Cohesive Resistance
Mechanical bond integrity measured in molten heat-seal polymers immediately following jaw release determines package survival on form-fill-seal packaging lines. Resistance to mechanical separation during the cooling phase defines hot tack strength, governing how effectively a molten polyolefin seal holds heavy or bulky contents before solidifying completely. Heat-sealable layers on paperboard cartons or flexible pouches experience immediate tensile stress when dense products drop into newly formed bags.
Inadequate molten cohesive force causes seal spring-back or complete joint opening before crystallization occurs.
Packaging Execution
Automated vertical form-fill-seal machines drop dry powders or liquid products onto bottom seals milliseconds after sealing jaws withdraw. High hot tack strength allows higher packaging speeds because line operators do not need to pause production while seals cool down to ambient temperature. Test procedures according to ASTM F1921 measure force required to pull apart a heat seal at specified dwell times and sealing pressures.
Polymer choice directly influences performance, with ionomers and metallocene polyethylene resins offering high initial cohesive force at lower sealing temperatures.
Thermal Window
Peak performance occurs within a specific temperature range bounded by the polymer melting point and the onset of thermal degradation. Lowering hot tack strength occurs when excess heat reduces melt viscosity before seal solidifying occurs.
