Acid/epoxy reaction catalyst screening for low temperature (120 °C) powder coatings

This paper describes efforts to identify and screen suitable acid/epoxy reaction catalysts for low temperature curing (≤120 °C) powder coatings including tertiary amines, ammonium compounds, and metal complexes. Thermal analysis techniques were developed to aid evaluation of catalyst efficacy and a statistical design of experiments was carried out to study several commercially available catalysts. In three different resin/crosslinker systems, the effect of catalyst type and loading were assessed and ranked in terms of kinetic responses including reaction rate, total heat-of-reaction, and extent-of-conversion. Isothermal kinetics modeling was also used to predict and compare reaction rates over a range of temperatures. Additionally, the susceptibility of each catalyzed system to thermal yellowing upon over-bake was evaluated.