Rheological Measurement Techniques for Coating Colors, with Reference to Runnability, 1997 Advanced Coating Fundamentals Symposium Proceedings

Engelhard Corporation

The ability to predict runnability of coating colors on a coater by making quick laboratory measurements has always presented a challenge to researchers in the paper coating industry. Rheology is the most logical and explored route. The necessary rheological measurements are not straightforward and high solids coating colors are rheologically complex.

Three kaolin-latex-CMC based coating colors were made down and various rheological functions were measured, in an effort that spanned ten laboratories, in four countries, over two continents!

The runnability of these three coating colors were then assessed on a Cylindrical Laboratory Coater™, runnability being defined as the minimum coating speed at which wet streaks begin to appear on the coated sheet. The rheological measurements were analyzed to determine which of these correlated with the trend observed as for runnability.

Several “low” shear rate measurements, such as the stress growth function and the stress relaxation function were found to correlate, as did results from the Mini-Blade viscometer in the “high’ shear rate regimes.