With the term “ghosting” we describe the presence of a faint image of a design that shows in areas where it was not intended to appear. Usually it is a repeated pattern on print along machine direction.
The main cause is attributable to the failure of replenishing, with fresh ink, the cells that discharged ink in contact with the plate while they return into ink chamber to be refilled.
This is typically connected to the use of anilox rolls with unbalanced engravings, having too deep cells and too high linescreen, resulting in insufficient ink transfer (and replenishment) properties of the anilox roll.
While there could be several possible -more or less palliative- adjustments within the ink, the most effective remedy is to use a different anilox with a better engraving ratio depth÷opening, typically ~1÷3, that allows better transfer and replenishment efficiency.
Other remedies might include the followings:
- increase ink flow and pressure within the chamber to facilitate cells replenishment
- control ink drying and prevent from ambient or blown air from interdeck driers (some retarder might help)
- avoid low viscosity: a higher viscosity slows the drying on anilox surface
- reduce doctor blade pressure alleviating friction and heat at the sheer point of the ink