JPH0625335B2 - Cool storage agent - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cold storage agent, and more specifically, to a water-containing hydrogel by adhering a polycarboxylic acid-based water-absorbing resin to a porous substrate and then allowing the resin to absorb water. The present invention relates to a cold storage agent formed by gelling and having excellent shape retention and durability.

(Prior Art) Regenerators are widely used in the food field and the like from the viewpoints of product temperature management and energy saving, since the temperature can be arbitrarily set by a refrigerant medium and can be reused. Conventionally, thixotropic viscous water-containing gel mixed with a storage medium such as natural gum in a bag-shaped container has been used as a regenerator, but in addition to the complete prevention of leakage of the contents, However, since it is a viscous material, it has a problem that it is inferior in moldability, and when it is cooled, it is solidified and deformed and inferior in shape retention.

In order to solve this problem, polyacrylic acid is ionically crosslinked with a polyvalent metal salt to obtain a hydrogel, a polyacrylic acid or a maleic acid-based polymer, which is crosslinked with a crosslinking agent such as a polyvalent epoxy compound or a polyvalent amine. A method using a hydrogel obtained by the above method has been developed (for example, Japanese Examined Patent Publication No. 57-2850).
No. 5, JP-A-57-14679). When the water-containing gel obtained by such a method is used as a regenerator, although it is superior in terms of moldability as compared to the viscous water-containing gel, the shape retention strength of the gel is not yet sufficient and the shape is changed by an external force. There was a problem when it changed or the gel broke and lost its shape retention property.

(Problems to be solved by the invention) Therefore, as a result of diligent efforts by the present inventors to develop a cool storage agent having excellent shape-retaining properties, a polycarboxylic acid-based water-absorbing resin was attached to a porous substrate, and then the It has been found that a cold storage agent excellent in shape retention and durability can be obtained by allowing a resin to absorb water to form a water-containing gel, and based on this finding, the present invention has been completed.

(Means for Solving Problems) Thus, according to the present invention, a polycarboxylic acid-based water-absorbing material is obtained by coating or impregnating a porous substrate with an aqueous solution containing a carboxylic acid-based polymer and a cross-linking agent, followed by heat treatment and drying. There is provided a cold storage agent obtained by depositing a resin and then allowing the resin to absorb water to form a hydrogel.

The polycarboxylic acid-based water absorbing resin used in the present invention is obtained by crosslinking a carboxylic acid-based polymer with a crosslinking agent and then drying it.

The carboxylic acid-based polymer is a water-soluble polymer which is a polymer of an α, β-unsaturated carboxylic acid monomer, a copolymer of the α, β-unsaturated carboxylic acid monomer and a copolymerizable ethylenically unsaturated monomer, or a salt thereof. Such a polymer usually has a number average molecular weight of 1,000 to
It has 1 million, preferably 2000-500,000.

The ratio of the α, β-unsaturated carboxylic acid monomer in the polymer can be appropriately selected, but is usually 20 mol% or more, preferably 30 mol% or more. Here, the α, β-unsaturated carboxylic acid monomer refers to an unsaturated carboxylic acid having a carboxyl group or an acid anhydride group or an anhydride thereof, and specific examples thereof include acrylic acid, methacrylic acid, maleic acid,
Examples include fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, citraconic anhydride and the like.

Further, the copolymerizable ethylenically unsaturated monomer may be any as long as it is radically polymerizable with the α, β-unsaturated carboxylic acid monomer, and specific examples thereof include ethylene, propylene, butene and 2- Methyl-butene-1,2-methyl-butene-2, hexene, octene, diisobutylene, decene, cyclopentene, cyclohexene, styrene, vinyltoluene, α-methylstyrene, coumarone, indene, methyl vinyl ether, ethyl acrylate, methacrylic acid Examples of polar or non-polar vinyl monomers such as methyl, vinyl acetate, vinyl alcohol, vinylpyrrolidone, acrylonitrile, vinylsulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid. These compounds may be used alone or in combination of two or more, and polyacrylic acid and an olefin-maleic anhydride copolymer are especially preferred.

The copolymer used in the present invention is not limited by its production method, but it is usually produced by radical polymerization according to a conventional method.

In the present invention, the water-soluble salt of the copolymer is used. Specific examples of such salts include alkali metals such as sodium and potassium, ammonium salts, amine salts and the like. Among them, the sodium salt is preferable from the economical aspect.

The aqueous solution of these copolymer salts can be obtained by synthesizing the copolymer and then subjecting it to hydrolysis and neutralization reaction in water in the presence of a base according to a conventional method.

The cross-linking agent used for cross-linking the copolymer salt to obtain a water-absorbent resin is a compound capable of reacting with two or more carboxyl groups, and specific examples thereof include calcium,
Polyvalent metals such as barium and aluminum, polyvalent epoxy compounds such as glycerin diglycidyl ether, ethylene glycol glycidyl ether, polyethylene glycol diglycidyl ether, polyethyleneimine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine And other polyvalent amines.

The mixing ratio of the copolymer salt and the cross-linking agent in the present invention can be appropriately selected depending on the required performance of the target object, but usually the cross-linking agent is 0.05 to 50 mol% with respect to the carboxyl group in the polymer salt. , Preferably 0.5 to 30 mol%.

The porous substrate used in the present invention may be any one as long as it can coat or impregnate the aqueous solution containing the carboxylic acid polymer and the crosslinking agent. Specific examples thereof include woven or non-woven fabrics made from paper, cotton, natural fibers, chemical fibers, synthetic fibers, etc., or natural foams having open cells, synthetic foams typified by polyurethane foams, and the like.

In the present invention, the method of adhering the water-absorbing resin to the porous substrate is 50 to 200 ° C., preferably 80 to 150, by coating or impregnating the porous substrate with an appropriate amount of an aqueous solution containing a carboxylic acid polymer and a crosslinking agent. It is carried out by heat treatment and drying at a temperature of ° C. The porous substrate to which the water-absorbent resin thus obtained is attached may be used in the form of a sheet or plate, or may be used in the form of strips having an appropriate shape depending on the purpose of use.

In the present invention, the cold storage agent is obtained by placing the porous base material to which the water-absorbing resin adheres in a suitable container such as a polyethylene bag, and then causing the water-absorbing resin to absorb water to form a water-containing gel. At that time, the cooling temperature of the obtained hydrous gel can be set by adding various additives to water in an appropriate amount according to the purpose. As such an additive, when melting and undergoing phase change from solid to liquid, any phase may be used as long as it has a property of absorbing a thermal energy from the surroundings and cooling the surroundings by a constant temperature. Examples thereof include sodium chloride, potassium chloride, calcium chloride, magnesium chloride, ethylene glycol, diethylene glycol, glycerin, 3-methyl-1.3,5-pentanetriol, polyethylene glycol, propylene glycol, polypropylene glycol and sorbitol. In addition, the components of the poultice such as menthol and the colorant may be dissolved or dispersed in water depending on the purpose of use of the cold storage agent.

(Effects of the Invention) Thus, according to the present invention, it is possible to obtain a hydrogel having excellent shape retention and durability as compared with the prior art.

(Example) Hereinafter, the present invention will be described more specifically with reference to Examples. Parts and% in Examples and Comparative Examples are based on weight unless otherwise specified.

Example 1 144 parts of a 20% aqueous solution of an isobutylene-maleic anhydride copolymer (Kuraray Isoprene Chemical Co., Ltd., Isoban 10) sodium salt (neutralization degree 0.78) was added to polyethylene glycol diglycidyl ether (Kyoeisha Yushi-Kagaku Kogyo). Epolite 400E manufactured by Co., Ltd.) 20% aqueous solution 7.
After adding 3 parts and mixing uniformly, it was impregnated with absorbent cotton.
Next, it was heated and dried in a hot air oven at 105 ° C. for 4 hours, and the obtained plate-like product was cut into 6 cm × 4 cm strips. This strip was put in a polyethylene bag (10 cm × 7 cm), 60 g of distilled water was injected, and the mixture was sealed so that water content would not evaporate and left at room temperature for 60 minutes to obtain a cold storage agent (I).

Example 2 A cold storage agent (II) was prepared in the same manner as in Example 1 except that 216 parts of a 20% aqueous solution of the copolymer salt used in Example 1 and 1 part of a 20% aqueous solution of tetraethylenepentamine were used. Obtained.

Example 3 144 parts of 20% aqueous solution of ethylene-maleic anhydride copolymer (molecular weight 100,000) sodium salt (degree of neutralization 0.7) and polyethylene glycol diglycidyl ether 20%
A cold storage agent (III) was obtained in the same manner as in Example 1 except that 8 parts of the aqueous solution was used.

Example 4 Acrylic acid polymer (A710, manufactured by Toagosei Kagaku Co., Ltd.)
0) Cooling agent (IV) was prepared in the same manner as in Example 1 except that 144 parts of an 8% aqueous solution of sodium salt and 8 parts of an 8% aqueous solution of polyethylene glycol diglycidyl ether were used.
Got

Example 5 A uniform solution of the copolymer salt and the cross-linking agent used in Example 1 was impregnated into a cellulosic non-woven fabric, and then the same operation as in Example 1 was carried out to obtain a cold storage agent (V).

Comparative Example 1 60 g of a uniform solution of the copolymer salt used in Example 1 and the crosslinking agent
Was poured into a polyethylene bag (10 cm × 7 cm) and sealed so as to prevent water from evaporating, and heated in a hot water bath at 60 ° C. for 2 hours to carry out a crosslinking reaction to obtain a cold storage agent (VI).

Comparative Example 2 60 g of a uniform solution of the copolymer salt used in Example 2 and the crosslinking agent
Except that the cold storage agent (V
II) was obtained.

Comparative Example 3 60 g of a uniform solution of the copolymer salt and the crosslinking agent used in Example 3
Except that the cold storage agent (V
I got III).

Comparative Example 4 60 g of a uniform solution of the copolymer salt used in Example 4 and the crosslinking agent
In the same manner as in Comparative Example 1 except that the cold storage agent (I
X) got.

Example 7 After bending each of the cold accumulating agents obtained in Examples 1 to 5 and Comparative Examples 1 to 30 at the center in the longitudinal direction, the presence or absence of cracks and the state of retaining the shape were examined, and the durability of the cold accumulating agent and The shape retention was evaluated. The results are shown in Table 1.

From Table 1, it can be seen that the cool storage agent of the present invention is excellent in durability and shape retention.

Example 8 Styrofoam insulation case (outer dimension: 330 mm x 260 mm)
X170mm, inside dimension 290mmx220mmx125mm) and 4 pieces of ham (750g) at 5 ℃ as food to be kept in advance-
Ten cool storage agents (I) frozen at 5 ° C. were put into the storage tanks, and changes in temperature with time were measured to evaluate the performance as the cool storage agents.

For comparison, the same operation was performed using the cold storage agent (VI),
The performance as a cold storage agent was evaluated.

The results are shown in Table 2.

From Table 2, it can be seen that the examples of the present invention have the same cold storage capacity as compared with the ordinary cold storage agent.

Claims (1)

[Claims] 1. A porous base material is coated or impregnated with an aqueous solution containing a carboxylic acid polymer and a cross-linking agent, heat-treated and dried to adhere a polycarboxylic acid resin, and then the resin is allowed to absorb water. A cold storage agent made by forming a water-containing gel.