Historically, bottles have been made from many different materials. Leather, ceramics and metals such as tin and pewter have all been used to create sealable containers that store and carry liquids. From the Eighteenth Century onwards, glass came to dominate the bottle industry. When plastic bottles were developed in the Twentieth Century, the drinks industry was keen to adopt this cheaper alternative. When it came to maximising strength and stability, there were some problems to overcome and these lead to a design feature of plastic drinks bottles that you might have overlooked.
The Bell Pepper Bottom
Take a look at the bottom of a plastics drinks bottle that contains a carbonated drink. You will see that it is comprised of multiple domes like the bottom of a bell pepper. A drinks bottle will typically have five domes arranged in a star pattern. Now compare the bottom of a bottle of still water or other non-carbonated drink. The base of the water bottle is flat. Why the difference?
From Glass to Plastic
Thick glass is strong enough to contain liquids that are stored under pressure. For this reason, Champagne bottles are made of heavier glass than bottles for still wine. When engineers first tried to put carbonated drinks into plastic bottles, the flat base couldn’t handle the pressure and popped out into one large hemisphere. These bottles could not then be stood upright on their base.
Two Solutions
The earliest solution to this problem was to use extra plastic to make a stand for the pressure-distorted bottle, but this negated the savings made by switching from glass to plastic in the first place. The bell pepper bottom solution was mathematically elegant - it could be proven to withstand the pressures from a shaken up soda-pop - and it allowed the bottle to stand upright in the fridge whilst using only minimally more plastic than a flat bottomed bottle.
Think you can come up with a better solution? Talk to our product development team at Coda Plastics Ltd. We can help you to design and produce your next-generation plastic drinks bottle. Call us on +44 1692 501020 or email sales@coda-plastics.co.uk.
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