UV ink explained: hard, flexible and specialist inks

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UV ink does not dry, it cures. As long as no UV light falls on it, it stays liquid. Only under the UV lamp does it crosslink into a solid film in a fraction of a second. If you understand how this works, you also understand why storage, ink type and white ink need so much attention.

What UV ink is made of

UV ink contains no solvent that has to evaporate. It consists of four main components, plus additives:

The shares vary considerably depending on the manufacturer and ink type. Clear varnish, for example, contains no pigment at all. What matters in practice: the photoinitiators also react to daylight and lamp light. That is why UV ink always belongs in dark containers.

Hard, flexible and in between

Most manufacturers offer at least two ink families.

Hard ink forms a very firm, scratch-resistant film. It is the standard ink for rigid materials such as metal, glass, acrylic, wood and hard plastics. On material that bends, however, it cracks.

Flexible (soft) ink stays stretchable after curing. It is intended for leather, synthetic leather, films, tarpaulins and soft plastics. Mimaki, for example, gives an elongation of up to 170 % for its flexible ink LUS-120. The price: the surface is softer and less scratch-resistant.

Some manufacturers also have a blend in their range that covers both reasonably well. With desktop machines there is often a flexible white ink as an interchangeable option, for example for leather or film.

Adhesion is not the same as scratch resistance

These two terms are often confused. Adhesion describes how well the ink holds to the material. Scratch resistance describes how hard the surface of the ink itself is. A hard ink can be very scratch-resistant and still flake off over large areas if the substrate was not prepared. Primer helps against poor adhesion; against scratches, a suitable ink, full curing and a layer of varnish help more.

Specialist inks

Besides CMYK and white there are further channels depending on the machine:

• Clear varnish (Varnish, Gloss): colourless, for gloss, protection and relief
• Primer as an ink channel: on some machines it is printed along directly instead of being applied by hand
• Light cyan, light magenta: for finer gradients in photos
• Orange, red, green: extend the colour gamut on some industrial machines

Which channels your machine has is stated in the data sheet.

Storage

UV ink is more sensitive than ordinary printer ink. Three things count:

Light. Store containers closed and dark. Even an open bottle on the workbench can start to cure at the edge.

Temperature. Manufacturers’ figures differ depending on the ink. Mimaki gives, for example, 0 to 20 °C or 5 to 35 °C depending on the ink. eufyMake states 15 to 35 °C and 30 to 70 % humidity for its cartridges. As a general rule: cool, but not frozen, and no strong fluctuations. Let cold ink come up to room temperature before inserting it.

Shelf life. Every bottle or cartridge has a date on it. Many manufacturers state about 12 months from manufacture. Expired ink can cure worse, change colour or clog the print head. So rather buy smaller quantities that you really use up.

Store cartridges upright and in their original packaging as long as they are not in the machine.

White ink settles

White ink contains titanium dioxide. These pigments are heavy and sink to the bottom over time. If that happens in the print head or in the tubes, nozzles clog. If white ink stands for too long, the sediment can become so solid that it can no longer be stirred up.

What you can do about it:

• Shaking: With machines without circulation, shake white ink before printing as the manufacturer states, often daily.
• Circulation (White Ink Circulation): Many machines pump the white ink through the system automatically at intervals. This only works if the machine stays switched on or wakes up regularly.
• Print regularly: Long pauses are particularly bad for white. More on this in Maintenance.

Original ink or third-party ink?

Third-party ink is much cheaper. But there are real risks:

• Warranty: Many manufacturers exclude damage caused by third-party ink from the warranty. Epson, for example, expressly advises against mixing other inks with its UV ink because lines and print heads can be damaged.
• Print head: The print head is the most expensive wear part. Wrong viscosity or incompatible ingredients can attack seals or clog nozzles permanently.
• Mixing: Never mix two inks in the same system. Anyone who switches has to flush the system completely.
• Colour profiles: The manufacturer’s ICC profiles only fit its own ink. With third-party ink you need your own profiles.
• Chips: Many cartridges have chips that detect third-party ink or can only be used once.

What does UV ink cost?

Prices vary widely. As a rough guide, as of 2026:

With desktop machines you often pay a multiple per litre. In return the quantities are small and the cartridges are easy to change. What that means per print is covered in UV running costs.

For business use

With small objects, ink is rarely the biggest cost factor. White, varnish and misprints make it more expensive. If you want to use third-party ink, weigh the possible print head replacement against the saving. And document the ink batch and material for every job. In the event of a complaint you then know what you printed on.

Next: Primer, Varnish and Which materials can you print on?.