01
First, define the failure precisely
| Observed symptom | Questions that narrow the investigation |
|---|---|
| Open or weak seal | Is the failure across the entire seal or localized? Does it peel at the interface, tear the film, or separate within a laminate? |
| Intermittent leak | Does frequency change by lane, jaw, roll, shift, speed, temperature, or time since startup? |
| Contaminated seal | What product is in the seal, when does it arrive, and do dust, crumbs, oil, liquid, or product temperature change seal formation? |
| Wrinkle or channel | Where does the wrinkle begin? Is web tracking, pouch presentation, product, gusset, zipper, jaw alignment, or tension creating a path? |
| Seal opens after filling | Does failure occur immediately while hot, after cooling, during product drop, in case packing, after a drop, or later in storage? |
| Delamination near seal | Is heat, pressure, chemistry, flexing, adhesive cure, or material interaction involved? Preserve the failure surface for analysis. |
02
Preserve evidence before adjusting the process
Failed packages
Keep failures as found. Mark the seal location, lane, direction, time, and observed event. Do not pull every failure apart before review.
Good comparison samples
Collect material made near the same time and from known good production, plus historical approved retains when available.
Traceability
Photograph roll or pouch labels and record supplier lot, roll, item, revision, lane, equipment, shift, operator, and case or pallet location.
Process conditions
Record actual temperature by zone, pressure, dwell, speed, tension, cooling, product temperature, room conditions, and every change made.
Frequency and pattern
Count failures and map them by time, lane, jaw, location, roll footage, and operating condition instead of relying on general descriptions.
03
Treat sealing as a system
Heat
Actual seal-interface temperature can differ from a controller setpoint. Warm-up, cycling, jaw coverage, speed, contamination, and heat transfer through the web matter.
Time
Dwell decreases as speed rises. A material may make an acceptable final seal at a slower cycle but lack hot strength when released quickly.
Pressure
Pressure must be present, even, and applied through aligned surfaces. Worn components, jaw deflection, buildup, or misalignment can create local channels.
Sealant
Seal initiation, operating window, hot tack, contamination tolerance, chemistry, and sealing to itself or another substrate all influence the result.
Geometry and presentation
Wrinkles, gussets, folds, zippers, fitments, pouch tracking, web tension, and product in the seal can prevent continuous contact.
Cooling and load
The seal may be stressed by product weight, trapped air, belts, guides, drops, or case packing before it develops final strength.
04
Run a controlled investigation
- Write a specific failure statement with location, timing, frequency, and failure mode.
- Compare failed and good samples and identify what changed in material, product, setup, equipment, environment, or handling.
- Check basic mechanical conditions: cleanliness, alignment, wear, pressure distribution, tension, tracking, timing, and actual temperatures.
- Rank likely mechanisms from the evidence. Choose the smallest test that can distinguish among them.
- Change one variable or one controlled group of variables while recording output, waste, speed, seals, and samples.
- Confirm the corrective action over enough time and material to show that the failure pattern is controlled.
- Update settings, specifications, preventive maintenance, training, or change-control documents so the learning survives the trial.
05
Match the test to the question
Seal strength, leak detection, burst, hot tack, visual inspection, and distribution tests answer different questions. Choose the method and acceptance criteria based on the package and failure mechanism. A single strong strip pulled from one location does not demonstrate that every production seal is continuous.
| Question | Possible evaluation |
|---|---|
| How much force separates the seal? | Seal-strength testing with controlled specimen preparation, width, pull rate, and tail-holding technique |
| Does a gross channel or leak exist? | Appropriate bubble-emission, pressure, vacuum, dye, or other package-integrity method |
| Will the seal hold while still hot? | Hot-tack evaluation related to release timing, product load, and production speed |
| Is the seal visually continuous? | Defined visual criteria under controlled lighting, including wrinkles, contamination, burn-through, channels, and seal width |
| Will the package survive handling? | Filled-package drop, compression, vibration, altitude, thermal, or distribution testing appropriate to the route |
FIELD CHECKLIST
Information to collect
Use this as a working prompt, then adapt the final specification or validation plan to the actual application.
- Failed and good samples preserved without destroying the failure surface
- Roll, pouch, lot, lane, equipment, shift, and time identification
- Exact seal location, failure mode, frequency, and timing
- Product, fill temperature, dusting, crumbs, oil, liquid, and headspace conditions
- Actual temperature, pressure, dwell, speed, tension, and cooling information
- Jaw condition, alignment, buildup, wear, timing, and pressure distribution
- Web or pouch presentation, tracking, wrinkles, gussets, zipper, and fitments
- Material structure, sealant, treatment, storage, age, and known changes
- One-variable trial plan and agreed success criteria
- Corrective action documented in the specification or operating standard
COMMON QUESTIONS
Questions worth resolving
Why do seals fail only when the line speeds up?+
Higher speed can reduce dwell, cooling time, registration margin, and the time available for product to clear the seal. The package may need stronger hot tack or a wider operating window, or the equipment and product timing may need adjustment.
Is seal strength the same as package integrity?+
No. Seal strength measures the force required to separate a test specimen under specified conditions. Package integrity asks whether the complete package maintains the required barrier or containment without channels, holes, fitment leaks, or other failure paths.
REFERENCES & TEST METHODS
Test methods and acceptance criteria should be selected for the actual application. These standards and technical sources support the principles discussed in this guide:
ASTM F88/F88M: Seal strength of flexible barrier materials↗ASTM D3078: Leaks in flexible packaging by bubble emission↗ASTM F2029: Laboratory heat seals for flexible barrier materials↗