JP2679732B2 - Water absorbing gel composition with excellent light resistance and heat resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water-absorbent gel composition which is stable with little deterioration over time even when exposed to light and in a high temperature atmosphere.

The water-retaining gel composition according to the present invention is a product obtained by swelling an aqueous solution containing a small amount of an ultraviolet absorber in a superabsorbent resin and is extremely stable against both light and heat. , In various fields of use, for example, regenerator,
Gels for heat storage agents, gels for fragrances, water retention gels for horticulture (ornamental), gels for artificial snow, waterproofing agents for outdoor civil engineering work, lubricants, and other materials that require light resistance and durability (heat resistance) It can be used effectively.

2. Description of the Related Art In recent years, highly water-absorbent resins have been proposed that absorb water of tens to hundreds of times their own weight. For example, a starch graft polymer (Japanese Patent Publication No. 53-46199, etc.), a cellulose modifier (Japanese Patent Publication No. 50-80376, etc.), a crosslinked product of a water-soluble polymer (Japanese Patent Publication No. 43-23462, etc.), Self-crosslinking alkali metal acrylate polymers (Japanese Patent Publication No. 54-30710, etc.), etc., which are used as absorbents for sanitary products, disposable paper diapers, etc., or water retention agents for agriculture and horticulture and other industries. Applications are being developed in a wide range of fields as materials for use.

However, although these superabsorbent resins have excellent ability to absorb a large amount of water and stability with time during drying, they are extremely poor in stability in a water-absorbed state. For example, if the water-absorbed gel-like material is exposed to sunlight, it often deteriorates and fluidizes within a few hours, and the gel-like material cannot retain its shape. Also, fill the gel-like material into a closed container without physical water evaporation,
Even when placed in a high-temperature atmosphere (80 ° C or higher), it takes a few hours to 24 hours
It may also deteriorate over time. Therefore, such a highly water-absorbent resin (water-absorbing gel) can be used for storage and storage, especially for horticultural (ornamental) water-retaining agents and cool storage agents (such as food cold-insulating films and molded containers). When used in fields requiring light resistance and heat resistance such as heat storage agents, waterproofing agents and lubricants for outdoor civil engineering work, artificial snow, etc. The durability is not sufficient, which is a major obstacle to practical use.

As a method of improving the light resistance and heat resistance of the water-absorbent gel,
A method of mixing carbon black or activated carbon with a super absorbent resin (Japanese Patent Laid-Open No. 59-38271) or a method of allowing a sulfoalkyl (meth) acrylate monomer to be present as a comonomer in an acrylic acid-based monomer, together with a crosslinking agent. A water-insoluble water-absorbent resin obtained by polymerization (JP-A-61-36309) and the like have been proposed.

However, by improving the resin itself by mixing substances such as carbon black and activated carbon with the super absorbent polymer itself or adding other substances as copolymerization components, the durability of the water-absorbent gel obtained from the resin is improved. The method of improving the property has a small effect and is still insufficient, which is a problem in practical use.

That is, in order to obtain a water-absorbent resin by synthesis, a mixture (carbon black or activated carbon) or a copolymerization monomer (sulfoalkyl (meth) acrylate) with a polymerizable monomer (acrylic acid-based monomer or the like) that can be the basis of the water-absorbent resin is used. The addition amount of the system monomers) is naturally limited, and if the addition amount is too large, the synthesis reaction (solubility in those solvents, reactivity (copolymerization, etc.) becomes difficult,
This is because the water-absorbent resin (including the mixture) obtained even if it could be synthesized would be one in which the original ability was significantly impaired.

Means for Solving the Problems The present inventors have conducted various studies in order to solve the above problems, and as a result, by absorbing an aqueous solution containing a small amount of an ultraviolet absorbent in a super absorbent polymer, The present invention has been completed by finding that the water-absorbent gel composition obtained is extremely stable to light and stable to heat.

That is, the light-absorbing gel composition excellent in light resistance and heat resistance according to the present invention is obtained by allowing a superabsorbent gel to absorb an aqueous solution containing a water-soluble ultraviolet absorber, To do.

The conventional method is to improve the superabsorbent resin itself and to attempt to improve the light resistance of the water-absorbent gel obtained therefrom, whereas the present invention is the superabsorbent resin itself. So, using any ordinary ordinary, the resin is fundamentally in terms of trying to impart light resistance and durability to the water-absorbing gel obtained by absorbing an aqueous solution having a light-absorbing ability. It is different.

Effect The water absorbing gel according to the present invention is extremely stable against light and heat. Therefore, the water-absorbing gel of the present invention can exhibit its excellent light resistance and heat resistance when used as, for example, an agricultural and horticultural water retention agent, a heat storage agent, a waterproofing agent for civil engineering work, a lubricant and the like.

Generally, UV absorbers absorb UV light from the outside and convert the absorbed energy into harmless forms such as heat, preventing incident light from reaching the photopolymerization initiation site of the target polymer. Have an effect.

Since the water-absorbent gel composition of the present invention contains a large amount of an aqueous solution containing such an ultraviolet absorber in the superabsorbent resin (in the cross-linking molecule) and absorbs water, the energy of ultraviolet rays from the outside It is effectively converted without degrading the water-absorbing gel.

In the case of the conventional improved super absorbent polymer, the ratio of the substances (carbon black, activated carbon, sulfoacrylate, etc.) added to impart light resistance and durability to the resin is about 50% for practical use. Is the limit, and if it is contained more than that, the original water-absorbing ability of the superabsorbent resin is remarkably reduced.

However, in the present invention, a super absorbent resin (a general one,
Since it is a system that absorbs an aqueous solution with a UV absorber concentration of 0.1 to 1 wt% at a water absorption ratio of 100 to 500 times), the UV absorber can be used up to about 500% in the resin and the water absorbing gel composition at that time Even when a product is prepared, the water absorption capacity (water absorption capacity) of the resin is hardly reduced and the original water absorption capacity of the resin can be maintained. From this, the water-absorbent gel composition of the present invention exhibits an excellent light resistance function, and the ultraviolet absorber used in the present invention can also improve heat resistance as a concomitant effect.

[Specific description of the invention]

Superabsorbent Resin The superabsorbent resin used in the present invention may be any water-insoluble superabsorbent resin. As an example, starch-acrylonitrile graft copolymer hydrolyzate, starch-acrylic acid graft polymer neutralized product, acrylic ester-vinyl acetate copolymer saponified product, crosslinked polyvinyl alcohol modified product, crosslinked product Examples thereof include polyethylene oxide modified products, partially neutralized poly (meth) acrylic acid salt crosslinked products, and crosslinked isobutylene-maleic anhydride copolymers.

Among these, acrylic acid and / or
Alternatively, a highly water-absorbent resin containing a carboxyl group based on methacrylic acid and / or a carboxylate group of an alkali metal is preferable.

Water-Soluble UV Absorber The water-soluble UV absorber used in the present invention is not particularly limited in its type, and is usually 300 to 400 μm as a wavelength region.
Any material may be used as long as it can efficiently absorb light in the range of m. Among such ultraviolet absorbers, benzophenone-based ones include (i) 2-hydroxybenzophenone-4-diglyceryl ether, (b) 2,2'-dihydroxybenzophenone-4-diglyceryl ether, (c) 2 -Hydroxybenzophenone-4,4'-bisglyceryl ether, (d) 2,2'-hydroxybenzophenone-4,4'-bisglyceryl ether, (e) 2-hydroxy-4-methoxy-5-sulfobenzophenone sodium salt , (To) 2,2'-dihydroxy-4,4'-dimethoxy-5
-Sulfobenzophenone sodium salt, (to) 2,2'-dihydroxy-4-methoxybenzophenone-5-sulfonic acid and the like. And as a benzotriazole type | system | group, (H) 2- (2'-hydroxy-4'-methoxy-
5'-sulfophenyl) benzotriazole sodium salt, (i) 2- (2'-hydroxy-4'-butoxy-
5'-sulfophenyl) benzotriazole sodium salt, and the like.

Of these, benzophenone-based and nonionic-based ones, that is, (i) to (d), are particularly preferable.

Production of Water-Absorbing Gel Composition The water-absorbing gel composition according to the present invention is produced by absorbing a UV absorbent solution in a highly water-absorbent resin. The concentration of the UV absorber in the aqueous solution is preferably 0.1 to 1.0% by weight with respect to water. If the concentration is less than 0.1% by weight, the light resistance and heat resistance are not improved much, and if it exceeds 1.0% by weight, it is markedly improved. Not only the effect is not recognized, but it is not advantageous in terms of cost.

Such an ultraviolet absorbent solution may be applied at the time when the water-absorbing gel is used, and there are various application methods. For example, it can be performed by immersing the super absorbent polymer in the ultraviolet absorbent solution or spraying the ultraviolet absorbent solution. Further, the number of times of application is not limited to once, and may be multiple times. When the ultraviolet absorbent solution is applied multiple times, the concentration of each application liquid may be the same or different.

The application rate of the ultraviolet absorbent solution depends on the type of super absorbent resin,
Saturated water absorption and application of water absorption gel, required light resistance,
It may be appropriately determined according to heat resistance, workability, cost and the like.

(Experimental example)

Example 1 A commercially available superabsorbent resin having a partially neutralized sodium polyacrylate crosslinked body as a main component (trade name "Diawet")
Mitsubishi Yuka Co., Ltd.) 1 g in ion-exchanged water 150 g 2-
Hydroxybenzophenone-4-diglyceryl ether
Water absorption swelling was carried out in an aqueous solution in which 1.0 g was dissolved to prepare a water absorption gel composition (1).

Example 2 1 g of the above diamond wet was added to 2 g of 150 g of ion-exchanged water.
-Hydroxy-4-methoxy-5-sulfobenzophenone sodium salt 0.6 g was put into an aqueous solution in which the product was dissolved and swollen by absorbing water to prepare a water-absorbing gel composition (2).

Example 3 The same operation as in Example 1 was carried out except that a commercially available superabsorbent resin (trade name “AQUALIC CA” manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.) was used instead of using the diamond wet of Example 1. A water-absorbent gel composition (3) was prepared.

Comparative Example 1 A highly water-absorbent resin was produced based on Example 1 described in JP-A-59-38271. That is, a 37% aqueous sodium acrylate solution was added to a double-arm kneader with a total volume of 2.5 liters.
956 g, 113 g of 80% acrylic acid aqueous solution, 0.8 g of methylenebisacrylamide and carbon black (Neo Spectra Mark II, 9 g of Columbia Carbon Co. were charged. The mixture was heated to 40 ° C. under a nitrogen atmosphere at a rotation speed of stirring of about 50 rpm for 10 minutes. % 50% aqueous solution of ammonium persulfate and 20 g of 10% aqueous solution of sodium hydrogen sulfite were added and polymerized, and heat was generated at the start of the polymerization, and the temperature reached 80 ° C about 10 minutes after the start of the polymerization. The aqueous solution of the monomer became a hydrous gel and was gradually subdivided by stirring.After 80 minutes from the start, the stirring was stopped and the subdivided black hydrous polymer (average particle size of about
(3 mm) was taken out and dried in a hot air dryer at 180 ° C. to obtain a comparatively super absorbent resin (1). 1g of this is 150g of deionized water
Was swelled with water to obtain a comparative water-absorbent gel (1).

Comparative Example 2 A highly water-absorbent resin was produced based on Example 2 described in JP-A-59-38271. That is, isobutylene-maleic anhydride copolymer 154 parts, caustic soda 64 parts and water 3
98 parts were mixed and heated and stirred at 90 ° C. for 2 hours to prepare a uniform aqueous solution. Next, 20 parts of powdered activated carbon (“Shirasagi M” manufactured by Takeda Pharmaceutical Co., Ltd.) and 2.5 parts of glycerin diglycidyl ether were added to this aqueous solution, and after mixing, the mixture was poured into a vat and a crosslinking reaction was carried out in a hot air dryer at 110 ° C. The mixture was aged and dried to obtain a black comparative super absorbent polymer (2). This 1g
Ion-exchanged water (150 g) was added to the mixture to absorb water and swell to obtain comparative water-absorbing gel (1).

Comparative Example 3 A highly water-absorbent resin was produced based on Example 1 described in JP-A-61-36309. That is, in a 500 ml cylindrical separable flask, 172.8 g (0.80 mol) of sodium salt of sulfoethyl methacrylate, 3.6 g (0.05 mol) of acrylic acid, 14.1 g (0.15 mol) of sodium acrylate, 0.154 g of N, N-methylenebisacrylamide were added. g (0.001 mol) and 260 g of water were charged and stirred to dissolve uniformly. After purging with nitrogen, heat to 40 ° C in a water bath and 1.0 g of 10% ammonium persulfate aqueous solution and 1% L-
0.5 g of an ascorbic acid aqueous solution was added, stirring was stopped, and polymerization was performed. After the initiation of polymerization, heat was generated and 40 minutes later, the temperature rose to 68 ° C. After confirming that the temperature of the polymerization system started to drop, the temperature of the water bath was raised to 90 ° C. and heating was continued for another hour. The hydrogel of the obtained water-absorbent resin was subdivided, dried in a hot air dryer at 150 ° C for 5 hours, and then pulverized to obtain a comparatively high water-absorbent resin (3).
I got To 1 g of this, 150 g of ion-exchanged water was added to cause swelling with water to obtain a comparative water-absorbing gel (3).

Comparative Example 4 150 g of ion-exchanged water was added to 1 g of a commercially available highly water-absorbent resin (trade name "Diawet" manufactured by Mitsubishi Petrochemical Co., Ltd.),
Comparative water-absorbing gel (4) was obtained by swelling with water.

Comparative Example 5 150 g of ion-exchanged water was added to 1 g of a commercially available highly water-absorbent resin (trade name "AQUALIC CA" manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.) to absorb water and swell to obtain a comparative water-absorbent gel (5).

[Evaluation test method]

1. Light resistance test (1) 50 g of each of the various water-absorbent gels obtained in Examples (1) to (3) and Comparative Examples (1) to (5) were placed in a 0.05 mm thick transparent polyethylene bag. Exposed to sunlight in the summer (July-August). The state of the water absorbing gel at that time was observed over time.
The results are shown in Table 1.

2. Heat resistance test 50 g of each of the water-absorbent gels of Examples (1) to (3) and Comparative Examples (1) to (5) were placed in a glass bottle, covered with a lid, and placed in a constant temperature bath at 90 ° C. to absorb water. The state of the gel was observed over time. The results are shown in Table-2.

Claims (1)

(57) [Claims] 1. A water-absorbent gel composition excellent in light resistance and heat resistance, which is obtained by allowing a highly water-absorbent resin to absorb an aqueous solution containing a water-soluble ultraviolet absorber.