Color ChangesRecent and ongoing developments in the equipment used for powder application have significantly reduced the time, effort and capital cost required for color changes. Efforts to increase application efficiency, streamline the powder delivery system and redesign the booth have all contributed to speeding up the color change process. Powder booths with plastic walls that repel rather than attract the powder, automated belts and sweepers that brush powder particles on the floor to recovery systems, and powerful bursts of air through the pumps and guns to clean the system have all helped to reduce color change operations, sometimes to 15 minutes or fewer. High-production powder systems apply over 20 different colors, with several color changes per day.
Coil CoatingCoil coating technology for powder continues to be developed. Coil coating is the process of coating one or both sides of flat metal sheets or strips on a continuous production line basis. The metal is then cut and post formed. Coil coating with powder can produce deep textures in a single pass, and visual effects not possible with liquid coil coating. It is used for a variety of products, such as appliances, light fixtures, window and door frames, solar sun screens, and other building components.
Blank CoatingPowder coating of pre-cut metal blanks that are post formed prior to final assembly remains a strong growth area, particularly in the appliance market. The process allows for complete edge wrap, uniform film thickness and high transfer efficiency, as blanks can be spaced only inches apart on the coating line.
Radiation CuringRadiation curing is the curing of a coating by means of exposure to electromagnetic waves or particles such as infrared (IR), ultraviolet (UV) or electron beam (EB). Radiation curing opens up new applications for powder coating of heat-sensitive substrates such as wood, wood-based materials, plastic parts and assembled components with heat-sensitive details by reducing the curing temperature to below 250ºF. The coating of metal substrates can also benefit from this technology, with lower energy and investment costs, shorter curing times, and higher line speeds in powder coil coating plants.
IR CuringInfrared ovens use radiant energy to cure the powder over the part, sometimes in as little as 30 seconds. The high heating rates possible in an infrared oven allow the surface to be heated without heating the entire substrate, providing a rapid heat up and quick cool down.
UV CuringUsing specially formulated powders, curing by ultraviolet light is achievable. The powder needs to be exposed to enough heat so it is molten when exposed to UV energy. The heat source is typically infrared, but convection heating can also be used. The coating is then exposed to a lamp that directs UV light onto the product. The photoinitiators in the coating absorb the UV energy from the ultraviolet light source and initiate a series of chemical reactions that rapidly convert the molten film to a solid cured finish in seconds.
Near Infrared CuringNewly developed near-infrared curing technology uses specially formulated powders, high-energy light sources and high focusing reflector systems, completing the powder coating and curing process within several seconds. Heat-sensitive assembled parts can benefit from near-infrared curing. This process also allows swift curing times on metal substrates with no film thickness limitations, especially with colors like yellow or red, which are difficult to cure in higher film thicknesses without current UV powder coatings.
Powder Coating of Wood ProductsWood products offering the greatest potential for powder coating are engineered wood materials like medium-density fiberboard (MDF) made of wood particles bonded with a synthetic resin. MDF is used to manufacture office furniture, ready-to-assemble furniture for the home and office, cabinets for kitchens and bathrooms, and store fixtures and displays. Barbecue trays made of MDF are also currently powder coated.
Some woods and wood products have enough moisture content to provide sufficient conductivity and can be coated directly. Wood parts can be blown off with compressed air to eliminate any surface contaminants. To enhance electrostatic attraction, wood can be pretreated with a liquid coat to improve adhesion, and the part can be preheated.
Curing of powder on MDF can be accomplished by infrared, a hybrid of infrared and convection ovens, or ultraviolet light in conjunction with infrared or convection ovens using specially formulated UV-curable powders.
Powder coating is more environmentally friendly than other traditional MDF coating practices such as vinyl films, multiple coats of liquid paint and laminates. Current lamination techniques also rely on edge-banding methods, difficult to do with odd shapes and angles. As office furniture manufacturers are moving away from simpler shapes such as squares and rectangles to more curved edges and interior “holes” to allow for drop-through of computer cords, powder coating will become an even more desirable coating option. Powder coating also offers a wider array of colors than laminates.
Electromagnetic Brush TechnologyA new application process called electromagnetic brush technology makes it possible to apply powder coatings at differential speeds and layer thicknesses on flat substrates. This process is similar to that used in copy machines and laser printers, with “toner” particles triboelectrically charged against the ferromagnetic “carrier” particles, and transported with mixing rollers to a rotating shell or drum, which has stationary magnets within it. The ferromagnetic particles form a chain as directed by the magnetic field lines, also called a magnetic brush. The substrate becomes powder coated as it passes by the magnetic brush and the electrostatic field is turned on. Thicker layers can be achieved by passing the substrate by the magnetic brush more than once. Potential application areas include the coating of coil, blanks and wood.
In-Mold CoatingAn in-mold powder coating process has been developed in which powder coating material is sprayed onto a heated mold cavity before the molding cycle begins. During the molding operation, the powder coating chemically bonds to the molding compound and produces a product with a coating that is chip and impact resistant.
In-the-Field Powder CoatingThermoplastic powders can be applied in the field, provided the substrate is clean and preheated properly. Bridge support columns and steel sidewalks have been coated successfully. Also, pipe joints coated in the shop have been shipped to the field, welded together and followed by the application of flamespray powder to the weld seams and pipe joints, creating a seamlessly coated pipe that is corrosion resistant.
Combining TechnologiesSome finishing operations have developed ways to use powder coating in tandem with liquid finishing lines, using powder basecoats and liquid topcoats, for example. This combined technology not only provides a more environmentally compliant finishing process than is available with a liquid-only finishing operation, but can result in new colors or effects not available with liquid or powder alone.
RoboticsAdvances in microprocessors and robotics are also allowing increased production in powder coating facilities. Robotics are typically used where an operation must be repeated for each workpiece on the line. The clearcoat being applied to BMW automotive body panels benefits from a complex series of twists and bends of a robotic gun, programmed even to shut the car door during the clearcoat application. When combined with analog powder output and voltage controls, robotics can adjust powder delivery settings in the midst of coating a part, maneuvers too difficult to accomplish manually.
Other InnovationsApplication equipment manufacturers are also working to develop equipment that will deliver lower film builds to increase yields, increase first pass transfer efficiency and further automate the powder coating application process.
Resent research and development has been directed toward online process monitoring as a prerequisite for automated control of powder coating lines, which will become more important with the increased demand for thin-film powder coatings.
All of these advances, plus the inherent advantages of working with powder, ensure that powder coatings will have a permanent and increasing share of the finishing market.