Flexographic Barrier Coating Viscosity Measurements for Aqueous Latex Formulations
Aqueous latex barrier performance depends on controlling dynamic high-shear viscosity to ensure complete anilox cell release and eliminate film pinholing.
Coaxial Cylinder Rheometer
Shear Measurement
Rotational test equipment governs fluid flow properties during container coating preparation and pigment dispersion. A coaxial cylinder rheometer evaluates the viscosity profiles of barrier dispersions and starch sizing agents by placing fluid samples in the annular gap between a fixed outer cup and a rotating inner bob. High shear rates during blade coating demand exact flow curve generation to prevent uneven film thickness across paperboard webs.
Bob rotation speed adjusts continuously to map non Newtonian fluid behavior under thermal stress. Starch migration problems occur when thermal profiles fluctuate during drying stages. Instrument calibration relies on certified viscosity standard oils maintained at strict laboratory temperatures.
Gap Geometry
Concentric cylinder design creates uniform shear stress distribution across the entire fluid height within the measuring cell. Narrow gap tolerances prevent velocity gradients from distorting measurement accuracy during high speed coating runs. Bob diameter relative to cup inner diameter sets the shear rate calculation factor for complex polysaccharide solutions.
Edge effects at the bottom of the cylinder require specialized conical geometries or guard rings to eliminate end errors in low viscosity lacquers.
Flow Curve
Viscosity data acquired during rotational ramps translates directly into pump sizing parameters for gravure printing stations. Shear thinning fluids display decreasing resistance as rotational speed increases inside the measuring chamber. Yield stress calculations determine whether a pigmented mineral coating resists gravitational sagging before ultraviolet curing lamps fix the layer.
Temperature control jackets maintain thermal equilibrium while shear forces alter internal fluid friction. Plant engineers use these flow curves to specify transfer pump capacities for water based barrier varnishes.