Radical photoinitiator technology for UV-cured coatings

摘要

Tony Heslop of Ciba Speciality Chemicals presented the second lecture of the 2004/05 season on Wednesday 13th October at Leeds University Department of Colour and Polymer Chemistry.A wet and windy Wednesday evening and competing against the England football match, Tony pulled in a capacity crowd.Tony Heslop has been working at Ciba for the past five years and introduced the lecture with a brief overview of Ciba's history and the many fields within the coatings industry that Ciba are involved. The lecture's main focus was on UV-cured photoinitiators, so basic theory on the free-radical process which is kick-started by UV exposure was explained. The advantages of this type of UV-cured coating, compared with the conventional solvent-borne system, is a faster line speed due to faster drying. However, the major advantage is the lack of solvent waste produced, although these benefits do come at a higher cost, and, in some cases, colour shade is reduced. The background theory to photoinitiators was then followed by a discussion about photoininitiators for surface cure and through cure. The mechanism of breakdown of Irgacure 184, a common photoinitiator used in clear topcoats due to its non-yellowing and excellent surface cure, was explained. The other products in the Irgacure and Darocur ranges used in surface cure were also presented, including the new Irgacure 754 used in high-solid water-borne coatings. The type of photoinitiator used in through cure absorbs greater UV light in the near UV/visible region of the electromagnetic spectrum compared with surface cure initiators. This is because this light has a higher penetration and thus can cure deeper into the coating. Ciba produce a large range of through-cure photoinitiators, with Irgacure 819 exhibiting four free radical sites when exposed to UV light, being recommended in many highly pigmented systems.