PETpla.net Insider 07 / 2017

BOTTLE MAKING 34 PET planet Insider Vol. 18 No. 07/17 www.petpla.net Stretch Blow Molding, part 4 Material Basics / Behaviour in the blow mould by Ottmar Brandau Ottmar Brandau has newly revised his book “Strech Blow Molding”, first published by hbmedia / PETplanet Publisher, and now re-issued in a second edition under the Elsevier imprint. PETplanet Insider is publishing extracts from successive chapters in a series of articles. Property data for PET Since the strain-hardening phase of the process is so important for bottle performance, correct preform design, temperature profile, and blow air timing are all necessary to guarantee the best bottle. If the inflated preform reaches the bottle mould during the pre-blow phase, orientation does not occur to a suf- ficient degree and the finished bottle might fail any number of tests (see Table 2.2). 2.6 Acetaldehyde (AA) in PET bottles AA is a natural sweetener that is present in all citrus fruits and is often used as sweetener in beverages. It is also a by-product of heating PET, especially heating it to melt tem- Relevant parameters IV, temperature, and co-polymer content all play a role in determining how far the material stretches during yielding and what force is required to stretch it further (Fig. 2.17). Tempera- ture conditioning allows the operator to improve the blow moulding process by making certain parts of the preform hotter or colder – changing the way in which they will stretch. The objective of preform design (or selection) and blow moulding processes is to properly match up the natural stretch ratio of the preform at the blow moulding conditions with the design stretch ratios of the preform/ bottle combination. Figure 2.17 Several factors at work, determining the natural stretch ratio.