Photolatent Bases: New Opportunities in Radiation Curing

摘要

Over the past decades, radiation curing has found an increasing number of industrial applications and still can be seen as most economic and ecologic among all coating technologies. Most photocurable applications are using radical photopolymerization processes that have some intrinsic disadvantages and limitations, e.g. oxygen inhibition or limited chemical diversity of suitable reactive building blocks. Base catalyzed curing mechanisms are well-known, e.g. for polyol-polyisocyanate or thiol-acrylate-polyester combinations. However, this approach is hitherto restricted to two-pack systems. The lack of efficient photolatent catalysts that can produce suitable bases upon irradiation while being stable in the absence of light forbids its use as one-pack photocurable formulations. In this paper several new concepts for the release of efficient base catalysts from their photolatent precursors upon irradiation will be discussed, allowing for one-pack formulation systems with a "cure on demand". The photogeneration of suitable bases, such as tertiary amines, amidines and imidazoles, as well as photolatent catalysts providing both radicals and an active base catalyst, suitable for hybrid-type resins, will be presented. Our recent developments on photolatent bases can now open up new dimensions for resin and coating manufacturers and provide end users with a huge variety of new resin types. Based on this technology platform, previously inaccessible curing mechanisms will re-open the door for conventional coating systems and allow the design of fully new resin types providing an improved coating performance.