JPH07224163A - Water absorbing resin and its production - Google Patents

Abstract

PURPOSE:To obtain a water absorbing resin useful for a sanitary material such as a diaper or a sanitary napkin, a water retaining material for soil, etc., having excellent water absorption properties and hydrolytic action by partially cross-linking a polysuccinimide with a diamine compound, etc., and then hydrolyzing. CONSTITUTION:(A) A polysuccinimide having preferably g 20,000 weight-average molecular weight is reacted with (B) a diamine compound selected from preferably lysine, ornithine, cystine, cysteamine and their derivatives. The reaction is finished before the reaction solution is gelatinized and the reaction product is hydrolyzed while adjusting to pH preferably 8.0-11.5 in an aqueous solution to give the objective water absorbing resin. The amount of the component B added is preferably 1-30mol%. The water absorbing resin is made water-soluble by treating in an aqueous solution of NaOH at pH 12 at 95 deg.C for two hours and has >=50 times water absorption amount of distilled water by a tea bag method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is obtained by reacting polysuccinimide (polyaspartic anhydride) with a diamine compound and then hydrolyzing the reaction product, or polysuccinic acid in an aqueous solution. The present invention relates to a water absorbent resin obtained by hydrolyzing a reaction product while reacting an imide and a diamine compound, and a method for producing the water absorbent resin.

[0002]

2. Description of the Related Art As a resin that absorbs a large amount of water, a polymer compound called a super absorbent resin is known. These highly water-absorbent resins have a water-soluble polymer as a starting material, but basically have a crosslinked structure that makes them water-insoluble. Specific examples of such a super absorbent polymer include starch-acrylonitrile graft polymer partial hydrolyzate, starch-acrylic acid graft polymer, cross-linked resin obtained by crosslinking acrylic acid with a copolymerizable cross-linking agent, and methyl methacrylate. -A hydrolyzate of a vinyl acetate copolymer, a polyvinyl alcohol-based or a polyethylene oxide-based cross-linked product, and the like, some of which have already been put into practical use (Masuda, F., "Superabs").
orient polymers-charaster
istis and trends in dev
“location of application”, C
hem. Econ. Engineer. Rev. , Vo
l. 15, pp. 19-23 (1983)).

These highly water-absorbent resins are used in the field of sanitary materials such as diapers and sanitary products, the field of agricultural materials such as soil water retention materials and sheets for raising seedlings, the field of foods such as food freshness-retaining agents and dehydrating agents, and building connections. It is used for a wide range of applications such as civil engineering and building materials such as prevention sheets and waterproof seals. Since these super absorbent polymers do not undergo hydrolysis, they exist semipermanently in water or soil.

However, this durability is a desirable property for some applications, but in the case of disposable applications represented by sanitary materials such as diapers and sanitary products, the material does not easily decompose into low-molecular weight substances, and therefore it is discarded. This is a problem when we consider the environmental conservation that follows.

On the other hand, some techniques for obtaining a water-insoluble water-absorbing polymer by cross-linking polyamino acids having excellent safety and degradability have been reported or disclosed.

After esterifying the carboxyl side chain of a monoaminodicarboxylic acid (acidic amino acid) such as polyaspartic acid or polyglutamic acid, the side chain is crosslinked with a diamine to produce a water-insoluble water-absorbing polymer. Techniques have been disclosed (Akamatsu et al., U.S. Pat. No. 3,948,863; Japanese Patent Publication No. 52-41309). In this technique, a polyamino acid in which a side chain of a carboxyl group is esterified is used as a starting material, and the starting material is brought into contact with a polyvalent amine to aminate a part of the ester group of the side chain of the polyamino acid, and It is different from other conventional techniques in that a part or all of the ester group in the reaction is converted into a carboxyl group or a salt thereof.

Water-insoluble poly (tyrosine-glutamic acid) has been reported (Overell et al., Journal.
al of Chemical Society, Pa
rtI, "Polymers of Some Bas"
ic and Acidicalpha-Amino-
Acids ", pp232-236, 1955). However, there is no disclosure about the possibility of applying the produced polypeptide to a water-insoluble hydrogel and the technique for achieving high water absorption capacity.

A technique for irradiating poly-γ-glutamic acid with γ-rays to crosslink the polymer to produce a water-insoluble water-absorbent polymer has been reported (Kunioka et al., Polymers Collection,
50, No. 10, 755 (1993)). From an academic point of view, this technique is interesting because it allows polyamino acids that are sensitive to heating to react at low temperatures. However, from an industrial point of view, the ⁶⁰ Co irradiation equipment required for this technique has an extremely large amount of shielding and is not realistic in that it requires management of leaked γ-rays after completion of irradiation. Further, from an economical point of view, polyglutamic acid as a starting material is expensive, which is a problem.

A technique of crosslinking an acidic amino acid polymer with lysine-diketopiperazine to produce a hydrophilic biodegradable polymer has been disclosed (Iwatsuki et al., JP-A-5-2794).
16). However, there is a problem in that it is difficult to prepare the cross-linking agent lysine-diketopiperazine.

A mixture of α-amino acids is dehydrated and condensed by heating to a high temperature of 150 ° C. or higher to form a protein-like protein (proteinoid) (Fox and Harada,
Science, vol. 128, p. 1214 (19
58) and; Am. Chem. Soc. , Vo
l. 82, pp. 3745-3751 (1959)).
In this synthesis, for unknown reasons, the presence of excess monoaminodicarboxylic acid (acidic amino acid) is necessary. However, at temperatures above 210 ° C., these amino acids are pyrolyzed and the usefulness of the excess monoaminodicarboxylic acid is lost (Fox and Wi).
ndsor, InternationalJourna
l of Quantum Chemistry; Qu
antum Biology, vol. 11, pp. 1
03-108 (1984)).

A technique for producing a water-soluble polypeptide by a dehydration condensation method by heating has been disclosed (Fox).
Et al., U.S. Pat. No. 4,996,292). However, there is no disclosure about the possibility of applying the produced polypeptide to a water-insoluble hydrogel and the technique for achieving a high water absorption capacity.

A technique has been reported in which a specific amino acid residue in an anionic polypeptide is crosslinked by a dehydration condensation method by heating. That is, a technique for producing a water-insoluble cross-linked polypeptide by heating glutamic acid and lysine, or aspartic acid or polyaspartic acid and lysine by a method of dehydration condensation by heating is disclosed (Donachy and Sikes, Special Table). Flat 6
-506244, U.S. Pat. Nos. 5,247,068 and 5,284,936).

However, the reaction temperature of the dehydration condensation by heating disclosed is 190 to 250 ° C., but this temperature range is extremely high for amino acids or polyamino acids, and the polymer produced by partial decomposition or side reaction is generated. This is a problem in that quality deterioration and coloring are unavoidable. Also, the water absorption capacity of the produced polymer is insufficient. Furthermore, as a technique for improving the water absorption capacity of the produced crosslinked polyamino acid, the polyamino acid is
A method of performing alkaline hydrolysis treatment at H11 to 12 and 80 to 95 ° C for 1 to 2 hours is disclosed. This is
The produced crosslinked polyamino acid is shown to be resistant to the water-insoluble hydrogel even under the alkaline treatment under such conditions, suggesting that the degradability is low.

[0014]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the problems of the prior art of the water absorbent resin as described above and to provide a highly water absorbent polymer having excellent water absorbing ability and resolution. is there.

[0015]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that polysuccinimide is partially crosslinked with a diamine compound and then hydrolyzed, or in an aqueous solution. It was found that a resin having excellent water absorbency and hydrolyzability can be obtained by hydrolyzing while reacting a polysuccinimide and a diamine compound, and completed the present invention.

That is, according to the present invention, polysuccinimide obtained by dehydration condensation of aspartic acid is reacted with a diamine compound in an aqueous solution or an organic solvent to partially crosslink and adjust the pH of the remaining imide portion. A method for obtaining a resin having excellent water absorption and hydrolyzability by performing alkaline hydrolysis while providing a water absorbent resin having excellent water absorption and hydrolyzability thus obtained Is.

The present invention will be described in more detail below.

The method for producing the polysuccinimide used in the present invention is not particularly limited, but it is usually produced by heating aspartic acid in the presence of phosphoric acid in a vacuum at 170 to 180 ° C. for dehydration condensation. . In order to obtain a higher molecular weight polysuccinimide, the polysuccinimide obtained as described above may be treated with a condensing agent such as dicyclohexylcarbodiimide. The molecular weight of the polysuccinimide may be such that the polymer after crosslinking becomes water-insoluble, and it is preferable that the weight average molecular weight is 20,000 or more.

The diamine compound used in the present invention has an amino group in the side chain represented by, for example, aliphatic diamine such as ethylenediamine and hexamethylenediamine, alicyclic diamine such as norbornenediamine, lysine and ornithine. Amino acids and their derivatives, cystine,
Examples include monoamino compounds represented by cystamine and the like, which are linked by a disulfide bond, and derivatives thereof. Among these, preferable are lysine, ornithine, cystine, cystamine and derivatives thereof, which are highly safe from polymer degradation products. Examples of the derivative include diketopiperazine, which is a cyclic dimer of lysine and ornithine, and esters of lysine, ornithine and cystine.

The diamine may be used in an amount such that the resulting polymer is substantially water-insoluble and exhibits high water absorption,
The amount is preferably 0.1 to 40 mol%, more preferably 1 to 30 mol%, based on the polysuccinimide. When the amount of the diamine used is reduced, the water solubility of the polymer is increased, and when the amount is increased, the water absorption is reduced. Therefore, depending on the purpose, by appropriately setting the amount of the diamine used, desired properties can be expressed. .

As a method of reacting the polysuccinimide and the diamine, there are a method carried out in an organic solvent and a method carried out in an aqueous solution.

[Method of reacting polysuccinimide and diamine in organic solvent] In the method of reacting polysuccinimide and diamine in an organic solvent, polysuccinimide and dimethylformamide (DMF) or dimethylacetamide (DMAc) are used. ), N-methylpyrrolidone (NM
P), dimethyl imidazolidinone (DMI), dimethyl sulfoxide (DMSO), sulfolane, or another aprotic polar organic solvent, and then diamine or a diamine solution of the organic solvent is added dropwise. At this time, the amount of the organic solvent used to dissolve the polysuccinimide is not particularly limited, but usually, the polymer concentration is 1 to 30 wt.
% To use.

The temperature at which the polysuccinimide and the diamine are reacted is not particularly limited, but usually room temperature is selected.

One of the important characteristics of the method used in the present invention is that the reaction is terminated before or just before the reaction mass changes to a jelly-like gel to the extent that stirring is substantially difficult. It is to select reaction conditions (reaction temperature, reaction time, reaction concentration, amount of diamine used, etc.). Thus, by terminating the reaction before or immediately before the reaction mass gels, the subsequent isolation operation can be realized very easily, and the production of a polymer having excellent water absorption can be realized. realizable. In contrast to the method used in the present invention, when the reaction mass gels, the hydrolysis reaction becomes insufficient, and as a result, it is difficult to obtain a polymer having a sufficiently high water absorption.

Isolation of the crosslinked polymer formed in the reaction includes
Known conventional isolation procedures such as recrystallization, reprecipitation, filtration,
Operations such as concentration can be used.

After the produced crosslinked polymer is isolated, the imide ring of the isolated crosslinked polymer is hydrolyzed. In the hydrolysis, it is possible to substantially maintain the stirring of the reaction system, the hydrolysis efficiency of the imide ring is sufficient, the hydrolysis degree of the amide bond of the main chain is small, and the pH can be controlled. If possible, the reaction conditions (reaction system, pH, temperature, polymer concentration, type of alkali, concentration of alkali, etc.) are not particularly limited.

The reaction system for hydrolysis of the crosslinked polymer is usually preferably a method of suspending the crosslinked polymer in an aqueous solution. The pH of the crosslinked polymer during hydrolysis is usually 8.0.
˜11.5 is preferable, and 9.0 to 11.0 is more preferable. When the value is lower than this preferable numerical range, the efficiency of hydrolysis of the imide ring becomes lower, and when the value is higher, the degree of hydrolysis of the amide bond in the main chain becomes larger. The polymer concentration during hydrolysis of the crosslinked polymer generally becomes faster as the amount of water increases, but when productivity is taken into consideration, the polymer concentration is preferably 0.5 to 10 wt%.

Specific examples of the alkali used for the hydrolysis of the crosslinked polymer include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and organic bases such as triethylamine, N-methylmorpholine, triethanolamine and diisopropylethylamine. can give.

The alkali used for the hydrolysis of the crosslinked polymer is usually used as an aqueous solution thereof, and its concentration is substantially sufficient for the hydrolysis of the imide ring and the degree of hydrolysis of the amide bond of the main chain. The concentration is not particularly limited as long as it is small and the pH can be controlled.
0.01 normal to 5 normal is preferable, and 0.1 to 2 normal is more preferable. When the value is lower than this preferable numerical range, the efficiency of hydrolysis of the imide ring becomes lower, and when the value is higher, the degree of hydrolysis of the amide bond in the main chain becomes larger.

[Method of reacting polysuccinimide and diamine in aqueous solution] A preferred embodiment of the reaction system of this method is a system in which polysuccinimide is suspended in water and reacted. The amount of water used in this suspension reaction system is not particularly limited as long as the stirring of the reaction system can be substantially maintained, but usually,
The weight ratio is preferably 6 to 20 times that of polysuccinimide. If the value is smaller than this preferable range, stirring becomes difficult, and if it is larger, the reaction rate of hydrolysis tends to be faster.

A preferred embodiment of the method of reacting polysuccinimide and diamine is a method of dropping a diamine or an aqueous solution of diamine into an aqueous suspension of polysuccinimide. When the diamine is present as a salt, it is preferably neutralized first and then added dropwise.

Also in the method of reacting polysuccinimide and diamine in an aqueous solution, hydrolysis is substantially
The stirring of the reaction system can be maintained, the efficiency of hydrolysis of the imide ring is sufficient, and the degree of hydrolysis of the amide bond of the main chain is small,
The reaction conditions (reaction system, pH, temperature, polymer concentration, type of alkali, concentration of alkali) are not particularly limited as long as it is possible to control pH.

While adjusting the pH by adding an alkali, the crosslinking reaction between the imide ring of polysuccinimide and the diamine proceeds, and at the same time, the remaining imide ring is hydrolyzed. The pH at this time is usually preferably 8.0 to 11.5,
9.0 to 11.0 is more preferable. The lower the value from this preferable range, the lower the efficiency of hydrolysis of the imide ring, and the higher the value, the greater the degree of hydrolysis of the amide bond in the main chain, which is not desirable.

When the method of reacting polysuccinimide and diamine in such an aqueous solution is adopted, as the reaction progresses, the polymer absorbs water and swells, so that it is necessary to maintain uniform stirring. It is preferable to add water. The amount of water added at this time is not particularly limited as long as stirring can be substantially maintained, but it is appropriately selected depending on the type and amount of the diamine to be added, but usually, the final polymer concentration is 0.1 to 2 wt%. It is preferable to adjust so that

The temperature at which the polysuccinimide and the diamine are reacted is not particularly limited, but is usually room temperature.

Specific examples of the alkali used in the reaction include:
Examples thereof include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and organic bases such as triethylamine, N-methylmorpholine, triethanolamine and diisopropylethylamine.

The alkali used in the reaction is usually used as an aqueous solution thereof, and the concentration thereof is substantially sufficient for the hydrolysis of the imide ring, the degree of hydrolysis of the amide bond of the main chain is small, and The concentration is not particularly limited as long as it can be controlled, but 0.01 to 5 normals is preferable, and 0.1 to 2 normals is more preferable. The lower the value from this preferable range, the lower the efficiency of hydrolysis of the imide ring, and the higher the value, the greater the degree of hydrolysis of the amide bond in the main chain, which is not desirable.

For the isolation of the crosslinked polymer formed in the reaction,
Known conventional isolation procedures such as recrystallization, reprecipitation, filtration,
Operations such as concentration can be used.

The appearance of the water-absorbent resin thus isolated is a colorless to pale yellow powder, and when it absorbs water, it becomes a transparent to colorless swollen gel.

[Characterization of Water-Absorbent Resin by Evaluation of Alkali Resistance] The water-insoluble cross-linked polypeptide water-absorbent resin can be characterized by the behavior of change from gel to water solubility by alkali treatment. As used in this application, the term "water-soluble" refers to a water-insoluble dry water-absorbent resin.
A dispersion liquid was prepared by adding sodium hydroxide and distilled water so as to have a pH of 12 by weight%, the dispersion liquid was treated at 95 ° C. for 2 hours, and then the residue collected by filtration with a filter paper having a retained particle diameter of 5 μm was dried. The weight is 10 times the dry weight of the original water absorbent resin.
% Or less.

The water-insoluble crosslinked polypeptide is improved in water absorption at a pH of 11 to 12 and at 80 to 95 ° C. for 1 to 2
A method of performing an alkaline hydrolysis treatment for a time is known (D
onachy and Sikes, Tokuyo Hyo 6-506244
Nos. 5,247,068 and 5,284,931.
No. 6). That is, it is shown that the crosslinked polyamino acid produced by this technique is resistant to the water-insoluble hydrogel even under the alkaline treatment under such conditions, suggesting that the degradability is low.

In contrast to the crosslinked polyamino acid produced by this technique, the water-absorbent resin of the present invention easily becomes water-soluble when subjected to the alkaline treatment under such conditions.

The difference in the behavior of the change from gel to water-soluble by the alkali treatment is that the primary, secondary or higher order structure of the water absorbent resin and the crosslinked state (density, uniformity, length of bridge, etc.). , Hydration property, charge state (density, balance, homogeneity, etc.), secondary bond (van der Waals bond, hydrogen bond,
It is considered to reflect molecular-level characteristics such as hydrophobic bond), and can also be used as a measure of hydrolysis property. Therefore, the difference in the behavior of the change from gel to water-soluble due to the alkali treatment can be evaluated as the difference in the overall molecular structure of the water-absorbent polymer.

[Methodology of Characterization of Water-Absorbent Resin by Evaluation of Water-Absorbency] The water-insoluble crosslinked polypeptide water-absorbent resin can be characterized by its water-absorbing behavior.

The maximum characteristic of the water-absorbent resin is literally its water-absorbing ability, and although the evaluation method for this characteristic is extremely important, it is not always standardized by those skilled in the art. It is not specified in Japanese Industrial Standards either. Therefore, even for the same sample, the results may vary greatly depending on the evaluation method, so it is necessary to select the optimum evaluation method according to the purpose. The water absorbing ability of the water absorbent resin is mainly classified into three types: suction force, holding force and gelling force. The suction force is, for example, the use of a paper towel or the like, the holding force is, for example, the use of a diaper, a sanitary napkin, a sanitary tampon or a soil water retention material, and the gelling force is, for example, the use of a sludge coagulant or the like. It becomes an index of practical performance (Water-absorbing polymer, Masuda, Kyoritsu Shuppan, 198
7 years, pp. 51-56).

Considering that the diapers, sanitary napkins, sanitary tampons, and water absorbent resins for soil water-retaining materials are the main applications, the holding power is a particularly important index. Against this background, tea bags that have the advantage of being highly correlated with the practical performance of diapers, sanitary napkins, sanitary tampons, and soil water retention materials, yet simple and highly reproducible In Japan, where water-absorbent resins are actively researched and developed, water-absorbing polymers are becoming the mainstream of water-absorbing capacity evaluation (water-absorbing polymer, Masuda, Kyoritsu Shuppan, 1987
51-56; Harada et al., JP-A-5-170835; Kurane et al., JP-A-5-301904).

Examples of methods for evaluating holding power other than the tea bag method include filtration method, centrifugal dehydration method, sheet method and blue dextran method (water-absorbing polymer, Masuda, Kyoritsu Shuppan, 1987, pp. 51-56). ). When considering the correlation with the practical performance of diapers, sanitary napkins, sanitary tampons, and soil water retention materials, the filtration method and centrifugal dehydration method may perform better than they actually are, depending on the type of water absorbent resin to be evaluated and the test conditions. May be evaluated considerably higher, and the blue dextran method or the sheet method may be evaluated as performance much lower than the actual performance. Therefore, when these evaluation methods are used to compare the relative performances of different types of water-absorbent resins, there is a possibility that results that faithfully reflect practical performances may not be obtained.

For example, an evaluation method other than the tea bag method is adopted, such as US Pat. No. 5,247,068, which evaluates the water absorbing ability of a water absorbent resin by adopting a centrifugal dehydration method of centrifuging at 1300 × g for 15 minutes. There is a case.

However, in the present application, from the background described above, the water absorption capacity of the water-absorbent resin was evaluated by employing the tea bag method, which has a very high correlation with practical performance and is simple and highly reproducible. The tea bag method adopted in the present application was based on the method described in JP-A-5-170835 and JP-A-5-301904.

[Characterization of Water-Absorbing Resin by Evaluation of Water-Absorbing Property] The water-absorbing resin of the present invention has an excellent water absorbing ability. The water-absorbent resin according to the present invention has a water absorption capacity of 50 times or more that of distilled water and 25 times or more that of physiological saline (0.9% by weight saline) when evaluated by the tea bag method. Since the water-absorbent resin according to the present invention exhibits high water-absorbing ability, diapers, sanitary material fields such as sanitary products, soil water retention materials, agricultural material fields such as nursery sheets, food freshness-retaining agents,
Food field such as dehydrating agents, civil engineering such as building connection prevention sheets
Can be widely used as a building material. Further, since it is easily hydrolyzed with an alkali, it can be easily discarded or recycled / reused by an alkali treatment after being used for these purposes.

[0051]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

GPC: The weight average molecular weight (Mw) of polysuccinimide was measured by GPC using polystyrene as a standard, and Mw of polyaspartic acid or a water-soluble polymer after hydrolysis was standardized with polyethylene oxide.

The water absorption was measured by the following method.

Tea bag method: Dry water-absorbent resin about 0.1
g is a non-woven tea bag (80 mm x 100 mm)
Then, the resin was swollen for a certain period of time by immersing it in excess distilled water or physiological saline, and then the tea bag was pulled up and drained for 1 minute, and the weight was measured. The weight when performing the same operation only with the tea bag, as a blank,
The value obtained when the value obtained by subtracting the weight of the blank and the weight of the dry resin from the weight after absorption became constant was divided by the weight of the water-absorbent resin to obtain a water absorption amount (g / resin 1).
g).

Centrifugation method: About 0.1 g of the dried water-absorbent resin was placed in a centrifuge tube whose weight was previously measured, and the resin was swollen by immersing it in excess distilled water or physiological saline for 1 hour, then 1300 × Centrifuge at g for 15 minutes. After removing the supernatant with a pipette, the weight was measured and the water absorption (g / resin 1
g) was determined.

<Example 1 (reaction of polysuccinimide and diamine in organic solvent)> 3.0 g of polysuccinimide having Mw = 83,000 was dissolved in 18 g of DMF to prepare a solution.
1.5 g of a DMF solution of 0.54 g of hexamethylenediamine (15 mol% / polysuccinimide) was added dropwise at room temperature. After 2 minutes had passed after the completion of the dropping, the reaction solution did not gel, and ethanol was added to this solution to cause reprecipitation, filtration and drying to obtain 2.5 g of a crosslinked polymer.

300 g of 1.6 g of the crosslinked polymer obtained
Was suspended in water, and a 2N NaOH aqueous solution was added dropwise to adjust the pH to 9 to 11 to hydrolyze the remaining imide ring. The obtained reaction suspension was discharged into ethanol, filtered and dried to obtain 1.4 g of a water absorbent resin.

<Example 2 (Reaction of polysuccinimide and diamine in organic solvent)> 20 g of lysine methyl ester dihydrochloride 1.8 g (15 mol% / polysuccinimide) was used.
It was suspended in g DMF and neutralized with 1.6 g triethylamine. 25 g of a solution prepared by dissolving 5.0 g of polysuccinimide having Mw of 94,000 in DMF was inserted into the solution, stirred for 1 hour at room temperature, 1.6 g of triethylamine was added dropwise, and the mixture was reacted at room temperature for 47 hours. Then, the reaction solution was filtered before gelling, and the filtrate was discharged into ethanol and dried to obtain 5.1 g of a crosslinked polymer.

500 g of 2.6 g of the crosslinked polymer obtained
Was suspended in water, and a 2N NaOH aqueous solution was added dropwise to adjust the pH to 9 to 11 to hydrolyze the remaining imide ring. The obtained reaction suspension was discharged into ethanol, filtered and dried to obtain 2.4 g of a water absorbent resin.

<Example 3 (Reaction of polysuccinimide and diamine in organic solvent)> The amount of lysine methyl ester dihydrochloride was 2.4 g (20 mol% / polysuccinimide).
The same operation as in Example 2 was carried out except that the desired water absorbent resin was obtained.

Example 4 (Reaction of polysuccinimide and diamine in organic solvent) The same operation as in Example 2 was carried out except that polysuccinimide having Mw of 188,000 was used to obtain desired water absorption. A resin was obtained.

<Example 5 (Reaction of polysuccinimide and diamine in organic solvent)> Using polysuccinimide with Mw = 16,000, the amount of lysine methyl ester dihydrochloride was 3.6 g (30 A desired water-absorbent resin was obtained by performing the same operation as in Example 2 except that (mol% / polysuccinimide) was used.

Example 6 (Reaction of polysuccinimide and diamine in aqueous solution) 3.0 g of polysuccinimide having Mw = 69,000 was suspended in 30 g of water, and the suspension was mixed with water. A solution in which 0.54 g of hexamethylenediamine (15 mol% / polysuccinimide) was dissolved in 2.0 g was slowly added dropwise at room temperature. After this time, add 2N NaO to the reaction suspension.
The remaining imide ring was hydrolyzed while dropping the aqueous H solution and adjusting the pH to 9-11. 300 g of water was added on the way and the reaction was carried out at 24 ° C. for 20 hours. The resulting reaction suspension was allowed to stand, the supernatant was removed, and the mixture was discharged into 1.5 liters of isopropyl alcohol (IPA), filtered and dried to obtain 2.4 g of a water absorbent resin.

The elemental analysis values of the resulting water absorbent resin are shown below.

[0065] <Example 7 (Reaction of polysuccinimide and diamine in aqueous solution)> A desired water-absorbent resin was obtained by the same operation as in Example 6 except that polysuccinimide having Mw of 168,000 was used. Obtained.

<Example 8 (Reaction of polysuccinimide and diamine in aqueous solution)> Example 6 except that the amount of hexamethylenediamine was 0.27 g (7.5 mol% / polysuccinimide). The same operation was performed to obtain the desired water absorbent resin.

<Example 9 (Reaction of polysuccinimide and diamine in aqueous solution)> Example 6 except that polysuccinimide having Mw = 108,000 was used and ethylenediamine was used instead of hexamethylenediamine. The same operation was performed.

The elemental analysis values of the resulting water absorbent resin are shown below.

[0069] <Example 10 (Reaction of polysuccinimide and diamine in aqueous solution)> 3.0 g of polysuccinimide having Mw of 108,000 was suspended in 30 g of water. On the other hand, cystamine
1.0 g of 2HCl (15 mol% / polysuccinimide) was dissolved in 6.0 g of water to prepare an 8% NaOH aqueous solution 4.7.
The solution neutralized with g was slowly added dropwise to the suspension at room temperature. After that, a 2N NaOH aqueous solution was added dropwise to the reaction suspension, and the remaining imide ring was hydrolyzed while adjusting the pH to 9 to 11. 300 g of water was added on the way and the reaction was carried out at 24 ° C. for 25 hours. The resulting reaction suspension was allowed to stand, the supernatant was removed, and then the mixture was discharged into 1.5 liters of IPA, filtered and dried to obtain 4.5 g of a water absorbent resin.

The elemental analysis values of the resulting water absorbent resin are shown below.

[0071] Comparative Example 1 10 g of polysuccinimide having Mw of 108,000 was dissolved in 60 g of DMF. To the solution, 8.8 g of a DMF solution containing 1.8 g of hexamethylenediamine (15 mol% / polysuccinimide) was added dropwise at room temperature. After the reaction was completed, the reaction solution gelled. Since a part of DMF exudes from the gel when left standing overnight, the gel was separated, washed with IPA and then dried to obtain 13 g of a crosslinked polymer.

The crosslinked polymer (5.5 g) was suspended in 130 g of water, and a 2N NaOH aqueous solution was added dropwise to adjust the pH to 9-11.
The imide ring was hydrolyzed while adjusting to. Reaction is 2
It was carried out at 4 ° C. for 50 hours. The resulting reaction suspension is allowed to stand,
After removing the supernatant, the mixture was discharged into 0.6 L of IPA, filtered and dried to obtain 3.5 g of a water absorbent resin.

The elemental analysis values of the resulting water absorbent resin are shown below.

[0074] <Comparative Example 2> The same operation as in Comparative Example 1 was performed except that polysuccinimide having Mw of 168,000 was used and ethylenediamine was used instead of hexamethylenediamine.

The elemental analysis values of the resulting water absorbent resin are shown below.

[0076] Comparative Example 3 1.8 g of lysine methyl ester dihydrochloride
(15 mol% / polysuccinimide) 20 g of DMF
And was neutralized with 1.6 g of triethylamine. 5.0 g of polysuccinimide with Mw of 108,000
Was added to DMF, 25 g of the solution was added, the mixture was stirred for 1 hour at room temperature, 1.6 g of triethylamine was added dropwise, and the mixture was reacted at room temperature for 50 hours to gel the reaction solution. The gel is taken out, washed with IPA, and then dried to give 6.8 g of crosslinked polymer.
Got

2.6 g of the obtained crosslinked polymer was suspended in 40 g of water, and 2N NaOH aqueous solution was added dropwise to adjust the pH to 9
The remaining imide ring was hydrolyzed while adjusting to -11. The reaction was carried out at 23 ° C. for 16 hours. The resulting reaction suspension was allowed to stand, the supernatant was removed, and then 0.5 liter of I
It was discharged to PA, filtered and dried to obtain 2.4 g of a water absorbent resin. The elemental analysis value of the obtained water absorbent resin is shown.

[0078] <Comparative Example 4> Polysuccinimide with Mw of 50 thousand 2.
9 g was suspended in 26 g of water, a 2N NaOH aqueous solution was added dropwise, and hydrolysis was performed while adjusting the pH to 9-11.
After neutralizing this, 2.0 g of aspartic acid and 1.4 g of lysine hydrochloride were added and reacted at 220 ° C. for 18 hours. To this, 500 g of water was added for sufficient swelling, washing and drying to obtain 1.9 g of a crosslinked polymer.

90 g of the obtained crosslinked polymer 0.90 g
Suspension in water, add 2N NaOH aqueous solution dropwise, and adjust to pH 9
Hydrolyzed at ~ 11. The obtained reaction suspension was filtered and dried to obtain 0.87 g of a brownish-colored water absorbent resin.

<Comparative Example 5> 4.1 g of sodium polyaspartate having Mw of 51,000 was suspended in 50 g of water, and HCl was added thereto.
After neutralizing with 0.92 g of lysine hydrochloride,
The reaction was carried out at 20 ° C. for 18 hours. To this, 500 g of water was added for sufficient swelling, filtration, washing and drying to obtain 3.5 g of a crosslinked polymer.

2.0 g of the obtained crosslinked polymer was suspended in 45 g of water, and the suspension was suspended in a pH 12 aqueous NaOH solution at 95 ° C. for 2 hours.
Hydrolyzed for hours. The obtained reaction suspension was filtered and dried to obtain 1.9 g of a brownish-colored water absorbent resin.

Table 1 shows the water absorption (g / resin 1 g) of the water-absorbent resins obtained in Examples 1 to 10 and Comparative Examples 1 to 5 measured by the tea bag method and the centrifugal separation method.

[0083]

[Table 1] <Example 11> 1.0 g of the water absorbent resin obtained in Example 2
Suspended in 30 g of a pH 12 aqueous NaOH solution at 95 ° C.
After being hydrolyzed for 2 hours, the polymer became water soluble.

<Example 12> 1.0 g of the water-absorbent resin obtained in Example 6 was suspended in 50 g of a 1N NaOH aqueous solution and hydrolyzed at 60 ° C. It became completely water-soluble after 1 hour of reaction. After that, Mw decreased with the passage of time. The results are shown in Table 2.

[0085]

[Table 2] <Comparative Example 6> 1.0 g of the water absorbent resin obtained in Comparative Example 4 was suspended in 30 g of an aqueous NaOH solution having a pH of 12, and the suspension was heated at 95 ° C for 2 hours.
The polymer remained a gel even after hydrolysis for a period of time.

FIG. 1 is a graph showing the alkali hydrolyzability of the polymers obtained in Example 2 and Comparative Example 5. That is, the change over time in the hydrolysis behavior when treated at pH 12 and 95 ° C. was determined by the residual ratio of the dried residue of the polymer collected by a filter paper having a retention particle size of 5 μm, and the weight average molecular weight of the polymer in the filtrate. evaluated.

[0087]

The novel water absorbent resin according to the present invention has excellent water absorbing ability and hydrolyzing ability. Further, according to the production method of the present invention, a water absorbent resin having such excellent characteristics can be easily produced. Since the water-absorbent resin according to the present invention has a high practical water-absorbing ability, it is used in the field of sanitary materials such as diapers and sanitary products, soil water-retaining materials, agricultural materials such as sheets for raising seedlings, food freshness-retaining agents, foods such as dehydrating agents It can be used in a wide range of fields such as civil engineering and building materials such as connection prevention sheets for buildings. Further, since it is easily hydrolyzed with an alkali, it can be easily discarded or recycled / reused by an alkali treatment after being used for these purposes. Furthermore, since it has excellent hydrolysis performance, it is a material that is friendly to the environment and living bodies.

[Brief description of drawings]

FIG. 1 is a graph showing the alkali hydrolyzability of the polymers obtained in Example 2 and Comparative Example 5.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiro Yamaguchi 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (10)

[Claims] 1. A method for producing a water absorbent resin, which comprises reacting a polysuccinimide and a diamine compound and then performing a hydrolysis reaction of a reaction product while adjusting pH in an aqueous solution. 2. The production method according to claim 1, wherein the polysuccinimide and the diamine compound are reacted with each other, and the reaction is terminated before the reaction solution gels. 3. A method for producing a water absorbent resin, which comprises hydrolyzing a reaction product while reacting a polysuccinimide and a diamine compound in an aqueous solution while adjusting pH. 4. The pH of the hydrolysis reaction is 8.0 to 11.5.
The manufacturing method according to claim 1 or 3, wherein 5. The diamine compound is lysine, ornithine,
The production method according to claim 1 or 3, which is selected from the group consisting of cystine, cystamine and derivatives thereof. 6. The method according to claim 1 or 3, wherein the polysuccinimide has a weight average molecular weight of 20,000 or more. 7. The addition amount of the diamine compound is 1 to 30 mo.
It is 1%, The manufacturing method of Claim 1 or 3. 8. A water absorbent resin produced by the method according to claim 1. 9. 95 ° C. in a pH 12 aqueous NaOH solution,
A water-absorbent resin, which becomes water-soluble by being treated for 2 hours. 10. The water absorbent resin according to claim 8, which has a water absorption amount of 50 times or more that of distilled water by a tea bag method.