SE470094B - Container lid and method of manufacture thereof - Google Patents

Description

In the case of glued label, special measures are required to remove the adhesive label from the first layer.

In order to provide a container lid which is easily recyclable, it is previously known to thermoform a lid of only a single layer of material and then directly print decor on this layer. Then the printing, however. must be performed after the lid has been thermoformed (to avoid the printed object being deformed or destroyed due to prevailing thermoforming temperatures) a problem arises in that standard offset printing no longer becomes possible because this type of standard offset high speed printing technology is normally industrial is made on a large flat sheet, while the small thermoformed lid has a raised flange for attachment to the container. Thus, special design of the offset equipment that can be used for the limited space available for the printing plates that must be inserted into the flat area of the lid surrounded by the raised flange is required.

In another technical field, that of container frames and troughs, unlike container lids, the additional problem arises regarding layers intended to provide strength and layers intended for decoration held together using hot melt adhesive type adhesives, which do not nor are they easily separable for recycling purposes. In order to overcome these problems, in our Swedish patent application no. 9200358-1, filed February 7, 1992, it has been proposed that the tray portion of a dimensionally stable container be given the required properties by forming the inner and outer material layers of thermoformable material, where the inner layer is given the required dimensional stabilizing properties and where the outer decorative layer is attached. to the former without the use of hot melt adhesives or other adhesives. In this way it is possible to use the same material for the inner and outer layers and to join them together using heat without the need for additional intermediate materials, thus providing an easily recyclable container.

In the present invention, the principles underlying the formation of container trays have been applied to the problems behind lid making.

EP-A-0 395 585 discloses a method for manufacturing trays or casings consisting of two layers of material, the outer layer being a label layer. However, this method requires the use of a heat shrinkable film for the outer layer which must be applied in a first step to a preforming tool in a hot state and. then inserted into the female portion of a mold. The material in both layers is completely different, which does not provide recyclability.

A further document EP-A-0 249 363 shows, in a first embodiment, a method in which a label and a lid can be combined without intermediate materials. However, the method relates to an injection molding method which has the consequence that molten plastic is inserted into a mold cavity.

The temperature of molten plastic is detrimental to the label layer and special measures must be taken in the form of protective patches applied to the label layer at places where the molten plastic material enters the mold. This increases the number of steps in the process and thereby also material and time costs.

SUMMARY OF THE INVENTION The invention provides a lid for a container having the features set forth in claim 1 and a method of manufacturing a container lid having the features of claim 10. Preferred features of the invention are defined in the dependency requirements.

The solution provided by the present invention enables the use of conventional thermoforming equipment and conventional offset printing equipment and avoids the need for adhesive, adhesive or mechanically formed connections between the layers. This is achieved using the heat stored in the first layer of material as it is heated for the purpose of softening and for thermoforming to the final closure lid configuration. Before the first heated layer is formed in the mold, the already printed second layer is placed with its printed surface lying on the cold female part of the mold in the thermoforming machine and its unprinted surface faces the superimposed heated first layer. During the formation of the heated first layer, the first layer is pressed against the second layer and the heat in the first layer provides a molten connection in the interface between the first layer and the second layer. Since the flat, cooled female portion of the mold faces the printed surface of the second layer, the pressure remains intact and undeformed.

By this method, the same material can be used for both the first and second layers of the lid, and since no adhesive layer is used between the layers, a perfectly recyclable container consisting of only one material can be provided. In connection with recycling, you only need to grind down the lid to create a new material source for re-manufacturing of lids / containers.

Various thermoformable. materials are already widely used 5. existing lid manufacturing technology such as PVC, polyethylene, polypropylene or plastic laminate, to name just a few. The lid and method of the invention are clearly not limited to any type of material, but any suitable thermoformable material may be used for the first layer as long as it can be bonded to the second layer of material only using of heat without binder of any kind between the surfaces of the layer. However, in order to achieve recyclability, the most useful form of container lid appears to be the one where both the first and second layer materials are non-laminate and where both materials are of the same type. This becomes even more advantageous when the container body part is also made of the same material, whereby separate recycling methods are not needed for containers and lids. In addition, one can fully maintain the benefits of standard flat sheet printing machines.

The invention will now be developed with reference to the drawings which show a preferred embodiment, this being only to be seen as an example of the invention without in any way limiting the scope of the invention, since many other embodiments are discernible within the scope of the appended claims.

BRIEF DESCRIPTION OF THE FIGURES: Fig. 1 shows a finished container lid with closing flange.

Fig. 2 shows a section through the lid along the line I-I in Fig. 1.

Fig. 3 shows a section through the lid, along the line I-I in Fig. 1, during thermoforming of the lid in the thermoforming mold.

DESCRIPTION OF A PREFERRED EMBODIMENT Fig. 1 shows a container lid according to the invention generally designated by the reference numeral 1. The container lid consists of two material layers, the first material layer 2 being a thermoformable film of suitable material for example PVC, polypropylene or polyethylene. The second material layer or label layer 3 of the lid is attached to the upper surface of the first material layer 2 without the use of any adhesive, hot melt adhesive compound or other additive material.

The second material or label layer is usually decorated thereon to enable identification of the product.

This decoration can be of any desired shape, for example bar code, general product information or an image of any kind.

The second material layer 3 consists of thermoplastic material of any suitable type. However, the first and second layers of material must be of the same material. The layers 2 and 3 are normally fastened to each other in the flat or substantially flat area of the first layer which is delimited by the upright rim 4 of the closing flange (generally designated lä in Fig. 1). The raised flange 4 is designed to enable resealing on an associated part of the container top edge and thereby some flexibility is provided in its structure for enabling elastic deformation over the associated container top edge. Some reinforcement of the inner part of the lid (normally at the corners) in the vicinity of the rim may be present if desired.

Part 5 of the lid indicates a substantially planar section of the lid flange formed around the outside of the raised rim 4, and said section may rest against a corresponding section on the top edge of the container. The section 5 continues in a further vertical or inclined section 5 'and terminates in a laterally projecting lip section 6, which if desired can be formed with a gripping tongue 7 for easy opening. Although certain portions 4, 5, 5 ', 6 and 7 have been indicated and described, it will be appreciated that the flange section A may be designed otherwise without departing from the spirit of the invention. Fig. 2 shows the container lid in cross section, the label layer 3 being attached to the central portion of the lid layer 2, which is substantially flat. A small gap has been shown between the edge of the label layer 3 and the rim 4, but if desired, a gap can be omitted. The thickness of the second material or label layer 3 is not of special importance but it is normally kept as thin as possible to avoid material waste. The thickness as such can normally be of the order of 20 μm but down to 10 μm if required or as large as 80 μm or larger if needed, while the thickness of the first layer is usually greater as this is used to provide dimensional stability of the lid section. An order of magnitude of the thickness in the range of 160 μm to 300 μm is normal, but it is obvious that larger or smaller thicknesses can be used as long as sufficient stability is maintained.

As can be seen, the label layer 3 or the second layer 3 is attached to the flat surface of the first material layer 2.

The label layer is usually printed using a standard offset printing machine for printing large sheets or webs of labels. The labels are cut out and then punched from the printed sheets to the desired label size.

The method of forming the lid from the two different material layers 2 and 3 will now be described with reference in particular to Fig. 3. A molding tool is used which has a female part consisting of mold elements 11 and 12 divided along the line 13. The second material layer 3 is pre-cut and is placed, as shown, on the mold part 11. Vacuum is established in the bores 10 in the mold part 11 so that the pre-cut material layer 3 is held in place. The film constituting the first material layer 2 has the shape of a continuous web and is driven from roll towards the mold and is heated by means of a heat source (not shown) normally located just outside the mold. Depending on the type of mold used, the first material layer 2 is formed either by vacuum only, or by means of a trade (not shown) of the forming machine which presses the film (first material layer) into the shown the mold of the female parts 11 and 12. With either method, the application of force against the film 2 will also effect the application of force downwards towards the second material layer 3 which lies with its printed surface against the mold, the heat and pressure from the first material layer 2 being such that the first layer of material is molecularly bonded to the second layer 3, without the need to add any material between the layers (for example hot melt adhesive). The mold is of course cooled so that the heated and shaped lid will not adhere to the mold, which obviously also gives the additional advantage that the printed surface of the second layer can directly contact the mold without damaging the printed object.

When this cycle has been completed, the mold is opened along line 13 by a vertical movement of the part 12 relative to the part 11, whereby the lid is ejected and punched and transported for storage.

With the known "traditional" method, the look consists of a layer which is first vacuum-formed and then printed.

Since the printing machine operates at a much higher speed than the thermoforming machine, several thermoforming machines work in parallel to feed a single printing machine in order to be able to preserve the economy of fast production.

However, stacking the thermoformed looks with flanges is required for the machine to be fed properly.

The required buffer zone for stacking lids, the problems of synchronization and the reliability of stacking and unstacking lids with flanges are significant problems, but the industry has previously considered these to be indispensable if one wishes to be able to manufacture a completely recyclable acceptable lid with decoration. By means of the method according to the invention, however, all these problems are avoided, since the flat, pre-cut, punched and dried label layers 3 are only placed in a conventional dispenser device for flat objects and then transferred into mold cavities, and the dispenser and transfer apparatus are of conventional type.

Claims (8)

10 15 20 25 30 35 470 094 10 Patent claims A container lid, wherein the lid is formed of a first material layer (2) and a second material layer (3), the first material layer (2) is thermoformed and the first (2) and second (3) material layers are attached to each other, characterized in that the material in the first and second material layers is the same, and that the first and second material layers are directly attached to each other by connecting their contacting surfaces by means of heat, without any intermediate material. Lid according to claim 1, characterized in that the first. the material layer (2) is thicker. than. the second layer of material (3). Lid according to claim 4, characterized in that the lid has a closing flange (A), that the closing flange is formed by the first material layer, and that the second material layer has a smaller surface area than the first material layer and is attached to the first material layer within the area bounded by the flange. Lid according to claim 3, characterized in that the closing flange is of the type which allows resealing after opening. Lid according to one of Claims 1 to 4, characterized in that the second material layer is a label layer provided with either print or decoration. 10 15 20 4'7U 094 ll A lid according to any one of claims 1 to 5, characterized in that the thickness of the first layer is in the range of 160 μm to 300 μm while the thickness of the second layer is in the range of 10 μm to 80 μm. A lid according to any one of claims 1 to 6, characterized in that the label layer is attached to the first layer over a relatively flat area. A method for manufacturing lids for containers, wherein the lid consists of two material layers (2,3), which are thermoformable and where the material in the first and second material layers is the same, the first (2) material layer being softened by the action of heat and then thermoformed on the second material layer, and the heat in the first material layer is sufficient to ensure secure bonding between the first material layer and the second material layer without the presence of any intermediate material.