Novel approach to the evaluation of dirt pickup resistance

 
Dirt pick-up resistance is a complex, dynamic phenomenon, which varies in magnitude and time with location. Its manifestation is dependent on several factors such as regional climate, local particle burden and formulation-dependent surface film properties. Dirt pick-up is based on a range of confounding particle transport, deposition, attachment, and release mechanisms. Fundamental concepts in particle and surface science coupled with Atomic Force Microscopy measurements for direct particle interactions were used to identify the dominant mechanisms and to develop a failure-mode-targeted accelerated test. The test, based on temperature-induced surface creep mechanism, showed good correlations with outdoor exposure data for a set of commercial paints with different sheens and for experimental paints for which formulation parameters (binder glass transition temperature, formula pigment volume concentration) are controlled. A path forward towards development of a comprehensive, yet practical understanding of dirt pickup resistance is proposed.