Volume 32, Issue 3 (May 2004)
UV Absorber Permanence and Coating Lifetimes
Delamination is the ultimate failure mechanism of a coating. Delamination times often are closely related to the dose of ultraviolet (UV) radiation reaching the substrate or primer, and this dose is related to the UV absorbing capability of the overlying coating. Organic UV absorbers are not permanent, and their photodegradation is an important factor in determining coating lifetime. The kinetics and some of the chemistry of UV absorber photodegradation have been studied extensively over the past decade and applied to coating lifetime prediction. Rates of UV absorber loss vary widely and are highly dependent on the coating matrix, so must be determined on a case-by-case basis. Simple zero- or first-order kinetic schemes give rates that are dependent on the initial absorbance of the sample. This paper discusses a more reliable kinetic equation and applies the rate constant to prediction of delamination times.