TPE Over-Moulding, also known as Overmoulding, refers to the process where TPE (Thermoplastic Elastomer) soft rubber material is injection moulded onto another material, usually a plastic, using an injection moulding machine. This can be achieved by employing a two-color injection moulding machine in a single-step process or using a conventional injection moulding machine with overmoulding dies to complete the process in two separate injections. Overmoulding is one of the most significant forming methods or applications for TPE. Through this technique, TPE's versatile functional properties, such as soft touch (e.g., handles and grips), slip resistance (e.g., wheels, coasters, non-slip mats, footpads), elasticity (e.g., buttons), sealing capabilities (e.g., composite seals), and other specialized features (e.g., foldable kitchenware and household items), can be fully exploited.

There are two main mechanisms for overmoulding, colloquially referred to as true bonding and false bonding, depending on the product's structure and the desired bonding effect.

True Bonding:
True bonding involves the actual fusion between the soft TPE and the hard plastic at the bonding interface. This occurs because TPE shares a similar polarity and some degree of compatibility with the hard plastic, causing the TPE to fuse with the hard plastic surface upon melting and enveloping it. The mechanism is somewhat analogous to welding in metals. After the bonding and subsequent cooling, the TPE and hard plastic form a cohesive, inseparable unit. Detaching them would require substantial force that could potentially damage the TPE material rather than cleanly removing the entire TPE component.

True bonding relies on chemical compatibility and interpenetration, whereas false bonding relies on physical mechanical interlocking. In terms of bonding strength, true bonding is superior to false bonding. However, TPE materials needed for true bonding typically come with a higher cost compared to those for false bonding. Commonly used TPE and TPR for true bonding are chosen based on the type and properties of the accompanying hard plastics, such as ABS, PA, PC, PC/ABS, PP, PS, etc. Besides TPE and TPR, other soft materials like TPV, TPU, and PVC can also be used for overmoulding purposes, but the unique soft feel of TPE and TPR makes them the preferred choice in many applications.

False Bonding:
In false bonding, TPE does not chemically bond to the hard plastic or other materials in the same manner as true bonding. Instead, a secure attachment is achieved through suitable overmoulding designs, such as complete encapsulation of the part or modifications to the hard component, like adding holes or recesses along the edges of the bonding area to enhance the grip between the TPE and the hard piece (also known as insert injection moulding). When TPE or TPR bonds to metal, it is considered false bonding. The feasibility of TPE replacing rubber for overmoulding on metal depends largely on the overmoulding structure. Higher hardness TPE is generally more conducive to bonding with metal.