Powder Coating on Wood and Wood Composites

摘要

The research project intending to introduce powder coating even into the wood industry entered completey new territory. The findings presented here result from intensive cooperation between industry partners and research institutes. At the Wilhelm Klauditz Institute the focus was on the interaction between the type of wood or wood infiltrates, the surface properties and the structure of the wood composites on the one hand and the wetting behaviour and the spreading of the powder melt on the other. The type of wood plays a decisive role in powder coating. MDF made from beech fiber is more suitable for powder coating than MDF made from spruce fiber. But even the raw density profile of the MDF has an all-important influence on its coatability with powder. For optimum spreading of the coat on the MDF surface, a high density of the topcoat should be aimed at. The Institut fuer Lacke und Farben (Institute for Coatings and Paints) developed the first foundations for a general coating process. The focus was first on low-temperature powders. However, it became clear that a temperature level of about 130℃ for film formation was too high. The available epoxy systems did not have any topcoat qualities. These insights lead to a new approach which consisted in dividing film formation into a spreading phase through infrared energy and a curing phase through UV radiation. The Institut fur Holztechnologie (Institute for Wood Technology) in Dresden carried out comprehensive studies on the improvement of electrostatic application. They were able to show that suitable pretreatments and also field-influencing measures make powder application on wood substrates possible. The most promising measure consists in using counter electrodes to generate counter charges on the reverse side of the workpiece thus creating charge equalization. The different properties of the wood composites, the many different shapes of the parts to be coated and the demands in the future field of application require different powder coating systems and application technologies. Fig. 13 shows the 3 different layer systems which can be derived from the research results.