Processing Machinery
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White spots of PP copolymer
Problem Phenomenon
Stress whitening appears at the stressed parts of impact copolymer PP products, especially obvious at bending locations.
Cause Analysis
Under stress, the rubber phase in the copolymer separates from the matrix interface to form micropores, which scatter light and appear white; excessive ejection or assembly stress can induce it.; during on-site investigation, verify item by item according to this mechanism to avoid blindly adjusting the machine based only on experience
Solution
①Reduce ejection and assembly stress; ②optimize the structure to avoid local over-stress; ③select a stress-whitening-resistant grade; ④check the balance of the demolding system.; after adjustment, continuously sample and verify the effect, and resume mass production after confirming stability
Key Takeaway
Stress whitening is a characteristic defect of impact PP; structural rounding and a low-stress process can effectively prevent it.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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