JP3107873B2 - Method for preventing temporal coloring of superabsorbent polymer and agent for preventing temporal coloring - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention is, deposition of the superabsorbent polymer
The present invention relates to a color prevention method and a coloring prevention agent . More specifically,
The present invention relates to a method for obtaining a superabsorbent polymer which is hardly colored with time even when stored under high temperature and high humidity for a long time, and a coloring inhibitor therefor .

[0002]

2. Description of the Related Art Superabsorbent polymers that absorb water tens to hundreds of times their own weight are widely used in paper diapers, sanitary napkins, and many other products.

Examples of such superabsorbent polymers include hydrolysates of starch-acrylonitrile graft polymers, starch-acrylic acid graft polymers, hydrolysates of vinyl acetate-acrylate copolymers, and polyacrylic acid. Crosslinked salts, carboxymethylated cellulose and the like are well known.

[0004]

However, since these superabsorbent polymers are colored brown or yellow when stored for a long period of time under high temperature and high humidity, products using these polymers have a markedly reduced commercial value during storage. There was a problem of doing.

Therefore, an object of the present invention is to solve the above-mentioned problem by adding an organic phosphoric acid compound or a salt thereof to a superabsorbent polymer.

[0006] The term "coloring" as used herein includes the meaning that the polymer is discolored.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to obtain a superabsorbent polymer which is hardly colored with time even when stored under high temperature and high humidity for a long time, and as a result, the present invention has been completed. .

According to the present invention , an organic phosphoric acid compound or a salt thereof is used as a coloring agent with time for a superabsorbent polymer .
This time coloring for superabsorbent polymer
It is characterized by adding 0.01 to 10% by weight of an inhibitor .

The superabsorbent polymer that can be used in the present invention includes, for example, a hydrolyzate of starch-acrylonitrile graft polymer, starch-
Acrylic acid graft polymer, hydrolyzate of vinyl acetate-acrylate copolymer, crosslinked polyacrylate, carboxymethylated cellulose and the like can be mentioned. Particularly preferred is a crosslinked polyacrylic salt in terms of absorption performance. The polymerization method and copolymerization component of the superabsorbent polymer are not particularly limited. Further, regarding the usage form of the superabsorbent polymer, there are a powder, a composite with a fibrous base, and the like, but there is no particular limitation.

[0010] In the present invention, an organic phosphoric acid compound or a salt thereof is added to the superabsorbent polymer as a coloring inhibitor with time . Ethylidenephosphonic acid; 1-hydroxyethylidene-1, 1
-Diphosphonic acid; aminotrimethylenephosphonic acid; ethylenediaminetetra (methylenephosphonic acid); diethylenetriaminepenta (methylenephosphonic acid); and particularly preferred are 1-hydroxyethylidene-1, 1-diphosphonic acid; ethylenediamine Tetra (methylenephosphonic acid); diethylenetriaminepenta (methylenephosphonic acid). Preferred salts include alkali metal salts such as Na salt and K salt, ammonium salts and amine salts. These compounds are known as a kind of sequestering agent.

Superabsorbent polymers containing a sequestering agent are disclosed in JP-A-56-89838 and JP-A-59-2300.
No. 46, JP-A 1-275661, and the like, for example, ethylenediaminetetraacetic acid (EDTA),
It has been clarified that the use of sodium tripolyphosphate or the like does not lower the water absorption performance even in the case of water containing salts and ions. However, according to the study of the present inventors, EDTA and sodium tripolyphosphate do not have a great effect on preventing the coloring with time of the superabsorbent polymer that is stored for a long time under high temperature and high humidity, which is the object of the present invention, and the present invention relates to the present invention. The object has been achieved for the first time by using the above specific compound.

In the present invention, each of the organic phosphoric acid compounds and salts thereof may be used alone or in combination. % By weight, more preferably 0.05%
~ 5% by weight. If it is less than 0.01% by weight, the effect of preventing coloration with time is poor, and if it exceeds 10% by weight, the water absorption performance is reduced. Therefore, these ranges are not intended by the present invention. The method for adding the organic phosphoric acid compound or a salt thereof is not particularly limited, and the solution can be added by a method of adding a solution thereof in the step of producing the superabsorbent polymer, or by spraying or impregnating the polymer after polymerization.

[0013] Other additives may be added to the superabsorbent polymer according to the present invention, if necessary. Among them, when another metal sequestering agent is used in combination, the effect of preventing the superabsorbent polymer intended for the present invention from being colored with time may be further improved.

[0014]

The superabsorbent polymer to which 0.01 to 10% by weight of an organic phosphoric acid compound or a salt thereof has been added has significantly less coloring with time even when stored under high temperature and high humidity, as compared with a non-added one.

The reason why this effect can be obtained is not clear, but a small amount of transition metal in the superabsorbent polymer is trapped by the organic phosphate compound or a salt thereof, whereby radical species are generated through the transition metal. It is considered that this would prevent undesired reactions such as decomposition of the superabsorbent polymer and cleavage of the polymer chain.

[0016]

Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

The amount of water absorption and the degree of coloring with time in Examples and Comparative Examples are determined by the following procedure. (How to determine water absorption) About 1 g of the superabsorbent polymer composition was placed in a 10 cm × 20 cm nylon mesh tea bag, and this was placed in a 1 liter beaker for 1 hour in a 0.9% by weight saline solution. After immersion and draining for 15 minutes, the amount of water absorption with respect to the weight of the polymer is determined by the following equation.

Water absorption (g / g) = (total weight after immersion (g)-weight of tea bag after immersion (g)) / (weight of superabsorbent polymer composition before immersion (g)) Evaluation method of coloring) The superabsorbent polymer composition was sealed in a polyethylene bag having a thickness of 60 μm and sealed in an atmosphere of 70 ° C. and 65% RH.
After storing for weeks and two weeks, the degree of coloring (YI value) is measured. To measure the degree of coloring, use “SM” manufactured by Suga Test Instruments Co., Ltd.
Color Computer ”(Model SM-5-1S-2B)
Is used.

Example 1 300 g of an aqueous solution of partially neutralized acrylic acid in which 60 mol% was converted to a potassium salt (monomer concentration: 30% by weight) was collected in a reaction vessel equipped with a stirring rod, a nitrogen blowing tube, and a thermometer. , N'-methylenebisacrylamide
15 g was added and completely dissolved. 1 under nitrogen atmosphere
3 g of a 0% by weight aqueous solution of 2,2'-azobis (N, N'-dimethyleneisobutyramide) hydrochloride was added, and the liquid temperature was lowered to 6%.
At 0 ° C., the polymerization proceeded gently. After 3 hours from the start of the polymerization, the reaction vessel was opened and the produced gel-like hydropolymer was taken out and pulverized to obtain a superabsorbent polymer.

Next, a 0.1% by weight aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid is uniformly sprayed and impregnated on the superabsorbent polymer, and then dried to give the superabsorbent polymer 1-hydroxyethyladenylate. A superabsorbent polymer composition to which ethylidene-1,1-diphosphonic acid was added was obtained. 1 -hydroxyethylidene- 1, for superabsorbent polymer,
The amount of 1-diphosphonic acid added was 0.3% by weight (1.5 × 10 ⁻⁵ mol added per 1 g of polymer).

The superabsorbent polymer composition was evaluated for water absorption and coloring with time, and the results are shown in Table 1.

Example 2 After producing a superabsorbent polymer in the same manner as in Example 1, an aqueous solution of ethylenediaminetetra (methylenephosphonic acid) was sprayed and impregnated in place of the aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid. After drying, a superabsorbent polymer was obtained. The amount of ethylenediaminetetra (methylenephosphonic acid) added to the superabsorbent polymer is 0.63
% By weight (1.5 × 10 ⁻⁵ mol added per 1 g of polymer). Table 1 shows the evaluation results.

Example 3 A 300 g aqueous solution of partially neutralized acrylic acid (monomer concentration: 30% by weight) in which 60 mol% was converted to a potassium salt was collected in a reaction vessel equipped with a stirring rod, a nitrogen blowing tube and a thermometer. , N'-methylenebisacrylamide
15 g, 5% by weight of 1-hydroxyethylidene-1, 1
-1.8 g of an aqueous solution of diphosphonic acid was added and completely dissolved. Under a nitrogen atmosphere, 3 g of a 10% by weight aqueous solution of 2,2′-azobis (N, N′-dimethyleneisobutyramidine) hydrochloride was added, and the temperature of the solution was raised to 60 ° C. to allow the polymerization to proceed gently. .

After 3 hours from the start of the polymerization, the reaction vessel is opened,
The resulting gel-like hydropolymer was taken out, dried and pulverized to obtain a superabsorbent polymer composition. The amount of 1-hydroxyethylidene-1,1-diphosphonic acid added to the superabsorbent polymer was 0.1% by weight (4.9 × 1 / g of polymer).
0 ^-6 mol added). The evaluation is shown in Table 1.

Example 4 N, N 'was added to 100 g of an aqueous solution of a partially neutralized acrylic acid in which 60 mol% was converted to a potassium salt (monomer concentration: 67%).
0.1 g of methylenebisacrylamide and 0.6 g of 30% by weight of hydrogen peroxide were added and completely dissolved. This was impregnated over the entire surface of a separately prepared 3 g of polyester nonwoven fabric, and kept at 40 ° C. in a thermostatic reactor. The amount of the impregnated monomer was 5 times the weight of the nonwoven fabric.

Next, a 0.5% by weight aqueous solution of L-ascorbic acid as a reducing agent was sprayed on the entire surface of the nonwoven fabric by a spray nozzle. L- against aqueous solution of partially neutralized acrylic acid
The amount of ascorbic acid added was 0.043% by weight.
Polymerization immediately occurred, and a superabsorbent polymer composite in which the superabsorbent polymer was strongly adhered to the polyester nonwoven fabric was obtained.

Further, a 1% by weight aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid is sprayed on the entire surface of the superabsorbent polymer composite, and dried to obtain 1% by weight of the superabsorbent polymer.
-A superabsorbent polymer composition to which -hydroxyethylidene-1,1-diphosphonic acid was added was obtained. The amount of 1-hydroxyethylidene-1,1-diphosphonic acid added to the superabsorbent polymer was 0.5% by weight (2.4 × 10 ⁻⁵ mol per 1 g of polymer).

The superabsorbent polymer composition was evaluated for water absorption and coloring with time, and the results are shown in Table 1.

Example 5 After producing a superabsorbent polymer composite in the same manner as in Example 4, an aqueous solution of diethylenetriaminepenta (methylenephosphonic acid) 7Na salt was replaced with an aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid. It was sprayed, impregnated and dried to obtain a superabsorbent polymer composition. The amount of diethylenetriaminepenta (methylenephosphonic acid) 7Na added to the superabsorbent polymer is 1.8% by weight (1 g of polymer).
2.4 × 10 ^-5 mol / mol). Table 1 shows the evaluation results.

Comparative Example 1 A superabsorbent polymer was produced in the same manner as in Example 1.
No aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid was added. Table 1 shows the evaluation results.

Comparative Example 2 A superabsorbent polymer was produced in the same manner as in Example 1,
Instead of the 1-hydroxyethylidene-1,1-diphosphonic acid aqueous solution, an ethylenediaminetetraacetic acid-4Na salt aqueous solution was sprayed, impregnated, and dried to obtain a superabsorbent polymer composition. The amount of ethylenediaminetetraacetic acid-4Na salt added to the superabsorbent polymer was 0.55% by weight (1.5 × 10 ⁻⁵ mol added per 1 g of polymer). The evaluation is shown in Table 1.

COMPARATIVE EXAMPLE 3 Instead of adding 1.8 g of a 5% by weight aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid in Example 3, a 5% by weight aqueous solution of ethylenediaminetetraacetic acid-4Na was added.
0.0 g was added. Otherwise, the procedure of Example 3 was repeated to prepare and evaluate a superabsorbent polymer composition. The amount of ethylenediaminetetraacetic acid-4Na added to the superabsorbent polymer was 0.55% by weight (1.5 × 10
^-5 mol added). The results are shown in Table 1.

Comparative Example 4 A superabsorbent polymer was produced in the same manner as in Example 4.
No aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid was added. Table 1 shows the evaluation results.

COMPARATIVE EXAMPLE 5 A superabsorbent polymer composite was produced in the same manner as in Example 4, followed by spraying and impregnating an aqueous solution of ethylenediaminetetraacetic acid-4Na salt in place of the aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid. And dried to obtain a superabsorbent polymer composition. The amount of ethylenediaminetetraacetic acid-4Na salt added to the superabsorbent polymer was 0.92% by weight (2.4 × 10 ^-5 mol added per gram of polymer). Table 1 shows the evaluation results.

[0035]

[Table 1] As is evident from Table 1, the superabsorbent polymer compositions obtained in the examples have a much smaller change in the degree of coloring (YI value) than the comparative examples, and coloring over time occurs even when stored under high temperature and high humidity. Hateful.

[0036]

Superabsorbent polymers superabsorbent polymer organic phosphoric acid compound, or by adding the salts according to the present invention is from Kunar coloring with time is difficulty occur under high temperature and high humidity, like this
If the superabsorbent polymer is used for a product whose appearance is important, its commercial value will not be impaired during the storage period.

Continuation of front page (72) Inventor Takashi Yamamoto 1-16-13 Kita-Kasai, Edogawa-ku, Tokyo Dai-ichi Pharmaceutical Co., Ltd. Tokyo Research and Development Center (56) References JP 1-275661 (JP, A) JP-A-2-117903 (JP, A) JP-A-1-13587 (JP, A) JP-A-1-180815 (JP, A) JP-A-62-215517 (JP, A) (Int.Cl. ⁷ , DB name) C08L 1/26-1/30 C08L 33/00-33/16 C08L 51/02 C08L 101/14 C08K 5/49-5/5399 CA (STN)

Claims (3)

(57) [Claims] 1. A method for preventing the superabsorbent polymer from coloring with time, comprising adding an organic phosphoric acid compound or a salt thereof to the superabsorbent polymer in an amount of 0.01 to 10% by weight.
Law . (2) Organic phosphoric acid compounds or salts thereof
And a colorant with time of a superabsorbent polymer. 3. The organic phosphate compound is 1-hydroxyethylidene-1,1-diphosphonic acid; ethylenediaminetetra (methylenephosphonic acid); diethylenetriaminepenta (methylenephosphonic acid) and / or a salt thereof. Prevention method described.