JPS6335644B2 - - Google Patents

Description

Detailed Description of the Invention The present invention involves reacting a monovalent metal hydroxide to a polymer containing a hydroxyl group to convert all or part of the hydrogen in the hydroxyl group into an alkali metal, and then forming a cyclic acid anhydride in an anhydrous state. The present invention relates to a method for producing a superabsorbent polymer obtained by reacting a carboxyl group and/or a metal salt thereof to the polymer by esterification, and simultaneously or thereafter generating a crosslinking bond.

Recently, many superabsorbent resins have been proposed that have ionizable groups such as carboxyl groups in their molecules and have a network-like structure due to intermolecular cross-linking.
It has begun to be used for various purposes such as sanitary napkins, water absorbing agents for disposable diapers, soil water retaining agents, dehydrating agents, and medical applications. Known examples of such resins include resins obtained by graft polymerizing acrylonitrile onto starch and hydrating the nitrile groups, resins obtained by graft polymerizing acrylic acid onto starch, and polyacrylic acid resins having intermolecular crosslinks. ing.
However, these super absorbent resins are not necessarily satisfactory because their raw materials are expensive, their carboxyl group content is low and their hydrophilicity or water absorption is insufficient, or their manufacturing methods are complicated. .

The present inventor conducted studies to improve these problems, and found that a polyvinyl alcohol-based polymer was reacted with a cyclic acid anhydride under anhydrous conditions, and a polymer into which carboxyl groups were introduced through esterification was an extremely useful hydrophilic polymer. discovered that a polymer with high water absorption performance can be obtained by forming intermolecular crosslinks in the polymer,
A patent application was filed first.

However, when the polyvinyl alcohol used as a raw material has a high degree of saponification, the reaction is difficult to proceed. Similar phenomena were observed when other hydroxyl group-containing polymers such as various starches, polysaccharides, and various celluloses were used. In addition, in the above-mentioned method, the carboxyl group introduced is in the acid type, and the resin obtained is acidic and has problems such as insufficient hydrophilicity and water solubility, and in many cases monovalent metal compounds, ammonia or ammonium A step of completely or partially neutralizing the carboxyl group with a compound, amine, or amine salt to form a carboxyl base salt was required.

As a result of repeated research on a method for modifying a hydroxyl group-containing polymer with a cyclic acid anhydride that does not have the above-mentioned difficulties, the present inventor found that
We have discovered that the above object can be achieved by reacting a hydroxide of a valent metal to replace all or part of the hydrogen in the hydroxyl group with an alkali metal, and then reacting the cyclic acid anhydride in an anhydrous state. It has arrived.

The hydroxyl group-containing polymer used in the present invention is a synthetic or natural polymer having a hydroxyl group in the molecule, or a modified product thereof, and includes not only powdered polymers but also fibrous materials, film materials, and the like. for example,
Polyvinyl alcohol polymers, various starches such as corn starch, wheat starch, tapioca starch, potato starch, oxidized starch, modified starches such as dextrin, various polysaccharides such as guar gum and locust bean gum, pulp, cotton, hemp, Examples include various celluloses such as sugarcane pulp and straw.

Examples of monovalent metal hydroxides used in the present invention include lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like. These are usually used in the form of concentrated aqueous solutions to treat hydroxyl group-containing polymers. The concentration is preferably in the range of 5 to 50% by weight, and the amount of the aqueous solution used is preferably in the range of 2 to 10 times the amount of the resin.

The cyclic acid anhydride used in the present invention is a polyhydric carboxylic acid anhydride having a cyclic structure, and specifically includes maleic anhydride, succinic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, and phthalic anhydride. Acids, trimellitic anhydride, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, hectic anhydride, etc. can be mentioned. The amount of these hydroxyl group-containing polymers used is preferably in the range of 10 to 500 parts by weight per 100 parts by weight of the polymer.

The reaction of a cyclic acid anhydride with a polymer in which hydrogen in a hydroxyl group is replaced with an alkali metal is usually carried out in a solvent that does not have reactivity with the cyclic acid anhydride. Examples of such solvents include benzene, toluene, xylene, hexane, cyclohexane, acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, and the like.
In addition, in order to facilitate the progress of the reaction, dimethyl sulfoxide, N-methylmorpholine/N-
A swelling agent such as an acetamide solution of oxide or lithium chloride can be used as a solvent, or a mixture of the above-mentioned solvent and swelling agent can also be used. The amount of these used is preferably in the range of 2 to 10 times the amount of the polymer.

The reaction of a monovalent metal hydroxide with a hydroxyl group-containing polymer in the present invention is usually carried out by immersing or dispersing the polymer in an aqueous solution of a monovalent metal hydroxide, and stirring is performed as necessary. . The treatment temperature is preferably in the range of room temperature to 100°C, and the treatment time is preferably in the range of several minutes to several hours. After the reaction, the aqueous solution is removed by methods such as decanting, filtration, centrifugation, and squeezing, and the remaining moisture in the polymer is removed by air drying, heat drying, vacuum drying, and the like. It is preferable to remove moisture as completely as possible. If water remains, it is not preferable because it will react with the cyclic acid anhydride in the next step and produce carboxylic acid as a by-product. The desired degree of substitution of hydrogen in the hydroxyl group with an alkali metal can be obtained by controlling the amount, concentration, treatment temperature, time, etc. of the aqueous alkali solution. Usually, the degree of substitution is preferably in the range of 10 to 100 mol%.

The next step of reaction with the cyclic acid anhydride is generally carried out by immersing or dispersing the polymer in the solvent, then adding and dissolving the desired amount of the cyclic acid anhydride, heating, and stirring. . Since the reaction proceeds in a heterogeneous system throughout, it is desirable to carry out the reaction under stirring so that the hydroxyl group-containing polymer is modified as homogeneously as possible. The reaction occurs when the alkali metal-substituted hydroxyl group or acid type hydroxyl group in the polymer is esterified, and a carboxyl group (salt) is introduced into the side chain of the polymer. At this time, by appropriately selecting the reaction temperature, reaction time, degree of esterification, type of cyclic acid anhydride, etc., it is possible to simultaneously carry out the diesterification reaction and introduce intermolecular cross-linking. In some cases, it is also possible to produce a polymer that does not contain crosslinks and heat-treat the polymer to introduce crosslinks. At this time, polyfunctional epoxy compounds, polyfunctional isocyanates, polyvalent metal compounds, polyvalent amines, polyfunctional methylol compounds (dimethylol urea, methylol melamine, etc.) can also be used as crosslinking agents. The heat treatment is carried out by heating the reaction mixture as it is, or after separating the resin from the reaction mixture and subjecting it to some form of molding, to 50 to 200°C, preferably 80 to 150°C. The heating time is usually several minutes to several hours, and the heating temperature and time are preferably selected so as to form one to several dozen crosslinks per polymer. Since the water absorption performance is significantly influenced by the crosslink density, it is preferable to control the crosslink density so as to obtain the desired water absorption capacity. As the reaction between the polymer and the cyclic acid anhydride progresses, the resin usually swells and becomes enlarged, making it possible to observe the reaction situation with the naked eye to some extent. Since the reaction proceeds almost quantitatively, the cyclic acid anhydride may be used in an amount necessary to bring the polymer to the desired degree of esterification. The degree of esterification is usually preferably in the range of 10 to 100 mol%. The reaction temperature is usually 30-200℃, preferably 50℃
~150℃ range. Reaction time is usually 10 minutes to 10
time, preferably in the range of 1 to 5 hours.

Usually, the reaction mixture after the reaction is in a state where the swollen modified resin is dispersed in the solvent, so it is possible to separate the resin part by methods such as filtration or centrifugation, and collect the filtrate for reuse. can. Finally, the resin is washed and dried.

The modified resin obtained as described above is usually in the form of a white or pale yellow powder, fiber, film, etc., and intermolecularly crosslinked resin is soaked in several times to hundreds of times its own weight of water for several seconds. It has excellent water absorption ability, absorbing water within minutes. Therefore, intermolecularly cross-linked products can be used as water-absorbing agents for sanitary napkins and disposable diapers, for dehydration of water in various organic solvents and petroleum, for dehydration and concentration of various emulsions, as water retention agents for soil, for fire extinguishing purposes, for medical purposes, etc. It is expected to have wide demand.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited only to these Examples.

Example 1 50 g of polyvinyl alcohol powder (polymerization degree 1700, saponification degree 99 mol%, particle size 100-200 mesh)
It was placed in a 500 c.c. wide mouth bottle, immersed in 400 c.c. of an 18% aqueous sodium hydroxide solution for 1 hour at room temperature, and as much liquid as possible was removed using a centrifuge. The obtained mercerized polyvinyl alcohol was dried under reduced pressure at 40°C to remove as much moisture as possible. Next, put all of the above mercerized polyvinyl alcohol into a 500 c.c. three-necked separable flask, add 30 g of maleic anhydride, 10 c.c. of dimethyl sulfoxide, and 190 c.c. of toluene, and stir the reaction at 120°C for 3 hours. I forced it. The reaction proceeded in a suspension system. The reaction mixture was filtered, dried and weighed. The yield was 88g.

1 g of this modified PVA powder was added to 1 portion of water, and the water was sufficiently absorbed. (Water absorption equilibrium was almost reached in 5 minutes.)
After lightly touching the gel with filter paper to remove excess adhering water, the weight of the water-absorbing gel was measured and found to be 200 g. One gram of modified PVA showed excellent water absorption performance, absorbing 200 times more water extremely quickly.

Example 2 50 g of guar gum was placed in a 500 c.c. wide-mouthed bottle, 400 c.c. of a 15% aqueous sodium hydroxide solution was added thereto, and the mixture was left to react at room temperature for 1 hour. The reaction mixture was centrifuged to thoroughly remove the liquid, and the solid portion was dried under reduced pressure at 40°C.

In a 500c.c. three-neck separable flask, 55g of the above mercerized guar gum, 30g of phthalic anhydride, N-
Add 20 c.c. of methylmorpholine/N-oxide and 180 c.c. of xylene and react at 130°C for 4 hours with stirring.
Introduction of carboxyl groups and intermolecular cross-linking were performed simultaneously. The reaction mixture was filtered, and the solid portion was washed with methanol, filtered, dried, and weighed to obtain 84 g of a light yellow powdery resin.

The obtained resin has cross-linked bonds, so water,
Although it is insoluble in hot water, it has the ability to absorb 250 times its own weight in water within a few minutes. In addition, artificial urine (urea; 1.94%, NaCl; 0.80%, _MgSO4 .
The liquid absorption of 7H ₂ O (0.11%, CaCl ₂ (0.06%)) was 80 times its own weight.

On the other hand, a commercially available super absorbent resin produced by grafting acrylonitrile onto starch and then adding water had a water absorption rate of 200 times higher.
The absorption rate of artificial urine was 30 times higher. Therefore, the resin of this example is extremely useful as a water-absorbing agent for paper diapers and sanitary napkins.

Example 3 Put 100g of cotton pulp into a 1000c.c. wide-mouth bottle and add 18%
800 c.c. of potassium hydroxide aqueous solution was added and allowed to stand at room temperature for 1 hour to react. The reaction mixture was centrifuged to thoroughly remove liquid, and the solid portion was dried under reduced pressure at 40°C to remove as much water as possible.

Next, put the entire amount of the above mercerized pulp, 100 g of phthalic anhydride, 80 c.c. of N-methylmorpholine/N-oxide, and 720 c.c. of xylene into a 500 c.c. wide-mouthed bottle.
The reaction was allowed to proceed at 130°C for 5 hours without stirring to simultaneously introduce carboxyl groups and diester crosslinking, filter the reaction mixture, wash the resin with methanol, dry and weigh to obtain 230 g of pale yellow fibrous material. Ta.

The resulting modified pulp is cross-linked and therefore insoluble in both water and hot water, but it has the ability to absorb 80 times its own weight in water within a few minutes, and maintains its fibrous form even when it absorbs water. Ta. Also, when mixed with untreated cotton pulp and made into a sheet, it becomes a good water absorbing material.
It was suitable for paper diapers, sanitary napkins, etc.

Claims (1)

[Claims] 1. A monovalent metal hydroxide is applied to a polymer containing a hydroxyl group to completely or partially replace the hydrogen of the hydroxyl group with an alkali metal, and then a cyclic acid anhydride is reacted in an anhydrous state to form a monovalent metal by esterification. 1. A method for producing a highly water-absorbing polymer, which comprises introducing a carboxyl group and/or a metal salt thereof into the polymer and generating a crosslink at the same time or after that.