Hot Seal Strength ASTM F1921

When it comes to packaging, ensuring the integrity of seals is paramount. The strength of these seals directly translates to the safety and quality of the packaged contents. One of the critical tests in this domain is the Hot Seal Strength, as defined by ASTM F1921. This standard is instrumental in evaluating the performance of heat seals under specified conditions.

Understanding Hot Seal Strength

Hot seal strength testing revolves around assessing the force required to peel or break a seal while it is still hot. This is particularly relevant for packages that are filled and sealed in a single, continuous process, such as vertical form-fill-seal operations. During this procedure, the heat seal must be strong enough to hold the contents immediately, without waiting for it to cool down to room temperature.

Procedure and Equipment

The standard procedure involves fixing a film sample between two specimen grips connected respectively to a load cell and a peeling actuator. The sample is then sealed under controlled conditions of temperature, pressure, and contact time. Following a predefined delay, the actuator peels the seal apart, and the maximum force recorded is termed the hot tack force.

The typical equipment used for this testing includes precision instruments to accurately measure these parameters. For more detailed information on the specifics of the instruments used, you can View Details

The Importance of ASTM F1921

ASTM F1921 provides a standardized methodology for determining hot seal strength. This ensures consistency and reliability across different tests and laboratories. Two key pieces of data are derived from this test: the threshold sealing temperature and the maximum peak force, both of which are critical for quality control in packaging operations.

Scope:
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 hot tack force.

Procedure:
The film sample is secured 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 hot tack 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).

Data:
Threshold sealing temperature; this is the minimum temperature at which the required hot tack strength is achieved. Seal strength, which is the maximum peak force.

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