Why Does the Trailing Edge Fade on a Sheetfed Press?
Trailing-edge fading on a sheetfed press is usually because a large solid area at the front has depleted the ink on the ink rollers and it cannot be replenished in time, or because the trailing-edge pressure is too light. It is not a paper whiteness variation: the gripper edge of the same sheet is normal, and it only gets lighter toward the back. First check whether there is a large solid area at the gripper edge, then discuss adding ink overall.
When the trailing edge prints light on a sheet-fed press, it is most likely that a large solid at the front has depleted the ink on the ink roller and it cannot be replenished later, or that the trailing-edge pressure is low. It is not a paper-white variation: on the same sheet, the gripper edge is normal, and only toward the back does it get lighter and lighter. First check whether there is a large solid at the gripper edge, then discuss increasing ink overall.
Front-to-Back on a Single Sheet
The amount of ink carried by each revolution of the ink roller is limited. If the gripper edge is a large solid, the ink on the roller is taken away; by the time it rotates to the trailing edge, the ink film is already thin, so solids and halftone dots at the trailing edge become light. If you remove the solid at the gripper edge, or move the large solid to the back, the trailing edge often recovers. This shows it is not that the ink formulation is insufficient overall.
Another case is when the pressure at both ends of the cylinder is acceptable, but the pressure in the trailing-edge direction has dropped. In this case, the entire trailing edge is light, and there is no correspondence of “the further behind a large solid, the lighter it gets.” When inspecting the sheet, read several points along the paper travel direction to distinguish these two.
Does Adding Ink Help?
| Light/dark distribution | More like | Do first |
|---|---|---|
| Light only after a large solid | Ink roller cannot replenish | Reduce ink in the front solid, or change the image position |
| Entire trailing edge strip is light, unrelated to the image | Pressure | Check trailing-edge pressure; do not add ink |
| Gripper and trailing edge equally light | Overall ink volume | Only then add this color according to the approved proof |
Do This First This Round
- Measure solids at the gripper edge, middle, and trailing edge along the paper travel direction.
- If only the area after a large solid is light, do not increase ink overall.
- If all three are light together, then add ink according to the approved proof.
