What are the precautions for using UV varnish?

UV varnish is a kind of transparent coating, widely applied in the printing industry. It delivers glossy, attractive surfaces with smooth texture. Many patterns on commercial packaging boxes show a shiny finish, which is achieved by applying varnish during UV‑printing.

When printing graphics, UV printers normally print white ink first, followed by color ink. Varnish is over‑sprayed onto the finished color‑ink pattern. It improves gloss and adhesion of the printed image and extends its service life.

What are the precautions for using UV varnish?

1. Store UV varnish in a well‑ventilated, dark environment at 20‑35 °C.
2. In poor printing environments, dust particles falling onto wet varnish will cause raised grain defects.
3. Do not mix UV varnishes from different manufacturers.
4. Moisture or contaminants on the printing substrate will result in bubbles in the cured varnish layer.

In addition, if UV varnish application is required, select a printer model equipped with varnish function before purchasing a UV printer.

There are two common varnish‑capable designs for UV flatbed printers: ‑ One design uses two reserved channels on the white‑ink printhead for varnish output. ‑ The other design adopts an independent dedicated printhead for varnish. The white‑ink, color‑ink and varnish printheads are arranged alternately.

For the first solution: if the varnish channels get clogged, the entire white‑ink printhead has to be replaced, leading to high running costs.

By contrast, printers with an independent varnish printhead cost slightly more at purchase. Nevertheless, even when the varnish printhead is clogged, the white‑ink and color‑ink printheads remain functional for printing.

Therefore, it is recommended to choose a UV printer fitted with a separate dedicated varnish printhead.