JPS6056608B2 - Manufacturing method of laminated film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a laminated film of a saponified ethylene-vinyl acetate copolymer.

Saponified product of ethylene-vinyl acetate copolymer (hereinafter referred to as E
Films of VA saponified materials (abbreviated as VA saponified materials) have excellent oxygen barrier properties, and are used in the food packaging field, etc., mainly as laminated films with other types of films, taking advantage of this property. However, since it is difficult to make a thin film of EVA saponified material, the EVA saponified film currently used is used as a relatively thick (15μ or more) unstretched film, and therefore the film exhibits hard and brittle properties. In addition, the thickness is often thicker than the required performance, resulting in high cost. Unlike other thermoplastic resins, EVA saponified resin has very strong hydrogen bonds. Since the stretching does not change much, and furthermore, the stretching shows neck stretching, the conventional biaxial stretching method used for stretching polyester, polypropylene, etc. cannot be directly applied as a thinning method.Alternative thinning method Although the uniaxial stretching method is possible, there are problems in terms of the mechanical strength of the product, workability, manufacturing cost, etc.
In view of this background, the present inventors have completed the present invention as a result of intensive research.

That is, the present invention makes it possible to make the EVA saponified film thick enough to suit the purpose of use and improve various properties, in other words, it does not need to be made thicker than necessary, thus reducing raw material costs, and is particularly suitable for food packaging. The purpose of the present invention is to provide a method for producing a laminated film of saponified EVA suitable for use in commercial applications, and its gist is to prepare a saponified ethylene-vinyl acetate copolymer that has been pre-stretched in one direction. A film of another thermoplastic resin is closely laminated on the uniaxially stretched film, and the laminate is heated within a temperature range of 60 to 160°C perpendicular to the stretching direction of the uniaxially stretched film of the saponified ethylene-vinyl acetate copolymer. The present invention relates to a method for producing a laminated film of a saponified ethylene-vinyl acetate copolymer, the film being stretched 2 to 7 times in the direction of . The present invention will be explained in detail below.

In the present invention, the saponified EVA is not only a saponified product of a copolymer of ethylene and vinyl acetate, but also contains one or more third components copolymerizable with ethylene and vinyl acetate (for example, propylene, etc.). , saponified products of multi-component copolymers obtained by copolymerization are also included.

In terms of oxygen barrier properties, transparency, moisture resistance, and extrusion moldability, these saponified EVA products have an ethylene content of 26 to 60 mol% and a saponification degree of 96 mol%.
The above is preferable. The primary stretching (uniaxial stretching) of these EVA saponified films can be carried out at a temperature in the range of 80 to 160° C. and at a magnification of 2 to 6 times.

The stretching ratio is preferably 3 times or more in order to make the film thinner and improve the strength in the stretching direction, and preferably 5 times or less in terms of stretchability.

The stretching temperature varies depending on the composition of the EVA saponified material, and the EVA
The lower the amount of ethylene in the saponified material A, or the higher the degree of saponification, the higher the temperature will be for stretching, but generally
~140 suitable C is preferred.

The thermoplastic resin film (hereinafter referred to as base film) laminated on the first stretched EVA saponified film may be polyvinyl chloride, vinyl chloride copolymer resin mainly composed of vinyl chloride, polyolefin such as polyethylene or polypropylene, or polyethylene. Terephthalate, ethylene
Easily stretched thermoplastic resin films such as polyester containing terephthalate as a main component, acrylonitrile copolymers such as acrylonitrile-styrene and acrylonitrile-butadiene, and polystyrene are used. I can stay.
These base films may be unstretched ones obtained by ordinary extrusion molding, but they may also be slightly uniaxially or biaxially stretched. Then, the film selected from these and the uniaxially stretched film of the saponified EVA can be laminated in close contact with each other by a known method such as an extrusion lamination method, a dry lamination method, or a heat adhesion method. . Lamination may be on one side or both sides of the EVA saponified film. The laminated film adhered in this way is stretched in a direction perpendicular to the stretching direction previously carried out for the EVA saponified uniaxially stretched film.

The stretching temperature at that time is within the range of 60 to 160'C, preferably within the range of 70 to 150'C. When this temperature is less than 60°C, non-uniform stretching occurs and a good stretched film cannot be obtained, and when the temperature exceeds 160°C, undesirable phenomena such as thermal deterioration occur. The stretching ratio of the laminated film must be in the range of 2 to 7 times.

If this magnification is less than 2 times, it will result in non-uniform stretching;
If it exceeds twice that, the film will break and a good laminated film cannot be obtained. In the present invention, it is practical to first stretch the saponified EVA material in the length direction of the film, and then stretch it after lamination in the width direction of the film.
Of course, it is also possible to do it in the opposite direction.

The stretched laminated film obtained as described above may be further heat-treated according to a conventional method depending on the purpose. Depending on the application, a sealant layer such as low-density polyethylene is further laminated. The laminated film thus obtained by the method of the present invention can be made into a thin film with a uniform thickness from EVA saponified material, which was conventionally considered difficult to be made into a thin film by biaxial stretching. It is possible to obtain a laminated film that has good mechanical strength without impairing its excellent oxygen barrier properties.

Biaxial stretching of EVA saponified film greatly improves its mechanical strength, water resistance, oxygen barrier properties, and other properties compared to unstretched films when compared at the same thickness.
It can be used with a thinner film than before. Furthermore, since the base material layer of the obtained laminated film is stretched only in one direction, it has tear propagation properties in that direction. It can be easily torn when opened, making it extremely desirable as a packaging material.

Next, examples and comparative examples of the method of the present invention will be explained.

Example 1 This example shows a case in which a base film is closely laminated on an EVA saponified film, and the temperature at which this is stretched is varied.

Saponified EVA (ethylene content: 34 mol%, degree of saponification: 99.7 mol%) is melt-extruded into a film, which is stretched 4 times in the longitudinal direction at a stretching temperature of 120°C to obtain a uniaxially stretched film.

On the other hand, unstretched films were obtained by melt-extruding polyvinyl chloride, polyester (polyethylene terephthalate), and polypropylene containing plasticizer 1CifI, respectively, and the combinations shown in Table 1 below were laminated by dry lamination, and then stretched. The film is stretched 3 times in the transverse direction while changing the temperature.

The resulting stretching conditions are shown in Table 1. In this table, the saponified EVA used in this example is abbreviated as EVA resin. In addition, the thickness of the film described in the table is the thickness before being stretched in the transverse direction. In the experiment shown in the table above, NO. l and NO. No. 7 was carried out under temperature conditions outside the scope of the present invention, resulting in non-uniform stretching and cutting, but No. 7 was conducted within the scope of the present invention. In Examples 2 to 6, the EVA saponified film was biaxially stretched and good products were obtained.

Example 2 This example shows an example in which a laminated film was obtained from a uniaxially stretched EVA saponified film, and the stretching ratio was varied when this was further stretched.

Saponified ethylene-vinyl acetate terpolymer (ethylene content 29.5 mol%, propylene content 2.5 mol%, saponification degree 99.5%) (in Table 2 below, ternary EVA
resin) and saponified ethylene-vinyl acetate copolymer (ethylene content 30 mol%, saponification degree 99.0
%) (abbreviated as EVA resin in Table 2 below) was melt-extruded to obtain each film, and each of these was stretched 3 times in the longitudinal direction at a stretching temperature of 110°C to obtain a uniaxially stretched film. On the other hand, unstretched films were obtained by melt-extruding polyvinyl chloride, polyester (polyethylene terephthalate), and polypropylene containing 5 parts of plasticizer, and laminated in the combinations shown in Table 2 below, then stretched under the stretching conditions shown in Table 2. Lateral stretching was performed. The stretching conditions are shown in Table 2. NO. whose stretching ratio falls within the range of the method of the present invention. 2-6
Although a uniform stretched film can be obtained in the example of NO. In Examples 1, 7, and 8, the laminates were stretched non-uniformly or broke, and good products could not be obtained.

Claims (1)

[Claims] 1. A uniaxially stretched film of a saponified ethylene-vinyl acetate copolymer that has been stretched in one direction in advance is closely laminated with another thermoplastic resin film, and this laminate is heated at 60 to 160°C.
The saponified ethylene-vinyl acetate copolymer is stretched 2 to 7 times in a direction perpendicular to the stretching direction of the uniaxially stretched film of the saponified ethylene-vinyl acetate copolymer within a temperature range of A method of manufacturing a laminated film.