Photocuring activity of several commercial, near UV activated photoinitiators in clear and pigmented systems

Some of the most important commercial near UV photoinitiators have been ana lyzed by UV spectroscopy to evaluate the type of electronic transitions occ urring upon absorption of light. Photocuring studies have been undertaken b y real time infrared spectroscopy (RTIR) in clear and pigmented (black, mag enta, cyan, and yellow) systems with UV and visible light at different phot oinitiator concentrations in the presence of air. Generally, the Type I pho tofrangmenting photoinitiators appear to operate more effectively under UV excitation when compared with the Type II thioxanthones, especially in pigm ented systems. There is a reasonable correlation between the UV and visible absorption properties of the respective initiators and their overlap with the excitation source.