In order to clarify the mechanism of orange peel defect generation in the sprayed paint films, high speed photographs were taken during spraying, and the changes in the surface unevenness after painting were observed by means of the direct shadow method and a newly developed quantitative method by use of “Orange Peel Tester”. The conclusions derived from the results are summarized as follows :
(1) Orange peel defects are not produced as a result of the evaporative convection in a wet paint film. The defects are due to incomplete elimination of unevenness formed during spraying, which remains even after setting and baking.
(2) Orange peel defects can be reduced by finer atomization, which diminishes the initial amplitude of the sprayed film. The defects can also be minimized by increase of the film thickness, decrease of the film viscosity and horizontal posture of the painted surface, which suggests some contribution of gravity on the film leveling.
View full abstract