When UV ink comes off during a tape test, the primer is often blamed first. However, poor adhesion can also result from the film surface, contamination, incomplete primer drying or incorrect UV curing.

Here, “adhesion promoter” refers to a primer applied before printing. No single grade is suitable for every plastic film.

Choose the Primer by Substrate

PET and BOPET films often benefit from a primer when direct UV ink adhesion is insufficient.

For corona-treated PET and BOPET, SA-235 PET film primer is designed to support UV ink adhesion, leveling and gloss.

BOPP, PP, OPP and PE have lower surface energy. Their surface-treatment level should be checked before coating.

For these films:

SA-248G provides a gloss printing surface.

SA-248M provides a matte finish.

Check the Process First

Before changing the primer, check:

Film surface treatment and cleanliness

Dust, oil or migrating slip additives

Primer coating and drying

UV ink thickness and curing energy

Surface treatment may decay during storage, so film from different batches can produce different results.

PP Film Application Example

In one pearlescent PP film application, UV ink showed poor adhesion when printed directly on the film. The original film was compared with a primed sample using the same ink and curing conditions.

Visible ink removal occurred on the unprimed film during the tape-peel test. The primed sample showed no visible ink removal in the same test.

Select Tests According to the Application

A dry tape test is useful for initial screening. If the printed film will face moisture, heat or repeated handling, water, rub, scratch and aging tests should also be included.

Primer selection should be based on the actual film, surface treatment, UV ink, production process and end-use conditions.

Contact: sales@sinogracechem.com