Development of High Appearance Water Borne Primer Surfacer Coating for Short Process Body Paint 2019-01-0189

"4 coat 3 bake (4C3B) painting system (E-coat paint/bake/primer paint /bake/Topcoat paint/bake system)" was general way for the automotive body painting system in the past. The efforts to shorten the painting process are progressing for the purpose of reducing CO2 generated in the manufacturing process. Since the beginning of the 2000s, the "Water borne 4 Coat 2 Bake (4C2B) Coating System, (without primer bake process)" started to get interested and used in automobile company. This environmentally compatible short process paint system can reduce VOC and CO2 emissions from the factory. In the waterborne 4C2B coating system, the water born basecoat will get painted wet on wet after pre-heat drying (80degreeC) of the water-based primer coating. For this reason the layer mixing will occur between the primer coating and the base coat. Compared to 4C3B coating system, where the primer is laminated, the paint appearance deterioration will occur more often in a 4C2B system. From this reason, there were only few cases where the water borne 4C2B painting system getting applied at a luxury car production line, where the high appearance is needed. In order to achieve the same external appearance as 4C3B in water borne 4C2B coating system, the key point is how to suppress the interfacial mixed layer of wet on wet paint coated with base coat. In this study, two curing agents (carbodiimide) are mixed with a polyester / melamine curing type water borne primer coating material (in a mixing device) and micro cross-linked in a preliminary drying process at 80degreeC., whereby an primer coating and a base coat. This technology method made it possible to achieve the same external appearance as the conventional 4C3B coating system.