The impact of rheological modifiers on water-borne coatings

While low volatile organic components (VOC) architectural coatings like interior wall or exterior façade paints are accepted to a large extent by the end-users, conventional solvent based alkyds are dominating in the area of high performance laquers. The lower acceptance of water-borne coatings corresponds to aesthetic problems like lower gloss, poorer flow and leveling as well as application disadvantages like shorter open-time, lower brush drag and limited weather conditions. To solve these problems it is mandatory to understand dispersions rheology and the different ways to adjust rheological properties of water-borne paints and laquers by special modifiers. In this paper a short review is given about the thickening mechanisms of three main groups of rheological modifiers (cellulose ethers HEC and HMHEC, acrylics ASE and HASE, and urethanes HEUR) in the presence of an acrylic and a polyurethane dispersion. Furthermore measurements on two model coatings are presented. These results allow a discussion about several factors which influence the coatings rheology and performance.