Plastic bottles

The usage of plastic bottles has increased dramatically over the last 20 years. While most soft drinks were still sold in glass bottles as late as 1975, plastic bottles have taken over this market at an incredible pace. Today, most of all soft drinks are sold in plastic bottles. The same is true for still water that is also sold mostly in plastic bottles already. New applications appear every day before our very eyes.

The idea of reheating a thermoplastic material and then stretching it to enhance its properties was first employed in extruded sheet in the 1930’s. But it took until the 1970s for Nathaniel Wyeth and his staff to blow the first PET bottle from an injection moulded PET perform at the DuPont company. At the same time Bekum Maschinenfabriken in Germany had commercialized a similar process, stretch blow moulding an extrusion blow moulded PVC perform in what we would call today a single-stage process. Oriented PVC has similar oxygen and water barrier, and even carbonation retention, than PET. Bekum’s OPVC machines featured a double carriage where one side blew a preform from an extruded parison that was then transferred to the other side where the bottle was stretched and blown. This yielded a lightweight bottle with superior properties and was successfully used to produce a variety of containers. However, 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.

Meanwhile in Europe the German company Gildameister (later to become SIG Corpoplast) and the French company Sidel were developing machines for PET production. Sidel had produced extrusion blow moulding machines using horizontal wheels. 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 1970’s Sidel started experimenting with the use of this concept in the PET stretch blow moulding process. By 1980 Sidel had built the first prototype machine that would start an unparalleled success in the blow moulding industry, propelling Sidel from a mid-size machine manufacturer to a billion Dollar company.

The reasons for the rapid success of plastic bottles are various:

• Light weight
• Cheap to manufacture and transport
• Environmentally friendly; this is often disputed but nevertheless true. The main reason is that it takes a lot less energy to produce a plastic bottle than it takes to produce a glass bottle because the temperatures used are much lower.
• Unbreakable and easy and safe to use

to name a few. Whether you like them or not, plastic bottles are here to stay.

Go to Blow Molding Consulting to learn more about plastic bottles.

1