WO2009030935A2

WO2009030935A2 - Method for coating and applying designs to substrates

Info

Publication number: WO2009030935A2
Application number: PCT/GB2008/003044
Authority: WO
Inventors: Sue Calver; Peter Kaczmar
Original assignee: Fira International Limited
Priority date: 2007-09-07
Filing date: 2008-09-08
Publication date: 2009-03-12
Also published as: WO2009030935A3; GB201005796D0; GB2465736A; GB0717463D0; GB2452545A

Abstract

The present invention provides a method of forming a coating on a lignocellulose substrate. The method comprises the steps of providing a lignocellulose substrate with a fusible powder disposed on a surface thereof, and applying laser radiation to fuse and, optionally, cure the powder to form a coating. The present invention also provides a lignocellulose substrate having on a surface thereof at least one coating formed in this way, as well as an item of furniture, a Braille sign, a wall panel and a floor panel comprising such a lignocellulose substrate.

Description

Method for coating and applying designs to substrates

The present invention relates to a method for applying a coating to, and forming designs on, wood or wood-based materials.

Wood and wood-based materials are commonly used in the building and furniture industries. Synthetic wood-based board materials typically comprise a matrix of lignocellulosic elements (e.g. in the form of chips, particles or fibres) bonded together by means of an adhesive agent. Lignocellulosic materials are typically composed of at least one of (preferably all of) cellulose, hemicellulose and lignin, and commonly derive from plant biomass or from recycling of materials that originally contained plant material. Suitable adhesives include, for example, a polyurethane, urea/formaldehyde, melamine-urea or phenolic resin. Examples of board materials produced in this way include medium density fibreboard (MDF) , particleboard and chipboard.

Furniture and items in the building industry are often made from a variety of components made from different substrates, e.g. wood and MDF, each with different visual characteristics. Manufacturers will often try to make a surface of an item more visually appealing either by coating and/or applying designs to the surface, often requiring several different operations. There are many ways of coating substrates known to those skilled in the art, for example, painting and powder coating. The main problem with using the current techniques for applying designs is that they are generally multi-step and complex, which greatly inflates manufacturing costs, slows throughput and increases the likelihood of manufacturing faults.

A common technique for covering MDF is to apply resin- bonded paper overlays. Designs may have been pre-applied to the overlays, thus making the MDF more visually appealing when the overlay covers the MDF.

One particular method of coating a metal substrate is to use a powder coating composition. Such compositions are advantageous compared to liquid paint, since they are virtually solvent-free and give off little, if any, volatile material during the application and curing processes. This means powder coatings contribute less to air pollution and are safer to use for workers applying the compositions, since they are not exposed to airborne solvents. Typically, a metal substrate is coated using powder coatings as follows: a dry, finely divided, free flowing, heat fusible powder is deposited on the surface of the substrate. Typical coating processes include electrostatic spray, fluidized bed, and electrostatic fluidized bed techniques, with electrostatic spray principally being used in the metal coating industry today. Following the coating step, the powder is then fused and cured on the substrate by external heating, which may be by placing the metal substrate in an oven and/or applying infrared radiation to the substrate.

Powders that are suitable for electrostatic spray coating of metals are not ideally suitable for use with temperature sensitive materials, such as lignocellulose materials. The reason for this is that the powder coatings generally require melting and curing temperatures in the region of 150 to 190 °C. While it is possible to coat synthetic lignocellulose materials such as MDF (medium density fibreboard) using powder coatings and curing them either by heating the substrate in an oven and/or the application of infrared radiation, such temperatures are detrimental to the physical and chemical properties of the lignocellulose materials.

Powder coating has been used as a finish in the metal industry for over 30 years, but recently thermally cured powders have been used as solvent-free coatings for wood- based materials. This technology is still relatively in its infancy and there are many common problems associated with thermally cured powder coat finishes (described below) .

Blistering may be caused by too much heat in the system, either from infrared lamps or, in the case of ultraviolet cured systems, from both IR and UV lamps.

Bubbles are often found within cured finishes or at the surface of a coating and are generally caused by the presence of air in the powder as it liquefies. The air typically results from outgassing (see below) from the substrate as it is heated to melt the powder.

A milky finish is a phenomenon of clear coatings which have been applied too thickly. This produces an opaque finish. However, this problem can also result from the formulation of the powder itself.

An off colour may be produced. The final powder finish colour can be influenced by the method of curing, especially - A -

by baking durations and curing temperatures. Off colours can particularly result from baking too long in the final oven cure phase or by curing in an oven that is too hot.

"Orange peel" is a surface effect which occurs where cured powder finishes resemble, as the name suggests, the texture of the skin of an orange. The main reason for this phenomenon is poor flow of the powder prior to curing, i.e. the powder has not been able to melt and create a smooth finish before passing into the crosslinking stage of the process. Reasons for this poor flow include passing the finish into the curing stage too soon.

Outgassing is an occurrence resulting from the release of gases from the substrate and/or the powder due to heating during the flowing and curing phases. Outgassing is evidenced by bubbles and pin holing.

Pin holing is a crater effect caused by bubbles bursting prior to the surface being cured.

Scorching occurs where a surface finish has been burnt during the process. This can occur within the ovens used to melt and flow the powders (both thermal and UV systems) or during the curing phase. The scorching can occur under both IR and UV lamps.

Warping of temperature sensitive substrates, such as wood-based panels, may occur when the heat required to melt, flow and (in the case of thermal powders) cure the coating is concentrated on one surface. Recently, powders with lower curing temperatures have been developed specifically for application to MDF materials. An example of such a powder coating may be found in EP 0 806 459 A2, which discloses a coating composition comprising imidazole and a polyamine with a curing temperature in the region of about 95 to about 110⁰C. Other references can be found in European Patent 371528 and United States Patent 5124387. It has been found that the low- curing-temperature compositions generally do not form a coating that is as hardwearing as the high-temperature- curing compositions. Additionally, the use of a powder coating on natural lignocellulose materials such as wood has not generally been successful due to outgassing.

A further disadvantage of the use of current powder coating techniques is that it is only possible to coat surfaces in a uniform colour. The use of powder coatings to form even simple designs on products has not been feasible on a commercial scale.

The present invention aims to overcome or at least mitigate at least some of the problems associated with the prior art.

The present invention will now be further described. In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. In a first aspect the present invention provides a method of forming a coating on a lignocellulose substrate. The method comprises providing a lignocellulose substrate with a fusible powder disposed on a surface thereof and applying laser radiation to fuse and, optionally, cure the powder to form a coating.

In a second aspect the present invention provides a further method of forming a coating on a lignocellulose substrate. The method comprises applying laser radiation to the surface of a lignocellulose substrate to form a texture thereon, applying at least one coating layer on the surface of said lignocellulose substrate, disposing a fusible powder on the surface of the coated substrate, removing excess powder from the surface, and fusing and, optionally, curing any remaining powder. The powder is preferably fused with a laser or by heating or by ultraviolet radiation.

In a third aspect the present invention provides a further method of forming a coating on a lignocellulose substrate. The method comprises forming at least one coating layer on a lignocellulose substrate and applying laser radiation to induce a colour change in at least a portion of said at least one coating layer.

In a fourth aspect the present invention provides a further method of forming a coating on a lignocellulose substrate. The method comprises applying laser radiation to the surface of a lignocellulose substrate to form a texture thereon, applying a fusible powder to the surface thereof, and fusing and, optionally, curing the powder to form a coating. The powder is preferably fused with a laser or by heating or by ultraviolet radiation.

The present invention will be described further with reference to the accompanying drawings, provided by way of example, in which:

Figure 1 shows a lignocellulose substrate provided with a coating and a design according to the method of the present invention. Figure 2 shows a substrate coated with a dark beige base coat. An ash surface decoration was applied in a vector scan by a laser that induced a colour change.

Figure 3 shows a substrate coated with a dark beige base coat. An ash surface decoration was applied in a bitmap scan by a laser that induced a colour change.

Figure 4 shows a substrate coated with a light beige base coat. An ash surface decoration was applied in a vector scan by a laser that induced a colour change.

Figure 5 shows a substrate coated with a light beige base coat. An ash surface decoration was applied in a bitmap scan by a laser that induced a colour change.

Figure 6 shows a substrate coated with a dark beige base coat and a second dark beige coat. An ash surface decoration was applied in a vector scan by a laser that induced a colour change.

Figure 7 shows a substrate coated with a dark beige base coat and a second dark beige coat. An ash surface decoration was applied in a bitmap scan by a laser that induced a colour change. Figure 8 shows a substrate coated with a light beige base coat and a second dark beige coat. An ash surface decoration was applied in a vector scan by a laser that was used to consolidate the upper layer.

Figure 9 shows a pre-etched MDF substrate coated with a light beige base coat and a second dark beige coat. A laser was used to consolidate the upper layer.

Figure 10 shows a substrate coated with a light beige base coat and a second dark beige coat. An ash surface decoration was applied by a vector scan with a laser which was used to consolidate the grain and lines. Figure 11 shows a pre-etched MDF substrate coated with a light beige base coat. A second dark beige coat was wiped level and remaining powder was cured.

The present inventors have found that the use of laser radiation to fuse and, optionally, cure a powder coating on a lignocellulose substrate has number of surprising advantages over simply heating the substrate in an oven and/or the application of infrared radiation. Because of the high intensity of the laser radiation, it has been found that the heat-curable powder requires only a very short period of exposure to the radiation for it to fuse and optionally cure, in the order of seconds or milliseconds, rather than minutes. Additionally, it has been found that is possible to focus the laser radiation so that only the surface is heated, in contrast with conventional powder coating methods, thus preventing deterioration of the interior of the substrate.

Fusing is the at least partial melting and combining, or agglomeration of discrete particles. Curing is a process whereby a chemical reaction, for example, crosslinking, occurs to bind discrete particles together. In one embodiment of the present invention the inventors have found that a laser can be used to effect a colour change in a coating applied to a lignocellulose substrate. In a preferred embodiment the colour change is effected by the use of the same laser radiation that is used to fuse, and, optionally, cure the powder coating disposed on the lignocellulose substrate. The use of a laser to effect a colour change has the advantage of providing a more attractive and varied appearance on the substrate whilst minimising the number of process steps that need to be conducted. Colour changes include changes in colour tone as well as lightening or darkening of the existing tone. The colour change can be strong or, alternatively, subtle shading.

Furthermore, because the laser radiation can be highly focused, it is possible to apply the laser radiation to a specific pre-determined part of the surface to form a design in the coating, i.e. fuse, cure or effect a colour change in only selected portions of the powder on the surface with the laser. Very sharp lines can be produced in this manner. Following creation of the design, the powder that has not been exposed to laser radiation, and hence has not been fused, can be easily removed from the surface, leaving the fixed design formed from the fused powder on the surface.

The laser radiation may be applied to a specific predetermined part of the surface to form a design in the coating. The designs can be created using computer software packages . The machine producing the laser may be programmed using known techniques to scan the surface in a certain design. The method may further comprise removal of non-fused powder from the surface following application of the laser radiation. This removal may be performed by conventional means .

The fusible powder may comprise a thermosetting material and/or a thermoplastic material. Thermosetting materials are known in the art and are materials in which the constituent molecules crosslink on the application of heat or radiation. Thermoplastic materials are known in the art and are materials, which melt, but do not undergo a chemical reaction, on the application of heat. Particles of the powder made from a thermoplastic material will, on application of the laser in the method of the present invention, melt and fuse together, thus forming the layer. The layer formed may be then be allowed to harden, either by allowing the substrate to cool, by applying further heating or laser radiation, or other techniques known in the art.

The powder may comprise any powder suitable for forming a coating on the application of heat or radiation. For example, the powder may be curable by heat and/or by ultraviolet radiation (400 - IOnm wavelength, more preferably 400 - 200nm)or infrared radiation (700nm - lmm, more preferably 1 - 20μm) . This heat-curable/fusible powder may comprise a thermosetting material selected from, but not limited to, polyester urethane, polyester triglycidyl isocyanurate (TGIC) , acrylic urethanes, acrylic hybrids (acidic functional resins) , glycidyl methacrylate acrylate (GMA) , epoxy functional resins, epoxy-based materials and epoxy/polyester coating powders. The powder may comprise a thermoplastic material selected from, but not limited to, polyamides, polyolefins, polyvinylchloride-based materials, polyester materials and polyvinylidene fluoride. The powder may optionally comprise a blend of two or more of the above materials. Most preferably, the powder comprises epoxy polyester resins. The foregoing powders can be used in combination with any embodiment or aspect of the present invention.

The heat-curable powder may be applied to the substrate by any of the processes known in the art. This may be as described in EP 0 806 459 A2. This document describes the use of electrostatic spraying of powders using the principle of electrostatic charging, using either the corona method or the triboelectric method. In the corona method, a charge is passed to the powder particles from ionized discharged air within the corona spray gun and the particles are then ejected from the gun onto the target object. In the triboelectric method, the powder particles are charged using friction by passing them over a surface, such as polytetrafluoroethylene, and then they are ejected from an electrostatic spray gun - this is generally the preferred method. The substrate may be preheated as required to increase adhesion of the particles to the surface. Alternatively the particles may also be applied using the fluidised bed method in which the substrate is passed into a fluidized bed containing the powder.

"Lignocellulose substrate" means a substrate that comprises a lignocellulose material. The lignocellulose substrate may comprise a material selected from paper, cardboard, wood, particleboard, OSB (Oriented Strand Board) and fibreboard. Preferably, the material comprises Medium Density Fibreboard. The foregoing substrates can be used in combination with any embodiment or aspect of the present invention.

In one embodiment the laser can be used to provide a surface texture to a lignocellulose substrate before a coating layer is applied thereon. In a preferred embodiment the raw lignocellulose substrate is etched by a laser. In another embodiment a coated substrate is etched by a laser. The texture that is applied may take the form of any pattern or design that results in the provision of a three dimensional surface on the substrate. In a preferred embodiment a textured surface has an etched regular pattern, an etched mock wood texture, a logo or a design. A pre- textured lignocellulose substrate may be used in combination with any of the embodiments or aspects of the present invention.

The powder may be disposed directly on the surface of the lignocellulose material of the substrate or, alternatively, other (non-lignocellulose) material may be disposed between the lignocellulose material and the powder. The other material may be in the form of a layer and may, for example, be produced using powder coatings, optionally by using the method of the present invention or using conventional techniques, or they may be produced using painting techniques or a surfacing foil.

In one embodiment where a pre-textured lignocellulose substrate is used, a powder is applied to at least a portion of a textured coated surface of the substrate. The surface is then processed, for example, by scraping, to remove any excess powder that is not within the grooves and indentations resulting from the pre-etched surface texture. The processing may be conducted by any means suitable to only remove powder that lies above the highest portions of the underlying textured coated substrate. The processing is preferably mechanical. A further step can then be conducted to fuse and, optionally, cure the powder that remains within the surface features of the substrate. This forms a partial further coating layer. In a preferred embodiment the further step is conducted by laser radiation in accordance with the main embodiment of the present invention. In another embodiment the powder can be fused and, optionally, cured thermally or by ultraviolet radiation. In a preferred embodiment the excess powder is removed with a doctor blade which mechanically scrapes the powder-covered surface of the substrate and removes all the powder lying above the uppermost features of the substrate or coated substrate.

In a preferred embodiment at least one coating layer is applied to a textured substrate. A further powder is applied thereon and powder that is not within the depressions on the surface is removed. The remaining powder is fused and, optionally, cured. This embodiment provides a surface having surprising depth of colour and texture whilst allowing for the provision of a hardwearing, optionally smooth, upper surface. In a preferred embodiment a translucent (optionally transparent) upper layer is formed over a coated textured substrate. This provides a hardwearing smooth surface whilst providing an appearance of a rough surface. Where the upper layer is translucent the depth of the layer will dictate its colour intensity. These effects are both attractive and functional. The wavelength of the laser is preferably selected so that it is readily absorbed by the powder being employed, causing it to fuse and optionally cure. When an infrared laser is used, the wavelength is preferably in the range 700nm - lmm, more preferably 1 - 20 μm. Typically commercially available sources are employed e.g. 355nm freguency tripled YAG lasers in the UV band, l.Oδum wavelength YAG lasers that are absorbed by dark coloured coatings and 10.6um wavelength CO₂ lasers are absorbed by nearly all polymers. Such lasers can be used in combination with any embodiment or aspect of the present invention. The focusing of the laser radiation is within the skill and knowledge of the skilled person.

The intensity of the laser beam can be varied by varying the laser power and/or by varying the size of the laser beam on the powder. Typically a smaller beam size, suitable for creating fine detail, is obtained by moving the focus close to the powder surface while a larger size, suitable for covering larger areas, is obtained by moving away from this position by a controlled amount. In addition the interaction of the laser beam and powder can be varied by altering the speed of the beam's traverse. Combinations of these parameters are selected so that the powder is preferably fused and optionally cured to the required standard while avoiding overexposure and resultant material degradation.

Optionally a stationary laser beam can be projected over an area and used to fuse and optionally cure the powder. The use of appropriate power levels allows this to be achieved rapidly, normally in a sub-second interval. Controlling the beam shape, by the use for example of masks, preferably projected, enables designs to be produced.

The same lasers used to fuse the powder can be used to texture and etch the surface of lignocellulose substrates as well as to effect any colour change.

In one embodiment there is disclosed a method of forming a coating on a lignocellulose substrate comprising forming at least one coating layer on a lignocellulose substrate, and applying laser radiation to induce a colour change in at least a portion of said at least one coating layer.

In another embodiment there is disclosed a method of forming a coating on a lignocellulose substrate comprising applying laser radiation to the surface of a lignocellulose substrate to form a texture thereon, applying a fusible powder to the surface thereof, and fusing and, optionally, curing the powder, preferably by laser, thermal or ultraviolet radiation, to form a coating.

Another embodiment relates to a method of forming a coating on a lignocellulose substrate comprising applying laser radiation to the surface of a lignocellulose substrate to form a texture thereon, applying at least one coating layer on the surface of the lignocellulose substrate, disposing a fusible powder on the surface of the coated substrate, removing excess powder from the surface, and fusing and, optionally, curing any remaining powder, preferably with a laser or by heating or by ultraviolet radiation. In one embodiment, any of the processes of the present invention can be used to create a wood effect on a lignocellulose substrate. In this way a hardwearing attractive wood-like product can be manufactured from cheap materials (e.g. MDF). Furthermore the processes of the present invention can be used to conceal joins between substrate sections when making furniture and/or panels. In this way complicated pieces may be made that appear to be made of a single piece of wood. Equally the technique can be used to give the impression of a joint where such a joint has not actually been employed.

Suitable wood effects preferably mimic the typical grain and surface appearance of a particular type of wood, for example, ash, beach, oak or even expensive woods like mahogany. The effects can also be made to simulate painted or stained wooden surfaces. A simulated wood surface that appears to have been painted will lessen the need to provide a fine detailed and extensive grain pattern. According to those embodiments where the substrate is pre-etched, it is possible to create a surface that has a 3D surface texture that matches or approximates to the apparent grain effect. Furthermore, in those embodiments including a filing powder layer, it is possible to give a finished product with subtle shading and colour graded properties resulting from the relative thickness of the fused powder filed portions and the light transmission properties of those portions.

The present invention further provides a lignocellulose substrate having on a surface thereof at least one coating formed by the application of laser radiation to a fusible powder disposed on the surface. The present invention further provides a lignocellulose substrate having a design on a surface thereof, the design having been formed from at least one coating formed by the application of laser radiation to a fusible powder disposed on the surface. The present invention also provides a lignocellulose substrate having at least one coating formed according to any method of the present invention.

The present invention further provides an item of furniture, a wall or floor panel or a Braille sign comprising a lignocellulose substrate having on a surface thereof at least one coating formed as herein described in accordance with an embodiment the present invention. The present invention still further provides an item of furniture, a wall or floor panel or a Braille sign comprising a lignocellulose substrate having a design on a surface thereof, the design having been formed as herein described in accordance with an embodiment the present invention.

An item of furniture or a wall or floor panel according to an embodiment the present invention may be preferably visually appealing and preferably hardwearing. Furthermore, it can be cheap to produce due to the reduced number of manufacturing steps compared to known methods. A Braille sign made according to an embodiment the present invention may be easily formed from several layers of a specific design. Such signs may be preferably cheap to produce and preferably hard wearing. Such signs could be produced quickly, the design pattern being controlled by a computer program. The process of the present invention allows intricate designs to be applied directly onto wood-based substrates using the coating polymer as the "ink" medium and has potential application in adding value to wood commodities through the application of designs which can be purely decorative or functional (Braille, barcoding etc) in nature.

The present invention will now be described further with reference to the following non-limiting examples.

Examples

Example 1

One embodiment of the invention utilises a solid state YAG laser capable of producing up to 70 watts of output power at a wavelength of l.Oβum. The output beam is steered over the electrostatically powder coated wood, MDF or other lignocellulose substrate by a pair of computer controlled mirrors and a focussing system. When fine detail is required the focus is arranged to be at the surface and the beam moves at typically 50 to 220mm/sec, depending upon the powder absorption characteristics. After each line the beam steps over by typically 0.1mm and the next line produced, the process being repeated until the required shape is created. For area coverage the focus is raised by 60mm to defocus the beam to produce a smoother finish, lowering the focus producing similar results. The laser power is adjusted to produce the best visible results and depends upon the powder absorption characteristics being typically in the 20 to 35W range. These parameters are examples and there are many other combinations of parameters and laser types possible. A working example of providing a design onto a standard grade MDF substrate will now be described. This example is shown in figure 1.

A wasp emblem was produced by first laying down a yellow background layer on standard grade MDF and then superimposing a black wasp outline layer. Both layers were produced using an electrostatic gun to apply the appropriate coloured powder coating followed by exposure to a computer controlled scanned YAG laser beam of 1.06um (near infrared) wavelength. However, the parameters used for the two layers were different as will be explained.

Absorption of the YAG laser is relatively low in paler powders making the production of a defect free yellow base layer difficult as the laser beam tends to be preferentially absorbed by surface features on the MDF. To overcome this problem the base laser processing was done with the laser focused 60mm above the sample surface. The resultant wider beam offered a less concentrated heat input which reduced the tendency to interact with surface features. The laser beam was moved at 100 mm/s with a step-over distance of 0.1 mm between adjacent passes. Laser lamp current was 18.6 A (equivalent to a power of about 30 Watts) in continuous mode .

After application of the continuous base layer the black powder was applied by electrostatic "spray" gun and the black wasp outline was fused into the black layer (see figure 1) . The powder that formed the black wasp outline absorbed the laser light strongly. As the design required detailed features to be produced, the processing was carried out with the laser beam focused at the surface of the MDF. The laser power was reduced to limit burning caused by the intense energy density of the resultant approximately 0.2 mm diameter focussed spot. The laser beam was moved at 100 mm/s with a step-over distance of 0.1 mm between adjacent passes but the lamp current was reduced to 14 A (equivalent to a power of about 12 Watts) in continuous mode.

Unfused powder was removed from the surface of the specimen using a compressed air line. Unfused powder collected from the surface in this manner was recovered for re-use .

Further Examples

A number of samples were prepared in accordance with the following table. The laser described in Example 1 was used to effect colour changes, consolidate powder and etch the surface of the substrate as indicated below.

V# Vector Scan Sample

B# Bitmap Scan Sample

CC Colour Change

Con Consolidation

5 LB Light Beige

DB Dark Beige

The effect and textures that were produced lignocellulose substrates according to the methods of the 10 present invention may be seen in Figures 2 - 11 which correspond to samples Vl - B5 respectively. Furthermore, the advantages and disadvantages of the various methods adopted can be summarised in the following table.

15 * Low for fill & wipe, high for laser consolidation .

In view of the foregoing, it can be seen that the use of a laser to provide a surface coating, effect a colour 20 change and/or pre-texture a substrate surface, provide a quick and efficient method of preparing coated lignocellulose substrates. The use of a laser allows the provision of subtle detail and the production of an attractive final product.

Claims

Claims :

1. A method of forming a coating on a lignocellulose substrate, the method comprising the steps of: (i) providing a lignocellulose substrate with a fusible powder disposed on a surface thereof, and (ii) applying laser radiation to fuse and, optionally, cure the powder to form at least one coating layer.

2. A method according to claim 1, wherein the laser radiation is applied to only a portion of the surface, to fuse or optionally cure the powder in this portion.

3. A method according to claim 1, wherein the laser radiation is applied to a specific pre-determined part of the surface to form a design in the coating.

4. A method according to any one of claims 1 to 3, wherein the laser radiation induces a colour change in the coating layer.

5. A method according to any one of the preceding claims, wherein laser radiation is applied to the surface of the lignocellulose substrate before the fusible powder is disposed thereon in order to form a texture on said surface.

6. A method according to claim 5, further comprising the steps of:

(iii) applying a further fusible powder on the coated surface, (iv) removing excess powder from the coated surface, and

(v) fusing and, optionally, curing any powder that remains within the texture of the surface.

7. A method of forming a coating on a lignocellulose substrate, the method comprising:

(i) applying laser radiation to a surface of a lignocellulose substrate to form a texture thereon, (ii) applying at least one coating layer on said surface of said lignocellulose substrate to form a coated substrate,

(iii) disposing a fusible powder on the surface of said coated substrate, (iv) removing excess powder from the surface, and

(v) fusing and, optionally, curing any remaining powder.

8. A method of forming a coating on a lignocellulose substrate, the method comprising:

(i) applying laser radiation to a surface of a lignocellulose substrate to form a texture thereon, (ii) applying a fusible powder to said surface, and (iii) fusing and, optionally, curing said fusible powder to form a coating.

9. A method according to any of the preceding claims, further comprising removal of non-fused powder from the surface following application of the laser radiation.

10. A method according to any of the preceding claims, wherein the fusible powder comprises a thermoplastic material and/or a thermosetting material.

11. A method according to claim 10, wherein the thermosetting material comprises an epoxy resin.

12. A method according to claim 11, wherein the thermoplastic material comprises a polyester resin.

13. A method according to any of claims 1 to 12, wherein the fusible powder is an epoxy polyester resin.

14. A method of forming a coating on a lignocellulose substrate, the method comprising:

(i) forming at least one coating layer on a lignocellulose substrate, and

(ii) applying laser radiation to induce a colour change in at least a portion of said at least one coating layer.

15. A method according to any one of the preceding claims, wherein the lignocellulose substrate comprises a material selected from paper, cardboard, wood, particleboard, OSB (Oriented Strand Board) and fibreboard.

16. A method according to claim 15, wherein the lignocellulose substrate comprises Medium Density Fibreboard.

17. A method according to any of the preceding claims, wherein the laser radiation has a frequency in the infrared range of the electromagnetic spectrum

18. A method according to any of the preceding claims, wherein the laser radiation is focused on the surface.

19. A method according to any of the preceding claims, wherein the laser radiation is focussed above or below the surface.

20. A method according to any of claims 5 to 8, wherein said texture is an etched pattern or an etched design.

21. A lignocellulose substrate having on a surface thereof at least one coating formed by the application of laser radiation to a fusible powder disposed on the surface.

22. A lignocellulose substrate having a design on a surface thereof, the design having been formed from at least one coating formed by the application of laser radiation to a fusible powder disposed on the surface.

23. A lignocellulose substrate according to claim 21 or 22, wherein the at least one coating has been formed using a method as defined in any one of claims 1 to 20.

24. An item of furniture comprising a lignocellulose substrate as defined in any of claims 21 to 23.

25. A Braille sign comprising a lignocellulose substrate having a design on a surface thereof, the design having been formed using a method as defined in any one of claims 1 to 20.

26. A wall or floor panel comprising a lignocellulose substrate as defined in any of claims 21 to 23.

27. A method for forming a coating on a lignocellulose substrate as substantially described herein.