INVESTIGATION OF THE FORMATION OF PHYSICAL DAMAGE ON AUTOMOTIVE FINISHES DUE TO ACIDIC REAGENT EXPOSURE

Automotive paints with clear-coat surfaces can be physically damaged b y exposure to acidic reagents produced in a smog chamber designed to r eproduce real environmental conditions. Visual and reflectance microsc opy observations show that deposition of material formed from the reac tion of the clear coat and the reagent drop occurs on the paint surfac e after the drop evaporates to a critical size, with the greatest depo sition occurring at the edge of the drop. This type of deposition sugg ests a free-energy minimization process favoring the formation of stab le nuclei at the reagent drop edge. With heating after the drop evapor ation to simulate exposure to the sun, a damaged area containing sulfu r that is in the shape of a circular ring is observed at the location of the deposits. The majority of the visual damage appears to result f rom an interaction between the deposit and the paint at elevated tempe ratures. Results from profilometry, scanning electron microscopy, and reflectance microscopy show that the damaged areas are ring-shaped cra cked blisters on the surface resulting from the clear coat separating into layers. (C) 1993 John Wiley & Sons, Inc.