Nozzle blockage: reading the test print and fixing the right thing

A nozzle check is not a pass/fail test. It is a diagnostic, and it tells you far more than whether nozzles are missing — it tells you why. Read it properly and you will stop running cleaning cycles at problems cleaning cannot fix.

Mimaki’s seven patterns

This is the most useful diagnostic table published by anyone in the industry, and almost nobody quotes it. Match what your test print looks like to the cause.

Note the last two. Deflection with a straight line means something is sitting on the plate and can be wiped. Deflection that looks curly and weak means the obstruction is inside the channel, and wiping will not reach it.

The cheapest test in the shop

Run three nozzle checks with a normal cleaning between each, and watch whether the gaps move.

• Dropouts that move around — air in the line. Check ink level, dampers, and every connection between cartridge and head. Cleaning will not fix air; it will just spend ink.
• Dropouts in the same place every time — dirty or blocked nozzles. Now cleaning is the right tool.

Two minutes of testing tells you which of two completely different repairs you are doing.

When to stop cleaning

Roland is explicit that cleaning has a cost: “Each level of cleaning consumes more ink than the previous level. If these levels of cleaning are performed too often, the print heads are likely to wear out; do not over clean at any level.”

A working rule: normal cleaning twice. If the same nozzles are still out, stop and diagnose. Escalating to powerful cleaning four times in a row is not persistence, it is wear.

Cleaning fluid: the mistake that gels your ink

Every shop has a bottle of isopropyl alcohol. Here is why it must not go near a UV head, in Mimaki’s own words:

“Aggregates are generated in the UV ink (ultraviolet curable ink) if it is mixed with water and alcohol. Do not let water or alcohol stick on the nozzle surface, cap, wiper, or anywhere near the head.”

The folklore says alcohol attacks seals. The real mechanism is worse and faster: alcohol crashes UV ink out of solution into a gel — precisely where a gel does maximum damage. You are not degreasing the head, you are solidifying the ink in it.

The manufacturers converge on the same instruction. Mimaki: “Do not use anything other than maintenance liquid 11 or 15.” Roland: “Never use gasoline, alcohol, thinner.” And on the linear guide specifically, Mimaki adds: “Do not wipe with ethanol.”

Use the maintenance fluid specified for your machine. It is not an upsell; it is formulated not to precipitate your ink.

Cotton buds destroy printheads

Roland says this twice, in two different manuals, which is a good sign of how often it happens: “Never use any implements other than the included cleaning sticks. Cotton swabs or other lint-producing items may damage the heads.”

And three rules for the sticks themselves:

• One stick per cleaning session.
• “Reusing cleaning sticks will reduce the printing quality.”
• “Do not put a used cleaning stick into the cleaning liquid” — that contaminates the bottle and you carry the debris back to the head next time.

Roland even lists “buildup of fibrous dust (lint) around the heads” as a named fault cause. A cotton bud leaves fibres on a surface you are forbidden to touch, next to nozzles measured in microns.

UV and solvent heads fail differently

Worth knowing if you run both, because the instinct from one machine is wrong on the other. Xaar: solvent inks “can dry out in the printhead”, so those machines spit at intervals to keep nozzles wet. But “This is less important in the case of UV-curable inks, because the ink can remain in the nozzles for hours or even days without ill effects, as long as they are not exposed to UV light or too much heat.”

So a solvent head’s enemy is evaporation, and a UV head’s enemy is light and heat. That is why the maintenance routines differ, and why leaving a UV machine open under workshop lighting is a genuine risk — covered in what actually kills a printhead. The broader difference between the ink families is in the UV, solvent or eco-solvent guide.

When it is not the nozzles at all

Plenty of “nozzle problems” are not nozzle problems. If the nozzle check is clean and the print still bands, the cause is feed calibration, bidirectional alignment or pass count — three different faults with three different fixes, all covered in reading UV print defects.

And if you keep losing the same nozzles no matter what you do, the answer is usually environmental rather than mechanical: dust, mist and static in the room. That is setting up the room.

What we are not going to tell you

Soak times. No manufacturer publishes one, so any figure you read — thirty minutes, overnight — is somebody’s habit presented as a specification. The same goes for encoder-strip cleaning fluids: no OEM names one, and getting it wrong is a warranty conversation.

And do not raise head voltage to recover a weak nozzle. Research on drop-on-demand jetting found that the probability of drawing air into the channel rises exponentially with drive amplitude. It may fire today at the cost of the channel.

Sources

• Mimaki Europe FAQ — nozzle check pattern taxonomy; UV ink aggregation with water and alcohol; approved maintenance liquids
• Roland DG user documentation — over-cleaning warning, cleaning stick rules, prohibited solvents, lint as a fault cause
• Xaar, Guide to Inkjet Printing — solvent vs UV drying behaviour in the nozzle
• arXiv:2205.06635 — bubble entrainment probability and drive amplitude