JPH04185322A - Multi-layer film - Google Patents

Abstract

PURPOSE:To improve the stretchability of saponified matter, the accuracy of ununiform section of the multi-layer film concerned and the dispersion of its thickness by a constitution wherein the multi-layer film concerned has a structure prepared by sandwiching saponified ethylene-vinyl acetate copolymer layer in between polyamide-based resin layers and mixed resin of nylon 6 and amorphous polyamide-based resin is employed as at least one of the polyamide-based resins. CONSTITUTION:The multi-layer film concerned has tree-layer structure consisting of polyamide-based resin layer, saponified ethylene-vinyl acetate copolymer layer, the ethylene content of which is 20-65mol% and the degree of saponification of which is 90% or more, and the polyamide-based resin layer. At least one layer of said polyamide-based resin layer of the multi-layer film concerned, which is formed in flat film and biaxially stretched in succession, is made of mixed resin layer consisting of 50-95wt.% of nylon 6 resin and 50-5wt.% of amorphous polyamide-based resin. In this case, the nylon 6 resin is preferably mixture consisting of 10-95 pts.wt. of aromatic polyamide resin to 100 pts.wt. of nylon 6 resin.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a flat multilayer film suitable as a packaging film.

<Conventional technology> Ethylene content is 920 to 65 mol% and saponification degree is 9.
Various multilayer films containing saponified ethylene-vinyl acetate copolymer (hereinafter referred to as saponified material) layers of 0% or more can be found here and there, but these are usually made into tube shapes by the inflation method, and are made using T-die, etc. Items extruded into a flat shape were not included. The reason for this is that saponified materials are usually difficult to stretch, and for this reason, stretching of flat films by the T-die method has not been common. On the other hand, film formation by the inflation method has other problems such as insufficient accuracy in thickness deviation and large variations in thickness.

<Means for Solving the Problems> Under these circumstances, the present inventors decided to pursue a flat multilayer film containing a saponified material layer, and by sandwiching the saponified material with polyamide resin layers. Considering the fact that the saponified product itself becomes easier to stretch, a mixed resin of 50 to 95 M% of nylon 6 resin and 50 to 5% by weight of amorphous polyamide resin is added to at least one of the polyamide resins. The present invention was finally arrived at by taking note of the fact that the use of a polyurethane resin makes it easier to stretch. That is, the present invention aims to improve the stretchability of the saponified material by adopting the above-mentioned basic structure, and thereby improve the uneven thickness accuracy and thickness variation of the multilayer film itself. In this article, we will discuss the methods to solve the problems in the following.

Polyamide resins according to the present invention include nylon 6, nylon 66, nylon 610, nylon 12, copolyamides such as nylon 6-66 copolymer, nylon 6-610 copolymer, and aromatic polyamides. Examples include resins, amorphous polyamide resins, and mixtures thereof, and there are no particular limitations. Nylon 6 here! ! What is fat?
-Caprolactam is a well-known product obtained by ring-opening polymerization. Furthermore, the aromatic polyamide resin is not particularly limited as long as it has a structure having an aromatic ring in the main chain and/or side chain, but it is usually preferable to have crystallinity, and more generally meta or polyamide resin. An example is a polyxylylene polymer obtained by polycondensation of xylylene diamine and a dicarboxylic acid having about 4 to 12 carbon atoms. Among them, polymethaxylylene adibanite synthesized from metaxylylene diamine and adipic acid is preferred, and such a polymer has properties such as gas barrier properties, low water absorption, and low moisture permeability.

At this time, a blend of nylon 6 resin and aromatic polyamide resin may be used, and the blending amount is 10 parts by weight of aromatic polyamide FM4 resin per 100 parts by weight of nylon 6 resin.
It is desirable that the amount is about 95 parts by weight, but it is not limited to this range and may be used by appropriately blending.

Furthermore, amorphous polyamide resin is a general term for those without crystallinity or those with poor crystallinity, and is not particularly limited, but generally has an aromatic ring in the main chain and/or side chain, etc. An example is semi-aromatic polyamide. Specific examples include polymers and ternary copolymers of dicarboxylic acids such as terephthalic acid and isophthalic acid and diamines such as hexamethylenecyamine, but there are no particular limitations. It has excellent gas barrier properties when wet, for example, certain amorphous polyamides have a 25 μm thickness.
O%RH oxygen permeability of 39cc/m”, 24h
r (23℃), 17cc/m” at 100%RH,
It is also possible to secure a value of about 24 hours (23°C).

The multilayer film according to the present invention includes a polyamide resin layer, an ethylene content of 20 to 65 mol%, and a saponification degree of 90.
% or more of a saponified ethylene-vinyl acetate copolymer layer and a polyamide resin layer, and at least one of the layers is a polyamide resin having a specific composition, There is no particular restriction on the total thickness, but an example is usually about 8 to 100 microns, preferably about 10 to 60 microns. In addition, the polyamide type mentioned above? ! There is no problem even if other appropriate third components are added to the fat or saponified material.

In this case, the structure of the multilayer film may be 3 or more layers, preferably about 3 to 7 layers. When creating multiple layers,
There are no particular restrictions on the resins used for the other layers, and various resin layers may be used in appropriate combinations. Examples of commonly used resins include olefin polymers. Such olefin polymers include, for example, homopolymers of olefins, mutual copolymers, copolymers with other copolymerizable polymers, such as other vinyl thread polymers, and modified copolymers of these. etc. can be exemplified. Specifically, for example, polyethylene of various densities ranging from low density to high density (including linear low density polyethylene), polypropylene, polybutene, mutual copolymers thereof, ionomer resins, ethylene-acrylic acid copolymers, ethylene- Vinyl acetate copolymer, modified polyolefin system I! Examples include l fats.

Here, modified polyolefin resins include single or copolymers of the above olefins, and derivatives such as maleic acid, fumaric acid, acrylic acid, other appropriate unsaturated carboxylic acids, or their acid anhydrides, esters, or metal salts. Typical examples include modified polymers obtained by copolymerizing, for example, graft copolymerizing, and the above-mentioned modified polymers alone or in mixtures with other components, such as other olefin polymers, are also included in the modified polyolefin resins. include. These modified polyolefin resins have excellent adhesive properties when multilayered! Other examples of such adhesive resins include ionomer resins, ethylene-ethyl-acrylate resins, ethylene-vinyl alcohol copolymers, etc., and there are no particular limitations.

Particularly preferred among the olefin polymers used are low density polyethylene, linear low density polyethylene, ionomer resins, modified polyolefin resins, ethylene-vinyl acetate copolymers, and the like. The above J-olefin polymers may be used alone or in combination of two or more. A layer made of such an olefin polymer can be conveniently used as a heat-sealing layer if necessary.

Gas barrier resins other than saponified materials can also be used in other layers! Examples of the WI4 resin having gas barrier properties include polyacrylonitrile resins, polyvinylidene chloride resins, and polyester resins.

Although it is clear from the above description that various combinations can be employed as the resins for each layer constituting the multilayer film, more preferable combinations are exemplified as follows.

In the following, each alpha head symbol represents the following resin.

A: Polyamide resin (3) Modified polyolefin resin C Olefin polymer D: Saponified product A/D/A, A/D/A/B/C1 C/B/A/D/A/B/C1 B /A/D/A/B/C5 A/D/B/A/B/C In addition, in the above multilayer film, B is □ using a different type of modified polyolefin resin. It goes without saying that the same type of olefin polymer may be used for C, and that different types of olefin polymers or the same type of C may be used.

It is also possible to use the above combinations in which B is replaced with an ionomer resin.

The thickness of the polyamide resin layer according to the present invention is usually 2 to 35 microns per layer, preferably 3 to 20 microns, and the thickness of the saponified material is usually 1 to 30 microns, preferably 2 to 20 microns, Adhesive properties added as required! The thickness of the tfr# layer and the olefin polymer layer may be set as appropriate. Of course, these descriptions are not particularly limited, and any values can be used as required.

Regarding the oxygen permeability of multilayer films, see 20. c/
m2.24H,atm (20"C165%RH) or less, preferably l0ec/m",24H,atm (20℃
, 65% RH) or less, but of course there are no particular restrictions on these values, and any value can be used as required.

Further, even if the multilayer film of the present invention has heat shrinkability, it may have poor heat shrinkage or substantially no heat shrinkage. The heat shrinkage rate or the heat shrinkage rate of a multilayer film that has poor heat shrinkability or substantially no heat shrinkability may be determined as appropriate.5 Although there are no particular restrictions, one example is heat shrinkability. If the material has a heat shrinkage rate of 5 to 50% in the longitudinal direction, preferably 10 to 30%, and 5 to 50% in the transverse direction, preferably 10 to 3% in a 90°C hot water bath for 30 seconds. can be,
If it has substantially no heat shrinkability or poor heat shrinkability, the heat shrinkage rate in a 90°C hot water bath for 30 seconds is less than 5% in the machine direction, preferably 0 to 3%, and 5% in the transverse direction. %, preferably about 0 to 3%.

In the present invention, a film is formed in a flat shape and successively biaxially stretched, and a specific example thereof will be described.The present invention may be formed into a film by coextrusion into a flat shape using a 5-T die. Film formation is not particularly limited, but is generally carried out by extrusion casting on a cooled chill roll, and the present invention is achieved by stretching the film thus formed either continuously or in a separate process. The stretching can be exemplified by a two-wheel stretching method, and the necessary stretching is generally performed by longitudinal stretching using a roll stretching machine and transverse stretching using a tenter stretching machine, but the stretching means is not particularly limited. The stretching conditions depend on the characteristics of the polymer used for the multilayer film and are not particularly limited, but usually the stretching conditions are 2 to 5 times in the longitudinal direction and 2 to 6 times in the transverse direction (the stretching order may be reversed, vertically and horizontally). Biaxial stretching can be exemplified, and the stretching temperature in the longitudinal direction is 6
0 to 120°C, preferably 70 to 100°C, transverse stretching temperature 70 to 180°C, preferably 100 to 1
An example is a range of 60°C.

After stretching, heat treatment is performed as necessary, but if a high degree of heat shrinkability is required, heat treatment may not be performed. The heat treatment may be carried out by any means, but it is generally carried out in a continuous process following the transverse stretching using a tenter stretching machine. When performing heat treatment, it is sometimes performed in a state where the width is reduced (relaxed) within 20%, preferably 3 to 10%, but of course, the width may be set to be the same as the width during transverse stretching, or The width of the heat treatment may be set to a width higher than that during horizontal stretching.The heat treatment temperature may be used to obtain a multilayer film with heat shrinkability or to obtain a multilayer film with poor heat shrinkage or substantially no heat shrinkage. The cases are different; the former is often carried out in a high temperature range, and the latter in a low temperature range. For example, in order to obtain a heat-shrinkable multilayer film, the heat treatment is carried out using a tenter stretching machine at less than 150°C, preferably at 80°C to 100°C.
Within the range of 30℃, and if necessary, within 20% in the width direction,
It is also possible to carry out the shrinkage in a state preferably in the range of 3 to 10%, and in order to obtain a multilayer film that does not have heat shrinkability or has poor heat shrinkability, heat treatment is carried out at 150° C. using a tenter stretching machine. Above, preferably 180-250℃
If necessary, it is possible to reduce the width by within 20%, preferably by 3 to 10%, but these values are just examples and are subject to particular restrictions. Not. When obtaining a film with heat shrinkability, heat treatment is carried out for the purpose of preventing natural shrinkage; (to suppress shrinkage) may have a slightly different purpose.

Applications of the multilayer film according to the present invention include food packaging materials such as meat, processed meat, retort foods, aquatic foods, microwave products, frozen foods, and other various packaging materials, as well as deep-drawn containers, etc. There are no particular restrictions on its use, and it can be applied to all fields.

When used as a packaging material, the packaging form can be opened into overlapping packaging, sleeve packaging, etc., or may be heat-sealed into a bag shape, but there is no particular restriction, but if it is made into a long tube-shaped film by applying a center seal. It can also be used as a packaging material by simply cutting it into a predetermined size, and such usage is also possible, and there are no particular restrictions.

The above is just an example of preferred embodiments of the present invention, and the present invention is capable of taking any embodiments without being limited to such descriptions.

<Example 1> Polyamide resin layer A containing nylon 6tll fat 90M amount % and amorphous polyamide resin 10i amount %, ethylene content 44 mol %, ethylene-vinyl acetate copolymer with saponification degree of 99% or more The combined saponified layer (melting point 164°C) D was coextruded from a T-die onto a chill roll with cooling water circulating in the order A/D/A to obtain a flat three-layer film, and then It was longitudinally stretched to 3 times using an 80"C roll stretching machine, then horizontally stretched to 3.5 times using a tenter stretching machine in an atmosphere of 140°C, and then the width was reduced by about 4% using the same tenter at 100°C. The thickness of the film thus obtained was A,
D, A = 5.5.5μ, and the heat shrinkage rate in hot water at 90°C for 30 seconds was 15% in the longitudinal direction and 20% in the transverse direction. These films had good thickness deviation accuracy and little variation in thickness. The oxygen permeability is 7 ee/m”, 2
4H, ATM (20°C, 65% RH).

<Comparative Example 1> A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that a polyamide polymer layer made of only nylon 6 was used in Example 1, and stretching was performed under the same conditions. Many tears occurred during tenter stretching, and stable stretching was not possible.

<Example 2> Using the same resin as in Example 1, a flat three-layer film was obtained by coextrusion using a chill roll with cooling water circulating from a T die in the order of A/D/A. Thereafter, it was longitudinally stretched 3 times in a roll stretching machine at 80°C, and further stretched to 14
It was laterally stretched 3.5 times using a tenter stretching machine in an atmosphere of 0°C, and then heat-set in an atmosphere of 210°C while reducing the width by about 4% using the same tenter. The thickness of the film thus obtained was A, D, A=5.5.5μ and 5.5μ.
The heat shrinkage rate in hot water at 90°C for 30 seconds was 1% in the longitudinal direction and 1% in the transverse direction. These films had good thickness deviation accuracy and little variation in thickness. In addition, the oxygen permeability is 7 cc/m", 24 H,at
m (20°C, 65% RH) and 4. cc/m”
, 24H, atm (20°C, 65% RH).

<Example 3> Practical] Using the same resin, A/D/A/B/C (in this case, B is a modified linear low-density polyethylene resin, and C is a linear low-density polyethylene resin) ) A heat-shrinkable multilayer film was obtained in the same manner as in Example 1, except that the film was made into a 5-layer film as shown in Example 1. (No. I above) In addition, as No. 2, a multilayer film with poor heat shrinkability was obtained in the same manner as in Example 1 except that the heat treatment was performed in an atmosphere of 210°C.

In Experiment Nos. 3 to 6 below, films were formed in the same manner, and the materials used, thickness, stretching temperature, and heat treatment temperature were set as shown in Table 1.

On this occasion.

LL is linear low density polyethylene LL, high melting point linear low density polyethylene LL t
L is a modified linear low-density polyethylene with a low melting point L is a mixture of modified linear low-density polyethylene and linear low-density polyethylene PA is a mixture of nylon 6 and amorphous polyamide resin (mixing ratio of Example 1) PP is polypropylene Modified PP is a mixture of modified polypropylene and polypropylene PA, and PA is a mixture of 100 parts by weight of nylon 6 resin, 50 parts by weight of aromatic polyamide resin, and 15 parts by weight (9.1% by weight) of amorphous polyamide resin. t is a nylon 6-nylon 66 copolymer.

As a specific example of the characteristics and preferred uses of the multilayer film obtained in this way, No. 1 is preferably used as a material for heat-shrinkable packaging for boiled foods, casings for processing, meat, general foods, etc. , No. 2 has the same characteristics as No. 1, and is preferably used in the non-shrinkable field of No. 1, as packaging materials for frozen foods, various foods, etc., and No. 3 is used for sealing. Items No. 4 are intended to increase strength, and Items No. 5 are intended to improve heat resistance and are suitable as packaging materials for retort food. No. 6 is particularly suitable as a packaging material for foods, etc., which requires a high degree of gas barrier property. The uses shown above are merely examples of preferred ones, and the present embodiment is not limited to such descriptions.

(Hereinafter referred to as "Jiba") <Effects of the Invention> Since the present invention uses a specific polyamide polymer layer as at least one layer in the multilayer film, it has good hot stretchability and can be stretched in a flat shape, increasing the stretching speed. There are also advantages such as the possibility of Furthermore, the film thus obtained has excellent thickness unevenness accuracy and little thickness unevenness, so it is suitable for use as a variety of packaging materials, and there are great expectations for its future use expansion.

For example, multilayer films with heat shrinkability can be provided, making them excellent for use in various shrink packaging applications.
It also has the effect of suppressing the generation of meat juices and the like over time by packaging the meat in close contact with it.

Furthermore, it is possible to provide multilayer films that have virtually no or poor heat shrinkability, or have low oxygen permeability, making them suitable for various packaging materials and all other fields. It also has the advantage of being adaptable, and is expected to have a wide range of uses in the future.

Claims (3)

[Claims] (1) Polyamide resin layer and ethylene content 20-6
It has at least a three-layer structure comprising a saponified ethylene-vinyl acetate copolymer layer with a saponification degree of 5 mol % and a saponification degree of 90% or more and a polyamide resin layer, and is formed into a flat film and sequentially biaxially stretched. At least one of the polyamide resin layers in the multilayer film made of nylon 6 resin and amorphous polyamide resin 5
A multilayer film characterized in that it is a mixed resin layer of 0 to 5% by weight. (2) The multilayer film according to claim 1, wherein the nylon 6 resin is a mixture containing 10 to 95 parts by weight of an aromatic polyamide resin based on 100 parts by weight of the nylon 6 resin. (3) The oxygen permeability of the multilayer film is 20_c_c/
m^2, 24H, atm (20℃, 65%RH) or less,
Preferably 10_c_c/m^2, 24H, atm (
The multilayer film according to claim 1, which has a temperature of 20° C., 65% RH or less.