Some military aircraft and shipboard surfaces, such as radomes, antennas, gun shields, wing leading edges, and helicopter blade leading edges are coated with a specialized erosion-resistant protective coating possessing strict performance requirements such as those specified in SAE AMS-C-83231A. Current specialized protective coatings typically contain up to 800 grams per liter of VOCs and high levels of HAPs such as xylene, toluene and methylisobutylketone (MIBK). These multi-component coatings are cured by chemical reaction, and once mixed, any excess materials must be disposed of as hazardous waste. In addition, many of these coatings contain isocyanates, which are hazardous and may be prohibited for use in the near future under the Prohibited and Controlled Chemical List (PCCL). There are currently no environmentally benign wear resistant coating alternatives that can meet performance requirements.
In addition to the environmental burden posed by these protective coatings, their use presents a significant production burden associated with application and cure times. The relatively thick coating required to ensure adequate performance means that multiple spray passes are made to achieve the final dry film thickness. With the relatively high solvent content of the coatings, a significant flash-off time is required between coating passes. As a result, the current coatings can take up to 12 hours to properly apply and 5 to 7 days to cure completely. Under less than ideal conditions, such as low humidity or temperatures, these cure times can increase significantly. These long cure times contribute to excessive backlogs in production and reduced availability to warfighters.
Thousands of gallons of these specialized coatings are used annually in the maintenance and repair of DoD weapon systems resulting in large cumulative releases of VOCs and HAPs. For example, Ogden Air Logistics Complex processes approximately 96 F-16 radomes a year, Warner Robins Air Logistics Complex reported processing up to 360 F-15 radomes and 240 C-130 radomes per year and Oklahoma City Air Logistics Complex processes approximately 100 KC-135 radomes and 24 B-52 radomes per year. Additionally, U.S. Navy aircraft such as the P-8A have over 100 radomes or antennas on the exterior of the aircraft that require periodic recoating.