Flexible, Low VOC, Chrome-Free Primer for Large Aircraft

Large aircraft present a particular challenge to corrosion preventative coatings due to amplified levels of stress from vibrations, cabin pressurization, and wing flexure.  Historically, corrosion prevention on large aircraft has relied on highly flexible polysulfide binder systems to prevent cracking around seams and fasteners and mitigate corrosion with chromated corrosion inhibitors.  With new regulations, the best performing polysulfide primers (e.g. PR-1432-GP) are no longer VOC compliant.  A new, reformulated version, PR-1432-GV, is VOC compliant, but is formulated with chromate corrosion inhibitors, which are coming under increased scrutiny due to their toxicity.

To meet the need for a large aircraft primer that is highly flexible, low VOC, and chrome-free, Luna Innovations Incorporated is developing a primer that is formulated with an innovative binder system that quickly cures with flexible crosslinkers at compliant levels of volatile organic compounds.  Luna’s flexible primer is a two component (2K) epoxy functional formulation with low viscosity (30 sec max Ford #4) for ease of spray application that is highly reactive to provide rapid film development.  Cure times meet the 5-hour recoat and 2-week ambient cure constraints per requirements in MIL-PRF-32239 for a Type 2, Class 2, Grade 1 primer.  Luna’s primer is suitable to protect various pretreated aluminum alloy substrates, and exhibits good intercoat adhesion to fielded topcoats, such as Desothane HS CA-9311 and Defthane APC ELT.  Initial performance results of Luna’s fully formulated primer indicate good elongation (40% elongation when tested by GE reverse impact), adhesion, fluid resistance, and corrosion resistance.  A full range of performance metrics will be addressed.