Sealing film failing to seal properly is one of the most frustrating issues on the production line. Leakage, detachment, false seals — the symptoms differ, but the root causes are often not the same. Based on service experience, Leadtra Packaging has identified the 5 most common causes.

1. Heat sealing temperature is set incorrectly

Too low, and the heat-seal layer doesn't fully melt — no effective bond forms between the film and bottle mouth, and it opens with a light touch. Too high, and the heat-seal layer overheats or even carbonizes, becoming brittle upon cooling and failing to seal just the same. Different film materials and bottle mouth materials require different optimal temperature ranges — you can't just copy parameters.

2. Uneven sealing pressure

Too little pressure, and the heat-seal layer doesn't press tightly against the bottle mouth, trapping air in between and creating a false seal. Too much pressure, and the film gets compressed or deformed, actually damaging the sealing layer. This is especially true for plastic bottles — excessive pressure can deform the bottle mouth locally, causing leaks right after sealing.

3. The bottle mouth isn't clean

Residual oil, moisture, or dust on the bottle mouth creates an isolation layer between the film and the bottle mouth during heat sealing. It looks sealed, but it's actually just resting loosely on top. This is one of the most common causes of false seals — and one of the easiest to overlook.

4. Film material doesn't match the bottle mouth material

Different bottle mouth materials have different affinities for the heat-seal layer. PET bottles and PE bottles require different adhesive formulations. Use the wrong one, and it either won't seal or won't tear open.

5. Equipment parameters or hardware aging

Aging induction coils, degraded capacitors, or excessive distance (air gap) between the coil and bottle mouth all lead to insufficient actual output power. The equipment looks like it's working normally, but the sealing effect has already been compromised.

Sealing failure is often not a single factor but several overlapping issues. When problems arise, it's advisable to troubleshoot item by item — first check temperature and pressure, then bottle mouth cleanliness, then confirm film material compatibility, and finally inspect equipment condition. If the problem persists after troubleshooting, send a sample to Leadtra Packaging — we'll help analyze the cause and match a solution.