Powder coatings are solvent-free, 100% solids coating systems that have been used as low VOC and low cost alternatives to traditional liquid coatings and paints.
Powder coating of metal parts is a common practice. It is difficult, however, to coat certain parts of a metal substrate, including edges and corners, for example, to obtain a uniform coating using typical powder coating processes, and edge corrosion is a common problem. Typically, when powder coatings are applied to metal parts, powder particles do not flow into corners, over edges, or into other recessed areas due to faraday cage effects. Moreover, when a powder coating composition is applied to a surface already coated with an uncured or non-gelled powder, surface charge tends to build up on the surface, leading to significant back ionization. This may result in undesirable electrostatic mixing of layers in the coating, and a consequent reduction in smoothness and gloss. Conventional systems that attempt to overcome faraday cage effects and back ionization problems typically require line modifications, modifications to the spray apparatus or changes to the physical characteristics of the powder composition itself. However, such methods typically lead to process inefficiency, increased costs and delay.
From the foregoing, it will be appreciated that there is a need for effective powder coating of metal parts, where faraday cage effects and back ionization are eliminated, and where the coating demonstrates excellent performance characteristics, such as excellent corrosion protection, including at the edges, and optimal surface smoothness or gloss, without significant equipment or line modification.