Root Cause Analysis and Mitigation of White Patch Formation in Automotive Headlamp

Abstract

Root cause analysis of the white patch formation on the headlamp lens of a particular automobile model was carried out. SEM, FTIR, and XPS techniques were used to analyze the white patch region. Headspace GCMS and TGA were used to analyze the volatiles and curing characteristics, respectively. The white patch region shows the presence of foreign deposits and chemical attacks in the form of undulation and holes on the polycarbonate lens surface. The holes due to the chemical attack on PC lens attributes to the degradation of the polycarbonate surface. GCMS analysis reveals the release of volatiles from the reflector materials and TGA reaffirmed the releases of it from base coating applied on the reflector. These volatiles permanently settle on the inner surface of the lens and attack leading to the hazy appearance/white patch formation. A minimal volatile release could be seen in all IR-UV curable base-coated reflectors. The volatiles generation in higher quantity and their deposition on the lens in the studied headlamp is a result of higher lamp temperature and insufficient breathing. Release of volatiles can be mitigated by adopting the thermal curing of the reflector and the deposition of such volatiles on different internal parts can be minimized by selecting an appropriate breathing mechanism to facilitate proper air circulation for a given lamp design and resultant temperature.