FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a lid for a container, which lid comprises an outer lid and an inner lid, which are rotatably connected to each other via a centrally positioned connection element, where the connection element serves as a force transferring means in an axial direction.

The present invention further relates to a lid for a container which lid comprises an outer lid and an inner lid, which outer lid and inner Kd are free to rotate relative to each other via a centrally positioned connection element, where the connection element serves as a force transferring means in at least an axial direction,

BACKGROUND OF THE INVENTION

PA 2003 01455 (not published) describes a Hd for a container, which lid comprises an outer lid and an inner lid, which are rotatably connected to each other via a centrally positioned connection element, where the connection element serves as a force transferring means in an axial direction. In the detailed description, an embodiment (Fig. 13) of an outer lid is described, in which Hd there is a projection that is turning down- wards toward the inner Hd. The bottom of the projection is equipped with at least one projection that extends into the connection element between the outer and inner lid.

The document described above describes different methods for making the connection between the outer and the inner lid. Some of the above mentioned methods are not effective in practical use because the outer Hd has an opening, which opening could be penetrated by oxygen or maybe bacterial contents of the air around the packaging during use or storage. Furthermore, methods for connecting the inner and the outer Hd where the outer Hd carries without holds the inner lid, are described, but there is no description on how the connection means in the outer lid is produced.

A lid of this type is also known from WO 00/56622, which describes an outer lid that contains an inner lid, where the inner lid is centrally attached to the outer lid with a rotatable connection element, which is made up from a flexible plastic material.

The document cited above describes a very primitive connection between an outer lid and an inner lid. This connection is mostly described as a kind of glue or rubber which makes a flexible connection. This method for connecting the inner and the outer lid is not usable in practical use.

US 3608764, US 3973690, US 4446979 and US 5503282 concern an outer lid and an inner lid, where the outer lid comprises a protrusion which is connected by rotating means towards the inner layer to allow the outer layer to rotate in relation to the inner layer.

DESCRIPTION / SUMMARY OF THE INVENTION

It is the object of the invention to provide a method for producing an outer lid that can easily and reliably be connected to an inner lid. A further object of the invention is to make a lid that can be mass produced in stamping process operating with a number of steps following each other with a very high stamping frequency.

This can be achieved if the manufacturing method comprises at least the following steps,, execution of at least one process for forming a projection, which process comprises at least one double operation, which double operation comprises a first stamp- ing in a matrix with a punch with a first large diameter and a first large rounding (large radius of curvature), and subsequently executing a second stamping with a punch that has substantially the same diameter and a second smaller rounding, placing the connection element around the projection, placing a rubber block inside the projection, a third stamping operation, where a punch is pressed toward the rubber block, while the projection is supported by supporting means from the opposite side, attachment of the inner lid to the connection element.

It is, hereby, achieved that material can be transported by a number of repeated punch operations from an outer diameter towards a centre section of a lid. The material is by repeated punching stressed and formed into a projection where repeated punching can reduce the diameter of a projection and increase the height of the projection without reducing the material thickness of the wall of the projection, hi this way, the projection can have a material thickness on the whole projection without a critical reduction of material thickness of the lid in any of the surrounding areas. Further in this process, a connection element is placed around the projection, and furthermore, the projection is deformed in a further punching process where the bottom of the projection by use of a piece of rubber is expanded so that the diameter of the projection in the bottom of the projection increases and, in this way, fastens the connection elements placed around it. A rotatable fastening can in this way be fixed to the outer lid, and the whole process as such can be done in a very fast mode of production.

The projection can be produced by a number of processes, which single process comprises at least one double operation. By repeating the punching process, more material can be transported from an outer diameter towards the centre where the projection is formed. By operating the double operations, a first punching which changes the outer diameter from a bigger to a smaller value is carried out with very rounded corners of the projection where the second operation is primarily changing the corners of the projection into a corner having a smaller radius.

The connection element can be ring shaped, and where the connection element comprises an inner ring, which inner ring is made up of a rigid material. It is hereby achieved that the ring of rigid material is placed over the part of the projection, which has an increased diameter due to the last punching process. This leads to a very stable fastening process for the connection means, and the rigid ring can be so strongly connected to the projection that rotation is carried out by the connection means around the inner ring as this is fixed. The rigid ring can be formed of a metal.

The connection element can comprise polypropylene (PP). It is, hereby, achieved that the connection element is made of a material that can easily be connected to the inner lid.

The connection element can be fixed to the inner lid, by a ultra sound welding process. It is hereby achieved that the inner lid can be connected to the connection element in a very effective way without using other chemical substances for the connection.

The connection element may alternatively be moulded together with the inner Hd, thus forming an integrated part of the inner Hd. It is, hereby, achieved that the connection element is connected to the inner Hd directly in the plastic forming machine where the connection element is produced.

The inner Hd can comprise a multilayer structure containing at least two layers, which are made up of different material. It is, hereby, achieved that the inner Hd is produced in a way where different materials at the upper and lower sides are selected in accordance with the use of the inner lid. For example, it is preferred that towards the outer Hd, the inner Hd could have a relatively low friction because the outer Hd when opening has to be rotated a few degrees before a venting of the container takes place, and the inner Hd is released.

The outer Hd can comprise a projection, which projection is placed in a central hole in the connection element, which connection element comprises a rigid ring placed around the opening and around the projection, where the projection in its lover parts are expanded in radial direction for fixing the rigid ring to the ¹ projection.

Herby can be achieved that a Hd can be formed with a central connection between an outer Hd and an inner Hd. This connection can transmit downwards-acting forces to the outer Hd, while the connection is form so that the outer Hd has freedom to rotate relative to the inner Hd. This allows the outer Hd to rotate during an opening process, where the outer Hd can comprise a protrusion acting below the edge of the inner Hd for generating an upwards generating force for lifting the edge of the inner Hd for venting the inner volume of a container covered by the Hd.

The force by which the stamping is performed in each part of the double process may be from 2500 N to 8000 N, preferably from 3000 N to 7000 N, more preferred from 4000 N to 6000 N, and even more preferred from 4500 N to 5500 N.

The force by which the third stamping operation performed may be from 1000 N to 2500 N, preferably from 1500 N to 2500 N, more preferred from 1700 N to 2200 N.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to the drawing, where fig. 1 shows a cut through a lid according to the invention, fig. 2 shows a part of a punch with large roundings and a part of an outer lid, fig. 3 shows a part of a punch with a small rounding and a part of an outer lid, fig. 4 shows an outer lid just before the lastpunching operation, fig. 5 shows a cut through as in fig. 4, but during the last punching operation, and fig. 6 shows a cut through of a central part of an outer Hd connected to an inner lid.

DETAILED DESCRIPTION / PREFERRED EMBODIMENT

Fig. 1 shows a cut through of a Kd 2 according to the invention. The lid 2 comprises an outer Hd 10 and an inner Hd 14. The outer Hd 10 comprises an outer circular region 8 which is flat, and the outer Hd 10 has a slope area 6 connected to a circular flat area 12 in which a projection 18 is formed. The connection element 16 is shown connected to the projection 18, which connection element 16 is connected to the inner lid 14.

The Hd 2 in fig. 1 will in use press the inner Hd 14 towards a container neck. If this container is closed in a situation where the content of the container and the container itself is heated for sterilising the content, the pressure in the container will by reduced by decreasing temperature, and the negative pressure will act as a forces pulling down the inner Hd 14. These forces are by the connecting element 16 converted so the active force at the inner Hd is also pulling down the outer Hd 10.

Fig. 2 shows a punch 22, which is supposed to operate together with a matrix 20 where a section of the outer lid 10 is shown between the punch 22 and the matrix 20. The punch 22 has a large diameter 24, and the punch has large rounding diameters in the front end 26.At the bottom of the figure, a second view of the cut through at the outer lid 10 is shown now having the projection 18. The projection 18 has a form according to the difference in form between the punch 22 and the matrix 20.

Fig. 3 shows the next operation with a new punch 30 having roundings 32 which roundings 32 have a relatively small diameter compared to the roundings described before. The punch has a diameter 24 which diameter is substantially the same as in the previous operation. The matrix 34 has a form according to the punch 30 with only the difference in size that is according to the thickness of the material of the outer lid 10.

Below is shown the outer lid 10 with the projection 18 after the punch operation. It is now seen that the corners of the projections of the inner lid are now relatively sharp.

The operation described in fig. 2 and 3 can be repeated where the diameter (24) of the punch (22,30) and the matrix (20,34) are reduced so that the projection (18) in the outer lid (10) is given a smaller diameter, and the height of the projection (18) can by a number of steps be increased.

Fig. 4 shows an outer lid 10 with a projection 18 surrounded by connection means 16 placed under a punch 50, where a matrix 42 supports the projection 18 from below. Inside the projection 18, a rubber block 40 is placed in the bottom of the projection 18. The connection means 16 comprises a rigid ring 46 placed outside the projection 18 and above the top of the rubber block 40.

Fig. 5 shows the punch 50 placed in the bottom of the projection 18, where the matrix 42 supports the projection 18 from below. The rubber block 40 is under pressure from the punch 50, and the rubber block 40 is being deformed so hard that also the lowest area of the projection 18 is deformed in radial directions so that a part of the projection 18 now has a an increasing diameter 48 just below the rigid ring 46. Hereby, the con-

necting element 16 is fixed towards the projection 18 but in a way, where the rotation of the connection means 16 is possible around the projection 18.

Fig. 6 shows a cut through of the central section of an outer lid 10 connected to an inner lid 14. The outer lid 10 with the projection 18 is connected to the connection element 16 by the increasing diameter 48 of the projection 18 below the rigid ring 46. The connection element 16 is connected to the inner lid 14 maybe by a welding process, or they may be moulded together in the manufacturing process. The inner lid 14 can comprise three different layers 70,71,72. The upper layer 70 of the inner lid 14 can be made of polypropylene, where the intermediate layer 71 can be made from EVOH while the lowermost layer 72 is formed by an elastomer or a soft polypropylene (PP) layer. Between the different layers 70, 71, 72 a binder may be provided. The inner layer can be made as a co-extruded multilayer product.

During operation of a lid closing an inner volume in a container, a subpressure will prevail in the inner volume of the container in relation to the surroundings. This sub- pressure will act on the inner lid 14 (fig. 1) with an evenly distributed force action in downwards direction, which will deflect the inner lid 14 whereby tension will arise on the inner lid 14 where the inner lid 14 bears against the packing edge. Retaining forces from possible jamming by means of outer lid 10 against the inner lid 14 over container lid 18 ensures against pulling down the inner lid into the container volume. However, a beginning opening of the outer lid 10 can entail reduction of the squeezing force between outer lid and inner lid, and airing of the volume between outer lid 10 and inner lid 14 may occur. Thereby the risk of downwards deflection of the inner lid 14 which may be pulled down into the container. This would be unsuitable for using the contents of the container. Therefore, fastening element 16, 18 is applied at the centre for preventing a deflection of the inner lid 14. During normal storage of a container with contents, the fastening element 16, 18 will deform the central area of the outer lid downwards which can be utilised for indicating subpressure in the container. By open- ing the lid, a projection of the outer lid will cause an upwards directed force pulling the inner lid towards the outer lid, whereby a passage to the inner volume of the container is created, equalising a subpressure, and further opening occurs by using very small forces from a person removing a lid on e.g. a glass.