Influence of additives segregation on surface composition of automotive coatings: Effects of an ethanol cleaning
Résumé
The automotive topcoat is constituted of a pigmented basecoat, covered by a transparent and shiny clearcoat. This layer protects the basecoat from the environment damage and determines the paint appearance. For white plain colour, the basecoat/clearcoat system is replaced by a layer of lacquer. The surface analyses are used to determine the influence of the topcoat composition on the adhesion of pressure-sensitive adhesives. X-ray photoelectron spectroscopy (XPS) and secondary ions mass spectrometry (ToF-SIMS) study the automotive topcoats chemistries. These analyses point out that polysiloxane additives are detected on the clearcoats but not on the lacquers. The impact of the different additives families (anti-UV agents and surface levelling additives) on the topcoat surface chemistry is identified. Moreover, the aluminium pigments do not appear on the metallic basecoat surface because of a siloxane additives layer, which also covers the polyester-polyurethane network. XPS studies on the basecoats covered by a clearcoat formulated without additive bring to the fore that the basecoat siloxane additives segregate towards the clearcoat/air interface during the curing process. The clearcoats additives can be removed with an ethanol cleaning according to the XPS analyses but this solvent cleaning is not able to remove all the additives from the basecoat surface, which seem to be partly cross-linked with the basecoat polyurethane network