Exploitable results
The need to improve coating performance on wooden joinery to a level where it can compete adequately against windows fabricated from substrates such as aluminium or PVC-u in terms of maintenance frequency is today regarded as a fundamental objective, the "holy grail" of the exterior wood protection industry. The quest for improved performance has, until now, focussed mainly on the development of increasingly sophisticated coating formulations. More recently, this has been accompanied by a shift of emphasis from on-site coating application towards pre-finishing at the factory. The tight controls available at the fabrication stage and the improved quality of application achievable from it mean that factory pre-finishing is a trend that is likely to continue and develop within the wood joinery industry for the foreseeable future.
These developments have resulted in improved quality of application although improvements in coating performance have not been as great as had been anticipated. The need to continually improve coating performance for exterior wood windows will always exist and alternative means to achieve this are beginning to be explored.
Flame plasma treatment is currently being investigated in a programme of research part-funded by the EC under the FAIR programme of research. It is being used by a consortium of European research partners, co-ordinate by TRADA Technology LTD as a method of modifying the surface of wood as a preliminary to the application of surface coatings. The technique is more commonly used in the plastics and automotive industries to improve the bonding of adhesives and inks to car panels and plastic containers. It involves momentarily passing a substrate intended for coating under a flame whose physical parameters are strictly controlled. The process does not burn or alter the appearance of the wood in any way but induces changes to the surface chemistry of the wood to occur which can affect the manner in which fluids applied to it can behave. In theory, improvements in the wetting properties of the wood surface should lead to better adhesion and film-forming properties which, it is hoped, will lead to improved coating performance without need of reformulation.
The next phase of the work will correlate improvements in wettability of the surface of the wood with the adhesion properties of coatings applied to surfaces treated in this manner.
Culmination of the research programme will be in the establishment of an in-line flame treatment process for wooden joinery. This will serve as a test bed for the technique in an actual factory environment and will be backed up by logistic and cost-analysis studies which will evaluate the cost benefits of the process in the context of a commercial manufacturing operation.
More information on this EC - FAIR research project can be found on our project web site http://www.tradatechnology.co.uk/eec/flame
The technique is used with considerable success commercially, and some studies on the enhancing effects of the technology on the adhesive properties of wood glues have been carried out. Very little work on wood finishes has been done using this technique although the prospect of its use in the wood joinery industry in enhancing the performance of exterior surface coatings to timber as part of a factory application process is seen as a promising one. The process is simple and cost effective to use, making it suited to wood manufacturing processes and one which can be integrated easily into an existing in-line manufacturing system with minimum disruption.
Preliminary studies using contact angle measurements of water droplets on wood surfaces as a means of studying wettability have examined Teak, Iroko, Douglas fir, pine, oak, meranti, beech and Western hemlock. These timbers have shown different levels of responsiveness to treatment with flame plasma and can be grouped into those, which show good improvement in wettability (oak, beech, Western hemlock, Teak and Iroko), and those that show inconclusive results (e.g. meranti). a decline in wettability (pine and Douglas fir). Meranti has for the moment produced.
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 a research effort intended to optimize the flame set-up for specific wood species of commercial importance in order to achieve maximum improvement in wood wettability. This will enable the establishment of a process template or treatment schedule suited for use in a commercial context for the treatment of specific timber species.
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