Injection Molding
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PP Tiger Stripe (Flow Mark)
Problem Phenomenon
Alternating light-dark tiger-stripe patterns appear on large-area PP parts such as automotive bumpers and door panels.
Cause Analysis
In impact copolymer PP, the rubber phase and matrix fluctuate in distribution under filling shear, forming periodic gloss differences; injection speed fluctuation and improper gate design can induce it.
Solution
①Optimize the injection speed profile to maintain a stable front; ②raise mold temperature and melt temperature; ③enlarge the gate to reduce shear fluctuation; ④if necessary, switch to anti-tiger-stripe grades.
Key Takeaway
Tiger stripes are flow imprints of rubber phase distribution—stable speed is the core.
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