JPH0360532B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object] The present invention relates to a method for producing an aqueous gel that can be produced at room temperature, has good transparency, excellent low and high temperature stability, and does not yellow under alkalinity.

[Prior art and drawbacks]

When a few percent of agar is placed in water, heated and dissolved to form an aqueous solution, and then cooled, it gels into a pudding-like aqueous gel. In addition, gelatin, alginic acid, carrageenan, etc. can be similarly gelatinized to obtain an aqueous gel.

These natural product gels require a step of heating and dissolving. Moreover, there is a drawback that the resulting gel is brittle and soft. Also, transparency is extremely poor. Gelatin also has the disadvantage of producing a glue odor.

Also, when boric acid or borax is added to an aqueous polyvinyl alcohol solution, an aqueous gel is obtained, but it is extremely soft and cannot be water-based if it freezes and thaws, is kept at high temperatures for a long time, or is frozen and then exposed to high temperatures repeatedly. There are drawbacks to doing so. Furthermore, there is a manufacturing disadvantage in that gelation tends to occur locally and it is difficult to obtain a uniform aqueous gel.

In addition, as a solution to the above-mentioned drawbacks, an aqueous solution of an acetoacetylated water-soluble polymer compound has an amine group, an aldehyde group, a hydrazide group,
There are aqueous gels that are crosslinked by adding a crosslinking agent containing functional groups such as epoxy groups and methylol groups, but depending on the type of crosslinking agent, there are some that do not gel at all at pH 9 or higher, and even if the gel Even if it becomes
At pH 9 or above, there were disadvantages such as poor gel stability, water separation over time, and easy yellowing.

Therefore, for example, if such a gel is used as a carrier for the disinfectant chlorine dioxide, the chlorine dioxide needs to be alkaline with a pH of 9 to 10 in order to maintain its stability, which can cause the gel to water apart or turn yellow. A problem arises.

Such yellowing is thought to be due to the gradual yellowing of unreacted amine groups, aldehyde groups, etc. of the crosslinking agent when the pH becomes 9 or higher.

[Means for Solving the Problem] In order to solve the above-mentioned problem, the present inventor earnestly
Conducted research on aqueous gels.

As a result, they discovered that the desired aqueous gel could be obtained by adding a specific crosslinking agent to an aqueous solution of acetoacetylated products of various water-soluble polymer compounds, and completed the present invention.

That is, the present invention provides an aqueous solution of a water-soluble polymer compound containing an acetoacetyl group with the formula: (However, R is H or CH ₃ ) This is a method for producing an aqueous gel characterized by adding a compound containing two or more groups and adjusting the pH of the solution to 9 or higher.

The acetoacetylated water-soluble polymer compound used in the present invention includes polyvinyl alcohol,
Hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, carboxymethylcellulose, or a water-soluble polymer compound such as starch is acetoacetylated.

These can be used alone or in combination.

Taking polyvinyl alcohol as an example, methods for acetoacetylating water-soluble polymer compounds include a method in which polyvinyl alcohol is dispersed in an acetic acid solvent, and diketene represented by the following formula is added thereto. There is a method in which polyvinyl alcohol is dissolved in a solvent such as dimethyl formaldehyde or dioxane in advance and diketene is added thereto, and a method in which polyvinyl alcohol is brought into direct contact with diketene gas or liquid diketene.

The degree of acetoacetylation of the acetoacetylated water-soluble polymer compound is suitably in the range of 1 mol% to 15 mol%, preferably 2 mol% to 12 mol%.

If it is less than 1 mol%, the crosslinking reaction will not proceed easily, making it difficult to obtain an aqueous gel, and if it exceeds 15 mol%,
Depending on the type of water-soluble polymer compound, it may become difficult to dissolve in water, which is undesirable.

Formula used in this invention: (However, R is H or CH ₃ ) Compounds containing two or more groups include diacrylates or dimethacrylates of polyhydric alcohols, such as ethylene glycol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylates, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, bisphenol A diglylyle ether diacrylate, ethoxylated bisphenol A diacrylate, and diacrylates or dimethacrylates of polyester polyols, e.g. It is a product of Toagosei Chemical Industry Co., Ltd., and has trade names such as Aronix-M6100, M6200, M6300, and M6500.

Among these compounds, those that are soluble in water or a water-soluble solvent are preferred, and particularly preferred are polyethylene glycol diacrylate or dimethacrylate in which the molecular weight of polyethylene glycol is 100 to 1000.

Although it is a guess, water-soluble polymer compounds containing acetoacetyl groups and compounds containing two or more CH ₂ =CR-CO-O- groups form a crosslinked structure by the reaction mechanism shown in the following formula, and contain water. to form an aqueous gel.

This reaction does not require any heating and proceeds rapidly at room temperature above pH 9 to produce a transparent aqueous gel. If the pH is less than 9, the reaction at room temperature is extremely slow and is not practical.

The aqueous gel of the present invention may contain a colorant or a colorant depending on the purpose.
Ultraviolet absorbers, antioxidants, antifreeze, water-soluble organic compounds, and the like can be included.

These reactions proceed at room temperature in 2 to 3 seconds, and an aqueous gel is produced. Of course, the type of acetoacetylated polymer compound, the degree of acetoacetylation,
The gelation time can be adjusted by adjusting the type and ratio of crosslinking agent used, the solution concentration of both, pH, etc.

In addition, by mixing a powdered acetoacetylated polymer compound and a powdered crosslinking agent, and adding an appropriate amount of water when necessary and stirring to dissolve,
Aqueous gels can be produced. Also, when either one is an aqueous solution, an aqueous gel can be produced simply by mixing and stirring the two.

According to the production method of the present invention, unlike agar and carrageenan, there is no need for the process of heating and melting and then cooling to gel. By simply stirring and mixing at room temperature, the product can be odorless, tough, and elastic. A transparent aqueous gel can be obtained, and an excellent aqueous gel that does not release water even when frozen and thawed, kept at high temperatures, or repeatedly subjected to high temperatures and freezing can be obtained.

The hardness of the resulting aqueous gel can be varied over a wide range, from fluid and soft to tough and elastic hard, by adjusting the type and proportion of the crosslinking agent, the concentration of both solutions, and pH. can be controlled. Therefore, the aqueous gel produced by the production method of the present invention can be used in a wide range of applications such as buffering materials, excipients, bumping agents, sound insulation materials, heat insulation materials, heat and cold insulation materials, bacterial culture media, and product window samples. Can be used.

〔Example〕

The present invention will be explained by giving Examples and Comparative Examples.

Example 1 To 50 parts by weight of a 10% aqueous solution of acetoacetylated polyvinyl alcohol with a degree of polymerization of 1700 and a degree of acetoacetylation of 6 mol%, 22 parts by weight of water and 10 parts by weight of ethanol were added and stirred. Add 4 parts by weight of polyethylene glycol diacrylate (trade name) manufactured by Synthetic Kagaku Kogyo Co., Ltd. and mix.

The pH at this time was 7. In this state, gelation did not occur even after being left at room temperature for 7 days. Next, about 4 parts by weight of a 1% aqueous sodium hydroxide solution was added to adjust the overall pH to about 10, and the mixture was left to stand at room temperature to obtain a colorless, transparent, elastic aqueous gel.

The gelation time was approximately 40 minutes, and the needle penetration depth into the gel after being left at room temperature for 3 days was 17 mm.

In addition, when this gel was left in a thermostat at 70°C for 72 hours and then placed in a -20°C freezer for 24 hours to undergo a high-temperature freezing cycle 10 times, no syneresis or yellowing was observed. There was no decrease in gel strength.

(Test method) Gelation time At room temperature (25℃), add and mix the crosslinking agent, and after adjusting the pH, the viscosity of the mixed liquid is 500 to 1000 cP using a BL type viscometer.
(the time it takes to reach the area where stirring is not possible).

Penetration depth The penetration depth of the probe into the gel when a static load of 200 g/cm ² is applied to a probe with a diameter of 4 mm.

(3 days after adding crosslinking agent and adjusting the mixing pH) Example 2 40 parts by weight of a 10% aqueous solution of acetoacetylated polyvinyl alcohol with a degree of polymerization of 2600 and a degree of acetoacetylation of 8 mol% was diluted by adding 40 parts by weight of water, and anion 2 parts by weight of surfactant and Aronix
Add 6 parts by weight of a mixture with 4 parts by weight of M6300 (trade name of polyester polyol diacrylate manufactured by Toagosei Chemical Industry Co., Ltd.) and uniformly dissolve. The pH at this time was 6.8.

In this state, gelation did not occur even after being left at room temperature for 7 days. Next, about 4 parts by weight of 2% soda carbonate was added to adjust the overall pH to about 10, and the mixture was left at room temperature to obtain a colorless, transparent, elastic aqueous gel.

The gelation time was approximately 30 minutes, and the penetration depth into the gel after being left at room temperature for 3 days was 11 mm.

Further, when this gel was subjected to high-temperature freezing cycles 10 times in the same manner as in Example 1, no syneresis or yellowing was observed, and there was no decrease in gel strength.

Claims (1)

[Claims] 1. In an aqueous solution of a water-soluble polymer compound containing an acetoacetyl group, the formula: A method for producing an aqueous gel, which comprises adding a compound containing two or more groups represented by R (R is H or CH ₃ ) to adjust the pH of the solution to 9 or higher.