Photoinitiators

A photographic plate coated with a layer of bitumen was exposed to sunlight for several hours; the image areas were cross-linked by the sunlight, thus becoming insoluble in the developer solution. The photopolymerization of unsaturated substances such as styrene was initiated with dithiocarbamate photoinitiators in combination with mercury lamps achieving very high degrees of conversion, whereas no photopolymerization at all was observed when irradiation was carried out without the dithiocarbamate photoinitiators. This chapter presents a simplified view on photoinitiators that provides a versatile guideline for a first selection of suitable substances. It discusses the various classes of photoinitiators commercially available with a special focus on their application properties in UV inkjet inks. An interesting approach is to use a liquid, surface-active photoinitiator with good water solubility; adhesion of the UV cured ink film to the plastic film was thus significantly improved.