Durability prediction of p-urethane clearcoats

Abstract

The durability of topcoats is dependent on a large number of factors such as polymer composition, stabilization package and the conditions during the weathering process. For obvious reasons, prediction of the long-term (5–10 years) durability of coatings is very important. Some background information concerning the weathering process as well as methods to trace the degradation during exposure is given. The rate-determining factor for the degradation of PUR coatings is photo-oxidation. The photo-oxidation rate (POR) is controlled by the polymer structure but also stabilizers such as hindered amine light stabilizers (HALS) have a large influence. The prediction of the durability of clearcoats is based on tracing of the POR and of the HALS longevity during exposure. The POR is measured using FTIR-PAS. The HALS longevity is determined by ESR. The results show that degradation can be detected much earlier compared to methods as gloss loss and time-to-cracking. Moreover, detection of differences between systems after short exposure times as well as prediction of the long-term durability are possible. Service life prediction (SLP) of clearcoats based on these chemical–analytical methods become more reliable as with the classical approach.