JPH11349826A - Production of polymeric absorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a with ease a polymeric absorbent excellent in the ability to absorb an aqueous electrolyte solution. SOLUTION: There is provided a process for producing a polymeric absorbent, comprising making an amino-containing high-molecular-weight polymer amphoteric and crosslinking the product with a crosslinking agent. It is desirable that the amino group contained in the amino-containing monomer is a tertiary amino group, and the amphoteric ion made amphoteric is of a betaine type. The amino- containing polymer is a copolymer of an amino-containing vinyl monomer with a carboxy or carboxylate-containing monomer. According to this process, a polymeric absorbent having a high ability to absorb an electrolyte solution irrespectively of the kind and concentration of the solution can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polymer absorbent, and more particularly, to a method for producing a polymer containing an amino group, wherein the polymer is amphoteric and then crosslinked. The present invention also relates to a method for producing a polymer absorbent that stably exhibits a high water absorption of an electrolyte solution.

[0002]

2. Description of the Related Art So-called polymer absorbents which absorb a large amount of water to swell and gel are absorbents such as disposable diapers, water retention materials for agriculture and horticulture, soil modifiers including salt damage prevention, water stopping agents, etc. It is frequently used in In particular, those that absorb an aqueous medium containing a high concentration of electrolytes such as seawater, urine, blood and saline soil groundwater, in addition to general civil engineering, absorbents such as disposable diapers and sanitary products,
It is important for waterproof pad, blood flow stopper, horticultural water retention material, etc.

Conventionally, it is known that sodium acrylate and starch / acrylic acid systems have excellent water absorbing performance. However, since the highly absorbent polymer is a polymer electrolyte, ions and pH of the absorbing solution are not so high. , The water absorption decreases. Therefore, they exhibit high water absorption performance with respect to distilled water, but have reduced absorption capacity with respect to the electrolyte solution.
Therefore, in order to improve the absorbability of the electrolyte solution, the polymer is modified with an anion such as a carboxyl group or a hydroxyl group, an anionic polymer modified with a cation such as an amino group, and the cation is incorporated into the molecule. Betaine-containing polymers modified with betaine containing anion and an anion have been developed.
For example, JP-A-2-119934 discloses a water-absorbing polymer of a monomer having a quaternary ammonium salt and a monomer having a carboxyl group, and JP-A-3-81310 discloses a quaternary polymer. As a water-absorbing polymer containing amine acrylic acid, Japanese Patent Application Laid-Open No. 5-230383 discloses a water-absorbing polymer of an anionic monomer and a cationic monomer. In particular, from the relationship between the number of dissociation points between the cationic group and the anionic group and the distance between the polar groups, etc., in a betaine-type zwitterionic water-absorbing polymer having an anion and a cation in close proximity in one molecule, It is suitably used for a water-absorbent article excellent in absorption of an aqueous electrolyte solution, in which the electrical neutrality is maintained and the hydrophilicity is not sharply reduced in the isoelectric region.

Therefore, taking advantage of this characteristic, Japanese Patent Application Laid-Open No.
No. 7,377, JP-A-7-76610 and JP-A-7-2427 disclose an absorbent resin comprising a betaine polymer obtained by polymerizing a betaine monomer having an inner salt.
No. 13, JP-A-8-27225, JP-A-8-27
No. 218065, JP-A-8-259628,
JP-A-9-31746 discloses a betaine polymer obtained by copolymerizing a betaine monomer, and JP-A-9-31746 particularly discloses a betaine monomer containing a betaine monomer as a constituent component and an electrolyte. A polymer absorber having excellent absorbency for an aqueous solution is disclosed.

[0005]

However, these betaine monomers have poor polymerizability, and when used for homopolymerization or copolymerization, they contain a very large amount of residual unreacted monomer low molecular weight uncrosslinked polymerization. It became a polymer and was difficult to use for water-absorbing articles. Therefore, development of a method for producing a polymer absorber which is excellent in water absorption of an electrolyte solution and easy to produce is desired.

[0006]

That is, the present invention provides a method for producing a polymer absorbent, which comprises ampholyzing an amino group-containing polymer and then crosslinking the polymer with a crosslinking agent. Further, the present invention provides the method for producing a polymer absorber, wherein the amino group contained in the amino group-containing polymer is a tertiary amino group, and the amphoteric amphoteric group is a betaine type. is there. Further, the present invention provides the method for producing a polymer absorber, wherein the amino group-containing polymer is a copolymer of an amino group-containing vinyl monomer and a carboxyl group (salt) -containing monomer. Things. The present invention also provides a method for producing the polymer absorber, wherein the amino group-containing polymer is a copolymer of an amino group-containing vinyl monomer and acrylic acid (salt). Further, the present invention provides a method for producing the polymer absorber, wherein the weight average molecular weight of the amino group-containing polymer is 10,000 to 10,000,000. In addition, the present invention provides a method for producing the polymer absorber, wherein the zwitterionic group is sulfobetaine or carboxybetaine.
Hereinafter, the present invention will be described in detail.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Amino Group-Containing Polymer The polymer used in the present invention is characterized by containing an amino group. The number of amino groups is not particularly limited as long as it is 1 or more, but can be appropriately selected according to the purpose of use, the degree of amphoteric conversion, and the like. The amino group contained in the polymer includes a primary amino group (—NH ₂ ) and a secondary amino group (> N
H) and a tertiary amino group (> N-).
This is because when a primary amino group or a secondary amino group is contained, amphoteric conversion of an amino acid type is easy, and when a tertiary amino group is contained, betaine formation is easy.
In the present invention, it preferably contains a tertiary amino group. This is because a betaine polymer can be easily obtained. The amino group contained in the polymer may be present in any of the main chain of the polymer and the graft chain when the polymer has a graft chain.

The weight average molecular weight of the polymer is 10,000
It is preferably from 10 to 10,000,000, and more preferably from 100,000 to 1,000,000.
When the molecular weight is lower than 10,000, the amount of the uncrosslinked body after crosslinking increases, and when the molecular weight is higher than 10,000,000,
This is because the crosslinking operation becomes complicated.

The polymer used in the present invention includes a tertiary amino group-containing vinyl monomer (a) and a carboxyl group (salt) -containing monomer (b), and these and other polymerizable monomers ( And a homopolymer of allylamine or alkyleneimine.

(A) Tertiary amino group-containing vinyl monomer (a) As the tertiary amino group-containing vinyl monomer, N, N-dimethylaminomethyl (meth) acrylate, N, N-diethylaminomethyl (meth) ) N, N- such as acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate
Dialkylaminoalkyl (meth) acrylate;
N-dimethylaminopropylacrylamide, N, N-
N, N-dialkylaminoalkylacrylamides such as diethylaminopropylacrylamide; imidazole-containing unsaturated vinyl monomers such as 1-vinylimidazole and 1-vinyl-2-methylimidazole; 2-vinylpyridine, 3-vinylpyridine, 4- Vinylpyridine, 3-
Examples thereof include pyridine-containing unsaturated vinyl monomers such as (2- (meth) acryloxy) ethoxycarbonylpyridine.
Any of these may be used alone, or two or more of these may be used in combination. In the present invention, among these, N,
N-dialkylaminoalkyl (meth) acrylate and N, N-dialkylaminoacrylamide are preferred, especially N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminomethyl (meth)
Acrylates, N, N-dimethylaminopropylacrylamide, are preferred. This is because it is easy to betain, and a polymer absorber having excellent absorbability can be obtained.

(B) Carboxyl group-containing monomer (b) Examples of the polymerizable monomer having a carboxyl group include (meth) acrylic acid, maleic acid, fumaric acid, maleic anhydride, itaconic acid, citraconic acid, Crotonic acid or salts thereof can be mentioned, and one or more of these can be used in combination. Here, as salts, these sodium, potassium, lithium, ammonium,
Examples include magnesium and calcium. In the present invention, as a polymerizable monomer containing a carboxyl group,
(Meth) acrylic acid or (meth) acrylate is preferred. As the (meth) acrylate, sodium (meth) acrylate, potassium (meth) acrylate,
Lithium (meth) acrylate is preferred. This is because polymerization is easy.

(C) Other polymerizable monomers (c) Other polymerizable monomers include amino groups, amide groups, imide groups, hydroxyl groups, sulfone groups, nitrile groups, aldehyde groups or oxy groups other than those described above. There are polymerizable monomers containing an alkylene group. These groups are contained in one molecule of the polymerizable monomer.
It may be contained as described above.

The polymerizable monomer containing an amino group includes allylamine, and the polymerizable monomer containing an amide group includes (meth) acrylamide, (meth) acrylacetylamide, and N-substituted alkylamide. Etc. Further, as a polymerizable monomer containing an imide group,
There are maleimide derivatives such as maleimide, methylmaleimide, ethylmaleimide, propylmaleimide, butylmaleimide, octylmaleimide, dodecylmaleimide, stearylmaleimide, phenylmaleimide, cyclohexylmaleimide, and vinylpyrrolidone.

As the polymerizable monomer having a hydroxyl group,
There are hydroxyalkyl (meth) acrylate compounds such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxypropyl (meth) acrylate, and hydroxopropyl (meth) acrylate, and hydroxyethyl acrylamide and allyl alcohol. Examples of the polymerizable monomer having a sulfone group include 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof, (meth) allylsulfonic acid or a salt thereof, vinylsulfonic acid or a salt thereof, styrenesulfonic acid or a salt thereof. And 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof, 2-hydroxy-3-butenesulfonic acid or a salt thereof, and a sulfonic acid group-containing monomer such as sulfoethyl (meth) acrylate.

Examples of the polymerizable monomer containing a nitrile group include vinyl monomers containing a nitrile group such as (meth) acrylonitrile. Aldehyde group-containing polymerizable monomers include aldehyde group-containing vinyl monomers such as (meth) acrolein. Further, other polymerizable monomers (c) include 4-methacrylamidopropyltrimethylammonium and N-vinyl-2-pyrrolidone.
Monomers containing a quaternary ammonium group; vinyl acetate, vinyl propionate, vinyl pivalate, vinyl benzoate,
Vinyl esters such as vinyl cinnamate; alkene monomers such as ethylene and propylene; aromatic vinyl monomers such as styrene and styrene sulfonic acid; alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; alkoxy polyalkylene glycols ( Nonionic hydrophilic vinyl monomers such as an alkylene oxide adduct of (meth) acrylate and (meth) acrylic acid can also be used. In addition to using one kind of these, two or more kinds may be used in combination. .

(D) Polymer and Polymerization Method As the amino group-containing polymer used in the present invention, a homopolymer of allylamine is preferred. When the amino group-containing polymer is a copolymer, a copolymer obtained by polymerization at the following ratio is preferred. That is, a carboxyl group-containing monomer or a carboxyl group metal salt-containing monomer (in the present invention, a carboxyl group (salt) is used for 0.1 to 80 parts by weight of the tertiary amino group-containing vinyl monomer (a). )
(B) preferably 0.1 to 90 parts by weight,
More preferably, (a) 10 to 50 parts by weight,
(B) 10 to 60 parts by weight.

Furthermore, in the present invention, (b) is preferably the total of acrylic acid and acrylate (also referred to as acrylic acid (salt) in the present invention), and more specifically, (b) B) 0.1 to 90 parts by weight of acrylic acid (salt) per 0.1 to 80 parts by weight, more preferably (a) 1
The amount of acrylic acid (salt) is 10 to 60 parts by weight based on 0 to 50 parts by weight. This is because a polymer absorbent having particularly excellent water absorbability can be easily obtained in this range. Further, as the amino group-containing polymer used in the present invention, the total of the above tertiary amino group-containing vinyl monomer (a) and acrylic acid (salt) is 10%.
In addition to 0 parts by weight, those obtained by copolymerizing the other polymerizable monomer (c) other than these in the range of 0.1 to 70 parts by weight are also preferable.

The amino group-containing polymer can be produced by a commonly used polymerization method. When the amino group-containing monomer is a copolymer of a tertiary amino group-containing monomer (a) and a carboxyl group (salt) -containing monomer (b) or the like, a carboxyl group (salt) -containing monomer is used. The monomer (b) may undergo hydrolysis during aqueous solution polymerization. Specifically, when a carboxyl group (salt) -containing monomer (b) that may cause hydrolysis during aqueous solution polymerization such as dimethylaminoethyl acrylate is used, the monomer is converted to a salt such as hydrochloride. After polymerization, or copolymerization with a carboxyl group-containing monomer (b) or the like which does not form a salt at a low hydrogen ion concentration of pH 7 or less to obtain an amino group-containing polymer and then amphoteric, for example, Betaine can be made. The mixing ratio of the tertiary amino group-containing vinyl monomer (a) and the carboxyl group (salt) -containing monomer (b) is (a)
The mixing ratio of the carboxyl group (salt) -containing monomer (b) having a degree of neutralization of 0.1 to 80 parts by weight is preferably 0.1 to 90 parts by weight, and more preferably (A) 5
The neutralization degree (b) is 10 to 60 parts by weight with respect to 0 parts by weight. When copolymerized with another polymerizable monomer (c) other than these, the total of the tertiary amino group-containing vinyl monomer (a) and the carboxyl group (salt) -containing monomer (b) is 100
Other polymerizable monomers other than these (c)
Preferably, 0.1 to 70 parts by weight is copolymerized.

In the present invention, after the amino group-containing polymer is amphoteric, the carboxyl group contained in the polymer may be converted into a salt. Specifically, as described above, after copolymerization in a state of a hydrogen ion concentration of pH 7 or less, the resulting polymer may be betaine-converted into betaine groups and the carboxyl groups contained therein may be converted into salts.

The above tertiary amino group-containing vinyl monomer (a)
And a carboxyl group (salt) -containing monomer (b) and optionally other polymerizable monomers (c)
May be any of alternating copolymerization, random copolymerization, block copolymerization and the like. Further, the homopolymer of these copolymers and allylamine may be prepared by any conventional radical polymerization method.
Therefore, bulk polymerization, aqueous precipitation polymerization, suspension polymerization, emulsion polymerization,
Either solution polymerization or reversed phase suspension polymerization may be used, and the method may be appropriately selected in consideration of the form of the obtained polymer.

The method of generating radicals includes a method using a radical polymerization catalyst, a method of irradiating radiation, an electron beam, and an ultraviolet ray. Examples of the radical polymerization catalyst include ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; organic peroxides such as t-butyl hydroperoxide and cumene hydroperoxide; and organic peroxides and azobisisobutyronitrile. Azo compounds such as azobiscyanovaleric acid, radical generators such as ammonium persulfate and persulfates such as potassium persulfate, and combinations of these radical generators with reducing agents such as sodium bisulfite and L-ascorbic acid. Redox-based initiators. In the present invention, it is preferable to use a redox-based initiator. This is because polymerization can be performed at a low temperature.

The amount of the radical generator used is not particularly limited, but is preferably 0.001 to 30% by weight, particularly preferably 0 to 30% by weight, based on the total weight of each monomer constituting the polymer. 0.01 to 10% by weight.

(E) Polyalkylenimine As the polymer used in the present invention, besides the above-mentioned polymers, polyalkylenimine which is a polymer of alkylene imine can be used. Here, the polyalkyleneimine can be obtained by polymerizing an alkyleneimine such as ethyleneimine, propyleneimine, 1,2-butyleneimine, 2,3-butyleneimine, or 1,1-dimethylethyleneimine by a conventional method, In addition to the homopolymers of these alkylene imines, there are polyalkylene imines obtained by mixing two or more of the above-mentioned alkylene imines, for example, a mixture of ethylene imine and propylene imine. Polyalkylenimines are branched by polymerization and usually contain a tertiary amino group in addition to a primary amino group and a secondary amino group in the structure. In the present invention, among these, polyethyleneimine is preferred.

(2) Amphoterization In the present invention, the amino group-containing polymer is amphoteric. By amphoteric, a polymer containing a primary amino group or a secondary amino group can be, for example, a polymer having an amino acid type amphoteric group, and a polymer containing a tertiary amino group is a betaine type polymer. It can be. When the amino group-containing polymer contains a secondary amino group or a primary amino group in addition to the tertiary amino group, depending on the purpose of use, water absorption performance, etc., for example, an amino acid type amphoteric group and betaine Both amphoteric groups and amphoteric groups may be amphoteric. On the other hand, even when only the tertiary amino group is contained,
In addition to the case where 00% is made into betaine, a part thereof may be made into betaine according to the degree of salt resistance required, and the rest may be made into a cationic group or a nonionic group.

(A) Betainelation The tertiary amino group contained in the polymer is sulfobetaine,
A suitable betaine can be appropriately selected depending on the purpose of use of the polymer absorber, such as sulfate betaine or carboxybetaine. As the betaine formation of the present invention, sulfobetaine formation and carboxybetaine formation are preferable. Sulfobetaination is performed because a polymer absorbent having excellent absorbability is obtained, and the tertiary amino group is formed with a sulfobetainating agent such as a halosulfonic acid salt or sultone.

Examples of the halosulfonate include 2-bromoethanesulfonate and 3-chloro-2-hydroxypropanesulfonate derived from epichlorohydrin and sodium bisulfite. Generally, the amount of the sulfobetain agent is preferably 0.1 to 2 mol, more preferably 0.3 to 1.2 mol, per 1 mol of the tertiary amino group.

Examples of the sultone include aliphatic sultone such as 1,3-propane sultone and 1,4-butane sultone, and aromatic sultone such as naphtha sultone. When sultone is used, the polymer is dissolved in a solvent, and 0.1 mol of sultone is added to 1 mol of the tertiary amino group.
２2 mol, particularly preferably 0.3-1.2 mol. The reaction system does not need to use a reaction catalyst. This is because sulfobetaine formation proceeds sufficiently.

The sulfobetaination is carried out by using a sulfobetainizing agent, quaternizing the tertiary amino group with allyl chloride, dibromoethane, benzylepichlorohydrin, etc., and then adding sodium bisulfite or A method of sulfonating with sodium sulfite can also be used. In the sulfonation of the present invention, it is preferable to use an aliphatic sultone such as 1,3-propane sultone and 1,4-butane sultone. This is because the reaction proceeds at a low temperature and does not produce a salt as a by-product.

Sulfate betainization can be carried out by using a cyclic sulfate instead of the sultone. Cyclic sulfates can be prepared by the sulfation of 1,3-diol and ethylene oxide. Further, quaternization can also be performed using an alkyl sulfate agent prepared from pyridine / SO ₃ complex, dioxane / SO ₃ complex or the like and ethylene oxide. Further, similarly to sulfobetaine, a method of quaternizing and then sulfating can be used. For example, when a tertiary amino group is
Grading followed by sulphation with chlorosulfonic acid gives sulfate betaine.

Carboxybetaination is carried out by combining a tertiary amino group with a carboxybetainizing agent such as monochloroacetic acid (salt), monochloroacetic ester, monobromophenylacetic acid or 4-bromobutanoic acid in a solvent such as water or isopropyl alcohol. The reaction can be carried out at a temperature of 10 to 100 ° C, particularly preferably 40 to 60 ° C. The carboxybetaine agent such as monochloroacetic acid (salt) is used in an amount of 0.1 to 2 mol, particularly preferably 0.3 to 1.5 mol, per 1 mol of the tertiary amino group.

Carboxybetaination can also be carried out by reacting a tertiary amino group with β-propiolactone or α, β-unsaturated fatty acid. Further, the tertiary amino group can be quaternized with halonitrile and then hydrolyzed to give carboxybetaine. In the present invention, it is preferable to use monochloroacetate or monochloroacetate such as sodium monochloroacetate for carboxybetainization.

In addition to the above, betaine can be obtained by reacting ethylene oxide with a complex of a tertiary amino group and a dibasic acid anhydride to obtain betaine having an ester bond. In addition, reprecipitation may be performed after betaine formation to wash unreacted betaine products.

(B) Other Amphoterization The amino group-containing polymer is obtained by saponifying the alkyl ester portion of the carboxyl group contained in the amino group-containing monomer to form an anionic group such as a carboxyl group or a salt thereof. Can be amphoteric to the amino acid form. When a cyano group is contained, the cyano group can be hydrolyzed with an alkali to form a carboxyl group or a salt thereof, and amphoteric to an amino acid type amphoteric group.

(3) Crosslinking The present invention is characterized in that the amphoteric polymer is subsequently crosslinked. The polymer absorber is cross-linked in the molecule, whereby the polymer absorber can maintain a swollen state without being dissolved in the medium, and the absorbency of the polymer absorber is improved.
For the introduction of cross-linking, a method of copolymerizing a polyfunctional cross-linking agent at the time of monomer polymerization, and then reacting the polyfunctional cross-linking agent with the uncross-linked polymer obtained by polymerizing the monomer to form a polymer absorber Although there is a method for obtaining the polymer, the present invention is characterized in that an uncrosslinked amino group-containing polymer is amphoteric and then crosslinked using a polyfunctional crosslinking agent. Thereby, a polymer having better absorption performance can be obtained than a polymer obtained by crosslinking at the time of monomer polymerization.

In order to introduce a crosslinked structure in the present invention, it is preferable to use a crosslinking agent having two or more functional groups which react with the polymer.

As the crosslinking agent, when the polymer used in the present invention contains a carboxyl group (salt) -containing monomer of (meth) acrylic acid or (meth) acrylate as a polymerizable monomer, , A polyfunctional compound having two or more functional groups capable of forming a chemical bond by reacting with a carboxyl group such as a hydroxyl group, an epoxy group, an amino group or a methylol group, for example, diglycidyl ether, glycerol diglycidyl ether, glycerol triglyceride Di- or triglycidyl compounds such as glycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether; glycol compounds such as ethylene glycol, propylene glycol, polyethylene glycol, and glycerol; Lumpur, trimethylolpropane,
Hydroxyl-containing compounds such as polyvinyl alcohol and pentaerythritol; ethanolamine, ethylenediamine,
Propylenediamine, trimethylolmelamine, polyethyleneimine, urea and the like can be used. Further, after crosslinking with formaldehyde, crosslinking with polyvalent metal ions can also be performed.

When the polymer has a hydroxyl group, a functional group capable of forming a chemical bond by reacting with a hydroxyl group such as a carboxyl group, an acid anhydride, an aldehyde group and an isocyanate group is used.
Polyfunctional compounds having at least one such as malonic acid, succinic acid, glutaric acid, malic acid, propane-1,2,3-tricarboxylic acid and their acid anhydrides, glyoxal, glutaraldehyde, hexamethylene diisocyanate, cyclohexane diisocyanate, etc. Can be used.

When the polymer has a nitrile group, a polyfunctional compound having two or more functional groups capable of forming a chemical bond by reacting with a nitrile group such as an amino group, for example,
Hydrazine, ethylenediamine, propylenediamine,
Butylenediamine, pentamethylenediamine, hexamethylenediamine, polyethylene glycol aminated at both ends, and the like.

When the polymer used in the present invention uses a copolymer of a tertiary amino group-containing vinyl monomer (a) with acrylic acid and acrylate, polyalkyleneimine or polyallylamine, It is preferable to use a glycidyl ether compound, an isocyanate compound, or a glycerol compound as a crosslinking agent.

The amount of the crosslinking agent used can be appropriately selected according to the required degree of crosslinking and the type of the polymer used. Generally, the crosslinking agent is used in an amount of 0.001 to 30% by weight, more preferably 0.01 to 30% by weight, based on 100 parts by weight of the betainized polymer.
10% by weight, particularly preferably 0.01 to 5% by weight, is used. This is because a polymer absorber excellent in water absorbency can be obtained in this range.

The crosslinking is carried out at a temperature of from 30 to 120 after addition of the crosslinking agent.
C., complete in 1-48 hours.

(4) Use The polymer absorbent produced according to the present invention is used as a water retention material by mixing it with a conventional absorbent resin or other water retention material in a portion of the soil that easily absorbs irrigation water and rainwater. can do. Further, the polymer absorber produced by the production method of the present invention is excellent in water absorption of a high electrolyte solution. For this reason, it can efficiently absorb electrolytes such as sweat, urine, and blood, and can be used as absorbents for disposable diapers and sanitary articles, waterproof pads, blood flow stoppers, and the like. In addition, seawater and salt water,
It can be used as a water retention material for horticulture, a salt soil improver, a waterproofing agent for underground and underwater cables, a waterproofing agent for steel pipe sheet piles, and the like.

[0043]

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples. In the examples, unless otherwise specified, "%" represents% by weight.

Example 1 12.8 g of 60 mol% neutralized sodium acrylate
And 80 g of deionized water were placed in a reaction vessel, and 7.2 g of dimethylaminoethyl acrylate was added thereto. Next, the reaction solution was bubbled with nitrogen while stirring, and nitrogen replacement was performed. At this time, the pH of the reaction solution was 5. Next, after adjusting the temperature of the reaction vessel to 50 ° C., 0.574 g of a 10% aqueous solution of sodium sulfite was added, and the mixture was stirred for 1 minute. Next, a 1% aqueous solution of L-ascorbic acid 0.17
7 g was added and stirred similarly. The reaction solution started polymerization after several minutes, and became a high viscosity polymer in about 20 minutes. After 3 hours, the polymer was removed and diluted with deionized water until the total amount was 300 g. When the molecular weight of the polymer was measured using GPC, the weight average molecular weight was 800,00.
It was 0.

Then, 6.14 g of propane sultone was added to the diluent containing the polymer, and the mixture was reacted at 70 ° C. for 2 hours with stirring to obtain betaine. Next, 2 g of propylene glycol diglycidyl ether was added, and the mixture was heated at 80 ° C. for 2 hours to perform crosslinking. As a result, a transparent crosslinked gel (A) was obtained.

The obtained crosslinked gel (A) was taken out and 1 m
2. Cut with scissors into m-square to form a 60 x 60 mm non-woven fabric.
00g, heat sealed on all sides and sealed.
After being immersed in 500 ml of the electrolyte solution of each concentration shown in 1 for 24 hours, it was taken out, drained with a centrifuge at 250 G for 3 minutes, and weighed. Next, the same operation was carried out without the crosslinked gel (A), and the blank amount of only the measured nonwoven fabric bag was subtracted to calculate the gel weight after liquid absorption. The absorption capacity was calculated by the following formula.

[0047]

## EQU1 ## Absorption ratio = (weight after draining (g) -amount of blank of nonwoven bag only (g)) / gel weight after drying Measurement of crosslinked gel (A) weight after drying: crosslinked gel (A) Cut into 1mm squares, 3.00g in a 30mm diameter aluminum dish
The gel was weighed and dried in an oven adjusted to 180 ° C. for 3 hours, and the weight was measured. The results are shown in Table 1.

Example 2 A polyethyleneimine aqueous solution (trade name “Epomin p-1000”, manufactured by Nippon Shokubai Co., Ltd., weight average molecular weight 7
230,000 (resin content 30%) was weighed and replaced with nitrogen. Then, the temperature was adjusted to 70 ° C. To this polymer solution, 30 g of 72.4 g of sodium monochloroacetate (50 mol% based on all amino groups of polyethyleneimine) was added.
The solution was stirred for 3 hours while dropwise adding the aqueous solution dissolved in deionized water over 30 minutes. This converted the tertiary amino group to betaine.

Next, 1.0 g of propylene glycol diglycidyl ether was added to the solution, and the mixture was stirred.
Crosslinking was performed at 2 ° C. for 2 hours to prepare a crosslinked gel (B).
Using the same method as in Example 1, the absorption capacity of the aqueous electrolyte solution was measured for the prepared crosslinked gel (B). The results are shown in Table 1.

Comparative Example 1 A reaction solution consisting of 34 g of 60 mol% neutralized sodium acrylate, 55 g of deionized water and 0.062 g of methylenebisacrylamide was placed in a reaction vessel. Next, the temperature was adjusted to 60 ° C. while degassing with nitrogen by bubbling with nitrogen. Thereafter, 0.56 g of azobiscyanovaleric acid was added, and polymerization was carried out at 60 ° C. for 20 hours.

The obtained crosslinked gel (C) was cut with a 1 mm square scissor, and dried with a reduced pressure drier at 60 ° C. for 4 hours. The dried polymer is pulverized and classified to 300 μm
Then, 0.20 g of the same non-woven fabric of 60 × 60 mm as that used in Example 1 was taken out, heat-sealed on all sides, and then added to 500 ml of each concentration of the electrolyte solution shown in Table-2. After being immersed for a period of time, it was taken out, drained with a centrifuge at 250 G for 3 minutes, and weighed. Next, the same operation was performed without the crosslinked gel (C), and the blank amount of only the nonwoven fabric bag measured was subtracted to calculate the gel weight after liquid absorption. The absorption capacity was calculated by the following formula. Table 2 shows the results.

[0052]

## EQU2 ## Absorption ratio = (weight after draining (g) -amount of blank of non-woven bag only (g)) / 0.20 (g) Comparative Example 2 Sodium acrylate 16 neutralized in a reaction vessel by 60 mol% 0.3 g, 96.2 g of deionized water, 0.039 g of methylenebisacrylamide, N, N-dimethyl-N- (3
-Acrylamidopropyl) -N- (3-sulfopropyl) ammonium internal salt, 17.6 g. Next, the temperature was adjusted to 60 ° C. while degassing with nitrogen by bubbling with nitrogen. Thereafter, 0.36 g of azobiscyanovaleric acid was added, and polymerization was carried out at 60 ° C. for 20 hours. The obtained crosslinked gel (D) was cut with scissors of 1 mm square, and dried at 60 ° C. for 4 hours with a reduced pressure drier. The dried crosslinked gel (D) is pulverized, classified, and
m to 500 μm particles. Using the same method as in Comparative Example 1, the obtained dried crosslinked gel (D) particles were measured for the absorption capacity of various electrolyte solutions. Table 2 shows the results.

[0053]

[Table 1]

[0054]

[Table 2]

Results In Example 1, since no betaine-containing monomer was used, in order to produce a betaine-containing polymer absorbent, 3 hours were required for synthesis of the polymer, 2 hours for betaine-ization, and 2 hours for crosslinking. It took a total of seven hours. In contrast, in Comparative Example 2,
In order to produce a betaine-containing polymer absorber using a betaine-containing monomer, it took 20 hours to synthesize the polymer. Therefore, in the production method of the present invention, an amphoteric polymer absorber could be easily produced. In Comparative Example 2 in which a copolymer reaction was carried out together with a crosslinkable monomer, the obtained polymer absorber had an absorptivity of 10% NaCl of 33.3, whereas the amino group-containing polymer had an absorptivity of 33.3. In Example 1 in which crosslinking was performed after amphoteric conversion, the obtained polymer absorber had the same absorption rate of 4
9.8, compared to Comparative Example 2 in which crosslinking was performed simultaneously during the polymerization of the amino group-containing polymer, by the crosslinking operation after the polymerization,
It has been found that a polymer absorber having an excellent absorption rate can be produced.

The polymer absorbent containing no cationic group of Comparative Example 1 is excellent in the absorbency of pure water, but decreases with an increase in salt concentration. On the other hand, the polymer absorbers obtained in Examples 1 and 2 according to the production method of the present invention contained betaine, which is an amphoteric group, and thus had excellent absorbability irrespective of salt concentration and type of salts.

In the production method of the present invention, cross-linking after polymerization is an essential requirement, and accordingly, 0.9% and 10% NaC with respect to the pure water absorbency of the polymer absorbent obtained in Example 2
The absorptivity ratio of the 1 solution was 0.85 and 1.1, respectively, and there was little change in the absorptivity with respect to the electrolyte solution concentration. On the other hand, the polymer absorbers obtained in Comparative Example 2 were 0.11 and 0.06, respectively, and the absorbability decreased as the concentration of the electrolyte solution increased. That is, it was found that by performing a crosslinking operation after amphoteric conversion of the amino group-containing polymer, a polymer absorber having a stable electrolyte absorption rate can be obtained regardless of a change in the concentration of the electrolyte solution.

[0058]

According to the present invention, there is provided a method for producing a polymer absorbent having high absorbency for an electrolyte solution.
In the present invention, since the non-amphotized high molecular weight polymer is amphoteric, the polymerization reaction is easy. Further, by amphotericizing the amino group-containing polymer and then crosslinking the polymer, a polymer absorbent having high absorbency to the electrolyte solution can be easily produced regardless of the type and concentration of the electrolyte.

Claims (6)

[Claims] 1. A method for producing a polymer absorber, comprising amplifying an amino group-containing polymer and then crosslinking the polymer with a crosslinking agent. 2. The polymer absorber according to claim 1, wherein the amino group contained in the amino group-containing polymer is a tertiary amino group, and the amphoteric zwitterionic group is a betaine type. Manufacturing method. 3. The polymer according to claim 1, wherein the amino group-containing polymer is a copolymer of an amino group-containing vinyl monomer and a carboxyl group (salt) -containing monomer. Manufacturing method of absorber. 4. The polymer according to claim 1, wherein the amino group-containing polymer is a copolymer of an amino group-containing vinyl monomer and acrylic acid (salt). Manufacturing method of absorber. 5. The method according to claim 1, wherein the amino group-containing polymer has a weight average molecular weight of 10,000 to 10,000,000. 6. The method according to claim 2, wherein the zwitterionic group is sulfobetaine or carboxybetaine.