Pigment dispersion degree and its evolution in storage

The current size of individual particles in most pigments is usually below 1μm; this ensures powerful forces of attraction causing the particles to cling to one another forming aggregates. If pigment dispersion stability is not appropriate, particles join again and form flocculates. It is important to know the initial degree of dispersion, its evolution during coating storage and the influence on its dry film anticorrosive properties. Several anticorrosive coatings were formulated starting from an epoxy resin as binder, tin tannates as inhibitor and a red iron oxide‐micronised talc mixture as inert pigment. Variables studied were pigment dispersion time and coating ageing time in storage. The degree of dispersion was determined by optical photomicroscopy to establish the shape and size of associated particles present in the system. The flow properties of anticorrosive coatings due to the different dispersion degree were evaluated through rheological tests. Coating film behaviour was also assessed for several dispersion times and ageing periods in laboratory, employing a salt spray (fog) cabinet and a 100 per cent relative humidity chamber.