Optimizing automotive coatings

The balancing act between adhesion energies, interfacial tensions, and spreading coefficients

The optimization of any coating process involves controlling the bulk rheology of the coating, the surface chemistry aspects of the coating, and the surface energetics of the solid. Here we share some recent work on the surface chemistry aspects of solvent based coatings used to color the plastisol materials which make up much of the interior of most automobiles – dashboards, door interiors, arm rests, and the like. Without surface treatment (corona, flame, plasma, or other) plastisol is a fairly hydrophobic (low surface polarity) and moderately low overall surface energy material, onto which the coating needs to properly spread (wet) and then adhere.

The goodness of adhesion needs to be considered in both, the short and the long term. The spreading coefficient of the coating on the substrate determines the uniformity of initial wetting. Coating/substrate adhesion energy (also known as work of adhesion) characterizes the short term bonding. And, coating/substrate interfacial tension – being that it represents the tension left in the formed bond (i.e. the bond’s potential to break) – characterizes long term adhesion. Any alteration of either the substrate surface or the coating changes all three of these important parameters. The trick is to optimize all three properties at once. This application report is an example case wherein we at KRÜSS helped a customer improve one particular color coating, based on studying these parameters relative to those of another coating which was known to have many less adhesion issues.

Download the full application report here: AR260