1992 Volume 65 Issue 10 Pages 605-611
Etched areas of acrylic-melamine film on real car bodies by rain were analyzed with 3 D roughness meter, SEM and micro-FTIR for the purposes of the reproduction of the etching in a laboratory and the elucidation of the etching mechanism.
The typical damage of a paint film was about 3 mm in diameter and its perimeter was etched deeply with maximum depth of about 1.2 μm.
The study of etching by the spot test with acid components in rain shows :
(1) Nitric and sulfuric acids caused damage but hydrochloric acid did not ;
(2) Area spotted with sulfuric acid was etched, while one spotted with nitric acid was swelled.
When acid drops get dry, hydrochloric and nitric acids evaporate, but sulfuric acid is concentrated.
The change of chemical structure of etched area is suggested that the triazine ring is hydrolyzed to water-soluble cyanuric acid through ammeline or ammelide derivatives by concentrated sulfuric acid.
