TL;DR

Doctor blade streaking produces ink lines or streaks in solid print areas. Replace the blade, verify blade material matches the ink system, and check anilox roll cleanliness.

What you might see

ink streaks or lines in solid print areas
streaks at consistent CD positions
streaks worsening as the run progresses
visible blade wear or nicking at the streak position

Likely causes

Tap to mark as ruled out

Nick or chip in the doctor blade creating a groove in the ink film
Incorrect blade material or hardness for the ink system causing rapid wear
Dried ink particle scoring the blade edge from a contaminated anilox
Blade holder bar distorted, creating uneven blade contact across the anilox width

Required tools

Cut-resistant gloves (blade-rated)
Replacement doctor blade (correct material and grade)
Anilox cleaner
Work light for blade edge inspection
LOTO kit

Safety first

Doctor blades are razor sharp. Use cut-resistant gloves at all times and never wipe a blade bare-handed.
Solvent cleaners for anilox rolls are flammable. Maintain ventilation and avoid ignition sources.

Procedure

7 steps · ~30 min

1
Stop the press and lock out before touching the doctor blade or blade holder.
Warning: Doctor blades are extremely sharp. Use cut-resistant gloves rated for blade handling. Never wipe a doctor blade bare-handed.
2
Remove the doctor blade and inspect the edge under a work light at a low angle for nicks, chips, or embedded particles.[1]
3
Replace the blade with the correct material and thickness for the ink system and anilox cell volume. Consult the press setup sheet for the approved blade specification.
4
Inspect the anilox roll surface for dried ink deposits or contamination at the streak position. Clean the anilox with the approved cleaner before installing the new blade.[1]
5
Inspect the blade holder bar for distortion or damage. A bent holder bar prevents uniform blade contact and causes streaking even with a new blade.
6
Install the new blade with uniform loading across the full width. Confirm the blade angle matches the specification for the anilox roll diameter.
7
Run a short test print and inspect for streaking before committing to the full run.

Sources

Bobst Bobst MASTER M5 / DM5 Flexo Press general technical documentation, Bobst
Flexographic press doctor blade management and anilox cleaning, general flexo printing practice (general)

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