Glossary · Accessories

UV printing

Primer (UV printing)

A thin, clear liquid that is wiped onto the material before printing. It ensures that the UV ink does not flake off smooth surfaces.

Explained in more detail

Primer acts as an adhesion promoter between the substrate and the UV ink. It is needed mainly for glass, ceramic, metal, stainless steel and many plastics such as PP, PE or silicone, whereas on wood, leather or coated boards it is often not needed. There are primers for specific groups of materials, and the right type depends on the substrate. It is applied thinly with a lint-free cloth or sponge, and depending on the product the primer must then flash off for a few minutes. Degrease the substrate beforehand, for example with isopropyl alcohol. Some printers can also print primer through a separate channel.

Where does the term come from?

The word comes from the English "to prime" = to prepare, which goes back to the Latin "primus" = the first. The primer is therefore the first layer, which prepares the substrate for everything that follows.

In practice

• Apply slightly beyond the later print area, so that the edges of the design also lie securely on primer.
• Thin is better: too much primer stays soft, forms streaks or visibly shines next to the design.
• Print promptly after flashing off; many primers lose effectiveness after a certain time.
• Check adhesion after half an hour at the earliest, and the cross-cut test to DIN EN ISO 2409 is more precise than adhesive tape.
• For PP and PE, normal plastic primers are usually not enough, and a special primer is needed; silicone remains unreliable even with it.

Not to be confused

Primer is not a cleaner: grease, fingerprints or release agents prevent adhesion even with primer. Always degrease beforehand.

Frequently asked questions

Do you need primer for wood?

Untreated wood usually accepts UV ink well and needs no primer. With varnished or oiled wood it depends on the coating, and only a test helps here.

How long must primer flash off?

Until the surface is no longer tacky, which is a few minutes for many products. The exact time is stated on the primer and can vary with temperature.