WATER ABSORBENT RESIN COMPOSITION, ABSORBENT, AND ABSORBENT ARTICLE

Abstract

The present invention provides a water absorbent resin composition which suppresses acetaldehyde odor, while being suppressed in coloring with time. A water absorbent resin composition which contains a hydrazide compound carrier and a water absorbent resin, wherein: the degree of yellowing is 10 or less if 2.0 g of this water absorbent resin composition is held at a temperature of 70° C. at a relative humidity of 90% for 7 days; and if 10.0 g of this water absorbent resin composition and 900 ml of a nitrogen gas having an acetaldehyde concentration of 20 ppm are sealed in a hermetically sealed bag having a volumetric capacity of 2 liters, the acetaldehyde concentration of the gas in the hermetically sealed hag measured after a lapse of one hour is 15 ppm or less.

Claims

1. A water-absorbing resin composition comprising: a supported hydrazide compound; and a water-absorbing resin, wherein: the water-absorbing resin composition has a yellow index of 10 or less when 2.0 g of the water-absorbing resin composition is held in an environment at a temperature of 70° C. and a relative humidity of 90% for 7 days, and the water-absorbing resin composition has an acetaldehyde concentration of 15 ppm or less when 10.0 g of the water-absorbing resin composition and 900 ml of nitrogen gas having an acetaldehyde concentration of 20 ppm are enclosed in a hermetically sealed bag having a volume of 2 liters and the acetaldehyde concentration of gas in the hermetically sealed bag after a lapse of 1 hour is measured.

2. The water-absorbing resin composition according to claim 1, wherein: the water-absorbing resin composition is in particulate form, and the supported hydrazide compound is present on at least one of a surface and an inside of the water-absorbing resin composition.

3. The water-absorbing resin composition according to claim 1, wherein a support of the supported hydrazide compound is at least one of silicic acid and a silicate.

4. The water-absorbing resin composition according to claim 1, wherein a content of the supported hydrazide compound is 0.001 to 10 mass %.

5. The water-absorbing resin composition according to claim 1, wherein a content of a hydrazide compound in the supported hydrazide compound is 0.1 to 30 mass %.

6. The water-absorbing resin composition according to claim 1, wherein the supported hydrazide compound has a median particle diameter of 0.01 to 100 μm.

7. An absorber comprising the water-absorbing resin composition according to claim 1.

8. An absorbent article comprising the absorber according to claim 7 held between a liquid-permeable sheet and a liquid-impermeable sheet.

Description

EXAMPLES

[0100] Hereinafter, the present invention will be described in detail with reference to an example and comparative examples. However, the present invention is not limited to the example.

[0101] The water-absorbing resin compositions obtained in the following example and comparative examples were evaluated in the following various tests. Hereinafter, each evaluation test method will be described.

[0102] <Median Particle Diameter>

[0103] The measurement was performed in an environment at a temperature of 25±2° C. and a humidity of 50±10%. JIS standard sieves were combined in the following order from the top: a sieve with an opening of 850 μm, a sieve with an opening of 600 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 150 μm, and a receptacle.

[0104] The water-absorbing resin composition, 50 g, was placed on the uppermost sieve of the combined sieves, and shaken for 10 minutes using a rotating and tapping shaker to perform classification. After classification, the mass of the water-absorbing resin composition retained on each sieve was calculated as a mass percentage with respect to the total amount, and the particle size distribution was determined. With respect to this particle size distribution, by cumulation of the mass percentages of the retained on the sieves in descending order of particle diameter, the relationship between the opening of the sieve and the cumulative value of the mass percentage of the water-absorbing resin retained on the sieve was plotted on a logarithmic probability paper. The plotted points on the probability paper were connected with a straight line, and a particle diameter corresponding to a cumulative mass percentage of 50 mass % was defined as a median particle diameter.

[0105] <Yellow Index of Water-Absorbing Resin Composition>

[0106] In an environment of a temperature of 25±2° C. and a humidity of 50±10%, 2.0 g of the water-absorbing resin composition was placed in a glass measuring container (cylindrical, inner diameter 3 cm). The yellow index of the water-absorbing resin composition was measured with a color difference meter (Color Meter ZE6000, manufactured by Nippon Denshoku Industries Co., Ltd.) in which X, Y, and Z, which are tristimulus values of a colorimetric color difference meter, had been corrected, using a white plate for standard use. The yellow index was calculated from X, Y, and Z (tristimulus values) of the obtained water-absorbing resin composition according to the following equation, and defined as an initial yellow index.

Yellow index=100×(1.2769×X−1.0592×Z)/Y

[0107] The test (accelerated test) of coloring of the water-absorbing resin composition over time was performed according to the following procedure. First, 2.0 g of a sample was uniformly placed in a glass container (cylindrical, inner diameter 3 cm, depth 1 cm), and the container was stored for 7 days in a tabletop thermo-hygrostat set at a temperature of 70±2° C. and a relative humidity of 90±2%. After a lapse of 7 days, the container was taken out from the thermo-hygrostat, and left for a while to be cooled to room temperature. The yellow index of the water-absorbing resin composition was measured with a color difference meter (Color Meter ZE6000, manufactured by Nippon Denshoku Industries Co., Ltd.). From X, Y, and Z (tristimulus values) of the obtained water-absorbing resin composition, the yellow index of the water-absorbing resin composition was calculated according to the following equation. The yellow index is shown in Table 1.

Yellow index=100×(1.2769×X−1.0592×Z)/Y

[0108] <Acetaldehyde Odor Suppression Test>

[0109] The acetaldehyde odor suppression test was performed in an environment of 25° C.±2° C. In a plastic petri dish having an inner diameter of 10 cm and a height of 1.5 cm, 10.00 g of the water-absorbing resin composition was placed. The petri dish containing the water-absorbing resin composition was placed in a 2L-Tedlar bag (with one port and a cap) equipped with a three-way cock with a silicone tube having an inner diameter of 5 mm interposed therebetween, and the bag was hermetically sealed by heat sealing. Then, the glass syringe (constant humidity glass syringe, 200 mL, manufactured by Tsuji Seisakusho Co., Ltd.) was connected to a three-way cock, and the entire amount of air in the Tedlar bag was withdrawn. Thereafter, 900 mL of a standard gas having an acetaldehyde concentration of 20±1 ppm (manufactured by Sumitomo Seika Chemicals Co., Ltd., nitrogen dilution, analytical value 19.3 ppm) was enclosed in the bag using the above-described glass syringe. After 60 minutes from the completion of enclosing of the acetaldehyde-containing gas, the three-way cock was removed from the Tedlar bag, a gas detection tube with the ends open (manufactured by GASTEC Corporation, detection tube: acetaldehyde 92L) was attached, and the acetaldehyde concentration in the Tedlar bag gas phase was measured. The measurement results are shown in Table 1.

Production of Water-Absorbing Resin

Production Example 1

[0110] A 2-L round-bottom cylindrical separable flask having an inner diameter of 11 cm and equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirring blade having two stages of 4-inclined paddle blades having a blade diameter of 5 cm as a stirrer was prepared. To this flask, 293 g of n-heptane as a hydrocarbon dispersion medium and 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hi-WAX 1105A) as a polymeric dispersant were added, the temperature was raised to 80° C. with stirring to dissolve the dispersant, and then the contents were cooled to 50° C.

[0111] On the other hand, in a beaker having an internal volume of 300 mL, 92.0 g (1.03 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed, 147.7 g of a 20.9 mass % aqueous sodium hydroxide solution was added dropwise while cooling with ice water to perform neutralization of 75 mol %, and then 0.092 g (Sumitomo Seika Chemicals Co., Ltd., HECAW-15F) of hydroxylethyl cellulose 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 thereto and dissolved, thereby preparing a first-stage aqueous monomer solution.

[0112] Then, the aqueous monomer solution prepared above was added to the separable flask and stirred for 10 minutes, after which a surfactant solution obtained by heating and dissolving 0.736 g of a sucrose stearate having an HLB of 3 (Mitsubishi Chemical Foods Corporation, Ryoto Sugar Ester S-370) as a surfactant in 6.62 g of n-heptane in a 20 mL-vial was further added. While stirring at a stirrer rotational speed of 550 rpm, the inside of the system was sufficiently purged with nitrogen, and then the flask was immersed in a water bath at 70° C. for 60 minutes to obtain a first-stage polymerization slurry solution.

[0113] On the other hand, in another beaker having an internal volume of 500 mL, 128.8 g (1.43 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed, 159.0 g of a 27 mass % aqueous sodium hydroxide solution was added dropwise while cooling with ice water to perform neutralization of 75 mol %, and then 0.103 g (0.381 mmol) of potassium persulfate as a water-soluble radical polymerization initiator and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal-crosslinking agent were added thereto and dissolved, thereby preparing a second-stage aqueous monomer solution.

[0114] While stirring at a stirrer rotational speed of 1000 rpm, the inside of the separable flask system was cooled to 25° C. Then the whole amount of the second-stage aqueous monomer solution was added to the first-stage polymerization slurry. After the inside of the system was purged with nitrogen for 30 minutes, the flask was immersed again in a water bath at 70° C. for 60 minutes to obtain a second-stage hydrous gel polymer.

[0115] To the hydrous gel polymer after the second-stage polymerization, 0.589 g of a 45 mass % aqueous pentasodium diethylenetriaminepentaacetate solution was added under stirring. Thereafter, the flask was immersed in an oil bath set at 125° C., and 257.7 g of water was removed to the outside of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of a 2 mass % aqueous solution of ethylene glycol diglycidyl ether as a post-crosslinking agent was added to the flask, and the contents were held at 83° C. for 2 hours.

[0116] Thereafter, the contents were dried by evaporation of n-heptane at 125° C. to obtain a particulate crosslinked polymer (dry product). This particulate crosslinked polymer was passed through a sieve with an opening of 850 μm, and 0.1 mass % of amorphous silica (Oriental Silicas Corporation, TOKUSIL NP-S) with respect to the mass of the particulate crosslinked polymer was mixed with the particulate crosslinked polymer to obtain 228.0 g of a particulate water-absorbing resin containing amorphous silica. The median particle diameter of the particulate water-absorbing resin was 352 μm.

Production of Water-Absorbing Resin Composition

Example 1

[0117] To 100 parts by mass of the water-absorbing resin obtained in Production Example 1, 0.100 parts by mass of a silicate compound on which a hydrazide compound was supported (Sinanen Zeomic Co., Ltd., Dushlite M, supported amount of hydrazide compound; 7 mass %, median particle diameter 6 μm) was powder-mixed to obtain a water-absorbing resin composition. The yellow index of this water-absorbing resin composition on the 7th day of the accelerated test was 9.5, and the acetaldehyde concentration in the gas phase after the acetaldehyde odor suppression test was 3 ppm.

Comparative Example 1

[0118] To 100 parts by mass of the water-absorbing resin obtained in Production Example 1, an aqueous malonic acid dihydrazide solution containing 0.007 parts by mass of malonic acid dihydrazide and 0.133 parts by mass of deionized water was added dropwise under stirring of the water-absorbing resin, and then the mixture was heated at 105° C. for 30 minutes. Then, the resultant was passed through a JIS standard sieve having an opening of 850 μm to obtain a water-absorbing resin composition. The yellow index of this water-absorbing resin composition on the 7th day of the accelerated test was 10.4, and the acetaldehyde concentration in the gas phase after the acetaldehyde odor suppression test was 18 ppm.

Comparative Example 2

[0119] To 100 parts by mass of the water-absorbing resin obtained in Production Example 1, an aqueous malonic acid dihydrazide solution containing 0.035 parts by mass of malonic acid dihydrazide and 0.665 parts by mass of deionized water was added dropwise under stirring of the water-absorbing resin, and then the mixture was heated at 105° C. for 30 minutes. Then, the resultant was passed through a JIS standard sieve having an opening of 850 μm to obtain a water-absorbing resin composition. The yellow index of this water-absorbing resin composition on the 7th day of the accelerated test was 14.6, and the acetaldehyde concentration in the gas phase after the acetaldehyde odor suppression test was 18 ppm.

Comparative Example 3

[0120] To 100 parts by mass of the water-absorbing resin obtained in Production Example 1, an aqueous malonic acid dihydrazide solution containing 0.070 parts by mass of malonic acid dihydrazide and 1.33 parts by mass of deionized water was added dropwise under stirring of the water-absorbing resin, and then the mixture was heated at 105° C. for 30 minutes. Then, the resultant was passed through a JIS standard sieve having an opening of 850 μm to obtain a water-absorbing resin composition. The yellow index of this water-absorbing resin composition on the 7th day of the accelerated test was 16.5, and the acetaldehyde concentration in the gas phase after the acetaldehyde odor suppression test was 18 ppm.

Comparative Example 4

[0121] To 100 parts by mass of the water-absorbing resin obtained in Production Example 1, 0.093 parts by mass of silicate (corresponding to the support used in Example 1, median particle diameter 6 μm) was powder-mixed to obtain a water-absorbing resin composition. The yellow index of this water-absorbing resin composition on the 7th day of the accelerated test was 20.6, and the acetaldehyde concentration in the gas phase after the acetaldehyde odor suppression test was 17 ppm.

Comparative Example 5

[0122] The water-absorbing resin obtained in Production Example 1 was used as it was as a water-absorbing resin of Comparative Example 5. The yellow index of this water-absorbing resin on the 7th day of the accelerated test was 9.8, and the acetaldehyde concentration in the gas phase after the acetaldehyde odor suppression test was 19 ppm.

TABLE-US-00001 TABLE 1 Yellow index of Acetaldehyde Supported hydrazide compound water-absorbing concentration after Addition amount resin odor suppression test Type (parts by mass) Day 0 Day 7 (ppm) Example 1 Silicate supported 0.100 6.2 9.5 3 malonic acid dihydrazide Comparative Malonic acid dihydrazide 0.007 6.4 10.4 18 example 1 Comparative Malonic acid dihydrazide 0.035 7.7 14.6 18 example 2 Comparative Malonic acid dihydrazide 0.070 7.4 16.5 18 example 3 Comparative Silicate 0.093 6.7 20.6 17 example 4 Comparative — 6.2 9.8 19 example 5