Computational analysis of surface‐tension‐driven coating‐defect flow

Bondline readout (BLRO) is a coating defect frequently exhibited on adhesively‐bonded, polymeric automotive body panels painted with high‐glamor/flow clearcoats. BLRO or telegraphing results from Marangoni‐type, surface‐tension‐driven flows. An efficient numerical code was developed to predict temperature‐ and concentration‐induced BLRO flows to use it as an effective tool for screening and developing potential clearcoat systems. Two numerical codes were developed: a 1‐D code based on the lubrication approximation; a 2‐D code based on the SIMPLER (Semiimplicit method for pressure‐linked equations revised) algorithm. The 1‐D code produced BLRO profiles in agreement with those predicted from the 2‐D code and those measured from BLRO flow experiments, thus confirming a proposed BLRO mechanism. Moreover, the 1‐D code was vastly more time‐efficient than the 2‐D code due to a severe time‐step stability limitation found with the latter.