A condition caused by slippage at the moment of impression between the substrate and plate. Slur is characterised by the smearing of the trailing edges of a printed image or by the appearance of a double image and can happen in both machine direction and across the web. However, slur is more common in the machine direction.
Causes:
- Mechanical problems;
- Poor tension control;
- Slippage of the substrate through the press caused by improper support of the sheet;
- Wrong undercut used.
Solutions:
- Check path rollers are running freely and that substrate is not dragging. Oil or lubricate, replace bearings or drive belt. Check chuck holding roll core is inflated or secure;
- Adjust tension to the correct level, check load cells and ensure all nips are set correctly. On a gearless press check the substrate is synchronised with the press speed, do not exceed manufacturer's recommended maximum repeat length tolerances. Ensure dryers are balanced correctly so exhaust does not suck in film;
- Check pull collars and belts are not worn or set wrongly. Check parallelism between the rollers. Check vacuum levels,
- Ensure that both the plate and tape thicknesses are the same as the undercut on the plate cylinder.
