Alternatives to cobalt dryers for paints
Cobalt organic salts are very good driers for paints but increasing concern about the hazard of cobalt compounds is arising, in general, made producers look for alternatives. Manganese driers currently represent the main alternative to cobalt, with their high drying power, although lower than that of cobalt. Their main disadvantage is the brown discoloration and yellowing of white and light-colour paints.
Manganese gives a longer drying time but better film hardness compared to cobalt based driers. An alternative example could be the manganese bis(2-ethylhexanoate) which can substitute naphthenic acids, cobalt salts (cobalt naphthenate) as drier. Similar salts (octoates/ ethyl hexanoates, naphthenates) of metals like iron or vanadium can also be used as alternatives. Additionally, driers can be used with low-chain aliphatic esters of oleic and linoleic acid (not classified as toxic or as VOCs) instead of usual aliphatic or aromatic solvents.