FI80236B - FLERSKIKTAD DJUPDRAGSFOLIE OCH DJUPFRYSBESTAENDIG VAKUUMDJUPDRAGSFOERPACKNING. - Google Patents

Abstract

1. Use of a multilayered co-extruded composite film (1') having two external layers (A, A') which correspond with regard to material and thickness and which comprise linear polyethylene or high-density polyethylene (low-pressure polyethylene, HDPE) and having two internal layers (B, B') which correspond with regard to material and thickness and which comprise an ethylene/methacrylic acid copolymer cross-linked with metal ions or an ethylene/vinyl acetate copolymer, in which film the external layers (A, A') are connected to the internal layers (B, B') by melt-bonding and the internal layers (B, B') are connected to one another by blocking, as self-supporting deepdrawn film, especially as film for the bottom part in the manufacture of deep-freeze-resistant vacuum deep-drawn packaging or vacuum deep-drawn packaging for sharp-edged packaged goods.

Description

80236

Multi-layer deep-drawing film and deep-freeze-proof vacuum deep-drawing package - Flerskiktad djupdragsfolie och djupfrysbeständig vakuumdjupdragsförpackning

The invention relates to multilayer deep-drawing films, in particular for the production of deep-freezing vacuum deep-drawing packages or vacuum-deep-drawing packages for sharp-edged products, and to a deep-freezing deep-drawing film with a foodstuff packaged together with a top film.

Multilayer deep-drawing films (lower films) for the production of deep-freeze-resistant packages according to the vacuum deep-drawing method are known. Laminates consisting of a polyamide film and a polyethylene layered on it are widely known. Such a film is excellently weldable due to its polyethylene layer, but it has the disadvantage that two working steps are usually required to produce these two film layers and one more step is required to join them. The crucial disadvantage is that in order to achieve sufficient puncture resistance, one of said film layers must be made of polyamide, which is a relatively expensive raw material.

Methods for making coextruded laminate films, the use of which makes it possible to produce a two- or multilayer film in a single operation, are also known. These methods mainly produce laminate films, which can be divided into three groups:

Hoses made using two or more annular nozzles which a) are used as such for the manufacture of packaging bags and b) hose films made in the same way, in which, however, the hose is cut and the film is used as a flat film.

In both cases, e.g. in the case of the use of two 2,80236 ring nozzles, films are formed which in each case consist of two interconnected layers. Such films and methods are known from DE-AS 11 36 818 and DE-PS 12 89 297.

c) Co-extruded laminate hoses, the different layers of which are joined together, eg by joining them together into a single laminate film so that their different layers can no longer be separated (DE-OS 19 66 466 and 21 02 377).

All of these multilayer films have the above-mentioned disadvantage, i.e. insufficient puncture resistance, if they do not use a relatively expensive polyamide material in at least one layer.

Another disadvantage of the known deep-drawing films, which occurs especially in complex deep-drawing molds, is due to the high space requirement of the polyamide or polyester layers. Therefore, the exact design of the deep-drawing film is not always possible.

The compound film described in Finnish patent application 831436 also belongs to the prior art. This patent application describes a film having two linear polymer outer layers of uniform material and thickness and two inner layers of uniform material and thickness consisting of metal ion crosslinked ethylene / methacrylate acid copolymer and ethylene / vinyl ethanol squeezing together.

This multilayer film is bonded by lamination to a single or multilayer carrier film and has proven to be very useful in puncture sensitive vacuum packs. When an ethylene / vinyl acetate copolymer is used for the inner layers, it contains up to 30% by weight, preferably 3 to 10% by weight of vinyl acetate.

When using multilayer films containing coextruded composite film with 3 80236 carrier films in addition to the composite film for vacuum packs, the total thickness of the composite film should be in the range of 80 to 250 etc. The thickness of the outer layer is preferably 1/2 to 4/5, while the inner layer is at least 1/5 and up to 1/2.

In connection with the compression joining of the inner layers, a bond is formed between these layers, which allows the layers to be mechanically separated from each other. Preferably, the bond strength between the layers does not exceed 100 cN / cm. Compression joining is performed according to the prior art using heat and pressure on a pair of press rollers.

By linear polymers used for the outer layers is meant polyethylenes which are prepared by copolymerizing ethylene with small amounts of alpha-olefin comonomers (C3 to C12). One such is LLDPE (linear-low-density polyethylene) having a density of 0.918 to 2245, preferably 0.930. Such a polyethylene has a melt index of between 0.2 and 4.0, preferably between 0.8 and 1.5.

Copolymers of ethylene for use in inner layers with vinyl acetate, respectively, ethylene / methacrylic acid copolymers crosslinked with metal ions, also called ionomer resins and marketed by Dupont under the trade name "Surlyn", are highly compressible, but still provide compressibility. i.e., both outer layers connected to the inner layers by fusion joints can, when both inner layers are compressed, move to a small extent relative to each other. In this case, in deep drawing, the outer layer forming the innermost part of the deep drawing mold, which is made of LDPE, for example, and which is fused to an inner layer of, for example, ethylene / vinyl acetate copolymer, is not automatically stretched an outer layer connected to the inner layer.

The object of the present invention is to obviate the above-mentioned known disadvantages, and to provide a packaging film with a very high strength and puncture resistance, which can be produced in one step from inexpensive raw materials, without the use of economically expensive materials. In particular, it is an object of the invention to provide a deep-drawn film, which in the context of the invention means a base film for a deep-drawing package, for freezable vacuum-deep-drawing packages, as well as for vacuum-deep-drawing packages for sharp-edged materials.

To accomplish this object, according to the invention, a coextruded composite film of the prior art is used as an independent deep-drawing film, in particular as a base film, for the production of , HDPE) and two inner layers of uniform material and thickness consisting of a metal ion crosslinked ethylene / methacrylic acid copolymer or an ethylene / vinyl acetate copolymer in which the outer layers are fused to the inner layers by melt bonding, and the inner layers.

Compared to known multilayer, deep-freeze-resistant vacuum deep-drawing packages or deep-drawing films for vacuum packaging of sharp-edged products, the deep-drawing film according to the invention is made of substantially cheaper raw materials than polyamide, such as linear polyethylene or high-ethylene ethylene ethylene / metakryylihappokopo-acrylate. Although the deep drawing film of the invention is not thicker than known deep drawing films, it is surprisingly equally tough and puncture resistant. The excellent strength of the deep-drawing film according to the invention is due, on the one hand, to the high mechanical impact resistance of the raw material groups 5,80236 used for the outer and inner layers, which in individual cases, e.g. linear-low-density polyethylenes (LLDPE) cN. The mechanical impact resistance of metal ion crosslinked ethylene / methacrylic acid copolymers, which are also suitable for the production of inner layers, is even higher, namely up to about 450 cN.

All figures for mechanical impact resistance given in the application are based on measurements according to ASTM D-1709-62 with a drop height of 650 mm and a film thickness of 25 μm.

On the other hand, the high puncture strength is due to the essential operation according to the invention of joining the surface of the outer layer of the coextruded hose to the inner layers by melt joining during extrusion, on the other hand only by compression.

For the purposes of the present invention, compression means that the inner layers adhere to one another in such a way that they are mechanically separable from one another. Preferably, the bond strength obtained by pressing the inner layers is at most 100 cN / cm. The pressing is expediently carried out using heat and pressure by means of a pair of compression rollers.

In contrast to the films known from DE-OS 21 02 377, in which the different layers of the finished laminate film are not specifically separable from each other, the mere compression joining of the inner layers of the deep-drawing film according to the invention provides tear prevention, which is explained as follows:

When the deep-drawing film according to the invention is subjected to a piercing stress, e.g. when a sharp-edged bone presses the deep-drawing film inside the deep-drawing package, a rupture may occur at the stress layer of the film layers - outer layer / inner layer - immediately adjacent to the stress point. In order to be able to break the other two layers of the 680236 deep drawing film according to the invention - inner layer / outer layer - the piercing force of the sharp-edged bone should again exceed the tear strength of the two layers in order to be able to tear these layers as well. However, since the tear strength of all planar structures is greater than their tear strength, a resistance force acts against the puncturing force of the bone at that point, which prevents the deep tension film according to the invention from tearing for a longer time and thus ensures that the package remains tight.

It is clear that in order to achieve an optimal deep-drawing behavior, the coextruded four-layer film according to the invention is left in an unstretched state.

By linear polyethylenes is meant, for the purposes of the invention, those polyethylenes which are prepared by copolymerizing ethylene with small amounts of olefin comonomers (C3 to C12). Particularly suitable is LLDPE (linear-low-density polyethylene) having a specific gravity of 0.918 to 0.945, preferably 0.922 to 0.930. This polyethylene has a melt index of 0.2 to 4.0, preferably 0.8 to 1.5. This class of material is particularly well suited for the purposes of the invention, since the multilayer deep-drawing film according to the invention is made particularly puncture-resistant due to the considerable toughness of LLDPE. For the same reason, HDPE having a specific gravity of at least 0.935, preferably 0.950 to 0.965 and a melt index of 0.2 to 4.0 is also an excellent raw material for the purposes of the invention.

The copolymers of ethylene with vinyl acetate used to make the inner layers according to the invention, i.e. ethylene / methacrylic acid copolymers crosslinked with metal ions, also called ionomer resins and marketed by Dupont under the trade name "Surlyn", are highly compressible but remain in the road during deep drawing. , in other words:

The two outer layers, which are joined together together with each inner layer by a fusion joint, 7 80236 still move slightly towards each other at the point where the inner layers are joined by pressing, so that during deep drawing the outer layer forming the deep drawing recess, e.g. , e.g., the inner layer made of ethylene / vinyl acetate copolymer does not automatically stretch as much as the second outer layer of multilayer film of the invention made of LDPE and combined with the inner layer of ethylene / vinyl acetate copolymer when the deep drawing recess is formed.

Although ethylene / methacrylic acid copolymers crosslinked with metal ions, of which sodium and zinc ion crosslinked are particularly preferred, have particularly good impact resistance and also excellent compression behavior, they are only used for some specific purposes, e.g. when extremely high puncture is required. strength or when a multilayer deep-drawing film is desired to be thin, as a result of which relatively thin inner layers must be made of a material with a particularly high mechanical impact resistance. However, ethylene / vinyl acetate copolymers have proven to be excellent for most purposes of the invention and are therefore highly preferred.

In a particularly preferred embodiment, the inner layers of the deep-drawing film according to the invention are made of an ethylene-vinyl acetate copolymer containing 8 to 35% by weight, preferably 15 to 28% by weight, of vinyl acetate. This ethylene / vinyl acetate copolymer having a melt index of 0.5 to 8, preferably 1.5 to 4 g / 10 min. At 190 ° C and a load of 2.16 kg measured according to DIN 53735, the use guarantees a particularly good melt bond with the outer layers of linear polyethylene or high-density polyethylene during coextrusion and makes the multilayer deep-drawing film very resilient and puncture-resistant.

β 80236

In another preferred embodiment of the present invention, the total thickness of the coextruded laminate film is 100 to 300 μm, with the proportion of outer layers being at most 4/5 and at least 1/2 and the proportion of inner layers at most 1/2 and at least 1/5. The total thickness of the film according to the invention used in deep-freeze-resistant deep-drawing packages has proven to be particularly suitable from 190 to 250.

In the following example and Figures 1-3, the invention will be explained in more detail without limiting the invention to the described embodiments.

Figure 1 shows a schematic cross-section of the two-layer blow hose shown.

Figure 2 shows a cross-section of the same hose, however in a compressed state.

Figure 3 shows a section of a vacuum-deep drawing package according to the invention, the lower film of which is a coextruded laminate film according to the invention.

In Fig. 1, the outer layer of the coextruded blow hose 1 is marked with A, A ', its inner layer with B, B'. The outer layer A, A 'is made of LLDPE with a mechanical impact resistance of 170 cN, a melt index of 1.0 and a specific gravity of 0.930, while the inner layers B, B' are made of an ethylene / vinyl acetate copolymer having a vinyl acetate content of 25% by weight and a melt index 3. Layers A and B are connected to each other by a fusion joint.

FIG. . The thickness of the outer layers A, A 'is 60 μm and that of the inner layers B, B' is 30 μm, so that their total thickness is 180 μm.

Figure 3 shows a deep freeze-resistant vacuum deep-drawing package 2 packed with goulash 5. The top film 3 is a two-layer laminate film known per se, made of a 30-μm-thick, non-oriented polyamide film and laminated with a 75-μm-thick non-oriented polyethylene film. The lower film 2 consists of the laminate film 1 '(compressed hose) according to the invention described in Figures 1 and 2.

Example:

The following example describes the use of a multilayer deep drawing film according to the invention for the packaging of a sharp-edged metal powder with a powder grain diameter of about 1 to 3 mm and marketed by Goldschmidt, Essen as a welding consumable under the trade name "Thermit".

The outer layers A, A 'of such a multilayer deep-drawing film are made of LLDPE having a specific gravity of about 0.92 and a melt index of 1. The thickness of each outer layer is 80.

The outer layers A, A 'are joined by melt bonding to the inner layers B, B' made of an ethylene acetate copolymer containing 8% by weight of vinyl acetate having a melt index of 1.5, while the inner layers B, B 'are joined together by compression. The thickness of each inner layer is 40 μm, so that the total thickness of the multilayer deep-drawing film is 240 μm.

As the packaging experiment showed, the described multilayer deep-drawing film has excellent puncture resistance with respect to sharp-edged metal powder even at temperatures below the freezing point.

Claims (3)

10 80236 A multilayer coextruded composite film (1 ') comprising two outer layers (A, A') of uniform material and thickness of linear polyethylene or high density polyethylene (low pressure polyethylene, HDPE) and two inner layers of material (B), of uniform thickness and thickness ') consisting of a metal ion crosslinked ethylene / methacrylic acid copolymer or an ethylene / vinyl acetate copolymer in which the outer layers (A, A') are joined to the inner layers (B, B ') by a melt bond and the inner layers (B, B' ) are joined together by compression, characterized in that the composite film is used as an independent deep-drawing film, in particular as a base film for the production of freezer-resistant vacuum deep-drawing packages or vacuum-deep-drawing packages for sharp-edged packaging products. Compound film according to Claim 1, characterized in that when the material of the inner layers (B, B ') is an ethylene / vinyl acetate copolymer, this copolymer contains 8 to 35% by weight, preferably 20 to 28% by weight, of vinyl acetate. Compound film according to Claim 1 or 2, characterized in that the total thickness of the compound film (1 ') is 100 to 300 μm, the outer layers (A, A') having a thickness of at most 4/5 and at least 1/2 and the inner layers (B, B) ') not more than 1/2 and not less than 1/5. lx 80236