How to Improve Flexographic Printing Quality: Design, Plates, Rollers and Inking

Fit a reverse-angle doctor blade system

Consistent ink metering from job to job depends on the inking system. Flexo presses use one of three arrangements: a two-roll system, a forward-angle doctor blade or a reverse-angle doctor blade. In the two-roll system, a fountain roller transfers ink to the anilox roller and the speed difference between the two meters the ink. The system also leaves a film of ink on the cell walls, and that film grows with press speed and ink viscosity, which makes the laydown unstable. A forward-angle blade forms a wedge of ink between the blade and the roller; hydraulic pressure lifts the blade as speed or viscosity rises, so the wall film becomes unpredictable again.

A reverse-angle blade wipes against the roller in the opposite direction of rotation, so the ink pressure pushes the blade toward the roller instead of lifting it away. With a reasonably accurate blade, only light pressure is needed. The cell walls come out clean, wear on both the roller and the blade stays low, and the metered volume is governed by the roller itself rather than by press speed or ink viscosity. For stable flexo quality on long production runs, the reverse-angle configuration is the system of choice.

Closing the remaining gaps

Quality in flexographic printing is built from many small decisions. A design reviewed against the limits of the process, a plate made by digital direct imaging, an anilox roller matched to the plate and the substrate, and a reverse-angle doctor blade system will take a shop most of the way. Operator training, consistent plate material and carefully selected substrates close the rest of the gap.