Blurry UV prints and ink mist (overspray)

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The print looks soft, text has a haze, and a fine ink mist lies next to the design. This overspray occurs when ink droplets do not land where they are meant to. Almost always it has to do with the path between nozzle and surface.

Cause 1: print gap too large

The most important point. The droplets from the print head are tiny and are slowed and deflected by the air on their way to the surface. The longer the path, the less accurately they land.

Mimaki recommends keeping the distance between the lowest and highest point of the print surface below 1.5 mm, and points out considerably more ink mist at distances above 2 mm. eufyMake also names height differences above 2 mm as a cause of blurry prints. For desktop machines, the exact values are in the manual.

What helps: Measure the height again or set it manually. Check whether the automatic measurement has picked up the right point.

Cause 2: uneven surfaces

Many printers measure the height at the highest point of the object and print everything at that height. If part of the object is lower, it turns out blurry there.

Typical cases:

• phone cases with a camera bump
• notebooks or folders with a raised corner
• slightly curved wooden discs or warped acrylic
• canvas that sags
• mugs and bottles that do not sit straight on the rotary attachment
• several objects of different heights in one pass

What helps: Lay objects flat and fix them with tape, even out the heights with spacers, and print only objects of the same height per pass. Jigs suit curved parts and series, see Positioning accurately. There are separate notes for mugs and bottles under Printing on round objects.

Cause 3: satellite droplets

A droplet does not always leave the nozzle as a single sphere. It is often followed by a small secondary droplet, the satellite. At a short gap it lands almost in the same place. At a large gap or with fast head movement it drifts away and forms a fine mist beside edges.

What helps: A small print gap and a slower mode. Partly faulty nozzles also produce crooked or atomised droplets. A nozzle check shows this, see Clogged nozzles on the UV printer.

Cause 4: draughts

The droplets are so light that even a slight draught deflects them. Fans, air conditioning, open windows or the exhaust of an air purifier right next to the printer make themselves felt.

What helps: Move the machine out of the airflow, keep the cover closed during printing, and position air purifiers so that they do not blow across the print table.

Cause 5: static charge

Plastics such as acrylic, PET films or protective films become electrically charged when peeled off or wiped. The charge attracts or repels the tiny droplets. The result is ink mist, speckles and ragged edges, often unevenly distributed across the object.

What helps:

• Do not rip off the protective film in one go right before printing
• Clean the surface with isopropyl alcohol, do not rub it dry
• Do not let the humidity get too low. In dry heated air in winter, static is much stronger.
• Professional machines have ionisers available as accessories, which neutralise the charge

Cause 6: speed and print mode

Fast modes move the head faster and print with fewer passes. The droplets carry more sideways momentum, and small deviations are more noticeable. In bidirectional mode, an offset between the forward and return pass can additionally create double edges.

What helps: Choose a quality mode. For double edges, run the bidirectional calibration. More on this under Banding in UV printing.

Ragged borders

If only the edges are untidy but the areas look good, other causes come into question:

• White shows through: The white layer is exactly as large as the design. The remedy is a small choke, see Preparing print data.
• Untidy cut-outs: Semi-transparent edge pixels get printed.
• Printing over the object edge: On sloping or rounded edges the gap suddenly grows, and mist forms there.
• Ink runs: On very smooth surfaces or with too little curing between the layers, droplets can run into each other.

For business use

Ink mist next to the design is immediately noticeable on light blanks and hardly removable. With series, it is worth checking the first part closely under a magnifier before you carry on printing. Objects of the same height, a suitable jig and a quiet location without draughts reduce rejects considerably. You should regularly remove ink mist from the print table and the underside of the head, otherwise it will later drip onto workpieces.

Quick checklist

1. Print height measured or set correctly?
2. Object flat, without raised corners or bumps?
3. Only objects of the same height in a pass?
4. No draught, cover closed?
5. Plastic statically charged? Clean with isopropyl alcohol, check the humidity.
6. Tried a quality mode instead of a fast mode?
7. Nozzle check clean?
8. For edge problems: choke and cut-outs checked?

Continue with: Positioning accurately and Clogged nozzles on the UV printer.