Extrusion & Post
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LLDPE blown film sharkskin melt fracture
Problem Phenomenon
Periodic rough ripples on the film surface, poor gloss, alleviated after raising temperature but not eradicated.
Cause Analysis
LLDPE viscosity is high, and die exit shear stress easily exceeds the critical value causing melt fracture; small die gap and low die temperature further aggravate shear.; During on-site troubleshooting, verify item by item according to this mechanism, avoiding blindly adjusting the machine based only on experience.
Solution
①Raise die lip temperature to reduce viscosity; ②widen the die gap; ③add fluoropolymer PPA processing aid; ④appropriately reduce extrusion output.; After adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability.
Key Takeaway
LLDPE is a high-incidence material for sharkskin; PPA aid can quickly eliminate it without modifying equipment, and works better with a wide die gap.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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