The Degradation Phenomenon of Coating Films in Weathering Test

Abstract

Several coating systems for outdoor structure (four different top coats) were subjected to outdoor exposure tests and accelerated weathering tests. The properties of the films were evaluated by surface appearance, gloss retention, SEM observation, and three-dimensional surface roughness measurement.
In addition to those, the adhesion strength of the films to a substrate and the dynamic contact angle on the topcoating surface were measured.
Correlations among those properties were obtained.
It was found that the top coatings became rough when the resins were decomposed by ultra-violet ray, which made the surface to retain more water. It was also found that the corrosive factor, such as water, oxygen, and chloride, penetrated undercoating from degraded top coating, which reduced the adhesivity and intercepting ability of the film.
As a conclusion, we assume that the topcoating that has poor weathering property affects anticorrosive property of the coating system.