Surface Energy Mismatch Dynamics in High Build Acrylic Varnish Jetting
Surface energy mismatch causes reticulation or edge slump in digital spot UV jetting, requiring balanced dynamic surface tension and LED pinning.
Viscosity Surge
Rheological Instability
Rheological anomalies characterized by rapid, temporary increases in fluid flow resistance occur in complex coating suspensions under critical shear conditions. In high-speed blade coating and flexographic ink circulation systems, a viscosity surge disrupts uniform fluid metering and damages application equipment. Dilatant flow behavior arises when high shear rates force dispersed pigment particles out of orderly flow lines into jammed structures.
Inter-particle friction increases exponentially, turning a fluid coating into a semi-solid paste inside pumping lines or metering nips. The sudden pressure spike can burst supply hoses and cause streaks on the moving paperboard web.
Process Disruption
Flow resistance spikes impair fluid transfer efficiency and degrade applied coating quality. When a viscosity surge occurs in paperboard coating formulations, high solids content and tight particle size distribution increase susceptibility to shear-thickening. Agglomeration of binder starches or synthetic thickeners under localized high shear zones initiates fluid structural buildup.
Recirculation pumps experience mechanical strain, leading to cavitation and flow rate fluctuations. Formulators introduce shear-stable dispersants and adjust solid concentrations to maintain Newtonian or shear-thinning flow characteristics across all processing speeds.
Shear Boundary
Shear-thickening behavior ceases when applied shear stress falls below the critical threshold required for particle jamming. Lowering line speed or enlarging metering gaps restores low fluid viscosity and normal flow properties. Maintaining operating parameters below the critical shear rate prevents sudden rheological transitions during production runs.