Material Drying
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PET drying 0.005% red line
Fenómeno del problema
Bubbles and water blisters appear in the PET sheet, transparency decreases, and '2079851475616104458 performance deteriorates
Análisis de la causa
PET is a strongly hygroscopic polycondensation polymer; when the moisture content exceeds the standard, hydrolysis occurs in the melting stage, and the molecular weight and intrinsic viscosity IV decrease; the moisture red line for sheet bubbles is 0.005% (50 ppm), far higher than that of general '2079851475616104452 materials
Solución
①Dehumidify and dry to a moisture content <0.005%; ②dew point below -40℃ with hot air in a closed-loop circuit; ③when water blisters appear, immediately adjust the drying temperature and time; after adjustment, take consecutive samples to verify the effect, and resume mass production only after confirming stability
Conclusión clave
The moisture red line for PET sheet is at the 50 ppm level rather than the percent level; hydrolytic viscosity reduction is irreversible, and drying is the first lifeline of sheet quality; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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