JPS6358868B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating material coated with a specific modified polyvinyl alcohol polymer and having excellent water absorption or hygroscopicity. More specifically, polyvinyl alcohol-based polymer (hereinafter simply referred to as
After preparing a solution by dissolving a carboxyl group-containing modified polyvinyl alcohol polymer (hereinafter simply abbreviated as modified PVA) obtained by reacting PVA (abbreviated as PVA) with a cyclic acid anhydride, in an appropriate solvent,
The present invention relates to a method for producing a coating material with excellent water absorption or hygroscopicity, which comprises applying the solution to various substrates or mixing it with various substrates, and then heat-treating the treated substrate. In recent years, as the use of hydrophilic polymer materials in the medical industry, food industry, and agricultural fields has progressed, polymer materials that are particularly water-insoluble and have hydrophilic or water-absorbing properties are being used as separation and purification materials such as various membranes and liquid chromatography carriers. It has come to be used as a culture medium for microorganisms and plants, as a medical material such as contact lenses and suture coverings, and in a variety of other applications that utilize its water absorption and water retention properties. Among these applications, it is desired that polymeric materials used in applications that utilize water absorption in particular have the ability to absorb as much water as possible in a short period of time upon contact with water.
So far, polymer materials for such uses include natural and synthetic polymers such as modified polyethylene oxide, cross-linked polyvinylpyrrolidone and sulfonated polystyrene, and saponified starch-acrylonitrile graft copolymers. Several materials using substances have been proposed. However, except for saponified starch-acrylonitrile copolymers, their water absorption capacity is small and they are not satisfactory as water-absorbing materials. Furthermore, even in the case of saponified starch-acrylonitrile graft copolymers, which have a water absorption capacity of more than 30 times their own weight, although various improvements have been made to their production methods, the process is relatively complicated. However, when used in a hydrated state for a long period of time, there are several practical problems, such as the possibility that the starch component will rot and the gel structure will be destroyed. On the other hand, the present inventors have previously discovered that modified PVA polymers whose side chains have been modified with cyclic acid anhydrides have various properties, ranging from water-soluble to water-insoluble water-absorbing polymers, depending on the manufacturing conditions. He discovered that these polymers could be made into polymers with the following characteristics, and filed a patent application (Japanese Patent Application No. 52-59083, [Japanese Unexamined Patent Publication No.
53-143691] Patent application 1977-85353 [Patent application 1977-
20073]). As a result of further research into a method for easily producing a polymeric material from such modified PVA that maximizes its water-absorbing ability and can be fully utilized in various fields of application, the present inventors have found that anhydrous PVA Carboxyl group-containing modified product obtained by reacting a PVA polymer with a cyclic acid anhydride in
The method consists of preparing a solution by dissolving PVA in a solvent, applying the solution to various substrates or mixing it with various substrates, and then heat-treating the treated substrate. The present inventors have discovered that the present invention is extremely advantageous in producing coating materials with properties, and have completed the present invention. The PVA-based polymers used as raw materials in the present invention include not only vinyl acetate, other various vinyl ester polymers, and those with a saponification degree of 50 to 100 mol% obtained by saponifying copolymers thereof; Copolymerized with 30 mol% or less of various unsaturated monomers, such as α-olefins, vinyl chloride, acrylonitrile, acrylamide, acrylic esters, and methacrylic esters, based on vinyl acetate and other various vinyl esters. Includes copolymers with a degree of saponification of 50 to 100 mol%. The PVA polymer to be subjected to the reaction is preferably in the form of a powder. Further, the degree of polymerization is preferably in the range of 100 to 5,000. Soluble modified PVA used in the present invention
There are five methods to obtain the following. 1. A PVA polymer is reacted with a cyclic acid anhydride in the presence or absence of an esterification catalyst such as sodium bicarbonate or triethylamine. however,
The amount of esterification catalyst used is 5% of PVA polymer.
% by weight or less. 2. A PVA polymer is reacted with a cyclic acid anhydride in the presence of monovalent metal hydroxides, alkoxides, salts, etc. However, the amount of monovalent metal hydroxide, alkoxide, salt, etc. used is equal to or less than the amount of the cyclic acid anhydride. 3. A PVA polymer is reacted with a cyclic acid anhydride in the presence of a tertiary amine. However, the amount of the tertiary amine used is equal to or less than the amount of the cyclic acid anhydride. 4 PVA polymer with monovalent metal hydroxide, alkoxide, salt, etc. and tertiary amine, 3
A cyclic acid anhydride is reacted in the presence of any of the class amine salts. However, the amount of monovalent metal hydroxide, alkoxide, salt, etc., tertiary amine, or tertiary amine salt used is equal to or less than the amount of the cyclic acid anhydride. 5. A cyclic acid anhydride is reacted with a PVA-based polymer in the presence or absence of an ester catalyst, and then one of monovalent metal hydroxides, alkoxides, salts, ammonia, ammonium salts, amines, and amine salts is reacted with a PVA-based polymer. Process with either. The treatment is carried out by dissolving the compound in a solvent to neutralize the carboxyl groups, or by simply mixing up to an equivalent amount of the compound with the carboxyl groups. The reaction is carried out in the absence of water as much as possible, but compounds with active hydrogen that are reactive with cyclic acid anhydrides are unsuitable as solvents for the reaction, and compounds without active hydrogen are not suitable. For example, benzene, toluene, hexane, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, etc. are used. Particularly suitable are toluene, dioxane, etc. When maleic anhydride is used in the reaction, since this compound has a low melting point, it can also function as a solvent. The amount of solvent used is
A suitable amount is 2 to 5 times that of the PVA polymer powder.
In the reaction, a predetermined amount of a cyclic acid anhydride is dissolved in a predetermined amount of a solvent, a predetermined amount of a PVA polymer, a catalyst, an additive, etc. are added, the mixture is stirred and dispersed, and the reaction is allowed to occur at a predetermined temperature for a predetermined period of time. Since the reaction proceeds in a heterogeneous system, it is preferable to carry out the reaction with sufficient stirring so that the PVA polymer is uniformly esterified. The reaction is preferably carried out under as mild conditions as possible, and the reaction temperature is between 30 and 150℃.
The temperature is preferably 50 to 100°C, and the reaction time is suitably 30 minutes to 10 hours, preferably 1 to 5 hours. The degree of esterification can be from 1 to 100 mol%, but for the purpose of the present invention, a degree of esterification from 5 to 50 mol% is preferred. Cyclic acid anhydrides used in the reaction include maleic anhydride, phthalic anhydride, trimellitic anhydride,
Examples include succinic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, and the like. Depending on the case, it is also possible to use a mixture of these. It is necessary to use the cyclic acid anhydride in an amount corresponding to the desired degree of esterification or more. In order to obtain the soluble modified PVA polymer used in the present invention,
In order to prevent the formation of crosslinks during the reaction, the degree of polymerization of the raw material PVA polymer must be selected, the reaction conditions as mild as possible, the aromatic cyclic acid anhydride selected, and the reaction of the cyclic acid anhydride Consideration needs to be given, such as reducing the amount. The reaction mixture is filtered, centrifuged, etc.
Separate the solids. The liquid is collected and reused. The solid part is washed with methanol, acetone, etc. and dried. Since the modified PVA polymer thus obtained is soluble in water or other solvents, it is dissolved in these solvents to prepare a solution. The solution concentration varies depending on the application and is difficult to define unconditionally, but 0.5% to 50% is usually suitable. The solution is applied to glass surfaces, paper surfaces, fiber surfaces, etc., or mixed with inorganic particles, sand, wood flour, etc., and then dried and heat treated. Drying is suitably carried out at a temperature of 100°C or lower. By appropriately controlling the conditions of the heat treatment, the crosslinking density can be adjusted, and the coating material can be given any water absorption or hygroscopicity. The heat treatment conditions vary depending on the degree of polymerization and modification of the modified PVA, the desired crosslinking density, etc., so it is difficult to define them unconditionally, but the heat treatment temperature is usually
It is appropriate to select the heat treatment time from 80°C to 250°C, preferably from 100°C to 200°C, and from 1 second to 2 hours, preferably from 1 minute to 1 hour. In addition, when method 1 mentioned above is adopted as a method for producing modified PVA, that is, a method in which a cyclic acid anhydride is reacted with a PVA polymer in the presence or absence of an ester catalyst, the coating material after heat treatment is It is also possible to treat with a hydroxide of a valent metal, ammonia, etc., or to mix an appropriate amount of a carbonate or bicarbonate of a monovalent metal during dissolution. By subjecting the modified PVA to the heat treatment described above, the modified PVA not only becomes intermolecularly crosslinked and firmly adheres to the base material, but also forms a coating material with good water absorption and hygroscopicity. Become. This coating material has an extremely wide range of uses in various fields such as anti-fogging glass and horticultural soil. The present invention will be specifically explained below using Examples. Example 1 50 g of PVA powder with a degree of polymerization of 1700 and a degree of saponification of 88 mol%, phthalic anhydride,
Baking soda was added in different amounts, dioxane was added as a solvent, and the mixture was reacted at 80°C for 4 hours.
The reaction mixture was washed repeatedly with filtrate and acetone and then dried. It was weighed and the modification rate (weight increase rate) was determined from the weight increase. All of the obtained modified PVA powders were soluble in water. The results are shown in Table 1.

[Table] Next, No. 1 and No. 2 modified PVA obtained above
Each was made into an aqueous solution with a concentration of 2% and applied to the surface of glass, dried at 100°C, and then heat-treated at 170°C for 30 minutes. The obtained modified PVA coating material was evaluated for antifogging ability and other performances. The results are shown in Table 2.

【table】

[Table] Separately, the swelling, solubility and hygroscopicity in water of the coating layer formed on the glass surface of No. 1 and No. 2 were investigated. The results are shown in Table 3. The water absorption rate and moisture absorption rate are values measured based on the weight of the coating layer.

[Table] From the above results, it can be seen that the coating material obtained in Example 1 has extremely unique performance in that it has excellent water absorption and hygroscopicity, and also has antifogging properties. Example 2 PVA powder 50 with a degree of polymerization of 500 and a degree of saponification of 80 mol%
g, maleic anhydride (40 g), sodium bicarbonate (17.2 g), and dioxane (200 c.c.), and the reaction was carried out at 70°C for varying times. The reaction mixture was washed repeatedly with filtrate and acetone and then dried. It was weighed and the modification rate was determined from the weight increase. The results are shown in Table 4.

[Table] Next, each of the four types of modified PVA powders (Nos. 3 to 6) obtained above was made into a 2% aqueous solution, applied to a glass plate, and heat-treated at 150°C for 10 minutes. The antifogging ability of the obtained coating material was investigated. The coating film formed on the surface of the glass plate was also examined for swelling, solubility, and hygroscopicity in water. The results are shown in Table 5. The anti-fog ability is at 90% humidity and 40℃.
It is expressed as the time required for water droplets to form on the surface after being left under these conditions, and the water absorption rate and moisture absorption rate are values measured based on the weight of the coated film.

[Table] From the above results, it can be seen that the coating material obtained in Example 2 has extremely unique properties such as excellent water absorption and hygroscopicity, and antifogging properties. Example 3 PVA powder 50 with a degree of polymerization of 1700 and a degree of saponification of 88 mol%
Using 100 cc., 20 g, or 40 g of phthalic anhydride, 2 g of triethylamine, and 100 cc. of dioxane and 100 cc. of toluene as solvents, the mixture was reacted at 80° C. for 4 hours. After repeated washing with filtrate and acetone, the two reaction mixtures were washed with an equivalent amount of phthalic anhydride involved in the reaction.
A 25% ammonia aqueous solution was added to convert the side chain carboxyl groups in the modified PVA into ammonium salts, followed by washing with acetone and drying. It was weighed and the modification rate was determined from the weight increase. All of the obtained modified PVA powders were soluble in water. The results are shown in Table 6.

[Table] Next, the two types of modified PVA powders (Nos. 7 to 8) obtained above were each dissolved in water to make a 1% aqueous solution. 100 g of each of these aqueous solutions was mixed with 100 g of standard sand, dried at 100°C, and then heat-treated at 170°C for 10 minutes. The water retention properties of the obtained treated sand were compared with that of untreated sand.

[Table] From the above results, it can be seen that the water retention capacity of the treated sand obtained in Example 3 was significantly improved, and a coating material with excellent water absorbency was obtained.

Claims (1)

[Claims] 1. After preparing a solution by dissolving modified polyvinyl alcohol containing a carboxyl group obtained by reacting a polyvinyl alcohol polymer with a cyclic acid anhydride in an anhydrous state in a solvent, the solution is applied to various substrates or A method for producing a water-absorbing or hygroscopic coating material, which comprises mixing it with a substrate and then heat-treating the treated substrate.