Separate four different failures before adjusting the press
“Poor ink adhesion” is often used for several faults that need different corrections.
- Wetting failure: The liquid ink pulls into beads, pinholes or reticulated areas before it forms a continuous film.
- Intercoat adhesion failure: One printed color or coating separates from another layer.
- Substrate anchorage failure: The complete ink film lifts cleanly from the BOPP, PE or PET surface.
- Cure or resistance failure: Print appears acceptable at first but scratches, blocks, transfers or fails after water, oil, chemicals, heat or time.
Start by identifying which layer separates. Use a magnifier on the failed area and compare the removed material, exposed film and remaining ink layers.
| Symptom | First checks | Do not assume |
|---|---|---|
| Ink beads or leaves pinholes while printing | Surface cleanliness, wetting, print side and ink surface tension | More ink or more impression will solve it |
| Tape lifts the complete ink film from clear film | Treatment/topcoat, contamination, ink compatibility and cure | A high dyne reading guarantees adhesion |
| Only one color or varnish separates | Intercoat compatibility and cure sequence | The facestock is the only cause |
| Ink scratches off immediately | Cure, ink film weight and substrate anchorage | Extra curing is always safe |
| Print passes initially but fails after conditioning | Cure development, migration, plasticizer or chemical exposure | The first press-side test represented end use |
| Failure appears only after filling or transport | Water, oil, chemicals, abrasion, heat and container flexing | The roll stock was defective on arrival |
| One side of a film prints and the other does not | Printable side, topcoat or one-side treatment | Both sides of a clear film are equivalent |
Why are BOPP, PE and PET difficult to print without the right surface?
Many plastic films have a relatively low-energy, nonporous surface. Liquid ink must wet that surface before its binder can anchor. Film suppliers may improve printability through corona or plasma treatment, a primer, or a purpose-designed topcoat.
These approaches are not interchangeable:
- Surface treatment changes the film surface to improve wetting and bonding. Its effect can reduce with time and handling.
- Primer provides an intermediate layer intended to bond to both film and a defined print system.
- Topcoat is a functional coating formulated for particular print technologies or performance requirements.
A topcoat that works with one UV flexographic ink set may not be the best choice for water-based flexo, thermal transfer, toner or digital inkjet. Confirm the exact printing process and ink system when ordering film label stock.
What does a dyne test tell you?
Dyne solutions or pens estimate how a test liquid wets the surface under a defined method. The result can help compare the print side, detect treatment loss or screen a suspect lot. It does not directly measure the bond strength between a cured ink and the film.
Treat the result as one piece of evidence because:
- contamination can distort the reading;
- operator timing and interpretation affect the result;
- a topcoated surface may not behave like untreated film;
- ink surface tension and chemistry still need to match the substrate;
- cure, ink thickness and end-use exposure can fail even when wetting looks acceptable.
There is no single correct dyne target for every BOPP, PE, PET, topcoat and ink combination. Use the facestock and ink suppliers’ recommendations for the exact construction. Read the dyne level definition before building it into an incoming inspection plan.
Common reasons ink peels from label film
1. The wrong side of the film was printed
Some clear or white films are treated or coated on only one side. Because both sides may look similar, a roll can be loaded with the non-printable side facing the ink station or a sheet sample can lose its orientation.
Keep side identification with every sample and roll. Mark the print side before cutting pieces from the web. If one side passes and the other fails under the same controlled test, confirm the construction with the supplier rather than treating the sides as equivalent.
2. Surface treatment has decayed or become contaminated
Treatment can change with storage time, heat and handling. Dust, oil, silicone, slip additives and contact with unsuitable packaging can interfere with wetting or anchorage. Contamination may be local, so average readings can miss isolated defects.
Compare an unopened section with web exposed to handling. Check several points across the width and along the roll using the approved method. If inline corona treatment is considered, confirm that the material and topcoat permit it. Over-treatment can damage a surface or create new print defects.
3. The topcoat does not match the print technology
“Topcoated film” is incomplete as a purchasing specification. The coating must be intended for the ink or toner system, cure method and required resistance. Ask whether the construction is approved for UV flexo, water-based flexo, letterpress, offset, toner, inkjet or thermal transfer, as applicable.
AllinLabel’s topcoat glossary explains the role of the printable coating. Use the supplier’s current datasheet for the actual compatibility claim.
4. Ink chemistry or additives are incompatible
An ink can wet the film and still develop weak adhesion. Binder chemistry, solvent or water balance, viscosity, pH for applicable systems, additives and overprint varnish can affect the final layer structure. Excess additive or an unapproved mix can change cure and intercoat adhesion.
Work with the ink supplier using the exact substrate code. “BOPP” is a polymer family, not a complete print specification.
5. The ink is under-cured or the film is overexposed
UV, LED-UV, water-based and solvent-based systems develop film properties differently. Lamp output, web speed, ink film weight, color density, dryer condition and oxygen inhibition can affect cure. More energy is not automatically better. Excess heat or cure energy may distort heat-sensitive films or reduce flexibility.
Record the actual press conditions and test after the supplier-specified cure or conditioning period. A result taken immediately off press may differ from a test after the printed web has cooled or completed cure development.
6. The end-use exposure exceeds the printed system
A label may pass a dry tape test and still fail when rubbed during filling, exposed to ice water, cooking oil, cleaning chemicals, sunscreen, alcohol or repeated squeezing. The required resistance comes from the combination of film, print surface, ink, cure and any protective coating or laminate.
Define the real contact conditions before choosing a corrective action. A laminate or varnish can protect print, but it should not be used to hide weak ink anchorage underneath.
How do BOPP, PE and PET differ in this diagnosis?
| Film family | Useful behavior in label applications | Print-adhesion consideration |
|---|---|---|
| BOPP | Good clarity, stiffness and moisture resistance for many rigid packages | Usually requires a defined printable surface; confirm treatment or topcoat and print side |
| PE | Conformable and suitable for many squeezable or flexible containers | Lower stiffness and container flexing can place more strain on ink and coatings; flexibility must be tested |
| PET | High strength, dimensional stability and heat/chemical performance in suitable grades | Smooth, durable surface still needs the correct treatment/topcoat and ink system |
These are family-level tendencies, not approval statements for a specific SKU. Thickness, orientation, additives, surface layer and coating can change performance within each family. Review Film Label Materials and the relevant BOPP, PE or PET construction.
A controlled print-adhesion troubleshooting workflow
Step 1: Lock down the identity of every layer
Record the facestock SKU and lot, printable side, topcoat or treatment, adhesive and liner. Then record the ink series, batch, additives, varnish or laminate and cure system. Generic descriptions such as “clear PP with UV ink” are not enough for a repeatable investigation.
Step 2: Preserve an unprinted control
Keep a clean, identified piece of unprinted material from the beginning, middle and end of the suspect roll. Handle test areas only by the edges and protect them from silicone paper, oil and dust.
Step 3: Check wetting before cure
Observe whether the ink forms a continuous layer at production viscosity and speed. Record beading, pinholes, crawling or edge retraction. If a dyne test is appropriate for the surface, follow the test-product and facestock supplier’s method.
Step 4: Record print and cure conditions
Document speed, ink film weight or anilox specification, dryer or lamp status, number of colors, sequence and web temperature where available. Do not change treatment, ink additives and cure energy in the same trial.
Step 5: Test after a defined conditioning period
Use consistent test timing. Depending on the job and supplier method, evaluate tape adhesion, scratch, rub, fold or crumple resistance and intercoat adhesion. Record the tape type, dwell, peel direction and number of rubs rather than writing only “pass.”
Step 6: Reproduce the real application
Print and convert the intended construction, apply it to the actual container and expose it to filling, condensation, chemicals, abrasion, squeezing and storage conditions that the finished label must survive. Use a representative trial roll, not only a flat hand sample.
| Controlled comparison | What to keep constant | What it helps isolate |
|---|---|---|
| Known good vs. suspect film lot | Ink, press, cure and test method | Material age, contamination or surface variation |
| Treated/topcoated side vs. opposite side | Same film piece and ink drawdown | Print-side identification and surface preparation |
| Current ink vs. supplier-approved ink | Film, cure and test | Ink/substrate compatibility |
| Current cure vs. verified cure window | Film and ink | Under-cure or excessive exposure |
| Dry test vs. end-use exposure | Printed sample and conditioning | Chemical, water, abrasion or flex resistance |
When should you use corona treatment, primer or a different film?
Consider inline corona when the film supplier confirms that the construction can be refreshed and the press can control treatment consistently. Confirm the maximum treatment and test interval for the exact material. Do not use corona as a universal repair for contamination or an incompatible topcoat.
Consider a primer or different topcoat when wetting is acceptable but ink anchorage remains poor with the approved cure. Match it to the print process and end use.
Consider a different facestock when the film’s flexibility, heat response, chemical resistance or available print surface cannot meet the full job. For example, a squeezable PE container may need a construction that remains flexible after printing, while a durable PET application may need stronger chemical and abrasion resistance.
What should be included in a film sample request?
- Container material, shape and whether it is rigid or squeezable
- Label dimensions and clear, white, metallized or opaque appearance
- Exact printing method and ink series
- Required topcoat, primer or corona-treatment compatibility
- White ink, varnish, foil, lamination or thermal-transfer requirements
- Application and service temperatures
- Water, oil, alcohol, chemicals, UV light and abrasion exposure
- Facestock thickness and stiffness requirements
- Adhesive, liner, roll width, core and winding direction
- Test method and acceptance criteria used by the printer or brand
Request the current technical datasheet and test the production ink set on the proposed construction. A sample approved for appearance but not for print resistance is not a complete qualification.
Technical references
Independent supplier documentation used as background reading. These companies do not endorse or certify AllinLabel.
Frequently asked questions
- Does a high dyne level guarantee ink adhesion?
- No. It indicates wetting behavior under a particular surface-tension test. Adhesion also depends on treatment or topcoat chemistry, ink binder, cure, contamination, ink thickness and end-use exposure.
- Can corona treatment restore old BOPP label film?
- It may refresh a compatible film surface, but only within the supplier and equipment limits. It cannot reliably remove contamination or make every topcoat compatible with every ink. Run a controlled print and resistance test after treatment.
- Why does ink pass a tape test and later rub off?
- The initial test may not represent final cure or service exposure. Water, oil, chemicals, abrasion, heat, plasticizer contact or container flexing can reveal a different weakness. Define and test the finished label system.
- Do clear BOPP films need a topcoat?
- They need a printable surface appropriate for the selected print technology. That may be a treatment, primer or topcoat depending on the construction and ink system. Confirm the exact SKU rather than relying on “clear BOPP” alone.
- Why does PE label film print differently from PET?
- They differ in surface chemistry, stiffness, heat response and flexibility. Those family-level differences affect handling and end-use stress, but the printable surface and coating of the exact grade remain decisive.
Request a printable film construction
Send AllinLabel the print technology, ink series, container, end-use exposure and finished roll specification. Ask which BOPP, PE or PET constructions have a suitable printable surface and which sample formats are available for press-side qualification. Start with the Material Selector or request a quote or sample.