Molding Process
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EMA Extruded Film Thick Edges and Thin Middle
Problem Phenomenon
EMA extruded film edges are 20-30% thicker than the middle, thickness showing a U-shaped distribution
Cause Analysis
Improper die flow channel design, low resistance and large flow at the edges; EMA melt elasticity swells more at the edges; air ring cooling has different effects at the edges
Solution
1) Adopt coat-hanger design for the die to balance the resistance between the middle and the edges; 2) Fine-tune the die gap, slightly larger in the middle and slightly smaller at the edges for compensation; 3) Slightly reduce the air volume at the air ring edges; 4) Add restrictor bars to adjust edge flow
Key Takeaway
U-shaped thickness is caused by die flow channel and swell differences; coat-hanger die and gap fine-tuning are key
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