Developments in raw materials Part 2: Protective pigments

For any paint or coating system performance in service is determined by the whole formulation, with each of the individual ingredients contributing either directly or by interaction to the overall balance of film properties. Within these constraints, paint formulators recognise that certain materials have a well defined role to play and in many instances a consideration of a coatings service requirements does largely dictate the initial approach to formulation. One such ‘key’ group of materials are the pigments added to anticorrosive paints to provide protection to metallic substrates under aggressive conditions of exposure. One group of these pigments inhibit corrosion by perturbing in one of a number of ways the chemical reactions that would otherwise occur on the substrate surface in the presence of water. Other types of protective pigments function by improving the barrier properties of the applied paint film so that water cannot readily permeate through and initiate corrosion reactions on the substrate. Pigments in this group typically have a flake‐like particle shape which enables a ‘leafing’ effect to be achieved within the liquid coating after application. The inhibitive types of pigment need to be in close proximity to the substrate to function properly, and accordingly these are normally placed in primer coats only. The flake pigments which reduce moisture permeation through the film are most effective if added in depth, and these are often added to severa or all of the coats comprising a system, or are included as the sole protective pigment in high‐build paints. Recent developments in both of these broad groups of inhibitive and flake pigments will be considered in this article.