Extrusion & Post
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LLDPE blown film bubble instability
Problem Phenomenon
LLDPE bubbles wobble more easily than LDPE, with large thickness deviation and uneven winding.
Cause Analysis
LLDPE molecular chains are linear and melt strength is lower than LDPE, so the bubble's anti-disturbance ability is weak; excessive melt temperature and insufficient cooling further weaken stability.; During on-site troubleshooting, verify item by item according to this mechanism, avoiding blindly adjusting the machine based only on experience.
Solution
①Blend in a small amount of low melt index LDPE to increase melt strength; ②control melt temperature to prevent excessive shear heat; ③improve cooling efficiency using cold air internal cooling; ④use a bubble stabilizer.
Key Takeaway
LLDPE bubble stability is inherently weaker than LDPE; blending LDPE is the most common improvement method, and combining with cooling and bubble stabilizing devices gives better results.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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