JPS6346096B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing superabsorbent resins. More specifically, a superabsorbent resin is obtained by heat-treating powder of a saponified copolymer of an unsaturated dicarboxylic acid monomer and vinyl ester with a specific particle size under specific conditions. 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, crosslinked polyvinylpyrrolidone, With the development of cross-linked sulfonated polystyrene, such materials have been used in the sanitary field, such as body fluid treatment products such as urine and blood, and in the fields of agriculture, civil engineering and construction, using their water absorption and water retention properties.
Furthermore, its use has been widely proposed in other fields. Among these resins, saponified starch-acrylonitrile grout copolymers and saponified copolymers of vinyl ester and ethylenically unsaturated carboxylic acids or derivatives thereof are attracting attention as having high water absorption performance. However, although these resins have a high absorption capacity for water, their absorption capacity for artificial urine and physiological saline, which correspond to body fluids such as urine and blood, is inferior to that of water. The ability to absorb aqueous liquids with high component concentrations, such as urine, tends to be significantly reduced. However, the present applicant previously filed a patent application in 1973 regarding a method for imparting water-holding properties to soil using modified polyvinyl alcohol obtained by saponifying and drying a maleic acid monomer-vinyl acetate copolymer. - Filed in 1930 (Japanese Unexamined Patent Publication No. 52-88168). That is, it has been found that by drying the modified polyvinyl alcohol, it is given the ability to absorb a large amount of water. The inventors of the present invention conducted further studies and found that the property of absorbing a large amount of water can be impaired only by heat-treating the modified polyvinyl alcohol powder having a particle size within a specific range under specific conditions. It was discovered for the first time that the ability to absorb large amounts of physiological saline and artificial urine was achieved, and the present invention was completed. As a known technique related to the present invention, Japanese Patent Publication No. 53-13495 discloses a method of drying a saponified copolymer of a vinyl ester and an ethylenically unsaturated carboxylic acid or its derivative in a water-containing state to impart water absorption properties. Disclosed in the official gazette. However, although it is possible to obtain a resin having a high water absorption capacity using this technique as described above,
Absorption capacity decreases for aqueous liquids containing high concentration of components such as artificial urine, and this invention is the first to achieve balanced absorption for water, physiological saline, and artificial urine. A resin with this ability can be obtained. In the present invention, there is no particular limitation on the method for producing a copolymer of a vinyl ester and an unsaturated dicarboxylic acid monomer alone or a mixture of two or more, but for example, the presence of a lower alcohol solvent such as methanol and a polymerization catalyst is required. Below, it is obtained by copolymerizing the monomer alone or a mixture of two or more types and vinyl ester, and the content of the monomer in the copolymer is in the range of 0.2 to 50 mol%, Preferably it is 1 to 30 mol%. If this content is too low, the absorption capacity will be poor,
Moreover, if it exceeds 50 mol%, it is difficult to obtain a high molecular weight polymer gel. The saponified product of the copolymer is obtained by saponifying the copolymer in an alcohol or alcohol-containing mixed medium using an acid catalyst such as sulfuric acid or hydrochloric acid, or an alkali catalyst such as caustic soda, caustic potash, soda carbonate, or an alkali metal alcoholate. can be obtained. It is desirable to increase the degree of saponification of the vinyl ester component to 70 mol% or more, preferably 90 mol% or more, and if the degree of saponification is too low, the affinity for water will be impaired, which is not preferable. Since the modified polyvinyl alcohol obtained by saponification as described above contains an alcohol content and a solvent such as an ester of the alcohol produced as a by-product during saponification, it is dried by heating at a temperature of 50 to 110°C. The resin in the present invention is produced by further processing the substantially dried resin powder at a temperature of 100 to 200°C for a period of 1 to 360°C.
It can be obtained by heat treatment under the conditions of 10 minutes. Since the heat treatment conditions are closely related to the particle size, degree of modification, and degree of saponification, it is preferable to appropriately select the above temperature and time conditions in consideration of these factors.
To specifically illustrate the relationship between the degree of modification, the degree of saponification, and the heat treatment temperature, the heat treatment temperature T (° C.) is expressed by the following formula. 200-1.5X-0.5YT120-0.3X-0.1Y Here, X represents the degree of modification (mol%) and Y represents the residual acetic acid group (mol%). Regarding particle size, heat treatment temperature, and time,
For particles with a relatively coarse particle size, it is preferable to carry out the treatment at a higher temperature within the above-mentioned range, and for particles with a fine particle size, it is preferable to carry out the temperature at a lower temperature within the above-mentioned range. The time may be relatively long for coarse grains, and relatively short for fine grains. The above conditions represent one embodiment of the heat treatment conditions of the present invention, and the present invention is not limited thereby. Specifically, the particle size of the resin powder obtained by heat-treating the substantially dried resin powder under the above-mentioned heat treatment conditions is
10 to 400 mesh (Japanese Industrial Standards standard sieve 10
(refers to particles with a particle size below mesh size and above 400 mesh size), preferably between 32 and 250 mesh size. If the particle size is too coarse, the degree of heat treatment will be non-uniform, and therefore it will not have the characteristics of the present invention, and if the particle size is too fine, it is not preferred for handling. In addition, once the substantially dried resin powder is heat treated as it is under the above conditions, it is classified and
A mesh particle size may be selected, or a material having a particle size of 10 to 400 mesh may be selected by classifying or pulverizing the substantially dried resin powder and heat-treating it under the above conditions. ,
The latter method is preferable in terms of uniformity of the degree of heat treatment. If the heat treatment temperature is too low, the heat treatment time becomes too long or the heat treatment effect is insufficient, which is undesirable. If the temperature is too high, the resin tends to deteriorate and decompose, which is undesirable. Through such heat treatment, the substantially dried resin is subjected to thermal history, thereby imparting the characteristics of the resin of the present invention, and it is difficult to obtain a resin having such characteristics by drying alone. When heat treatment is carried out, the powder is heated while being stirred, or heated air or a non-volatile gas is blown into the powder to leave it still or fluidized, or it is carried out in a fluidized state. It is desirable to employ a method in which the heat treatment is carried out in a fluidized state, since this method allows for uniformity of the degree of heat treatment. Further, heat treatment may be performed in the presence of water vapor, solvent vapor, etc., or even in the presence of a high boiling point solvent. Vinyl esters in the present invention include vinyl formate, vinyl acetate, vinyl propionate, vinyl stearate, etc., with vinyl acetate being preferred. Examples of dicarboxylic acid monomers include maleic acid,
Examples include dicarboxylic acids such as itaconic acid, fumaric acid, glutaconic acid, and allylmalonic acid, their anhydrides, and their monoalkyl esters such as methyl, ethyl, and propyl, which may be used alone or in a mixture of two or more. It will be done.
Among these, maleic acid monoalkyl esters are preferred. Furthermore, in addition to the above monomer, a monomer copolymerizable with vinyl ester, such as crotonic acid, (meth)
Unsaturated monocarboxylic acids such as acrylic acid and their esters, α- such as ethylene and propylene
Olefin, (meth)allyl sulfonic acid, ethylene sulfonic acid, olefin sulfonic acid such as sulfonic acid malate, sodium (meth)allyl sulfonate, sodium ethylene sulfonate, sodium sulfonate (meth)acrylate, sodium sulfonate (monoalkyl olefin sulfonic acid alkali salts such as sodium disulfonate alkyl maleate, amide group-containing monomers such as N-methylol acrylamide and acrylamide alkyl sulfonic acid alkali salts, as well as N-vinylpyrrolidone,
A small amount of N-vinylpyrrolidone derivatives or the like may also be used in combination. Examples of the method of using the resin of the present invention as a sanitary absorbent material include: 1) Sprinkling the resin powder into an absorbent layer of crepe paper, crushed pulp, or the like. 2) After treating an absorbent layer such as crepe paper or crushed pulp with water or a water-based adhesive, the resin is added thereto and fixed with or without pressure bonding.
3) Sprinkle the resin onto a sheet-like material (plastic film, fibrous sheet). Alternatively, after the addition, the mixture is further wrapped in the sheet-like material to form a sandwich sandwich. 4) The sheet material is treated with water or a water-based adhesive, the resin is added thereto, and the sheet is fixed with or without pressure bonding. Or further wrapped in the sheet-like material to form a sandwich sandwich. There are also combinations of these. The resin of the present invention has a well-balanced absorption capacity for water, physiological saline, and artificial urine. It is suitable for use as materials (bandages, gauze, etc.). In addition, water absorbing materials for civil engineering and construction, agriculture and fisheries fields,
It is also suitable for a wide range of uses as a water retaining material. Next, the present invention will be specifically explained with reference to Examples. In the examples, "part" means "part by weight" and "%" means "% by weight." Example 1 A methanol solution of a monomethyl maleate-vinyl acetate copolymer having a monomethyl maleate content of 5 mol% was saponified in the presence of caustic soda to obtain a saponified product slurry with a degree of saponification of the vinyl acetate component of 95 mol%, Wet cake after solid-liquid separation was heated to 110
It was dried in a hot air dryer at ℃ to obtain a modified polyvinyl alcohol powder with a volatile content of 0.5%. Among the powders, those having a particle size of 100 to 200 mesh were heat-treated in a hot air circulation dryer at 130° C. for 120 minutes to obtain resin (A). Add a certain amount of resin (A) to distilled water, physiological saline (9.0 parts of NaCl dissolved in 1 part of distilled water), artificial urine (19.4 parts of urea, 8.0 parts of NaCl, 1.1 parts of MgSO ₄ 7H ₂ O).
(1 part and 0.6 parts of Cacl ₂ dissolved in 1 part of distilled water)
Pour and disperse into each, and heat at room temperature (approximately 20℃) for 40 to 60 minutes.
After standing for a period of time, the swollen gel was taken out, and the weight of the swollen gel was measured after suction. The amount of distilled water absorbed is
200 (g/g), absorption amount of physiological saline is 28 (g/g),
The amount of artificial urine absorbed was 30 (g/g). The absorption amount here was determined by the following formula. Absorption amount (g/g) = swollen gel weight (g) / sample weight (
g) Example 2 The modified polyvinyl alcohol powder in Example 1 with a particle size of 48 to 100 mesh was heat-treated at 140°C for 60 minutes in the same dryer as in Example 1 to obtain resin (B). Obtained. When the absorption amount of distilled water, physiological saline, and artificial urine was determined using resin (B) in the same manner as in Example 1, the absorption amount of distilled water was 200 (g/g),
The amount of physiological saline absorbed was 26 (g/g), and the amount of artificial urine absorbed was 28 (g/g). Control Example 1 Particle size of substantially dry modified polyvinyl alcohol powder (volatile content 0.5%) in Example 1: 100
Using ~200 mesh, as in the example,
When the absorption amount of distilled water, physiological saline, and artificial urine was determined, the resin was almost completely dissolved in all of them. Control Example 2 When the absorbed amount of distilled water, physiological saline, and artificial urine was determined in the same manner as in the example using saponified vinyl acetate-methyl acrylate copolymer, the absorbed amount of distilled water was 415 (g The absorption amount of physiological saline was 23 (g/g), and the absorption amount of artificial urine was 16 (g/g).
(g/g). In particular, it is clear that the amount of artificial urine absorbed is inferior to that of the Examples. Control Example 3 Using a saponified starch-acrylonitrile graft product, the absorption amount of distilled water, physiological saline, and artificial urine was determined in the same manner as in the example, and the absorption amount of distilled water was 85 (g/g ), the amount of saline absorbed is
17 (g/g), and the amount of artificial urine absorbed was 9 (g/g), both of which were inferior to the Examples. Example 3 A vinyl acetate copolymer containing 5 mol% of monomethyl maleate and 5 mol% of monomethyl itaconate was saponified in the same manner as in Example 1 to obtain a saponified product with a degree of saponification of 90 mol%, and then dried. A modified polyvinyl alcohol powder was obtained. 48 to 100 mesh of the powder was dried at 130% x 30 in the same dryer as in the example.
Resin (C) was obtained by heat treatment under the conditions of 10 minutes. The resin (C)
The absorbed amounts of distilled water, physiological saline, and artificial urine were determined in the same manner as in the examples. The results are shown in Table 1. The results of Examples 1 to 3 and Control Examples 1 to 3 are listed in Table 1. 【table】

Claims (1)

[Claims] 1. Unsaturated dicarboxylic acid monomer (excluding unsaturated dicarboxylic acid dialkyl ester) alone or 2.
Mixture of species or more 0.2-50 mol%, vinyl ester
A substantially dried powder of modified polyvinyl alcohol having a saponification degree of 70 mol% or more obtained by saponifying a copolymer consisting of 99.8 to 50 mol% and having a particle size of 10 to 400 mesh is heated at a temperature of 100 to 200°C. A method for producing a superabsorbent resin, characterized by heat treatment under conditions of 1 to 360 minutes. 2. The production method according to claim 1, wherein the unsaturated dicarboxylic acid monomer is an unsaturated dicarboxylic acid, an unsaturated dicarboxylic anhydride, or an unsaturated dicarboxylic acid monoalkyl ester. 3. The manufacturing method according to claim 1, wherein the vinyl ester is vinyl acetate.