TPE overmolding considerations and process tips shared

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

　　Examples of TPE overmolding

　　A. One kind of two-component molding or two-color injection molding is realized on a two-color injection molding machine, in which the hard plastic (hard plastic) is injected into the product, and then jumped to the corresponding mold cavity of another injection cylinder on a two-color machine by mold flip, and the part is used as an insert to inject TPE on it to form an integrated dual-material product. In two-color injection molding, the first step of the hard plastic is still hot when it is injected, immediately into the second cavity of the 2K injection molding machine, the intermediate transfer process also did not absorb moisture, both easy to be high-temperature TPE melt in the surface ablation of ultra-thin layer, but also no water vapor in the surface is adsorbed influence, conducive to the formation of TPE and the material chemical bonding, strengthening the bonding force.

　　B. Another kind of two-step injection molding, in one injection molding machine to mold the hard plastic, the part as an insert into another mold, and then injected with TPE. two-step injection molding, the hard plastic in the middle after the stop hair, transfer process, the material will cool, moisture absorption or contamination. For polar hard plastic such as PC, PBT, PET, POM, especially strong polar hard plastic such as nylon 6, nylon 66 and other materials, the surface of the product will absorb moisture and cause the material to form hydrogen bonds with water molecules, resulting in the TPE can not effectively form intermolecular bonds with the surface molecules of hard plastic, the bonding force of the package will be reduced, showing the poor effect of the package.

　　Process technology sharing

　　1.TPE high temperature, in the TPE material processing allowed range, as far as possible to choose a higher barrel (melt) temperature, so that the TPE will have enough heat to ablate the surface of the hard plastic material.

　　2. Hard plastic high mold temperature, hard plastic as inserts in the mold cavity as high as possible to maintain the hard plastic temperature, so that the TPE high-temperature melt cooling is slow, there is enough heat, enough time to ablate hard plastic to form a super thin layer of mutual solubility.

　　3. TPE high injection speed, in the premise of not producing TPE flying edge, as far as possible to use high injection speed to TPE melt injection. As long as the TPE in the hard plastic surface spreading time is short, in the molding cycle will have a longer time to ablate the hard plastic surface; In addition, the friction between the TPE and the hard surface friction heat, TPE melt temperature cooling also slows down, longer time for contact and ablate the hard plastic surface; Finally, high screw speed will make the melt viscosity shear thinning, surface tension decreases, conducive to spreading in the hard plastic surface. Finally, the TPE of wrapping polar hard plastic, certainly also polar formula, do not pay attention to moisture, the same affect the bonding effect of wrapping.