JP2000290381A - Production of water-absorbent resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a highly biodegradable water-absorbent resin excellent in water absorption characteristics by dispersing a biodegradable water- absorbent resin in a hydrophobic organic solvent in the presence of a surfactant, adding a hydrophilic or water-soluble crosslinker to the resultant suspension and heating the suspension to crosslink the vicinity of the surface of the resin. SOLUTION: A hydrophilic or water-soluble crosslinker reactive with two or more functional groups of a water-absorbent resin is used. A water-absorbent resin mainly comprising a polyamino acid and/or its salt, especially polyaspartic acid and/or its salt, is preferable. Preferably, the polyamino acid and/or its salt has a wt. average mol.wt. of 3,000 or higher. The resin may be a crosslinked one sand/or a radiation-cured one and/or a partially cured one. A suitable amount of the surfactant, preferably a nonionic surfactant, is 0.01-50 pts.wt. based on 100 pts.wt. hydrophobic organic solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a surface-crosslinked water-absorbing resin. More specifically, the present invention relates to a method for producing an absorbent resin having excellent water absorption properties such as water absorption, water absorption speed, and swelling gel strength, and having high biodegradability.

[0002]

2. Description of the Related Art Polyacrylate partially crosslinked products, starch acrylic acid copolymer hydrolysates, vinyl alcohol-acrylic acid copolymers and the like are conventionally known as water-absorbing resins. In addition, these water-absorbing resins are used in a wide variety of fields such as sanitary fields such as diapers and sanitary products, medical fields, civil engineering and construction fields, food fields, industrial fields, soil modifying agents, and agricultural and horticultural fields. It is used for

[0003] The properties desired of the water-absorbing resin for such uses include high water absorption, salt resistance, low water-soluble content, high water absorption rate, high swelling gel strength and the like. However, the relationship between these properties does not necessarily show a positive correlation, and in particular, the absorption capacity is opposite to the salt resistance, low water soluble content, water absorption rate and swelling gel strength, and the higher the water absorption capacity, the more these Characteristics are degraded. In addition, some of the materials having a high water absorption capacity form so-called "mamako" when they come into contact with an aqueous liquid, so that water does not diffuse throughout the water-absorbing resin and the absorption speed is extremely low.

[0004] In order to improve these properties, there is known a method of further cross-linking the vicinity of the surface of a water-absorbent resin in a partially cross-linked polyacrylate or a hydrolyzate of a starch acrylic acid copolymer. Specifically, a method in which a water-absorbent resin powder and a hydrophilic crosslinking agent are directly mixed and, if necessary, subjected to a heat treatment (JP-A-58-180233, JP-A-59-1)
89103, JP-A-61-16903),
Water-absorbent resin, in a mixed solvent of water and a hydrophilic organic solvent,
Alternatively, a method of reacting with a hydrophilic crosslinking agent in an inert solvent in the presence of water (JP-B-60-18690, JP-B-61-48521), a method in which a water-absorbing resin is added in the presence of a surfactant A method of dispersing in a hydrophobic organic solvent, adding a hydrophilic cross-linking agent and reacting (Japanese Patent Publication No. 5-81610, Japanese Patent Application Laid-Open No. 5-15634) and the like are known.

However, the above-mentioned polyacrylic acid (salt)
Absorbent materials containing as a main component hardly have biodegradability. Therefore, when the absorbent material is disposed of as waste, for example, if it is landfilled, it is not decomposed by bacteria or microorganisms in the soil, and may cause environmental health problems such as environmental pollution. That is, an absorbent material containing polyacrylic acid (salt) as a main component has a problem with respect to environmental conservation after disposal.

[0006] As biodegradable water-absorbing resins, natural resins such as polysaccharides and polyamino acid resins are known. As natural resins such as polysaccharides, it is known that hyaluronic acid and polysaccharides produced from microorganisms belonging to the Alcaligenes family have high water absorption (Japanese Patent Application Laid-Open No. 4-200389). Further, as an inexpensive polysaccharide-based water-absorbing resin using cellulose or starch as a raw material, a water-absorbing resin obtained by mixing a polysaccharide with an amino acid and drying by heating is known (JP-A-8-8979).
No. 6). As for the polyamino acid-based resin, a water-absorbing resin obtained by hydrolyzing a partially crosslinked product of polyaspartic acid with a polyamine (JP-A-7-309943,
JP-A-9-169840), a water-absorbent resin in which the polyamine compound is an amino acid such as lysine, ornithine, cystine and cystamine (JP-A-7-224163), and a crosslinking agent such as a diepoxy compound such as ethylene glycol glycidyl ether. Water absorbent resin (Polym.Mate
r.Sci.Eng., 79, 232, 1998). In addition, polyaspartic acid (JP-A-9-202825), polyglutamic acid (JP-A-6-322358), polylysine (JP-A-8-175901), and a mixed solution of polyglutamic acid and polylysine (J. Appl. Polym.S
ci., 58, 807, 1995), a method of irradiating γ-radiation to obtain a cross-linked polyamino acid is known.

[0007] These water-absorbing resins having biodegradability also have the same problem as the water-absorbing resin containing polyacrylic acid (salt) as a main component when the above-mentioned properties are improved.

[0008] There is hardly any specific report as a method for improving the water absorption properties of a water-absorbing resin having biodegradability in a well-balanced manner. The only known method is to crosslink the vicinity of the surface of a water-absorbent resin, which is a polysaccharide crosslinked by amino acids, with a surface crosslinker (Japanese Patent Application Laid-Open No. 8-196901). However, in this technique, it is difficult to directly spray or drop and mix the crosslinking agent on the dried water-absorbing resin, and to distribute the crosslinking agent uniformly on the surface of the resin. Easy to be.

Therefore, a method for improving the water absorption properties of a biodegradable water-absorbing resin in a well-balanced manner and a satisfactory resin as the resin have not been obtained at present.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to uniformly crosslink the surface of a biodegradable water-absorbing resin, thereby improving water absorption properties, such as water absorption, water absorption speed, and swollen gel strength. Another object of the present invention is to provide a method for producing an absorbent resin having high biodegradability.

[0011]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a biodegradable water-absorbing resin can be dissolved in a hydrophobic organic solvent in the presence of a surfactant. To the functional group of the water-absorbent resin.
Add a hydrophilic or water-soluble crosslinking agent that can react with more than one,
By heating and crosslinking the vicinity of the surface of the water-absorbent resin, it is possible to obtain a water-absorbent resin having excellent water absorption properties such as water absorption, water absorption speed, and swelling gel strength, and having high biodegradability. They have found and completed the present invention.

That is, [I] The present invention relates to a method in which a suspension in which a biodegradable water-absorbing resin is dispersed in a hydrophobic organic solvent in the presence of a surfactant is added to a functional group of the water-absorbing resin. A method for producing a water-absorbent resin, characterized in that a hydrophilic or water-soluble crosslinker capable of reacting with two or more of the above is added and heated to crosslink the vicinity of the surface of the water-absorbent resin. [II] The present invention provides the method for producing a water-absorbent resin according to the above [I], wherein the biodegradable water-absorbent resin is a resin comprising a polyacidic amino acid and / or a salt thereof. [III] The present invention provides the method for producing a water-absorbent resin according to claim 1 or 2, wherein the surfactant is a nonionic surfactant, [IV]
In the present invention, the water-absorbent resin has a water absorption capacity of physiological saline of 10
It is intended to provide a method for producing a water-absorbent resin according to any one of the above [I] to [III], wherein the resin is g / g or more.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a method for preparing a suspension of a water-absorbent resin obtained by dispersing a water-absorbent resin in an inert hydrophobic organic solvent in the presence of a surfactant. Is achieved by adding, dispersing, and reacting a reactive cross-linking agent to cross-link the surface vicinity.
It consists of the following five steps.

That is, (1) in the presence of a surfactant,
The water-absorbent resin having biodegradability is uniformly dispersed in a hydrophobic organic solvent so that the surfactant does not substantially penetrate into the water-absorbent resin. Obtaining a suspension coated with an activator; (2) adding a hydrophilic or water-soluble crosslinking agent capable of reacting with two or more of the functional groups of the water-absorbent resin to the suspension; A step of dispersing the crosslinking agent into fine droplets in the suspension by the surfactant and dispersing the droplets uniformly; (3) the crosslinking agent crosslinks the surface of the water-absorbent resin and the interior of the water-absorbent resin; Contacting and reacting the agent without substantially penetrating the agent; (4) a mixture of the surface-crosslinked water-absorbent resin, the crosslinking agent and the surfactant is separated from the organic solvent, and the surface is crosslinked. The water-absorbing resin and the cross-linking agent do not react significantly, or under such conditions as to react Comprising the step of reducing by mechanical means and (5) the particle size of the optionally dry surface crosslinked absorbent resin; 燥 to process.

The biodegradable water-absorbing resin used in the present invention is not particularly limited, but includes natural resins such as the above-mentioned polysaccharides and polyamino acid resins. Among these biodegradable water-absorbing resins, it is preferable to use a polyacidic amino acid and / or a salt thereof as a main component in terms of a balance between water absorption performance and biodegradability.

The polyacid amino acid resin used in the present invention includes polyglutamic acid and / or a salt thereof,
Polyaspartic acid and / or its salts, their copolymers, derivatives and mixtures thereof can be used as the main component. Among these, polyaspartic acid and / or a salt thereof are more preferred.

The molecular weight of the polyacidic amino acid and / or its salt is preferably a high molecular weight in order to obtain a water-insoluble crosslinked product, and is preferably 3,3 in weight average molecular weight.
000 or more, and more preferably 5,000 or more.

The method for producing the polyacid amino acid and / or salt thereof is not particularly limited. For example, (a) a method of producing poly-γ-glutamic acid by culturing a poly-γ-glutamic acid-producing bacterium in a medium containing L-glutamic acid, and (b) heating and dehydrating and condensing D / L-aspartic acid A method for producing polyaspartic acid and / or polyaspartate,
(C) a method for producing polyaspartic acid and / or polyaspartate by subjecting D / L-aspartic acid to thermal dehydration condensation in the presence of a catalyst such as phosphoric acid;
(D) a method for producing polyaspartic acid and / or polyaspartic acid salt by subjecting D / L-aspartic acid to heat dehydration condensation in a suitable solvent in the presence of a catalyst such as phosphoric acid, (e) maleic anhydride A method for producing polyaspartic acid and / or polyaspartic acid via an acid, fumaric acid, malic acid and the like and ammonia through a maleimide, maleamide, maleamic acid or ammonium maleate, (f) maleic anhydride,
A method in which ammonia is reacted with fumaric acid, malic acid, or the like under heat to produce maleimide, maleamide, or ammonium maleate, and polyaspartic acid and / or polyaspartate is produced in the presence of a catalyst such as phosphoric acid.

These reactions are shown below for L-aspartic acid.

[0020]

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The biodegradable water-absorbing resin used in the present invention may be a crosslinkable compound and / or a crosslinked product by radiation and / or as long as the object of the present invention is not impaired.
Alternatively, it may be a partially crosslinked product.

Examples of the crosslinking compound include an epoxy crosslinking agent, a polyamine crosslinking agent, an oxazoline crosslinking agent, an aziridine crosslinking agent, a carbodiimide crosslinking agent, a polyhydric alcohol, an isocyanate crosslinking agent, and a protein.

Among these, epoxy crosslinking agents include:
Ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin-1,3
Examples thereof include diglycidyl ether, polyethylene glycol diglycidyl ether, and bisphenol A-epichlorohydrin type epoxy resin.

Examples of the polyamine crosslinking agent include linear aliphatic polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexamethylenediamine, and polyetherpolyamine; mensendiamine; isophoronediamine; 4-aminocyclohexyl)
Methane 3,9-bis (3-aminopropyl) -2,4
Cycloaliphatic polyamines such as 8,10-tetraoxane pyro [5,5] undecane, m-xylenediamine, p-
Examples thereof include aromatic polyamines such as xylene diamine, polyamides obtained from dimer acid and aliphatic polyamine, and basic amino acids such as lysine.

As the oxazoline crosslinking agent, 2,2'-bis (2-oxazoline), 2,2'-bis (3-methyl-2-oxazoline), 1,4-bis (2- (4-methyl-5 -Phenyloxazoline)) benzene, 2,2 ′
-(1,4-phenylene) -bis (2-oxazoline), 2,2 ′-(1,3-phenylene) -bis (2-
Oxazoline).

Examples of the aziridine crosslinking agent include 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate] and diphenylmethane-bis-
4,4-N, N'-ethyleneurea, hexamethylene-
Bis-ω, ω-N, N′-ethyleneurea, tetramethylene-bis-N, N′-ethyleneurea, triphenylmethane-4,4 ′, 4 ″ -tetramethylene-bis-N,
N'-ethyleneurea, p-phenylenebisethyleneurea, m-toluylene-bis-N, N'-ethyleneurea, carbonylbisaziridine and their methyl derivatives, 2- (1-aziridinyl) ethyl-methacrylate and copolymers thereof Coalescence is exemplified.

Examples of the carbodiimide compound include dicyclohexylcarbodiimide, diphenylcarbodiimide, di- (diisopropyl) phenylcarbodiimide and the like, and a so-called isocyanate group-containing carbodiimide compound represented by the following general formula. (A)

[0028]

Embedded image

(However, R ₅ in the formula represents an aromatic or aliphatic divalent linking group.) Alternatively, a compound derived from the compound (A) and containing no isocyanate group, General formula

[0030]

Embedded image

(However, R ₅ in the formula represents an aromatic or aliphatic divalent linking group, and R ₆ represents an alkyl group, an aralkyl group or an oxyalkylene group.)
And a carbodiimide compound such as a carbodiimide compound (B) containing no hydrophilic group or containing a hydrophilic group.

Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, triethanolamine, polyoxypropylene and oxyethyleneoxypropylene blocks. Examples include polymers, pentaerythrol, and sorbitol.

Examples of the isocyanate crosslinking agent include tolylene diisocyanate (TDI), phenylene diisocyanate (PPDI), diphenylmethane diisocyanate (MDI), hydrogenated MDI, polymeric MDI, tolidine diisocyanate (TODI), hexamethylene diisocyanate (HDI), and isophorone. Diisocyanate (IPDI), xylylene diisocyanate (XD
I), lysine diisocyanate (LDI), tetramethylene xylene diisocyanate (TMXDI), triphenylmethane triisocyanate, tris (isocyanate phenyl) thiophosphate, undecane triisocyanate, lysine ester triisocyanate,
1,8-diisocyanate-4-isocyanatomethyloctane, bicycloheptane triisocyanate, and urethane-modified, allophanate-modified, buret-modified, isocyanurate-modified, carbodiimide-modified, blocked isocyanates, mixtures thereof and the like. Is exemplified.

The proteins are not particularly limited as long as they have two or more amino groups as side chains which react with polysuccinimide, and peptides having a molecular weight of 100 or more are also included here. Also, the origin of the protein is not limited, and (a) a protein separated and recovered from a culture such as a bacterium, a yeast, a filamentous fungus, or an animal cell;
(B) proteins recovered from plant tissues and animal tissues such as soybean, wheat, papaya, milk, pancreas, liver, hair and bone; and (c) amino acids containing two or more amino acids having two amino groups such as lysine. And synthetic proteins prepared by thermal polymerization. Of these proteins, those which are easily recovered and purified, and which are easily available and inexpensive, are preferable.Examples of proteins that satisfy such conditions include, for example, glutenin, oryzin, zein, casein, glue, gelatin, and soybean. Soy protein and the like are exemplified. Among them, proteins mainly containing globulin recovered from soybean are most preferable because they can be easily recovered and purified and are inexpensive.

The form of these crosslinkable compounds is not particularly limited, but is preferably a liquid. Alternatively, any solid may be used as long as it is soluble in a suitable solvent.

The radiation includes, for example, α ray, β ray
Radiation, γ-ray, electron beam, neutron beam, X-ray, charged particle beam and the like.

The hydrophobic organic solvent used for suspending the water-absorbing resin is not particularly limited as long as it is inert to polymerization and other reactions. For example, n-
Aliphatic hydrocarbons such as pentane, n-hexane, n-heptane and n-octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclooctane and decalin; chlorobenzene, bromobenzene, carbon tetrachloride,
Halogenated hydrocarbons such as 1,2-dichloroethane; and aromatic hydrocarbons such as benzene, toluene, and xylene. Of these, n-hexane, cyclohexane, chlorobenzene, toluene and xylene are preferred. One or more of these can be used.

The amount of the hydrophobic organic solvent to be used is 50 to 2,000 parts by weight, preferably 70 to 1,000 parts by weight, per 100 parts by weight of the water-absorbing resin.

The surfactant used in the present invention includes:
Examples include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, and polymeric surfactants.

As the nonionic surfactant, for example,
Sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyglycerin fatty acid ester,
Polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ester, polyoxyethylene acyl ester, sucrose fatty acid ester and the like can be mentioned.

Examples of the anionic surfactant include, for example,
Higher alcohol sulfates, alkyl naphthalene sulfonates, alkyl polyoxyethylene sulfates, dialkyl sulfosuccinates, and the like.

Further, examples of the cationic surfactant include alkyl quaternary ammonium salts and alkylamine salts. Examples of the amphoteric surfactant include:
Alkyl betaine, lecithin and the like can be mentioned, and as the high molecular surfactant, for example, a polymer having a lipophilic carboxyl group and the like can be mentioned. One of these surfactants
Species or two or more can be used.

Among these surfactants, nonionic surfactants are preferred because they uniformly adhere to the surface of the water-absorbent resin and the surface of the water-soluble crosslinking agent, and uniformly disperse the resin and the crosslinking agent in a hydrophobic organic solvent. Activators are preferred, and those having an HLB value in the range of 3 to 10 are more preferred.

The use amount of these surfactants is suitably in the range of 0.01 to 50 parts by weight based on 100 parts by weight of the hydrophobic organic solvent. If the amount is less than 0.01 part by weight, it is difficult to perform a uniform crosslinking reaction on the surface of the water-absorbent resin with a hydrophilic or water-soluble crosslinking agent, and if it exceeds 50 parts by weight, an effect commensurate with the amount used is obtained. Absent.

The hydrophilic or water-soluble crosslinking agent used in the present invention is not particularly limited as long as it is a hydrophilic or water-soluble compound which can react with two or more functional groups of the water-absorbing resin. Specifically, for example, an epoxy crosslinking agent,
Examples include a polyamine crosslinking agent, an oxazoline crosslinking agent, an aziridine crosslinking agent, a carbodiimide crosslinking agent, a polyhydric alcohol, and an isocyanate crosslinking agent. Specific examples include the compounds described above. Of these, epoxy crosslinking agents, polyamine crosslinking agents, and polyhydric alcohols are preferred.

The amount of the hydrophilic or water-soluble crosslinking agent to be used depends on the type thereof, but is generally 0.01 to 5% by weight based on the water-absorbing resin. If this amount is 0.
When the content is less than 01% by weight, no surface crosslinking effect appears,
If it exceeds 5% by weight, the water absorption performance may decrease.

In the present invention, a method of adding and mixing a hydrophilic or water-soluble crosslinking agent to a suspension of a water-absorbent resin includes:
There is no particular limitation, and examples thereof include a method in which a hydrophilic or water-absorbing crosslinking agent is added to a suspension of the water-absorbing resin with stirring.

In the present invention, in order to crosslink the vicinity of the surface of the water-absorbent resin with a hydrophilic or water-soluble crosslinker, a temperature determined according to the type of the hydrophilic or water-soluble crosslinker using the water-absorbent resin is used. Should be kept. For example, a method in which a suspension of a mixed water-absorbent resin is generally kept at 10 to 250 ° C., preferably 50 to 200 ° C. to cause a crosslinking reaction, or in the presence of a surfactant, a hydrophilic or water-soluble crosslinking agent is used. Addition
After separating the water-absorbent resin from the mixed suspension of the water-absorbent resin by filtration or the like, a method of performing a heat treatment of the water-absorbent resin by using a usual dryer, a heating furnace, or the like may be used.

The surface-crosslinked biodegradable absorbent resin according to the present invention is excellent in both water absorption and biodegradability.

The water absorption performance is determined by the water absorption test method (JIS K-722) of the superabsorbent resin specified in Japanese Industrial Standards.
It can be measured by a test of the amount of water absorption by the tea bag method according to 3). When evaluated by the tea bag method, the absorbent resin according to the present invention has a water absorption capacity of 50 times or more with respect to ion-exchanged water and 10 times or more with respect to physiological saline (0.9% by weight physiological saline).

Furthermore, since the water-absorbent resin according to the present invention has biodegradability that can be decomposed by bacteria and microorganisms in the soil, it can be decomposed only by burying in the soil. For this reason, disposal is simple and excellent in safety, and does not cause environmental health problems such as environmental pollution.

Accordingly, the surface-crosslinked biodegradable absorbent resin of the present invention can be applied to all uses of conventionally known water-absorbent resins. For example, hygiene fields such as sanitary articles such as diapers and sanitary articles, medical fields for use in antibacterial agents, or agriculture and horticulture as civil engineering and construction fields, food fields, industrial fields, soil modifying agents, water retention agents, etc. It can be used in various fields such as fields.

[0053]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited by these examples. Incidentally, the water absorption capacity described in the examples,
The water absorption rate, swelling gel strength, and biodegradability were measured by the following methods. Water absorption capacity: In the examples, the water absorption capacity of the resin is based on Japanese Industrial Standards, JIS
It carried out based on the water absorption test method of the superabsorbent resin described in K-7223. That is, 0.50 g of the dried water-absorbent resin (1.00 g with respect to a 0.9% by weight aqueous sodium chloride solution) was put into a tea bag (200 mm × 100 mm) made of 255 mesh nylon shear, and
After immersing in 000 ml of ion-exchanged water or 0.9% sodium chloride aqueous solution to swell the resin for a certain period of time,
The tea bag was pulled up, drained for 10 minutes, and weighed. The measurement was performed using the weight obtained when the same operation was performed using only the tea bag as a blank. Water absorption ratio W
(G / g) is the mass a (g) of the sample, the tea bag containing the sample is immersed for a predetermined time, the mass b (g) after draining,
A tea bag containing no sample was immersed for a predetermined period of time, and calculated from the average value c (g) of the mass after draining according to the following equation.

[0054]

(Equation 1)

(B) Water absorption rate: artificial urine (1.9% by weight of urea, 0.8% by weight of sodium chloride, 0.1% by weight of calcium chloride).
1% by weight, containing 0.1% by weight of magnesium sulfate) 20m
1.0 g of the water-absorbing resin was added to 1 l, and the time until the absorbent resin absorbed all artificial urine and the fluidity of the swollen gel was lost was defined as the water absorption rate. (C) Swelled gel strength 1 g of water-absorbent resin dried in a 100 ml beaker
And 20 g of a 0.9% sodium chloride aqueous solution, and the mixture was gently stirred and left at room temperature for 1 hour to obtain a swelled gel swelled 20-fold. A glass plate was placed on the swelling gel, a weight of 1 kg was placed on the swelling gel, and allowed to stand for a few minutes. The presence or absence of seepage of the aqueous solution from the swelling gel was visually checked. (D) Biodegradation rate: The biodegradability test was performed according to a modified MITI test. That is, the water-absorbent resin as a test substance was added to 200 ml of the basic culture solution so as to have a concentration of 100 ppm, and the activated sludge was added to have a concentration of 30 ppm. Then, keep the basal culture at 25 ° C. in the dark,
The cells were cultured with shaking for 28 days. During the above period, the amount of oxygen consumed by the activated sludge was measured periodically to obtain a biochemical oxygen demand (BOD) curve. Biodegradation rate (%)
Are the biochemical oxygen demand A (mg) of the test substance (polymer composition) obtained from the BOD curve, and the blank obtained from the BOD curve, that is, the oxygen demand B (mg) of the basal culture solution. From the total oxygen demand (TOD) C (mg) required to completely oxidize the test substance,

[0056]

(Equation 2)

Calculated according to

REFERENCE EXAMPLE 100 g of L-aspartic acid and 50% of 85% phosphoric acid were placed in a 1 L metal separable flask.
g at a reaction temperature of 180 ° C. and a reduced pressure of 600 Pa.
The reaction was carried out for 3.5 hours with stirring. After completion of the reaction, 400 ml of DMF was added to the flask to uniformly dissolve the reaction product. The resulting solution was dropped into 1.5 L of ion-exchanged water to reprecipitate the formed resin, and then the slurry was pulverized by a mixer and filtered under reduced pressure. After filtration, washing was performed until the pH of the ion-exchanged water became neutral.
And dried with hot air for 24 hours to obtain 72.5 g of a white powder. As a result of measuring the obtained resin by GPC, the weight average molecular weight was 125,000.

3 g of the obtained white powder was suspended in 20 g of DMF, and 10 mg of hexamethylene diamine was added thereto.
Added to the solution dissolved in 10 g. The mixture obtained after the addition was stirred at room temperature for 10 hours to react. Next, this reaction mixture was dropped into 400 g of ion-exchanged water, and the obtained precipitate was filtered under reduced pressure, washed with water, dried with hot air at 100 ° C. for 15 hours, and partially crosslinked with an anhydrous polyacid amino acid 2.8.
g was obtained.

2 g of this partially crosslinked product was added to ion-exchanged water 10
The solution was added to a solution prepared by dissolving 0.8 g of sodium hydroxide in 0 g, stirred at room temperature for 3 hours, and hydrolyzed to obtain a viscous liquid. 600 ml of methanol was added to this solution, and the resulting precipitate was filtered under reduced pressure, washed with methanol, and heated at 60 ° C. for 1 hour.
After drying under reduced pressure for 2 hours, 1.5 g of a white powdery resin was obtained.

[Example 1] In 300 ml of cyclohexane, 30 g of the water-absorbent resin obtained in the reference example and 2 g of Rheodol SP-S10 [sorbitan monostearate HLB = 4.7 manufactured by Kao Corporation] as a surfactant were vigorously stirred. In addition to shaking, a suspension of the water-absorbent resin was prepared, and dissolved oxygen was expelled by blowing nitrogen gas.

Separately, 50 g of cyclohexane and 0.5 g of sorbitan monolaurate as a surfactant and 0.2 g of hexamethylene diamine as a hydrophilic cross-linking agent are added under vigorous stirring to obtain a cyclohexane dispersion of hexamethylene diamine. Was.

This dispersion was added to the above-mentioned suspension of the water-absorbent resin under stirring at room temperature, mixed, and filtered. The obtained solid was placed in a hot-air dryer at 180 ° C. and heat-treated for 30 minutes to obtain a target surface-crosslinked biodegradable absorbent resin.

Table 1 shows the measurement results of the water absorption capacity, water absorption rate, swelled gel strength, and biodegradation rate of the obtained water-absorbent resin.

Example 2 In Example 1, the surfactant Rheodol SP-S10 used for preparing the suspension of the water-absorbent resin and the dispersion of the hydrophilic crosslinking agent was used without changing the amount used. , Reodol TW-L120 [Polyoxyethylene sorbitan monolaurate HL manufactured by Kao Corporation]
B = 16.7], and the other operations were the same to obtain a surface-treated biodegradable absorbent resin.

Table 1 shows the measurement results of the water absorption capacity, water absorption rate, swelling gel strength, and biodegradation rate of the obtained water-absorbent resin.

[Example 3] The hydrophilic cross-linking agent used in Example 1 was changed to ethylene glycol glycidyl ether without changing the amount used, and the same operation was carried out except for the above, and the surface-treated biodegradation was performed. A water-absorbent resin was obtained.

Table 1 shows the measurement results of the water absorption capacity, water absorption rate, swelling gel strength, and biodegradation rate of the obtained water-absorbent resin.

Comparative Example 1 For comparison, the water absorption ratio, water absorption rate, swelling gel strength, and biodegradability of the water-absorbent resin obtained in Reference Example were measured. The results are shown in Table 1.

Comparative Example 2 A suspension of a water-absorbent resin was prepared by adding 30 g of the water-absorbent resin obtained in the Reference Example to 300 ml of cyclohexane under strong stirring and shaking, and nitrogen gas was blown to remove dissolved oxygen. I was kicked out.

Separately, 0.2 g of hexamethylenediamine as a hydrophilic crosslinking agent was added to 50 g of cyclohexane under strong stirring and shaking to obtain a cyclohexane dispersion of hexamethylenediamine.

0.2 g of hexamethylene diamine was added to the suspension of the water-absorbent resin under stirring at room temperature.
After adding and mixing an aqueous solution dissolved in ml, the mixture was filtered. The obtained solid is placed in a hot air drier at 180 ° C.
Heat treatment was performed for 0 minutes to obtain the desired surface-crosslinked biodegradable absorbent resin.

Table 1 shows the measurement results of the water absorption capacity, water absorption rate, swelling gel strength, and biodegradation rate of the obtained water-absorbent resin.

[0074]

[Table 1]

：: No seepage is seen. ×: Seepage is seen.

[0076]

The water-absorbent resin obtained by the production method of the present invention is excellent in various water-absorbing properties such as water absorption, water absorption speed, and swelling gel strength, and has high biodegradability.
Since the above-mentioned water-absorbent resin has biodegradability that can be decomposed by bacteria and microorganisms in the soil, it is decomposed only by burying in the soil. For this reason, disposal is simple and excellent in safety, and does not cause environmental health problems such as environmental pollution. Therefore, the biodegradable absorbent resin of the present invention,
It is applicable to all uses of conventional water-absorbing resins.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C08L 101: 00 (72) Inventor Yoshiki Hasegawa 3-2-15 Higashi Mikuni, Yodogawa-ku, Osaka-shi, Osaka − 308 F term (reference) 4F070 AA54 AB13 AC38 AC43 AC46 AE14 GA06 GA10 4G066 AA10D AA33D AA50A AB02D AB06D AB07A AB07D AB09D AB10D AC22D AC27B AC35B BA35 BA36 BA38 CA43 EA05 FA05 FA14 FA20 FA21

Claims (4)

[Claims] 1. A reaction in which a biodegradable water-absorbing resin is dispersed in a hydrophobic organic solvent with two or more functional groups of the water-absorbing resin in the presence of a surfactant. A method for producing a water-absorbent resin, which comprises adding a hydrophilic or water-soluble crosslinkable agent and heating the same to crosslink the vicinity of the surface of the water-absorbent resin. 2. The method for producing a water-absorbent resin according to claim 1, wherein the biodegradable water-absorbent resin is a resin comprising a polyacid amino acid and / or a salt thereof. 3. The method according to claim 1, wherein the surfactant is a nonionic surfactant. 4. The water-absorbing resin according to claim 1, wherein the water-absorbing resin has a water absorption capacity of 10 g / g or more.
The manufacturing method described in the item.