JPH0531362A - Manufacture of water-absorptive agent - Google Patents

Abstract

PURPOSE:To easily obtain a water-absorptive agent which is hard to move and drop off when it is compounded with cellulose fibers and thus expected to have a synergistic effect on the water-absorptive function. CONSTITUTION:The surface of water-absorptive particles having a carboxyl group is treated with a cross-linking agent having two or more functional groups which are able to form a covalent bond by reaction with the carboxyl group to cross-link a part of the carboxyl group and, after that, the particles are mixed with a cationic high molecular compound having 2000 or more weight average molecular weight and able to form an ionic bond by reaction with the carboxyl group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a novel water absorbing agent. More specifically, the present invention relates to a method for producing a water-absorbing agent which has excellent water-absorbing properties by itself and, when combined with cellulose fibers, exhibits an extremely excellent water-absorbing effect.

[0002]

2. Description of the Related Art In recent years, a water-absorbent resin that absorbs several tens to several hundreds of times its own weight of water has been developed. Various water-absorbent resins have been used for applications requiring water absorption or water retention, such as fields, industrial fields such as dew condensation prevention, and cold insulation materials. As the water-absorbent resin, a cross-linked product of an acrylate cross-linked polymer or a starch-acrylate graft polymer is known.

Since the water-absorbent resin is generally in the form of powder, it is rarely used alone, and is used in combination with hydrophilic cellulose fibers such as crushed pulp and paper. In applications where a large amount of water is absorbed in a short period of time, such composite formation is particularly necessary in order to prevent the water-absorbing resin alone from absorbing the water within a short period of time and spreading the water. Cellulose fiber holds a powdery water-absorbent resin, or because it takes time for the water-absorbent resin to absorb ambient water, it holds water around the water-absorbent resin particles by that time, or , Has a function of evenly distributing water to the water-absorbent resin particles distributed by the capillary phenomenon.

Many proposals have hitherto been made on methods for improving the water absorption rate of the water absorbent resin itself and the water absorption under pressure. For example, Japanese Examined Patent Publication No. 63-19215 discloses a method in which a water-absorbent resin powder having a carboxyl group is mixed with a polyvalent amine compound and heat-treated as necessary to crosslink the molecular chains near the surface. In Japanese Patent Publication No. 1-17411, a water-absorbent resin powder having a carboxyl group, a polyhydric alcohol, and one or more compounds selected from the group consisting of water and a hydrophilic organic solvent are added. 0.001 to 10 parts by weight of polyhydric alcohol and 0.0 of compound per 100 parts by weight
A method of mixing at a ratio of 1 to 8 parts by weight and heating at a temperature of 90 ° C. or higher to react the water-absorbent resin powder with a polyhydric alcohol to crosslink the molecular chains near the surface of the water-absorbent resin powder. Is disclosed. In JP-A-57-44627, two water-absorbent resins containing an acrylic acid alkali salt as a constituent component of a polymer are dispersed in a mixed solvent of water and a hydrophilic organic solvent to react with a carboxylate group. A method of adding a cross-linking agent having the above functional group (for example, ethylene glycol diglycidyl ether) to cross-link is disclosed. In JP-A-60-163956, a crosslinking agent (in the presence of a water-absorbent resin containing a monomer unit having a carboxylate as a constituent component of a polymer and an inert inorganic powder (hydrous silicon dioxide powder, etc.)) A diglycidyl ether-based compound, a polyvalent metal salt, a haloepoxy-based compound, an aldehyde-based compound, an isocyanate-based compound, etc.) and water are absorbed and then heated under stirring to carry out a crosslinking reaction and distilling off water. Has been done. In JP-A-60-36516, a hydrophilic monomer [(meth) acrylamide, N, N-dimethylaminoethyl) having a reactive functional group is added to a superabsorbent resin having a carboxyl group having a water content adjusted to 50% by weight or less. A nitrogen-containing vinyl monomer such as methacrylate; an oxygen-containing vinyl monomer such as 2-hydroxyethyl methacrylate; a sulfonate-containing vinyl monomer such as vinyl sulfonate; a nitrile group-containing vinyl monomer such as acrylonitrile; ing. JP-A-60-
In JP-A-255814, a cross-linking agent (diglycidyl ether compound, polyvalent metal salt and haloepoxy) is stirred under stirring a water-absorbent resin containing a monomer unit having a carboxylate as a constituent of a polymer and an inert inorganic powder. System compound) and water (70 to solid content of water-absorbent resin)
(Corresponding to 200 wt. In JP-A-2-248404, the side chain is-
A method of crosslinking a water-insoluble superabsorbent resin having a COOM group (M is a hydrogen atom or an alkali metal atom) with a reaction product of epihalohydrin with ammonia or amines is disclosed.

[0005]

However, although the water-absorbent resin modified by these publicly known techniques improves the water-absorbent property of the water-absorbent resin itself to some extent, it is composited with the cellulose fiber in actual use as described above. In that case, the water absorption property was not sufficient. This drawback is that, for example, when a water absorbent resin is used for a part of the water absorbent body of a paper diaper, the water absorbent resin that has swollen after urine absorption due to the movement of the wearer moves or falls off, which is as expected. Is known for its current state of not having water absorption performance. Such a phenomenon that the water-absorbent resin moves or falls off is a major obstacle when the water-absorbent resin is used for various purposes. It can be said that an ideal water-absorbent resin is one that can sufficiently bring out a synergistic effect with a material of a composite partner such as cellulose fiber in actual use, but such a thing has not yet been obtained.

The present invention provides a method for producing a water absorbing agent which is less likely to move or fall off when it is combined with a cellulose fiber, and which is therefore expected to have a synergistic effect on water absorbing performance. Is an issue.

[0007]

In order to solve the above problems, the present invention provides two or more functional groups capable of reacting the surface of a water-absorbent resin particle having a carboxyl group with the carboxyl group to form a covalent bond. The particles are treated with a cross-linking agent having a group to cross-link some of the carboxyl groups, and then the particles are
Provided is a method for producing a water-absorbing agent, which is capable of reacting with a carboxyl group to form an ionic bond with a cationic polymer compound having a weight average molecular weight of 2000 or more.

The water absorbent resin which can be used in the present invention is required to have a carboxyl group. Examples of such a water-absorbent resin include acrylic acid cross-linked polymers, vinyl alcohol-acrylic acid acid cross-linked copolymers, starch-acrylic acid acid graft polymer cross-linked materials, maleic anhydride grafted polyvinyl alcohol cross-linked materials, Examples thereof include alkali salt cross-linked products of carboxymethyl cellulose, which can be preferably used in the present invention. Although the amount of the carboxyl group contained in the water absorbent resin is not particularly limited, it is preferable that the carboxyl group is present in an amount of 0.01 equivalent or more per 100 g of the water absorbent resin. Suitable water-absorbent resin particles are, for example, JP-A-57-
34101, JP-B-58-35605, JP-B-62-16135, JP-B-2-14361, JP-A-62-144748, JP-A-62-
It is disclosed in Japanese Patent No. 54751, Japanese Patent Laid-Open No. 63-21902, and the like. Particularly preferred are acrylate cross-linked polymer particles having a degree of neutralization of 50 to 95 mol% from the viewpoint of water absorption performance, and the polymerization method is not particularly limited.

The shape of the water-absorbent resin particles used in the present invention may be spherical, scaly, pulverized amorphous or granular. The size of the particles is usually 10 to 1000.
It is in the range of μm, preferably in the range of 20 to 840 μm. Particles of less than 10 μm may cause so-called gel blocks when the water-absorbent resin particles in the water absorbent swell, and particles of more than 1000 μm may give the water absorbent a rugged feel during use.

The crosslinking agent used in the present invention is not particularly limited as long as it is a compound having two or more functional groups capable of reacting with the carboxyl group of the water absorbent resin to form a covalent bond. The two or more functional groups need not be the same as each other. Examples of such a functional group include an epoxy group, an aldehyde group, and a hydroxyl group. Examples of the cross-linking agent include polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycerin triglycidyl ether; haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; glutaraldehyde and glyoxal. Aldehydes; polyols such as glycerin, pentaerythritol, ethylene glycol, polyethylene glycol and the like can be mentioned, and they can be used alone or in combination of two or more kinds. The cross-linking agent is preferably water-soluble and is used in the form of being dissolved in an aqueous solution or a mixed solvent of water and a hydrophilic organic solvent such as ethanol.

The amount of the crosslinking agent used is appropriately in the range of 0.01 to 10 parts by weight with respect to 100 parts by weight of the water absorbent resin.
If the amount of the cross-linking agent is less than 0.01 parts by weight, the crosslinking may be insufficient, and if it exceeds 10 parts by weight, the residual amount of the carboxyl groups capable of ionic bonding may be insufficient. The cationic polymer compound used in the present invention is a compound capable of reacting with a carboxyl group of a water absorbent resin to form an ionic bond and having a weight average molecular weight of at least 2000. And a weight average molecular weight of 5,000 or more is preferable, and a weight average molecular weight of 10,000 or more is more preferable. The cationic polymer compound having a weight average molecular weight of 2000 or more used in the present invention is not limited to those exhibiting a single maximum value (peak) in the molecular weight analysis by gel permeation chromatography, and a plurality of maximum values (peak) Even if it shows, the weight average molecular weight may be 2000 or more. If a cationic polymer compound having a weight average molecular weight of less than 2000 is used, or if an anionic polymer compound or a nonionic polymer compound is used without using a cationic polymer compound, modification as a water absorbing agent is insufficient, In addition, there is a problem that adhesion to the cellulose fiber is insufficient.

In the present invention, as the cationic polymer compound, a compound containing at least one selected from a primary amino group, a secondary amino group, a tertiary amino group and salts thereof is preferably used. In this case, the amino group salt is a salt in which the amino group nitrogen is neutralized with an inorganic acid or an organic acid. Examples of the inorganic acid that can be used for neutralization include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and the like.
Examples of the organic acid include formic acid, acetic acid, propionic acid, p-toluenesulfonic acid and the like.

Specific examples of the cationic polymer compound include, for example, polyethyleneimine, modified polyethyleneimine crosslinked with epihalohydrin to a water-soluble range, polyamine, polyamidoamine modified by grafting ethyleneimine, and protonated polyamide. Amine, polyetheramine, polyvinylamine, modified polyvinylamine, polyalkylamine, polyvinylimidazole, polyvinylpyridine, polyvinylimidazoline, polyvinyltetrahydropyridine, polydialkylaminoalkylvinylether, polydialkylaminoalkyl (meth) acrylate, polyallylamine, and Cationic polyelectrolytes such as these salts.

The amount of the cationic polymer compound used is preferably 0.1 to 3 with respect to 100 parts by weight of the water absorbent resin particles.
It is in the range of 0 parts by weight, more preferably in the range of 0.3 to 20 parts by weight, and most preferably in the range of 0.5 to 10 parts by weight. If the amount of the cationic polymer compound is less than 0.1 parts by weight, the synergistic effect when it is complexed with the cellulose fibers may be insufficient, and if it exceeds 30 parts by weight, the absorption capacity of the resulting water-absorbing agent may be lowered. May invite. The cationic polymer compound is water-soluble and is used in the form of a powder, an aqueous solution, or dissolved in a mixed solvent of water and a hydrophilic organic solvent such as ethanol.

The method for producing the water absorbing agent of the present invention can be carried out, for example, by the following method. That is, first, the surfaces of the water absorbent resin particles are crosslinked with a crosslinking agent. At this time, the covalently crosslinked layer should not be bonded to all of the carboxyl groups on the particle surface, and some of the carboxyl groups should be left for ionic bonding. Therefore, in the step of forming a crosslinked layer by this covalent bond,
The aqueous liquid containing the cross-linking agent is used in an amount that does not entirely cover the surface of the water-absorbent resin particles (for example, an amount such that the weight ratio of the cross-linking agent to the water-absorbent resin is within the above range),
It is important that they are mixed. The mixture of the water-absorbent resin particles and the crosslinking agent is heat-treated at a temperature in the range of 40 to 250 ° C. for 1 to 120 minutes, for example, to form a crosslinked layer by covalent bonds on the surface of the water absorbent resin particles. Subsequently, the particles are mixed with the cationic polymer compound. In this mixing, heating is not always required, and the water-absorbent resin is mixed with the aqueous solution containing the cationic polymer compound or the cationic polymer compound powder. As a result, the desired water absorbing agent is obtained. When an aqueous liquid containing a cationic polymer compound is used, the ion-bonded layer is formed on the surface of the water-absorbent resin particles by mixing. When the cationic polymer compound powder is used, water is added during or after the mixing to form an ionic bond layer on the surface of the water absorbent resin particles. When mixed with water such as an aqueous liquid, it may be dried by heating or the like after the mixing, if necessary.

In the present invention, the order of the treatment using the crosslinking agent and the treatment using the cationic polymer compound is important. The effect of the present invention cannot be obtained if the covalent bond cross-linking layer is provided after the ionic bond layer is provided, or if both layers are provided at the same time. Further, if only the ionic bond layer is provided and no covalent bond crosslinked layer is provided, or if only the covalent bond crosslinked layer is provided and no ionic bond layer is provided, the effect of the present invention cannot be obtained.

In the present invention, the aqueous liquid containing the cross-linking agent and the mixture of the aqueous liquid containing the cationic polymer compound and the water-absorbent resin particles can be mixed in various forms (for example, the cross-linking agent and the cationic polymer). It is carried out by immersing the particles in each aqueous solution of the polymer compound, mixing the droplets of each aqueous solution with the particles, spraying each aqueous solution into a mist and mixing with the particles). For this mixing, for example, a high-speed stirring mixer, an airflow mixer, a tumbling mixer,
Devices such as kneaders can be used. During the mixing, it is possible to coexist with an organic powder such as cellulose powder and an inorganic powder such as fine particle silica. Further, the obtained water absorbing agent may be dried if necessary.

By combining the water-absorbing agent obtained by the above method with cellulose fibers, for example, a water-absorbing material suitable as an absorbent layer for sanitary materials can be obtained. Examples of the cellulose fibers include wood pulp fibers such as mechanical pulp, chemical pulp, semi-chemical pulp, and dissolving pulp from wood, artificial cellulose fibers such as rayon and acetate, and the like. The preferred cellulose fiber is wood pulp fiber. These cellulose fibers may partially contain synthetic fibers such as nylon and polyester.

In order to obtain a water absorbing body from the water absorbing agent and the cellulose fiber obtained by the above method, for example, a method in which a water absorbing agent is sprinkled on a paper or a mat made of cellulose fiber and sandwiched by these, a cellulose fiber and water absorbing Known means for obtaining a water absorbent body can be appropriately selected, such as a method of uniformly blending agents. Preferred is a method in which the water absorbing agent and the cellulose fibers are dry-mixed and then compressed. By this method, it is possible to remarkably prevent the water absorbing agent from falling off from the cellulose fiber. The compression is preferably performed under heating, and the temperature range is, for example, 50 to 200 ° C.

The water-absorbing agent obtained by the production method of the present invention is less likely to fall from the material of the composite partner such as cellulose fiber even after absorbing water and swelling, and is excellent in water-absorbing property. It can be used as a water absorbent and water retention agent. Examples of the water absorbent / water retaining agent include the following. (1) Water-absorbing and water-retaining agent for absorbent articles Paper diapers, sanitary napkins, incontinence pads, medical pads and the like.

(2) Agricultural and horticultural water retention agents Substitutes for water moss, soil reforming and improving agents, water retention agents, agricultural chemical effect lasting agents, etc. (3) Water retention agent for buildings Dew condensation prevention agents for interior wall materials, cement additives, etc. (4) Other release control agents, cold storage agents, disposable body warmers, sludge coagulants, food freshness retention agents, etc.

[0022]

[Function] The surface of the water-absorbent resin particles having a carboxyl group is treated with a crosslinking agent having two or more functional groups capable of reacting with the carboxyl group to form a covalent bond to crosslink part of the carboxyl group. As a result, the water-absorbent resin particles are less likely to form mamako, and the water-absorbent resin itself has improved water-absorbing performance. Moreover, after the treatment with the crosslinking agent, the particle surface is mixed with a cationic polymer compound capable of reacting with a carboxyl group to form an ionic bond. The cationic polymer compound reacts with the carboxyl groups remaining on the particle surface in the presence of water, and the water-absorbent resin particles are reacted in the presence of water (not only in liquid water but also in the gas phase such as the atmosphere). With water (so-called moisture is also possible), it is easy to stick to the material of the composite partner such as cellulose fiber. As a result, even when water is absorbed, the water-absorbent resin is unlikely to move in the composite partner material such as cellulose fiber or fall off from the material. Such an effect is possible only by performing the above processing.

[0023]

EXAMPLES Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to the following examples.
In the following, mere “%” means “% by weight” and “part” means “part by weight”. -Synthesis example of water-absorbent resin particles-Sodium acrylate 74.95 mol%, acrylic acid 2
37% of an acrylate-based monomer consisting of 5 mol% and 0.05 mol% of trimethylolpropane triacrylate
% Aqueous solution of 4000 parts and 2.0 parts of ammonium persulfate and 0.08 parts of L-ascorbic acid were polymerized in a nitrogen atmosphere at 30 to 80 ° C. to obtain a gel-like water-containing crosslinked polymer. The obtained water-containing gel-like crosslinked polymer was dried with a hot air dryer at 150 ° C., pulverized with a hammer mill, and sieved with a 20 mesh (Tyler's standard sieve. The same applies hereinafter) wire mesh to obtain a 20 mesh passed product. This is called water-absorbent resin particle (a).

-Example 1- 100 parts of the water-absorbent resin particles (a) was mixed with glycerin 0.
After 5 parts, 2 parts of water and 2 parts of ethyl alcohol were added and mixed, the mixture was heated at 210 ° C. for 10 minutes to obtain a water-absorbing polymer A in which the vicinity of the surface was secondarily cross-linked. Furthermore, for 100 parts of the water-absorbent polymer A obtained, polymine SK (modified polyethyleneimine having a weight average molecular weight of about 100,000, BASF
(Manufactured by 20% aqueous solution) was added and mixed, dried by heating at 120 ° C. for 10 minutes, and then sieved with a 20 mesh sieve to obtain a 20 mesh passed product. This is called a water absorbing agent (1).

Example 2-For 100 parts of the water-absorbent polymer A obtained in Example 1,
A water absorbing agent (2) was obtained by adding and mixing 5 parts of a 30% aqueous solution of Epomin P-1000 (polyethyleneimine having a weight average molecular weight of about 70,000, manufactured by Nippon Shokubai Co., Ltd.). The water absorbing agent (2) obtained was in the form of powder.

Example 3-For 100 parts of the water-absorbent polymer A obtained in Example 1,
A water absorbing agent (3) was obtained by adding 1.7 parts of a 30% aqueous solution of Epomin P-1000 (polyethyleneimine having a weight average molecular weight of about 70,000, manufactured by Nippon Shokubai Co., Ltd.). The water absorbing agent (3) was in powder form.

Example 4-For 100 parts of the water-absorbent polymer A obtained in Example 1,
10 parts of a 30% aqueous solution of Epomin SP-200 (polyethyleneimine having a weight average molecular weight of about 10,000, manufactured by Nippon Shokubai Co., Ltd.) was added and mixed, and after heating and drying at 120 ° C. for 20 minutes, it was sieved with a 20 mesh sieve. A 20-mesh pass product was obtained. This is called a water absorbing agent (4).

Example 5 To 100 parts of the water-absorbent resin particles (a), 8 parts of a 10% aqueous solution of ethylene glycol diglycidyl ether (Denacol EX-810 manufactured by Nagase Kasei Co., Ltd.) was added and mixed, and then 120 Heat treatment was performed at 30 ° C. for 30 minutes to obtain a water-absorbent polymer B in which the vicinity of the surface was secondarily crosslinked. The property of the water-absorbent polymer B was powder. Further, the resulting water-absorbent polymer B
Copolymer powder of dimethylaminoethyl acrylate-acrylamide-acrylic acid (100 parts by weight) (dimethylaminoethyl acrylate / acrylamide / acrylic acid = 30/60/10 molar ratio, weight average molecular weight about 1)
3 parts of the material (passed through 1,000,000 and 100 mesh) was added and mixed to obtain a water absorbing agent (5).

-Example 6-For 100 parts of the water-absorbent polymer A obtained in Example 1,
4 of polyallylamine hydrochloride (weight average molecular weight of about 60,000, product name PAA-HCL-10L manufactured by Nitto Boseki Co., Ltd.)
7.5 parts of 0% aqueous solution was added and mixed, heated and dried at 120 ° C. for 10 minutes, and then sieved with a 20 mesh sieve to obtain a 20-mesh passing product. This is called a water absorbing agent (6).

-Example 7-For 100 parts of the water-absorbent polymer A obtained in Example 1,
Polyethyleneimine Polyethyleneglycol block copolymer (ethyleneimine / ethyleneglycol = 50 /
12.5 parts of a 40% aqueous solution having a molar ratio of 50 and a weight average molecular weight of about 80,000) was added and mixed, and after heating and drying at 120 ° C. for 10 minutes, it was sieved with a 20 mesh sieve to obtain a 20 mesh passed product. . This is called a water absorbing agent (7).

-Example 8-For 100 parts of the water-absorbent polymer A obtained in Example 1,
20 parts of a 30% aqueous solution of Epomin P-1000 (polyethyleneimine having a weight average molecular weight of about 70,000, manufactured by Nippon Shokubai Co., Ltd.) was added and mixed, and the mixture was heated and dried at 120 ° C. for 10 minutes, and then sieved with a 20 mesh sieve. A 20-mesh pass product was obtained. This is called a water absorbing agent (8).

-Comparative Example 1- The water absorbent resin particles (a) were used as a comparative water absorbent (1). -Comparative Example 2-The water-absorbent polymer A obtained in Example 1 was sieved with a 20-mesh sieve to obtain a 20-mesh passed product. This is referred to as a comparative water absorbing agent (2).

Comparative Example 3-For 100 parts of the water-absorbent polymer A obtained in Example 1,
Add 10 parts of a 30% aqueous solution of ethylenediamine and mix,
After heating and drying at 120 ° C. for 10 minutes, it was sieved with a 20-mesh sieve to obtain a 20-mesh passed product. This is called a comparative water absorbent (3).

Comparative Example 4-For 100 parts of the water-absorbent polymer A obtained in Example 1,
10 parts of a 30% aqueous solution of Epomin SP-012 (polyethyleneimine having a weight average molecular weight of about 1,200, manufactured by Nippon Shokubai Co., Ltd.) was added and mixed, and the mixture was dried by heating at 120 ° C. for 10 minutes, followed by sieving with a 20 mesh sieve. To obtain a 20-mesh pass product. This is referred to as a comparative water absorbing agent (4).

Comparative Example 5-For 100 parts of the water-absorbent polymer A obtained in Example 1,
N-100 powder (nonionic acrylamide polymer having a weight average molecular weight of about 17 million, manufactured by Mitsui Cyanamid Co., Ltd., 100 mesh passing product) was added and mixed in 3 parts,
A comparative water absorbing agent (5) was obtained.

-Comparative Example 6- Epomin P-1 was added to 100 parts of the water-absorbent resin particles (a).
000 (polyethyleneimine having a weight average molecular weight of about 70,000,
33.4 parts of a 30% aqueous solution (produced by Nippon Shokubai Co., Ltd.) was added and mixed, dried by heating at 120 ° C. for 20 minutes, and sieved with a 20 mesh sieve to obtain a 20 mesh passed product.
This is called a comparative water absorbent (6).

Comparative Example 7 Epomin P-1 was added to 100 parts of the water-absorbent resin particles (a).
000 (polyethyleneimine having a weight average molecular weight of about 70,000,
10 parts of a 30% aqueous solution of Nippon Shokubai Co., Ltd. was added and mixed, and the mixture was dried by heating at 120 ° C. for 10 minutes, and then glycerin 0.5
Parts, 2 parts of water and 2 parts of ethyl alcohol were added and mixed, followed by heat treatment at 210 ° C. and sieving with a 20-mesh sieve to obtain a 20-mesh pass product. This is called a comparative water absorbing agent (7).

-Examples 9 to 16 and Comparative Examples 8 to 14-Water absorbing agents (1) to (8) obtained in Examples 1 to 8 and Comparative water absorbing agent (1) obtained in Comparative Examples 1 to 7 The water absorption characteristics of (7) to (7) were compared by the following method. The results are shown in Table 1. (Water absorption capacity) About 0.2 g of a water absorbing agent was uniformly put in a non-woven tea bag type bag (40 mm x 150 mm), immersed in a large excess of physiological saline (0.9% saline) and left for 30 minutes. . As a result, the water absorbing agent in the bag became a swollen gel. The tea bag type bag containing the swollen gel was drained and weighed. With the absorbed weight of only the tea bag type bag as the blank, the value obtained by subtracting the value obtained by subtracting the blank weight from the weight after absorbing water by the weight of the water absorbing agent is the water absorption ratio [g /
g].

(Aspiration amount) 1 g of a water absorbing agent was added to artificial urine (composition: 1.9% urea, 0.8% salt, 0.1% calcium chloride,
16 sheets of toilet paper (55 mm x 75 mm) dipped in 20 ml of an aqueous solution containing 0.1% magnesium sulfate)
Add to the top and let it absorb for 10 minutes, then collect the swollen gel,
The weight was defined as the suction amount [g / g].

[0040]

[Table 1]

As shown in Table 1, the water absorbing agents obtained in the examples had a high water absorption capacity and a high suction amount. The suction amount is
It is an index of water absorption rate, and high value means that water absorption rate is high. Among the water-absorbing agents obtained in Comparative Examples, those in Comparative Examples 2 to 5 show the same water-absorption capacity and suction amount as those in Examples. However, in Comparative Example 1, since the water-absorbent resin particles (a) are as they are, the suction amount is low,
In Comparative Example 6, since the cross-linking agent was not cross-linked, the amount of suction was low, and in Comparative Example 7, the cross-linking agent was tried to be cross-linked after the treatment with the cationic polymer compound. Was low.

-Example 17- 100 parts of the water absorbing agent (1) obtained in Example 1 and crushed pulp
Dry mix 100 parts in a mixer and then batch type empty
Air-making on a wire screen using a gas-making machine
To obtain a web having a size of 10 cm × 20 cm. The obtained wafer
The upper and lower surfaces of the knob are 0.0013 g / cm²The tissue
It is clamped with a taper, and then the pressure is 2 kg / cm. ²For 1 minute
And the basis weight is about 0.05 g / cm²To obtain the water absorber (1)
It was

-Examples 18-24 and Comparative Examples 15-1
8-Water absorbing agents (2) to (8) obtained in Examples 2 to 8 and Comparative Example 2 in which the water absorption capacity and the suction amount were the same as those of the Examples.
Using the comparative water absorbing agents (2) to (5) obtained in Nos. 5 to 5, water absorbing bodies (2) to (8) and comparative water absorbing bodies (1) to (4) were obtained in the same manner as in Example 17. In the examples, the water absorber and the water absorbing agent are used so as to have the same number, and in the comparative example,
The numbers of the comparative water absorbents are given in ascending order of the numbers of the comparative water absorbents.

-Examples 25-32 and Comparative Examples 19-2
2-Water absorbing bodies (1) to (8) obtained in Examples 17 to 24 and comparative water absorbing body (1) to be obtained in Comparative Examples 15 to 18
(4) was evaluated by the following method to evaluate the absorption characteristics of the water absorbing body. The results are shown in Table 2. (Absorbed amount under pressure) As shown in FIG. 1, a container 4 equipped with an outside air suction pipe 2 placed on a balance 1 and containing a physiological saline 3 of 0.9% concentration, and a container 4 of this container 4 An apparatus comprising a reverse funnel 6 communicating with a physiological saline storage section by a conduit 5 and having a plate (perforated plate) 7 having a liquid supply hole with a diameter of 10 mm fixed at the center of the top of the reverse funnel 6 is used. Then, the water absorbing body 8 is placed on the perforated plate 7, and the weight 9 is placed on the water absorbing body 8, and after 30 minutes, the absorption amount (absorption amount under pressure) of the water absorbing body under a load of 30 g / cm ^{2 is} measured. It was measured. In addition, the water absorbent used had been previously cut into a circle having a diameter of 9 cm.

(Release rate of water-absorbing agent) While stirring 100 cc of physiological saline in a 100 cc beaker (using a 45 mm stirrer and stirring at 100 rpm), a water absorbent cut into 2 cm x 4 cm was charged. After 10 minutes of stirring, the water absorbing body was taken out, the weight of the water absorbing agent dropped into the physiological saline was measured, and the drop rate of the water absorbing agent was determined by the following formula 1.

[0046]

[Equation 1]

[0047]

[Table 2]

As is clear from Table 2, the water absorbing body using the water absorbing agent obtained by the production method of the present invention is excellent in the absorption amount under pressure and the falling rate of the water absorbing agent is remarkably improved. Since the comparative water absorbent (1) used the water absorbing agent that was only surface-crosslinked with the crosslinking agent, the drop rate was high. Since the comparative water absorbent (2) used the water absorbing agent using ethylenediamine instead of the cationic polymer compound, the drop rate was high. In Comparative Water Absorber (3), a water absorbing agent using a low molecular weight polyethyleneimine having a weight average molecular weight of less than 2000 was used in place of the cationic polymer compound, and therefore the dropout rate was high. In Comparative Water Absorber (4), since the water absorbing agent using the nonionic polymer compound instead of the cationic polymer compound was used, the dropout rate was high.

[0049]

According to the manufacturing method of the present invention, a water-absorbing agent which exhibits excellent water-absorbing properties by itself can be obtained. Moreover, this water absorbing agent also has an excellent effect that it does not drop off or move even if it absorbs water and swells when it is combined with cellulose fibers to form a water absorbing body. Since this water absorbent body does not move or drop off the water absorbent even after absorbing the liquid, it is possible to remarkably improve the twist of the water absorbent body, which has been common in the past. Therefore, the water absorbing agent obtained by the present invention is particularly useful for water absorbing articles such as disposable diapers, sanitary napkins and incontinence pads.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus for measuring an absorption amount of a water absorbent body under pressure.

[Explanation of symbols]

1 Balance 2 Outside air intake pipe 3 physiological saline 4 containers 5 conduits 6 reverse funnel 7 Aperture plate 8 Water absorber 9 weights

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tadao Shimomura             5-8 Nishiomitabicho, Suita City, Osaka Prefecture             Central Research Institute of Nippon Shokubai

Claims (7)

[Claims] 1. A surface of a water-absorbent resin particle having a carboxyl group is treated with a cross-linking agent having two or more functional groups capable of reacting with the carboxyl group to form a covalent bond, so that a part of the carboxyl group is treated. A method for producing a water-absorbing agent, which comprises crosslinking and then mixing the particles with a cationic polymer compound having a weight average molecular weight of 2000 or more, which can react with a carboxyl group to form an ionic bond. 2. The method for producing a water absorbing agent according to claim 1, wherein a compound having two or more functional groups of at least one selected from an epoxy group, an aldehyde group and a hydroxyl group is used as the crosslinking agent. 3. The method for producing a water absorbing agent according to claim 2, wherein at least one selected from polyglycidyl ethers, haloepoxy compounds, polyaldehydes and polyols is used as the crosslinking agent. 4. The cationic polymer compound contains at least one selected from a primary amino group, a secondary amino group, a tertiary amino group and salts thereof, any one of claims 1 to 3. A method for producing the water absorbing agent according to claim 1. 5. The method for producing a water absorbing agent according to claim 4, wherein the cationic polymer compound is at least one selected from polyethyleneimine, polyamidoamine, polyetheramine, polyvinylamine, and polyallylamine. 6. The method according to claim 1, wherein the particles treated with the crosslinking agent are mixed with the cationic polymer compound in the presence of water to react with the carboxyl groups remaining on the surface of the particles. Manufacturing method of the water-absorbing agent. 7. The method for producing a water absorbing agent according to claim 6, which is dried after being reacted with a carboxyl group.