JPS63242344A - Acrylic water absorbent and its preparation - Google Patents

Abstract

PURPOSE:To impart an excellent film forming property, by preparing a water absorbent from an acrylic copolymer consisting of an acrylic acid monomer and a hydrophilic unsaturated carboxylic ester monomer whose carboxyl group is substituted with a specific group. CONSTITUTION:A copolymer is obtained by a monomer mixture wherein 3-35wt.% of an acrylic acid type monomer, 35-97wt.% of a hydrophilic unsaturated carboxylic ester type monomer and 0-50wt.% of an acrylic acid type alkyl ester monomer are compounded. The obtained copolymer is neutralized with an alkali metal base, an ammoniacal compound or amine and crosslinked by a crosslinking agent to obtain an acrylic water absorbent. This water absorbent has excellent film forming capacity and can be formed into a film by a solution coating system and the water absorbing film composed of the water absorbent itself can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention consists of a copolymer containing an acrylic acid monomer and a hydrophilic unsaturated carboxylic acid ester monomer, which can be formed into a film. This invention relates to an acrylic water absorbing agent and a method for producing the same.

Conventional technologies and problems Polymer-based water absorbing agents are typically used in disposable diapers and feminine hygiene products, but among their various uses, they are most commonly used in the form of films and sheets. In such cases, the various polymer-based water-absorbing agents that have been proposed so far do not have film-forming ability themselves, so they can be used in the form of granules or powder to be used as water-absorbing paper. Generally, methods have been used to make sheets by sandwiching them with fibers or mixing them between fibers.However, with these methods, it is difficult to obtain a transparent body, the water absorption points are uneven, and the thickness is too high. There were problems in that it was not suitable for various uses in terms of thickness, etc., and that it required a lot of effort to manufacture.

For this reason, attempts have been made to form a film by dispersing a water-absorbing agent in a resin solution that fosters film-forming ability, such as ethylene-vinyl acetate copolymer, and to form a film by mixing a plasticizer with a polymer-based water-absorbing agent. An attempt to
No. 41357), but in all cases, water absorption properties such as water absorption amount and water absorption rate deteriorate, and a satisfactory water absorbent film has not yet been obtained.

Means for Solving the Problems The present inventors have conducted intensive research to develop a polymer-based water-absorbing agent that itself exhibits excellent film-forming ability. The present inventors have discovered that the object can be achieved by using a special copolymer composed of a saturated carboxylic acid ester monomer, and have completed the present invention.

That is, the present invention consists of an acrylic copolymer containing an acrylic acid monomer and a hydrophilic unsaturated carboxylic acid ester monomer, and the carboxyl group of the copolymer is an alkali metal salt or an ammonium salt. or form an amine salt,
and an acrylic water-absorbing agent characterized by being cross-linked, 3 to 35% by weight of an acrylic acid monomer, 35 to 97% by weight of a hydrophilic unsaturated carboxylic acid ester monomer, and an acrylic acid-based monomer. Alkyl ester monomer 0-50% by weight
An acrylic-based copolymer obtained by polymerizing monomers having a blending ratio of A method for producing a water absorbing agent is provided.

Excellent water absorption ability is imparted based on the alkali metal salt, ammonium salt or amine salt of the acrylic acid component. In addition, based on hydrophilic unsaturated carboxylic acid ester components,
The resulting copolymer has a low glass transition point (which gives it film-forming ability as well as water absorption ability.Furthermore, when an acrylic acid-based alkyl ester monomer is added, the resulting copolymer has a low glass transition point). The film-forming ability of the polymer is improved, and the physical properties of the resulting film, such as elasticity, can be easily adjusted.

Examples of Constituent Elements of the Invention The acrylic water absorbing agent of the present invention comprises an acrylic acid monomer,
It consists of a copolymer polymerized using a hydrophilic unsaturated carboxylic acid ester monomer and, if necessary, an acrylic acid alkyl ester monomer.

As the acrylic acid monomer, acrylic acid or methacrylic acid may be used alone or in combination.

Further, as the hydrophilic unsaturated carboxylic acid ester monomer, one having an alkoxy ether bond or a hydroxyl group in the molecule is used.

As a hydrophilic unsaturated carboxylic acid ester monomer having an alkoxy ether bond in the molecule, formula 1: HO-
←CH2-～-〇→CH2H (in the formula ■, m is 1 to 4,
n is an integer from 1 to 3. ) Formula I[:HO→CH2CH
2O￥→CH YunaH (in the formula ■, p is 2 to 6, n is 1 to 3
is an integer. ) H3 (In formula (1), y is an integer of 1 to 6, and n is an integer of 1 to 3.) One or two ether bonds consisting of an alkoxy group having 3 or less carbon atoms in the molecule. Examples include esters of the above-mentioned monohydric alcohols and unsaturated carboxylic acids.

Specific examples of the monohydric alcohols described above include formula I; 2-
Methoxyethyl alcohol, 2-methoxypropyl alcohol, 3-methoxypropyl alcohol, 4-methoxybutyl alcohol, 2-ethoxyethyl alcohol,
3-ethoxypropyl alcohol, 2-propoxyethyl alcohol, formula ■; diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monoethyl ether, Formula ■: Dipropylene glycol monomethyl ether Propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diethylene glycol monoethyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether , tripropylene glycol monopropyl ether, etc.
I can give you 1.

Examples of unsaturated carboxylic acids include unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid, and unsaturated dicarboxylic acids such as maleic acid and itaconic acid. In particular,
Unsaturated monocarboxylic acids are preferably used, and unsaturated dicarboxylic acids are preferably used in combination.

On the other hand, hydrophilic unsaturated carboxylic acid ester monomers having a hydroxyl group in the molecule include 2-hydroxymethyl group,
Examples include esters of unsaturated carboxylic acids such as acrylic acid and methacrylic acid having hydroxyl group-containing groups such as 2-hydroxyethyl and 2-hydroxypropyl groups.

On the other hand, acrylic acid-based alkyl ester monomers that may be used as necessary include those having 3 to 1 carbon atoms, such as propyl, butyl, or 2-ethylhexyl groups.
Examples include esters of acrylic acid or methacrylic acid having 4, preferably 4 to 9 alkyl groups.

The proportion of monomers used in the copolymerization treatment is 3 to 35% by weight of acrylic acid monomer, preferably 5 to 33% by weight,
Appropriate amounts are 35 to 97% by weight of the hydrophilic unsaturated carboxylic acid ester monomer, preferably 40 to 85% by weight, and 0 to 50% by weight of the acrylic acid alkyl ester monomer, preferably 40% by weight or less. If the blending ratio of the acrylic acid monomer is less than 3% by weight, the water absorbing agent obtained will have poor water absorption ability, and if it exceeds 35% by weight, it will be difficult to obtain a copolymer that can form an elastic film. . In addition, if the blending ratio of the hydrophilic unsaturated carboxylic acid ester monomer is less than 35% by weight, it is necessary to balance the film-forming ability and water-absorbing ability of the water-absorbing agent obtained. The agent becomes poor in its water absorption capacity. On the other hand, if the blending ratio of the optional acrylic acid alkyl ester monomer exceeds 50% by weight, the resulting water absorbing agent will have poor water absorbing ability.

In addition, each of the monomers described above may be used alone, or two or more types may be used in combination. Further, the polymerization treatment can be carried out in a conventional manner when obtaining an acrylic acid polymer. Therefore, known polymerization initiators such as persulfates, organic peroxides, and redox initiators can be used.

The acrylic water absorbing agent of the present invention is obtained by neutralizing a copolymer made of the above monomers with an alkali metal base, an ammonia compound, or an amine. That is, the carboxyl group of the copolymer is neutralized with an alkali metal salt, ammonium salt, or amine salt. Thereby, it can be made to have excellent water absorption ability. The degree of neutralization of carboxyl groups is 20 mol% or more, preferably 40 mol%
Above all, 40 to 95 mol% is suitable. If the degree of neutralization is less than 20 mol%, the resulting acrylic water absorbing agent may have poor water absorbing ability. Note that even if the degree of neutralization is set to 95 mol % or more, no substantial difference in water absorption capacity is observed.

Examples of alkali metal bases used in the neutralization treatment include alkali metal salt forming substances such as sodium salts and potassium salts represented by sodium hydroxide and potassium hydroxide, and examples of ammonia compounds include ammonia and aqueous ammonia. Examples of the amine include monoamines and polyvalent amines such as monoethanolamine, jetanolamine, triethanolamine, hexamethylenediamine, and tetramethylenehexamine.

The acrylic water-absorbing agent of the present invention is made by subjecting the above-described copolymer to a crosslinking treatment so that it can maintain a water-absorbing state without completely dissolving in water. Crosslinking treatment is generally performed using a crosslinking agent. The appropriate amount of the crosslinking agent is 0.01 to 1 part by weight, preferably 0.03 to 0.7 part by weight, per 100 parts by weight of the copolymer. Its blending amount is 0.01
If it is less than 1 part by weight, the crosslinking density will be low and the amount of components dissolved in water will be large, resulting in poor water absorption ability. On the other hand, if it exceeds 1 part by weight, the crosslinking density becomes too high, resulting in swelling (and thus poor water absorption ability).

Known crosslinking agents are used, examples of which include triglycidyl isocyanurate, alicyclic glycidyl esters having a terminal 1,2-epoxy group, alicyclic glycidyl ethers, bisphenols, aliphatic, etc. Epoxy compounds represented by low molecular weight epoxy compounds such as melamine, methylolmelamine, polymethylolmelamine such as di(tri, tetra, penta, hegiza) methylolmelamine, alkylated methylolmelamine such as methylated methylolmelamine, etc. Examples include polyfunctional compounds such as melamine compounds represented by melamine derivatives. Among these, epoxy compounds having two or more glycidyl groups in the molecule, polymethylolmelamine, alkylated methylolmelamine, and the like are preferably used.

Note that the crosslinking treatment can be sufficiently carried out by heating when drying the copolymer solution.

The acrylic water absorbing agent of the present invention itself has film-forming ability, so for example, a neutralizing agent and a crosslinking agent are added to the reaction solution from which the copolymer is obtained, and this is applied onto a liner, conveyor, etc. A film of uniform thickness can be obtained by a conventional method such as evaporating the solvent. The obtained film generally has excellent transparency, and when it contains an acrylic acid alkyl ester component, it has particularly excellent elasticity.

The acrylic water absorbing agent of the present invention can be applied to paper, nonwoven fabric, synthetic resin,
It can be applied to a supporting base material such as metal or wood to form a laminate sheet or the like. Alternatively, an impregnated sheet can be obtained by impregnating and adhering it to the structure of a porous material such as a nonwoven fabric or a resin foam.

In this case, a water-absorbing sheet with a large surface area and a high water absorption rate can be obtained.

Effects of the Invention The acrylic water-absorbing agent of the present invention has excellent film-forming ability, and can be formed into a good film even by solution coating.

As a result, it is possible to obtain a water-absorbing film made of the water-absorbing agent itself, and it can also be used as a laminating agent, coating agent, impregnating agent, spraying agent, etc., and can be applied to various uses as a water-absorbing treatment agent. Can be done.

Examples Example 1 20 parts of acrylic acid (parts by weight, the same applies below), 140 parts of 2-methoxyethyl acrylate, 40 parts of 2-ethylhexyl acrylate, 0.6 parts of benzoyl peroxide, and 444 parts of toluene. was polymerized in a 1e capacity flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas blowing nozzle at 59-62° C. for 12 hours under a nitrogen stream. The viscosity of the obtained reaction solution was 1120 boise (B-type rotational viscometer,
Rotor No., 6.4 rpm.

30°C).

Next, 114.5 parts of isopropyl alcohol was added to the reaction solution, and then 14 parts of potassium hydroxide (00 g
An aqueous solution containing 1-0.03 parts of triglycidyl isocyanurate was gradually added dropwise to 100 parts of the reaction solution, and the resulting solution was placed on release paper. A water-absorbing film with a thickness of about 50 μm was obtained by coating the film on the water and drying it.

Example 2 60 parts of acrylic acid and 1 part of 2-ethoxyethyl acrylate
00 parts of butyl acrylate, 40 parts of hendiyl peroxide, 240 parts of toluene, and 60 parts of isopropyl alcohol were polymerized in the same manner as above, and the viscosity was 365 poise (as measured by a B-type rotational viscometer). , rotor No., 5.4
A reaction solution with rpI of 11 and 30° C. was obtained.

Next, 37 parts of isopropyl alcohol was added to 100 parts of the reaction solution.
After adding 5 parts and 25 parts of water, an aqueous solution of 5.33 parts of sodium hydroxide (0.8 equivalent to carboxyl group) dissolved in 20 parts of water was gradually added dropwise, and then 0.024 parts of triglycidyl isocyanurate was added. A water-absorbing film with a thickness of about 5 hm was obtained by adding a 1% by weight aqueous solution containing 1% by weight, coating the resulting solution on a release paper, and drying it.

Example 3 Polymerization was carried out in the same manner as above using 30 parts of methacrylic acid, 140 parts of 2-hydroxyethyl acrylate, 30 parts of isobutyl acrylate, 1 part of benzoyl peroxide, 210 parts of toluene, and 90 parts of methyl alcohol. processed and the viscosity is 6
50 Boise (B type rotational viscometer, rotor No., 6.4r
pm, 30°C) was obtained.

Next, 37.5 parts of methyl alcohol and 25 parts of water were added to 100 parts of the reaction solution, and then 2 parts of sodium hydroxide was added to 5 parts of water.
．． An aqueous solution containing 23 parts (0.8 equivalents to carboxyl groups) of ethylene glycol diglycidyl ether was gradually added dropwise, and then 0.04 part of ethylene glycol diglycidyl ether was added, the resulting solution was coated on release paper, and this was dried. Approximately 50μ thick
A water-absorbing film of m was obtained.

Example 4 A water-absorbing film was obtained in the same manner as in Example 1, except that a solution prepared by dissolving 9.33 parts of potassium hydroxide (0.6 equivalents to carboxyl groups) in 20 parts of water was used.

Example 5 A water-absorbing film was obtained in the same manner as in Example 1, except that a solution prepared by dissolving 6.22 parts of potassium hydroxide (0.4 equivalents to carboxyl groups) in 13.3 parts of water was used.

Example 6 A water-absorbing film was obtained in the same manner as in Example 1, except that a solution prepared by dissolving 3.11 parts of potassium hydroxide (0.2 equivalents to carboxyl groups) in 6.66 parts of water was used.

Example 7 A solution prepared by dissolving 12.44 parts of potassium hydroxide (0.8 equivalents to carboxyl groups) in 26.7 parts of water was used, and glycerin polyglycidyl ether o, tss part was used instead of triglycidyl isocyanurate. A water-absorbing film was obtained in the same manner as in Example 1, except that .

Example 8 The amount of glycerin polyglycidyl ether used was 0.03
A water-absorbing film was obtained in the same manner as in Example 7, except that the amount was 1 part.

Example 9 The amount of glycerin polyglycidyl ether used was 0.01
A water-absorbing film was obtained in accordance with Example 7 except that the amount was 55 parts.

Example 10 After adding 37.5 parts of isopropyl alcohol and 25 parts of water to 100 parts of the reaction solution obtained in Example 2, 13.5 parts of triethanolamine (0.8 equivalents to carboxyl group) and methyl etherification were added. 0.024 part of methylolmelamine was added, and the resulting solution was coated on a release paper and dried to obtain a water-absorbing film with a thickness of about 50 μm.

Example 11 Same as Example 1 except that the amount of acrylic acid used was 25 parts, the amount of 2-methoxyethyl acrylate was 175 parts, methanol was used instead of toluene, and 2-ethylhexyl acrylate was not used. A water absorbent film with a thickness of about 5 hm was obtained in the same manner.

All of the water-absorbing films obtained in the above examples were transparent without defects such as holes, and had excellent flatness without wavy irregularities. Moreover, the thickness was almost uniform. Furthermore, it did not break even when bent (especially those obtained in Examples 1 to IO had excellent elasticity).

Approximately 1 g (dry product) of the water absorbent films obtained in Evaluation Test Examples 1 to 11
was immersed in 3000 g of distilled water, left at room temperature for about 12 hours, filtered through a 200-mesh filter cloth, measured the weight of the remaining gel, and calculated the weight per 1 g of water-absorbent film. This value was converted into water absorption capacity.

The results are shown below.

Example water absorption capacity

Claims (1)

[Scope of Claims] 1. Consisting of an acrylic copolymer containing an acrylic acid monomer and a hydrophilic unsaturated carboxylic acid ester monomer, the carboxyl group of the copolymer is an alkali metal salt, An acrylic water absorbing agent that forms an ammonium salt or an amine salt and is crosslinked. 2. The water absorbing agent according to claim 1, wherein the acrylic acid monomer is acrylic acid or methacrylic acid. 3. The water absorbing agent according to claim 1, wherein the hydrophilic unsaturated carboxylic acid ester monomer has an alkoxy ether bond or a hydroxyl group. 4. The water absorbing agent according to claim 1, wherein the acrylic copolymer also contains an acrylic acid alkyl ester monomer as a copolymerization component. 6. The water absorbing agent according to claim 1, wherein 20 mol% or more of the carboxyl groups are in the form of a salt. 7. The water absorbing agent according to claim 1, which is formed into a film, a laminate film, or an impregnated sheet. 8. A monomer consisting of a blending ratio of 3 to 35% by weight of an acrylic acid monomer, 35 to 97% by weight of a hydrophilic unsaturated carboxylic acid ester monomer, and 0 to 50% by weight of an acrylic acid alkyl ester monomer. A method for producing an acrylic water absorbing agent, which comprises neutralizing a copolymer obtained by polymerizing a polymer with an alkali metal base, an ammonia compound, or an amine, and crosslinking the copolymer with a crosslinking agent. 9. 0.01 to 1 crosslinking agent per 100 parts by weight of copolymer
9. A method according to claim 8, using parts by weight. 10. The method according to claim 8, wherein the crosslinking agent is an epoxy compound having two or more glycidyl groups in the molecule, polymethylolmelamine, or alkylated methylolmelamine.