Laminated sheets and deep-drawn containers made therefrom.

The present invention relates to thermoforming shrinkable composite films made from copolyamides and ethylene copolymers, which are particularly suitable for packaging foods, such as meat and sausage products, on thermoforming systems.

Composite films made of polyamides, preferably PA-6 and polyethylene, have already been used for food packaging. However, when these composite films are used as vacuum packaging on deep-drawing systems, wrinkles appear around the packaged product. These folds not only interfere optically, but can also easily cause damage to the packaging due to puncturing under mechanical stress.

There is therefore a considerable need to provide thermoformed packaging, in particular food packaging, which has a wrinkle-free appearance.

Surprisingly, this is achieved with the composite films according to the invention, which are shrinkable by deep drawing<ul id="ul0001" list-style="none"><li>1) at least one layer of at least one copolyamide with at least 50% by weight ε-capro</li><li>lactam units and a melting temperature in the range of 75-215 ° C, preferably 160-200 ° C, and optionally an ethylene / vinyl alcohol copolymer and / or ionomer resin,</li><li>2) at least one heat-sealable layer of an ethylene copolymer of at least 50 mol% of ethylene units and</li><li>3) optionally an adhesive or adhesion promoter layer which is customary between layers 1) and 2)</li></ul>consists.

The invention further relates to wrinkle-free thermoformed packaging, in particular for foodstuffs such as sausage and meat, which have been produced from the composite films according to the invention.

For the production of layer 1), copolyamides composed of at least 50 wt.

To produce the layer 2) suitable for surface sealing, copolymers of ethylene and α, B-unsaturated monomers, such as, for example, α, B-unsaturated monocarboxylic acids with C₃-C₅which are composed of at least 50 mol% of ethylene can be used. The copolymers preferably contain 2-25 mol% of α, B-unsaturated monocarboxylic acid units, which are optionally partly or completely present as alkali metal, alkaline earth metal or Zn salt such as Zn and / or Ca salts. The melt index of the copolymers should be in the range of 0.5-40 g / 10 min, preferably 1.5-5.0 g / 10 min measured in accordance with DIN 53 735. Be particularly preferred_C.o-polymers of ethylene (meth) acrylic acid with 2-25 mol%, preferably at least 10 mol%, of (meth) acrylic acid units, which can be present as zinc and / or Ca salts (ionomer resins).

Modified ethylene / vinyl acetate copolymers with 2-40% by weight, preferably with 3-10% by weight, vinyl acetate units are also suitable for producing layer 2). However, preference is also given to quaternary polymers which consist of approximately 71 to 90% by weight of ethylene, 3 to 9% by weight of an aliphatic, ethylenically unsaturated carboxylic acid with C.₃-C₅, 1 to 20 wt .-% of an ester of an aliphatic, ethylenically unsaturated carboxylic acid with alcohols, the C₁-C_acontain, as well as from 0.3 to 5 wt .-%, preferably 0.8 to 3 wt .-% isobutylene, the sum of the wt .-% must be 100 in each case. These are particularly preferably ethylene-vinyl acetate copolymers which, in addition to vinyl acetate units, consist of 71-90% by weight of ethylene, 3-9% by weight of acrylic acid, 1-20% by weight of the t-butyl ester of acrylic acid and 0.8 -3% by weight of isobutylene are built up.

In particular when using the vinyl acetate copolymers mentioned to produce the heat seal layer, the bond should be applied by means of a conventional adhesion promoter layer 3), preferably based on the ionomer resins described above, between the carrier film made of copolyamides and the heat seal layer made of ethylene copolymers or on the basis of the ethylene / vinyl acetate copolymer described above .

It is also possible to add the ionomer resins to the copolyamides in an amount of 5-30% by weight so as to increase the bond strength.

Gas permeability, especially for 0₂ To lower it, it is advantageous to add to the copolyamides ethylene vinyl acetate with 50-80% by weight vinyl acetate units, which are at least 90% saponified, in amounts of 5-30% by weight and to produce the carrier film therefrom.

The composite films according to the invention should have a thickness of 90-300 μm, preferably 160-250 μm, in order to give sufficiently stable thermoformed packaging. A thickness of 40-120 μm, preferably 60-100 μm, and a thickness of 50-200 μm, preferably 100-180 μm, should be maintained for the copolyamide layer.

The composite films according to the invention are produced by customary processes, preferably by coextrusion according to the film blowing process, and are expanded 1: 2 - 1: 6, preferably 1: 3-1: 4, in order to ensure a volume shrinkage of at least 40% after deep-drawing the packaging .

The packaging, preferably for food, such as sausage or meat, is produced on the conventional thermoforming packaging machines from the composite films according to the invention.

In order to obtain wrinkle-free packaged products, the following treatment methods of the thermoformed packaging according to the invention are available:<ul id="ul0002" list-style="none"><li>a) The filled thermoformed packaging is evacuated in the machine and then sealed. Then it is shrunk for 1-5 seconds at 80-100 ° C, preferably 85-95 ° C by immersion in a water bath.</li><li>b) The filled, sealed deep-drawing packaging is briefly subjected to a hot air treatment at 170-240 ° C, preferably at 220-240 ° C, preferably in a hot air or superheated steam tunnel.</li><li>c) It is also possible to effect the shrinkage by contact heat in the thermoforming packaging machine. For this purpose, the packaging, which is already filled, is sealed using a suitable sealing tool for surface sealing - ideally at the top and bottom - in the vacuum chamber of the thermoforming machine and at the same time brought to shrinkage. The surface sealing also serves the purpose of preventing juice from escaping, which is often observed in many foods.</li></ul>

The packaging according to the invention not only has a wrinkle-free appearance, but is also distinguished by improved mechanical strength, puncture resistance and flexural strength, since the corners of the film trough thinned out by deep drawing regain considerable thickness and mechanical strength as a result of the shrinking process. This is accompanied by a reduction in the gas and water vapor permeability of the trough and thus a longer shelf life of the food.

example 1

From a copolyamide 6/12 from 98% by weight ≤-caprolactam and 2% by weight laurolactam or from a copolyamide 6 / 6.6 from 85% ε-caprolactam and 15% by weight hexamethylene diamine / adipic acid or from a copolyamide composed of 96% by weight £-caprolactam and 4% by weight isophorediamine / isophthalic acid and from an ethylene (meth) acrylic acid copolymer with a melt index of 5.0 g / 10 min (Surlyn® is made by coextrusion under the following conditions Laminated film produced: temperatures in the mold 235-240 ° C, in the extruder (for layer 1) 230-245 ° C, at a speed of 50 rpm, (for layer 2) 235_-240 ° C at a speed of 70 rpm; Take-off speed approx. 9 m / min, inflation ratio 1: 2. The total film tube thickness achieved here is 160 µm.

Example 2

For a composite film consisting of a copolyamide 6/12 layer (as in example 1) and an ethylene-vinyl acetate copolymer layer, with 8% by weight vinyl acetate units and with a melt index of 1.3 g / 10 min. the layers are produced under the same conditions as in Example 1 by the film blowing process and the two film layers are bonded to one another by means of a commercially available polyurethane-based adhesive.

Example 3

Layer 1) of a composite film consisting of a mixture of 10% by weight of a commercially available ionomer resin, 20% by weight of an ethylene-vinyl alcohol copolymer (70% by weight of vinyl alcohol) and 20% by weight of copolyamide 6/12 (as in Ex. 1) and layer 2) consisting of an ethylene-vinyl acetate copolymer with a VAc content of 8% by weight are produced as blown films under the same conditions as described in Example 1 and bonded to one another using a commercially available polyurethane-based adhesive ( Layer 3).

<tables id="tabl0001" num="0001"><img file="EP0062822A2_D0001.tif" /></tables>