2,4,6-Trimethylbenzoyl-diphenyl-phosphineoxide. Acts as a highly efficient free radical type I solid photoinitiator. It is used to initiate the UV polymerization of styrene-based unsaturated polyesters and acrylic resins. It can be used as the sole photoinitiator or in combinations with other photoinitiators, like e.g. hydroxy ketones. It produces two kinds of free radicle, benzoyl and phosphorous radicle, which can both induce polymerization reaction so that TPO has a quick speed to solidify UV system.
2-Isopropylthioxanthone. Acts as a highly efficient free radical type II photoinitiator. It is used to initiate the photopolymerization of chemically unsaturated prepolymers, e.g. acrylates, in combination with mono- or multi-functional vinyl monomers. It is usually combined with amine synergists or cationic photoinitiator to increase the depth and hardness of film.