New Trends in UV Curing

Abstract

We present an overview of the use of photochemistry applied to polymerization and crosslinking reactions by radical or cationic process used for thin film technologies and more generally for coatings. Industrially, most of the formulations used are initiated by radical mechanism. Since the discovery by J. Crivello of iodonium and sulfonium salts, the market has been oriented to use cationic systems to crosslink monomers/ oligomers. One of the main advantage of such a system is that it is not sensitive to the presence of oxygene as it is for radical mechanisms. An overview of a photosensitive formulation is presented i.e. photoinitiators, photosensitisers, monomers and/or oligomers mainly used by formulators and additives. A new technique which has been developed to study and optimise any photosensitive formulation – differential phto calorimetry DPC – and which permits to determine kinetic parameters such as enthalpy, degree of conversion, rate constant, Arrhenius parameters, etc. is also describe. Some of the main characteristics and properties of UV cured polymers like acrylates, epoxides, vinylethers and others are correlated with their structures and the photocuring conditions. Applications to thin film technologies based on acrylates, epoxides and silicones is presented. A promising area of research which opens a new route for the obtention of new structure of alternating copolymers for coatings without the use of photoinitiator and based on charge transfer complex CTC is also presented.