Extrusion & Post
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LDPE Film Sharkskin
Problem Phenomenon
Periodic ripples like sharkskin appear on the film bubble surface, and the gloss of transparent film is lost
Cause Analysis
Melt fracture is a manifestation of extrusion shear stress exceeding the critical value; die temperature too low or resin melt index too low both trigger it; the elastic melt of LDPE long branched chains is sensitive to this
Solution
① Raise the die temperature by 10-20℃; ② switch to high melt index resin; ③ add fluorinated elastomer processing aid PPA; after adjustment, take continuous samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
The essence of sharkskin is the shear critical; the three routes of raising die temperature, changing melt index, and adding PPA are selected according to cost; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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