Powder Coating Process

Powder coating is a dry finishing process that uses finely ground particles of pigment and resin that are electrostatically charged and sprayed onto electrically grounded parts. The charged powder particles adhere to the part and are held there until melted and fused into a uniform coating in a curing oven.

Since its introduction more than 40 years ago, powder coating has grown in popularity and is now widely used by many manufacturers of common household and industrial products. In North America, it is estimated that more than 5,000 finishers apply powder to produce high-quality, durable finishes on a wide variety of products. Powder coated finishes resist scratches, corrosion, abrasion, chemicals and detergents, and the process can cut costs, improve efficiency and facilitate compliance with environmental regulations.

Because powder coating materials contain no solvents, the process emits negligible, if any, volatile organic compounds (VOCs) into the atmosphere. It requires no venting, filtering or solvent recovery systems such as those needed for liquid finishing operations. Exhaust air from the powder booth can be safely returned to the coating room, and less oven air is exhausted to the outside, making powder coating a safe, clean finishing alternative and saving considerable energy and cost.

Theoretically, 100% of the powder coating over-spray can be recovered and reused. Even with some loss in the collection filtering systems and on part hangers, powder utilization can approach 95%. Over-sprayed powder can be reclaimed by a recovery unit and returned to a feed hopper for re-circulation through the system. The waste that results is negligible, and can be disposed of easily and economically.

Powder coating requires no drying or flash-off time, so parts can be racked closer together on a conveyor and more parts can be coated automatically. It is very difficult to make powder coating run, drip or sag, resulting in significantly lower reject rates for appearance issues.

Powder coating operations can be implemented with additional cost savings because they require minimal operator training and supervision. Employees typically prefer to work with dry powder rather than liquid paints, and housekeeping problems and clothing contamination are kept to a minimum. Also, compliance with federal and state regulations is easier, saving both time and money. In short, powder coating can provide the Five E’s: economy, efficiency, energy savings, environmental compliance and an excellent finish.

There are two basic types of powder coatings: thermoplastic and thermosetting. Thermoplastic powders melt and flow when heat is applied but they continue to have the same chemical composition once they cool and solidify. Thermosetting powder coatings also melt when exposed to heat, but they then chemically cross-link within themselves or with other reactive components. Thus the cured coating has a different chemical structure than the basic resin. Thermosetting coatings are heat-stable and, unlike thermoplastic powders, will not soften back to the liquid phase when re-heated.

The main driver in the development of powder coating materials was the pursuit of an environmentally friendly alternative to solvent-laden paints. In pursuit of a sprayable, low-VOC coating, Dr. Pieter g. de Lange of The Netherlands developed the process of hot melt compounding in a z-blade mixer. This made powder coating much more consistent. De Lange also developed the electrostatic spray application method for thermoset powder coatings in 1960. Using compressed air to “fluidize” the dry powder material, he was able to spray the coating and provide a decorative film. The process was introduced in the United States in the 1960s and rapid growth continued for the next 30 years. More information on powder materials is available in the article "Powder Chemistries."