JPS6017378B2 - Method for improving transparency of saponified ethylene-vinyl acetate copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ethylene-vinyl acetate copolymer (hereinafter referred to as EVA
This paper relates to a method for improving the transparency of saponified products.

More specifically, the present invention relates to a method of providing a saponified EVA product with good transparency by contacting the saponified EVA product with a solution containing sulfuric acid.

Saponified EVA has superior properties such as thermal stability, mechanical strength, and solvent resistance compared to EVA, which is its raw material, and is prized in various fields.

In addition, a wide range of performance can be obtained by selecting the type of EVA that is the raw material for saponified EVA and the saponified material.
It has diversity. On the other hand, when the degree of saponification of EVA saponified products is relatively high, transparency becomes poor when used as a film or molded product, and its uses are limited.
There is a strong desire to improve the transparency of highly saponified VA products.

It is generally said that this decrease in transparency of highly saponified EVA is caused by increased crystallinity, and was thought to be somewhat fateful.

However, the present inventors have continued to study the improvement of the transparency of saponified EVA from various angles;
Surprisingly, it was discovered that this object could be achieved by a simple treatment of contacting a saponified EVA product with a solution containing sulfuric acid, leading to the present invention.

The present invention will be specifically explained below.

The saponified EVA used in the present invention is one manufactured by a known method.

That is, after forming a homogeneous system in a good solvent for EVA such as benzene or toluene, or as a heterogeneous system in a poor solvent for EVA such as methanol or ethanol, or heating the EVA without a solvent. A saponified EVA product obtained by subsequently adding an alkali catalyst such as sodium hydroxide or sodium methoxide can be used.

In addition, as EVA saponified product, ethylene units are 50 to 9.
Highly saponified compositions ranging from 0 to 35% by weight of pinyl acetate units and from 7 to 5% by weight of vinyl alcohol units are used.

In the present invention, the sulfuric acid solution with which the saponified EVA is contacted contains 0.5 to 5% by weight of sulfuric acid and has 1 to 4 carbon atoms.
or a mixed solution of a lower alcohol having 1 to 4 carbon atoms and water (alcohol/water,
~2/8 (weight ratio)) is used.

In addition, the amount used is 100~
50% by weight is practically preferred. The temperature and time when the sulfuric acid solution is brought into contact with the saponified EVA of the present invention are not particularly limited, but from a practical standpoint, the temperature range is from 10°C to 80°C,
Times ranging from 4 to 12 hours are preferred. The method of the present invention can be applied to already commercialized EVA saponified powder, pellets, films, molded products, etc.

Furthermore, it can be incorporated into the manufacturing process of EVA saponified products, for example, in the cleaning process, and is an extremely practical method for improving the transparency of EVA saponified products. The remarkable improvement in transparency of saponified EVA according to the present invention by a sulfuric acid solution is unique, as it is not observed by contact with methanol or with a hydrochloric acid solution of methanol, as will be clearly shown in the examples below.

The reason for this improvement in transparency is not clear, but the degree of saponification did not change due to contact with the sulfuric acid solution, and the presence of sulfur was not observed in the saponified product after contact, so the possibility of a chemical change is unlikely. Rather, it is surmised that this is due to some kind of physical change that subtly affects optical aspects in particular.

In addition, the EVA saponified product with good transparency obtained by the present invention can be applied not only to the uses of conventional EVA saponified products but also to uses that require further transparency. Examples are given below to demonstrate the effectiveness of the present invention, but the scope of the present invention is not limited thereby.

Example 1 A saponification degree of 8 was produced by an alkaline saponification reaction of EVA with an ethylene content of 7% by weight and a vinyl acetate content of 2% by weight.
10 pieces of 5 mol % saponified powdered EVA were placed in a 500 mm glass reaction vessel with a 5 mol % layer, and an ethanol solution containing sulfuric acid was added thereto for 4 hours at 80°C.

Subsequently, the saponified EVA product was filtered out, washed with methanol, and then dried at 60°C under reduced pressure for two hours. Obtained EV
The transparency of the saponified product A was determined by ASTM
-1003-52. The measured light transmittance was 90%, which shows a significant improvement in transparency compared to the light transmittance of the saponified EVA material before treatment (79%) measured under the same conditions. The degree of saponification of the saponified EVA product after the treatment was the same as that of the saponified EVA product before the treatment, and the presence of sulfur due to sulfuric acid was not observed in the saponified EVA product after the treatment. Comparative Example 1 All experiments were carried out under the same conditions as in Example 1 except that sulfuric acid was not used.

The light transmittance of the final saponified EVA was 79%, which was the same as that of the starting saponified EVA. Comparative example
2 All experiments were carried out under the same conditions as in Example 1 except that hydrochloric acid was used instead of sulfuric acid.

The light transmittance of the final saponified EVA product was 81%, which was not significantly different from the light transmittance of the starting saponified EVA product. Note that the difference in light transmittance between Examples and Comparative Examples is not due to the difference in residual sodium acetate, which is one factor that deteriorates transparency.

Example 2 All experiments were carried out under the same conditions as in Example 1 except that the amount of sulfuric acid added was changed.

The light transmittance of the final saponified EVA product was 90%, and a saponified EVA product with good transparency was obtained. Example 3 A saponified powdered EVA with a total saponification degree of mol % produced by an alkaline saponification reaction of EVA with an ethylene content of 7 a weight % and a vinyl acetate content of 2 crane weight % was added to a glass with a fly dressing layer. The mixture was charged into a reaction vessel, and 30 methanol solution containing sulfuric acid was added thereto, and the mixture was heated at 50°C for 6 hours.

Subsequently, the saponified EVA product is filtered out, washed with methanol, and then dried at 60 qo under reduced pressure for 2 hours.

The light transmittance of the obtained saponified EVA was 91%,
A significant improvement in transparency can be seen compared to the light transmittance of the saponified EVA material before treatment, which was 81%. Comparative Example 3 All experiments were carried out under the same conditions as in Example 3 except that sulfuric acid was not used.

The light transmittance of the final saponified EVA was 81%, which was the same as that of the starting saponified EVA. Comparative example
4 All experiments were carried out under the same conditions as in Example 3 except that hydrochloric acid was used instead of sulfuric acid.

The light transmittance of the final saponified EVA product was 83%, which was not significantly different from the light transmittance of the starting saponified EVA product. Example 4 All experiments were carried out under the same conditions as in Example 3 except that the treatment temperature was set to room temperature and the treatment time was changed to 1 hour.

The final saponified EVA had a light transmittance of 91%, and a saponified EVA with good transparency was obtained. Example 5 In Example 3, the methanol solution was mixed with water and methanol (1
All experiments were conducted under the same conditions except that a mixed solution of /1) (weight ratio) was used.

The final saponified EVA had a light transmittance of 91%, and a saponified EVA with good transparency was obtained.

Claims (1)

[Claims] 1. Saponified ethylene-vinyl acetate copolymer is dissolved in sulfuric acid with 0.0% sulfuric acid.
Ethylene, which is characterized in that it is brought into contact with a solution of a lower alcohol having 1 to 4 carbon atoms or a mixture of a lower alcohol having 1 to 4 carbon atoms and water containing 5 to 5% by weight.
Method for improving transparency of saponified vinyl acetate copolymer. 2. The saponified ethylene-vinyl acetate copolymer has a composition of 50 to 90% by weight of ethylene units, 0 to 35% by weight of vinyl acetate units, and 7 to 50% by weight of vinyl alcohol units. Method. 3. The method according to claim 1 or 2, in which the solution containing sulfuric acid is used in an amount of 100 to 500% by weight based on the saponified ethylene-vinyl acetate copolymer. 4. The method according to claim 1, 2 or 3, wherein the saponified ethylene-vinyl acetate copolymer containing sulfuric acid is brought into contact at a temperature of 10 to 80°C.