A comparison of two cellulosic thickeners in coating colors at different temperatures: flow behavior and coating performance

The water-soluble polymer (i.e. the thickener) is a vital component of a co ating color and is mainly used to control the flow behavior and the water r etention of the color. Variations in these properties may be reflected in t he quality of the final dry coating layer. A crucial factor influencing coa ting color flow and dewatering is the temperature. In this study, the influ ence of coating color temperature on the rheological properties and on the pilot coating performance of offset-grade coating colors was evaluated. Two types of cellulosic thickener, carboxymethyl cellulose (CMC) and ethyl hyd roxyethyl cellulose (EHEC), were compared at two suspension temperatures (2 3 degreesC and 43 degreesC). In addition, the coating color formulations we re varied with respect to the type of styrene-butadiene latex (T-g 10 degre esC and 22 degreesC) and the solids content (65 and 61 weight-%). In all co lors, the amount of thickener was adjusted to give a Brookfield viscosity o f 1000 mPas. Coating at 43 degreesC gave a higher surface roughness accompa nied by a lower gloss. When the CMC was replaced by EHEC, static dewatering decreased, but the high-shear viscosity increased, as did the blade load d uring coating. Lower toughness and higher gloss were obtained using EHEC.