Dispersant Technology for Red and Yellow Iron Oxides

摘要

Pigment concentrates have always been a modern and flexible way to produce colored paints. Especially in waterborne applications. these concentrates have to be suitable for a broad range of different binder technologies. Because of that, the concentrate formulations are usually free of binders and offer a broad compatibility. Furthermore, the demands in terms of storage stability, color strength and cost efficiency are very high. These demands are addressed directly to the additive technology. The additive is expected to provide outstanding viscosity reduction in order to achieve high pigment loadings and the most economic grind. It has to stabilize the viscosity over long periods of time and has to develop maximum color strength to avoid underutilizing any expensive pigments. Iron oxides are the most important pigment class when it comes to decorative coatings. The difficulty in iron oxides lies in the shape and not the wetting of the pigment. Iron oxide yellow tends to give dilatant rheology, which can be a disaster when automatically dosing in a dispensing machine. On the other hand, iron oxide red tends to increase in viscosity over time in pigment concentrates. This article explains the different structures of wetting and dispersing additives that could be used in waterborne, binder-free pigment concentrates for iron oxides. The stability and wetting of the pigment concentrates will be reflected by the viscosity reduction, storage stability and coloristic properties. The zeta potential is used for characterizing the wetting behavior and dispersing efficiency. Guidelines for formulating iron oxide pigments will be provided at the end.