Injection Molding
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PET Preform White Haze Crystallization (Slow Cooling)
Problem Phenomenon
The preform, especially the middle and lower part of the body, presents a milky white hazy turbidity and loses transparency; the white haze cannot be eliminated after blowing.
Cause Analysis
Insufficient cooling rate after injection or melt temperature too high causes PET to form spherulitic crystallization in the mold; the crystallized zone scatters light producing white haze, and this defect cannot be reversed in the blowing process.
Solution
①Reduce the melt temperature to within the process window; ②strengthen mold cooling (mold temperature 5~15℃) and shorten cooling time; ③check whether the hot runner is locally overheated; ④improve rapid cooling efficiency after injection.
Key Takeaway
White haze crystallization is an irreversible defect and must be prevented at the preform injection stage; controlling melt temperature and cooling rate is the core, and preforms with white haze should be directly scrapped.
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