Extrusion & Post
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Insufficient orientation degree of PET film
Problem Phenomenon
The refractive index difference between the longitudinal and transverse directions of PET biaxially stretched film is insufficient; orientation degree is inadequate and strength is on the low side.
Cause Analysis
The draw ratio is too small (longitudinal <3 times, transverse <3 times); stretching temperature is on the high side, molecular chains relax too fast and orientation is eliminated.
Solution
Appropriately increase the draw ratio; reduce stretching temperature (operate at 10-20°C above Tg); accelerate the cooling rate after stretching to fix the orientation.
Key Takeaway
PET film orientation degree determines film strength; draw ratio and temperature are the core parameters.
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