Cobalt based driers are the most commonly used primary catalysts in alkyd coatings as they promote fast drying and lead to hard coatings. However, several studies have suggested potential reclassification of cobalt-based alkyd driers. Therefore, cobalt based driers are being replaced by alternatives, e.g. based on iron or manganese. In practice primary driers (Co, Mn, or Fe) are used in combination with secondary driers (e.g. Ca, Zr) to enhance drying of the film. Coating formulators aim for a high drying speed and hardness development. However, each combination of primary and secondary driers leads to a different oxidative drying pattern resulting in variations in the crosslink density and hardness development. In this study we have systematically investigated the effect of two secondary driers, Calcium (Ca) and Zirconium (Zr), on curing behavior when added to different primary driers (Co, Mn, and Fe) using a high spatial resolution NMR set-up. As expected, we observed increased drying speed and higher crosslink densities when adding these secondary driers. While calcium showed to promote the front speed, zirconium showed to increase the measured crosslink density. The behavior seems to be generic as this was seen for all three the primary driers.
Volume 121, 14 July 2017, Pages 262–273