Chemical resistance of waterborne epoxy/amine coatings

Waterborne epoxy/amine coatings, compared to solvent-based, show considerably lower chemical resistance. This fact is often blamed on hydrophilic emulsifiers or crosslinking agents remaining inside the coating after curing. To judge this assertion, the influence of surfactants and hardeners, as well as various other parameters were investigated. Surfactants appear just to influence the solvent resistance slightly. The main responsibility for the poor resistance to other chemicals – especially acids – lies with unreacted amine curing agents and/or water trapped inside the coating, and, most important, an inhomogeneous film structure due to insufficient coalescence during the curing process. Incremental improvements are possible by using excess epoxy, increasing the film thickness, or curing at elevated temperatures. The latter forces water out of the coating, drives the epoxy/amine reaction to completion, and also somewhat improves the coalescence. However, the resistance can still not be enhanced to the level of a solvent-based system. But although there seem to be inherent limitations to the chemical resistance of waterborne epoxy systems, for many practical applications it is adequate.