Nest generation of aircraft coatings systems

The current generation of aircraft coatings had its basis in the polymer te chnologies of the 1970s and the use of chromate-based metal pretreatments a nd primers. There have been some incremental improvements in the epoxy and polyamide oligomers used in the primers as well as the isocyanates and flex ible polyols used in topcoats, plus increases in the volume solids of the c oatings to continue minimally meeting environmental requirements, but no tr uly new technologies have been developed and applied to aircraft coatings s ince that time. However, because of increasing economic and environmental p ressures, this situation will soon change. Also, the U.S. Air Force is seek ing a coating system that will have an ultimate lifetime of 30 years for ma intenance cost control and fleet sustainability. The first change in the pr esent coatings system will be in the pretreatments plus primers that curren tly constitute the metal protection system for the high strength Al alloys used for aircraft. For military aircraft, these alloys will continue to be Al 2024 T-3 and Al 7075-T6, heat-treated metals that have phase-separated r egions rich in reactive metals such as Cu, Mg, and Zn, There are several ne w technologies now under consideration for such metal protection including conductive polymers as primers without Cr-based metal pretreatments, sol-ge l based pretreatments and primers, plasma polymer metal pretreatments, and organo-modified aluminum oxide particles. Each of these technologies has sh own some promise for Cr replacement, but each presently has a weakness that needs to be corrected for immediate usage. For the topcoat system, fluorin ated polyols and improved use of UV-absorbers and light stabilizers will pr obably be the first changes implemented, with ceramer and other new crossli nking systems the most likely next polymer matrix candidates. The target fo r the entire coatings system is to have drastically improved wet-adhesion d ue to a covalently bonded system that has a gradient in composition that go es continuously from metal to metal oxide to mixed metal oxide/organic poly mer to high-performance UV-stable organic polymer. The materials cost for s uch a system may be quite high, but the maintenance cost savings will much more than offset these costs.