Powder Coating Center

The technology for coating products with dry powder rather than conventional liquids has been available since the 1950s. The powder used for the process is a mixture of finely ground particles of pigment and polymeric resin. The powder is either sprayed electrostatically onto a surface to be coated, or the substrate is dipped into a fluidized bed of suspended powder. The powders adhere to a preheated substrate surface in the fluidized bed process, or they adhere electrostatically in the spray process. When heated further in a curing oven, the particles flow and fuse into a strong, adhering coating. The result is a high quality coating with an attractive finish and excellent durability.

The growth of powder coatings has been dramatic during the last two decades with new applications continually being developed for both industrial and consumer related markets. The growth can be attributed to the powder coating industry meeting customers' demands with a two-pronged attack:

1. The development of new formulations and
2. The development of advanced equipment and application processes.

These developments have created many new market opportunities and helped overcome finishing obstacles that were common in the early days of the powder coating industry.

Powder coatings have been shown to possess significant durability and resistance to abrasion, corrosion, scratching, and chemicals when compared to liquid coatings. Powder coatings stay bright with less fading, and color selection is virtually unlimited with high and low gloss, metallic, and clear finishes available. Texture selections range from smooth surfaces to wrinkled or matte finishes, and rough textures are available for hiding surface imperfections. Thick coatings can be achieved quickly and efficiently.

Although the final properties of the powder coatings are often superior to liquid coating systems, the reason for the fast growth of this technology has been more related to the evidence that powder coatings maximize production, cut costs, improve efficiencies, and offer maximum compliance with increasing stringent environmental regulations - factors all related to the end-user's bottom line.

Environmental advantages have led the way for the conversion of liquid coatings to powder coatings. Powder coating contains no solvent, and thereby the process emits negligible, if any, polluting volatile organic compounds (VOCs) into the atmosphere. Furthermore, the processes used for powder coating do not require venting, filtering, or solvent recovery as is necessary with liquid finishing. Costs are saved because there is less need for heating outside air to supply oven exhaust air, and most of the powder coating over-spray can be retrieved and re-used.

Table 1 summarizes the advantages and disadvantages of powder coatings. Recent developments in materials and process technology have greatly minimized the disadvantages that are listed here. These developments are summarized in this article.

Advantages	Disadvantages
No solvents so that VOCs are nil	Very thin coatings (less than 1.0 mil) are difficult because of pinholes
Exhaust air from the coating booth can be returned to the coating room, thus less oven air is exhausted to the outside	Frequent color changes could entail extensive downtime
Over-spray (up to 98%) can be retrieved and reused	Storage and handling of powder requires special climate controls
No drying or flash time required so that parts can be racked closer together	Color matching and color uniformity is somewhat more difficult than with liquid coatings
Easily adapted to continuous, automatic processes	Uniformity of coating thickness is sometimes difficult to maintain
Coating does not run, drip, or sag, thereby lowering rejection rates	Cure temperatures required for some powders are too high for temperature sensitive parts
Minimum operator training and supervision	Powder coating is difficult on sharp corners
Thick coatings are easily possible	Conversion from liquid coating processes is expensive
High throughput / output options	Inside corners have low film thickness owing to the Faraday cage effect
Simple clean-up and maintenance