Citation
Bean, J. (2002), "Powder coating wood without pretreatment", Pigment & Resin Technology, Vol. 31 No. 3. https://doi.org/10.1108/prt.2002.12931caa.002
Publisher
:Emerald Group Publishing Limited
Copyright © 2002, MCB UP Limited
Powder coating wood without pretreatment
The UK's Furniture Industries Research Association (FIRA) has been leading a project to develop a new range of MDF panels that enable a powder finish to be applied without the need for expensive and time-consuming pretreatment. FIRA worked closely with powder coating materials manufacturers and application equipment manufacturers – Sonneborn & Rieck and Nordson, for example.
Entitled Fibrecharge: Development of wood composite fibreboard with improved electrical conductivity,the project was DTI-funded and included the board manufacturer Nexfor.
As it is an electrostatic process, wood is not an ideal substrate for powder coating because of its poor electrical conductivity. This problem is is partially overcome by expensive pretreatment involving the use of heating and coating with electrically conductive primers. The principal aim of the Fibrecharge project was to develop a wood based composite board with sufficient conductivity to allow the consistent electrostatic application of a powder coated finish, without the need for pretreatment.
Investigations were carried out using various additives within the board material to improve surface conductivity. It was essential to find an additive that not only provided the required conductivity but also did not affect the characteristics of the finished panel or raise the cost of manufacture to a prohibitive level. Full-scale production trials have been carried out with the selected formulation, using coloured, textured and clear coatings, and the board is about to be launched onto the general market. A major advantage of the newly developed product is that substantially less powder is required per unit area than with current methods.
FIRA has also been working on the development of special powder coatings for use on solid wood; both hard varieties such as oak, ash and sycamore, and soft types such as pine and larch. This project, called Envirocoat, also had DTI backing and was aimed to reduce the VOC emissions of UK furniture manufacturers, who in total emit around 16,000 tonnes of volatile compounds from solvent based coatings every year. The adoption of more powder coatings as a surface finish will, of course, help to minimize these emissions.
The Envirocoat project was designed to develop and optimise powder coating systems that facilitate the effective and consistent finishing of solid wood substrates for furniture, and also for the increasingly popular wooden laminate flooring. However, the aesthetic qualities of 'real' wood which are fundamental to the market value of finished products make it more difficult to produce a powder coated surface free from defects. The difference in colour and porosity between the growth rings and knots prevents finishes that currently perform to UK and other European standards. The Envirocoat project was aimed at overcoming the problem and FIRA says it has produced encouraging results for some hardwood applications but has also shown that the technique has a long way to go before being suitable for softwoods.