Aerospace primers with the ability to accommodate flexing and vibrations of aircraft are widely used for corrosion resistance, especially on large aircraft, and leading edge protection. Historically, high flexibility polysulfide primer systems with chromated corrosion inhibitors have provided this protection, but increasingly stringent air quality regulations and a desire to eliminate chrome as a corrosion inhibitor are driving a search for new flexible primers.Â
Luna is developing a new class of VOC compliant, chrome-free, corrosion resistant primers to meet the dual needs of environmental acceptability and high flexibility. To provide this advanced performance, Luna is utilizing a novel coating binder system based on glycidyl carbamate (GC) resin technology. The GC model provides epoxy type reactivity, pot life, and adhesion combined with flexibility, weathering, and chemical resistance typical of polyurethane systems, making them excellent candidates for the preparation of highly flexible, low VOC coatings systems.Â
The Luna primer is a two component, epoxy functional coating system that can be mixed and applied with conventional equipment. The coating is brushable out of the container, or can be thinned with Oxsol 100 for spray application. With either application process, the coating is ready for recoat within five hours.
Through internal and third party testing, Luna is evaluating the performance of the flexible aerospace primer, and initial results indicate that it meets many of the MIL-PRF-32239 performance criteria.
 Key advantages of Luna’s flexible primer include:
- Environmentally Acceptable – Luna’s flexible primer uses a non-chrome inhibitor package
- Flexibility – The novel GC resin chemistry of the coating binder system provides 40% flexibility without the use of polysulfides or polythioethers
- Low Temperature Flexibility – The coating performs well over a range of temperatures, meeting low temperature flexibility requirements
- Heat Resistance – The Luna primer passes heat resistance testing (1†mandrel bend after four hours exposure) at both 121 °C (250 °F) and 177 °C (350 °F)
- Adhesion – After water immersion, the Luna primer retained a passing 5A rating on X-scribe adhesion, equivalent to COTS aerospace primers
- Corrosion Resistance – In testing at Luna, the flexible primer demonstrates comparable corrosion resistance to COTS non-chrome aerospace primersÂ
Luna has successfully demonstrated the feasibility of formulating a non-chrome flexible primer using novel coating binder technology. This approach has a number of advantages which can benefit many aerospace applications. Luna continues the development and optimization of the coating system and expects to scale up the binder and coating formulation for large scale demonstration and validation testing in the future.
This material is based on work supported by the United States Air Force, specifically the Air Force Office of Scientific Research, under Contract No. FA9550-09-C-0150. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the United States Air Force.
