SE502080C2 - Packaging material, method of making it, containers consisting of such material and use of the material for the manufacture of containers - Google Patents

Abstract

A flexible packaging material for making dimensionally-stable containers, intended especially for food and exhibiting barrier qualities, comprises a stiffening, polymeric core layer (1) which on both sides has a protective layer (2, 3) of polymeric material connected thereto. The core layer (1) consists of a foamed thermoplastic and has a thickness that makes up about 70-95 % of the total thickness of the material, while the protective layer or layers (2, 3) consist of non-foamed thermoplastic and make up the remainder of the thickness of the material. A container made of this material has a trough element with a circumferential flange, as well as a lid element with a corresponding circumferential flange. These flanges are applicable against each other, and at least the one flange is provided with an adhesive for original sealing of the container. In a method for producing the packaging material, the core layer (1) is brought to a viscosity (iv) of 0.68-0.82 before the lamination, and the protective layers (2, 3) are brought to a viscosity (iv) of 0.68-0.72. The lamination is so controlled that the difference in viscosity (iv) between the core layer (1) and the protective layers (2, 3) at all times exceeds 0.04. The packaging material is primarily used for making dimensionally-stable liquid-tight containers, which are produced by thermoforming or other mechanical processing and which exhibit barrier qualities.

Description

502 080 10 15 20 25 30 35 2 the packing contents cannot be used. Another disadvantage is that a table pack of this kind consists of different materials, namely plastic and metal (aluminum) and in some cases also paper and / or cardboard.

This is extremely negative from a recycling and environmental point of view. point.

There is thus a need for a new packaging material. material which, without the use of metal foil, exhibits satisfactory barrier properties at the same time cheaper than the corresponding packaging material coming on the market.

Given that several European countries are planning to introduce a packaging tax based on packaging weight, the market is increasingly demanding packaging materials rial. Many countries also have very strict regulatory requirements that all packaging must consist of easy recycling bare material.

There is therefore also a need for a new packing material which, with satisfactory barrier creates and at a low price can be given a much easier execution than has hitherto been possible. Of recycling For reasons of convenience, the packaging produced in the case consist of a single material.

Packaging itself has already been proposed. material without Al foil, and an example of this is shown in ' SE-B-468 635 with the equivalent EP-A-494 594. This known packaging material consists of a relatively thick, rigid frame layer, which has one on each side thin protective or barrier layer. The body layer consists of one mixture of plastic and filler, where the plastic is preferably shall be a polyolefin, for example polyethylene or propene. As a filler it is proposed primarily chalk, and Other pesticides include talc, mica and clay.

The amount of filler in the backing layer should be 50-80% of the backing total weight of the layer, preferably about 65% by weight. Protective the layers shall consist of a mixture of plastics of the same kind as the plastic in the backing layer and a plastic of another kind. 10 15 20 25 30 35 502 080 3 However, this packaging material does not respond against the demands that the market will make in terms of lightweight packaging, as the filler in the the layer rather makes this material heavier than comparable previously known packaging materials, with or without Al foil.

As further examples of background technology can be mentioned SE-B-467 772 with the equivalent EP-A-494 595, which is described over a packaging material similar to that discussed above.

Prior art also includes US-A-4 657 811, which describes ver one of three layers of plastic film, specially designed for the production of garbage bags. The disadvantages intended to removed by means of the proposed plastic film hangs together garbage bags are usually made in very thin and flexible plastic material, which means that garbage bags they do not have such rigidity that they can stand on their own loading. The garbage bag simply collapses.

Therefore, in the above-mentioned US patent, a material is proposed built up of a core layer (core layer) consisting of a foamed thermoplastic, which on each side has a thin polyethylene skin layer. It frothed the backing layer is intended to have a certain stiffening effect.

However, the plastic film made up of these three layers is very thin and not suitable for the manufacture of liquid-tight, dimensionally stable packaging containers for e.g. shortening. The known three-layer film has a thickness of only about 20-60 pm, where the frame layer should have a thickness of about 6-38 μm while each outer layer should have one thickness of about 6-13 pm.

It will be readily appreciated that in the U.S. patent proposed the three-layer film does not have to exhibit such properties initially discussed, as this known film is intended to be used mainly for garbage bags. On due to its very small thickness, this is probably known plastic film can not be used as packaging at all foodstuffs. 502 10 15 20 25 30 35 080 4 The object of the present invention is therefore that instruct a process for the manufacture of a materials, by means of those discussed above the disadvantages are eliminated and the demands of the market in terms of low weight and low price are met.

The resulting packaging material should be without need of metal foil ensure satisfactory barrier characteristics.

Furthermore, a packaging container made of the resulting material can be original sealed or sealed without any need for metal foil. Packaging the container shall consist of as few parts and materials as possible and thereby be easily recyclable.

The object of the invention is thus to provide one rational process for the production of packaging material and to provide a use of the packing material for the production of dimensionally stable, liquid-tight containers that exhibit barrier properties.

These and other purposes, which will be apparent from subsequent description, has now according to the invention achieved through a procedure generally defined in subsequent claim 1 and in a preferred variant in requirement 2.

The invention will be described in more detail in the following with reference to the accompanying drawings, which show working examples.

Fig. 1 schematically shows a cross section through a packing material prepared according to a preferred embodiment embodiment of the invention, Fig. 2 shows a partial section of a container consisting of the packaging material in Fig. 1.

Fig. 3 schematically shows a plant for manufacturing packaging material.

Fig. 1 shows a cross section through a packaging material prepared in accordance with a preferred embodiment embodiment of the invention. The material comprises a rigid giving polymeric backing layer 1 (eng. core layer) as on 10 15 20 25 30 35 502 080 5 each side has an associated barrier or protective layer 2, 3 (skin layer) of polymeric material. For achievement of low weight includes the intermediate body layer 1 a foamed thermoplastic, preferably a thermoplastic plastic polyester. The density lowering foaming achieved by a per se known foaming foaming agent is blended into the polyester. In it cases where the foaming agent is based on plastic, include the granules which, when heated, produce gas bubbles (e.g. carbon dioxide), which expand the polyester. Preferably is degree of foaming of the backing layer 1 such that its density is at least 20% lower than the density of the protective layers 2, 3, which may preferably comprise an unfoamed, thermoplastic polyester. From a recycling point of view, it is preferred that 1 and the protective layers 2, 3 are based on the same thermal plastic, preferably a polyester. The packaging material must have a thickness in the approximate range 125-2500 μm altogether. according to the purpose of the packaging to be manufactured hence.

In order to achieve good dimensional stability, good properties and low weight, it should be mainly of foamed polyester consisting of the backing layer 1 have a thickness that constitutes about 70-95% of the total thickness of the packaging material, in the case mainly consisting of unfoamed polyester the protective layers 2, 3 constitute the rest of the packaging material thickness. Practical trials with these conditions met have given very good results.

A liquid-tight and dimensionally stable container consisting of a packaging material prepared according to the invention can be made up of only two parts, namely a trough shaped part 4 and a lid 5 which can be tightly closed thereby (see Fig. 2). Such a trough part 4 has at its opening one circumferential flange 6, which after filling is applied to a corresponding circumferential flange 7 on the lid part 5. At least one of the flanges is provided with an adhesive to achieve such a tight original closure of the container that no sealing by means of metal foil is required. 502 080 10 15 20 25 30 35 6 When closing the container, clamping jaws (not shown) are used. de) against the flanges 6, 7 at a temperature of about 180-200 ° C and for a period of 0.5-1 s. pressure of about 2-5 N / mmz a very reliable orientation is achieved final closure of the container. In order not to be harmed the clamping jaws, the flanges 6, 7 on their outside can have a thin coating of a protective varnish (not shown).

By applying the adhesive or glue only on one of the circumferential flanges 6, 7 becomes the glue-coated surface is very limited, which gives large savings of glue. In the case of a similar original closure, prior art, the entire inside of the lid has been provided with a so-called thermal varnish for adhesion to trough the flange of the part. The container according to the invention is limited the glued surface to only the contact surface between the flanges sarna 6, 7.

It should be noted that the container 4 described above, 5 further have means (not shown) for resealing, e.g. through a snap function.

In a container that is specifically designed for shortening the trough part 4 has a material thickness in the range 300-1200 μm, preferably 450-1000 μm and most preferably 550-700 μm. At In the same application, the lid part 5 has a material thickness in range 125-400 μm, preferably 150-300 μm and all preferably 200-240 um.

At another container specially designed for yoghurt, the tray part 4 can have a material thickness up to 2500 μm, while the lid part 5 may be thinner and have a material thickness corresponding to what is stated above for a shortening container.

If a packaging tray is thermoformed from the material in downward direction with respect to Fig. 1, comes the protective layer 2 to form the inner layer of the trough while the protective layer 3 more to form the outer layer of the trough. If the trough is to be used for cooking fat, the inner layer 2 must of course be resistant, and it must also form a barrier against oxygen gas and water / steam. Usually this inner layer is colored 10 15 20 25 30 35 502 080 7 2 with white color. The body layer 1 is preferably dyed gray color to obtain light barrier. Also the outer layer 3 can be colored, for example for decorative reasons. It should be It is pointed out that in some circumstances the outer layer 3 can be omitted if the required barrier properties is obtained only by means of the inner layer 2 and the body layer 1.

Fig. 3 schematically shows a plant at which the method according to the invention can be applied. Construction includes three silos 8-10 for polyester, three dryers 11-13 and four tanks 14-17 for paint granules and foam as will be described in more detail below.

Furthermore, the plant contains three extruders 18-20, one mold head 21, three cooling rollers 22-24, a thickness gauge 25, a reindeer cutting device 26, a mill 27 and a termination winding device 28.

Silon 8 contains so-called new product in the form of polyester with a viscosity of about 0.8, i.e. the iv value is on average about 0.8 (English intrinsic viscosity). This is fed via the dryer 11 polyester to the extruder 18, from which the material from which shall form the backsheet 1 is fed to the mold head 21. To the backsheet extruder 18 is fed foaming agent from the tank 16 and, where applicable, paint granules from the tank 17. Silon 10 also contains novelty in the form of polyester with lower iv value, namely on average about 0.7. Via torken 13 matas this polyester to the extruder 19 for making the inner layer 2 and the extruder 20 for producing the outer layer 3. Possible dyeing of the outer layer 3 obtained by paint granules from the tank 14, and on the correspondingly, the inner layer 2 can be dyed by means of granules from the tank 15. From the extruders 18-20 they are fed three materials to the mold head 21, in which the materials laminated at a temperature of about 200-300 ° C. Via cooling rollers 22-24, the web of material is fed on to the winding order 28, which forms intermediate layers before thermoforming (not shown) by the packaging containers. 502 080 10 15 20 25 30 35 8 In the reindeer cutting device 26, the web of material is edge-cut and the material waste is fed to the mill 27, from which crushed material is returned to the silo 9 and via the dryer 12 back to the extruder 18, in which the backing layer material das. In the crushed polyester material as in this way returned in the process, the molecular chains have been broken such that the iv value is less than 0.8 and in some cases also less than 0.7. This recycling of crushed poly- ester provides the ability to control the process at an extreme expediently, as described below.

The backsheet material leaving the extruder 18 can by controlling the above-mentioned feedback, one is imparted iv value in the approximate range 0.68-0.82, ie before the lamination in the mold head 21. The polyester to be peeled form the protective layers 2, 3 after the extruders 19 and 20, respectively is always added in the form of new product with an iv value of approx 0.68-0.72. Through the above-described return of crushed material for the backing layer material, the lamination in the mold head 21 is controlled in such a way that the difference between the iv value of the backing layer and the iv value of the protective layers always is greater than 0.04. Thereby a very good lami- nering.

The thickness gauge 25 can by feedback (not shown) also used to control the one described above the process. ' Practical experiments, in which the inventive concept basic ideas tested, have given very good results. For- gaskets with up to 50% lower total weight than the equivalent known packaging has been produced with fully acceptable mechanical properties and barrier properties. In the experiments has been used on the market using polyester materials with a density of about 1.33 kg / dm3. By foaming of the backing layer, its density can be easily reduced by approx 20-40%.

In conclusion, it should be pointed out that the invention is by no means is limited to the embodiments described therein previous, but several modifications thereof are conceivable within the framework of the inventive concept which will be 10 15 20 25 30 35 502 080 9 pressure in the appended claims. Other thermoplastics can of course used, and further must be pointed out that minor deviations from those stated in the following claims intervals are conceivable without one for that matter deviates from the inventive concept.

Claims (2)

502 10 15 20 25 30 35 080 10 PATENT CLAIMS A process for the production of a flexible packaging material, which is to be formed by thermoforming or other mechanical processing into dimensionally stable containers, consisting mainly of foamed polyester backing layers, in particular for foodstuffs, and consisting of one (1), which on one side or provided on both sides with a relatively thinner protective layer (2, 3) which consists mainly of unfoamed polyester, the body layer (1) being produced in a first extruder (18) and the protective layer (s) (2, 3) being produced in a second extruder (20) or a second pair of extruders (19, 20), the layers (1-3) being joined and laminated in a mold head (21) at a temperature in the approximate range 200-300 ° C and the layers ( 1-3) after lamination forms a web of material, characterized in that the polyester which is to form the backing layer (1) before lamination is imparted with a viscosity (iv) in the approximate range 0.68-0.82; that the polyester which is to form the protective layer (s) (2, 3) before the lamination is imparted to a viscosity (iv) in the approximate range 0.68-0.72; and that the lamination in the mold head (21) is controlled in such a way that the difference between the viscosity of the body layer (1) and the viscosity (iv) of the protective layer (s) (2, 3) is always greater than 0.04. 2. A method according to claim 1, characterized in that the web of material formed during lamination is that the waste formed during the edge cutting is fed to a mill (27) wet edge cut in an edge cutting device (26), where it is crushed, that the crushed waste is dried in a dryer (12) and that the crushed, dried waste is returned to the first extruder (18), where the backing layer (1) is produced.