerization. From the viewpoint of ease of polymerization control and the water-absorbing properties of the desiccant, aqueous solution polymerization or reverse suspension polymerization is preferred, aqueous solution polymerization is more preferred, and continuous aqueous solution polymerization is even more preferred. Reverse suspension polymerization is described in International Publication No. 2007 / 004529, International Publication No. 2012 / 023433, etc. Furthermore, continuous aqueous solution polymerization can produce desiccant in high yields. Specific examples include continuous belt polymerization described in US Patent No. 4,893,999, US Patent No. 6,906,159, US Patent No. 7,091,253, US Patent No. 7,741,400, US Patent No. 8,519,212, Japanese Patent Application Publication No. 2005-36,100, and continuous kneader polymerization described in US Patent No. 6,987,151, etc.

[0112] As one embodiment of the aqueous solution polymerization, the temperature of the monomer aqueous solution at the start of polymerization is adjusted to be above 10°C and below 30°C.

[0113] Preferred methods for the continuous aqueous solution polymerization include high-temperature initiation polymerization, high-concentration polymerization, and foaming polymerization. High-temperature initiation polymerization involves setting the temperature of the monomer aqueous solution at polymerization initiation to preferably 30°C or higher, more preferably 35°C or higher, further preferably 40°C or higher, and particularly preferably 50°C or higher (the upper limit being the boiling point of the monomer aqueous solution). High-concentration polymerization involves setting the monomer concentration at polymerization initiation to preferably 30% by mass or higher, more preferably 35% by mass or higher, further preferably 40% by mass or higher, and particularly preferably 45% by mass or higher (the upper limit being the saturation concentration of the monomer aqueous solution).

[0114] Furthermore, while the above-mentioned polymerization methods can be carried out in an air atmosphere, from the viewpoint of the desiccant's color, it is preferable to carry them out in an atmosphere of inert gases such as nitrogen or argon (with an oxygen concentration of less than 1% by volume). It should be noted that the dissolved oxygen in the monomer aqueous solution is also preferably replaced beforehand with an inert gas (dissolved oxygen content less than 1 mg / L (=ppm)).

[0115] [2-3] Gel pulverization process

[0116] This step involves pulverizing the hydrogel obtained in the polymerization step to obtain granular hydrogel (hereinafter also referred to as "granular hydrogel"). It should be noted that, in order to distinguish it from the "pulverization" in the pulverization step below, this step is referred to as "gel pulverization".

[0117] The gel pulverization refers to using gel pulverizers such as kneaders, meat grinders, and shredders to adjust hydrogels to a specified size.

[0118] Regarding the implementation methods and working conditions for gel pulverization, the contents described in International Publication No. 2011 / 126079 are preferably applicable to this invention. It should be noted that when the polymerization method is kneading polymerization, the polymerization step and the gel pulverization step are performed simultaneously. Furthermore, when particulate hydrogels are obtained during the polymerization step in reverse suspension polymerization, spray polymerization, or droplet polymerization, the gel pulverization step is considered to be performed simultaneously with that polymerization step. Additionally, in this invention, by means of the gel pulverization step, amorphous, fragmented water-absorbing resins and water-absorbing agents can be obtained.

[0119] [2-4] Drying process

[0120] This process involves drying the hydrogel and / or granular hydrogel obtained in the polymerization and / or gel pulverization processes to a desired resin solids composition to obtain a dried polymer. This resin solids composition is determined by the loss on drying (the change in mass when 1 g of absorbent resin is heated at 180°C for 3 hours), preferably 80% by mass or more, more preferably 85% to 99% by mass, further preferably 90% to 98% by mass, and particularly preferably 92% to 97% by mass.

[0121] Examples of drying methods for the hydrogels and / or granular hydrogels include: heating drying, hot air drying, vacuum drying, fluidized bed drying, infrared drying, microwave drying, drum dryer drying, drying based on azeotropic dehydration with hydrophobic organic solvents, and high-humidity drying using high-temperature steam. From the viewpoint of drying efficiency, hot air drying is preferred, and belt drying, which involves hot air drying over a ventilation belt, is more preferred.

[0122] From the viewpoint of the color of the water-absorbing resin and the water-absorbing agent, and the drying efficiency, the drying temperature (hot air temperature) for the hot air drying is preferably 120°C to 250°C, and more preferably 140°C to 200°C. It should be noted that drying conditions other than the drying temperature, such as the hot air velocity and drying time, can be appropriately set according to the moisture content, total mass, and solid composition of the granular hydrogel to be dried. When performing belt drying, the conditions described in International Publication No. 2006 / 100300, International Publication No. 2011 / 025012, International Publication No. 2011 / 025013, and International Publication No. 2011 / 111657 can be appropriately applied.

[0123] Furthermore, 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 this range, the physical properties of the resulting water-absorbing resin and water-absorbing agent can be set within the desired range. In addition, the physical properties of the water-absorbing resin as an intermediate product can also be set within the desired range.

[0124] [2-5] Crushing process, grading process

[0125] This process involves pulverizing the dried polymer obtained from the drying process (pulverization process) and adjusting it to a desired particle size range (grading process) to obtain water-absorbing resin powder (base polymer). Through the pulverization process following drying, amorphous, fragmented water-absorbing resin and water-absorbing agent can be obtained. Pulverization can be performed more than twice as needed.

[0126] Examples of pulverizers used in the aforementioned pulverizing process include: high-speed rotary pulverizers such as roller mills, hammer mills, screw mills, and pin mills; or vibrating mills, knuckle-type pulverizers, and cylindrical mixers. From the viewpoint of pulverizing efficiency, roller mills are preferred. Furthermore, multiple of these pulverizers may be used in combination.

[0127] Methods for particle size adjustment in the grading process include sieve grading using a JIS standard sieve (JIS Z8801-1 (2000)) and air classifying. From the perspective of grading efficiency, sieve grading is preferred. It should be noted that particle size adjustment of water-absorbing resins and desiccant is not limited to the pulverizing and grading processes; it can also be implemented in polymerization processes (especially reverse suspension polymerization, droplet polymerization, etc.) or other processes (e.g., granulation processes, micronized powder recovery processes).

[0128] [2-6] Surface crosslinking process

[0129] This process involves further setting a highly crosslinked portion on the surface layer of the base polymer obtained through the aforementioned processes. It comprises a mixing process, a heat treatment process, and, if necessary, a cooling process. In this surface crosslinking process, free radical crosslinking, surface polymerization, and a crosslinking reaction with a surface crosslinking agent occur on the surface of the base polymer, thereby obtaining a (surface-crosslinked) water-absorbing resin.

[0130] [2-6-1] Mixing process

[0131] This process involves mixing a solution containing a surface crosslinking agent (hereinafter referred to as "surface crosslinking agent solution") with a base polymer in a mixing device to obtain a humidified mixture.

[0132] (Surface crosslinking agent)

[0133] In one embodiment of the present invention, a surface crosslinking agent is used during surface crosslinking. Specifically, the surface crosslinking agent described in U.S. Patent No. 7,183,456 can be cited as an example. Considering reactivity, at least one surface crosslinking agent can be selected from these surface crosslinking agents. Furthermore, from the viewpoints of operability of the surface crosslinking agent and water-absorbing properties of the water-absorbing agent, it is preferable to select an organic compound having two or more functional groups that react with carboxyl groups and forming covalent bonds.

[0134] More specifically, the following can be listed as surface crosslinking agents: 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, glycerol, polyglycerol, 1,6-hexanediol, 1,5-... Polyols such as hexanediol, 1,4-hexanediol, 1,3-hexanediol, 1,2-hexanediol, 2,3-hexanediol, 2,4-hexanediol, diethanolamine, and triethanolamine; polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyallylamine, and polyethyleneimine; halogenated epoxy compounds and condensates of polyamines and halogenated epoxy compounds; oxazoline compounds such as 1,2-ethylenebisoxazoline and oxazolidinones. Compounds; 1,3-dioxolane-2-one (ethylene carbonate), 4-methyl-1,3-dioxolane-2-one, 4,5-dimethyl-1,3-dioxolane-2-one, 4,4-dimethyl-1,3-dioxolane-2-one, 4-ethyl-1,3-dioxolane-2-one, 4-hydroxymethyl-1,3-dioxolane-2-one, 1,3-dioxane-2-one, 4-methyl-1,3-dioxane-2-one, 4,6-dimethyl-1 Alkyl carbonate esters such as 3-dioxepan-2-one and 1,3-dioxepan-2-one; polyglycidyl compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidyl; oxetane compounds and vinyl ether compounds. Preferred surface crosslinking agents include: polyol compounds such as propylene glycol and 1,3-propanediol; alkyl carbonate esters such as ethylene carbonate; polyglycidyl compounds such as ethylene glycol diglycidyl ether; and polyamines such as diethylenetriamine.

[0135] The amount of the surface crosslinking agent (the total amount in cases of multiple applications) relative to 100 parts by weight of the base polymer is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, even more preferably 0.01 to 2 parts by weight, even more preferably 0.1 to 1.8 parts by weight, and still more preferably 0.5 to 1.5 parts by weight. By setting the amount of the surface crosslinking agent within this range, an optimal crosslinking structure can be formed on the surface layer of the base polymer, thereby obtaining a highly absorbent resin or absorbent agent. In addition, adjusting the amount of the surface crosslinking agent according to its type is also effective in rationalizing the gel packing density of the absorbent resin or absorbent agent.

[0136] 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 is preferably 0.1 to 20 parts by weight relative to 100 parts by weight of the base polymer, more preferably 0.3 to 15 parts by weight, and even more preferably 0.5 to 10 parts by weight. By setting the amount of water within this range, the operability of the surface crosslinking agent solution is improved, and the surface crosslinking agent can be uniformly mixed into the base polymer.

[0137] Alternatively, the surface crosslinking agent solution can be prepared by combining a hydrophilic organic solvent with the water as needed. In this case, the amount of hydrophilic organic solvent used is preferably small to avoid producing an unpleasant odor, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, further 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 achieving adequate surface crosslinking, a hydrophilic organic solvent can 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 the base polymer.

[0138] Examples of hydrophilic organic solvents include: lower alcohols (e.g., 1-3 carbon atoms) such as methanol and isopropanol; ketones such as acetone; ethers such as dioxane; amides such as N,N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide.

[0139] (Mixed methods, mixed conditions)

[0140] Regarding the mixing of the base polymer and the surface crosslinking agent solution, the following method is selected: the surface crosslinking agent solution is prepared in advance, preferably by spraying or dripping the solution onto the base polymer for mixing, and more preferably by spraying the solution onto the base polymer for mixing.

[0141] [2-6-2] Heat treatment process

[0142] This step involves heating the humidified mixture obtained in the mixing step to induce a crosslinking reaction on the surface of the base polymer.

[0143] The heat treatment of the humidified mixture can be performed by heating the mixture in a static state or by using a dynamic force such as stirring to heat it in a flowing state. However, in terms of achieving uniform heating of the humidified mixture as a whole, heating under stirring is preferred. From this viewpoint, heat treatment apparatuses for performing the heat treatment can include paddle dryers, multi-finned dryers, tower dryers, etc.

[0144] From the viewpoints of the type and amount of surface crosslinking agent and the water absorption performance of the water-absorbing agent, the heating temperature in this process is preferably 150°C to 250°C, more preferably 170°C to 250°C, and even more preferably 180°C to 230°C. Furthermore, the heating time is at least 5 minutes, preferably at least 7 minutes. As an upper limit, it 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 aforementioned range improves the water absorption performance of the obtained water-absorbing agent, which is therefore preferable.

[0145] [2-6-3] Cooling process

[0146] This step is an arbitrary step that is added as needed after the heat treatment step. This step involves forcibly cooling the high-temperature water-absorbing resin after the heat treatment step to a specified temperature, so as to quickly end the surface cross-linking reaction.

[0147] [2-7] Chelating agent addition process

[0148] One aspect of the present invention comprises a chelating agent in its water-absorbing resin composition. The chelating agent can be added to monomers, hydrogels, dried polymers, base polymers (water-absorbing resin powder), or surface-crosslinked water-absorbing resins. In one embodiment of the invention, the chelating agent is added after a polymerization step, after a gel pulverization step, after a pulverization / gradation step, or after a surface crosslinking step. Adding it after the surface crosslinking step is particularly preferred. The addition of the chelating agent after the surface crosslinking step can be done simultaneously with or sequentially with the copper silicate.

[0149] In one embodiment of the present invention, the amount of chelating agent, calculated as active ingredient, is 10 ppm to 1000 ppm, 20 ppm to 800 ppm, 30 ppm to 600 ppm, 40 ppm to 500 ppm, 50 ppm to 300 ppm, 60 ppm to 200 ppm, or 70 ppm to 150 ppm relative to the water-absorbing resin.

[0150] In one embodiment of the present invention, heat treatment may be performed after the addition of the chelating agent. The preferred heat treatment temperature is, for example, 45°C to 75°C, 50°C to 70°C, or 55°C to 65°C. The heat treatment time 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-mentioned heat treatment may be performed after the addition of the chelating agent, followed by the addition of copper silicate.

[0151] [2-8] The process of adding copper silicate

[0152] One aspect of the present invention provides a water-absorbing resin composition containing copper silicate. Copper silicate can be added to hydrogels, dried polymers, base polymers (water-absorbing resin powder), or surface-crosslinked water-absorbing resins. In one embodiment of the invention, copper silicate is added after a polymerization step, after a gel pulverization step, after a pulverization / gradation step, or after a surface crosslinking step. Adding it after the surface crosslinking step is particularly preferred. As a result, the presence ratio of copper silicate on the surface of the water-absorbing resin is higher than the presence ratio inside the water-absorbing resin. Therefore, in one embodiment of the present invention, a water-absorbing resin composition in which the presence ratio of copper silicate on the surface of the water-absorbing resin is higher than the presence ratio inside the water-absorbing resin can be provided.

[0153] In one embodiment of the present invention, the amount of copper silicate used relative to the water-absorbing resin is 0.01% to 10% by mass, 0.05% to 9% by mass, 0.1% to 8% by mass, 0.2% to 7% by mass, 0.3% to 6% by mass, 0.4% to 5% by mass, 0.5% to 4% by mass, 0.6% to 3% by mass, or 0.7% to 2% by mass.

[0154] In one embodiment of the invention, no intentional heat treatment is performed after the addition of copper silicate.

[0155] [2-9] Steps for adding anti-staining agents or urine resistance improvers

[0156] Generally, absorbent resins also tend to stain and deteriorate easily. Therefore, in this invention, to prevent staining and deterioration, an anti-staining agent or a urine resistance (weather resistance) improver selected from inorganic or organic reducing agents (especially sulfur-based inorganic reducing agents) may also be included. The amount used is preferably 0 to 3 parts by weight, more preferably 0.001 to 1 part by weight, and particularly preferably 0.05 to 0.5 parts by weight, relative to 100 parts by weight of the absorbent resin, based on solid content. This preferred amount is consistent with the preferred content in the absorbent resin composition. That is, according to one embodiment of the invention, in the absorbent resin composition, the content of the anti-staining agent or the urine resistance improver is each independently 0 to 3 parts by weight, more preferably 0.001 to 1 part by weight, and particularly preferably 0.05 to 0.5 parts by weight, relative to 100 parts by weight of the absorbent resin. They are added to monomers, hydrogels, dry polymers, powders, etc., and the addition process is appropriately determined after the polymerization process. However, since the reducing agent in them is consumed during polymerization, it is preferred to add them after polymerization, more preferably after drying, and especially after surface crosslinking.

[0157] Examples of usable inorganic or organic reducing agents (particularly sulfur-based inorganic reducing agents) include sulfur-based reducing agents, particularly sulfites or bisulfites, as illustrated in U.S. Patent Application Publication No. 2010 / 0062252.

[0158] [2-10] Other processes

[0159] In addition to the above-mentioned processes, this invention may include, as needed, a granulation process, a sizing process, a micro-powder removal process, a micro-powder recovery process, a micro-powder reuse process, a process for adding other additives, and an iron removal process. Furthermore, it may also include at least one process selected from conveying, storage, bundling, and refrigeration processes.

[0160] It should be noted that the granulation process includes a step of classifying and removing the micropowder after the surface cross-linking process, or a step of classifying and pulverizing the micropowder when it aggregates beyond the desired size due to the presence of superabsorbent resin. Furthermore, the micropowder reuse process includes a step of forming the micropowder directly or during the granulation process into large hydrogels, and then adding them to the hydrogels or the like as raw materials in any step of the superabsorbent resin manufacturing process.

[0161] Furthermore, in the process of adding the anti-coloring agent or the urine resistance improver, in order to impart various functions to the absorbent, one or more other additives selected from organic powders such as oxidants and metal soaps, pulp, thermoplastic fibers, etc., may be added together with the anti-coloring agent or the urine resistance improver, or added in place of the anti-coloring agent or the urine resistance improver. Additionally, these other additives may be mixed simultaneously with or separately from the surface crosslinking agent. That is, the absorbent resin composition of the present invention may also contain such other additives.

[0162] [3] Characteristics of water-absorbing resin compositions

[0163] [3-1] Other properties of the water-absorbing resin composition

[0164] In one embodiment of the present invention, the water-absorbing resin composition preferably also possesses the following properties.

[0165] (3-1-1) Mass-average particle size (D50)

[0166] In one embodiment of the present invention, the mass-average particle size (D50) of the water-absorbing resin composition is preferably 300 μm or more, more preferably 305 μm or more, further preferably 310 μm or more, and particularly preferably 315 μm or more. Additionally, it is preferably 600 μm or less, more preferably 550 μm or less, further preferably 500 μm or less, and particularly preferably 450 μm or less. The range of this mass-average particle size (D50) can be any combination of the above-mentioned upper and lower limits.

[0167] By setting the mass-average particle size (D50) of the absorbent resin composition within the aforementioned range, the unpressurized absorbance ratio (CRC) and pressurized absorbance ratio (AAP) of the absorbent resin composition can be well controlled in a balanced manner in one embodiment of the invention described below. That is, by setting it within the aforementioned range, the unpressurized absorbance ratio (CRC) and pressurized absorbance ratio (AAP) can be increased, while the particle size of the absorbent resin can be suppressed, thereby improving skin feel and wearing experience when used in absorbent articles such as disposable diapers and sanitary napkins.

[0168] (3-1-2) CRC (Absorption Ratio without Pressure)

[0169] In one embodiment of the present invention, the CRC (centrifuge retention capacity) of the water-absorbing resin composition is typically 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. There is no particular limitation on the upper limit, and a higher value is preferred; however, from the viewpoint of balancing 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, as a representative range of the above-mentioned CRC (centrifuge retention capacity), it can be appropriately selected within the range of the above-mentioned upper and lower limits. For example, any range such as 5 g / g to 70 g / g, 20 g / g to 50 g / g, or 24 g / g to 45 g / g can be selected.

[0170] When the CRC (Chemical Reabsorbent Composite) is less than 5 g / g, the absorbency of the absorbent resin composition is low, making it unsuitable as an absorbent material for absorbent products such as diapers. Furthermore, when the CRC exceeds 70 g / g, the absorption rate of bodily fluids such as urine and blood decreases, making it unsuitable for high-absorbency diapers. It should be noted that the CRC can be controlled using internal cross-linking agents, surface cross-linking agents, etc.

[0171] (3-1-3) AAP (Water Absorption Ratio under Pressure)

[0172] In one embodiment of the present invention, the AAP (average absorbency 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, even more preferably 12 g / g or more, preferably 14 g / g or more, even more preferably 18 g / g or more, even more preferably 22 g / g or more, even more preferably 25 g / g or more, even more preferably 28 g / g or more, and even more preferably 30 g / g or more. There is no particular limitation on the upper limit, but it is preferably 40 g / g or less, 35 g / g or less, or 33 g / g or less.

[0173] When the AAP content is less than 5g / g, the absorbency decreases when pressure is applied to the absorbent material during actual use in diapers and similar products, making it unsuitable as an absorbent material for absorbent items such as diapers. It should be noted that AAP can be controlled using particle size, surface cross-linking agents, etc.

[0174] [4] Uses of water-absorbing resin compositions (absorbent, absorbent layer)

[0175] The absorbent resin composition of the present invention is preferably used primarily as an absorbent body (absorbent layer) for absorbent articles such as disposable diapers and sanitary napkins, and more preferably as an absorbent body (absorbent layer) for absorbent articles in which a large amount is used per absorbent article. Therefore, in one embodiment of the present invention, an absorbent body containing an absorbent resin composition and hydrophilic fibers is provided.

[0176] The absorbent refers to an absorbent formed by molding the absorbent resin composition into sheets, fibers, tubes, etc., preferably into sheets to form an absorbent layer. In addition to the absorbent resin composition of the present invention, absorbent materials such as pulp fibers, adhesives, and nonwoven fabrics may also be used during molding. In this case, the amount of absorbent 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. When the core concentration is less than 20% by mass, the amount of absorbent resin composition used is small, and for example, it may not be sufficient to impart deodorizing properties to the diaper as a whole, which is not preferred.

[0177] When manufacturing the absorbent of the present invention from a water-absorbing resin composition and hydrophilic fibers, the manufacturing method is not particularly limited. For example, the following method can be used: dry mixing the water-absorbing resin composition and hydrophilic fibers in a ratio equal to the aforementioned core concentration using a mixer such as a stirrer; forming the resulting mixture into a mesh shape by, for example, air forming; and then compressing it as needed. The absorbent is preferably compressed to a density of 0.001 g / cc to 0.50 g / cc and a basis weight of 0.01 g / cm³. 2 ~0.20g / cm 2 The range.

[0178] [5] Absorbent items

[0179] The absorbent article of the present invention includes the absorbent body (absorbent layer), which typically has a liquid-permeable surface sheet and a liquid-impermeable back sheet. Examples of absorbent articles include disposable diapers and sanitary napkins. Therefore, in one embodiment of the present invention, an absorbent article having an absorbent body, a liquid-permeable surface sheet, and a liquid-impermeable back sheet is provided.

[0180] In one embodiment of the present invention, when the absorbent article is, for example, a disposable diaper, the disposable diaper is manufactured by sandwiching an absorbent containing a water-absorbing resin composition between a liquid-permeable upper pad that is in contact with the skin when worn and a liquid-impermeable lower pad that is on the outside when worn. It should be noted that the disposable diaper also includes components known to those skilled in the art, such as adhesive tape for securing the disposable diaper after wearing.

[0181] It should be noted that, in addition to the disposable diapers and sanitary napkins, the absorbent resin composition of the present invention can also be suitably used for pets and portable toilets.

[0182] The present invention includes the following schemes and methods.

[0183] 1. A water-absorbing resin composition comprising a water-absorbing resin, a copper silicate, and a chelating agent.

[0184] 2. The water-absorbing resin composition according to 1, wherein the chelating agent contains at least one compound selected from the group consisting of amino polycarboxylic acids, amino polyphosphates and their salts.

[0185] 3. The water-absorbing resin composition according to 1 or 2, wherein the copper silicate is present in a higher proportion on the surface of the water-absorbing resin than in the interior of the water-absorbing resin.

[0186] 4. The water-absorbing resin composition according to any one of 1 to 3, wherein the copper silicate is composed of an amorphous structure.

[0187] 5. The water-absorbing resin composition according to any one of 1 to 4, wherein the solubility of the copper silicate in ion-exchanged water at 25°C is less than 0.5 g / 100 mL H2O.

[0188] 6. The water-absorbing resin composition according to any one of 1 to 5, wherein the copper silicate contains sulfur atoms.

[0189] 7. The water-absorbing resin composition according to any one of 1 to 6, wherein copper accounts for 50% or more by mass of all the polyvalent metal components contained in the copper silicate.

[0190] 8. The water-absorbing 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.

[0191] 9. An absorbent comprising a water-absorbing resin composition according to any one of 1 to 8 above.

[0192] 10. An absorbent article comprising an absorbent body according to claim 9, a liquid-permeable surface sheet, and a liquid-impermeable back sheet.

[0193] Example

[0194] The present invention will now be described in more detail through 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 the examples are also included within the scope of the present invention. It should be noted that, unless otherwise specified, the electrical equipment used in the examples and comparative examples, as well as in the determination of the various properties of the water-absorbing resin and the water-absorbing resin composition, uses a 200V or 100V / 60Hz power supply. Unless otherwise specified, the various properties of the water-absorbing resin and the water-absorbing resin composition are determined at room temperature (20℃~25℃) and a relative humidity of 50±5%RH. Furthermore, for convenience, "liter" is sometimes written as "l" or "L", and "mass%" is written as "wt%".

[0195] [Manufacturing Example 1]

[0196] A monomer aqueous solution was prepared by mixing 67.0 parts by weight of a 37% sodium acrylate aqueous solution, 10.2 parts by weight of acrylic acid, 0.084 parts by weight of polyethylene glycol diacrylate (with an average molar addition of 9 ethylene oxides), and 22.0 parts by weight of water. Nitrogen gas was blown into the monomer aqueous solution in a butt to reduce the dissolved oxygen content to below 0.1 ppm. The temperature of the monomer aqueous solution was then adjusted to 18°C ​​under a nitrogen atmosphere. Subsequently, 0.16 parts by weight of a 5% sodium persulfate aqueous solution, 0.16 parts by weight of a 5% 2,2'-azobis(2-amidinylpropane) dihydrochloride aqueous solution, 0.15 parts by weight of a 0.5% L-ascorbic acid aqueous solution, and 0.17 parts by weight of a 0.35% hydrogen peroxide aqueous solution were added dropwise with stirring. Polymerization was initiated immediately after the addition of hydrogen peroxide. Stirring was then stopped, and the monomer temperature reached its peak temperature of 85°C after 10 minutes. Next, the tank was immersed in a hot water bath at 80°C and matured for 10 minutes. The resulting transparent hydrogel-like crosslinked polymer was then pulverized using a meat grinder. The refined hydrogel-like crosslinked polymer (particulate hydrogel) was then spread on a 50-mesh (300μm mesh) metal grid and dried in hot air at 180°C for 30 minutes to obtain a dried polymer.

[0197] The obtained dried polymer was pulverized using a pulverizer and classified into polymers that passed through a 500 μm sieve and remained on a 105 μm sieve, thereby obtaining a water-absorbing resin powder.

[0198] A surface crosslinking agent solution 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 isopropanol was mixed into 100 parts by mass of the obtained water-absorbing resin powder and heated at 180°C for 40 minutes to obtain surface-crosslinked water-absorbing resin particles.

[0199] [Example 1]

[0200] 1.0 part by mass of a 1.0% (w / w) trisodium diethylenetriaminepentaacetate aqueous solution was added to 100 parts by mass of the surface-crosslinked absorbent resin particles obtained in Manufacturing Example 1, and the mixture was heated at 60°C for 30 minutes. Then, 1.0 part by mass of copper silicate (A) (volume average particle size: 7 μm, solubility in ion-exchanged water at 25°C: 0 g / 100 mL H₂O) satisfying the atomic ratio and weight ratio of Si shown in Table 1 below was added to obtain a mixture. The mixture was then passed through a JIS standard sieve with a mesh size of 850 μm to obtain the absorbent resin composition (1). The results of the determination of various physical properties of the obtained absorbent resin composition (1) are shown in Table 5. The copper silicate (A) is composed of an amorphous structure.

[0201] It should be noted that the atomic number ratio and weight ratio were determined using SEM-EDS analysis with a scanning electron microscope. Specifically, an image of the additive was obtained using a JCM-6000 Neoscope desktop scanning electron microscope (manufactured by Nippon Electronics Corporation) at a magnification of 1000x, and the atomic number ratio and weight ratio of the constituent elements of the additive were analyzed by energy-dispersive X-ray spectroscopy (EDS).

[0202] [Example 2]

[0203] The 1.0% by mass trisodium diethylenetriaminepentaacetic acid aqueous solution was replaced with a 1.0% by mass pentasodium ethylenediaminetetra(methylenephosphonic acid) aqueous solution, and the water-absorbing resin composition (2) was otherwise obtained in the same manner as in Example 1. The results of the determination of various physical properties of the water-absorbing resin composition (2) are shown in Table 5.

[0204] [Example 3]

[0205] The copper silicate (A) was replaced with copper silicate (B) with the atomic ratio and weight ratio relative to Si shown in the table below (volume average particle size: 3 μm, solubility in ion-exchanged water at 25°C: 0 g / 100 mL - H2O), otherwise, the water-absorbing resin composition (3) was obtained in the same manner as in Example 1. The results of the determination of various physical properties of the water-absorbing resin composition (3) are shown in Table 5. The copper silicate (B) is composed of an amorphous structure.

[0206] [Table 1]

[0207]

[0208] [Comparative Example 1]

[0209] The comparative absorbent resin (1) was obtained in the same manner as in Example 1, except that 1.0 parts by weight of 1.0% trisodium diethylenetriaminepentaacetate aqueous solution was replaced with 1.0 parts by weight of water and no copper silicate (A) was added. The results of the determination of various physical properties of the comparative absorbent resin (1) are shown in Table 5.

[0210] [Comparative Example 2]

[0211] Without the addition of copper silicate (A), the comparative absorbent resin composition (2) was obtained in the same manner as in Example 1. The results of the determination of various physical properties of the comparative absorbent resin composition (2) are shown in Table 5.

[0212] [Comparative Example 3]

[0213] Without the addition of chelating agents, the comparative absorbent resin composition (3) was obtained in the same manner as in Example 1. The results of the determination of various physical properties of the comparative absorbent resin composition (3) are shown in Table 5.

[0214] [Comparative Example 4]

[0215] The 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 H₂O) that satisfies the atomic ratio and weight ratio of Si shown in Table 2 below. Otherwise, the comparative absorbent resin composition (4) was obtained in the same manner as in Example 1. The results of the determination of various physical properties of the comparative absorbent resin composition (4) are shown in Table 5.

[0216] [Table 2]

[0217]

[0218] [Comparative Example 5]

[0219] The copper silicate (A) was replaced with copper gluconate (II) (which has a solubility of 30 g / 100 mL H2O in ion-exchanged water at 25 °C), and the comparative absorbent resin composition (5) was otherwise obtained in the same manner as in Example 1. The results of the determination of various physical properties of the comparative absorbent resin composition (5) are shown in Table 5.

[0220] [Comparative Example 6]

[0221] The copper silicate (A) was replaced with sodium copper chlorophyllin (solubility of 1 g / 100 mL-H2O in ion-exchanged water at 25 °C), and the comparative absorbent resin composition (6) was otherwise obtained in the same manner as in Example 1. The results of the determination of various physical properties of the comparative absorbent resin composition (6) are shown in Table 5.

[0222] [Comparative Example 7]

[0223] The copper silicate (A) was replaced with a copper oxide-zinc oxide composite aluminosilicate (copper and zinc-supported zeolite) (trade name: Dushlite CZU, manufactured by Sinanen Zeomic Co., Ltd., average particle size = 4 μm) that satisfies the atomic ratio and weight ratio relative to Si shown in Table 3 below. Otherwise, the comparative absorbent resin composition (7) was obtained in the same manner as in Example 1. The results of the determination of various physical properties of the comparative absorbent resin composition (7) are shown in Table 5.

[0224] [Table 3]

[0225]

[0226] [Evaluation of the water-absorbing resin composition]

[0227] (a) Mass average particle size (D50)

[0228] The mass average particle size (D50) of the water-absorbing resin composition was determined according to the particle size analysis method of EDANA WSP220.2, using sieves with mesh sizes of 850 μm, 710 μm, 600 μm, 500 μm, 300 μm, 150 μm, and 45 μm from top to bottom.

[0229] (b) Absorption Ratio (CRC) without Pressure

[0230] The CRC of the water-absorbing resin composition was determined according to the EDANA method WSP241.3 (10).

[0231] (c) Absorption rate under pressure (AAP 0.3psi)

[0232] The AAP of the absorbent resin composition was determined according to the EDANA method NWSP 242.0.R2 (15). The loading was at 0.3 psi (= 21 g / cm³). 2 The evaluation was conducted at a pressure of 2.06 kPa.

[0233] (d) Evaluation of the deodorizing performance of human urine

[0234] 2.0g of the absorbent resin (or absorbent resin composition) obtained in the above examples or comparative examples was mixed with 4.0g of wood pulp to prepare a simple absorbent. The simple absorbent was placed in a 250ml capped polypropylene cup, and 50ml of human urine collected from multiple adults was added. The urine used was urine collected within 2 hours of excretion. The container was capped, and the simple absorbent was kept at 40°C. Three hours after the liquid absorption began, the cap was opened, and a panel of 20 adults smelled the odor from approximately 3cm above the top of the cup to determine the deodorizing effect. The determination was made using the following criteria, with each person scoring on a 6-point scale, and the average score was calculated.

[0235] [Table 4]

[0236]

[0237] (e) Methanethiol (MM) concentration

[0238] 1. Place 5g of the water-absorbing resin composition into a mayonnaise jar (manufactured by Yamamura Glass Co., Ltd., Japan, outer diameter 62mm, height 109.2mm, capacity 241.8mL), add 25g of 0.9% sodium chloride aqueous solution, and allow it to swell.

[0239] 2. Cap the mayonnaise jar and place it in a paint shaker (No. 488 Experimental Disperser, manufactured by Toyo Seiki Co., Ltd.). Then, shake the paint shaker at 800 cycles / min for 1 minute, and then stop.

[0240] 3. Add 1g of 0.1% sodium methanethiol aqueous solution (a commercially available reagent prepared by diluting a 15% sodium chloride aqueous solution with a 0.9% sodium chloride aqueous solution) to the mayonnaise bottle.

[0241] 4. After sealing the mayonnaise jar and storing it at 30°C for 1 hour, open the lid and use a test tube to measure the concentration of methanethiol in the upper part of the jar.

[0242] (f) Increase rate of methanethiol (MM) concentration

[0243] In section 4 above, the storage temperature was changed to 40°C. All other procedures were performed, and the concentration of methanethiol (MM) at 40°C was measured. The increase in MM concentration due to the temperature increase was calculated using the following formula.

[0244] The percentage increase in MM concentration due to temperature rise [%] = {(MM concentration at 40℃) / (MM concentration at 30℃) - 1} × 100.

[0245] [Table 5]

[0246]

[0247] <Discussion>

[0248] Comparative Example 1 is a blank test using only absorbent resin, in which neither urine odor nor methanethiol odor was suppressed.

[0249] As can be seen from the comparison of Comparative Examples 1 and 2, the application of chelating agents alone in the absorbent resin is insufficient to suppress urine odor. Furthermore, as shown in Examples 1-3, only by combining chelating agents and copper silicates in the absorbent resin can both urine odor and methanethiol odor be suppressed. It is also worth noting that the absorbent resin compositions of Examples 1-3 can suppress the regeneration of methanethiol odor even when the storage environment becomes high.

[0250] As shown in Comparative Example 4, even when copper-free silicates are applied to the absorbent resin, the odors of urine and methanethiol cannot be suppressed.

[0251] As shown in Comparative Examples 5 and 6, even when non-silicate water-soluble copper compounds are applied to the absorbent resin, they cannot suppress the odors of urine and methanethiol.

[0252] As shown in Comparative Example 7, when an inorganic antibacterial agent, which is made by loading antibacterial metals such as copper and zinc onto an inorganic compound, is applied to a water-absorbing resin, it can suppress urine odor and methanethiol odor to a certain extent. However, when the storage environment becomes high temperature, the methanethiol odor that was once suppressed will reappear.

[0253] As described above, by combining copper silicate with a chelating agent and applying it to absorbent resin, the following effects can be achieved: compared with the past, it can further improve the reduction of urine odor and also inhibit the regeneration of odor in high temperature environments.

[0254] This application is based on Japanese Patent Application No. 2023-143714, filed on September 5, 2023, the entire disclosure of which is incorporated herein by reference.

Claims

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

2. The water-absorbing resin composition according to claim 1, wherein, The chelating agent contains at least one compound selected from the group consisting of amino polycarboxylic acids, amino polyphosphates, and their salts.

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

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

5. The water-absorbing resin composition according to any one of claims 1 to 4, wherein, The solubility of the copper silicate in ion-exchanged water at 25°C is less than 0.5 g / 100 mL H2O.

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

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

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

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

Images