Optimization of automotive clearcoat application properties.

Abstract

The present project is made by AkzoNobel Car Refinishes and Chemical Engineering department of Universidad de Barcelona collaboration. This is focused on automotive clearcoat properties improvement. Throughout history the use of plastic in the vehicle manufacture has increased due to its low cost, its low weight and its resistance. Due to plastic surface is in contact with chemistry and climatic agents this surface needs to be protected. One of the protective layer applied on the plastic surface is the clearcoat. Clearcoats must have some properties and pass some requirements to warrant a quality cover. Binders are a clearcoat component which are responsible of the clearcoat properties; it is common using different types of resins to get optimal properties. In the automotive industry clearcoats are applied in the painting line with the substrate in a vertical position. At time of application clearcoats are subjected to high efforts, that’s why they have a low viscosity. In order to dry the clearcoats film thinners have to evaporate so after the application the substrate with the clearcoat applied remains vertically while thinners are evaporating. If the clearcoat viscosity does not grow quickly, it is common that steaks appear on the paint layer, causing a paint defect called sagging. To avoid this problem the clearcoat used in this project incorporates antisagging binders (SCA) which are poliurea crystals. When the effort stops between the molecules of poliurea intermolecular links are established, making a tridimensional structure in the clearcoat that provide viscosity to the clearcoat film applied. On the other hand after having applied the film clearcoat it must flow (level) enough in order to have a good appearance. When the clearcoat has dried some automobile pieces are packed, the clearcoat needs to have hardness enough to avoid packaging marks. In this project AkzoNobel clearcoat the addition of cellulose acetate butyrate in an AkzoNobel commercial clearcoat formulation is studied to obtain a hardness and appearance improvement and sagging reduction. On the other hand it is studied how CAB addition affects on packaging marks, on a commercial clearcoat polish and on abrasion resistance.