The benefits of powder coating wood and medium density fiber board (MDF)
The powder coating of wood and medium density fiber board (MDF) is a disruptive technology that is set to open new markets. Specifically, the many benefits of powder coatings, normally thought as applicable only to metals can now be conferred to wood and other temperature sensitive substrates. Examples of these benefits are improved adhesion, chemical resistance, scratch resistance, improved durability and a significant lowering of volatile organic content (VOC). In addition, irregular shaped objects, edges and borders can be painted at a significantly reduced production cost. Instead of multiple layers, sanding and mechanical preparation, a lot less effort is required.
While there are many benefits to powder coating including greater chemical- and humidity resistance, scratch resistance, durability and longevity, cost efficiency, high end look, environmentally friendly (low VOC) and easy maintenance (STP Performance Coatings, n.d.). These advantages are realized by investing in the necessary equipment such as ovens and electrically charged spray guns and fluidized bed feeding systems to feed the powders to the applicator guns. Normally this would put off potential smaller investors but if the number of SMME’s in Asia and Africa are anything to go by, this is not a significant hurdle. Still, there are some risks involved in the actual coating process that has to be carefully considered such as touch-up, the speed of application and the correct amount of powder to apply. In addition, the baking process has to be carefully controlled to minimize under- or over baking.
In order to develop powder coatings for wood and MDF, a number of additional challenges are faced. Chief amongst these is the fact, that unlike metal, wood, MDF and plastic are not conductive. Powder coating of these objects require enhancing the conductivity such as exposing wood to an initial source of heat to drive moisture (at least 8%) to the surface or by spraying a conductive primer onto the object that has to be powder coated (Lin, n.d.), (ONOYAMA et al., 2005). This primer can be applied in various ways including as a water-based primer or as an epoxy- or polyurethane coating. In addition, the chemistry associated with each conductive primer may differ considerably from highly filled conductive metal coatings, quaternary ammonium compounds to inorganic compounds that facilitate charge transport. Non-conductive parts can sometimes be preheated and sprayed hot with conventional powder, or an in-mold process can be applied in which a mold is electrically charged and heated, powder is applied and melted and then exposed to the part to be coated. Successive layers of resin can be applied and later mechanically smoothed.
While facilitating conductivity in non-conductive substrates can be achieved by highly sophisticated chemistries, the next significant hurdle remains the heat sensitivity of the object that requires coating. Wood, MDF and plastics cannot endure exposure to high temperatures or excessive exposure times to high temperatures. A major chemical process that affects all of these non-metallic surfaces remains oxidative degradation. Therefore, ways to address low curing powder coatings is of great importance. An additional point to remember is that low temperature curing, according to owners of smaller companies, requires additional controls that are not necessarily universally available or accessible. Hence, powder coating companies in Europe, the USA and some Asian countries may have access to this technology in response to drivers such as the requirement for lower energy and more environmentally friendly alternatives, requirements that are sometimes at odds with each other. In other places in the world such as South Africa, the technology may contribute to the survival of the powder coating business in general.
