TL;DR
Registration error between print colors is caused by web tension variation, plate mount error, or driven roller slip. Check web tension, verify plate position, and inspect all drive rollers before re-registering.
What you might see
- color-to-color misregister visible on print
- registration error increasing over the run
- register mark gaps inconsistent
- one color drifting in MD or CD
Likely causes
Web tension variation causing the web to stretch or relax between print units
Printing plate mounted off-register on the plate cylinder
Drive roller contamination causing web slip between units
Press speed variation from a drive fault affecting one print unit
Required tools
- Registration measurement tool or loupe
- Tension meter or press tension display
- Roller cleaning solvent
- Nitrile gloves
Safety first
- Keep hands clear of rotating cylinders and nips during register checks while the press is running.
- Solvent cleaners are flammable. Use with ventilation and away from ignition sources.
Procedure
- 1
Pull a register mark read from the current output. Measure the register error in both MD and CD for all color combinations.[1]
- 2
Check web tension readouts at each print unit. Tension variation above 5% between units will cause register drift.
- 3
Inspect all driven rollers and nip rollers in the web path for contamination or slipping. Clean roller surfaces with approved cleaner.[1]
- 4
Verify plate position on the misregistering color. Check that the plate is mounted flat, fully seated, and at the correct angular position.
- 5
Confirm press speed is consistent across all print units by checking the drive speed feedback from the control panel.
- 6
If tension variation is confirmed, check the dancer or tension control system for the affected interunit span.
- 7
After corrections, re-register all colors from the lead color and run a test sheet to confirm register is within specification.
Sources
Bobst Bobst MASTER M5 / DM5 Flexo Press general technical documentation, Bobst
Flexographic press register control and web tension management, general flexo printing practice (general)
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