Kojima, K. and Ogawa, T., "The Development of Primer Process-less Paint System (4WET Paint System by Using Waterborne Chipping Primer)," SAE Technical Paper 2014-01-1046, 2014, doi:10.4271/2014-01-1046.
The CO2 emission from automobile plants is large. A majority of this quantity comes from the body painting process. A breakdown of CO2 emissions from the painting process shows the significant impact of painting process equipment such as the oven used to cure paint and the air conditioning facilities used to maintain controlled temperature and humidity on CO2 emissions. It was concluded, therefore, that shortening these processes will effectively promote the reduction of CO2 emissions.Removing the primer process means that the basecoat (BC) and clearcoat (CC), which provide color and marketability, would be applied on the E-coat directly. By the removing the primer several issues are raised such as stone chipping resistance, weather durability, color variation and appearance. By contrast, this 3Wet painting system applies two coats of waterborne basecoat, dividing it up into 1-Base and 2-Base and then CC, in order to achieve both targets, quality and color variation.For severe corrosion areas, chipping primer (CP) is applied to keep chipping resistance before the application of 1-Base. Also waterborne chipping primer is required in VOC regulated regions, especially in US. Therefore the most unique feature of this paint process is “4-WET” process. During workability some defects such as popping and sagging can occur affecting the appearance, since three waterborne materials are applied as thick film. So it is necessary to set the viscosity of each layer.The developed 4Wet paint system has achieved primer process removal without the limitation of color variations.