JPH0121164B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a highly water-absorbing polymeric material (hereinafter referred to as hydrogel) that has the ability to absorb a large amount of water. The objective is to provide a hydrogel capable of absorbing water. In recent years, as the use of hydrophilic polymer materials in the medical industry, food industry, and agricultural fields has progressed, hydrogels that are particularly water-insoluble and have hydrophilic or absorbent properties are being used as separation and purification materials such as various membranes and liquid chromatography carriers. It has come to be used as an enzyme-immobilized carrier, a culture medium for microorganisms and plants, a medical material such as contact lenses and suture coverings, and a variety of other uses that utilize water absorption and water retention. Among these applications, hydrogels used particularly in fields that utilize water absorption or water retention are desired to have the ability to absorb as much water as possible in a short period of time upon contact with water. In particular, hydrogels used in sanitary products such as sanitary products and diapers are required to have a high water absorption rate upon contact with water. Typical methods for producing hydrogels include:
Methods of crosslinking water-soluble polymeric substances using a crosslinking agent, substituting some of the hydrophilic groups with lipophilic groups to make them water-insoluble, and other methods are known. Crosslinked products of acrylic acid, polyvinylpyrrolidone, sulfonated polystyrene, sodium polyacrylate, etc., cellulose derivatives, saponified polyacrylonitrile products, saponified products of starch-acrylonitrile graft copolymers, or vinyl esters and ethylenically unsaturated carboxylic acids or Several materials using natural or synthetic polymeric substances, such as saponified copolymers with derivatives thereof, have been proposed. The water absorption rate of these hydrogels is influenced by their surface area. In other words, for a given volume (weight), if the hydrogel particles are large, the sum of their surface areas will be smaller than that of smaller particles. The time it takes to absorb water becomes slower. Conversely, the finer the hydrogel particles, the larger the sum of their surface areas, the larger the contact area when they come into contact with water, and the faster the rate of water absorption. Also, when comparing particles of similar size, amorphous and porous particles have a larger surface area and a faster water absorption rate than spherical particles. However, if the hydrogel particles are small, a so-called "sticky" phenomenon occurs when they come into contact with water, and the water absorption rate may not necessarily increase. In view of the above-mentioned circumstances, the present inventors conducted extensive studies to increase the water absorption rate of hydrogels, and arrived at the present invention. An object of the present invention is to provide a hydrogel with a high water absorption rate that can quickly swell with water without causing a lump phenomenon when it comes into contact with water even if the hydrogel has a small particle size. According to the present invention, a crosslinked product of polyacrylic acid and/or an alkali metal salt of polyacrylic acid or a copolymer thereof is brought into contact with a mixed solvent of a hydrophilic organic solvent and water, and then the solvent is removed and dried. The resulting lumps are pulverized into granules, or a crosslinked product of polyacrylic acid and/or an alkali metal salt of polyacrylic acid or a copolymer thereof is swollen with water, brought into contact with a hydrophilic organic solvent, and then the solvent is removed. It is obtained by removing and drying the resulting lumps and pulverizing them into granules. Furthermore, polyethylene oxide, polyethylene glycol, polyoxyethylene derivatives, dialkyl sulfosuccinates, or mixtures of these and higher fatty acids or higher fatty acid esters that are solid at room temperature are dissolved or dispersed in the organic solvent, and the lumps are treated in the same manner. This results in a product with even faster water absorption. The present invention will be explained in detail below. The crosslinked products of polyacrylic acid and/or alkali metal salts of polyacrylic acid or their copolymers used in the present invention absorb water and swell from several times to several thousand times, but do not dissolve in water. be.
Examples of the alkali metal salt of polyacrylate include sodium polyacrylate and potassium polyacrylate. In order to produce a crosslinked product, known crosslinking means are used. For example, a crosslinking agent having two or more polymerizable unsaturated bonds may be added to acrylic acid or
Alternatively, an alkali metal salt of acrylic acid may be added at the time of polymerization to carry out the crosslinking reaction at the same time as the copolymerization. Specific examples of crosslinking agents include polyallyl compounds such as diallyl phthalate, diallyl maleate, diallyl terephthalate, triallyl cyanurate, and triallyl phosphate, divinylbenzene, N,N'-methylenebisacrylamide, ethylene glycol diacrylate, and polyethylene. Examples include polyvinyl compounds such as glycol acrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, and glycerin trimethacrylate. Further, self-crosslinking may be carried out during polymerization without using a crosslinking agent. Alternatively, the crosslinking reaction may be carried out by irradiation with radiation or the like. Further, as a method for polymerizing acrylic acid and/or an alkali metal salt of acrylic acid, a known method can be applied. That is, usually aqueous solution polymerization,
It is synthesized by radical polymerization using emulsion polymerization (reverse-phase emulsion polymerization), suspension polymerization (reverse-phase suspension polymerization), or bulk polymerization. In particular, when an aqueous solution of acrylic acid or/and an alkali metal salt of acrylic acid is dispersed and polymerized in an organic solvent that does not dissolve in water (for example, hexane, toluene, etc.), small spherical particles are formed. At that time, dispersion stabilization during polymerization can be achieved by using a dispersion stabilizer or surfactant that dissolves in an organic solvent. When this polymerization method is combined with the production method of the present invention, a hydrogel with particularly high water absorption rate can be obtained. Further, there is no particular restriction on the degree of polymerization of the crosslinked product of polyacrylic acid and/or alkali metal salt of polyacrylic acid or a copolymer thereof used in the present invention. There is also no particular restriction on particle size, but
As mentioned above, in order to increase the water absorption rate, it is necessary to reduce the particle size, but if the particle size is reduced,
In some cases, the "mamako" phenomenon occurs and the water absorption rate is rather slowed down, and in such cases, applying the present invention has a significant effect.Therefore, the particle size is preferably 500μ or less.Furthermore, 350μ or less is particularly effective.In the present invention The hydrophilic organic solvent used is an organic solvent that is compatible with water, and examples include methanol, ethanol, propanol, and acetone.The ratio of the hydrophilic organic solvent and water used is 90 to 40:10. -60 (by weight), preferably 75-50:25-50 (by weight).It is also possible to partially mix a water-insoluble organic solvent, but if the solvent after mixing is It must be in a range that shows hydrophilicity, that is, a range that does not cause two-layer separation even when mixed with water at the above mixing ratio.Also, the amount of water must be within the range where polyacrylic acid or/and alkali metal salt of polyacrylic acid or polyacrylic acid alkali metal salt or The amount is preferably the same to 4 times the amount (weight) of the crosslinked copolymer.Also, the polyethylene oxide used in the present invention has a molecular weight of 150,000 or more, and the polyethylene glycol has a molecular weight of 600 or more. Examples of polyoxyethylene derivatives include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether, polyoxyethylene octyl phenol ether, Examples include polyoxyethylene alkyl phenol ethers such as polyoxyethylene nonyl phenol ether, polyoxyethylene acyl esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monostearate, and polyoxyethylene sorbitan monooleate. Examples of dialkyl sulfosuccinates include sodium di(2-ethylhexyl) sulfosuccinate. Examples of higher fatty acids that are solid at room temperature include stearic acid and palmitic acid. Examples of higher fatty acid esters that are solid at room temperature include wax and glycerin. Examples include monostearate. The amount used thereof is in the range of 0.001% to 50% by weight based on the crosslinked product. Preferably, it is in the range of 0.01% to 20% by weight. More preferably,
It ranges from 0.01% to 10% by weight. As mentioned in the introduction, the hydrogel of the present invention obtained by the method described above can quickly absorb water and swell without causing the swelling phenomenon when it comes into contact with water. . Moreover, it does not impair the water absorption rate that hydrogel originally has. It is useful in various sanitary materials where water absorption speed is especially important, such as disposable diapers, tampons, sanitary cotton, hot towels, and napkins. A high water absorption rate is also desirable for hydrogels in other fields, so they can be used as water separation agents in oil, other dehydration or drying agents, water retention agents for plants and soil, liquid chromatography carriers, and other water absorbing agents. , is suitably used in various applications that utilize water retention. The hydrogel with a high water absorption rate of the present invention may contain a coloring agent as long as it does not adversely affect its properties.
Flavors, other additives, and various inorganic and organic fillers can be added. Additionally, the hydrogels of the present invention can be used in combination with paper, fibers, cloth, and other dissimilar materials. EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. In addition, the water absorption rate in the examples was expressed as water absorption rate=gel weight after absorption/dry gel weight. Moreover, parts represent parts by weight. In addition, the water absorption rate is as follows: Put 50 c.c. of water in a beaker with a water absorption rate of 100 c.c., add 0.5 g of hydrogel while stirring,
The time required for all the water to be absorbed and the fluidity of the water to disappear was measured and expressed as such. Example 1 Put 30 parts of water into a polymerization tank and add sodium hydroxide.
6.7 parts were added and dissolved while stirring. While cooling with ice, 15 parts of acrylic acid was gradually added and neutralized with stirring. Add 0.0522 parts of potassium persulfate and 0.0085 parts of N,N'-methylenebisacrylamide. Plus sorbitan monolaurate (HLB8.0)
0.9 parts and 66 parts of n-hexane were added, and polymerization was carried out at 60°C for 3 hours while stirring. After polymerization, let stand, remove the hexane layer, and add to a solution of 0.5 parts of polyoxyethylene nonylphenol ether (HLB14.5) and 50 parts of methanol while stirring, and the hydrogel will precipitate. The solvent is filtered off and a mass is obtained after drying at 80° C. for 15 hours.
Grind it into granules and sieve it to size it.
A powder of 177μ to 250μ was obtained. Its water absorption rate is 620g/
It was hot at g. The water absorption rate was 10 seconds. Example 2 Put 30 parts of water into a polymerization tank and add sodium hydroxide.
6.7 parts were added and dissolved while stirring. While cooling with ice, 15 parts of acrylic acid was gradually added and neutralized with stirring. Add 0.0522 parts of potassium persulfate and 0.0085 parts of N,N'-methylenebisacrylamide. Plus sorbitan monolaurate (HLB8.0)
0.9 parts and 66 parts of n-hexane were added, and polymerization was carried out at 60°C for 3 hours while stirring. After polymerization, let it stand, remove the hexane layer, and add methanol while stirring.
When added to 50 parts, the hydrogel precipitates. After filtering off the solvent and drying at 80° C. for 15 hours, a mass is obtained. It was ground into granules and sized through a sieve to obtain a powder of 177μ to 250μ. Its water absorption rate is
It was 620g/g. Water absorption speed reached 13 seconds. Comparative example 1 Add 30 parts of water to a polymerization tank and add sodium hydroxide.
6.7 parts were added and dissolved while stirring. While cooling with ice, 15 parts of acrylic acid was gradually added and neutralized with stirring. Add 0.0522 parts of potassium persulfate and 0.0085 parts of N,N'-methylenebisacrylamide. Plus sorbitan monolaurate (HLB8.0)
0.9 parts and 66 parts of n-hexane were added, and the mixture was polymerized at 60°C for 3 hours with stirring. After completion of polymerization, solid-liquid separation was performed and dry hydrogel powder was obtained by drying under reduced pressure at 80°C for 15 hours. Water absorption rate is 620g/g
The water absorption rate was 16 seconds. Example 3 In Example 1, polyethylene oxide, polyethylene glycol, a polyoxyethylene derivative, a dialkyl sulfosuccinate, or a mixture thereof with a higher fatty acid or higher fatty acid ester was used in place of 0.5 part of polyoxyethylene nonylphenol ether. Table 1 shows the water absorption rate and water absorption rate.

[Table] Example 4 10 parts of the dry hydrogel synthesized in Comparative Example 1 was taken and added to a mixed solvent consisting of 30 parts of methanol and 20 parts of water. Leave to stand at room temperature for 10 minutes, remove the supernatant, and dry at 80°C for 15 hours to obtain a lump.
Grind it into granules and sieve it to size it.
A powder of 177μ to 250μ was obtained. Its water absorption rate is 600g/
It was hot at g. The water absorption rate was 12 seconds.

Claims (1)

[Claims] 1. A crosslinked product of polyacrylic acid or/and an alkali metal salt of polyacrylic acid or a copolymer thereof is brought into contact with a mixed solvent of a hydrophilic organic solvent and water, and then the solvent is removed and dried. A method for producing a highly water-absorbing polymeric material with a high water absorption rate, which comprises pulverizing the obtained lump into granules. 2. The hydrophilic organic solvent is a hydrophilic organic solvent in which polyethylene oxide, polyethylene glycol, polyoxyethylene derivatives, dialkyl sulfosuccinates, or a mixture of at least one of these and higher fatty acids or higher fatty acid esters that are solid at room temperature are dissolved or dispersed. A method for producing a super absorbent polymer material having a high water absorption rate according to claim 1. 3 A crosslinked product of polyacrylic acid and/or an alkali metal salt of polyacrylic acid or a copolymer thereof is swollen with water, brought into contact with a hydrophilic organic solvent, the solvent is removed, and the resulting mass is dried. A method for producing a highly water-absorbing polymeric material that has a high water absorption rate and is characterized by pulverizing it into granules. 4. The hydrophilic organic solvent is a hydrophilic organic solvent in which polyethylene oxide, polyethylene glycol, polyoxyethylene derivatives, dialkyl sulfosuccinates, or a mixture of at least one of these and higher fatty acids or higher fatty acid esters that are solid at room temperature are dissolved or dispersed. A method for producing a super absorbent polymeric material having a high water absorption rate according to claim 3.