An Investigation Of The Weathering Durability Of Aerospace Exterior Coating Systems

Exterior aerospace coating systems serve both a decorative and protective function, providing airline branding and differentiation while offering corrosion, fluid, and UV resistance.  The current generation of commercial aerospace polyurethane topcoats has an expected service life of approximately three to five years, limited primarily by color shift and loss of gloss.  In order to reduce the environmental impact and maintenance costs of stripping and repainting aircraft, the goal for the next generation of exterior aerospace coating systems is a service life of eight to ten years.   One approach towards achieving this goal is to replace conventional monocoat topcoat systems with basecoat/clearcoat systems, where the pigment is incorporated into the basecoat to provide color and hide while the clearcoat provides gloss, weathering protection, and chemical resistance.  The automotive industry has achieved significant enhancements in durability with basecoat/clearcoat technology; however, the service environment for aircraft differs from automotive in several important ways, including temperature and intensity of solar radiation.  In order to examine whether basecoat/clearcoat systems offer enhanced durability in aerospace environments, studies of accelerated artificial weathering, natural outdoor weathering, and in-service performance are being conducted.  After 4000 kJ (@350nm) of accelerated weathering in accordance with SAE J2527 using boro/boro filters, no significant differences were observed between white monocoats and white basecoat/clearcoat systems, as assessed with color and gloss measurements.  However, weathering to similar dosages by two other methods - 1) a new experimental accelerated protocol; and 2) natural exposure in Florida - both show enhanced durability for basecoat/clearcoats as compared with monocoats, without introducing any new failure modes such as interlayer delamination and cracking.  With respect to performance in service, data for first-generation basecoat/clearcoat systems are limited; however, clearcoats applied over monocoats show significant gloss retention up to at least seven years.