Molding Process
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PET Bottle White Haze (Crystallization Type)
Problem Phenomenon
The outer surface of the bottle body shows overall or banded white haze, and transparency decreases.
Cause Analysis
When PET stays above about 115℃ and cools slowly, the molecules gain crystallization ability, forming microcrystals that scatter light; excessive heating and insufficient ventilation make the preform surface temperature exceed the threshold.
Solution
①Lower the corresponding lamp power or increase ventilation, and control the preform surface temperature below the crystallization threshold; ②in the two-step method, locate the corresponding lamp zone for adjustment; ③in the single-step method, increase holding pressure/cooling time; ④avoid static baking of preforms in the oven.
Key Takeaway
White haze = overheating crystallization, pearlescence = cold stretching; the two directions are opposite, do not adjust in reverse.
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