Field of the Invention The invention relates to a container, a method and a mould for producing the container, the container comprising a skeleton structure comprising a top rim and supporting legs, the container further comprising a bottom structure and a substrate; said supporting legs connecting said top rim with said bottom structure, said substrate extending between said supporting legs and defining walls and bottom parts of said container, said skeleton structure being made from a polymer material,

Background of the invention When designing and producing polymer material packaging solutions such as single-use food containers, the weight/volume of material used is of great importance. It is desirable to produce a packaging with a material weight or volume as low as possible. This will among others help to reduce transportation costs and protect the environment by reducing the amount of raw mate- rial used.

To reduce the material volume, international patent application WO2008/035162 suggests a special structure of a pan for containing foodstuff. The structure comprises rigid supporting means for supporting the pan structure and lightened coating means to coat the supporting structure.

Another important aspect when designing a polymer packaging is the amount of polymer material used. It is desirable to reduce the amount of polymer material to a minimum. Reducing the volume of a structure is only one approach for reducing the amount of polymer material used. Reducing the material volume creates significant challenges in injection moulding and other moulding techniques. Due to the nature of plastics the thickness of a moulded product can only be reduced to a certain minimum. When a very low product thickness is specified the flow of the molten plastic material in the mould becomes a problem. Reductions of the material thickness beyond a critical minimum thickness will among others result in poor surface quality, lower strength and poorly looking products. Within the limits of known packaging designs and productions methods it has not been possible to reduce the amount of polymer used beyond a certain practical limit. A need however exists, for further reductions in the amount of polymer used in packaging solutions.

Summary of the invention

Disclosed herein is a container wherein the amount of polymer used is reduced, this being achieved by the skeleton structure being made form a polymer material containing an amount of filler. An advantage in this respect is that the amount of polymer material used in the construction of the container can be reduced.

In one embodiment, the said substrate is being made from a polymer material containing an amount of filler.

In another embodiment, the bottom structure is an integrated part of the skeleton structure.

In still another embodiment, the structure is made form a polymer material containing between 75 % and 95 % by weight of filler.

In a further embodiment, the substrate is made from a polymer material containing between 75 % and 95 % by weight of filler. Disclosed herein is further a method for producing a skeleton structure 7 made form a polymer material containing an amount of filler, by injection moulding. This is achieved by the polymer material being mixed with filler before the polymer material is injected into a mould. An advantage in this respect is that the amount of polymer material used in the construction of the container can be reduced.

In one embodiment, the polymer material is mixed with between at least 30 by weight of the filler, or even between 55% and 95% by weight of the filler, before the polymer material is injected into a mould. Disclosed herein is still further a mould having one or more cavities for injection moulding a container comprising a skeleton structure 7 made from a polymer material containing an amount of filler. This is achieved by the one or more cavities preferably having a minimum cross-sectional dimension of in the order of at least 0.4 mm, preferably in the order of 1 -2.5 mm in case of a filler content higher than 50% by weight, whereby preferably at least the supporting legs will have a corresponding thickness. The maximum thickness of the supporting legs for foodstuff containers typically will be in the order of 3-6 mm. These and other characteristics and advantages of the invention are described especially in the figures, the specification and the claims.

The use of high filler amounts in a plastics material for injection moulding of conventional lidded thin-walled small size plastics containers, such as con- tainers for foodstuffs as shown in e.g. WO 07071252, is generally not possible due to the very small container wall thickness where the small mould cavity width restricts flow of the molten plastics material containing the filler through the mould cavity, as this premixed material is injected into the mould under pressure. These flow characteristics may give rise to undesirable variations in the material strength throughout the container. With a skeleton container the wall thickness of the legs is generally larger than the wall of a conventional thin-walled container having a comparable internal volume, such as the one disclosed in WO 07071252, without adding to the total volume of plastics material used and while still maintaining the same structural strength.

Brief description of the drawings

In the following, the invention will be described in greater detail with reference to embodiments shown by the enclosed figures. It should be empha- sized that the embodiments shown are used for example purposes only and should not be used to limit the scope of the invention.

Fig. 1 is a perspective view of a container according to an embodiment of the invention,

Fig. 2 is a perspective view of a container according to another embodiment of the invention,

Fig. 3 is a perspective view of a container according to yet another embodi- ment of the invention,

Fig. 4 is a cross section of a mould cavity according to an embodiment of the invention, Fig. 5 is a cross section of a mould cavity according to another embodiment of the invention, and

Fig. 6 is a cross-sectional view through a mould for making one embodiment of the container.

Detailed description of the embodiments With reference to Fig. 1 there is shown a container 4 according to an embodiment of the invention. The container 4 comprises a plastic material skeleton structure 7, a plastic material bottom structure 3 and a substrate 10 and defines a hollow cavity for containing content such as food stuff.

The skeleton structure 7 comprises a top rim 1 and supporting legs 2. The top rim 1 defines an opening through which content can be introduced into the container 4. The skeleton structure 7 provides a high structural rigidity to the container 4.

The supporting legs 2 extend between the top rim 1 and the bottom structure 3. In the shown embodiments according to the invention the supporting legs are connected to the corners of the bottom structure 3 and the top rim 1 . The supporting legs 2 may need to be able to withstand considerable forces induced both by the content of the container itself and from other containers during stacking. The supporting legs 2 thus are a vital part of the construction. Side and bottom areas of the container are defined by a thin lining or covering, in the present text referred to as a substrate 10, such as a polymer film of a preferred thickness between 0.05-0.1 mm. The substrate 10 is arranged in between the supporting legs 2 and at the plane of the bottom structure 3 as shown in fig. 1 ; preferably, the substrate is a single web extending con- tinuously along the inside or outside of the container and being joined to either the inside or outside of the supporting legs. The substrate 10 creates a fluid tight container and thus protects the content of the container from conditions induced by the surroundings. Preferably the film defining the substrate 10 is a continuously extending film extending on the inside or outside of the supporting leg 2 and bottom structure 3, and being integrally connected therewith such as through an IML (in mould labelling) process. The supporting legs 2 are designed with a special geometry to enhance the structural rigidity and facilitate the moulding process. As shown in fig. 1 the supporting legs 2 have a substantially planar surface 5 extending from the bottom structure 3 to the top rim 1 . The supporting legs 2 have corners 6 extending along the length of the longitudinal sides of the planar surfaces 5. These corners 6 may help to increase the strength of the supporting legs 2. Further, the geometry of the planar surfaces 5 might be optimized to enhance structural capabilities.

According to the embodiment shown in fig. 1 , the bottom structure 3 constitutes a cross like structure connecting the supporting legs 2. In the embodiment shown in fig. 2, the supporting structure comprises an intermediate piece 1 1 having ends expanding towards the supporting legs 2. In fig. 3 the bottom structure 3 comprises additional supporting elements 12 extending between the supporting legs 2.

Fig. 4 shows a cross section of a simplified injection mould according to an embodiment of the invention. A male mould part 20 and a female mould part 21 define a mould cavity 22. As shown, the distance between the surface of the male mould part 20 and the female mould part 21 is decreasing in the direction from the mould section defining the bottom structure 3 towards that defining the top rim 1 . A molten plastic material with a filler is injected under pressure through injection gate 23. With the one or more injection gates 23 arranged in the bottom part of the skeleton structure, the decreasing distance between the surfaces of the male mould part 20 and the female mould part 21 in the direction away from the gate 23, possibly even starting where the bottom structure is formed will facilitate the moulding process. The decreasing distance creates a better flow of molten material inside the mould cavity. By reducing the above internal mould part distance e.g. undesirable curing can be avoided and an amount of filler in the polymer composition is possible with the filler uniformly reaching even the parts of the container most remote from the gate 23. Depending on the position of the one or more injection gates 23, the decreasing mould distance could alternatively be inverse. The one or more injection gates 23 could e.g. be arranged near the top rim 1 of the container 4 and the mould distance decreasing from the top rim 1 towards bottom structure 3. Alternatively the one or more injection gates 23 could be arranged somewhere along the supporting legs 2 and the mould distance increasing from the one or more injection gates 23 towards both the top rim 1 and the bottom structure 3.

The decreasing distance between the surfaces of the male mould part 20 and the female mould part 21 shown in figs. 4 and 5, results in a container 4 having legs with an decreasing minimum cross-sectional dimension i.e. decreasing material thickness towards the rim 1 .

By applying a construction comprising a structural skeleton 7 and a separate substrate 10, customised properties can be assigned to both the skeleton 7 and a the substrate 10. This can be of great advantage in relation to both production and functional properties. In an embodiment of the invention this is utilised by having a structural skeleton with a relatively large material thickness. By increasing the material thickness a polymer containing an amount of filler can be used for injection moulding. The structural skeleton is manufactured by injection moulding using e.g. polyethylene (PE), polyethylene terephthalate (PET) or polypropylene (PP) containing a filler. The filler con- tent is in the range of between 30 % and 95 % by weight and the filler could e.g. be calcium carbonate, talc, chalk, Mica or nano-clay but is not limited hereto. By using larger amounts of filler the strength of the construction could be improved and polymer consumption reduced. According to an embodiment of the invention, the substrate 10, defining sides and bottom of the container 4, is comprised by two layers, namely a first layer containing a polymer material, such as HDPE, with a filler, and a second metal or polymer material layer, such as of PET. The first layer is laminated onto the second layer. The second layer provides a barrier that may also protect the first layer, in particular when having a filler material such as calcium carbonate, from being attacked by any aggressive substance held in the container. The first layer could e.g. be of a composition containing 75 %-95 % by weight calcium carbonate and 5%-25% by weight HDPE, preferably 85% by weight calcium carbonate and 15% by weight HDPE. This substrate could also be used independently of whether or not the material used for the skele- ton structure comprises filler; independent claims may be drawn on this aspect.

According to an embodiment of the invention the substrate 10 is arranged on the inside of the skeleton structure 7. Alternatively the substrate 10 could be arranged on the outside of the skeleton structure 10 or incorporated into the skeleton structure 7 and bottom structure 3. By having the substrate on the inside, the content of the container is out of contact with the skeleton structure 7 and bottom structure 3. This reduces material requirements associated with the skeleton structure 7 and bottom structure 3 and could e.g. facilitate the use of recycled plastics.

Fig. 5 shows a schematic horizontal cross-sectional view through the mould of fig. 4, showing a configuration for forming a skeleton structure 7 where the supporting legs 2 at the corners 6 have inwardly facing ribs.

It is to be noted that the figures and the above description have shown the example embodiments in a simple and schematic manner.