Real-time monitoring of paint curing by surface potential measurement with corona discharge

Real-time monitoring of the cure state of sprayed paint is important for industrial painting processes to determine appropriate leveling and drying times. Paints contain pigment, resin, solvent, and other additives. The solvent is generally conductive and is finally evaporated during the paint curing process, which results in a change in the electrical properties of the painted layer, from conductive to insulative. Therefore, we propose a technique to measure the cure state of a painted layer from the change in its surface resistance. The measurement apparatus includes a corona charger and surface potential probes. The surface resistance can be estimated from the increase in potential during corona charging. The degree of cure Dc is determined as a function of the surface potential. Pencil hardness, which is a general measure of the degree of cure, was also measured for comparison. A linear relationship between Dc and the pencil hardness was determined for various paints, which suggests the degree of cure can be monitored according to Dc estimated from surface potential measurements.