NZ527833A - Application of powder paint using dielectric brush to charge powder, and rotating screen - Google Patents

Abstract

Brush 7 of dielectric material electrostatically charges powder 10. Rotating perforated drum screen 6 is electrically conductive and not earthed and is positioned above the substrate to be coated. Typically the substrate is then passed through oven 8.

Description

52783 NEW ZEALAND PATENTS ACT, 1953 No: 527833 Date: 26 August 2003 COMPLETE SPECIFICATION COATING METHOD AND APPARATUS I, DARREN JOHN BLADE, a New Zealand citizen of 1 Kaikoura Street, Glendene, Auckland, New Zealand, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: FIELD OF THE INVENTION The invention relates to an improved method and apparatus for powder coating a substrate. More particularly the invention relates to coating a substrate with an image coat to decorate the surface with a pattern, image or texture.

BACKGROUND The electrostatic application of solid paint (powder form) has remained largely unchanged for the last 30 years. Metal sheet or section substrates for painting are first pre-treated to degrease, clean, and/or enable the powdered paint to properly adhere to the surface of the substrate. The coating process is performed by electrostatically charging the powder in order to make the powder adhere to the surface of the earthed substrate. The substrate is then covered by spraying the powdered paint in an even layer before being placed into an oven where the substrate is heated until the powder sinters then melts and polymerises over the surface of the substrate. The electrostatic application process of the powder paint is generally one of two types, being: corona charging, or tribo charging and are well established in the powder coating industry.

Interest has developed in recent years for the application of powder coatings to coiled substrates as well as sheet and section substrates of metallic or non-metallic materials. The main focus of this interest has been the application of uniform colours and there does not exist an, economical and efficient means of powder coating a pattern, image or texture onto a section or coil substrate. Texture is usually applied to a substrate by passing it between embossing rolls which impart the desired texture, however this process is costly and suffers from high wear rates.

SUMMARY OF THE INVENTION It is an object of the invention to provide a method of coating a substrate with an image, pattern or texture that goes some way to overcoming the above mentioned disadvantages or at least provides the industry with a useful choice.

In a first aspect the present invention consists in a method of coating a substrate comprising: electrostatically applying at least one coat of a powder paint to said substrate by: electrostatically charging a powder using a brush of a dielectric material, passing said powder through a substantially cylindrical electrically conductive and not earthed screen, while rotating the screen and advancing said substrate past said screen, and maintaining said substrate earthed.

Intellectual Property Office ot H Z. - 4 APR 2006 RECEIVED In a further aspect the invention consists in a method of coating a substrate comprising: applying at least one background coat of a first paint to said substrate, applying at least one image coat of at least a second powder paint to said substrate overtop said background coat, wherein said at least one image coat is applied to said substrate electrostatically through an electrically conductive and not earthed screen.

In a further aspect the invention consists in, in apparatus for coating a substrate, the improvement comprising: means for electrostatically applying at least one coat of a powder paint to said substrate, having a brush of a dielectric material for electrostatically charging said powder a substantially cylindrical electrically conductive and not earthed screen positioned above a carrier for said substrate, and a drive adapted to rotate said screen as it deposits said image coat on said substrate.

In a further aspect the invention consists in apparatus for coating a substrate comprising: means for applying at least one background coat of a first paint to said substrate, means for electrostatically applying at least one image coat of a powder paint to said substrate including an electrically conductive and not earthed screen positioned above a carrier for said substrate.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic drawing of the coating process of the present invention applied to a coil coating line.

Intellectual Property Office of M.Z. - 4 APR 2006 RECEIVED _4- Figure 2 is an enlarged view of the rotary screen station of the schematic of Figure 1.

Figure 3 is a perspective view of the rotary screen station according to a preferred embodiment of the present invention.

Figure 4 is a perspective view of a planar screen of an alternative embodiment.

Figure 5 is a schematic diagram illustrating alternative embodiments for various stages in the coating process Figure 6 is a schematic diagram illustrating further alternative embodiments for various stages in the coating process.

Figure 7 is a schematic diagram illustrating further alternative embodiments for various stages in the coating process.

Figure 8 is a schematic diagram illustrating further alternative embodiments for various stages in the coating process.

DETAILED DESCRIPTION The coating process described is suitable for applying an image, pattern effect, and/or texture to a substrate or object, which is inherently electrically conductive (for example a metallic substrate) or alternatively, is non-conductive and is pre-treated in order to impart conductivity to the surface of the substrate. An example of pre-treating processes are the degreasing, washing and phospho-chromating of aluminium sections before the application of the base power coat. Other pre-treating processes, many of which are already known in the powder coating industry, may also be suitable, depending on the requirements of the substrate utilised (for example, whether conductive or not).

While the coating process that will be described refers mainly to a tribo charging method of applying a base powder coat, it will be appreciated by those skilled in the art that the base coat may also be applied by a corona method or electro-magnetic brush method (EMB) as is known, in the art without departing from the scope of the present invention. Where the image coat is to be applied over a charged base coat, the polarity of the base coat must match the polarity of the image coat in order to avoid shorting and maintain image quality. Therefore the method and polarity of the process chosen to apply the image coat will be at least in part influenced by the method and polarity of the base coat application method. In 3 0 AUS 2034 the most preferred embodiment, positively tribo charging the base coat and image coat layers is preferred.

The method described is suitable for the coating of heat sensitive substrates capable of withstanding temperatures of up to approximately 140°C, and solid paints (powder) that contain (or largely contain) no solvents and are thermally curable at temperatures less than approximately 140°C, or alternatively with solid paints that melt at less than approximately 100°C and are curable by electron beam (EB) or electromagnetic radiation, e.g. infa-red or ultra-violet. It will also be appreciated that it may be advantageous or more convenient to use powder coating materials that cure at higher temperatures depending on the particular requirements and/or where the substrate is capable of withstanding higher temperatures, for example where the substrate is metallic. The method of the invention is therefore applicable to many different types of substrates including wood, plastic, ceramic, mineral, glass, metal, and metal alloys or composite structures which may include a number of these materials.

A first preferred embodiment of the method and apparatus for coating and decorating substrates will now be described with reference to Figures 1 to 3. The substrate 2 is prepared for coating (not shown) as is known in the art, according to the type of substrate, to improve the finished coatings adhesion to the substrate and/or corrosion resistance. Figure 1 illustrates a coating line generally indicated by the numeral 1. In this embodiment, the substrate 2 is unwound from a supply coil 3 and proceeds down the coating line 1 before being wound onto storage coil 4, after the coating and decorating process has been completed. As the substrate 2 proceeds down the coating line 1, it proceeds through a number of stations. At station 15a tribo charging powder gun 5 applies a first layer of a coloured powdered solid paint 9 to the substrate 2. It is envisaged that it may be desirable or necessary to apply more than one background coat prior to the application of the image coat on the substrate 2. The powder of the background coat 9 is electro-statically held to the grounded substrate 3 as it passes onto the next (image) coating process. It should be noted that according to the preferred embodiment of the present invention, it is not necessary to partially cure the background coating before the image coat is applied, and therefore there is no heating or curing step immediately following the base coat station 15. This is particularly preferred in conjunction with a coil coating process as the length of the line can be significantly reduced. Alternatively, an intermediate step may be introduced between the coating steps, to partially cure the base coat.

» The substrate progresses through an image coat station 16. To apply the image, pattern and/or texture to the surface of the substrate, the solid paint (powder) of the image coat 10 is applied through a screen 6, located above the surface of the substrate to be coated. The application screen 6 is preferably in the form of a rotating drum having a large number of small perforations in the outer surface through which the powder particles can pass. It is preferred that the minimum size of the perforations or apertures are at least the maximum size of the powder particles. In this way the resolution of the image coat can be adjusted. The image powder is made to a preferred particle size distribution and/or modified by additives such as fumed silicas or fumed AI2O3 to prevent the powder form blocking the screen. The particle size of the solid paint is preferably less than 80 microns having an average particle size between 10 and 35 microns.

The drum may be formed from a fine metal wire mesh or alternatively may be constructed from a cylindrical metal sheet filled with small perforations. For a continuous image, a rotary screen such as that manufactured by Stork Prints BV of Boxmeer in the Netherlands for the textile printing industry and distributed under the name RotaMesh® is preferred as it is electro formed in nickel and does not have a prominent edge joining seam on its curved surface. This enables continuous lengths of substrate such as that in a coil coating line to have continuous images applied, which is a particularly advantageous feature of the present invention when applied to a coil coating line. Alternatively, a drum screen is also well suited to coating non-continuous sections such as sheets. Examples, of images that might be applied are a continuous wood grain or stone effect or other repeated pattern including a uniform colour.

For a non uniform image coat, the screen is prepared for example, by the application of a photo emulsion or capillary film which is then allowed to dry or set. In order to apply the image coat in a desired pattern, the perforations in the drum which are sealed by the emulsion may be selectively opened, for example by etching the emulsion using known apparatus such as Stork Prints' LEX, or ecoLEN, or MAX systems to make the stencilled image. In this process the screen is mounted into the etching machine which rotates the screen at a high rate while it etches across the width of the screen, selectively opening some of the perforations in the drum 6 to form the pattern (ablation method).

At station 16, as the powder passes over the rotary screen 6, the powder particles pass through the open mesh and deposit onto the substrate in the desired pattern. The diameter of the drum 6, will determine the size of the image which can be applied before the image Intellectual P^perty repeats itself on subsequent rotations of the drum. Office of Z. - <1 APR 2® RECEIVED Referring to Figure 2, a charging brush 7 is located inside the cylindrical screen 6. The charging brush 6 is arranged in a substantially vertical radial orientation and brushes against the inside lowermost portion of the rotating screen drum 6. Where the hole pattern is formed, according to a method such as outline above, the image defining emulsion is preferably applied to the outside of the drum 6 in order to reduce the tendency for the brush 6 to rub the emulsion off the drum, thereby degrading the image. The brush 7, is made from a dielectric material and is preferably nylon, polypropylene or PTFE, however other dielectric materials may also be used. Depending on the polarity of the base coat, the charging brush is constructed of a suitable material chosen for its position on the dielectric scale, to ensure the correct polarity of charge to the image coat powder.

It is envisaged that the charging brush 7 may also be a composite material, where for example the dielectric material is provided as a coating over a base material. The charging brush 7 is electrically earthed. The powder paint 11 is fed in front of the brush 7 contact area, evenly along the length of the cylindrical screen 6. The brush remains stationary while the cylindrical screen 6 revolves about the brush 7. The bristles of the charging brush 7 preferably contact the screen with a force less than 20kg/m ' to tribo charge the image powder particles, and to urge the powder though the screen.

The screen is fabricated from a conductive material, and is not earthed. In this way the powder paint 11 is tribo charged with little or no loss of charge to the cylindrical screen 6, and the distribution of charge is substantially even. In order to ensure that the screen remains electrically isolated (i.e. not earthed), the screen 6 does not contact the substrate 2 during the application of the powder paint and is rotatably mounted in insulating supports. A drive is provided to rotate the drum. Preferably the drum is rotated at a speed and in a direction so that the tangential speed of the drum skin matches the advance speed and direction of the substrate. The distance between the outer surface of the screen 6 and the substrate 2, is preferably no more that 50mm and no less than 0.5mm. In a most preferred embodiment the separation gap is between 5 and 20mm.

Figure 3 illustrates a substrate 2 supported by rollers on a section of coil line 1, as it passes beneath a rotary screen 6. The stationary charging brush 7 is mounted within the cylindrical rotating screen 6 and spans its entire width. The solid paint 10, having been charged with the charging brush 7, is electrostatically attracted to the grounded substrate 2, through the open perforations in the cylindrical screen 6, and is held on the substrate 2 by the 3 0 A'J3 7rn BCrrri Mr- i-v electrostatic charge.

After the complete image coat is electrostatically applied to the substrate 2, it proceeds to heating station 17. At station 17 it passes through oven 8 (or electromagnetic curing stage) for the final curing step before the substrate is allowed to cool and is rewound onto coil 4 for storage. It will be appreciated that the precise nature of the curing step will depend on the nature of the powder paint, and substrate, and is known in the art. For the illustrated continuous process it will be appreciated that a tunnel oven of length appropriate to the advance speed of the substrate and melt and curing time of the paint will be necessary.

With reference to Figure 4, an alternative preferred embodiment of the present invention will now be briefly described. Figure 4 is a perspective view of the image coating process wherein the screen 12 is substantially planar in-shape. It will be appreciated by those skilled in the art that applying a pattern to the planar screen is less difficult than applying a pattern to a rotary screen such as that described in the previous embodiment. However, it will also be appreciated that a planar screen is more suited to applying a pattern or texture to a section or non-continuous substrate. However, a planar screen may be used for applying an image coat to a continuous coil. An alternative example process of selectively opening the perforations in a screen is similar to that previously described for a rotating screen. A positive film is placed on the emulsion side of the screen and exposed to UV light which hardens the emulsion in the areas required. The screen is then washed to remove the unhardened emulsion thereby selectively opening perforations in the screen and producing the stencilled image. Alternatively, capillary film may also be used in place of a liquid emulsion as is known in the art. Suitable capillary films, for example, are made by Kissel + Wolf GmbH. The fabrication of a planar screen may be analogous to that of a rotary screen. Usually a metal frame has a screen mesh stretched over it to produce the planar screen. Suitable conductive meshes for fabricating the screens include stainless steel, for example, produced by Asada in Japan or a metalised polymer mesh.

In the embodiment illustrated in Figure 4, the planar screen 12 is stationary and the charging brush 13 moves along the planar screen 13 in the directions of arrow 14. In this way the powder particles are tribo charged and electrostatically applied to the grounded substrate through the open apertures in the patterned screen.

It is to be appreciated that the processes described and illustrated are by way of example only and are not intended to be limiting. There are many variations possible, such as, but not limited to those described below.

For example the charging brush may be cylindrical in shape and be radially bristled. In this alternative embodiment it is important that the diameter of the brush is relatively small so that the powder is urged through the screen (rotary or planar) along a thin line in order to maintain an accurate image.

The first powder coat or background base coat may be applied by a corona charging method such as illustrated schematically in Figure 5. Alternatively, the first background base powder coat may be applied by any method known in the art and does not form part of the present invention. For example, Figure 6 illustrates the application of the first base powder coat via an electromagnetic brush method. However, as discussed earlier, the polarity of the base coat(s) and image(s) coat must be the same and the image coat powder speed to be corona charged rather than tribo charged.

During the tribo charging of the image powder on the screen it is important that the bulk of the powder is charged to the same polarity. This is required in order to stop the build-up or blocking of the screen perforations with charged powder of the incorrect polarity. By applying a variable voltage potential to the screen it is possible to correct this blocking problem. Additionally it is has been found to allow the varying of the contrast of the applied image also.

In an alternative embodiment, applying the basecoat via the corona method; the following image coat is also applied using substantially the corona method. A voltage potential is applied to the conductive screen 6; this causes the screen to act as a large electrode to cause electric field lines between the screen and the earthed substrate, the second electrode. The screen charges the powder in this embodiment as it passes thru the screen and follows the electric field lines between the screen and substrate where the powder then electrostaticly adheres.

With reference to Figure 7 and 8, two further methods of applying the base coat are illustrated. In Figure 7 the base coat is applied by spraying a liquid paint or slurry and subsequent drying the liquid fraction before the image coat is applied. In Figure 8 the liquid paint or slurry is applied by a roller and the liquid fraction is subsequently dried off before the image coat is applied overtop the base coat by the method described in the present invention.

Following the image coating of the substrate 2, further images may be applied, for example a different solid paint colour may be added in subsequent image coats. In this way a multi coloured graphic image may be obtained. Additionally using the present invention the solid paint could be luminescent effect solid paint or a blend of metallic, or ceramic, or photo luminescent "effect" pigments blended or bonded to the solid paint. In this way artistic and creative images, pattern effects and/or textures may be applied. The imaged solid paint may be melt fused to the substrate before another image coat is applied, or the image coats may be applied sequentially and then melt fused together and/or cured using thermal or combination thermal and electromagnetic radiation curing methods. Additionally, a non-image solid paint may also be applied, for example a clear coat prior to the final curing step.

The solid paints largely contain binders comprising one or more of the following polymer types although many types and hybrids including but not limited to acrylic, epoxy, hydroxyl-alkyl-amide, polyester, polyurethane, or silicone, are also suitable. The powder coating material used for the process according to the invention can be any thermal curing or electromagnetic radiation curing powder that is suitable for the substrate in question, comprising the known powder binders, cross-linking agents, pigments and/or additives. The resulting coating may be a smooth finish, a textured finish or a metallic effect. Examples of powder coating compositions that can be cured with UV-radiation are described in EP-A 739922, EP-A 702067 or EP-A 636660. Examples of powder coating compositions that are suitable for being cured by means of near infra red (NIR) radiation are described in WO 99/41323.

In order to control the tribo-electric charge, the imaging powder coating may include additives such as those disclosed in US Patent 6,113,980 e.g. Tinuvin 144, Tinuvin 111 FD of Ciba. Examples of other types of additives for controlling the electrostatic charge effect are Texaquat 900, and Texaquat 3226 from Henkel. These products are particularly useful for allowing build up of powder on powder before curing without resulting in the phenomenon known as back ionisation.

Fumed silica and/or aluminium oxide may also be included as a powder dry flow additive. Cabot Corporation sells examples of fumed silica under the tradename "Cab-O-Sil" e.g. Cab-O-Sil TS530. Degussa Corporation sells an example of aluminum oxide under the tradename "Aluminum Oxide C", and also sells fumed silica under the tradename "Aerosil" e.g. "AEROSIL 200", "AEROSIL R-972". — The image application, method and apparatus allows the manufacture of images, pattern effects, and/or texture on heat insensitive substrates able to withstand temperatures of 140°C or alternatively higher temperature curing powder coating materials may be used depending on particular requirements and/or where the substrate is capable of withstanding higher temperatures, particularly where the substrate is metallic.

According to one aspect of the invention the coating process includes a rotating conductive screen for depositing powder for an image coat onto a continuously advancing substrate. This allows for efficient image or texture application on effectively continuous materials, such as a coil of metal sheet.

According to another aspect of the invention the image coat is deposited on top of an unfired background coat. The background powder and image powder are fixed and cured at the same stage of the process. This effectively excludes an intervening curing step and associated equipment providing a substantial saving in production line cost and size.

Claims (47)

1. A method of coating a substrate comprising: electrostatically applying at least one coat of a powder paint to said substrate by: electrostatically charging a powder using a brush of a dielectric material, passing said powder through a substantially cylindrical electrically conductive and not earthed screen, while rotating the screen and advancing said substrate past said screen, and maintaining said substrate earthed.

2. A method as claimed in claim 1 including rotating said cylindrical screen at a speed such that the tangential speed of said screen surface matches the advance speed of said substrate.

3. A method as claimed in either claim 1 or claim 2 wherein procuring a relative advance comprises moving said substrate below a fixed, but rotating said screen.

4. A method as claimed in any one of claims 1 to 3 further comprising curing said coat after said application of said coat.

5. A method as claimed in claim 4 wherein said curing step comprises heating said substrate in an oven.

6. A method as claimed in claim 4 wherein said curing step comprises exposing said image coat to Ultra Violet light.

7. A method as claimed in claim 4 wherein said curing step comprises exposing image coat to infra red or near infra red light.

8. A method as claimed in any one of claims 1 to 7 wherein said substrate is advanced past said screen separated by a distance between 0.5mm and 50mm.

9. A method as claimed in any one of claims 1 to 8 wherein said brush is substantially stationary and does not rotate with said screen, such that said brush contacts said screen at an inner lowermost portion of said screen.

10. A method as claimed in any one of claims 1 to 9 wherein said screen includes an array of perforations and said method includes a preparatory step of preparing said screen to have selected perforations blocked and others open, such that in use said powder can pass through said open perforations and deposit on said substrate in a pattern.

11. A method of coating a substrate comprising: ! Office - ♦ An 2006 5EJCEIVE -13- applying at least one background coat of a first paint to said substrate, applying at least one image coat of at least a second powder paint to said substrate overtop said background coat, wherein said at least one image coat is applied to said substrate electrostatically through an electrically conductive and not earthed screen.

12. A method as claimed in claim 11 including a curing step after said application of said image coat to fix said at least one background coat and said at least one image coat to said substrate.

13. A method as claimed in claim 12 wherein said curing step comprises heating said substrate in an oven.

14. A method as claimed in claim 12 wherein said curing step comprises exposing said coated substrate to Ultra Violet light.

15. A method as claimed in claim 12 wherein said curing step comprises exposing said coated substrate to an infra red process.

16. A method as claimed in claim 11 wherein applying a first paint comprises applying a charged powder to said substrate.

17. A method as claimed in any one of claims 11 to 16 wherein during said step of applying said image coat said screen is maintained spaced from said substrate by a distance between 0.5mm and 50mm.

18. A method as claimed in any one of claims 11 to 17 wherein said powder is statically charged by a brush of a dielectric material and applied to said substrate through said screen.

19. A method as claimed in any one of claims 11 to 18 wherein said screen includes a number of perforations such that said powder can pass through said perforations and deposit on said substrate in a pattern.

20. A method as claimed in any one of claims 11 to 19 wherein said screen is cylindrical and is rotated over said substrate such that said powder is electrostatically deposited on said substrate, and said substrate is advanced past said screen.

21. A method as claimed in claim 20 when dependent on claim 18 wherein said brush is substantially stationary and does not rotate with said screen, such that said brush contacts said screen at an inner lowermost portion of said screen; and applying said image coat comprises -14- advancing said substrate relative to said screen and rotating said screen above said advancing substrate.

22. Apparatus for coating a substrate, comprising: means for electrostatically applying at least one coat of a powder paint to said substrate, having a brush of a dielectric material for electrostatically charging said powder a substantially cylindrical electrically conductive and not earthed screen positioned above a carrier for said substrate, and a drive adapted to rotate said screen as it deposits said coat on said substrate.

23. Apparatus as claimed in claim 22 including a carrier for supporting and earthing said substrate, said carrier adapted to advance said substrate such that said screen passes along said substrate.

24. Apparatus as claimed in claim 23 wherein said drive is adapted to rotate said screen cylinder at a speed such that the tangential speed of the screen surface matches an advance speed of said carrier.

25. Apparatus as claimed in either claim 22 or claim 23 including a curing station downstream of said means for applying said coat.

26. Apparatus as claimed in claim 25 wherein said curing station comprises an oven.

27. Apparatus as claimed in claim 25 wherein said curing station comprises a source of UV light.

28. Apparatus as claimed in claim 25 wherein said curing station comprises a source of IR light. Intellectual Property Office ot »m Z. - h APR 2006 RECEIVED - 15-

29. Apparatus as claimed in claim 24 wherein said screen is separated from said carrier such that the surface of said screen will be spaced from an intended said substrate by a distance between 0.5mm and 50mm.

30. Apparatus as claimed in any one of claims 22 to 29 wherein said brush is fixed and does not rotate with said screen, and is located such that said brush contacts said screen at an inner lowermost portion of said screen.

31. Apparatus as claimed in any one of claims 22 to 30 wherein said screen includes an array of perforations some said perforations being blocked by a blocking agent and others being open such that said powder can pass through said open perforations and deposit on said substrate in a pattern.

32 Apparatus for coating a substrate comprising: means for applying at least one background coat of a first paint to said substrate, means for electrostatically applying at least one image coat of a powder paint to said substrate including an electrically conductive and not earthed screen positioned above a carrier for said substrate.

33. Apparatus as claimed in claim 32 including a carrier for supporting and earthing said substrate, said carrier adapted to advance said substrate such that said screen passes along said substrate.

34. Apparatus as claimed in either claim 32 or claim 33 including a curing station downstream of said means for applying said image coat.

35. Apparatus as claimed in claim 34 wherein said curing station comprises an oven. -16-

36. Apparatus as claimed in claim 35 wherein said curing station comprises a source of UV light.

37. Apparatus as claimed in claim 35 wherein said curing station comprises a source of IR light.

38. Apparatus as claimed in claim 33 wherein said screen is separated from said carrier such that the surface of said screen will be spaced from an intended said substrate by a distance between 0.5mm and 50mm.

39. Apparatus as claimed in any one of claims 32 to 38 including a brush of dielectric material for statically charging said powder and assisting said powder to penetrate said screen.

40. Apparatus as claimed in claim 39 wherein said screen is substantially cylindrical and said brush is fixed and does not rotate with said screen, and is located such that said brush contacts said screen at an inner lowermost portion of said screen; and said apparatus includes a drive adapted to rotate said screen as it deposits said image coat on said substrate.

41. Apparatus as claimed either claim 39 or 40 wherein said drive is adapted to rotate said screen cylinder at a speed such that the tangential speed of the screen surface matches an advance speed of said carrier.

42. Apparatus as claimed in any one of claims 32 to 41 wherein there is no curing or heating station between said means for applying at least one background coat and said means for applying said image coat.

43. Apparatus as claimed in any one of claims 22 to 30 wherein said screen includes an array of perforations some said perforations being blocked by a blocking agent and others being open such that said powder can pass through said open perforations and deposit on said substrate in a pattern. la-L iy -17-

44. A method of coating a substrate substantially as herein described with reference to and as illustrated by any one or more of Figures 1 to 3 or 6.

45. A method of coating a substrate substantially as herein described with reference to and as illustrated by any one or more of Figures 5 to 8.

46. An apparatus for coating a substrate substantially as herein described with reference to and as illustrated by any one or more of Figures 1 to 3.

47. An apparatus for coating a substrate substantially as herein described with reference to and as illustrated by any one or more of Figures 1 or 2. DATED THIS %0 DAY OF fkAau£4- AGENTS FOR THE APPLICANT