JPH10324750A - Purification of water-absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-absorbing resin that has excellent gel strength and get surface improved in its stickiness by washing a get of the water- absorbing resin, which is swollen with water or the like, by using water and/or a water-miscible organic solvent. SOLUTION: A water-absorbing resin gel is swollen with water, when necessary, a mixture thereof with a water-miscible organic solvent as ethanol and the swollen gel is rinsed with water and/or a water-miscible organic solvent. This water-absorbing resin is preferably a partial hydrolyzate of crosslinked polyacrylic acid, starch-acrylic acid graft copolymer, 2-acrylamido-2- methylpropanesulfonic acid and acrylic acid crosslinked product, or cross-linked poly(amino acid) and the like. The amount of the water and a water-miscible organic solvent to be used for swelling the resin is preferably 0.001-10-fold volume of that of the distilled water or purified water for the resin absorption. In addition, the amount of water and/or a water-miscible organic solvent for washing the gel is preferably 1-50-fold that of the resin weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying a water-absorbing resin. Specifically, by removing water-soluble components,
The present invention relates to the production of a water-absorbent resin having excellent gel strength after water absorption, high gel strength, and high water-absorbing power with respect to an aqueous solution containing salt.

[0002]

[Prior art]

[Technical background of water-absorbent resin] A water-absorbent resin is a resin that can absorb tens to thousands of times as much water as its own weight.
Sanitary articles such as disposable diapers, breast milk pads, disposable rags, dressing materials for wound protection, medical underpads, medical supplies such as cataplasms, pet sheets, portable toilets, gel fragrances, gel deodorants, and sweat-absorbing fibers , Household goods such as disposable body warmers, shampoos, gels for setting, toiletries such as moisturizers, water retention materials for agriculture and horticulture, life-extending agents for cut flowers, floral foam (fixing material for cut flowers), nursery beds for nursery, water Agricultural and horticultural products such as cultivation, vegetation sheet, seed tape, fluid sowing, dew condensation prevention agricultural sheet, freshness retaining material for food tray, food wrapping material such as drip absorbent sheet, cold insulator, fresh vegetable transportation Materials for transportation such as water-absorbent sheets, building materials for preventing dew condensation, sealing materials for civil engineering and construction, sludge preventing agents for shield method, concrete admixtures,
Materials for civil engineering and construction such as gaskets and packing, sealing materials for electronic devices such as optical fibers, waterproof materials for communication cables, materials for electric devices such as ink jet recording paper, coagulants for sludge, dehydration of gasoline and oils, and water removal. It is used in a wide range of fields such as water treatment agents such as agents, printing pastes, water-swellable toys, and artificial snow.

[0003] Further, by utilizing the sustained-release properties of the chemicals, it is expected to be used in applications such as sustained-release fertilizers, sustained-release pesticides, and sustained-release drugs.

Further, it is expected to be used as a humidity control material by utilizing its hydrophilicity and an antistatic agent by utilizing its charge retention.

[Prior art relating to water-absorbing resin] Examples of the water-absorbing resin used in such applications include, for example,
Crosslinked polyacrylic acid partially neutralized product (JP-A-55-8430)
No. 4, U.S. Pat. No. 4,625,001), a partially hydrolyzed starch-acrylonitrile copolymer (JP-A-46-439).
No. 95), a starch-acrylic acid graft copolymer (JP-A-51-125468), and a hydrolyzate of a vinyl acetate-acrylate copolymer (JP-A-52-14689).
No.), copolymerized crosslinked product of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid (European patent 00681)
No. 89), a crosslinked polymer of a cationic monomer (US Pat. No. 4,906,717), a hydrolyzate of a crosslinked isobutylene-maleic anhydride copolymer (US Pat. No. 4,389,513)
Etc. are known.

[0006] However, these water-absorbing resins include saline,
For solutions containing salts such as urine, sweat, and seawater, the osmotic pressure, which is the driving force of water absorption, is reduced, so the amount of water absorption is significantly reduced, the gel strength is low, and the gel becomes sticky over time. doing.

Many studies have been made to solve the above-mentioned disadvantages of the water-absorbing resin. For example, as a method for improving the gel strength and the stability over time of the gel, a method of incorporating oxalic acid into a water-absorbing resin (Japanese Patent Application No. 5-289699),
A method in which zirconium oxide having an average particle size of 1 μm or less is contained in a water-absorbing resin (Japanese Patent Application No. 5-120678), and a method in which a polyvalent metal sulfate is contained in a water-absorbing resin (Japanese Patent Application No. 5-206).
-282708), a method of incorporating an oxygen-containing reducing inorganic salt and / or an organic antioxidant into a water-absorbing resin (Japanese Patent Application Laid-Open No. 63-118375), and a method of including an oxidizing agent in a water-absorbing resin (Japanese Patent Application Laid-Open No. No. 63-127754), a method of incorporating a sulfur-containing reducing agent into a water-absorbing resin (Japanese Patent Laid-Open No. 63-27).
No. 2349), a method in which a metal chelating agent is contained in a water-absorbing resin (JP-A-63-146964), and a method in which a radical chain inhibitor is contained in a water-absorbing resin (JP-A-63-1).
No. 5266), a method in which a phosphinic acid group or a phosphonic acid group-containing amine compound or a salt thereof is contained in a water-absorbing resin (Japanese Patent Application Laid-Open No. 1-275661), and a method in which a polyvalent metal oxide is contained in a water-absorbing resin (Japanese Patent Application Laid-open No. 64-29257
), A method of coexisting a water-soluble chain transfer agent during the polymerization of a water-absorbing resin (JP-A-2-255804, JP-A-3-17
No. 9008) has been proposed.

[0008] However, in any of the reports, in applications where these resins are actually used, the improvement is not sufficient, the gel strength is low, the surface is sticky, and it is not practical. As a method for improving the gel strength and stability over time of the water-absorbent resin, a method of increasing the cross-link density of the water-absorbent resin is generally known. Was not a typical solution.

A method of further crosslinking the vicinity of the surface of the water-absorbent resin (JP-A-58-180233, JP-A-59-189)
No. 103, JP-A-51-136588 and JP-A-61-136.
No. 211305) and a method in which an inert inorganic powder is present during the crosslinking reaction (Japanese Patent Application Laid-Open No. 60-163956).

Although the physical properties of the water-absorbing resin are improved by these methods, the cross-linking agent used tends to remain on the resin surface. Therefore, when a compound such as an epoxy compound or an isocyanate compound is used, the type of the cross-linking agent In some cases, a new safety issue may arise. Therefore, a method of reducing the residual surface cross-linking agent (JP-A-3-195705)
However, an extremely complicated process was required, and the reduction of the residual surface crosslinking agent was insufficient.

On the other hand, as a method for solving the drawbacks such as a decrease in water absorption of a conventional aqueous solution containing a salt of a polymer-type water-absorbing resin, a method of graft-polymerizing a hydrophilic monomer to a polysaccharide (JP-A-56-76419, JP-A-56-76481
No. 3), a method in which a hydrophilic monomer is graft-polymerized to a polysaccharide and further subjected to a heat treatment if necessary (Japanese Patent Publication No. 3-6888).
No. 9), a method of crosslinking the polysaccharide itself (Japanese Patent Application Laid-Open No.
No. 5137, JP-A-58-79006, JP-A-60-1985.
No. 58443), a method using a cellulose derivative (JP-A-49-128987, JP-A-50-85689),
JP-A-54-163981, JP-A-56-28755
JP-A-58-1701, JP-A-60-94401
And JP-A-61-589364), and a method of cross-linking and insolubilizing a polysaccharide containing uronic acid or a salt thereof (JP-A-56-5137).

However, it is hard to say that the salt water absorbing ability has been sufficiently improved by any of these methods.

On the other hand, in the case of a nonionic water-absorbing resin such as cross-linked polyvinyl alcohol, cross-linked polyacrylamide, cross-linked polyhydroxyethyl methacrylate, cross-linked polyethylene glycol, cross-linked polypropylene glycol, etc., there is little decrease in water absorption with respect to a solution containing a salt. However, it was not useful because its absolute water absorption was small.

However, it is hard to say that the salt water absorbing ability has been sufficiently improved by any of these methods.

That is, in the field of application of the above-mentioned water-absorbing resin, a solution containing a salt is often targeted.
It has been desired to develop a material exhibiting a high absorption amount even in the presence of a salt. In addition, polymerized water-absorbing resins such as cross-linked polyacrylic acid and cross-linked polyacrylamide use monomers that are highly toxic to human skin and the like. Consideration has been made, but it is difficult to completely eliminate it. In particular, it is expected to be more difficult in production on an industrial scale.

As described above, the conventional water-absorbent resin has low gel strength, sticky surface, poor stability over time,
There is a safety problem that a surface cross-linking agent such as an unpolymerized monomer or an epoxy compound remains. Still another problem is that the water-absorbing properties of the aqueous solution containing a salt are not sufficient, and there has been a strong demand for improvement of these properties.

[Technical background of water-absorbing resin having biodegradability] On the other hand, in recent years, biodegradable polymers have attracted attention as "earth-friendly materials", and it has been proposed to use this as a water-absorbing resin. ing.

Examples of the water-absorbing resin having biodegradability used in such applications include, for example, a crosslinked product of polyethylene oxide (JP-A-6-157795), a crosslinked product of polyvinyl alcohol, and a crosslinked product of carboxymethyl cellulose (US Pat. No. 4650716), crosslinked alginic acid,
Crosslinked starch, crosslinked polyamino acid and the like are known.
Among these, crosslinked polyethylene oxide and crosslinked polyvinyl alcohol have low water absorption, and are not suitable especially when used as materials for products requiring high water absorption such as sanitary products, disposable diapers, disposable rags, and paper towels.

Further, since these compounds can only be biodegraded by special bacteria, biodegradation is slow or not at all under general conditions.
When the molecular weight is further increased, the decomposability extremely decreases.

In addition, crosslinked saccharides such as crosslinked carboxymethylcellulose, crosslinked alginic acid, crosslinked starch, etc.
Since the molecule contains many strong hydrogen bonds, the interaction between molecules and between polymers is strong, so that the molecular chains cannot be opened widely and the water absorbing ability is not high.

[Technical background of polyamino acid-based water-absorbing resin] On the other hand, a resin obtained by crosslinking a polyamino acid is biodegradable and thus is friendly to the global environment. It has been shown that it is digested and absorbed, does not show antigenicity in the living body, and that the decomposition products have no toxicity.

As an example of description of such a resin, poly-γ
A method for producing a resin having a high water-absorbing ability by irradiating glutamic acid with γ-rays has been reported (Kunioka et al., Journal of Polymers, Vol. 50, No. 10, p. 755 (1993)). However, from an industrial point of view, the 60Co irradiation equipment used in this technology requires a large-scale equipment to shut off radioactivity, and requires sufficient consideration for its management. Absent. Another problem is that polyglutamic acid as a starting material is expensive.

Also, methods for obtaining a hydrogel by crosslinking an acidic amino acid have been reported [Akamatsu et al., US Pat. No. 3,948,863 (corresponding to Japanese Patent Publication No. 52-41309), Iwatsuki et al., JP-A-5-279416. ]. Further, it has been reported that a crosslinked amino acid resin is used as a water-absorbing polymer (Sikes et al., JP-A-6-506244; US Pat. Nos. 5,247,068 and 5,284,936; Suzuki et al.
JP-A-7-309943, Harada et al., JP-A-8-598
No. 20).

However, in any of these reports, these resins are not practical because of insufficient water absorption and salt water absorption.

[Background of the technical idea of the present inventors] As described in JP-A-7-224163, the present inventors reacted polysuccinimide with a crosslinking agent to form A technique for producing a crosslinked polyaspartic acid-based resin having a high salt water absorption ability by hydrolysis is disclosed. The present inventors have also disclosed in Japanese Patent Application Laid-Open No. 9-16984.
As described in No. 0, after cross-linking the polysuccinimide, the remaining imide ring is hydrolyzed in a uniform mixed solvent of a water-miscible organic solvent and water, whereby the cross-linking with high salt water absorption ability is performed. A technique for producing a polyaspartic acid-based resin has been disclosed.

The crosslinked polyaspartic resin obtained by these techniques is very useful because it is earth-friendly and has a high water absorption capacity. However, even in such a crosslinked polyaspartic acid-based resin, improvement in gel strength,
There is room for further improvement in terms of prevention of stickiness of the gel surface and improvement of water absorption capacity for aqueous solutions containing salts.

[0027]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned conventional problems and to obtain a highly water-absorbent resin having excellent gel strength and improved gel surface tackiness. It is to provide a method.

[0028]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that monomers, oligomers, water-soluble polymers and inorganic or organic salts contained in a resin reduce water absorption and gel strength. And found that the performance of the water absorbent resin was reduced. That is, if these impurities are removed, the water absorption capacity of the resin, such as the water absorption and the gel strength, is improved.

The method of the present invention solves these problems and is a method for obtaining a superabsorbent resin. The present inventors have conducted intensive studies to solve the above problems, and as a result, have completed the present invention. That is, the present invention relates to a water-absorbent resin characterized in that a gel of a water-absorbent resin swollen with water or with water and a water-miscible organic solvent is washed with water and / or a water-miscible organic solvent. Purification method, removing water-soluble components by washing the gel of the water-absorbent resin swollen with water or with water and a water-miscible organic solvent with water and / or a water-miscible organic solvent. A method for purifying a water-absorbent resin characterized by the following, and water, or, with water and a water-miscible organic solvent, a gel of a water-absorbent resin swollen,
A method for purifying a water-absorbent resin, comprising reprecipitating with a water-miscible organic solvent.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. [1] Water Absorbent Resin The water absorbent resin used in the present invention is not particularly limited,
Crosslinked polyacrylic acid partially neutralized product, starch-acrylonitrile copolymer partially hydrolyzed product, starch-acrylic acid graft copolymer, vinyl acetate-acrylic acid ester copolymer hydrolyzed product, 2-acrylamide-2- Crosslinked copolymer of methylpropanesulfonic acid and acrylic acid, crosslinked product of cationic monomer, crosslinked isobutylene-maleic anhydride copolymer, polyethylene oxide crosslinked product, polyvinyl alcohol crosslinked product, carboxymethylcellulose crosslinked product,
Examples thereof include crosslinked alginic acid, crosslinked starch, and crosslinked polyamino acid.

Among these, crosslinked polyacrylic acid partially neutralized product, starch-acrylic acid graft copolymer, copolymerization of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid, which has high water absorbing ability and is advantageous in terms of cost. A crosslinked product, a crosslinked product of a cationic monomer, a crosslinked isobutylene-maleic anhydride copolymer, and a carboxymethylcellulose crosslinked product having biodegradability friendly to the global environment, an alginic acid crosslinked product, a starch crosslinked product, and a polyamino acid crosslinked product are preferable. Particularly preferred are partially crosslinked polyacrylic acid partially neutralized products, starch-acrylic acid graft copolymers, copolymerized crosslinked products of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid, and crosslinked polyamino acids.

[1-1] Crosslinked polyacrylic acid-based resin The crosslinked polyacrylic acid-based water-absorbing resin used in the present invention is not particularly limited. Generally, acrylic ester, acrylic amide and methacrylic acid are used. , Methacrylic ester, methacrylamide, acrylonitrile, 2-acrylamido-2-methylpropanesulfonic acid, hydroxymethyl methacrylate, vinyl acetate, cationized acrylate, cationized methacrylate, vinylsulfonic acid, maleic anhydride, maleic acid, fumaric acid And the like.

[1-2] Cross-Linked Polyamino Acid Resin The cross-linked polyamino acid-based water-absorbing resin used in the present invention is not particularly limited, but generally, cross-linked polyaspartic acid, cross-linked polyglutamic acid, cross-linked polylysine and There are copolymers of these polymers with other amino acids.

Specific examples of the amino acid component as a copolymer include, for example, 20 kinds of essential amino acids, a series of α
-Amino acids, neutral amino acids, acidic amino acids, ω-esters of acidic amino acids, basic amino acids, N-substituted basic amino acids, and aspartic acid-L-phenylalanine dimer (aspartame). The α-amino acid may be an optically active form (L-form, D-form) or a racemic form. Among these, crosslinked polyaspartic acid and crosslinked polyglutamic acid having high water absorption are preferable, and crosslinked polyaspartic acid suitable for industrial production is particularly preferable. The method for producing the crosslinked polyaspartic acid is not particularly limited, but generally, a method of crosslinking polyaspartic acid with a polyglycidyl compound, a polyisocyanate compound, a polyaziridine compound, or the like, and partially opening polysuccinimide with a polyamine. After ring cross-linking, there is a method of hydrolyzing with an alkali, a method of polymerizing in the presence of an acidic amino acid and / or an oligomer of an acidic amino acid and a cross-linking agent. However, a polysuccinimide capable of obtaining a resin having a high water absorption is partially converted to a polyamine. After ring-opening and crosslinking, a method of hydrolysis with an alkali is preferred.

[2] Purification of Water Absorbent Resin The method of purifying a water absorbent resin of the present invention is a method of washing or reprecipitating a gel of a water absorbent resin with water and / or a water-miscible organic solvent.

By this purification method, the water absorbing ability and gel strength of the water absorbing resin are improved. This is presumably because water-soluble components that deteriorate the properties of the resin, such as monomers, oligomers, and inorganic or organic salts, contained in the resin gel are removed.

As a specific example of this cleaning treatment, the following 2
There are two ways.

[2-1] A method of filtering and washing a gel of a water-absorbent resin swollen with water or a mixture of water and a water-miscible organic solvent using water and / or a water-miscible organic solvent.

[2-2] A method of washing a gel of a water-absorbent resin swollen with water or a mixture of water and a water-miscible organic solvent by reprecipitation using a water-miscible organic solvent.

These methods [2-1] and [2-2] can be applied to a solid water-absorbing resin in an isolated state, that is, water or water such as a wet cake, a press cake, and a slurry. And a water-absorbing resin containing an organic solvent. Here, in [2-1], in the case of the water-absorbing resin in a solid state, the solid temporarily undergoes a gel form when washed with water or a water-miscible organic solvent. Included in the invention. In [2-2], when the polymer is reprecipitated, it can be carried out while suppressing the degree of swelling of the gel depending on the conditions. However, this case is also essentially the same as the technique of the present invention, Included in the present invention.
In other words, the purification method of the present invention is characterized by temporarily passing through a gel polymer, and the gel may be in a state of completely absorbing a solvent or in a state of an opaque slurry which is partially absorbed. Including. Furthermore, there is no particular limitation on the length of time that the water-absorbent resin is in a gel state.

Hereinafter, these methods [2-1] and [2-2] will be described.

[2-1] A method of filtering and washing the gel using water and / or a water-miscible organic solvent In this method, for example, the gel is swollen with water or a mixture of water and a water-miscible organic solvent. The water absorbent resin gel
The gel is filtered using water and / or a water-miscible organic solvent, and the filtered hydrogel is washed with water and / or a water-miscible organic solvent. By this filtration, impurities smaller than the mesh of the filter medium can be removed by filtration, and, if desired, the remaining impurities can be removed by further washing.

The water-miscible organic solvent used is not particularly limited as long as it is an organic solvent miscible with water. Specific examples thereof include alcohols such as methanol, ethanol, propanol, isopropanol, butanol, 2-methoxyethanol, and 2-ethoxyethanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and dipropylene glycol; Ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, cyclic ethers such as tetrahydrofuran and dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, N
-Methylpyrrolidone, N, N'-dimethylimidazolidinone, dimethylsulfoxide, sulfolane and the like. Among these, in particular, the obtained water-absorbent resin is easy to dry, and in that the solvent hardly remains in the resin after drying,
Alcohols such as methanol, ethanol, propanol, isopropanol and butanol are preferred.

The amounts of water and the water-miscible organic solvent used for swelling the resin are not particularly limited as long as they can swell the resin sufficiently. The degree of swelling of a resin changes according to the water absorption capacity of the resin. In particular, in this method, it is preferable to swell using excess distilled water or pure water. However, it is not economical to use too much water. From such a point, the amount of distilled water or pure water to be used is preferably 0.001 to 10 times by weight, more preferably 0.02 to 5 times by weight of the amount of distilled water or pure water absorbed by the resin. The amount of water and / or water-miscible organic solvent used for washing the gel of the resin after swelling is not particularly limited, but from the viewpoint of washing effect and economy, 1 to 50 times the weight of the resin. Is preferred, and 3 to 20 times by weight is particularly preferred. When a mixed solution of water and a water-miscible organic solvent is used to wash the gel of the resin after swelling, the ratio between the two is not particularly limited. It is preferred that the content be at least 10% by weight. Here, when the ratio of the organic solvent is increased, the gel shrinks, and the resin is reprecipitated as in [2-2].

The material used for filtration is not particularly limited, and examples thereof include a steel sieve, a nylon nonwoven fabric, and a glass filter. The size of the mesh of the filter is preferably 50 μm to 2 mm, and 100 μm
１1 mm is more preferred. If the size of the eyes is appropriately increased, the filtration rate is increased, and if the size is appropriately reduced, the recovery rate of the gel is increased.

The filtration may be performed while the liquid to be filtered is allowed to stand, may be performed while stirring, or may be performed while vibrating or rotating the entire filter. The filtration may be performed at normal pressure, under pressure, or under reduced pressure.

The method of washing the gel may be a usual washing method, or a method in which a hydrogel obtained by filtration is further sludged with distilled water or pure water, followed by filtration and washing with water. In the sludge method, the number of operations is large, but the cleaning efficiency is large.

Also, the gel that has fallen through the mesh during filtration precipitates at the bottom and can be recovered and used.

The gel after filtration and washing is dried as it is or reprecipitated with a water-miscible organic solvent, and the precipitate is collected and dried.

The water-miscible organic solvent used for the reprecipitation is not particularly limited, but is generally methanol, ethanol, propanol, isopropanol, butanol, or the like.
Alcohols such as 2-methoxyethanol and 2-ethoxyethanol, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol and dipropylene glycol; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; tetrahydrofuran and dioxane Cyclic ether, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, N, N′-
Dimethylimidazolidinone, dimethylsulfoxide, sulfolane and the like can be mentioned. Of these, methanol, ethanol, propanol, isopropanol, and acetone are preferred because they can be obtained at low cost.

[2-2] Method of washing the gel by reprecipitation using a water-miscible organic solvent In this method, for example, a water-absorbing material swollen with water or a mixture of water and a water-miscible organic solvent is used. Resin gel,
The resin is reprecipitated by draining into a water-miscible organic solvent, or the resin is reprecipitated by charging the gel with a water-miscible organic solvent.

The swelling of the water-absorbing resin may be performed in the same manner as in the method [2-1] described above.

When the gel is reprecipitated by discharging it into a water-miscible organic solvent, the viscosity of the gel before discharging may be adjusted, if necessary. For example, increasing the proportion of water contained in the gel increases the viscosity of the gel, while increasing the proportion of the water-miscible organic solvent decreases the viscosity of the gel,
It becomes a slurry. Since the slurry is transferred when discharging, the viscosity of the slurry is preferably low. However, the discharging method is not particularly limited, and the discharging time is not limited. In the method in which the water-miscible organic solvent is charged into the gel or the slurry containing the gel, the resin may agglomerate during the charging to form a firm mass. It is necessary to pour in or pulverize with a high-speed mixer with a blade after solidification.

Examples of the water-miscible organic solvent used for reprecipitation of the gel include acetone, methyl ethyl ketone, methanol, ethanol, propanol, butanol, heptanol, ethylene glycol, propylene glycol, 1,2-dimethoxyethane and methoxymethanol. ,
2-methoxyethanol, tetrahydrofuran, dioxane, N, N-dimethylaminoformamide, N, N-
Dimethylaminoacetamide, dimethylsulfoxide,
N, N-dimethylimidazolidinone, sulfolane, N-
Methylpyrrolidone and the like. From an industrial point of view, acetone, methanol and ethanol, which are highly safe and easy to recover, are preferred. These may be used alone or in combination of two or more. Further, it may be the same as or different from the water-miscible organic solvent used for swelling the resin. Further, if necessary, water may be contained.

The amount of the water-miscible organic solvent used in the reprecipitation is not particularly limited as long as the gel is reprecipitated, and may be a complete precipitate or a gel. Although depending on the type of the solvent, generally, it is preferably 0.5 to 10 times by weight, more preferably 1 to 5 times by weight of the resin. It is uneconomical to use more.

The method of mixing the gel swollen with water or a water-miscible organic solvent and the water-miscible organic solvent used for reprecipitation is not particularly limited, and a general method can be used.

For example, there is a method in which a gel swollen with water or a water / water-miscible organic solvent is discharged into the water-miscible organic solvent or reprecipitated by inserting the water-miscible organic solvent.

The viscosity of the discharged gel can be changed as required. For example, when the proportion of water increases, the viscosity of the gel increases. Conversely, when the proportion of the water-miscible organic solvent increases, the viscosity of the gel decreases and the gel becomes a slurry.

The discharging method is not particularly limited, and the discharging time is not limited. For the reprecipitated resin, a liquid / solid separation method in ordinary chemical synthesis can be applied. For example, filtration,
Decantation, centrifugation, etc.

The method for drying these resins is not particularly limited, but may be hot air drying, drying with specific steam, microwave drying, reduced pressure drying, drum dryer drying, azeotropic drying in a hydrophobic organic solvent. Drying can be performed by a known method such as drying by dehydration. Drying temperature is 20 ~ 200 ℃
Is preferable, and 50 to 120 ° C. is more preferable.

The obtained resin may be subjected to surface crosslinking and granulation, if necessary.

[3] Form of Use of Water Absorbent Resin The form of use of the water absorbent resin is not particularly limited, and may be used alone or in combination with other materials.

For example, a method of kneading a thermoplastic resin and molding by injection molding or the like, a method of mixing a monomer of a constituent resin with a water-absorbent resin resin and an initiator as required, and polymerizing with light or heat, etc. And water-absorbent resin dispersed in a solvent,
There are a method of casting and removing the solvent, a method of mixing and mixing the prepolymer and the water-absorbent resin, and a method of mixing and crosslinking the polymer and the water-absorbent resin.

The resin composition of the present invention is not particularly limited as a molded product, and can be used as a solid, a sheet, a film, a fiber, a nonwoven fabric, a foam, a rubber and the like.
The molding method is not particularly limited.

On the other hand, the water-absorbing resin used in the present invention may be a single compound or a composite obtained by combining with another material. Although the structure of the composite is not particularly limited, for example, a method of sandwiching between pulp and nonwoven fabric, a method of forming a sandwich structure, a method of forming a multilayer structure using a resin sheet and a film as a support, and a method of casting into a resin sheet to form a two-layer structure There are methods.

The water-absorbing resin used in the present invention may be used in combination with two or more other water-absorbing resins, if necessary. If necessary, an inorganic compound such as salt, colloidal silica, white carbon, ultrafine silica, titanium oxide powder, or an organic compound such as a chelating agent may be added. Further, an oxidizing agent, an antioxidant, a reducing agent, an ultraviolet absorber, an antibacterial agent, a bactericide, a fungicide, a fertilizer, a fragrance, a deodorant, a pigment and the like may be mixed.

The resin of the present invention can be used as a gel or a solid. For example, water retention materials for agricultural and horticultural use, cut flowers,
When used as a gel fragrance, a gel deodorant, etc., it is used as a gel, and a paper diaper absorber is used as a solid.

[4] Use of water-absorbent resin The use of the water-absorbent resin is not particularly limited, but it can be used for any of the conventional water-absorbable resins.

For example, sanitary articles such as sanitary articles, disposable diapers, breast milk pads, disposable rags, dressings for protecting wounds, medical articles such as medical underpads, cataplasms,
Pet seats, portable toilets, gel air fresheners, gel deodorants, sweat-absorbing fibers, household items such as disposable warmers, toiletries such as shampoos, set gels, moisturizers, and water retention materials for agriculture and horticulture. Agricultural and horticultural supplies such as cut flower prolonging agent, floral foam (cutting flower fixing material), nursery beds, hydroponic cultivation, vegetation sheets, seed tape, fluid seeding, dew condensation prevention agricultural sheets, food tray freshness Food packaging materials such as holding materials, drip-absorbent sheets, cold insulation materials, transportation materials such as water-absorbent sheets for transporting fresh vegetables, building materials for preventing dew condensation, sealing materials for civil engineering and construction, and anti-sludge agents for shield method Construction materials such as concrete admixtures, gaskets and packing, sealing materials for electronic devices such as optical fibers, waterproof materials for communication cables, and electrical devices such as recording paper for inkjet. Wood, sludge coagulants, gasoline,
Dehydration of oils, water treatment agents such as water removers, printing pastes, water-swellable toys, artificial snow, sustained-release fertilizers, sustained-release pesticides, sustained-release agents, humidity regulators, antistatic agents, etc. No.

[0070]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the examples. In the following Examples and Comparative Examples, “parts” means “parts by weight”.

In the examples, the water absorption was measured by the tea bag method, and the gel strength of the water absorbent resin gel was measured by the steel ball standing method.

Hereinafter, these measuring methods will be described.

(1) Tea Bag Method The amount of water absorption was measured for distilled water and physiological saline. That is, in the case of distilled water, about 0.05
Parts, physiological saline, about 0.1 part of water-absorbent resin is put into a non-woven tea bag (80 mm x 50 mm), immersed in excess solution, and the resin swells with distilled water and physiological saline for 1 hour. After that, in the case of artificial urine, after 10 minutes, the tea bag was pulled up and drained for 1 minute, and the weight was measured. Assuming that the same operation was performed using only a tea bag as a blank, the value obtained by subtracting the weight of the blank and the weight of the water-absorbent resin from the measured value was divided by the weight of the water-absorbent resin. ). The physiological saline is a 0.9% by weight aqueous sodium chloride solution.

(2) Steel ball standing method 250 parts of physiological saline was added to 5 parts of the water-absorbing resin, and the mixture was gelled for 1 hour.
The maximum diameter when the gel did not sink for 0 seconds was defined as the gel strength of the gel.

Example 1 In a nitrogen stream, 5 parts of a polysuccinimide having a weight average molecular weight of 96,000 was dissolved in 20 parts of N, N-dimethylformamide (DMF), and lysine methyl ester dihydrochloride 1 was dissolved. 2. 8 parts and triethylamine
One part was added and the mixture was stirred at room temperature for 20 hours. 100 parts of methanol was added to the reaction product, and the mixture was stirred at room temperature for 2 hours to loosen the formed gel. The resulting precipitate was collected by suction filtration and washed with methanol and then with water to obtain a wet cake of crosslinked polysuccinimide.

This wet cake of crosslinked polysuccinimide was suspended in 30 parts of distilled water and 90 parts of methanol.
An 8% by weight aqueous solution of sodium hydroxide was added dropwise so that the pH of the suspension was in the range of 11 to 12.
The alkaline aqueous solution was continued to be added until the temperature did not decrease. p
After H stopped decreasing, dilute hydrochloric acid was added until the pH of the reaction solution reached 7. The resulting precipitate was gelled by adding 50 parts of distilled water, gelled, filtered through a sieve having openings of 425 μm, washed sufficiently with distilled water, and dried,
As a result, 6.9 parts of a crosslinked polyaspartic acid-based resin as a water-absorbing polymer was obtained. The water absorption of the crosslinked polyaspartic acid resin was 490 times with distilled water and 62 times with physiological saline. The gel strength was 20/16 inch.

Example 2 In the same manner as in Example 1, the crosslinked polysuccinimide was hydrolyzed and neutralized. Thereafter, 15 parts of distilled water and 15 parts of methanol were added to the precipitate to cause gelation. The obtained gel was filtered using a sieve having an opening of 200 μm, washed twice with 15 parts of 50% by weight methanol water, dried and dried to obtain a crosslinked polyaspartic acid-based resin as a water-absorbing polymer. 7.2 parts were obtained. The water absorption of this crosslinked polyaspartic acid-based resin is 5
It was 50 times with physiological saline and 64 times. The gel strength was 20/16 inch.

Example 3 In the same manner as in Example 1, the crosslinked polysuccinimide was hydrolyzed and neutralized. Thereafter, 15 parts of distilled water and 18 parts of methanol were added to the precipitate to gel into a slurry. The obtained gel was gradually charged into 50 parts of methanol over 30 minutes to reprecipitate the gel. This was collected and dried to obtain 7.7 parts of a crosslinked polyaspartic acid-based resin as a water-absorbing polymer.
The water absorption of the crosslinked polyaspartic acid resin was 450 times with distilled water and 61 times with physiological saline. The gel strength was 20/16 inch.

Example 4 Using 10 parts of a cross-linked polyacrylic resin (Aqualic CAW, manufactured by Nippon Shokubai Co., Ltd.), gelled with 30 parts of water and 30 parts of methanol.
The treatment was performed in the same manner as in Example 3. The water absorption of this water-absorbing polymer was 580 times with distilled water and 61 times with physiological saline.
The gel strength at this time was 20/16 inch.

Example 5 A disposable disposable diaper “Eliele Friend” (manufactured by Daio Paper Co., Ltd.) was decomposed to obtain a water absorbent resin. Gelation was carried out using 10 parts of this resin, and treatment was carried out in the same manner as in Example 1. The water absorption of this water-absorbing polymer was 1010 times with distilled water and 72 times with physiological saline. The gel strength at this time was 24/16 inch.

Comparative Example 1 In the same manner as in Example 1, the crosslinked polysuccinimide was hydrolyzed and neutralized. Thereafter, the precipitate is dried at 60 ° C. as it is, and after pulverization, a crosslinked polyaspartic acid-based resin 7.6 as a water-absorbing polymer is obtained.
Got a part. The water absorption of this crosslinked polyaspartic acid-based resin was 160 times with distilled water and 37 times with physiological saline. The gel strength was 8/16 inch.

[Comparative Example 2] The crosslinked polyacrylic acid resin used in Example 4 (manufactured by Nippon Shokubai Co., Ltd., Aquaric C)
When the water absorption of AW) was measured without performing the washing treatment, the water absorption was 350 times with distilled water and 55 times with physiological saline. The gel strength at this time was 12/16 inch.

[Comparative Example 3] The disposable disposable diaper “Eliele Friend” used in Example 5 (Daio Paper Co., Ltd.)
The water absorption of the water-absorbent resin was measured without performing the washing treatment. The water absorption was 750 times with distilled water and 63 times with physiological saline. The gel strength at this time was 16/16 inch.

[Comparison and Consideration of Examples 1 to 5 and Comparative Examples 1 to 3] In Comparative Example 1, the gel of the crosslinked polyaspartic acid resin was used without washing or reprecipitation, so that the water absorption was And the gel strength was poor. In contrast, in Examples 1 to 3, in each case, the gel of the crosslinked polyaspartic acid-based resin was washed or reprecipitated, so that a high water absorption was exhibited, and the crosslinked polyasparagine excellent in gel strength was also obtained. The acid was obtained.

In Comparative Example 2, since the gel of the crosslinked polyacrylic acid resin was used without washing or reprecipitation, the water absorption was slightly low and the gel strength was inferior. In contrast, in Example 4, the gel of the crosslinked polyacrylic acid-based resin was reprecipitated, so that a crosslinked polyacrylic acid having a high water absorption and excellent gel strength was obtained.

Furthermore, in Comparative Example 3, since the gel of the water-absorbent resin was used without washing or reprecipitation, the water absorption was slightly low and the gel strength was inferior. In contrast, in Example 5, the gel of the water-absorbent resin was washed, so that a water-absorbent resin that exhibited high water absorption and excellent gel strength was obtained.

The gel of a water-absorbing resin such as a crosslinked polyaspartic acid-based resin or a crosslinked polyacrylic acid obtained by hydrolysis is washed with water and / or a water-miscible organic solvent, or By reprecipitation with a water-miscible organic solvent, it was confirmed that a water-absorbing resin excellent in water absorption and gel strength could be obtained.

[0088]

As described above, according to the purification method of the present invention, the gel has a high gel strength and a high water absorption, which is useful as a water absorbent used for disposable diapers, agricultural and horticultural uses, and the like. Thus, a water-absorbent resin having improved gel surface tackiness can be obtained.

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI C08G 73/10 C08G 73/10

Claims (9)

[Claims] 1. A method of washing a water-absorbent resin gel swollen with water or with water and a water-miscible organic solvent, using water and / or a water-miscible organic solvent. Purification method. 2. A water-soluble component is removed by washing a water-absorbent resin gel swollen with water or with water and a water-miscible organic solvent with water and / or a water-miscible organic solvent. A method for purifying a water-absorbent resin, comprising: 3. A method for purifying a water-absorbent resin, comprising re-precipitating a gel of a water-absorbent resin swollen with water or with water and a water-miscible organic solvent with a water-miscible organic solvent. 4. The method for purifying a water-absorbent resin according to claim 1, wherein the water-miscible organic solvent is an alcohol. 5. The method according to claim 1, wherein the water-absorbent resin is a biodegradable resin. 6. The method for purifying a water-absorbent resin according to claim 1, wherein the water-absorbent resin is a crosslinked polyamino acid. 7. The method for purifying a water-absorbing resin according to claim 1, wherein the water-absorbing resin is a crosslinked polyaspartic acid-based resin. 8. The method for purifying a water-absorbent resin according to claim 1, wherein the water-absorbent resin is a cross-linked poly (meth) acrylic acid. 9. A water-absorbent resin purified by the method according to claim 1.