Generally, electrostatic coating is a coating method in which: an electrostatic field (lines of electric force) is formed by applying a high voltage between a coating object and an electrode on a coating device side with the coating object being an earth electrode and the electrode on the coating device side being an cathode; paint particles are negatively charged; and the paint is thus made to efficiently adhere to the coating object by electrostatic force. Effects such as an improvement in coating efficiency (reduction of a coating time due to an improvement in coating throwing power) and an improvement in transfer efficiency (reduction of a paint usage amount due to an improvement in ratio of amount of paint adhering to a coating object) can be obtained from the electrostatic coating.
Moreover, since the coating object in the electrostatic coating is an electrode, the coating object needs to be electrically conductive. In a case of performing the electrostatic coating on a non-electrically conductive object, the following techniques are used.                Electrical conductivity is imparted to a raw material by mixing an electrically-conductive material or an electrically-conductive agent.        Electrical conductivity is imparted to the coating surface by applying an electrically-conductive film such as a conductive primer.        Low electrical conductivity is temporarily imparted to the coating surface by performing antistatic treatment such as application of surfactant.        Low electrical conductivity is imparted to the coating surface by grounding the coating surface and using an electrically-conductive paint.        An electrostatic capacitance is increased by applying an electrically-conductive material to a back surface of the coating object or bringing the electrically-conductive material close to the back surface of the coating object (potential fall with respect to a charge amount).        
Imparting electrical conductivity to the coating surface by applying an electrically-conductive film such as a conductive primer is most commonly employed particularly in a technique of performing electrostatic coating on a surface of a polypropylene (PP) material of a front bumper, a rear bumper, and the like which accounts for the most of coating on resin parts of an automobile.
USPTO Backgrounds
USPTO Backgrounds