Banding in UV printing: causes and fixes
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Banding means fine light or dark stripes that run through the motif at regular intervals. They are most noticeable on solid areas and gradients. The causes range from clogged nozzles to badly calibrated axes, and the problem can usually be narrowed down with a few tests.
First, read the stripes
Before you change any settings, look closely at the stripes:
| Appearance | Likely cause |
|---|---|
| Light lines, one colour missing in places | Nozzle dropout in that colour channel |
| Light lines in all colours, even spacing | Step or feed calibration too large |
| Dark lines, even spacing | Feed too small, passes overlap |
| Slightly doubled edges, blurry lines | Bidirectional calibration or print head distance |
| Stripes only in the white | White ink has settled or white nozzles are clogged |
| Stripes only with one motif | Cause more likely in the file |
Cause 1: Nozzle dropout
The most common cause. If individual nozzles drop out, ink is missing at those positions, and every pass produces a light line.
What helps: Print a nozzle check. Missing or crooked lines in the test pattern show the affected channel. Then start a cleaning and repeat the test. More on this in the article Clogged nozzles on a UV printer.
Air bubbles in the ink lines after a cartridge change, or a very low fill level, can also make nozzles drop out briefly. Many devices have a function for filling or flushing the lines for this.
Cause 2: Step or feed calibration
The print head prints the motif in swaths. After each swath, the object or the head moves on by a precisely defined distance. If this step is not exactly right, gaps (light stripes) or overlaps (dark stripes) appear between the swaths.
What helps: Run the step calibration (often called “Step”, “Feed” or “Vorschub”) from the maintenance menu. The device prints a test pattern, and you pick the value with the most even result. After transport, a move or a change of print plate, this calibration is always worthwhile.
Cause 3: Print mode and passes
Fast modes print with few passes. Each swath then applies a lot of ink at once, and small deviations become visible. Modes with more passes spread the ink over several swaths, which compensate for each other.
What helps: Try a quality mode with more passes. If the banding disappears, the cause is more likely in the calibration or the nozzles and is merely masked by the slower mode.
Cause 4: Print head distance
If the distance between print head and surface is too large, the droplets travel further and land less accurately. The swaths no longer line up cleanly. This often shows as stripes combined with blur.
What helps: Measure or set the height again and lay the object flat. Mimaki, for example, recommends keeping the difference between the lowest and highest point of the print surface under 1.5 mm. More on this under Blurry UV print and ink mist.
Cause 5: Bidirectional calibration
In bidirectional mode, the head prints on the way out and the way back. If the two directions are not precisely matched, the droplets land slightly offset. The result is blurry edges and fine stripes.
What helps: Run the bidirectional calibration (also “Bi-D” or head alignment) in the maintenance menu. If that does not help, switch to unidirectional printing as a test. This is slower, but shows whether the problem lies here. Epson gives the same advice for its printers.
Cause 6: White ink
White ink contains heavy pigments (titanium dioxide) that settle. If it is not moved regularly, varying amounts of pigment come out of the nozzles. The result is uneven, streaky white areas that show through the colour.
What helps: Shake the white ink or let it circulate as the manufacturer specifies, and print a white area on scrap material until the white comes out evenly, and only then print the actual object.
Cause 7: Room climate
UV ink becomes more viscous in the cold. This can make nozzles fire irregularly. eufyMake, for example, recommends a room temperature of 18 to 22 °C for its printer. Other manufacturers give similar ranges, and the exact values are in the manual.
Cause 8: The file
Not every stripe comes from the printer:
- Heavily compressed JPGs have block patterns that look like stripes in print
- Gradients with too few colour steps show breaks (“stair-stepping”)
- Upscaled images can form patterns
Test: Print a different, known-good motif. If it is stripe-free, the cause lies in the first file. How to set up your data cleanly is covered under Preparing print data.
For business use
Slight banding is hardly noticeable on photos on wood, but immediately visible on solid areas on acrylic or on company logos. Print a nozzle check before every run and include a test piece for critical jobs. Regular maintenance, as described in the article Maintaining UV printers, is cheaper than any misprint.
Quick checklist
- Nozzle check printed? Fix missing lines first by cleaning.
- Stripes even in all colours? Run the step calibration.
- Quality mode with more passes tested?
- Print height correct, object flat?
- Bidirectional calibration run, or unidirectional tested?
- White ink shaken or circulated?
- Room not too cold?
- Cross-checked with a different motif?
Continue with: Clogged nozzles on a UV printer and Maintaining UV printers.