PETpla.net Insider 03 / 2017

BOTTLE MAKING 37 PET planet Insider Vol. 18 No. 03/17 www.petpla.net Part 1: A short history of stretch blow moulding / Material basics Stretch Blow Molding by Ottmar Brandau Ottmar Brandau has newly revised his book, first published by hbmedia / PETplanet Publisher, and now re-issued in a second edition under the Elsevier imprint. PETplanet Insider will be publishing extracts from successive chapters in a series of articles in forthcoming issues. 1. A short history of stretch blow moulding OPVC machines featured a double carriage where one side blew a pre- form from an extruded parison that was then transferred to the other side where the bottle was stretched and blown (see fig. 1.1). This yielded a lightweight bottle with superior prop- erties and was successfully used to produce a variety of containers. How- ever, PVC became environmentally suspect and PET is not suited to a process that requires what extrusion blow moulders call ‘hang strength’, the ability of the material to sustain shape at melt temperature against gravity. Another problem with the PVC process was its inability to be scaled up easily. Figure 1.1 Bekum’s double-sided extru- sion stretch-blow machine for PVC where preforms are blown in the inner carriages and bottles in the outer ones. Photo courtesy of Bekum America Cor- poration. Meanwhile, several US-based companies had developed machin- ery to produce stretch-blown PET bottles. Cincinnati Milacron’s RHB-5 machine reheated preforms neck-side up, in four lanes, then stretched and blew them in a four-cavity mould. All moulds moved at the same time and machines of this type are referred to as linear or in-line machines. Initially, output was limited to 2,800 bottles per hour (bph) but later versions boosted output to 4,000bph before Cincinnati stopped producing them in the early nineties. Meanwhile in Europe, the German company Gildameister (later to become Corpoplast and today KHS Corpoplast) and the French company Sidel were developing machines for PET production (see fig. 1.2). Sidel produced extrusion blow moulding machines using horizontal wheels. The idea of reheating a thermo- plastic material and then stretch- ing it to enhance its properties was first employed in extruded sheet in the 1930s. However, it took until the 1970s for Nathaniel Wyeth and his staff at DuPont to blow the first polyethylene terephthalate (PET) bottle from an injection moulded PET preform. At the same time, Bekum Maschinenfabriken in Germany had commercialised a similar process, stretch-blow moulding an extrusion blow-moulded PVC preform in what is now known as a singlestage pro- cess. Oriented PVC has oxygen and water barriers, and even carbonation retention, similar to PET. Bekum’s