JPS63122778A - Aqueous gel for cold insulation - Google Patents

Abstract

PURPOSE:To obtain the titled gel having shelf stability, not releasing water even by repetition of freezing and thawing, by producing aqueous gel obtained by reacting a mixture of PVA, an organic acid, glutardialdehyde, a melting point lowering agent and water in a specific ratio, as a main agent. CONSTITUTION:The aimed gel consisting of (A) 3-20wt% PVA (preferably one having high polymerization degree and saponification degree and concentration of aqueous solution of PVA is preferably 10-50wt%), (B) 0.5-5.0wt% organic acid (e.g. acetic acid, citric acid, etc.), (C) 0.01-0.5wt% glutardialdehyde shown by the formula OHCCH2CH2CH2CHO, (D) 0-20wt% melting point lowering agent (e.g. polyhydric alcohol such as propylene glycol, etc.) and (E) the rest of water.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aqueous cold gel that is pre-cooled to a low temperature and used to cool objects or the human body when necessary. This relates to an aqueous gel for cold storage that does not release water even after repeated use.

[Prior art and its disadvantages] Ice packs that are sol-like or liquid-like at low or normal temperatures are
If a bag or container is damaged during storage or use, the contents will flow out and wet or stain the surrounding area, so ice packs that are gel-like at room temperature are preferred, and polyvinyl alcohol-based water-based gels are preferred from the standpoint of safety and toxicity. Attention has been paid.

It is known that polyvinyl alcohol can be turned into an aqueous gel by a gelling agent such as phenol, naphthol, Congo red, pyrogallol, boric acid, or metal salts.

However, when such a strong gelling agent is used, the gelation reaction occurs rapidly, so a gel is formed partially, making it difficult to obtain a uniform aqueous gel, and a gel containing air bubbles is likely to be formed. It's difficult to get rid of that air. Furthermore, if the obtained gel is stored for a long period of time or repeatedly frozen and thawed, there is a drawback that the gel contracts and syneresis occurs.

In addition, formaldehyde is used as a gentle gelling agent.
Aldehydes such as acetaldehyde and glyoxal are known, but gelation takes a very long time and is not practical. In order to achieve gelation within a practical time using this method, additional heating and cooling steps must be added.

Moreover, the temperature conditions for heating are difficult; at high temperatures, partial gels are formed and it takes a long time to change the aqueous gel uniformly at low temperatures.

Instead of heating and cooling, there is a method of adding inorganic acids such as sulfuric acid, hydrochloric acid, or nitric acid to make it strongly acidic, but since the strong acid remains even after gelation, if the container is damaged and the gel is exposed, food may be damaged. This is not desirable as there is a risk of harm due to contact with the human body.

It is also known that a gel can be formed by leaving an aqueous solution of polyvinyl alcohol with a high degree of saponification at a low temperature of -20° C. and freezing it. In this case, in order to obtain a strong gel, it is necessary to freeze at a low temperature for a long time or to repeat several cycles of freezing and thawing, making the manufacturing process extremely complicated. Furthermore, this gel has the disadvantage that if it is left at room temperature or higher for a long period of time, the gel becomes soft and turns into a sol.

To prevent this, a method of vacuum dehydrating the frozen gel has been considered, but the process becomes even more complicated. Another drawback of this method is that it cannot be gelled after being packed into bags.

[Means for Solving the Problems] The present inventors have conducted various studies in order to solve these problems. In other words, as mentioned above, in order to uniformly gel an aqueous polyvinyl alcohol solution at room temperature within an appropriate time using aldehydes, which are gentle gelling agents, it is necessary to make the polyvinyl alcohol solution highly acidic. Therefore, in order to avoid this, organic acids that are harmless to the human body and food were used, but formaldehyde, acetaldehyde, and glyoxal all had slow gelation reactions and were not practical.

Further research revealed that only glutardialdehyde, when used in combination with an organic acid, can produce a homogeneous polyvinyl alcohol aqueous gel at room temperature within a reasonable amount of time, and that the gel has good storage stability and can be frozen and thawed. They discovered that water separation does not occur even after repeated steps, and completed the present invention.

That is, the present invention comprises 3 to 20% by weight of polyvinyl alcohol, 0.5 to 5.0% by weight of an organic acid, 0.01 to 0.5% by weight of glutardialdehyde, and 0 to 20% by weight of a melting point depressant.
This is an aqueous gel for cold preservation whose main ingredient is an aqueous gel obtained by reacting a mixture consisting of % by weight and the balance water.

According to the present invention, the viscosity of the mixture before gelation is set to 100 to 1
It can be adjusted within a range of about 0,000 eP (25°C), and the gelation time at room temperature is about 30 minutes to about 24 minutes.
Since it can be adjusted within a time range, it can be changed depending on the work method and work process.

A stable homogeneous gel with good dimensional stability can be obtained very easily by simply filling the above mixture into a predetermined container or bag and leaving it at room temperature.

The resulting aqueous gel has sufficient strength to withstand deformation and does not soften even at high temperatures.

In addition, it has gel properties that are extremely suitable as a cold storage agent, such as no shape change or syneresis due to long-term storage, and no shrinkage or syneresis due to repeated freezing and thawing.

The degree of polymerization and degree of saponification of the polyvinyl alcohol used in the present invention are not particularly defined, but the higher the degree, the better. The concentration of the polyvinyl alcohol aqueous solution used for the gelling reaction varies depending on the degree of polymerization and saponification, but is suitably 10 to 5.96°.

The blending ratio also varies widely, ranging from 3 to 20% by weight in the aqueous gel.
is appropriate. If it is less than 3% by weight, the aqueous gel will have sufficient strength. If it exceeds 20% by weight, the viscosity will not only increase and workability will deteriorate, but the amount of water will decrease, resulting in poor cooling effect. do not have.

Examples of organic acids used in the present invention include acetic acid, propionic acid, oxalic acid, maleic acid, succinic acid, malic acid, citric acid,
These include tartaric acid and ascorbic acid.

The appropriate blending ratio is 0.5 to 5.0% by weight in the aqueous gel; if it is less than 0.5% by weight, the gelation time will be long and it is not practical, and if it exceeds 5.0% by weight, it will rapidly Because it gels, it not only becomes difficult to work with, but also makes it difficult to change the gel uniformly.

Glutaric dialdehyde is an aldehyde with the structural formula shown below.

0HCC) I2CII2 Ct12CHO This aldehyde alone, together with the organic acids mentioned above, acts as a suitable gelling agent for polyvinyl alcohol. Other aldehydes cannot gel an aqueous polyvinyl alcohol solution within a practical time even when used in combination with an organic acid.

The amount of glutardialdehyde used in the aqueous gel is 0.01~
0.5% by weight is appropriate; if it is less than 0.01% by weight, the strength of the gel will be insufficient, and if it exceeds 0.5% by weight, shrinkage of the gel and syneresis will easily occur.

Therefore, in this gelation reaction, a homogeneous aqueous gel suitable for cold storage gel can be obtained within a practical gelation time only in the presence of both an organic acid and glutardialdehyde; The reaction is extremely slow and is not practical at all.

When a combination of glutardialdehyde and a strong acid is used, gelation proceeds rapidly, a uniform aqueous gel cannot be obtained, and the strong acid remains, which has an adverse effect. Of course, the combination of an aldehyde other than glutardialdehyde, such as formaldehyde, acetaldehyde, glyoxal, etc., with an organic acid requires an extremely long gelation time and is not practical, as described above.

The purpose of using a melting point depressant in the present invention is to adjust the freezing temperature of the aqueous gel, and polyhydric alcohols and/or salts are used. The more it is used, the lower the freezing temperature will be.

The polyhydric alcohols used include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and glycerin, and the effect of lowering the freezing temperature differs depending on the type. In addition, the salts used include Na(J, NH4Cal,
Examples include salts such as NH4NO3 and CaCj2.

If the amount used is too large, the water content will decrease and the cooling effect will be reduced, so it is preferable to limit the amount to about 20% by weight at most.

If desired, a deodorant, a preservative, an anti-pepper agent, a coloring agent, a fragrance, a filler, and the like can be appropriately mixed into the aqueous gel for cold preservation of the present invention.

[Example] Next, the present invention will be explained with reference to Examples and Comparative Examples.

Example 1 Polyvinyl alcohol with a degree of polymerization of 1,700 and a degree of saponification of 88 mol% 9.75 parts by weight Citric acid 1.25 parts by weight Glutaric dialdehyde 0.10 parts by weight Water
An aqueous gel for cold storage obtained by reacting a mixture consisting of 88.90 parts by weight.

This product was manufactured as follows.

2.5 f of a 50% aqueous solution of citric acid was added to 65 parts by weight of an aqueous solution in which 15 parts by weight of polyvinyl alcohol with a degree of polymerization of 1,700 and a degree of saponification of 88 mol% was completely dissolved in 85 parts by weight of water.
r parts and 31.5 parts of water were added and stirred, and then, while stirring, 1 part by weight of a 10% aqueous glutardialdehyde solution was added and mixed.

This mixture exhibited a viscosity of 1,500 cP at 25°C.

When this mixed solution was poured into a predetermined container and left to stand at room temperature, a strong, transparent, and uniform cooling gel was transformed in about 3 hours.

Example 2 Polyvinyl alcohol with a degree of polymerization of 1,400 and a degree of saponification of 99 mol% 7 parts by weight of succinic acid
1.5 parts by weight Glutaric dialdehyde 0.1 ffif 1 part Propylene glycol 10 parts by weight Water
An aqueous gel for cold storage obtained by reacting a mixture consisting of 81.4 parts by weight.

This product was manufactured as follows.

10 parts by weight of propylene glycol, 3 parts by weight of a 50% aqueous succinic acid solution, and water were added to 70 parts by weight of an aqueous solution in which parts by weight of polyvinyl alcohol IO having a degree of polymerization of 1,400 and a degree of saponification of 99 moles and 96 moles were completely dissolved in 90 parts by weight of water. 16 parts by weight were added and stirred, and then 1 part by weight of a 10% aqueous glutardialdehyde solution was added and mixed while stirring.

This liquid mixture exhibited a viscosity of 500 cP at 25°C.

When this mixed solution was poured into a predetermined container and left to stand at room temperature, a strong, transparent, and uniform cooling gel was transformed in about 5 hours.

Comparative Example 1 In Example 1, when 1.25 parts by weight of water was substituted for 1.25 parts by weight of citric acid, no reaction occurred and no gel was obtained even after being left at room temperature for 48 hours.

The manufacturing method was the same as in Example 1.

Further, the viscosity of the mixture was 1.400 cP at 25°C.

Comparative Example 2 In Example 1, when 0.10 parts by weight of water was substituted for 0.10 parts by weight of glutardialdehyde, no reaction occurred and no gel was obtained even after being left at room temperature for 48 hours.

The manufacturing method was the same as in Example 1.

Further, the viscosity of the mixture was 1,500 cP at 25°C.

Comparative Example 3 In Example 1, when 0.10 parts by weight of glyoxal was substituted for 0.10 parts by weight of glutardialdehyde, no reaction occurred and no gel was obtained even after being left at room temperature for 48 hours.

The manufacturing method was the same as in Example 1.

The viscosity of the mixture was 1,500 cP at 25°C.

Comparative Example 4 In the production method of Example 1, 50% citric acid aqueous solution 2
．． When 1 part by weight of a 10% glutardialdehyde aqueous solution was added under stirring in the same manner except that 2.5 parts by weight of 50% sulfuric acid was substituted for 5 parts by weight, rapid gelation occurred in some parts and the mixture was uniform. I couldn't change the gel.

Comparative Example 5 (Example using boric acid) Polyvinyl alcohol with a degree of polymerization of 1,400 and a degree of saponification of 99 mol%. 7 parts by weight of boric acid.
2 parts by weight Sodium hydroxide 0.2 parts by weight Propylene glycol
1 Offi parts water
An aqueous gel for cold storage obtained by reacting a mixture consisting of 80.8 parts by weight.

This product was manufactured as follows.

In the production method of Example 2, instead of 3 parts by weight of 50% succinic acid aqueous solution, 16 parts by weight of water, and 1 part by weight of glutardialdehyde, 2 parts by weight of boric acid and 0.2 parts by weight of sodium hydroxide were added to 17.8 parts by weight of water. At room temperature, 20 parts by weight of the aqueous solution dissolved in 50% of polyvinyl alcohol were added to a mixed solution of 70 parts by weight of a 10% aqueous solution of polyvinyl alcohol with a degree of polymerization of 1.400 and a degree of saponification of 99 mol% and 10 parts by weight of propylene glycol in a predetermined container. The mixture was quickly stirred and left to stand. Immediately after mixing, gelation occurred, resulting in a partially solidified aqueous gel. The gel became somewhat homogeneous by being left at room temperature for one day, but air bubbles mixed in during gelation remained as they were.

Comparative Example 6 (Example of aqueous gel other than polyvinyl alcohol) An aqueous gel was produced according to Example 1 of JP-A-55-184278.

That is, 10 parts by weight of propylene glycol was added to 5 parts by weight of guar gum, and after wetting, 80 parts by weight of water was added.
Mixing was continued for about 10 minutes using a kneader to prepare a colloidal water dispersion of guar gum. On the other hand, after dispersing 2 parts by weight of corn starch in 10 parts by weight of water, approximately 80 parts by weight of corn starch was dispersed in 10 parts by weight of water.
℃ to prepare an aqueous dispersion of pregelatinized starch. The aqueous dispersion of pregelatinized starch thus prepared was added to the above aqueous dispersion of guar gum, stirred and mixed in a kneader until a homogeneous state was obtained, and then 0.15 parts by weight of boric acid was added. An aqueous solution obtained by dissolving the above in 10 parts by weight of water was added, and the mixture was stirred and mixed to obtain an aqueous gel.

Comparative Test The aqueous gels of Examples 1 and 2 and Comparative Examples 5 and 6 were subjected to comparative tests on gel appearance, shape retention, storage stability, freezing temperature, freeze-thaw stability, and cold storage time.

The results were as shown in Table 1.

Test method (1) Preparation of samples The gels of Examples and Comparative Examples were heated vertically at 20 On+m.
A polyethylene container with a width of 1.5001111 was filled with 500 g of gel to form a gel, thereby producing a plate-shaped cold gel with a thickness of approximately 17 mm, and was used for testing.

(2. Gel Shape Retention A plate-shaped gel sample was stood vertically and left at room temperature for 7 days, and the fluidity of the gel was observed.

○: No fluidity Δ: Slight flow ×: Flows and collects at the bottom (3) Stability of gel on storage The sample was left at 70° C. for 7 days, and the water separation rate was measured when the sample was returned to room temperature.

080 to 0.5% Q: 0.5 to 5% 625 to 10% The water separation rate was measured after repeating 10 cycles as one cycle.

010-0.5% 0: 0.5-5% 625-10% The time required for the surface temperature to reach 10°C was measured.

Claims (1)

[Claims] 1 3-20% by weight of polyvinyl alcohol and 0% organic acid
．． 5-5.0% by weight and 0.01 glutardialdehyde
-0.5% by weight, 0-20% by weight of a melting point depressant, and the balance water.