JPS6132139B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a transparent, high gas barrier laminated film with little curling and good elasticity. Conventionally, a composite film with good gas barrier properties consists of three layers: a specific ethylene-vinyl acetate copolymer (hereinafter referred to as "saponified material"), a modified polyolefin, and polypropylene, and the polypropylene layer is biaxially connected to other layers. For example, JP-A No. 52-54784 is known, in which two layers are uniaxially stretched. However, this type of composite film had the disadvantage of curling from the saponified layer to the polypropylene layer due to the hygroscopic nature of the saponified material. This curling phenomenon tended to be promoted in harmony with the fact that the saponified layer and modified polyolefin layer were uniaxially stretched. Furthermore, it is extremely difficult to reduce the thickness of the modified polypropylene layer to 0.8 μ or less when industrially produced at practical speeds of 20 to 100 m/min, which may impede the transparency of the composite film. Moreover, it was also inhibiting the elasticity of polypropylene, which is originally good. This is because modified polypropylene generally has a maximum thickness of 12 to 15μ when melt extruded from a die, while it is extremely difficult to stretch saponified polypropylene more than 15 times at the above-mentioned practical speed. Even if polypropylene was uniaxially stretched together with a saponified material, the thickness could not be less than 0.8 μm, and the above-mentioned defects could not be corrected. As a result of intensive research to improve the above-mentioned drawbacks, the present inventors have finally found a waist with less curling phenomenon.
We have succeeded in providing a method for producing a transparent laminated film with good gas barrier properties. That is, in the present invention, a two-layer film obtained by co-extrusion laminating polypropylene and an adhesive polyolefin resin, or by melt-extruding laminating an adhesive polyolefin resin on a polypropylene film, is stretched 2 to 12 times in the warp direction, and then Further, on the adhesive polyolefin resin surface of the two-layer film, an ethylene content of 25 to 60 mol%,
This invention relates to a method for producing a laminated film, characterized in that saponified ethylene-vinyl acetate copolymers having a saponification degree of 90% or more are laminated by melt extrusion and then stretched 5 to 15 times in the opposite direction. The polypropylene according to the present invention refers to polypropylene and a copolymer of this and other α-olefins such as ethylene, and crystalline polypropylene is particularly preferred. In addition, saponified products have an ethylene content of 25 to 60 mol%, preferably 30 to 50 mol%, and a degree of saponification of 90% or more, preferably 95% or more, and those that fall outside this range are unsuitable for the present invention. It is. Furthermore, adhesive polyolefin resins are polyolefins such as polyethylene, polypropylene, copolymers thereof, or copolymers of these with other α-olefins, vinyl acetate, etc., and inorganic compounds such as acrylic acid, maleic acid, and fumaric acid. At least one selected from saturated carboxylic acids or their derivatives such as acid anhydrides and esters in an amount of 10 ^-4 to 10% by weight, preferably 10 ^-3 to
This is a resin containing a modified polyolefin that has been graft copolymerized in a range of 5% by weight, and may be composed only of the modified polyolefin, or a modified polyolefin mixed with an unmodified polyolefin and/or a third party. It may be something you have done.
Particularly preferred examples include polypropylene, ethylene-propylene copolymers, etc., which have a high melting point and are made by graft copolymerizing maleic anhydride, and can exhibit the effects of the present invention well. The stretching ratio according to the present invention is 2 to 12 times in the warp direction, preferably 3 to 7 times, and 5 to 15 times in the weft direction, preferably 7 to 12 times. It is not usable because it causes undesirable phenomena on the surface. The stretching temperature is preferably 90 to 160°C in the warp direction and 130 to 190°C in the weft direction, preferably 110 to 140°C in the warp direction and 140 to 170°C in the weft direction. It is preferable to carry out the process to the extent that it is melted and does not adhere to stretching rolls or the like. Furthermore, stretching in the weft direction is preferably carried out by a tenter method, and the stretching speed is 20 to 100 m/min, preferably 50 to 80 m/min.
It is necessary to carry out the stretching at m/min. If the value is less than this, the productivity will decrease, and if it is more than this, it will become unsuitable for stretching, which is not preferable. In the production method according to the present invention, it is most desirable to melt-extrude and laminate the "saponified material" onto a warp-stretched two-layer film. In addition, it goes without saying that the extrusion of a saponified material into a film and its continuous lamination on the two-layer film also falls within the scope of the "melt extrusion lamination" according to the present application. Naturally, this also applies when melt-extrusion laminating an adhesive polyolefin resin to the polypropylene film according to the present invention. The thickness of the adhesive polyolefin layer is 0.8 to 0.1 μ, preferably 0.2 to 0.5
If it is 0.8μ or more, transparency will be impaired, and if it is 0.1μ or less, adhesiveness will be poor. Generally, this value is extremely difficult to achieve for ordinary gas barrier laminated films produced at the above-mentioned drawing speed, and this value is fully guaranteed only in the present invention. Incidentally, by taking a value for this thickness as in the present invention, the following effects can be expected. In other words, in general, the thinner the laminated film (coating) is, the less variation in thickness that occurs during stretching. Even if the clips hold only the edges of the polypropylene layer 1, it is possible to stretch the polypropylene layer 1 to a uniform thickness, and the lamination state after stretching is also good and thick, as shown in Figure 2. It was also uniform. By doing this, when collecting the ears later, it is only necessary to collect the ears having the clip retaining marks made of only the polypropylene layer along the chain line 4 in Figure 2, which is extremely effective for collecting waste. It is true. On the other hand, in the conventional method, the modified polyolefin layer cannot be thinned, so even if only the polypropylene layer is stretched by clipping as described above, the state at the time of lamination is as shown in Figure 3 due to the effect of the tensile stress. As shown in Fig. 3, the unevenness makes it difficult to obtain thickness accuracy, and it is impossible to collect only the polypropylene layer when collecting the ears. It was necessary to remove even the parts where the layers were stacked. Since the recovered ear part is a mixture of three substances and is tightly attached, it lacks compatibility and lacks transparency, so it has been difficult to find its useful value. However, according to the present invention, these It is also extremely useful, such as being able to solve shortcomings all at once. The present invention is as described above, and since the gas barrier laminated film produced by the production method of the present invention is less prone to curling, it has excellent bag-making properties and packaging suitability especially when applied as a packaging film, and is suitable for automatic machines. Effective. Furthermore, it has high transparency and good elasticity, so it has an extremely wide range of applications ranging from general packaging to special packaging, and has special effects such as sufficient heat sealing strength and no delamination. The laminated film according to the present invention has particularly good gas barrier properties and heat sealability, so it is suitable for general packaging and special packaging for fresh foods, etc., but it can of course be applied to other appropriate uses. Next, examples of the present invention will be described. Example 1 Extruded crystalline polypropylene film (thickness
1060μ), maleic anhydride to polypropylene
An adhesive polyolefin resin (melting point: 160°C) consisting of a mixture of 5 parts of 3.5% by weight graft copolymer and 95 parts of polypropylene is melt-extruded and laminated to a thickness of 40μ, and then laminated by 5 times in the warp direction at approximately 130°C. A uniaxially stretched two-layer film was obtained. In addition to the adhesive polyolefin layer of such a two-layer film,
A saponified ethylene-vinyl acetate copolymer with a 30μ ethylene content of 40 mol% and a saponification degree of 98% was melt-extruded and laminated, and then heated at a speed of 50 m/min to 160 m/min.
The film was stretched 10 times in the latitudinal direction at ℃ to obtain a laminated film. The thickness of this film was 25μ, of which the thickness of the adhesive polyolefin layer was 0.8μ. Example 2 A laminated film was obtained in the same manner as in Example 1 so that only the adhesive polyolefin layer had a thickness of 0.2μ. Comparative Example 1 Using the same resin as in Example 1, a uniaxially stretched polypropylene film with a thickness of 205 μm was melt-extruded and laminated with an adhesive polyolefin resin with a thickness of 15 μm and a saponified material with a thickness of 30 μm. A laminated film with an adhesive polyolefin layer having a thickness of 1.5 μm was obtained by stretching in the weft direction in the same manner as above. The thicknesses of the other two layers were the same as in Example 1. Comparative Example 2 An attempt was made to melt-extrude and laminate an 8μ adhesive polyolefin film using the same method as in Comparative Example 1, but extrusion film formation was not possible. Comparative Example 3 The stretching ratio in the weft direction was set to 16 using the same method as Comparative Example 1.
When the amount was doubled, cracks appeared in the saponified layer, making it impossible to obtain a good film. Comparative Example 4 The same resin as in Example 1 was introduced into one die from three extruders to obtain a three-layer coextruded film,
After that, under the same stretching conditions as in Example 1, 2
When axially stretched, cracks appeared in the saponified layer and a good film could not be obtained. As is clear from the above examples and comparative examples, it is difficult to extrude adhesive polyolefin into a film of 12μ or less, and on the other hand, it is difficult to stretch ``saponified material'' to more than 15 times. It can be seen that it is impossible to reduce the thickness of the adhesive polyolefin layer to 0.8μ or less. On the other hand, the material of the present invention can have a thickness of 0.2μ, and as shown in Table 1, the material of the present invention has particularly remarkable effects compared to the conventional material.

【table】

[Table] Example 3 In the method of Example 1, the three materials were laminated as shown in Figure 1, and only the polypropylene layer was clipped in a tenter and stretched in the weft direction. After stretching, the lamination was as shown in Figure 2. It was possible to recover only the polypropylene layer when cutting the ears with good edges. Comparative Example 5 In the method of Comparative Example 1, the three materials were laminated as shown in Fig. 1, and only the polypropylene layer was held in a tenter with clips and then weft-stretched. There were irregularities. Therefore, in order to cut the ears, the third
As shown by the chain line in the figure, it was necessary to cut out the parts where the three parts were glued together, which caused various problems in reusing the ears.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the state of lamination when three parts are laminated, Fig. 2 is a sectional view showing the state of cutting the ears after stretching, and Fig. 3 is a sectional view showing the state of laminating the three parts. FIG. 3 is a cross-sectional view showing the state of lamination after stretching by a conventional method. DESCRIPTION OF SYMBOLS 1... Polypropylene layer, 2... Adhesive polyolefin resin layer, 3... "Saponified material" layer, 4...
...Ear cut line, 5...Laminated film, 6...
Traces of tenter clips.

Claims (1)

[Claims] 1 A two-layer film formed by co-extrusion lamination of polypropylene and adhesive polyolefin resin, or melt extrusion lamination of adhesive polyolefin resin on polypropylene film, or lamination in the form of a film by extrusion, is laminated in the warp direction. Stretched 2 to 12 times, and then coated with an ethylene content of 25 to 25% on the adhesive polyolefin resin surface of the two-layer film.
A saponified ethylene-vinyl acetate copolymer with a saponification degree of 60 mol% or more is laminated by melt extrusion or in the form of a film, and then laminated in the latitudinal direction for 20 to 30 minutes.
A method for producing a laminated film, characterized in that the adhesive polyolefin layer is stretched 5 to 15 times at a speed of 100 m/min to a thickness of 0.1 to 0.8 μm.