Plate Plugging in Water-Based Flexography: Fluid Mechanics of the Press Nip.

The role of various factors such as press operation, printing plate geometry, and ink properties in plugging or filling-in of printing plates in water based flexography has been investigated. The most commonly observed initial plugging at the leading edge of the type and halftones is explained using the flow equations for a thin liquid film in a nip, using representative values for the pressure gradient in the nip, ink viscosity, and nip gap thickness. Plugging at the trailing rather than the lading edge may result from excessive nip pressure and from excessive ink film thickness; both of which also contribute to the total amount of plugging. The amount of ink recovered from a severely plugged plate agree with the calculations.