It is virtually impossible to alter the polarity of nylon; thus, the approach shifts to modifying the polarity of TPE. To increase the polarity of TPE, grafting materials are utilized, such as SEBS modified with strongly polar maleic anhydride.

According to the principles of solubility and Fluid Solubility Parameter (SP), TPE must have a similar polarity and good compatibility with the substrate material to successfully achieve successful overmolding.

The surface tension and compatibility of materials are meaningful only in liquid or molten states. During overmolding, a sufficient molding temperature must be provided so that TPE with coating properties can deliver the intended bonding effect. If the temperature is too low, there will be no compatibility (melting erosion, interphase structure alteration, or molecular-level penetration) or chemical reactions at the interface of the two phases, and no change to the surface tensions can occur, resulting in poor overmolding outcomes.

Based on the above analysis, the following points can be summarized:

1. Compatibility between TPE and the hard plastic structural components must match, with similar molecular solubility leading to better molecular compatibility.
   
2. In design, sharp corners should be avoided as much as possible to ensure good contact between TPE and the hard plastic part, thereby enhancing bonding effectiveness.
   
3. Proper venting should be implemented to prevent gas entrapment within the mold cavity.
   
4. The thickness of TPE should be balanced with the desired tactile feel.
   
5. The melt temperature of TPE must be maintained to ensure proper bonding.
   
6. TPE material should be pre-dried before processing to reduce water marks on the product surface and achieve uniform coloration.
   
7. The selected color masterbatch should have a carrier resin compatible with both the TPE and the structural material.
   
8. Smooth surfaces should receive special treatment to increase the bonding contact area between the soft and hard plastics and strengthen the adhesive effect.
   
9. TPE must exhibit good flowability as the ratio of TPE coating layer thickness to its overall size is small, requiring it to flow through longer paths and thin-walled sections in the mold.
   
10. The flow length-to-thickness ratio of TPE should be less than 150:1.
   
11. High-quality adhesives should be employed.