In-depth study of drying solvent-borne alkyd coatings in presence of Mn- and Fe- based catalysts as cobalt alternatives

Abstract

As a result of potential reclassification of cobalt-based alkyd driers, many studies have been conducted to find suitable alternatives as primary driers in alkyd paints. Some commercial replacements are currently available. A systematic investigation on the oxidative drying of solventborne alkyd coatings with commercial cobalt-free driers has been performed, a cobalt-based drier as a reference and an iron-based drier and two manganese-based driers. This work investigates how these driers influence the molecular network development and mechanical properties of the final films from the moment of application to full drying. High spatial resolution NMR profiling allows tracing the depth-resolved crosslinking during drying, and is used for the first time in conjunction with time-resolved ATR-FTIR and standard methods like the Beck-Koller (BK) drying test, König hardness and DMA. Based on the results from these different techniques, we found correlations between the drying pattern of driers and properties such as the drying rate, the overall and depth-resolved crosslink density and hardness development. This study shows that front drying works best to obtain densely crosslinked hard films. In the case of demanding a fast drying, a drier promoting homogeneous drying without an induction period is preferred, still resulting in a film with a reasonable crosslink density and hardness.