A New Approach to Understanding Rheological Additives
With spray application, an optimum compromise has to be found between good vertical flow characteristics (to achieve an adequate film thickness) and good leveling (to obtain a smooth finish). For this reason, in the low-shear range, the viscosity must be set just high enough to prevent vertical flow. At the same time, the viscosity should be kept as low as possible to ensure good leveling. Inappropriate rheological control might be the reason for building curtains or runners that will strongly impact the quality of the resulting surface coating (Figures 2a and 2b).
Adequate effectiveness of modern thickeners is not only extremely important in the field of emulsion paints, but it also plays a major role in industrial coating systems. Unlike emulsion paints, which are usually applied by brush or roller, industrial coatings are normally applied by spraying or dipping. With spray application, an optimum compromise has to be found between good vertical flow characteristics and good leveling. It is logical that in such cases, use is frequently made of an associative thickener that has more of a pseudoplastic rheology profile. In parallel with this, however, it must have a certain efficacy in the high-shear range in order to ensure satisfactory spray application.