Few people realize what it takes to bring a bottle to life. From the initial design to the final product, the design team in question works closely with plastic bottle manufacturers to ensure their idea stays as close as possible to their original vision. But the process in between remains somewhat of a mystery. Just what does it take to manufacture a plastic bottle?
Before we dive into the logistics, let’s talk a little bit about different types of plastic bottles. The material used to create some plastic bottles is called polyethylene terephthalate, or PET for short. PET is a thermoplastic polymer, making it a perfect material for manufacturing plastic bottles because it is lightweight and robust. PET is made of petroleum hydrocarbons, the product of a chemical reaction between terephthalic acid and ethylene glycol. These reactions form long polymer chains, which are quite reliable when bundled together.
However, not all PET is created equal; it must go through a rigorous set of tests before it can be used in manufacturing. Several factors that are tested include transparency, gloss, shatter resistance, thickness, and pressure resistance. Two common impurities that appear during the polymerization process are diethylene glycol and acetaldehyde. While the former usually appears only in negligible, trace amounts, the latter can affect the taste of the bottle’s contents if too much is present. One last important test these bottles undergo is carbon dioxide permeability testing. This part tests the bottle to see if carbon dioxide leaks through – a crucial step when producing bottled soda.
Now that we know a little about the stuff that goes into plastic bottle manufacturing, let’s take a look at how the bottles are made. The first step in the plastic bottle-making process is the stretch blow moulding. It’s a little like glassblowing, but with plastic instead. A long, thin mould of hot plastic is blown and stretched into a bottle mould. This long, thin mould of plastic has an unusual name, actually: parison. A long, thin rod known as a mandrel is then forced into the mould, creating a pocket of pressurized air. This pocket of air pressure forces the plastic in the first mould into a larger, second mould – and that’s how you achieve the bottle shape.
The hot mould must then be cooled very quickly. There are a couple of ways to achieve this: the mould can either be indirectly cooled by coursing cold water through the pipes surrounding the mould, or directly cooled by blowing pressurized air or carbon dioxide on the moulds themselves. Once the bottles are set and cooled, they can be removed from their moulds for packaging.
It is also possible to produce custom plastic bottles. This customization changes the process a little bit and is often a collaboration between the manufacturer and the product’s design team. Whilst the design team might think ‘the sky is the limit’ when it comes to their dream bottle, it is up to the engineers manufacturing the bottles to create a reliable product that is safe for commercial use. This takes close collaboration between parties to obtain the optimum product considering all factors of purpose, design, manufacture and cost.
Design teams may also fail to consider some critical practicalities during the initial stages of the process. For example, the chemical composition of the liquid expected to fill the bottles may determine the shape and size of the bottle. It may also determine the type of closure used on the cap. How thick should the container be? Should it be transparent or opaque? All of these properties must be carefully selected, as design problems could pose problems and cost a lot of money in the future.
Close attention to detail is also required in designing the closure. The moulding process depends on whether the closure opening should face the same direction as the bottle label and the desired function of the cap based on contact material with the product, dispensing options and branding or decoration. This is why design teams benefit by by working closely with the engineering team in the beginning phases of the bottle-making process, ensuring manufacturing capabilities, materials and costs are also taken into consideration.
Who knew so much thought went into making custom plastic bottles? Yet it should come as no surprise that the most mundane objects often require the most attention and detail in their production process. Their careful engineering and design are what make them such reliable staple products in everyday life. So next time you take a swig from a soda bottle, thank the people behind it. Otherwise, you’d have carbon dioxide leaking all over you!
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