The vast majority of the commercially available UV coating systems are based on free radical curing systems. A minority employ ionic curing processes but these will be left for a later article.
The choice of photoinitiator for coating applications is primarily determined by:
1. curing efficiency
2. matching of spectral characteristics
3. binder chemistry
4. coating film thickness
5. compatibility with the binder formulation
6. pigments and additives
7. solvents
8. cost
The speed of coating production lines is normally much slower as than the cure speed of the photoinitiator. Only in high speed coating production, such as that of optical fibres, does the actual cure speed (reactivity) of the photoinitiator need to be considered.
Hence for most coating applications, curing efficiency is more related to the degree of cure at the surface and that of the bulk of the coating (through-cure).
Each of these parameters is now considered. Three types of mercury lamps are most commonly used in UV curing of coatings...