JPH062769B2 - Method for producing super absorbent polymer with excellent salt resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a highly water-absorbent resin excellent in salt resistance capable of highly absorbing an electrolyte solution and stably retaining the absorbed electrolyte solution. It is about law. More specifically, the present invention relates to a method for producing a bead-like superabsorbent resin which can rapidly absorb an electrolyte solution regardless of the type and concentration of the electrolyte and can retain these absorbents without being exposed from the resin by external pressure.

[Conventional technology]

Conventionally, paper, pulp, sponge, etc. have been used in the fields of sanitary materials (sanitary napkins, disposable diapers) and agriculture and forestry as water-absorbing or water-retaining materials, but these materials also have low water-absorbing ability and are once absorbed. A large part of the water is easily squeezed out by the external pressure.

Therefore, various developments have been made on superabsorbent resins capable of absorbing and retaining a large amount of water with a slight weight and used as sanitary materials. These resins include starch graft polymers (Japanese Patent Publication No. 53-46199), cross-linked polyacrylates (Japanese Patent Publication No. 54-30710), and the like, and the present inventors have proposed a further improved water absorbing material. (JP-A-57-158210,
JP-A-59-62665).

[Problems to be solved by the invention]

However, since the above super absorbent polymer is an anionic polymer electrolyte, even if it exhibits a high water absorption capacity for a low concentration electrolyte solution of 1% by weight or less or distilled water, an electrolyte solution of 1% by weight or more is used. Has a major drawback that the water absorption is significantly reduced. In the fields of sanitary napkins, which are the main applications of superabsorbent polymers, sanitary materials such as paper diapers, and agricultural and forestry fields such as soil water retention agents, most of the target absorbing liquids are electrolyte solutions, and many types of salts ( Monovalent and polyvalent salts), and their salt concentrations are various. Therefore, it has been desired to develop a highly water-absorbent resin that can be preferably used under these circumstances, that is, a highly water-absorbent resin that has excellent salt resistance, water absorption rate, and gel strength.

So far, an amphoteric type resin has been developed for the purpose of absorbing an electrolyte solution, and the technical content thereof has been disclosed in Japanese Patent Laid-Open No. 154710/1983, but aqueous solution polymerization is adopted therein. However, there is a drawback in that it is difficult to remove the heat of polymerization and to stir the solution due to the increase in viscosity during the polymerization, and the physical properties of the obtained resin are likely to be non-uniform. further,
The polymerization product becomes a rubbery substance containing water and requires complicated steps such as subsequent crushing and drying, and fine powder is easily generated in the product due to crushing, so the so-called "Mamako"
It also has a drawback that the water absorption ability is lowered due to a phenomenon.

[Means for solving problems]

The present inventor, as a result of intensive research to address the above problems, found a highly water-absorbent resin having excellent absorption ability in a wide concentration range regardless of the type of electrolyte, with respect to an electrolyte solution, and completed the present invention. did.

That is, in the present invention, the acidic vinyl monomer (A component) and the basic vinyl monomer (B component) are used in a molar ratio A: B = 2.
A monomer aqueous solution was prepared so as to have a composition ratio of 0:80 to 80:20, and this was dispersed and suspended in a hydrophobic solvent in the presence of a dispersant, and a water-soluble radical polymerization initiator was added thereto. The monomer is added and copolymerized, and then the water content of the resin is adjusted to 10 to 35% by weight, and two or more functional groups capable of reacting with the acidic group or basic group in the copolymer are added. It is intended to provide a method for producing a beaded superabsorbent polymer having excellent salt resistance, which is characterized in that it is crosslinked with a crosslinking agent contained therein.

The acidic vinyl monomer according to the present invention is a compound having an acidic group such as a carboxyl group and a sulfonic acid group in one molecule and a polymerizable vinyl group, and examples thereof include acrylic acid, methacrylic acid, and itacone. Acid, maleic anhydride, 2-
Examples thereof include acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, acrylicsulfonic acid, methallylsulfonic acid, and the like.

The basic vinyl monomer according to the present invention is a compound having in one molecule a basic group such as a primary amino group, a secondary amino group and a tertiary amino group, and a polymerizable vinyl group. , For example, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, dimethylaminopropyl acrylamide, 2-vinylpyridine, 4-vinylpyridine, dimethylallylamine, diallylmethylamine, etc. I can name it.

In the present invention, the kind of the monomer is not limited, and a combination of three or more kinds of the above monomers may be used. The molar ratio of the acidic vinyl monomer (A) and the basic vinyl monomer (B) may be A: B depending on the conditions of the object to be absorbed.
= 20: 80 to 80:20, but considering physical properties such as absorption capacity, A: B = 30: 70 to 70:
A range of 30 is preferred. Furthermore, a resin obtained by copolymerizing a nonionic water-soluble vinyl monomer such as 2-hydroxyethyl (meth) acrylate or acrylamide within a range that does not deteriorate the performance of the resin can also be used in the method of the present invention. Further, when a copolymer is produced using the above-mentioned monomer, addition of a very small amount of crosslinking agent does not prevent the effect of the present invention.

As a method of obtaining a resin having excellent water absorption properties by copolymerizing the above monomers, in the present invention, since it is required to control the water content in the water-containing resin fat, usually,
After synthesizing the resin, a dehydration step is required. Therefore, when the above monomers are copolymerized, it is preferable to use W / O suspension polymerization from the viewpoint of workability afterwards. W / O
As a protective colloid (dispersant) for suspension polymerization,
Sorbitan resin acid esters such as sorbitan monostearate and sorbitan monolaurate, and cellulose ethers such as ethyl cellulose and benzyl cellulose, cellulose acetates such as cellulose acetate and cellulose butyrate, maleated polybutadiene, maleated polyethylene, and maleated α-olefin. And the like, and any one or more of these may be used. A polymer dispersant that gives a large particle size is desirable in view of the particle size of the obtained polymer and measures against dust. The hydrophobic solvent used at that time is an aliphatic hydrocarbon such as hexane, heptane, or octane, an alicyclic hydrocarbon such as cyclohexane, methylcyclohexane, or decalin, an aromatic hydrocarbon such as benzene, toluene, xylene, or chlorobenzene. , Halogenated hydrocarbons such as brombenzene and dichlorobenzene.

The concentration of the aqueous monomer solution including the acidic vinyl monomer, the basic vinyl monomer, and the nonionic water-soluble vinyl monomer can be varied within a wide range, and is generally 30 to 7
It is 0% by weight. The upper limit depends particularly on the solubility when both monomers are mixed, but the lower limit is generally not lower than the above value for economic reasons. A water-soluble initiator such as persulfate is used as the radical polymerization initiator. Although the amount of the radical polymerization initiator used varies depending on the type of the monomer, it is generally preferably about 0.01 to 5% by weight based on all the monomers.

Since suspension polymerization has a large heat removal effect, a high-molecular-weight resin can be easily obtained, and a bead-shaped resin can be obtained, and fine powder is less likely to be generated, so dust countermeasures are unnecessary,
In addition, it is possible to obtain a resin having uniform performance among particles, which is a preferable method in terms of product form as a highly water-absorbent resin.

In the method of the present invention, a particularly important requirement is that the water content in the resin hydrate when the crosslinking reaction is carried out by adding the crosslinking agent is within the range of 10 to 36% by weight (the total amount of the resin hydrate). To control. More preferably, 15
Control in the range of ~ 30% by weight. When the water content in the resin is out of the above range, the water absorption amount and / or the water absorption speed is inferior, and the remarkable effect of the present invention cannot be obtained. In the present invention, an acidic vinyl monomer and a basic vinyl monomer aqueous solution are used to concentrate the resin obtained by the W / O suspension polymerization method to control the water content within the above range. You can achieve the effect of
A highly water-absorbent resin having excellent water absorption amount, water absorption speed, gel strength, and excellent salt resistance can be obtained.

The crosslinking agent used in the present invention may be any compound as long as it is a compound having two or more functional groups capable of reacting with an acidic group or a basic group. Examples of such cross-linking agents include polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycerin triglycidyl ether, epichlorohydrin, haloepoxy compounds such as α-methylchlorohydrin, glutaraldehyde, and polyglycol such as glyoxal. Aldehydes, etc. can be mentioned.

The addition amount of the cross-linking agent varies depending on the kind of the cross-linking agent and the kind of the polymer, but is usually 0.01 to 5.0% by weight with respect to the polymer in an appropriate range. If the addition amount of the cross-linking agent is less than 0.01% by weight, the effect of addition is not sufficiently exhibited, and when water is absorbed, the gel becomes semi-dissolved. On the other hand, when the amount is more than 5.0% by weight, the crosslink density becomes high and the water absorption amount is lowered, which is not intended by the present invention.

The fat obtained by the present invention has a high water absorption capacity for various electrolyte solutions in a wide concentration range. Especially when compared with conventional anionic superabsorbent resins, for example, MgSO ₄ , CaC
It has a remarkably high water absorption capacity for polyvalent electrolytes having a valence of 2 or more such as l ₂ and Al ₃ SO ₄ . Therefore, it can be used as a solidifying agent for water-containing substances containing high concentrations of electrolytes such as industrial waste and sewage, which were difficult to apply with conventional anion-type superabsorbent resins, including the fields of sanitary materials and agriculture and forestry. Widely available.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

The water absorption amount in the following examples and comparative examples is a value obtained by the following operation. That is, about 1 g of resin is dispersed in a large excess of an absorbing electrolyte solution, sufficiently swelled, and then passed through a wire mesh of 80 mesh to obtain the swelled resin weight.
It is a value obtained by measuring (W) and dividing this value by the initial resin weight (Wo).

That is, the water absorption amount (g / g) = W / Wo. The water absorption rate was represented by the amount of electrolyte solution absorbed by 0.3 g of resin in 10 minutes.

Examples 1 to 3 A 500 ml four-necked round bottom flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a nitrogen gas introducing tube was charged with 230 ml of cyclohexane and 1.0 g of still cellulose N-200 (manufactured by Herquiles) 75 The temperature was raised to ° C. Separately, dissolve 12.0 g of acrylic acid and 26.2 g of dimethylaminoethyl methacrylate in 70 g of distilled water in an Erlenmeyer flask.
% 5% hydrochloric acid was added. Further, 0.02 g of ammonium persulfate was added as a polymerization initiator and uniformly dissolved, and the monomer aqueous solution was added to the above 4-necked flask under a nitrogen atmosphere to 1.
After dripping for 5 hours to polymerize, at 70-75 ℃
It was left for 0.5 hour to complete the polymerization. After this, the water content in the resin suspended in cyclohexane was 35% (Example 1) and 25% by azeotropic dehydration (cyclohexane was refluxed).
(Example 2) and 20% (Example 3) were controlled. Then, each of them was mixed with 0.02 g of ethylene glycol diglycidyl ether in 1 ml of water to prepare an aqueous solution.
After adding at 3 ° C. and maintaining at this temperature for 2 hours, cyclohexane was removed, and the resin was dried under reduced pressure at 80 to 100 ° C. to obtain a super absorbent polymer having a center particle size of 100 to 350 μm.

Example 4 Polymerization was carried out according to Example 1. However, the same procedure as in Example 1 was conducted except that acrylic acid 20 g, dimethylaminoethyl methacrylate 20 g, and 35% hydrochloric acid 2 g were used in the monomer portion, and the water content of the resin was 22% by azeotropic dehydration after the completion of the polymerization. A highly water-absorbent resin having a diameter of 100 to 350 μm was obtained.

Example 5 Polymerization was carried out according to Example-1. However, 0.05 g of V-50 (manufactured by Wako Pure Chemical Industries; 2,2'-azobis (2-amidinopropane) dihydrochloride) was used as an initiator, and N,
0.003 g of N'-methylenebisacrylamide was added.
After polymerization, the water content in the resin was controlled to 25% by azeotropic dehydration, and then an aqueous solution prepared by dissolving 0.15 g of polyethylene glycol diglycidyl ether (n = 9) in 1 ml of water was added at 73 ° C., and this temperature was maintained for 3 hours. After standing, cyclohexane was removed, and the resin was dried under reduced pressure at 80 to 100 ° C. to obtain a highly water-absorbent resin having a center particle size of 100 to 350 μm.

Example 6 Polymerization was carried out according to Example 1. However, in the monomer portion, 11.5 g of vinyl sulfonic acid was used instead of acrylic acid, and 20 g of diethylaminoethyl methacrylate was used instead of dimethylaminoethyl methacrylate. After completion of the polymerization, the water content of the resin was adjusted to 25% by azeotropic dehydration. The same operation as above was performed to obtain a highly water-absorbent resin having a central particle diameter of 100 to 350 μm.

Example 7 Polymerization was carried out according to Example 1. However, in the monomer part, 27 g of 2-acrylamido-2-methylpropanesulfonic acid was used in place of acrylic acid, and 15 g of 4-vinylpyridine was used in place of dimethylaminoethyl methacrylate. After the completion of polymerization, the water content of the resin was changed to 20 by azeotropic dehydration.
%, The same operation as in Example 1 is performed, and the central particle size is 1
A highly water-absorbent resin having a particle size of 00 to 350 μm was obtained.

Comparative Example 1 Polymerization was carried out according to Example-1. However, 0.02 g of ethylene glycol diglycidyl ether was added to the aqueous monomer solution to carry out crosslinking simultaneously with polymerization. After completion of the polymerization, cyclohexane was removed, and the resin was dried under reduced pressure at 80 ° C to 100 ° C to obtain a highly water-absorbent resin having a center particle size of 100 to 350 µm.

Comparative Example 2 Polymerization was carried out according to Example-1. However, an aqueous solution prepared by dissolving 0.03 g of ethylene glycol diglycidyl ether in 1 ml of water was added after controlling the water content in the resin to 45% by azeotropic dehydration, and the mixture was kept at 73 ° C. for 2 hours. After completion of the cross-linking reaction, cyclohexane was removed and the resin was
Dry under reduced pressure at 0 ° C to 100 ° C to obtain a median particle size of 100 to 3
A highly water-absorbent resin of 50 μm was obtained.

Comparative Example 3 12.0 g of acrylic acid and 26.2 g of dimethylaminoethyl methacrylate were dissolved in 70 g of distilled water, and 5 g of 35% hydrochloric acid was added. Furthermore, N, N-methylenebisacrylamide was added to 0.0
5 g was added and uniformly dissolved. This aqueous solution was transferred to a 500 ml separable flask equipped with a stirrer, a reflux condenser and a nitrogen gas inlet tube, and 0.02 g of ammonium persulfate was added as an initiator under a nitrogen atmosphere, and the temperature was raised and kept at 70 ° C. As the polymerization proceeds, the system thickens and becomes impossible to stir. When it becomes impossible to stir, stop stirring and
The mixture was allowed to stand at ℃ for 2 hours and then cooled to obtain a rubbery hydropolymer. This was dried at 80 ° C. under reduced pressure and pulverized to obtain a powdery resin.

Comparative Example 4 The water absorption amount and the water absorption speed were compared using a commercially available water absorbent resin and a crosslinked product of sodium polyacrylate (trade name: AQUAKEEP 10SH-P; manufactured by Iron Manufacturing Chemical).

Water absorption amount, water absorption rate of various electrolyte solutions of each superabsorbent resin obtained in Examples 1 to 7 and Comparative Examples 1 to 4, and 100
Table 1 shows the results of the presence or absence of collapse of the absorbed resin under the pressure of g / cm ² .

From Table 1, it is clear how the resin obtained according to the present invention has excellent salt resistance and excellent water absorption properties.

(Effect of the invention) Generally, the physical properties required for a super absorbent resin include 1) water absorption amount, 2) water absorption speed, 3) gel strength, and 4) shape, and it is necessary to satisfy all these physical properties. It can be said to be an excellent super absorbent polymer.

As shown concretely in Examples and Comparative Examples, the resin obtained by the present invention has a high water absorption capacity for various electrolyte solutions in a wide concentration range. In particular, when compared with conventional anionic superabsorbent resins, for example, MgSO ₄ , CaC
It has a remarkably high water absorption capacity for polyvalent electrolytes having a valence of 2 or more such as l ₂ and Al ₃ SO ₄ . Therefore, even in the field of hygiene materials, the field of agriculture and forestry, it is difficult to deal with conventional anion-type highly water-absorbent resins, and even for water-containing substances containing high-concentration electrolytes such as industrial waste and sewage, It can be used widely as a solidifying agent and the like.

Claims (4)

[Claims] 1. An acidic vinyl monomer (component A) and a basic vinyl monomer (component B) are used in a molar ratio A: B = 20: 80 to.
An aqueous monomer solution was prepared so that the composition ratio was 80:20, and this was dispersed in a hydrophobic solvent in the presence of a dispersant,
After suspending and adding a water-soluble radical polymerization initiator to this to copolymerize the monomers, the water content of the resin is reduced to 10%.
To 35% by weight, and beads having excellent salt resistance characterized by being crosslinked with a crosslinking agent having two or more functional groups capable of reacting with an acidic group or a basic group in the copolymer. For manufacturing a highly absorbent resin. 2. A group of acidic vinyl monomers consisting of acrylic acid, methacrylic acid, itaconic acid, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid and methallylsulfonic acid. The method for producing a highly water-absorbent resin according to claim 1, which is one kind or two or more kinds selected from the following. 3. The basic vinyl monomer is dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, dimethylaminopropyl acrylamide,
The method for producing a highly water-absorbent resin according to claim 1, which is one kind or two or more kinds selected from the group consisting of 2-vinylpyridine and 4-vinylpyridine. 4. A cross-linking agent having two or more functional groups capable of reacting with an acidic group or a basic group is polyglycidyl ether,
The method for producing a super absorbent polymer according to claim 1, which is a haloepoxy compound or a polyaldehyde.