JPH0623400B2 - Reinforced hydrogel and cold storage agent using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a hydrogel having excellent shape-retaining property and a cold storage agent using the same, and more specifically, a carboxylic acid polymer reinforced with a porous substrate. And a cold storage agent using the same.

(Prior Art) Hydrous gel is used as a material suitable for various applications such as a cold storage agent, a heat insulating material, a fragrance, and a cushioning material, and in particular, it has been expected in recent years as a cold storage agent.

The regenerator is widely used in the food field and the like from the viewpoints of product temperature management and energy saving, because the temperature can be arbitrarily set by the regenerator and can be reused. Conventionally, thixotropic viscous water-containing gel, which is a mixture of natural gum and a storage medium, enclosed in a bag-shaped container has been used as a regenerator, but these do not completely prevent leakage of contents. However, since it is a viscous material, it has a problem that it is solidified and deformed when it is cooled, resulting in poor shape retention.

Also, as conventional hydrous gel, natural gum, agar,
Most of them were made from gelatin as a raw material, but in recent years, synthetic polymer materials have been attracting attention from the viewpoints of rot resistance and durability. As such a synthetic polymer material, a hydrogel obtained by cross-linking a polycarboxylic acid-based water-soluble polymer such as polyacrylic acid, for example, polyacrylic acid and a salt thereof is used as a polyvalent metal such as magnesium chloride or calcium chloride. Hydrous gels obtained by ionic crosslinking using salts, hydrous gels obtained by crosslinking polyacrylic acid or maleic acid polymers with a crosslinking agent such as polyvalent epoxy compounds or polyvalent amines, etc. have been developed (for example, JP-B-57-28505, JP-A-57-14679
No.).

When the water-containing gel obtained by such a method is used as a regenerator, it is superior in terms of moldability as compared with a natural water-containing gel, but the shape retention strength of the gel is not yet sufficient and the shape changes due to external force. However, there is a problem that the gel breaks and loses its shape retention property.

(Problems to be solved by the invention) Therefore, as a result of intensive studies to solve the above-mentioned drawbacks, the present inventors have obtained a hydrogel excellent in shape retention and durability when a porous substrate is used as a reinforcing material. However, they have found that the hydrous gel has excellent performance as a cold storage agent, and have completed the present invention based on this finding.

(Means for Solving Problems) Thus, according to the present invention, as the first invention, a porous substrate is coated or impregnated with an aqueous solution containing a carboxylic acid polymer and a crosslinking agent, and then a crosslinking reaction is performed. A hydrogel reinforced with a porous substrate obtained as described above is obtained by applying or impregnating an aqueous solution containing a carboxylic acid polymer and a cross-linking agent on a porous substrate as a second invention and then performing a cross-linking reaction. There is provided a regenerator composed of a hydrous gel reinforced with a porous substrate.

The carboxylic acid-based polymer used in the present invention is a polymer of an α, β-unsaturated carboxylic acid monomer, a copolymer with an ethylenically unsaturated monomer copolymerizable with the α, β-unsaturated carboxylic acid monomer, or a salt thereof, which is water-soluble. It is a thing. Such polymers usually have a number average molecular weight of 1,000 to 1,000,000, preferably 2,000 to 5
Have 0 million.

The ratio of the α, β unsaturated carboxylic acid monomer in the polymer can be appropriately selected, but is usually 10 mol% or more, preferably 2 mol% or more.
It is 0 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, and maleic acid. , 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 Methyl acid, vinyl acetate,
Examples thereof include polar or non-polar vinyl monomers such as acrylic acid, 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 kinds.

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.

An aqueous solution of these copolymer salts can be obtained by synthesizing the copolymer and then performing 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 shape-retaining hydrogel is a compound capable of reacting with two or more carboxyl groups, and specific examples thereof include:
Calcium, barium, polyvalent metals such as aluminum, glycerin diglycidyl ether, ethylene glycol glycidyl ether, polyvalent epoxy compounds such as polyethylene glycol diglycidyl ether, polyethyleneimine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, penta Examples thereof include polyamines such as ethylene hexamine.

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 is usually 3 to 50 mol% of the cross-linking agent based on the carboxyl groups in the polymer salt, preferably Is 5 to 30 mol%. When the amount of the cross-linking agent is small, a water-containing gel having a shape-retaining property cannot be obtained. On the contrary, when the amount of the cross-linking agent is large, the unreacted part of the cross-linking agent may remain, resulting in poor economy.

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 fabric made of paper, natural fiber, chemical fiber, synthetic fiber, or the like, or natural foam having open cells, or synthetic foam typified by polyurethane foam.

The reinforced hydrous gel of the present invention is prepared by uniformly mixing the carboxylic acid polymer and the cross-linking agent in the presence of water, and then coating or impregnating the porous substrate with an appropriate amount at a temperature of 5 to 100 ° C, preferably 10 to 80 ° C. It is obtained by crosslinking. The water content of the crosslinked product may be appropriately selected depending on the performance required of the target product, but is usually 60 to 99.5% by weight, preferably 7% in the reaction mixture.
It is 0 to 98% by weight.

In the present invention, the cooling temperature of the resulting hydrogel can be set by adding an appropriate amount of various additives to water according to the purpose of the hydrogel when producing the hydrogel. 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. For example sodium chloride,
Examples thereof include 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. Also,
The ingredients of the poultice such as menthol, the colorant and the like can be appropriately dissolved or dispersed in water depending on the purpose of use of the hydrous gel.

(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. This water-containing gel is particularly excellent in performance as a cold storage agent,
It can also be effectively used as a heat insulating material, a fragrance material, a cushioning material and the like.

(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 an 8% 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 Co., Ltd.). 73 parts of 8% aqueous solution of Eporite 400E manufactured by Co., Ltd. was added and mixed uniformly, and 60 g of the solution was put into a polyethylene bag (10 cm) into which a urethane foam sheet (9.5 cm × 6.5 cm × 1.0 cm) was previously inserted. (7 cm), and the urethane foam sheet was sufficiently impregnated. Next, remove air bubbles, seal the water to prevent evaporation, and place in a water bath at 60 ° C for 2 minutes.
The mixture was heated for a period of time to carry out a crosslinking reaction to obtain a reinforced hydrous gel (I).

Example 2 A reinforced hydrogel was prepared in the same manner as in Example 1 except that 216 parts of an 8% aqueous solution of the copolymer salt used in Example 1 and 9.9 parts of an 8% tetraethylenepentamine aqueous solution were used. I
I) got.

Example 3 Implemented except that 144 parts of an 8% aqueous solution of ethylene-maleic anhydride copolymer (molecular weight 100,000) sodium salt (neutralization degree 0.7) and 81 parts of an 8% polyethylene glycol diglycidyl ether aqueous solution were used. The same operation as in Example 1 was carried out to obtain a reinforced hydrous gel (III).

Example 4 Acrylic acid polymer (A710, manufactured by Toagosei Kagaku Co., Ltd.)
0) A reinforced hydrous gel (IV) was obtained in the same manner as in Example 1 except that 144 parts of an 8% aqueous solution of sodium salt and 81 parts of an 8% aqueous solution of polyethylene glycol diglycidyl ether were used.

Example 5 60 g of a uniform solution of the copolymer salt used in Example 1 and the crosslinking agent
Cellulosic nonwoven fabric (9.5 cm x 6.5 cm x 0.2 c
m) Three pieces were applied and inserted into a polyethylene bag (10 cm x 7 cm). Next, Example 1 is sealed so that water does not evaporate.
A cross-linking reaction was carried out in the same manner as above to obtain a reinforced hydrogel (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 a crosslinking reaction was carried out in the same manner as in Example 1 to obtain a hydrogel (VI).

Comparative Example 2 60 g of a uniform solution of the copolymer salt used in Example 2 and the crosslinking agent
A hydrogel (VII) was obtained in the same manner as in Comparative Example 1 except that was used.

Comparative Example 3 60 g of a uniform solution of the copolymer salt and the crosslinking agent used in Example 3
A hydrogel (VIII) was obtained in the same manner as in Comparative Example 1 except that

Comparative Example 4 60 g of a uniform solution of the copolymer salt used in Example 4 and the crosslinking agent
A hydrous gel (IX) was obtained in the same manner as in Comparative Example 1 except that was used.

Example 7 After bending each hydrous gel 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 hydrous gel and The shape retention was evaluated. The results are shown in Table 1.

From Table 1, it can be seen that the hydrogel 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 pieces of the reinforced hydrous gel (I) frozen at 5 ° C. were put, the time-dependent change in temperature was measured, and 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 are excellent as a cold storage agent.

Claims (2)

[Claims] 1. A hydrogel reinforced with a porous base material obtained by coating or impregnating an aqueous solution containing a carboxylic acid polymer and a crosslinking agent on the porous base material, and then carrying out a crosslinking reaction. 2. A hydrogel reinforced with a porous base material obtained by applying or impregnating an aqueous solution containing a carboxylic acid polymer and a cross-linking agent on the porous base material, followed by a crosslinking reaction. Cold storage agent.