Hot Seal Strength (Hot Tack) of Thermoplastics ASTM F1921 method B data for optimizing heat seals in film and flexible packaging materials.

Hot tack measures the strength of heat seals formed between thermoplastic surfaces of flexible webs, immediately after the seal has been made and before it cools to room temperature. This property is important since this situation frequently occurs on vertical form-fill-seal packaging. In this process, the contents are dropped into the bag immediately after the horizontal seal bars have opened. Since the content can be heavy, the hot seal must be able to withstand high loads, thus requiring a high hottack force.

The film sample is fixed in the upper specimen grip which is connected to a load cell and the lower specimen grip which is connected to a peeling actuator. The film sample is inserted between the sealing bars by means of a specimen insertion mechanism. A seal is made under defined conditions of temperature, contact time and pressure. At the end of the sealing time, and after a preset delay time, the peeling actuator moves down with a preset speed and peels the hot seal totally apart. The maximum force required to peel or break the seal is the hottack force.

Specimen size:
A rectangular specimen is used. The specimen width may be either 25 mm, 15 mm or 1.00 inch. Specimen length must be adequate for the testing machine (range of 30 to 35 cm; 12 to 14 in).

Threshold sealing temperature; this is the minimum temperature at which the required hot tack strength is reached.

Seal strength, which is the maximum peak force.

The hot tack temperature range, this is the temperature range in which the required hottack strength is obtained.

Failure Mode (Equivalent to ASTM F88)

**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Standards can be obtained from appropriate standards authorities.

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