INTERFACE-ENGINEERED PARYLENE-C COATING FOR CORROSION PROTECTION OF COLD-ROLLED STEEL

Vacuum-deposited poly(chloro-p-xylylene), or parylene C, can be used f or corrosion protection of cold-rolled steel (CRS) through interface e ngineering. Interface engineering replaces galvanizing, zinc phosphati ng, and cathodic electrocoating (E-coating). Parylene C polymer has ex cellent bulk properties, including its moisture barrier, toughness, an d electrical insulation characteristics, but Its poor adhesion to most smooth or nonporous substrates has restricted its application Parylen e C coating applied directly to a CRS surface does not provide corrosi on protection because there is no adhesion between the film and the su bstrate. It was shown that adhesion could be improved to the extent pa rylene-coated CRS panels performed as good as, if not better than a co ntrol (E-coat/zinc phosphate/electrogalvanized steel [EGS]) under cond itions of a commercial scab corrosion test. Improvement was achieved b y placing an interlayer of plasma polymer to provide interfacial bondi ng to the CRS surface and the parylene C film. The interface engineeri ng involved in-situ consecutive vacuum processes consisting of: the re moval of oxides by (argon + hydrogen) plasma, the direct current (DC) cathodic plasma polymerization of trimethylsilane (TMS), the in-situ c athodic polymerizatlon of methane on the plasma polymer of TMS (in the parylene reactor), and the deposition of parylene C.