JPH02180988A - Low-temperature insulant - Google Patents

Abstract

PURPOSE:To prepare a low-temperature insulant which is unflowable, nonsticky, stable and hardly perishable, which does not flow out from a broken bag and does not stick to food through into contact with it, and which comprises a hydrogel of a polyvalent metal salt of carboxymethylcellulose. CONSTITUTION:A low-temperature insulant comprising a hydrogel of a polyva lent metal salt of carboxymethylcellulose obtd. by gelling sodium carboxymethylcellulose with a polyvalent metal ion. Said hydrogel, contg. neither protein nor fat, is hardly perishable and hardly flowable because it has a strong three-dimensional structure as a result of the ion reaction, so that it can provide a stable low-temperature insulant which does not exhibit a remarkably viscosity decrease or syneresis, both usually caused by the disappearance of crosslinkage upon irradiation with light. As it is prepd. at a concn. of 1.5-5% which is lower than the value (4-15%) required in preparing an insulant from other water-sol. polymers, it can utilize a large amt. of heat of melting of water to the max. and thus can keep its cooling effect for a long time.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a cold pack that is used for the purpose of keeping fresh foods such as seafood, ham, vegetables, juice, wine, blood, etc. fresh and cold during distribution. It is related to.

(Prior Art) Traditionally, seafood has been distributed in boxes with ice. However, since ice is melted water, its cooling time is short, and there is a point U when the melted water comes into contact with foods and stains them, or leaks to the outside.

In order to compensate for these drawbacks, in recent years, polyethylene bags or plastic containers filled with a liquid or gel-like material and frozen have come into widespread use as ice packs.

Among these, gel-like products are mainly used for those filled with liquid because there is a risk that the contents may leak out if the bag breaks and contaminate food products.

Gel compositions to be filled into cold bags or plastic containers include guar gum, polyvinyl alcohol, sodium polyacrylate, polyacrylamide, sodium carboxymethyl cellulose, sodium alginate, starch, starch graft-polymerized with acrylic acid or acrylamide, etc. High viscosity aqueous solutions of water-soluble polymers, or hydrogels obtained by crosslinking these water-soluble polymers with inorganic salts such as borates or organic crosslinking agents are used.

However, a high viscosity aqueous solution of a water-soluble polymer has the disadvantage that it gradually flows out when a cold bag ruptures or a plastic container is damaged, and since it is sticky, it adheres to foods and stains them.

On the other hand, guar gum and polyvinyl alcohol formed into precious wood with borate and gelled do not have stickiness but still have fluidity. Therefore, the contents may leak out if the bag breaks, or even if the bag does not break, the contents may flow and change shape, so it may be frozen in an irregular shape, making it impossible to pack it inside insulation material. It had the following drawbacks.

Furthermore, guar gum contains proteins, fats, etc., and serves as a nutritional source for microorganisms, so it also has disadvantages such as being susceptible to spoilage during preparation or distribution.

In addition, crosslinked products of polyvinyl alcohol, sodium polyacrylate, polyacrylamide, and crosslinked products made by graft polymerizing acrylonitrile or acrylic acid to starch have no stickiness and have little fluidity, but they can be filled into bags etc. It is easily broken by touching it with your hands or due to vibrations during transportation, and if a gel-like material sealed in a bag is exposed to sunlight, the crosslinks will come off and the viscosity will become significantly lower.
There is a drawback that the liquid substance separates from the gel-like substance. Furthermore, there is a risk that the liquid released when the bag is torn may flow out and contaminate food products and the like.

These water-soluble polymers and crosslinked polymers usually have a 4 to
They are used at a concentration of 15%, and their addition in large amounts reduces the latent heat of fusion when used as a cold pack, which also has the disadvantage of shortening the cooling time, which is its original function.

(Problems to be Solved by the Invention) In the present invention, the ice pack has fluidity and adhesiveness, so that even if the bag is torn during distribution, the gel-like substance will not flow out, and even if it comes into contact with food, etc., it will not stick. To provide a cold pack made of a stable gel-like material that does not cause viscosity reduction or syneresis due to decomposition or light, etc. Furthermore, in order to enhance its original cold storage ability, the present invention provides a cold pack that forms a gel-like substance at the lowest possible concentration.

(Means for Solving the Problems) The present invention is a cold pack made of an aqueous gel of carboxymethyl cellulose polyvalent metal salt. That is, it is a cold pack made of an aqueous gel of carboxymethylcellulose polyvalent metal salt, which is made by gelatinizing sodium carboxymethylcellulose with polyvalent metal ions.

Commercially available CMC is used as sodium carboxymethyl cellulose (hereinafter abbreviated as CMC) used in the present invention. The average of that carboxymethyl group! degree of conversion (hereinafter referred to as D
(abbreviated as S) is 0.30 to 2.50, preferably 0.5
0 to 1.50. CMC with a DSffio of 30 or less is difficult to dissolve in water, and a CMC with a DS of 0.50 or more completely dissolves in water to form a gel-like substance with a beautiful appearance. on the other hand,
When CMC with a DS of 2.50 or more is gelled with polyvalent metal ions, intramolecular crosslinking predominates due to the presence of many carboxymethyl groups in the molecule, and gelation due to intermolecular three-dimensional crosslinking occurs. At the beginning, it becomes a weak gel. This tendency is thought to occur even when the DS is 2.50 or less;
．． If it is 50 or less, the object of the present invention can be achieved. However, it is more desirable to set the DSL to 50 or less because a harder gel can be obtained.

In addition, the viscosity of a 1% aqueous solution of CMC (25°C, 60 rpm
) is preferably in the range of 10 to 10,0OOcps, 10
If the concentration is less than cps, the molecular chains are too short to form a three-dimensional structure, and an aqueous gel with the desired hardness cannot be obtained unless the concentration is high.

CMC of 10.000 cps or more has a high viscosity itself, making it difficult to mix uniformly with a crosslinking agent and making it difficult to obtain a uniform aqueous gel. This is because if the concentration is lowered to 1.5% or less, it will be difficult to obtain an aqueous gel with the desired hardness.

The metal salt used as a gelling agent for CMC can be a polyvalent metal salt that forms a three-dimensional crosslinked structure, such as an aluminum compound, iron compound, or chromium compound, but the coloring characteristic of metal salts may be observed. Judging from the economical and other considerations, it is preferable to use an economically available aluminum compound that forms a colorless and transparent gel. Potassium alum, aluminum acetate, aluminum sulfate, aluminum nitrate, etc. can be used as the aluminum compound. .

In addition, when preparing the cold pack composition of the present invention, preservatives, colorants, polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin, and sorbitol, sodium chloride, and potassium chloride for adjusting the freezing temperature (cold storage temperature) are used. The addition of salts such as , sodium nitrate, and sodium sulfate is also included within the scope of the present invention.

It is also possible to use other water-soluble polymers such as guar gum, polyvinyl alcohol, sodium acrylate, etc. in combination with CMC.

(Effect of the invention) These aqueous gels of CMC polyvalent metal salts do not contain substances that cause putrefaction, such as proteins and fats, so they are less likely to putrefy, and they also have a strong three-dimensional structure due to ionic reactions. Therefore, it is possible to form a stable ice pack that has almost no fluidity and does not cause significant viscosity reduction or syneresis due to decrosslinking due to light or the like.

In addition, the aqueous gel of CMC polyvalent metal salt can be prepared at a lower concentration of 1.5-5% than the 4-15% for water-soluble polymers, which maximizes the large heat of fusion of water. It has the feature of being able to keep cold for a long time, which is the most important function as a cold pack. This is because CMC is a rod-shaped polymer, so its molecules spread widely in solution.
This is thought to be because it is easy to form a large three-dimensional structure.

(Example) The present invention will be explained below with reference to Examples. Here, parts indicate parts by weight, and % indicates weight %.

Example I DS0.65.1% aqueous solution 100 parts of CMC having a viscosity of 420 cps as a 3% aqueous solution is charged into a 300 ml beaker. Potassium alum A I K (30
4) Add 10.8 parts of a 5% aqueous solution of 2'12 H20 little by little while stirring, and continue stirring for 1 to 2 minutes. Thereafter, it was immediately filled into a plastic bag and left to stand for 3 to 6 hours to prepare the ice pack. The physical properties of the prepared cold pack are listed in the table.

Comparative Examples 1 to 3 Cold packs were prepared in the same manner as in Example 1 using CMC having different DS and viscosity. The physical properties of the prepared cold pack are listed in the table.

Examples 2 to 6 Cold packs were prepared in the same manner as in Example 1 by changing the DS, viscosity and amount of CMC used, and the amount of potassium alum added. The physical properties of the obtained ice pack are listed in the table.

Comparative examples 5 to 7 The physical properties of a commercially available ice pack are shown as a comparative example.

5 (1) Hardness Cut a gel-like material into 2 cm cubes, place a cylindrical rod with a contact area of 1 - in the center of the gel-like material, and place a predetermined weight on top of the rod. A weight was placed on the gel-like material, and the hardness was measured by the total weight [g] of the cylinder and weight when the cylinder penetrated or broke into the gel-like material.

It seems that the weight of the ice pack should be 30 g/- or more.

(2) 1oot of fluid gel-like material WfOcm, width 9 cm, thickness 0
．． The mixture was filled into a polypropylene bag of 0'l/m, heat-sealed, fixed with a clip on one side of the plastic bag, and hung for 4 hours.

The shape change at this time was evaluated based on the following criteria.

O: No change in shape Δ: Slight change in shape The degree of this was evaluated using the following criteria.

O: Does not adhere to fingers at all Δ: Slightly adheres to fingers ×: Significantly adheres to fingers (4) Cooling time Pack 20 g of gel-like material into a bag made of polypropylene, -2
After leaving it in the freezer at 0℃ for 20 hours and completely freezing, the temperature
Leave it in a thermostat at 5℃, and use a Teflon rod (5LI) from time to time.
Determine the presence or absence of thawing using Ii + diameter) and measure the cold storage time (minutes).

(5) Fill a polypropylene bag with 20g of water-repelling gel and -20g
After repeating freezing for 20 hours at °C and thawing for 4 hours at 25 °C five times, the syneresis state was evaluated according to the following criteria.

○: No syneresis at all Δ: 1 syneresis X: Significant syneresis (6) 20 g of putrid gel-like material was filled into a polypropylene bag, left at room temperature for 30 days, and the presence or absence of putrefaction was confirmed. When rK fails, mold growth and viscosity reduction and syneresis are observed.

O: No rotting X: Rotting observed (7) The photostable gel material was filled into a polypropylene bag and left under sunlight three times for 8 hours. Subsequent state changes were evaluated using the following criteria.

○: No change Δ: Release slightly to make it softer. ×: Significant syneresis and viscosity reduction

Claims (1)

[Claims] A cold pack made from an aqueous gel of carboxymethyl cellulose polyvalent metal salt.