How to Judge Halos Around Flexographic Text
A pale edge around the outer contour of flexo text means pressure has squeezed ink out of the strokes. For fine text, barcodes, and strokes smaller than 6 pt, as soon as this edge appears, the run should be stopped, because the stroke width has already changed. A very narrow squeeze-out at the edge of a large solid area can be kept if the customer has given written approval; without written approval, reduce pressure as well.
A faint halo around flexographic text is ink squeezed out of the strokes by pressure. Fine text, barcodes, and strokes smaller than 6 pt should stop the run as soon as this ring appears, because the stroke width has already changed. A very narrow squeeze-out at the edge of a large solid can stay if the customer has given written approval; without written approval, reduce pressure as well.
How does this halo form?
The printing plate presses too far into the material, and the ink has nowhere to go, so it is squeezed out from the edges of the strokes as a ring of ink lighter than the text. This ring is the same color as the text, so it is not misregistration. Under a magnifier, there is no paper white separating the light edge from the dark stroke; they are connected. Misregistration, by contrast, will reveal another color beside it, or expose a ring of paper white.
If the pressure is high enough to squeeze a halo out of fine text, the bar width of the barcode has usually already exceeded tolerance. So do not pass a halo on fine text just because it is “still legible.” A squeeze-out at the edge of a large solid does not change any text. Some customers allow a very narrow one in their dirt/speck or edge chart, but it must be written down, and you cannot carry it over from the previous order.
Stop or keep?
| Where the halo is | Action |
|---|---|
| Fine text, barcodes, strokes smaller than 6 pt | Stop; reduce pressure, then recheck bar width |
| Edge of a large solid, if the work order states it is allowed | Keep it to that width; if it exceeds it, reduce pressure |
| Not stated on the work order | Reduce pressure; do not assume it can stay |
First steps for this run
- Confirm that the light edge and the text are the same color and that there is no paper white between them. Only then is it a halo.
- Check the smallest text and barcodes first, not the large headings.
- Reduce pressure until the light edge disappears, then recheck the barcode; do not just check whether the text is still there.
