JPS60228124A - Manufacture of laminated and oriented film - Google Patents

Abstract

PURPOSE:To obtain the titled film whose gas barrier properties are favorable, by making biaxial orientation of an unoriented and laminated film at a time, which is constituted with a saponified article of a polypropylene/ethylene-vinyl acetate copolymer laminated through coextrusion method. CONSTITUTION:After aqueous latex or a solvent solution of (B) polyvinylidene chloride series has been applied to at least one side of an unoriented and laminated film constituted with a saponified article of a polypropylene ethylene- vinyl acetate copolymer laminated through a (A) coextrusion method, an aimed film is obtained by making biaxial orientation of the laminated film at a time. As for percent of stretch, moreover, 3-3.5 times in a longitudinal direction and 3-4 times in a lateral direction are suitable for the titled film.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a laminated biaxially stretched film of a polypropylene film and a saponified ethylene vinyl acetate copolymer (hereinafter referred to as EVOH) film.

EVOH film is relatively easy to mold, and its moisture resistance has been improved to some extent among polyvinyl alcohol films, and its original gas barrier properties have not been lost, making it highly suitable as a food packaging film. It is a material that has

(Prior Art) However, the EVOH film remains disadvantageous in that under high humidity conditions, its structure relaxes and its gas barrier properties deteriorate due to its water absorption properties. In particular, this tendency becomes stronger in copolymer compositions containing less ethylene component in order to maintain heat resistance and gas barrier properties under low humidity conditions.By biaxially stretching the EVOH film, these drawbacks can be overcome to some extent. Although improved, it is unlikely to be a sufficient barrier material in application fields with severe conditions.

Further, the stretched EVOH film has low bending strength, which is a serious drawback as a packaging film.

(Problems to be Solved by the Invention) The inventors of the present invention have conducted intensive research on a method for economically manufacturing EVOI (films that take advantage of their excellent qualities and eliminate the above-mentioned drawbacks), and have invented the present invention. reached the method.

In other words, in order to cover the moisture resistance and bending pinhole resistance of CVOH film, biaxially oriented polypropylene films are laminated, and both are laminated by co-extrusion and co-stretched, thereby making it possible to create a polypropylene film in post-processing. This is a method of producing laminated films at a much lower cost than laminating.

When stretching a single film, the optimum stretching ratio is quite different between a polypropylene film and an EVOH film. Generally, a polypropylene film is stretched five times or more in both the longitudinal and transverse directions, and cannot be stretched uniformly if it is less than five times. On the other hand, the stretching ratio of the cvou film is that of a general copolymer composition.

It is about three times as large both in length and width. However, the present inventors have found that when they are laminated by a coextrusion method and then co-stretched by a simultaneous biaxial stretching method, by considering the selection of the adhesive, the EVO
It has been found that polypropylene can be uniformly stretched even at a stretching ratio of 1, that is, a stretching ratio of about 3 times in both the length and width, and that a practically sufficient orientation effect can be obtained. This is because the stretching stress of EVOH is large, so the stretching deformation behavior is dominated by EVO)I, and polypropylene is uniformly stretched according to the deformation of EVOll.

Note that this is only possible with the simultaneous biaxial stretching method, and it is difficult to stretch EVOII with the two-stage biaxial stretching method.
Furthermore, even if the ethylene component in EVO)I is increased to improve the stretchability, the two will peel off due to the shear stress generated on the adhesive surface during stretching.

(Means for Solving the Problems) EVOll, which is a component of the present invention, has an ethylene content of 25 to 50 mol% and a saponification degree of 98% or more. The lower the ethylene content, the better the quality of the laminated stretched film in terms of barrier properties and heat resistance, but the lower the co-stretchability with polypropylene. On the other hand, if the ethylene content becomes too high, the quality of the barrier properties will decrease,
Furthermore, the stretching stress decreases, making uniform stretching difficult.

The polypropylene used in the method of the present invention is polypropylene homopolymer or 80% polypropylene homopolymer.
These are copolymerized with other α-olefins, etc., and include those containing additives such as lubricants and antistatic agents.

By providing a polyvinylidene chloride (hereinafter referred to as PVDC) layer on one or both sides of the polypropylene/EVO11 laminated film, the barrier performance of the film obtained by the method of the invention is further improved. In this case as well, PVDC
The barrier performance of PVDC is improved by laminating them before stretching and co-stretching to provide an orientation effect. p here
VOC is a copolymer of vinyl chloride, acrylonilyl, acrylic ester, etc. without changing the basic performance of polyvinylidene chloride, and these PVDCs are water-based latex.

Applied as a solvent solution. The higher the polyvinylidene chloride component, the better the barrier performance, but the bottling life of the latex or solution becomes too short and the uniformity of application decreases.

The thickness ratio of polypropylene and E V O11 film is suitably in the range of 2:8 to 6:4, and the optimum composition ratio is determined depending on the purpose of use. PVO on one or both sides
cm, the thickness of the PVDC layer is stretched.

After crystallization, a range of 0.5 to 2μ is passed.

Further, the effects of the present invention are most clearly exhibited when the total thickness of the laminated film is in the range of 15 to 30 μm after stretching.

(effect) Next, the operation of the method of the present invention will be explained.

Lamination of polypropylene and EVO)I film is basically carried out using a coextrusion device that is a combination of three extruders and a three-layer T-die. The third extruder is for adhesive resin poured between the polypropylene layer and the EVOH layer, and modified polyolefin resin is generally used as the adhesive resin.

Since shearing force acts on the interface during the biaxial stretching process and may impair adhesion, sufficient care must be taken in selecting the type of adhesive resin and the layer thickness. It may be desirable to use a crosslinkable adhesive if particular adhesive strength is required.

When providing an additional pvoc layer on one or both sides of the polypropylene/EVOI+ laminated film, coat one or both sides of the polypropylene/F, VOII laminated non-oriented film obtained by coextrusion with a PVDC aqueous latex or solvent solution, and at least apply After drying until the surface is no longer sticky, it is fed into a stretching machine. Application is done by air knife method, gravure roll method, and reverse roll method.

Drying is performed using a bar code method, etc., and drying is performed in an arch type, floating type, etc. drying oven. The primary purpose of applying PVOC before stretching and then stretching is to also orient the PVO layer to improve barrier performance, but the other effect is that this method can be used without anchoring. EVO) I/PVDC, polypropylene/PνD
It was found that the adhesion between C was improved. The reason for this is not clear even to the inventors, but it is thought that it is related to the effect of the high temperature heat treatment performed after stretching. In addition, when applying PVOC water-based latex to the EVOI-1 surface, the water in the coating liquid migrates into the EVOI and plasticizes the EVOI.
The effect of increasing the stretchability of I+ is recognized.

A non-oriented laminated film having a polypropylene/EVOH structure or a film coated with PVDC is fed into a simultaneous biaxial stretching machine and stretched.

A simultaneous biaxial stretching machine is a machine in which both ends of an unoriented film are held by clips attached to an endless link chain, and the clips are heated to the stretching temperature in a preheating zone where they advance in parallel.
In the next stretching zone, the distance between the opposing clips widens in a divergent manner, resulting in stretching in the transverse direction, and at the same time, the pinch between the clips in the machine direction gradually increases, increasing the speed of clip advancement, resulting in stretching in the longitudinal direction. Next to the stretching zone is a heat treatment zone where the clips run in parallel at a constant speed and are blown with high temperature hot air.
Here, the stretched film is heat set.

The stretching ratio is suitably 3 to 3.5 times in the longitudinal direction and 3 to 4 times in the transverse direction, and the stretching temperature is selected from the range of 90 to 150°C. The heat treatment temperature must be lower than the lower of the melting point of polypropylene and the melting point of EVOI+.

Next, the method of the present invention will be specifically explained with reference to Examples.

(Example) Examples L2 and 3 and Comparative Example Polypropylene, EVOIL with ethylene content of 30 mol%
Three types of non-oriented laminated films with different thickness configurations were obtained by melting a carboxylic acid-modified polyolefin adhesive using three extruders, extruding it using a multi-manifold type three-layer gouer, and rapidly cooling it using a cooling roll. The obtained film was fed into a simultaneous biaxial stretching machine and stretched simultaneously on two wheels to 3.0 times in the longitudinal direction and 3.3 times in the transverse direction to obtain three types of laminated stretched films. Thickness structure of the obtained film (the thickness of the adhesive layer is 0.5 to 1 μm)
) E V O1 manufactured from raw material EνOH with the same physical properties as
A comparison with 1 single film is shown in the table.

As is clear from the table in Table 1, the film of the present invention has greatly improved bending resistance without significantly losing the oxygen gas barrier properties of the VOI+ film.

Example 4 After manufacturing a polypropylene/EVO11 laminated non-oriented film in the same manner as in Example 1, a PVDC aqueous latex containing 92% by weight of vinylidene chloride component was stretched on the EVOI surface to form a 1.5μ PVDC layer. The film was coated and dried as described above, and then simultaneously biaxially stretched in the same manner as in Example 1. Oxygen gas permeation rate (cc/r) of the obtained film
d・24hr) is less than 0.5 at 65% I'll, and is less than 2.0 even at 100% R11, and the amount of water vapor permeation (
g/r+(·24hr) was 3.0 or less, which was extremely excellent.

(Effect of the invention) The heat-treated film is trimmed at both edges and then rolled up to become a product. The trimmed edges are EVOI (by making it a single unit, it can be easily recycled. A biaxially stretched laminated film. If necessary, the film is subjected to post-treatments such as corona treatment, pre-UV irradiation aging, etc. The laminated stretched film thus obtained is printed and further laminated with a wet film to become a packaging material.

In the present invention, a polypropylene film is laminated onto an EVOH film that has excellent barrier performance but has shortcomings in moisture resistance and bending pinhole resistance, and these shortcomings can be overcome using an economical method of co-extrusion and co-stretching. The industrial value of this technology is extremely large.

Patent applicant: Unitika Co., Ltd.

Claims (1)

[Claims] 1. A method for producing a laminated stretched film, which comprises simultaneous two-wheel stretching of an unoriented laminated film composed of a saponified polypropylene/ethylene-vinyl acetate copolymer laminated by a coextrusion method. 2. After coating an aqueous latex or solvent solution of polyvinylidene chloride resin on at least one side of a non-oriented laminated film composed of saponified polypropylene/ethylene vinyl acetate copolymer laminated by coextrusion method, the laminated film is simultaneously The manufacturing method according to claim 1, characterized in that axial stretching is carried out.