Applications and properties of amine synergists in uv and eb curable coatings

A number of studies have been carried out to investigate the photo-oxidation and photoyellowing phenomena which occur in various multifunctional acrylated systems. The complex formulations of radiation curable resins complicate our understanding of the mechanisms involved. For example, high concentrations of photoinitiators in UV curable resins will often dominate the subsequent photo reactions and contribute significantly to photoyel lowing. With regard to photo-oxidative stability, hydrogen abstracting type photoinitiators such as benzophenone are more detrimental than the photogramenting types such as the benzoin ethers. Other factors include the use of tertiary amines as co-synergists, which also contribute towards the photoyellowing phenomenon and photostability of the resin and these may be free or reacted with acrylate groups in the resin. In earlier , it was found that whilst the use of tertiary amines contributed significantly toward the subsequent photoyellowing of resins, they nevertheless markedly improved their photo-oxidative stability. The yellowing was associated with hydroperoxidation of the amine, resulting in the formation of conjugated unsaturated carbonyl products which absorb strongly in the UV region with a maximum at 275 nm. The latter, on the other hand, was associated with ability of the amine to scavenge oxygen effectively and operate as an effective sacrificial site for hydrogen-atom abstraction reactions, thus protecting the resin structure. These observations were also extended to Photomer 4116 where it was found that hydroperoxides are the key initiators of the photoyellowing phenomenon but not in photo-oxidations. In this paper, we have examined the postcured photoyellowing and properties of a number of different dialkylamine terminated diacrylate resins prepared via a Michael reaction of the corresponding secondary amine with a trifunctional monomer Photomer 4094, and compared the results with our standard amine synergist Photomer 4116.