JPS637203B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polymeric materials (hereinafter referred to as hydrogels) that have the ability to absorb and retain large amounts of water. In recent years, as the use of hydrophilic polymer materials has progressed in the medical industry, food industry, and agricultural fields, hydrogels that are insoluble in water and have hydrophilic or water-absorbing properties have been 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 its water absorption and water retention properties. Among these applications, hydrogels used particularly in application 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. Methods for producing hydrogels for such uses include crosslinking water-soluble polymeric substances using a crosslinking agent, replacing some of the hydrophilic groups with lipophilic groups, and modifying them to make them water-insoluble. Methods such as crosslinking of polyethylene oxide, polyacrylic acid, polyvinylpyrrolidone, sulfonated polystyrene, sodium polyacrylate, etc., cellulose derivatives, polyacrylonitrile, or starch-acrylonitrile graft copolymers have been used to date. Several materials using natural or synthetic polymeric substances, such as saponified materials, have been proposed. However, saponified starch-acrylonitrile graft copolymers, self-crosslinking acrylic acid alkali metal salt polymers, vinyl esters previously proposed by the present inventors, or combinations of these with ethylene and ethylenically unsaturated carboxylic acids or derivatives thereof Except for saponified copolymers or neutralized polymers obtained by polymerizing acrylic acid or methacrylic acid in the presence of polyvinyl alcohol, their water absorption capacity is small and they are not satisfactory as water-absorbing materials. . Furthermore, in the case of saponified starch-acrylonitrile graft copolymers that have a relatively high water absorption ability, although various improvements have been made to the manufacturing method, the process is relatively complicated and takes a long time. When used in a water-containing 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. Generally, the highly water-absorbent hydrogels that have been proposed so far have flexibility in a moderately hygroscopic state, but exhibit extreme inflexibility and brittleness in a dry state. For this reason, it is very easy to break when handled in a dry state, and when used for applications that come into contact with the human body, it has poor adhesion to the skin and lacks flexibility, which significantly inhibits the feel of the product. There are drawbacks. The saponified copolymer of (ethylene)-vinyl ester-ethylenically unsaturated carboxylic acid or its derivatives proposed by the present inventors does not have the above-mentioned drawbacks, is water-insoluble, and moreover swells quickly upon contact with water. It has the ability to hold large amounts of water, and
Although the hydrogel has excellent flexibility even in a dry state, the manufacturing process requires a saponification reaction of the vinyl ester unit in the copolymer, which poses a problem in terms of economic efficiency. In order to solve these problems, we proposed neutralized acrylic acid or methacrylic acid polymers in the presence of polyvinyl alcohol, but it was necessary to handle a highly viscous polyvinyl alcohol aqueous solution in the manufacturing process, and the operability was not fully satisfactory. It's not a thing. Self-crosslinking type acrylic acid alkali metal salt polymers do not have the above-mentioned drawbacks and have the ability to absorb and retain large amounts of water.
It is necessary to remove a large amount of polymerization heat released in a short period of time, which poses a problem in terms of process control. It is known that hydrogels can be obtained by copolymerizing acrylic acid or its salts with a crosslinking agent (US Pat. No. 3,669,103; Polymer Processing, 21 ,
693 (1972); Japanese Patent Publication No. 53-46389). However, when polymerization is carried out rapidly, self-crosslinking occurs and the water absorption capacity does not increase. In addition, by reducing the amount of polymerization initiator or using it in combination with polymerization retarders and inhibitors,
If the polymerization is carried out gently, a highly water-absorbent hydrogel can be obtained, but due to the low reaction rate of the monomer, demonomerization steps such as washing are required, and an economically improved manufacturing method is required. Be expected. In view of the above-mentioned circumstances, the present inventors have conducted further studies on a method for producing a product that has high water absorption and safety, is inexpensive and simple, and have arrived at the present invention. An object of the present invention is to provide a method for producing a hydrogel that can quickly absorb and retain a large amount of water. Another object is to provide a method for producing hydrogels in a cheap and simple manner. Another purpose is to provide a method for producing a highly safe hydrogel that increases the reaction rate of monomers and has a low content of unreacted monomers. Other advantages and objectives will become apparent from the description below. According to the present invention, a crosslinking agent having two or more polymerizable unsaturated groups and acrylic acid or its salt or methacrylic acid or its salt are copolymerized, and at that time, the polymerization initiator is divided into two or more times. The present invention provides a method for producing a highly water-absorbent hydrogel, which is characterized in that it facilitates the removal of polymerization heat and reduces unreacted monomers by charging the same. In the present invention, it is essential to polymerize by adding the polymerization initiator two or more times, and it is also essential to neutralize the carboxyl group of acrylic acid or methacrylic acid in advance at the monomer stage or at the polymer stage. That is. The present invention will be explained in detail below. A known method can be used to copolymerize acrylic acid or methacrylic acid or a salt thereof and a crosslinking agent having two or more polymerizable unsaturated bonds. That is, it is usually synthesized by radical polymerization using bulk polymerization, emulsion polymerization (inverse emulsion), or suspension polymerization (inverse suspension). In particular, organic solvents that do not dissolve in water or dissolve polyacrylic acid, polymethacrylic acid or their salt compositions (e.g. toluene, hexane, etc.)
The heat of polymerization can be easily removed by polymerizing while stirring a mixed aqueous solution of acrylic acid or methacrylic acid or a salt thereof and a crosslinking agent as a dispersion medium.
The polymerization initiator added after the third initiator easily permeates into the copolymer, and unreacted monomers can be further reacted. The resulting hydrogel is granular. At that time, dispersion stabilizers and surfactants may be used, but in order to obtain spherical hydrogels, HLB3~
It is preferable to use sorbitan fatty acid ester, sucrose fatty acid ester, or glycerin fatty acid ester of No. 6. Examples of the crosslinking agent used in the present invention include polyallyl compounds such as diallyl phthalate, diallyl maleate, diallyl terephthalate, triallyl cyanurate, and triallyl phosphate, divinylbenzene, N,N'-methylenebisacrylamide, ethylene glycol diacrylate, Examples include polyvinyl compounds such as ethylene glycol dimethacrylate and glycerin trimethacrylate. In particular, water-soluble crosslinking agents such as N, N′-
Methylenebisacrylamide is preferred. When using a crosslinking agent, the amount added varies depending on the type of crosslinking agent, but it is usually appropriate to use it in the range of 0.001 to 20 mol%, preferably 0.003 to 1 mol%, based on the total amount of monomers. . As the polymerization initiator, generally known radical polymerization initiators can be used. azonitrile such as azobisisobutyronitrile, alkyl peroxide such as t-butyl peroxide, cumene hydroperoxide, etc.
Dialkyl peroxides such as di-t-butyl peroxide, acyl peroxides such as acetyl peroxide, lauroyl peroxide, stearoyl peroxide, benzoyl peroxide, t-butyl peroxyacetate, t-butyl peroxide Isobutyrate, t-
Examples include peroxy esters such as butyl peroxypivalate, ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, hydrogen peroxide, ammonium persulfate, potassium persulfate, and cerium () salts. Particularly desirable are water-soluble initiators such as hydrogen peroxide, ammonium persulfate, potassium persulfate, and cerium () salts. The amount of the polymerization initiator used is in the range of 0.0001 to 0.1 mol% for the first time based on the total amount of monomers,
From the second time onward, the amount is in the range of 0.01 to 5 mol%. There are no particular restrictions on polymerization conditions, but the polymerization temperature is 150℃ or less, usually 10 to 80℃ for the first polymerization using a polymerization initiator, and thereafter
The temperature is 50-150℃. There is also no limit to the polymerization pressure. In the method of the invention, the crosslinking agent is copolymerized with acrylate or methacrylate, or with acrylic acid or methacrylic acid, and then neutralized with alkali. The above-mentioned acrylate or methacrylate or neutralized product of polymerized acrylic acid or methacrylic acid is preferably a salt whose carboxyl group is represented by the following formula. ―CO Y ⁺ where Y is Na, K,

[Formula] (R ₁ , R ₂ , R ₃ , R ₄ are hydrogen or alkyl having 1 to 4 carbon atoms,
At least one of the alkanol group, aralkyl group having 6 to 8 carbon atoms, and aryl group is hydrogen. )or

[Formula]. Among these, particularly preferred are those in which Y is Na, K, or NH ₄ , with Na being the most preferred. The alkalis used for neutralization correspond to the above salts, and include sodium hydroxide, potassium hydroxide, ammonia, and organic amines. Examples of organic amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, iso-propylamine, di-n-propylamine, di-iso-propylamine, tri-n
-propylamine, tri-iso-propylamine,
t-butylamine, n-butylamine, iso-butylamine, di-t-butylamine, di-n-butylamine, di-iso-butylamine, tri-t
-butylamine, tri-iso-butylamine, tri-n-butylamine, monoethanolamine,
Examples include diethanolamine, triethanolamine, mono-isopropanolamine, di-isopropanolamine, tri-isopropanolamine, cyclohexylamine, benzylamine, aniline, and pyridine. The neutralization reaction may or may not use a solvent. Regarding the reaction conditions, the same conditions as those for conventional neutralization reactions of carboxylic acids are used, and there are no particular restrictions, but the reaction temperature is preferably 200°C or less, preferably 10 to 60°C. There is no particular restriction on the reaction pressure. The amount of alkali used in the neutralization reaction is 0.3 to 2 times the theoretical amount required for neutralization, preferably 0.5
Use ~1.0x. Specific examples of salts of acrylic acid and methacrylic acid include sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, ammonium acrylate, ammonium methacrylate, trimethylamine salt of acrylic acid, trimethylamine salt of methacrylic acid. , triethylamine salt of acrylic acid, triethylamine salt of methacrylic acid, tri-n-propylamine salt of acrylic acid, tri-n-butylamine salt of acrylic acid, and the like. As mentioned in the introduction, the hydrogel of the present invention obtained by the method described above usually has the ability to absorb more than 100 times its own weight in water. It varies depending on the type and amount of the substance, if any. For example, PH
Regarding absorption capacity for different types of water, pH is 8.
It has the highest absorption capacity for water around ~10%, and in this case, it can absorb more than 500 times its own weight in water. Furthermore, in a pH range of 5 or less, the water absorption capacity is significantly reduced. However, when the material that has been immersed in an acidic solution is immersed in an alkaline solution again, its water absorption capacity is completely restored. Furthermore, when a salt such as NaCl is added to a highly water-absorbing gel, it releases a large amount of water. In other words, it exhibits reversible changes in water absorption and water release depending on changes in water PH and salt concentration. Furthermore, since the hydrogel of the present invention has relatively good flexibility even in a dry state, it has a significantly improved feel on the skin compared to conventional hydrogels. The superabsorbent hydrogel of the present invention as described above has the following advantages. In other words, it is transparent, has little coloring, contains only a very small amount of unreacted monomer in the hydrogel, is almost non-toxic, and is therefore useful for various sanitary materials, such as disposable diapers, etc.
It is expected that it can be used without any problems in applications that come into contact with the human body, such as tampons, sanitary cotton, hot towels, and napkins.It also has excellent gel strength in a hydrated state, and the gel structure will not break even after long-term use. Therefore, it can be used in various industrial applications, such as as a water-in-oil separation agent, other dehydration or desiccation agents, or as a water-retaining agent such as plants and soil, liquid chromatography carrier, and other water-absorbing and water-retaining properties. The superabsorbent hydrogel of the present invention has the advantage that it can be suitably used for various applications, and that it can be produced industrially very easily and can be molded into various shapes depending on the application. . Coloring agents, fragrances, other additives, and various inorganic and organic fillers can be added to the hydrogel of the present invention as long as they do not adversely affect its properties. 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. In addition, parts represent parts by weight. Example 1 133 parts of water was placed in a polymerization tank, and 44.7 parts of sodium hydroxide was added and dissolved with stirring. While cooling with ice, 100 parts of acrylic acid was gradually added and neutralized with stirring. Add 0.0667 part of potassium persulfate and 0.01 part of N,N'-methylenebisacrylamide. Furthermore, 6 parts of sorbitan monostearate and 470 parts of n-hexane were added and polymerized at 60°C for 1 hour with stirring. Furthermore, an aqueous solution of 0.58 parts of ammonium persulfate dissolved in 5 parts of water was continuously added dropwise for 1 hour, and polymerization was continued at 60° C. for 4 hours including the time for addition. After the polymerization was completed, solid-liquid separation was performed and dried under reduced pressure to obtain a dry hydrogel powder. The obtained hydrogel was spherical and had a water absorption rate of 850 (g/g).
The amount of unreacted acrylic acid monomer was 330 ppm.
The unreacted monomer was quantified by gas chromatography using a column with PEG1000 as the liquid phase after extracting acrylic acid with toluene in the presence of sulfuric acid. Comparative Example 1 A hydrogel was produced in the same manner as in Example 1 except that ammonium persulfate was not added in the formulation shown in Example 1. The water absorption rate of the obtained hydrogel was 860 g/g, and unreacted monomers were
It was 1000ppm. Comparative Example 2 Polymerization was carried out using the charging recipe of Comparative Example 1, and after solid-liquid separation, the polymer was washed with 400 parts of methanol and dried under reduced pressure to obtain a dry hydrogel. The water absorption rate of the obtained hydrogel was 870 g/g, and the amount of unreacted monomer was 370 ppm. Example 2 100 parts of water is placed in a polymerization tank, and 70 parts of ammonium acrylate is added. Additionally, 0.01 part of N,N'-methylenebisacrylamide and potassium persulfate.
Add 0.06 parts. Sorbitan monostearate 6
1 part and 470 parts of n-hexane were added, and polymerization was carried out at 60°C for 1 hour while stirring. An aqueous solution containing 5 parts of water and 0.5 parts of ammonium persulfate was continuously added dropwise to this solution for 1 hour, and polymerization was further carried out at 60° C. for 4 hours. After the polymerization was completed, dry hydrogel powder was obtained by separating solid and liquid and drying under reduced pressure. The water absorption rate of the obtained hydrogel was 700 (g/g), and the amount of unreacted monomer was 250 ppm. Example 3 150 parts of toluene is placed in a polymerization tank, and 7 parts of polyvinyl acetate (degree of polymerization: 2000) and 0.9 parts of sorbitan monostearate are added and dissolved. A solution prepared by dissolving 20 parts of acrylic acid, 0.03 part of potassium persulfate, and 0.002 part of N,N'methylenebisacrylamide in 30 parts of water is added dropwise to the toluene solution with stirring.
Polymerization was carried out at 60°C for 1 hour while stirring, and an aqueous solution of 0.2 parts of ammonium persulfate dissolved in 5 parts of water was continuously added dropwise for 1 hour, and polymerization was further carried out at 60°C for 4 hours including the dropwise addition time. After polymerization, filter and remove solids with methanol.
Add to a solution of 9 g of sodium hydroxide dissolved in a solution of 500 parts of water and 50 parts of water, and stir at room temperature for 30 minutes.
Strain and dry. The water absorption rate was 560 g/g, and the amount of unreacted monomer was 90 ppm.

Claims (1)

[Claims] 1. Copolymerization of acrylic acid or methacrylic acid and a crosslinking agent having two or more polymerizable unsaturated groups, at which time a radical polymerization initiator is added in two or more portions, and the resulting copolymer is A method for producing a super-absorbent polymer material, characterized by neutralizing a polymer. 2. A compound obtained by neutralizing acrylic acid or methacrylic acid is copolymerized with a crosslinking agent having two or more polymerizable unsaturated groups, and at that time, a radical polymerization initiator is added in two or more portions. A method for producing a super absorbent polymer material.