Definitional Parameter
Thermal parameters identify the lowest temperature at which a heat sealable coating or film achieves a specified bond strength. Determining the heat seal initiation temperature is necessary for optimizing the speed of packaging lines and ensuring the integrity of the final seal. It marks the transition from a non-tacky state to one where the polymer chains can interdiffuse across the interface.
Testing Procedure
Testing involves sealing two layers of material at increasing temperatures while keeping the dwell time and pressure constant. The heat seal initiation temperature is reached when the resulting bond can withstand a defined peel force without failing.
Production Influence
A lower starting temperature allows for faster machine speeds because the required heat can be transferred to the interface more quickly. If the heat seal initiation temperature is too high, the substrate might be damaged or scorched before a proper bond is formed. This value is heavily influenced by the chemistry of the coating, including the type of resin and the presence of any waxes or fillers.
Converters select specific grades based on whether they need a quick tack for high speed form fill and seal machines or a robust seal for heavy duty applications. Regular calibration of the sealing jaws is necessary to ensure the laboratory results match the conditions on the factory floor.
