Performance Comparison of Modified MIL-PRF-85285 Topcoats

Paint and de-paint operations account for a large portion of the hazardous waste produced by DoD aviation, and de-painting/repainting operations are often performed because of visible changes in the color, gloss, or chalking of the topcoat after weathering due to environmental exposures.  The current topcoat for the majority of military aerospace applications is MIL-PRF-85285, a polyurethane high-solids formulation.  The products qualified to MIL-PRF-85285 are tested for initial gloss and color, and tested for color change after 500 hours in Xenon-Arc accelerated weathering exposure.  Newer, modified topcoats have been indicated in DoD and industry testing to have better weatherability and cleanability than legacy products qualified to the MIL-PRF-85285 specification.  However, no requirements or performance criteria existed to determine ‘advanced performance’ per MIL-PRF-85285.  Based on these claims, the modified topcoats (advanced performance topcoats – APC’s) were assessed head to head against traditional coatings formulations. A polyurethane chemical agent resistant coating (CARC) qualified to MIL-DTL-64159 was also included in the testing for reference. This effort examined polyurethane topcoats for corrosion, humidity, weatherability, cleanability, and adhesion properties.  These evaluations were conducted with both flat gray and high-gloss white colors applied over high-solids and water-reducible primers, in both chromated and non-chromated pigments.  The cost of the modified coatings is approximately 20-30% greater than more traditional formulations, and it was necessary to determine any benefits to the use of the modified topcoats.  Results indicate that improved weathering resistance is achieved with certain modified formulations, and quantifiable testing requirements were established for specification validation testing.