HEAT SEAL TESTERS AND HOT TACK TESTERS

A heat sealer and hot tack tester are critical laboratory instruments that evaluate the optimal heat sealing properties of your packaging materials. Measure your temperature, pressure, and dwell time parameters with a calibrated laboratory heat sealer (ASTM F2029) to create your test specimen. Then peel the seal apart to determine the cooled seal strength (ASTM F88) or hot tack strength (ASTM F1921).

FAQs ABOUT HEAT SEAL AND HOT TACK TESTING

What is the difference between heat seal strength and hot tack strength?

Heat seal strength usually refers to the force required to separate a seal after it has cooled. Hot tack strength measures the seal’s resistance to separation shortly after formation, before it reaches ambient temperature. These measurements assess different stages of seal performance. Testing cooled seals helps evaluate finished seal strength, whereas hot tack testing assesses whether the seal can withstand forces applied while it is still hot.

Do I need a laboratory heat sealer, a seal strength tester, or a hot tack tester?

The right equipment depends on whether you need to make a controlled seal, measure its strength after cooling, or assess its strength while hot. A laboratory heat sealer prepares specimens under controlled sealing conditions. A seal strength tester measures the force required to separate a prepared seal. An instrumented hot tack tester combines sealing and strength measurement within a controlled sequence, allowing testing before the seal cools.

Which standards apply to heat seal and hot tack testing?

Three relevant standards address different parts of the testing process:

• ASTM F2029 covers laboratory preparation of heat seals and the evaluation of sealability using seal strength data.
• ASTM F88/F88M measures the force required to separate a cooled seal in flexible barrier materials and identifies the specimen’s failure mode.
• ASTM F1921/F1921M covers instrumented measurement of hot tack strength before the seal cools to ambient temperature.

These standards are not interchangeable.

How do I determine the optimum heat sealing temperature, pressure, and dwell time?

Use a controlled laboratory test programme to evaluate sealing temperature, pressure, and dwell time (the period during which the sealing jaws contact the material). Measure seal performance across the selected conditions to identify a suitable operating window rather than a single setting. Laboratory results provide a starting point for production trials, not a substitute for them: differences in jaw design, sealing area, and operating speed can affect how results transfer to manufacturing equipment.

Why is hot tack testing important for form-fill-seal packaging?

Hot tack testing assesses whether a newly formed seal can resist forces applied before it has cooled. In form-fill-seal packaging, sealed areas may experience disruptive loads while still hot. Insufficient hot tack can therefore cause a seal to separate during the packaging cycle. Testing helps compare materials and sealing conditions where early seal strength is critical, using a controlled delay between seal formation and strength measurement.

Can a seal have good strength after cooling but insufficient hot tack?

Yes. A seal’s strength while hot is not necessarily the same as its strength after cooling. A material may produce an acceptable cooled seal but provide insufficient resistance to separation during the earlier, hotter stage of the packaging cycle. Where seals are loaded before cooling, evaluate both hot tack and cooled seal strength rather than relying on the cooled result alone.

Can heat seal and hot tack testing help compare recyclable or mono-material packaging films?

Yes. These tests can help compare the sealing performance of candidate films, including structures being considered for recyclable packaging. Evaluate each material over a relevant range of sealing conditions, using consistent preparation and measurement procedures. Compare cooled seal strength and hot tack where both matter to the process. The results characterise sealing performance – they do not, by themselves, establish recyclability or the suitability of the complete package.

What factors affect the repeatability of heat seal and hot tack test results?

Repeatability depends on controlling specimen preparation, sealing conditions, and the measurement procedure. Relevant variables include specimen dimensions, temperature, pressure, dwell time, grip arrangement, and separation speed. For hot tack testing, the delay between sealing and measurement is particularly important. For ASTM F88/F88M testing, use a consistent specimen-support technique throughout a test series. Follow the selected method and record the conditions alongside the results.

Does a strong heat seal mean the package is leak-tight?

No. Seal strength and leak integrity are related but different properties. A seal strength test measures the force required to separate a specimen containing the seal; it does not demonstrate that the entire package is free from leaks. Where package integrity is a requirement, use an appropriate integrity or leak test alongside strength testing. Select the method according to the packaging materials, package design, and defects you need to detect.

How do I choose the right heat seal or hot tack tester for my application?

Start with the measurement you need: controlled seal preparation, cooled seal strength, hot tack strength, or a combination. Then confirm the applicable test method, material structure, specimen dimensions, sealing conditions, force range, and reporting requirements. For hot tack testing, also consider control of the cooling delay and test speed. Share your material and packaging-process details with RDM Test Equipment to discuss a suitable instrument configuration.