Extrusion & Post
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LLDPE blown film sharkskin
Problem Phenomenon
Periodic ripples like sharkskin appear on the bubble surface, and transparent film loses gloss
Cause Analysis
LLDPE has high melt fracture sensitivity; too low die temperature or too low resin melt index triggers it; narrow MWD lacks shear thinning, making the critical shear rate lower; when troubleshooting on site, verify item by item according to this mechanism to avoid blindly adjusting the machine based only on experience
Solution
①Raise die temperature by 10-20°C; ②switch to high melt index resin; ③add fluoroelastomer processing aid PPA; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
LLDPE sharkskin is harder to cure than LDPE; raising die temperature, changing melt index and adding PPA often need to be combined; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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