An In-Depth Factory Analysis: The Impact of Poor Adhesion of TPE Materials on Finished Products

On the production floor for TPE material overmolded products, poor adhesion is one of the most common causes of batch scrapping and customer complaints leading to returns. When the bond between the soft rubber layer and the rigid substrate fails to meet the design strength requirements, the problem often extends beyond mere “delamination.” It cascades through five areas—structure, sealing, appearance, durability, and functionality—ultimately turning a TPE material finished product that should have been acceptable into scrap. The following is a layer-by-layer breakdown of this failure.

I. Structural Separation

The most direct manifestation of adhesive failure is the inability to form an effective bond between the TPE layer and the substrate. Under load, the overmolded layer may peel off entirely or develop localized blisters or voids, with a noticeable looseness when pressed. The edges are prone to curling, creating gaps between the overmolded layer and the substrate. This phenomenon indicates that the two layers remain separated, failing to meet the design objectives of the overmolding process.

II. Loss of Sealing

For products that rely on TPE overmolding to achieve a seal—such as waterproof plugs, automotive headlight seals, and outdoor connector housings—microscopic gaps at the bonding interface become pathways for moisture and dust to penetrate. Once the seal is compromised, internal components face risks such as short circuits, corrosion, and fogging. At this point, the TPE material’s inherent weather resistance and elasticity can no longer function effectively, as the sealing system as a whole has failed.

III. Abnormal Texture and Appearance

Areas with poor overmolding adhesion produce a hollow sound when pressed, accompanied by the sound of air being squeezed between the delaminated layers, which directly affects the user’s perception of the product’s sturdiness. Visually, delamination often manifests as localized whitening, a hazy appearance, or color discrepancies due to abnormal light refraction; peeling edges further compromise the product’s overall aesthetic and refinement.

IV. Insufficient Long-Term Durability

Even if the product barely passes visual inspection at the time of shipment, weak bonding carries the risk of gradual failure over the product’s service life. Differences in the thermal expansion coefficients between hard and soft plastics mean that repeated expansion and contraction caused by changes in ambient temperature will cause the weak bond interface to gradually peel away, eventually leading to complete separation. Such failures often become apparent only after the user has used the product for some time; the costs and impact of addressing them are far greater than those of intercepting them during production.

V. Interruption of Functional Transmission

In components involving power transmission or cushioning—such as the outer rings of casters, coupler elastomers, and shock-absorbing pads—the bond between the TPE material and the substrate is responsible for transmitting torque or impact loads. A weak bond can cause slippage at the interface, preventing effective torque transmission and reducing the ability to absorb impact energy, which directly affects the equipment’s functional output.

How can you determine if the bond is reliable?

First, peel test: Peel the overmolded layer away from the substrate and observe whether the fracture occurs within the material itself rather than at the interface. A smooth separation at the interface indicates insufficient adhesion.

Second, cross-section inspection: Cut a slice perpendicular to the interface and examine the transition layer under a microscope to check for voids or gaps.

Third, peel strength test: Measure peel strength using a tensile tester to obtain quantitative data as a basis for judgment.

In summary, when addressing adhesion issues from a materials perspective, the root cause often lies in the overmolding material’s insufficient affinity for the substrate, rather than relying solely on adjustments to the injection molding process. Zhongsuwang’s overmolding tpe materials are formulated to match common substrates such as PC, PA, and ABS, reducing the risk of adhesion failure at the compatibility level. Both the peel strength and the retention rate of adhesion after aging have been systematically verified.