JPH0229084B2 - KOKYUSUISEIJUSHINOSEIHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a water-insoluble superabsorbent resin that absorbs several hundred times its own weight of water by copolymerizing a water-soluble monomer with a divinyl compound. Traditionally, pulp products have been used to absorb and retain water. However, the amount of water absorbed by pulp is about 10 times its own weight, and in order to absorb and retain a large amount of water, a large amount of pulp is required, resulting in a very bulky product, and it also applies pressure to the material that has absorbed water. It had the disadvantage of easily separating water. Therefore, various efforts have been made to develop super absorbent resins that absorb and retain large amounts of water with a small weight.
This super absorbent resin absorbs and retains several hundred times its own weight in water, and furthermore, it has the characteristic that it forms a stable gel in the absorbed state and does not separate water even if a certain amount of pressure is applied. These superabsorbent resins are used in disposable diapers, napkins, microbial culture media, water retention agents for gardening, etc.
It has a wide range of uses. As super absorbent resins that have already been developed, starch graft polymers (Tokuko Showa)
53-46199) Cellulose modified product (Unexamined Japanese Patent Publication 1973-
80376), but starch graft polymers have the disadvantage that if they are used as a hydrogel for a long period of time, the starch may rot, and cellulose modified products do not absorb much water compared to cellulose. have. The present inventors conducted extensive research to overcome this drawback, and as a result, they arrived at the present invention. That is, the present invention provides a monomer (A) in which the molar ratio of acrylic acid and acrylamide is in the range of 70:30 to 100:0, and 70 mol% or more of the acrylic acid is ammonium, amine, or alkali metal salt. and 0.005 parts by weight of acrylic acid and acrylamide.
A super absorbent resin characterized by carrying out aqueous solution polymerization with ~0.05 parts by weight of a water-miscible or water-soluble divinyl compound (B) and 0.5 to 10 parts by weight of polystyrene (C) with a particle size of 5 μm or less as essential ingredients. It is related to the manufacturing method. Regarding the monomer (A) which is an essential component of the present invention,
If the molar ratio of acrylamide is increased outside this range, that is, when the acrylic acid content is less than 70 mol%, the strength of the hydrogel will increase, but the water absorption capacity will decrease.
Furthermore, if the degree of neutralization is less than 70 mol%, the dissociation of carboxyl groups will not be sufficient and a decrease in water absorption capacity will be observed. The base required for neutralization is not particularly limited, but monovalent cations are preferred. Examples of the water-miscible or water-soluble divinyl compound (B) include N,N-methylenebis(meth)acrylamide, tetraethylene glycol di(meth)acrylate, decaethylene glycol di(meth)acrylate, etc. , N,N-methylenebisacrylamide is industrially preferred. The amount of divinyl compound (B) is 0.005 to 100 parts by weight when the sum of the weights of acrylic acid and acrylamide is 100 parts by weight.
It is preferably 0.05 part by weight; if it is less than this range, the hydrogel will be in a semi-dissolved state, and if it is more than this, the degree of crosslinking will increase, and in both cases the water absorption capacity will decrease. Furthermore, an important feature of the present invention is that the aforementioned monomer (A)
In aqueous solution polymerization of and divinyl compound (B),
This means that polystyrene (C) with a particle size of 5 μm or less coexists as an essential component. Polystyrene during polymerization
The superabsorbent resin obtained by coexisting (C) showed a remarkable increase in water absorption capacity. Although the reason for this improvement in water absorption capacity is not clear, it is speculated that the fine polystyrene particles provide a site for polymerization, resulting in the synthesis of a superabsorbent resin with higher performance. The amount of polystyrene coexisting is preferably in the range of 0.5 to 10 parts by weight per 100 parts by weight of acrylic acid and acrylamide, and the particle size is also 5 μm.
The following is preferable; outside this range, no improvement in water absorption capacity can be expected. Polystyrene with a diameter of 5 μm or less can be obtained by ordinary emulsion polymerization, and a predetermined amount of the polystyrene emulsion may be dispersed and coexisted during polymerization. In polymerizing the product of the present invention, any commonly used initiator, such as redox type or azo type, may be used, and the initiator is not limited to a specific initiator. Further, the polymerization concentration is not particularly limited and can be selected in any concentration range, but in consideration of the drying process, it is advantageous to carry out the polymerization at a concentration as high as possible. For example, it is also possible to carry out polymerization with a highly concentrated aqueous solution of about 70%, evaporate the water by the heat of polymerization, and directly carry it to the pulverization process without going through the drying process. Furthermore, the initiation temperature is not particularly limited, as the temperature at which polymerization is initiated differs depending on the type of initiator, so long as the polymerization is initiated at a temperature higher than the temperature at which the initiator functions. Next, the present invention will be explained in more detail based on Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Example 1 52.7 g of acrylic acid and 17.3 g of acrylamide were dissolved in 20 g of distilled water, and 32.8 g of potassium hydroxide was added to this.
was added to partially neutralize 80 mol% of acrylic acid.
Add N,N-methylenebisacrylamide to this.
Add 0.007g and further polystyrene emulsion with an average particle size of 0.5μm (polystyrene concentration 50%)
5g of was added and stirred to make it homogeneous. Next, as an initiator, add 10 c.c. of an acetone solution containing 0.7 g of 2,2'-azobisisobutyronitrile.
added. This solution was placed in a box-shaped container (Teflon-treated glass fiber material) heated in a constant temperature water bath at 80°C. As the temperature of the solution rose, the polymerization reaction started, and water was evaporated by the generated heat of polymerization, yielding a highly water-absorbent resin as a porous white solid with a very low water content. Example 2 20.8 g of acrylamide was dissolved in 49.2 g of acrylic acid, and 28.0 g of 29% ammonia water was added thereto.
70 mol% of acrylic acid was neutralized. N, N to this
- Added 0.01 g of methylenebisacrylamide, and further added 3 g of polystyrene emulsion (polystyrene concentration 50%) with an average particle size of 1 μm, and stirred to make the mixture uniform. Next, 2,2'-azobis(2-amidinopropane) hydrochloride was used as an initiator.
A solution of 0.7 g dissolved in 5 g of distilled water was added.
This solution was placed in the aforementioned box-shaped container heated in a constant temperature water bath at 80°C and heated to initiate polymerization.
As the polymerization reaction progressed, water was evaporated by the generated heat of polymerization, and a highly water-absorbent resin was obtained as a porous white solid with a very low water content. Example 3 70g of acrylic acid was dissolved in 20g of distilled water, and 40.8g of potassium hydroxide was added to dissolve 75g of acrylic acid.
Neutralized mole %. Add 0.007g of N,N-methylenebisacrylamide to this, and further
2 g of 5 μm polystyrene emulsion (polystyrene concentration 50%) was added and stirred to make it homogeneous.
Next, 10 c.c. of an acetone solution containing 0.7 g of 2,2'-azobisisobutyronitrile was added as an initiator. This solution was placed in the aforementioned box-shaped container heated in a constant temperature water bath at 80°C and heated to initiate polymerization. Water was evaporated by the heat of polymerization generated as the polymerization reaction progressed, and a super absorbent resin was obtained as a porous white solid with a very low water content. Comparative Example 1 A super absorbent resin was obtained by polymerizing in the same manner as in Example 1 except that the polystyrene emulsion was not added. Comparative Example 2 Polymerization was carried out in the same manner as in Example 2, except that the polystyrene emulsion was not added, to obtain a super absorbent resin. Comparative Example 3 Polymerization was carried out in the same manner as in Example 3, except that the polystyrene emulsion was not added, to obtain a super absorbent resin. Example 4 The polymers obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were directly pulverized without going through a drying process to obtain powdered superabsorbent resins. The following tests were conducted to examine the water absorption performance of each powder. Add 1 g of super absorbent resin powder (20 to 400 mesh) to 2 parts of distilled water while stirring.
After leaving it for 1 hour, it was passed through a 100 mesh sieve, and the amount of water absorbed was measured from the amount of liquid. The results are shown in Table 1 in terms of water absorption capacity (water absorption amount ÷ weight of added super absorbent resin). From this, it was found that the product of the present invention had significantly superior water absorption performance compared to the comparative example. 【table】

Claims (1)

[Claims] 1. Acrylic acid and acrylamide in a molar ratio of 70:
Monomer (A) in the range of 30 to 100:0, and 70 mol% or more of acrylic acid is ammonium, amine, or alkali metal salt, and 0.005 to 100 parts by weight of acrylic acid and acrylamide. 0.05 parts by weight of a water-miscible or water-soluble divinyl compound (B) and 0.5 to 10 parts by weight of acrylic acid and acrylamide.
A method for producing a super absorbent resin characterized by carrying out aqueous solution polymerization using polystyrene (C) having a particle size of 5 μm or less in parts by weight as an essential component.