What is ink misting, and why are there ink dots in blank areas?
Ink misting is when ink is thrown off from the gaps between rollers and fine dots land outside the image area, even on the machine and adjacent sheets. Dots outside the image area that do not repeat according to the printing plate are ink misting. Dots inside the image area that repeat at the circumference are dirt on the plate or roller, not ink misting. High speed and ink that is too long are the most likely to throw it off.
Ink fly is ink thrown out in the gap between rollers, with fine dots landing outside the image area, even on the machine and adjacent sheets. Dots outside the image area that do not repeat according to the plate are ink fly. Dots inside the image area that repeat at the circumference are dirt on the plate or roller, not ink fly. High speed and ink that is too long are the most likely to throw it out.
Why there are dots in blank areas
When two rollers separate, the ink filament is pulled apart, and the broken bit flies out. The higher the speed and the longer the ink, the farther it flies. So these dots do not need the plate involved; they appear on blank areas, paper edges, even guards. If you wipe dots off the paper, they are back the next minute, because the source is in the roller nip, not on the paper.
If dots only appear inside the image, and are in the same relative position on every revolution, that is a particle on the plate or roller; treat it as a repeating defect and measure the circumference. Ink fly dots are scattered, and do not align from one sheet to the next.
Don't wipe the wrong place
| Where is the ink dot | Do consecutive sheets align? | Action |
|---|---|---|
| Outside the image, also on the machine | Not aligned | Reduce speed, shorten the ink |
| Fixed position inside the image | Aligned | Measure circumference, check plate and rollers |
| Only a line at the paper edge | Not aligned | Still ink fly or ink thrown from the roller end; check ink volume at that end |
Do these first this round
- Check the guards and blank edges. If there are new fine dots there, it is ink fly.
- First reduce speed and see whether the dots decrease. If they decrease, do not wash the plate.
- If the dots are still numerous after reducing speed, then shorten the ink for this color, and note this speed limit.
