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.
