PETpla.net Insider 08 / 2014

PREFORM PRODUCTION 28 PET planet insider Vol. 15 No. 08/14 www.petpla.net Drying of PET- Bottles, preforms and closures, part 13 Manufacture of PET Preforms Although this book will not detail every aspect of the injection moulding of PET preforms, we will give an overview of some aspects that are critical to designers. PETplanet insider is publishing extracts from successive chap- ters of Ottmar Brandau’s “Bottles, Preforms and Closures”, which was first published by hbmedia. A newly revised version is reissued under the Elsevier imprint. Because PET is hygroscopic, it must be dried before it can be injected. The maximum amount of water that can be in the resin when it is in the extruder throat is 50ppm. This residual moisture will react with the PET in the extruder and lead to an acceptable drop of 0.03–0.04 in IV. Higher moisture levels will lead to much higher IV drops, rendering the material unsuitable for the application (Fig. 2.10). The correct drying parameters are a combination of time and temperature at a certain airflow. Modern dryers are able to generate the required airflow of 4m 3 /h/kg h (1 cfm/lb h). Under these conditions, proces- sors must calculate or determine by practi- cal experiment what the residence time of the resin in the hopper is for a given job. To do this practically, a handful of colour pellets is placed on top of the resin in the 0 50 100 150 200 250 300 350 400 1.2 1.0 0.8 0.7 0.6 1.2 1.0 0.9 0.8 PPM Water Final IV Initial IV Fig. 2.10