Effects of Atomization on the Particle Size, Appearance, and Composition of Automotive OEM Basecoats

Color uniformity in the automotive paint industry is a very important attribute. Previous work to better understand the factors responsible for basecoat color variation has concluded that dried film composition is the most important factor. This work continues to support that conclusion, and in addition, describes quantitatively how final film composition can be modified by small changes in the atomization of the basecoat.

Using an air-blast paint spray atomizer and a silver (aluminum flake containing) waterborne basecoat, sixteen (16) spray applied films were analyzed by inductively coupled plasma - atomic emission spectroscopy (ICP-AES) for pigment content. Analysis found that the ratio of “effect” to “color” pigments in the films (i.e., metallic flakes vs. colored pigments) changed by more than 60% when changes were made to the conditions of spray application; fluid flow [100 vs. 400 g/min.], shaping air flow [25 vs. 50 psi cap], and atomizing air flow [40 vs. 60 psi cap]. These results are significant as perceived color is highly correlated to the concentration of aluminum in the film. Formulation specialists can typically detect color differences in coatings when films vary in composition by less than 2%. For the casual observer, this lower limit is approximately 5%.