The heat sealability of plastic films is assessed by defining a heat seal window. Heat seals or welds are prepared using an RDM HSE-3 hot bar heat sealer - satisfying the requirements of ASTM F2029.
Replicate heat seals are prepared using a matrix of sealing temperature, dwell time and pressure. The resulting seals are first assessed subjectively, then using a tensile test machine to determine the optimum sealing conditions. The tensile strength of heat seals is determined in accordance with ASTM F88. ASTM F88 is also used in the validation of the seal strength of packaging for medical devices.
In addition to the sealing of plastic films, the heat sealability of heat seal blister boards is assessed by replacing one of the heated jaws with a resilient unheated jaw. Determination of a heat seal window forms part of Smithers Pira technical investigations into heat seal and blister board pack failures.
ASTM F 2029 details standard practices for making heat seals for the determination of the heat sealability of flexible webs as measured by seal strength.