Self-healing coatings are made by incorporating microcapsules (60 - 150 microns in diameter) that contain film-formers and corrosion inhibitors into the paint primers at the time of coating application. When coating is scratched, the microcapsules break and spill their corrosion inhibitors and film formers, which protect the underlying steel substrates from corrosion, and repair some of the coating damage. Five (5) different types of inhibitors/film formers were tested, and three (3) different techniques for application of the coatings with microcapsules were evaluated. Accelerated testing of the self-healing coatings on steel was conducted by scribing and subjecting them to ASTM D-5894 testing in the laboratory to simulate the environmental effects of salt spray and ultraviolet exposure, in conjunction with electrochemical impedance spectroscopy (EIS). The effect on coating adhesion resulting from adding the microcapsules was also ascertained. Changes in EIS parameters were determined at the end of each week of ASTM D-5894 exposure. EIS results were correlated with undercutting at the scribe. Growth of coating damage at the scribe was arrested in self-healing coatings with all microcapsule formulations compared to control samples. The performance of some microcapsules evaluated in this study was found to be dependent on the method of application.
Keywords: corrosion, coatings, microcapsules, self-healing, ASTM D 5894, electrochemical impedance spectroscopy (EIS)