1. Diagnostic Approach to Blown Film Defects
Film extrusion quality depends on a precise balance between thermal melt temperature, polymer viscosity, mechanical alignment, and ambient cooling airflow. When defects occur, rapid diagnosis minimizes resin scrap and machine downtime.
2. Die Lines & Surface Streaks
Die lines appear as continuous longitudinal streaks along the film bubble. Primary root causes include degraded polymer carbon deposits on the die lip or metallic scratches on the die land. Solution: Perform die lip brass scraping, clean melt filter screens, or purge with high-viscosity cleaning resin.
3. Interfacial Shear & Melt Fracture (Sharkskin)
Melt fracture manifests as a rough, hazy surface texture caused by high shear stress at the die lip exit. Solution: Increase die lip gap, elevate die zone temperatures by 5°C–10°C, or add fluoroelastomer polymer processing aids (PPA).
4. Film Thickness Gauge Variation
Cross-direction (CD) gauge variation creates hard bands on finished film rolls. Solution: Check air ring levelness using a precision spirit level, clean clogged air ring baffles, align die center mandrel, and adjust oscillating haul-off unit.
5. Unmelted Gels & Contamination Spots
Gel spots ruin optical transparency and cause pinholes during heat sealing. Solution: Increase screw backpressure by using finer mesh filter screens (e.g., 80/100 mesh) and inspect barrel temperature profiles for cold zones.