The present invention relates to a tray, especially a tray for holding foodstuffs.

Numerous foodstuffs, such as ready meals or animal food, are sold in aluminium trays. The inside of the tray is typically coated with a plastic material in order to enable it to be sealed. A plastic material used for this purpose must be designed such that no compounds from the plas- tic material which might be harmful to health or might alter the taste or are disadvantageous in any other way are released into the foodstuffs to be packed.

Food trays made of aluminium are known in the state of the art, where, for example, their inside surfaces are coated thinly with polypropylene.

One problem associated with the use of aluminium trays for food packaging is that the trays can easily be mechanically deformed. During transport of the packaged foodstuffs from the factory to the place of sale or from the place of sale to the consumer, the packaging may suf- fer unsightly dents, for example because of knocks or other mechanical effects. In this way, the visual impression of the packaged foodstuffs on the shop shelf is drastically impaired.

In order to counter mechanical deformation of this kind, aluminium trays with a large wall thickness of about 150 μm have so far been used, the inside surfaces of which are coated with a polypropylene layer about 30 μm thick. The great thickness of the aluminium walls is in- tended to prevent the formation of dents and other types of deformation. A disadvantage here is that large amounts of aluminium are required. The manufacture of alu- minium materials, however, requires a great deal of energy and hence involves high manufac- turing costs and has a major impact on the environment.

It is accordingly one object of the present invention to provide a tray which overcomes the disadvantages of the state of the art. In particular, the object is to provide a tray for foodstuffs which exhibits improved resistance to mechanical deformation and which at the same time can be produced in an environmentally friendly manner with lower manufacturing costs.

This problem is solved by a tray comprising, in this order: a first inner polymer layer, a sec- ond polymer layer and an outer aluminium layer, the first inner polymer layer having a thick- ness in a range from 200 - 400 μm, the second polymer layer having a thickness in a range from 20 - 40 μm and the outer aluminium layer having a thickness in a range from 40 - 80 μm.

The first inner polymer layer and the second polymer layer are separated from one another by an intermediate layer, which is typically created in that the two polymer layers are formed in different, successive operations, for example in that the second polymer layer is formed on the outer aluminium layer in a first operation, and, preferably after the second aluminium layer has cooled, the first inner polymer layer is formed in a second operation. The intermediate layer formed in this way can be observed in a simple manner, such as by cutting the tray per- pendicularly to the layers and inspecting the cut surface under a microscope.

According to one aspect of the present invention, a tray is prepared with the first inner poly- mer layer having a thickness in a range from 250 - 350 μm.

According to a further aspect of the present invention, a tray is prepared with the second polymer layer having a thickness in a range from 25 - 35 μm. In addition, the present invention preferably comprises a tray with the outer aluminium layer having a thickness in a range from 40 - 60 μm.

According to yet another aspect, the present invention relates to a tray wherein the first inner polymer layer and/or the second polymer layer comprises polypropylene and/or polyethylene, preferably polypropylene.

In addition, the invention relates particularly preferably to a tray wherein the first inner poly- mer layer and/or the second polymer layer consists of polypropylene and/or polyethylene, preferably polypropylene.

Furthermore, the invention preferably provides a tray wherein the first inner polymer layer is a layer produced by injection moulding.

in addition, the invention preferably provides a tray wherein the second polymer layer is a layer applied by lamination and/or coextrusion.

One embodiment is characterised by the fact that on the upper peripheral rim it has a sealing region formed by the second polymer layer, which projects above the first inner polymer layer in the sealing region, and that the tray can be sealed with a lid.

The invention also relates to the use of such a tray for holding foodstuffs, especially animal food or ready meals.

It has surprisingly been found that the tray of the invention exhibits unusually great resistance to mechanical deformation and at the same time contains a considerably smaller amount of aluminium compared to the state of the art. In this way, the tray of the invention can surpris- ingly be manufactured at considerably lower cost and in an environmentally friendly manner.

The shape of the tray of the invention is of no particular significance. All suitable and stan- dard shapes of tray for holding, for example, foodstuffs can be used, i.e. with round, rectangu- lar or square cross-sections, for example.

According to the invention, it may be particularly preferable that first of all an aluminium tray of suitable size and shape and with a wall thickness in accordance with the invention is manu- factured. On the inside of that tray, a thin polymer film about 20 - 40 μm thick can be applied by single or double-sided lamination. That polymer layer serves as a sealing medium. The sealing rim produced in this way is stable, even though there are only relatively thin PP and aluminium layers present.

A second polymer layer, which in accordance with the invention can advantageously be ob- tained by injection moulding processes, is applied to the thin polymer layer, which is applied directly onto the aluminium. This thicker polymer layer can advantageously be manufactured in a separate process step by injection moulding, in that the aluminium tray, with the second polymer layer applied, is placed in the injection moulding mould, in order for the thicker polymer layer to be produced in the injection moulding machine / the mould.

According to the invention, it may further be contemplated that the thicker first inner polymer layer is not used in the sealing region, but only fills out the interior of the tray body. "Sealing region" here means the region by which a connection to a lid or cover can be made in an appropriate manner. A thin aluminium foil, for example, which is fused with the sealing re- gion of the food tray, can serve as a cover. In addition to the methods of producing the polymer layers explicitly mentioned (single or double-sided lamination, injection moulding), any other suitable method known in the state of the art for producing polymer layers can also be used in accordance with the invention.

The first inner polymer layer and the second polymer layer may have different chemical com- positions and may accordingly differ in their chemical and physical properties. It is, however, likewise contemplated in accordance with the invention that the two polymer layers have the same or a similar chemical structure and accordingly have substantially the same or similar chemical and physical properties.

Further features and advantages of the tray of the invention will become clear from the fol- lowing detailed description of a preferred embodiment, with reference to the Figures, where

Fig. 1 is a cross-section of a tray in accordance with the invention; and

Fig. 2 is an enlarged partial view of the cross-section of Fig. 1 , especially of the upper part of the tray comprising the sealing region.

Referring to Figures 1 and 2, the tray of the invention will be explained in the following, tak- ing a preferred embodiment as an example.

Fig. 1 is a schematic view of the complete cross-section of a tray in accordance with the in- vention 1. Fig. 2 shows a detail of the cross-section of the tray 1 enlarged on a scale of 20: 1, which is marked with a circle in the upper right-hand corner of Fig. 1. The tray comprises a first inner polymer layer 2, a second polymer layer 3 and an outer aluminium layer 4. Fig. 2 likewise shows a schematic view of a sealing region 5, which merely comprises the outer alu- minium layer 4 and the second polymer layer 3. The features of the invention disclosed in the above description and in the claims and drawing can be essential to implementing the invention in its various embodiments both individually and in any combination.