When polyethylene bag seals fail, identify where and when the failure occurs before changing the bag or the machine settings. A weak seal, a tear beside a seal, and a leak through a wrinkle are different problems. Useful troubleshooting separates material, equipment, product contamination, and handling conditions rather than assuming one cause.
This approach applies both to seals made during bag manufacturing and closures made on a customer's packing line. The first step is to establish which operation created the affected seal.
Locate the failure precisely
Save representative failed bags and, when available, acceptable bags from the same production period. Photograph the damage before pulling the package apart. Mark the orientation, affected edge, and location relative to the product.
Determine whether the bonded surfaces separate, the film tears beside the sealed area, or a small channel remains through the closure. Also check whether the damage is actually a puncture elsewhere in the package.
Record when it was discovered: immediately after sealing, during packing, after storage, or at the customer. Those observations help distinguish a problem that exists at closure from one that develops under load. Follow your quality procedures for identifying and containing affected product while the investigation proceeds.
Compare the current run with a known good run
Start with documented differences rather than a list of guesses. Compare the material lot, approved specification, equipment, line speed, product condition, operators' observations, and maintenance history.
A useful investigation asks what changed and when. Was there a new bag lot, a maintenance intervention, a different fill weight, or a change in product temperature? Did the issue begin at startup or only after the line had been running?
Keep failed and acceptable samples traceable to these details. “The bags split” gives a supplier very little to investigate. A description such as “the customer-applied top seal opens after filling, while the factory bottom seal remains intact” narrows the discussion substantially.
Check the sealing area before adjusting heat
Observe how the bag reaches the sealing position. Product in the closure area, folded film, uneven tension, or a poorly presented bag mouth may interfere with consistent contact.
Check whether failures cluster near a gusset, overlap, fold, or location where product is likely to collect. Compare lightly filled and fully filled packages within the approved operating range. An overfilled bag may leave insufficient clean material for closure or place immediate stress on the new seal.
Have trained personnel inspect equipment condition using the manufacturer's procedures. Cleaning, maintenance, and adjustment must follow the site's safety requirements. Do not bypass guards, reach into operating sealing equipment, or treat additional heat as a substitute for resolving contamination or alignment.
Review the sealing process as a set of variables
Temperature, contact time, and pressure may all be relevant, depending on the equipment. Impulse sealing also requires attention to the specified heating and cooling cycle. The displayed setting is not a substitute for checking how the process is actually performing.
For example, Audion's temperature-controlled sealing equipment distinguishes systems by the process variables they control. That reinforces the need to understand the specific machine rather than borrow settings from a different line.
Ask the equipment supplier or qualified process personnel to help establish an appropriate operating window. Changing several settings at once can obscure the cause of a problem. Use an approved trial plan, record each change, and compare results against predefined criteria.
Confirm that the material matches the approved requirement
Review the bag construction, specified thickness and tolerance, seal configuration, and relevant material or surface changes. Do not assume two bags are interchangeable because they have similar dimensions or both are described as polyethylene.
Ask the bag supplier to compare the affected material with the approved specification and retained samples when available. Provide the actual failure samples, not only a purchase order number. Where the problem concerns a factory-made seal, the supplier's production and inspection information may be important to the review.
Laboratory evaluation can help compare constructions. ASTM F2029 addresses making laboratory heat seals to evaluate heat sealability. Its scope makes clear that laboratory results do not validate production equipment. A promising laboratory result still needs an appropriate trial on the intended line.
Distinguish seal strength from leakage
A seal-strength result answers a different question from a package leak evaluation. Treating either one as a complete substitute for the other can leave the actual failure unexplained.
ASTM F88/F88M measures the force needed to separate a specimen containing a seal and identifies the failure mode. It does not turn a few tested strips into proof that every part of a finished package is free of leaks.
The quality team should choose methods appropriate to the package and failure being investigated. Preserve details such as specimen location, conditioning, test method, and acceptance criteria. Avoid comparing results from different methods as though they were interchangeable. Do not claim compliance with an ASTM method unless the applicable procedure has actually been followed.
Check what happens after the seal is made
Sometimes the sealing operation appears consistent, but the closed bag is stressed before it can withstand the next operation. Observe how packages are lifted, transferred, compressed, cooled, stacked, or placed in an outer container.
Look for equipment edges and handling points that repeatedly contact the same location. Check whether the product pulls against the closure or whether the bag is being used to carry a load it was not designed to support.
A handling issue may require a change in support, fit, or process sequence rather than a different seal setting. Confirm the proposed correction through the full workflow, including storage and distribution conditions when they are relevant to the failure.
Common bag seal troubleshooting questions
Should we increase sealing temperature first
Not automatically. Inspect the failure, bag presentation, material, and equipment condition before making controlled adjustments. Follow the machine manufacturer's instructions and the site's approved process.
Does a strong seal prove that the package cannot leak
No. Seal-strength testing and leak evaluation address different characteristics. Select appropriate checks for the package's intended function and the failure being investigated.
What should we send the bag manufacturer
Provide failed and acceptable samples, lot identification, the approved specification, photographs, failure location, timing, and relevant process details. State whether the affected seal was made by the bag manufacturer or on your line.
Bring the evidence to Champion Plastics
Champion Plastics manufactures polyethylene bags and films for business applications. If a bag or seal is not performing as expected, contact Champion Plastics with the sample and process information behind the problem. Call 800-526-1230 to discuss the packaging requirements and how to share materials for review.