UV Curable Coatings for Exterior Exposure

UV curable coatings are based on acrylate chemistry, but unlike conventional acrylate coatings, they are reputed to have poor outdoor durability. The objectives of this project were to identify the important factors influencing the outdoor durability of UV curable coatings and to put forward guidelines for achieving improved durability.

Four hypotheses were considered during the project:

• UV curable coatings employ multifunctional acrylates with a variety of chemical backbones, often not found in conventional acrylate chemistry. Such species may be more susceptible to photo-oxidation.
• Free radical curing systems usually polymerise very rapidly on exposure to UV radiation, a process which results in significant contraction, leading to stresses in the coating detrimental to adhesion. Further, the rapid solidification gives rise to occluded acrylate groups which may be photo-oxidatively reactive and reduce the effective crosslinking and Tg of the resultant coating.
• Photoinitiators are needed to promote cure effectively on exposure to UV radiation. However, UV absorbing species (unreacted photoinitiator or breakdown products) remain in the coating after cure. These are still able to produce radicals and may initiate degradation reactions.
• UV curing is typically undertaken in air. Radicals formed near the surface can react with oxygen to form peroxides and hydroperoxides which may begin the photodegradation pathway.

From the study of the above hypotheses and their consequences, a number of recommendations for improved durability were proposed.

Further Information

If you are interested in this, or any other project, please contact Richard Holman.