Extrusion & Post
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LLDPE Blown Film Sharkskin
Problem Phenomenon
Periodic fine roughness (sharkskin) appears on the LLDPE film surface, gloss drops severely, and it is more obvious during high-speed production.
Cause Analysis
LLDPE molecular chains are linear, melt viscosity is high, and there is no long branched chain lubrication, so the shear stress at the die lip outlet easily exceeds the critical value and surface melt fracture occurs; the higher the line speed, the more severe it is.
Solution
① Raise the die temperature by 3~5℃; ② reduce the line speed; ③ add a fluorinated processing aid (PPA) to form a lubricating layer on the die wall; ④ polish the die lip to reduce resistance; ⑤ blend with LDPE when necessary to improve processability.
Key Takeaway
LLDPE sharkskin = high viscosity meeting high shear, and PPA is the standard solution.
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