US Patent 9044779 Method for applying a powder coating

A method for the application of at least two different powder coating layers to a substrate comprising the steps of application of a first powder coating layer followed by the application of a second powder coating layer, without any substantial curing of the first powder coating layer prior to the application of the second powder coating layer, followed by the simultaneous curing of the first powder coating layer and the second powder coating layer, wherein the first powder coating layer is applied to the substrate using a corona charging system and the second powder coating layer is applied to the substrate using a tribo charging system, or the first powder coating layer is applied to the substrate using a tribo charging system and the second powder coating layer is applied to the substrate using a corona charging system and the first powder coating layer and second powder coating layer have an opposite electrostatic polarity.