Water-borne, silicone- based paints for protecting metal structures against corrosion have been developed as substitutes for traditional anticorrosion paints that contain large amounts of volatile organic solvents. It is desirable to reduce the volatile-organic-compound (VOC) contents of paints in order to reduce the associated pollution, toxicity, flammability, and problem of compliance with environmental regulations. The VOC contents of the present water-borne, silicone-based paints are less than 200 g/L. An additional desirable feature of these paints is that they can be applied without need for prior application of primers to ensure adhesion.
Paints of this type were formulated and tested for sprayability, dry-film adhesion, inhibition of corrosion, resistance to abrasion, flexibility, and resistance to weathering. Several formulations were found to continue to be effective in inhibiting corrosion on aluminum and stainless steel after 1,000 hours of corrosion exposure according to two American Society for Testing and Materials (ASTM) standard tests: ASTM B117 (a salt-spray test) and ASTM G85 (also known as the prohesion test — a test that involves cycles of alternate drying and spraying with a sulfate-rich solution).
In these tests, the water-borne, silicone-based paints performed as well as did flexible solvent-borne paints. The waterborne, silicone-based paints were found to be stable in that they exhibited shelf lives of more than one year. The drying time for these paints at ambient temperature is typically less than one hour. Coating films derived from optimized formulations of the water-borne, silicone-based paints were found to be flexible at temperatures down to –60 °C, to resist simulated outdoor weathering, and to protect metals against attack by acids. The best results were obtained with acryliclatex/silicone emulsion blends formulated with low-toxicity corrosion inhibitors and extender pigments.
This work was done by Francis L. Keohan, Marcela Samsel, Melissa Perkins, Murty Bhamidipati, and Michael Goodwin of Cape Cod Research, Inc., for Kennedy Space Center. For further information, contact the Kennedy Commercial Technology Office at 321-867-8130.