Extrusion & Post
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EVOH extruded film longitudinal stripes
Problem Phenomenon
Continuous stripes 1-3mm wide on the EVOH extruded film surface along the extrusion direction
Cause Analysis
Local damage or uneven gap at the die lip; unstable flow generated in melt stagnation zones inside the die; pressure fluctuation at the screw front end
Solution
1) Check die lip flatness and gap uniformity ±0.01mm; 2) Clean the die interior to remove carbonized matter in stagnation zones; 3) Install a gear pump on the extruder to stabilize melt pressure; 4) Polish the die lip to Ra<0.1μm
Key Takeaway
Longitudinal stripes are caused by die defects and pressure fluctuations; die maintenance and pressure stabilization are key
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