The lowest sealing temperature at which a seal reaches a stated onset or strength criterion under defined test conditions.
Also called: heat-seal initiation temperature; HSIT; seal onset temperature.
Is seal initiation temperature the melting point?
No. Seal initiation concerns the appearance of a bond meeting a stated strength criterion after a defined sealing and test sequence. It can occur below the sealant melting point for a particular laminate. The melting transition and a measured bond are different observations; their relationship depends on the material and method.
Check the criterion in the material report: first measurable strength and attainment of a specified minimum strength need not define the same onset. Compare SIT values only on a compatible method and criterion.
A published onset is not a complete production recipe. Retain the material pair, dwell, pressure, heating arrangement and strength-test conditions. Reaching an initiation criterion is different from reaching a later strength plateau or the required production outcome.
Evaluate strength, opening behaviour, appearance and integrity over the proposed operating range. A low SIT describes an onset under stated conditions, rather than all of these production outcomes.