Overmolding in the field of TPE thermoplastic elastomers is a special type of overmolding. And what is overmolding? Simply put, overmolding can be plastic over plastic, or soft rubber over plastic, or soft rubber over soft rubber.

　　There are two main means to realize overmolding. 1:

　　1. a two-component molding or called two-color injection molding, that is, in the two-color injection molding machine to achieve, will be a material injected into the product, and then in the two-color machine by the mold flip jump to another injection plastic cylinder corresponding to the mold cavity, the part to do as a panel, the injection of another material in the top of the formation of the integration of dual-material products. The injection molding machine is a double barrel, double mold cavity, the injection process is two materials at the same time the production of products, only one cavity of the products will be used as inserts into the next cavity.

　　2. The other is two-step injection molding, in which one material is molded in one injection molding machine, the part is put into another mold as an insert, and then the second material is injected.

　　Methods to achieve overmolding (including overmolding) can be physical snap methods and chemical methods.

　　In the former case, for example, the overmolding (overmolding) is realized by the design of the clips, the surface rolling, the surface tapping, and then the overmolding of the second material. This method of material bonding is characterized by strong adhesion at the physical connection area and little adhesion outside the physical connection area.

　　Chemical methods rely on the molecular affinity between the two materials, the bonding force of the chemical bond, the two materials bonded together to form a single part, two or more.

　　While physical snap and chemical bonding methods are often used together in practical applications, it is clear that achieving a chemical bond between two materials is the preferred method that is more secure and offers greater design freedom.

　　Such strong chemical bonding includes intermiscibility of molecules or molecular chain segments, osmosis, penetration, and molecular entanglement.

　　To achieve bonding at the molecular chain segment level of TPE/hard plastic, it is also critical to do the following three things:

　　1. the polarity of the TPE material is similar to that of the hard plastic (otherwise it is not possible to intermelt, penetrate and penetrate in the melt state);

　　2. The surface tension of the TPE material is less than the surface tension of the hard plastic (otherwise the TPE melt will not be able to spread out on the surface of the hard plastic insert);

　　With regard to surface tension, it is easy to understand when you think about mercury shrinking into a ball on its own on the surface of glass, while water droplets can spread out on the surface of glass;

　　3. TPE melt in the mold cavity along the hard plastic surface flow, the cooling process releases heat, can quickly and effectively melt the hard plastic surface layer can be interpenetrated to form a thin layer.