JP2960495B2 - Water absorbing agent and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a water absorbing agent having improved properties such as water absorption rate and gel strength, and a method for producing the same.

A water-absorbing agent composed of a polyacrylate or the like absorbs water several hundred times its own weight and has a high absorbency for urine and blood, and is therefore used for sanitary napkins, disposable diapers and the like.

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

The water-absorbing agent is usually put into practical use in the form of powder, fiber, or film. The performance of the water-absorbing agent is evaluated by properties such as water absorption rate, water absorption ratio, and gel strength.A soft gel having a high water absorption ratio has poor water absorption speed and gel strength, while
Hard gels having excellent water absorption rate and gel strength tend to have a low water absorption capacity. As a practical problem when using a water absorbing resin powder having a carboxyl group as a water absorbing agent,
The generation of "mamako" can be mentioned. When “mamako” is generated, the portion of the resin powder that contacts the water absorbs and swells to form a massive gel, which hinders penetration into the water. In addition, even when only one powder particle is viewed, a tendency is observed that the gel on the surface portion impedes the penetration of water into the inside and the water absorption rate decreases.
Such a phenomenon is remarkable in a soft gel having a high water absorption ratio.

In order to prevent the "makoko" phenomenon, a method has been proposed in which the surface of the resin particles is treated with a crosslinking agent as described below to form the surface of the resin particles into a permeable hard gel.
As a first method, there is a method of using a polyvalent epoxy compound or the like as a crosslinking agent (Japanese Patent Publication No. 59-6669, Japanese Patent Publication No. 60-18690, Japanese Patent Publication No. 61-48521), and a second method. As a method, a method of using a polyhydric alcohol as a cross-linking agent (Japanese Patent Publication No. 1-17411, Japanese Patent Application Laid-Open No. 58-180233) is known.

[Problems to be Solved by the Invention] Powder of a water-absorbing resin having a carboxyl group is liable to cause "clams" at the time of water absorption, and properties such as water absorption capacity, water absorption speed, and gel strength are not always compatible, and therefore, The above-described secondary crosslinking (treatment of the surface of the resin with a crosslinking agent) is essential.

The first method is effective in preventing "makoko" and is effective in improving the water absorption rate and gel strength, but has the disadvantage that the crosslink density varies greatly and the water absorption ratio is considerably reduced. was there.

On the other hand, the above-mentioned second method is effective in improving the water absorption capacity and gel strength, but has a disadvantage that the water absorption rate is not sufficient and the resin is exposed to a high temperature for a long time at the time of crosslinking, so that the resin is significantly deteriorated. Was.

[Means for Solving the Problems] In order to solve the above problems, various cross-linking agents and cross-linking methods were examined. As a result, an improved water-absorbing agent having practical properties balanced and an improved method for producing the same were found. Thus, the present invention has been completed.

That is, the present invention relates to (1) a water-absorbing agent obtained by crosslinking the surface of a water-absorbing resin having a carboxyl group with a monoepoxy compound having a hydroxyl group, and (2) a water-absorbing resin having a carboxyl group. The present invention relates to a method for producing a water-absorbing agent, characterized by adding a monoepoxy compound having the following to carry out a crosslinking treatment.

 Hereinafter, the present invention will be described in detail.

As the water-absorbing resin having a carboxyl group, various ones can be used, and there is no particular limitation, and a resin having a carboxyl group and being substantially insoluble in water but capable of absorbing water and swelling. Any can be used.
Preferably, Polymers having a structural unit represented by, for example, acrylic acid-acrylate crosslinked polymer, starch-acrylic acid graft crosslinked polymer, starch-acrylonitrile graft polymer hydrolyzate, vinyl acetate-acrylic acid And saponified ester copolymers.

Usually, the carboxyl group contained in these polymers is
50-95% is in a state neutralized as an alkali metal salt.

Particularly preferred water-absorbing resins having a carboxyl group include acrylic acid 5 to 50 mol%, alkali metal acrylate 45 to 94 mol%, crosslinker 0.01 to 5 mol%, and other ethylenically unsaturated monomers 0 to 5 mol%. 10 mol% polymer. Examples of the alkali metal acrylate include a sodium salt and a potassium salt of acrylic acid. As the crosslinking agent, various known crosslinking agents can be used. For example, methylene bis (meth) acrylamide, divinylbenzene, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, In addition to divinyl compounds and polyacrylate compounds such as glycerin di (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tri (meth) acrylate and dipentaerythritol hexa (meth) acrylate, diglycidyl compounds and polyhydric alcohols Is mentioned. Other optional ethylenically unsaturated monomers include, for example, methacrylic acid and its salts, (meth) acrylamide, (meth) acrylonitrile, and alkyl esters of (meth) acrylic acid.

Examples of the monoepoxy compound having a hydroxyl group include glycidol, ethylene glycol monoglycidyl ether, propylene glycol monoglycidyl ether, glycerin monoglycidyl ether, trimethylolpropane monoglycidyl ether, diethylene glycol monoglycidyl ether, polyethylene glycol monoglycidyl ether, and polypropylene glycol. Examples include, but are not limited to, monoglycidyl ether, p-xylylene glycol monoglycidyl ether, and the like.

The amount of the monoepoxy compound to be 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 it 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 a monoepoxy compound having a hydroxyl group.

As a method of impregnating the surface portion of the water-absorbent resin having a carboxyl group with the monoepoxy compound, for example, spraying an aqueous solution containing the monoepoxy compound while stirring the water-absorbent resin powder, or the resin powder with an organic solvent Various methods can be adopted such as adding an aqueous solution containing a monoepoxy compound after dispersing, or adding an organic solvent solution containing an epoxy compound to a water-absorbing resin containing 5 to 50% by weight of water, There is no particular limitation. Alternatively, a method in which a monoepoxy compound having a hydroxyl group is added to the resin powder and mixed with a usual mixer, for example, a V-type mixer, a screw-type mixer, a ribbon-type mixer, or the like may be used. Among these methods, the method of impregnating the surface of the water-absorbent resin with the monoepoxy compound in the form of an aqueous solution containing the same is particularly preferable.

Before adding the aqueous solution containing the monoepoxy compound,
If the water-absorbing resin is dispersed in an organic solvent in advance, uniform impregnation is performed, and preferable results are obtained.

By appropriately selecting the amount of the aqueous solution of the monoepoxy compound to be added or the amount of the organic solvent, it is possible to impregnate the surface of the water-absorbent resin mainly 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 a portion near the surface. As the organic solvent, methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, isopropyl ether, acetonitrile and the like are used.

The organic solvent is usually used in an amount of preferably 1 to 50 parts by weight, particularly preferably 3 to 30 parts by weight, based on 100 parts by weight of the water absorbent resin. 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 with respect to water is used. Preferably 5
Used up to 30 parts by weight.

By subjecting the impregnated resin thus obtained to a cross-linking treatment, the water-absorbing agent of the present invention whose surface is mainly cross-linked by a monoepoxy compound having a hydroxyl group 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 the epoxy group and the carboxyl group occurs by heating to 50 ° C. or more, and the reaction between the hydroxyl group and the carboxyl group occurs by heating to 100 ° C. or more. Therefore, in the present invention, preferably 100
It is sufficient to heat at 〜250 ° C., particularly preferably 150-200 ° C. for 0.1-10 hours.

By using the method of the present invention, water absorption capacity is good,
The water absorption speed is high, the gel at the time of water absorption is not sticky, and a water absorbing agent having high gel strength can be easily produced. The water-absorbing agent according to the present invention is a sanitary material such as paper diapers, sanitary napkins,
It is useful as a material for a water retention agent for soil, a water stopping agent for civil engineering construction, an anti-condensation agent, a poultice, a poultice, a desiccant, a moisture regulator, and the like.

[Examples] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the examples and comparative examples, “parts” indicates “parts by weight”.

Example 1 To 233 parts of a 43% aqueous solution of an acrylic monomer composed of 75 parts of sodium acrylate, 24.7 parts of acrylic acid and 0.09 part of methylenebisacrylamide, 0.03 part of ammonium persulfate and 0.01 part of sodium hydrogen sulfite were added, and the mixture was added in a nitrogen atmosphere
The mixture was allowed to stand still at 30 to 100 ° C. for 5 hours to obtain a gel-like hydrated polymer. The gel-like hydropolymer was dried with a hot air dryer at 170 ° C., and then sieved with an 18-mesh wire net to obtain an 18-mesh passing product (powder A).

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

Comparative Example 1 To 40 parts of the powder A obtained in Example 1, 0.2 part of ethylene glycol diglycidyl ether, 4 parts of water, and 8 parts of methanol
The mixture was added while stirring, and dried by heating at 170 ° C. for 40 minutes to obtain a water absorbing agent X.

Example 2 To 40 parts of the powder A obtained in Example 1, 4 parts of acetone was added to decompose, and a solution prepared by dissolving 0.1 part of glycidol in 4 parts of water was added thereto and mixed. The obtained mixture was dried by heating with a hot air dryer at 150 ° C. for 50 minutes to obtain a water absorbing agent F.

Comparative Example 2 0.8 parts of glycerin and 40 parts of powder A obtained in Example 1 were mixed with water.
A mixed solution of 0.8 parts and 0.8 parts of ethyl alcohol was added with stirring. This is dried by heating at 180 ° C. for 30 minutes.
I got

Example 3 300 parts of n-hexane was placed in a reactor, and 0.7 part of sorbitan monostearate was dissolved. Next, in this, 30 parts of acrylic acid was dissolved in 40 parts of water, and then neutralized with 12.5 parts of sodium hydroxide, and further added and dispersed with a monomer aqueous solution obtained by dissolving 0.05 part of potassium persulfate. Keep in 5
Polymerization was carried out for hours.

After completion of the polymerization, the resultant was dried under reduced pressure to obtain powder B. Powder B (40 parts) was dispersed in tetrahydrofuran (10 parts), a solution of glycerin monoglycidyl ether (0.3 part) dissolved in water (4 parts) was added thereto, and the mixture was heated and dried at 180 ° C. for 30 minutes to obtain a water absorbing agent G.

Example 4 To 40 parts of the powder B obtained in Example 3, 10 parts of ethanol was added and dispersed, and a solution prepared by dissolving 2 parts of polyethylene glycol monoglycidyl ether (molecular weight: 450) in 3 parts of water was added and mixed. Then, the resultant was dried by heating at 190 ° C. for 10 minutes to obtain a water absorbing agent H.

Example 5 To 40 parts of the powder B obtained in Example 3, 10 parts of dioxane was added and dispersed, and a mixed solution of 0.4 part of glycidol and 2 parts of water was added and mixed, and dried by heating at 150 ° C. for 50 minutes to absorb water. Agent I was obtained.

Example 6 The polymerization was carried out according to Example 3. However, 1.9 parts of an isobutylene-maleic anhydride copolymer (viscosity average molecular weight: about 10,000) was used instead of sorbitan monostearate. After completion of the polymerization, the resultant was dried under reduced pressure to obtain a powder C containing 15% by weight of water.
A mixed solution of 0.2 part of ethylene glycol monoglycidyl ether and 5 parts of methanol was added to 40 parts of powder C, mixed well, and heated and dried at 160 ° C. for 40 minutes to obtain a water absorbing agent J.

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

Application Example 1 Water absorbing agents E to K obtained in Examples 1 to 7, untreated powder A
Table 1 shows the water absorption capacity, water absorption rate, gel strength, and the presence or absence of "mamako" of the water absorbing agents X to Y obtained in Comparative Examples 1 to 2 and Comparative Examples 1 and 2.

Example 8 75 parts of sodium acrylate, 24.8 parts of acrylic acid and 0.1 of polyethylene glycol diacrylate (molecular weight 302)
To 250 parts of a 40% aqueous solution of an acrylic monomer composed of 5 parts, 0.03 part of ammonium persulfate, 0.5 part of 35% hydrogen peroxide and L
-Add 0.01 part of ascorbic acid, and add 20 to 100 in a nitrogen atmosphere.
The resulting mixture was allowed to stand for polymerization at ℃ to obtain a gel-like hydrated polymer. This gel-like hydropolymer was dried with a hot-air dryer at 180 ° C., and then sieved with an 18-mesh wire net to obtain an 18-mesh passing product (powder L).

To 40 parts of this powder L, 4 parts of methanol was added and dispersed, and a solution of 0.16 part of glycidol dissolved in 2.0 parts of water was added thereto and stirred. The obtained mixture was dried by heating with a hot air dryer at 180 ° C. for 30 minutes to obtain a water absorbing agent N.

Example 9 Potassium persulfate was added to 233 parts of a 43% aqueous solution of an acrylic monomer composed of 75 parts of sodium acrylate, 24.9 parts of acrylic acid, and 0.05 part of dipentaerythritol acrylate.
3 parts, 35% hydrogen peroxide 0.1 part and L-ascorbic acid 0.01
The polymerization was allowed to proceed at 20 to 100 ° C. in a nitrogen atmosphere to obtain a gel-like hydropolymer. This gel-like hydropolymer was dried with a hot-air dryer at 150 ° C., and then sieved with an 18-mesh wire net to obtain an 18-mesh passing product (powder M).

To 40 parts of this powder M, 8 parts of methanol was added and dispersed, and a solution of 0.24 part of glycidol dissolved in 2.0 parts of water was added and stirred. The obtained mixture was dried by heating with a hot air drier at 150 ° C. for 50 minutes to obtain a water absorbing agent O.

In any of the above Examples and Comparative Examples, those obtained at the time before the heating and drying after the addition of the monoepoxy compound having a hydroxyl group impregnate the surface portion of the water-absorbent resin with the monoepoxy compound having a hydroxyl group. It was what was done.

Application Example 2 Water-absorbing agents N and O obtained in Examples 8 to 9 and untreated powder
Table 2 shows the water absorption ratios of L and M, water absorption speed, gel strength, and the presence or absence of “Mamako”.

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

○ Water absorption capacity 200 g of 0.9% salt solution was added to 0.5 g of water absorbing agent or powder, and after 1 hour, the solution was filtered through a 200-mesh wire gauze, the weight of the resin absorbed was weighed, and the weight was divided by the weight before absorbing water. Ask for.

○ G1 glass filter with diameter of 7cm and diameter of 1.4cm as water absorption rate measuring device
Connect the graduated examiner to the U-shape. 0.3 g of the water-absorbing agent or powder is spread evenly on a glass filter, and artificial urine is added at an equal water level, and the water absorption after 1 minute, 5 minutes and 20 minutes is measured by reading the drop of the water level. Artificial urine is 1.94 g urea, 0.08 g salt,
0.11 g of magnesium sulfate and 0.06 g of calcium chloride in pure water
Dissolve in 97.09g to make 100g.

○ Weigh 2 g of water-absorbing agent or powder in a beaker with a gel strength of 200 ml.
After adding methanol, 40 g of pure water is added at a stretch and stirred to form a water-absorbing gel. Thereafter, a columnar adapter having a diameter of 6 cm is placed on the gel in the beaker, compressed with Tensilon, and the strength at which the gel starts to flow is measured. The gel strength is represented by the stress per unit area of the cylinder.

In addition, for "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.

〔The invention's effect〕

The water-absorbing agent of the present invention is a water-absorbing agent exhibiting good performance in terms of water absorption capacity, water absorption speed and gel strength, and having a balance of practical properties such as no occurrence of "makoko".

Continuation of the front page (56) References JP-A-2-253845 (JP, A) JP-A-1-113406 (JP, A) JP-A-61-213206 (JP, A) JP-A-63-199205 (JP) , A) JP 60-18690 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01J 20/00-20/34

Claims (4)

(57) [Claims] 1. A water-absorbing agent obtained by crosslinking the surface of a water-absorbing resin having a carboxyl group with a monoepoxy compound having a hydroxyl group. 2. A method for producing a water-absorbing agent, comprising adding a monoepoxy compound having a hydroxyl group to a water-absorbing resin having a carboxyl group, followed by 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, wherein the crosslinking treatment is a heating treatment at a temperature of 100 to 250 ° C.