Powder coatings on wood

Citation

Bean, J. (2000), "Powder coatings on wood", Pigment & Resin Technology, Vol. 29 No. 2. https://doi.org/10.1108/prt.2000.12929baa.001

Powder coatings on wood

Powder coatings on wood

Keywords: Powder coatings, Coatings, Wood

It is more than a year since we commented on the development of powder coatings which are suitable for application to wood. Pioneers of this development in the UK are Sonneborn & Rieck, long-time specialists in wood finishes.

At the close of the century the company installed a £275,000 plant at its Chesterfield factory, primarily for the development of powder coatings for wood. The plant is already producing results, says the company, and has recently produced a new powder coating for a specialist European plywood. The plant includes equipment for pre-mixing, extrusion, micronisation, spray application and curing, and will be used to examine every aspect of wood powder coatings, with the aim of extending the range and type of finishes available.

The new powder coatings are said to have already proved highly successful when used on MDF. They are being used commercially for office furniture and for prefinished MDF panels supplied to a number of customers in the furniture and shopfitting sectors. They are claimed to offer a number of advantages: only a single coat is required to provide a durable finish; they are VOC-free and create virtually no waste. Curing temperatures are lower than for conventional wet finishes and an extensive variety of colours is available. The new finishes are also said to provide an especially effective and cheaper alternative to the use of paper and foils.

Improving wood coating performance by flame plasma

Another development in improving coating performance on wood involves flame plasma treatment to modify the surface of wood before the application of a coating. The objective is to improve coating performance on wooden joinery to a level where it can compete against aluminium and PVC-u in maintenance frequency. The flame plasma system is the subject of an EC research project co-ordinated by TRADA Technology and including Oxford Brooks University (UK), Stichting Hout Research (The Netherlands), Centre Technique du Bois et de l'Ameublement (France), CATAS (Italy), Sherman Treaters Ltd (UK), manufacturers of flame and corona discharge equipment.

The flame plasma technique is used in the plastics and automotive industries to improve the bonding of adhesives and inks to plastic containers and car panels. The substrate for coating is passed under a strictly controlled flame. The process does not burn or alter the appearance of the wood in any way but induces changes to the surface chemistry which can affect how fluids subsequently applied to the surface behave. In theory, improvements in the wetting properties of the wood surface should lead to better adhesion and film-forming.

Some studies have been carried out on how the technology enhances the adhesive properties of wood glues, but very little work has been done on wood finishes, despite the fact that there is the prospect of a considerable benefit as part of a factory application process. Simple and cost-effective, the process is well suited to wood manufacturing and can be easily integrated into existing in-line manufacturing systems.

Preliminary studies, using contact angle measurements of water droplets on wood surfaces to assess wettability, have examined teak, iroko, Douglas fir, pine, oak, meranti, beech and western hemlock. These timbers have shown different levels of responsiveness to flame plasma treatment and can be grouped into those with good improvement in wettability (oak, beech, western hemlock, teak and iroko), inconclusive results (meranti) and negative (pine and Douglas fir). The programme has also examined the effects of a number of timber variables such as density, heartwood, sapwood and moisture content on the effectiveness of the plasma treatment. This has been followed by research to ascertain the optimum flame set-up for specific commercially important species which will enable a process template or treatment schedule to be drawn up.

The next phase is to correlate improvements in the wettability of the treated wood surfaces with the adhesion properties of coatings applied to them. The culmination will be to establish an in-line flame treatment process for timber joinery as a test bed in an actual factory environment. This will be backed by logistic and cost-analysis studies to evaluate the benefits in a commercial manufacturing operation.

Growth predicted for global coating market

A report from Market Tracking International Ltd says that further consolidation and specialisation of the global paint industry was expected to occur by the end of 1999, while markets in Eastern Europe and China are anticipated to emerge as the world's fastest growing. These are the key findings of their report on the global coatings industry, entitled World Paint Companies 1999.

In terms of market growth the emerging regions of Eastern Europe and the vast Chinese region are forecast to experience the strongest paint demand rates over the next five years, followed by the former high growth markets of Asia-Pacific.

The Chinese paint market is forecast to emerge as the world's fastest growing over the next five years, with paint production volumes forecast to increase by an average rate of some 12 per cent per annum.

Although many Asian markets have been witnessing declining paint demand, growth was predicted to return by the end of 1999. Moreover, with the potential for further economic expansion still in place and with underlying population growth, longer-term prospects beyond the year 2000 are still promising in most Asian markets.

The same is also true for Eastern Europe where recovery in paint demand has been marked in recent years. Whereas paint production levels decreased by an average of 3 per cent per annum between 1993-97, they are forecast to increase by an average rate of 3 per cent over the next five years. Growth is expected to be particularly strong in Poland, with paint production levels forecast to grow by an average rate of 9 per cent per annum in the coming five years.

Market Tracking International Ltd, 7 Archway Business Centre, Wedmore Street, London N19 4RU. Tel: +44 (0)171 263 1365; Fax: +44 (0)171 272 8525.

John Bean