Since the early days of epoxy chemistry, the standard primer based on a “1-type” solid epoxy resin combined with a polyamidoamine has dominated the field of corrosion protection. Besides the excellent corrosion protection properties, several other attributes have led to the success of this type of system:
These systems, however, require an induction period, a period of time that allows the epoxy and curing agent (binder) to react to some degree before the coating is applied. This increases the compatibility of the binder components and results in improved performance of the coating. The need for an induction period can be reduced or eliminated by modification of the hardener (e.g., adducts).
From a performance point of view, there are few reasons to change this system. The main drivers for new development today are legal or environmental aspects. Solvents are a major contributor to formation of ground-level ozone (“smog”), an air pollutant partially responsible for environmental and health problems.(1) Unfortunately, this 1-type/polyamidoamine system requires a substantial amount of solvent to be applied (approximately 50% v/v for spray application). The EPA, California’s South Coast Air Quality Management District (SCAQMD) and many European countries have established solvent reduction programs forcing formulators and applicators to reduce the amount of VOC in their coatings. Private companies and industry groups have also agreed to reduce their VOC output respectively, and set limits for their product lines by evaluating alternative environmentally friendly technologies such as: waterborne, high-solids, solvent-free and powder coatings.
Everyone agrees that less VOC is better for the environment. However, there are often technical reasons why this seemingly simple goal can be very difficult, if not unlikely, to achieve. This paper presents a low-VOC, waterborne, anticorrosive primer for heavy-duty corrosion protection.