Container with closing membrane   

Abstract: In a container with an externally protruding annular flange which delimits an opening and is delimited by a beaker edge, and with a film-like closing membrane which, forming a common annular connecting surface delimited by an inner ring edge and an outer ring edge, is sealed against the flange to close the opening, and which can be peeled off the flange and is delimited by a membrane edge with a tear-off tab protruding beyond the beaker edge, the closing membrane, starting from the tear-off tab protrudes freely beyond the outer ring edge of the connecting surface and the distance of the membrane edge to the outer ring edge starting from the tear-off tab, on both sides of the tear-off tab up to an angle of at least 45° in relation to a diameter line running in a tear-off direction (x), diminishes constantly to zero.

The invention concerns a container with an externally protruding, annular flange which delimits an opening and is delimited by a beaker edge, and with a film-like closing membrane which, forming a common annular connecting surface delimited by an inner ring edge and an outer ring edge, is sealed against the flange to close the opening, and which can be peeled off the flange and is delimited by a membrane edge, with a tear-off tab protruding beyond the beaker edge.

It is known to provide containers, such as for example deep-drawn, injection-moulded or otherwise formed containers, at their opening with a flat annular flange and to close such containers with a lid, in particular after filling, wherein the lid or closing membrane lies across the full surface of the flange and for example is attached tightly sealing and peelable by sealing or gluing to the flange. Such containers, dishes, menu trays for example with one or more compartments, beakers, small packings etc. are known for example for packing foodstuffs of all types, e.g. dairy products, in particular yoghurt, whipping cream, sour cream, coffee cream, finished preparations of salads or semi- or full preserves, precooked or otherwise prepared meals, drinks such as fruit and vegetable juice or drinking water.

The lids, boards or closing membranes are for example punched out of an endless film-like lid material and stacked. The lid stacks are supplied to a packaging machine and the separated or unstacked lids with a sealing layer are continuously sealed by means of a sealing tool onto the container edge of the previously filled containers in the flange region of the container. The lids are often embossed or fitted with spacers when processed from magazines. Alternatively, the lid film can also be processed from a roll and punched out together after sealing with the beaker.

Normally the lid material is sealed flush to the beaker edge and the lid is typically raised at a tear-off tab. By pulling the tear-off tab, the lid is detached from the seal flange by peeling without tearing and thus preventing a complete opening of the container. However opening the lid leads to a particularly unfavourable pull angle in which the film is easily torn. Here the tensile force on opening the lid acts particularly strongly on the lid edge so that the lid no longer peels from the beaker but tears. The tendency to tear is particularly high at the start of the tear-off process as the lid edge here requires particularly little force to tear. As opening progresses, the risk of tearing increasingly diminishes.

The tearing of the lids or closing membranes on opening constitutes an irritation to the consumer. Tearing also prevents further thinning of the lid material as this would cause even more tearing due to the lower tear force required.

A relatively firm seal e.g. above 8 Nm/15 mm and the typical flush sealing of the lid film with the outer beaker edge contribute particularly greatly to tearing, as the lid film is virtually torn away from the seal edge. Here the relatively low tear or tear progression resistance of the lid materials, in contrast to the high tensile strength of the lid material, acts directly on the edge of the lid.

The tearing of the lid material can be prevented by increasing the material thickness or by lamination with tear-resistant films. Both solutions substantially increase the costs.

WO 2008/0116444 A1 discloses, to prevent tearing in peelable lids sealed to a container edge, reinforcing the lid edge e.g. by folding at least in the critical region.

For lid rings for crimping onto cans, WO 2008/068326 A1 discloses in one embodiment that the sealing film which is sealed to the lid ring to prevent tearing of the film edge during the pull-off process has an edge strip extending over the entire edge of the film and protruding beyond its fixing region. In another embodiment the closing film has “ears” protruding externally beyond the fixing region on both sides of the grip tab.

The solutions offered in the prior art are associated with an additional material usage and hence higher costs.

The invention is based on the object of designing, in a container of the type cited initially, the connection of closing membrane with the container such that with only slightly greater material use, opening is possible without tearing the membrane.

The solution to this task according to the invention is that the closing membrane, starting from the tear-off tab, protrudes freely beyond the outer ring edge of the connecting surface and the distance of the membrane edge to the outer ring edge, starting from the tear-off tab, diminishes constantly to zero on both sides of the tear-off tab up to an angle of at least 45° in relation to a diameter line running in a tear-off direction.

Preferably, the distance of the membrane edge to the outer ring edge of the connecting surface diminishes constantly to zero up to an angle of around 90°.

The solution according to the invention overcomes the possibility of tearing with a low tearing resistance. The gradual transition of the tear-off tab allows the necessary resistance of the closing membrane over the sealing edge to be kept very low and leads to an additional material consumption of only around 1%.

The tear resistance can also be reduced in that the connecting surface between the flange and closing membrane is reduced in the region of the tear-off tab, e.g. by a narrower design. In practice this can be achieved for example by a corresponding step in the flange.

On sealing beaker materials, depending on sealing medium and conditions, very high tear-off forces can occur. The tear-off force differs greatly over the periphery of the beaker and is characterised in particular by a strong rise at the start of the opening process and on tearing the membrane away when the container is opened. This second rise in tensile force can be ignored as usually the membrane is left on the container at the rear end of the periphery by the consumer.

The first very strong tension rise is achieved in the moment where the unsealed edge region of the tear-off tab of the lid reaches the so-called collision point on the sealed container edge. With very strong seals, with a flush seal all round of the membrane with the beaker edge, it is even often observed that the tab is separated from the remainder of the lid.

Surprisingly, it has now been shown that by avoiding a run-up of the tab edge at the beaker edge, said tension peak can be substantially reduced. Thus the beaker can be opened with less force and much more evenly. After half opening, the avoidance of the collision point between lid edge and beaker edge is not required as the rear lid periphery does not run towards the beaker edge but due to the modified pull direction, is merely peeled away from this.

In a first embodiment, the common annular connecting surface is arranged concentric to the beaker edge and the outer ring edge of the connecting surface substantially coincides with the beaker edge.

In this embodiment, starting from and to both sides of the tear-off tab, there is a protrusion of the closing membrane over the beaker edge in the region of a first flange half. This protrusion can if necessary be avoided by a flange or beaker edge formed eccentric in this region.

In a second embodiment, the common annular connecting surface is arranged on the diameter line running starting from the tear-off tab in the tear-off direction, eccentrically to the annular flange by a shift dimension directed away from the tear-off tab, and the edge of the closing membrane apart from the tear-off tab substantially coincides with the beaker edge.

Instead of an eccentric shift of the annular connecting surface to the flange, in this embodiment the flange or beaker edge can be formed eccentric.

Depending on the requirements imposed, the lid material can comprise various materials. Typical examples are metal foils coated with plastic on one or both sides. Other lid materials contain or consist of plastics in the form of monofilms or multilayer laminates. Further lid materials can consist of cellulose-containing materials such as cellular glass or paper. Laminates of metal and plastic films can also be used. To seal the lid material to the container edge, the lid material is usually coated over the full surface with a sealing layer such as a sealing lacquer, a sealable extrusion layer or a sealing film, wherein the sealing layer is arranged on the side facing the inside on the finished packaging, i.e. facing towards the container interior. In non-metallic films or metal films protected completely against corrosion, however, annular or partially applied sealing layers are also possible.

The containers are usually formed from plastic by deep-drawing or injection-moulding. Suitable containers can also be made by deep-drawing of lacquered or extrusion-coated films of metal or of metal/plastic laminates.

Further advantages, features and details of the invention arise from the description below of preferred embodiment examples and with reference to the drawing which depicts schematically in

FIG. 1 a section through a container with flange and closing membrane sealed against the flange;

FIG. 2 a view onto the rear of the flange of the container in FIG. 1 in view direction Y, with a closing membrane sealed against the flange in a first manner;

FIG. 3 a view onto the rear of the flange of the container in FIG. 1 in view direction Y, with a closing membrane sealed against the flange in a second manner.

A container 10 shown in FIG. 1 in the form of a beaker of plastic to receive yoghurt, for example, has a base 12 and protruding from this a side wall 14 delimiting a filling product volume. The side wall 14 extends upward from the base 12, in the example shown with an outwardly directed angle of incline, and at its end remote from the base transforms into a horizontally outwardly projecting annular flange 16. The transition of the side wall 14 into the annular flange 16 delimits a container opening 18. The free end of the flange 16 forms a container edge 20. Sealed to the annular flange 16 is a film-like board or closing membrane 22 which is peelable from the flange 16 and tightly seals the container opening 18. The seal is achieved with a sealing tool with an annular or full-surface die and leads to a common annular connecting surface 28 delimited by an inner ring edge 24 and an outer ring edge 26 between flange 16 and closing membrane 22. The closing membrane 22 which is delimited by a membrane edge 21 at one point has a tear-off tab 23 protruding from the container edge 20.

In a first type of connection between flange 16 and closing membrane 22 shown in FIG. 2, the seal is achieved such that the common annular connecting surface 28 between flange 16 and closing membrane 22 is arranged concentric to the flange 16, and the outer edge 26 of the annular connecting surface 28 substantially coincides with the beaker edge 20. Starting from the tear-off tab 23, the closing membrane protrudes beyond the outer ring edge 26 of the annular connecting surface 28 and hence also beyond the beaker edge 20, wherein the distance between the edge 21 of the closing membrane 22 and the beaker edge 20 diminishes constantly to zero on both sides of the tear-off tab 23, over a first flange half up to an angle of 90° on both sides to a diameter line defining a tear-off direction x. Over the next second flange half, the membrane edge 21 runs coincident with the beaker edge 20 or the outer ring edge 26 of the annular connecting surface 28. To guarantee peeling of the closing membrane 22 without risk of tearing, the membrane edge 21 should protrude beyond the beaker edge 20 up to at least an angle of around 45° on both sides.

In a second type of connection between flange 16 and closing membrane 22 shown in FIG. 3, the seal is achieved so that the common annular connecting surface 28 between flange 16 and closing membrane 22 is arranged eccentrically to the annular flange 16 on the diameter line running from the tear-off tab 23 in the tear-off direction x, by a shift dimension a directed away from the tear-off tab 23, and the edge 21 of the closing membrane 22, apart from the tear-off tab 23, substantially coincides with the beaker edge 20. On both sides of the tear-off tab 23, the closing membrane 22 which is coincident with the beaker edge 20 protrudes beyond the outer ring edge 26 of the annular connecting surface 28, wherein the distance between the edge 21 of the closing membrane 22 and the outer ring edge 26 of the annular connecting surface 28 diminishes constantly to zero on both sides of the tear-off tab 23, over the first flange half up to an angle of 90° on both sides to the diameter line defining the tear-off direction x. Over the next second flange half, the membrane edge 21 runs substantially coincident with the beaker edge 20 or the outer ring edge 26 of the annular connecting surface 28. To guarantee peeling of the closing membrane 22 without risk of tearing, the membrane edge 21 in this variant too should protrude beyond the outer ring edge 26 of the annular connecting surface 28 up to at least an angle of around 45° on both sides.

The closing membranes shown in the drawing have a circular round form corresponding to beakers with a circular round opening. The invention is not however restricted to these examples but comprises also other geometric container openings and lid shapes such as e.g. oval and polygonal shapes.