JPH0859820A - Water-absorptive resin and its manufacture - Google Patents

Abstract

PURPOSE: To obtain a water-absorptive resin that is excellent in ability of absorbing aqueous liquids and is biodegradable, by crosslinking an acidic polyamino acid with a basic polyamino acid. CONSTITUTION: An acidic polyamino acid ]e.g. a polyaspartic acid (salt)] and a basic polyamino acid (e.g. glycine-lysine) are mixed and heated to obtain a water-absorptive resin. This water-absorptive resin is excellent both in water absorptive ability and biodegradability and can retain the water absorptive ability under pressure, so that it can be used, for example, in the field of hygiene to be used as a hygiene material for sanitary articles, paper diapers, and the like as well as in the medical field, the field of civil engineering and construction, the field of food, the industrial field, and the field of agriculture and horticulture and can also be used as an oil-water separating material, a waste liquor absorbing material, a vibration-damping material, a sound-absorbent material. Since this water-absorptive resin is biodegradable, for example, by fungi and microorganisms in the soil, when it is simply buried in the soil, it is decomposed. Therefore, it can be simply discarded, is excellent in safety, and will not cause such a problem as environmental pollution.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a water absorbent resin and a method for producing the same. More specifically, it relates to a water-absorbent resin having excellent water-absorbing ability of an aqueous liquid and biodegradability, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, water-absorbent resins have been used not only as sanitary materials such as disposable diapers and sanitary products, but also in the medical field such as body fluid absorbents, civil engineering materials such as sealing materials (water blocking materials) and dew condensation prevention materials. -It is used in a very wide variety of fields, such as the field of construction, the field of food such as freshness-retaining materials, the field of industry such as dehydrating agents that remove water from solvents, and the field of agriculture and gardening such as greening. Various synthetic or semi-synthetic water-absorbent resins have been proposed according to these applications.

Of these various water-absorbent resins proposed, generally, a cross-linked polyacrylic acid (salt) -based totally synthetic water-absorbent resin has excellent water-absorbing ability and is inexpensive.
Widely used. However, a crosslinked polyacrylic acid (salt) -based water-absorbing resin (for example, JP-A-62-54751) has some photodegradability in a water-absorbing state, but almost no biodegradability. Therefore, when the water-absorbent resin is treated as a waste, for example, if it is disposed in a landfill, it is not decomposed by bacteria and microorganisms in the soil, which causes environmental health problems such as environmental pollution. That is, the crosslinked polyacrylic acid (salt) -based water-absorbent resin has a problem in disposal.

Therefore, various kinds of semi-synthetic water-absorbent resins such as (cross-linked) starch derivatives, (cross-linked) carboxymethyl cellulose, cross-linked hyaluronate, cross-linked alginate and the like have been proposed as biodegradable water-absorbent resins. (For example, JP-A-49-128987, JP-A-50-85689, JP-A-54-163981, JP-A-56-5137, JP-A-56-28755, Japanese Laid-Open Publication No. 57-137301,
JP 58-1701, JP 60-58443, JP
60-94401, JP-A-61-89364, JP-A-4-1614
31, JP-A 5-49925, JP-A 5-123573, JP-B-55-500785).

[0005]

However, the conventional water-absorbent resin, that is, the semi-synthetic water-absorbent resin, is biodegradable in the case of non-crosslinking, but is inferior in water-absorbing ability. Further, when the semi-synthetic water-absorbent resin is crosslinked to improve the water-absorbing ability, the biodegradability of the water-absorbent resin after crosslinking is significantly reduced. Therefore, the conventional water-absorbent resin has a problem that it is inferior in either water absorption capacity or biodegradability, and cannot be provided with a performance satisfying both of them. Therefore, the above-mentioned conventional water-absorbent resin is limited in applicable fields.

A water-absorbent resin obtained by graft-polymerizing a natural monomer with a hydrophilic monomer has also been proposed (see, for example, Japanese Patent Laid-Open Publication No. Sho.
56-76419 publication). However, the water absorbent resin is insufficient in both water absorption capacity and biodegradability.

Therefore, a water-absorbent resin excellent in both water-absorbing ability and biodegradability and a method for producing the same have been desired. That is, the present invention has been made in view of the above conventional problems, the object thereof is excellent in both water absorption capacity and biodegradability, moreover, it is possible to maintain the water absorption capacity even under pressure. It is to provide a resin and a manufacturing method thereof.

[0008]

Means for Solving the Problems In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies on a water-absorbent resin excellent in both water-absorbing ability and biodegradability and a method for producing the same. It was found that the water-absorbent resin obtained by mixing with a basic polyamino acid and heating has excellent performance which the above-mentioned conventional water-absorbent resins do not have, and completed the present invention.

That is, the water absorbent resin of the invention according to claim 1 is characterized in that, in order to solve the above problems, an acidic polyamino acid is crosslinked with a basic polyamino acid.

In order to solve the above-mentioned problems, the water-absorbent resin according to the second aspect of the present invention is the water-absorbent resin according to the first aspect, wherein the ratio of the basic polyamino acid to 100 parts by weight of the acidic polyamino acid is 0.1. It is characterized by being in the range of 100 parts by weight to 100 parts by weight.

In order to solve the above problems, the water-absorbent resin according to the third aspect of the present invention is the water-absorbent resin according to the first or second aspect, wherein the acidic polyamino acid is polyaspartic acid (salt). It has a feature.

[0012] In order to solve the above-mentioned problems, the water-absorbent resin according to a fourth aspect of the present invention is the water-absorbent resin according to the first, second or third aspect, wherein the water absorption capacity of physiological saline is 5 g / g or more. Moreover, the biodegradation rate is 10% or more.

In order to solve the above-mentioned problems, the method for producing a water-absorbent resin of the present invention is characterized in that an acidic polyamino acid is mixed with a basic polyamino acid and heated.

In order to solve the above-mentioned problems, the method for producing a water-absorbent resin according to a sixth aspect of the present invention is the method for producing a water-absorbent resin according to the fifth aspect, wherein an acidic polyamino acid and a basic polyamino acid are used. It is characterized in that an amino acid is added to the mixture.

In order to solve the above-mentioned problems, the method for producing a water-absorbent resin according to the invention of claim 7 is the method of claim 5 or 6.
In the method for producing a water-absorbent resin described, the heating temperature is 100
It is characterized by being in the range of ℃ to 300 ℃.

The present invention will be described in detail below. The acidic polyamino acid used as a raw material in the present invention is not particularly limited, but a linear compound is preferable because it has excellent biodegradability. The acidic polyamino acid in the present invention means a polyamino acid having more carboxyl groups than amino groups in one molecule.

Specific examples of the above-mentioned acidic polyamino acids include polyaspartic acid, polyglutamic acid, copolymers of aspartic acid and glutamic acid, copolymers of acidic amino acids with other amino acids, and these. Examples thereof include salts and esters. These acidic polyamino acids may be used alone, or two or more kinds may be appropriately mixed and used. Among these acidic polyamino acids, polyaspartic acid and salts and esters thereof are preferable. Examples of the above-mentioned salts include alkali metal salts such as sodium salt and potassium salt, ammonium salt and the like.

The above-mentioned acidic polyamino acid has a molecular weight of several thousands.
The range of tens of millions is preferable, and the range of tens of thousands to millions is more preferable. When the molecular weight of the acidic polyamino acid is smaller than the above range, the water absorbing ability of the resulting water absorbent resin does not reach the desired performance, which is not preferable. Further, when the molecular weight of the acidic polyamino acid is larger than the above range, the resulting water absorbent resin is inferior in biodegradability, which is not preferable. The method for producing the acidic polyamino acid is not particularly limited.

The basic polyamino acid used for crosslinking the acidic polyamino acid in the present invention is not particularly limited. In addition, the basic polyamino acid in the present invention means a polyamino acid in which the number of amino groups in one molecule is larger than the number of carboxyl groups.

Specific examples of the above-mentioned basic polyamino acids include dimers containing basic amino acids such as glycine-lysine, lysine-glycine, alanine-lysine and lysine-phenylalanine, polylysine and polyarginine. , A copolymer of lysine and arginine, a copolymer of a basic amino acid and another amino acid, and the like. These basic polyamino acids may be used alone or in an appropriate mixture of two or more kinds. Also,
The basic polyamino acid may form a salt with an inorganic acid, an organic acid or the like.

The molecular weight of the basic polyamino acid is preferably in the range of several hundreds to several hundreds of thousands, and low molecular weight oligopeptides such as dimers are more preferable. If the molecular weight of the basic polyamino acid is smaller than the above range, the water absorbing ability of the resulting water absorbent resin does not reach the desired performance, which is not preferable. Further, when the molecular weight of the basic polyamino acid is larger than the above range, the resulting water absorbent resin is inferior in biodegradability, which is not preferable. The method for producing the basic polyamino acid is not particularly limited.

The amount of the basic polyamino acid used with respect to the acidic polyamino acid is not particularly limited, and may be appropriately set depending on the type of acidic polyamino acid or the type of basic polyamino acid used. Specifically, for example, with respect to 100 parts by weight of the acidic polyamino acid, the basic polyamino acid may be used in the range of 0.1 parts by weight to 100 parts by weight, preferably 1 part by weight to 50 parts by weight. Can be used in. When the amount of the basic polyamino acid used is less than 0.1 part by weight, the water absorbing ability of the resulting water absorbent resin does not reach the desired performance, and the water absorbent resin after water absorption becomes unfavorable. Further, when the amount of the basic polyamino acid used is more than 100 parts by weight, the water absorbing ability of the water absorbent resin obtained is inferior, which is not preferable.

The water absorbent resin according to the present invention can be obtained by mixing an acidic polyamino acid with a basic polyamino acid and heating them, that is, by crosslinking the acidic polyamino acid with the basic polyamino acid. That is, when both are mixed and heated, a dehydration reaction (thermal condensation reaction) occurs between the carboxyl group of the acidic polyamino acid and the amino group of the basic polyamino acid to form an amide bond. Since the basic polyamino acid has at least two amino groups, it is possible to crosslink two or more molecules of the acidic polyamino acid to form a network structure by forming the amide bond. . Therefore, the basic polyamino acid acts as a diamine-type cross-linking agent on the acidic polyamino acid. When an acidic polyamino acid ester is used, a thermal condensation reaction occurs between the acidic polyamino acid ester and the basic polyamino acid to form an amide bond.

As described above, the water-absorbent resin according to the present invention is crosslinked by the amide bond to form a network structure. Therefore, the crosslinking point can be relatively easily produced by the enzyme produced by soil bacteria or microorganisms. Cleaves. Therefore, the water absorbent resin according to the present invention exhibits excellent biodegradability.

By using infrared absorption spectrum (IR) and the like, it can be confirmed that the ester bond disappears when, for example, an acidic polyamino acid ester and a basic polyamino acid are mixed and heated. This allows
It can be confirmed that the amide bond is formed between the acidic polyamino acid and the basic polyamino acid.

In the method for producing a water absorbent resin according to the present invention, an amino acid may be added as a third component when the acidic polyamino acid is crosslinked with the basic polyamino acid. Examples of the above amino acids include α-amino acids and β-amino acids.
Amino acids, γ-amino acids, unsaturated amino acids and the like can be used. These amino acids are not particularly limited, but specifically, for example, glycine,
Alanine, phenylalanine, leucine, isoleucine, valine, methionine, cystine, cysteine, serine, threonine, aspartic acid, glutamic acid, α-
Aminoadipic acid, aminomalonic acid, α-aminopimelic acid, α-aminosebacic acid, β-methylglutamic acid, ornithine, lysine, arginine, histidine, β
-Alanine, β-phenylalanine, β-aminobutyric acid,
α-methyl-β-aminopropionic acid, isoserine, β
-Tyrosine, taurine, α-aminoacrylic acid, α-aminocrotonic acid and the like. These amino acids may be used alone, or two or more kinds may be appropriately mixed and used. In addition, for amino acids having optical isomers, any of the d-form, the l-form, and a mixture of the two can be used. By adding the above amino acid, an amide bond is formed between the amino acid and the acidic polyamino acid or the basic polyamino acid, and the main chain is extended, so that the water absorption capacity such as the water absorption capacity of the water absorbent resin is further improved. To do.

When an amino acid is added, the amount of the amino acid used with respect to the acidic polyamino acid is not particularly limited, and depending on the type of acidic polyamino acid or basic polyamino acid or the type of amino acid used, It may be set appropriately. Specifically, for example, acidic polyamino acid
The amino acid may be used within the range of 1 to 100 parts by weight with respect to 100 parts by weight. When the amount of the amino acid used is less than 1 part by weight, the effect of adding the amino acid is hardly exhibited, which is not preferable. On the other hand, if the amount of the amino acid used is more than 100 parts by weight, the water absorbing ability of the resulting water absorbent resin is poor, which is not preferable.

When the acidic polyamino acid is crosslinked with the basic polyamino acid, it is preferable that both are uniformly and sufficiently mixed so that a uniform crosslinking reaction is carried out. The method for mixing the acidic polyamino acid and the basic polyamino acid is not particularly limited, and for example, a method of mixing both solids (dry mixing method), a method of mixing both in a slurry state, either one Various methods such as a method of making the slurry state and adding the other to this, a method of mixing both in an aqueous solution state, a method of making one of them into an aqueous state and adding the other to this, and mixing can do. Of these mixing methods, a method of mixing both in an aqueous solution state, one of which is in an aqueous solution state,
The method of adding the other to this and mixing is preferable.

Even when an amino acid is added to a mixture of an acidic polyamino acid and a basic polyamino acid,
The above mixing method can be adopted. In this case, the amino acid may be added to the acidic polyamino acid in advance,
It may also be added to the basic polyamino acid. further,
Amino acids may be added to the mixture of both. in short,
The amino acid may be added before heating.

In the above mixing method, that is, the method for producing the water absorbent resin, water as a solvent is used as necessary. And, the amount of water used in the above manufacturing method,
It may be appropriately set in consideration of the types and solubilities of the acidic polyamino acid and the basic polyamino acid.

For example, when the acidic polyamino acid or the basic polyamino acid is used as the aqueous solution, the concentration of the acidic polyamino acid aqueous solution or the basic polyamino acid aqueous solution is not particularly limited. However, when the concentration is extremely low, the amount of the aqueous solution becomes large and, for example, the aqueous solution must be heated for a long time in order to remove water, so that the production efficiency decreases. Further, when the concentration is extremely high, the viscosity of the aqueous solution becomes high, and it becomes difficult to uniformly and sufficiently mix the aqueous solution, that is, the acidic polyamino acid and the basic polyamino acid, which is preferable. Absent.

The above heating temperature is preferably in the range of 100 ° C to 300 ° C, more preferably in the range of 200 ° C to 300 ° C. By heating at a temperature within the above range, a cross-linking reaction occurs between the acidic polyamino acid and the basic polyamino acid, and an amide bond is formed. That is, a three-dimensional mesh structure is formed. If the heating temperature at the time of carrying out the crosslinking reaction is lower than 100 ° C., the above crosslinking reaction hardly progresses, which is not preferable. Further, if the heating temperature is higher than 300 ° C., acidic polyamino acids, basic polyamino acids and the like are decomposed and colored, which is not preferable. The heating method is not particularly limited,
For example, various methods such as a method of irradiating with far infrared rays, a method of irradiating with microwaves, a method of using a hot air dryer or a reduced pressure dryer can be adopted.

The heating time is not particularly limited, depending on the type of acidic polyamino acid and basic polyamino acid, the heating temperature, the desired physical properties of the water absorbent resin, and the like.
It may be set appropriately. Specifically, for example, the heating temperature is
If it is in the range of 200 ℃ ~ 300 ℃, the heating time is
It may be 1 minute to 1000 minutes, preferably 5 minutes to 500 minutes.

As the method for producing the water absorbent resin according to the present invention, an acidic polyamino acid is made into an aqueous solution, and the basic polyamino acid and, if necessary, the amino acid are added and mixed uniformly and sufficiently. After that, a method of obtaining a solid, that is, a water absorbent resin by heating the mixture to carry out a crosslinking reaction and removing water from the mixture to dry the mixture is preferable. Further, when the mixture is dried, it is preferable that the water content is 5% by weight or less, that is, the water content of the water absorbent resin is 5% by weight or less. By setting the water content to 5% by weight or less,
It is possible to obtain a water absorbent resin having an excellent water retention capacity under pressure. When removing water from the above mixture, a solid-liquid separation operation such as suction filtration may be performed.

The water absorbent resin obtained by the above method is
The water absorption capacity of the aqueous liquid (physiological saline) is 5 g / g or more, and the biodegradation rate is 10% or more. Further, even under pressure, it is possible to retain an aqueous liquid that is several times its own weight or more. Therefore, the water-absorbent resin is excellent in both water absorption capacity and biodegradability and can maintain the water absorption capacity even under pressure. The methods for measuring these various properties of the water absorbent resin will be described in detail in the examples in the latter part.

The above water-absorbent resin may be granulated into a predetermined shape, or may have various shapes such as irregular crushed shape, spherical shape, scale shape, fibrous shape, rod shape, and lump shape. Good. Further, the water absorbent resin may be primary particles,
Further, it may be a granulated body of primary particles. The particle size and the granulation method for granulating the water absorbent resin into a predetermined shape are not particularly limited. Further, in the above water-absorbent resin,
In order to improve the water absorption property, for example, the permeability and dispersibility of the aqueous liquid, the water absorption rate, etc., various processes and modifications (modification) may be performed.

The water absorbent resin obtained by the above method is
It can be used not only in the sanitary field such as sanitary materials such as disposable diapers, sanitary products and various cleaning tools, but also in a very wide variety of fields as shown below.

That is, the water-absorbent resin is used in the medical field such as a body fluid absorbent at the time of surgery, a wound protector, etc .; a sealing material (water blocking material) at the time of the shield construction method, a concrete curing material, a gel water bag,
Civil engineering / construction fields such as dew condensation prevention materials; Food fields such as drip absorption materials for meat and fish and freshness preservation materials, freshness preservation materials such as vegetables;
Industrial fields such as dehydrating agents that remove water from solvents; soil and water retaining materials for greening, agricultural and horticultural fields such as seed coating materials, and oil / water separators and waste liquid absorbents. It can be used in a very wide variety of fields, such as anti-vibration material, sound insulation material, household sundries, toys and artificial snow.

The above water-absorbent resin has a biodegradability capable of being decomposed by bacteria, microorganisms and the like in the soil, so that it can be decomposed only by burying it in the soil. Therefore, it is easy to dispose of, is excellent in safety, and does not cause environmental hygiene problems such as environmental pollution. Therefore, the water-absorbent resin can be applied to all the uses of the conventionally known water-absorbent resin.

Since the water-absorbent resin is particularly excellent in biodegradability and safety, among the above fields, the hygiene field, medical field,
Suitable for the food field. The composition of the water-absorbent resin (that is, the type of acidic polyamino acid, basic polyamino acid, etc.) may be appropriately selected so that optimum performances corresponding to these applications can be obtained.

Further, in order to improve processability and quality performance, the water-absorbent resin may contain inorganic fine particles such as silica fine particles or a filler made of pulp fiber, if necessary; activated carbon or iron phthalocyanine derivative, Deodorant or deodorant mainly composed of zeolite adsorbed vegetable essential oil etc .; fragrance; antibacterial agent mainly composed of metal such as silver, copper, zinc, etc., bactericide, fungicide, preservative; An oxygen absorber (antioxidant); a surfactant; a foaming agent; a fragrance, etc. may be added. By adding these additives, various functions can be imparted to the water absorbent resin. The addition amount of the above-mentioned additive depends on the kind of the additive but is 0.01% by weight to 5% by weight with respect to the water absorbent resin.
It may be in the range of about wt%. The method of adding the additive is not particularly limited.

[0042]

According to the above constitution, the water-absorbent resin is made by cross-linking the acidic polyamino acid with the basic polyamino acid, has a water absorption capacity of 5 g / g or more and a biodegradation rate of physiological saline. It is 10% or more. Therefore, the water-absorbent resin is excellent in both water absorption capacity and biodegradability and can maintain the water absorption capacity even under pressure. The above water-absorbent resin is not only used as a sanitary field such as sanitary materials such as paper diapers and sanitary items, but also, for example, in the medical field, civil engineering / construction field, food field, industrial field, agriculture / horticultural field, etc. Can be used in a very wide variety of fields such as oil-water separators, waste liquid absorbers, vibration-proof materials, sound-proof materials, household sundries, toys, and artificial snow. Since the water absorbent resin has biodegradability that can be decomposed by bacteria and microorganisms in the soil, it is decomposed only by burying it in the soil. Therefore, it is easy to dispose of, is excellent in safety, and does not cause environmental hygiene problems such as environmental pollution.

Further, according to the above method, the acidic polyamino acid is mixed with the basic polyamino acid and the mixture is heated to crosslink, so that the water absorbent resin having the above-mentioned excellent performance can be produced.

[0044]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these. The various properties of the water absorbent resin were measured by the following methods. In addition, "part" described in the comparative example
Indicates “part by weight”.

(A) Water absorption capacity 0.2 g of water-absorbent resin is used as a non-woven tea bag bag (40 mm
(150 mm) and then immersed in a 0.9 wt% sodium chloride aqueous solution (physiological saline). After 60 minutes, the tea bag type bag was pulled up and drained for a certain period of time, and then the weight W ₁ (g) of the tea bag type bag was measured. Further, the same operation was performed without using the water absorbent resin, and the weight W ₀ (g) of the tea bag type bag at that time was measured. Then, from these weights W ₁ and W ₀ , the water absorption capacity (g) is calculated according to the following equation: water absorption capacity (g / g) = (weight W ₁ (g) -weight W ₀ (g)) / water absorbent resin weight (g). / g) was calculated.

(B) Water Retention Amount Under Pressurization The tea bag type bag containing the swollen water absorbent resin after measuring the water absorption capacity was set in a centrifuge. Then, after dehydration was performed at a rotation speed of 1500 rpm (centrifugal force: 200 G) for 10 minutes, the weight W ₃ (g) of the tea bag type bag was measured. Further, the same operation was performed for the tea bag type bag containing no water absorbent resin, and the weight W ₂ (g) of the tea bag type bag at that time was measured. Then, from these weights W ₃ · W ₂ , the following formula, water retention under pressure (g / g) = (weight W ₃ (g) -weight W ₂ (g)
) / Water absorbent resin weight (g), the water retention capacity under pressure (g / g) was calculated.

(C) Biodegradation rate The biodegradation test was carried out using the modified MITI (Ministry of Internation).
al Trade and Industry) test. That is,
In 200 ml of basal culture solution as a composition solution specified in the section of biochemical oxygen consumption in JIS K-0102,
A water-absorbent resin as a test substance was added to 100 ppm, and activated sludge was added to 30 ppm. Then, this basal culture solution was kept at 25 ° C. in the dark and cultured for 28 days with stirring. Then, during the culturing period, the amount of oxygen consumed by the activated sludge is periodically measured to obtain a biochemical oxygen demand (BOD: Biochemical
Oxygen Demand) curve was determined.

The biodegradation rate (%) is the biochemical oxygen demand A (mg) of the test substance (water-absorbing resin) obtained from the above BOD curve and the blank obtained from the BOD curve, that is, the basal culture solution. Oxygen consumption B (mg) and total oxygen demand (TOD: Total) required for complete oxidation of the test substance
Oxygen Demand) C (mg) and calculated according to the following formula, biodegradation rate (%) = {(A−B) / C} × 100.

Example 1 5 g of water was put into a 100 ml beaker, and sodium polyaspartate (molecular weight: 80,000) 0.60 g as an acidic polyamino acid and glycine-lysine (dimer as a basic polyamino acid) ) Monohydrochloride 0.
26 g and 0-l-aspartic acid as amino acid.
An aqueous solution was prepared by dissolving 29 g.

Then, the above aqueous solution is dried using a dryer.
A dried product was obtained by heating at 200 ° C. for 4 hours. The dried product was crushed to obtain a water absorbent resin. The water absorption capacity, the water retention capacity under pressure, and the biodegradation rate (hereinafter referred to as various performances) of the obtained water absorbent resin were measured. These values (hereinafter simply referred to as results) are shown in Table 1.

Example 2 Glycine in Example 1
Reaction and operation similar to those in Example 1 except that 0.12 g of polylysine as a basic polyamino acid was used instead of 0.26 g of lysine (dimer) monohydrochloride, and the heating time was changed from 4 hours to 2 hours. Then, a water absorbent resin was obtained. Various performances of the obtained water absorbent resin were measured. The results are also shown in Table 1.

Example 3 5 g of water was placed in a 100 ml beaker, and 0.55 g of 50% partially neutralized sodium polyaspartate (molecular weight: 80,000) as an acidic polyamino acid was added to the beaker.
An aqueous solution was prepared by dissolving 0.26 g of glycine-lysine (dimer) monohydrochloride as a basic polyamino acid.

Then, the above aqueous solution is dried using a dryer.
A dried product was obtained by heating at 200 ° C. for 2 hours. The dried product was crushed to obtain a water absorbent resin. Various performances of the obtained water absorbent resin were measured. The results are also shown in Table 1.

Example 4 Glycine in Example 3
The same reaction and operation as in Example 3 were carried out except that 0.10 g of polylysine as a basic polyamino acid was used in place of 0.26 g of lysine (dimer) monohydrochloride to obtain a water absorbent resin. Various performances of the obtained water absorbent resin were measured. The results are also shown in Table 1.

Comparative Example 1 Glycine in Example 1
Lysine (dimer) monohydrochloride 0.26g instead of glycine
The same reaction and operation as in Example 1 were carried out except that 0.081 g and lysine 0.159 g were used to obtain a compound for comparison. However, this comparative compound was soluble in water and therefore could not be used as a water absorbent resin.

Comparative Example 2 A 2 L four-neck round bottom flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a nitrogen gas blowing tube was used as a reactor. In this reactor, 1150 ml of cyclohexane and ethyl cellulose (Hercules Co., Ltd .: trade name ethyl cellulose N-200)
I loaded 9.0g. Then, nitrogen gas was blown into the reaction system to expel the dissolved oxygen, and then the reaction liquid was heated to 75 ° C.

On the other hand, 65.8 g of 98% by weight sodium hydroxide was dissolved in 200 g of ion-exchanged water to prepare an aqueous sodium hydroxide solution. Then, 150 g of acrylic acid contained in another flask was neutralized with the above aqueous sodium hydroxide solution while cooling the flask. The concentration of the aqueous sodium acrylate solution was 45% by weight. Next, to this aqueous solution, 0.5 g of potassium persulfate as a polymerization initiator and 0.15 g of N, N'-methylenebisacrylamide were added. The ratio of the polymerization initiator to acrylic acid was 0.1% by weight. Then, nitrogen gas was blown into the aqueous solution to expel dissolved oxygen.

This aqueous solution was placed in the dropping funnel described above, and 1
The aqueous solution was added dropwise to the reaction solution over time. After the dropping is completed,
The reaction was continued for 1 hour while maintaining the reaction solution at 75 ° C. After the reaction was completed, cyclohexane was distilled off under reduced pressure, and the swollen polymer was taken out.

The resulting swollen polymer was dried under reduced pressure at 80 ° C. to 100 ° C. to obtain a water absorbent resin for comparison.
The various performances of the obtained comparative water absorbent resin were measured. The results are also shown in Table 1.

[Comparative Example 3] 50 parts of corn starch and 300 parts of water were charged into a reactor equipped with a stirrer, a thermometer, and a nitrogen gas blowing tube. This reaction solution
The mixture was stirred at 50 ° C for 1 hour under a nitrogen stream. Then, the reaction solution
After cooling to 30 ° C., acrylic acid 20 parts, sodium acrylate 80 parts, N, N-methylenebisacrylamide 0.02
Part and ammonium persulfate 0.1 which is a polymerization initiator
Parts and 0.01 parts of sodium bisulfite were added to initiate the polymerization. Then, after reacting at a reaction temperature of 30 ° C. to 80 ° C. for 4 hours, the hydrogel polymer was taken out.

The obtained hydrogel polymer was dried with hot air at 120 ° C. Then, the dried product was pulverized to obtain a comparative water-absorbent resin composed of a starch graft polymer. The various performances of the obtained comparative water absorbent resin were measured. The results are also shown in Table 1.

[0062]

[Table 1]

As is clear from the results of Examples 1 to 4 and Comparative Examples 2 to 3, the water-absorbent resin according to this example has a water-absorbing ability as compared with the conventional water-absorbent resin. Excellent in both water absorption capacity and biodegradability, and
It was found that the water absorption capacity can be maintained even under pressure.

[0064]

EFFECTS OF THE INVENTION According to the above constitution, the water-absorbent resin is made by cross-linking the acidic polyamino acid with the basic polyamino acid, has a water-absorption capacity of 5 g / g or more of physiological saline, and is biodegradable. The rate is 10% or more. Therefore, the water absorbent resin has an effect that it is excellent in both water absorbing ability and biodegradability, and can maintain the water absorbing ability even under pressure.

The above water-absorbent resin is not only used in the field of hygiene for sanitary materials such as disposable diapers and sanitary products, but also in the fields of medicine, civil engineering / construction, food, industry, agriculture / horticultural fields. Further, it can be used in a very wide variety of fields such as oil / water separating material, waste liquid absorbing material, vibration insulating material, sound insulating material, household sundries, toys, artificial snow, etc. Since the water absorbent resin has biodegradability that can be decomposed by bacteria and microorganisms in the soil, it is decomposed only by burying it in the soil. For this reason, it is easy to dispose of, is excellent in safety, and does not cause environmental hygiene problems such as environmental pollution.

Further, according to the above-mentioned method, the acidic polyamino acid is mixed with the basic polyamino acid, and the mixture is heated to crosslink, so that the water absorbent resin having the above-mentioned excellent performance can be produced. Therefore, the above method has an effect that it is suitably used as a method for producing a water absorbent resin.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyuki Nishibayashi 1) 992, Nishioki, Nishihama, Kohama, Aboshi-ku, Himeji City, Hyogo Prefecture

Claims (7)

[Claims] 1. A water-absorbent resin comprising an acidic polyamino acid crosslinked with a basic polyamino acid. 2. The water absorbent resin according to claim 1, wherein the ratio of the basic polyamino acid to 100 parts by weight of the acidic polyamino acid is in the range of 0.1 parts by weight to 100 parts by weight. 3. The water absorbent resin according to claim 1 or 2, wherein the acidic polyamino acid is polyaspartic acid (salt). 4. The water absorbent resin according to claim 1, 2 or 3, wherein the water absorption capacity of physiological saline is 5 g / g or more and the biodegradation rate is 10% or more. 5. A method for producing a water absorbent resin, which comprises mixing an acidic polyamino acid with a basic polyamino acid and heating the mixture. 6. The method for producing a water absorbent resin according to claim 5, wherein the amino acid is added to a mixture of the acidic polyamino acid and the basic polyamino acid. 7. The method for producing a water absorbent resin according to claim 5, wherein the heating temperature is in the range of 100 ° C. to 300 ° C.