Optimizing purging time at product change in blown film extrusion by selective modification of process parameters

During the product change from colored into colorless especially at blown film extrusion, long purging times arise because of the long continuing colour haze. The purging behavior has been investigated in low density polyethylene (LDPE) films under variation of the process parameters mass flow rate and temperature. Our analysis shows that the improved purge process control and variation of the process parameter modifications during the purging process reduce the purging time and substandard goods compared to the conventional arrangements. Also the study examines the influence of different color pigments into the purging behaviour.