Rheology Modifiers for Improved Applied Hide and Smooth Finish in Low-VOC Emulsion Paints

By Anne Koller, Pol Storme

One of the needs of the decorative paints market is the achievement of maximum hiding—the opacity that the end user perceives—with a minimum of paint coats. There are several tools designed to maximize hiding, such as the use of polymeric opacifiers* and pre-composite polymers,† which adsorb onto titanium dioxide (TiO2) to optimize its efficiency.

Hydrophobically modified ethoxylate urethanes (HEURS) and hydrophobically modified alkali swellable emulsions (HASE) rheology modifiers have also been developed to improve flow and leveling and therefore improve applied hiding. These rheology modifiers are efficient from low to high shear rate viscosity. The applied hiding of a paint is represented by the equation in Figure 1. It is the sum of intrinsic opacity brought by the level of TiO2 and the polymeric technologies plus the paint thickness that is controlled by rheology.

To this equation, one must subtract the negative effect due to lack of leveling, which creates low spots in the dry paint film, leading to low opacity. Newly developed rheology modifiers** were designed to maximize paint leveling and surface smoothness and improve applied hiding.