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.
Anilox Spitting
Deflection Mechanism
Flexographic printing processes utilize a doctor blade to wipe excess ink from a ceramic engraved roller before impression. When hydrodynamic force lifts the doctor blade from the roller surface, anilox spitting occurs as ink drops escape onto the substrate. The fluid accumulates on the trailing edge of the blade, forming large drops that the air boundary layer pulls onto the web.
Ink viscosity and roller cell geometry interact to create a lifting pressure under the blade, which leads to intermittent separation. This separation occurs primarily at high press speeds when the shearing force of the ink exceeds the mechanical tension of the doctoring assembly.
Production Impact
Defective print runs result from uncontrolled droplet release, which appears as random specks or long horizontal trails of ink across the printed paperboard. Flecks of ink ruin the visual appeal of packaging and render barcode scans unreliable during later distribution steps. Excessive blade lift often forces a reduction in press speed, which lowers hourly throughput and drives up production costs.
Operational Control
Mechanical adjustment of blade thickness and chamber pressure reduces the risk of hydroplaning. Operators choose stiffer blades or decrease the ink viscosity to keep the blade in contact with the roller. Decreasing the ink surface tension also helps to minimize drop formation at the blade edge.