Exploring the properties and performance of Lewis base organocatalysts in epoxy/polyester hybrid low-cure powder coatings

Abstract

Low-cure powder coating (LCPC) is a novel, 100 % solvent-free, low-energy coating suitable for heat-sensitive substrates. The inclusion of a curing catalyst in the formulation effectively lowers the curing temperature and time. However, the structural morphology, physical and chemical properties and catalytic mechanism of catalysts still significantly constrain the research and application of LCPC. In this study, we reveal and conclude that the curing catalyst commonly used in LCPC is essentially Lewis base organocatalysts with well crystal form and particle sizes on the order of several tens of microns. The experimental results show the incorporation of different types of Lewis catalysts results in varying curing and surface performance in coatings. Increasing catalyst concentration from 0.08 % to 0.2 % improves curing efficiency at lower temperatures but negatively affects the visual quality of coating films. The HOMO-LUMO energy gap and density functional theory (DFT) transition state calculation indicate that the addition of imidazole type and quaternary ammonium salt type catalysts effectively reduces the activation energy of the curing reaction by promoting the epoxy ring opening via proton transfer and negative halogen ions, respectively. This study represents a systematic and mechanistic exploration of organocatalysts and their impact on LCPC, addressing a gap in academic research and providing insights for future developments in LCPC.