Printing colours without ink

Home Technologist 13 Printing colours without ink

Inspired by the wing of a butterfly, Danish scientists are developing a technology to mass-produce structural colours. 

Laser printers of the future could work without ink cartridges. Technology University of Denmark researcher, Anders Kristensen, came up with the first printing technique to mass-produce what are known as structural colours. These colours, as opposed to pigments, are produced solely by nanostructures, which absorb and reflect specific light wavelengths depending on their shape. This mechanism is responsible for the sparkling blue of the Morpho butterfly’s wings. “To paint the surface of objects like credit cards, pens or cars, first, we create nanoscopic pillars of plastic, which are only 60 nanometres thick – 1,500 times thinner than a human hair”, explains Kristensen. “Then, we coat it with a semi-conductor called Germanium. Finally, a pulse of laser light melts the Germanium just enough to modify its shape and produce the desired colour.”

This technology could be used to store information and enhance security. Thanks to its high resolution (127,000 dots per inch against around 300 for smartphones), watermarks, invisible to the naked eye, could be printed on passports or banknotes to discourage counterfeiting. They would also be more durable because, unlike pigments or dyes, structural colours do not fade. “Its main application would be mass customisation. People would buy the exact same car but the colour palette of interior elements could be changed simply by firing lasers at it”, says Kristensen. Alas, the printer cannot be released soon because Kristensen still needs to fix a major issue: the current palette does not include green.

By Anne-Sophie Dubey

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