1. Appearance of Automotive Coatings
- Author
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Marcy E. Zimmer, Jun Lin, and Jingguo Shen
- Subjects
Cure rate ,Materials science ,business.industry ,Automotive industry ,02 engineering and technology ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Coating ,Compatibility (mechanics) ,engineering ,Surface structure ,Composite material ,0210 nano-technology ,business ,Curing (chemistry) ,Shrinkage - Abstract
A few concepts related to the development of surface structure and how it can affect the appearance of automotive coatings are discussed. These concepts include flow and leveling, substrate telegraphing, gradient of drying or curing, and inter-layer compatibility in multi-layer systems. While flow and leveling is essential to achieve excellent coating appearance, volume shrinkage is the driving force for telegraphing substrate texture. Gradients of cure (both intra-layer and inter-layer) and wrinkle formation are the fundamental mechanisms for surface structure formation in low-bake systems. For multi-layer systems, inter-layer ingredient migration and mismatch of cure rates between the neighboring layers can disrupt the interfacial structure and create structures on the topmost surface, typically a clearcoat. For systems where multiple layers are sprayed wet-on-wet-on-wet (3-W) and baked simultaneously, all the factors above influence appearance. To achieve the best system appearance for high temperature baking conditions, an addition-reaction crosslinking chemistry is superior to condensation crosslinking chemistry. This is due to addition-reaction chemistry providing lower overall volume shrinkage and a prolonged flow and leveling period based on the slower cure rate of the system used in this study.
- Published
- 2017