Modulus and chemical mapping of multilayer coatings

Thermoplastic olefins (TPOs) are polymeric materials utilized for interior and exterior automotive parts. These materials are often painted to protect and enhance their appearance. TPO materials possess a low surface energy because of the aliphatic backbone, and adhesion promoters (APs), such as chlorinated polyolefins, are used to increase paint adhesion and improve paint performance. The impact of the AP structure and processing conditions on the mechanical properties and degree of interpenetration was investigated on cross sectioned coatings. The AP structure was varied by the chlorine content and molecular weight for the same TPO and polyester acrylic, melamine-cured paint system. Two different processing conditions were investigated. Mechanical properties were measured using depth-sensing indentation. Long-range diffusion of coating components across each interface was verified with confocal Raman microscopy. The AP interfaces, AP/base coat and AP/TPO, were chemically and mechanically sharp at the 1 mum lateral resolution of both techniques. Depth-sensing indentation measured a modulus gradient across the top coating cross section. The free air surface of the top coat had a higher modulus than the interior. Processing conditions and polishing to prepare the cross section for measurements were found to affect only the control AP.