Knock on Wood

Posted on Monday, June 1, 2015

Powder coating wood substrates is nothing new. Specifically, powder coatings have been applied to medium density fiberboard (MDF) since the late 1990s. A couple hurdles had to be overcome to make this a commercial reality. Engineers had to decipher a process to electrostatically apply powder to a not-so-conductive surface. And chemists needed to develop chemistries that melted and cured at temperatures that would not damage this heat sensitive substrate. Both challenges were met and a few pioneers built finishing lines using powder coatings on MDF.

Achieving conductivity on the board required preheating the board, which caused moisture to exude to the surface. The combination of water and other board components provided enough conductivity to successfully apply powder with relatively conventional application equipment.
Powder formulators established two schools of thought. One approach was to design lower melt point polymers and catalyze them for complete cure at 250 to 275°F. The careful utilization of infrared (IR) energy allowed the coating to reach surface temperatures high enough to elicit cure without soaking the board with excess heat.
Other formulators used a unique cross pollination of powder polymers and ultraviolet (UV) cure chemistry. Resin scientists took relatively normal looking solid polymers and fixed radiation curable chemical groups on them. Powder formulators found the right photoinitiators, pigments and additives to allow these polymers cure with light rather than heat energy. This process requires the powder layer to be melted and fused, and then uses high intensity UV light to cure the coating.
The first adopters of powder coated MDF were microwave cabinet makers and office furniture manufacturers. Since the turn of the century, additional MDF powder coaters have slowly emerged to support a broad array of end uses, including garage cabinets, wall partitions, doors, point of purchase displays, picture frames and medical carts. Manufacturers have realized the versatility of using powder to coat an irregular machined surface and the coating performance advantages that avoid the seams required with commonly used laminates. Furthermore, powder provides better heat and moisture resistance than PVC thermofoils.
So what does the future hold for this distinctive and high performance coating technology? Finishing experts are not standing still. Advancements and refinements in application equipment have already taken place at some of the major suppliers of spray and recovery equipment. Infrared technology has advanced and equipment specifically designed to melt and cure powder is now available including electric, gas and gas catalytic options. Chemists have pushed the chemistry envelope by creating faster curing and smoother powder formulas to provide even better process efficiency and film performance.
Not only is the industry expanding the reach of powder coated MDF into broader markets, but new wood composite substrates are being investigated for powder finishing. A new generation of composites based on wood fibers and plastic materials are emerging as components for fabricated goods such as outdoor furniture, decking and window and door frames. Powder coating materials are being developed that provide good adhesion and film performance for these end uses. Meeting the demands of these applications will be daunting, but, “knock on wood,” I think the powder coating technologists are up to the task.
Kevin Biller is technical editor of Powder Coated Tough and the president of The Powder Coating Research Group. He can be reached at kevinbiller@yahoo.com.