High Shear Rheology Calibration Procedures for Aqueous Latex Anilox Evacuation
Calibrating capillary rheometers with Bagley and Mooney corrections ensures precise aqueous latex transfer from anilox cells, preventing spatters and excess coat weight.
Dilatancy
Rheological Shear
Fluid mechanics under high mechanical stress governs how coating suspensions behave during high-speed blade application. Dilatancy describes the distinct hydrodynamic phenomenon where apparent viscosity increases under intense shear rates because suspended mineral particles pack tightly and lose their lubricating liquid film. Modern paper mills monitor this rheological shift closely during pigment coating preparation to prevent high shear equipment jamming.
Formulators adjust dispersant levels and binder ratios to control shear thickening behavior before the mixture reaches the high-speed coating head. High-speed curtain coaters and blade applicators demand stable low viscosity profiles at the application nip to avoid catastrophic coating streaks and web breaks.
Viscosity Spike
Hydrodynamic resistance escalates sharply once critical shear thresholds are exceeded inside the applicator gap. Dilatancy forces pigment slurries to dilate rapidly as asymmetric shear forces disrupt orderly particle layers and create dilatant structures that trap fluid in expanding void spaces. Coating kitchens evaluate this resistance profile using rotational viscometers across stepped rotational speeds to chart the precise onset of shear thickening.
Converting operations maintain strict tolerances on pigment particle size distribution to prevent premature viscosity spikes that overload circulation pumps and damage metering rods.
Shear Boundary
Critical shear limits define the operational boundary where fluid flow transitions from stable liquid behavior to solid-like plug resistance. Dilatancy occurs when interstitial water fails to fill the expanding spaces between tightly jammed pigment aggregates under extreme mechanical deformation. Packaging converters avoid this boundary by specifying high shear stable formulations that maintain uniform film thickness across high-speed printing and coating lines.
Poorly controlled pigment slurries exceed this critical limit inside narrow application nips, causing severe coating weight variations and downstream drying failures.