Abstract
The new generation clear coats introduced in the automotive industry have improved scratch and mar resistance. It is believed that those properties are related to the introduction of new binder technologies leading to higher film cross-link densities. This was relatively easy to accomplish in the automotive industry because baking temperatures are well above the glass-transition temperature (Tg) of the final clear coat film. In car repair coatings, the cross-linking takes place under conditions where the intermediate and/or final film Tg values are above the curing temperature. Such formulations result in vitrification during the drying process, a transition during which chemical cure and solvent release are slowed down substantially. The chemical cure can be improved through more reactive and/or higher functional binders, but this shifts the gel point to shorter times in the drying cycle which may lead to more solvent entrapment, resulting in low film hardnesses and paint defects. This paper describes the overall properties of 2K-refinish clear coats based on linear versus branched, random and graft acrylic polyols. The authors will try to correlate overall properties with theoretical predictions and practical results.
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