Cobalt (Co) soaps, or more accurately, cobalt carboxylates, is the collective description for a range of partially soluble compounds formed by cobalt in combination with a range of organic acids. These typically have a carbon chain with between 8 and 10 carbon atoms; the most common being ethylhexanoate (C8), isononanoate (C9) and neodecanoate (C10) or, in selected applications, natural naphthenates.
These substances are used as a primary drier or siccative in alkyd resin-based paints that make up about 40% of the market and are used widely for both decorative and functional end uses. An example of a typical linseed oil-based alkyd resin is given in Figure 1. The coatings sector today is well versed in the regulatory issue that cobalt has come to present. Working in close co-operation with paint makers, research and development groups have found some solutions, and a number of paint makers already make claim to being “cobalt-free,” but how did we get there, where are we now and how do these developments inform the next step?