Why does the TPE/TPR encapsulated PC break?

1. The crack of the PC piece (fracture)

Those who are familiar with engineering plastics know that the problem of cracking of PC (polycarbonate) is very common. PC parts are prone to cracking problems, 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 orientation 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.

When the TPE and TPR are overmolded and encapsulated with PC parts, the internal stress is only manifested in the encapsulated TPE due to the large internal stress inside the PC. Or when TPE is used for encapsulation, the TPE encapsulation part has a large area, and the TPE coating layer shrinks during the encapsulation molding, and the thickness of the PC part is thinner. The shrinkage of the TPE coating layer will affect the internal stress. It plays a role in fueling the PC, causing cracks in 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.

2. Cracking of TPE/TPR coating

TPE/TPR encapsulated PC, TPE coating rupture (crack), this occurs, usually after a period of plastic molding. The reason for TPE and TPR crack is mainly TPR. The aging resistance of TPE is poor. After a long time, the material is aged and cracked.

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