Material Drying
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Improper PET drying process
Problem Phenomenon
After conventional hot-air drying treatment, the preforms still show bubbles and white haze; after switching to dehumidifying drying, the problem disappeared, confirming that the drying method did not match.
Cause Analysis
PET is a strongly hygroscopic polyester, and ordinary hot-air drying cannot reduce the moisture content below 50 ppm; if any of drying temperature, time, or dew point fails to meet the standard, moisture will remain.
Solution
①Use a dehumidifying dryer with dew point ≤ -40℃; ②dry at 150~180℃ × 4~6 h; ③convey the hot material in a sealed manner after drying to prevent secondary moisture absorption; ④regularly calibrate the moisture content.
Key Takeaway
PET drying must use dehumidification rather than ordinary hot air; the three elements of dew point, temperature, and time are indispensable, and preventing secondary moisture absorption after drying is equally critical.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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