Banding Only in Certain Zones — Mechanical Issues (EP.2) ARTJET 2026

A high-volume order using a jig

• Every time a new smartphone model launched, we needed to print and deliver official cases on a tight deadline.
• The printer ran 24 hours a day, and we built a custom jig to streamline the workflow.
• We were using the full flatbed area for printing — but strangely, banding with a color inconsistency kept appearing in one specific zone.

Where the banding occurred

• We were printing on transparent PC sheets, each measuring 350×250mm.
• With a flatbed size of 600×900mm, we loaded 4 PC sheets per print cycle.
• Looking at the printed output, the color inconsistency appeared in the second zone — around the Y-axis 550mm mark on the flatbed.

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• It was barely visible head-on, but when viewed at an angle, the color inconsistency became clearly visible in the light.

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Initial theories

• The Y-axis is belt-driven, so the first thought was: “Is this just a limitation of belt-driven movement?”
• Another theory: “Is it more sensitive because we’re using bidirectional printing rather than unidirectional?”
• With no time to investigate further, we raised the G mask by one level to reduce the visible banding and kept the job running.

The next morning, all overnight prints were banding-free.

• We had no explanation. “Why is it gone?”
• During the day, our own staff had been operating the machine. Overnight, contract workers had run it.
• We started looking at the differences between how each group worked.

What the night shift did differently

• The contract workers had never used a UV printer before, so we gave them the safest, most careful set of instructions.
• Before printing: place all 4 PC sheets on the flatbed, confirm positioning, then start the print.
• After the print cycle finishes: remove all printed sheets, reload 4 new sheets, and start again.
• We specifically told them not to touch any substrates while printing was in progress — only handle materials after the cycle was fully complete.
• Even with the G mask raised, our daytime prints still showed faint banding — but the overnight output had none. In fact, when the G mask was restored to its original setting, the overnight prints were still banding-free.

The cause was in the workflow itself.

A colleague noticed several anomalies while working.

• “Sometimes the banding shows up in zone 4, sometimes zone 5, and sometimes not at all. I tried waiting until all 4 sheets were done before removing anything — and the banding was gone.”
• “Is it because removing the substrate weakens the fan suction? Or does touching the flatbed physically shift the Y-axis feed value slightly?”
• Our best assessment: removing the front substrate causes a brief drop in suction, momentarily lifting the sheet — or the physical force of swapping substrates affects Y-axis feed. The bidirectional printing mode may also have made the system more sensitive.
• To save time, we had been swapping the front 2 PC sheets while the printer was still printing the rear 2 sheets.
• That physical disturbance during the swap was the cause of the color banding.

Why solid color is so hard to get right

• One of the most demanding image types for a UV printer is not fine text — it’s solid color: a single, uniform tone such as a solid blue or red.
• With solid color, even the slightest change in conditions becomes immediately visible to the human eye.
• By contrast, fine text or images with multiple mixed colors are comparatively forgiving.
• This is why swapping substrates mid-print causes no visible issue when printing ballpoint pen designs or other fine-text images.

If you swap substrates mid-print to speed up production, we strongly recommend avoiding this practice during solid color jobs. For fine-text or small-image prints such as ballpoint pen designs, it is generally not a problem.