DESCRIPTION: The Environmental Protection Agency has issued rigid guidance to reduce, and ultimately eliminate chromium in aerospace protective coatings, with intent to protect the environment and workforce health.  The most effective flexible primer in use on aircraft throughout DoD is a high VOC, chromate polysulfide primer.  Standard epoxy and polyurethane primers provide protection of smaller aircraft, but significant flexure on large aircraft structures leads to coating cracks around the seams and fasteners.  These coating cracks expose the metallic substrates allowing penetration from water and other corrosion causing chemicals. The resulting corrosion damages both the aircraft’s skin and surrounding coating causing significant time and manpower to remove the corrosion, repair any damage, and reapply protective coatings.

A VOC compliant (350 g/L) chromium-free flexible primer will allow for more durable and longer lasting protection for the large aircraft which make up a significant portion of the Air Force fleet.  Further, such a primer would be the final piece in a completely chromium-free outer mold line coating system comprised of a surface pretreatment, flexible primer, and topcoat.  Proposed coatings must be free of chromium and cadmium, capable of enduring 60 percent elongation without cracking before and after 3000 hrs of Xenon-arc exposure, incorporate a proven non-chromate corrosion inhibitor, be compatible with standard Air Force coating equipment, and comply with relevant EPA and OSHA standards for aerospace coatings. The primer must also be combined with a suitable chromium-free pretreatment and top coat, and meet the requirements of MIL-PRF-32239A.
 

PHASE I: Develop at least one laboratory formulation for a high-flexibility, VOC compliant (350 g/L), chrome-free primer.  Demonstrate that the primer when teamed with a suitable non-chromate pretreatment and topcoat can pass the flexibility and dry time requirements of MIL-PRF-32239A, Type 1, Class 2, Grade 1.
 

PHASE II: Modify the best formulations from Phase I and demonstrate the primers when teamed with a suitable non-chromate pretreatment and topcoat can pass standard DoD corrosion tests (as described in MIL-PRF-32239A and MIL-PRF-23377) while still passing the requirements from Phase I.
 

PHASE III DUAL USE APPLICATIONS: Select the best coating systems from Phase II, mature the formulation, and demonstrate performance in a relevant environment.  Generate a five-gallon batch and deliver to the government for further testing.  Develop and deliver plans for scale-up and large-scale production.
 

REFERENCES:

1. MIL-PRF-32239A, Type 1, Class 2, Grade 1: Contains the requirements the coating system developed under this effort must meet in order to be used on DoD aircraft.
 

2. T.O. 1-1-8: A general series technical order that authorizes the use of the latest revision of MIL-PRF-32239.