A METALLIC OBJECT PROVIDED WITH AREAS OF CONTRASTING APPEARANCE

Abstract: The present invention relates to a process for making visually contrasting structures on a metallic substrate (1), characterized in that the substrate which is coated with a single coloured layer (2) is partially subjected to the energy of a laser beam in such a way that a transparent remainder (3) of the layer is maintained on the treated area; a metallic substrate which is provided with visually contrasting structures, characterized in that a single coloured layer is present on part of the substrate, while on the remaining part of the substrate in place of this layer a single transparent layer which is substantially thinner as compared to the single coloured layer is present; and containers and cans made from the said substrate.

Description: A METALLIC OBJECT PROVIDED WITH AREAS OF CONTRASTING APPEARANCE The present invention relates to metallic substrates having visually contrasting surfaces which are suitable e.g. for the production of containers such as beverage cans and the like or are such containers . The following process is presently used to produce two-coloured logos, labels or the like on a metallic substrate: Two epoxy resin-type lacquer layers which have differing colours are applied onto the metallic substrate one after the other. Then, the upper one of the two layers is fully removed by laser ablation, so that in those areas in which the upper lacquer has evaporated the lower lacquer layer contrasting in its colour can be seen. This process is expensive, since the metallic substrate has to be provided with resin, coating it twice in separate operating cycles. This is a rather slow and tedious process, e.g. when the metallic substrate shall be coated in the form of a plate or sheet. This is due to the fact that the equipment used for coating has to be cleaned thoroughly between the application of each differently coloured layer and that the application of the second layer requires the continuous production process to be interrupted at that time, thus greatly reducing the capacity of the manufacturing line. However, until now there was no other method of applying two differently coloured layers of an epoxy resin-type lacquer onto a metallic substrate when production shall be carried out on a large scale. It is the object of the invention to provide a process which is faster and cheaper as compared to the above process and suitable for high volume production. This object is achieved by coating the metallic substrate with only one single coloured layer and partially, i.e. in the desired areas, removing (evaporating) this layer incompletely by laser irradiation. Surprisingly it has been found that treating the layer with a laser beam, the energy of which is lower as compared to the prior art, results in an incomplete removal of the coating. A thin transparent "skin" or film remains which is substantially thinner than the lacquer layer. Since this skin is surprisingly translucent, the colour of the metallic substrate becomes visible, so that visual contrasts appear. Pig. 1 schematically illustrates the process according to the invention and the resulting product: A metallic substrate 1 is fully coated with a coloured layer 2 prior to laser ablation (A) . Having evaporated the coloured layer, a remaining transparent layer 3 which is substantially thinner than the original coloured layer is shown in B in the areas 4 where the laser beam stroke. In contrast thereto, fig. 2 illustrates the known process mentioned in the introductory part, in which, under the (first) coloured layer 2 ' , the metallic substrate 1' comprises a second, differently coloured layer 5' which is directly applied onto the substrate (A'). It follows from B' that the striking of the laser beam results in the full evaporation of the first coloured layer in the affected areas 4' whereas the majority of the second layer 5' is maintained, so that the colour of the second layer 5 ' becomes visible for a viewer in the areas 4 ' . In principle, the thickness of the coloured layer can be chosen freely and is determined by common considerations (scratch resistance, price, etc.). While in prior known processes the thickness of the lower coloured layer was usually 3 - 4 μm and the layer on top thereof was thinner {e.g. about 0.5 to 2 μm) , the thickness of the only and coloured layer of the invention may for example be the same or less (e.g. about 2 to 4 μm, preferable less than 3 μm) compared to what was usual in known processes. Due to the laser ablation, a considerably thinner layer (e.g. having a thickness of only 1/6 to 1/3) remains, e.g. when a layer having a thickness of 3 μm is processed by the laser ablation, this may yield a transparent layer having a thickness of about 0.6 μm. In the process according to the invention, laser ablation may be carried out according to conventional methods. For example, the laser ablation is effected by applying a mask or stencil which covers, or vice versa exposes, letters, words, logos, figures or the like or by a printing method, e.g. printing in a dot-matrix form. The energy to be actually generated can easily be calculated by a person skilled in the art and depends on the layer thickness. Of course, higher energy will lead to greater ablation. When the upper layer of the prior art is compared with the single layer of the present invention, the energy to be generated is markedly lower than the one used in the prior art when the layers have equal thickness. Therefore, it suffices to use an NO laser for carrying out the process according to the invention. The adjustment is made such that the greater part (see above) of the coloured layer is removed from the exposed areas and the remaining skin becomes transparent in these areas, so that the metallic substrate appears as the second colour so that it appears as if it were a two-colour print. The fact that a transparent remaining layer is actually maintained by means of the process according to the invention can easily be proved by way of experiments in which the processed substrates are treated with copper sulphate. The single coloured layer may be a common lacquer, e • . g . an epoxy resin-type lacquer. As far as the colours are concerned, there is no restriction, dark colours being especially suitable due to the better contrast with the metallic translucent substrate (e.g. aluminum, steel) . Since laser ablation does not effect complete evaporation of the exposed areas of the coloured layer in the process according to the invention, the remaining thinner and colourless layer ("skin") acts as a protective layer protecting the metal from atmospheric influences and/or as a contact barrier vis-a-vis any other substances which could attack the metal, and thus also as a protection against corrosion. New coated metal sheets can be produced in a simple way by means of the process according to the invention. These sheets are anti -corrosive as well as have an attractive graphic form. In addition to the production of two-dimensional metal substrates, the process is also suited for the production of metal containers such as cans which are either "painted" according to the invention after shaping or produced from metal sheets treated according to the invention. Optionally, specific areas of the containers or cans may be treated according to the invention, e.g. the bottom and/or the tab. Thus, e.g. the back side of the tab may be provided with a very small mark which serves for the manufacturer or insiders as an identification or the like.

Claims: Claims : 1. A process for making visually contrasting structures on a metallic substrate, characterized in that the substrate which is coated with a single coloured layer is partially subjected to the energy of a laser beam in such a way that a transparent remainder of the layer is maintained on the treated area. 2. A process according to claim 1, wherein the coloured layer comprises an epoxy resin-type lacquer. 3. A process according to claim 1 or 2 , wherein those areas of the coated substrate which are not subjected to the laser beam are covered by a mask. 4. A process according to claims 1 or 2 , wherein the laser beam ablation is carried out by means of printing in a dot-matrix form. 5. Metallic substrate which is provided with visually contrasting structures, characterized in that a single coloured layer is present on part of the substrate, while on the remaining part of the substrate in place of this layer a single transparent layer which is substantially thinner as compared to the single coloured layer is present. 6. Metallic substrate according to claim 5, characterized in that the single coloured layer is an epoxy resin-type lacquer. 7. Metallic substrate according to claim 5 or 6 , characterized in that the transparent layer which is substantially thinner than the coloured layer has been prepared by exposing the single coloured layer to the light of a laser beam. 8. Container, at least partially consisting of a metallic substrate according to any one of claims 5 to 7. 9. Beverage can at least partially consisting of a metallic substrate according to any one of claims 5 to 7. 10. Beverage can comprising a tab which consists at least partially of a metallic substrate according to any one of claims 5 to 7. 11. Beverage can according to claim 10, characterized in that the single coloured layer is present on at least the back side of the tab and in that the single transparent layer is only present on the back side of the tab.

Inventors: EDWARDS DYLAN, EDWARDS, DYLAN
Applicants: EDWARDS DYLAN, SCHMALBACH LUBECA, EDWARDS, DYLAN, SCHMALBACH-LUBECA AG
Application year: 1997
Main classification: B44C1
IPC codes: B41M5, B44C1, B44C3, B65D1, B65D25