What is UV printing? How UV printers work
are explained briefly when you hover over or tap them.
A UV printer prints colour directly onto wood, metal, acrylic, glass, leather or plastic. The ink does not dry; it cures under UV light in a fraction of a second. This lets you print on objects that would not fit in any normal printer.
The principle
Technically, a UV printer is an inkjet printer. A piezo print head fires tiny droplets onto the material. Right next to the print head sits a UV LED lamp that passes over the freshly printed area.
The ink contains liquid acrylates and so-called photoinitiators. When UV light of the right wavelength hits it, the photoinitiators start a chemical reaction: the liquid components cross-link into a solid plastic film. This is called curing. Hardly anything evaporates, and the ink stays on the surface completely.
Current machines almost always work with UV LEDs in the range of around 365 to 405 nm, often around 395 nm. Which wavelength is right depends on the photoinitiators in the ink. For this reason you should only use ink that is approved for your machine.
The result: no waiting for drying, no smearing, and you can print several layers directly on top of each other.
Types: flatbed, roll, UV DTF
| Type | How it works | Typical for |
|---|---|---|
| Flatbed | Material lies on a table, the head travels over it | Panels, signs, phone cases, small parts |
| Roll (roll-to-roll) | Material runs from the roll through the machine | Films, banners, wallpaper, more large-format |
| UV DTF | Printing onto a transfer film, which is then stuck on | curved or awkward objects |
Many desktop machines are flatbed printers with add-on modules: a rotary unit for bottles and cups and, in some cases, a film option for UV DTF. More on this in UV DTF explained.
Print heads in rough terms
Epson print heads are common in the desktop and entry-level range. Some are heads that originally come from photo printers (for example XP600 or TX800), others are industrial heads such as Epson’s i-series. Larger production machines often use heads from Ricoh, Kyocera or Konica Minolta. Brands such as Mimaki or Roland DG build their own systems around such heads.
Three points matter most to you as a user: how many colour channels a head has, how sensitive it is to drying out and what a replacement head costs. Print heads are wear parts.
Colour channels: CMYK, white, varnish
- CMYK: Cyan, magenta, yellow and black together make up the colours.
- White: covers dark or transparent substrates so that the colours stand out on them. Without white, colours would be barely visible on black wood or clear acrylic.
- Varnish (gloss): a clear ink for shine, protection or tactile effects.
Some machines have additional light colours (light cyan, light magenta) or a primer channel. How white, colour and varnish are printed on top of each other is explained in Colour, white and varnish.
What you can and cannot print on
Solid surfaces that are smooth to slightly textured are well suited: wood, acrylic, aluminium, coated metal, glass, ceramic, leather, plastics such as ABS or PVC, slate, cork, paper and cardboard.
Difficult or unsuitable:
- Textiles that get washed: The cured ink is stiff and cracks.
- Soft, highly stretchy materials: silicone, rubber, thin films without special ink.
- Very smooth, non-polar plastics such as PP or PE: without a primer the ink adheres poorly.
- Very tall objects: Every machine has a maximum print height.
- Food contact: The inside of cups, plates or boards is off limits. More on this in UV printing safety.
Glass, metal and smooth plastics often need a primer so that the print lasts.
Limits of the process
Feel: The ink sits as a thin film on the surface. On smooth materials you can feel the edge of a print, especially with white and several layers. That can be intended (relief) or a nuisance.
Outdoor durability: Indoors, UV printing is very robust. Outdoors, sun, rain and temperature changes take their toll. Colours can fade and adhesion to glass or metal can weaken. How long a print lasts depends on ink, primer, varnish and substrate. Manufacturer figures usually apply to ideal conditions.
Flexibility: Standard UV ink is rather hard once cured. If the material is bent, the print can crack. Flexible inks exist for films and leather, but they are less scratch-resistant.
Maintenance: UV ink must not be left standing in the head. White settles and has to be circulated regularly. If you only print every few weeks, you are more likely to struggle with clogged nozzles.
Typical uses
- Personalised gifts: name plates, wood pictures, phone cases, key rings
- Signage and advertising: signs, displays, samples, small runs
- A replacement for screen printing or pad printing for small quantities
- Printed 3D prints, acrylic stands, game components
- Prototypes for packaging and labels
For business use
UV printing is worthwhile above all where every piece is different and small quantities are wanted. The ink itself is usually not the biggest cost per piece. Blanks, rejects, set-up time and maintenance weigh more heavily. Before selling, clarify how your product will be used: a sign for indoors is uncritical, but a bottle opener that ends up in the dishwasher quickly leads to complaints.
Next: UV printing, DTF or sublimation? and UV printing safety.