Thermal Aging Tests for TPE Overmolding Compounds: A Focused Checklist

The focus of thermal aging tests for TPE overmolding compounds differs from that of standard TPE materials. While standard materials are evaluated for changes in properties such as hardness, strength, and appearance, overmolding compounds have an additional critical factor: whether the overmolded interface remains bonded at high temperatures.

In actual failure cases, problems with overmolded parts are more often caused not by material aging itself, but by a decline in interfacial adhesion after aging, leading to delamination and warping. Therefore, when evaluating TPE overmolding compounds through thermal aging testing, the focus should be on adhesion stability. Now, Zhongsu Wang shares this with you.

I. Mechanical Property Retention Is the Minimum Requirement

Changes in tensile strength and elongation at break reflect how well the TPE overmolding compounds withstand high temperatures. The industry-standard threshold is a retention rate of no less than 50% after aging; scenarios with higher requirements demand 70% or more. If this metric is not met, nothing else matters, as the material itself has already failed.

II. Adhesion Peel Test Is the Primary Acceptance Criterion

After aging, overmolded parts must undergo peel testing to observe the failure location. Before aging, failure occurs within the TPE matrix itself; after aging, it shifts to a smooth separation at the interface, indicating that thermal aging has compromised the bonding system. This shift suggests that the compatibilizer or compatibilizing components in the overmolding compound lack sufficient heat resistance, and the risk of delamination at the end-user level will become evident once mass production begins. For TPE overmolding compounds, this test is more targeted than simply examining the material’s physical properties.

III. Appearance and Dimensional Changes as Auxiliary Assessment Criteria

After aging, test specimens must not exhibit noticeable discoloration, chalking, or cracking; the edges of the overmolded parts must not peel up, and there must be no visible gaps. For sealing-type overmolded parts, compression set and hardness changes must also be evaluated to confirm that they can still rebound after being subjected to high temperatures and pressure. While these are auxiliary assessment criteria, they reflect the overall condition of the overmolding material under actual operating conditions.

IV. Combined Testing Under Special Conditions

Outdoor overmolded parts undergo supplementary UV aging testing; automotive interior components undergo SAE J2527 high-temperature cycling testing; and medical overmolded parts are tested for dimensional and bond stability after steam sterilization at 121°C. The closer the test conditions are to the actual operating environment, the more valuable the results are as a reference.

In summary, the acceptance testing for thermal aging of TPE overmolding compounds primarily involves ensuring both the material’s mechanical properties and the integrity of the interface bond. Focusing solely on the material’s aging performance while neglecting the long-term stability of the overmolding interface can easily lead to delamination issues during subsequent use. Only by establishing acceptance criteria based on the product’s actual operating conditions can TPE overmolding compounds maintain long-term reliability in complex environments.