AU2004203662B2 - Powder Coating Procedures - Google Patents

Description

I -Z Regulation 3.2

AUSTRALIA

PATENTS ACT, 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventors: Address for service in Australia: Invention Title: CLIMATE COATING LIMITED JEFFREY WILLIAM STEWART A J PARK, Level 11, 60 Marcus Clarke Street, Canberra ACT 2601, Australia Powder Coating Procedures The following statement is a full description of this invention, including the best method of performing it known to us.

2 The present invention relates to methods of powder coating heat sensitive substrates, products that result from such methods, heat sensitive substrates powder coated in two layers and related methods, products, sub-assemblies and assemblies.

A range of heat sensitive substrates are encountered which require an effective surface coating.

Existing surface coating regimes that rely upon powder coating are those hereinafter shown in Figures 1 and 2. Each involves either preheating (either with radiant infrared or with convection heat or combination of both) or the application of a liquid primer coating prior to the presentation of the powder coating thereto.

PCT/EP96/03264 of MIDASLR (published as WO97/05965) discloses a method for coating surfaces in general, and decorating them with powders of various colours characterised by: applying to the surface to be decorated, previously treated for this application, a layer of powdered coating material of colour corresponding to the desired background for the decoration to be obtained, heating the surface treated in this manner to a temperature lower than the backing temperature of the powdered coating material, but sufficient to fix it to the surface to be decorated, applying to the surface prepared in this manner at least one powder of colour corresponding to the coloured motif to be reproduced, distributing it in accordance with the desired pattern of this motif, subjecting the surface treated in this manner to final baking for a time and at a temperature sufficient to securely fix said powder to said surface.

WO97/05965 whilst speaking in respect of a heating temperature for at least the preliminary powder coating of from 75 to 90 0 C is silent as to how this can be achieved other than to refer to a traditional powder coating line having pairs of catalytic heating panels, heating lamps, ultraviolet lamps, etc between which the two surfaces to be decorated is passed.

The present invention recognises an advantage for heat sensitive substrates where a conveyor advance of a product can be passed plural infrared sources thereby, in each passage passed the plural sources, to elicit a desirable effect but with the temperatures being controllable by the relativity of the conveyor speed to the intensity and output of each infrared source and the spacing of them mutually apart. In addition, there is also seen an advantage, for the purpose of temperature control, of having one or more of the infrared sources controlled as to output by, for example, its own pulsing of its maximum output.

3 Thereafter one prior art regime cures the thus applied powder coating with infrared radiation and/or with convention heat thereby to provide the coated component.

Another procedure relies upon thermal melting and flowing of the powder coat reliant on infrared radiation and/or convection heat and thereafter a UV curing step thereby to provide the coating component.

Such prior art procedures provide adequate coatings for many substrates but not for heat sensitive substrates which present gassing difficulties and/or are liable to damage owing to the heats that may be required by such processes. Difficulties can compound at edges and profiled regions.

As used herein "heat sensitive substrates" include any substrate of a kind where such conventional processes tend to be less than optimal. One such substrate is that frequently referred to as "engineered wood substrates" typified plywood by many resin bound lignocellulosic fibrous composites MDF, particle board, OSB, LBL, etc.) or even some such compositions not requiring an added resin system hardboard). Other heat sensitive fibres include carbon fibres. Such carbon fibre/resin systems can be degraded as far as strength is concerned is subjected to excessive heats. Other heat sensitive substrates include any less tolerant to temperature than, say, EWS or as intolerant to temperature as EWS.

As used herein "powder coating" includes or refers to any procedure where electrostatic attachment of a coating material ("powder") is involved irrespective of whether or not the coating material is in a solids and/or liquid form (a true powder) prior to any cure or drying thereof.

As used herein the term "and/or" means "and" or "or" or, where permitted by the context, both.

As used herein the term following a noun means either or both the singular and plural forms of that noun.

Reference herein to a "powder" (subject to the foregoing comment in respect of powder coating) preferably includes any powder of a kind capable of at least a partial cure under the action of heat such as that derived from an IR (infrared) source and in the case of the second powder coating a powder both or either capable of being cured by a IR heating source and/or melted and/or melded with an IR heating source and being cured in that molten and/or the post molten state under the action of a UV source.

15-NOU-006 12:10 fA J PRRK 64 9 3566990 P.05/22 4

INO

0 O Reference herein to "preheating" is preferably (but not necessarily) to ensure sufficient conductivity for subsequent powder deposition reliant on electrostatic attachment.

z Likewise partial cure heating, etc.

tt As used herein "cure" (and related words such as "curing") includes polymerisation, etc. or other chemical reformation, irrespective of whether or not to completion.

As used herein the terms "pulse" or "pulsed" mean, in respect of exposure to infrared \O radiation, subjection to oscillating heat and relaxation periods ("Oscillating Relaxation

\O

en Periods" or During the relaxation period or periods (arising from movement relative 0 to plaques, or vice versa, rather than heating control of the plaques) the energy absorbed by 10 the coating (immediate surface of the product exposed) is allowed to uniformly disperse 0 across the previously irradiated surface e.g as shown in Figure 5 as opposed to Figure 4 hereof. Nonetheless, prior art type pulsing plaques can be used (and preferably are used), in addition, to provide some semblance of heating control for the non relaxation periods (e.g as in Figure 6).

"ORP" includes both the singular or plural.

The present invention recognises an advantage to be derived from a sequential coating procedure.

In one aspect the invention is a method of coating a substrate to provide a product which comprises or includes the steps of heating the substrate sufficiently to enable its powder coating, applying a coating of a powder ("the first powder coating") at least to an entire surface of the sufficiently heated substrate, partially heat curing the first powder coating on said entire surface, applying a subsequent powder coating (whether the same type of powder or different) ("the second powder coating") to the entire surface of the partially cured and still sufficiently heated first powder coating on said entire surface of the substrate, and either heat curing or (ii) heating and UV curing the second powder coating, wherein at least steps to occur sequentially whilst the substrate or coated substrate is on a conveyor, and wherein at least one of the step partial heat curing of first powder coating, and COMS ID No: SBMI-05356561 Received by IP Australia: Time 10:17 Date 2006-11-15 15-NOU-2006 12:10 A J PARK 15-NIJ-200 1210 3 PRK64 9 3566990 P.06/22 O(1I) the step heat curing or step (ii) heating of at least the second powder coating z involves movement of the coated substrate relative to plural infrared radiant heat sources spaced to provide a movement caused pulsing of exposure to the heating effect of such heat sources of the coated surface involved.

Preferably the curing of the second powder coating involves movement relative to plural infrared radiant heat sources.

INO Preferably the curing of the second powder coating completes the curing of the first 0 powder coating.

Preferably at least one of the heat sources itself is a pulsing infrared radiant heat O source.

Preferably said movement is continuous.

Alternatively, but less preferred, said movement is intermittent.

Preferably step is a heat curing step.

In another aspect the invention is any product being a substrate coated by a method as hereinbefore described.

A preferred form of the present invention will now be described with reference to the accompanying drawings in which, Figure 1 shows a prior art powder coating procedure when being used less than optimally with a heat sensitive substrate, Figure 2 like Figure I shows a conventional powder coating procedure being used less than optimally with a heat sensitive substrate, Figure 3 shows processes of the present invention, Figure 4 shows Temperature build up in a conventional IR pulse plaque oven, Figure 5 shows (e.g with two relaxation periods by way of example) the lesser T build up using (preferably pulsed IR plaques) serially separated so as to provide relaxation periods, and Figure 6 is a flow diagram showing as the powder coated product passes through the IR the product is subjected to oscillating heat and relaxation periods. During the relaxation COMS ID No: SBMI-05356561 Received by IP Australia: Time 10:17 Date 2006-11-15 EDITORIAL NOTE There are no pages 6 to 14.

I period the energy absorbed by the coating (immediate surface of the product) is allowed to uniformly disperse across the previously irradiated surface.

The following for the type of powder coatings can be used for either or both coatings and are preferably of the resin/binder type. These include powder coatings based on the following resin chemistries (including variations thereof, and not limited to): Polyester Epoxy Epoxy Polyester Polyester hydroxyalkylamide Polyurethane Acrylic Epoxy-Acrylate Acrylo-Polyurethane Acrylo-Polyester.

Additionally they can include powder coatings that may contain flexibility modifying additives for example those based on core/shell acrylic rubber.

When processing HSS we have found it preferably to use a heating source that is controllable and directly able in which to localise and thus minimise heat transfer into the substrate but make it conductive enough to powder coat evenly.

To solve this problem we have evolved two techniques of advantage in the procedures of the present invention.

1. Dual Coating (2 stage application optionally single or double pass) 2. Electromagnetic Radiation Pulsing (ERP), preferably IR with ORP or ORPs.

PROCESS OVERVIEW: The process involves the pre-conditioning of the substrate which in one embodiment is an engineered wood substrate (EWS). This is achieved by way of applying a minimum level of heat to increase conductivity of the EWS, whilst not unduly diminishing its physical integrity.

A first "dusting" layer of powder of a powder coating system is applied to the EWS (approximately 30-40 microns), this is then followed by a "green cure" melt, flow partial curing) of the dusting layer by way of an IR heating, which blocks off and seals the

EWS.

"I

16 A secondary coat of powder coating is then applied (approximately 50-60 microns) over the dusting coat.

The final thickness of the powder coating, then being approximately 80-100 microns, which is then cured to the specification required.

The final curing preferably ensures (e.g with ORP) that the EWS does not receive too high a level of IR heat input. This involves only allowing just enough heat be absorbed by the powder coating so as to polymerise it to the level specified. Too much heat will result in offgassing, cracking and degradation of the EWS, which will lead to post cure cracking (PCC) and loss of the EWS mechanical properties such as "screw-ability".

A PREFERRED PROCEDURE: The EWS is preferably loaded on to the coating conveyor's line at the loading zone.

The EWS is prepared by removing any loose particles from its surface by way of air jets, denibbler, brush or the like. This process provides a smooth surface, free from objects that would disrupt the final coated film.

The EWS undergoes pre-treatment by passing it thru a booster oven. This booster oven is preferably IR heating (with or without ORP) but could also be convection heating or a combination IR/Convection. The booster oven raises the EWS temperature to a predetermined level prior to powder coating.

The EWS enters the "dusting" booth where a layer of powder is deposited on one or more of its surfaces. The dusting layer is ideally between 30 and 40 microns, but could be anywhere between 20 and 60 microns. The powder particles adhere to the grounded and warm EWS.

The dust coated EWS passes next through the "green cure" oven where the powder is heated to bring about melting, flow-out and allow partial polymerisation of the powder. This is preferably with IR radiation using ORP.

Following the green cure oven the EWS enters a second powder coating booth where a new layer of powder is deposited on the previously coated surfaces. The new layer is ideally between 50 and 60 microns but could be anywhere between 40 and 80 microns. The powder particles adhere to the grounded and still warm EWS.

The fully coated EWS enters the IR Pulse Plaque Oven configured to provide ORP where the heat is directed to the surface in such a way so as to largely only heat the combined powder layer.

By employing a "Dual Coating" technique (whether within a single or double pass operation), a significant reduction in coating defects is achieved. This reduction in the number of defects ultimately addresses appearance and performance needs. This lowers the overall reject rate of powder coated EWS. By dust coating the EWS first we are sealing the substrate and reducing dehydration of the EWS in order to provide us with an evenly conductive surface for the final coat.

By using this method we are able to achieve repeatedly, uniform and consistent film builds.

The ORP technique was developed to limit heat transfer into the substrate whilst allowing the powder increased dwell time in which to cure. By way of this process the two main issues of supplying a pre-finished totally cured HSS are addressed, 1. Limiting heat build-up in the HSS 2. Provide an environment in which the powder can go through its three states of Melt, Flow and Cure.

Use of the ORP technique coupled with the particular pulsing plaque layout (Fig 1) for the IR pulse oven, we lower the heat intensity on the substrate, leaving the integrity of the substrate intact as well as evening the energy out across all six edges of a usual panel type product, which allows us to achieve a uniform cure of the powder.

A process layout, which enables us to apply powder to a wide range of HSS including but not limited to plywood and MDF, is used which will not jeopardise the integrity of the products being processed.

Suitable powders for powder coatings include those available from each of: Orica Powder Coating Limited 31 B Hillside Road Wairau Valley Auckland 1310 Ameron (New Zealand) Limited Monahan Road Mt Wellington Auckland 1006 18 Dulux Powder Coatings 51 Winterton Road Clayton VIC 3168 Australia Akzo Nobel Powder Coatings Akzo Nobel Pty Limited 51 McIntyre Road Sunshine, Melbourne Victoria 3020 Australia DuPont Powder Coatings USA, Inc 9800 Genard Rd.

Houston, TX 77041

USA

Tigerwerk Lack u.Farbenfabrick Gmbh Co. KG Negrellistr. 36 4600 Wels Austria Suitable platens include those available from each of platen manufacturers: Catalytic Industrial Systems 2 0 th and Sycamore Independence, KS 67301, USA Vulcan Catalytic Systems Portsmouth Business Park 207 High Point Road, PO Box 555 Portsmouth, RI 02071-0855

USA

1 'I 19 Heraeus Noblelight GmbH HeraeusstraBe 12-14 63450 Hanau Germany Infratech-USA 939 North Vernon Avenue, Azusa CA 91702

USA

Suitable UV sources include those sources available from any of: Fusion UV Systems, Inc 910 Clopper Road Gaithersburg, MD 20878-1357

USA

Nordson Corp., UV Curing Systems 555 Jackson St.

Amherst OH 44001-2496

USA

Heraeus Noblelight GmbH HeraeusstraBe 12-14 63450 Hanau Germany

Claims (1)

15-NDV-2006 12:15 A J PARK 15-NIJ-006 12:1 P 1 PRK4 9 3566990 P.18/22 o THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A method of coating a substrate to provide a product which comprises or includes o the steps of Z heating the substrate sufficiently to enable its powder coating, applying a coaling of a powder ("the first powder coating") at least to an entire surfiace of the sufficiently heated substrate, partially heat curing the first powder coating on said entire surface, IND(d) applying a subsequent powder coating (whether the same type of powder or o different) ("the second powder coating") to the entire surface of the partially cured and still sufficiently heated first powder coating on said entire surf-ace of the o substrate, and either heat curing or (ii) heating and UV curing the second powder coating, wherein at least steps to occur sequentially whilst the substrate or coated substrate is on a conveyor, and wherein at least one of the step partial heat curing of first powder coating, and (1I) the step heat curing or step (ii) heating of at least the second powder coating involves movement of the coated substrate relative to plural infrared radiant heat sources spaced to provide a movement caused pulsing of exposure to the heating effect of such heat sources of the coated surface involved. 2. A method of claim 1 wherein the curing of the second powder coating involves movement relative to plural infrared radiant heat sources. 3. A method of claim 1 or 2 wherein the curing of the second powder coaling completes the curing of the first powder coating. 4. A method of any one of the preceding claims wherein at least one of the heat sources itself is a pulsing infrared radiant heat source. A method of any one of the preceding claims wherein said movement is continuous. 6. A method of any one of claims I to 4 wherein said movement is intermittent. 7. A method of any one of the preceding claims wherein step is a heat curing step. 8. Any product being a substrate coated by a method of any one of claims I to 7. COMB ID No: SBMI-05356561 Received by IP Australia: Time 10:17 Date 2006-11-15