Hot Seal Strength (Hot Tack) evaluation of Thermoplastic Polymers and Blends Comprising the Sealing Surfaces of Flexible Webs is done by ASTM F1921. Seal strength, the maximum peak force, threshold sealing temperature, and hot tack temperature range are determined for a thermoplastic polymeric material.
ASTM F1921 test used to measure the strength of heat seals formed between thermoplastic surfaces of flexible webs. The seal is quickly measured after it has been created and before it cools to room temperature. This characteristic is significant because such situations often occur on vertical form-fill-seal packaging. The contents are released into the bag instantly after the horizontal seal bars have been opened in the procedure. The content can be heavy and also the hot seal has to deal with high loads, so a high hot tack force is required to overcome such obstacles.
For ASTM F1921 test, the film sample is used which is fixed in the upper sample grip. The sample is linked to a load cell and the lower sample grip is linked to a peeling actuator. Then, the film sample is placed between the sealing bars. This is achieved by a sample insertion mechanism. Under specified conditions of temperature, pressure, and contact time, a seal is prepared. At the final sealing time, after a predetermined delay time, the peeling actuator proceeds down with a predetermined speed and peels the hot seal completely apart. Hot tack force is used to determine the maximum force required to break or peel the seal.
Generally, a rectangular sample is used. The sample width can be either 25 mm, 15 mm, or 1.00 inch. The length of the sample must be between 250 and 350 mm.
Seal strength; the maximum peak force.
Threshold sealing temperature; the minimum temperature at which the required hot tack strength is reached.
Hot tack temperature range; the temperature range in which the required hot tack strength is acquired.Failure Mode (Similar to ASTM F88)