Print and packaging troubleshooting
Common production problems, what usually causes them, what to check first, and how to stop them coming back.
How to use this
Every defect below follows the same shape: what it looks like, what usually causes it, what to check in order, and what prevents it returning. Work down the checks rather than changing several things at once, because two simultaneous adjustments make the result impossible to interpret.
One principle applies throughout: measure before adjusting. A press corrected by eye against a drifting reference will drift further.
Colour variation through the run
Looks like: colour on target at start up, drifting away over the run, or differing between rolls or pallets.
Usual causes: ink viscosity changing as solvent evaporates, anilox or cylinder wear, doctor blade pressure or angle, ink temperature, substrate variation between batches, press speed changes.
Check in this order:
- Viscosity, measured and recorded rather than judged
- Whether the drift correlates with speed changes or stoppages
- Substrate batch and roll changes against the timeline
- Anilox cell condition, and whether it has been measured recently
- Doctor blade pressure, wear and contact angle
Prevention: automatic viscosity control where available, a measurement routine at fixed intervals, and recorded values so drift is visible before the customer sees it. Use the Delta E calculator to compare readings against your reference.
Misregistration
Looks like: colours not aligned, white gaps at edges, text with coloured fringes.
Usual causes: web tension, substrate stretch, plate mounting accuracy, cylinder or sleeve condition, distortion applied incorrectly, register system not tracking.
Check in this order:
- Whether it is constant or varying. Constant points at mounting or plate length, varying points at tension
- Tension settings through the unwind, print units and rewind
- Plate mounting accuracy and whether the mounter is calibrated
- Distortion factor, and crucially whether it has been applied twice
- Substrate behaviour, particularly thin films under tension
Prevention: consistent tension profiles by substrate, a mounting procedure that is followed, and one agreed place where distortion is applied. The plate distortion calculator shows what the compensation should be.
Dot gain and tonal change
Looks like: midtones heavier than the proof, shadows filling in, images losing separation.
Usual causes: impression pressure set too high, plate relief or durometer, anilox volume relative to the plate screening, ink strength, substrate absorbency.
Check in this order:
- Impression. Excess impression is the most common single cause in flexo
- Whether the curve applied in the workflow matches the current press condition
- Anilox volume against the plate screen ruling
- Plate type and relief against what the job needs
Prevention: set impression by procedure rather than by feel, recalibrate when plate type or anilox changes, and verify with a measured control strip rather than by looking at the image.
Mottling and uneven solids
Looks like: patchy, cloudy or grainy solid areas rather than an even lay.
Usual causes: insufficient ink transfer, anilox too fine or worn, plate surface screening absent on large solids, substrate surface energy too low, drying too aggressive.
Check: substrate surface treatment level first, because on film it is often the answer. Then anilox volume, plate surface screening on solid areas, and ink formulation with your supplier.
Prevention: check treatment level on arrival and again before running, since it decays with storage time.
Pinholes
Looks like: small unprinted specks within a solid.
Usual causes: low surface tension on film, contamination such as dust, silicone or oil, air entrapment in ink, drying too fast at the nip.
Check: treatment level, cleanliness of the substrate path, ink filtration and foaming, and whether the problem follows a particular roll.
Prevention: treatment verification, housekeeping around the unwind, and defoamer only on supplier advice rather than as a habit.
Banding and streaks
Looks like: bars or lines across or along the web, repeating at a regular interval.
Usual causes: mechanical, most often. Gear marks, bearing wear, roller runout, sleeve damage, doctor blade nicks or dried ink on the blade.
Check: measure the repeat distance of the banding. A repeat that matches a cylinder circumference identifies the component immediately. Blade related streaks usually run in the web direction and move when the blade is adjusted.
Prevention: maintenance schedule driven by measurement, blade inspection at changeover, and not running damaged sleeves because the job is urgent.
Poor ink adhesion
Looks like: ink lifting on tape test, scuffing in transit, failure at lamination.
Usual causes: surface treatment below the required level, wrong ink system for the substrate, residual solvent, contamination, insufficient drying or curing.
Check: treatment level with dyne solution or pen, ink and substrate compatibility with your supplier, dryer temperatures and air flow, and residual solvent if lamination is involved.
Prevention: record treatment levels on arrival, agree ink systems per substrate rather than per press, and test adhesion during the run and not only at the end.
Frequently asked questions
Why does colour drift during a print run?
Most often because ink viscosity changes as solvent evaporates, or because press speed changed, or because a new substrate batch came on. Anilox wear and doctor blade condition are slower causes. Measuring and recording at fixed intervals makes the difference visible before a customer sees it.
What causes misregistration in flexo printing?
Web tension and substrate stretch are the usual causes when it varies, while plate mounting and plate length are the usual causes when it is constant. Distortion applied twice, once in the workflow and again in the artwork, is a frequent and easily missed error.
What is the first thing to check for heavy dot gain?
Impression pressure. Excess impression is the most common single cause in flexographic printing, and it is also the cheapest thing to correct before looking at curves, anilox or plates.
How do I identify the source of banding?
Measure the distance between the bands. If it matches the circumference of a cylinder or roller, that component is the source. Streaks running in the web direction usually point to the doctor blade instead.
Why does ink fail an adhesion test?
Surface treatment below the level the ink needs is the most frequent cause on film, and treatment decays during storage. Ink and substrate mismatch, residual solvent and inadequate drying are the other common reasons.
Related tools and reading
Working on something specific? Send me the process, the substrate and what you have already tried, and I will tell you where to start. Get in touch or message me on WhatsApp.