Formulation, Curing Kinetics and Properties of Photocurable Epoxy Resins

Epoxy is widely used in industry as coatings, composites, reinforced structural materials, and insulations for medium and high voltage electrical equipment due to favorable mechanical properties, excellent breakdown strength, and high thermal and chemical stability. Epoxy is most often thermally cured, but photocurable epoxy has attracted increasing attention because photopolymerization is a solvent-free and energy efficient process that can be carried out under ambient environment. With increasing interest in additive manufacturing, epoxy photopolymerization is an attractive option for parts with demanding electrical and mechanical requirements in the realm of 3D printing. Cationic photopolymerization of epoxy benefits from recent development in chemistry. Moreover, other advantages, such as excellent adhesion strength, low shrinkage, and long history of applications in insulation products, make photocured epoxy a preferred choice for industrial applications. This study reviewed literatures on formulations of photocurable epoxy and their impact on curing kinetics as well as properties of the final cured products. The mechanical and dielectric properties of photopolymerized epoxy are of importance for applications in electrical insulation. These properties are closely related to the resin chemistry and determined by resultant epoxy network. Cationic photopolymerization of epoxy shows attractive prolonged dark-curing, satisfactory curing kinetics and sufficient dielectric and mechanical properties of final products. This technology has enormous potential in electrical industry for insulation manufacturing with complex form factors.