JPH0623218B2 - Super absorbent resin manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a highly water-absorbent resin.

Conventionally, highly water-absorbent resins have been widely used in fields such as disposable diapers and sanitary napkins. It is also used as a contact lens and a medium for microorganisms and plants.

2. Description of the Related Art Conventionally, this type of highly water-absorbent resin has been produced by carrying out a water-in-oil type reverse phase suspension polymerization of an unsaturated carboxylic acid such as acrylic acid or methacrylic acid in the presence of a crosslinking agent. It was

As examples thereof, those disclosed in, for example, JP-A-57-94011 and JP-A-59-62665 are known.

In these methods, an unsaturated carboxylic acid monomer such as (meth) acrylic acid and a crosslinking agent are dissolved in water, the aqueous solution is suspended in an organic solvent, and the reverse phase suspension polymerization reaction is performed in the aqueous phase. It was awakening.

Problems to be Solved by the Invention However, in this method, since the crosslinking agent is contained in the aqueous phase, the entire polymer in the aqueous phase is uniformly crosslinked. As a result, the strength of the gel becomes low, and if the degree of cross-linking is increased, the water absorption capacity will decrease and the water absorption rate will also decrease.

Further, in the method described in JP-A-57-94011, since a carboxyl group-containing polymer having an affinity for an organic solvent is used as the dispersant, the dispersant is transferred to the organic solvent. Since the unsaturated carboxylic acid is partially dissolved therein, a part of the reaction may proceed in the organic solvent and the gelled product may adhere to the inner surface of the reaction vessel.

The present invention has been made in view of the above circumstances, is a method for producing a highly water-absorbent resin having a high gel strength and a large water absorption capacity and a high water absorption rate, and further the reaction proceeds in the aqueous phase. However, it is an object of the present invention to provide a method for producing a highly water-absorbent resin in which gel does not adhere to a reaction container.

Means for Solving the Problems The present invention provides a method for producing a highly water-absorbent resin, which comprises polymerizing acrylic acid and / or an alkali metal acrylate by a water-in-oil type reverse phase suspension polymerization method. 2-
Hydroxyethyl or 2-hydroxyethyl methacrylate, acrylic acid or methacrylic acid and 4 to 18 carbon atoms
With an ester of an alkyl alcohol of, a copolymer is used as a dispersant, and an ester of acrylic acid or methacrylic acid containing glycidyl methacrylate or a hydroxyl group is added to the solvent phase in the reverse phase suspension polymerization. It is a feature.

The main component of the resin obtained in the present invention is polyacrylic acid or its alkali metal salt obtained by polymerizing acrylic acid and / or an alkali metal salt of acrylic acid.

The alkali metal is sodium or potassium.

Then, the acrylic acid and / or the alkali metal acrylate is polymerized in the water phase by a water-in-oil type reverse phase suspension polymerization method.

In the present invention, as a dispersant, a copolymer of 2-hydroxyethyl acrylate or 2-hydroxymethyl methacrylate and an ester of acrylic acid or methacrylic acid and an alkyl alcohol having 4 to 18 carbon atoms is used. , Used as a hydroxyl group-containing polymer.

In the present invention, a crosslinkable monomer is used. This crosslinkable monomer is a monomer having two or more functional groups capable of reacting with the carboxyl group in the polymer, such as glycidyl methacrylate or a hydroxyl group-containing (meth) acrylic acid ester. Can be mentioned. Furthermore, examples of the hydroxyl group-containing (meth) acrylic acid ester include polyethylene glycol mono (meth) acrylic acid.

Then, this crosslinkable monomer is added to the solvent phase in the inverse suspension polymerization.

Action When the acrylic acid and / or the alkali metal acrylate is polymerized according to the present invention, the action of the dispersant causes the acrylic acid and / or the alkali metal acrylate to be confined in the aqueous phase without migration to the organic solvent. In addition, the gel can be efficiently polymerized without the gel sticking to the inner surface of the reaction vessel.

Since the crosslinkable monomer is added to the organic solvent phase, the crosslinkable monomer acts only on the surface of the polymer produced in the aqueous phase to crosslink, and the degree of internal crosslinking is low. Becomes

EFFECTS OF THE INVENTION Therefore, according to the present invention, only the surface of the gel particle is crosslinked and the degree of crosslinking inside is low, so that the gel has high strength and the inside can contain a sufficiently large amount of water. Therefore, the highly water-absorbent resin obtained by the present invention has a large water absorption capacity,
The water absorption rate becomes faster.

In addition, since the gel does not adhere to the reaction vessel during the polymerization reaction, the yield is high and the operation is easy.

Example 1 210 g of toluene in a separable flask having a capacity of 500 ml.
, 2-hydroxyethyl methacrylate 45 g, butyl acrylate 2 while heating under toluene reflux conditions
5 g, lauryl methacrylate 70 g, and tertiary butyl peroxyacetate 1.5 g as a polymerization initiator
The mixture obtained by mixing is added dropwise over 2 hours. After the dropping was completed, the polymerization was continued for another 3 hours to obtain a hydroxyl group-containing polymer having a solid content of 40%, a hydroxyl value of 138 and a viscosity of 2100 cps.

Next, in a separable flask having a volume of 1, 348 g of cyclohexane and 7.2 g of the hydroxyl group-containing polymer (solid content 2.88 g) polymerized in the above step are charged and heated to 60 ° C. Next, 188.5 g of a 40% sodium acrylate aqueous solution, 14.5 g of acrylic acid and 34 g of distilled water were mixed into this flask, and 0.2 g of potassium persulfate was further added.
And the dissolved solution is added. Further, a solution prepared by dissolving 0.04 g of glycidyl methacrylate in 6 g of cyclohexane was added, and polymerization was carried out at 60 ° C. for 3 hours.

After completion of the reaction, the polymer particles were separated by passing and vacuum dried at 70 ° C. to obtain a dry fine particle gel.

Example 2 In a toluene in the same separable flask as in Example 1, 26 g of 2-hydroxyethyl acrylate, 21 g of ethyl methacrylate, 40 g of lauryl methacrylate, 53 g of stearyl methacrylate and 53 g of tertiary as a polymerization initiator were added. A mixture obtained by mixing 2 g of butyl peroxyacetate was added dropwise over 2 hours, and then polymerized in the same manner as in the example to obtain a solid content of 40%, a hydroxyl value of 89, and a viscosity of 950 cp.
A hydroxyl group-containing polymer of s was obtained.

Next, in a separable flask having a volume of 1, 348 g of cyclohexane and 7.2 g of the hydroxyl group-containing polymer (solid content 2.88 g) polymerized in the above step are charged and heated to 60 ° C. Next, 188.5 g of a 40% sodium acrylate aqueous solution, 14.5 g of acrylic acid and 22 g of distilled water were mixed into this flask, and 0.2 g of potassium persulfate was further added.
And the dissolved solution is added. There, polyethylene glycol methacrylate (PEG # 200) 0.14
What was dissolved in 6 g of cyclohexane was added, and 60
Polymerization was carried out at ℃ for 3 hours.

After completion of the reaction, the polymer particles were separated by passing and vacuum dried at 70 ° C. to obtain a dry fine particle gel.

Comparative Example 1 In a separable flask having a volume of 1, cyclohexane 34 was added.
Charge 8g and sorbitan monostearate 4g, 6
Heat to 0 ° C. There, 188.5 g of 40% sodium acrylate aqueous solution, acrylic acid 14.5 g and distilled water 34
g, mixed with 0.06 g of ethylene dimethacrylate as a crosslinking agent, and further added with 0.2 g of potassium persulfate.
Was added with stirring, and the polymerization was continued at 60 ° C. for 3 hours.

After completion of the reaction, the polymer particles were separated by passing and vacuum dried at 70 ° C. to obtain dry fine particle gel.

Comparative Example 2 As a cross-linking agent in Comparative Example 1, the same procedure as in Comparative Example 1 was carried out except that 0.04 g of methylenebisacrylamide was added instead of ethylene dimethacrylate, to obtain a dry fine particle gel.

Regarding the resins obtained in Test Examples 1 and 2 and Comparative Examples 1 and 2, the water absorption capacity for pure water and 0.9% saline solution, and
The water absorption rate by the suction method for 0.9% saline was measured.

Test results The results of the test were as follows.

Claims (1)

[Claims] 1. A method for producing a highly water-absorbent resin, which comprises polymerizing acrylic acid and / or an alkali metal acrylate by a water-in-oil type reverse phase suspension polymerization method, comprising: 2-hydroxyethyl acrylate or methacrylic acid- A copolymer of 2-hydroxyethyl and an ester of acrylic acid or methacrylic acid and an alkyl alcohol having 4 to 18 carbon atoms is used as a dispersant, and glycidyl methacrylate or a hydroxyl-containing acrylic acid or methacrylic acid is used. The ester
A method for producing a highly water-absorbent resin, which comprises adding to a solvent phase in the reverse phase suspension polymerization