Air must leave the pack without weakening the sleeve
PE shrink film around a sleeve sealed pack needs a controlled route for air to escape as the bundle enters the tunnel and the film shrinks.
If air cannot escape, the pack can balloon, wrinkle or shrink unevenly. If too much air escapes too quickly, the bundle can lose tension or expose a weak seal. The correct answer depends on film, pack shape, perforation method, bullseye size and tunnel airflow.
Factors that affect air escape
| Variable | Possible effect | What to check |
|---|---|---|
| Perforation position | Can help air escape but may change pack tightness. | Perforation location in relation to seal and product edges. |
| Bullseye size | Large openings can reduce side retention; small openings can trap air. | Finished pack photos from each side. |
| Film width and overlap | Affects seal strength, air release and finished sleeve position. | Approved roll width and finished bundle dimensions. |
| Tunnel airflow | Too little or too much airflow can show as wrinkles, holes or distortion. | Stable tunnel recipe from accepted samples. |
| Pack spacing | Uneven loading can change heat exposure and shrink result. | Line speed, pitch and transfer consistency. |
How to trial perforation and air release
- Approve the film roll specification before changing tunnel settings.
- Run representative packs through the sleeve sealer and tunnel.
- Separate air-trapping faults from weak-seal faults.
- Inspect each side of the cooled bundle, not only the top view.
- Keep accepted and rejected samples with the recorded settings.
Questions buyers ask about perforation
Does every sleeve pack need perforated film?
No. Perforation is a process variable rather than a universal requirement. The need depends on pack size, film, tunnel airflow, bundle shape and the amount of air trapped during shrinking.
A trial should confirm whether perforation improves the finished bundle without weakening the sleeve.
Can too much air escape make a pack loose?
Yes. If the film, perforation pattern or end openings release air in the wrong way, the pack may finish loose even when the tunnel is applying heat.
Loose packs should be checked against film width, shrink behaviour, bullseye, pack support and the tunnel recipe.