The Influence of Pigment Concentration, Particle Size Distribution, and Aspect Ratio, PaperCon 2016

Paper coating colors are non-Newtonian suspensions that are subjected to high shear rates during blade coating applications. The rheological behavior has been linked as a potential cause of runnability issues. There are several important factors that control the rheology of a suspension such as size distribution, aspect ratio, solids content, and other additives. However, there has not been a clear understanding of the interaction of these factors on the rheology given in the literature.

Particle size analysis on five different pigments with a range of aspect ratios was completed using two different techniques. A new parameter, ω, was devised using the results from the particle size analysis data which was used to characterize the pigments. The maximum packing fraction for each of the pigments were determined by two different methods. The rheology was also examined for the pigments in the shear rate range of 2,000 to 23,000 s-1. Three viscosity-volume fraction equations were fit to the experimental data. The maximum packing fraction that fit the experimental results was different than the measured values. An analysis of the maximum packing fraction and the intrinsic viscosity was completed to demonstrate the dependence on shape factor, α, or the new parameter, ω. New expressions were developed to estimate the viscosity at 10,000 s-1 based upon the Krieger-Dougherty equation using the volume fraction, centrifuged packing fraction and either α or ω.  

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