JPS6034562B2 - Method for producing hydrogel with excellent water absorption - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a hydrogel having the ability to absorb a large amount of water, and its purpose is to use it as various water-absorbing materials or in a swollen state after absorbing water. The object of the present invention is to provide a hydrogel that can be suitably used as a gel material.

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 enzyme-immobilized carriers, culture media for microorganisms and plants, medical materials 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.

Methods for producing hydrogels for such uses include crosslinking a water-droppable polymer material with a crosslinking agent, modifying it to be water-insoluble by substituting some of the hydrophilic groups with lipophilic groups, and other methods. This method is known, and so far, crosslinked materials such as polyethylene oxide, polyacrylic acid, polyvinylpyrrolidone, sulfonated polystyrene, and sodium polyacrylate, cellulose derivatives, polyacrylonitrile, or starch-acrylonitrile graft copolymers have been used. Several materials have been proposed using natural or synthetic polymeric substances such as saponified materials. However, except for saponified products of starch-acrylonitrile graft copolymers, their water absorption capacity is small and they are not satisfactory as water-absorbing materials.

In addition, in the case of saponified starch-acrylonitrile graft copolymers with relatively high water absorption ability,
Although various improvements have been made to the manufacturing method,
If the process is relatively complicated or if it is 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. In addition, although the high-grade aqueous hydrogels that have been proposed so far have flexibility in a moderately hygroscopic state, they 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 in applications that come in contact with the human body, it has disadvantages such as poor adhesion to the skin and poor flexibility, which significantly inhibits the feel of the product. There is.

The present inventors focused on the above problems, and found that water-insoluble,
In addition, we investigated a method for producing hydrogels that swell quickly on contact with water and have the ability to retain large amounts of water and have excellent flexibility even in dry conditions. A patent application has been filed under the heading that a hydrogel made from water-insoluble water by saponifying a copolymer with an unsaturated carboxylic acid or its derivative has extremely excellent properties.

The present inventors have further investigated the method for producing a hydrogel made of the above-mentioned copolymer, and found that a copolymer of ethylene, vinylester, and ethylenically unsaturated carboxylic acid or its humble conductor, which has a crosslinked structure, has a crosslinked structure. The present invention was completed based on the discovery that a water-independent high-grade aqueous gel with significantly improved gel strength could be obtained by saponifying the coalescence.

It is generally known that gel materials having water absorption properties can be obtained by crosslinking water-soluble polymers using various crosslinking agents.

In this case, the degree of crosslinking and water absorption capacity are in a contradictory relationship; if the degree of crosslinking is increased to the point where it is water-insoluble, non-tacky in a water-containing state, and has the ability to form a gel with a certain degree of strength, the water absorption capacity will sharply decrease. In many cases, the usefulness as a water-absorbing material is lost. However, according to the method of the present invention, it is extremely easy to industrially produce a hydrogel that absorbs an extremely large amount of water, usually more than one pea of its own weight, has high gel strength in a hydrated state, and is stable for a long time. can be obtained.

Conventionally, copolymers of ethylene, vinylester, and ethylenically unsaturated carboxylic acids or their derivatives, and their saponified products having certain compositions or components have been used as water-soluble adhesives or plastic materials with low gas permeability, etc. It is known to be used in

However, it is not known that a water-insoluble superabsorbent hydrogel can be obtained by the method defined in the present invention. The copolymer used in the present invention can be produced by any known method.

It is usually synthesized by radical polymerization using solution polymerization, emulsion polymerization, or suspension polymerization.
Otherwise, it has a large effect on the flexibility of the dried gel.
Therefore, in order to obtain a hydrogel as the object of the present invention, the composition of the copolymer before saponification must be within a defined range, that is, the vinylester component (
X), ethylenically unsaturated carboxylic acid or its derivative component (Y), and ethylene component (Z) in a molar ratio of X:Y=20:
It needs to be in the range of 80-80:20 Z:(x+Y):0.1:99.9-15:85.

If the ratio of (Y) is small, the water absorption capacity of the obtained hydrogel will be extremely low, and if it is too large, the gel strength in a water-containing state will be reduced.

The usually preferred ratio of X:Y is 30:70 to 70:30,
More preferably, it is in the range of 40:60 to 60:40.
Furthermore, as the ratio of the ethylene component (Z) increases, the flexibility of the gel in a dry state increases, but when the above ratio is exceeded, the water absorption rate decreases extremely, and in that case, it is no longer suitable for the purpose of the present invention. is not suitable.

The usually preferred ratio of (Z) is Z:(X+Y) of 1:99.
~10:90, more preferably 3:97~7:93. Examples of the vinyl ester used to produce the copolymer starting material include vinyl acetate, vinyl propionate, and vinyl stearate, but it is usually preferable to use vinyl acetate.

Examples of ethylenically unsaturated carboxylic acids or derivatives thereof include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, maleic anhydride, itaconic anhydride and their esters, acrylamide, Examples include methacrylamide, among others, acrylic acid, methacrylic acid, and their methyl, ethyl, n-propyl,
These are lso-propyl-, n-butyl-, t-butyl esters, acrylamide, and methacrylamide. The copolymer of ethylene, vinyl ester, and ethylenically unsaturated carboxylic acid or its derivatives having a crosslinked structure used in the present invention can be obtained either simultaneously with the synthesis of the copolymer or by crosslinking after synthesis. I can do it.

Usually, when the former method is used, it is carried out by adding a crosslinking agent having two or more polymerizable unsaturated bonds in the molecule to carry out a crosslinking reaction simultaneously with copolymerization.

．． On the other hand, when carrying out a crosslinking reaction using a copolymer, it can be carried out by either a method of crosslinking by radiation irradiation or addition of a radical generator, or a method of using these in combination with a crosslinking agent as described above. I can do it. The above crosslinking reactions are carried out in the presence or absence of a solvent in any case.

In this case, when a radical generator is used as a catalyst, it is sufficient to add the catalyst in an amount of 0.001 mol or less to 5 mol % based on the total amount of copolymerized monomers or copolymer. In addition, when using a crosslinking agent, the amount added varies depending on the type of crosslinking agent, but it is usually used in the range of 0.005 mol% to 20 mol% based on the total amount of copolymer monomers or copolymer. Appropriate.

Examples of such 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 ethylene glycol diacrylate. Examples include polyvinyl compounds such as methacrylate, glycerin trimethacrylate, allyl acrylate, and allyl methacrylate.
The hydrogel of the present invention can be obtained by saponifying the crosslinked copolymer obtained by the above method using a well-known saponification method.

At this time, the copolymer is saponified in a solvent, preferably in a swollen state. Usually, it is preferable to use a suitable alkaline substance in alcohol or an organic mixed solvent containing alcohol as a main component, but water or a water-alcohol mixture may also be used as the solvent. Generally, examples of the alkaline substance include compounds such as alkali metal hydroxides and alcoholates such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, and potassium methylate.

However, when the saponification reaction is carried out using a water-containing solvent, preferred alkali substances are alkali metal hydroxides. For the purpose of the present invention, it is necessary that the saponified copolymer having a crosslinked structure contains at least a hydroxyl group and a carboxylate group in its molecule.

Therefore, the degree of saponification may be within a range that satisfies the above conditions, but in order to obtain a hydrogel that is water insoluble and has a high water absorption ability, for example, ethylene having a crosslinked structure, In the case of using a copolymer of pinyester and ethylenically unsaturated carboxylic acid ester as a starting material, 50 mol% or more, preferably 90 mol% or more of the vinylester component of the copolymer,
30 mol% of ethylenically unsaturated carboxylic acid ester component
The above content is preferably 70 mol% or more. In addition, the water absorption capacity of the superabsorbent hydrogel obtained by the method of the present invention is determined not only by the components and composition of the crosslinked copolymer and the degree of crosslinking or saponification, but also by the saponified copolymer. The degree of salt formation of the ethylenically unsaturated carboxylic acid component in the copolymer also has a large influence.

That is, the water absorption capacity generally increases as the degree of salt formation increases.

In other words, the water absorption capacity of the hydrogel can be varied by changing the degree of salt formation.

Salt-forming substances used in this case include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal hydroxides such as calcium hydroxide and magnesium hydroxide; ammonium hydroxide; , trimethylamiso; mono, di, triethylamine; mono, di, triisopropylamine; mono,
D, triethanolamine; mono, di, triisopro/enolamine; N,N-dimethylethanolamine; N,N-dimethylisopro/gnolamine; N,N-diethylethanolamine; N,N-diethylisof.

B/Gnolamine; N-methylethanolamine, N
-Methylisof. Examples include b/f-nolamine, N-ethylethanolamine, cyclohexylamine, benzylamine, aniline, pyridine, and other organic amines. Preferred salt forms are alkali metal salts, ammonium salts, and organic amine salts.

As mentioned in the introduction, the hydrogel of the present invention obtained by the method described above usually has the ability to absorb water of one tonne or more of its own weight; If it contains a substance, it changes depending on the type and amount of that substance.

For example, regarding the absorption capacity for water with different pH,
It has the highest absorption ability for nearby water with a pH of 8 to 1.
In this case, it is possible to absorb more than 50M sound of water than its own weight. Furthermore, as the pH moves away from this range, the water absorption capacity decreases, and the decrease in water absorption capacity is particularly significant in the pH range below 5. When exposed to water, the water absorption capacity is completely restored.Also, highly water-absorbed gels are
It has the property of releasing a large amount of water when salts such as these are added. In other words, it exhibits a reversible change in water absorption and water release depending on changes in water pH and salt concentration. As described above, the hydrogel of the present invention is used as a particularly suitable water-absorbing material when absorbing water with a pH in the range of approximately 5 to 12, and its water-absorbing ability is determined by the degree of crosslinking, composition and components of the copolymer starting material, It can be changed by changing the degree of oxidation, etc.

Furthermore, the hydrogel of the present invention is useful not only as a material for absorbing water, but also as an absorbent material for other liquids. For example, when the final salt form of the copolymer is an organic amine salt, it is excellent against not only water but also polar organic solvents, water-alcohol, water-acetone, and other mixed liquids of organic solvents and water. Hydrogels with various absorption capacities can be obtained by selecting the salt form. Furthermore, since the hydrogel of the present invention has relatively good flexibility even in a dry state, it has significantly improved feel to the skin layer compared to conventional hydrogels.

The superabsorbent hydrogel of the present invention as described above has the following advantages.

First of all, it is transparent, has little coloring, and is almost non-toxic, as can be easily estimated from its molecular structure, so it can be used as a variety of sanitary materials, such as disposable diapers, tampons, sanitary cotton, and hot towels. However, it is expected that it can be used in areas that come into contact with the human body, such as napkins, without any problems.Secondly, it has excellent gel strength in a water-containing state, and the gel structure will not break down even after long-term use. This makes it suitable for various industrial applications, such as water-in-oil separation agents, other dehydration or drying agents, water retention agents for plants and soil, liquid chromatography carriers, and other water-absorbing agents.
Suitable for use in various applications that utilize water retention;
Thirdly, it has the advantage of being extremely easy to manufacture industrially and being able to be molded into various shapes depending on the intended use. 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 by these in any way.

In addition, the water absorption rate or absorption rate in the examples is (water absorption (
Yield) rate = weight of gel after absorption/weight of dry gel).

Example 1 A polymerization tank was charged with 300 g of water in which 3 g of partially saponified polyvinyl alcohol was dissolved as a dispersion stabilizer, and then 60 g of vinyl acetate and 40 g of methyl acrylate were added to this aqueous solution.
Penzoyl peroxide 0.5 as polymerization initiator and polymerization initiator
In the evening, add and disperse a mixed solution of 0.1 g of divinylbenzene as a crosslinking agent, and after sufficiently replacing the air in the polymerization tank with nitrogen and ethylene, maintain the internal temperature at 6500 and pressurize ethylene to 10k9/kg. Then, suspension polymerization was carried out for 6 hours.

The obtained copolymer has a methyl acrylate component of approximately 46 mol%.
It contained about 48 mol% of vinyl acetate component, about 5 mol% of ethylene component, and the insoluble content in benzene solvent was 8% by weight.

Next, the cross-linked copolymer was dispersed in 300 ml of methanol, 70 ml of NaOH aqueous solution was added thereto, and a saponification reaction was carried out at 6000 ml for 5 hours.

After the reaction was completed, the saponified product was washed with methanol and heated repeatedly to remove free NaH, and then dried under reduced pressure to obtain a spherical powder. The saponification degree of the saponified product is about 91 mol%, and the infrared absorption spectrum shows -COO at 1570 arc-1.
- It had strong absorption based on The hydrogel in the form of a Na salt thus obtained was insoluble in water, swelled quickly in water, and had a water absorption rate of 420 tons. It was also stable for a long time even in excess water and maintained excellent gel strength. Example 2~
3 Table 1 shows the liquid absorption properties of the hydrogels obtained by converting the Na salt hydrogel obtained in Example 1 into ammonium salt and triethylamine salt.

Table 1 Example 4 Polymerization was carried out in the same manner as in Example 1 except that divinylbenzene was used overnight to obtain a crosslinked copolymer with a benzene residual content of 9% by weight.

Next, the copolymer was saponified in the same manner as in Example 1 to obtain a hydrogel with a degree of saponification of 90 mol.

The obtained gel had a water absorption rate of 309/night and had excellent gel strength and stability. Example 5 60% of vinyl acetate, 40% of methyl acrylate, 0.59% of penzoyl peroxide as a polymerization initiator, and 0.2% of triethylene glycol dimethacrylate as a crosslinking agent.
Polymerization was carried out in the same manner as in Example 1 using aqueous solution, and the methyl acrylate component was about 46 mol% and the vinyl acetate component was about 47 mol%.
A benzene-insoluble copolymer containing about 6 mol % of ethylene was obtained.

Next, the crosslinked copolymer was saponified under the same conditions as in Example 1 to obtain spherical hydrogel beads with a degree of saponification of about 92 mol%.

This Na salt-form hydrogel was insoluble in water, quickly absorbed water and swelled, and absorbed 500 tons of water. It was stable for a long time in an equilibrium water absorption state and had excellent gel strength. In addition, the gel converted to triethylene amine salt is 4
Absorbed water on 20/evening and methanol on 909/evening.
Example 6 Example 1 except that methyl methacrylate 509, vinyl acetate 50 and divinylbenzene 1 were used as a crosslinking agent.
A copolymerization reaction was carried out in the same manner as above to obtain a penzene-insoluble copolymer containing about 49 mol % of methyl methacrylate component, about 43 mol % of vinyl acetate component, and about 7 mol % of ethylene component.

Next, the copolymer was saponified in the same manner as in Example 1 to obtain a hydrogel with a saponification degree of 88 mol%. The resulting hydrogel had excellent stability and gel strength and absorbed 120 t/d of water. Example 7 A polymerization tank was charged with 0.5 parts of divinylbenzene, 50 parts of vinyl acetate, 200 parts of water, 0.5 parts of potassium persulfate, and 1 part of a /ionic surfactant, and after replacing with ethylene, the internal temperature was lowered. Keep it at 60oo,
Ethylene was introduced under pressure to 8k9/cm, and acrylic acid was added dropwise to react for 5 hours, and after the addition of acrylic acid was completed, the reaction was continued for another hour.

The composition of the obtained copolymer was approximately 48 mol% vinyl acetate.
, the acrylic brewing component was about 46 mol%, and the ethylene component was about 5 mol%.

Next, the above copolymer was dispersed in 300 ml of methanol, 40 ml of NaOH aqueous solution was added, and a saponification reaction was carried out at 6000 ml for 5 hours.

After the saponification reaction, free NaOH was removed by washing with methanol, and the mixture was dried under reduced pressure to obtain a fine hydrogel powder. The water absorption rate of this hydrogel was 490 pm/pm. Example 8 Methyl acrylate component 40 mol%, vinyl acetate component 53
A copolymer of ethylene, methyl acrylate, and vinyl acetate having a composition of 100% by mole and an ethylene component of 100% was foamed with 0.5% of Q,Q-vistar sharybutylperoxydiisopropylbenzene as a radical generator. Azodicarbonamide was added as an agent, and the mixture was mixed uniformly for 10 minutes at 12,000 using a hot roll.

Next, this mixture was molded into a film using a hot press molding machine, and cross-linked and foamed at 170 oo. The resulting foamed sheet had a thickness of one layer, a foaming ratio of 10 times, and was insoluble in benzene.

Next, the foamed sheet was cut into a size of 5 pieces x 5 pieces, soaked in a saponification solution consisting of 100 parts of methanol and 20 parts of NaOH aqueous solution, and saponified at 60 degrees for 8 hours. It was washed and dried under reduced pressure.

The degree of saponification was about 85 mol%. The foam-like hydrogel thus obtained had excellent flexibility even in a dry state and had a water retention capacity of 100 μm.

Claims (1)

[Claims] 1. A method for producing a hydrogel with excellent water absorption by saponifying a crosslinked copolymer of ethylene, vinyl ester, ethylenically unsaturated carboxylic acid or its transparent conductor. 2 Molarity of vinyl ester component (X), ethylenically unsaturated carboxylic acid or its derivative component (Y), and ethylene component (Z) in a copolymer of ethylene, vinyl ester, and ethylenically unsaturated carboxylic acid or its derivative The manufacturing method according to claim 1, wherein the ratio is X:Y=20:80 to 80:20 Z:(X+Y)=0.1:99.9 to 15:85.