Optimizing Thermoforming Process Windows Using Strain Hardening Rheology Metrics
Strain hardening rheology metrics define thermoforming process windows by predicting extensional melt strength to eliminate corner thinning and sheet sag.
Side Wall Banding
Meaning
Horizontal rings or lines appearing on the outer surface of a blow-moulded container indicate fluctuations in parison inflation or material distribution. This cosmetic defect, known as side wall banding, occurs when the extrusion speed or inflation pressure is unstable. It can also be caused by temperature variations in the extrusion die or mould cooling channels.
The defect is particularly visible in high-gloss or transparent packaging products.
Visual Quality
Unacceptable aesthetic variations along the container surface often lead to immediate rejection by quality control teams. While side wall banding does not always ruin the container, it can make it look cheap or flawed to the consumer. Maintaining a uniform visual appearance is important for premium consumer brands.
Process Optimization
Adjusting the blow pressure and blow time can resolve the underlying instabilities that cause the lines. By optimizing these parameters, the moulder can eliminate side wall banding without changing the resin grade. Ensuring a consistent melt temperature is also necessary to keep the parison flowing evenly.
Mechanical Consequence
Uneven material distribution in the container walls creates localized thin spots that are susceptible to crushing under vertical loads. If side wall banding is severe, the thin regions can collapse during the filling or stacking operations. This weakness reduces the top-load capacity of the finished bottle.