Over the last 30+ years, powder coating has revolutionized the finishing industry by providing a superior, durable, environmentally friendly finish, particularly for metal products such as appliances, automotive parts, sporting goods andcountless other products.
Technological advancements in powder coating materials and application and curing methods have also brought the advantages of powder coating to heat sensitive substrates. Powder coating is now used on a variety of products that were impossible a few years ago.
One of the biggest breakthroughs for powder in the heat sensitive substrate market is on medium density fiberboard, or MDF, a combination panel bonding particles of wood with a synthetic resin. MDF is very suitable for powder coating application because of its low porosity and homogeneous surface. MDF products include office furniture, kitchen and bath cabinets, doors, store fixtures and displays, barbecue trans and ready-to-assemble furniture for the office and home.
Powder coating is revolutionizing the MDF market because it offers design freedoms other finishing methods and laminating processes just can't provide. Powder coating provides a beautiful, durable, seamless finish in every color of the rainbow. And, powder coating protects MDF products from chips, stains, spills, and scratches.
Meeting the Challenges of Heat Sensitive Substrates
Some woods and wood products such as MDF have sufficient and consistent moisture content to provide conductivity and can be coated directly. Wood parts that require sanding can be cleaned with compressed air to remove any surface contaminants. To enhance electrostatic attraction, wood can be pretreated with a spray solution that provides a conductive surface. The part is then preheated to a desired coating temperature, which solvents or partially melts the powder when it is applied and helps the powder adhere to the part where it melts a little on impact. A uniform board surface temperature allows for high transfer efficiency and a consistent appearance.
For powder application, an electrostatic charge is applied from the spray gun to deposit powder on the MDF surface. Powder materials for MDF can be either thermal cure products of UV-cured powders. Thermal cure powders rely on infrared ovens, convection ovens or hybrid ovens that combine infrared and convection heating. The thermal energy melts the powder so it will flow into a level film and eventually cure, or crosslink, into a finished film.
With specially formulated UV-curable powders the melt and flow can be separated from the curing process and requires minimal heat to cure the powder. After the parts enter an infrared or convection oven where the coating melts and flows for two to ten minutes, the board is exposed to ultraviolet light for just a few seconds for final curing and hardening of the finish. Then the parts cool naturally or in a cooling tunnel before they are unloaded from the coating line.
Powder Coating Fills a Need for MDF Products
Many office furniture makers are moving away from standard shapes such as squares and rectangles to more rounded corners and contoured edges, with interior circles and ellipses to allow for computer cords to drop through. They are also offering seamless desktop coatings and a variety of colors and effects. Powder coating can accommodate these shapes, while other lamination techniques that rely on edge-banding methods cannot. And, powder application is a one-step finishing process, not requiring successive coats or a long time to dry.