In TPE overmolding (secondary injection molding), a key point involves ensuring that TPE adheres well to the substrates being overmolded, such as PP, ABS, PC, or PA. To facilitate good bonding, according to the principle of chemical similarity, it is pivotal that the TPE possesses a polarity closely resembling that of the substrate, enabling molecular chain fusion between the TPE and the substrate. Hence, the nature of the substrate determines the TPE formulation, and the parameters of the secondary injection molding process – such as the secondary injection temperature – significantly affect the bond strength between the TPE and the underlying material.

TPE Overmolding Formulations and Characteristics:

TPE Formulations:
For diverse substrates like PP, PC, ABS, or PA, unique TPE formulations and grades are necessary. As such, it is wise to partner with a robust TPE manufacturer, since TPE distributors or traders often possess only cursory knowledge of TPE formulations.

Overmolding Various Substrates:
When overmolding PP, a polymer with very low polarity, an SEBS-based TPE is particularly compatible due to its comparable polarity. Therefore, for PP overmolding, a standard TPE formulation is usually sufficient without requiring any additional polar modifiers. Although TPEs designed for PP overmolding are quite adaptable, the secondary injection molding temperature remains vital. An appropriate injection temperature should be used to guarantee adequate fluidity of the TPE and swift encapsulation onto the PP surface, creating a rapid fusion layer that fosters strong adhesion between the TPE and PP, while avoiding thermal distortion of the PP component during the molding process. The suggested secondary injection molding temperatures for PP overmolding are between 170°C and 220°C. Note: For PP overmolding applications, it is not advised to utilize SBS as the base material for TPE modification.