How to Perform a Hot Tack Test in 5 Steps – ASTM F1921 Guide

The hot tack test is designed to evaluate the strength of seals made by materials that are still hot. In many packaging operations, materials are sealed while in a heated state. If these seals are too weak, they could break during further processing, leading to product loss or contamination. This test ensures that packaging materials can endure the stresses that occur right after sealing, preventing such failures.

This testing is particularly critical for vertica form-fill-seal operations, where heat-sealed areas of packages are subjected to forces while still in a hot state. The hot tack test measures the force needed to peel apart a sealed area, revealing how well the material resists these disruptive forces.

By understanding the hot tack testing process, manufacturers can ensure that their packaging materials will hold up during production, transport, and shelf life.

Hot Tack Testing Process: Step-by-Step Guide Based on ASTM F1921

1. Preparation of Test Specimens

Before beginning the test, it’s essential to prepare the test specimens properly. ASTM F1921 specifies that the specimen should be cut to a standardized width, typically 15 mm or 25 mm, to ensure consistent results. The specimens should be cut in the machine direction (MD) or transverse direction (TD), depending on the expected stress direction of the seal.

2. Setting Up the Testing Machine

The test requires a specialized machine equipped with heated jaws, capable of sealing the specimens at defined temperatures, pressures, and dwell times. The hot tack tester should have the following capabilities:

Precise control of jaw temperatures and sealing pressure
A set speed for grip separation
Automatic activation of the testing cycle upon seal jaw opening

For the best results, ensure that the machine is calibrated according to the manufacturer’s specifications, including parameters like seal bar temperature, pressure, and withdrawal rate.

3. Sealing the Specimens

Once the specimen is placed in the machine, the jaws apply pressure to seal the two strips of material. The temperature and pressure settings are carefully controlled, and the dwell time (the duration of heat application) should be appropriate for the thickness of the material being tested. Commonly used dwell times range from 0.5 to 1 second, depending on the film’s thickness.

4. Measuring Hot Tack Strength

After sealing, the grips holding the unsealed ends of the specimen begin to separate at a controlled rate. As the sealed strip is pulled apart, the force required to break the seal is recorded. This force is referred to as the hot tack strength. ASTM F1921 outlines two primary methods for this:

Method A (Fixed Delay): Measures hot tack strength at various time intervals after the jaw opening, which reflects the cooling curve of the material.
Method B (Variable Delay): Measures the peak hot tack strength after a delay, providing insight into how material strength changes over time after sealing.

5. Analyzing Test Results

The hot tack strength is plotted against time or temperature to generate a hot tack curve. This curve is critical for determining how the material performs under various sealing conditions. The test results can be used to identify the optimal sealing parameters for a specific material, ensuring the seal strength is maintained during packaging operations.

For companies looking for reliable hot tack testers, Cell Instruments offers advanced solutions like the Hot Tack Tester Series. These instruments are designed to provide accurate, repeatable results, ensuring that your materials meet industry standards like ASTM F1921.