Printing problems on plastic film do not always come from the same part of the process.

Ink may shrink immediately after transfer. A printed layer may look normal but fail a tape test after drying. Some problems only appear after water exposure, rubbing or when the press reaches normal production speed.

During troubleshooting, it is useful to recordwhen the defect first appearsbefore changing several ink parameters at the same time.

Printing Defects at Different Stages

The same defect can involve more than one factor, especially when the substrate, ink and primer are changed at the same time.

Ink Shrinkage and Bare Spots During Printing

Shrinkage, fisheyes and bare areas are usually visible soon after the ink reaches the film.

Fine lines and small text often show the problem before large printed areas do. A solid block may still look acceptable, while thin lines start to break or characters become incomplete.

Printing speed can make the difference more obvious. A film may run normally during a slow trial and show uneven coverage once the press returns to production speed.

Check the film currently running on the press, together with ink viscosity, surface tension and leveling.

PP, PE and PET can behave quite differently on press, so the substrate should be identified clearly during troubleshooting.

When the Print Looks Good but Adhesion Is Poor

Sometimes the ink transfers evenly and the printed surface looks normal after drying, but the coating comes off during a tape test or later processing.

That is no longer mainly a wetting problem.

Primer compatibility, ink chemistry and drying or curing conditions need more attention.

A print can have good appearance and still have weak adhesion, so visual inspection alone is not enough for applications where the printed film will be converted, laminated or handled further.

Problems Revealed by Water and Handling

Some weaknesses do not appear on the printing line.

A printed film may pass the initial inspection but turn white, lose adhesion or become unstable after contact with water.

Mechanical handling can expose a different problem. Rewinding, slitting, transportation and packaging may cause scratching or rub-off even when the print looked good when it left the press.

The test method should follow the final use of the film. If the finished material will be exposed to moisture or repeated handling, those conditions should be included during evaluation.

Matching the Primer to the Film

Anhui Sinograce Chemical uses different water-based modified acrylic primer systems for different film substrates.

SA-235is developed for PET/BOPET UV printing, with emphasis on ink acceptance, adhesion and leveling.

Both products fall within the same viscosity range, yet they are intended for different substrates. Product selection should follow the film and required performance, not viscosity alone.

Information Worth Recording During Troubleshooting

When a printing problem occurs, record a few details before making a major adjustment:

Film type

Pretreatment condition

Ink system

Printing speed

Stage at which the defect appears

Appearance of the defect

Primer coating and drying conditions

Final performance requirement

For example, “poor printing on PP” gives very little information.

“PP film, UV ink, fine lines break only at production speed while solid areas remain acceptable”gives a much clearer direction for testing.

For primer evaluation, Anhui Sinograce Chemical recommends testing with the actual film, ink system and production conditions.

Product data are useful for initial selection, but the final recommendation should still be checked with the customer's actual film, ink and printing conditions.

FAQ

1. Why does ink shrink or form fisheyes on plastic film?

Ink shrinkage or fisheyes usually appear when the ink does not wet the film evenly. Film condition, pretreatment, ink viscosity, surface tension and printing speed can all affect the result.

2. Why does the print look good but fail after drying?

If the printed surface looks uniform but peels during a tape test or later processing, the main issue may be adhesion rather than initial wetting. Primer compatibility, ink chemistry and drying or curing conditions should be checked.

3. Why does printed film turn white after water exposure?

Whitening after water contact can indicate insufficient water resistance in the complete film–primer–ink system. The test should reflect the actual moisture or water exposure expected in the final application.

4. Can the same primer be used for PP, PE and PET films?

Not always. PP, PE, OPP and BOPP have different surface characteristics from PET/BOPET. Primer selection should follow the substrate, ink system and required final performance rather than viscosity or solids alone.