JPS6321532B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an absorbent for concentrated aqueous solutions of inorganic salts using a specific copolymer. Conventional so-called superabsorbent resins that absorb and swell in large amounts of water relative to their own weight include saponified copolymers of vinyl acetate and unsaturated dicarboxylic acid monomers, starch-acrylonitrile graft copolymers, and sodium acrylate. Many polymer compounds are known, such as -methyl acrylate-starch copolymer, saponified products of sodium acrylate-methyl acrylate-vinyl acetate terpolymer, and sodium polyacrylate. It is being considered that its ability to absorb body fluids such as blood can be used in the field of sanitary materials, and its water absorption and water retention properties can be used in fields such as agriculture, horticulture, and civil engineering. The present inventor conducted a detailed study on the absorption performance of these conventionally known superabsorbent resins, and found that low concentration aqueous salt solutions such as water, artificial urine, and physiological saline, and high concentration aqueous salt solutions close to the saturated solubility of salts. There is a specificity in its absorption performance, and saponified products made by copolymerizing vinyl acetate and unsaturated dicarboxylic acid monomers in a specific ratio have the same absorption capacity for water as other known superabsorbent resins. Although the water absorption rate is rather slow, they have discovered the novel fact that they exhibit an extremely high absorption capacity for concentrated aqueous salt solutions, and have utilized this fact to complete the present invention. That is, the absorbent of the present invention is vinyl acetate 50 to 99.8
Mol% and unsaturated dicarboxylic acid monomer 50~
The base material is a copolymer with a proportion of 0.2 mol % and a heat-treated copolymer in which 70 mol % or more of the vinyl acetate component has been saponified. Vinyl acetate is required at least 50 mol%, and its 70
Mole %, preferably 90 mole % or more, must be saponified. If the vinyl acetate and degree of saponification are outside the above ranges, the gel strength will decrease and the insolubilization will be insufficient, which is not preferred. Unsaturated dicarboxylic acid monomer: 0.2 to 50 mol%,
Preferably it is 0.5 to 15 mol%. If it is less than 0.2 mol%, a water-insoluble superabsorbent resin cannot be obtained, and if it exceeds 50 mol%, there is a tendency for the absorption performance to decrease, making it unsuitable. Such an absorbent is prepared by carrying out conventional solution polymerization of vinyl acetate and an unsaturated dicarboxylic acid monomer to form a copolymer in the proportions within the above range. The obtained copolymer is saponified to a predetermined ratio using an alkali catalyst such as caustic soda, caustic potash, soda carbonate, or an alkali metal alcoholate. Since the obtained saponified product contains solvents during solution polymerization and solvents such as acetic esters produced as by-products in the saponification reaction, it is heated and dried at a temperature of 50 to 110°C to remove them. Furthermore, heat treatment of the powder obtained by heating and drying has the advantage that the absorption capacity can be improved several to several tens of times. The heat treatment conditions are selected from the range of 1 to 360 minutes at a temperature of 110 to 200°C in an air or inert gas atmosphere. The obtained resin is a powder, but those with an appropriate particle size are selected and ground to an appropriate particle size for practical use. Examples of the unsaturated dicarboxylic acid monomer in the present invention include maleic acid, fumaric acid, itaconic acid,
Examples include glutaconic acid, allylmalonic acid, and their monoesters and diesters such as methyl, ethyl, and propyl. Further, other copolymerizable monomers may be copolymerized as long as the amount is small. The absorbent of the present invention is mainly composed of the above-mentioned specific copolymer, but also contains silicic anhydride, calcium carbonate, magnesium carbonate, kaolin, diatomaceous earth,
Inorganic fillers such as titanium oxide and alumina, polyvinyl alcohol, polyethylene oxide, sodium polyacrylate, cellulose derivatives, starch, etc. may be blended depending on the purpose. Specific examples of the inorganic salts of the present invention include sodium carbonate, potassium carbonate, sodium potassium carbonate, sodium bicarbonate, potassium bicarbonate, lithium chloride, calcium chloride, aluminum chloride, manganese chloride, iron chloride, cobalt chloride, nickel chloride, Copper chloride, zinc chloride, aluminum bromide, calcium bromide, manganese bromide, iron bromide, cobalt bromide, nickel bromide, copper bromide, zinc bromide, aluminum iodide, calcium iodide, chromium iodide,
Manganese iodide, iron iodide, cobalt iodide, nickel iodide, aluminum nitrate, calcium nitrate, iron nitrate, cobalt nitrate, nickel nitrate, zinc nitrate, ammonium nitrate, sodium chlorate, potassium chlorate, calcium chlorate, bromate Sodium, potassium bromate, calcium hypochlorite,
Examples include sodium perchlorate, magnesium perchlorate, calcium perchlorate, and nickel perchlorate. The concentration of aqueous solutions of these salts varies depending on the type of salt, so it cannot be determined unconditionally, but the features of the present invention generally apply to concentrated aqueous solutions in the range of 5% by weight or more, preferably 10% by weight or more up to saturated solubility. can be demonstrated. The absorbent of the present invention can be prepared by adding it to a concentrated aqueous solution of the above-mentioned salts, by mixing the salt and the absorbent in advance and then mixing it with water, or by allowing the absorbent to absorb the necessary water in advance. , followed by mixing salts, etc. Since the absorbent of the present invention has the above-mentioned features, it can be used, for example, as a heat storage agent, a dry cell electrolyte, etc., and can exhibit excellent effects. Next, the absorbent of the present invention will be explained by giving an example. Example 1 Absorbent 1 Monomethyl maleate content 2.2 mol%,
Powder absorbent 2 prepared by heat-treating a monomethyl maleate-vinyl acetate copolymer saponified product with a saponification degree of vinyl acetate component of 93.7 mol% at 145°C for 2 hours. Monomethyl maleate content: 4.0 mol%.
Powder obtained by heat-treating saponified monomethyl maleate-vinyl acetate copolymer with a degree of saponification of the vinyl acetate component at 95.8 mol% at 130°C. 22g of Absorbent 1 was added to 483g of a 41.4% aqueous solution of anhydrous calcium chloride, and the mixture was heated at 60°C. The mixture was stirred at After 1 hour, Absorbent 1 had completely absorbed the aqueous calcium chloride solution, and the whole had a gel-like appearance, with no aqueous solution being observed. A similar experiment was conducted using Absorbent 2, and similar results were obtained when 21g was added. As a control example, a sodium acrylate-methyl acrylate-starch copolymer (copolymer composition 5.5:
2.0:2.5), saponified product of sodium acrylate-methyl acrylate-vinyl acetate terpolymer (copolymer composition: 5.0:3.5:1.5, degree of saponification 98 mol%), and sodium polyacrylate. As a result, the amounts of absorbent required to completely form a gel were 147 g, 519 g, and 221 g, respectively. Example 2 An experiment was conducted using Absorbent 1 in the same manner as in Example 1 except that the type and concentration of salts were changed. The results are shown in Table 1.

【table】

[Table] Example 3 In place of the absorbent in Example 1, a dimethyl maleate-itaconate-vinyl acetate copolymer consisting of 5.0 mol% dimethyl maleate, 5.0 mol% itaconic acid, and 95.2 mol% saponification degree of vinyl acetate component was used. As a result of a similar experiment using the combined saponified product, similar results were obtained when 24 g of the absorbent was added.

Claims (1)

[Claims] 1 Heat treatment of a copolymer containing 50 to 99.8 mol% of vinyl acetate and 50 to 0.2 mol% of an unsaturated dicarboxylic acid monomer, and in which 70 mol% or more of the vinyl acetate component has been saponified. An absorbent for a concentrated aqueous solution of inorganic salts, which is characterized in that the main ingredient is