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Heat-seal jaw temperature must exceed the sealant melt point because heat has to conduct through the outer layers within the dwell time. Thicker films and shorter dwell both require a higher jaw setting, which is why the same laminate seals at a much lower temperature on a slow machine than on a fast one.
Jaw temperature
Jaw temperature = sealant melt point + thickness allowance + short-dwell allowance
Available dwell
Dwell available = (60 / packs per minute) x jaw closed fraction
Seal integrity for food, pharmaceutical and sterile packaging must be validated by seal strength and leak testing against the applicable standard, not set from a calculation alone.
Above the sealant's optimum the layer thins and can burn through, and the outer web distorts. Seal strength typically peaks then falls, so a seal window must be established by testing across temperature.
Temperature, pressure and dwell time. All three interact — increasing pressure or dwell often allows a lower temperature, which is gentler on the film and on product in the seal area.