Progress in the development of cobalt-free drier systems

Driers are used in air-drying coating systems to catalyze the polymerization process. Cobalt-carboxylates are the most widely used driers. However, cobalt compounds may indirectly be implicated as carcinogen suspects as a result of studies in the U.S.A. in the national toxicology program using cobalt sulphate heptahydrate. Hence, Germany is no longer granting the Blue Angel award to cobalt-containing paints. Other transition metal carboxylates such as based on manganese or iron show much lower catalytic effects and cannot equalize cobalt as a catalyst in autoxidation polymerization reactions. The effect of various organic chelating ligands on the catalytic properties of manganese in autoxidation processes was investigated experimentally in air-drying paints. The activity of manganese is strongly effected by organic ligands. New manganese based coordination compounds enable the formulation of Co-free air-drying paints, which show good drying performances and improved color retention.