Extrusion & Post
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MP film excessive heat shrinkage
Problem Phenomenon
MP film heat shrinkage at 80°C >12%, exceeding the 5% dimensional stability requirement
Cause Analysis
MP extrusion orientation released after heating causing large shrinkage; MP thermal expansion coefficient large; film cooling froze a large amount of orientation stress
Solution
1) reduce extrusion draw ratio to reduce 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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