JPS5820971B2 - Water absorbent resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a water-absorbing resin composition, and more specifically, c.
The present invention relates to a water-absorbing resin composition comprising a saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as saponified EVA) and a water-soluble polymer.

With the diversification of uses for plastic materials, it has become necessary to impart hydrophilicity and water absorption properties to thermoplastic resins, which were originally hydrophobic.

Such modification of hydrophobic resins can usually be carried out by the following three methods.

1) Introduction of hydrophilic groups by polymer reaction 2) Mixing of hydrophilic compounds 3) Mixing of hydrophilic polymers Among these methods, method The drawback is that large-scale improvements cannot be expected because it is difficult to introduce in large quantities.

Method 2) is easy to carry out and can be carried out at low cost in some cases, so it is useful when it is desired to improve the hydrophilicity even slightly.

However, mixing hydrophilic compounds with thermoplastic resins generally has drawbacks such as a decrease in mechanical properties.
There are problems with mixing large quantities.

Method 3) also has the same drawbacks as method 2).

Moreover, since hydrophilic polymers are usually not thermoplastic, mixing them with thermoplastic resins results in poor dispersion and often impairs the transparency of the thermoplastic resin.

In this way, thermoplastic resins can be added without sacrificing other properties.
It was not an easy technique to impart hydrophilicity and water absorption properties.

The present inventors had previously researched blends of saponified EVA and water-soluble polymers, and happened to discover that a certain type of EVA
We discovered that when a saponified material is blended with a certain type of water-soluble polymer, they are mixed uniformly without impairing the properties of the original saponified EVA material, and it is also possible to blend a large amount of the water-soluble polymer. .

That is, a water-absorbing resin composition was easily obtained by blending the saponified EVA and the water-soluble polymer.

Moreover, it has been found that the resin composition can also be a good adhesive component for metals and other polymeric materials.

In this way, the resin composition is being used as a composition having both water absorption and adhesive properties in films, molded products, foams, adhesives, etc. However, if it comes into contact with water or is used in water, it may contain moisture. It has been found that the water-soluble polymer contained in the composition may be gradually extracted by water, and the performance of the composition may change over time.

In order to solve these problems, the present inventors conducted extensive research and found that using a combination of polyacrylic acid and polyvinylpyrrolidone as water-soluble polymers has good water absorption and adhesive properties. Moreover, they found that it was not extracted by water.

That is, the present invention relates to a novel composition containing saponified EVA, polyacrylic acid, and polyvinylpyrrolidone as essential components.

The present invention will be explained in detail below.

The saponified EVA according to the present invention is obtained by saponifying EVA containing 80 to 98 moles of ethylene by a known method using an acid or alkali catalyst.

The degree of saponification is preferably 20 degrees or more.

If the degree of saponification is low and the content of hydroxyl groups is too small, it will not be possible to mix uniformly with the water-soluble polymer, resulting in a decrease in transparency and mechanical properties.

The only property required for the polyacrylic acid and polyvinylpyrrolidone used with EVA saponification is that they are soluble in water.

The effects of the present invention can be fully exhibited as long as the molecular weight is about 1000 or more and exhibits a starch syrup-like appearance at room temperature.

The amount of these water-soluble polymers used is 10% of the EVA saponification product.
The range of 2 to 200 parts by weight is preferable for 0 parts by weight.

The ratio of polyacrylic acid to polyvinylpyrrolidone can be varied depending on the purpose as long as it is in the range of 1:10 to 10:1.

The EVA saponification product and the water-soluble polymer are mixed using a known mixing device such as a heating roll or a Banbury.

At this time, it is preferable to supply the high molecular weight water-soluble polymer to the kneading device in the form of an aqueous solution, since uniform mixing can be achieved.

Further, during kneading, it is preferable to add known additives such as antioxidants, heat stabilizers, antistatic agents, lubricants, and processing aids.

The composition obtained by kneading the saponified EVA and the water-soluble polymer as described above can be used in the form of a film or a mold using various known molding machines.

In that case, the skin absorbs moisture or dries depending on the surrounding humidity, but no sweating is observed.

Further, the composition of the present invention can be blended or laminated with other thermoplastic resins and used for the purpose of modifying them.

As described above, the present invention relates to obtaining a water-absorbing composition by kneading with a water-soluble polymer.

However, the effect of the composition of the present invention is not only to provide water absorption, but also to improve the adhesion of saponified EvA as described below.

In other words, the adhesion of saponified EVA to cellulosic substances and metals has been known for a long time, but by blending it with polyacrylic acid or polyvinylpyrrolidone, the adhesion to cellulosic substances and metals is further improved. It is.

As described above, the present invention can further expand the applications of synthetic resins because it easily provides a composition with high water absorption properties, and is therefore considered to be extremely important.

Examples of the present invention will be described below.

Example 1 Melt index (
MI ) is 18. ! 6 kg of 7/10 ethylene-vinyl acetate copolymer, 18 kg of methanol, and 700 g of sodium hydroxide were charged into a 507 reactor, and the 70
The saponification reaction was carried out at °C for 3 hours.

After the reaction was completed, the product was filtered and dried to give 88.6 moles of ethylene, 1.0 moles of vinyl acetate, and 10 moles of vinyl alcohol.
．． 4.9 kg of saponified EVA consisting of 4 moles was obtained.

This saponified EVA 30.9, 160 g of a 30% aqueous solution of polyacrylic acid (manufactured by Wako Tsumugi Pharmaceutical Co., Ltd.), and 22 g of polyvinylpyrrolidone were roll-kneaded at 170° C. for 25 minutes, and after cooling, the mixture was powdered using a pulverizer.

<Measurement of water absorption> Precisely weigh a certain amount of the powder and place it in a desiccator with water in the bottom.
The water absorbency was expressed by the increased weight (weight) after being left at room temperature for one day.

Measurement of Extraction Rate of Water-Soluble Polymer> Approximately 5 g of the powder is accurately weighed, left for one day at room temperature with 10 ml of water, filtered, washed with water, dried under vacuum at 50° C. for 48 hours, and weighed.

Since the reduced weight corresponds to the water-soluble polymer extracted by water, the percentage with respect to the weight of the water-soluble polymer in the powder before extraction was calculated and taken as the extraction rate.

The water absorption measured as described above was 16.3%, and the extraction rate with water was 0.6%.

Comparative Example 1 In Example 1, a roll cross-wire was carried out in the same manner as in Example 1 without using polyvinylpyrrolidone, and the material was pulverized to form a powder.

When the water absorption and extraction rate of this powder were measured in the same manner as in Example 1, the water absorption was 10.2 m and the extraction rate was 33.5.
%Met.

Approximately 1/3 of the polyacrylic acid contained in the composition
You can see that it is washed out by water.

Example 2 Instead of the saponified EVA used in Example 1, ethylene 8
EVA containing 8.6 moles of vinyl acetate, 8.0 moles of vinyl acetate and 3.4 moles of vinyl alcohol, and an MI of 25 g/10 min.
Using 50 g of saponified material, 170 g of 30% aqueous solution of polyacrylic acid and 25 g of polyvinylpyrrolidone were added.
Roll crossing was carried out at ℃ for 25 minutes.

When it was powdered in the same manner as in Example 1 and the water absorption and water extraction rate were measured, values of 11.3% and 1.2% were obtained.

For comparison, roll kneading was carried out in the same manner without using polyvinylpyrrolidone, and the water absorption and extraction rate of the powder were measured and found to be 3.4% and 10.8%.

Claims (1)

[Scope of Claims] 1. A water-absorbing resin composition comprising a saponified ethylene-vinyl acetate copolymer, polyacrylic acid, and polyvinylpyrrolidone. 2. The ethylene content is within the range of 80 to 98 moles,
Claim 1, which uses a saponified ethylene-vinyl acetate copolymer in which 20% or more of the acetate groups are converted to hydroxyl groups.
composition of the term. 3. The composition according to claim 1 or 2, wherein 2 to 200 parts by weight of polyacrylic acid and 00 parts by weight of human polyvinylpyrrolidone are used per 100 parts by weight of saponified ethylene-vinyl acetate copolymer.