Yes. And it's often the kind of effect where it "looks sealed, but actually isn't."

How do oil and moisture compromise the seal?

The heat-seal layer of the sealing film needs direct contact with the bottle mouth surface — melting, bonding, and cooling under high temperature to form a strong seal. But oil and moisture create an invisible barrier film on the bottle mouth surface, separating the heat-seal layer from the bottle mouth. The result: the heat-seal layer melts, but doesn't actually bond with the bottle mouth — it just sits loosely on top.

This type of seal has a name: a "false seal." It looks sealed, but in reality, it opens with a light touch, leaks when inverted, and detaches during transport vibration.

Where do oil and moisture come from?

Oil: contents splashing onto the bottle mouth during filling; lubricating oil dripping from equipment; grease from operators' hands contacting the bottle mouth. Moisture: bottles not thoroughly dried after washing; high workshop humidity causing condensation on bottle mouths; contents with high moisture content splashing during filling.

How serious is the impact?

False seals caused by oil lead to full-circumference failure — the larger the oil-contaminated area, the larger the failed area. Moisture-induced seal strength reduction is more subtle — water droplets vaporize instantly during sealing, forming tiny bubbles. After cooling, these bubbles become voids, allowing moisture to seep in through invisible micro-pores, causing subsequent seal detachment.

How to solve it?

Add a bottle mouth wiping or blowing step before sealing; check filling nozzles for drips; ensure thorough drying after bottle washing; have operators wear clean gloves; regularly clean conveyor belts and bottle-gripping devices to prevent oil transfer.

The most effective approach is prevention — keeping the bottle mouth clean and dry before sealing is far easier than discovering problems afterward and having to fix them.

If you're unsure whether your bottle mouth cleanliness meets standards, send your bottles to Leadtra Packaging. We'll run sealing tests to see how much oil or moisture is affecting the results, and provide targeted solutions. No two production lines are exactly alike — without testing, it's hard to give a one-size-fits-all answer.