Development of High Appearance Water Born Primer Surfacer Coating for Short Process Body Paint

4C3B (4 coat 3 bake) painting system (see Figure 1) which needs a bake process after the primer surfacer paint was very general and common process for the automotive body painting system. In the beginning of the 2000s, 4C2B painting system (Reference 1) was developed which changed the oven after the primer surfacer paint to a pre heat area, so it can reduce the carbon dioxide (Figure 1, and Figure 2). But unfortunately in this 4C2B painting system, the base coat will be painted on the primer surfacer paint wet-on-wet. By that reason, the appearance deterioration will occur often. The authors used a low temperature crosslinking agent “Polycarbodiimide” to a water born primer surfacer paint, to control the viscosity of primer surfacer paint at the pre heat area. Controlling the viscosity is important to avoid the layer mixing of the primer surfacer paint and the base coat which makes appearance deterioration. Taking control of the primer surfacer paint viscosity, the high appearance in 4C2B process have achieved.