JPH08151453A - Production of film excellent in rubber elasticity - Google Patents

Abstract

PURPOSE: To obtain a film excellent in flexibility, processibility, rubber elasticity, and recovery from stretching. CONSTITUTION: A film excellent in rubber elasticity is produced by partially cross-linking a compsn. comprising an ethylene-vinyl acetate copolymer. a styrenic thermoplastic elastomer, and an org. peroxide. forming the partially cross-linked compsn. into a film, and stretching and relaxing the resulting film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a film which is excellent in flexibility and processability as well as in rubber elasticity and elongation recovery, and a film obtained by the method. The film having such characteristics is preferably used in the fields of sanitary materials, stretch packaging and the like.

[0002]

2. Description of the Related Art The properties of a polyolefin film can be widely changed by various modifications. Particularly, in the field where the film is required to have flexibility, a film formed from a copolymer of ethylene and a vinyl ester or an unsaturated carboxylic acid ester, or a copolymer of ethylene and an α-olefin is generally known. (For example, JP-A-2-276831). However, the films obtained from these ethylene copolymers have the drawback of poor rubber elasticity.

On the other hand, as the thermoplastic elastomer rich in rubber elasticity, styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, styrene-isoprene copolymer, ethylene-propylene elastomer are preferable. Are known. However, although they are thermoplastic, the films obtained are inferior to those made of polyolefins in terms of processability.

Therefore, in order to make the best use of these characteristics as they are, a polyolefin resin and a styrene thermoplastic resin elastomer are blended, and further an organic peroxide is blended in order to improve the compatibility and processability of the blended resin. Then, a method of partially cross-linking the above-mentioned compounded resin and molding a film from the obtained cross-linked resin was proposed.

[0005]

However, the film obtained by the above-mentioned method has a problem that the rubber elasticity and the stretch recovery property are not satisfactory.

In view of the above points, it is an object of the present invention to provide a film which is excellent in flexibility and workability as well as rubber elasticity and extension recovery.

[0007]

The method for producing a film according to the present invention has been devised to achieve the above object.
A method of partially cross-linking a composition comprising an ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVA), a styrene-based thermoplastic resin elastomer and an organic peroxide, and molding a film from the obtained cross-linked resin is obtained. The film is stretched and relaxed.

In the method of the present invention, a composition comprising EVA, a styrene thermoplastic resin elastomer and an organic peroxide is EVA having a vinyl acetate content of 5 to 40% by weight.
A composition comprising 30 to 70% by weight, 70 to 30% by weight of a styrene-based thermoplastic resin elastomer, and 200 to 2000 ppm of organic peroxide based on 100 parts by weight of the total amount of the above resins is preferable.

The EVA used in the method of the present invention preferably has a vinyl acetate content of 5 to 40% by weight. When the vinyl acetate content is 5% by weight or less, the flexibility of the obtained film is poor, and when it is 40% by weight or more, the blocking property of the composition is high. EVA melt flow rate (MF
(Abbreviated as R) is preferably 1 to 50 g / 10 minutes.

Examples of the styrene-based thermoplastic resin elastomer include styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated styrene-isoprene- Examples thereof include styrene block copolymers, but hydrogenated ones are preferable from the viewpoint of thermal stability.

The compounding ratio of EVA and styrene type thermoplastic resin elastomer is preferably 30 to 70% by weight of EVA and 70 to 30% by weight of styrene type thermoplastic resin elastomer. When EVA is less than 30% by weight, the processability of the obtained film is poor, and when it is 70% by weight or more, the flexibility and rubber elasticity of the film are poor. A particularly preferred blending ratio is
EVA is 40 to 60% by weight, and styrene-based thermoplastic resin elastomer is 60 to 40% by weight.

Organic peroxides used for partial crosslinking include t-butylcumyl peroxide, dicumyl peroxide, α, α'-bis (t-butylperoxy-m).
-Isopropyl) benzene, 2,5-dimethyl-2,5
-Di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-
3, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, 1,1-di-t-butyl peroxide, t-butyl perbenzoate, di-t-butyl peroxide and the like. However, these may be used alone or in combination. The amount of organic peroxide added is E
Sum of VA and styrene thermoplastic elastomer 10
It is preferably 200 to 2000 ppm with respect to 0 part by weight. If the addition amount is less than 200 ppm, the obtained film is inferior in rubber elasticity and processability, and if it is 2000 ppm or more, a large amount of gel is formed and a good film cannot be obtained. A particularly preferable amount of addition is in the range of 400 to 1500 ppm.

The partial crosslinking of the resin with the organic peroxide is
This can be achieved by thoroughly mixing VA, a styrene elastomer and an organic peroxide, and then thoroughly kneading the compounded resin with an extruder, a kneader, a Banbury mixer, a hot roll or the like at a temperature not lower than the decomposition temperature of the organic peroxide.

A crosslinked resin obtained by partially crosslinking a composition comprising EVA, a styrene thermoplastic resin elastomer and an organic peroxide is easily formed into a film by a conventional method such as inflation or T-die casting. . A preferable film thickness is 10 to 100 μm.

To improve rubber elasticity, the film is stretched and relaxed. The stretching of the film can be realized by stretching the film between a pair of rolls that are close to each other and have different rotation speeds, or by fixing one end and pulling the other end. The former method is preferable because continuous production of films can be carried out. The stretching range is, for example, 50 to 30 at room temperature.
It is preferably 0%. If the elongation is less than 50%, a sufficient effect of improving the rubber elasticity cannot be obtained, and if it is more than 300%, the film may be broken or permanently deformed. The stretching temperature is 5
It is preferably below 0 ° C, particularly at room temperature. At 50 ° C or higher, permanent deformation of the film occurs. The relaxation of the film is preferably performed immediately after stretching. For relaxation, the stretched film may be left alone.

[0016]

In the production method of the present invention, a composition comprising EVA, a styrene-based thermoplastic resin elastomer and an organic peroxide is partially crosslinked, a film is formed from the obtained crosslinked resin, and then the film is stretched. EV to relax
It is possible to obtain a film which makes good use of the characteristics of both A and the styrene-based thermoplastic resin elastomer as they are, and is also excellent in rubber elasticity and extension recovery.

[0017]

Example 1 Vinyl acetate content 10% by weight, MFR 10 g / 10 min E
40% by weight of VA (Tosoh Ultrasen 541),
Hydrogenated styrene-butadiene-styrene block copolymer (Clayton G1657 manufactured by Shell Chemical Co., Ltd.) 60% by weight
And a composition obtained by adding 600 ppm of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane (Perhexa 3M manufactured by Nippon Oil Co., Ltd.) as an organic peroxide to 100 parts by weight of the above compound. The resin was partially crosslinked by extruding the resin using an extruder at 160 ° C.
The obtained cross-linked resin was mixed with a T-die cast molding machine 3
It was formed into a 0 μm film. This film was rolled at the original length of 20 at 30 ° C using a pair of rolls with a speed ratio of 1: 3.
Stretched to 0%. Immediately thereafter, the film was relaxed. The physical properties of the obtained film were measured. Table 1 shows the measurement results.

Comparative Example 1 A film was formed in the same manner as in Example 1. However, the film was not stretched or relaxed. The physical properties of the obtained film were measured. Table 1 shows the measurement results.

Example 2 A crosslinked resin was prepared in the same manner as in Example 1 except that benzoyl peroxide was used as the organic peroxide, and this was molded into a 50 μm film using an inflation molding machine. The obtained film was stretched by 100% at 40 ° C. by the same apparatus as in Example 1 and then immediately relaxed. The physical properties of the obtained film were measured. Table 1 shows the measurement results.

Comparative Example 2 A film was formed in the same manner as in Example 2. However, the film was not stretched or relaxed. The physical properties of the obtained film were measured. Table 1 shows the measurement results.

[0021]

[Table 1]

[0022]

Since the production method of the present invention is constituted as described above, it is possible to obtain a film which is excellent not only in flexibility and workability but also in rubber elasticity and extension recovery.

Claims (1)

[Claims] 1. A method of partially crosslinking a composition comprising an ethylene-vinyl acetate copolymer, a styrene-based thermoplastic resin elastomer and an organic peroxide, and molding a film from the obtained crosslinked resin. A method for producing a film having excellent rubber elasticity, which comprises stretching and relaxing the film.