EP1563916A2

EP1563916A2 - Apparatus and method for powder coating of a wood-based substrate using infrared radiation

Info

Publication number: EP1563916A2
Application number: EP20050250341
Authority: EP
Inventors: William Peter Miller; David Francis Miller
Original assignee: MILLER Dolores Mary
Current assignee: MILLER Dolores Mary
Priority date: 2004-01-22
Filing date: 2005-01-24
Publication date: 2005-08-17
Also published as: GB0401328D0

Abstract

The present invention relates to an apparatus and process for coating a substrate with a coating material, in particular to an apparatus and process for powder coating a substrate such as a wood based substrate (eg medium density fibreboard (MDF)), using IR-radiation and to a method for processing a product.

Description

The present invention relates to an apparatus and process for coating a substrate with a coating material, in particular to an apparatus and process for powder coating a substrate such as a wood based substrate (eg medium density fibreboard (MDF)), and to a method for processing a product.
MDF board is manufactured from wood fibres which when mixed with binders and other additives are compressed and cured to provide a solid board which may be used inter alia in the building industry. The quality of MDF board varies considerably even amongst premium quality board. Inconsistencies in quality may become apparent during the various heating steps involved in powder coating. Some boards are more tolerant to heat than others but generally speaking improper heat treatment may lead to poor powder coating, gassing or cracking. When conventional heating systems such as hot air or electric systems are used to condition MDF and/or for melting and curing the powder, a number of drawbacks exist and the method is generally considerably unstable and unpredictable. Direct irradiation by catalytic heaters reduces but does not eliminate these drawbacks.
One conventional method for powder coating MDF is largely described in EP-A-0933140. This firstly involves preheating raw board with catalytic heaters to bring moisture to the surface where it assists in electrostatic transfer of powder from an application gun onto the surface of the board to create a generally satisfactory condition to assist powder adhesion (whilst generally minimising complete dry out). In one particular arrangement, the catalytic heaters are placed in a frame inside a metallic tunnel structure which resembles a hexagonal shaped enclosure which can vary in height, width and length. The heaters are fitted into recesses in stainless steel sheeting separated in the horizontal and vertical plane by gaps of various sizes dependent on their design, type, size and number. The heaters emit long wave infrared radiation and are fitted in a manner such that the heat is directed onto both sides of the MDF board as it travels down the tunnel. The stainless steel in the gaps between the heaters reflect back the infrared radiation towards the opposite side of the tunnel. However, underheating or overheating can prevent the powder from adhering properly to even the highest quality board. This is particularly true for a routed board or a board into which a design has been cut. In such cases, the areas in which the board has been routed or cut are thinner than the remainder of the board and can dry out excessively during heating. Moreover due to the fact that the surface temperature of the heaters is higher than that of the stainless steel in the gaps, there is greater heat pick up in a part of the board at which heat from the heater is directed than in a part of the board at which heat reflected from the stainless steel is directed. Thus heat striping can occur and this is worsened by the inconsistent quality of even the highest quality available boards. Furthermore, it is difficult to control the exact temperature of each catalytic heater since there may be inherent variations in heat output which exacerbate inconsistencies in heat pick up by the board as it passes along the tunnel.
After then carrying out powder application (eg spraying) in a non-heated zone, the board is moved by conveyor into a hotter zone where the powder melts. This step requires considerable heat penetration into the powder/substrate to effect a change in the powder from a dry state to a hot wet state and is usually carried out by a series of catalytic heaters to directly irradiate the board from both sides. Catalytic heaters flow the powder more easily and evenly than other heating means. After the powder melts, the board is then passed through a curing tunnel which stabilises the temperature of the powder/board and cures the flowed powder by direct irradiation using catalytic heaters. This gives reasonable results but not without drawbacks. In particular, difficulties in controlling all of the heaters in the curing section may make it troublesome to satisfy the requirements of different boards and powder colours/types and lead to an inconsistent finished quality.
Although millions of powder coated MDF panels are in worldwide use, the shortcomings in the powder coating steps have been accepted as the norm and inconsistencies in product appearance and finish are largely tolerated. However, next generation powders for applying to MDF represent new challenges in coating and curing. When properly cured, such powders are smoother and match foil coated boards very well. Although they open up new markets, they are not ideally suited for coating by conventional heating apparatuses.
The present invention seeks to improve coating of substrates such as wood based substrates by irradiating the substrate exclusively with reflected infrared radiation.
Thus viewed from one aspect the present invention provides an apparatus for coating a substrate with a coating material comprising:
at least one zone adapted to irradiate the substrate substantially exclusively with reflected infrared radiation.
The present invention advantageously makes it possible to avoid heat shock (and therefore cracking) and to achieve a consistent and uniform coating of all currently available powder formulations irrespective of the characteristics of the substrate.
The substrate may be natural or synthetic. The substrate may be a wood-based substrate such as medium density fibreboard (MDF), high density fibreboard (HDF), chipboard, hardboard, blackboard or timber board. Other suitable substrates are paper based, card based, metallic or plastic substrates. Even vulnerable or heat sensitive substrates such as light gauge metals and wet paint and powder coated plastics may be coated by the apparatus of the invention.
The substrate may be clay and the coating material may be a glaze.
In a preferred embodiment, the substrate is a wood-based substrate. The present invention in this embodiment serves advantageously to eliminate heat shock and dry out even where the wood-based substrate is routed, recessed or cut.
The coating material may be a solvent (eg water) based or solid (eg powdered) coating material. A preferred coating material is a powder, particularly preferably a flowable powder. The coating material may be a paint (eg a GRP paint), lacquer, sealant, stain, varnish, ink, rubber or glue. The coating may be decorative and/or protective.
In a preferred embodiment, the coating material is a flowable powder, the substrate is a wood-based substrate and the apparatus comprises:
a conditioning zone for heating the wood based substrate to a pre-conditioning temperature, wherein the conditioning zone is adapted to irradiate the wood based substrate substantially exclusively with reflected infrared radiation. Exploiting substantially totally reflected infrared radiation advantageously makes it possible to avoid heat shock, drying out or heat striping even for sensitive or routed boards.
Irradiating the wood based substrate substantially exclusively with reflected infrared radiation in the conditioning zone typically raises the wood based substrate to a preconditioning temperature in the range 60-80°C. The conditioning zone may be further adapted to directly irradiate the wood based substrate with infrared irradiation to raise it to an elevated conditioning temperature (eg 160-180°C). The elevated conditioning temperature may be sufficient to elevate the electrical conductivity at the surface of the substrate.
The apparatus may further comprise a powder distribution zone for distributing (eg spraying) powder onto the surface of the wood based substrate. The powder distribution zone is generally unheated and on leaving the conditioning zone, the temperature of the wood based substrate may drop typically to 40-60°C.
In a preferred embodiment, the coating material is a flowable powder, the substrate is a wood-based substrate and the apparatus comprises:
a curing zone for curing the flowable powder at or above the minimum curing temperature, wherein the curing zone is adapted to irradiate the wood based substrate substantially exclusively with reflected infrared radiation. In this embodiment, over cure and under cure is avoided and the curing zone is more easily controlled in terms of temperature pick up by the powder/wood based substrate leading to a more uniform cure.
In a particularly preferred embodiment, the curing zone includes:
(a) a flowing zone for converting the flowable powder into a flowed powder at a first temperature; and
(b) a stabilising zone for stabilising the flowed powder at a second temperature below the first temperature and at or above the minimum curing temperature, wherein one or both of the flowing zone and stabilising zone is adapted to irradiate the wood based substrate substantially exclusively with reflected infrared radiation.
In a preferred embodiment, the coating material is a flowable powder, the substrate is a wood-based substrate and the apparatus comprises:
(1) a flowing zone for converting the flowable powder into a flowed powder at a first temperature, wherein the flowing zone is adapted to irradiate the wood based substrate directly with infrared irradiation; and
(2) a stabilising zone for stabilising the flowed powder at a second temperature below the first temperature and at or above the minimum curing temperature, wherein the stabilising zone is adapted to irradiate the wood based substrate substantially exclusively with reflected infrared radiation.
Typically the first temperature is in the range 160-190°C. Typically the second temperature is in the range 130-140°C.
The or each zone may be a walled zone such an oven. The substrate may be stationary or may move linearly or rotate. The substrate may be agitated or turned over to assist coating. For example, the or each zone typically takes the form of an elongate tunnel (eg a hexagonal or box-like tunnel) or an essentially box-like enclosure (ie with entry and exit doors) into which the substrate may be introduced or through which the substrate may be conveyed by conventional conveyor means (eg flat bed or monorail). It is envisaged that conventional box oven enclosures, semi enclosures and drying rooms could be readily adapted into a zone according to the apparatus of the invention. The air in the elongate tunnel may be recirculatory.
The substrate may be irradiated substantially exclusively with reflected infrared radiation by judiciously siting and fixing one or more sources of infrared radiation in the zone. The one or more sources of infrared radiation may be one or more heaters such as catalytic heaters, naked flame infrared sources or electric infrared sources. The one or more heaters may be adapted to provide flash heating. Typically the one or more sources of infrared radiation emit long wave infrared radiation. Preferably the one or more sources of infrared radiation are one or more catalytic heaters (eg Bruest catalytic heaters available from the applicants Miller, Miller and Miller for the present application).
In any zone, the one or more sources of infrared radiation may have the same or different output. For example, in the conditioning zone it may be useful to have a plurality of sources of infrared radiation with a ramped output (eg to create a gradual or stepped increase in temperature along the zone).
Preferably the one or more sources of infrared radiation are mounted such that the radiative face of each source of infrared radiation is adjacent to and faces one or more discrete reflective surfaces. Where there is a plurality of discrete reflective surfaces, the or each source of infrared radiation is preferably mounted such that the infrared radiation with which the substrate is substantially exclusively irradiated is reflected substantially only from the nearest (and optionally the second nearest) discrete reflective surface. The or each discrete reflective surface may adopt any convenient regular or irregular shape (eg angled, flat, rounded, convex or concave shape).
The discrete reflective surface may be a reflective wall. Preferably the one or more sources of infrared radiation are mounted such that the radiative face of each source of infrared radiation is adjacent to and faces one or more (eg two) reflective walls (eg adjacent to and facing a side wall, the floor or the ceiling or adjacent to and facing a side wall and the ceiling or a side wall and the floor). Where there is a plurality of reflective walls, the or each source of infrared radiation is preferably mounted such that the infrared radiation with which the substrate is substantially exclusively irradiated is reflected substantially only from the nearest (and optionally the second nearest) reflective wall.
By way of example, one or more walls of a walled zone may be at least partially (preferably wholly) composed of or lined with a reflective material such as a reflective metal, metal alloy or metal composite. Preferably the or (preferably) each reflective wall is wholly composed of or lined with a reflective material. Preferably the or (preferably) each reflective wall is composed of or lined with a reflective metal, particularly preferably stainless steel.
The precise angle at which the radiative face is disposed to a discrete reflective surface (eg reflective wall), the precise distance from the discrete reflective surface (eg reflective wall) and the separation of the sources of infrared radiation may be readily empirically determined for optimum effect by the skilled person. The angle, distance and separation may depend inter alia on the type and size of the substrate and the heating temperature required. For example, if there is too great a distance between sources of infrared radiation, a long region of substantially exclusively reflected infrared radiation zone exists with a greater likelihood of cold spots. Other influential factors such as temperature, output and the gas pressure and flow to catalytic heaters may equally be readily optimised by the skilled person.
Preferably the one or more sources of infrared radiation are mounted such that the radiative face of each source of infrared radiation faces a discrete reflective surface in a manner such as to aggregate a substantially linear region of substantially exclusively reflected infrared radiation zone (a "reflective region") to the rear of the radiative face of each source of infrared radiation. By passing the substrate through the reflective region, it is possible to avoid heat shock and to achieve a consistent and uniform coating of currently available powder formulations. Typically the radiative face of the or each source of infrared radiation is at a distance of between 6 and 24 inches from the reflective wall to create a stable and uniform reflective region.
The one or more sources of infrared radiation may be wall mounted. For example, one or more sources of infrared radiation may be mounted on both side faces of the zone. Typically the one or more sources of infrared irradiation are mounted at the upper and lower ends of the side faces of the zone. For a box-like enclosure, the one or more sources of infrared radiation may be mounted at or near to the junction of two surfaces (for example a side wall and a floor or a side wall and a ceiling). For example, there may be a first source of infrared radiation mounted at or near to the junction of a side wall and the ceiling and a second source of infrared radiation mounted at or near to the junction of the opposing side wall and the ceiling. Alternatively for example, there may be a first source of infrared radiation mounted at or near to the junction of a side wall and the ceiling, a second source of infrared radiation mounted at or near to the junction of the side wall and the floor, a third source of infrared radiation mounted at or near to the junction of the opposing side wall and the ceiling and a fourth source of infrared radiation mounted at or near to the junction of the opposing side wall and the floor. Alternatively for example, there may be a first source of infrared radiation mounted at or near to the junction of a first side wall and the ceiling, a second source of infrared radiation mounted at or near to the junction of the second side wall opposite the first side wall and the ceiling, a third source of infrared radiation mounted at or near to the junction of a third side wall and the ceiling and a fourth source of infrared radiation mounted at or near to the junction of the fourth side wall opposite to the third side wall and the ceiling. Alternatively for example, there may be a first source of infrared radiation mounted at or near to the junction of a first side wall and the ceiling, a second source of infrared radiation mounted at or near to the junction of the second side wall opposite the first side wall and the ceiling, a third source of infrared radiation mounted at or near to the junction of a third side wall and the ceiling and a fourth source of infrared radiation mounted at or near to the junction of the fourth side wall opposite to the third side wall and the ceiling, together with a fifth source of infrared radiation mounted at or near to the junction of the first side wall and the floor, a sixth source of infrared radiation mounted at or near to the junction of the second side wall and the floor, a seventh source of infrared radiation mounted at or near to the junction of the third side wall and the floor and an eighth source of infrared radiation mounted at or near to the junction of the fourth side wall and the floor.
It has been noted that the present invention may use a fewer number of heaters than conventional heaters. For example, on average in the conditioning zone of the apparatus of the present invention, four heaters are used in each two metre section (minimum height 4ft, maximum height 12ft) whereas 12 heaters are used in each six foot long and eight foot high section of the conditioning zone of a conventional heater. For example, on average in the curing zone of the apparatus of the present invention, four heaters are used in each six foot long by twelve foot (or less) high section whereas 12 heaters are used in each six foot long and eight foot high section of the curing zone of a conventional heater. The desirability of a fewer number of heaters (up to 80%) is that heat control is more straightforward and reliable and that energy consumption may be reduced by 60-80% with lower emissions. Additionally there are less ancillary components such as electrical wiring, gas piping and gas solenoids.
Viewed from a further aspect the present invention provides a process for coating a substrate with a coating material comprising:
irradiating the substrate substantially exclusively with reflected infrared radiation in at least one step of the process.
In a preferred embodiment, the coating material is a flowable powder, the substrate is a wood-based substrate and the process comprises:
irradiating the wood based substrate substantially exclusively with reflected infrared radiation in a preconditioning step. Irradiating with reflected infrared radiation in the preconditioning step typically raises the wood based substrate to a temperature in the range 60-80°C. The preconditioning step may be followed by a conditioning step in which the wood based substrate is irradiated directly with infrared irradiation to raise it to an elevated conditioning temperature (eg 160-180°C). Preferably the elevated conditioning temperature is sufficient to elevate the electrical conductivity at the surface of the substrate.
The process may further comprise:
distributing (eg spraying) a coating material (eg a powder) onto the surface of the substrate (eg a wood based substrate).
In a preferred embodiment, the coating material is a flowable powder, the substrate is a wood-based substrate and the process comprises:
irradiating the substrate substantially exclusively with reflected infrared radiation to a temperature at or above the minimum curing temperature of the flowable powder.
In a particularly preferred embodiment, the coating material is a flowable powder the substrate is a wood-based substrate and the process comprises:
(a) converting the flowable powder into a flowed powder at a first temperature; and
(b) stabilising the flowed powder at a second temperature below the first temperature and at or above the minimum curing temperature,
In a preferred embodiment, the coating material is a flowable powder, the substrate is a wood-based substrate and the process comprises:
irradiating the wood based substrate directly with infrared radiation to convert the flowable powder into a flowed powder at a first temperature; and
irradiating the wood based substrate substantially exclusively with reflected infrared radiation to stabilise the flowed powder at a second temperature below the first temperature and at or above the minimum curing temperature.
Typically the first temperature is in the range 160-190°C. Typically the second temperature is in the range 130-140°C.
Viewed from a yet further aspect the present invention provides a coated substrate obtainable or obtained by a process as hereinbefore defined.
Viewed from an even still further aspect the present invention relates to a method for processing a product comprising:
irradiating the product substantially exclusively with reflected infrared radiation in at least one step of the method.
The step of the method may be a conditioning, drying, curing, hardening, dehydration, moisture removal or solvent removal step. The product may be a pharmaceutical product (eg in tablet form), rubber, building products (eg plaster), fabric, paper, clay, wood chips, sawdust, oat grain, vegetables, biscuits (eg water biscuits or biscuit derived from flower or grain products (eg rusk used for sausage making)). For example, the method may be used to condition clay (prior to entry into the kiln), to remove solvents/chemicals from wood chips, sawdust, oats grain, vegetables or biscuits, to condition biscuit derived from flower or grain products (eg rusk used for sausage making), to condition, form or dry a pharmaceutical product or to cure or condition rubber.
Preferably the product is a composite product (eg a carbon fibre composite product). Particularly preferably the composite product is an aircraft product (eg a product used in the aircraft construction industry).
Preferably the step of the method is a curing step. Particularly preferably the step of the method is a low temperature curing step eg a temperature in the range 30 to 80°C, preferably 40 to 60°C.
In a preferred embodiment, the product is an aircraft product and the method further comprises:
applying a curable paint composition to the aircraft product;
irradiating the product substantially exclusively with reflected infrared radiation so as to cure the paint composition.
The present invention will now be described in a non-limitative sense with reference to the accompanying Figures in which:
Figure 1 illustrates schematically in cross-section an oven of an embodiment of the apparatus of the present invention.
In Figure 1 is illustrated schematically an oven of an embodiment of the present invention designated generally by reference numeral 1. The oven 1 comprises side walls 3a, 3b spaced part by a ceiling 4b and floor 4a in the form of a walled, box-like enclosure 2. Each of the side walls 3a and 3b, the end walls (not shown) and the ceiling 4b is lined with reflective stainless steel.
Four catalytic heaters 5a-d are mounted respectively near to each of the junctions of the side wall 3a and floor 4a, floor 4a and side wall 3b, side wall 3b and ceiling 4b and ceiling 4b and side wall 3a. The angle of the heaters 5a-d to the nearby reflective surfaces is about 45° and the respective radiative faces 6a-6d are directed outwardly towards the nearby side wall and the radiation (as shown by the arrows X) reflects off the side walls 3a and 3b towards the centre of the enclosure 2 (as shown by arrows Y) where it aggregates into a reflective region.
A wood based board 8 passes through the reflective region by conventional conveyor means (not shown) where it is exposed on both faces 8a and 8b to uniform heating by totally reflected infrared radiation. By varying the temperature the oven 1 may be used as a conditioning zone, a curing zone or a flowing zone. Three such ovens 1 may be used in sequence to effect coating of the wood based board 8 with a powder and such an arrangement is described in the following Example.

Example

The board arrives at a main conditioning oven at room temperature where it is subjected to direct IR radiation by catalytic heaters in order to raise the temperature to 160°-180°C. Alternatively and optimally the board arrives at the main conditioning oven at an elevated temperature in the range 60-80°C having been subjected to indirect IR irradiation in accordance with the invention by catalytic heaters in a preconditioning phase.
As the board leaves the main conditioning oven, the temperature drops gradually to about 40-60°C as it enters a coating booth where powder is applied to the board in a conventional manner. The board leaves the powder booth and enters the flow oven where the temperature is elevated by direct irradiation to 160-190°C. When flow of the powder is initiated, the board leaves the flow oven causing the temperature to drop to 130-150°C. On entry into and conveyance along the curing oven, the temperature of the board is maintained at 130-140°C by indirect irradiation in accordance with the invention.

Claims

An apparatus for coating a substrate with a coating material comprising:

at least one zone adapted to irradiate the substrate substantially exclusively with reflected infrared radiation.
An apparatus as claimed in claim 1 wherein the substrate is a wood-based substrate and the coating material is a flowable powder.
An apparatus as claimed in claim 2 comprising:

a conditioning zone for heating the wood based substrate to a pre-conditioning temperature, wherein the conditioning zone is adapted to irradiate the wood based substrate substantially exclusively with reflected infrared radiation.
An apparatus as claimed in claim 2 comprising:

a curing zone for curing the flowable powder at or above the minimum curing temperature, wherein the curing zone is adapted to irradiate the wood based substrate substantially exclusively with reflected infrared radiation.
An apparatus as claimed in claim 4 wherein the curing zone includes:

(a) a flowing zone for converting the flowable powder into a flowed powder at a first temperature; and

(b) a stabilising zone for stabilising the flowed powder at a second temperature below the first temperature and at or above the minimum curing temperature, wherein one or both of the flowing zone and stabilising zone is adapted to irradiate the wood based substrate substantially exclusively with reflected infrared radiation.
An apparatus as claimed in claim 2 comprising:

(1) a flowing zone for converting the flowable powder into a flowed powder at a first temperature, wherein the flowing zone is adapted to irradiate the wood based substrate directly with infrared irradiation; and

(2) a stabilising zone for stabilising the flowed powder at a second temperature below the first temperature and at or above the minimum curing temperature, wherein the stabilising zone is adapted to irradiate the wood based substrate substantially exclusively with reflected infrared radiation.
An apparatus as claimed in any preceding claim wherein the or each zone takes the form of an elongate tunnel or an essentially box-like enclosure into which the substrate is introduced or through which the substrate is conveyed by a conveyor means.
An apparatus as claimed in any preceding claim wherein the one or more sources of infrared radiation are mounted such that the radiative face of each source of infrared radiation is adjacent to and faces one or more discrete reflective surfaces.
An apparatus as claimed in any preceding claim wherein the one or more sources of infrared radiation are mounted such that the radiative face of each source of infrared radiation is adjacent to and faces a plurality of discrete reflective surfaces, wherein the or each source of infrared radiation is mounted such that the infrared radiation with which the substrate is substantially exclusively irradiated is reflected substantially only from the nearest discrete reflective surface.
An apparatus as claimed in claim 8 or 9 wherein the discrete reflective surface is a reflective wall.
An apparatus as claimed in any preceding claim wherein the or each zone is a walled zone, wherein one or more walls of the walled zone is at least partially composed of or lined with a reflective material.
An apparatus as claimed in any preceding claim the one or more sources of infrared radiation are mounted such that the radiative face of each source of infrared radiation faces a discrete reflective surface in a manner such as to aggregate a substantially linear region of substantially exclusively reflected infrared radiation zone to the rear of the radiative face of each source of infrared radiation.
An apparatus as claimed in any preceding claim wherein the one or more sources of infrared radiation are wall mounted at the upper and lower ends of the side faces of the zone.
An apparatus as claimed in any preceding claim wherein the one or more sources of infrared radiation are mounted at or near to the junction of two surfaces.
An apparatus as claimed in any preceding claim wherein

(a) a first source of infrared radiation is mounted at or near to the junction of a side wall and the ceiling and a second source of infrared radiation is mounted at or near to the junction of the opposing side wall and the ceiling or

(b) a first source of infrared radiation is mounted at or near to the junction of a side wall and the ceiling, a second source of infrared radiation is mounted at or near to the junction of the side wall and the floor, a third source of infrared radiation is mounted at or near to the junction of the opposing side wall and the ceiling and a fourth source of infrared radiation is mounted at or near to the junction of the opposing side wall and the floor or

(c) a first source of infrared radiation is mounted at or near to the junction of a first side wall and the ceiling, a second source of infrared radiation is mounted at or near to the junction of the second side wall opposite the first side wall and the ceiling, a third source of infrared radiation is mounted at or near to the junction of a third side wall and the ceiling and a fourth source of infrared radiation is mounted at or near to the junction of the fourth side wall opposite to the third side wall and the ceiling or

(d) a first source of infrared radiation is mounted at or near to the junction of a first side wall and the ceiling, a second source of infrared radiation is mounted at or near to the junction of the second side wall opposite the first side wall and the ceiling, a third source of infrared radiation is mounted at or near to the junction of a third side wall and the ceiling and a fourth source of infrared radiation is mounted at or near to the junction of the fourth side wall opposite to the third side wall and the ceiling, together with a fifth source of infrared radiation mounted at or near to the junction of the first side wall and the floor, a sixth source of infrared radiation mounted at or near to the junction of the second side wall and the floor, a seventh source of infrared radiation mounted at or near to the junction of the third side wall and the floor and an eighth source of infrared radiation mounted at or near to the junction of the fourth side wall and the floor.
A process for coating a substrate with a coating material comprising:

irradiating the substrate substantially exclusively with reflected infrared radiation in at least one step of the process.
A process as claimed in claim 16 wherein the coating material is a flowable powder, the substrate is a wood-based substrate and the process comprises:

irradiating the wood based substrate substantially exclusively with reflected infrared radiation in a preconditioning step.
A process as claimed in either of claims 16 or 17 wherein the coating material is a flowable powder, the substrate is a wood-based substrate and the process comprises:

irradiating the substrate substantially exclusively with reflected infrared radiation to a temperature at or above the minimum curing temperature of the flowable powder.
A process as claimed in claim 18 comprising:

(a) converting the flowable powder into a flowed powder at a first temperature; and

(b) stabilising the flowed powder at a second temperature below the first temperature and at or above the minimum curing temperature,

wherein either or both of steps (a) and (b) is carried out by irradiating the wood based substrate substantially exclusively with reflected infrared radiation.
A process as claimed in any of claims 16 to 19 wherein the coating material is a flowable powder, the substrate is a wood-based substrate and the process comprises:

irradiating the wood based substrate directly with infrared radiation to convert the flowable powder into a flowed powder at a first temperature; and

irradiating the wood based substrate substantially exclusively with reflected infrared radiation to stabilise the flowed powder at a second temperature below the first temperature and at or above the minimum curing temperature.
A coated substrate obtainable or obtained by a process as defined in any of claims 16 to 20.