Development of Rheologically Controlled Waterborne Basecoats

Public awareness toward the environment has been increasing recently. Accordingly, volatile organic compounds from automotive coating processes must be decreased to protect the environment. Various environmental regulations are already being enforced in many countries and it's expected that the rules will become tighter every year. For this reason, the usage of waterborne basecoats has increased recently. But the introduction of waterborne basecoats has some difficulties such as the requirement of strict temperature and humidity control. So, the application of waterborne basecoats has been inferior to that of solventborne basecoats. We have conducted an investigation, putting emphasis on the viscosity characteristics of waterborne basecoats and reached the conclusion that the following factors are important for applying waterborne basecoats:

• During spray application, the paint indicates shear thinning behavior. In other words, viscosity of the paint decreases with increasing shear rate.
• As the on-part-NV varies, the viscosity of the paint should not fluctuate significantly.

Based on these conclusions, dispersion type waterborne basecoats which can achieve high application properties have been developed. As a result, it's the author's opinion that waterborne paint will become a leading product for global automotive applications.