Staining Behavior of an Anti-Graffiti Polyurethane Clear Coating against Accelerated Weathering Test
Apermanent anti-graffiti clear polyurethane coating, using a silicone additive, was prepared and studied. Various techniques, such as contact angle measurements and EDX were employed to characterize and investigate the surface properties of the coatings. The results revealed that with inclusion of silicon additive to clear coating, according to Wu method, surface free energy was decreased from 45.13 mJ/m2 for neat clear polyurethane film to 25.25 mJ/m2 in a coating containing 5% additive. With inclusion of higher mole percentage of additive, surface energies remained constant as revealed by EDX technique, which was considered to be due to the excessively covered surface by silicone additive. Ageing under UV radiation revealed that the inclusion of additive up to 5 mole percentage could improve the anti-graffiti property during the first few aging cycles. However, by increasing the number of aging cycles and higher concentration of silicone additive, the rate of degradation in coatings increased. The results showed that PU5% has the best anti-graffiti and ageing properties among other compositions.