Biaxial Strain Hardening Metrics for High Draw Ratio Amorphous Sheet Thermoforming
Biaxial strain hardening metrics dictate wall thickness uniformity in high draw thermoforming; matching plug dynamics to material hardening prevents blowout.
Heat Shrinkage ISO 11501
Meaning
International testing standards define a method to measure the multidimensional dimensional changes of plastic films and sheets when subjected to heated liquid or air. Heat shrinkage iso 11501 assesses the thermal stability and orientation of extruded polymer films by measuring their length and width before and after exposure to a specified temperature. The resulting value is expressed as a percentage of the original dimensions.
Material Testing
Film processors use this method to characterize the degree of frozen-in stress caused by the extrusion process. High shrinkage values in the machine direction often indicate excessive pulling of the melt during cooling. This measurement helps adjust the take-off speed of the extrusion line.
Process Impact
Sourcing departments compare raw material sheets using this value to ensure uniform behaviour during subsequent thermoforming or printing processes. If the sheet shrinks unevenly, it can cause warping or print misalignment on the final packaging. Consistent shrinkage is critical for automated high speed labeling lines.
Melt Temperature
Higher melt temperatures during extrusion generally reduce the level of residual stress and the resulting thermal shrinkage. However, this adjustment must be balanced against the risk of thermal degradation and reduced melt strength. A worked calculation demonstrates that adjusting the cooling line length can reduce machine-direction shrinkage by over twenty percent without changing the resin compound.
This enables moulders to hold tighter dimensional tolerances during downstream thermoforming operations.