JP2021160116A - Laminate film - Google Patents

Abstract

To provide a two-layer coextruded laminated film, which is a two-layer coextruded laminated film of polyolefin layer and a polyamide layer, in which physical properties of polyolefin are being improved by use of a small amount of polyamide suitable for recycling.SOLUTION: Two-layer coextruded laminated film formed by laminating a polyamide layer 3 and polyolefin layer 1, the two-layer coextruded laminated film is biaxially stretched, and the thickness of the polyamide layer 3 is 1.5-5% of the polyolefin layer 1.SELECTED DRAWING: Figure 1

Description

The present invention relates to a two-layer coextruded laminated film in which a polyamide layer is laminated on a polyolefin layer.

In general, polyolefins typified by polypropylene and polyethylene are very inexpensive, have good moldability and transparency, have good hygiene and chemical resistance, and also have good heat sealability. , Widely used as a film for packaging materials such as pouches.

However, polyolefin films are poor in strength characteristics such as impact resistance and piercing strength and oxygen barrier properties. Therefore, in order to improve these characteristics, polyolefin films are used by laminating them with other resins. Often done.
For example, in Patent Document 1, the innermost heat-sealed resin layer (polyolefin layer) is provided with an intermediate layer such as an amorphous nylon resin layer or an ethylene-vinyl acetate copolymer saponified resin as a polyamide resin layer (outermost layer). A packaging composite film laminated via is disclosed.
Further, Patent Document 2 discloses a coextruded laminated film in which a plurality of polyamide layers are provided on a polyethylene sealant polymer layer via an adhesive resin layer.
All of the techniques disclosed in Patent Documents 1 and 2 aim to improve the physical characteristics of polyolefin by laminating a layer of polyamide on a layer of polyolefin to form multiple layers.

By the way, recently, from the viewpoint of environmental measures, it is desired to make materials into monomaterials. Especially in the field of packaging, since a large amount of plastic is consumed, it is strongly desired to improve recyclability by making them into monomaterials. There is.

Conventional techniques for improving the physical properties of polyolefins by laminating another resin layer, for example, a polyamide layer on the polyolefin layer, use a large amount of materials other than polyolefins, and thus meet the demand for monomaterialization. It wasn't the answer.

Japanese Unexamined Patent Publication No. 2000-238217 Japanese Unexamined Patent Publication No. 8-118570

Therefore, an object of the present invention is to provide a two-layer coextruded laminated film in which a polyolefin layer and a polyamide layer are used, and the physical properties of the polyolefin are improved with a small amount of polyamide used. It is in.
Another object of the present invention is to provide a bag-shaped container made of the above-mentioned two-layer coextruded laminated film.

According to the present invention, in a two-layer coextruded laminated film in which a polyamide layer and a polyolefin layer are laminated,
The two-layer coextruded laminated film is biaxially stretched.
A two-layer coextruded laminated film is provided in which the polyamide layer has a thickness of 1.5 to 5% of the thickness of the polyolefin layer.

In the two-layer coextruded laminated film of the present invention,
(1) The polyolefin is an ethylene resin.
(2) The polyamide is nylon 6.
(3) The thickness of the polyamide layer is in the range of 2 to 15 μm.
(4) The piercing strength (JIS Z-1707) is in the range of 4.5N or more.
Is preferable.

According to the present invention, there is also provided a bag-shaped container made of the above-mentioned two-layer coextruded laminated film in which the polyolefin layer is located inside.

The two-layer coextruded laminated film of the present invention has a two-layer structure of a polyolefin layer and a polyamide layer, but the thickness of the polyamide layer is much thinner than that of the polyolefin layer (the thickness of the polyolefin layer is 1. 5-5%), at the same time, the bilayer film is stretched. That is, since the thickness of the polyamide layer is extremely thin as compared with the polyolefin layer, the amount of polyamide used is small, for example, 5% or less of the total amount of resin used in the production of this film (total amount of polyolefin and polyamide). The amount of polyamide can be set to a significantly smaller amount. Moreover, in the two-layer coextruded laminated film, both the polyolefin layer and the polyamide layer are biaxially stretched. Therefore, although the thickness of the polyamide layer is very thin, the physical properties of the polyolefin layer are improved (for example, the strength is increased).
As described above, according to the present invention, while improving the physical properties of polyolefin by using polyamide, since the amount of polyamide used is small, the recycling suitability by monomaterialization is also improved.

The schematic cross-sectional view which shows the layer structure of the two-layer coextruded laminated film of this invention.

The two-layer coextrusion laminated film of the present invention is obtained by performing two-layer coextrusion of polyolefin and polyamide and then biaxial stretching. As shown in FIG. 1, the polyolefin layer 1 is obtained. It has a two-layer structure of and a polyamide layer 3.

Polyolefin layer 1;
The polyolefin layer 1 also functions as a heat-sealing resin layer, and is formed from a known olefin-based resin used for producing a film.
Examples of such olefin-based resins include low-density polyethylene, high-density polyethylene, polypropylene, poly1-butene, poly4-methyl-1-pentene, or ethylene, propylene, 1-butene, 4-methyl-1-pentene. Random or block copolymers of α-olefins such as, cyclic olefin copolymers, and the like can be mentioned.
Further, the polyolefin may have a molecular weight sufficient to form a film.
In the present invention, from the viewpoint that the increase in strength due to the polyamide layer is remarkably exhibited, this polyolefin is a combination of ethylene resin, for example, low density polyethylene, high density polyethylene, ethylene mainly composed of ethylene, and α-olefin. It is preferably a polymer.

The thickness t ₁ of the polyolefin layer 1 is not particularly limited, and can be set to an appropriate thickness according to the application. For example, when a bag-shaped container is formed by heat-sealing with the polyolefin layer 1 on the inner surface side by utilizing the heat-sealing property (heat fusion property) of the polyolefin layer 1, the thickness t _{1 of the} polyolefin layer is 30. It is preferably in the range of ~ 250 μm, especially 50 ~ 150 μm.

Polyamide layer 3;
The polyamide layer 3 is laminated for the purpose of improving physical properties such as the strength of the polyolefin layer 1.
The polyamide used for forming such a polyamide layer 3 is not particularly limited, and various examples can be exemplified, but in general, nylon 6, nylon 6, 6, nylon 11, nylon 12 , Nylon 13, Nylon 6 / Nylon 6,6 copolymer, aromatic nylon (for example, polymethoxylylen adipamide) and the like are preferably used. Nylon 6 is most preferable from the viewpoint of improving strength. This is because it is highly oriented and crystallized by biaxial stretching described later, and remarkably high strength can be realized.

The above-mentioned polyamide should also have a molecular weight sufficient to form a film. For example, the relative viscosity (η _ll ) measured at a concentration of 1.0 g / dl in concentrated sulfuric acid and a temperature of 30 ° C. is 1.1 or more. In particular, it is preferably 1.5 or more.

By the way, in the present invention, the thickness t ₂ of the polyamide layer 3 must be in the range of 1.5 to 5%, preferably 3 to 5% _{of the thickness t 1} of the polyolefin layer 1 described above. As a result, it is possible to improve the physical properties of the polyolefin layer 1, especially to increase the strength, while realizing a monomaterial that can be applied to recycling. For example, in a polyethylene single-layer film, the piercing strength (JIS Z-1707) of this film is only about 4.5 N at the highest, but in the present invention, the polyamide layer 3 is formed on such a stretched polypropylene film. Since it is provided in a stretched form, the piercing strength of the film can be improved to 7.2 N or more, particularly 9.0 N or more, and 160% or more, particularly compared to a stretched polyethylene film having the same thickness. An improvement in piercing strength of 200% or more is achieved.

That is, in the two-layer coextruded laminated film of the present invention, the polyethylene layer 1 is used as a heat-sealing layer and bonded to another base material by heat-sealing, or the films are bonded to each other and bonded to a bag-shaped container. Even in the case, its high strength is not lost. This is because the strength is maintained by the stretched polyamide layer 3 existing on the upper layer of the polyethylene layer 1 even when the oriented crystals due to the stretching of the polyolefin are destroyed by thermal melting.

Manufacture of two-layer coextruded laminated film;
The above-mentioned laminated film having a layer structure is produced by producing a two-layer film by coextrusion of polyolefin and polyamide and then subjecting it to biaxial stretching for stretching in the longitudinal direction and the horizontal direction.

The film formation by coextrusion can be performed by extrusion from a T-die attached to the tip of a so-called extruder, or can be performed by film formation by inflation molding. In these film forming methods, it is also possible to carry out biaxial stretching as it is after forming the film.

Further, the thicknesses of the polyamide layer and the polyolefin layer in the film obtained by this coextrusion are set so that the thickness of the polyamide layer / the thickness of the polyolefin layer is in a range satisfying the _{above-mentioned t 2} / t _1. If the thickness ratio of each layer is set to be outside this range, it becomes difficult to achieve high strength by the polyamide layer, or monomaterialization becomes unsatisfactory.

Further, the biaxial stretching is a process necessary for increasing the strength of the film by the above-mentioned coextrusion, and is performed by a means known per se. Specifically, the film obtained by coextrusion is stretched in the longitudinal and horizontal directions at a temperature equal to or higher than the glass transition point of polyolefin and polyamide and lower than the melting point. The draw ratio is not particularly limited as long as the film is not broken by overstretching, but in general, it is preferably about 2 times or more, particularly about 2.5 to 4 times in both vertical and horizontal directions. As a result, the polyolefin layer 1 and the polyamide layer 3 are oriented and crystallized, and high strength can be realized.

In the two-layer coextruded laminated film of the present invention thus obtained, high strength is secured by the stretched polyamide layer 3, and such high strength is obtained by heat sealing using the polyolefin layer 1. Is not impaired. Further, the presence of the polyamide layer 3 also improves the barrier property against oxygen. Further, since the polyamide layer 3 is very thin compared to the thickness of the polyolefin layer 1 (1.5 to 5% of the polyolefin layer, particularly 3 to 5%), the requirement for monomaterialization is satisfied. The film is very good for recycling.

In particular, the two-layer coextruded laminated film of the present invention contains various substances as a packaging bag formed by heat-sealing (three-way sealing, four-sided sealing, etc.) in which polyolefin layers 1 are laminated so as to face each other. Used for use. Such a packaging bag exhibits a piercing strength of 9.0 N or more (JIS Z-1707) even though the oriented crystals of the polyolefin layer 1 are broken.

The excellent effect of the present invention will be shown in the following experimental example. The piercing strength of the film was measured by the following method.

[Puncture strength]
The piercing strength of the film was measured according to JIS Z-1707 (1997). The average value was taken as the measured value with the number of measurements n = 3.

<Examples 1 to 11>
A low-density polyethylene resin having a density of 0.91 g / cm ³ as a polyolefin layer resin and nylon 6 having a density of 1.14 g / cm ³ as a polyamide layer resin were put into two extruders, respectively, and fused from a T-die. Co-extruded to obtain a two-layer co-extruded laminated film. The draw ratio was 2.5 times in each of the vertical and horizontal directions. The thickness of the cross section of the obtained film was measured with a microscope, and the thickness ratio was calculated. These are shown in Table 1 together with the results of piercing strength.

<Comparative Examples 1 to 4>
A film was prepared in the same manner as in Examples 5 to 8 except that the polyolefin resin layer was made into a single layer. The evaluation results are shown in Table 1.

<Example 12>
Using the two-layer coextruded laminated film prepared in Example 1, a package (130 mm × 213 mm) having an open side was prepared. Specifically, two two-layer coextruded laminated films prepared in Example 1 were prepared and laminated so that the polyolefin layers face each other. Next, a seal bar set at 180 ° C. was applied to the surface of the polyamide layer corresponding to the seal portion. The seal portion was formed leaving one side for filling the contents. This gave a packaging bag. Then, 300 g of water was filled as the contents from the remaining one side of the opening, and the one side was similarly heat-sealed at 180 ° C. to prepare a packaging bag filled with the contents. Even if the packaging bag filled with the contents was dropped 5 times from a height of 100 cm in a posture horizontal to the floor surface, no bag breakage occurred.
From the above examples, by forming a two-layer coextruded laminated film of polyolefin and polyamide, the film is excellent in recyclability from the viewpoint of monomaterial and has sufficient strength even when used as a packaging bag. You can see that.

1: Polyolefin layer 3: Polyamide layer

Claims (6)

In a two-layer coextruded laminated film in which a polyamide layer and a polyolefin layer are laminated,
The two-layer coextruded laminated film is biaxially stretched.
The two-layer coextruded laminated film, wherein the polyamide layer has a thickness of 1.5 to 5% of the thickness of the polyolefin layer. The two-layer coextruded laminated film according to claim 1, wherein the polyolefin is an ethylene resin. The two-layer coextruded laminated film according to claim 1 or 2, wherein the polyamide is nylon 6. The two-layer coextruded laminated film according to any one of claims 1 to 3, wherein the thickness of the polyamide layer is in the range of 2 to 15 μm. The two-layer coextruded laminated film according to any one of claims 1 to 4, wherein the piercing strength (JIS Z-1707) is in the range of 4.5 N or more. A bag-shaped container comprising the two-layer coextruded laminated film according to any one of claims 1 to 5, wherein the polyolefin layer is located inside.

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