SELF-healing coatings

Abstract

The efficacy of a "self-healing" corrosion protection coating system for use on steel enclosures for outdoor equipment has been investigated. Urea formaldehyde microcapsules (60-150 microns in diameter) that contained several types of film forming compounds (healants) and corrosion inhibitors were mixed into commercially available coatings systems. Laboratory tests showed that when the coating system was damaged by abrasion, the microcapsules broke open and released their film forming and corrosion inhibiting compounds, thus initiating the self-healing process, in which the damaged area of the coating is covered and repaired, and corrosion of the substrate is inhibited. Steel substrates coated with these self-healing systems were scribed and laboratory tested according to ASTM D 5894, in which the specimens are alternately subjected to salt spray and ultraviolet exposure. The coated test specimens were evaluated with respect to undercutting at the scribe in accordance with ASTM D 1654. The undercutting was reduced from 2.12 mm to 0.46 mm at the scribe by using microcapsules containing phenolic vamish, a long chain polyester diluent, a second carrier/diluent based on high molecular weight hydrocarbons and a corrosion inhibitor. Electrochemical impedance spectroscopy (EIS) tests showed that the incorporation of self-healing microcapsules resulted in significantly higher impedances for exposed coatings than for similar coatings containing no microcapsules.