Extrusion & Post
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LDPE Blown Film Melt Fracture Sharkskin
Problembeschreibung
The film surface shows wavy periodic patterns, commonly called sharkskin, with reduced transparency and gloss.
Ursachenanalyse
The melt viscosity is high, forming a velocity gradient inside the die that forcibly drags the surface layer, showing wavy patterns after freezing; low die gap temperature, small gap, and low melt index all aggravate it.
Lösung
①Raise temperature settings to improve flowability; ②Raise die lip temperature to reduce viscosity; ③Widen the die gap to weaken the velocity gradient; ④Use PPA processing aid or blend in an appropriate amount of LDPE to improve rheology.
Wichtigste Erkenntnis
Sharkskin is the surface manifestation of shear instability; raising temperature, widening the gap, and adding additives are quick countermeasures, while adjusting resin rheological properties is the fundamental solution.; After confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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