WO2013078648A1

WO2013078648A1 - Methods of powder coating

Info

Publication number: WO2013078648A1
Application number: PCT/CN2011/083252
Authority: WO
Inventors: Wai Suen WONG; Kim Yung HUNG
Original assignee: Superl Technology Limited
Priority date: 2011-11-30
Filing date: 2011-11-30
Publication date: 2013-06-06

Abstract

The present invention provides a method of powder coating a heat-sensitive item having an edge, which includes sealing the edge against moisture loss from the item, applying powder to a surface of the item, and curing the powder. The present invention also provides another method of powder coating a heat-sensitive item, the method including applying a powder to a surface of the item, heating the surface in a melting stage for between about 60 seconds and about 90 seconds such that the surface has a surface temperature that reaches a maximum that is above a curing temperature to melt the powder, and heating the surface in a curing stage to maintain the surface temperature at the curing temperature for between about 120 seconds and about 180 seconds to cure the powder.

Description

Methods of Powder Coating

FIELD OF THE INVENTION

The present invention relates to methods of powder coating heat- sensitive items, and in particular, items made of wood-based materials. BACKGROUND OF THE INVENTION

The process of powder coating metal items by spraying a coating of powder onto the items and then heating the coating of powder to cure the coating has been used for about 50 years. The process involves spraying a coating of powder onto an item, heating or baking the coating of powder to 200°C so that the powder melts, flows and then bonds to the item. Advantages of the process include that no solvents are necessary, no harmful substances are discharged during the process, and the powders used do not contain heavy metals and are non-toxic. Thus, the powder coating process is environmentally-friendly and relatively safe.

The powder coating process has been applied to synthetic board since the end of the 1990s. However, although the powder coating process, with the high temperature baking required, is excellent when applied to metal, there are many problems when it is applied to synthetic board and other heat-sensitive items. Synthetic board includes synthetic wood or engineered wood board, such as fiberboard, particleboard, chipboard, medium density fiberboard (MDF), and hardboard. One as yet unresolved problem with items made of these types of materials is the cracking and distortion that results from high temperature baking. One particular aspect of this problem is edge cracking. This occurs, for example, around the edges of a board being powder coated. It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

SUMMARY OF THE INVENTION

The present invention, in a first aspect, provides a method of powder coating a heat- sensitive item having an edge, the method including:

sealing the edge against moisture loss from the item;

applying powder to a surface of the item; and

curing the powder.

Preferably, the edge is sealed by applying an edge strip to the edge. Preferably, the edge strip is bonded to the edge. Preferably, the edge strip is bonded to the edge by gluing the edge strip to the edge. Preferably, the edge strip and the glue are blanched after gluing the edge strip to the edge. The edge strip and the glue are preferably blanched at a temperature between about 80°C and about 220°C.

Preferably, the glue is a hotmelt adhesive. Preferably, the glue is a hotmelt adhesive that reacts with moisture to increase the bond strength between the item and the edge strip.

Preferably, the edge strip is made of one or more of paper, melamine paper, and kraft paper.

Preferably, after applying powder to the surface of the item, the method includes:

heating the surface in a melting stage for between about 60 seconds and about 90 seconds such that the surface has a surface temperature that reaches a maximum that is above a curing temperature to melt the powder; and heating the surface in a curing stage to maintain the surface temperature at the curing temperature for between about 120 seconds and about 180 seconds to cure the powder.

Preferably, the powder has a rated curing temperature of between about 120°C and about 150°C. In one embodiment, the powder has a rated curing temperature of about 150°C.

In one embodiment, the surface temperature reaches a maximum of between about 155°C and about 175°C in the melting stage. Preferably, the surface temperature reaches a maximum of between about 160°C and about 170°C in the melting stage.

In one embodiment, the curing temperature is between about 130°C and about 160°C. Preferably, the curing temperature is between about 140°C and about 150°C.

Preferably, the item has a relative humidity of between about 5% to about 7% before the powder is applied to the surface of the item.

Preferably, the item is preheated such that the item has a relative humidity of between about 5% to about 7%. Preferably, the item is preheated to a temperature of between about 60°C and about 120°C for about 90 seconds.

In one embodiment, the item has a relative humidity of between about 6% and about 8% before preheating.

In one embodiment, the item has a temperature of about 25 °C before preheating.

Preferably, the item has a temperature of between about 40°C and about 55°C before the powder is applied to the surface of the item. Preferably, the item is heated by moving the item through a heating oven having a melting zone corresponding to the melting stage and a curing zone corresponding to the curing stage.

Preferably, the item is heated using infrared radiation.

In one embodiment, the infrared radiation is supplied by an infrared radiation source producing an average power distribution of about 25kW/m during the melting stage.

In one embodiment, the infrared radiation is supplied by an infrared radiation source producing an average power distribution of about lOkW/m during the curing stage.

Preferably, the infrared radiation source includes one or more infrared lamps spaced apart over an area to produce the average power distribution. Preferably, the surface is the entire outer surface of the item. Preferably, the cured powder has a hardness of at least 2H.

Preferably, the board is made of wood or wood-based material. In one embodiment, the item is made of engineered wood. In another embodiment, the item is made of one or more of fiberboard, particleboard, chipboard, medium density fiberboard, and hardboard. In one embodiment, the item is made of medium density fiberboard and the powder forms a coating having a thickness of between about 80 micrometres and about 90 micrometres. Preferably, the method is used a second time to form a second coating having a thickness of between about 60 micrometres and about 70 micrometres. Preferably, one or both of the first and second coatings is sanded, and the overall thickness of the first and second coatings is between about 100 micrometres and about 140 micrometres. In another embodiment, the item is made of melamine faced chipboard and the powder forms a coating having a thickness of between about 80 micrometres and about 100 micrometres.

In a second aspect, the present invention provides a method of powder coating a heat- sensitive item, the method including:

applying a powder to a surface of the item;

heating the surface in a melting stage for between about 60 seconds and about 90 seconds such that the surface has a surface temperature that reaches a maximum that is above a curing temperature to melt the powder; and

heating the surface in a curing stage to maintain the surface temperature at the curing temperature for between about 120 seconds and about 180 seconds to cure the powder.

In one embodiment, the item has a temperature of about 25 °C before preheating. Preferably, the item has a temperature of between about 40°C and about 55°C before the powder is applied to the surface of the item.

Preferably, the item is heated by moving the item through a heating oven having a melting zone corresponding to the melting stage and a curing zone corresponding to the curing stage.

Preferably, the item is heated using infrared radiation. In one embodiment, the infrared radiation is supplied by an infrared radiation source producing an average power distribution of about 25kW/m during the melting stage.

Preferably, the infrared radiation source includes one or more infrared lamps spaced apart over an area to produce the average power distribution.

Preferably, the surface is the entire outer surface of the item. Preferably, the cured powder has a hardness of at least 2H.

In one embodiment, the item has an edge and the method includes sealing the edge against moisture loss from the item before applying powder to the surface of the item. Preferably, the edge is sealed by applying an edge strip to the edge. Preferably, the edge strip is bonded to the edge. Preferably, the edge strip is bonded to the edge by gluing the edge strip to the edge. Preferably, the edge strip and the glue are blanched after gluing the edge strip to the edge. The edge strip and the glue are preferably blanched at a temperature between about 80°C and about 220°C.

Preferably, the glue is a hotmelt adhesive. Preferably, the glue is a hotmelt adhesive that reacts with moisture to increase the bond strength between the board and the edge strip.

Preferably, the edge strip is made of one or more of paper, melamine paper, and kraft paper. Preferably, the item is made of wood or wood-based material. In one embodiment, the item is made of engineered wood. In another embodiment, the item is made of one or more of fiberboard, particleboard, chipboard, medium density fiberboard, and hardboard.

In one embodiment, the item is made of medium density fiberboard and the powder forms a coating having a thickness of between about 80 micrometres and about 90 micrometres. Preferably, the method is used a second time to form a second coating having a thickness of between about 60 micrometres and about 70 micrometres. Preferably, one or both of the first and second coatings is sanded, and the overall thickness of the first and second coatings is between about 100 micrometres and about 140 micrometres.

In another embodiment, the item is made of melamine faced chipboard and the powder forms a coating having a thickness of between about 80 micrometres and about 100 micrometres. In a third aspect of the present invention, there is provided a heat- sensitive item to be powder coated, the heat- sensitive item having an edge sealed against moisture loss from the item.

Preferably, the edge has an edge strip. Preferably, the edge strip is bonded to the edge. Preferably, the edge strip is bonded to the edge with a glue. Preferably, the edge strip and the glue were blanched. The edge strip and the glue were preferably blanched at a temperature between about 80°C and about 220°C.

BRIEF DESCRIPTION OF THE FIGURES

Preferred embodiments in accordance with the best mode of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Fig. 1 is a perspective view of an oven used in a powder coating process in accordance with a preferred embodiment of the present invention, where the oven is for heating an item that has been coated with powder;

Fig. 2 is an end view of the oven of Fig. 1;

Fig. 3 is a cross-sectional side view of the oven of Fig. 1;

Fig. 4 is a cross-sectional side view of the oven of Fig. 1 showing a wall inside the oven fitted with infrared tubes to form an infrared radiation source; Fig. 5 is a graph showing the surface temperature of the item as the item proceeds through the oven;

Fig. 6 is another graph showing the surface temperature of the item as the item proceeds through the oven; Fig. 7 is a further graph showing the surface temperature of the item as the item proceeds through the oven;

Fig. 8a is a perspective view of an item to be powder coated in a powder coating process in accordance with a preferred embodiment of the present invention, shown before edge strips are bonded to the edges of the item; Fig.8b is a plan view of the item of Fig. 8b; and

Fig. 9 is a plan view of the item of Fig.8, shown after the edge strips have been bonded to the edges of the item using a glue.

DETAILED DESCRIPTION OF THE BEST MODE OF THE INVENTION

Referring to the figures, there is depicted a method of powder coating a heat-sensitive item 1. The method includes applying a powder 2 to a surface 3 of the item 1, heating the surface 3 in a melting stage for between about 60 seconds and about 90 seconds such that the surface 3 has a surface temperature that reaches a maximum that is above a curing temperature to melt the powder 2, and heating the surface 3 in a curing stage to maintain the surface temperature at the curing temperature for between about 120 seconds and about 180 seconds to cure the powder 2. The powder 2 can be any suitable low temperature powder. Such a powder typically has a rated curing temperature of between about 120°C and about 150°C. One particular powder that has been applied quite successfully has a rated curing temperature of about 150°C.

It is preferred that in the melting stage, the surface 3 is heated for between about 60 seconds and about 90 seconds such that the surface 3 has a surface temperature that reaches a maximum of between about 155°C and about 175°C to melt the powder 2. More preferably, the surface 3 is heated in the melting stage for between about 60 seconds and about 90 seconds such that the surface 3 has a surface temperature that reaches a maximum of between about 160°C and about 170°C to melt the powder 2.

It is preferred that the curing temperature is between about 130°C and about 160°C. More preferably, the curing temperature is between about 140°C and about 150°C.

Throughout the present specification, a "heat-sensitive item" means an item which is affected by the heating required in traditional powder coating processes in such a way that the item contains defects, such as cracking, distortion, bubbling, surface unevenness, and structural weakening, that detract from the quality, aesthetics, and performance of the item. Depending on the colour of the powder 2, the amount of time the item 1 spends in the melting stage and the curing stage can be adjusted. This is because different colours absorb heat energy at different rates and adjusting the time the item 1 spends in the melting and curing stages ensures that similar heat energies are absorbed by powders of different colour. For example, it has been found that black coloured powder requires shorter times, white coloured powder requires longer times, and yellow coloured powder requires even longer times.

The heating can be carried out by moving the item 1 through a heating oven 4 having a melting zone 5 corresponding to the melting stage and a curing zone 6 corresponding to the curing stage. In the present embodiment, infrared radiation is used to heat the item 1. However, other methods such as using ultraviolet radiation, radiant heat, and convective heat can be employed in other embodiments. In one embodiment, the infrared radiation is supplied by an infrared radiation source producing an average power distribution of about 25kW/m during the melting stage. In another embodiment, the infrared radiation is supplied by an infrared radiation source producing an average power distribution of about lOkW/m during the curing stage. These average power distributions can be produced by having the infrared radiation source include one or more infrared lamps 7 spaced apart over an area.

In the present embodiment, the heating oven 4 includes two opposing walls 8 between which the item 1 moves. Each wall 8 includes a plurality of infrared lamps 7 distributed over an area of the wall to produce the desired average power distribution. For example, 25 infrared lamps each rated at lOkW can be evenly distributed over an area of one of the walls 8 measuring 5m in length and 2m in height. The item 1 is suspended on an overhead conveyor 9 that moves the item 1 between the walls and along the length of the walls 8 through the heating oven 4. The melting zone 5 is defined by an initial length of the walls 8 beginning from an end of the heating oven 4 through which the item 1 first enters the heating oven 4. The curing zone 6 is defined by a subsequent length of the walls 8 beginning from the end of the melting zone 5. In some embodiments, the walls 8 can be moved towards or away from each other to adjust the distance between the opposing faces of the walls 8. This allows adjustment of the heating energy that impacts the surface 3, and therefore, the adjustment of the resulting surface temperature of the surface 3, so that the desired surface temperatures can be achieved in different environmental conditions.

It is preferred that the item 1 has a relative humidity of between about 5% to about 7% before the powder 2 is applied to the surface of the item 1. In this regard, in a preferred embodiment of the method of the present invention, the item 1 is also preheated such that the item has a relative humidity of between about 5% to about 7%.

In one embodiment, the item 1 is preheated to a temperature of between about 60°C and about 120°C for about 90 seconds. Typically, the item 1 has a relative humidity of between about 6% and about 8% before preheating. Also typically, the item 1 has a temperature of about 25 °C before preheating. The preheating is such that the item has a temperature of between about 40°C and about 55°C before the powder 2 is applied to the surface 3 of the item 1.

Many applications require the entire outer surface of the item 1 to be powder coated. Thus, in many embodiments of the present invention, the surface 3 is the entire outer surface of the item 1. Embodiments of the present invention are well suited to items 1 that are made of wood or wood-based materials. These materials are heat- sensitive and particularly prone to the problems described above of cracking, distortion, bubbling, surface unevenness, structural weakening, and other defects that detract from the quality, aesthetics, and performance of the item, when subjected to the high temperature baking required in traditional powder coating processes. These materials include engineered wood, such as fiberboard, particleboard, chipboard, medium density fiberboard (MDF), and hardboard. However, the present invention is not limited to these specific materials and can be applied to other heat-sensitive materials. In one embodiment which has been found to perform well, the item 1 is made of medium density fiberboard and the powder forms a coating having a thickness of between about 80 micrometres and about 90 micrometres. This first coating is sanded and the method of the present invention described above is used a second time to form a second coating having a thickness of between about 60 micrometres and about 70 micrometres. With the sanding of the first coating, this results in the overall thickness of the first and second coatings being between about 100 micrometres and about 140 micrometres. In other embodiments, the second coating can also be sanded, with or without sanding the first coating.

In another embodiment which has been found to perform well, the item 1 is made of melamine faced chipboard (MFC) and the powder forms a coating having a thickness of between about 80 micrometres and about 100 micrometres. Only one coating is required in this particular embodiment, and this coating can also be sanded.

The methods provided by the present invention result in a cured powder 2 that has a hardness of at least 2H. Also, it has been found that when the methods of the present invention are applied to a plurality of heat- sensitive items, a defect rate of less than 3% can be achieved, that is, less than 3% of the plurality of heat-sensitive items have defects after the items are powder coated using the methods of the present invention. This is a vast improvement from the defect rate of 30% that is typical of prior methods of powder coating heat-sensitive items.

One particular application of the present invention is for the powder coating of an item 1 having an edge 10. One particular example is an item 1 in the form of a board having an edge 10. Typically, boards have two opposite major faces 11 with an edge 10 that is between the faces and extends around the perimeter of the faces. Boards are often flat with the two opposite major faces 11 being substantially flat. In many applications, the major faces 11 have features such as grooves, channels, holes, splines, ribs, raised or indented patterns, and attachments. Such features can also be included on the edge 10. Boards can have one or more edges 10. To simplify referencing, any reference to a "board" in this specification also refers to boards having a plurality of edges 10 and any reference to an "edge" in this specification also refers to one or more, or all, of the edges 10 of boards having a plurality of edges.

The powder coating of furniture pieces is becoming more and more popular. Thus, it is envisaged that popular applications of the present invention will be those where items, such as the boards described above, are assembled to form furniture pieces. Where boards such as those described above are used in these applications, the features noted above that are located on the major faces 11 and the edge 10 are used to facilitate attachment of one board to one or more other boards in order to allow assembly of the boards to form furniture pieces. It was noted above that the methods provided by the present invention result in a cured powder 2 that has a hardness of at least 2H. This is particularly desirable for the furniture pieces described above.

With boards, and other items having an edge, one particular problem is water or moisture loss through an edge of the board. This can lead to defects such as edge cracking and bubbling. In view of this, the present invention also provides a method of powder coating a heat- sensitive item having an edge which includes sealing the edge against moisture loss from the item through the edge before applying powder to the item. Thus, the sealing of the edge also occurs before curing the powder. The method of powder coating the item that is performed after sealing the edge against moisture loss from the item can be any suitable method of powder coating, and can be, but is not limited to, the method of powder coating a heat- sensitive item described above in the present specification. Thus, in a preferred embodiment of the method of powder coating a heat- sensitive item having an edge, in which the edge is sealed against moisture loss from the item before applying powder to the item, the item is the heat- sensitive item 1 described above, having the major faces

11 and the edge 10. Preferably, the edge 10 is sealed by applying an edge strip 12 to the edge. The edge strip

12 can be bonded to the edge 10. For example, the edge strip can be bonded to the edge 10 by gluing the edge strip 12 with a glue 13 to the edge. Any suitable glue can be used to glue the edge strip to the edge 10. A preferred glue is a hotmelt adhesive. Even more preferred is a hotmelt adhesive that reacts with moisture to increase the bond strength between the board and the edge strip. One specific example of this type of moisture reactive hotmelt adhesive is Kleiberit PUR hotmelt adhesive supplied by KLEBCHEMIE GmbH & Co. KG.

In one embodiment, the edge strip and the glue are blanched after gluing the edge strip to the edge 10. More particularly, in one embodiment, the edge strip and the glue are blanched at a temperature between about 80°C and about 220°C. Blanching ensures that the glue seals and solidifies appropriately. In particular, blanching drains water from the glue, and accelerates curing and attachment between the edge strip and the edge 10, which reduces processing time. The edge strip can be made of any suitable material, such as one or more of paper, melamine paper, and kraft paper.

It has been found that an edge strip having a thickness of between about 0.03mm and about 5mm is preferable. The edge strip is matched to the board. For example, for an item 1 in the form of a board having a length of 600mm, a width of 400mm, and an edge thickness of 18mm, the required length of the edge strip is 2m. The edge strip can be attached to the edge 10 either manually or with the aid of machinery, and can be attached to items of various shapes, such as rectangular and round boards. The edge strip can be coated with glue for attachment to the edge 10. The edge strip and the glue are then blanched to securely attach the edge strip to the edge. The corners of the board can then be polished. After a quality inspection, the powder 2 is then applied to the item 1 and cured.

As well as ameliorating defects such as edge cracking and bubbling due to moisture loss from the board, the use of the edge strip has also been found to assist in the leveling of the edge 10, which reduces processing time. For example, this can reduce the time required for any polishing required. The present invention also provides a heat- sensitive item to be powder coated, the heat- sensitive item having an edge sealed against moisture loss from the item through the edge, as best shown in Fig. 9. In a preferred embodiment, the item is the item 1 described above having the edge 10.

The edge 10 has the edge strip 12. The edge strip 12 is bonded to the edge 10. In particular, the edge strip is bonded to the edge with the glue 13. The edge strip 12 and the glue 13 were blanched. More particularly, the edge strip 12 and the glue 13 were blanched at a temperature between about 80°C and about 220°C.

The glue 13 is a hotmelt adhesive. More particularly, the glue 13 is a hotmelt adhesive that reacts with moisture to increase the bond strength between the item and the edge strip. As above, one specific example of this type of moisture reactive hotmelt adhesive is Kleiberit PUR hotmelt adhesive supplied by KLEBCHEMIE GmbH & Co. KG. The edge strip 12 is made of one or more of paper, melamine paper, and kraft paper.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention can be embodied in many other forms. It will also be appreciated by those skilled in the art that the features of the various examples described can be combined in other combinations.

Claims

1. A method of powder coating a heat- sensitive item having an edge, the method including: sealing the edge against moisture loss from the item;

applying powder to a surface of the item; and

curing the powder.

2. A method according to claim 1 wherein the edge is sealed by applying an edge strip to the edge.

3. A method according to claim 2 wherein the edge strip is bonded to the edge.

4. A method according to claim 3 wherein the edge strip is bonded to the edge by gluing the edge strip to the edge.

5. A method according to claim 4 wherein the edge strip and the glue are blanched after gluing the edge strip to the edge.

6. A method according to claim 5 wherein the edge strip and the glue are blanched at a temperature between about 80°C and about 220°C.

7. A method according to any one of claims 4 to 6 wherein the glue is a hotmelt adhesive.

8. A method according to any one of claims 4 to 7 wherein the glue is a hotmelt adhesive that reacts with moisture to increase the bond strength between the item and the edge strip.

9. A method according to any one of claims 2 to 8 wherein the edge strip is made of one or more of paper, melamine paper, and kraft paper.

10. A method according to any one of claims 1 to 9 wherein after applying powder to the surface of the item, the method includes:

11. A method according to claim 10 wherein the powder has a rated curing temperature of between about 120°C and about 150°C.

12. A method according to any one of claims 10 wherein the powder has a rated curing temperature of about 150°C.

13. A method according to any one of claims 10 to 12 wherein the surface temperature reaches a maximum of between about 155°C and about 175°C in the melting stage.

14. A method according to any one of claims 10 to 12 wherein the surface temperature reaches a maximum of between about 160°C and about 170°C in the melting stage.

15. A method according to any one of claims 10 to 14 wherein the curing temperature is between about 130°C and about 160°C.

16. A method according to any one of claims 10 to 14 wherein the curing temperature is between about 140°C and about 150°C.

17. A method according to any one of claims 1 to 16 wherein the item has a relative humidity of between about 5% to about 7% before the powder is applied to the surface of the item.

18. A method according to claim 17 wherein the item is preheated such that the item has a relative humidity of between about 5% to about 7%.

19. A method according to claim 18 wherein the item is preheated to a temperature of between about 60°C and about 120°C for about 90 seconds.

20. A method according to any one of claims 18 to 19 wherein the item has a relative humidity of between about 6% and about 8% before preheating.

21. A method according to any one of claims 18 to 20 wherein the item has a temperature of about 25 °C before preheating.

22. A method according to any one of claims 17 to 21 wherein the item has a temperature of between about 40°C and about 55°C before the powder is applied to the surface of the item.

23. A method according to any one of claims 1 to 22 wherein the item is heated by moving the item through a heating oven having a melting zone corresponding to the melting stage and a curing zone corresponding to the curing stage.

24. A method according to any one of claims 1 to 23 wherein the item is heated using infrared radiation.

25. A method according to claim 24 wherein the infrared radiation is supplied by an infrared radiation source producing an average power distribution of about 25kW/m during the melting stage.

26. A method according to any one of claims 24 to 25 wherein the infrared radiation is supplied by an infrared radiation source producing an average power distribution of about lOkW/m during the curing stage.

27. A method according to any one of claims 25 to 26 wherein the infrared radiation source includes one or more infrared lamps spaced apart over an area to produce the average power distribution.

28. A method according to any one of claims 1 to 27 wherein the surface is the entire outer surface of the item.

29. A method according to any one of claims 1 to 28 wherein the cured powder has a hardness of at least 2H.

30. A method according to any one of claims 1 to 29 wherein the board is made of wood or wood-based material.

31. A method according to claim 30 wherein the item is made of engineered wood.

32. A method according to claim 31 wherein the item is made of one or more of fiberboard, particleboard, chipboard, medium density fiberboard, and hardboard.

33. A method according to claim 32 wherein the item is made of medium density fiberboard and the powder forms a coating having a thickness of between about 80 micrometres and about 90 micrometres.

34. A method according to claim 33 wherein the method is used a second time to form a second coating having a thickness of between about 60 micrometres and about 70 micrometres.

35. A method according to claim 34 wherein one or both of the first and second coatings is sanded, and the overall thickness of the first and second coatings is between about 100 micrometres and about 140 micrometres.

36. A method according to claim 32 wherein the item is made of melamine faced chipboard and the powder forms a coating having a thickness of between about 80 micrometres and about 100 micrometres.

37. A method of powder coating a heat-sensitive item, the method including:

applying a powder to a surface of the item;

38. A method according to claim 37 wherein the item has an edge and the method includes sealing the edge against moisture loss from the item before applying powder to the surface of the item.