Extrusion & Post
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LLDPE blown film machine-direction strength
Problem Phenomenon
Film machine-direction tensile strength is insufficient, tearing along the machine direction during packaging use
Cause Analysis
Too small a draw ratio gives insufficient molecular orientation in the machine direction; too high melt temperature breaks molecular chains; too fast cooling rate causes uneven crystallization; LLDPE itself is stronger than LDPE but this must be realized through process
Solution
①Increase draw ratio to 1.5-3 times to enhance orientation; ②lower barrel rear-zone temperature to prevent degradation; ③adjust frost line to optimize cooling gradient; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
LLDPE machine-direction strength is pulled by the draw ratio; the 1.5-3 times orientation range plus temperature protection is needed to realize the performance advantage; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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