Associative Thickeners for Viscosity Retention upon Tinting
Rheology is an important topic in waterborne paints. Compared to solventborne paints, there is a greater variation of thickeners like cellulose ethers, acrylates, bentonite clays or the group of associative thickeners. In high-quality waterborne paints the associative thickeners are gaining an important role relative to the other thickeners. This is due to their unique benefits that lead to better leveling, better brush drag and reduced spatter in wet application. They also impart better water resistance to the dried paint film. These properties are achieved due to their general chemical structure.
Associative thickeners are polymers that are based on water-soluble polymers. These can be acrylate polymers, cellulose ethers or, for the top-quality nonionic products, polyethyleneglycol. These are capped with water-insoluble hydrophobic groups like fatty alcohols, for example. In water solution or in emulsion, these polymers form a network that increases the viscosity. The water-soluble backbone polymer is dissolved in water. The hydrophobic caps are adsorbed onto the hydrophobic emulsion polymer particles, or they form micelle structures with hydrophobes from other polymers. As each associative thickener polymer contains at least two hydrophobic caps, the result is a three-dimensional network within the emulsion. This increases the viscosity. Mainly the high- and mid-shear viscosity are affected. Therefore, it improves antispatter and brush drag more than all other thickeners. (Figure 1)