JPH0586251A - Highly water-absorbable polymer composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition hardly causing coloring even when stored for a long period under high temperature and humidity and used for paper diaper, sanitary napkin, etc., by blending a highly water-absorbable polymer with an organophosphoric acid compound of a specified amount. CONSTITUTION:The objective composition is obtained by blending (A) a highly water-absorbable polymer, preferably consisting of a crosslinked product of a polyacrylic acid salt with (B) 0.01-10wt.% (preferably 0.05-5wt.%) organophosphoric acid compound (salt), preferably, consisting of 1- hydroxyethylidene-1, 1-diphosphonic acid, ethylenediamine tetra(methylene phosphonic acid), diethylenetriaminepenta-(methylene phosphonic acid) and/or its alkali metal salt, ammonium salt or amine salt.

Description

Detailed Description of the Invention

[0001]

This invention relates to superabsorbent polymer compositions. More specifically, it relates to a highly water-absorbent polymer composition which is less likely to be colored over time even when stored under high temperature and high humidity for a long time.

[0002]

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

Examples of such superabsorbent polymers include starch-acrylonitrile graft polymer hydrolysates, starch-acrylic acid graft polymers, vinyl acetate-acrylic acid ester copolymer hydrolysates, and polyacrylic acid. Cross-linked salts, carboxymethylated cellulose and the like are well known.

[0004]

By the way, since these superabsorbent polymers are colored brown or yellow when stored for a long time under high temperature and high humidity, the products using these polymers have remarkably reduced commercial value during storage. There was a problem to do.

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

The coloring referred to herein includes the meaning that the polymer is discolored.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to obtain a superabsorbent polymer which is difficult to be colored over time even if it is stored under high temperature and high humidity for a long time, and as a result, the present invention has been completed. ..

In the present invention, the organic phosphoric acid compound or its salt is 0.01 to 10% by weight based on the superabsorbent polymer.
It is characterized by being added.

Here, examples of the super absorbent polymer which can be used in the present invention include starch-acrylonitrile graft polymer hydrolyzate and starch-
Examples thereof include an acrylic acid graft polymer, a hydrolyzate of a vinyl acetate-acrylic acid ester copolymer, a polyacrylate crosslinked product, and carboxymethyl cellulose. Particularly preferred is a crosslinked polyacrylic salt in terms of absorption performance. The polymerization method and the copolymerization component of the super absorbent polymer are not particularly limited. Further, regarding the usage form of the superabsorbent polymer, there are powder, a composite with a fibrous substrate, and the like, but there is no particular limitation.

In the present invention, an organic phosphoric acid compound or a salt thereof is added to the above superabsorbent polymer to give a superabsorbent polymer composition. Organic phosphoric acid compounds include ethylidenephosphonic acid; 1-hydroxyethylidene-1,1-diphosphonic acid; aminotrimethylenephosphonic acid; ethylenediaminetetra (methylenephosphonic acid);
Diethylenetriaminepenta (methylenephosphonic acid) and the like can be mentioned, but particularly preferred are 1-hydroxyethylidene-1,1-diphosphonic acid; ethylenediaminetetra (methylenephosphonic acid); diethylenetriaminepenta (methylenephosphonic acid). Preferable salts include alkali metal salts such as Na salt and K salt, ammonium salts, and amine salts. These compounds are known as a type 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 No. 1-275661, etc., for example, ethylenediaminetetraacetic acid (EDTA),
It has been clarified that the use of sodium tripolyphosphate or the like does not reduce the water absorption performance even in the case of water containing salts and ions. However, according to the studies by the present inventors, EDTA and sodium tripolyphosphate have no significant effect on the prevention of coloration over time of the superabsorbent polymer which is the object of the present invention for long-term storage under high temperature and high humidity. The purpose was achieved only by using the above specific compound.

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

If desired, other additives may be added to the superabsorbent polymer composition of the present invention. In particular, when other metal sequestering agents are used in combination, the effect of preventing coloration with time of the superabsorbent polymer, which is the object of the present invention, may be further improved.

[0014]

The superabsorbent polymer composition of the present invention containing 0.01 to 10% by weight of an organic phosphoric acid compound or a salt thereof has a coloring property over time which is higher than that of the composition without addition of color even when stored under high temperature and high humidity. Are extremely few.

Although the reason why this effect is obtained is not clear, by capturing a trace amount of the transition metal in the superabsorbent polymer composition by the organic phosphoric acid compound or its salt, the radical species is mediated by the transition metal. It is considered that this is because it is possible to prevent undesired reactions such as decomposition of the superabsorbent polymer and breakage of the polymer chain from occurring.

[0016]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

The water absorption and the degree of coloration over time in the examples and comparative examples are determined by the following procedure. (How to obtain water absorption amount) About 1 g of a super absorbent polymer composition was placed in a 10 cm × 20 cm nylon mesh tea bag, which was placed in a 1 liter beaker to obtain a concentration of 0.9.
After immersing in a physiological saline solution of weight% for 1 hour and draining for 15 minutes, the water absorption amount with respect to the own weight of the polymer is determined by the following formula.

Water absorption (g / g) = (total weight after immersion (g) -tea bag weight after immersion (g)) / (weight of super absorbent polymer composition before immersion (g)) Coloring evaluation method) The superabsorbent polymer composition was placed in a polyethylene bag having a thickness of 60 μm and hermetically sealed at 70 ° C.
It is stored in an atmosphere of 65% RH for 1 week and 2 weeks, and then the degree of coloring (YI value) is measured. A "SM color computer" (model SM-5-1S-2B) manufactured by Suga Test Instruments Co., Ltd. is used for the measurement of the coloring degree.

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

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

With respect to this highly water-absorbent polymer composition, the water absorption amount and coloration with time were evaluated, and the results are shown in Table 1.

Example 2 A superabsorbent polymer was prepared in the same manner as in Example 1, and then an ethylenediaminetetra (methylenephosphonic acid) aqueous solution was sprayed and impregnated in place of the 1-hydroxyethylidene-1,1-diphosphonic acid aqueous solution. Then, it was dried to obtain a super absorbent polymer. The amount of ethylenediaminetetra (methylenephosphonic acid) added to the superabsorbent polymer is 0.63.
It was a weight% (1.5 × 10 ⁻⁵ mol was added per 1 g of the polymer). The evaluation results are shown in Table 1.

Example 3 300 g of a partially neutralized acrylic acid aqueous solution (monomer concentration 30% by weight) in which 60 mol% was a potassium salt was sampled in a reaction vessel equipped with a stir bar, a nitrogen blowing tube, and a thermometer, and further N , N'-methylenebisacrylamide 0.
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 2,2′-azobis (N, N′-dimethyleneisobutyramidine) hydrochloride aqueous solution was added, and the liquid temperature was set to 60 ° C. to allow the polymerization to proceed gently. ..

3 hours after the initiation of polymerization, the reaction vessel was opened,
The resulting gel-like hydropolymer was taken out, dried and pulverized to obtain a super absorbent polymer composition. The amount of 1-hydroxyethylidene-1,1-diphosphonic acid added to the superabsorbent polymer was 0.1% by weight (4.9 × 1 per 1 g of the polymer).
Was 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 partially neutralized acrylic acid in which 60 mol% was a potassium salt (monomer concentration 67%).
-Methylenebisacrylamide (0.1 g) and 30% by weight of hydrogen peroxide (0.6 g) were added and completely dissolved. This was impregnated onto the entire surface of a separately prepared 3 g of polyester nonwoven fabric and kept at 40 ° C. in a constant temperature reaction tank. The amount of the impregnated monomer was 5 times the weight of the nonwoven fabric.

Next, a 0.5 wt% L-ascorbic acid aqueous solution as a reducing agent was sprayed onto the entire surface of the non-woven fabric using a spray nozzle. L- for partially neutralized acrylic acid aqueous solution
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, 1% by weight of an aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid was sprayed on the entire surface of the superabsorbent polymer composite and dried to form a superabsorbent polymer.
A highly water-absorbent 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 added per 1 g of polymer).

The water absorption amount and coloration over time of this highly water-absorbent polymer composition were evaluated, 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 used instead of the aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid. It was sprayed, impregnated and dried to obtain a super absorbent polymer composition. The amount of diethylenetriaminepenta (methylenephosphonic acid) 7Na salt added to the superabsorbent polymer was 1.8% by weight (1 g of the polymer).
Per 2.4 × 10 ⁻⁵ mol). The evaluation results are shown in Table 1.

Comparative Example 1 A superabsorbent polymer was produced in the same manner as in Example 1, except that
No 1-hydroxyethylidene-1,1-diphosphonic acid aqueous solution was added. The evaluation results are shown in Table 1.

Comparative Example 2 After producing a superabsorbent polymer 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 the polymer). The evaluation is shown in Table 1.

Comparative Example 3 Instead of adding 1.8 g of a 5 wt% 1-hydroxyethylidene-1,1-diphosphonic acid aqueous solution in Example 3, 5 wt% of an ethylenediaminetetraacetic acid-4Na aqueous solution 1 was added.
0.0 g was added. Otherwise in the same manner as in Example 3, a superabsorbent polymer composition was produced and evaluated. The amount of ethylenediaminetetraacetic acid-4Na added to the superabsorbent polymer was 0.55% by weight (1.5 × 10 5 per 1 g of the polymer).
^-5 mol). The results are shown in Table 1.

Comparative Example 4 A superabsorbent polymer was prepared in the same manner as in Example 4, except that
No 1-hydroxyethylidene-1,1-diphosphonic acid aqueous solution was added. The evaluation results are shown in Table 1.

Comparative Example 5 A superabsorbent polymer composite was prepared in the same manner as in Example 4, and then an ethylenediaminetetraacetic acid-4Na salt aqueous solution was sprayed and impregnated in place of the 1-hydroxyethylidene-1,1-diphosphonic acid aqueous solution. And dried to obtain a super absorbent 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 1 g of the polymer). The evaluation results are shown in Table 1.

[0035]

[Table 1] As is clear from Table 1, in the superabsorbent polymer compositions obtained in Examples, the change in coloring degree (YI value) is much smaller than that in Comparative Examples, and coloring over time occurs even when stored under high temperature and high humidity. Hateful.

[0036]

EFFECTS OF THE INVENTION A superabsorbent polymer composition obtained by adding an organic phosphoric acid compound or a salt thereof to a superabsorbent polymer is less likely to be colored over time even under high temperature and high humidity. Even if it is used, its commercial value will not be lost during the storage period.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Yamamoto 1-16-13 Kitakasai, Edogawa-ku, Tokyo Daiichi Pharmaceutical Co., Ltd. Tokyo Research and Development Center

Claims (2)

[Claims] 1. A superabsorbent polymer composition comprising an organic phosphoric acid compound or a salt thereof in an amount of 0.01 to 10% by weight based on the superabsorbent polymer. 2. The organic phosphoric acid compound is 1-hydroxyethylidene-1,1-diphosphonic acid; ethylenediaminetetra (methylenephosphonic acid); diethylenetriaminepenta (methylenephosphonic acid) and / or salts thereof. The superabsorbent polymer composition described.