JPH0762149A - Water absorbent resin composition - Google Patents

Abstract

(57) [Summary] [Structure] A water absorbent resin composition obtained by adding aluminum isopropoxide powder to a water absorbent resin powder. [Effect] Since the gel strength and the water absorption amount are improved, a high water absorption amount can be secured under pressure. Moreover, since the treatment can be performed without using a dispersion medium, the number of steps and the manufacturing cost can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbent resin composition, and more particularly to a water-absorbent resin composition having an improved hydrogel strength.

[0002]

2. Description of the Related Art Since water-absorbent resins have a high water absorption capacity and excellent water retention ability, they are widely used not only in hygiene products such as diapers and sanitary products but also in fields such as agriculture, gardening, food and medicine. Has been done. Generally, a water absorbent resin is required to have high gel strength in addition to high water absorption and water retention. When the gel strength of the water-absorbent resin is weak, for example, in the case of diaper products, the water-containing gel becomes pasty, and the baby may lose its shape due to the weight and movement of the baby, which may cause diaper leakage. Further, when the gel strength is weak, the water-containing gel becomes large in stickiness, the wet back is deteriorated, and the diaper quality is deteriorated.

Therefore, conventionally, it has been performed to increase the gel strength by treating the water absorbent resin. That is, in JP-A-58-42602, a hydrophilic cross-linked polymer having a hydroxyl group or a carboxyl group is dispersed in a dispersion medium of methanol or ethanol, and the surface is further cross-linked with a cross-linking agent such as a polyvalent metal salt. It is disclosed that the water absorption rate and the gel strength are increased.

However, in this method, there is a risk of fire, explosion, toxicity, etc. by using a large amount of a dispersion medium of methanol and ethanol, and the solvent must be completely removed after the surface treatment. There was a problem of poor productivity. Therefore, the present applicant previously prepared a powdery polyacrylic acid-based water-absorbent resin in the presence of polyhydric alcohol such as polyethylene glycol and water,
It has been proposed to treat with an aluminum compound capable of reacting with it (JP-A-63-270741). That is, the use of such a polyhydric alcohol having a high boiling point has an advantage that there is no risk of fire and toxicity and that water is simply removed by drying, which is preferable in terms of productivity.

These cross-linking treatments not only increase the water absorption rate, but also serve to increase the strength of the hydrogel. In particular, the strength of the hydrous gel has a correlation with the amount of water absorption under pressure, and as the gel strength increases, the amount of water absorption increases under pressure. In addition, when the gel strength is weak, the water-absorbent gel becomes pasty, and the baby may lose its shape due to the weight and movement of the baby, which may cause diaper leakage. Furthermore, when the gel strength is weak, the water-absorbent gel becomes large in stickiness, so-called wet back deteriorates, and the diaper quality deteriorates.

[0006]

In the case of diaper products, for example, the weight of the baby is actually used, and therefore, those having a high water absorption amount under pressure are preferable, and therefore a water absorbent resin having a high gel strength is desired. . However, when the water-absorbent resin is subjected to the above-mentioned cross-linking treatment, the strength of the hydrous gel is improved, but the water absorption amount is decreased, which may result in insufficient water absorption under pressure.

Further, in any of the above processing methods, since a solvent such as alcohol is used as the dispersion medium, it is necessary to remove the dispersion medium after the processing. for that reason,
There is a problem that the number of processes increases and the production cost also increases. The main object of the present invention is to solve the above technical problems and to provide a water absorbent resin composition having a large water absorption and an excellent gel strength.

Another object of the present invention is to provide a water-absorbent resin composition which can be treated without using a dispersion medium and which can reduce the number of steps and manufacturing costs.

[0009]

The water-absorbent resin composition of the present invention is characterized in that aluminum isopropoxide powder is added to the water-absorbent resin powder. According to the present invention, since aluminum isopropoxide has deliquescent and is decomposed by water, after mixing with the water absorbent resin,
Aluminum isopropoxide is decomposed and activated by the moisture in the air and reacts with the surface of the water absorbent resin powder. As a result, the gel strength of the water-absorbent resin is improved, but surprisingly, in the present invention, even if the gel strength of the water-absorbent resin is increased, it has an unexpected effect of suppressing the decrease in water absorption. Was found. Such an effect is first achieved by using aluminum isopropoxide and is not observed when using other aluminum compounds such as aluminum chloride.

Further, according to the present invention, since solid powders are mixed with each other, it is not necessary to use a dispersion medium such as polyhydric alcohol as in the prior art, and a drying step after the treatment is required to remove the dispersion medium. There is also the effect of not doing. As the water-absorbent resin used in the present invention, various conventionally used water-absorbent resins such as cross-linked polyethylene oxide, cross-linked polyvinyl alcohol, cross-linked polyacrylic acid and its salt, cellulose-acrylic acid graft copolymer. And salts thereof, hydrolysates of starch-acrylonitrile graft copolymers, and the like, and in particular, polyacrylic acid-based water-absorbing water-absorbent polymers or copolymers having acrylic acid or acrylate monomer units in the main chain. It is preferable to use a resin.

Examples of such polyacrylic acid-based polymers include polyacrylic acid, polyacrylic acid salts, and copolymers of acrylic acid and acrylic acid salts. Here, examples of the polyacrylic acid salt and the salt portion of the acrylic acid salt include alkali metal salts such as sodium salt and potassium salt, and organic base salts such as ammonium salt. Further, in order to improve properties such as hydrophilicity, it is a copolymer of a polymer having a monomer unit of acrylic acid or acrylate in its main chain and acrylamide, N-vinylpyrrolidone, 2-hydroxyethyl methacrylate or the like. May be.

Further, the water-absorbent resin is preferably a cross-linked one, and known cross-linking means can be used for the cross-linking. For example, by heating a copolymer with a cross-linking monomer such as N-methylol acrylamide, by using an oxidizing catalyst such as potassium peroxosulfate, or by using N, N having two or more polymerizable unsaturated bonds. It is possible to crosslink by adding a crosslinking agent such as'-methylenebisacrylamide, ethylene glycol diacrylate during the polymerization.

Usually, a method is employed in which, if necessary, another copolymerizable monomer and the above-mentioned crosslinking agent are added to an aqueous solution of acrylic acid or an acrylic acid salt to carry out polymerization.
Since the polymer obtained by this method solidifies into a lump when dried, it is pulverized using a pulverizer into a particle size of a size suitable for a super absorbent polymer material. Since the polymer obtained by emulsion polymerization or suspension polymerization has a small spherical shape, it may be used as it is, or may be further pulverized into fine particles before use.

Further, in the present invention, a commercially available water-absorbent resin powder is used as it is as the water-absorbent resin powder,
Even if aluminum isopropoxide powder is added thereto, the effect of improving water absorption and gel strength can be obtained. Therefore, it is optimal for remedying the disadvantage that the gel strength is weak when a commercially available water-absorbent resin having a low gel strength but a large water absorption amount is used. Further, the present invention can be applied to a defective product having poor gel strength generated in the process of manufacturing a water absorbent resin to obtain a water absorbent resin composition having excellent gel strength and water absorption.

The particle size of the water absorbent resin powder in the present invention is
In the Tyler standard sieve, 5-400 mesh product is preferable, 16-150 mesh product (about 110-1000μ)
m) is more preferred. The aluminum isopropoxide powder in the present invention preferably has a small particle size in order to increase the water absorption amount and gel strength, but if the powder is too fine, it may agglomerate into lumps. Therefore, the preferable particle size of the aluminum isopropoxide powder is 16 to 6 on the Tyler standard sieve.
00 mesh product, especially 200 mesh product (75 μm)
It is the following.

The amount of the aluminum isopropoxide powder added to the water absorbent resin powder is 100 water absorbent resin powder.
It is preferably 0.1 to 5 parts by weight with respect to parts by weight.
If the added amount of aluminum isopropoxide powder exceeds 5 parts by weight, the water absorption tends to decrease, and if the added amount is less than 0.1 part by weight, the improvement of the strength of the hydrogel cannot be recognized.

The aluminum isopropoxide powder is added to the water-absorbent resin powder by a dry method without using a solvent or the like. The mixing means for the both powders is not particularly limited, and any known mixing means can be adopted, and examples thereof include a Nauter mixer, a ribbon blender, a conical blender, a Henschel mixer, and a liquor.

The water-absorbent resin composition of the present invention thus obtained can be applied to various uses, and is particularly suitable for uses requiring high water absorbency and gel strength. Examples of such applications include sanitary materials such as diapers and sanitary products, medical materials such as water retaining materials for poultices, seed germination aids, agricultural materials such as water retaining materials for soil, and dew condensation prevention materials for interior materials. Examples include building materials, cosmetics, and cosmetic materials such as water retention materials such as fragrances.

[0019]

【Example】

Example 1 and Comparative Examples 1 to 6 Commercially available super absorbent polymer "Aquamate AQ-200A"
[Polyacrylic acid-based polymer manufactured by Sekisui Plastics Co., Ltd.,
The particle size is in the range of 16 to 150 mesh (Tyler standard sieve, the same applies hereinafter), and 42 mesh is the center] to 100 g.
0.5 g of the additive shown in 1 was added and uniformly mixed with a small stirrer to obtain each water-absorbent resin composition. Among the additives used, aluminum isopropoxide had a particle size of 1
It was a 50-mesh product (106 μm) fine powder, and other additives were also pulverized in a mortar so that the particle diameters were almost the same.

The water absorption and gel strength of each of the obtained samples were measured. The results are also shown in Table 1. The water absorption and gel strength were measured by the following methods. (1) Measurement of water absorption amount A commercially available coffee filter is folded, a sample (Xg) is put in it, and after dipping in 0.9% saline for a certain period of time, its weight (Yg) is measured including the coffee filter. did. On the other hand, the weight (Zg) of the coffee filter itself that absorbed water was measured in advance, and the water absorption amount (times) was calculated from the following formula.

[0021]

[Equation 1] Water absorption amount (times) = (Y−Z) / X (2) Measurement of gel strength 60 g of 0.9% saline solution was added to a 100 ml beaker,
While stirring with a magnetic stirrer, 2 g of the water-absorbing polymer compound was added to cause gelation. After allowing the generated gel to stand for 8 hours, the hardness of the gel was measured using a card meter (manufactured by Iio Denki Co., Ltd.).

[0022]

[Table 1]

As is clear from Table 1, in Comparative Examples 2 to 6, the water absorption amount and the gel strength are almost the same as or slightly lower than those of Comparative Example 1 in which the additive is not added. There is no point in doing it. On the other hand, in Example 1, by adding aluminum isopropoxide powder as an additive, the gel strength is significantly improved without lowering the water absorption amount. Examples 2-3 and Comparative Examples 7-8 80% acrylic acid aqueous solution 75.0 parts by weight, 48.6% sodium hydroxide aqueous solution 54.9 parts by weight, deionized water 5
6.1 parts by weight were mixed to prepare an aqueous monomer solution having a neutralization degree of 80%.

Next, 1023 g of the obtained monomer aqueous solution
1% N, N'-methylenebisacrylamide aqueous solution 9
After adding g, the dissolved oxygen was replaced with nitrogen gas. Then, 33 g of 1% potassium persulfate, 40 g of 1% potassium pyrosulfate and 25 g of 0.04% glyoxal aqueous solution.
Were sequentially added and mixed over 15 seconds. Note that the above 0.0
4% glyoxal aqueous solution is glyoxal (40%
An aqueous solution, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was diluted 100 times with water.

The obtained mixed solution was poured into a box-shaped container (15 cm in length, 20 cm in width, 4 cm in height) (made of SUS, inner surface treated with tetrafluoroethylene resin), and polymerization was carried out using a water bath at a temperature of 35 ° C. A hydrogel was obtained. This hydrogel was dried with a drum dryer to form flakes, which were crushed with a pin mill to obtain a water-absorbent resin powder composed of an acrylic acid-acrylate copolymer cross-linked product and having an average particle size of 42 mesh.

Then, the obtained water-absorbent resin powder is shown in Table 2.
It was treated with a treatment liquid having the composition shown in. That is, 200 g of the water-absorbent resin powder was added to a small stirrer with a capacity of 1 liter
Was added, and the treatment liquids shown in Table 2 were added dropwise at room temperature while stirring. After completion of dropping, stirring was continued for further 3 minutes, and the obtained resin was dried at 140 ° C. until the water content became 7%.
Dried at a temperature of.

The resin thus obtained was divided into two equal parts, and one of them was put into a small stirrer again, and the particle size was 150 mesh (106
0.5 g of aluminum isopropoxide powder (μm) was added, and the mixture was stirred for 5 minutes so as to be uniform to obtain water absorbent resin compositions (Examples 2 and 3). The water absorption amount and gel strength of this water absorbent resin composition were measured in the same manner as in Example 1. Further, the water absorption amount and the gel strength were similarly measured for the remaining samples (Comparative Examples 7 and 8) which were not equally treated with the aluminum isopropoxide powder and which were divided into two parts. The test results are also shown in Table 2.

[0028]

[Table 2]

From Table 2, it is possible to improve the gel strength of the water-absorbent resin whose surface is cross-linked by adding aluminum isopropoxide powder without decreasing the water absorption. Recognize. Comparative Examples 9-10 80 g of each water-absorbent resin of Comparative Examples 7 and 8 was placed in a small stirrer, the same treatment as described above was performed as shown in Table 3, and the water absorption amount and gel strength were measured in the same manner as described above. The test results are also shown in Table 3.

[0030]

[Table 3]

It can be seen from Table 3 that the water-absorbent resin is improved in gel strength as compared with the water-absorbent resins of the original Comparative Examples 7 and 8 by the crosslinking treatment again, but the water absorption amount is decreased. Examples 4-6 and Comparative Examples 11-13 100 g of commercially available super absorbent polymer powder was put in a small stirrer,
0.5 g of 150-mesh aluminum isopropoxide powder was added and uniformly mixed for 5 minutes to obtain water-absorbent resin compositions (Examples 4 to 6). The water absorption amount and gel strength of this water absorbent resin composition were measured in the same manner as in Example 1.

Further, as a control, the same tests were carried out for those to which aluminum isopropoxide powder was not added (Comparative Examples 11 to 13). The test results are shown in Table 4.

[0033]

[Table 4]

As shown in Table 4, it is understood that the gel strength can be improved without lowering the water absorption amount even by adding the aluminum isopropoxide powder to the commercially available super absorbent polymer. Test Example (1) Examination of Particle Size of Aluminum Isopropoxide Powder The particle size used in Example 2 was 150 mesh (106 μm).
m) instead of the aluminum isopropoxide powder, 1
6 mesh (1000 μm) and 42 mesh (35
(5 μm) aluminum isopropoxide powder was added, and a water-absorbent resin composition was prepared in the same manner as in Example 2, and the water absorption amount and gel strength were measured in the same manner as in Example 1. (2) Examination of Addition Amount of Aluminum Isopropoxide Powder The particle size used in Example 2 was 150 mesh (106 μm).
Amount of aluminum isopropoxide powder of m.
Instead of 5 parts by weight, a water absorbent resin composition was prepared in the same manner as in Example 2 except that various addition amounts shown in Table 5 were added, and the water absorption amount and gel strength of each were the same as in Example 1. Measured.

Table 5 shows the test results of the above (1) and (2).

[0036]

[Table 5]

As shown in Table 5, the smaller the particle size of the aluminum isopropoxide powder is, the more the gel strength is improved. However, even if the particle size is large, the gel strength is improved as compared with the additive-free powder (Comparative Example 7). is doing. The amount of aluminum isopropoxide powder added is preferably in the range of 0.1 to 5 parts by weight. When the amount is less than this, the effect of addition is not obtained, and when it is more than this, the water absorption decreases. .

[0038]

As described above, according to the present invention, both the gel strength and the water absorption amount can be increased by adding the aluminum isopropoxide powder to the water absorbent resin powder. Therefore, since a high water absorption amount can be secured under pressure, it is particularly suitable for applications such as diapers.

Further, according to the present invention, since the water absorbent resin can be treated without using a dispersion medium, the number of steps and the manufacturing cost can be reduced.

Claims (1)

[Claims] 1. A water-absorbent resin composition comprising a water-absorbent resin powder and aluminum isopropoxide powder added thereto.