The key point of TPE overmolding (secondary injection molding) is to make the TPE and the covered substrate (hard plastic, so called) PP, ABS, PC, PA, etc. to be well covered and bonded. In order to make TPE and hard plastic bond well, according to the principle of chemical compatibility, the key is that TPE and hard plastic should have similar polarity, so that TPE and hard plastic can be fused at the molecular chain level. Therefore, the type of hard plastic determines the formulation of TPE, and the secondary injection molding process (such as the temperature of the secondary injection, etc.) directly affects the adhesion of TPE and hard plastic. The following detailed analysis:

　　1. TPE formulation

　　Different hard plastics, such as PP, PC, ABS, PA, etc., need different TPE formulations and models. Therefore, it is recommended to find a strong TPE manufacturer to cooperate, TPE dealers or traders usually know little about the TPE formula.

　　2. Different hard plastic wrapping.

　　1.PP overmolding

　　PP is a very weak polarity plastic, and the polarity of TPE is very close to that of SEBS base material. Therefore, the most conventional TPE formulation can be directly used for PP overmolding without adding additional polarity modifiers. Although TPE is the most common type of PP, the secondary injection molding temperature is also very important to ensure the fluidity of TPE and fast coating on the surface of PP with sufficient injection temperature. The recommended temperature for secondary injection molding is 170~220℃. Note: PP overmolding, SBS is not recommended as TPE modified base material. 2.

　　2. ABS, PC overmolding

　　ABS and PC are weak to medium polarity plastics, with TPE there is a certain polarity difference. By adding modifier (TPU) in the formula, the polarity of TPE can be improved, thus improving the adhesion of TPE with ABS and PC. In addition, the secondary injection temperature is recommended to be 180~230℃. The specific processing can be adjusted according to the actual situation.

　　3. PBT, PET overmolding

　　PBT, PET semi-crystalline plastic, polarity and ABS, PC similar. 220 ℃ PBT melting point, PET melting point is as high as 260 ℃, the need for TPE has a higher melt temperature. Therefore, the TPE overmoulding PBT and PET, the required overmoulding secondary injection temperature is higher than overmoulding ABS and PC. Bonding difficulty to be greater.

　　4. PA6, PA66 overmolding

　　PA6, PA66 for semi-crystalline strong polar plastic, requires a higher temperature and energy to form a fusion layer on the surface of the hard plastic. PA6 melting point of 240 ℃, PA66 melting point of 260 ℃. To form a strong bond, the TPE needs to have a higher melt temperature. Generally, TPE overmelt PA6, overmelt secondary injection temperature 230 ~ 250 ℃, TPE overmelt PA66, the need for 240 ~ 270 ℃ overmelt temperature. In addition, PA6, PA66 easy to absorb water, these are unfavorable factors for overmolding bonding.

　　5. POM overmolding

　　POM overmolding. although the melting point of POM is not high, only 180 ℃. But because of its high crystallinity, to form a fusion layer on the cladding surface, requiring high energy, while the self-lubricating nature of POM, is not conducive to TPE material in the POM hard plastic parts on the surface of the fast cladding. Therefore, the POM cladding, in the country, I have not heard of a TPE manufacturers say that the cladding firm.

　　Lastly, I would like to summarize and add that the adhesion between TPE and PP, ABS, PC, PA and other plastics depends on the TPE formula and the suitable coating process. In addition, for PA6, PA66, PBT and other high melting point plastics, preheating of hard plastic parts before secondary injection is beneficial to the bonding of TPE and hard plastics. In the secondary injection molding with high injection temperature (to TPE does not degrade as the limit), high injection speed, so that TPE has as much energy and time to achieve the cladding fusion with PA6, PA66, PBT and other hard plastic parts, so as to form a good bond.

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