JPS6340801B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing superabsorbent resins. More specifically, to produce a saponified copolymer containing vinyl acetate, dialkyl maleate, and ethylenically unsaturated carboxylic acid monomer (excluding dialkyl ethylenically unsaturated dicarboxylic acid ester) in a specific ratio. It is characterized by: In recent years, resins that highly absorb water or aqueous liquids,
For example, saponified starch-(meth)acrylonitrile graft copolymers, crosslinked polyethylene oxide, starch-acrylamide grafts, saponified copolymers of vinyl ester and ethylenically unsaturated carboxylic acid or its derivatives under specific conditions. With the development of treated products, cross-linked products of polyvinylpyrrolidone, cross-linked products of sulfonated polystyrene, and reaction products of polyvinyl alcohol and cyclic acid anhydrides, such materials are being used in the sanitary field such as products for treating body fluids such as urine and blood. In addition, its use in the fields of agriculture, horticulture, civil engineering, architecture, separation of water in organic solvents, adsorption separation of heavy metals, and many other fields is proposed by utilizing its absorption and water retention properties. has been done. However, when looking at the manufacturing methods for these superabsorbent resins, many of the manufacturing processes are extremely complicated and require special treatments and operations.
For example, in Japanese Patent Publication No. 53-13678, an alkali-saponified copolymer of a vinyl ester and an ethylenically unsaturated carboxylic acid or its derivative is isolated by adjusting the pH, and PH
It is dissolved by conditioning and further dried under specific conditions. Also, starch-acrylonitrile graft copolymer saponified products, starch-acrylonitrile graft copolymer saponified products,
Acrylic acid grafted products use a special grafting catalyst to graft acrylonitrile and acrylic acid onto starch, and their absorption capacity is also unsatisfactory. The inventors of the present invention have conducted intensive studies to obtain a resin with a simple production method and excellent absorption capacity, and have found that (a) vinyl acetate and (b) dialkyl maleate, as well as (c) Copolymers consisting of a specific proportion of ethylenically unsaturated carboxylic acid monomers (excluding dialkyl esters of ethylenically unsaturated dicarboxylic acids) can be prepared by saponifying the resulting copolymer only by alkali saponification. The present invention was completed based on the discovery that the compound has high absorption performance. The method for producing a superabsorbent resin in the present invention includes (a) 70 to 98 mol% of vinyl acetate, (b) 1 to 10 mol% of dialkyl maleate, (c) ethylenically unsaturated carboxylic acid monomer ( However, (excluding (b))) is a copolymer obtained by random copolymerization of 1 to 20 mol%, which is saponified with an alkali, and then 80 mol% or more of vinyl acetate, which is the component (a), is saponified. It is something. At least 70 mol% of vinyl acetate in (a) is required, and 80 mol% or more of it, preferably 90 mol% or more, must be saponified. If the amount of vinyl acetate and the degree of saponification deviate from the above ranges, the gel strength will decrease and the insolubilization will be insufficient, which is not preferable. The maleic acid dialkyl ester (b) is present in an amount of 1 to 10 mol%. If it is less than 1 mol %, a water-insoluble highly swelling resin cannot be obtained, and if it exceeds 10 mol %, there is a tendency for the absorption capacity to decrease, which is inappropriate. The ethylenically unsaturated carboxylic acid monomer (including ethylenically unsaturated monocarboxylic acid, ethylenically unsaturated dicarboxylic acid, and ethylenically unsaturated dicarboxylic acid monoalkyl ester) in (c) is 1 to 20 mol%.
It is. A water-insoluble swellable resin can also be obtained by alkaline saponification of a copolymer containing only two components (a) and (b), but the absorption capacity is insufficient and the addition of component (c) Absorption capacity increases. Therefore, the higher the amount of component (c), the better, but if it exceeds 20 mol %, it is unsuitable because non-heat treatment tends to result in insufficient insolubilization. The average degree of polymerization of the saponified terpolymer is preferably 500 or more, preferably 500 to 3,000. When it is less than 500, the absorption function decreases. There is no particular limit on the upper limit, but if it exceeds 3000, it becomes difficult to manufacture in practice and industrial production becomes difficult. The method for producing a superabsorbent resin in the present invention uses the three components (a), (b), and (c), and the ratio of the three components (a), (b), and (c) is within the above range. Ordinary solution polymerization is carried out to obtain a random copolymer. For example, in the presence of a lower alcohol solvent such as methanol and a polymerization catalyst,
Copolymerize the three components (a), (b), and (c). The obtained copolymer is saponified using an alkali catalyst such as caustic soda, caustic potash, soda carbonate, or an alkali metal alcoholate. The degree of saponification is aimed at saponifying 80 mol% or more of the vinyl acetate component as described above. Since the obtained saponified product contains solvents such as the solvent during solution polymerization and 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, when the powder obtained by heating and drying is subjected to heat treatment such as dry heat treatment or wet heat treatment, the degree of insolubilization increases, but there is a tendency that the absorption capacity decreases. Therefore, depending on the purpose and use, a material with a high degree of insolubilization may be required even if the absorption capacity is slightly inferior, and in that case, it is desirable to employ the above-mentioned heat treatment. The heat treatment conditions are preferably appropriately selected from conditions such as an inert gas atmosphere, a temperature of 110 to 200°C, and a time of 1 to 360 minutes. The obtained superabsorbent resin is in the form of a powder, but those with an appropriate particle size are selected and ground to an appropriate particle size for practical use. The maleic acid dialkyl ester (b) in the present invention includes dialkyl maleic acid esters such as methyl, ethyl, and propyl, and these may be used alone or in combination of two or more. Among them, dimethyl maleate is preferred. (c) The ethylenically unsaturated carboxylic acid monomers are those excluding the ethylenically unsaturated dicarboxylic acid dialkyl esters such as the aforementioned maleic acid dialkyl esters. Namely, unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, glutaconic acid, and allylmalonic acid, and their monoalkyl esters such as methyl, ethyl, and propyl, as well as acrylic acid,
Examples include unsaturated monocarboxylic acids such as methacrylic acid and crotonic acid, which may be used alone or in combination of two or more. Among these, unsaturated dicarboxylic acids are preferred. Furthermore, α-olefins such as ethylene and propylene, olefin sulfonic acids such as (meth)allylsulfonic acid, ethylenesulfonic acid, and sulfonic acid malate, sodium (meth)allylsulfonate, sodium ethylenesulfonate, and sodium sulfonate (meth)acrylate. , olefin sulfonic acid alkali salts such as sodium sulfonate (monoalkyl maleate), sodium disulfonate alkyl maleate, N
- A small amount of amide group-containing monomers such as methylol acrylamide and alkali salts of acrylamide alkyl sulfonic acids, as well as N-vinylpyrrolidone and N-vinylpyrrolidone derivatives, may be used in combination. The superabsorbent resin obtained by the production method of the present invention can be used in combination with other known superabsorbent resins. Furthermore, it may contain inorganic fine particles such as silicic anhydride, calcium carbonate, magnesium carbonate, barium carbonate, kaolin clay, diatomaceous earth, and feldspar powder, as well as metal oxide powders such as titanium oxide and alumina. It may also contain other water-soluble resins such as polyvinyl alcohol, polyethylene oxide, sodium polyacrylate, cellulose derivatives, starch, starch derivatives, polyacrylamide, polyvinylpyrrolidone, etc. depending on the intended use. The saponified terpolymer obtained by the production method of the present invention can be applied to all known uses of superabsorbent resins. For example, in the hygiene field such as sanitary napkins, tampons, and disposable diapers, in the agriculture, forestry and horticulture field such as soil damage water retention agents, water retention for seeds and seedlings, in the civil engineering and construction field such as water stop agents, anti-condensation agents, and muddy water coagulants, and in organic solvents. It can be used in a wide range of applications in the chemical industry, such as water separation, emulsion latex concentration, and heavy metal adsorption, as well as enzyme fixation, fire extinguishing agents, food packaging materials, and humidity control agents. Next, the present invention will be specifically explained using examples. In addition, "parts" in the examples represent "parts by weight" unless otherwise specified. Example 1 1500 parts vinyl acetate, 17.7 parts dimethyl maleate
1, 265 parts of methanol and 3 parts of azobisisobutyronitrile were charged into a reactor, stirred and heated, and under reflux (65°C) 83.2 parts of dimethyl maleate and 86.1 parts of itaconic acid were each added separately in a methanol solution. The mixture was added dropwise and polymerized for 7 hours, and when the polymerization rate reached 70%, the polymerization was stopped. Thereafter, it was purified according to a conventional method. The amount of dimethyl maleate in the obtained vinyl acetate/dimethyl maleate/itaconic acid copolymer was 5.0 mol%, and the amount of itaconic acid was 5.0 mol%. Next, a 30% by weight methanol solution of the copolymer was placed in a kneader, and the itaconic acid component was neutralized with NaOH.
8% of 0.09 molar equivalent to vinyl acetate component
A NaOH methanol solution was added and saponification reaction was carried out at 40°C for 3 hours. Thereafter, it was filtered, washed with methanol, and dried at 55°C to obtain a powder with a viscosity of 48 to 170 mesh. Saponification degree is 95.2 mol%, average polymerization degree 2100
It was hot. Using the obtained superabsorbent resin powder,
Absorption capacity for pure water and physiological saline was measured.
The results are shown in Table 1. Example 2 A saponified vinyl acetate/dimethyl maleate/acrylic acid copolymer was obtained in the same manner as in Example 1 except that itaconic acid was replaced with acrylic acid. Dimethyl maleate amount is 5.0 mol%, acrylic acid amount is 5.0
The degree of saponification was 98.0 mol%, and the average degree of polymerization was 1500. The absorption capacity was measured in the same manner as in Example 1, and the results are shown in Table 1. Example 3 A saponified vinyl acetate/dimethyl maleate/monomethyl maleate copolymer was obtained in the same manner as in Example 1 except that itaconic acid was replaced with monomethyl maleate. The amount of dimethyl maleate is 3.2 mol%, the amount of monomethyl maleate is 9.5 mol%, the degree of saponification is 93.4 mol%, the average degree of polymerization
It was 2700. The absorption capacity was measured in the same manner as in Example 1, and the results are shown in Table 1. Reference Example The absorption capacity of a starch-acrylic acid graft material known as a superabsorbent resin was measured in the same manner as in the example, and the results are shown in Table 1. 【table】

Claims (1)

[Claims] 1 (a) 70 to 98 mol% vinyl acetate, (b) 1 to 10 mol% maleic acid dialkyl ester, and (c) ethylenically unsaturated carboxylic acid monomer (excluding ethylenically unsaturated dicarboxylic acid dialkyl ester) )1～
A method for producing a superabsorbent resin, which comprises saponifying a copolymer obtained by random copolymerization of 20 mol% with an alkali to saponify 80 mol% or more of the vinyl acetate component.