GB2290734A

GB2290734A - Marking a surface

Info

Publication number: GB2290734A
Application number: GB9413221A
Authority: GB
Inventors: Keith Edward Crush; Michael Sargent
Original assignee: INDELIBLE MARKING SYSTEMS LIMI
Current assignee: INDELIBLE MARKING SYSTEMS LIMI
Priority date: 1994-07-01
Filing date: 1994-07-01
Publication date: 1996-01-10
Also published as: GB9413221D0

Abstract

To mark a surface, a stencil 12 is first stuck to the surface to be marked which is then grit-blasted. The result is that the part of the surface exposed by the cut-out area of the stencil is actually roughened by the grit-blasting, whereas the part of the surface protected by the stencil is not roughened. A coating composition is then applied over the stencil, and the coating adheres to the roughened part of the surface which has been grit-blasted. The stencil is then removed. <IMAGE>

Description

MARKING A SURFACE This invention relates to a method of marking a surface, and to apparatus for marking a surface. The marking is intended to be permanent and to act as a deterrent to the theft of an article, the surface of which is thus marked.

Permanent security markings of this type are applied either by 'branding' a surface with a branding iron having the desired message, or by acid etching of a surface in desired pattern. Both of these methods have the disadvantage that complicated designs cannot be accurately applied, the techniques being generally limited to simple lettering.

According to the invention, there is provided a method of marking a surface, the method comprising the steps of a) adhering a stencil to the surface to be marked, the material of the stencil being such that it will not be destroyed by grit-blasting; b) grit-blasting the surface through the cut-out area of the stencil; c) 'applying a coating composition to the grit blasted area; and d) removing the stencil.

The coating composition can be for example an ink, a paint or a grout filler. It may be colourless but containing an ultra-violet sensitive component which shows up under ultraviolet light. It is preferred to first apply a colourless UV sensitive composition and then to apply a coloured ink.

The stencil may have more than one cut-out area. Different cut-out areas can be coated with different coloured coating compositions, or it may be possible to apply different colours within one cut-out area.

Grit-blasting of the surface ensures that the surface being marked is interrupted so that the coating composition is applied to a part of the surface where the outer surface layer has been removed. This both aids adhesion of the coating composition to the surface and also means that removal of the marking can only be done by removing a significant amount of further material from the surface.

The grit-blasting can be carried out at pressures and with grit sizes in accordance with the nature of the surface to be marked. Most surfaces can be marked with this method, including plastics, glass, metal, stone and wood. For example, on a painted metal surface it is possible to control the grit-blasting so that either only the paint film is interrupted, or so that the paint film is completely removed in the cut-out area of the stencil and so that the underlying metal surface is interrupted.

The coating composition is preferably allowed to dry before the stencil is removed. The area of the marking can finally be cleaned up by rubbing with a solvent to remove any remaining adhesive from the area to which the stencil has been adhered. The solvent will also remove any excess ink or paint.

The invention also provides equipment for marking a surface, the equipment comprising a stencil having a cut-out area, and a pressure-sensitive adhesive on one surface, and gritblasting apparatus, the material of the stencil being such that it will not be destroyed by the operation of the gritblasting apparatus.

The cut-out area will correspond in shape to the desired mark to be marked on the surface.

The material of the stencil is preferably a plastics film which can be cut to form a stencil of any desired shape, preferably using conventional die/stencil cutting technology. The ability of the stencil to resist destruction when subjected to grit-blasting appears to derive from a resilient characteristic of the film, whereby the film compresses resiliently when in it is struck by grit to absorb some of the kinetic energy of the grit. The film is however preferably thin (between 50 Am and 200 ym is suitable, with 75 to 100 ptm being preferred). A suitable material is a soft vinyl, particularly the material sold under the name ASLAN by Allprint Supplies Ltd of Slough, England.

The material has a pressure sensitive adhesive on one face which will be protected by a peelable backing sheet before use. The adhesive should be such that the stencil can be removed from any surface after grit-blasting, leaving no or substantially no adhesive residue on the surface.

The grit blasting apparatus can be any suitable apparatus capable of operating in the range 10 - 200 psi. The pressure used and the grit specification chosen will depend very much on the nature of the surface being marked. For a hard plastic surface, for example a computer casing, a pressure of about 50 psi would be used with a silicon carbide grit with a grain size of approximately 600 ym (Grit No F30 as sold by Norton Materials UK of Ipswich, England).

Use of the method and/or apparatus set forth above allows a permanent marking to be applied to virtually any surface with a high definition, so that fine lines can be marked and sharp edges produced. It is possible to reproduce company logos and scripts to a high standard, so that the application of the marking does not spoil the appearance o= the article to which it is applied.

The marking can be applied on site, because the grit blasting apparatus is portable and articles to be marked do not need to be moved in order for the marking to be applied.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view showing apparatus in accordance with the invention in use; and Figure 2 shows a cross-section through the apparatus at the beginning of blasting; Figure 3 shows the same view as in Figure 2, but after blasting has taken place; and Figure 4 shows the surface after blasting and application of a coating.

Figure 1 shows a surface 10 to which a marking is to be applied. The surface can for example be on the outside of a computer casing or other high-value, readily portable article vulnerable to theft.

A stencil 12 is made with the design of the marking. The stencil is a flexible plastics film which has been cut through to form cut-out areas 14 which form an image of the marking. The film is supplied from the film manufacturer with a self-adhesive backing layer on one face. The film can be cut to form the stencil without removing it from the backing layer, and the redundant parts of the film can then be removed. Next, the front face of the film is covered with a self-adhesive cover sheet.

To apply the stencil to a surface, the backing sheet is removed and the stencil with its cover sheet is pressed against the surface. The adhesive layer on the film adheres to the surface. The cover layer is then removed. The cover layer is required to hold in place until application, the centres of letters (for example the centre of the letter D in Figure 1) or other stencil parts which are not connected to the rest of the film.

The nozzle 16 of a grit blasting apparatus is then brought up to the surface. The apparatus can be a standard grit blasting apparatus, and the details and functioning of this apparatus are readily available to those familiar with grit blasting. When blasting takes place, the grit which penetrates through the cut-out areas 14 in the stencil 12 will cause removal of material from the surface 10. However the grit which impinges on the uncut areas of the stencil will 'bounce off' the stencil without significantly damaging the stencil and in particular without damaging the sharp edges of the cut-out areas. Depending on the size of the stencil, it may be necessary to move the nozzle 16 over the surface to ensure that all the cut-out areas of the stencil are covered. If the cut-out areas of the stencil approach the edges of the stencil it may be desirable to mask around the stencil to prevent blasting of parts of the surface which are not intended to be marked.

The grit-blasting apparatus can have a suction system operating within a schematically shown hood 18 to retrieve and recycle the grit after it has been propelled against the surface 10. Such suction systems are known in the art.

When blasting is completed, the surface will appear as shown in Figure 3, with slightly cratered areas 20 where the cutout areas 14 of the stencil lie. Next ink 22 (or any other coating composition) is applied, over the stencil, so that the ink stains the cratered areas 20. The ink can be applied by brush or with a fibre tipped pen. A DV sensitive ink can be applied as a first coat, followed by a pigmented ink. When the ink is dry, the stencil is peeled off the surface leaving a copy of the stencil outline permanently marked on the surface.

The marking is very difficult to remove without permanently damaging the surface 10. The inclusion of a transparent DV sensitive ink means that even if a thief is successful in removing the coloured ink, the presence of the marking can be revealed under DV light. Furthermore the roughening of the surface by blasting will itself be visible unless the surface is ground away.

The method described here is simple to operate and can be applied quickly and without mess to form a permanent mark of high visual quality.

Claims

1. A method of marking a surface, the method comprising the steps of a) adhering a stencil to the surface to be marked, the material of the stencil being such that it will not be destroyed by grit-blasting; b) grit-blasting the surface through the cut-out area of the stencil; c) applying a coating composition to the grit blasted area; and d) removing the stencil.

2. A method as claimed in Claim 1, wherein the coating composition is an ink.

3. A method as claimed in Claim 1, wherein the coating composition is a paint.

4. A method as claimed in Claim 1, wherein the coating composition is a grout filler.

5. A method as claimed in any preceding claim, wherein the coating composition is colourless but contains an ultraviolet sensitive component which shows up under ultra-violet light.

6. A method as claimed in any one of Claims 1 to 4, wherein a colourless W sensitive composition is applied first to the grit blasted area, followed by the application of a coloured ink.

7. A method as claimed in any preceding claim, wherein the stencil has more than one cut-out area.

8. A method as claimed in Claim 7, wherein different cutout areas are coated with different coloured coating compositions.

9. A method as claimed in any preceding claim, for marking a painted surface, wherein the grit-blasting is controlled so that only the paint film is interrupted.

10. A method as claimed in any one of Claims 1 to 8, for marking a painted surface, wherein the grit-blasting is controlled so that the paint film is completely removed in the cut-out area of the stencil and so that the underlying surface is interrupted.

11. A method as claimed in any preceding claim, wherein the coating composition is allowed to dry before the stencil is removed.

12. Equipment for marking a surface, the equipment comprising a stencil having a cut-out area, and a pressuresensitive adhesive on one surface, and grit-blasting apparatus, the material of the stencil being such that it will not be destroyed by the operation of the grit-blasting apparatus.

13. Equipment as claimed in Claim 12, wherein the cut-out area corresponds in shape to the desired mark to be marked on the surface.

14. Equipment as claimed in Claim 12 or Claim 13, wherein the material of the stencil is a plastics film which can be cut to form a stencil of any desired shape using conventional die/stencil cutting technology.

15. Equipment as claimed in any one of Claims 12 to 14, wherein the film has a thickness of between 50 im and 200 ym.

16. Equipment as claimed in any one of Claims 12 to 14, wherein the film has a thickness of between 75 ym and 100 ym.

17. Equipment as claimed in any one of Claims 12 to 16, wherein the material of the stencil is a soft vinyl.

18. Equipment as claimed in any one of Claims 12 to 17, wherein the material of the stencil is the material sold under the name ASLAN by Allprint Supplies Ltd of Slough, England.

19. Equipment as claimed in any one of Claims 12 to 18, wherein the material has a pressure sensitive adhesive on one face protected by a peelable backing sheet before use.

20. Equipment as claimed in Claim 19, wherein the adhesive is such that the stencil can be removed from any surface after grit-blasting, leaving no or substantially no adhesive residue on the surface.

21. Equipment as claimed in any one of Claims 12 to 20, wherein the grit blasting apparatus is capable of operating in the range 10 - 200 psi.

22. Equipment as claimed in any one of Claims 12 to 21, wherein the grit blasting apparatus is portable and can be readily moved to the location of the articles to be marked which do not need to be moved in order for the marking to be applied.

23. A method of marking a surface, the method being substantially as herein described with reference to the accompanying drawings.

24. Equipment for marking a surface, the equipment being substantially as herein described with reference to the accompanying drawings.