Injection Molding
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Yellowing and Black Specks in PE Injection Molded Products
Problem Phenomenon
Natural-color PE parts turn yellow, or light-colored parts show black specks and black streaks, resulting in poor appearance.
Cause Analysis
Excessive melt temperature or too long residence time causes thermal degradation yellowing; material accumulated in dead spots of the barrel/hot runner carbonizes and falls off to form black specks; regrind contamination and high-temperature idling with heat preservation also introduce them.
Solution
①Lower the melt temperature to a reasonable range and shorten residence time; ②Thoroughly purge the machine and disassemble and clean dead spots; ③Avoid prolonged high-temperature idling of the barrel; ④Check the cleanliness of raw material and regrind; ⑤Evaluate whether the antioxidant system matches.
Key Takeaway
PE yellowing and black specks = 'excessive heat history + dead spot carbonization': lower temperature and shorten time to prevent yellowing, purge the machine and check material to prevent black specks; for intermittent black specks, focus on checking equipment dead spots instead of repeatedly fiddling with the process.
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