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Cationic energy curing systems are used today in different industrial applications such as coatings, release coatings and graphic arts. Coatings are primarily clear for protection of the exterior of packaging materials: mainly metals but also plastics and they take advantage of the use of cycloaliphatic diepoxyde and standard triarylsulfonium hexafluorophosphate I). Release coatings are based on epoxy functional silicone resins and uses lipophilic diaryl iodonium salts specially designed for the incorporation into this kind of formulations. The use of cationic UV curing in graphic arts seemed very promising up to the mid of '90s and tried to compete with the most widely used radical curing for its excellent resistance properties, adhesion to difficult substrates and reduced migration characteristics. In particular the increased use of narrow web flexo printing onto plastic substrates seemed to boost this technology. The discovery of release of aromatic hydrocarbons of toxicological concern as photodecomposition product of (I) had a dramatic effect in development of this application.
