A good seal is essential for successful POF shrink packaging.
If the seal is weak, burns through, or the film breaks during shrinking, the problem may be related to the film, sealing machine, sealing temperature, or shrink tunnel settings.
Understanding when the problem occurs is the first step to finding the right solution.
Common POF Shrink Film Sealing Problems
1. Weak Seal or Seal Opens Easily
A weak seal is usually caused by insufficient heat, sealing time, or pressure.
Common causes include:
Sealing temperature is too low
Sealing time is too short
Insufficient sealing pressure
Dirty or worn sealing blade
Incorrect film positioning
Unsuitable film thickness or specification
Solutions
Check the sealing temperature, time, and pressure first. Clean the sealing blade and replace damaged Teflon tape if necessary.
Do not simply increase the temperature to the maximum, as excessive heat can damage the film.
2. Seal Burns or Develops Holes
If the sealing area becomes burned, brittle, or develops holes, the sealing temperature or contact time may be too high.
Possible causes include:
Excessive sealing temperature
Excessive sealing time
Excessive pressure
Damaged sealing blade
Reduce the sealing temperature or sealing time gradually and check the sealing components.
3. Film Breaks After Shrinking
Sometimes the seal looks normal after sealing, but the film breaks after passing through the shrink tunnel.
In this situation, two factors should be checked first:
Excessive shrink tunnel temperature
If the tunnel temperature is too high, the film may become damaged and break during shrinking.
Insufficient air escape
If there are not enough perforations or air-escape holes, air can become trapped inside the package. During heating and shrinking, the trapped air can create excessive pressure and cause the film to rupture.
Therefore, if the film breaks after shrinking, check:
Shrink tunnel temperature
Number and size of air-escape holes
Perforation condition
Film thickness
Airflow and conveyor speed
For products that trap more air, proper perforation is especially important.
Recommended Sealing Temperature for POF Film
Sealing temperature depends on the film type and packaging machine.
As a general starting point, we recommend:
| Film Type | Sealing Temperature |
|---|---|
| Standard POF | Around 180°C |
| Cross Linked POF | Around 190°C |
Cross Linked POF generally requires a higher sealing temperature because it is more difficult to cut through during the sealing process.
These are starting recommendations. The actual temperature may need to be adjusted according to film thickness, sealing time, pressure, machine speed, and sealing blade condition.
Standard POF vs. Cross Linked POF
Cross Linked POF Shrink Film generally provides higher seal strength and better puncture resistance than Standard POF.
It can also achieve a shrink rate of 75% or more, while Standard POF generally reaches around 60%.
For demanding applications, Cross Linked POF can provide more stable performance during sealing and shrinking.
However, correct machine settings are still important.
Sealing Temperature vs. Shrink Tunnel Temperature
Sealing temperature and shrink tunnel temperature are two different parameters.
Sealing temperature: used to seal and cut the film.
Standard POF: around 180°C
Cross Linked POF: around 190°C
Shrink tunnel temperature: used to shrink the film around the product.
For Standard POF, a typical starting range is around 115°C–140°C.
The actual tunnel temperature depends on film thickness, product size, tunnel design, airflow, and conveyor speed.
How to Troubleshoot POF Film Problems
A simple method is to determine when the problem occurs.
If the seal is weak immediately after sealing:
Check:
Temperature + Time + Pressure + Sealing Blade
If the film breaks only after shrinking:
Check:
Shrink Temperature + Air Escape + Perforation + Film Thickness
Change one parameter at a time during testing. This makes it easier to identify the actual cause.
Conclusion
Most POF shrink film sealing problems can be solved by correctly matching the film with the sealing machine and shrink tunnel.
If the seal is weak, check the sealing temperature, time, pressure, and sealing blade.
If the film breaks after shrinking, check the shrink tunnel temperature and whether enough air can escape from the package.
For demanding applications, Cross Linked POF can provide higher seal strength, better puncture resistance, and shrinkage of 75% or more.
The key is not simply using more heat, but finding the right combination of film, sealing temperature, machine settings, shrink tunnel conditions, and air escape.
FAQ
Why is my POF shrink film seal weak?
Common causes include low sealing temperature, short sealing time, insufficient pressure, or a dirty sealing blade.
Why does POF film break after shrinking?
The shrink tunnel temperature may be too high, or there may not be enough perforations for trapped air to escape.
What is the recommended sealing temperature for POF film?
As a starting point, Standard POF is around 180°C, while Cross Linked POF is around 190°C.
What is the shrink tunnel temperature for POF film?
For Standard POF, a typical starting range is around 115°C–140°C, depending on the film, product, and shrink tunnel.
Is Cross Linked POF stronger than Standard POF?
Cross Linked POF generally provides higher seal strength and puncture resistance and can achieve a shrink rate of 75% or more.
