JPH05261873A - Polyamide type heat-shrinkable multilayered film for tray container package - Google Patents

Abstract

PURPOSE:To especially enhance pinhole resistance and gas barrier properties by successively laminating a polyamide resin layer, a modified polyolefin adhesive resin layer and a polyolefinic resin layer and specifying the compsn. or various conditions of the polyamide resin layer. CONSTITUTION:A polyamide heat-shrinkable film for a tray container package is constituted of a multilayered plastic film containing a multilayered structure wherein a polyamide layer, a modified polyolefin adhesive resin layer and a polyolefinic resin layer are provided in this order so as to be adjacent to each other. The polyamide resin layer is formed from a compsn. consisting of 20-80wt.% of a xylylenediamine type polyamide resin and 80-20wt.% of other polyamide resin. The total thickness of the film is set to 10-40mum. Further, the oxygen permeability of the film within a total humidity region and a water bonded state is set to 100cc/m<2>.day.atm or less. By this constitution, pinhole resistance and gas barrier properties are especially enhanced.

Description

Detailed Description of the Invention

[0001]

The polyamide-based heat-shrinkable multilayer film for tray container packaging of the present invention is used as a packaging film for processed meat products such as ham and sausage, and processed fish products such as kamaboko, which are placed on a tray container. used. That is, the present invention uses a horizontal pillow type automatic wrapping machine to cover foods placed on a tray containing an oxygen scavenger with a shrink film having an excellent gas barrier property, and deaerate the internal air. After that, the invention relates to a barrier shrink film intended to obtain a shrink-wrapped package which is heat-sealed and passed through a heat-shrink tunnel to obtain a tight shrink package. Note that such a packaging method is hereinafter referred to as "barrier shrink packaging".

[0002]

2. Description of the Related Art Hams currently placed in tray containers. As a packaging film for processed meat products such as sausages and processed fish products such as kamaboko, stretch films of vinyl chloride resin are used as wrap films, but the problem is that the storage period is short because of poor gas barrier properties. Also, there is a problem of global environmental pollution due to generation of chlorine gas at the time of waste incineration, and there has been an urgent need for a film or packaging system that can replace it.

That is, recently, as such a packaging system, an automatic packaging system by degassing and shrinking packaging, that is, "barrier shrink packaging" has been developed, and as described in Japanese Patent Application Laid-Open No. 58-136442, shrinkage is performed. As the film, ethylene-vinyl acetate copolymer / ethylene-vinyl alcohol copolymer / ethylene-
A multilayer film of vinyl acetate copolymer is used, but this has a problem of poor pinhole resistance.
In these packages, if there are pinholes, the contents are oxidized and discolored, and the poor pinhole resistance means a fatal defect.

Further, these packages are generally left under low temperature and high humidity, and under such conditions, external moisture and moisture from the package accumulate on the film surface and water adheres thereto. In the case where the core layer is an ethylene-vinyl alcohol copolymer, the gas barrier property is significantly lowered due to the moisture absorption of the ethylene-vinyl alcohol copolymer. However, it is desired that the gas barrier property is excellent even under high humidity. For example, in the case of an ethylene-vinyl alcohol copolymer having an ethylene content of 32 mol% in the above-mentioned multi-layered film, generally,
It is composed of 5-6μ thickness, but it is thicker than 1
Even at 0 μ, the elementary transmittance is 100 cc / m ² due to the moisture absorption of the ethylene-vinyl alcohol copolymer. day. at
m (20 ° C) or more. In addition, in the storage test results of the beef and processed meat products by the present inventors, the oxygen permeability is 1
00 cc / m ² . day. If it is less than atm, the preservability is excellent, but if it exceeds this, discoloration easily appears.

Resins having excellent pinhole resistance include nylon-6, nylon-66 and nylon-12.
Etc., and a multilayer heat shrinkable film of this and a polyolefin is described in Japanese Examined Patent Publication No. 1-43626, which has a poor gas barrier property even under low humidity, and is under high humidity and in a state where water is attached. Then, the oxygen transmission rate is 100cc
/ M ² . day. There is a problem that the temperature easily exceeds the atm (20 ° C.) or more, and the contents easily discolor. The present invention has been completed with the object of solving these problems.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention provides a heat-shrinkable polyamide polyamide multilayer film for tray container packaging, which has excellent pinhole resistance and gas barrier properties.

[0007]

In order to solve the above-mentioned problems, the present inventor has found that xylylenediamine type polyamide (hereinafter referred to as "MX nylon") is not easily affected by humidity and is excellent in gas barrier property. The present invention has been completed.

That is, the present inventor
The multi-layer heat-shrinkable film for a tray container package of the present invention was completed, paying attention to the fact that the gas barrier property is not significantly reduced even in the entire humidity range and in the state where water is attached.

That is, the heat-shrinkable film of the present invention is
The polyamide resin layer, the modified polyolefin-based adhesive resin layer, and the polyolefin-based resin layer are multilayer plastic films including a laminated structure in which they are adjacent in this order, and the polyamide resin layer contains 20 to 80 weight of the xylylenediamine-based polyamide resin. %, Other polyamide resins 80 to 20
% By weight, the total thickness of the film is 10 to 40 μm, and the oxygen transmission rate is 100 cc / m ^{2 in} the entire humidity range and in the state where water is attached. day. It is characterized by being atm or less.

In the present invention, the xylylenediamine type polyamide resin, that is, "MX nylon" means metaxylylenediamine alone or 60% of metaxylylenediamine.
Mixed xylylenediamine with para-xylylenediamine containing the above is used as a diamine component, and one or more of α, ω-straight chain aliphatic dibasic acid having 6 to 12 carbon atoms such as adipic acid and sebacic acid. It is a polyamide resin synthesized by the polycondensation reaction of.

The other polyamide resin is a kind of polyamide resin selected from nylon-6, nylon-66, nylon-10, nylon-11 and nylon-12, or
A polyamide compound composition comprising a copolymer or a blend of two or more of these.

It is suitable that the composition of the polyamide resin is 20 to 80% by weight of MX nylon and 80 to 20% by weight of other polyamide resin, and when the content of MX nylon is less than 20% by weight, it adheres to high humidity and water. The oxygen transmission rate in this state is 100 cc / m ² . day. This is because the gas barrier property exceeds atm and the gas barrier property is poor, and when it exceeds 80% by weight, the film becomes too hard, and 40 to 60% by weight is preferable.

The modified polyolefin-based adhesive resin is obtained by copolymerizing an olefin homopolymer or copolymer with an unsaturated carboxylic acid such as maleic acid, fumaric acid or acrylic acid or a derivative thereof such as an acid anhydride or ester. For example, a modified polymer obtained by graft copolymerization, which includes modified low-density polyethylene, modified linear low-density polyethylene, modified ethylene-
Examples thereof include vinyl acetate copolymer and modified polypropylene.
The modified polyolefin-based adhesive resin may be one of these or other polyolefins, that is, low density polyethylene, linear low density polyethylene, extremely low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer. , Ethylene-methyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid copolymer or ionic copolymer of ethylene-methacrylic acid copolymer and metal Coalesce, polypropylene, propylene-ethylene copolymer, propylene-butene copolymer,
Blends with propylene-ethylene-butene terpolymers are also included.

The polyolefin-based resin includes a polyolefin-based resin selected from the above-mentioned polyolefins or a polyolefin-based compounded composition comprising a blend of two or more of these. Since MX nylon alone is inferior in heat-sealing property, it becomes easy to form a bag by forming a multilayer with the above-mentioned polyolefin.

The total thickness of the film of the present invention is 10-40.
If it is less than 10 μm, the strength of the film is weak and the suitability for automatic packaging is poor, and if it exceeds 40 μm, it is excessively packaged in terms of cost. Therefore, a film having a thickness in this range is suitable for shrink-wrapping of food. The thickness of the polyamide resin layer of the present invention is 5 to 20 µ, and if it is less than 5 µ, the oxygen permeability is 100 even when the MX nylon content is 80% by weight, which is the highest.
cc / m ² . day. If the thickness exceeds 20 μm, the film becomes too hard and the tray is deformed when contracted. Therefore, the thickness in this range is suitable. The heat-shrinkable film of the present invention has a shrinkage ratio of more than 10% both longitudinally and laterally after 10 seconds after being placed in an atmosphere at a temperature of at least 100 ° C. in order to shrink the animal meat processed product after it is automatically packaged. This is because if it is less than this, the shrinkage finish cannot be finished neatly.

The constitution of the present invention is a multilayer plastic film having a laminated structure in which a polyamide resin layer, a modified polyolefin-based adhesive resin layer, and a polyolefin-based resin layer are adjacent in this order. Adhesive resin layer / polyolefin resin layer, and polyolefin resin layer / modified polyolefin adhesive resin layer / polyamide resin layer / modified polyolefin adhesive resin layer / polyolefin resin layer, etc. Depending on the situation, more layers may be formed.

As the method for producing the film of the present invention, polyamide resin, modified polyolefin adhesive resin, polyolefin resin and the like are melt-extruded from a laminating die by a co-extrusion method, cooled and solidified to 60 to 100 ° C.
Reheating to a stretching temperature within the above temperature range, biaxial stretching at least twice in the longitudinal direction and at least two times in the transverse direction, and then cooling. The coextrusion method for the multilayer sheet is preferably either a tubular extrusion using an annular die or a flat extrusion using a T die using a plurality of extruders, but is not particularly limited. When a multilayer sheet is melt extruded into a tube shape from an annular die, the tube is immersed in a water tank to cool and solidify the tube, and the tube is reheated to a stretching temperature of 60 to 100 ° C and a take-up roll is used in the longitudinal direction. Stretch it 2 times or more, and in the lateral direction, put compressed air into the tube to expand the tube.
By simultaneously stretching the film twice or more, a film having a good appearance can be manufactured. The stretching ratio is not particularly limited, but in general, a stretching ratio of 2.5 to 4.0 times is used in each of the longitudinal direction and the transverse direction, but the shrinkability is easily obtained. Therefore, it is desirable that at least one of them has a draw ratio of 3 times or more. In addition, the film of the present invention, when left to stand naturally, has a natural shrinkage that the film itself has, which deteriorates the deformation and the surface state. Therefore, in order to prevent this, heat treatment is performed so as not to deteriorate the heat shrinkage property so much. It is more preferable to reduce the amount of natural shrinkage.

Further, what is necessary is to add a tackifier, an antifogging agent, an antistatic agent, an antiblocking agent, etc. to the polyolefin resin layer of the present invention to form a heat-shrinkable film similar to a stretch film. Not hindered.
Examples of the tackifier include rosin or its derivative, terpene resin, petroleum resin, coumarone-indene resin, and hydrogenated resins thereof.

Further, the method for measuring the physical properties of the film in the present invention will be described below. 1. Pinhole resistance Rotation angle: 5/4 rotation, Stroke: 150mm Gelbo flex tester, sample: 200mm × 280mm, 5 ℃
Was bent 2000 times and the number of pinholes was measured. 5 or less pinholes were judged to be good, and pinholes above this were judged to be defective.

2. Heat shrinkage rate A film cut into a square with a length and width of 10 cm is 100
It was immersed in a glycerin bath at 0 ° C for 10 seconds and calculated by the following formula. ((10−X) / 10) × 100 = Heat Shrinkage (%) Note that X is the dimension of the sample after immersion in glycerin. In the evaluation, a heat shrinkage rate of 10% or more was good and a heat shrinkage rate of less than 10% was bad.

3. Tray container wrapping Using a horizontal pillow type automatic wrapping machine, food wrapped in a tray containing oxygen absorber is wrapped with shrink film, and after deaerating the air inside, heat sealing is performed. Length of about 1m
The product is passed through a heat shrink tunnel set at 120 ° C. for about 5 seconds to obtain a shrink package. Those with excellent tension and no deformation of the tray were evaluated as good, and those with tension or deformation of the tray were evaluated as poor.

4. Oxygen permeability Measured using an Oxtran 10/50 manufactured by Mocon.
The oxygen transmission rate with water adhered was measured by sandwiching the both sides of the sample with water-absorbing paper, and then sandwiching both sides with a PE film having a thickness of 20 μm in a chamber of Octran 50/50. .. Oxygen permeability is 100
cc / m ² . day. Atm or less was judged to be good, and exceeding this was judged to be bad.

[0023]

INDUSTRIAL APPLICABILITY The polyamide-based heat-shrinkable multilayer film for tray container packaging of the present invention is excellent in gas barrier property, pinhole resistance, and tightness property, and therefore is excellent in storability and appearance, and is a barrier shrink. Most suitable as a packaging film.

[0024]

[Examples and Comparative Examples] Examples and comparative examples will be shown below.
The contents of the present invention will be described more specifically. The present invention is
Of course, the matters described in the examples are not limiting.

Examples 1 to 11 and Comparative Examples 1 to 4 As shown in Examples and Comparative Examples shown in Table 1, Table 2 and Table 3, the core layer is a polyamide resin and the intermediate layer is a modified polyolefin adhesive. A laminated tubular unstretched raw material in which both outer layers of the resin were made of a polyolefin resin was obtained by a coextrusion method. This was drawn at a stretching temperature of 90 ° C. in a length of 3 times and a width of 3.3
The film was double-axially stretched by an inflation method to obtain a gas barrier shrink film. The pinhole resistance, heat shrinkage, tray container wrapping property, and gas barrier property of this film were measured.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

Here, LL: Linear low-density polyethylene (Ultzex manufactured by Mitsui Petrochemical) Modified LL: Modified linear low-density polyethylene (Admer manufactured by Mitsui Petrochemical) EVA: Ethylene-vinyl acetate copolymer (Evatate manufactured by Sumitomo Chemical) ) Modified EVA: Modified ethylene-vinyl acetate copolymer (Novatech manufactured by Mitsubishi Kasei) LD: Low density polyethylene (Sumikasen manufactured by Sumitomo Chemical) Modified LD: Modified low density polyethylene (Admer manufactured by Mitsui Petrochemical) MX: Metaxylylenediamine Polyamide (Mitsubishi Gas Chemical nylon MXD6) N-6: Nylon-6 (Toray CM1021) N-6.66: Nylon-6.66 copolymer (Toray C
M6041) N-6.12: Nylon-6.12 copolymer (Toray C
M6541).

In Comparative Example 1, since the amount of MX nylon mixed was small, the gas barrier property was poor, and in Comparative Example 2, the amount of MX nylon mixed was too large, and the pinhole resistance was poor.
In Comparative Example 3, since the polyamide layer is too thin, the gas barrier property is inferior. In Comparative Example 4, the polyamide layer is too thick, so that the shrinkage stress is too strong and the tray is deformed.

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Claims (7)

[Claims] 1. A polyamide resin layer, a modified polyolefin-based adhesive resin layer, and a polyolefin-based resin layer are multilayer plastic films including a laminated structure in which they are adjacent in this order, and the polyamide resin layer is a xylylenediamine-based polyamide resin. Is 20 to 80% by weight, the other polyamide resin is 80 to 20% by weight, and the total thickness of the film is 10
Is about 40 μ, and the oxygen permeability is 100 cc / m ^{2 in} the entire humidity range and in the state where water is attached. day. A polyamide-based heat-shrinkable multi-layer film for a tray container package, wherein the heat-shrinkable polyamide-based multi-layer film has a thickness of atm or less. 2. The polyamide-based heat-shrinkable multilayer film for tray container packaging according to claim 1, wherein the xylylenediamine-based polyamide resin is a polyamide resin synthesized by a polycondensation reaction of meta-xylylenediamine and adipic acid. .. 3. A polyamide compound composition comprising another polyamide resin selected from nylon-6, nylon 66 and nylon 12, or a copolymer or blend of two or more of these polyamide resins. The polyamide-based heat-shrinkable multi-layer film for a tray container package according to claim 1. 4. The polyamide-based heat-shrinkable multilayer film for tray container packaging according to claim 1, wherein the modified polyolefin-based adhesive resin is a modified linear low-density polyethylene or a blend of the linear low-density polyethylene and the linear low-density polyethylene. 5. The modified polyolefin adhesive resin is a modified ethylene-vinyl acetate copolymer or ethylene-vinyl acetate copolymer.
The polyamide heat-shrinkable multilayer film for tray container packaging according to claim 1, which is a blend with a vinyl acetate copolymer. 6. The polyolefin resin is one kind of polyolefin resin selected from low density polyethylene, linear low density polyethylene, extremely low density polyethylene, and ethylene-vinyl acetate copolymer, or two or more kinds of these. The polyamide heat-shrinkable multilayer film for tray container packaging according to claim 1, which is a polyolefin-based compounded composition comprising a blended product. 7. The heat-shrinkable polyamide-based multilayer film for tray container packaging according to claim 1, wherein the polyamide resin layer has a thickness of 5 to 20 μm.