JPS6216132B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water-absorbing and water-retaining material made by uniformly mixing a water-absorbing polymer with a soft resin or rubber. Soft resins or rubbers are hydrophobic materials, and there has been a demand for imparting water absorbing and water retaining properties to these base materials. Various methods have been proposed for this purpose. For example, there are known methods such as chemically treating the surface of the base material to increase its hydrophilicity, and methods of coating or mixing a water-absorbing substance on the surface of the base material. Among them, the method using a water-absorbing substance is relatively easy to implement, and a method for imparting water-absorbing and water-retaining properties characterized by mixing a water-absorbing substance to a base material has already been described in JP-A-53-91086. has been done. However, since the water-absorbing ability of the water-absorbing polymer is higher than that of the base material, there is a problem in that the water-absorbing polymer absorbs water by itself, expands, and separates from the base material. More specifically, the water-absorbing polymer located near the surface of the base material in contact with water undergoes volumetric expansion due to water absorption and falls off from the surface of the base material. Such a phenomenon occurs sequentially from the surface to the inside, and continues until all the water-absorbing polymers are separated and fallen off from the base material. As a result, the surface of the base material not only becomes rough, but also the water-absorbing substance falls off and the water-retaining and water-absorbing properties of the base material disappear, making it impossible to achieve the intended purpose. As a result of intensive research into water-absorbing and water-retaining materials that do not have such drawbacks, the present inventors found that the average particle diameter
By uniformly dispersing a specific water-absorbing polymer in the form of fine powder of 100 μm or less in a soft resin and rubber, we succeeded in obtaining the water-absorbing and water-retaining material that is the object of the present invention. The present invention uses soft resin and rubber;
It is essential to use a specific finely powdered water-absorbing polymer. It was completely unexpected that dropping of the water-absorbing polymer during water absorption could be prevented by satisfying this essential requirement. The reason for this is not clear, but due to a good balance between the elasticity of the soft resin and rubber and the elasticity of the specific finely powdered water-absorbing polymer after water absorption, both coexist in the same base material and are able to separate and fall off. It seems that it will not reach . The water-absorbing polymer used in the present invention is desirably highly absorbent and can absorb 50 times or more its own weight of pure water. If a water-absorbing polymer with a water-absorbing property lower than 50 times is used, the performance as a water-absorbing and water-retaining material will be poor, which is not preferable. Further, it is desirable that the particle size is as small as possible, and the smaller the particle size, the better the material can be obtained in which the water-absorbing polymer does not fall off during water absorption. In other words, the average particle size of the fine powder water-absorbing polymer is 100
It is not preferable that it exceed μ, and it is more desirable that it be 50 μ or less. The water-absorbing polymer used in the present invention is mainly composed of vinyl ester (X) and ethylenically unsaturated carboxylic acid or its derivative (Y), with a molar ratio of X:Y = 20:80 to 80:20. saponified copolymers or polyvinyl alcohol/acrylate graft copolymers, which have high strength after water absorption and are useful in increasing the stiffness of the water-absorbing and water-retaining materials of the present invention when water is absorbed. . Since it has excellent rigidity when water is absorbed, the water-absorbing and water-retaining material of the present invention has excellent effects such as high tensile strength and high swelling pressure. The soft resin used in the present invention is an ethylene-vinyl acetate copolymer, a saponified ethylene-vinyl acetate copolymer, an ethylene-isobutylene copolymer, an ethylene-acrylate copolymer, a vinyl chloride polymer, and a saponified ethylene-vinyl acetate copolymer. Vinyl copolymers, etc. Examples of rubber include ethylene-propylene copolymer, polybutadiene, polyisoprene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, and natural rubber. The water-retaining and water-absorbing material of the present invention is produced by uniformly dispersing and mixing a finely powdered water-absorbing polymer and a soft resin or rubber by a mechanical method. Examples of mechanical dispersion mixing methods that can be applied to the present invention include roll kneading, Banbury kneading, extruder kneading equipped with a Dalmage type screw, and extruder kneading. The water-retaining and water-absorbing material of the present invention can be used for water stop agents, dew condensation prevention wall materials, medical sanitary materials, and the like. In the present invention, a coloring agent, a foaming agent, a crosslinking agent, a filler, etc. may be mixed and used as necessary. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto. The water absorption rate and water retention rate in the Examples are based on the following definitions and test methods, respectively. Water absorption rate (g/g) = weight of water-absorbed base material/weight of dry base material Water retention rate (g/g) = water-absorbed base material was wrapped in a 300 mesh wire mesh and centrifuged at 100G for 10 minutes. Subsequent water absorption rate In addition, the tensile test and measurement of swelling pressure of the water absorbent sheet in the examples were carried out as follows. Tensile test of water-absorbing sheet Water-absorbing polymer is mixed with soft resin or rubber,
The uniformly dispersed sheet was immersed in water for 24 hours, and the water-absorbing sheet was subjected to a tensile test according to JISK-6301. Measurement of swelling pressure Using a 2 mm thick sheet obtained by press molding, a 20 x 20 mm square test piece was cut out from the sheet, sandwiched between iron plates with a gap of 2 mm, and immersed in water. The swelling pressure generated was measured. Example 1 0.7 mol of vinyl acetate, 0.5 mol of methyl acrylate, 0.03 mol of ethylene glycol diacrylate as a crosslinking agent, and 0.02 mol of benzoyl peroxide as a polymerization initiator were mixed, and 3 g of partially saponified polyvinyl alcohol was used as a dispersion stabilizer.
and 300 ml of water containing 10 g of NaCl, and suspension polymerization was carried out at 65°C for 6 hours. Next, 10 g of the above copolymer was dispersed in 200 ml of methanol, 40 ml of 40% NaOH aqueous solution was added, and 60 g of the above copolymer was dispersed in 200 ml of methanol.
It was saponified at ℃ for 5 hours. The degree of saponification was approximately 91 mol%. The resulting water-absorbing polymer has a spherical shape with a diameter of 20 to 200 microns, is insoluble in water, and has a water absorption rate of 550 times. By sieving, the particles were separated into two types of particle size: 100μ or more and 100μ or more. 100 parts of a water-absorbing polymer was added to 100 parts of an ethylene-vinyl acetate copolymer (Evatate R-5011 manufactured by Sumitomo Chemical) and mixed for about 10 minutes at room temperature by roll kneading. Then, test pieces with a thickness of 1 mm were obtained by press molding at 100°C. After this test was immersed in water, water absorption, water retention,
Changes in shape were determined. (Table 1)

[Table] As is clear from Table 1, a uniform swollen body was obtained when a finely powdered polymer of 100 μm or less was used. On the other hand, when the particle size exceeds 100μ, there is a drawback that the water-absorbing polymer falls off from the surface during water absorption. Example 2 0.5 g of benzoyl peroxide was added as a polymerization initiator to 60 g of vinyl acetate and 40 g of methyl acrylate, and this was dispersed in 300 ml of water containing 3 g of partially saponified polyvinyl alcohol and 10 g of NaCl as a dispersion stabilizer, and the mixture was heated at 65°C for 6 hours. Suspension polymerization was carried out. 8.6g of this copolymer with 200g of methanol and 10g
The suspension was suspended in a saponification solution consisting of water and 40 ml of 5N NaOH, and the saponification reaction was carried out at 25°C for 1 hour, and then the temperature was further raised to 65°C and the saponification reaction was carried out for 5 hours. After thorough washing with methanol, the product was dried under reduced pressure to obtain 6.8 g of spherical dry saponified material having a particle size of 20 to 300 μ. Water absorption rate is 750
g/g. 100 parts of the water-absorbing polymer thus obtained was added to 100 parts of ethylene propylene rubber (Espren 501A), and the mixture shown in Table 2 was kneaded for about 15 minutes using a 6-inch roll to form an unvulcanized compound. was formed. This compound is heated at 160℃ in a steam press machine.
Vulcanization was performed for 15 minutes to obtain a test piece with a thickness of 1 mm. After this test piece was immersed in water for 24 hours, water absorption and change in shape were determined. The water-absorbing polymer was classified into two types with average particle diameters of 75μ and 200μ.

[Table] Example 3 Using the water-absorbing polymer obtained in Example 2 and the vinyl chloride resin, the formulations shown in Table 3 were kneaded for 20 minutes in a mulch machine. The paste sol thus obtained was applied to a thickness of 300 μm on paper, heated at 120° C. for 1 minute to form a semi-gel, and then heat-treated at 200° C. for 3 minutes to obtain foamed paper. The water absorption and water retention properties of the foamed paper thus obtained were as shown in Table 3.

[Table] Example 4 Pour 200 ml of water into a polymerization tank, add 10 g of polyvinyl alcohol (degree of polymerization 1750, degree of saponification 88%), and dissolve while stirring. Add 0.135 g of potassium persulfate, then add 16.4 g of acrylic acid, and polymerize at 60° C. for 1 hour with stirring. After polymerization, add the polymerization solution to 1000ml of methanol and 1000ml of water.
When added to a solution of 13.5 g of caustic soda, a precipitate is formed. The precipitate was collected, dried under reduced pressure at 80°C for 5 hours, and heat treated. By treating with hot air at 120°C for 1 hour, a water-absorbing polymer with a water absorption rate of 709 times was obtained. This was ground with a jet mill and the particle size was 80μ.
The following fine powder water-absorbing polymer was obtained. This fine powder water-absorbing polymer is made of ethylene-vinyl acetate copolymer (Evatate R5011, manufactured by Sumitomo Chemical).
After roll kneading for 10 minutes at room temperature, the mixture was press-molded to obtain a 3 mm thick sheet. Physical property values are shown in Table 4. After absorbing water, the sheet swells uniformly and can be used as a water stopper or wall material to prevent condensation.

【table】

[Table] Example 5 100 parts of the water-absorbing polymer according to the present invention obtained in Example 1 with a particle size of 100μ or less was dispersed in 100 parts of ethylene-vinyl acetate copolymer, and a mixture was prepared at 100°C to a thickness of 2.
Tensile tests and swelling pressure measurements were conducted on the water-absorbing sheet using sheets press-molded to a diameter of 5 mm.
The results are shown in the table. Example 6 A sheet with a thickness of 2 mm was obtained in the same manner as in Example 5, except that the water-absorbing polymer according to the present invention obtained in Example 2 and having a particle size of 100 μm or less was used. This water-absorbing sheet was subjected to a tensile test and swelling pressure measurement, and the results are shown in Table 5. Example 7 A sheet with a thickness of 2 mm was obtained in the same manner as in Example 5, except that the water-absorbing polymer according to the present invention obtained in Example 4 and having a particle size of 80 μm or less was used. This water-absorbing sheet was subjected to a tensile test and swelling pressure measurement, and the results are shown in Table 5. Comparative Example Example 5 except that a crosslinked polyacrylate polymer water absorbent polymer with a particle size of 100μ or less (water absorption rate: 500 times) was used instead of the water absorbent polymer of the present invention used in Example 5. Using a 2 mm thick sheet obtained in the same manner as in Example No. 5, a tensile test and swelling pressure measurement of the water absorbent sheet were carried out, and the results are shown in Table 5.

[Table] As is clear from the results in Table 5, the ethylene/vinyl acetate copolymer sheet in which the water-absorbing polymer of the present invention is dispersed has a cross-linked polyacrylate-based water-absorbing polymer dispersed therein. Because of its superior rigidity during water absorption, the water-absorbing sheet had a high tensile strength and a high swelling pressure.

Claims (1)

[Scope of Claims] 1. A compound consisting of vinyl ester (X) and ethylenically unsaturated carboxylic acid or its derivative (Y) in a molar ratio of X:Y=20:80 to 80:20. A water-absorbing and water-retaining material characterized by uniformly dispersing a finely powdered water-absorbing polymer, which is a saponified polymer or a polyvinyl alcohol acrylate graft copolymer, in a soft resin or rubber. 2. The water-absorbing and water-retaining material according to claim 1, wherein the soft resin is an ethylene copolymer and a vinyl chloride polymer. 3. The water-absorbing and water-retaining material according to claim 1, wherein the water-absorbing polymer has an average particle size of 100 μm or less.