High-Performance, Cost-Effective Rheology Modifiers for the Coatings Industry
Formulators of waterborne coatings, whether architectural or industrial, face many hurdles as they try to comply with environmental concerns and maintain high performance.
One class of chemical additives that plays a key role in the development of high-performance coatings is rheology modifiers. Rheology modifiers are essential for application properties, as well as to enhance storage and stability. They can affect processing, color performance and how customers perceive the quality of the paint. Rheology modifiers can thicken or alter the rheology of a coating in a number of ways. Associative and associated thickening mechanisms are the primary ways in which coatings obtain a rheological profile.
The associative mechanism is quite familiar and is caused predominately by hydrophobic portions of thickener molecules interacting and bonding with the surface of latex particles. These interactions are further influenced by surfactants, coalescing solvents and pigments, but are primarily driven by the thickener-latex polymer particle interaction. Advantages of this mechanism include higher viscosity under high-shear regimes such as roller, brush and spray application leading to good film build and low spatter. The disadvantages are that certain associative thickeners such as hydrophobically modified ethoxylate urethanes (HEUR) are not always the most cost-effective method of thickening paint. The thickening efficiency of HEURs is directly related to the amount of latex available for association. Therefore, high-PVC coatings, such as flat and satin types, generally use a different mechanism for thickening. Earlier types of polyurethane (HEUR) rheology modifiers have been known to cause color development problems. Newer generation HEUR rheology modifiers are more compatible with colorants, and viscosity change is minimized.