Powder coating has been around since the 1950s. But in recent decades, this "dry painting" technology has improved dramatically that today it is an economically viable and preferable process for coating a countless variety of products without liquid solvents. Thousands of manufacturers are now powder coating producers ranging from automobile parts and vacuum cleaners to roofing tiles and decorative glass bottles with strong, colorful, durable surfaces.

Environmentally, the advantages of powder coating over liquid, solvent-based paint are obvious. Powder coating requires less energy and emits virtually no volatile organic compounds (VOCs) or hazardous air pollutants (HAPs), eliminating the need for expensive pollution control equipment. In addition, powder overspray can be recovered or reused, the process generates little or no hazardous waste compared with the problematic sludge left over by liquid paint.

Powder coating even costs less to apply than liquid paint. The initial capital costs are slightly higher — but subsequent operating costs are substantially lower. According to a 1990 PCI study, the applied cost for using conventional solvent painting is 6.06 cents per square foot, compared with 4.28 cents per square foot for powder coating. Not surprisingly, powder coating has captured over 10% of the total industrial finishing market in North America, and 15% of the market where it directly competes with liquid finishes.

What is powder coating? Finely-ground, electrostatically-charged particles of pigment and resin are sprayed onto electrostatically-grounded surfaces, where they adhere. The dry powder particles are then heated and permanently fused to the surface in an oven.

Like all industrial coating processes, powder coating involves a pretreatment operation to ensure that the surface is clean and free of grease, dust, dirt, and rust. To improve adhesion, phosphatizing and chromatizing may also occur. After drying, parts then enter the spray booth. The powder coating is applied using pneumatic pumps and manual or automatic electrostatic powder spray guns. The parts then enter a curing oven, where the powder melts, flows, and cures onto the convection surface of the part. Curing ovens use either gas or electricity ovens, infrared ovens, or a combination of the two.

Many coatings can be cured at temperatures between 121°C to 177°C (250°F to 350°F), in 15 to 30 minutes. It is virtually impossible to have drips, runs, or sags when applying powder coatings, meaning that many fewer products are rejected or required repainting.

During the 1950s, powder was primarily being used to coat pipe for corrosion. The early process involved dipping heated parts into a vat, where the powder was fluidized by hot air. The coatings were usually vinyl or epoxy, with thickness of 6 to 40 mils.

Electrostatic spraying technology developed in the 1960s allowed the application of much thinner layers of powder and made it possible to coat parts that could not be heated or dipped in a fluidized bed. Today polyesters, polyester/urethanes, epoxy-polyester hybrids, acrylics, and polyvinylidene resin systems can all be utilized.

Powders are being developed to compete with almost every market that has traditionally been held by liquid coatings. For example, powder coating has replaced porcelain enamel on many washer and dryer parts. These technological improvements have transformed powder coating into an efficient, cost-effective process for coating surfaces ranging from metal and glass to ceramics and even wood.

Powder coatings are available in virtually every color including clearcoats and metallics, and in a variety of gloss levels and textures. Curing temperatures have been lowered to the point where heat need not damage most temperature-sensitive parts of items being coated.

Another major efficiency of the powder coating process is the ability to recover and reuse powder. Air and water pollution problems are eliminated in well-operated facilities. Because solvents are not released into the air in the powder coating booth, that air can be circulated back into the plant, saving a considerable amount of energy, especially in winter. Unlike liquid coating, almost 100% of oversprayed powder can be collected and reused. Powder spray booths are designed to allow efficient and quick cleaning for color changes, with minimal production down-time.

Additional advantages include lower labor costs, because the process has fewer critical operating parameters to monitor (such as viscosity or pH), and greater operating efficiency, because parts can be passed through the production line racked closer together on the conveyor line.

The list of products coated with powder is extensive and includes automotive parts, industrial pipe, appliances, sporting goods equipment, outdoor furniture and farm implements. Customized coating of individual items is provided by about a fifth of the 5,000 powder coating systems in operation in the United States.

Exciting new powder coating innovations are underway, including coil and inmold coating. Advances in robotics, microprocessors and infrared curing will allow even greater use of highly efficient, cost-effective and environmentally-friendly powder coating technology. Powder coating truly is the technology of the future, here today.