“Fluoro-Fab: Accelerating UV Testing to Keep Colours True”
At A&I coatings, we use ASTM G154 as the standard for analyzing our high durability fluoropolymer topcoats, accelerating the degradation process by using the fluorescent ultraviolet lamps UVB-313 in an 8-hour exposure, 4 hours condensation cycle at 40 oC. The procedure is not intended to mimic natural sunlight exposure, but to use the harsher UV wavelengths to accelerate the degradation process. This allows for fast comparative testing of topcoats designed for outdoor exposure.
In the photos below, we are comparing the standard pigmented fluoropolymer (left, panel #1) with the pigmented fluoropolymer having an additional clear fluoropolymer topcoat (right, panel #2). The panels were exposed to over 10,000 hours of the 8-hour UVB-313, 4 hours condensation cycle and show that although they have similar gloss level reduction, the colour change (DE) is higher in the left panel #1. This result has given us insight into how the clear topcoat can improve the overall colour stability of the fluoropolymer when exposed to harsh UV wavelengths over time.
A&I Coatings has found that 4,000 hours of QUV-B testing provides a reasonable
correlation to approximately 20 years of Australian UV exposure, with 10,000
hours representing an estimated 50 years, noting that this is based on
accelerated testing conditions rather than direct equivalence to natural sunlight.
These results demonstrate that the coating is able to maintain its original
appearance more effectively over time, with improved colour stability and long-
term performance under harsh UV exposure.
The UVB-313 lamps are very useful when comparing UV resistance of resins, pigment bases, inorganic fillers, or even catalyst loading. An average year estimate could be useful and give viewers a better gauge of what 10,000 hours in the QUVB represents, we just need to make sure that it is stated that the wavelength distribution and irradiance of UVB-313 are not directly comparable to natural sunlight. See ASTM 154 Image below of spectral power Distributions of UVB Lamps & Sunlight. See ASTM 154 Image below of spectral power Distributions of UVB Lamps & Sunlight:
For more information or technical questions on high performance polyurethanes and fluoropolymers, please call us on 1800 727 865 or email helpdesk@aicoatings.com.
