MOTTLED PRINT
Mottled print is a common problem , when trying to print good quality consistent solids in flexo. The surface of the print appears like orange peel, with inconsistent colour and non-uniform appearance
Cause
Printing form with uneven or un-clean surface
Ink viscosity or concentration, too low
Residual chemicals from the plate-making process, still on surface
Dirty or scratched impression cylinder
In-correct ink transfer on the printing form or substrate
Ink not wetting on printing form or substrate
Solution
1 Increase the printing pressure between the printing form and substrate
2 Increase the ink viscosity or ink film thickness.
3 Modify ink to correct viscosity or opacity. Check the balance of solvent in the ink. If necessary change the ink
4 Wash the printing form to remove residual chemicals. If necesary remake the printing form
5 Properly clean the impression cylinder
6 Use softer or more compatible plate or cushion tape
7 Check surface treatment of the substrate
Helmut Mathes, troubleshooting defects supplied curtesey of Flexo & Gravure Int''l 2011
INK TRANSFER - ANILOX
The shape and consistency of anilox cells makes a huge impact on ink transfer and cleanliness of the inking process to the printing plate.
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DIRTY ANILOX
Dried ink in anilox cells, can cause significant change in print densities. The FlexoStar laser can clean dried ink from even the smallest cells.
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