JPH0615574B2 - Method for producing water absorbent resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a water absorbent resin, and more specifically,
The present invention relates to a method for producing a water-absorbent resin capable of efficiently producing a water-absorbent resin having excellent water-absorbing properties and gel strength.

<Problems to be solved by the prior art and invention> In recent years, in the fields of hygiene products, medicines, cosmetics, agriculture, foods, civil engineering, household products, etc., as water-absorbing materials and water-retaining materials,
Water-absorbent resins that can highly absorb water are used.
Examples of such water-absorbent resin include cross-linked polyethylene oxide, cross-linked polyvinyl alcohol, cross-linked polyacrylic acid and its salt, cellulose-acrylic acid graft copolymer and its salt, starch-acrylonitrile graft copolymer hydrolyzate. Etc. are known. Further, in order to enhance the gel strength and water retention after absorbing water, a water-absorbent resin having a large gel strength can be obtained by copolymerizing acrylic acid or an alkali metal acrylate and a crosslinkable monomer having copolymerizability with the above monomer. There are attempts to manufacture. However, the reactivity of the acrylic acid-based monomer and the crosslinkable monomer also varies depending on the pH of the reaction system and the like, which causes a problem in copolymerizability. Further, in order to obtain a water absorbent resin having a uniform composition and a crosslink density and to reduce the residual monomer concentration, it is necessary to strictly adjust the temperature, pH and the like of the reaction system to improve the productivity. Have difficulty. Further, when the water-containing gel obtained as described above is dried and pulverized to produce a powdery water-absorbent resin, the water-containing gel is hydrophilic, rich in water retention, and crosslinked,
It is not economical because desorption of water is not easy and a large amount of heat is required in the drying process. Furthermore, according to the above method, since the gel strength of the water-absorbent resin is defined by the degree of crosslinking of the crosslinkable monomer, when a resin having low gel strength is obtained, the gel strength and water retention of the water-absorbent resin are increased. Is difficult.

Further, the acid-based water-absorbent resin, in order to increase the water absorption rate,
Although it is usually used in the form of a powder, there is a problem that the powder agglomerates (Mamako phenomenon) at the time of water absorption and the contact area with water becomes small, so that the original water absorbing performance of the water absorbent resin cannot be exhibited.

In order to solve the above problems, a method of dispersing the powdery polyacrylic acid-based water-absorbent resin in a mixed solvent of water and a hydrophilic organic solvent such as methanol, and crosslinking with a crosslinking agent such as ethylene glycol diglycidyl ether ( JP-A-57-44627) or a water-absorbent resin obtained by crosslinking a powdery water-absorbent resin having a carboxy group with a crosslinking agent such as a polyvalent glycidyl ether compound (JP-A-59-189103). See the bulletin).

However, according to the former method, since a large amount of an organic solvent such as methanol is used, an uneconomical step of removing a large amount of the solvent is carried out after the cross-linking treatment. However, it is difficult to manufacture industrially safely and the cost is high.

Further, the latter water-absorbent resin, since a small amount of the crosslinking agent is added directly to the powdery water-absorbent resin or the like, it is difficult to uniformly distribute the crosslinking agent on the entire surface of the powdery water-absorbent resin. However, there is a problem that a portion with excessive cross-linking or insufficient cross-linking occurs locally, and the Mamako phenomenon is likely to occur in the water absorption process, so that sufficient water absorption characteristics are not exhibited.

In addition, in order to increase the water absorption performance and reduce changes in water absorption characteristics and the like due to changes over time and repeated use, a method of crosslinking a water-containing substance of a water-absorbing resin having a carboxy group with a polyglycidyl ether compound is known. (JP 62-
50305 gazette).

However, according to the above method, not only is it necessary to adjust the water content of the water-absorbent resin to a specific range, but it is industrially difficult to uniformly contain a specific amount of water in the resin. Further, since the water-absorbent resin contains water, in the cross-linking step, lumps that are aggregates of the water-absorbent resin are likely to occur, and not only the uniform cross-linking treatment is not possible,
It is difficult to obtain the water absorbent resin in good yield. Further, in order to adjust the water content to a specific range, it is necessary not only to adopt a reverse phase suspension polymerization method using an organic solvent, but also to remove the used organic solvent, which is not economical. There is.

<Objects of the Invention> The present invention has been made in view of the above problems, and without using an organic solvent such as a lower alcohol, the powdery water-absorbent resin does not aggregate and become uniform during the crosslinking treatment. Even if it is a water-absorbent resin that can be cross-linked and has insufficient water absorption characteristics, it is excellent in water absorption characteristics such as water absorption speed and water absorption, gel strength after water absorption, water retention, etc. An object of the present invention is to provide a method for producing a water-absorbent resin that can efficiently produce a water-absorbent resin that is not present at low cost.

<Means for Solving the Problem> In order to solve the above problems, the method for producing a water-absorbent resin of the present invention, in the presence of a polyhydric alcohol and water, powdery water-absorbing water having a carboxy group or a carboxylate group. The functional resin is treated with an aluminum compound capable of reacting with the water absorbent resin and a crosslinking agent having two or more functional groups capable of reacting with the water absorbent resin. After the above treatment, the residual water is removed by means such as heating, and the powder is preferably used in the form of powder.

The present invention will be described in detail below.

The water absorbent resin used in the present invention may be a polymer having a carboxy group and / or a carboxylate group, and examples thereof include a hydrolyzate of a starch-acrylonitrile graft polymer and a starch-acrylic acid graft polymer. Examples of the partially neutralized product, vinyl acetate-saponified acrylic acid ester copolymer, carboxymethyl cellulose, isobutylene-maleic anhydride copolymer, partially neutralized polyacrylic acid, or cross-linked products of these polymers are exemplified. It Among the above water-absorbent resins, a polyacrylic acid-based water-absorbent resin composed of a polymer or copolymer having at least a monomer unit of acrylic acid or acrylate in its main chain is particularly preferable.

Examples of the polyacrylic acid-based polymer comprising a polymer or a copolymer having at least acrylic acid or an acrylic acid salt monomer unit in the main chain include polyacrylic acid, polyacrylic acid salt, and acrylic acid-acrylic acid salt. Examples thereof include copolymers. Examples of the salt portion of the acrylic acid salt and the polyacrylic acid salt include alkali metal salts such as sodium salt, potassium salt and lithium salt, organic base salts such as ammonium salt, triethylamine salt and pyridine salt.

These polymers may have acrylamide, N-vinylpyrrolidone,
It may be a copolymer with 2-hydroxyethyl methacrylate or the like. Further, the above-mentioned polymer is preferably a cross-linked polymer, and known cross-linking means can be adopted in the production of the cross-linked product. For example, self-crosslinking by heating a self-crosslinking polymer copolymerized with a crosslinkable monomer such as N-methylolacrylamide, or using an oxidizing catalyst such as potassium persulfate, N, N'-methylenebisacrylamide, 2 such as ethylene glycol diacrylate
It is carried out by adding a crosslinking agent having at least one polymerizable unsaturated bond during the polymerization. The above-mentioned polymer is usually produced by adding other copolymerizable monomer and the above-mentioned cross-linking agent to an aqueous solution of acrylic acid and / or an acrylic acid salt, and then polymerizing the resulting mixture. Therefore, it is pulverized by a pulverizer to an appropriate particle size. Regarding the particle size, a Tyler standard sieve having a particle size of preferably 5 to 400 mesh, more preferably 10 to 200 mesh is used. Although emulsion polymerization or suspension polymerization yields small spherical particles, it may be further pulverized.

Examples of the polyhydric alcohol used in the present invention include ethylene glycol, 2,2-propanediol, 1,3-propanediol and butanediol (for example, 1,2-butanediol, 1,3-butanediol, 1, 4-butanediol, 2,3-butanediol, etc., pentanediol (eg, 1,5-pentanediol, 1,3-pentanediol, 2,3-pentanediol, etc.), hexanediol (eg, 1,6) -Hexanediol,
2,5-hexanediol, etc.), 2-methyl-2,4-
Diols such as pentanediol and 2-methyl-2,3-butanediol; glycerin, trimethylolpropane, hexanetriol (for example, 1,2,6-hexanetriol, 1,3,5-hexanetriol, etc.),
Triols such as triethanolamine; tetraols such as pentaerythritol and diglycerin; pentaols such as glucose and furanose; hexaols such as sorbit and mannite; octaols such as sucrose; lower of the above compounds Alkylene oxide adducts; lower alkylene oxide copolymers and the like are exemplified. You may use these polyhydric alcohols in mixture of 2 or more types.

Examples of the lower alkylene oxide include ethylene oxide (hereinafter, referred to as EO), propylene oxide (hereinafter,
PO)), butylene oxide, and other alkylene oxides having 2 to 4 carbon atoms. Examples of the polyhydric alcohols to which these lower alkylene oxides are added include:
Diethylene glycol, triethylene glycol, polyethylene glycol [average molecular weight (hereinafter referred to as MW): 200, 300, 400, 600, 1000, 2
, 6000, etc.], dipropylene glycol, tripropylene glycol, polypropylene glycol [M
W: 200, 400, 1000, 2000, 4000
Etc.], glycerin-EO adduct [MW: 400, 60
0, 1000, 3000, 4000, etc.], glycerin-
PO adduct [MW: 400, 600, 1000, 300
0, 4000, etc.], glycerin-EO (50) / PO
(50) Random adduct [MW: 2600, etc.], glycerin-PO (80) -EO (20) block adduct [M
W: 3000 etc.], trimethylolpropane-EO adduct, trimethylolpropane-PO adduct, pentaerythritol-EO adduct, pentaerythritol-PO.
Examples thereof include an adduct and a sorbit-EO adduct. The lower alkylene oxide copolymer includes random copolymers and block copolymers. For example, polypropylene glycol EO adducts [MW: 2400, 31
00, 4000, etc.] can be exemplified.

In the above compounds, for example, glycerin-EO (5
0) / PO (50) random adduct means a compound obtained by reacting a mixture of 50% by weight of EO and 50% by weight of PO (all of which are based on total alkylene oxide) and glycerin at random. Glycerin-P
O (80) -EO (20) block adduct means that 80% by weight of PO is added to glycerin and then 20% by weight of EO is added.
(Any weight% has the same meaning as described above).

Among the above polyhydric alcohols, preferred are ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, 2-methyl-2,4-pentanediol, hexanetriol, glycerin, pentaerythritol, sorbit,
Polyethylene glycol, polypropylene glycol,
Examples thereof include glycerin-EO adduct, glycerin-PO adduct, pentaerythritol-EO adduct, pentaerythritol-PO adduct, sorbit-EO adduct, and the like, more preferably ethylene glycol, propanediol, butanediol, pentane. Diol, hexanediol, 2-methyl-2,4-pentanediol,
Examples include hexanetriol and polyethylene glycol.

The amount of the polyhydric alcohol added is 0.01 to 50% by weight, preferably 0.1 to 50% by weight, with respect to the water absorbent resin.
It is in the range of 20% by weight, and more preferably in the range of 1 to 10% by weight. If it is less than 0.01% by weight, the effect of addition is not observed, and if it exceeds 50% by weight, the water absorption capacity is lowered or the fluidity of the powder is lowered, which is not preferable.

The water-absorbent resin obtained by using a compound of the above polyhydric alcohols to which a lower alkylene oxide is not added has very good fluidity of the powdery water-absorbent resin before water absorption.

The water used together with the polyhydric alcohol is not particularly limited, for example, ion-exchanged water, distilled water, tap water or the like can be used, and the amount of water used is an amount sufficient to dissolve or disperse the aluminum compound or It may be used in an amount of 1 to 10 times (weight), preferably 1 to 8 times (weight), and more preferably 2 to 6 times (weight) with respect to the aluminum compound.

The aluminum compound may be any aluminum compound capable of reacting with the carboxy group or the carboxylate group of the water absorbent resin, and these aluminum compounds act as a crosslinking agent on the surface of the water absorbent resin. Examples of the aluminum compound include aluminum salts such as aluminum chloride, aluminum nitrate, aluminum sulfate, aluminum phosphate and aluminum acetate; aluminum hydroxide; aluminum isopropoxide, aluminum ethoxide, aluminum-tertiary-butoxide and the like. Examples thereof include aluminum alkoxide, and two or more kinds may be mixed and used. Among them, aluminum hydroxide sol, especially when used in the cross-linking reaction in the state of aluminum hydroxide gel immediately after precipitation, has high reactivity, it is possible to increase the gel strength without significantly impairing water absorption, and unnecessary residue is removed. It never happens. The above-mentioned sol or gel state can be suitably obtained by reacting an aluminum salt with an aluminate or an aluminum salt with an alkali metal hydroxide in the presence of water.

The aluminum compound is 0.1 with respect to the water absorbent resin.
-40% by weight, preferably 0.2-20% by weight, more preferably 0.25-10% by weight. If the addition amount is less than 0.1% by weight, the crosslinking is insufficient to prevent the mamako phenomenon and the like, and if the addition amount exceeds 40% by weight, the surface crosslinking becomes excessive and the water absorption decreases.

Further, the cross-linking agent having two or more functional groups capable of reacting with the water absorbent resin may be any one capable of reacting with the carboxy group and / or the carboxylate group of the water absorbent resin. Examples of the crosslinking agent include aldehyde compounds such as glutaraldehyde and glyoxal; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; haloepoxy compounds such as epichlorohydrin and epibromohydrin; ethylene glycol diglycidyl ether and diethylene glycol diether. Glycidyl ether, polyethylene glycol diglycidyl ether,
Examples thereof include epoxy compounds such as propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, polyglycerin polyglycidyl ether, pentaerythritol polyglycidyl ether, and sorbitol polyglycidyl ether. Of the above-mentioned crosslinking agents, epoxy compounds are preferable from the viewpoint of reactivity and the like.

The cross-linking agent is used in an appropriate amount depending on the desired water absorption characteristics, gel strength, etc., but is used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, based on 100 parts by weight of the water absorbent resin. To be done. If the amount of the cross-linking agent is less than 0.01 part by weight, not only the effect due to the cross-linking does not appear remarkably, but also the powdery water-absorbent resin aggregates into a lump-like lump during the cross-linking process, which makes it difficult to uniformly process. . On the other hand, if it exceeds 10 parts by weight, the crosslink density increases and the water absorption capacity decreases.

The method for producing a water absorbent resin of the present invention is a powdery water absorbent resin having a carboxy group and / or a carboxylate group in the presence of a polyhydric alcohol and water, an aluminum compound capable of reacting with the water absorbent resin, and It is carried out by treating with a crosslinking agent having two or more functional groups capable of reacting with the water absorbent resin. More specifically, for example, in the presence of a polyhydric alcohol and water, it is made by mixing the powdered water-absorbent resin with the aluminum compound and the cross-linking agent and drying, for example, in a mixer By adding or spraying a resin prepared by dissolving or dispersing a desired amount of polyhydric alcohol, an aluminum compound and a cross-linking agent in water while stirring, and thoroughly mixing and drying in a dryer. A water absorbent resin is produced. In addition, a method of preparing an aqueous solution or dispersion of a polyhydric alcohol, an aluminum compound and a cross-linking agent and adding them to the resin at the same time, or adding a polyhydric alcohol solution, an aluminum compound solution and a cross-linking agent solution in an appropriate order It may be.

The mixing means is not particularly limited, Nauta mixer,
A conventional mixer such as a ribbon blender, a conical blender, a Henschel mixer, and a liquor mixer can be used.

After the above treatment, residual water is removed by means such as heating and drying, but the polyhydric alcohol, which is a high boiling point component, remains in the water absorbent resin.

In the above steps, the crosslinking reaction temperature of the aluminum compound is not particularly limited, but is usually room temperature to 100 ° C., preferably room temperature to 60 ° C., and the reaction time is 1 to 12
It is 0 minutes, preferably 2 to 30 minutes. Further, the cross-linking of the water-absorbent resin with the cross-linking agent can be carried out at an appropriate temperature depending on the type of the cross-linking agent, the desired water-absorption property, gel strength, etc.
To 250 ° C, preferably 70 to 200 ° C, in the case of an isocyanate compound 0 to 200 ° C, preferably room temperature to 15
0 ° C., 30 to 200 ° C. in the case of haloepoxy compound, preferably 50 to 150 ° C., 50 in the case of epoxy compound
It is carried out at a temperature of ~ 250 ° C, preferably 70-200 ° C.

Further, the drying is a conventional dryer, for example, a hot air circulation dryer,
Using a vacuum dryer or the like, room temperature to 150 ° C, preferably 70
It is performed at ~ 120 ° C. In addition, you may perform the said drying process and a crosslinking process simultaneously at the temperature suitable for the said crosslinking reaction. Further, calcium chloride, zinc nitrate or the like may be added in order to improve fluidity at the time of mixing, cross-linking characteristics and the like.

Incidentally, without using a cross-linking agent, in the presence of a polyhydric alcohol and water, when treated with the aluminum compound, a water-absorbing resin having excellent water-absorbing properties such as water-absorption rate and water-absorption amount can be obtained. Of water-soluble resin is still insufficient in gel strength and water retention after water absorption. Further, when the crosslinking treatment is carried out using a crosslinking agent in the absence of the polyhydric alcohol or the aluminum compound, the powdery water-absorbent resin aggregates into a lump during the crosslinking treatment, and it is difficult to uniformly perform the crosslinking treatment. On the other hand, by treating the water-absorbent resin with the aluminum compound and the crosslinking agent in the presence of the polyhydric alcohol and water, the powdery water-absorbent resin may be aggregated into a lump during the crosslinking treatment. It is possible to produce a water-absorbent resin that is not only excellent in water absorption characteristics such as water absorption rate and water absorption, fluidity before water absorption, but particularly gel strength and water retention, and can be uniformly crosslinked. . Further, since it is possible to introduce a cross-linked structure after the above treatment without introducing a cross-linked structure to the water-absorbent resin in advance, even if the water-absorbent resin does not have sufficient gel strength, etc., be subjected to the above-mentioned treatment. This makes it possible to produce a water absorbent resin having the above-mentioned properties, particularly gel strength and water retention.

The preferred embodiments of the method for preparing the treatment liquid used in the present invention are as follows.

(A) When aluminum chloride and an aluminum salt alkali metal salt such as sodium aluminate are used as the aluminum compound (1) A predetermined amount of aluminum chloride hexahydrate is added to water with stirring and dissolved.

(2) Then, a predetermined amount of sodium aluminate is gradually added with stirring.

(3) Immediate white turbidity and formation of aluminum hydroxide, the viscosity of which once rises and loses fluidity, but when stirring is continued, it becomes a viscous liquid with fluidity again. Usually, it is preferable to stir for 20 minutes or more.

(4) A treatment liquid is prepared by adding a predetermined amount of polyhydric alcohol and a cross-linking agent to this liquid and stirring the mixture to obtain a uniform liquid. The polyhydric alcohol and the cross-linking agent may be added to the initial water.

(B) When aluminum chloride and an alkali metal hydroxide such as sodium hydroxide are used as the aluminum compound (1) A predetermined amount of sodium hydroxide is dissolved in water.

(2) Then, while stirring, a predetermined amount of aluminum chloride
Hexahydrate is gradually added.

(3) Thereafter, the same processing as (3) and (4) in (A) above is performed.

The treatment liquid thus prepared is preferably used in a proportion of 100 to 750 parts by weight, preferably 150 to 500 parts by weight, of the powdery water-absorbent resin with respect to 100 parts by weight of the treatment liquid. Further, since the aluminum hydroxide precipitates and separates when the treatment liquid is left standing, it is preferable to use the treatment liquid in a state of stirring and dispersing at the time of use.

The water absorbent resin obtained by the production method of the present invention is used in the form of powder, and the particle size thereof is 5 to 50 on Tyler standard sieve.
It is about 0 mesh, preferably 10 to 200 mesh. If necessary, use by adding additives such as fine powder silica, fluidity aids such as talc, extenders, antioxidants, fungicides, bactericides, fragrances, colorants, deodorants, etc. You may.

<Operation and Effect of Invention> As described above, according to the method for producing a water absorbent resin of the present invention, a powdery water absorbent resin having a carboxy group and / or a carboxylate group in the presence of a polyhydric alcohol and water. Since the water absorbent resin is treated, the powdery water absorbent resin does not agglomerate to form a lump at the time of the treatment, and the crosslinking treatment can be uniformly performed, so that the water absorbent resin having excellent water absorbing performance can be manufactured. More specifically, the water-absorbent resin obtained by the method of the present invention has, for example, a high water-absorption amount and water-absorption rate not only for water but also for solutions containing salts, such as urine and human discharge liquid such as blood. It is possible to rapidly absorb urine, blood and the like. Further, since the gel strength after absorbing water is remarkably high, it is possible to retain water in a stable shape, and it is excellent in water retention. Furthermore, since the Mamako phenomenon does not occur during water absorption, the water absorption speed can be significantly increased. Moreover, even if the water absorbent resin has insufficient properties such as gel strength, the gel strength can be remarkably increased by subjecting it to the above treatment.

Further, according to the method for producing a water absorbent resin of the present invention, a water absorbent resin excellent in water absorbing performance and the like can be efficiently and inexpensively produced. That is, according to the production method of the present invention, the crosslinking step does not use a large amount of an organic solvent such as alcohol, does not require a solvent recovery step, etc., and in the presence of the polyhydric alcohol and water, the aluminum compound and the crosslinking By cross-linking with an agent, the gel strength and the like can be increased even with a water-absorbent resin having insufficient performance, so in the production of the polymer constituting the water-absorbent resin, a production method for increasing the productivity is used. Not only can it be adopted, but the crosslinking treatment can be performed uniformly without causing lumps, the cost can be reduced, and the water absorbent resin can be produced safely and industrially by a simple operation.

Since it has the advantages as described above, the water-absorbent resin obtained by the production method of the present invention can be used in various applications, has a high water absorption amount and a high water-absorption rate, and is excellent in water retention and gel strength after water absorption. , Sanitary materials such as paper diapers, sanitary napkins, sanitary tampons, paper towels, medical products such as water retaining materials for poultices, seed germination aids, agricultural materials such as water retaining materials for soil, anti-condensation materials for interior materials, etc. Can be used as a building material, a cosmetic material such as a water retaining material such as a cosmetic or a fragrance.

<Examples> Examples and comparative examples of the present invention will be shown below, but the present invention is not limited to these examples. In the examples,% means% by weight unless otherwise specified.

The performance test of the water absorbent resin was performed by the following method.

a) Measurement of water absorption amount A sample (Xg) is put into a commercially available fold-folded coffee filter and immersed in 0.9% saline for a certain time, and then the weight (Yg) including the coffee filter is measured. On the other hand, the weight (Zg) of the water-absorbed coffee filter itself was measured in advance, and the water absorption amount (times) was obtained from the following formula.

Water absorption amount (times) = (Y−Z) / X b) Measurement of gel strength To a 200 ml beaker was added 97.5 g of 0.9% saline, and 2.5 g of a water absorbent resin was added while stirring with a magnetic stirrer. Add and gel. 24 gel generated
After standing for 3 hours, the diameter will change from 3/16 inch to 1/1
Steel balls for JIS standard ball bearings, which are increased by 6 inches, are sequentially placed on the gel surface and continued until they settle in the gel. However, the steel balls that have not settled are removed before the next steel ball is steeled. In this way, the maximum diameter of the steel balls that did not settle was taken as the gel strength.

Preparation of water absorbent resin to be tested 75% by weight of 80% acrylic acid, 54.9 parts by weight of 48.6% sodium hydroxide and 56.1 parts by weight of deionized water are mixed to obtain an aqueous acrylate solution having a neutralization degree of 80%. Was prepared.

The container containing 1023 g of the aqueous acrylate solution was replaced with nitrogen, and 33 g of 1% ammonium persulfate was added and mixed. A box-shaped container (SUS, inner Teflon coat) with a length of 4 cm, a width of 20 cm, and a height of 15 cm.
The resulting viscous liquid is obtained by pouring the mixture into a drum dryer having a surface temperature of 130 ° C., and the resulting viscous liquid is heated for 30 minutes using a water bath at 60 ° C. Completion and drying were performed simultaneously. The obtained flaky resin was pulverized with a pin mill and then classified to obtain a powdery water-absorbent resin of 16 to 145 mesh. The water content of the powdery water-absorbent resin was 8.8%.

Examples 1 to 7 and Comparative Examples 1 to 3 The obtained powdery water absorbent resins were treated with a predetermined amount of a treatment liquid having the composition shown in the table. That is, the treatment liquid shown in the table was added to the powdery water-absorbent resin with high-speed stirring, and after stirring for 2 to 3 minutes, the resin was dried in a drier until the water content became about 7%.

In the treatment liquid, the aluminum hydroxide gel was prepared from aluminum chloride hexahydrate and sodium aluminate (Example 1 and Comparative Examples 1 and 2),
The ones prepared from aluminum chloride hexahydrate and sodium hydroxide (Examples 2 to 7) were used. Further, in Comparative Examples, a treatment liquid containing no crosslinking agent (Comparative Example 1), a treatment liquid containing no polyhydric alcohol (Comparative Example 2) and a treatment liquid containing no aluminum compound (Comparative Example 3) were used.

The composition of the treatment liquid, the amount used, and the properties of the resulting water-absorbent resin are shown in the table.

As shown in the table, the gel treated with the treatment liquid containing no crosslinking agent had a low gel strength. Further, when treated with a treatment liquid containing no polyhydric alcohol or aluminum compound, the powdery water-absorbent resin is aggregated into a lump during the treatment, which makes it impossible to uniformly treat the water-absorbing amount and gel. It was difficult to measure the strength.

On the other hand, the water-absorbent resins treated with the treatment liquids of Examples 1 to 7 had large water absorption and gel strength. Further, in the treatment step with the treatment liquid, it was found that the powder of the water absorbent resin in each of the Examples can be uniformly cross-linked without agglomeration, and the water absorbent resin can be efficiently produced. did.

Claims (6)

[Claims] 1. A powdery water-absorbing resin having a carboxyl group or a carboxylate group in the presence of a polyhydric alcohol and water, an aluminum compound capable of reacting with the water-absorbing resin and a water-absorbing resin capable of reacting 2 A method for producing a water absorbent resin, which comprises treating with a crosslinking agent having the above functional group. 2. The method for producing a water absorbent resin according to claim 1, wherein the water absorbent resin is a polyacrylic acid water absorbent resin. 3. The production of a water absorbent resin according to claim 2, wherein the polyacrylic acid water absorbent resin is a polymer having at least a monomer unit of acrylic acid or an alkali metal acrylate in the main chain. Method. 4. The method for producing a water absorbent resin according to claim 1, wherein the aluminum compound is aluminum hydroxide. 5. The water-absorbing material according to claim 4, wherein the aluminum hydroxide is an aluminum hydroxide gel produced by the reaction of an aluminum salt and an aluminate, or an aluminum salt and an alkali metal hydroxide. Resin manufacturing method. 6. The method for producing a water absorbent resin according to claim 1, wherein the crosslinking agent is an epoxy compound.