Extrusion & Post
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Delamination of PP products overmolded with TPE/TPU
Problem Phenomenon
After two-shot molding (overmolding) of PP substrate with TPE/TPU soft rubber, the soft-hard rubber joint delaminates and peels.
Cause Analysis
PP and TPE/TPU have different shrinkage rates, and the mold is not designed for differential shrinkage, causing interfacial stress; during two-shot molding, the substrate temperature is low and the interface is not fully fused, or the soft rubber grade does not match PP—all cause insufficient bonding force and delamination.
Solution
①Select a special TPE/TPU grade that can chemically bond with PP; ②design the mold with differential shrinkage compensation for the two materials; ③preheat the PP substrate before two-shot molding to increase the interface temperature; ④optimize the soft rubber injection temperature and speed to ensure interfacial fusion; ⑤perform peel strength verification.
Key Takeaway
For PP overmolding delamination, grasp the three points of 'grade matching + interface temperature + differential shrinkage': the soft and hard rubbers must be bondable, the substrate must be preheated, and the mold must be designed for differential shrinkage—all three are indispensable.
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