Various environmental factors (temperature, humidity, light/salt exposure, etc.) act in complex ways to degrade the corrosion protection performance of coating films. However, it is difficult to evaluate the individual and combined effects of all these factors. On the other hand, corrosion protection performance has a strong correlation with the impedance of coating films, which corresponds to the resistance to the flow of electrical charges in the coating. Therefore, the effects of light irradiation on the penetration behavior of moisture and salt into the coating films were investigated. As a result, it was found that material changes due to light irradiation accelerated the penetration of water and/or salt, thus decreasing the impedance. When water and/or salt penetrated into the coating films, a peak in the DRT (Distribution of Relaxation Times) spectrum was observed at relaxation times less than 10−1 s.
Horie et al. (Tue,) studied this question.