Extrusion & Post
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Longitudinal Stripes on PU Extruded Film
Problem Phenomenon
Continuous stripes 1-3mm wide along the extrusion direction on PU extruded film surface
Cause Analysis
Die lip local damage or gap uneven; melt stagnation zone in the die producing unstable flow; pressure fluctuation at the screw front
Solution
1) Check die lip flatness and gap uniformity ±0.01mm; 2) Clean the die interior to remove stagnation zone carbides; 3) Install a gear pump on the extruder to stabilize melt pressure; 4) Polish die lip to Ra<0.1μm
Key Takeaway
Longitudinal stripes are caused by die defects and pressure fluctuation; die maintenance and pressure stabilization are key
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