Banding, orange peel and adhesion failure: reading UV print defects

Banding is not one fault. It is at least five, they look similar, and they have completely different fixes — which is why shops lose afternoons cleaning heads at a problem that was never in the head. Diagnose in order and most of it resolves quickly.

The order to diagnose in

1. Nozzle check. Rules the head in or out in a minute.
2. Print the same file unidirectionally. If it cleans up, it is alignment or head height.
3. Run the feed-correction pattern.
4. Run the bidirectional pattern at the actual media height you are printing at.
5. Then look at encoder, dampers and the room.

Doing these out of order is how people end up replacing a head that was fine.

Banding 1 — nozzles

Signature: irregular, often a fine line or a lightened streak that follows a specific nozzle position, and it shows in the nozzle check.

The seven-pattern diagnostic table — including how to tell debris on the nozzle from debris inside it — is in reading the test print. If the nozzle check is clean, stop cleaning and move on.

Banding 2 — media feed

Roland states the cause plainly: “Horizontal bands are caused by the subtle changes in the movement distance that occur when feeding the media depending on the media’s thickness.” The correction procedure asks you to pick the value with “the smallest gaps and overlaps.”

Epson describes the symptoms as “horizontal banding”, “uneven tint” and “stripes”, and notes the calibration must be redone if media width, tension or suction changes.

Signature: regularly pitched — one band per pass, at exactly the swath height — running the full width, and persisting with a perfect nozzle check. Overlap shows as a dark line, underfeed as a light one.

One trap worth knowing: Roland warns that the RIP setting can override the printer’s own feed value. If you corrected it at the machine and nothing changed, check whether the RIP is sending its own.

Banding 3 — bidirectional alignment

Signature: doubled or shadowed edges, worse on fine detail and text, and it disappears when you print in one direction only.

Because it depends on the distance the drop flies, it reappears every time substrate thickness changes. That is geometry, not drift — explained in what pass count really means.

Banding 4 — pass count

Here is the discriminator, because this shares a pitch with feed error and the two get confused constantly:

• Feed error responds to a numeric feed correction, and changes when media thickness changes.
• Pass-count banding is unaffected by the feed value, and only improves with more passes.

If the feed correction makes no difference at any value, you are asking the machine to do the job in fewer passes than the artwork tolerates.

Banding 5 — the lamp

Reported widely in the trade rather than documented by manufacturers, so treat it as a hypothesis to test rather than established fact: where the lamp is wide relative to the pass, a strip of ink can receive a second dose on the following pass, curing differently from its neighbours and showing as a band.

Testable: change pass count or lamp power and see whether the pitch moves. Related physics in UV LED vs mercury curing.

Orange peel

A dimpled, slightly textured surface on what should be flat gloss.

We can tell you what is verifiable about the mechanism, and we will be clear about where it stops. UV ink “will not dry by evaporation and/or absorption”, and the cured film is “between 5 and 40 µm” — the full applied thickness, because nothing left. So the drop topography that lands on the surface is the topography you keep, unless it levels first. Monomers are deliberately selected for “good flow, leveling”, which tells you levelling is a real, finite, formulated-for process.

Marabu’s list of operator-side cure variables is the useful part: “the dryer’s design, age, and performance, as well as the number of lamps and the ink deposit… the colour shade, the substrate, and the printing speed.”

What to try, as shop practice rather than sourced instruction: reduce ink deposit or total ink limit; slow down; check whether the lamp is curing sooner or harder than it needs to; and test on a smoother substrate to separate material texture from print texture.

We could not obtain a manufacturer technical note explaining orange peel in UV inkjet. The common explanation — that cure outruns levelling and freezes the drop shape — is almost certainly right, and we are not going to present it as sourced when it is not.

Adhesion failure

The most important thing about adhesion failure is that most of it is not failure. Two ink manufacturers independently specify that final adhesion is reached after 24 hours.

A tape test ten minutes after printing will fail a job that passes the next morning. Full detail — surface energy, primers, the tin side of float glass, and how to run the test properly — is in will the ink stick?

Under-cure, and the standard that refuses to give you a number

The solvent-rub test for cure is ASTM D5402, and its own scope is remarkable:

“This practice does not specify the solvent, number of double rubs, or expected test results” — “The coating manufacturer may specify…”

And the caveat that matters even more:

“the level of solvent resistance by itself does not indicate full cure and some coatings become solvent resistant before they become sufficiently cured for service.”

So the standard tells you to ask your ink supplier for the number. Anyone quoting a universal MEK double-rub count for UV ink is quoting folklore.

Two practical consequences. First: an under-cured UV print does not improve overnight. “The polymerization will not continue after UV/EB exposure.” If it is tacky, that is under-cure, not drying, and time will not fix it.

Second, and this is the one for an established shop: Marabu lists cure as depending on the dryer’s “design, age, and performance.” Emitters lose output over their life, and the ink maker says so in writing. A print that cured properly last year may not cure now at the same settings. If cure has drifted gradually rather than suddenly, measure the lamp before you change the ink.

Other defects worth naming

• Colour shifting between runs. Mimaki attributes this to “using profile with mismatched print mode settings” and instructs: “always use profile with its originally specified print mode.” If the same file printed differently on Tuesday, check the mode before the ink.
• Nozzle deflection. Straight but off-target means debris on the surface; curly and weak means debris inside. Different fixes.
• Ink bleed on heated machines — insufficient heater temperature.

What we deliberately do not claim

A universal MEK double-rub count. The thumb-twist test as a standard — we found no citation for it at all; it is shop practice. Mottling, coalescence, satellite drops and gloss banding as sourced mechanisms. And the idea that you can over-cure ink into brittleness by running lamps hot: the shrinkage and brittleness trade-off in UV chemistry is formulated in at the monomer level, not something a machine setting induces.

If a defect on your machine does not match anything here, that is worth a conversation rather than another cleaning cycle — service and support covers how a fault gets handled and what the common ones actually are.

Sources

• Roland DG documentation — feed correction cause and procedure, RIP override warning, bidirectional correction
• Epson documentation — feed calibration symptoms and triggers; unidirectional test
• Mimaki — nozzle check patterns, profile and print mode mismatch, deflection causes
• Allnex — UV ink does not dry by evaporation; cured film thickness; monomer selection for flow and levelling; no post-exposure polymerisation
• Marabu — cure dependent on dryer design, age and performance; 24-hour final adhesion
• ASTM D5402-19R24 — solvent rub practice scope and its explicit refusal to specify solvent, rub count or result