Cutting-Edge Approaches to Coating Wood

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
One of the biggest breakthroughs for powder in the wood market is the use of engineered wood materials such as MDF, medium density fiberboard. MDF is very suitable for powder coating because of its low porosity and homogeneous surface. It lends itself easily to both thermal and UV methods of curing powder coating.

Thermal curing relies on infrared ovens, convection ovens or hybrid ovens that combine infrared and convection heating. The MDF board is heated to bring moisture to the surface. Specially formulated low-temperature-curing thermoset powder is sprayed onto the part. 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,” said Rich Saddler, engineering manager for office furniture manufacturer Herman Miller Inc., based in Zeeland, Michigan. “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, and the production line must be set up so the UV rays hit all the surfaces. After the parts enter an infrared or convection oven where the coating melts and flows (for 2-10 minutes) the board is exposed to ultraviolet light for just a few seconds for final curing and hardening of the finish. The UV light cure induces a chemical reaction in the powder, like exposing a roll of film to light. Then the parts cool naturally or in a cooling tunnel before they are unloaded from the coating line.

Powder Coating Fills a Need
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. Office furniture makers have moved away from standard shapes such as squares and rectangles to more rounded corners and contoured edges with interior circular or elliptical holes to allow for computer cords to drop through. Powder coating can accommodate these shapes, while current lamination techniques–which rely on edge-banding methods–cannot. And powder coating is a one-step finishing process, not requiring successive coats or long drying times.

Reformulating the Powders
“The real advances are in new powder coating formulations,” said Jim Pelc, president of Capital Components, a Sacramento, California-based company that powder coats wood and works with its powder supplier to develop powders for a variety of heat treatment lines.

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,” said Mr. Pelc, “because the new powder coated surfaces withstand much more heat from a kitchen oven or range.” 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 to benefit from new powder formulations include children’s furniture and healthcare tables and counters that have powder coated surfaces without seams or hard edges, which can be difficult to keep clean.

Natural Wood Next?
Along with special powder formulations and advanced heat-treatment methods, a critical element in the success of the powder coating process is the specially engineered, medium density fiberboard (MDF) wood product that is being coated. Natural wood doesn’t work as well as MDF, because each supply of raw-wood planks or sheets has a different fiber density and moisture content. Powder coating requires a uniform density.

While no one has yet come up with an economical process to powder coat natural wood, that doesn’t mean powder manufacturers and heating-element suppliers aren’t busy experimenting with the possibilities. The natural wood market is enticing because it could open up new marketing avenues into home furniture, flooring, high-end office furniture and decorative wood-grain cabinets.

According to Greg Bocchi, Executive Director of The Powder Coating Institute, “Working with natural wood requires lower powder melting temperatures. Powder manufacturers are finding ways to get the temperature down using convection and infrared. Up to now, powder manufacturers and raw material suppliers have been successful in the laboratory.” When the technology is refined, Mr. Bocchi said, it could open up the market for clear (powder) coating over natural wood for the higher-end furniture and cabinet market.

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, ash and beech 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. Research engineers are also studying the use of powder on paper-laminated MDF, laminated flooring and particleboard.

Natural, hard wood may have a bright, new powder coating future, industry marketing managers say, but engineered wood (MDF) is here to stay and will continue to expand into new markets.

Designers Delighted
“The biggest thing coming through now,” said Herman Miller’s Rich Saddler, “is the flexibility the powder coating techniques give designers to open up ways to create new products for such things as work surfaces, cabinet doors and drawer fronts, file cabinet fronts, shelves and bookcases. All told, it will help keep the costs down and give us nice looking, more durable surfaces.”

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’s 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.