Water-absorbing resin composition

Abstract

Provided is a water-absorbing resin composition having an excellent deodorizing effect.　The water-absorbing resin composition contains 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, and in the entire water-absorbing resin composition, the sum (x + y) of the content x (mass %) of the organic acid and the content y (mass %) of the porous deodorant is 0.5 mass % or more.

Description

Water absorbent resin composition

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

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

[0003] As such a water-absorbent resin, a cross-linked polymer having structural units derived from acrylic acid and its neutralized salt is known, and has excellent water-absorbing capacity. Since the raw material, acrylic acid, is easily available industrially, the cross-linked polymer has many advantages, such as consistent quality, low cost production, and resistance to decay and deterioration, and is therefore considered to be a preferred water-absorbent resin.

[0004] On the other hand, absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads are mainly composed of an absorbent core arranged in the center to absorb and retain body fluids such as urine and menstrual blood excreted from the body, a liquid-permeable surface sheet (top sheet) arranged on the side that comes into contact with the body, and a liquid-impermeable back sheet (back sheet) arranged on the opposite side that comes into contact with the body. The absorbent core is usually composed of hydrophilic fibers such as pulp and a water-absorbent resin.

[0005] When such an absorbent is used as, for example, a sanitary material, the absorbent may emit unpleasant odors such as ammonia after absorbing body fluids, particularly urine, blood, sweat, and the like.

[0006] Japanese Patent Application Laid-Open No. 2001-323155

[0007] When urine is absorbed by the absorbent material, the urea in the urine is broken down by the action of urease contained in the urease-producing bacteria, generating ammonia.

[0008] The present inventors attempted to inactivate urease by lowering the pH of urine using an organic acid, thereby inhibiting the decomposition reaction of urea by urease and suppressing the generation of ammonia. However, through their investigations, the present inventors discovered a problem in that the pH of urine lowered by the organic acid shifts to the neutral side due to the pH buffering action of the water-absorbent polymer particles in the absorbent, weakening the urease inactivation action of the organic acid and preventing a sufficient deodorizing effect from being achieved.

[0009] A main object of the present invention is to provide a water-absorbing resin composition having an excellent deodorizing effect.

[0010] The present inventors have conducted extensive studies to solve the above-mentioned problems. As a result, they have found that, in a water-absorbent resin composition containing water-absorbent polymer particles, an organic acid and a porous deodorant are used in combination, and the ratio (X / Y) of the organic acid content X (parts by mass) to the porous deodorant content Y (parts by mass) is set to a predetermined ratio or more, and further, the sum (x+y) of the organic acid content x (% by mass) and the porous deodorant content y (% by mass) in the entire water-absorbent resin composition is set to a predetermined ratio or more, whereby the water-absorbent resin composition exhibits a high deodorizing function against ammonia. The present invention is an invention that has been completed based on such findings and through further extensive studies.

[0011] That is, the present invention provides the following configurations. Item 1. A water-absorbent resin composition comprising an organic acid, a porous deodorant, and water-absorbent polymer particles having structural units derived from a neutralized salt of an ethylenically unsaturated monomer, wherein a ratio (X / Y) of a content X (parts by mass) of the organic acid to a content Y (parts by mass) of the porous deodorant is 1.0 or more, and a sum (x+y) of a content x (% by mass) of the organic acid and a content y (% by mass) of the porous deodorant in the entire water-absorbent resin composition is 0.50% by mass or more. Item 2. A 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. Item 3. Item 4. A 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. Item 5. An absorbent article comprising an organic acid, a porous deodorant, and water-absorbent polymer particles, wherein 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, 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-absorbent polymer particles is 0.5 mass% or more.

[0012] According to the present invention, it is possible to provide a water-absorbing resin composition having an excellent deodorizing effect.

[0013] FIG. 1 is a schematic diagram of a device for measuring the amount of saline solution absorbed under a load of 4.14 kPa.

[0014] In this specification, the term "comprising" includes "consisting essentially of" and "consisting of". Furthermore, in this specification, "(meth)acrylic" means "acrylic or methacrylic", and "(meth)acrylate" means "acrylate or methacrylate". Furthermore, "water-soluble" means exhibiting a solubility of 5% by mass or more in water at 25°C.

[0015] In addition, in this specification, a numerical value connected with "~" means a numerical range that includes the numerical values ​​before and after "~" as the lower limit and upper limit. When multiple lower limit values ​​and multiple upper limit values ​​are listed separately, any lower limit value and upper limit value can be selected and connected with "~".

[0016] 1. Water-absorbent resin composition The water-absorbent resin composition of the present invention is a water-absorbent resin composition containing an organic acid, a porous deodorant, and water-absorbent polymer particles, characterized in that 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 more, and the sum (x + y) of the organic acid content x (% by mass) and the porous deodorant content y (% by mass) in the entire water-absorbent resin composition is 0.5% by mass or more. The water-absorbent resin composition of the present invention having such characteristics exhibits an excellent deodorizing effect. The water-absorbent resin composition of the present invention will be described in detail below.

[0017] As mentioned above, the present inventors attempted to inactivate urease by lowering the pH of urine with an organic acid, thereby inhibiting the decomposition reaction of urea by urease and suppressing the generation of ammonia. However, through their studies, the present inventors discovered a problem in that the pH of urine lowered by the organic acid shifts to the neutral side due to the pH buffering action of the water-absorbent polymer particles in the absorbent, weakening the urease inactivation action of the organic acid and preventing a sufficient deodorizing effect from being achieved. Furthermore, the present inventors have conducted extensive studies and have found that, in a water-absorbent resin composition containing water-absorbent polymer particles, an organic acid and a porous deodorant are used in combination, and further, the ratio (X / Y) of the organic acid content X (parts by mass) to the porous deodorant content Y (parts by mass) is set to 1.0 or more, and the sum (x+y) of the organic acid content x (% by mass) and the porous deodorant content y (% by mass) in the entire water-absorbent resin composition is set to 0.5% by mass or more, whereby the organic acid and the porous deodorant function synergistically, and the water-absorbent resin composition exhibits a high deodorizing function against ammonia. This can be considered to be because the porous deodorant suppresses the pH buffering action of the water-absorbent polymer particles (more specifically, the pH buffering action of the portion derived from the neutralized salt of the water-soluble ethylenically unsaturated monomer contained as a constituent unit of the water-absorbent polymer particles), and the urease inactivation action of the organic acid is suitably exhibited, so that the water-absorbent resin composition exhibits a high deodorizing function against ammonia and the like.

[0018] In the water-absorbent resin composition of the present invention, at least a part of the organic acid (for example, 20% by mass to 100% by mass, 50% by mass to 100% by mass, 80% by mass to 100% by mass, 90% by mass to 100% by mass, 95% by mass to 100% by mass, or 100% by mass of the total organic acid) may be disposed on the surface of the water-absorbent polymer particle, and at least a part of the organic acid may penetrate into the interior of the water-absorbent polymer particle. Further, in the water-absorbent resin composition of the present invention, at least a part of the porous deodorant (for example, 20% by mass to 100% by mass, 50% by mass to 100% by mass, 80% by mass to 100% by mass, 90% by mass to 100% by mass, 95% by mass to 100% by mass, or 100% by mass of the total porous deodorant) may be disposed on the surface of the water-absorbent polymer particle. In the water-absorbent resin composition of the present invention, at least a part of the organic acid and at least a part of the porous deodorant may be disposed on the surface of the water-absorbent polymer particle.

[0019] (Organic Acid) The organic acid is a component that lowers the pH of urine absorbed in the absorbent material.

[0020] The organic acid may have a pH of a 10% by mass aqueous solution measured by the following method of, 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.

[0021] The organic acid may include, for example, 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, or at least one selected from the group consisting of tartaric acid, citric acid, malic acid, and maleic acid. The organic acid preferably includes at least tartaric acid, which the inventors believe is difficult to adsorb to porous deodorants (i.e., easily lowers the pH of urine). 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 thought to be difficult to adsorb to porous deodorants. The organic acid contained in the water-absorbent resin composition may be one type or two or more types.

[0022] From the viewpoint of more suitably exerting the effects of the present invention, when the organic acid is particulate, the median particle diameter (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 size), volume basis) of the organic acid can be measured using a laser diffraction particle size distribution measuring device.

[0023] In the entire water absorbent resin composition of the present invention, the sum (x+y) of the content x (mass%) of the organic acid and the content y (mass%) of the porous deodorant is 0.50 mass% or more. From the viewpoint of more suitably exhibiting the effects of the present invention, the sum (x+y) is 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 1.2 ...20 mass%, 0.53 mass% to 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% to 2.00% by weight, 0.59% to 1.50% by weight, 0.59% to 1.40% by weight, 0.59% to 1.30% by weight, 0.59% to 1.20% by weight, or 0.59% to 1.00% by weight. In addition, when the organic acid is in a particulate form, if the sum (x+y) of the content x (mass%) of the organic acid and the content y (mass%) of the porous deodorant is large, the organic acid and the porous deodorant tend to come into contact with each other and rub against each other, which tends to generate fine powder (in other words, the degree of dust generation increases), and the handleability of the water absorbent resin composition may decrease. In consideration of the degree of dust generation, the sum (x+y) is preferably 1.50 mass% or less.

[0024] Furthermore, from the viewpoint of more suitably 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 mass% to 1.20 mass%, 0.30 mass% to 1.00 mass%, 0.30 mass% to 0.80 mass%, 0.40 mass% to 1.20 mass%, 0.40 mass% to 1.00 mass%, 0.40 mass% to 0.80 mass%, 0.45 mass% to 1.20 mass%, 0.45 mass% to 1.00 mass%, or 0.45 mass% to 0.80 mass%. Note that, since the water absorption rate of the water absorbent resin composition tends to decrease when the content x (mass%) of the organic acid is large, taking this into consideration, the upper limit of the content x (mass%) is preferably 1.00 mass%.

[0025] In the water-absorbent 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 more suitably exerting 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 consideration of the influence of the organic acid on the water absorption rate of the water-absorbing resin composition, the upper limit of the ratio (X / Y) is preferably 12.0.

[0026] As described above, in the water-absorbent resin composition of the present invention, when the organic acid is in a particulate form, the organic acid may be arranged on the surface of the water-absorbent polymer particle (i.e., the organic acid may be present on the surface of the water-absorbent polymer particle). For example, by mixing the water-absorbent polymer particle and the particulate organic acid in a solid phase state, the organic acid can be attached to the surface of the water-absorbent polymer particle, and the organic acid can be arranged on the surface of the water-absorbent polymer particle.

[0027] (Porous Deodorant) The porous deodorant is a porous deodorant.

[0028] From the viewpoint of more suitably exerting the effects of the present invention, the porous deodorant may contain at least one selected from the group consisting of zeolite, activated carbon, silicon dioxide, silicate, titania, alumina, aluminum hydroxide, and magnesium hydroxide, or may contain at least one selected from the group consisting of zeolite, activated carbon, and silicon dioxide. In particular, since activated carbon is thought to be difficult to adsorb organic acids, the porous deodorant preferably contains at least activated carbon, and the proportion (mass %) thereof is, for example, 80% by mass to 100% by mass, 90% by mass to 100% by mass, or 95% by mass to 100% by mass.

[0029] 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.

[0030] The median particle size (D50 (median size), volume basis) of the porous deodorant can be measured using a laser diffraction particle size distribution measuring device, and specifically, it is a value measured by the method described in the examples.

[0031] The shape of the porous deodorant may be, for example, pulverized or cylindrical, and is preferably pulverized.

[0032] The BET specific surface area of ​​the porous deodorant is 100 m 2 / g to 3000m 2 / g, 100m 2 / g~2500m 2 / g, 100m 2 / g to 2000m 2 / g, 100m 2 / g~1500m 2 / g, 500m 2 / g to 3000m 2 / g, 500m 2 / g~2500m 2 / g, 500m 2 / g to 2000m 2 / g, 500m 2 / g~1500m 2 / g, 1000m 2 / g to 3000m 2 / g, 1000m 2 / g~2500m 2 / g, 1000m 2 / g to 2000m 2 / g or 1000m 2 / g~1500m 2 If the BET specific surface area of ​​the porous deodorant is too large, the pores become finer, which may reduce the strength of the porous deodorant and increase the dust generation rate described above. Therefore, the upper limit of the BET specific surface area is set to 2000 m 2 / g.

[0033] The BET specific surface area of ​​the porous deodorant can be measured using a specific surface area measuring device, and specifically, it is a value measured by the method described in the examples.

[0034] In order to more effectively exert the effects of the present invention, the activated carbon used as the porous deodorizer is preferably activated carbon 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 phenol groups. Activated carbon having polar functional groups on its surface is commercially available, for example, as activated carbon for liquid phase use and activated carbon for water treatment.

[0035] Examples of sources of activated carbon include coconut shells, infusible or carbonized organic materials, and infusible resins such as phenolic resins. Examples of organic materials include polyacrylonitrile, pitch, polyvinyl alcohol, and cellulose. Among these, activated carbon is preferably derived from wood (sawdust), coconut shells, or pitch (e.g., coal pitch).

[0036] From the viewpoint of more suitably exhibiting the effects of the present invention, the content y (mass%) of the porous deodorant in the water absorbent resin composition of the present invention is 0.05 mass% to 0.50 mass%, 0.05 mass% to 0.40 mass%, 0.05 mass% to 0.35 mass%, 0.05 mass% to 0.30 mass%, 0.07 mass% to 0.50 mass%, 0.07 mass% to 0.40 mass%, 0.07 mass% to 0.35 mass%, 0.07 mass% to 0.30 mass%, 0.08 mass% to 0.50 mass%, 0.08 mass% to 0.40 mass%, 0.08 mass% to 0.35 mass%, 0.08 mass% to 0.30 mass%, 0.10 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% ~0.50 wt%, 0.20 wt%~0.40 wt%, 0.20 wt%~0.35 wt%, 0.20 wt%~0.30 wt%, 0.25 wt%~0.50 wt%, 0.25 wt%~0.40 wt%, 0.25 wt%~0.35 wt%, or 0.25 wt%~0.30 wt%.

[0037] 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%.

[0038] Here, the loss on drying of the porous deodorant is a value measured in accordance with JIS K1474:2014.

[0039] The pH of the porous deodorant may be, for example, 2.0 to 12.0, 2.0 to 11.0, 2.0 to 8.0, 2.0 to 6.0, 2.0 to 5.0, 3.0 to 12.0, 3.0 to 11.0, 3.0 to 8.0, 3.0 to 6.0, 3.0 to 5.0, 4.0 to 12.0, 4.0 to 11.0, 4.0 to 8.0, 4.0 to 6.0, or 4.0 to 5.0. If the porous deodorant is acidic, the cooperation of the porous deodorant and the organic acid makes it easier to inactivate urease, and the effects of the present invention can be more favorably achieved. From this perspective, the upper limit of the pH of the porous deodorant may be 6.0 or 5.0.

[0040] Here, the pH of the porous deodorant is a value measured in accordance with JIS K1474:2014.

[0041] As described above, in the water-absorbing resin composition of the present invention, it is preferable that the porous deodorant is disposed on the surface of the water-absorbing polymer particle (i.e., the porous deodorant is present on the surface of the water-absorbing polymer particle). For example, by mixing the water-absorbing polymer particle and the porous deodorant in a solid phase state, the porous deodorant is attached to the surface of the water-absorbing polymer particle, and the porous deodorant can be disposed on the surface of the water-absorbing polymer particle.

[0042] Next, the water-absorbent polymer particles (water-absorbent resin particles) contained in the water-absorbent resin composition of the present invention will be described in detail.

[0043] (Water-absorbent polymer particles) The water-absorbent polymer particles contained in the water-absorbent resin composition of the present invention are constituted by crosslinking a polymer of a water-soluble ethylenically unsaturated monomer, i.e., a crosslinked polymer having a structural unit derived from a water-soluble ethylenically unsaturated monomer.

[0044] The water absorption speed of the water-absorbing polymer particles by the Vortex method may be, for example, 1 second to 80 seconds, 1 second to 60 seconds, 1 second to 40 seconds, 10 seconds to 80 seconds, 10 seconds to 60 seconds, 10 seconds to 40 seconds, 20 seconds to 80 seconds, 20 seconds to 60 seconds, or 20 seconds to 40 seconds.

[0045] The water absorption rate of the water-absorbent polymer particles measured by the Vortex method is a value measured by the method described in the examples.

[0046] The saline water retention capacity of the water-absorbent polymer particles may 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.

[0047] The physiological saline water absorption amount of the water-absorbent polymer particles 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.

[0048] The saline water retention capacity of the water-absorbent polymer particles and the saline water absorption capacity under a load of 4.14 kPa are values ​​measured by the method described in the Examples.

[0049] The median particle diameter of the water-absorbing polymer particles is, 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 400 μm, 260 μm to 850 μm, 260 μm to 600 μm, 260 μm to 550 μm, 260 μm to 500 μm, 260 μm to 450 μm, 260 μm to 400 μm, 280 μm to 850 μm, 280 μm to 600 μm, 280 μm to 550 μm, 280 μm to 500 μm, 280 μm to 450 μm, 280 μm to 400 μm, 300 μm to 850 μm, 300 μm to 600 μm, 300 μm to 550 μm, 300 μm to 500 μm, 300 μm to 450 μm, or 300 μm to 400 μm.

[0050] In addition, the water-absorbing polymer particles may be in a form consisting of a single particle, or may be in a form (secondary particle) in which fine particles (primary particles) are aggregated. The shape of the primary particles may be approximately spherical, irregularly crushed, plate-like, etc. In the case of primary particles produced by reversed-phase suspension polymerization, examples thereof include approximately spherical single particle shapes having a smooth surface shape such as a perfect sphere, an oval sphere, etc.

[0051] The median particle size of the water-absorbing polymer particles can be measured using a JIS standard sieve, and specifically, it is a value measured by the method described in the examples.

[0052] The water-absorbing polymer particles have a constituent unit derived from a neutralized salt of a water-soluble ethylenically unsaturated monomer. Typical polymerization methods for polymerizing a water-soluble ethylenically unsaturated monomer include aqueous solution polymerization, emulsion polymerization, and reversed-phase suspension polymerization. In the aqueous solution polymerization, polymerization is carried out by heating an aqueous solution of the water-soluble ethylenically unsaturated monomer while stirring as necessary. In the reversed-phase suspension polymerization, polymerization is carried out by heating the water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium while stirring.

[0053] An example of a method for producing the water-absorbing polymer particles will be described below.

[0054] As a specific example of the method for producing water-absorbing polymer particles, there can be mentioned a method for producing water-absorbing polymer particles by inverse phase suspension polymerization of water-soluble ethylenically unsaturated monomer in hydrocarbon dispersion medium, which comprises the steps of carrying out polymerization in the presence of a radical polymerization initiator, and surface-crosslinking the hydrogel-like substance obtained by polymerization in the presence of a surface-crosslinking agent.In addition, in the method for producing water-absorbing polymer particles of the present invention, an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomer as required to form the hydrogel-like substance having an internal crosslinking structure.

[0055] <Polymerization Step> [Water-Soluble Ethylenically Unsaturated Monomer] Examples of the water-soluble ethylenically unsaturated monomer include (meth)acrylic acid (in this specification, "acrylic" and "methacrylic" are collectively referred to as "(meth)acrylic", the same applies hereinafter) and salts thereof; 2-(meth)acrylamido-2-methylpropanesulfonic acid and salts thereof; nonionic monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(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 quaternized products thereof. Among these water-soluble ethylenically unsaturated monomers, (meth)acrylic acid or a salt thereof, (meth)acrylamide, and N,N-dimethylacrylamide are preferred, and (meth)acrylic acid and a salt thereof are more preferred, from the viewpoint of industrial ease of availability, etc. These water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more.

[0056] Among these, acrylic acid and its salts are widely used as raw materials for water-absorbing polymer particles, and these acrylic acid and / or its salts may be copolymerized with the above-mentioned other water-soluble ethylenically unsaturated monomers for use. In this case, it is preferable that acrylic acid and / or its salts are used as the main water-soluble ethylenically unsaturated monomer in an amount of 70 to 100 mol% based on the total water-soluble ethylenically unsaturated monomers.

[0057] The water-soluble ethylenically unsaturated monomer may be dispersed in a hydrocarbon dispersion medium in the form of an aqueous solution and subjected to reversed-phase suspension polymerization. By forming the water-soluble ethylenically unsaturated monomer into an aqueous solution, the dispersion efficiency in the hydrocarbon dispersion medium can be increased. The concentration of the water-soluble ethylenically unsaturated monomer in this aqueous solution is preferably in the range of 20% by mass to the saturated concentration or less. The concentration of the water-soluble ethylenically unsaturated monomer is more preferably 55% by mass or less, even more preferably 50% by mass or less, and even more preferably 45% by mass or less. Meanwhile, the concentration of the water-soluble ethylenically unsaturated monomer is more preferably 25% by mass or more, even more preferably 28% by mass or more, and even more preferably 30% by mass or more.

[0058] When the water-soluble ethylenically unsaturated monomer has an acid group, such as (meth)acrylic acid or 2-(meth)acrylamido-2-methylpropanesulfonic acid, the acid group may be neutralized in advance with an alkaline neutralizing agent, as necessary. 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. These alkaline neutralizing agents may be used in the form of an aqueous solution to simplify the neutralization operation. The alkaline neutralizing agents described above may be used alone or in combination of two or more.

[0059] 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 %, even more preferably 40 to 85 mol %, and still more preferably 50 to 80 mol %, as the degree of neutralization with respect to all acid groups possessed by the water-soluble ethylenically unsaturated monomer.

[0060] [Radical Polymerization Initiator] Examples of the radical polymerization initiator added to 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-t-butyl peroxide, t-butylcumyl peroxide, t-butyl peroxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, and hydrogen peroxide, as well as 2,2'-azobis(2-amidinopropane) dihydrochloride and 2,2'-azobis[2-(N-phenyl)propane]. Examples of the radical polymerization initiator include azo compounds such as 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). Among these radical polymerization initiators, potassium persulfate, ammonium persulfate, sodium persulfate, and 2,2'-azobis(2-amidinopropane) dihydrochloride are preferred from the viewpoints of ease of availability and handling. These radical polymerization initiators may be used alone or in combination of two or more. The radical polymerization initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid.

[0061] The amount of radical polymerization initiator used is, for example, 0.00005 to 0.01 mole per mole of the water-soluble ethylenically unsaturated monomer. By using such an amount, it is possible to avoid a rapid polymerization reaction and complete the polymerization reaction within an appropriate time.

[0062] [Internal Crosslinking Agent] The internal crosslinking agent can be one that can crosslink the polymer of the water-soluble ethylenically unsaturated monomer used, such as (poly)ethylene glycol ("(poly)" refers to both the presence and absence of the prefix "poly"). the same applies hereinafter)], unsaturated polyesters obtained by reacting polyols such as diols and triols, such as (poly)propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, and (poly)glycerin, with unsaturated acids, such as (meth)acrylic acid, maleic acid, and fumaric acid; bisacrylamides such as N,N-methylenebisacrylamide; di(meth)acrylic acid esters or tri(meth)acrylic acid esters obtained by reacting polyepoxides with (meth)acrylic acid; di(meth)acrylic acid carbamyl esters obtained by reacting polyisocyanates, such as tolylene diisocyanate and hexamethylene diisocyanate, with hydroxyethyl (meth)acrylate; allylated starch, allylated cellulose, diallyl phthalate, N,N',N''-triallyl isocyanurate, divinyl Examples of the compound include a compound having two or more polymerizable unsaturated groups such as benzene; a diglycidyl compound such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, and the like, and a polyglycidyl compound such as a triglycidyl compound; an epihalohydrin compound such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; a compound having two or more reactive functional groups such as an isocyanate compound such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; and an oxetane compound such as 3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, and 3-butyl-3-oxetane ethanol. Among these internal cross-linking agents, it is preferable to use a polyglycidyl compound, it is more preferable to use a diglycidyl ether compound, and it is preferable to use (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, or (poly)glycerin diglycidyl ether.These internal crosslinking agents may be used alone or in combination of two or more.

[0063] The amount of the internal crosslinking agent used is preferably 0.000001 to 0.02 mol, more preferably 0.00001 to 0.01 mol, even more preferably 0.00001 to 0.005 mol, and still more preferably 0.00005 to 0.002 mol, relative to 1 mol of the water-soluble ethylenically unsaturated monomer.

[0064] [Hydrocarbon Dispersion Medium] Examples of hydrocarbon dispersion media include aliphatic hydrocarbons having 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. Among these hydrocarbon dispersion media, n-hexane, n-heptane, and cyclohexane are particularly preferred because they are easily available industrially, have stable quality, and are inexpensive. These hydrocarbon dispersion media may be used alone or in combination of two or more. As an example of a mixture of hydrocarbon dispersion media, a commercially available product such as Exxol Heptane (manufactured by ExxonMobil Corporation; contains 75 to 85% by mass of hydrocarbons such as heptane and its isomers) can also be used to obtain favorable results.

[0065] The amount of hydrocarbon dispersion medium used is preferably 100 to 1500 parts by mass, and more preferably 200 to 1400 parts by mass, per 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage, from the viewpoints of uniformly dispersing the water-soluble ethylenically unsaturated monomer and facilitating control of the polymerization temperature. As will be described later, the reversed-phase suspension polymerization is carried out in one stage (single stage) or in multiple stages of two or more stages, and the above-mentioned first stage polymerization refers to the polymerization reaction in the first stage of single-stage polymerization or multi-stage polymerization (the same applies hereinafter).

[0066] [Dispersion stabilizer] (Surfactant) In the reversed-phase suspension polymerization, a dispersion stabilizer can be used to improve the dispersion stability of the water-soluble ethylenically unsaturated monomer in the hydrocarbon dispersion medium. A surfactant can be used as the dispersion stabilizer.

[0067] Examples of surfactants that can be used include sucrose fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropyl alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl gluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkyl allyl ethers. Among these surfactants, sorbitan fatty acid esters, polyglycerin fatty acid esters, and sucrose fatty acid esters are particularly preferred from the standpoint of dispersion stability of the monomer. These surfactants may be used alone or in combination of two or more.

[0068] The amount of surfactant used is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, per 100 parts by mass of the first stage water-soluble ethylenically unsaturated monomer.

[0069] (Polymer-Based Dispersant) As a dispersion stabilizer used in reversed-phase suspension polymerization, a polymer-based dispersant may be used in combination with the surfactant described above.

[0070] 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, and ethylhydroxyethyl cellulose. Among these polymeric dispersants, it is particularly preferable to use 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 from the viewpoint of dispersion stability of the monomer. These polymeric dispersants may be used alone or in combination of two or more.

[0071] 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, per 100 parts by mass of the first stage water-soluble ethylenically unsaturated monomer.

[0072] [Other Components] In the method for producing water-absorbing polymer particles, if desired, other components may be added to the aqueous solution containing the water-soluble ethylenically unsaturated monomer to carry out reversed-phase suspension polymerization. As other components, various additives such as a thickener and a chain transfer agent can be added.

[0073] For example, a thickener can be added to an aqueous solution containing a water-soluble ethylenically unsaturated monomer to carry out reversed-phase suspension polymerization. By adjusting the viscosity of the aqueous solution by adding a thickener in this way, it is possible to control the median particle size obtained in the reversed-phase suspension polymerization.

[0074] Examples of usable thickeners include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, (partially) neutralized polyacrylic acid, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, etc. If the stirring speed during polymerization is the same, the higher the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution, the larger the primary particles and / or secondary particles of the resulting particles tend to be.

[0075]

[0033] In performing the 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 or polymeric dispersant) may be added either before or after the addition of the aqueous monomer solution, as long as it is before the start of the polymerization reaction.

[0076] Among these, from the viewpoint of easily reducing the amount of hydrocarbon dispersion medium remaining in the obtained water-absorbent polymer particles, it is preferable to disperse an aqueous monomer solution in a hydrocarbon dispersion medium in which a polymeric dispersant has been dispersed, and then further disperse a surfactant therein, and then carry out polymerization.

[0077] Such reversed-phase suspension polymerization can be carried out in one stage or in two or more stages, and is preferably carried out in two or three stages from the viewpoint of increasing productivity.

[0078] When carrying out reversed-phase suspension polymerization in two or more stages, after carrying out reversed-phase suspension polymerization in the first stage, a water-soluble ethylenically unsaturated monomer is added to the reaction mixture obtained in the polymerization reaction in the first stage and mixed, and reversed-phase suspension polymerization in the second and subsequent stages can be carried out in the same manner as in the first stage.In the reversed-phase suspension polymerization in each stage from the second stage onwards, it is preferable to carry out reversed-phase suspension polymerization by adding a radical polymerization initiator in addition to the water-soluble ethylenically unsaturated monomer within the molar ratio of each component to the water-soluble ethylenically unsaturated monomer as described above, based on the amount of the water-soluble ethylenically unsaturated monomer added during the reversed-phase suspension polymerization in each stage from the second stage onwards.In addition, in the polymerization in the second and subsequent stages, an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomer as needed.

[0079] 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, shortening the polymerization time, thereby improving economic efficiency, and easily removing the heat of polymerization to smoothly carry out the reaction.

[0080] <Surface cross-linking step> Next, the water-absorbent polymer particles of the present invention can be obtained by adding a surface cross-linking agent to the hydrogel-like substance having an internal cross-linked structure obtained by polymerizing a water-soluble ethylenically unsaturated monomer, and cross-linking (surface cross-linking reaction).This surface cross-linking reaction is preferably carried out in the presence of a surface cross-linking agent after the polymerization of the water-soluble ethylenically unsaturated monomer.In this way, by carrying out surface cross-linking reaction on the hydrogel-like substance having an internal cross-linked structure after the polymerization, the cross-linking density near the surface of the water-absorbent polymer particles can be increased, and water-absorbent polymer particles with improved performances such as water absorption capacity under load can be obtained.

[0081] Examples of the surface cross-linking agent include compounds having two or more reactive functional groups. For example, polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetanemethanol and 3-ethyl-3-oxetane Oxetane compounds such as methanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, and 3-butyl-3-oxetaneethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; ethylene carbonate, propylene carbonate, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl and hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]adipamide. Among these surface cross-linking agents, polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether are preferred.These surface cross-linking agents may be used alone or in combination of two or more.

[0082] 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 further preferably 0.0001 to 0.002 mol, relative to 1 mol of the total amount of the water-soluble ethylenically unsaturated monomers used in the polymerization.

[0083] As a method for adding the surface crosslinking agent, the surface crosslinking agent may be added as it is or as an aqueous solution, or, if necessary, may be added as a solution using a hydrophilic organic solvent as a solvent. Examples of the hydrophilic organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, etc.; ketones such as acetone, methyl ethyl ketone, etc.; ethers such as diethyl ether, dioxane, tetrahydrofuran, etc.; amides such as N,N-dimethylformamide, etc.; sulfoxides such as dimethyl sulfoxide, etc. These hydrophilic organic solvents may be used alone, or two or more types may be used in combination, or as a mixed solvent with water.

[0084] The timing of addition of the surface crosslinking agent may be after the polymerization reaction of the water-soluble ethylenically unsaturated monomer has almost completely finished, and the surface crosslinking agent is added in the presence of water in a range of preferably 1 to 400 parts by mass, more preferably 5 to 200 parts by mass, still more preferably 10 to 100 parts by mass, and still more preferably 20 to 60 parts by mass, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer. Note that the amount of water means the total amount of water contained in the reaction system and water used as necessary when adding the surface crosslinking agent.

[0085] 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 of the surface crosslinking reaction is preferably 1 to 300 minutes, and more preferably 5 to 200 minutes.

[0086] <Drying step> After the above-mentioned reversed-phase suspension polymerization, a drying step may be included in which water, hydrocarbon dispersion medium, etc. are removed by distillation by applying energy such as heat from the outside. When dehydrating the hydrogel after reversed-phase suspension polymerization, the system in which the hydrogel is dispersed in the hydrocarbon dispersion medium is heated, and water and the hydrocarbon dispersion medium are once distilled out of the system by azeotropic distillation. At this time, if only the distilled hydrocarbon dispersion medium is returned to the system, continuous azeotropic distillation is possible. In this case, the temperature in the system during drying is maintained below the azeotropic temperature with the hydrocarbon dispersion medium, which is preferable from the viewpoint of preventing deterioration of the resin. Subsequently, water and the hydrocarbon dispersion medium are distilled off to obtain water-absorbent polymer particles. By controlling the treatment conditions of the drying step after this polymerization to adjust the amount of dehydration, it is possible to control the various properties of the obtained water-absorbent polymer particles.

[0087] In the drying step, the drying treatment by distillation may be carried out under normal pressure or under reduced pressure. Moreover, from the viewpoint of increasing the drying efficiency, it may be carried out under a gas flow such as nitrogen. 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, even more preferably 80 to 140°C, and even more preferably 90 to 130°C. Moreover, 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.

[0088] In addition, when the surface cross-linking step using a surface cross-linking agent is carried out after the polymerization of monomers by reverse phase suspension polymerization, the drying step by distillation described above is carried out after the surface cross-linking step is completed. Alternatively, the surface cross-linking step and the drying step may be carried out simultaneously.

[0089] The water-absorbent resin composition of the present invention may contain additives according to the purpose. Examples of such additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, radical chain inhibitors, antioxidants, antibacterial agents, etc. For example, the fluidity of the water-absorbent resin composition can be further improved by adding 0.05 to 5 parts by mass of amorphous silica as inorganic powder to 100 parts by mass of the water-absorbent polymer particles. The additives are preferably hydrophilic or water-soluble.

[0090] In the water-absorbing resin composition of the present invention, the content of the water-absorbing 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.

[0091] The water-absorbent resin composition of the present invention can be produced, for example, by mixing the water-absorbent polymer particles, the organic acid, and the porous deodorant in a solid phase.

[0092] 2. Absorbent body, absorbent article The water-absorbent resin composition of the present invention constitutes an absorbent body used in hygiene materials such as sanitary products and disposable diapers, and is suitable for use in absorbent articles containing the absorbent body. The absorbent article of the present invention is an absorbent article containing an organic acid, a porous deodorant, and water-absorbent polymer particles, wherein 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 more, and the sum (x+y) of the organic acid content x (% by mass) and the porous deodorant content y (% by mass) based on the total amount of the organic acid, the porous deodorant, and the water-absorbent polymer particles is 0.5% by mass or more. The more detailed configuration of the absorbent article of the present invention can be set in the same way as for the water-absorbent resin composition described above.

[0093] Here, the absorbent using the water-absorbent resin composition of the present invention contains the particulate water-absorbent resin composition of the present invention. The absorbent may further contain hydrophilic fibers. Examples of the configuration of the absorbent include a sheet-like structure in which water-absorbent polymer particles are fixed on a nonwoven fabric or between multiple nonwoven fabrics, a mixed dispersion obtained by mixing the particulate water-absorbent resin composition and hydrophilic fibers to form a uniform composition, a sandwich structure in which the particulate water-absorbent resin composition is sandwiched between layers of hydrophilic fibers, and a structure in which the particulate water-absorbent resin composition and hydrophilic fibers are wrapped in tissue. The absorbent may also contain other components, such as adhesive binders such as heat-fusible synthetic fibers, hot-melt adhesives, and adhesive emulsions, to improve the shape retention of the absorbent.

[0094] 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, even more preferably 20 to 90% by mass, and even more preferably 30 to 80% by mass.

[0095] Examples of hydrophilic fibers include cellulose fibers such as cotton-like pulp obtained from wood, mechanical pulp, chemical pulp, and semi-chemical pulp, artificial cellulose fibers such as rayon and acetate, and fibers made of synthetic resins such as hydrophilically treated polyamide, polyester, and polyolefin. The average fiber length of the hydrophilic fibers is usually 0.1 to 10 mm, or may be 0.5 to 5 mm.

[0096] 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) through which liquid can pass and a liquid-impermeable sheet (back sheet) through which liquid cannot pass. The liquid-permeable sheet is arranged on the side that comes into contact with the body, and the liquid-impermeable sheet is arranged on the opposite side that comes into contact with the body.

[0097] Examples of liquid-permeable sheets include nonwoven fabrics such as air-through, spunbond, chemical-bond, and needle-punched types 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.

[0098] 3. Additional Notes This specification includes at least the inventions shown in (1) to (12) below. (1) A water-absorbent resin composition comprising an organic acid, a porous deodorant, and water-absorbent polymer particles having a constitutional unit derived from a neutralized salt of an ethylenically unsaturated monomer, wherein a ratio (X / Y) of a content X (parts by mass) of the organic acid to a content Y (parts by mass) of the porous deodorant is 1.0 or more, and a sum (x+y) of a content x (% by mass) of the organic acid and a content y (% by mass) of the porous deodorant in the entire water-absorbent resin composition is 0.50% by mass or more. (2) 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 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. The water-absorbing resin composition according to (1),(3) 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-absorbing resin composition is 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 1.3. 0 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%, 0.53 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 quality The water-absorbing resin composition according to (1) or (2) above, which has a content of from 0.59% to 1.50% by mass, from 0.59% to 1.40% by mass, from 0.59% to 1.30% by mass, from 0.59% to 1.20% by mass, or from 0.59% to 1.00% by 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, titania, alumina, aluminum hydroxide, and magnesium hydroxide. (5) The water-absorbent resin composition according to any one of (1) to (4) above, wherein the organic acid has a pH of 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, wherein 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, and the sum (x+y) of the content x (% by mass) of the organic acid and the content y (% by 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% by mass or more.(8) 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 to 15.0, 2.0 to 1 The absorbent article according to (7) above, wherein the elastic modulus is 2.0, 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. (9) The sum (x+y) of the content x (mass%) of the organic acid and the content y (mass%) of the porous deodorant in the organic acid, the porous deodorant, and the water-absorbing polymer particles as a whole is 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%, 0.53 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 1.50 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%, the absorbent article according to (7) or (8) above. (10) The absorbent article according to any one of (7) to (9) above, wherein the porous deodorant comprises at least one selected from the group consisting of zeolite, activated carbon, silicon dioxide, silicate, titania, alumina, aluminum hydroxide, and magnesium hydroxide. (11) The absorbent article according to any one of (7) to (10) above, wherein the organic acid has a pH of 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 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.

[0099] 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.

[0100] The following water-absorbent polymer particles, activated carbon as a porous deodorizer, and water-absorbent resin compositions obtained in Examples and Comparative Examples were evaluated by the following various tests. Unless otherwise specified, the measurements were carried out in an environment of a temperature of 25±2°C and a humidity of 50±10%.

[0101] [Production Example of Water-Absorbent Polymer Particles] A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a capacity of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm as a stirrer. 293 g of n-heptane was placed in this flask as a hydrocarbon dispersion medium, and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hiwax 1105A) was added as a polymer dispersant. The mixture was heated to 80 ° C. with stirring to dissolve the dispersant, and then cooled to 50 ° C. Separately, 92.0 g (1.03 mol) of an 80.5 mass% aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed in a 300 mL beaker, and while cooling with ice water, 147.7 g of a 20.9 mass% aqueous sodium hydroxide solution was added dropwise to carry out 75 mol% neutralization. Thereafter, 0.092 g of hydroxyl ethyl cellulose (Sumitomo Seika Chemicals Co., Ltd., HEC AW-15F) as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a water-soluble 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 liquid. The aqueous liquid prepared above was then added to a separable flask and stirred for 10 minutes. A surfactant solution prepared by heating and dissolving 0.736 g of sucrose stearate with an HLB of 3 (Ryoto Sugar Ester S-370, Mitsubishi-Kagaku Foods Corporation) as a surfactant in 6.62 g of n-heptane in a 20 mL vial was then added, and the system was thoroughly purged with nitrogen while stirring at a stirrer rotation speed of 550 rpm. The flask was then immersed in a water bath at 70°C to raise the temperature, and polymerization was carried out for 60 minutes, thereby obtaining a first-stage polymerization slurry.

[0102] On the other hand, 128.8 g (1.43 mol) of an 80.5 mass% aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed in another 500 mL beaker, and while cooling with ice water, 159.0 g of a 27 mass% aqueous sodium hydroxide solution was added dropwise to carry out 75 mol% neutralization, and then 0.103 g (0.381 mmol) of potassium persulfate as a water-soluble 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 liquid.

[0103] The contents of the separable flask system were cooled to 25°C while stirring at a stirrer speed of 1000 rpm, and then the entire amount of the second-stage aqueous liquid was added to the first-stage polymerization slurry liquid. The atmosphere in the system was replaced with nitrogen for 30 minutes, and the flask was again immersed in a water bath at 70°C to raise the temperature, and a polymerization reaction was carried out for 60 minutes to obtain a hydrogel polymer.

[0104] Thereafter, the flask was immersed in an oil bath set to 125°C, and 260.1 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane. Thereafter, 4.42 g (0.507 mmol) of a 2 mass% aqueous solution of ethylene glycol diglycidyl ether was added as a surface crosslinking agent to the flask, and the mixture was maintained at 83°C for 2 hours.

[0105] Thereafter, n-heptane was evaporated at 125°C to dry the mixture, and the mixture was 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 diameter of 362 µm, and a saline water absorption capacity of 20 ml / g under a load of 4.14 kPa.

[0106] [Evaluation of Water-Absorbent Polymer Particles] <Saline Water Retention Capacity> A cotton bag (membrane 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% by mass aqueous sodium chloride solution (saline) was poured into the cotton bag containing the water-absorbent polymer particles all at once, taking care not to allow the bag to swell. The top of the cotton bag was tied with a rubber band and allowed to stand for 30 minutes to allow the water-absorbent polymer particles to swell. After 30 minutes, the cotton bag was dehydrated for 1 minute using a dehydrator (Kokusan Co., Ltd., product number: H-122) set to a centrifugal force of 167 G, and the mass Wd (g) of the cotton bag containing the swollen gel after dehydration was measured. The same procedure was performed without adding the water-absorbent polymer particles, and the empty mass We (g) of the cotton bag when wet was measured, and the saline water retention capacity was calculated using the following formula. Saline water retention capacity (g / g) = [Wd - We] / 2.0

[0107] <Measurement of water absorption rate of pure water by Vortex method> 50±0.1 g of pure water adjusted to a temperature of 25±0.2°C in a thermostatic water bath was weighed into a 100 ml beaker and stirred with a magnetic stir bar (8 mmφ×30 mm without ring) to generate a vortex at a rotation speed of 600 rpm. 2.0±0.002 g of water-absorbent polymer particles were added to the physiological saline solution at once, and the time (seconds) from the addition of the water-absorbent polymer particles to the time when the vortex on the liquid surface converged was measured, and this time was taken 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.

[0108] <Median particle size (particle size distribution)> 50.0 g of water-absorbent polymer particles were used for measuring the median particle size (particle size distribution). JIS standard sieves were combined in the following order from top to bottom: a sieve with an opening of 850 μm, a sieve with an opening of 500 μm, a sieve with an opening of 425 μm, a sieve with an opening of 300 μm, a sieve with an opening of 250 μm, a sieve with an opening of 180 μm, a sieve with an opening of 150 μm, and a tray. The water-absorbent polymer particles were placed on the top sieve of the combination, and classified by shaking for 20 minutes using a rotary shaker. After classification, the mass of the water-absorbent polymer particles remaining on each sieve was calculated as a mass percentage relative to the total amount to determine the particle size distribution. Regarding this particle size distribution, the particles remaining on the sieve were integrated in descending order of particle diameter, and the relationship between the sieve opening and the integrated value of the mass percentage of the water-absorbent polymer particles remaining on the sieve was plotted on a logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle diameter corresponding to an integrated mass percentage of 50 mass% was determined as the median particle diameter.

[0109] <Water absorption amount of physiological saline solution under a load of 4.14 kPa> The water absorption amount of physiological saline solution under a load of 4.14 kPa (water absorption amount under load) was measured using a measuring device schematically shown in Figure 1. The measurement was performed twice for one type of water-absorbent polymer particle, and the average value was calculated. The measuring device includes a burette unit 1, a clamp 3, a conduit 5, a stand 11, a measurement table 13, and a measurement unit 4 placed on the measurement table 13. The burette unit 1 has a burette tube 21 with a scale, a rubber stopper 23 that seals the opening at the top of the burette tube 21, a cock 22 connected to the tip of the bottom of the burette tube 21, and an air introduction tube 25 and a cock 24 connected to the bottom of the burette tube 21. The burette unit 1 is fixed with a clamp 3. The flat measurement table 13 has a through-hole 13a with a diameter of 2 mm formed in its center, and is supported by a height-adjustable stand 11. The through hole 13a of the measuring table 13 and the cock 22 of the burette part 1 are connected by a conduit 5. The inner diameter of the conduit 5 is 6 mm.

[0110] The measurement unit 4 has a Plexiglas cylinder 31, a polyamide mesh 32 adhered to one opening of the cylinder 31, and a weight 33 movable up and down within the cylinder 31. The cylinder 31 is placed on the measurement table 13 via the polyamide mesh 32. The inner diameter of the cylinder 31 is 20 mm. The opening 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, and can apply a load of 4.14 kPa (0.6 psi) to the water-absorbent polymer particles 10a uniformly arranged on the polyamide mesh 32 as described later.

[0111] First, the stopcocks 22 and 24 of the burette part 1 were closed, and 0.9% by mass physiological saline solution adjusted to 25°C was poured into the burette tube 21 through the opening at the top of the burette tube 21. Next, the top opening of the burette tube 21 was sealed with a rubber stopper 23, and then the stopcocks 22 and 24 were opened. The inside of the conduit 5 was filled with 0.9% by mass saline solution 50 while preventing the inclusion of air bubbles. The height of the measurement table 13 was adjusted so that the height of the water surface of the 0.9% by mass saline solution 50 that had reached the through-hole 13a was the same as the height of the upper surface of the measurement table 13. After the adjustment, the height of the water surface of the 0.9% by mass saline solution 50 in the burette tube 21 was read on the scale of the burette tube 21, and this position was designated as the zero point (the reading at 0 seconds).

[0112] In the measurement section 4, 0.10 g of water-absorbent polymer particles 10a were uniformly arranged on a polyamide mesh 32 in a cylinder 31, a weight 33 was placed on the water-absorbent polymer particles 10a, and the cylinder 31 was installed so that its center coincided with the conduit opening at the center of the measurement table 13. The amount of saline solution reduced in the burette tube 21 (i.e., the amount of saline solution absorbed by the water-absorbent polymer particles 10a) Wc (ml) 60 minutes after the water-absorbent polymer particles 10a began to absorb saline solution from the conduit 5 was read, and the saline solution absorption capacity of the water-absorbent polymer particles 10a under a load of 4.14 kPa was calculated by the following formula: saline solution absorption capacity under a load of 4.14 kPa (ml / g) = Wc (ml) / mass of water-absorbent polymer particles (g)

[0113] [Preparation of Organic Acid] Particulate L-tartaric acid (manufactured by Wegochemical, median particle size 206 μm) was prepared as an organic acid.

[0114] [Evaluation of Organic Acid] <Measurement of pH of Organic Acid> 5.0 g of organic acid and 45.0 g of ion-exchanged water were weighed into a 100 mL plastic beaker. A stirring bar (8 mmφ × 30 mm) was placed in the beaker, and the mixture was stirred at 400 rpm using a magnetic stirrer for 1 hour. The electrode of a portable pH meter (manufactured by HORIBA, pH / ORP METER D-72, electrode model 9625) was inserted into the beaker to a depth of 2.5 cm, 1 cm from the inner wall. The electrode was allowed to stand for several minutes after insertion, and the stabilized value was recorded as the pH of a 10% by mass aqueous solution of the organic acid.

[0115] <Median particle size of organic acid> 10 g of organic acid was sieved using a continuous fully automatic ultrasonic vibration sieving measuring device (Robot Sifter RPS-205, manufactured by Seishin Enterprise Co., Ltd.), sieves with JIS standard openings of 850 μm, 500 μm, 425 μm, 300 μm, 212 μm, 106 μm, 75 μm, and 45 μm, and a tray under sieving conditions of a frequency of 80 Hz, a pulse interval of 1 second, and a classification time of 2 minutes. The mass of particles remaining on each sieve was calculated as a mass percentage relative to the total amount. The mass percentages of particles remaining on each sieve were integrated in descending order of particle size, and the relationship between the sieve opening and the integrated value of the mass percentage of particles remaining on the sieve was plotted on logarithmic probability paper. The plots on the probability paper were connected with a straight line to determine the particle size corresponding to a cumulative mass percentage of 50% by mass, and this was taken as the median particle size.

[0116] [Preparation of activated carbon] BET specific surface area: 1345 m 2 Activated carbon (Carborafine-6, manufactured by Osaka Gas Chemicals Co., Ltd.) having a molecular weight of 1000 kJ / 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 shape was prepared.

[0117] [Evaluation of Activated Carbon] <Median Particle Diameter of Activated Carbon (Laser Diffraction)> The median particle diameter (D50 (median diameter), volume basis) of the activated carbon used was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD2300).

[0118] <BET specific surface area of ​​activated carbon> 0.1 g of the activated carbon to be measured was dried using a pretreatment device (MicrotracBel, BELPREP VAC II) under degassing conditions of heating and vacuum evacuation at 60°C for 24 hours. Thereafter, an adsorption isotherm was measured at a temperature of 77 K using nitrogen gas as the adsorption gas using a specific surface area measurement device (MicrotracBel, BELSORP MINI II), and the specific surface area was determined from a multi-point BET plot, which was taken as the BET specific surface area of ​​the activated carbon.

[0119] [Production of Water-Absorbent Resin Composition] <Example 1> To 100 parts by mass of the water-absorbent polymer particles obtained in 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 using a cross rotary mixer manufactured by Meiwa Kogyo Co., Ltd. under conditions of a rotation speed of 50 rpm and a revolution speed of 50 rpm, thereby obtaining a water-absorbent resin composition.

[0120] Example 2 A water-absorbing resin composition was obtained in the same manner as in Example 1, except that the amount of activated carbon added was changed to 0.30 parts by mass.

[0121] Example 3 A water-absorbing 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.

[0122] 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 parts by mass and the amount of activated carbon added was 0.30 parts by mass.

[0123] Example 5 A water-absorbing 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.

[0124] Comparative Example 1 A water-absorbing resin composition was obtained in the same manner as in Example 1, except that the amount of L-tartaric acid added was 0.25 parts by mass and the amount of activated carbon added was 0.05 parts by mass.

[0125] 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.

[0126] 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 0.25 parts by mass and the amount of activated carbon added was 0.30 parts by mass.

[0127] 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 0.25 parts by mass and no activated carbon was added.

[0128] 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 0.50 parts by mass and no activated carbon was added.

[0129] 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 0.75 parts by mass and no activated carbon was added.

[0130] 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 1.00 parts by mass and no activated carbon was added.

[0131] Comparative Example 8 A water-absorbent resin composition was obtained in the same manner as in Example 1, except that no L-tartaric acid was added and the amount of activated carbon added was 0.05 parts by mass.

[0132] Comparative Example 9 A water-absorbent resin composition was obtained in the same manner as in Example 1, except that no L-tartaric acid was added and the amount of activated carbon added was 0.10 parts by mass.

[0133] Comparative Example 10 A water-absorbent resin composition was obtained in the same manner as in Example 1, except that no L-tartaric acid was added and the amount of activated carbon added was 0.20 parts by mass.

[0134] Comparative Example 11 A water-absorbent resin composition was obtained in the same manner as in Example 1, except that no L-tartaric acid was added and the amount of activated carbon added was 0.30 parts by mass.

[0135] Reference Example 1 The water-absorbing polymer particles obtained in the Production Example were used as Reference Example 1.

[0136] [Evaluation of Water-Absorbent Resin Composition] <Ammonia Generation 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. Furthermore, urease (manufactured by MERCK Corporation, 50% glycerin solution derived from jack bean, 1000 U / mL) was diluted with distilled water to prepare a urease solution at 2 U / mL. 1.00 g of the water-absorbent resin composition or water-absorbent polymer particles was placed in a sterile Petri dish (diameter 88 mm, height 17 mm), and a test liquid (prepared by mixing 45.0 mL of the above-mentioned artificial urine with 1.0 mL of urease solution) was added to swell the sample. After adding the test liquid, the sample was sealed in a 2 L polyester sampling bag (PAAAK2, manufactured by GL Sciences Co., Ltd.), the air inside the bag was removed, and 900 mL of dry air was added instead. The sample was then stored at 35°C, and after 24 hours, the ammonia concentration was measured using a gas detector tube (ammonia 3 L, 3 La, 3 M, manufactured by Gastec Corporation). This measured value and the deodorizing rate calculated from the following formula 1 are shown in Table 1. Formula 1: Deodorizing rate (%) = [(ammonia concentration of Reference Example 1 - ammonia concentration of Example or Comparative Example) / ammonia concentration of Reference Example 1] x 100

[0137] <Dust Generation Rate Test> A glass suction bottle with a capacity of 500 mL was prepared. A stainless steel hopper (top inner diameter 88 mm × foot inner diameter 18 mm) was set so that the height from the bottom of the suction bottle to the discharge outlet of the hopper was 180 mm, and the suction port of the suction bottle and a dust generation meter (manufactured by Shibata Scientific Co., Ltd., Digital Indicator LD-5R type) were connected with a glass tube (inner diameter 7.7 mm × length 300 mm). 3.0 g ± 0.1 g of a water-absorbent resin composition was charged into the hopper as a sample, and the start button of the dust generation meter was pressed at the same time as the damper of the hopper was pulled out, and the counter after 1 minute (counter (A) for the sample) was recorded. A blank test was performed before measuring the sample to determine the counter (B) during the blank test, and the dust generation rate was calculated using the following formula: dust generation rate (cpm) = A - B In the formula, A represents the counter (cpm) for the sample, and B represents the counter (cpm) during the blank test. The dust generation rate was measured 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.

[0138]

[0139]

[0140] As shown in Table 1, for example, the deodorizing rate of Comparative Example 11 (containing no organic acid) in which the content y of the porous deodorant in the water-absorbent resin composition is 0.30% by mass is 47%, and the deodorizing rate of Comparative Example 5 (containing no porous deodorant) in which the content x of the organic acid in the water-absorbent resin composition is 0.50% by mass is 17%. In contrast, the deodorizing rate of Example 2 in which the content y of the porous deodorant in the water-absorbent resin composition is 0.30% by mass and the content y of the organic acid is 0.50% by mass is as high as 72%, and it is understood that a synergistic effect between the organic acid and the porous deodorant is exerted, which cannot be predicted from the results of Comparative Examples 5 and 11 (the sum of the deodorizing rates of Comparative Examples 5 and 1 is 64%). The synergistic effect of the deodorizing rate of the water absorbent resin composition shown in Table 2 is obtained by dividing the deodorizing rate of the Example by the sum of the deodorizing rates of the Comparative Examples in which each deodorizer was used alone, and for example, the synergistic effect of Example 2 is a value calculated by deodorizing rate of Example 2 (72) / (deodorizing rate of Comparative Example 11 (47)+deodorizing rate of Comparative Example 5 (17)). When the reference value of 1.00 is exceeded, it can be said that a synergistic effect is exerted.

[0141] Furthermore, although the addition of an additive to water-absorbent polymer particles usually tends to slow down the water absorption rate, it is understood from the results shown in Table 2 that the water-absorbent resin compositions of Examples 1 to 5 maintain water absorption rates close to that of Reference Example 1 (containing no deodorant). It is also understood from the results shown in Table 2 that, among the water-absorbent resin compositions of Examples 1 to 5, Examples 1, 3, and 5 are excellent in dust generation rate, and Example 1 is particularly excellent.

[0142] REFERENCE SIGNS LIST 1 burette part 3 clamp 4 measuring part 5 conduit 10a water-absorbent polymer particles 11 stand 13 measuring table 13a through-hole 21 burette tube 22 cock 23 rubber stopper 24 cock 25 air introduction tube 31 cylinder 32 polyamide mesh 33 weight 50 saline solution

Claims

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

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

3. The water-absorbent resin composition according to claim 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.

4. An absorbent article comprising an organic acid, a porous deodorant, and water-absorbing polymer particles, wherein 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 more, and the sum (x+y) of the organic acid content x (% by mass) and the porous deodorant content y (% by mass) based on the total amount of the organic acid, the porous deodorant, and the water-absorbing polymer particles is 0.5% by mass or more.

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