One shot matte powder coatings

 
"Achieving very low gloss appearances is challenging in powder coatings. The best appearance is obtained by a one shot matte (OSM) approach. Covestro has developed a novel acid functional OSM system. In this paper we describe the processes taking place during cure for the formation of the low gloss appearance. The OSM powder coating formulation comprises two polyester resins with a large reactivity difference together with an hydroxyalkyl amide crosslinker. Upon cure phase separation takes place, forming domains which are primarily composed of the two different resins with crosslinker. The crosslinker is initially homogeneously distributed in the powder paint, but during cure the crosslinker migrates from the low reactive domain to the high reactive domain. Thereby Thereby reducing the domain size of the low reactive resin. This so-called ripening leads to a final domain distribution and the domains are set by crosslinking. Upon cooling these domains lead to roughening of the surface due to non-homogeneous shrinkage in the coating itself which leads to matting. By controlling these processes, the degree of matting can be tuned. For acid functional OSM system this phase separation process is more difficult to control than for hydroxy functional resins with urethane crosslinking. In this paper the route to obtain a dead matte coating with this acid functional system will be explained. "