JPH0733818A - Modified highly water-absorbing resin and its production - Google Patents

Abstract

PURPOSE:To obtain the subject resin, having the crosslinked vicinity of the surface and excellent in absorptivity and initial absorption rate by treating and reacting a water absorbing resin with an aqueous solution of an alkylene oxide adduct, etc., of a monohydric alcohol and a crosslinking agent having plural functional groups. CONSTITUTION:This water-absorbing resin is obtained by treating and reacting (A) water absorbing resin particles composed of cross linked polymer, etc., of an ethylenicallly unsaturated monomer containing acrylic acid and/or an acrylate as main constituent units with (B) a water-soluble compound composed of a compound which is an alkylene oxide adduct of a monohydric alcohol and has 100-1000 molecular weight, an alkali metallic salt of a 2-6C organic acid and 4-8C cyclic lactams, etc., and (C) a cross linking agent, having two or more functional groups reactive with the component (A) and composed of a polyglycidyl ethereal compound, a polyhydric alcoholic compound and a polyamine-based compound, etc. The vicinity of the surface is crosslinked and resultant resin is excellent in absorptivity and initial absorption rate and good in the dry feeling of a gel after absorbing water.

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 modified superabsorbent resin and a superabsorbent resin obtained by the method. More specifically, the vicinity of the surface of the water-absorbent resin particles is treated with an aqueous solution of a water-soluble compound having a specific property and a crosslinking agent,
The present invention relates to a method for producing a modified superabsorbent resin by a cross-linking reaction, and a superabsorbent resin obtained by the method and having a large absorption capacity under both unpressurized and pressurized conditions.

[0002]

2. Description of the Related Art Conventionally, superabsorbent resins have been widely used for sanitary products, sanitary materials such as disposable diapers, and soil water retention agents. Examples of such a super absorbent resin include, for example, polyacrylate crosslinked products, self-crosslinked polyacrylic acid salts,
Starch-acrylic acid salt graft copolymer crosslinked product, vinyl alcohol-acrylic acid salt copolymer, hydrolyzate of acrylamide copolymer crosslinked product, neutralized product of crosslinked isobutylene-maleic anhydride copolymer, carboxymethylcellulose salt Substantially water-insoluble cross-linked polymers, such as the cross-linked products described above, are known.

The main method for obtaining a water-absorbent resin is to slightly cross-link a water-soluble resin to make it water-insoluble. The cross-linking method is to add a cross-linking agent at the time of polymerizing a hydrophilic monomer. There are known methods such as cross-linking at the same time as polymerization and inter-molecular cross-linking by reacting a water-soluble polymer with a cross-linking agent. In the water-absorbent resin obtained by these crosslinking methods, the amount of the crosslinking agent used is as small as possible in order to enhance the absorption capacity. Due to this effect, this water-absorbent resin has weak gel strength and has a low absorption capacity under pressure. Furthermore, a water-soluble component coexists inside the water-absorbent resin, which reduces the absorption rate, reduces the stability of the water-absorbent gel due to the elution of the water-soluble component after absorption, and deteriorates the dry feel of the water-absorbent gel. Is coming. On the other hand, there is also a method of increasing the crosslinking density by increasing the amount of the crosslinking agent used, but uniform crosslinking at a high density is not preferable because the basic performance of the water absorbent resin is reduced.

As a method for solving these problems, there have been proposed methods for further cross-linking and modifying the water-absorbent resin particles, as exemplified in the following. A method in which a water-absorbent resin is dispersed in a large amount of an organic solvent having a low boiling point and a molecular weight such as alcohols, ketones and ethers containing water, and a cross-linking agent is added to cross-link (JP-A-57-4).
No. 4627) A method in which a crosslinking agent is added to a water-containing material of a water-absorbent resin having a water content adjusted to 10 to 40% by weight for crosslinking (JP-A-59-6).
No. 2665) A method in which a water-absorbent resin is made to absorb a cross-linking agent and water in the presence of an inorganic powder, and then the mixture is heated with stirring to simultaneously carry out a cross-linking reaction and water removal (JP-A-60-163956).
No.) 1 part by weight of water-absorbent resin is dispersed in a large amount of a hydrophilic inert solvent having a boiling point of 100 ° C. or more and crosslinked in the presence of 1.5 to 5.0 parts by weight of water and an inert inorganic powder. Method (JP-A-60-147475)

[0005]

However, among the above-mentioned reforming methods, the above-mentioned methods can give water-absorbent resins having an improved absorption rate, but require a step of removing a large amount of low-boiling organic solvents. Therefore, it is hard to say that this method is suitable for industrial use. Further, since these low-molecular weight organic solvents have high permeability into the water-absorbent resin particles, the cross-linking agent penetrates into the center of the water-absorbent resin particles together with the organic solvent and water and is crosslinked into the resin interior. , The absorption performance may decrease. Furthermore, in the process of removing the organic solvent, the cross-linking agent penetrates into the central part of the water-absorbent resin particles together with the concentrated water and is cross-linked to the inside of the resin, which may lead to a decrease in the absorption performance or the concentrated water. There is a problem in that workability is poor because agglomeration easily occurs between the water-absorbent resin particles to form lumps.
Even in the method of, since the water content of the water-absorbent resin is high,
The cross-linking agent penetrates into the center of the resin and is cross-linked to the inside of the resin, which reduces the absorption performance and causes a problem that agglomeration easily occurs between the water-absorbent water-absorbent resin particles to form a lump. There is. In the method of and, it is possible to prevent aggregation of the water-absorbent resin particles to each other to some extent due to the presence of the inorganic powder, but since the cross-linking agent is adsorbed not only to the water-absorbent resin but also to the inorganic powder, the crosslinking becomes uneven. It may happen that it is hard to get enough performance. Furthermore,
In this method, since a large amount of water, which is 1.5 to 5.0 times that of the water-absorbent resin, is used, the cross-linking agent penetrates even into the central part of the water-absorbent resin hydrous material, resulting in a decrease in absorption performance. There is.

[0006]

Means for Solving the Problems The present inventors have
As a result of diligent research to solve the problems in the modification method such as, even if the water-absorbing resin particles treated with a crosslinking agent in the state of an aqueous solution, due to the presence of a water-soluble compound of a specific property, The method for producing a modified superabsorbent resin capable of efficiently and homogeneously cross-linking the vicinity of the surface of resin particles without causing agglomeration of, and the modified superabsorbent resin obtained by this method, The present invention has been accomplished by discovering that it is a highly water-absorbent resin having a large absorption capacity and an excellent initial absorption rate under both unpressurized and pressurized conditions.

That is, the present invention relates to the water absorbent resin particles (A)
Is treated with an aqueous solution of the following water-soluble compound (B) and the following cross-linking agent (C) and reacted to obtain resin particles whose surface vicinity is cross-linked. And a high absorption rate obtained by this method, which has an absorption capacity of not less than 50 times against physiological saline and an absorption capacity of not less than 30 times against physiological saline. It is a water absorbent resin. Water-soluble compound (B): selected from the group consisting of an alkylene oxide adduct of a monohydric alcohol (1), a monovalent salt of an organic acid (2) and a lactam (3), and (A) and (C) Inactive one or more water-soluble compound Crosslinking agent (C): Crosslinking agent having two or more functional groups capable of reacting with (A)

In the present invention, the water-absorbent resin particles (A) are substantially water-insoluble resins that absorb a large amount of water and swell when contacted with water to form a hydrogel. The particles are (water-absorbent resin). Such a water-absorbent resin is not particularly limited, but examples thereof include crosslinked products of partially neutralized polyacrylic acid, self-crosslinked partially neutralized polyacrylic acid, and starch-acrylic acid salt graft copolymer crosslinked products. , A hydrolyzate of a starch-acrylonitrile graft polymer crosslinked product, a vinyl alcohol-acrylic acid salt copolymer, an acrylic acid salt-acrylamide copolymer crosslinked product or a hydrolyzate of an acrylic acid salt-acrylonitrile copolymer crosslinked product, Acrylate and 2-acrylamide-2
-Methyl propane sulfonate copolymer crosslinked products, crosslinked isobutylene-maleic anhydride copolymer neutralized products, carboxymethylcellulose salt crosslinked products, and the like, and one or more resins. In addition, in the above, as the salt, sodium salt, potassium salt, ammonium salt, amine salt and the like are used. Among these, preferable ones are water-absorbent resins having a carboxyl group and / or a carboxylate group, particularly acrylic acid and / or an acrylic acid salt as a main constituent unit, in view of the absorption characteristics of the finally obtained superabsorbent resin. Is a cross-linked polymer of an ethylenically unsaturated monomer,
The water-absorbent resin particles are substantially water-insoluble. In the present invention, the water content of the water absorbent resin particles (A) is usually 12
It is not more than 7% by weight, preferably not more than 7% by weight.

The shape of the water-absorbent resin particles (A) is not particularly limited, and depending on the production method, pearl-like particles obtained by reverse phase suspension polymerization, scaly particles obtained by drum-drying, and resin lumps are crushed. Examples thereof include the obtained rock-like or amorphous shape, and the shape of granules of these particles, and the like. The particle size is also not particularly limited and is usually about 10-1,
000 microns, preferably about 100-850 microns and having an average particle size of 300-700 microns.

In the present invention, the water-soluble compound (B) is
Alkylene oxide adduct of monohydric alcohol (1),
One or more water-soluble compounds selected from the group consisting of monovalent salts of organic acids (2) and lactams (3) and inert to (A) and (C). Examples of (1) include, for example, ethylene oxide adduct of methanol, ethylene oxide adduct of ethanol, ethylene oxide adduct of isopropyl alcohol, ethylene oxide adduct of butyl alcohol, propylene oxide adduct of methanol, ethylene of methanol. Examples thereof include oxide / propylene oxide adducts. Here, the monohydric alcohol component preferably has 1 to 5 carbon atoms, and the alkylene oxide component preferably has 2 to 4 carbon atoms in the alkylene group. Furthermore, the molecular weight of the compound is preferably in the range of 100 to 1,000. When the molecular weight is less than 100, the water-absorbing resin particles have high permeability, so that the water-absorbing resin particles may permeate into the central part of the water-absorbing resin particles to be cross-linked to the inside of the resin, resulting in a decrease in absorption performance. On the other hand, when the molecular weight exceeds 1,000, the powder fluidity of the superabsorbent resin obtained may be deteriorated due to the remaining of the highly viscous water-soluble compound. Examples of (2) include alkali metal salts, alkaline earth metal salts, amine salts, and ammonium salts of organic acids, such as sodium acetate, potassium acetate, ammonium acetate, sodium propionate, potassium propionate, and propionic acid. Examples thereof include ammonium, sodium lactate, potassium lactate and the like. The organic acid preferably has 2 to 6 carbon atoms. Examples of (3) include β-propiolactam, γ-butyrolactam, δ-valerolactam, ε-caprolactam and the like. The lactams preferably have about 3 to 9 carbon atoms. Among those exemplified as (B), more preferable are ethylene oxide adducts of monohydric alcohols having 1 to 5 carbon atoms and compounds having a molecular weight of 100 to 1000, and alkali metals of organic acids having 2 to 6 carbon atoms. They are salts and cyclic lactams having 4 to 8 carbon atoms. Particularly preferred is an ethylene oxide 2-10 mol adduct of a monohydric alcohol having 1 to 4 carbon atoms and a molecular weight of 100 to 50.
0 compound.

In the present invention, the concentration of the aqueous solution of the water-soluble compound (B) can be variously changed depending on the type of (B), but the water-absorbent resin particles (A) are absorbed into the aqueous solution (B) after 2 minutes. It is preferable to set the concentration of (B) so that the liquid volume is 10 ml / g or less, particularly 5 ml / g or less. Here, the liquid absorption amount is the liquid absorption amount after 2 minutes with respect to the (B) aqueous solution of (A), and this liquid absorption amount is the demand machine tester (Scientific Machine).
& Supply Co. (Manufactured by the company). This concentration can be variously changed depending on the kind of (B), but is usually 5 to 60% by weight, preferably 10
˜50% by weight, more preferably 15-40% by weight. In particular, when (1) is used as (B), 15
-40% by weight, and when (2) or (3) is used as (B), the range of 10-35% by weight is preferable. When the concentration is less than 5% by weight, 2 with respect to (A) (B) aqueous solution
The liquid absorption after a minute may exceed 10 ml / g. In this case, when (A) is treated with the (B) aqueous solution and the cross-linking agent (C) described later, (A) becomes a semi-swelled state, and swollen particles tend to agglomerate to form a lump. It becomes difficult to uniformly crosslink the vicinity of the surface, and workability also deteriorates. On the other hand, if the concentration exceeds 60% by weight,
In order to secure the water content necessary for the cross-linking reaction of (A) and (C), a large amount of the water-soluble compound (B) is used, which is uneconomical. The powder fluidity may deteriorate.

In the present invention, the amount of the aqueous solution (B) used with respect to the water absorbent resin particles (A) is the type and concentration of (B),
It can be variously changed depending on the type and amount of the cross-linking agent (C) used.
And usually 100: (1-10), preferably 100:
(2-8), particularly preferably 100: (2-5). When the ratio of this (B) aqueous solution is less than 1, it becomes difficult to carry out the crosslinking reaction uniformly. When it exceeds 10, not only does the crosslinking reaction take time, but the aqueous solution (B) gradually penetrates to the vicinity of the center of (A) together with the crosslinking agent (C), and the crosslinking reaction proceeds to the center. It may impair the absorption performance and is not practical.

In the present invention, the crosslinking agent (C) is
It is a compound having two or more functional groups capable of reacting with (A), and such compounds can be used without particular limitation. Particularly, a water-soluble crosslinking agent is preferably used. Examples of the cross-linking agent (C) include polyglycidyl ether-based compounds, haloepoxy-based compounds, polyaldehyde-based compounds, polyhydric alcohol-based compounds and polyamine-based compounds, and these may be used in combination of two or more. .

Specific examples of the polyglycidyl ether compound include ethylene glycol diglycidyl ether,
Examples thereof include propylene glycol diglycidyl ether, glycerin-1,3-diglycidyl ether, glycerin triglycidyl ether, polyethylene glycol diglycidyl ether, and 1,6-hexanediol diglycidyl ether. Specific examples of the haloepoxy compound include epichlorohydrin and α-methylepichlorohydrin. Specific examples of polyaldehyde compounds include glutaraldehyde and glyoxal. Specific examples of the polyhydric alcohol compound include glycerin, ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, diethanolamine and triethanolamine. Specific examples of the polyamine-based compound include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamide resin which is a reaction product of polyamine and fatty acid, polyamine epichlorohydrin resin,
Examples thereof include polyamide polyamine epichlorohydrin resin. Among the examples of the cross-linking agent (C), preferred are polyglycidyl ether compounds, polyhydric alcohol compounds and polyamine compounds. More preferable ones are ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin-1,3-diglycidyl ether, glycerin triglycidyl ether, and polyamine, since the reaction temperature is low and it is economical in terms of energy cost. These are epichlorohydrin resin and polyamide polyamine epichlorohydrin resin.

In the present invention, the amount of the cross-linking agent (C) used varies depending on the type of (C), the type of (A) and the degree of cross-linking thereof, the performance target of the resulting modified superabsorbent resin, and the like. Is (A) :( C) (weight ratio), and is usually 10
0: (0.01 to 5), preferably 100: (0.05
To 3), particularly preferably 100: (0.1 to 2). If the ratio of (C) is less than 0.01, the effect of addition will not be sufficiently exhibited, while if it is more than 5, the crosslinking density will be too high, leading to a decrease in absorption.

In the present invention, the water absorbent resin particles (A)
To treat (B) aqueous solution and (C)
In general, the mixture of the aqueous solution (B) and the mixture (C) is sprayed or dropped and then mixed. However, the (B) aqueous solution and the (C) are not mixed in advance,
It is also possible to use (A) in the form of simultaneous treatment or separate treatment.

The apparatus used for mixing the aqueous solutions (A), (B) and (C) may be a conventional mixer, for example, a cylindrical mixer, a screw mixer, a screw extruder, a turbulator. Examples thereof include a riser, a Nauta type mixer, a V type mixer, a ribbon type mixer, a double arm type kneader, a fluid type mixer, an air flow type mixer, a rotary disk type mixer and a roll mixer. Heating is usually required to react the mixture of (A), (B) aqueous solution and (C) obtained by treating as described above. Moreover, you may perform the said mixing and heating simultaneously. The reaction is a cross-linking reaction of (A) and (C). For this heating, a dryer or a heater, for example, a flash dryer, a rotary dryer, a paddle dryer, a disk dryer, a fluidized bed dryer, a belt dryer, a Nauter heater, an infrared dryer or the like is used. be able to.

The temperature for heat treatment varies depending on the type and amount of (C) used and the amount of water used in (B) aqueous solution, but is usually 80 to 230 ° C., preferably 100 to 210.
℃. In particular, polyglycidyl compounds such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin-1,3-diglycidyl ether, and glycerin triglycidyl ether as crosslinking agents; polyamine compounds such as polyamine epichlorohydrin resin and polyamide polyamine epichlorohydrin resin. When used, heat treatment temperature is 100-1
It is preferable because it can be heat-treated at a relatively low temperature of 80 ° C. When a polyhydric alcohol compound is used as the cross-linking agent, it is usually necessary to perform heat treatment at a high temperature of 180 to 210 ° C. in order to allow the cross-linking reaction to proceed sufficiently and uniformly. If the temperature is lower than 80 ° C., it takes a long time for heating, which is not economical, and depending on the type and amount of (C) used, the crosslinking reaction does not proceed to a sufficient extent to exhibit the effects of the present invention. There is. If the temperature exceeds 230 ° C, coloring or thermal decomposition of the super absorbent polymer may occur.

The heat treatment time varies depending on the type and amount of (C) used, the amount of water used in the aqueous solution (B), the temperature of heat treatment, etc., but is usually 2 minutes or more, preferably 5 to 60 minutes. If the time is less than 2 minutes, the heat treatment temperature is often required to be high, which is not economical, and depending on the type and the amount of (C) used, the effect of the present invention may be sufficient. The cross-linking reaction may not proceed up to this point. This heating can be carried out in vacuum or in an inert gas atmosphere, if necessary. By heating in a vacuum or in an inert gas atmosphere, it becomes possible to suppress coloring, oxidation, thermal deterioration and the like of the super absorbent polymer. Examples of the inert gas stream include nitrogen, helium, carbon dioxide gas and the like.

In the present invention, the use of the aqueous solution (B) makes it difficult for the cross-linking agent (C) to penetrate into the water-absorbent resin particles (A), so that the concentration of the cross-linking agent on the surface of the water-absorbent resin particles is reduced. It is considered that it is possible to effectively crosslink mainly in the vicinity of the surface of the water absorbent resin particles.
On the other hand, when a conventionally proposed low-boiling organic solvent having a relatively small molecular weight is used instead of (B), the aqueous solution of the organic solvent penetrates into (A).
Not only near the surface of the water-absorbent resin particles but also inside thereof are cross-linked, leading to a decrease in absorption performance. Generally, when the surface of the water-absorbent resin particles is cross-linked to the inside thereof, if the degree of cross-linking is low, the absorption capacity without load can be increased, but the absorption capacity under load tends to decrease. Further, if the degree of crosslinking is high, the absorption capacity under pressure can be increased to some extent, but the absorption capacity without pressure decreases. In the present invention, the vicinity of the surface of the water-absorbent resin particles can be efficiently cross-linked, so that a water-absorbent resin having a high initial absorption rate and a high absorption capacity both under no pressure and under pressure can be produced.

Regarding the depth of cross-linking from the surface of the water-absorbent resin particles in the vicinity of the surface of the present invention cross-linked with a cross-linking agent, (A)
Although it varies depending on the particle size of, the performance target of the modified superabsorbent resin to be obtained, it is usually 40% or less, preferably 20% or less, and more preferably 10% or less of the radius of (A).

The superabsorbent resin of the present invention is obtained by the method of the present invention, and its absorption characteristics can be controlled according to the purpose of use, but the absorption capacity without load to physiological saline is usually 50. More than twice, preferably 55
It is at least 30 times, and the absorption capacity with respect to physiological saline under pressure is 30 times or more, preferably 35 times or more. In addition, the physiological saline means an aqueous solution of sodium chloride (concentration: 0.85 to
0.95% by weight). Therefore, since it has excellent absorbency, when the same absorbency is required, a small amount can be used, bulkiness does not increase, and cost can be reduced. Furthermore, the highly water-absorbent resin of the present invention has a small amount of water-soluble components, has a good dry feeling of gel after absorbing water, and shows a dry feel, for example, the surface of a paper diaper after urination when used in a paper diaper or the like. Feels good.

The superabsorbent resin of the present invention can be used as a preservative, fungicide, bactericide, antioxidant, ultraviolet absorber, colorant, fragrance, deodorant, at any stage in the method of the present invention. It is possible to add inorganic fine powder (fine powder silica or the like), organic fibrous substance (pulp powder or the like), or the like.

[0024]

The present invention will be further described below with reference to Examples and Comparative Examples, but the present invention is not limited to these. The initial absorption rate and absorption capacity without pressure, the initial absorption rate and absorption capacity under pressure, and the dry feeling of the water-absorbent gel were measured by the following methods. Hereinafter, unless otherwise specified,% means% by weight.

Initial unpressurized absorption rate and absorption capacity: 250
1g of super absorbent resin was placed in a tea bag made of mesh nylon net, immersed in physiological saline (concentration 0.9% by weight) for 5 minutes and 60 minutes, and then drained for 15 minutes to increase the weight. To measure. The absorption amount after 5 minutes of immersion was defined as the initial unloaded pressure of physiological saline, and the absorption amount after 60 minutes of immersion was defined as the unpressurized absorption capacity of physiological saline.

Initial absorption rate and absorption capacity under pressure: 250
Put 0.1 g of super absorbent resin into a cylindrical plastic tube (inner diameter 30 mm, height 60 mm) with a nylon mesh net on the bottom, and 20 g / cm2 on top of this resin.
A weight having an outer diameter of 30 mm is placed so that the load becomes. A plastic tube containing a water-absorbent resin is immersed in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline with the nylon net side facing down and left to stand. The weight of the superabsorbent resin absorbed by the physiological saline solution is measured after 5 minutes and 60 minutes. The value 10 times the absorption after 5 minutes was used as the initial absorption rate under pressure against physiological saline, and 10 times the absorption after 60 minutes.
The doubled value was taken as the absorption capacity under pressure against physiological saline.

Dry sensation of water-absorbent gel: The surface of the water-absorbent gel for which the absorption capacity against physiological saline was measured was touched with a finger, and the dry sensation was evaluated according to the following four criteria. ◎: Good dry feeling ○: Slightly inferior, but satisfactory dry feeling △: Poor dry feeling, slightly sticky feeling ×: Great sticky feeling

Example 1 72.95 mol% sodium acrylate, acrylic acid 2
25% aqueous solution of acrylate monomer consisting of 7 mol% and methylenebisacrylamide 0.05 mol% 1,
000 parts with 0.1 part of hydrogen peroxide and 0.03 part of ascorbic acid in a nitrogen atmosphere at a polymerization initiation temperature of 10 ° C.
Then, adiabatic polymerization was carried out by standing to obtain a gel polymer. After drying this gel polymer with a drum dryer set at 180 ° C.,
Water-absorbent resin particles (a) were obtained by pulverizing to a particle size of 20 to 145 mesh. 100 parts of water-absorbent resin particles (a) were placed in a juicer mixer having a capacity of 2,000 ml and, while continuing stirring, 4 parts of an aqueous solution of a cross-linking agent in which 10% by weight of ethylene glycol diglycidyl ether was dissolved in a 15% by weight aqueous solution of sodium propionate. (0.4 parts with respect to the water absorbent resin (a)) was added and mixed sufficiently. The obtained mixture was heat-treated at 150 ° C. for about 20 minutes to obtain the superabsorbent polymer (1) of the present invention.

Example 2 Using the water-absorbent resin particles (a) obtained in Example 1, 15% by weight of sodium propionate in Example 1 was replaced by the kind and the amount of the water-soluble compound described below. Super absorbent polymers (2) to (6) were obtained in the same manner as in Example 1. That is, in the case of the superabsorbent resin (2), 30% by weight of sodium propionate, in the case of the superabsorbent resin (3), 25% by weight of sodium lactate, and in the case of the superabsorbent resin (4), In the case of the highly water-absorbent resin (5), 30% by weight of ethylene oxide 3 mol adduct of methanol is added.
20% by weight of an ethylene oxide 3 mol adduct of butanol and 25% by weight of ε-caprolactam in the case of the super absorbent resin (6) were used.

Example 3 100 parts of the water-absorbent resin particles (a) obtained in Example 1 were placed in a juicer mixer having a capacity of 2,000 ml and, while continuing stirring, to a 30% by weight aqueous solution of a 3 mol adduct of ethylene oxide with methanol. 3 parts of an aqueous solution of a crosslinking agent in which 10% by weight of polyamide polyamine epichlorohydrin resin was dissolved (0.3 parts with respect to the water absorbent resin (a)) was added and sufficiently mixed. The obtained mixture was heat-treated at 150 ° C. for about 20 minutes to obtain the superabsorbent polymer (7) of the present invention.

Example 4 Using the water-absorbent resin particles (a) obtained in Example 1, Example 1
The ethylene glycol diglycidyl ether in Example 1 was replaced with the cross-linking agent described below, and the heat treatment temperature of the mixture was adjusted to 1
Superabsorbent polymers (8) to (10) were obtained in the same manner as in Example 1 except that the temperature was changed to 90 ° C. That is, glycerin was used for the super absorbent polymer (8), polyethylene glycol 200 was used for the super absorbent resin (9), and triethylenetetramine was used for the super absorbent resin (10).

Example 5 Using the water-absorbent resin particles (a) obtained in Example 1, Example 1
Example 1 except that 4 parts by weight of the aqueous solution of the crosslinking agent in 7 was used.
A super absorbent resin (11) was obtained in the same manner as in.

Example 6 Instead of the water absorbent resin particles (a) of Example 1, starch-
Highly water-absorbent resin (12) in the same manner as in Example 1 except that water-absorbent resin particles (b) [Sanyo Chemical Co., Ltd., Sunwet IM-1000] of a cross-linked sodium acrylate graft copolymer are used. Got

Comparative Example 1 A comparative water absorbing agent (1) was obtained in the same manner as in Example 1 except that sodium propionate was not added to the aqueous solution of the crosslinking agent.

Comparative Example 2 A comparative water absorbing agent (2) was obtained in the same manner as in Example 1 except that ethylene glycol diglycidyl ether was not added to the aqueous solution of the crosslinking agent.

Comparative Example 3 In Example 1, sodium propionate was not added, and ethylene glycol diglycidyl ether was added to 2 parts.
A comparative water absorbing agent (3) was obtained in the same manner as in Example 1 except that 20 parts by weight of a cross-linking agent aqueous solution was used.

Comparative Example 4 A comparative water absorbing agent (4) was obtained in the same manner as in Example 1 except that the same amount of isopropyl alcohol was used instead of sodium propionate.

Water-absorbent resin particles (a) and (b) obtained in Examples 1 to 6 and Comparative Examples 1 to 4 and super-water-absorbent resin (1)
-(12) and comparative water-absorbing agents (1)-(4) were measured for initial absorption rate and absorption capacity without pressure, initial absorption rate and absorption capacity under pressure, and dry feeling of the water-absorbent gel. The results are shown in Table 1 together with the state of the water absorbent resin during the crosslinking reaction.

[0039]

[Table 1]

From Table 1, the following is clear. Super absorbent polymers (1) to (1) obtained in Examples 1 to 6
In 2), compared with the water-absorbent resin particles (a) and (b) before the reaction, the dry feeling of the water-absorbent gel and the initial absorption rate and absorption capacity under pressure are dramatically improved. Further, the super absorbent resin (1) obtained in Examples 1 to 6
~ (12), compared with the comparative water-absorbing agent (1) ~ (4) obtained in Comparative Examples 1 to 4, the dry feeling of the water-absorbing gel, the initial absorption rate under pressure and the absorption capacity are dramatically increased. Has improved. Moreover, the comparative water-absorbing agents cause aggregation during the reaction except for (2). Comparative absorbent (2) in good condition during reaction
Is a water-absorbent resin particle (a) because no crosslinking agent is used.
It shows almost the same performance as.

[0041]

The method of the present invention has the following effects. The method of the present invention is an industrially simple method, and the modified superabsorbent resin of the present invention can be produced at low cost. The aqueous solution of (B) is hardly absorbed by the water-absorbent resin particles in a short time. Therefore, in the process of treating the water-absorbent resin particles with the aqueous solution of (B) and the crosslinking agent, agglomeration occurs between the resin particles to form a lump. The workability is good. Even if the cross-linking agent is treated in the state of an aqueous solution, the cross-linking agent hardly penetrates into the inside of the resin particles due to the presence of (B), so that the cross-linking agent concentration on the surface of the resin particles becomes high. As a result, the vicinity of the surface of the particles can be crosslinked uniformly and efficiently. Generally, in the case where the water-absorbent resin particles are cross-linked even in the interior thereof, if the degree of cross-linking is low, the absorption capacity without pressure can be increased, but the absorption capacity under pressure tends to decrease. On the other hand, if the degree of crosslinking is high, the absorption capacity under pressure can be increased to some extent, but the unabsorbed absorption capacity decreases. Since no organic solvent is used, the step of removing the organic solvent is unnecessary. As in the case of using an aqueous solution of a low molecular weight organic solvent as a solvent for the cross-linking agent, not only the vicinity of the surface of the water-absorbent resin particles but also the inside thereof are cross-linked and the absorption performance is not deteriorated.

The superabsorbent resin of the present invention obtained by the method of the present invention has the following characteristics. It has an excellent absorption capacity in both unpressurized and pressurized situations. The water-absorbent resin particles do not become muddy when brought into contact with water, and have an excellent initial absorption rate. Since it has excellent absorbency as described above, when the same absorbency is required, a small amount can be used, bulkiness does not increase, and cost can be further reduced. The amount of water-soluble components is small, the dry feel of the gel after water absorption is good, and it shows a dry feel. Therefore, when used in a paper diaper or the like, the feel of the surface of the paper diaper after urination becomes good. Since the method of the present invention also causes crosslinking between particles, the superabsorbent resin obtained has the advantage that the content of fine powder is small. Therefore, dust is hardly generated when the resin is handled, workability is good, and there is no concern about dust inhalation, which is safe for workers.

Because of the above effects, the superabsorbent resin of the present invention obtained by the method of the present invention is
Use in contact with the human body such as sanitary materials (diapers for children and adults, sanitary napkins, incontinence pads, etc.); Use in contact with food products such as freshness-retaining materials, cold storage materials, drip absorbents; Removal agent for water in oil , Desiccants; water retention agents for plants and soil; coagulants such as sludge; anti-condensation agents; waterproofing materials and packing materials for civil engineering and construction; water blocking materials for electric cables and optical fiber cables. .

Claims (12)

[Claims] 1. A water-absorbent resin particle (A) is treated with an aqueous solution of the following water-soluble compound (B) and the following cross-linking agent (C) and reacted to obtain a resin particle in which the vicinity of the surface is cross-linked. A method for producing a modified superabsorbent resin characterized by: Water-soluble compound (B): selected from the group consisting of an alkylene oxide adduct of a monohydric alcohol (1), a monovalent salt of an organic acid (2) and a lactam (3), and (A) and (C) Inactive one or more water-soluble compound Crosslinking agent (C): Crosslinking agent having two or more functional groups capable of reacting with (A) 2. The method according to claim 1, wherein the concentration of the (B) aqueous solution is 5 to 60% by weight. 3. The weight ratio of (A) and (B) aqueous solution is 1
It is 00: (1-10), The manufacturing method of Claim 1 or 2. 4. The weight ratio of (A) to (C) is 100:
(0.01-5), The manufacturing method in any one of Claims 1-3. 5. (B) is a compound having an alkylene oxide adduct of a monohydric alcohol and having a molecular weight of 100 to 1,000, an alkali metal salt of an organic acid having 2 to 6 carbon atoms and 4 to 8 carbon atoms. The method according to any one of claims 1 to 4, wherein the method is at least one selected from the group consisting of cyclic lactams. 6. The compound according to claim 1, wherein (B) is a compound having 2 to 10 mol of ethylene oxide with a monohydric alcohol having 1 to 4 carbon atoms and having a molecular weight of 100 to 500. Manufacturing method. 7. The concentration of the aqueous solution of (B) is (B) of (A).
The production method according to any one of claims 1 to 6, wherein the amount of liquid absorbed after 2 minutes with respect to the aqueous solution is 10 ml / g or less. 8. The method according to claim 1, wherein the reaction temperature is 80 ° C. to 230 ° C. 9. (A) is a cross-linked polymer of an ethylenically unsaturated monomer having acrylic acid and / or acrylate as a main constituent unit, and is substantially water-insoluble water-absorbent resin particles. The manufacturing method according to claim 1. 10. (C) is at least one selected from the group consisting of polyglycidyl ether compounds, polyhydric alcohol compounds and polyamine compounds.
9. The production method according to any one of 9. 11. (C) is ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin-1,3-diglycidyl ether
The method according to any one of claims 1 to 10, wherein the reaction temperature is 100 to 180 ° C, and the reaction temperature is 100 to 180 ° C, which is at least one selected from the group consisting of polyglycerin triglycidyl ether, polyamine epichlorohydrin resin, and polyamide polyamine epichlorohydrin resin. 12. An absorption obtained by the method according to any one of claims 1 to 11, which has a non-pressurized absorption capacity of 50 times or more for physiological saline, and an absorption capacity of 30 times or more for physiological saline under pressure. A modified superabsorbent resin having characteristics.