In the Phase I study of Zero Volatile Organic Compounds (VOC) Aircraft Coatings (Contract Number FA8650-07-M-5029), the feasibility to formulate environmentally safe, high performance, dual-cure (UV cure followed by air dry) urethane gloss topcoat as well as conventional fast dry two-component chromate-free epoxy primer, was demonstrated by preliminary results. The 100% solids non-chromate primer was based on liquid epoxies and aliphatic amine hardeners. A solvent-free hyper-dispersant was used to reduce the application viscosity. Non-chromate corrosion inhibitor packages were employed in the formulas. These two-component epoxy primer candidates had a maximum of 30 Ford #4 Cup viscosity under the ambient temperature. These application viscosities are very similar to that of the widely used MIL-PRF-23377J primers. These new non-chromate primers have quick dry characteristics and a 2h pot life. The primer films passed a 20% G.E. elongation. Also, a 100% solids, UV curable, urethane and polyester acrylates, gloss white topcoat was investigated. To reduce the film shrinkage during UV curing, a dual cure system was chosen. The current proto-type UV cure, two-component urethane systems are based on reactive diluents, low viscosity polyester acrylates and hydroxy functional urethane acrylates, and isocyanate prepolymers. Photo-initiators for surface cure and through-cure are incorporated in the formulas. These systems can be cured by UV radiation followed by ambient temperature cure or the reverse. A sprayable white topcoat with 60o gloss of 85 units can be formulated. These topcoats have good intercoat adhesion over the above mentioned 100% solids epoxy primers.
Keywords: Zero Voc, Chromate-Free, Dual Cure Topcoat, Epoxy Primer, Urethane Topcoat
