Cutting-Edge Approaches to Coating Wood
The development of powder coating on natural wood and heat-resistant coatings has taken several big steps forward.
By Greg Bocchi
Powder coating has been used with great success in the metal finishing industry for decades. But when manufacturers first began to powder coat wood, they ran into challenges. The heat required for the powder coating process sometimes damaged the wood, and the non-uniform density of the wood products resulted in finishes that were uneven and unacceptable.
By reducing the heat requirements, developing a uniform-density wood product and experimenting with different powder formulations, manufacturers and their suppliers are now able to powder coat a wide range of wood products including office furniture, kitchen and bathroom cabinets, entertainment centers and ready-to-assemble furniture.
Taming the Heat
Thermal curing relies on infrared ovens, convection ovens or hybrid ovens that combine infrared and convection heating. The thermal energy melts the powder, allowing it to flow out evenly and eventually cure, or crosslink, into a finished film.
“We are taking powder coating, applying it to MDF and curing it with thermal energy,” says Rich Saddler, engineering manager for Herman Miller Inc. of Zeeland, MI. “The powder coating we are using produces the smoothness and gloss range our products require, and it works well with our current thermal system.”
With the UV method, the melt and flow can be separated from the curing process and minimal heat is required to cure the powder. The surface must be in direct line of sight, however, and the production line must be set up so the UV rays hit all the surfaces. Every UV powder operation needs thermal heat to melt the powder so the UV can cure it. The heat source is typically infrared, but convection heating can also be used.
In a typical UV operation, the product is first preheated to make it electrostatically grounded by drawing the moisture to the surface. Then the powder is applied to the product part with the highest temperature reaching 120F. After the powder is applied, it goes through a melt-and-flow oven with infrared and convection heat and then into a UV-light chamber where it is cured. The UV-light cure induces a chemical reaction in the powder, which is like exposing a roll of film to light, and the powder is cured.
The whole process keeps heat at the lowest possible levels. Using UV in powder coating provides more design flexibility for such products as office furniture and cabinets, which in turn, allows designers to use curved, linear shapes and a whole host of colors, textures and glosses. At this time, industry sources say, there are several production lines using UV curing, and the process is expected to expand over the next few years as more companies realize the benefits of the technology.
Reformulating the Powders
As powder manufacturers continue to juggle their formulas to require less heat, the resulting product coatings can stand up to heat better than previous applications.
“This is especially good for kitchen cabinets because the new powder-coated surfaces withstand much more heat from a kitchen oven or range,” Pelc says. “Previously, if you were using rigid thermofoil, you had to leave a six-inch space on each side of the oven. Now you can put your cabinets right up against the oven and save a lot of space.”
Other products that benefit from new powder formulations include children’s furniture, healthcare tables and counters that have powder-coated surfaces without seams or hard edges, making them easier keep clean.
Natural Wood Next?
While no one has come up with an economical process to powder coat natural wood, that does not mean powder manufacturers and heating-element suppliers are not busy experimenting with the possibilities. The natural wood market is enticing because it could open up marketing avenues into home furniture, flooring, high-end office furniture and decorative wood-grain cabinets.
Working with natural wood requires lower powder-melting temperatures. Powder manufacturers are working to find ways that will get the temperature down using convection and infrared ovens. Thus far, powder manufacturers and raw material suppliers have been successful in a laboratory setting. When the technology is refined, it could open up the market for clear powder coating over natural wood for the higher-end furniture and cabinet markets.
The powder manufacturers are eager to get the kinks out of clear coating natural wood surfaces because it will provide another tool for wood-product designers to work with. They will be able to show beautiful natural oak, maple and beach grains for kitchen and bathroom cabinet surfaces. Some industry sources believe the market for solid, natural wood could be huge and just around the corner.
Natural, hardwood may have a bright, new, powder coating future, industry marketing managers say, but MDF is here to stay and will continue to expand into new markets.
There is a rising level of excitement in the powder coating industry as suppliers and fabricators keep coming up with new ways to reduce production heat levels, develop new powder mixtures and create better quality, engineered wood products. It is reaching the point where designers of furniture, cabinets and work surfaces are asking for new surfaces, new colors and new glosses to develop products for their constantly changing markets. The powder coating industry is working overtime to keep them happy.
Greg Bocchi is the executive director of The Powder Coating Institute of Alexandria, VA. He can be reached at (703) 684-1770 or visit www.powdercoating.org.
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