Extrusion & Post
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Excessive Heat Shrinkage of PU Film
Problem Phenomenon
PU film heat shrinkage at 80°C >12%, exceeding the 5% dimensional stability requirement
Cause Analysis
PU extrusion orientation released upon heating causing large shrinkage; PU coefficient of thermal expansion large; film cooling froze large amounts of orientation stress
Solution
1) Reduce extrusion draw ratio to decrease orientation freezing; 2) Anneal film at 60-80°C to release orientation stress; 3) Add 5-10wt% rigid resin to reduce heat shrinkage; 4) Biaxial stretching process to balance orientation
Key Takeaway
Film heat shrinkage is caused by orientation freezing; reducing draw ratio and annealing are key
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