JPH0487638A - Water absorbent and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a water absorbent excellent in the water absorption magnification, the water absorption speed and the strength of a gell by adding mono- epoxy compounds having hydroxyl group into the water absorptive resin having carboxyl group, thereby subjecting the resin to a cross-linking treatment. CONSTITUTION:Into the resin having carboxyl group and substantially insoluble in water but having swelling property by the absorption of water (e.g. acrylic acid-acrylic acid salt-based cross-linked polymer), an aqueous solution incorporating mono-epoxy compound having hydroxyl group is impregnated into the surface part of the water absorptive resin. Before the addition of the above- mentioned aqueous solution, by dispersing previously the water absorptive resin by using an organic solvent, homogeneous impregnation and faborable results are obtained. The water absorbent is obtained by the cross-linking treatment of impregnated resin (heat treatment of impregnated resin) by using cross-linking agent such as methylene bis(meth) acrylamide. By this method, the performance excellent in the water absorption magnification, the water absorption speed and the gell strength are exhibited and the absorbent without generating an undissolved lump of product is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a water absorbing agent with improved properties such as water absorption rate and gel strength, and a method for producing the same.

Water-absorbing agents made of polyacrylates and the like absorb several hundred times their own weight in water and have a high ability to absorb urine and blood, so they are used in sanitary napkins, disposable diapers, and the like.

[Prior Art] Various types of water absorbing agents have been known so far, but polyacrylate-based resins are the mainstream.

Water-absorbing agents are usually put into practical use in the form of powder, fibers, or film. The performance of water absorbing agents is evaluated by properties such as water absorption rate, water absorption capacity, and gel strength. Soft gels with high water absorption capacity have poor water absorption rate and gel strength, while hard gels with excellent water absorption rate and gel strength have poor water absorption rate and gel strength. There is a tendency for the water absorption capacity to be low.

A practical problem when using a water-absorbing resin powder having a carboxyl group as a water-absorbing agent is the formation of "mamako". When "mamako" is formed, the part of the resin powder that comes into contact with water absorbs water and swells, forming a lumpy gel, which prevents water from penetrating into the interior. Furthermore, even when looking only at powder particles, there is a tendency that the gel on the surface prevents water from penetrating into the interior, resulting in a decrease in water absorption rate. This phenomenon is remarkable in soft gels with high water absorption capacity.

In order to prevent the "mamako" phenomenon, a method has been proposed in which the surface portion of the resin particle is treated with a crosslinking agent to form a permeable hard gel as described below. The first method is to use a polyvalent epoxy compound as a crosslinking agent (Japanese Patent Publication No. 596696, Japanese Patent Publication No. 60-18
690, Japanese Patent Publication No. 61-48521), and a second method uses a polyhydric alcohol as a crosslinking agent (Japanese Patent Publication No. 1-17411, Japanese Patent Publication No. 17411/1982).
-180233) is known.

Problems to be Solved by the Invention C] Water-absorbing resin powders having carboxyl groups tend to cause "stickiness" when absorbing water, and also have poor water absorption capacity, water absorption rate,
Properties such as gel strength are not necessarily compatible, so secondary crosslinking (treatment of the surface of the resin with a crosslinking agent) as described above is essential.

The first method mentioned above is effective in preventing "stickiness" and improving the water absorption rate and gel strength, but it has the drawbacks of large variations in crosslinking density and a considerable decrease in water absorption capacity. was there.

On the other hand, the second method described above is not effective in improving water absorption capacity and gel strength, but has the disadvantage that the water absorption rate is not sufficient and the resin is exposed to high temperatures for a long time during crosslinking, resulting in significant deterioration of the resin. Ta.

[Means to solve the problem]

In order to solve the above problems, we investigated various crosslinking agents and crosslinking methods, and found that
The present invention was completed by discovering an improved water-absorbing agent and a method for producing the same.

That is, the present invention provides (1) a water-absorbing agent obtained by crosslinking the surface portion of a water-absorbing resin having a carboxyl group using a monoepoxy compound having a hydroxyl group; The present invention relates to a method for producing a water-absorbing agent, which comprises adding a monoepoxy compound having the following properties for crosslinking treatment.

The present invention will be explained in detail below.

Various types of water-absorbing resins having carboxyl groups can be used, and there are no particular limitations. Resins that have carboxyl groups and are substantially insoluble in water but have the ability to absorb water and swell. You can use either one. Preferred examples include polymers having a structural unit represented by H-CH2OOH, such as acrylic acid-acrylate crosslinked polymers and starch-based crosslinked polymers.
Examples include acrylic acid graft crosslinked polymers, starch-acrylonitrile graft polymer hydrolysates, and saponified vinyl acetate-acrylic acid ester copolymers.

Usually, 5 of the carboxyl groups contained in these polymers are
0 to 95% is in a neutralized state as an alkali metal salt.

Particularly preferable water-absorbing resins having carboxyl groups include acrylic acid 5 to 50 mol%, acrylic acid alkali metal salt 45 to 94 mol%, crosslinking agent 001 to 5 mol%, and other ethylenically unsaturated monomers θ to 10 mol % of polymer is mentioned. Examples of the alkali metal salts of acrylic acid include sodium salts and potassium salts of acrylic acid. Various known crosslinking agents can be used as the crosslinking agent, for example,
Methylene bis(meth)acrylamide, divinylbenzene, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin di(meth)acrylate, pentaerythritol tetra(meth)acrylate, di Examples include divinyl compounds and polyacrylate compounds such as pentaerythritol tri(meth)acrylate and dipentaerythritol hexa(meth)acrylate, as well as diglycidyl compounds and polyhydric alcohols. Examples of other optional ethylenically unsaturated monomers include methacrylic acid and its salts, (meth)acrylamide, (meth)acrylonitrile, and alkyl esters of (meth)acrylic acid.

Examples of monoepoxy compounds having a hydroxyl group include:
Glycidol, ethylene glycol monoglycidyl ether, propylene glycol monoglycidyl ether,
Glycerin monoglycidyl ether, trimethylolbromonomonoglycidyl ether, diethylene glycol monoglycidyl ether, polyethylene glycol monoglycidyl ether, polypropylene glycol/b
Monoglycidyl ether, p-xylylene glyco-) I
Examples include, but are not limited to, t-monoglycidyl ether and the like.

The amount of the monoepoxy compound used is usually 0.01 to 10% by weight, preferably 0.1 to 5% by weight based on the resin.

The monoepoxy compound having a hydroxyl group may be added as is, or may be added after being dissolved in water, an organic solvent, or a mixed solution of water and an organic solvent.

When adding a monoepoxy compound having a hydroxyl group, it is preferable to adopt a method of impregnating the surface of the water-absorbing resin having a carboxyl group with the monoepoxy compound having a hydroxyl group.

Examples of methods for impregnating the surface of a water-absorbing resin having a carboxyl group with a monoepoxy compound include spraying an aqueous solution containing a monoepoxy compound while stirring the water-absorbing resin powder, or soaking the resin powder in an organic solvent. Various methods can be adopted, such as adding an aqueous solution containing the monoepoxy compound after dispersion, or adding an organic solvent solution containing the epoxy compound to a water-absorbing resin containing, for example, 5 to 50% by weight of water. Not particularly limited. Alternatively, a method may be employed in which a monoepoxy compound having a hydroxyl group is added to a resin powder and mixed using a conventional mixer such as a V-type mixer, a screw-type mixer, a ribbon-type mixer, or the like. Among these methods, the method of impregnating the surface of the water-absorbing resin with a monoepoxy compound in the form of an aqueous solution containing the monoepoxy compound is particularly preferred.

If the water-absorbing resin is previously dispersed in an organic solvent before adding the aqueous solution containing the monoepoxy compound, uniform impregnation can be performed and favorable results can be obtained.

By appropriately selecting the amount of the aqueous solution of the monoepoxy compound or the amount of the organic solvent to be added, it is possible to impregnate mainly the surface portion of the water-absorbing resin with the monoepoxy compound or the aqueous solution containing the same.

Here, the surface portion means not only the outer surface of the resin but also the portion near the surface. As the organic solvent, methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, isopropyl ether, acetonitrile, etc. are used.

The organic solvent is usually used preferably in an amount of 1 to 50 parts by weight, particularly preferably 3 to 30 parts by weight, based on the weight of the water absorbent resin IN. As the aqueous solution containing the monoepoxy compound, an aqueous solution or a solution containing preferably 10% by weight or less of an organic solvent based on water is used.
It is preferably used in an amount of 3 to 50 parts by weight, particularly preferably 5 to 30 parts by weight.

By crosslinking the impregnated resin thus obtained, the water absorbing agent of the present invention whose surface portion is crosslinked mainly with a monoepoxy compound having hydroxyl groups can be obtained. The crosslinking treatment is usually performed by heating the impregnated resin.

By heating, the epoxy group in the monoepoxy compound reacts with the carboxyl group contained in the water-absorbing resin to form an ester bond, while the remaining hydroxyl group reacts with the carboxyl group of the water-absorbing resin by further heating. to form a crosslinked structure. At this time, the reaction between epoxy groups and carboxyl groups occurs by heating to 50°C or higher, and the reaction between hydroxyl groups and carboxyl groups occurs by heating to 100°C or higher. Therefore, in the present invention, it is sufficient to heat preferably at 100 to 250°C, particularly preferably at 150 to 200°C for 01 to 10 hours.

By using the method of the present invention, it is possible to easily produce a water-absorbing agent that has a good water-absorbing ability, a high water-absorbing rate, a non-sticky gel upon water absorption, and a high gel strength. The water-absorbing agent according to the present invention can be used as materials for sanitary materials such as disposable diapers and sanitary napkins, water-retaining agents for soil, water-stopping agents for civil engineering and construction, anti-condensing agents, poultices, poultices, desiccants, and moisture regulators. It is useful as

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Note that "parts" in Examples and Comparative Examples indicate "parts by weight."

Example 1 To 233 parts of a 43% aqueous solution of an acrylic monomer consisting of 75 parts of sodium acrylate, 24.7 parts of acrylic acid, and 0.09 parts of methylenebisacrylamide, 0.03 part of ammonium persulfate and 0.01 part of sodium bisulfite were added. was added and polymerized by standing at 30 to 100° C. for 5 hours in a nitrogen atmosphere to obtain a gel-like hydropolymer. This gel-like hydrous polymer
After drying in a hot air dryer at 170° C., it was sieved through an 18-mesh wire mesh to obtain a material that passed through the 18-mesh mesh (powder A).

To 40 parts of this powder A, 8 parts of methanol was added and dispersed, and a solution of 0.2 parts of ethylene glycol monoglycidyl ether dissolved in 4 parts of water was added and stirred. The resulting mixture was heated and dried in a hot air dryer at 170° C. for 40 minutes to obtain water absorbing agent E.

Comparative Example 1 To 40 parts of the powder A obtained in Example 1, 02 parts of ethylene glycol diglycidyl ether, 4 parts of water, and 8 parts of methanol were added.
The mixture was added with stirring and dried by heating at 170° C. for 40 minutes to obtain water absorbing agent X.

Example 2 4 parts of acetone was added to 40 parts of the powder A obtained in Example 1 and dispersed, and a solution of 0.1 part of glycidol dissolved in 4 parts of water was added and mixed. The resulting mixture was heated to 150
Water absorbing agent F was obtained by heating and drying for 50 minutes in a hot air dryer at .degree.

Comparative Example 2 08 parts of glycerin was added to 40 parts of the powder A obtained in Example 1,
A mixed solution of 08 parts of water and 08 parts of ethyl alcohol was added while stirring. This was heated and dried at 180°C for 30 minutes,
A water absorbing agent Y was obtained.

Example 3 300 parts of n-hexane was placed in a reactor, and 0.7 parts of sorbitan monostearate was dissolved therein. Next, an aqueous monomer solution obtained by dissolving 30 parts of acrylic acid in 40 parts of water, neutralizing it with 115 parts of caustic soda, and further dissolving 0.05 part of potassium persulfate was added and dispersed, and the mixture was dispersed under a nitrogen stream. The temperature was maintained at 65°C and polymerization was carried out for 5 hours.

After the polymerization was completed, powder B was obtained by drying under reduced pressure. 840 parts of powder was dispersed in 10 parts of tetrahydrofuran, a solution of 0.3 parts of glycerin monoglycidyl ether dissolved in 4 parts of water was added thereto, and the mixture was heated and dried at 1110°C for 30 minutes to obtain water absorbing agent G.
I got it.

Example 4 10 parts of ethanol was added to 840 parts of the powder obtained in Example 3 for dispersion, and a solution of 2 parts of polyethylene glycol monoglycidyl ether (molecular weight 450) dissolved in 3 parts of water was added and mixed. Then, water absorbent H was obtained by heating and drying at 190° C. for 10 minutes.

Example 5 To 840 parts of the powder obtained in Example 3, 1 part of dioxane Il was added and dispersed, a mixed solution of 04 parts of glycidol and 2 parts of water was added and mixed, and the mixture was heated and dried at 150°C for 50 minutes to absorb water. Formulation I was obtained.

Example 6 Polymerization was carried out according to Example 3. However, 1.9 parts of isobutylene-maleic anhydride copolymer (viscosity average molecular weight: 10.000) was used instead of sorbitan monostearate. After completion of polymerization, dry under reduced pressure to obtain powder C containing 15% by weight of water.
I got it. A mixed solution of 02 parts of ethylene glycol monoglycidyl ether and 5 parts of methanol was added to 40 parts of powder C, mixed well, and dried by heating at 160° C. for 40 minutes to obtain water absorbing agent J.

Example 7 Polymerization was carried out according to Example 6. However, before the completion of polymerization, 0.01 part of glycidol was added and dried under reduced pressure to obtain a powder. Add and disperse 10 parts of methanol to 40 parts of powder D,
A mixed solution of 0.2 parts of glycidol and 2 parts of water was added to this, mixed well, and dried by heating at 160° C. for 40 minutes to obtain water absorbing agent K.

Application example 1 Untreated powder A was added to the water absorbing agent E- obtained in Examples 1 to 7.
Table 1 shows the water absorption capacity, water absorption rate, gel strength, and presence or absence of "mamako" of the water absorbing agents X-Y obtained in -D and Comparative Examples 1 and 2.

Table 1 Example 8 Sodium acrylate 75m, acrylic acid 24.8m and polyethylene glycol diacrylate (molecular weight 3[
12) [40 of acrylic monomer consisting of 1.15 parts
% aqueous solution, 0.03 part of ammonium persulfate,
05 parts of 35% hydrogen peroxide and 0.0 parts of L-ascorbic acid
1 part was added and polymerized by standing at 20-10°C (1°C) in a nitrogen atmosphere to obtain a gel-like water-containing polymer. After drying this gel-like water-containing polymer in a hot air dryer at 180°C, it was dried with a 18-mesh wire mesh. It was sieved to obtain a material that passed through 18 meshes (powder L).

To 40 parts of this powder L, 4 parts of methanol was added and dispersed, and a solution of 0.16 parts of glycidol dissolved in 2 parts and 0 parts of water was added and stirred. The resulting mixture was heated to 180°C.
The mixture was heated and dried in a hot air dryer for 30 minutes to obtain a water absorbing agent N.

Example 9 To 233 parts of a 43% aqueous solution of acrylic monomers consisting of 75 parts of sodium acrylate, 249 parts of acrylic acid and 1.05 parts of dipentaerythritol triacrylate,
0.03 part of potassium persulfate, 11 parts of 35% hydrogen peroxide, and 0.01 part of L-ascorbic acid were added, and the mixture was polymerized by standing at 20 to IN°C in a nitrogen atmosphere to obtain a gel-like hydropolymer.

After drying this gel-like hydrous polymer in a hot air dryer at 150°C, it was sieved through an 18-mesh wire mesh, and the material passing through the 18-mesh mesh (
Powder M) was obtained.

8 parts of methanol was added to 8 parts of this powder M2O for dispersion, and a solution of 0.24 parts of glycidol dissolved in 2.0 parts of water was added and stirred. The resulting mixture, 15
It was heated and dried in a hot air dryer at 0° C. for 50 minutes to obtain water absorbing agent O.

In addition, in any of the above Examples and Comparative Examples, the monoepoxy compound having a hydroxyl group is impregnated on the surface of the water-absorbing resin when the monoepoxy compound having a hydroxyl group is added and before heating and drying. It was something that was done.

Application example 2 Water absorption capacity, water absorption rate, gel strength, and “mamako” of water absorbing agents N, ○, and untreated powder lily and M obtained in Examples 8 and 9
Table 2 shows the presence or absence of

Table 2 The water absorption capacity, water absorption rate, and gel strength were measured as follows.

Add 200g of 09% saline to 0.5g of water absorbing agent or powder, filter after 1 hour through a 200 mesh wire mesh, weigh the absorbed resin, and divide this by the weight before water absorption. Find the magnification.

○61 glass filter with diameter 7an and diameter 1 as water absorption rate measuring device
．． Connect test tubes with scales from four countries in a U shape. Spread 0.3 g of the water-absorbing agent or powder evenly on a glass filter, add artificial urine to the same water level, and measure the absorbed amount after 1 minute, 5 minutes, and 20 minutes by reading the drop in the water level. Artificial urine contains urea 1.9
4g, salt 0.80g, magnesium sulfate 0.11
g and 006 g of calcium chloride are dissolved in 97.09 g of pure water to make 100 g.

Weigh 2 g of water absorbing agent or powder into a 200 ml beaker, add 2 g of methanol, and then add 40 g of pure water and stir to form a water absorbing gel.

Then, place a cylindrical adapter with a diameter of 6 (1111) on top of the gel in the beaker, compress it with Tensilon, and measure the strength when the gel starts to flow.Gel strength is expressed as stress per unit area of the cylinder. .

Regarding "Mamako", 100 parts by weight of water was added to 1 part by weight of the water-absorbing agent powder, and the presence or absence of "Mamako" was examined.

"Effects of the Invention" The water-absorbing agent of the present invention exhibits good performance in terms of water-absorbing capacity, water-absorbing rate, and gel strength, and is a water-absorbing agent with well-balanced practical properties, such as not causing "stickiness". be.

Claims (4)

[Claims] (1) The surface part of the water-absorbing resin having a carboxyl group,
A water absorbing agent that is crosslinked using a monoepoxy compound having a hydroxyl group. (2) A method for producing a water-absorbing agent, which comprises adding a monoepoxy compound having a hydroxyl group to a water-absorbing resin having a carboxyl group for crosslinking treatment. (3) The method for producing a water-absorbing agent according to claim 2, wherein the addition of the monoepoxy compound having a hydroxyl group impregnates the surface portion of the water-absorbing resin with the monoepoxy compound having a hydroxyl group. (4) The method for producing a water absorbing agent according to claim 2 or 3, wherein the crosslinking treatment is a heat treatment at a temperature of 100 to 250°C.