Water-absorbent resin composition

Abstract

Provided is a water-absorbent resin composition having an excellent deodorizing effect. A water-absorbent resin composition containing an organic acid, a porous deodorant, and water-absorbent polymer particles, the ratio (X / Y) of the content X (parts by mass) of the organic acid to the content Y (parts by mass) of the porous deodorant being 1.0 or more, the sum (x + y) of the content x (mass%) of the organic acid and the content y (mass%) of the porous deodorant in the entire water-absorbent resin composition is 0.50 mass% or more.

Description

Technical Field

[0001] The present invention relates to a water-absorbent resin composition, and more particularly to a water-absorbent resin composition constituting an absorbent body suitable for use in sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads. Background Art

[0002] In recent years, water-absorbent resins have been widely used in sanitary materials such as diapers, sanitary napkins, and incontinence pads.

[0003] As such water-absorbing resins, cross-linked polymers containing structural units derived from acrylic acid and its neutralized salts are known to have excellent water absorption capacity. Furthermore, since acrylic acid, the raw material, is readily available industrially, these cross-linked polymers offer numerous advantages, including consistent quality, low-cost production, and resistance to spoilage and degradation. Therefore, they are considered to be preferred water-absorbing resins.

[0004] Meanwhile, absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads primarily consist of an absorbent core positioned in the center to absorb and retain body fluids such as urine and menstrual blood; a liquid-permeable topsheet (top sheet) positioned on the side that contacts the body; and a liquid-impermeable backsheet (back sheet) positioned on the opposite side. The absorbent core is typically composed of hydrophilic fibers such as pulp and a water-absorbent resin.

[0005] When such absorbent bodies are used in sanitary materials, for example, unpleasant odors such as ammonia may be generated from the absorbent bodies that have absorbed body fluids, particularly urine, blood, sweat, and the like.

[0006] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Laid-Open No. 2001-323155 Summary of the Invention Technical problem to be solved by the invention When urine is absorbed by the absorbent, the urease in the urine is broken down by the action of urease possessed by urease-producing bacteria, producing ammonia.

[0007] The present inventors attempted to inactivate urease by lowering the pH of urine using organic acids, thereby inhibiting the urease-induced urea decomposition reaction and suppressing ammonia production. However, their research revealed the following problem: the pH buffering effect of the water-absorbing polymer particles in the absorbent core shifted the pH of urine lowered by the organic acids toward neutrality, weakening the urease-inactivating effect of the organic acids and preventing a sufficient deodorizing effect.

[0008] The main object of the present invention is to provide a water-absorbent resin composition having an excellent deodorizing effect.

[0009] Technical solutions to technical problems The present inventors conducted intensive research to address the above-mentioned issues. As a result, they discovered that, in a water-absorbent resin composition containing water-absorbent polymer particles, by using an organic acid and a porous deodorant in combination, and by ensuring that the ratio (X / Y) of the organic acid content X (parts by mass) to the porous deodorant content Y (parts by mass) is at least a predetermined ratio, and further ensuring that the sum (x+y) of the organic acid content x (mass %) and the porous deodorant content y (mass %) in the entire water-absorbent resin composition is at least a predetermined ratio, the water-absorbent resin composition exhibits a high deodorizing function against ammonia. The present invention was completed as a result of further intensive research based on this finding.

[0010] That is, the present invention provides an invention having the following configuration.

[0011] Item 1. A water-absorbent resin composition comprising an organic acid, a porous deodorant, and water-absorbent polymer particles having a structural unit derived from a neutralized salt of an ethylenically unsaturated monomer, The ratio (X / Y) of the content X (parts by mass) of the organic acid to the content Y (parts by mass) of the porous deodorant is 1.0 or more, The sum (x+y) of the content x (mass %) of the organic acid in the entire water-absorbing resin composition and the content y (mass %) of the porous deodorant is 0.50 mass % or more.

[0012] Item 2. The water-absorbent resin composition according to Item 1, wherein a ratio (X / Y) of the content X (parts by mass) to the content Y (parts by mass) is 12.0 or less.

[0013] Item 3. The water-absorbent resin composition according to Item 1 or 2, wherein the sum (x+y) of the content x (mass %) of the organic acid and the content y (mass %) of the porous deodorant is 1.50 mass % or less.

[0014] Item 4. An absorbent article comprising an organic acid, a porous deodorant, and water-absorbing polymer particles, The ratio (X / Y) of the content X (parts by mass) of the organic acid to the content Y (parts by mass) of the porous deodorant is 1.0 or more, The sum (x+y) of the content x (mass %) of the organic acid and the content y (mass %) of the porous deodorant based on the total amount of the organic acid, the porous deodorant, and the water-absorbing polymer particles is 0.5 mass % or more.

[0015] Effects of the Invention According to the present invention, a water-absorbent resin composition having an excellent deodorizing effect can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the device for measuring the water absorption of physiological saline under a load of 4.14 kPa. DETAILED DESCRIPTION

[0017] In this specification, the term "comprising" includes "consisting essentially of" and "consisting of." Furthermore, in this specification, "(meth)acrylic acid" refers to "acrylic acid or methacrylic acid," and "(meth)acrylate" refers to "acrylate or methacrylate." It should be noted that "water-soluble" means a solubility of 5% by mass or greater in water at 25°C.

[0018] In addition, in this specification, the numerical value connected by "-" means the numerical range including the numerical values ​​before and after "-" as the lower limit and upper limit. When multiple lower limits and multiple upper limits are separately described, any lower limit and upper limit can be selected and connected by "-".

[0019] 1. Water-absorbent resin composition The water-absorbent resin composition of the present invention is characterized by comprising an organic acid, a porous deodorant, and water-absorbent polymer particles; the ratio (X / Y) of the organic acid content X (parts by mass) to the porous deodorant content Y (parts by mass) is 1.0 or greater; and the sum (x + y) of the organic acid content x (mass %) and the porous deodorant content y (mass %) in the entire water-absorbent resin composition is 0.5 mass % or greater. The water-absorbent resin composition of the present invention, possessing these characteristics, exhibits excellent deodorizing effects. The water-absorbent resin composition of the present invention is described in detail below.

[0020] As described above, the present inventors attempted to inactivate urease by lowering the pH of urine using organic acids, thereby inhibiting the urease-induced urea decomposition reaction and suppressing ammonia production. However, the present inventors' research revealed the following problem: the pH of urine lowered by the organic acids shifts toward neutrality due to the pH buffering effect of the water-absorbing polymer particles in the absorbent body, weakening the urease-inactivating effect of the organic acids and preventing a sufficient deodorizing effect. Furthermore, the present inventors have conducted extensive research and discovered that, in a water-absorbent resin composition containing water-absorbent polymer particles, by combining an organic acid and a porous deodorant, and further increasing the ratio (X / Y) of the organic acid content (X (parts by mass) to the porous deodorant content (Y (parts by mass)) to 1.0 or greater, and further increasing the sum (x + y) of the organic acid content (x (mass%)) and the porous deodorant content (y (mass%)) in the entire water-absorbent resin composition to 0.5 mass% or greater, the organic acid and the porous deodorant function synergistically, resulting in the water-absorbent resin composition exhibiting a high deodorizing effect against ammonia. This is presumably because the porous deodorant suppresses the pH buffering effect of the water-absorbent polymer particles (more specifically, the pH buffering effect derived from the neutralized salt of the water-soluble ethylenically unsaturated monomer contained as a structural unit of the water-absorbent polymer particles), thereby effectively inactivating urease due to the organic acid, and thus enabling the water-absorbent resin composition to exhibit a high deodorizing effect against ammonia and the like.

[0021] In the water-absorbent resin composition of the present invention, at least a portion of the organic acid (e.g., 20% to 100% by mass, 50% to 100% by mass, 80% to 100% by mass, 90% to 100% by mass, 95% to 100% by mass, or 100% by mass of the total organic acid) can be disposed on the surface of the water-absorbent polymer particles, or at least a portion of the organic acid can penetrate into the interior of the water-absorbent polymer particles. Furthermore, in the water-absorbent resin composition of the present invention, at least a portion of the porous deodorant (e.g., 20% to 100% by mass, 50% to 100% by mass, 80% to 100% by mass, 90% to 100% by mass, 95% to 100% by mass, or 100% by mass of the total porous deodorant) can be disposed on the surface of the water-absorbent polymer particles. In the water-absorbent resin composition of the present invention, at least a portion of the organic acid and at least a portion of the porous deodorant can be disposed on the surface of the water-absorbent polymer particles.

[0022] (Organic acid) Organic acids are components that lower the pH of urine absorbed by the absorbent.

[0023] The pH of a 10% by mass aqueous solution of the organic acid measured by the following method may be, for example, 1.0 to 6.0, 1.0 to 4.0, 1.0 to 3.0, 1.0 to 2.0, 1.5 to 6.0, 1.5 to 4.0, 1.5 to 3.0, or 1.5 to 2.0.

[0024] The organic acid may include, for example, at least one selected from tartaric acid, citric acid, malic acid, maleic acid, fumaric acid, succinic acid, acetic acid, and propionic acid. It may also include at least one selected from tartaric acid, citric acid, malic acid, and maleic acid. The organic acid preferably includes at least tartaric acid, as the present inventors speculate that it is less likely to be adsorbed by porous deodorants (i.e., it tends to lower urine pH). In this case, the proportion of tartaric acid may be 70% to 100% by mass, 80% to 100% by mass, 90% to 100% by mass, or 95% to 100% by mass of the organic acid. Tartaric acid is preferably in the L-form, as it is believed to be less likely to be adsorbed by porous deodorants. The water-absorbent resin composition may contain only one organic acid or two or more.

[0025] From the viewpoint of better exerting the effects of the present invention, when the organic acid is in a granular form, the median particle size (D50 (median diameter), volume basis) of the organic acid may be 20 μm to 600 μm, 20 μm to 500 μm, 20 μm to 400 μm, 20 μm to 300 μm, 50 μm to 600 μm, 50 μm to 500 μm, 50 μm to 400 μm, 50 μm to 300 μm, 100 μm to 600 μm, 100 μm to 500 μm, 100 μm to 400 μm, 100 μm to 300 μm, 150 μm to 600 μm, 150 μm to 500 μm, 150 μm to 400 μm, or 150 μm to 300 μm. The median particle size (D50 (median diameter), volume basis) of the organic acid can be measured using a laser diffraction particle size distribution analyzer.

[0026] The sum (x+y) of the content x (mass %) of the organic acid in the entire water-absorbent resin composition of the present invention and the content y (mass %) of the porous deodorant is 0.50 mass % or more. From the perspective of further exerting the effects of the present invention, the sum (x+y) may be 0.50 mass % to 2.00 mass %, 0.50 mass % to 1.50 mass %, 0.50 mass % to 1.40 mass %, 0.50 mass % to 1.30 mass %, 0.50 mass % to 1.20 mass %, 0.50 mass % to 1.00 mass %, 0.53 mass % to 2.00 mass %, 0.53 mass % to 1.50 mass %, 0.53 mass % to 1.40 mass %, 0.53 mass % to 1.30 mass %, 0.53 mass % to 1.20 mass %, 0. % to 1.00 mass%, 0.56 mass% to 2.00 mass%, 0.56 mass% to 1.50 mass%, 0.56 mass% to 1.40 mass%, 0.56 mass% to 1.30 mass%, 0.56 mass% to 1.20 mass%, 0.56 mass% to 1.00 mass%, 0.59 mass% to 2.00 mass%, 0.59 mass% to 1.50 mass%, 0.59 mass% to 1.40 mass%, 0.59 mass% to 1.30 mass%, 0.59 mass% to 1.20 mass%, or 0.59 mass% to 1.00 mass%. Note that when the organic acid is in particulate form, if the sum (x + y) of the organic acid content x (mass %) and the porous deodorant content y (mass %) is large, the organic acid and the porous deodorant are more likely to come into contact and rub against each other, resulting in the generation of fine powder (in other words, increased dust generation), which may reduce the handleability of the water-absorbent resin composition. Considering this dust generation, the sum (x + y) is preferably 1.50% by mass or less.

[0027] Furthermore, from the perspective of further exerting the effects of the present invention, the content x (mass %) of the organic acid in the entire water-absorbent resin composition of the present invention may be 0.30% to 1.20% by mass, 0.30% to 1.00% by mass, 0.30% to 0.80% by mass, 0.40% to 1.20% by mass, 0.40% to 1.00% by mass, 0.40% to 0.80% by mass, 0.45% to 1.20% by mass, 0.45% to 1.00% by mass, or 0.45% to 0.80% by mass. Note that as the content x (mass %) of the organic acid increases, the water absorption rate of the water-absorbent resin composition tends to decrease. Therefore, in view of this, the upper limit of the content x (mass %) is preferably 1.00% by mass.

[0028] In the water-absorbing resin composition of the present invention, the ratio (X / Y) of the content X (parts by mass) of the organic acid to the content Y (parts by mass) of the porous deodorant is 1.0 or more. From the viewpoint of better exhibiting the effects of the present invention, the ratio (X / Y) may be 1.0 to 15.0, 1.0 to 12.0, 1.0 to 10.0, 1.0 to 8.0, 1.0 to 6.0, 1.5 to 15.0, 1.5 to 12.0, 1.5 to 10.0, 1.5 to 8.0, 1.5 to 6.0, 2.0 to 15.0, 2.0 to 12.0, 2.0 to 10.0, 2.0 to 8.0, 2.0 to 6.0, 2.5 to 15.0, 2.5 to 12.0, 2.5 to 10.0, 2.5 to 8.0, 2.5 to 6.0, 3.0 to 15.0, 3.0 to 12.0, 3.0 to 10.0, 3.0 to 8.0, or 3.0 to 6.0. In addition, considering the influence of the organic acid on the water absorption rate of the water-absorbent resin composition, the upper limit of the ratio (X / Y) is preferably 12.0.

[0029] As described above, in the water-absorbent resin composition of the present invention, when the organic acid is in particulate form, the organic acid can be disposed on the surface of the water-absorbent polymer particles (i.e., the organic acid is present on the surface of the water-absorbent polymer particles). For example, by mixing the water-absorbent polymer particles and the particulate organic acid in a solid phase, the organic acid adheres to the surface of the water-absorbent polymer particles, thereby disposing the organic acid on the surface of the water-absorbent polymer particles.

[0030] (Porous deodorant) Porous deodorant is a porous deodorant.

[0031] To better demonstrate the effects of the present invention, the porous deodorant may contain at least one selected from zeolite, activated carbon, silica, silicates, titanium dioxide, alumina, aluminum hydroxide, and magnesium hydroxide, or may contain at least one selected from zeolite, activated carbon, and silica. In particular, since it is presumed to be less susceptible to adsorption of organic acids, the porous deodorant preferably contains at least activated carbon, with the proportion (mass %) being, for example, 80% to 100%, 90% to 100%, or 95% to 100%.

[0032] The median particle size of the porous deodorant may be 1 μm to 100 μm, 1 μm to 80 μm, 1 μm to 60 μm, 10 μm to 100 μm, 10 μm to 80 μm, 10 μm to 60 μm, 15 μm to 100 μm, 15 μm to 80 μm, 15 μm to 60 μm, 20 μm to 100 μm, 20 μm to 80 μm, or 20 μm to 60 μm.

[0033] The median particle size (D50 (median diameter), volume basis) of the porous deodorant can be measured using a laser diffraction particle size distribution analyzer. Specifically, it is a value measured by the method described in Examples.

[0034] The shape of the porous deodorant is, for example, a crushed shape or a cylindrical shape, and preferably a crushed shape.

[0035] The BET specific surface area of ​​porous deodorants can be 100m 2 / g~3000m 2 / g、100m 2 / g~2500m 2 / g、100m 2 / g~2000m 2 / g、100m 2 / g~1500m 2 / g、500m 2 / g~3000m 2 / g、500m 2 / g~2500m 2 / g、500m 2 / g~2000m 2 / g、500m 2 / g~1500m 2 / g、1000m 2 / g~3000m 2 / g、1000m 2 / g~2500m 2 / g、1000m 2 / g~2000m 2 / g or 1000m 2 / g~1500m 2 When the BET specific surface area of ​​the porous deodorant is too large, each pore becomes finer, thereby reducing the strength of the porous deodorant and possibly increasing the dust generation rate. Therefore, the upper limit of the BET specific surface area is preferably 2000 m 2 / g.

[0036] The BET specific surface area of ​​the porous deodorant can be measured using a specific surface area measuring device, and specifically, is a value measured by the method described in Examples.

[0037] To maximize the effectiveness of the present invention, the activated carbon used as the porous deodorant is preferably one having polar functional groups (hydrophilic functional groups) on its surface (i.e., hydrophilic activated carbon). Examples of polar functional groups include hydroxyl groups, carboxyl groups, and phenolic groups. Activated carbon having polar functional groups on its surface is commercially available, for example, as liquid phase activated carbon and water treatment activated carbon.

[0038] Examples of sources for activated carbon include coconut shells, infusible or carbonized organic materials, and infusible resins such as phenolic resins. Examples of organic materials include polyacrylonitrile, asphalt, polyvinyl alcohol, and cellulose. Among these, preferred sources for activated carbon are wood (sawdust), coconut shells, and asphalt (e.g., coal tar).

[0039] From the viewpoint of better exerting the effects of the present invention, the content y (mass %) of the porous deodorant in the water-absorbent resin composition of the present invention may be 0.05% by mass to 0.50% by mass, 0.05% by mass to 0.40% by mass, 0.05% by mass to 0.35% by mass, 0.05% by mass to 0.30% by mass, 0.07% by mass to 0.50% by mass, 0.07% by mass to 0.40% by mass, 0.07% by mass to 0.35% by mass, 0.07% by mass to 0.30% by mass, 0.08% by mass to 0.50% by mass, 0.08% by mass to 0.40% by mass, 0.08% by mass to 0.35% by mass, 0.08% by mass to 0.30% by mass, 0.10% by mass % to 0.50 mass%, 0.10 mass% to 0.40 mass%, 0.10 mass% to 0.35 mass%, 0.10 mass% to 0.30 mass%, 0.15 mass% to 0.50 mass%, 0.15 mass% to 0.40 mass%, 0.15 mass% to 0.35 mass%, 0.15 mass% to 0.30 mass%, 0.20 mass% to 0.50 mass%, 0.20 mass% to 0.40 mass%, 0.20 mass% to 0.35 mass%, 0.20 mass% to 0.30 mass%, 0.25 mass% to 0.50 mass%, 0.25 mass% to 0.40 mass%, 0.25 mass% to 0.35 mass%, or 0.25 mass% to 0.30 mass%.

[0040] The loss on drying of the porous deodorant may be, for example, 0.1% to 15.0%, 0.1% to 10.0%, 0.1% to 5.0%, 0.5% to 15.0%, 0.5% to 10.0%, 0.5% to 5.0%, 1.0% to 15.0%, 1.0% to 10.0%, or 1.0% to 5.0%.

[0041] Here, the loss on drying of the porous deodorant refers to a value measured in accordance with JIS K1474:2014.

[0042] The pH of the porous deodorant can be, for example, 2.0-12.0, 2.0-11.0, 2.0-8.0, 2.0-6.0, 2.0-5.0, 3.0-12.0, 3.0-11.0, 3.0-8.0, 3.0-6.0, 3.0-5.0, 4.0-12.0, 4.0-11.0, 4.0-8.0, 4.0-6.0, or 4.0-5.0. It should be noted that if the porous deodorant is acidic, the synergistic effect of the porous deodorant and the organic acid makes it easier to inactivate urease, thereby further enhancing the effects of the present invention. From this perspective, the upper limit of the pH of the porous deodorant can be 6.0 or 5.0.

[0043] Here, the pH of the porous deodorant refers to a value measured in accordance with JIS K1474:2014.

[0044] As described above, in the water-absorbent resin composition of the present invention, the porous deodorant is preferably disposed on the surface of the water-absorbent polymer particles (i.e., the porous deodorant is present on the surface of the water-absorbent polymer particles). For example, the porous deodorant can be disposed on the surface of the water-absorbent polymer particles by mixing the water-absorbent polymer particles and the porous deodorant in a solid phase so that the porous deodorant adheres to the surface of the water-absorbent polymer particles.

[0045] Next, the water-absorbing polymer particles (water-absorbing resin particles) contained in the water-absorbing resin composition of the present invention will be described in detail.

[0046] (Water-absorbent polymer particles) The water-absorbent polymer particles contained in the water-absorbent resin composition of the present invention are composed of a cross-linked polymer of a water-soluble ethylenically unsaturated monomer, that is, a cross-linked polymer having a structural unit derived from a water-soluble ethylenically unsaturated monomer.

[0047] The water absorption rate of the water-absorbing polymer particles by a vortex method may be, for example, 1 to 80 seconds, 1 to 60 seconds, 1 to 40 seconds, 10 to 80 seconds, 10 to 60 seconds, 10 to 40 seconds, 20 to 80 seconds, 20 to 60 seconds, or 20 to 40 seconds.

[0048] The water absorption rate of the water-absorbent polymer particles by the vortex method is a value measured by the method described in Examples.

[0049] The physiological saline water retention capacity of the water-absorbing polymer particles can be, for example, 20 g / g to 60 g / g, 20 g / g to 55 g / g, 20 g / g to 50 g / g, 25 g / g to 60 g / g, 25 g / g to 55 g / g, 25 g / g to 50 g / g, 30 g / g to 60 g / g, 30 g / g to 55 g / g, or 30 g / g to 50 g / g.

[0050] The amount of water absorbed by the water-absorbent polymer particles in physiological saline under a load of 4.14 kPa may be, for example, 10 mL / g to 40 mL / g, 10 mL / g to 35 mL / g, 10 mL / g to 30 mL / g, 13 mL / g to 40 mL / g, 13 mL / g to 35 mL / g, 13 mL / g to 30 mL / g, 15 mL / g to 40 mL / g, 15 mL / g to 35 mL / g, or 15 mL / g to 30 mL / g.

[0051] The physiological saline water retention capacity and the physiological saline water absorption capacity under a load of 4.14 kPa of the water-absorbent polymer particles are values ​​measured by the methods described in Examples.

[0052] The median particle size of the water-absorbing polymer particles may be, for example, 150 μm to 850 μm, 150 μm to 600 μm, 150 μm to 550 μm, 150 μm to 500 μm, 150 μm to 450 μm, 150 μm to 400 μm, 200 μm to 850 μm, 200 μm to 600 μm, 200 μm to 550 μm, 200 μm to 500 μm, 200 μm to 450 μm, 200 μm to 400 μm, 240 μm to 850 μm, 240 μm to 600 μm, 240 μm to 550 μm, 240 μm to 500 μm, 240 μm to 450 μm, 240 μm to 50 ... μm~400μm, 260μm~850μm, 260μm~600μm, 260μm~550μm, 260μm~500μm, 260μm~450μm, 260μm~400μm, 280μm~850μm, 280μm~600μm, 280μm~5 50μm, 280μm~500μm, 280μm~450μm, 280μm~400μm, 300μm~850μm, 300μm~600μm, 300μm~550μm, 300μm~500μm, 300μm~450μm or 300μm~400μm.

[0053] In addition to being composed of single particles, the water-absorbing polymer particles may also be formed by agglomerating fine particles (primary particles) (secondary particles). Examples of primary particle shapes include roughly spherical shapes, irregularly shaped fragments, and plate-like shapes. For primary particles produced by reversed-phase suspension polymerization, examples include roughly spherical single particles with smooth surface shapes, such as true spheres and ellipsoids.

[0054] The median particle size of the water-absorbing polymer particles can be measured using a JIS standard sieve, and specifically, is a value measured by the method described in Examples.

[0055] The water-absorbent polymer particles have structural units derived from a neutralized salt of a water-soluble ethylenically unsaturated monomer. Typical polymerization methods for polymerizing water-soluble ethylenically unsaturated monomers include aqueous solution polymerization, emulsion polymerization, and reversed-phase suspension polymerization. In aqueous solution polymerization, an aqueous solution of a water-soluble ethylenically unsaturated monomer is stirred and heated as needed to polymerize the monomer. In reversed-phase suspension polymerization, a water-soluble ethylenically unsaturated monomer is heated in a hydrocarbon dispersion medium while stirring to polymerize the monomer.

[0056] An example of a method for producing the water-absorbing polymer particles will be described below.

[0057] Specific examples of methods for producing water-absorbent polymer particles include methods that involve producing water-absorbent polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, comprising a polymerization step in the presence of a free radical polymerization initiator and a surface crosslinking step of the resulting hydrogel in the presence of a surface crosslinking agent. In the method for producing water-absorbent polymer particles of the present invention, an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomer, as needed, to produce a hydrogel having an internally crosslinked structure.

[0058] <Polymerization process> [Water-soluble ethylenically unsaturated monomer] Examples of water-soluble ethylenically unsaturated monomers include (meth)acrylic acid (in this specification, "acrylic acid" and "methacrylic acid" are collectively referred to as "(meth)acrylic acid"; the same shall apply hereinafter) and its salts; 2-(meth)acrylamide-2-methylpropanesulfonic acid and its salts; nonionic monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-hydroxymethyl(meth)acrylamide, and polyethylene glycol mono(meth)acrylate; and amino group-containing unsaturated monomers such as N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide, and their quaternized products. Among these water-soluble ethylenically unsaturated monomers, (meth)acrylic acid or its salts, (meth)acrylamide, and N,N-dimethylacrylamide are preferred, and (meth)acrylic acid and its salts are more preferred, from the perspective of industrial availability. These water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more.

[0059] Among them, acrylic acid and its salts are widely used as raw materials for water-absorbing polymer particles. These acrylic acid and / or its salts are sometimes copolymerized with the other water-soluble ethylenically unsaturated monomers mentioned above. In this case, acrylic acid and / or its salts are preferably used as the main water-soluble ethylenically unsaturated monomer in an amount of 70 to 100 mol % relative to the total water-soluble ethylenically unsaturated monomers.

[0060] The water-soluble ethylenically unsaturated monomer can be dispersed in a hydrocarbon dispersion medium in the form of an aqueous solution and provided for reverse suspension polymerization. By forming an aqueous solution, the water-soluble ethylenically unsaturated monomer can improve the dispersion efficiency in the hydrocarbon dispersion medium. The concentration of the water-soluble ethylenically unsaturated monomer in the aqueous solution is preferably in the range of 20% by mass to below the saturation concentration. In addition, the concentration of the water-soluble ethylenically unsaturated monomer is more preferably 55% by mass or less, further preferably 50% by mass or less, and even more preferably 45% by mass or less. On the other hand, the concentration of the water-soluble ethylenically unsaturated monomer is more preferably 25% by mass or more, further preferably 28% by mass or more, and even more preferably 30% by mass or more.

[0061] When a water-soluble ethylenically unsaturated monomer has an acid group, such as (meth)acrylic acid or 2-(meth)acrylamide-2-methylpropanesulfonic acid, it is also possible to use a monomer whose acid group has been pre-neutralized with an alkaline neutralizing agent, as needed. Examples of such alkaline neutralizing agents include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate; and ammonia. Furthermore, to simplify the neutralization process, these alkaline neutralizing agents can be used in the form of aqueous solutions. It should be noted that the above-mentioned alkaline neutralizing agents can be used alone or in combination of two or more.

[0062] The degree of neutralization of the water-soluble ethylenically unsaturated monomer with the alkaline neutralizing agent is preferably 10 to 100 mol %, more preferably 30 to 90 mol %, further preferably 40 to 85 mol %, and even more preferably 50 to 80 mol % relative to all acid groups of the water-soluble ethylenically unsaturated monomer.

[0063] [Free radical polymerization initiator] Examples of the radical polymerization initiator added in the polymerization step include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-tert-butyl peroxide, tert-butyl isopropyl peroxide, tert-butyl peroxyacetate, tert-butyl peroxyisobutyrate, tert-butyl peroxypivalate, and hydrogen peroxide; and 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(N-phenylamidino)propane] Azo compounds such as dihydrochloride, 2,2'-azobis[2-(N-allylamidino)propane] dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and 4,4'-azobis(4-cyanovaleric acid) are preferred. Among these free radical polymerization initiators, potassium persulfate, ammonium persulfate, sodium persulfate, and 2,2'-azobis(2-amidinopropane) dihydrochloride are preferred from the perspective of easy availability and ease of handling. These free radical polymerization initiators may be used alone or in combination of two or more. Furthermore, the above-mentioned radical polymerization initiator can also be used in combination with a reducing agent such as sodium sulfite, sodium bisulfite, ferrous sulfate, and L-ascorbic acid to be used as a redox polymerization initiator.

[0064] The amount of the radical polymerization initiator used is, for example, 0.00005 to 0.01 mol per 1 mol of the water-soluble ethylenically unsaturated monomer. By satisfying this amount, a rapid polymerization reaction can be avoided and the polymerization reaction can be terminated at an appropriate time.

[0065] [Internal crosslinking agent] Examples of the internal crosslinking agent include crosslinking agents capable of crosslinking polymers of water-soluble ethylenically unsaturated monomers used, such as (poly)ethylene glycol [the expression "(poly)" indicates both the presence and absence of the prefix "poly"]. The same applies to the following], unsaturated polyesters obtained by reacting diols, triols and other polyols such as (poly)propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane and (poly)glycerol with unsaturated acids such as (meth)acrylic acid, maleic acid and fumaric acid; bisacrylamides such as N,N-methylenebisacrylamide; di(meth)acrylates or tri(meth)acrylates obtained by reacting polyepoxide with (meth)acrylic acid; di(meth)acrylate carbamoyl esters obtained by reacting polyisocyanates such as toluene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth)acrylate; allylated starch, allylated cellulose, diallyl phthalate, N,N',N''-triallyl isocyanurate, divinylbenzene and the like having two Compounds having more than one polymerizable unsaturated group; diglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerol diglycidyl ether, and polyglycidyl compounds such as triglycidyl compounds; epihalohydrin compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; isocyanate compounds such as 2,4-toluene diisocyanate and hexamethylene diisocyanate, and compounds having two or more reactive functional groups; oxetane compounds such as 3-methyl-3-hydroxymethyloxetane, 3-ethyl-3-hydroxymethyloxetane, 3-butyl-3-hydroxymethyloxetane, 3-methyl-3-hydroxyethyloxetane, 3-ethyl-3-hydroxyethyloxetane, and 3-butyl-3-hydroxyethyloxetane. Among these internal crosslinking agents, polyglycidyl compounds are preferred, diglycidyl ether compounds are more preferred, and (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerol diglycidyl ether are even more preferred. These internal crosslinking agents may be used alone or in combination of two or more.

[0066] The amount of the internal crosslinking agent used is preferably 0.000001 to 0.02 mol, more preferably 0.00001 to 0.01 mol, further preferably 0.00001 to 0.005 mol, and even more preferably 0.00005 to 0.002 mol, relative to 1 mol of the water-soluble ethylenically unsaturated monomer.

[0067] [Hydrocarbon dispersion medium] Examples of hydrocarbon dispersion media include aliphatic hydrocarbons with 6 to 8 carbon atoms, such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane; alicyclic hydrocarbons, such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, and trans-1,3-dimethylcyclopentane; and aromatic hydrocarbons, such as benzene, toluene, and xylene. Of these hydrocarbon dispersion media, n-hexane, n-heptane, and cyclohexane are particularly preferred due to their industrial availability, stable quality, and low cost. These hydrocarbon dispersion media can be used alone or in combination of two or more. Suitable results can also be achieved using commercially available products such as Exxsol Heptane (manufactured by ExxonMobil Corporation; hydrocarbons containing 75-85% by mass of heptane and its isomers) as an example of a mixture of hydrocarbon dispersion media.

[0068] The amount of the hydrocarbon dispersion medium used is preferably 100 to 1500 parts by mass, and more preferably 200 to 1400 parts by mass, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage, from the perspective of uniformly dispersing the water-soluble ethylenically unsaturated monomer and facilitating polymerization temperature control. It should be noted that, as described below, reversed-phase suspension polymerization is carried out in a single stage (single stage) or in multiple stages of two or more stages, and the first stage polymerization described above refers to the polymerization reaction in the single stage polymerization or multistage polymerization (the same shall apply hereinafter).

[0069] [Dispersion stabilizer] (Surfactant) In the reversed-phase suspension polymerization, a dispersion stabilizer may be used to improve the dispersion stability of the water-soluble ethylenically unsaturated monomer in the hydrocarbon dispersion medium.

[0070] As surfactant, for example, sucrose fatty acid ester, polyglycerol fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerol fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkyl allyl formaldehyde condensation polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropylene alkyl ether, polyethylene glycol fatty acid ester, alkyl glucoside, N-alkyl glucamide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, the phosphoric acid ester of polyoxyethylene alkyl ether, the phosphoric acid ester of polyoxyethylene alkyl allyl ether etc. can be used. Among these surfactants, from the dispersion stability aspect of monomer, particularly preferably use sorbitan fatty acid ester, polyglycerol fatty acid ester, sucrose fatty acid ester. These surfactants can be used alone, and two or more can also be used in combination.

[0071] The amount of the surfactant used is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage.

[0072] (Polymer dispersant) Furthermore, as a dispersion stabilizer used in reversed-phase suspension polymerization, a polymeric dispersant may be used together with the above-mentioned surfactant.

[0073] Examples of polymeric dispersants include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified EPDM (ethylene-propylene-diene terpolymer), maleic anhydride-modified polybutadiene, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, maleic anhydride-butadiene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose, etc. Among these polymeric dispersants, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene-propylene copolymer are particularly preferred from the perspective of monomer dispersion stability. These polymeric dispersants may be used alone or in combination of two or more.

[0074] The amount of the polymeric dispersant used is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage.

[0075] [Other ingredients] In the method for producing water-absorbing polymer particles, other components may be added to the aqueous solution containing the water-soluble ethylenically unsaturated monomer as needed to carry out reversed-phase suspension polymerization. Various additives such as thickeners and chain transfer agents may be added as other components.

[0076] For example, a thickener may be added to an aqueous solution containing a water-soluble ethylenically unsaturated monomer to perform reversed-phase suspension polymerization. By adding a thickener and adjusting the viscosity of the aqueous solution, the median particle size obtained in the reversed-phase suspension polymerization can be controlled.

[0077] As thickeners, for example, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, (partially) neutralized polyacrylic acid, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, etc. It should be noted that, if the stirring speed during polymerization is constant, the higher the viscosity of the aqueous solution of the water-soluble ethylenically unsaturated monomer, the larger the primary and / or secondary particles of the resulting particles tend to be.

[0078] [Inverse suspension polymerization] In reversed-phase suspension polymerization, for example, an aqueous monomer solution containing a water-soluble ethylenically unsaturated monomer is dispersed in a hydrocarbon dispersion medium in the presence of a dispersion stabilizer. In this case, the dispersion stabilizer (surfactant, polymeric dispersant) can be added either before or after the addition of the aqueous monomer solution, provided it is before the start of the polymerization reaction.

[0079] Among them, from the viewpoint of easily reducing the amount of hydrocarbon dispersion medium remaining in the obtained water-absorbing polymer particles, it is preferred to disperse the monomer aqueous solution in the hydrocarbon dispersion medium in which the polymeric dispersant is dispersed, and then further disperse the surfactant before conducting polymerization.

[0080] Such reversed-phase suspension polymerization can be carried out in one stage or in multiple stages of two or more stages. However, from the viewpoint of improving productivity, it is preferably carried out in two to three stages.

[0081] Under the situation of carrying out reversed-phase suspension polymerization with the multistage more than two stages, after carrying out the reversed-phase suspension polymerization of the first stage, in the reaction mixture obtained by the polyreaction of the first stage, add water-soluble ethylenically unsaturated monomers and mix, carry out the reversed-phase suspension polymerization after the second stage with the method identical with the first stage.In the reversed-phase suspension polymerization in each stage after the second stage, preferably except water-soluble ethylenically unsaturated monomers, the amount of the water-soluble ethylenically unsaturated monomers that free radical polymerization initiator adds during the reversed-phase suspension polymerization in each stage after the second stage is as benchmark, add in the scope of the mol ratio of above-mentioned each composition relative to water-soluble ethylenically unsaturated monomers, carry out reversed-phase suspension polymerization.It should be noted that, in the polymerization after the second stage, as required, also internal crosslinking agent can be added in the water-soluble ethylenically unsaturated monomers.

[0082] The reaction temperature of the polymerization reaction is preferably 20 to 110° C., more preferably 40 to 90° C., from the viewpoints of rapidly progressing the polymerization and shortening the polymerization time to improve economic efficiency, and easily removing the polymerization heat to smoothly progress the reaction.

[0083] Surface cross-linking process Next, the water-absorbent polymer particles of the present invention are obtained by adding a surface crosslinking agent to a hydrogel having an internally crosslinked structure obtained by polymerizing a water-soluble ethylenically unsaturated monomer, and performing crosslinking (surface crosslinking reaction). This surface crosslinking reaction is preferably performed in the presence of a surface crosslinking agent after polymerization of the water-soluble ethylenically unsaturated monomer. By subjecting the hydrogel having an internally crosslinked structure to a surface crosslinking reaction after polymerization, the crosslink density near the surface of the water-absorbent polymer particles can be increased, resulting in water-absorbent polymer particles having improved properties such as water absorption capacity under load.

[0084] Examples of surface crosslinking agents include compounds having two or more reactive functional groups. Examples include: polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, trimethylolpropane, glycerol, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerol; polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerol diglycidyl ether, (poly)glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether; halogenated epoxy compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; isocyanate compounds such as 2,4-toluene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-hydroxymethyloxetane, 3-ethyl-3-hydroxymethyloxetane, 3-butyl-3-hydroxymethyloxetane, 3-methyl-3-hydroxyethyloxetane Oxetane compounds such as cyclobutane, 3-ethyl-3-hydroxyethyloxetane, and 3-butyl-3-hydroxyethyloxetane; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds (e.g., alkylene carbonate) such as ethylene carbonate, propylene carbonate, 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-1,3-dioxane-2-one, and 1,3-dioxolane-2-one; and hydroxyalkylamide compounds such as bis[N,N-bis(β-hydroxyethyl)]adipamide. Among these surface crosslinking agents, polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerol diglycidyl ether, (poly)glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether are preferred. These surface crosslinking agents may be used alone or in combination of two or more.

[0085] The amount of the surface crosslinking agent used is preferably 0.00001 to 0.01 mol, more preferably 0.00005 to 0.005 mol, and even more preferably 0.0001 to 0.002 mol, based on 1 mol of the total amount of the water-soluble ethylenically unsaturated monomers used in the polymerization.

[0086] The surface crosslinking agent can be added as is or as an aqueous solution. Alternatively, it can be added as a solution containing a hydrophilic organic solvent as needed. Examples of hydrophilic organic solvents include lower alcohols such as methanol, ethanol, n-propanol, and isopropanol; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether, dioxane, and tetrahydrofuran; amides such as N,N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. These hydrophilic organic solvents can be used alone, in combination of two or more, or as a mixed solvent with water.

[0087] The surface crosslinking agent can be added after the polymerization reaction of the water-soluble ethylenically unsaturated monomer has almost completely completed. The addition is preferably performed in the presence of 1 to 400 parts by mass of water, more preferably 5 to 200 parts by mass of water, further preferably 10 to 100 parts by mass of water, and even more preferably 20 to 60 parts by mass of water, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer. It should be noted that the amount of water refers to the total amount of water contained in the reaction system and the water used as needed when adding the surface crosslinking agent.

[0088] The reaction temperature in the surface crosslinking reaction is preferably 50 to 250° C., more preferably 60 to 180° C., further preferably 60 to 140° C., and even more preferably 70 to 120° C. The reaction time in the surface crosslinking reaction is preferably 1 to 300 minutes, more preferably 5 to 200 minutes.

[0089] <Drying process> After the reversed-phase suspension polymerization, a drying step may be included to remove water, the hydrocarbon dispersion medium, and the like by distillation using external application of energy such as heat. When dehydrating the hydrogel after reversed-phase suspension polymerization, the system containing the hydrogel dispersed in the hydrocarbon dispersion medium is heated to temporarily remove the water and hydrocarbon dispersion medium from the system by azeotropic distillation. In this case, continuous azeotropic distillation can be performed by returning only the distilled hydrocarbon dispersion medium to the system. This method maintains the temperature of the system during drying below the azeotropic temperature of the hydrocarbon dispersion medium, which is preferred for minimizing resin degradation. Subsequently, the water and hydrocarbon dispersion medium are distilled off to obtain water-absorbing polymer particles. By controlling the treatment conditions in this post-polymerization drying step and adjusting the amount of water removed, the properties of the resulting water-absorbing polymer particles can be controlled.

[0090] In the drying step, the drying treatment by distillation can be carried out under normal pressure or under reduced pressure. In addition, from the perspective of improving drying efficiency, it can also be carried out under a stream of nitrogen or the like. When the drying treatment is carried out under normal pressure, the drying temperature is preferably 70 to 250°C, more preferably 80 to 180°C, further preferably 80 to 140°C, and even more preferably 90 to 130°C. When the drying treatment is carried out under reduced pressure, the drying temperature is preferably 40 to 160°C, more preferably 50 to 110°C.

[0091] It should be noted that, when a surface crosslinking step using a surface crosslinking agent is performed after polymerization of the monomers by reversed-phase suspension polymerization, the drying step using distillation described above is performed after completion of the surface crosslinking step. Alternatively, the surface crosslinking step and the drying step may be performed simultaneously.

[0092] The water-absorbent resin composition of the present invention may contain additives depending on the intended purpose. Examples of such additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, free radical chain reaction inhibitors, antioxidants, and antimicrobial agents. For example, the addition of 0.05 to 5 parts by mass of amorphous silica as an inorganic powder per 100 parts by mass of the water-absorbent polymer particles can further improve the fluidity of the water-absorbent resin composition. It should be noted that these additives are preferably hydrophilic or water-soluble.

[0093] In the water-absorbent resin composition of the present invention, the content of the water-absorbent polymer particles (excluding additives) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0094] The water-absorbent resin composition of the present invention can be produced by, for example, mixing water-absorbent polymer particles, an organic acid, and a porous deodorant in a solid phase state.

[0095] 2. Absorbents and absorbent articles The water-absorbent resin composition of the present invention constitutes an absorbent body used in sanitary products such as sanitary products and disposable diapers, and is suitable for use in absorbent articles containing such absorbent bodies. The absorbent article of the present invention comprises an organic acid, a porous deodorant, and water-absorbent polymer particles. The ratio (X / Y) of the organic acid content (parts by mass) to the porous deodorant content (parts by mass) is 1.0 or greater, and the sum (x + y) of the organic acid content (x) and the porous deodorant content (y) based on the total amount of the organic acid, the porous deodorant, and the water-absorbent polymer particles is 0.5% or greater. The absorbent article of the present invention can be configured in a more detailed manner similar to the water-absorbent resin composition described above.

[0096] Here, the absorbent body using the water-absorbent resin composition of the present invention comprises the particulate water-absorbent resin composition of the present invention. The absorbent body may further comprise hydrophilic fibers. Examples of absorbent body configurations include sheet structures in which water-absorbent polymer particles are fixed to a nonwoven fabric or between multiple nonwoven fabrics; mixed dispersions obtained by mixing a particulate water-absorbent resin composition and hydrophilic fibers to form a uniform composition; sandwich structures in which a particulate water-absorbent resin composition is sandwiched between layers of hydrophilic fibers; and structures in which a particulate water-absorbent resin composition and hydrophilic fibers are wrapped in tissue paper. It should be noted that the absorbent body may contain other components, such as heat-fusible synthetic fibers, hot-melt adhesives, adhesives such as adhesive emulsions, etc., to improve the shape-retaining properties of the absorbent body.

[0097] The content of the water-absorbent resin composition in the absorbent body is preferably 5 to 100% by mass, more preferably 10 to 95% by mass, further preferably 20 to 90% by mass, and even more preferably 30 to 80% by mass.

[0098] Examples of hydrophilic fibers include cellulose fibers such as cotton pulp, mechanical pulp, chemical pulp, and semi-chemical pulp obtained from wood, man-made cellulose fibers such as rayon and cellulose acetate, and fibers made of hydrophilically treated synthetic resins such as polyamide, polyester, and polyolefin. The average fiber length of the hydrophilic fibers is generally 0.1 to 10 mm, or 0.5 to 5 mm.

[0099] The absorbent article of the present invention can be produced by holding an absorbent body using the particulate water-absorbent resin composition of the present invention between a liquid-permeable sheet (top sheet) and a liquid-impermeable sheet (back sheet). The liquid-permeable sheet is positioned on the side that contacts the body, and the liquid-impermeable sheet is positioned on the side opposite to the body.

[0100] Examples of liquid-permeable sheets include air-through, spunbond, chemically bonded, and needle-punched nonwoven fabrics made of fibers such as polyethylene, polypropylene, and polyester, as well as porous synthetic resin sheets. Examples of liquid-impermeable sheets include synthetic resin films made of resins such as polyethylene, polypropylene, and polyvinyl chloride.

[0101] 3. Additional Notes This specification includes at least the inventions described in the following (1) to (12). (1) A water-absorbent resin composition comprising an organic acid, a porous deodorant, and water-absorbent polymer particles having a structural unit derived from a neutralized salt of an ethylenically unsaturated monomer, The ratio (X / Y) of the content X (parts by mass) of the organic acid to the content Y (parts by mass) of the porous deodorant is 1.0 or more, The sum (x+y) of the content x (mass %) of the organic acid in the entire water-absorbing resin composition and the content y (mass %) of the porous deodorant is 0.50 mass % or more. (2) The water-absorbent resin composition according to (1), wherein the ratio (X / Y) of the content X (parts by mass) to the content Y (parts by mass) is 1.0 to 15.0, 1.0 to 12.0, 1.0 to 10.0, 1.0 to 8.0, 1.0 to 6.0, 1.5 to 15.0, 1.5 to 12.0, 1.5 to 10.0, 1.5 to 8.0, 1.5 ~6.0, 2.0~15.0, 2.0~12.0, 2.0~10.0, 2.0~8.0, 2.0~6.0, 2.5~15.0, 2.5~12.0, 2.5~10.0, 2.5~8.0, 2.5~6.0, 3.0~15.0, 3.0~12.0, 3.0~10.0, 3.0~8.0 or 3.0~6.0. (3) The water-absorbent resin composition according to (1) or (2), wherein the sum (x+y) of the content rate x (mass %) of the organic acid and the content rate y (mass %) of the porous deodorant in the entire water-absorbent resin composition is 0.50% by mass to 2.00% by mass, 0.50% by mass to 1.50% by mass, 0.50% by mass to 1.40% by mass, 0.50% by mass to 1.30% by mass, 0.50% by mass to 1.20% by mass, 0.50% by mass to 1.00% by mass, 0.53% by mass to 2.00% by mass, 0.53% by mass to 1.50% by mass, 0.53% by mass to 1.40% by mass, 0.53% by mass to 1. % to 1.30 mass%, 0.53 mass% to 1.20 mass%, 0.53 mass% to 1.00 mass%, 0.56 mass% to 2.00 mass%, 0.56 mass% to 1.50 mass%, 0.56 mass% to 1.40 mass%, 0.56 mass% to 1.30 mass%, 0.56 mass% to 1.20 mass%, 0.56 mass% to 1.00 mass%, 0.59 mass% to 2.00 mass%, 0.59 mass% to 1.50 mass%, 0.59 mass% to 1.40 mass%, 0.59 mass% to 1.30 mass%, 0.59 mass% to 1.20 mass%, or 0.59 mass% to 1.00 mass%. (4) The water-absorbent resin composition according to any one of (1) to (3) above, wherein the porous deodorant comprises at least one selected from the group consisting of zeolite, activated carbon, silicon dioxide, silicate, titanium dioxide, aluminum oxide, aluminum hydroxide, and magnesium hydroxide. (5) The water-absorbent resin composition according to any one of (1) to (4) above, wherein the pH of the organic acid is 1.0 to 6.0, 1.0 to 4.0, 1.0 to 3.0, 1.0 to 2.0, 1.5 to 6.0, 1.5 to 4.0, 1.5 to 3.0, or 1.5 to 2.0. (6) The water-absorbent resin composition according to any one of (1) to (5) above, wherein the organic acid comprises at least one selected from the group consisting of tartaric acid, citric acid, malic acid, maleic acid, fumaric acid, succinic acid, acetic acid, and propionic acid. (7) An absorbent article comprising an organic acid, a porous deodorant and water-absorbing polymer particles, The ratio (X / Y) of the content X (parts by mass) of the organic acid to the content Y (parts by mass) of the porous deodorant is 1.0 or greater, and the sum (x+y) of the content x (mass %) of the organic acid and the content y (mass %) of the porous deodorant, based on the total amount of the organic acid, the porous deodorant, and the water-absorbing polymer particles, is 0.5 mass % or greater. (8) The absorbent article according to (7), wherein the ratio (X / Y) of the content X (parts by mass) to the content Y (parts by mass) is 1.0 to 15.0, 1.0 to 12.0, 1.0 to 10.0, 1.0 to 8.0, 1.0 to 6.0, 1.5 to 15.0, 1.5 to 12.0, 1.5 to 10.0, 1.5 to 8.0, 1.5 to 6 .0, 2.0-15.0, 2.0-12.0, 2.0-10.0, 2.0-8.0, 2.0-6.0, 2.5-15.0, 2.5-12.0, 2.5-10.0, 2.5-8.0, 2.5-6.0, 3.0-15.0, 3.0-12.0, 3.0-10.0, 3.0-8.0 or 3.0-6.0. (9) The absorbent article according to (7) or (8), wherein the sum (x+y) of the content rate x (mass %) of the organic acid and the content rate y (mass %) of the porous deodorant in the total of the organic acid, the porous deodorant, and the water-absorbing polymer particles is 0.50% by mass to 2.00% by mass, 0.50% by mass to 1.50% by mass, 0.50% by mass to 1.40% by mass, 0.50% by mass to 1.30% by mass, 0.50% by mass to 1.20% by mass, 0.50% by mass to 1.00% by mass, 0.53% by mass to 2.00% by mass, 0.53% by mass to 1.50% by mass, 0.53% by mass to 1.40% by mass, 0.53% to 1.30% by mass, 0.53% to 1.20% by mass, 0.53% to 1.00% by mass, 0.56% to 2.00% by mass, 0.56% to 1.50% by mass, 0.56% to 1.40% by mass, 0.56% to 1.30% by mass, 0.56% to 1.20% by mass, 0.56% to 1.00% by mass, 0.59% to 2.00% by mass, 0.59% to 1.50% by mass, 0.59% to 1.40% by mass, 0.59% to 1.30% by mass, 0.59% to 1.20% by mass, or 0.59% to 1.00% by mass. (10) The absorbent article according to any one of (7) to (9) above, wherein the porous deodorant contains at least one selected from the group consisting of zeolite, activated carbon, silicon dioxide, silicate, titanium dioxide, aluminum oxide, aluminum hydroxide, and magnesium hydroxide. (11) The absorbent article according to any one of (7) to (10) above, wherein the pH of the organic acid is 1.0 to 6.0, 1.0 to 4.0, 1.0 to 3.0, 1.0 to 2.0, 1.5 to 6.0, 1.5 to 4.0, 1.5 to 3.0, or 1.5 to 2.0. (12) The absorbent article according to any one of (7) to (11) above, wherein the organic acid includes at least one selected from the group consisting of tartaric acid, citric acid, malic acid, maleic acid, fumaric acid, succinic acid, acetic acid, and propionic acid.

[0114] Example The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0115] The water-absorbing polymer particles described below, activated carbon as a porous deodorant, and the water-absorbing resin compositions obtained in the Examples and Comparative Examples were evaluated using the following various tests. Unless otherwise specified, measurements were performed at a temperature of 25±2°C and a humidity of 50±10%.

[0116] [Production Example of Water-Absorbent Polymer Particles] A 2L, round-bottomed, cylindrical separable flask with an inner diameter of 11 cm and a volume was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen inlet tube, and a stirring blade with four inclined blades of 5 cm in diameter in two stages. 293 g of n-heptane as a hydrocarbon dispersion medium was added to this flask, along with 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., HI-WAX1105A) as a polymeric dispersant. The mixture was heated to 80°C while stirring to dissolve the dispersant, and then cooled to 50°C. Separately, 92.0 g (1.03 mol) of an 80.5 mass % aqueous solution of acrylic acid as a water-soluble ethylenically unsaturated monomer was placed in a beaker with an internal volume of 300 mL. While cooling with ice water, 147.7 g of a 20.9 mass % aqueous solution of sodium hydroxide was added dropwise to neutralize the mixture to 75 mol %. Then, 0.092 g of hydroxyethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a water-soluble free radical polymerization agent, and 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare a first-stage aqueous solution. The aqueous solution prepared above was then added to a separable flask and stirred for 10 minutes. A surfactant solution prepared by dissolving 0.736 g of HLB 3 sucrose stearate (Ryoto Sugar Ester S-370, Mitsubishi Chemical Foods Co., Ltd.) in 6.62 g of n-heptane by heating was then added to a 20 mL vial. While stirring at 550 rpm, the system was thoroughly purged with nitrogen. The flask was then immersed in a 70°C water bath, the temperature was raised, and polymerization was carried out for 60 minutes to obtain a first-stage polymerization slurry.

[0117] Meanwhile, in another beaker with an internal volume of 500 mL, 128.8 g (1.43 mol) of an 80.5 mass % aqueous solution of acrylic acid as a water-soluble ethylenically unsaturated monomer was taken and, while cooling with ice water, 159.0 g of a 27 mass % aqueous solution of sodium hydroxide was added dropwise. After 75 mol % neutralization, 0.103 g (0.381 mmol) of potassium persulfate as a water-soluble free radical polymerization initiator and 0.0117 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare a second-stage aqueous solution.

[0118] While stirring at a stirrer speed of 1000 rpm, the separable flask system was cooled to 25°C. The entire amount of the second-stage aqueous liquid was then added to the first-stage polymerization slurry. After the system was purged with nitrogen for 30 minutes, the flask was again immersed in a 70°C water bath to raise the temperature, and a polymerization reaction was carried out for 60 minutes to obtain a hydrogel polymer.

[0119] The flask was then immersed in an oil bath set at 125°C. Azeotropic distillation of n-heptane and water was performed, and 260.1 g of water was expelled from the system while the n-heptane was refluxed. Then, 4.42 g (0.507 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was maintained at 83°C for 2 hours.

[0120] The n-heptane was then evaporated and dried at 125°C, and the particles were passed through a sieve with an opening of 850 μm to obtain 226.6 g of water-absorbent polymer particles. The water-absorbent polymer particles had a saline water retention capacity of 42 g / g, a water absorption rate of 39 seconds, a median particle size of 362 μm, and a saline water absorption capacity of 20 ml / g under a load of 4.14 kPa.

[0121] [Evaluation of water-absorbent polymer particles] <Water retention capacity of saline solution> A cotton bag (cotton broadcloth No. 60, 100 mm wide x 200 mm long) containing 2.0 g of water-absorbent polymer particles was placed in a 500 ml beaker. 500 g of a 0.9% sodium chloride aqueous solution (physiological saline) was poured into the bag containing the water-absorbent polymer particles all at once, without forming a lump. The bag was then tied with a rubber band at the top and allowed to stand for 30 minutes to allow the water-absorbent polymer particles to swell. After 30 minutes, the bag was dehydrated for 1 minute using a dehydrator (Kokusan Co., Ltd., Product No. H-122) set to a centrifugal force of 167 G. The mass of the dehydrated bag, including the swollen gel, Wd (g), was measured. The same procedure was repeated without adding the water-absorbent polymer particles, and the empty mass of the wet bag, We (g), was measured. The saline water retention was calculated using the following formula.

[0122] Water retention of saline solution (g / g) = [Wd-We] / 2.0 <Measurement of Pure Water Absorption Rate Using Eddy Current Method> In a constant-temperature water bath, 50 ± 0.1 g of pure water, adjusted to 25 ± 0.2°C, was weighed into a 100 mL beaker and stirred with a magnetic stir bar (8 mm φ × 30 mm ringless) at 600 rpm to create a vortex. 2.0 ± 0.002 g of water-absorbent polymer particles were added all at once to the saline solution. The time (in seconds) from the addition of the water-absorbent polymer particles until the vortex at the liquid surface converged was measured and used as the water absorption rate of the water-absorbent polymer particles. This water absorption rate is also expressed as the vortex method or vortex time.

[0123] <Median particle size (particle size distribution)> 50.0 g of water-absorbent polymer particles were used for median particle size (particle size distribution) measurement. JIS standard sieves were assembled, starting from the top, in the following order: 850 μm mesh sieve, 500 μm mesh sieve, 425 μm mesh sieve, 300 μm mesh sieve, 250 μm mesh sieve, 180 μm mesh sieve, 150 μm mesh sieve, and a receiving tray. Water-absorbent polymer particles were placed in the top sieve of the assembly and shaken for 20 minutes using a Ro-Tap shaker for classification. After classification, the mass percentage of water-absorbent polymer particles remaining on each sieve relative to the total mass was calculated to determine the particle size distribution. The particle size distribution was calculated by accumulating the particles on the sieves in order from the particle size with the largest particle size. The relationship between the sieve mesh size and the cumulative mass percentage of water-absorbent polymer particles remaining on the sieves was plotted on logarithmic probability paper. The plots on the probability paper were connected with a straight line, and the particle diameter corresponding to 50% by mass of the cumulative mass percentage was defined as the median particle diameter.

[0124] <Water absorption of physiological saline solution under a load of 4.14 kPa> Water absorption of saline solution under 4.14kPa load (water absorption under load) Figure 1 The measurement is performed using a measuring device schematically shown in FIG. Two measurements are performed on one type of water-absorbent polymer particles, and the average value is obtained. The measuring device comprises a burette portion 1, a fixture 3, a catheter 5, a stand 11, a measuring table 13, and a measuring portion 4 placed on the measuring table 13. The burette portion 1 has a burette 21 with a scale, a rubber stopper 23 that tightly covers the opening at the top of the burette 21, a stopcock 22 connected to the front end of the lower portion of the burette 21, and an air inlet tube 25 and a stopcock 24 connected to the lower portion of the burette 21. The burette portion 1 is fixed by the fixture 3. The flat measuring table 13 has a through hole 13a with a diameter of 2 mm formed in its center, and is supported by the stand 11 with a variable height. The through hole 13a of the measuring table 13 and the stopcock 22 of the burette portion 1 are connected via the catheter 5. The inner diameter of the catheter 5 is 6 mm.

[0125] The measuring unit 4 comprises a cylinder 31 made of organic glass, a polyamide mesh 32 bonded to one opening of the cylinder 31, and a weight 33 movable vertically within the cylinder 31. The cylinder 31 is placed on the measuring table 13 via the polyamide mesh 32. The inner diameter of the cylinder 31 is 20 mm. The mesh size of the polyamide mesh 32 is 75 μm (200 mesh). The weight 33 has a diameter of 19 mm and a mass of 119.6 g. As described later, it can apply a load of 4.14 kPa (0.6 psi) to the water-absorbing polymer particles 10a uniformly arranged on the polyamide mesh 32.

[0126] First, close the stopcock 22 and stopcock 24 of the burette section 1, and inject 0.9% by mass saline solution adjusted to 25°C into the burette 21 from the upper opening. Next, after tightly capping the upper opening of the burette 21 with the rubber stopper 23, open the stopcock 22 and stopcock 24. Fill the interior of the catheter 5 with 0.9% by mass saline solution 50 so as not to introduce air bubbles. Adjust the height of the measuring table 13 so that the height of the water surface of the 0.9% by mass saline solution reaching the through hole 13a is the same as the height of the upper surface of the measuring table 13. After adjustment, read the height of the water surface of the 0.9% by mass saline solution 50 in the burette 21 using the scale on the burette 21, and use this position as the zero point (the reading at 0 seconds).

[0127] In the measuring unit 4, 0.10 g of water-absorbent polymer particles 10a were evenly distributed on a polyamide mesh 32 within a cylinder 31. A weight 33 was placed on the water-absorbent polymer particles 10a. The cylinder 31 was positioned so that its center aligned with the catheter opening at the center of the measuring table 13. The amount of saline solution reduced in the burette 21 (i.e., the amount of saline solution absorbed by the water-absorbent polymer particles 10a) Wc (ml) was read 60 minutes after the water-absorbent polymer particles 10a began absorbing saline solution from the catheter 5. The saline absorption capacity of the water-absorbent polymer particles 10a under a load of 4.14 kPa was calculated using the following formula.

[0128] Water absorption capacity of saline solution under 4.14 kPa load (ml / g) = Wc (ml) / mass of water-absorbent polymer particles (g) [Preparation of organic acid] Granular L-tartaric acid (manufactured by Wegöchemical Co., Ltd., median particle size 206 μm) was prepared as an organic acid.

[0129] [Evaluation of organic acids] <pH Measurement of Organic Acids> In a 100 mL plastic beaker, weigh 5.0 g of an organic acid and 45.0 g of ion-exchanged water. Place a stirring bar (8 mm diameter x 30 mm) in the beaker and stir at 400 rpm using a magnetic stirrer for 1 hour. Then, insert the electrode of a portable pH meter (HORIBA, pH / ORP METER D-72, electrode model 9625) 1 cm from the inner wall of the beaker to a depth of 2.5 cm. After inserting the electrode, let it stand for several minutes. The stable value is used as the pH of a 10% by mass aqueous solution of the organic acid.

[0130] <Median Particle Size of Organic Acid> Using a continuous, fully automatic sonic vibration sieve analyzer (Robot Shifter RPS-205, manufactured by Seishin Enterprise Co., Ltd.), sieves with JIS standard mesh sizes of 850 μm, 500 μm, 425 μm, 300 μm, 212 μm, 106 μm, 75 μm, and 45 μm, and a tray, sieving was performed at a frequency of 80 Hz, a pulse interval of 1 second, and a classification time of 2 minutes. The mass percentage of particles remaining on each sieve relative to the total mass was calculated. The mass percentage of particles remaining on each sieve was accumulated, starting with the largest particle size. The relationship between the sieve mesh size and the cumulative mass percentage of particles remaining on the sieve was plotted on logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle size corresponding to 50% of the cumulative mass percentage was determined and used as the median particle size.

[0131] [Preparation of activated carbon] Prepared BET specific surface area of ​​1345m 2 / g, a median particle size of 46 μm, an ignition residue of 0.4%, a loss on drying of 3.2%, a pH of 4.9, and a crushed activated carbon (Carboraffin-6, manufactured by Osaka Gas Chemicals Co., Ltd.).

[0132] [Evaluation of activated carbon] <Median particle size of activated carbon (laser diffraction)> The median particle size (D50 (median diameter), volume basis) of the activated carbon used was measured using a laser diffraction particle size distribution analyzer (SALD2300, manufactured by Shimadzu Corporation).

[0133] <BET specific surface area of ​​activated carbon> 0.1 g of the activated carbon to be measured was dried using a pretreatment apparatus (BELPREP VAC II, manufactured by Microtrac Bel) at 60°C under degassing conditions with heated vacuum exhaust for 24 hours. An adsorption isotherm was then measured at 77 K using a specific surface area measuring apparatus (BELSORP MINI II, manufactured by Microtrac Bel) using nitrogen as the adsorption gas. The specific surface area was calculated from the multipoint BET curve and used as the BET specific surface area of ​​the activated carbon.

[0134] [Production of Water-Absorbent Resin Composition] <Example 1> To 100 parts by mass of the water-absorbent polymer particles obtained in the production example, 0.5 parts by mass of the above-mentioned L-tartaric acid as an organic acid and 0.1 parts by mass of the above-mentioned activated carbon as a porous deodorant were added, and the mixture was rotated for 30 minutes at an autorotation speed of 50 rpm and an orbital speed of 50 rpm using a cross-rotation mixer manufactured by Meiwa Industry Co., Ltd., to obtain a water-absorbent resin composition.

[0135] <Example 2> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the added amount of the activated carbon was changed to 0.30 parts by mass.

[0136] <Example 3> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was changed to 1.0 part by mass.

[0137] <Example 4> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was 1.00 part by mass and the amount of activated carbon added was 0.30 part by mass.

[0138] <Example 5> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was changed to 0.75 parts by mass and the amount of activated carbon added was changed to 0.20 parts by mass.

[0139] Comparative Example 1 A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was changed to 0.25 parts by mass and the amount of activated carbon added was changed to 0.05 parts by mass.

[0140] Comparative Example 2 A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was 1.00 parts by mass and the amount of activated carbon added was 0.05 parts by mass.

[0141] Comparative Example 3 A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was changed to 0.25 parts by mass and the amount of activated carbon added was changed to 0.30 parts by mass.

[0142] Comparative Example 4 A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was changed to 0.25 parts by mass and activated carbon was not added.

[0143] <Comparative Example 5> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was changed to 0.50 parts by mass and activated carbon was not added.

[0144] <Comparative Example 6> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was changed to 0.75 parts by mass and activated carbon was not added.

[0145] <Comparative Example 7> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the amount of L-tartaric acid added was changed to 1.00 parts by mass and activated carbon was not added.

[0146] <Comparative Example 8> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the L-tartaric acid was not added and the amount of activated carbon added was changed to 0.05 parts by mass.

[0147] <Comparative Example 9> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the L-tartaric acid was not added and the amount of activated carbon added was changed to 0.10 parts by mass.

[0148] <Comparative Example 10> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the L-tartaric acid was not added and the amount of activated carbon added was changed to 0.20 parts by mass.

[0149] <Comparative Example 11> A water-absorbent resin composition was obtained in the same manner as in Example 1 except that the L-tartaric acid was not added and the amount of activated carbon added was changed to 0.30 parts by mass.

[0150] <Reference Example 1> As Reference Example 1, the water-absorbing polymer particles obtained in the Production Example were used.

[0151] [Evaluation of water-absorbent resin composition] <Ammonia production inhibition test> Artificial urine was prepared by dissolving 25.0 g of urea, 9.0 g of sodium chloride, 0.6 g of magnesium sulfate heptahydrate, 0.7 g of calcium lactate, 4.0 g of potassium sulfate, 2.5 g of ammonium sulfate, and 0.1 g of L-cystine in 958.1 g of distilled water. Separately, urease (1000 U / mL of a 50% glycerol solution derived from jack bean, manufactured by Merck) was diluted to 2 U / mL in distilled water to prepare a urease solution. 1.00 g of the water-absorbent resin composition or water-absorbent polymer particles was placed in a sterile petri dish (88 mm diameter, 17 mm height). A test solution (prepared by mixing 45.0 mL of the artificial urine and 1.0 mL of the urease solution) was added to swell the sample. After adding the test solution, the sample was sealed in a 2 L polyester sampling bag (PAAAK2 manufactured by GL Sciences Co., Ltd.). The air in the bag was purged, and then 900 mL of dry air was added. The samples were then stored at 35°C, and after 24 hours, ammonia concentrations were measured using a gas detector tube (GASTEC Corporation, Ammonia 3L, 3La, 3M). The measured values ​​and the deodorization rate calculated using the following formula 1 are shown in Table 1.

[0152] Formula 1: Deodorization rate (%) = [(ammonia concentration of Reference Example 1 - ammonia concentration of Examples or Comparative Examples) / ammonia concentration of Reference Example 1] × 100 <Dust generation test> Prepare a 500mL glass suction flask. Set a SUS hopper (88mm top inner diameter x 18mm foot inner diameter) so that the height from the bottom of the flask to the hopper's discharge port is 180mm. Connect the suction port of the flask to a dust meter (digital indicator LD-5R, manufactured by Shibata Scientific Co., Ltd.) via a glass tube (7.7mm inner diameter x 300mm length). Place 3.0g ± 0.1g of the water-absorbent resin composition as a sample into the hopper. Pull out the hopper's damper while pressing the start button on the dust meter. Record the count after one minute (count for sample (A)). Perform a blank test before measuring the sample. Calculate the count during the blank test (B) and calculate the dust emission using the following formula.

[0153] Dust emission (cpm) = AB Where A represents the counts (cpm) for the sample, and B represents the counts (cpm) for the blank test. The above dust generation measurement was performed three times for each sample, and the average value was used as the dust generation rate for that sample. The results are shown in Table 2.

[0154] [Table 1] [Table 2] As shown in Table 1, for example, Comparative Example 11 (containing no organic acid), in which the porous deodorant content y in the water-absorbent resin composition was 0.30 mass%, achieved a deodorization rate of 47%, while Comparative Example 5 (containing no porous deodorant), in which the organic acid content x in the water-absorbent resin composition was 0.50 mass%, achieved a deodorization rate of 17%. In contrast, Example 2, in which the porous deodorant content y in the water-absorbent resin composition was 0.30 mass% and the organic acid content y was 0.50 mass%, achieved a deodorization rate as high as 72%. The results for Comparative Examples 5 and 11 (the combined deodorization rates of Comparative Examples 5 and 1 were 64%) demonstrate the unexpected synergistic effect of the organic acid and the porous deodorant. The synergistic effect of the deodorization rate of the water-absorbent resin composition shown in Table 2 is the deodorization rate of the example divided by the sum of the deodorization rates of the comparative examples using each deodorant alone. For example, the synergistic effect of Example 2 is calculated as the deodorization rate of Example 2 (72) / (the deodorization rate of Comparative Example 11 (47) + the deodorization rate of Comparative Example 5 (17)). If the value exceeds the reference value of 1.00, it can be said that the synergistic effect is exerted.

[0155] While the addition of additives to water-absorbent polymer particles typically slows the water absorption rate, the results shown in Table 2 demonstrate that the water-absorbent resin compositions of Examples 1 to 5 maintain water absorption rates close to those of Reference Example 1 (which does not contain a deodorant). Furthermore, the results shown in Table 2 demonstrate that, among the water-absorbent resin compositions of Examples 1 to 5, Examples 1, 3, and 5 exhibit excellent dust generation, with Example 1 being particularly excellent.

[0156] Description of Reference Numerals 1. Burette 3. Fixture 4 Measurement unit 5 Catheter 10a Water-absorbing polymer particles 11 racks 13. Measuring platform 13a Through hole 21 burette 22 cock 23 rubber stopper 24 cock 25 Air inlet pipe 31 Cylinder 32 Polyamide mesh 33 Counterweight 50 Salt water.

Claims

1. A water-absorbent resin composition, characterized in that comprising an organic acid, a porous deodorant, and water-absorbing polymer particles having structural units derived from a neutralized salt of an ethylenically unsaturated monomer, The ratio X / Y of the content X (parts by mass) of the organic acid to the content Y (parts by mass) of the porous deodorant is 1.0 or more. The sum of the content x (mass %) of the organic acid in the entire water-absorbing resin composition and the content y (mass %) of the porous deodorant, that is, x+y, is 0.50 mass % or more.

2. The water-absorbent resin composition according to claim 1, wherein The ratio of the content X (parts by mass) to the content Y (parts by mass), that is, X / Y, is 12.0 or less.

3. The water-absorbent resin composition according to claim 1 or 2, wherein The sum of the content rate x (mass %) of the organic acid and the content rate y (mass %) of the porous deodorant, ie, x+y, is 1.50 mass % or less.

4. An absorbent article, characterized in that: Contains organic acid, porous deodorant and water-absorbing polymer particles, The ratio X / Y of the content X (parts by mass) of the organic acid to the content Y (parts by mass) of the porous deodorant is 1.0 or more. The sum of the content x (mass %) of the organic acid and the content y (mass %) of the porous deodorant based on the total amount of the organic acid, the porous deodorant, and the water-absorbing polymer particles, i.e., x+y, is 0.5 mass % or more.

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