WATER ABSORBENT RESIN COMPOSITION, ABSORBENT, AND ABSORBENT ARTICLE

Abstract

Provided is a water absorbent resin composition which is capable of suppressing unpleasant odors, while having excellent fluidity. A water absorbent resin composition according to the present invention contains a water absorbent resin and a hydroxamic acid or a salt thereof.

Claims

1. A water-absorbent resin composition comprising: a water-absorbent resin; and hydroxamic acids represented by the following general formula (1): ##STR00003## wherein R represents a linear or branched C1 to C7 alkyl group, a phenyl group, a hydroxyphenyl group, an amino group, a naphthyl group, a pyridyl group, an aromatic alkyl group having a butoxy group, alkyl group having a benzamide structure, or an alkyl group having a phenylcarbamoyl group.

2. The water-absorbent resin composition according to claim 1, wherein the hydroxamic acids represented by the general formula (1) are contained in the form of an alkali metal salt or an ammonium salt.

3. The water-absorbent resin composition according to claim 1, wherein the hydroxamic acids or salts thereof are at least one selected from the group consisting of acetohydroxamic acid, salicylhydroxamic acid, octanohydroxamic acid, benzohydroxamic acid, hydroxyurea, 2-(4-butoxyphenyl) acetohydroxamic acid, 1-naphthohydroxamic acid, 3-pyridinecarbohydroxamic acid, suberoylanilide hydroxamic acid, 4-(dimethylamino)-N-[7-(hydroxyamino)-7-oxoheptyl]benzamide, sodium acetohydroxamic acid, sodium octanohydroxamic acid, and sodium benzohydroxamic acid.

4. The water-absorbent resin composition according to claim 1, wherein the content of the hydroxamic acids or salts thereof is in a range of 0.01 to 5 parts by mass per 100 parts by mass of the water-absorbent resin.

5. An absorbent material comprising the water-absorbent resin composition according to claim 1 and a hydrophilic fiber.

6. An absorbent article comprising the absorbent material according to claim 5 held between a liquid-permeable sheet and a liquid-impermeable sheet.

Description

EXAMPLES

[0074] Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. However, the present invention is not limited to the examples.

[0075] Water-absorbent resins obtained in the following examples and comparative examples were evaluated using the tests described below. Each of the testing methods for evaluation will be hereinafter described.

<Median Particle Diameter>

[0076] JIS standard sieves having mesh sizes of 850 m, 600 m, 500 m, 425 m, 300 m, 250 m, and 150 m, and a receptacle were combined in that order from the top.

[0077] 50 g of the water-absorbent resin was placed on the top sieve of the combined sieves, and shaken for 20 minutes with a Ro-Tap shaker to conduct classification. After the classification, the particle size distribution was determined by calculating the mass of the water-absorbent resin remaining on each sieve as the mass percentage relative to the total mass. With regard to this particle size distribution, the mass percentage of the water-absorbent resin remaining on each sieve was integrated in descending order of particle diameter. Thereby, the relationship between the sieve mesh size and the integrated value of the mass percentage of the water-absorbent resin remaining on each sieve was plotted on logarithmic probability paper. The plots on the probability paper were connected with straight lines, and a particle diameter equivalent to 50% by mass of the integrated mass percentage was determined as the median particle diameter.

<Water Content>

[0078] About 2 g of the water-absorbent resin was precisely weighed out (mass Wa (g) of the water-absorbent resin before drying) in a previously weighed aluminum foil case (No. 8). The above sample was dried for 2 hours with a hot-air dryer (from ADVANTEC) set at an internal temperature of 105 C. Thereafter, the dried sample was allowed to be cooled in a desiccator, and the mass Wb (g) of the water-absorbent resin after drying was measured. The water content of the water-absorbent resin was calculated by the following equation:

water content (%)=[[WaWb]/Wa]100

<Ammonia Generation Suppression Test>

[0079] 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, and 2.5 g of ammonium sulfate in 1.0 kg of distilled water. Also, 1.0 mL of urease (1000 U/ml of a 50% glycerin solution originating from Sword Bean (Canavalia gladiata) manufactured by MERCK) was diluted with distilled water 500 times to prepare a urease solution. 1.0 g of each sample (water-absorbent resin compositions of Examples 1 to 8 and a water-absorbent resin of Comparative Example 1) was placed in a sterile petri dish and added with a test liquid (prepared by mixing 30.0 g of the artificial urine with 1.0 mL of the above urease solution) to swell the sample. After the test liquid was added, the sample was sealed in a 2 L Tedlar bag, air in the bag was evacuated, and instead of the air, 900 mL of dry air was added into the bag. Subsequently, storage was performed at 30 C., and after 24 hours, the amount of generated ammonia was measured using a gas detecting tube (from Gastec Corporation, ammonia 3L, 3La, 3M). The measurement value (200 ppm) is taken as 100.0% (generation amount of Comparative Example 1), and the results are shown in Table 1.

<Flowability Test>

[0080] A spatula angle was measured with a powder tester PT-N (from Hosokawa Micron Corporation), and the flowability of the water-absorbent resin compositions of Examples 3 and 7 as representative examples and the water-absorbent resin of Comparative Example 1 was evaluated. The spatula angle is an inclination angle of a side of a resin powder deposited on a spatula, refers to an angle required to move the powder in a stationary state, and is one of indicators of flowability. It means that the smaller the value of the spatula angle, the better the flowability. The measurement procedure was performed according to an instruction of the powder tester. The measured values of the spatula angle are shown in Table 2.

<Production of Water-Absorbent Resin>

Production Example 1

[0081] A 2 L cylindrical round-bottomed separable flask equipped with a stirrer, two sets of paddle blades, a reflux condenser, a dropping funnel, and a nitrogen gas inlet tube was provided. This flask was charged with 340.0 g of n-heptane, and then 0.92 g of a sucrose stearate (Ryoto sugar ester S-370 from Mitsubishi-Kagaku Foods Corporation) and 0.92 g of a maleic anhydride-modified ethylene-propylene copolymer (Hi-wax 1105A from Mitsui Chemicals, Inc.) were added thereto. The mixture was heated with stirring to 80 C. to dissolve the surfactant, and then cooled to 50 C.

[0082] Separately, 92.0 g (1.02 mol) of an 80% by mass aqueous solution of acrylic acid was placed in 500-mL Erlenmeyer flask, and 146.0 g of a 21% by mass aqueous solution of sodium hydroxide was added dropwise with external cooling to accomplish 75 mol % neutralization. Then, 0.11 g (0.41 mmol) of potassium persulfate as a radical polymerization initiator and 8.10 mg (0.046 mmol) of ethylene glycol diglycidyl ether as an internal-crosslinking agent were added and dissolved. As a result, a first-stage aqueous monomer solution was prepared.

[0083] The entire amount of the first-stage aqueous monomer solution was added to the separable flask, and the inside of the system was sufficiently replaced with nitrogen. Thereafter, the flask was immersed in a water bath at 70 C. to raise the temperature, and the first-stage polymerization was carried out for 30 minutes, thereby obtaining a first-stage reaction mixture.

[0084] Separately, 128.8 g (1.43 mol) of an 80% by mass aqueous solution of acrylic acid was placed in another 500-mL Erlenmeyer flask, and 159.0 g of a 27% by mass aqueous solution of sodium hydroxide was added dropwise with external cooling to accomplish 75 mol % neutralization. Then, 0.16 g (0.59 mmol) of potassium persulfate as a radical polymerization initiator and 6.62 mg (0.038 mmol) of ethylene glycol diglycidyl ether as an internal-crosslinking agent were added and dissolved. As a result, a second-stage aqueous monomer solution was prepared.

[0085] The first-stage reaction mixture was cooled to 28 C., the second-stage aqueous monomer solution at the same temperature was added into the system, and the flask was kept at 25 C. for 30 minutes while the internal of the system was replaced with nitrogen. Thereafter, the flask was again immersed in a water bath kept at 70 C. to raise the temperature, and the second-stage polymerization was carried out for 30 minutes.

[0086] After the second-stage polymerization, the temperature of the reaction mixture was raised in an oil bath at 125 C. to distill 248.0 g of water out of the system while refluxing n-heptane by azeotropic distillation of water and n-heptane. Then, 4.42 g (0.51 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added, and the post-crosslinking reaction was carried out at 80 C. for 2 hours. Thereafter, the temperature of the reaction mixture was raised in an oil bath at 125 C., and n-heptane was evaporated and dried to obtain 230.5 g of a water-absorbent resin. The median particle diameter of the water-absorbent resin was 400 m, and the water content of the water-absorbent resin was 8%.

Example 1

[0087] Acetohydroxamic acid as hydroxamic acids was added to and mixed with the water-absorbent resin obtained in Production Example 1 in an amount of 0.05 parts by mass per 100 parts by mass of the water-absorbent resin to produce a water-absorbent resin composition.

Example 2

[0088] A water-absorbent resin composition was produced in the same manner as in Example 1 except that the addition amount of acetohydroxamic acid was 0.1 parts by mass per 100 parts by mass of the water-absorbent resin.

Example 3

[0089] A water-absorbent resin composition was produced in the same manner as in Example 1 except that the addition amount of acetohydroxamic acid was 0.5 parts by mass per 100 parts by mass of the water-absorbent resin.

Example 4

[0090] A water-absorbent resin composition was produced in the same manner as in Example 1 except that the addition amount of acetohydroxamic acid was 1.0 part by mass per 100 parts by mass of the water-absorbent resin.

Example 5

[0091] Salicylhydroxamic acid as hydroxamic acids was added to and mixed with the water-absorbent resin obtained in Production Example 1 in an amount of 0.05 parts by mass per 100 parts by mass of the water-absorbent resin to produce a water-absorbent resin composition.

Example 6

[0092] A water-absorbent resin composition was produced in the same manner as in Example 5 except that the addition amount of salicylhydroxamic acid was 0.1 parts by mass per 100 parts by mass of the water-absorbent resin.

Example 7

[0093] A water-absorbent resin composition was produced in the same manner as in Example 5 except that the addition amount of salicylhydroxamic acid was 0.5 parts by mass per 100 parts by mass of the water-absorbent resin.

Example 8

[0094] A water-absorbent resin composition was produced in the same manner as in Example 5 except that the addition amount of salicylhydroxamic acid was 1.0 part by mass per 100 parts by mass of the water-absorbent resin.

Example 9

[0095] Octanohydroxamic acid as hydroxamic acids was added to and mixed with the water-absorbent resin obtained in Production Example 1 in an amount of 0.5 parts by mass per 100 parts by mass of the water-absorbent resin to produce a water-absorbent resin composition.

Example 10

[0096] Benzohydroxamic acid as hydroxamic acids was added to and mixed with the water-absorbent resin obtained in Production Example 1 in an amount of 0.5 parts by mass per 100 parts by mass of the water-absorbent resin to produce a water-absorbent resin composition.

Example 11

[0097] Sodium acetohydroxamic acid as hydroxamic acids was added to and mixed with the water-absorbent resin obtained in Production Example 1 in an amount of 0.5 parts by mass per 100 parts by mass of the water-absorbent resin to produce a water-absorbent resin composition.

Example 12

[0098] Sodium octanohydroxamic acid as hydroxamic acids was added to and mixed with the water-absorbent resin obtained in Production Example 1 in an amount of 0.5 parts by mass per 100 parts by mass of the water-absorbent resin to produce a water-absorbent resin composition.

Example 13

[0099] Sodium benzohydroxamic acid as hydroxamic acids was added to and mixed with the water-absorbent resin obtained in Production Example 1 in an amount of 0.5 parts by mass per 100 parts by mass of the water-absorbent resin to produce a water-absorbent resin composition.

Comparative Example 1

[0100] The water-absorbent resin produced in Production Example 1 was used as it is as the water-absorbent resin of Comparative Example 1.

TABLE-US-00001 TABLE 1 Hydroxamic acids Addition Ammonia generation amount (%) amount after 24 hours (part(s) (Ammonia generation amount of Type by mass) Comparative Example 1: 100%) Comparative 100.0 Example 1 Example 1 0.05 15.0 Example 2 Acetohydroxamic acid 0.1 7.5 Example 3 0.5 1.0 Example 4 1.0 0.3 Example 5 Salicylhydroxamic acid 0.05 40.0 Example 6 0.1 32.5 Example 7 0.5 1.8 Example 8 1.0 1.0 Example 9 Octanohydroxamic acid 0.5 0.3 Example 10 Benzohydroxamic acid 0.5 0.5 Example 11 Sodium acetohydroxamic acid 0.5 2.5 Example 12 Sodium octanohydroxamic acid 0.5 0.5 Example 13 Sodium benzohydroxamic acid 0.5 0.5

TABLE-US-00002 TABLE 2 Flowability test (Spatula angle ) Comparative Example 1 48.2 Example 3 33.8 Example 7 35.6