2002 Volume 75 Issue 5 Pages 209-213
A new treatment for a rapid weatherability test method for coatings has been studied. Nine alkyd-melamine coatings films containing TiO2 pigment were subjected to UV irradiation of 97 W/m2 (300-400 nm) in aqueous solutions of 3.0-wt% hydrogen peroxide, 5.0-wt% sodium hypochlorite and 1.0-wt% sodium peroxocarbonate for 50 h at 40°C, and gloss and surface morphology were examined. Four coatings were formulated from different resins with a TiO2 pigment, the other five coatings were formulated from different organic pigments with a TiO2 pigment and a resin. These films were also outdoor-weathered in Okinawa for 2 years.
Gloss was decreased with treatment time. SEM observation showed that the gloss loss resulted from formation of small pits by resin loss around TiO2 pigment. The same results were obtained in all cases of oxidizing agents and coatings. The formation of pits is observed in every outdoor-weathered coatings film. Thus our treatment is a rapid method to reproduce outdoor degradation. The resin loss around TiO2 pigment is supposed to be caused by photocatalytic oxidation enhanced by oxidizing agents.
