PETpla.net Insider 03 / 2017

BOTTLE MAKING 38 PET planet Insider Vol. 18 No. 03/17 www.petpla.net In a wheel machine, each individual mould cavity opens and closes in sequence and machines of this type are called rotary machines. In the late 1970s, Sidel started experimenting by using this concept in the PET stretch blow moulding process. By 1980, Sidel had built the first prototype that would initiate unparalleled success in the blow moulding industry, propelling Sidel from a mid-size machine manu- facturer to a billion dollar company. Today, companies such as Krones, Smiform, and Sipa have all devel- oped rotary machines of their own and his competitive pressure has driven prices down, opening new applica- tions for bottle blowing. Blow moulding speeds have also driven costs down: While 1,000 bottles/cavity/hour (b/c/h) was the benchmark for many years, today’s machines feature outputs of up to 2,200 b/c/h. The first ‘killer application’ for PET was the 2l bottle for carbonated soft drinks (CSD), introduced in 1978. The first bottles featured a dome- shaped bottom ideally suited to sus- tain internal pressures that routinely reach 5bar (70 PSI). This required an additional plastic component, called a base cup, to be glued to the bottom in a secondary operation in order for the bottle to stand up. However, cost and recycling considerations (glue resi- due) encouraged the development of a one-piece bottle. The breakthrough came with the design of the so-called Petaloid base: a thick, mostly amor- phous centre disk surrounded by five blown feet. Granted as patent to the Continental Can Company in 1971, it caused controversy with three other patents and litigation ensued for several years. It took until the early 1990s before one-piece bottles came off the conveyors of reheat stretch- blow moulding machines and were completely replaced two-piece bottles within a few short years. By the mid-1990s, soft drink companies agreed to lower shelf-life requirements and so opened the way for the extremely successful launch of 20oz and 500ml containers. At the time of writing, water and a whole new line of beverages that did not even exist a few years ago, are the key drivers for PET growth. Hot-fill juices and the so-called Neutra- ceuticals have raised the demands imposed on today’s PET bottles and the industry has responded with a wealth of new technologies. Recent developments aim to eliminate the unsightly vacuum panels needed for controlled shrinkage of the PET bottle during cooling of a hot-filled product. Multilayer preforms and coating technologies increase shelf life and, therefore, open the way for even smaller CSD packages and the replacement of glass in a new set of applications. At this time, it is unclear whether coatings or multi- layer technologies will prevail as the preferred choice of packaging, but it is this author’s opinion that a variety of methods will be required to meet an ever-increasing variety of packag- ing demands. On the horizon we can see PET entering the retort arena, used for packages that typically need expo- sure to 125°C (257°F) for a number of minutes and are currently all filled in cans and glass. The PET bottle’s crystallinity levels will have to be sub- stantially increased to allow the use of PET here. At this time, the highest temperature PET is being exposed commercially is 95°C (203°F). Barrier enhancements will allow extended shelf life milk and other goods that require a long shelf life to be pack- aged in PET. Improved ways of injecting preforms and blowing bot- tles will extend the industry’s ability to deliver a safe, environmentally sound, and economical package to consumers. Figure 1.2 Rotary high-speed machines such as this blow moulder produce the bulk of PET bottles. Photo courtesy of KHS Corpoplast. .com 100815dmyL