Issues with Cracking in PC Parts and TPE/TPR Overmolding Solutions
Time of issue:2024-10-23
Issues with Cracking in PC Parts and TPE/TPR Overmolding Solutions:
Those familiar with engineering plastics will recognize that cracking in PC (polycarbonate) parts is a common issue. The propensity for PC parts to crack primarily stems from internal stresses developed during the manufacturing process. During molding, PC material experiences forced molecular orientation, but due to the presence of inflexible aromatic ring structures, molecular deorientation becomes challenging after cooling.
If deorientation is not properly managed during the molding process—such as through low mold temperatures, insufficient holding pressure times, or inadequate cooling—the molecules cannot relax and deorient sufficiently, leading to internal stress in the final product. When these internal stresses reach a critical level (greater than the force required to initiate cracking), the PC part will develop cracks.
When TPE (thermoplastic elastomer) or TPR (thermoplastic rubber) are used for overmolding on PC parts, the existing internal stresses within the PC can exacerbate the situation. Additionally, if the area covered by the TPE layer is large and the PC part is thin, the contraction of the TPE layer during overmolding can intensify the effect of the internal stresses, causing the PC part to crack.
Solution: When molding PC parts, use high mold temperatures, extend holding and cooling times appropriately to minimize or eliminate internal stresses.
Another issue arises with cracking in the TPE/TPR overmolded layer. This type of cracking typically appears some time after the overmolding process has been completed. The cause of cracking in TPE/TPR layers is often due to poor aging resistance, which leads to material degradation over time.
Solution: Use TPE/TPR grades with better aging resistance to improve the material’s ability to withstand cracking due to aging.
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