Dr Michelle Dickinson, also known as Nanogirl, is an Auckland University nanotechnologist who is passionate about getting Kiwis hooked on science. Photo / Jason Oxenham
Dr Michelle Dickinson, also known as Nanogirl, is an Auckland University nanotechnologist who is passionate about getting Kiwis hooked on science. Photo / Jason Oxenham
This week the Reserve Bank announced new, upgraded banknotes that it will be releasing to increase the level of security and try to stay ahead of the counterfeiters.
I'll admit that as a contactless credit card fan I rarely use cash and really haven't sat down with a $5 note to study its high-tech features. However, looking into our new, vibrantly coloured notes, they contain a lot more science than you might think.
New Zealand banknotes are made of a plastic called polypropylene, the same plastic that's used for lunch boxes. We are one of only a few countries that use plastic banknotes. Many, including the UK and US, still use a paper banknote made up of a blended cotton and linen mix that crumples easily. Paper banknotes also have open pores deriving from the natural cotton structure, which act like pockets for holding oil and dirt.
Our plastic notes are much cleaner, with research showing they harbour four times less bacteria on their surface than paper notes. If you are a germaphobe, our notes are washable, can withstand boiling water and up to 100C dry heat.
If the bacteria don't convince you, then maybe the life-cycle analysis will, as making banknotes out of plastic is also better for the environment. They produce a 32 per cent reduction in global warming potential and 30 per cent reduction in primary energy demand, compared with paper notes.
Our new banknote starts its life as raw polypropylene pellets which are heated up and inflated into a stretched tube through a process called biaxial orientation blow moulding. The tube is then slowly cooled and passed through rollers to flatten it into a film resulting in a stronger, more tear-resistant 0.1mm thick plastic that lasts at least two and a half times longer than paper notes.
The transparent film is then coated in coloured ink using a gravure printing process, taking care to leave an inkless part for a transparent window security feature.
The window then has an embossed, metallised hologram image of a bird, map of New Zealand and silver fern hot stamped into its centre, which changes colour and appearance depending on the angle you view it from.
The hologram's 3D effect is caused by closely spaced lines within the image which cause the reflecting light to bend and diffract differently when it's tilted, as well as the shiny reflection from a thin layer of vapourised aluminium coated on the surface.
The new $10 bank note. Photo / Supplied
Thirty tonnes of force are then applied to the note in a process called intaglio printing which puts on the next layer of colour. This uses a special ink which is heavily pressed into a physical shape, forming a raised layer that you can feel.
This produces a tactile texture on both the portrait picture and denomination number on the note, so when you run your finger across it you can feel the printed shapes on the surface. It helps visually impaired people tell the notes apart.
After texturing, letterpress printing is used to add a different serial number to allow each note to be identified. Then a final layer of varnish is applied to seal and waterproof the notes before they are cut and packaged.
So there you have it - not only are our new bank notes jam-packed with anti-counterfeiting technology, tactile texture, 3D light-diffracting holograms and bug-resistant surfaces but they are also better for the environment by lasting longer and being recyclable.
I've always tried to be smart with my money but I've just realised how smart our money is.
This column is sponsored by Callaghan Innovation to promote coverage of science and innovation. The views are the author's own.
