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