Why does the TPE over molding PC injection molding product crack ?

- Jul 05, 2019-

Why does the TPE over molding with PC  product crack ?


  Why the TPE  over molding PC is broken is a headache that is often encountered. Whether the tpe encapsulated part is broken or the PC part is broken. Asia Billion believes that the user's problem should be that the cracks in PC parts are mostly.


1. The crack of the PC piece


  The problem of cracking of PC (polycarbonate) is very common. PC parts are prone to cracks, mainly due to internal stresses in the parts. The PC material undergoes forced molecular orientation during molding, but after molding cooling, it is very difficult to cause molecular misorientation due to the presence of a poorly compliant benzene ring structure. Therefore, when the PC parts are molded, the de-orientation measures are improperly handled, such as low mold temperature setting, insufficient cooling and holding time, etc., and the molecules cannot be fully relaxed and de-oriented, and the products will have internal stress after molding. When the stress reaches a certain level (greater than when the cracking force), the PC part will crack. In addition, it is necessary to check whether the PC part is subjected to a large injection pressure or a crushing and fracturing between the product and the mold during the overmolding in the encapsulation process. In this case, it is necessary to re-strengthen the mold.


   When TPE and TPR are overmolded and encapsulated PC parts, due to the large internal stress inside the PC part, the damage of this internal stress appears just when the TPE is encapsulated, or when TPE is used, the TPE package The rubber part has a large area, and the TPE coating shrinks during the molding process, and the thickness of the PC part is thinner. The shrinkage of the TPE coating layer will play a role in promoting the internal stress, thereby causing PC parts. 

Solution: When molding PC parts, try to use high mold temperature, properly extend the holding pressure and molding cooling time, and minimize or eliminate internal stress. Or strengthen the mold fiting to prevent product crushing and fracturing.


2. Cracking of TPE/TPR coating


  TPE, TPR encapsulated PC, TPE coating rupture (crack), this happens, usually after a period of plastic molding. The reason for TPE and TPR cracks is mainly due to the poor aging resistance of TPE and TPR. It takes a long time to cause aging cracking of TPE materials.


Solution: Use TPE and TPR product grades with excellent aging resistance to improve the aging crack resistance of the material.

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