The sealing film is applied, and everything looks normal. But after a period of storage or transport, leakage appears. This isn't a problem with any single step — it's the result of several factors overlapping. Based on common cases, Leadtra Packaging helps you sort out the main causes of leakage.

Incorrect sealing parameters — the most common cause

If the temperature is too low, the heat-seal layer doesn't fully melt, and the sealing film merely "rests" on the bottle mouth without forming a true bond. If the temperature is too high, the heat-seal layer overheats or even carbonizes, becoming brittle upon cooling and cracking under stress. Pressure is equally critical — insufficient pressure prevents the sealing film from pressing tightly against the bottle mouth, trapping air in between; excessive pressure compresses the film too thin, actually damaging the sealing layer. These three parameters must be matched to the sealing film and bottle mouth material — you can't just copy settings.

Bottle mouth condition — easily overlooked

Residual oil, moisture, or dust on the bottle mouth creates an isolation layer between the sealing film and the bottle mouth during heat sealing. It looks sealed, but it's actually a false seal — opens with a light touch, leaks when inverted. This is one of the most common yet most easily overlooked causes of leakage.

Mismatch between sealing film and 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 seal strength will be insufficient — the seal may detach after transport vibrations.

The test of the transport phase

Even if the seal is qualified, stacking, jostling, and temperature fluctuations during transport can gradually compromise the seal. This is especially true for sealing film whose heat seal strength is at a critical threshold — it doesn't leak normally, but problems emerge once it's on the road.

Leakage causes are often not singular. When troubleshooting, follow this order: first check sealing parameters, then bottle mouth cleanliness, then confirm sealing film compatibility, and finally evaluate transport conditions. If the problem persists after troubleshooting, send a sample to Leadtra Packaging — we'll help analyze the cause and match a solution.