Low VOC has been the driver for R&D for decades. Lowering molecular weight of resins and crosslinking after application in order to lower VOCs has become standard practice in the industry. Sagging of the paint film with such low molecular weights is also well known. In metallic coatings, metal orientation is also an important consideration. In high-performance coatings, several rheology modifiers have been used for sag control and proper metal orientation. For automotive coatings in North America, silica is commonly used; while in Europe, the use of urea crystals (sag control agents – SCAs) is predominant, and the use of microgels is prevalent in Japan. Each of these technologies has its own benefits and limitations.
Edge coverage is another phenomenon that is very important in high-performance coatings. When paint is applied on objects with corners, the Laplace pressure causes paint to flow away from the sharp edge, resulting in bad edge coverage. The risks of coating edges, especially for marine and protective coatings, have been previously discussed.1,2 Sag control agents with thixotropic behavior are known to prevent the paint from flowing away and provide improved edge coverage.3