JPH07179613A - Production of modified water-absorbing resin - Google Patents

Abstract

PURPOSE:To coat a specific water-absorbing resin powder with a cross-linker uniformly in a short time to impart excellent water absorption rate and gel strengths to the resin by placing the powder on a specific support and immersing the powder together with the support in a soln. contg. the cross-linker. CONSTITUTION:A water-absorbing carboxylated resin powder 11 is placed on a box-shaped support having many openings smaller than the particle size of the powder, lowered together with the support in the direction of the arrow A into a soln. 11 comprising water and/or a hydrophilic org. solvent and a cross-linker, a compd. having at least two carboxyl-reactive groups. immersed in the soln. for a specified time, and pulled up together with the support in the direction of the arrow B. Thus, the powder is coated with the cross-linker in a short time, giving a water-absorbing resin improved in the balance among water-absorption capacity, water-absorption rate, and gel strengths.

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 water absorbent resin, and more specifically, to improve properties of the water absorbent resin powder such as water absorption rate and gel strength. The present invention relates to a method for producing a modified water absorbent resin in which a crosslinked structure is introduced in the vicinity of the surface.

[0002]

2. Description of the Related Art In recent years,
BACKGROUND ART Water-absorbent resin powders are used in various fields such as sanitary napkins, paper diapers, and other sanitary materials that absorb body fluids and water retention agents. Examples of this type of water-absorbent resin powder include carboxymethyl cellulose crosslinked products and starch-
Hydrolyzates of acrylonitrile graft polymers, partially crosslinked polyethylene oxides, partially crosslinked polyacrylates, vinyl alcohol-acrylate copolymers and the like are known.

Properties desired for the above water-absorbent resin powder include a high water absorption capacity, an excellent water absorption rate, a high gel strength when hydrated, and an excellent absorption power for sucking an aqueous liquid from a substrate containing the aqueous liquid. Is mentioned. However, these characteristics do not necessarily show a positive correlation between them, and in particular, the water absorption capacity and the water absorption speed, the gel strength and the absorption capacity are in a contradictory relationship, and the higher the water absorption capacity, the higher the water absorption speed. There is a problem in that the physical properties such as are deteriorated.

Therefore, as a method of improving the balance between the above properties, a method of crosslinking the surface of the water absorbent resin with a crosslinking agent has been proposed. As the crosslinking agent, polyhydric glycidyl ethers, polyhydric alcohols, polyhydric aldehydes, polyhydric isocyanates, polyhydric amines, polyhydric metal salts, haloepoxy compounds and the like are used.

In order to improve the effect of improving the water-absorbent resin by the above-mentioned cross-linking agent, it is necessary to coat the surface of the water-absorbent resin with the cross-linking agent uniformly and to react them.
Various methods for uniformly coating the surface of the water-absorbent resin with a cross-linking agent have been proposed so far, and specific examples thereof include the following.

A method in which a water-absorbent resin is dispersed in a hydrophobic organic solvent, a hydrophilic organic solvent or a mixture of water and a hydrophilic organic solvent and a cross-linking agent is added to carry out the reaction (JP-A-57-44).
627, JP-A-58-42602, JP-B-60-18690). A method of spraying and dropping a cross-linking agent or a mixed solution of a cross-linking agent and a diluent while stirring the water-absorbent resin powder in a mixer (Japanese Patent Publication No. Sho 6).
2-16135, JP-A-60-163956, JP-A-1-297430). Method of contacting the water-absorbent resin powder and the cross-linking agent in an air stream (JP-A-3-8400, JP-A-4-246403)
Issue).

However, in the above method, in order to uniformly coat the surface of the water-absorbent resin with the crosslinking agent,
At least a few minutes to several tens of minutes is required, and further, continuous operation cannot be performed by the above method, and when the continuous operation is attempted, it is difficult to control the amount of the crosslinking agent to be coated. There is also a problem that it is difficult to obtain a water-absorbent resin having uniform water-absorbing properties.

In the above method, the cross-linking agent can be brought into contact with the water-absorbent resin continuously in a short time, but it is difficult to uniformly coat the cross-linking agent on the surface of the water-absorbent resin. There is a problem.

That is, various methods of forming a crosslinked layer in the vicinity of the surface of the water-absorbent resin have been tried so far in order to improve various properties of the water-absorbent resin in a well-balanced manner. It is not a method that is industrially sufficiently satisfactory.

Therefore, an object of the present invention is to coat a surface of a water-absorbent resin powder with a crosslinking agent in a short time and continuously, and to balance the water absorption capacity with the water absorption rate, gel strength and absorption capacity. It is an object of the present invention to provide a method for producing a modified water-absorbent resin capable of obtaining a water-absorbent resin having improved properties.

[0011]

Means for Solving the Problems As a result of various studies to solve the above-mentioned problems, the present inventors found that the water-absorbent resin powder was dipped in a specific immersion liquid to carry out crosslinking, The inventors have found that the objects can be achieved and have completed the present invention.

That is, in the present invention, the water-absorbent resin powder (A) having a carboxyl group is placed on a support having a large number of voids smaller than the particle size of the water-absorbent resin powder (A), and then the The water-absorbent resin powder (A) is added to the support together with water and / or
Alternatively, the water-absorbent resin powder is immersed in an immersion liquid (B + C) composed of a solvent (B) made of a hydrophilic organic solvent and a crosslinking agent (C) having two or more functional groups capable of reacting with a carboxyl group. The present invention provides a method for producing a modified water-absorbent resin, which comprises cross-linking (A).

The method for producing the modified water absorbent resin of the present invention will be described in detail below. In the text, "%" means "% by weight" unless otherwise specified. The water-absorbent resin powder (A) used in the present invention is a polymer or copolymer usually used as a water-absorbent resin and containing a carboxyl group in the constituent components of the polymer or copolymer. It can be used without particular limitation as long as it is, for example, a self-crosslinking polyacrylic acid partially neutralized product, a crosslinked product of a polyacrylic acid partially neutralized product, a starch-acrylic acid graft copolymer part. Examples thereof include a hydrate, a hydrolyzate of a starch-acrylonitrile graft copolymer, a saponified product of an acrylic ester-vinyl acetate copolymer, and a carboxyl group-containing crosslinked polyvinyl alcohol-modified product.

The amount of carboxyl groups contained in the water-absorbent resin powder (A) is not particularly limited, but the carboxyl group is 0.01 equivalent or more per 100 g of the water-absorbent resin powder (A), and further, It is preferably present in an amount of 0.1 equivalent or more.

The particle size of the water absorbent resin powder (A) is preferably in the range of 20 to 3000 μm.

In order to prepare the water-absorbent resin powder (A), a known method for producing a water-absorbent resin is used without any particular limitation. The polymerization method in this case is reverse phase suspension polymerization or aqueous solution. Polymerization and the like can be exemplified, but various polymerization methods can be used without particular limitation.

The water content of the water-absorbent resin powder (A) is preferably not more than 300%, more preferably not more than 150% in the present invention, but the outermost surface of the absorbent resin powder (A) is preferable. In order to crosslink the vicinity, it is preferable to use 10% or less, particularly 3% or less.

The support used in the present invention is not particularly limited in material, shape and the like as long as it has a void smaller than the particle diameter of the water absorbent resin powder (A), but the material is Particularly preferred are wire mesh, cloth, and the like.
The shape is not particularly limited as long as the water-absorbent resin powder (A) does not fall down (in the immersion liquid), and examples thereof include a box shape, a belt shape, a sieve shape, and a bag shape. The size of the voids in the support is arbitrary as long as it is smaller than the particle size of the water-absorbent resin powder (A), but is 10 to 350.
μm is preferable, and the porosity [space area / total area] is preferably 0.2 to 0.9.

In the present invention, the immersion liquid (B + C) for immersing the water-absorbent resin powder is a solvent (B) composed of water and / or a hydrophilic organic solvent and a cross-link having two or more functional groups capable of reacting with a carboxyl group. The immersion liquid (B + C) composed of the agent (C).

Examples of the hydrophilic organic solvent used in the solvent (B) include methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, acetone and dioxane. Among them, methyl alcohol, ethyl alcohol, n-propyl alcohol and iso-propyl alcohol are preferable.

The mixing ratio of water to the hydrophilic organic solvent in the solvent (B) is such that water: hydrophilic organic solvent = 0: 100.
It can be arbitrarily changed in a wide range of 100: 0 (weight ratio). However, when it is desired to crosslink only the vicinity of the outermost surface of the water absorbent resin powder (A), it depends on the water content of the water absorbent resin powder (A), the immersion time and the concentration of the crosslinking agent in the immersion liquid.
It is preferable to use the solvent (B) in which water: hydrophilic organic solvent = 0: 100 to 40:60 (weight ratio).

The crosslinking agent (C) that can be used in the immersion liquid (B + C) is not particularly limited as long as it is a crosslinking agent having two or more functional groups capable of reacting with a carboxyl group. However, the following compounds and the like can be preferably exemplified, and among them, polyvalent glycidyl ether compounds are particularly preferable.

Ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene Polyhydric glycidyl ether compounds such as glycol diglycidyl ether; ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylol Propane, diethanolamine,
Polyethanol compounds such as triethanolamine, polyoxypropylene, polyvinyl alcohol, oxydiethylene propylene block copolymer, pentaerythritol and sorbitol; haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin: ethylenediamine, diethylenetriamine, triethylenetetramine , Tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine and other polyvalent amine compounds;
2'-bishydroxymethylbutanol-tris [3-
(1-aziridinyl) propionate], 1,6-hexamethylenediethyleneurea, diphenylmethane-bis-4,4′-N, N′-diethyleneurea and other polyvalent aziridine compounds, 2,4-toluylene diisocyanate,
Polyvalent isocyanate compounds such as hexamethylene diisocyanate.

The concentration of the cross-linking agent (C) in the immersion liquid (B + C) depends on the kind of the cross-linking agent, but in general,
0.001 to 90 wt%, preferably 0.01 to 50 wt%
Is. If the concentration is less than 0.001 wt%, the effect of the cross-linking agent cannot be recognized unless it is immersed for a long time.
Manufacturing time becomes long and it is not industrially preferable. Further, if the concentration of the cross-linking agent exceeds 90 wt%, it becomes difficult to control the coating amount of the cross-linking agent on the surface of the water absorbent resin powder (A), which is not preferable. Also, the crosslinking agent concentration is usually 9
If it exceeds 0 wt%, the water-absorbing capacity is large because the surface of the water-absorbent resin powder (A) is coated or impregnated with the crosslinking agent in a large amount even if the immersion time or the solvent (B) is variously changed. Decrease, and further by dipping the cross-linking agent (C)
Adheres to the surface of the water-absorbent resin powder (A) in a large amount, a plurality of water-absorbent resin powders (A) are cross-linked after heat treatment.
Since they may be strongly adhered / aggregated to each other and handling thereafter may be difficult, it is preferably within the above range.

In order to carry out the method for producing a modified water absorbent resin of the present invention, the water absorbent resin powder (A) is placed on the support and then the water absorbent resin powder is placed. (A) together with the support is immersed in the immersion liquid (B + C) to crosslink the water absorbent resin powder (A).

Here, the water-absorbent resin powder (A) can be used as it is after being polymerized by the above-mentioned preparation method, or after being dried and classified. Any route may be used, such as using a product adjusted to have the above-mentioned preferable water content.

The method of placing the water-absorbent resin powder (A) on the support is not particularly limited, and the amount of the water-absorbent resin powder (A) is placed on the support. It is preferably 0.1 to 10 g per 10 cm ^{2 of} body area.

Next, the above immersion will be described with reference to FIGS. Here, FIG. 1 is a schematic view showing an embodiment of a batch type immersion method using a box-shaped support as a support, and FIG. 2 is a continuous type using a belt-shaped support as a support. It is the schematic which shows the aspect of the immersion method. Figure 1
And, as shown in FIG. 2, the above-mentioned dipping can be performed by a batch system or a continuous system.

In the batch type dipping method, as shown in FIG. 1, the water-absorbent resin powder 1 is placed inside a box-shaped support 10.
1 is then placed, and then the support 10 is lowered in the direction of the arrow A to immerse the support 10 together with the water-absorbent resin powder 11 in the immersion liquid 12 filled in the container 13 to obtain the water-absorbent resin powder 11 Can be carried out by immersing the substrate 10 in the arrow B direction after immersing the substrate for a predetermined time. The immersion time at this time is preferably in the range of 0.1 to 30 seconds, more preferably 0.5 to 10 seconds.

Further, in the continuous dipping method, as shown in FIG.
As shown in FIG. 3, the water-absorbent resin powder 21 is placed on the belt-shaped support 20, and then the support 20 is moved in the direction of arrow A to bring the water-absorbent resin powder 21 together with the support 20 into the container 23.
The water-absorbent resin powder 11 is continuously dipped by immersing it in the dipping liquid 22 filled in the container for a predetermined time. The immersion time at this time is preferably in the range of 0.1 to 30 seconds, more preferably 0.5 to 10 seconds.

Further, the water-absorbent resin powder (A) and the immersion liquid (B + C) in the above-mentioned immersion are the above-mentioned immersion liquid (B + C) 20 with respect to 10 g of the water-absorbent resin powder (A).
It is preferably 0 to 1000 ml.

The coating and impregnation amount of the cross-linking agent on the surface of the water-absorbent resin powder (A) depends on the immersion time, the concentration of the cross-linking agent in the immersion liquid, the solvent in the immersion liquid and the initial water content of the water-absorbent resin. Can be changed.

After the above immersion, it is preferable to carry out a heat treatment usually at 40 to 250 ° C. to smoothly carry out the crosslinking reaction.

In the present invention, the organic solvent (D) is sprayed on the water absorbent resin powder (A) before the water absorbent resin powder (A) is immersed in the immersion liquid (B + C). Workability, especially work time can be shortened,
It is preferable to add this operation from the viewpoint of workability.

Examples of the above-mentioned spraying method include a spray method and a showering method.

Examples of the organic solvent (D) include methyl alcohol, ethyl alcohol, n-propyl alcohol,
iso-propyl alcohol, n-butyl alcohol,
Examples thereof include iso-butyl alcohol, acetone, dioxane and the like, among which methyl alcohol, ethyl alcohol, n-propyl alcohol and iso-propyl alcohol are preferable.

When the organic solvent (D) is sprayed and coated on the water absorbent resin powder (A) before immersion, the wettability between the water absorbent resin powder (A) and the immersion liquid (B + C) increases,
The water absorbent resin powder can be easily immersed in the immersion liquid. Although it is not always necessary to spray the organic solvent (D), unless the organic solvent (D) is sprayed onto the water absorbent resin powder (A) before immersion, the water absorbent resin powder floats on the surface of the immersion liquid especially at the initial stage of immersion. However, the water-absorbent resin powder may not be instantly dipped in the immersion liquid and the working time may have to be extended. Therefore, in order to smoothly perform the immersion treatment, it is preferable to spray the organic solvent (D). .

The amount of the organic solvent (D) sprayed is 10 to 20 with respect to 100 g of the water absorbent resin powder (A).
It is preferably in the range of 0 ml.

The modified water-absorbent resin obtained as described above preferably has a surface vicinity (mainly on the surface side of the polymer particles, which does not exclude crosslinking inside). A water-absorbent resin which is coated with a cross-linking agent and cross-linked, and has a good balance between the water absorption amount and the water absorption speed. Specifically, the water absorption [equilibrium swelling water absorption (g / g)] is in the range of 30 to 80, and the water absorption rate [water absorption representing water absorption rate (ml / 3 minutes)] is 6 to
It is a modified water absorbent resin having a range of 20.

[0040]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Unless otherwise specified, “%” in the text means “% by weight”.

The test methods used in the examples and comparative examples are as follows. [Measurement Method of Equilibrium Swelled Water Absorption] 1 g of the water absorbent resin is dispersed in a large excess of physiological saline (0.9% saline), and the water absorbent resin is swollen until the water absorption reaches an equilibrium state. After that, the physiological saline is filtered through a wire mesh of 80 mesh, the weight (W) of the swelling resin obtained is measured, and this value is divided by the resin weight W ₀ before water absorption, that is, W The value of / W ₀ was taken as the equilibrium swelling water absorption (g / g).

[Measurement Method of Water Absorption Amount Representing Water Absorption Rate] Using a device (Demand Wettability Tester) shown in FIG. 3 which is generally known as a device for carrying out the DW method, as shown in FIG. Resin spraying table 2 (70 mmφ, No. 2 filter paper with glass filter N with the liquid level of W set to the same water level)
0.3 g of the resin P is sprayed on the table placed on the o. 1), and the water absorption amount at the time of spraying the resin is 0, and the water absorption amount after 3 minutes (this water absorption amount is the water level of the physiological saline W). (Measured by a burette scale indicating the amount of decrease in water) was measured, and this value was taken as the water absorption amount (ml) representing the water absorption speed.

Example 1, Comparative Example 1 Acrylic acid 72.
After 1 g was diluted with 32.0 g of water and neutralized with 98.9 g of a 30 wt% sodium hydroxide aqueous solution while cooling, 2.
10.7 g of an 8 wt% potassium persulfate aqueous solution and 0.36 g of ethylene glycol diglycidyl ether were added to make a uniform solution to prepare a monomer / initiator / crosslinking agent aqueous solution.

Separately, 283 ml of cyclohexane was placed in a 500 ml flask equipped with a reflux condenser, a dropping funnel, a stir bar, and a nitrogen introducing tube, and 1.06 g of ethyl cellulose (manufactured by Hercules, trade name, "N-100"). Was added, and the mixture was stirred (300 rpm) and dispersed, the flask was replaced with nitrogen, and the temperature was raised to 75 ° C. After the temperature was raised, the monomer / initiator / crosslinking agent aqueous solution was added dropwise thereto for 1.5 hours. After the dropwise addition was completed, the temperature was maintained at 75 ° C. for 0.5 hour to complete the polymerization, and then the products were separated and dried under reduced pressure to obtain 87.6 g of acrylic acid (sodium) polymer A. . The obtained polymer A was sieved to 10
It was fractionated to 6 to 360 μm. Further, the water content of the separated polymer A was dried at 120 ° C. for 24 hours under a reduced pressure of 0.5 mmHg and was determined by the following equation to be 3% or less. [(Weight before drying−weight after drying) / (weight after drying)] × 1
00

Next, 5 g of the separated polymer A (water-absorbent resin powder) [water content of 3% or less] was placed on a box-shaped metal net having voids of 106 μm, and 5 ml of ethyl alcohol (EtOH) was placed thereon. After spraying, it was immersed for 1 second in a 1% ethyl alcohol solution of ethylene glycol diglycidyl ether, which is an immersion liquid. After immersion, under reduced pressure, 150 ℃
In, a cross-linking reaction was carried out by heat treatment for 3 hours to obtain a modified water absorbent resin.

Equilibrium swelling water absorption and water absorption representing the water absorption rate were measured for the modified water absorbent resin thus obtained.
The results are shown in [Table 1]. In addition, as Comparative Example 1,
Similarly, for the water-absorbent resin powder (polymer A separated as above) before being immersed in the crosslinking agent solution, the equilibrium swelling water absorption amount,
The amount of water absorption representing the water absorption rate was measured. The results are also shown in [Table 1].

[Examples 2 to 4] Modified water absorbent resins were obtained in the same manner as in Example 1 except that the cross-linking agent concentration and immersion time shown in Table 1 were used. about,
The equilibrium swelling water absorption and the water absorption representing the water absorption rate were measured. The results are shown in [Table 1].

Example 5, Comparative Example 2 Acrylic acid 72.
After 1 g was diluted with 32.0 g of water and neutralized with 98.9 g of a 30 wt% sodium hydroxide aqueous solution while cooling, 2.
10.7 g of 8 wt% potassium persulfate aqueous solution was added to make a uniform solution to prepare a monomer / initiator aqueous solution.

Separately, 283 ml of cyclohexane was placed in a 500 ml flask equipped with a reflux condenser, a dropping funnel, a stir bar, and a nitrogen introducing tube, and polyoxyethylene dodecyl ether sulfuric acid ester sodium salt (average ethylene oxide addition mole number = 3) was added. 1.5 g of a 25 wt% aqueous solution was added, and the mixture was stirred (300 rpm) and dispersed, the flask was purged with nitrogen, and the temperature was raised to 75 ° C. After raising the temperature, the monomer /
The aqueous initiator solution was added dropwise over 1.5 hours. After completion of dropping, stir at 75 ° C for 1.5 hours, then at 80 ° C for 4 hours.
Polymerization was carried out, and then the product was separated and dried under reduced pressure to obtain 88.1 g of acrylic acid (sodium) polymer B. The obtained polymer B was further fractionated by a sieve to 106 to 360 μm. Further, the water content of the separated polymer B was measured in the same manner as in Example 1, and it was 3% or less.

Next, 5 g of the separated polymer B (water-absorbent resin powder) [water content of 3% or less] was placed on a box-like metal net having voids of 106 μm, and ethyl alcohol (E
After spraying 5 ml of tOH), it was immersed for 1 second in a 1% ethyl alcohol solution of ethylene glycol diglycidyl ether as an immersion liquid. After the immersion, a heat treatment was performed under reduced pressure at 150 ° C. for 3 hours to cause a crosslinking reaction to obtain a modified water absorbent resin.

Physical properties of the obtained modified water absorbent resin were measured in the same manner as in Example 1. The results are shown in [Table 1].
Shown in. In addition, as Comparative Example 2, the same measurement was performed for the water-absorbent resin powder (polymer B separated as described above) before being immersed in the crosslinking agent solution. The results are also shown in [Table 1].

[Examples 6 to 11] Modified water absorbent resins were obtained in the same manner as in Example 5 except that the concentration of the cross-linking agent and the immersion time shown in Table 1 were used, and the physical properties were measured. The results are shown in [Table 1].

[Examples 12 to 16] The separated polymer A (water-absorbent resin powder) obtained in Example 1 was swollen with ion-exchanged water to the water content shown in [Table 1], and the resulting swelling was obtained. 10 g of the polymer A prepared above was placed on a box-shaped metal net having a gap of 106 μm, 5 ml of ethyl alcohol was sprayed on it, and then immersed in a 5% ethyl alcohol solution of ethylene glycol diglycidyl ether as a dipping solution for 5 seconds. did.
After the immersion, heat treatment was performed under reduced pressure at 150 ° C. for 3 hours to obtain a modified water absorbent resin. Physical properties of the modified water absorbent resin thus obtained were measured in the same manner as in Example 1. The results are shown in [Table 1].

Example 17 10 g of the separated polymer B (water-absorbent resin powder) obtained in Example 5 was placed on a wire net having voids of 106 μm, and 15 ml of ethyl alcohol was sprayed on it. It was immersed for 1 second in a 5% aqueous solution of ethylene glycol diglycidyl ether, which is an immersion liquid. After the immersion, heat treatment was performed under reduced pressure at 150 ° C. for 3 hours to obtain a modified water absorbent resin. Physical properties of the modified water absorbent resin thus obtained were measured in the same manner as in Example 1. The results are shown in [Table 1].

[Examples 18 to 20] Solvent for immersion liquid (B)
Was changed as shown in [Table 1], and a modified water absorbent resin was obtained in the same manner as in Example 17, and the physical properties of the obtained modified water absorbent resin were measured in the same manner as in Example 1. . The results are shown in [Table 1].

Example 21 10 g of the separated polymer B obtained in Example 5 was placed on a box-like metal net having a void of 106 μm, and 10 ml of ethyl alcohol was sprayed on it, which was a dipping solution. It was immersed in a 5% methyl alcohol (MeOH) solution of ethylene glycol diglycidyl ether for 5 seconds. After the immersion, heat treatment was performed under reduced pressure at 150 ° C. for 3 hours to obtain a modified water absorbent resin. Physical properties of the modified water absorbent resin thus obtained were measured in the same manner as in Example 1. The results are shown in [Table 1].

Example 22 A modified water absorbent resin was obtained in the same manner as in Example 21 except that the dipping solution was a 5% iso-propyl alcohol (IPA) solution of ethylene glycol diglycidyl ether. Physical properties of the modified water absorbent resin thus obtained were measured in the same manner as in Example 1. The results are shown in [Table 1].

[0058]

[Table 1]

Next, the embodiments of the present invention and related related items will be listed. [1] Water-absorbent resin powder having a carboxyl group (A)
Is placed on a support having a large number of voids smaller than the particle diameter of the water-absorbent resin powder (A), and then the water-absorbent resin powder (A) together with the support is mixed with water and / or a hydrophilic organic compound. The water-absorbent resin powder (A) is immersed by immersing it in an immersion liquid (B + C) composed of a solvent (B) made of a solvent and a crosslinking agent (C) having two or more functional groups capable of reacting with a carboxyl group. A method for producing a modified water-absorbent resin, which comprises cross-linking.

[2] The organic solvent (D) is sprayed onto the water absorbent resin powder (A) before the water absorbent resin powder (A) is immersed in the immersion liquid (B + C). 1. The method for producing the modified water absorbent resin according to 1. [3] The method for producing a modified water absorbent resin according to claim 1, wherein the concentration of the crosslinking agent (C) in the immersion liquid (B + C) is 0.001 to 90 wt%. [4] The method for producing a modified water-absorbent resin according to claim 1, wherein the support is made of wire mesh or cloth.

[5] The method for producing a modified water absorbent resin according to claim 1, wherein the hydrophilic organic solvent is methyl alcohol, ethyl alcohol, n-propyl alcohol or iso-propyl alcohol. [6] The organic solvent (D) is methyl alcohol, ethyl alcohol, n-propyl alcohol or iso-
The method for producing a modified water absorbent resin according to claim 2, wherein the modified water absorbent resin is propyl alcohol. [7] The modified water absorbent according to claim 1, wherein the water absorbent resin powder (A) has a water content of 3% or less, and only the hydrophilic organic solvent is used as the solvent (B). Resin manufacturing method. [8] The mixing ratio of water to the hydrophilic organic solvent in the solvent (B) is such that water: hydrophilic organic solvent = 0: 100 to 4
It is 0:60 (weight ratio), The manufacturing method of the modified water absorbent resin of Claim 1 characterized by the above-mentioned.

[0062]

EFFECT OF THE INVENTION According to the method for producing a modified water absorbent resin of the present invention, the surface of the water absorbent resin powder can be coated with a crosslinking agent in a short time and continuously. It is possible to obtain a water absorbent resin having an improved balance between gel strength and absorbency. That is, according to the present invention,
The water-absorbent resin powder is placed on the above support, and the crosslinking agent is efficiently applied to the surface of the water-absorbent resin powder by a short time treatment such as never before such as immersing the dipping solution containing the cross-linking agent in a few seconds. The modified water-absorbent resin powder, which can be uniformly coated and obtained by subjecting it to a crosslinking reaction after heat treatment and the like, becomes a material having an excellent water absorption rate and gel strength.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a batch-type dipping method using a box-shaped support as a support.

FIG. 2 is a schematic view showing an embodiment of a continuous dipping method using a belt-shaped support as a support.

FIG. 3 is a schematic diagram showing a Demand Wettability Tester generally known as an apparatus for performing the DW method.

Claims (2)

[Claims] 1. A water absorbent resin powder (A) having a carboxyl group is placed on a support having a large number of voids smaller than the particle diameter of the water absorbent resin powder (A), and then the water absorbent resin powder. An immersion liquid (A) comprising (A) together with the support, a solvent (B) composed of water and / or a hydrophilic organic solvent, and a crosslinking agent (C) having two or more functional groups capable of reacting with a carboxyl group ( A method for producing a modified water-absorbent resin, comprising immersing the water-absorbent resin powder (A) in B + C) to cross-link the water-absorbent resin powder (A). 2. The water absorbent resin powder (A) is sprayed with an organic solvent (D) before the water absorbent resin powder (A) is immersed in the immersion liquid (B + C). A method for producing the modified water absorbent resin described.