Five testing modes
The MAGMA test system performs five types of tests:
- Hot tack test
- Heat seal test
- Combined hot tack and heat seal test
- Pre-aged seal (heat seal only)
- Post-aged test (tensile test only)
It follows the test methods in ASTM F1921 and provides test data well beyond the ASTM standard. With its many modes of operation the MAGMA test instrument is designed to deliver maximum flexibility and versatility.
Hot tack test
The strength of a hot seal at a defined time after the seal is formed is known as its hot tack. It is measured before the seal comes to ambient temperature.
In form-fill-seal packaging applications, understanding hot tack properties is important. The freshly-formed package seal must resist the stresses of machinery handling during the first second or less from exiting the seal jaws to being delivered to the conveyor belt. During this period the seal is cooling and its strength is increasing.
The MAGMA test system measures the packaging film’s heat seal strength versus time during this critical interval, and thus characterizes the hot tack behavior of the heat seal as a cooling curve. The system performs the measurement by first sealing the film sample under the specified conditions of jaw temperature, jaw pressure and dwell time. As soon as the jaws open, the test system immediately withdraws the film under very high speed and immediately performs a tensile test. From that tensile data the cooling curve is created and discrete seal forces are recorded, typically at 250ms and 500ms.
Heat seal test
A heat seal test determines the strength of the packaging film’s heat seal after stabilizing at ambient temperature. In this mode MAGMA operates the same as in the hot tack test mode, until the hot seal has been withdrawn from the jaws. But instead of immediately doing a tensile test, MAGMA automatically cools the seal to ambient temperature for a programmable length of time using a selectable amount of air flow. Once cooled the seal is pealed apart with the resulting tensile data recorded for creating the strength profile.
Combined hot tack and heat seal test
Combining hot tack and heat seal tests saves substantial time when curves for both are needed. In the combined mode, at each temperature step the Pilot software prompts the operator to load specimens for either the hot tack test or heat seal test. After both tests are run, Pilot automatically increments to the next temperature where both test modes are run. This saves valuable time as compared to waiting for temperatures to increment and stabilize for all temperature steps in separate heat seal and hot tack tests.
Pre-aged seal (heat seal only)
This mode is heat seal only, where the operator inserts the test specimens into the system as normal. The system forms the seal under the programmed conditions of temperature, pressure and dwell, and then stops. The seal is not peeled apart as is done in a complete test. Rather, the operator removes the sealed film for age-conditioning and for later testing in the post-aged mode.
Post-aged test (tensile test only)
When used in this mode, the MAGMA test system acts as a tensile tester to peel apart pre-aged heat seal samples to measure their strength. Samples that have been sealed and aged the required time are simply inserted into the system for peel testing.