Accumulation of excess ink on and around the plate surface, especially in regard to small type and halftones.
Causes:
– Specks of pigment or foreign matter;
– Type, design or screen incorrect
– Ink solvent balance wrong;
– Plate incorrectly made;
– Improper nip settings;
– Pick and offset from a previous colour;
– Inking too heavy;
– Uncontrolled ink viscosity and/or pH range;
– Low fountain roll durometer.
Solutions:
– Use well dispersed inks, free of large particles. Ensure pump and pipework is clean, sieve ink;
– Check design for suitability for flexo work;
– Use recommended solvent mixtures;
– Ensure relief is correct and edges not cupped. If plate is too soft change to a harder durometer;
– Increase pressure settings of fountain roll nip or doctor blade assembly;
– Adjust solvent speeds between colours, ensure interstage drier is balanced;
– Maintain ink viscosity and ensure anilox roller is correct;
– Maintain proper ink viscosity and/or pH range. Ensure ink tray covers are used;
– Use higher roll durometer.
