Extrusion & Post
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LLDPE blown film sharkskin
Fenómeno del problema
Periodic ripples like sharkskin appear on the bubble surface, and transparent film loses gloss
Análisis de la causa
LLDPE has high melt fracture sensitivity; too low die temperature or too low resin melt index triggers it; narrow MWD lacks shear thinning, making the critical shear rate lower; when troubleshooting on site, verify item by item according to this mechanism to avoid blindly adjusting the machine based only on experience
Solución
①Raise die temperature by 10-20°C; ②switch to high melt index resin; ③add fluoroelastomer processing aid PPA; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Conclusión clave
LLDPE sharkskin is harder to cure than LDPE; raising die temperature, changing melt index and adding PPA often need to be combined; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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