Cracking of TPE/TPR Overmolding and PC Components: Causes and Solutions
Time of issue:2024-11-26
#### 1. Cracking of TPE Overmolded Layer
When TPE is overmolded onto PC (Polycarbonate), the TPE overmolded layer may develop cracks after some time. The primary reason for these cracks is the poor aging resistance of TPE, which leads to material degradation and cracking over time.
**Solution:** Use TPE grades with excellent aging resistance to improve the material's performance against aging and cracking.
#### 2. Cracking of PC Components
Those familiar with engineering plastics know that cracking in PC components is quite common. The main cause of cracks in PC parts is internal stress. During the molding process of PC materials, forced molecular orientation occurs. However, due to the rigid benzene ring structure present in PC, it is difficult for molecules to relax and reorient themselves after cooling.
Therefore, if the measures for molecular relaxation during the molding of PC parts are not properly handled—such as setting the mold temperature too low, or insufficient holding pressure and cooling time—the molecules will not be able to relax and reorient sufficiently. As a result, the finished product will retain internal stress. When this internal stress exceeds a certain level (greater than the cracking force), the PC part will crack.
When TPE is overmolded onto a PC component that already has significant internal stress, this stress can manifest during the TPE overmolding process. Additionally, if the TPE overmolded area is large, the TPE layer will contract during molding. If the PC component is relatively thin, the contraction of the TPE overmolded layer can exacerbate the effect of internal stress, leading to cracking of the PC part.
**Solution:** During the molding of PC components, use higher mold temperatures, appropriately extend holding pressure and cooling times, and strive to minimize or eliminate internal stress as much as possible.
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