JPH02120339A - Production of water-absorptive resin - Google Patents

Abstract

PURPOSE:To obtain a water-absorptive resin which can absorb pure water and an aqueous electrolyte solution at a high absorption speed and has an ability to diffuse them by sulfonating a polystyrene foam to its inside. CONSTITUTION:A polystyrene foam is sulfonated with at least one member selected from among fuming sulfuric acid, chloro or fluoro-sulfonic acid and sulfur trioxide, and the product is optionally converted into a salt. As the polystyrene, a homopolymer or a copolymer with butadiene or acrylonitrile can be used and it is desirable that it has a comonomer content above 40mol%. As the polystyrene foam, a waste of a heat-insulation material or a cushioning material can be used. As the fuming sulfuric acid, commercially available 20-30% fuming sulfuric acid can be used as such. The sulfonation is usually carried out at 90-100 deg.C for about 3-8hr. The sulfur content of the product is about 16-21% for all of these sulfonating agents and can reach such a degree as to be sulfonated to the inside or near. As the neutralizing agent, an alkali is usually used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a water-absorbing resin that has a high absorption rate (and diffusivity) of pure water and an aqueous solution of an electrolyte, such as a saline solution.

[Conventional technology]

In recent years, many chemical materials have been used for water-absorbing resins.
Moreover, its application fields are wide-ranging, from food and agriculture to medical use.

Various compositions of conventional water-absorbent resins are known, but the main ones are starch-acrylonitrile graft copolymer hydrolysates, starch-acrylic acid graft copolymers, and water-soluble monomer acrylics. Examples include acid soda, acrylamide polymers, and hydrolysates of methyl methacrylate-vinyl acetate copolymers.

These water-absorbing resins weigh 20 to 100 times their own weight in pure water.
It has about 0 times the water absorption capacity. However, the water absorption capacity of these resins is extremely reduced when it comes to the water absorption capacity of electrolyte solutions. For example, in 0.9% saline, the water absorption capacity is reduced to about 1/10 of that in pure water.

On the other hand, regarding the water absorption rate, the time from when the water absorbent resin starts absorbing water until it reaches a certain saturated state is approximately 5 minutes. The water absorption rate changes depending on the shape of the water absorbent resin and the wettability of the surface.

The smaller the particle size, the larger the surface area and the faster the water absorption rate. However, if the particle size is simply made smaller, only the surface will become wet, resulting in a so-called "sticky texture" and the water absorption rate will decrease. In order to prevent this "stickiness", improved methods have been proposed in which the resin surface is treated with quaternary ammonium salts, nonionic surfactants, etc., but these methods are not fully satisfactory. Furthermore, although the water-absorbing resin has water-absorbing ability, it has poor liquid diffusivity.

Therefore, when used in sanitary napkins and disposable diapers, which are currently widely used, a method is used in which the capillary action of pulp fibers is used to first diffuse the liquid and then absorb it.

[Problem to be solved by the invention]

The problem to be solved by the present invention is to eliminate each of the above-mentioned difficulties of conventional water absorbent resins. The goal is to develop

[Means for Solving the Problem] As a means for solving this problem, a polystyrene foam is actively sulfonated into the inside of the foam using at least one of fuming sulfuric acid, chloro or fluorosulfonic acid, and sulfur trioxide. This is achieved by using a sulfonated polystyrene foam obtained by oxidation and its inorganic and organic salts as a water-absorbing resin.

That is, as a result of various studies in order to improve each of the drawbacks of the conventional water-absorbing resins mentioned above, the present inventors have developed a solution by sulfonating the polystyrene foam, which is originally hydrophobic, or by adding salt to the polystyrene foam. This results in a resin foam having water absorption properties, and the present inventors have discovered that this water-absorbing resin has a high water absorption rate for pure water, an electrolyte aqueous solution, or a saline solution, and also has water absorption and diffusivity, leading to the completion of the present invention.

[Structure and operation of the invention]

It has been little known in the past that polystyrene foam can be sulfonated by treating it with at least one of fuming sulfuric acid, chloro or fluorosulfonic acid, and sulfur trioxide (hereinafter referred to as sulfonating agents) as described above. It is only known that a polystyrene foam whose surface is sulfonated using a small amount of chlorosulfonic acid can be used as a soil improvement material. Originally, polystyrene foam is a foam consisting of almost closed pores, and it is a common belief in this type of industry that even if this foam is sulfonated, only the surface thereof will be sulfonated.

However, according to the research of the present inventors, when polystyrene foam was actively sulfonated to the inside with a sulfonating agent, it was surprisingly possible to sulfonate the polystyrene foam to almost no extent without damaging the individual cells of the foam. It has been discovered that the sulfonated polystyrene foam can be sulfonated to the inside, and that the water absorption rate of this sulfonated polystyrene foam reaches more than 90% of the total water absorption capacity within 30 seconds. The present invention was completed based on these new facts.

[Structure and operation of the invention] The polystyrene used in the present invention may be a homopolymer or a copolymer with butadiene, acrylonitrile, etc., but the effects of the present invention are more likely to be exhibited as the polystyrene content is higher. .

The ratio of styrene to other monomers in the above-mentioned copolymer is 40 mol% or less, preferably 10% by mole or less.
It is about 20 mol%. There are no particular limitations on the form of the copolymer, including block copolymerization, graft copolymerization, and other random copolymerization.

In the present invention, it is essential to use foamed polystyrene. Various polystyrene foams can be used as long as they are foamed, and it is particularly preferable to use the polystyrene foam itself, and it is preferable to avoid pulverized polystyrene foams. Polystyrene foam can be used in packaging materials that are inexpensive and easily available, such as cushioning materials such as sorted, ribbon-shaped, and block-shaped materials, as well as molded objects such as plate-shaped insulation materials, cases, picture objects, containers, etc. It is also possible to utilize already finished polystyrene foam.

In particular, since the present invention uses polystyrene foam, conventional waste materials that have been used as insulation and cushioning materials can also be used, which is significant in that it has developed a new use for waste materials.

The fuming sulfuric acid used in the present invention is 20 to 30% oleum, and a commercially available product can be used as is.

Although chlorosulfonic acid is commonly used, fluorosulfonic acid can also be used. Although liquid sulfur trioxide is used as the sulfur trioxide, it is also possible to react in a gaseous state. Conditions for the reaction between the polystyrene foam and these acids are such that the inside of the foam can be positively sulfonated.

There is no particular limitation as long as the inside can be sulfonated, but
For example, usually 90-100°C, preferably 95-100°C
When the reaction is carried out for about 3 to 8 hours at 00'C, and for more than 72 hours, preferably for about 72 to 240 hours at room temperature, the sulfur content of the product will be 16 to 2 for any sulfonating agent.
The sulfonated range reaches 1%, almost to the inside.

The polystyrene foam treated with the sulfonating agent is washed with water until sulfate ions are no longer detected, neutralized if necessary to form a salt, and dried according to a conventional method.

The method of neutralizing to form a salt is not limited in any way, and may be carried out according to a conventional method. The neutralizing agent in this case is usually an alkali, and examples of the alkali used for neutralization include -a alkali and alkaline earth metal hydroxides, or ammonia and alkyl amines, such as organic amines such as ethanolamine. Preferably used.

The sulfonated polystyrene foam or its salt according to the present invention is a solid having a cell structure like the raw material polystyrene foam. For example, reference drawing 1 shows micrographs (magnification: 1
00 times). However, the drawing (A) shows the raw materials in the same drawing (B).
1 shows a foam of the present invention, and the polystyrene foam shown in (A) of Reference Drawing 1 is "Aspac" manufactured by Asahi Kasei ■. Reference drawing 2 also means the same thing; (A) in this drawing 2 is a commercially available bead-shaped polystyrene foam, and (B) is a sulfonated product up to the inside thereof.

As is clear from these Reference Drawings 1 and 2, there is almost no change in the cell structure in either case, and it is clearly revealed that the cell structure is sulfonated to the inside while maintaining the original cell structure.

Furthermore, the sulfonated polystyrene foam and its salts of the present invention are hydrophilic but water-insoluble.

In addition, while the raw material polystyrene foam is hydrophobic, sulfonated polystyrene foam or its salt (hereinafter simply referred to as sulfonated polystyrene foam) is hydrophilic, and the cell structure that makes up the foam is hydrophilic. Because it itself is hydrophilic, it can quickly absorb and retain water, and its water absorption amount reaches about 20 to 80 times its own weight. As described above, the sulfonated polystyrene foam according to the present invention has excellent water retention properties because it has a large water absorption amount, has a cell structure, and easily releases absorbed water.

As explained above, the resin of the present invention has excellent water absorbency and diffusivity, but this is true not only for water but also for electrolyte aqueous solutions.
Ct, ω, other Ca C1,2, M g CjL2
The concentration is about 0.1% by weight or more, preferably about 15% by weight or less.

[Example] Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples.

Example 1 20g of polystyrene foam and 400ml of 25% oleum
was added and reacted for 8 hours at 95-100''C while shaking occasionally to wet the surface of the polystyrene. After the reaction, the solid content was poured into water and washed repeatedly until no sulfate ions were detected in the washing solution. A sulfonated polystyrene foam was obtained by drying at 60 to 70'C.The sulfur content of this was 19.0%.The water absorption amount of the water absorbent resin according to this example after 24 hours was 33.4 g/g. The water absorption rate and the water absorption rate of 0.9% sodium chloride aqueous solution are shown in Tables 1 and 2, respectively.
It was found that when the resin according to this example, which had a cylindrical shape of 1 diameter and 2 slopes, was placed on a glass plate and one end of the resin was immersed in water, it was easily diffused.

Example 2 50-chlorosulfonic acid was added to 3.0 g of polystyrene foam.
was added and reacted at 95 to 100°C for 8 hours.

After the reaction, the solid content was poured into water and thoroughly washed. After washing with water until the washing liquid became neutral, it was neutralized with an aqueous sodium hydroxide solution and dried at 60 to 70°C to obtain a sodium salt of sulfonated polystyrene foam. The sulfur content of this was 16.0%. The water absorption amount of the resin according to this example after 24 hours was 28.4 g/g, and the water absorption rate was 0.9 g/g.
% absorption rate of sodium chloride aqueous solution is shown in Tables 1 and 2, respectively.
As shown in the table. In addition, the length according to this example is 20
When a cylindrical resin with an M1 diameter of 2 m was placed on a glass plate and one end of the resin was immersed in water, it was observed that the water easily diffused and rose.

Example 3 2.2 g of polystyrene foam was mixed with 10.2 g of liquid sulfur trioxide.
9 g was added and reacted at room temperature for 10 days. After that, the reactant was poured into water and thoroughly washed with water until the washing became neutral.
It was neutralized by adding calcium hydroxide and dried at 60-70°C. The sulfur content of the calcium salt of the resulting sulfonated polystyrene foam was 201%. this thing 2
The amount of water absorbed after 4 hours was 25.4 g/g, and the water absorption rate was 0.
．． The water absorption rates of 9% aqueous sodium chloride solutions are shown in Tables 1 and 2, respectively. Furthermore, when the cylindrical resin of this example with a length of 15 mm and a diameter of 2 + nm was erected on a glass plate and one end was immersed in water, it was observed that the water easily diffused and rose.

Comparative example 20% sodium hydroxide aqueous solution 18g in 80g of acrylic acid
Neutralize by gradually adding 0g of N,N''methylenebisacrylamide, 0.1g of potassium peroxodisulfate
g and 0.05 g of sodium hydrogen sulfite were added thereto, and the mixture was poured into a container, replaced with nitrogen gas, and left for 3 nights. The obtained sodium polyacrylate gel was cut into pieces of 100 to 12
Dry at 0°C. This water-absorbing resin is approximately the same size as the resin of the example of the present invention (length 10 to 20 mm).
, diameter 2 to 3 mm), the water absorption amount after 24 hours is 8
The water absorption rate and the absorption amount of 0.9% sodium chloride aqueous solution at 7.5 g/g are shown in Tables 1 and 2, respectively. In addition, this resin was cut into a rectangular column with a length of 20 mm and a side of 2 mm, stood on a glass plate, and one end of the column was immersed in water.
No increase in diffusion was observed.

++1L Table 1 shows the water absorption rate (%) at each time when the water absorption after 24 hours is taken as 100%, and Table 2 shows the water absorption rate (%) when the water absorption after 10 minutes is taken as 100%. Time 0.
The absorption ratio of 9% saline is shown.

Table 1 Table 2

Claims (1)

[Claims] A method for producing a water-absorbing resin, which comprises sulfonating a polystyrene foam with at least one of fuming sulfuric acid, chloro- or fluorosulfonic acid, and sulfur trioxide to form a salt if necessary.