A team of scientists from the University of Cambridge has published plans for a laser “unprinter”, which vaporizes toner used in printing to leave a clean sheet of paper.
This idea of reusing printed paper has been around for sometime, and it’s possible if you are willing to use expensive coated paper. Toshiba recently showed off a printer that can erase its own single colour toner off normal paper, but this technique has limitations. With Toshiba’s system the ink is heated to make it disappear, but the technique leaves a residue and the same paper can only be reused five times.
Toshiba’s ‘e-blue’ toner is similar to old thermal fax paper as it fades under the right type of light. However this only applies if you buy their magic toner. The Cambridge project ambition is to develop a different method which would remove conventional toner from conventional paper in order to allow the re-use of the paper – a different approach to the same old problem.
The Cambridge team’s unprinter can work with any laser printed or photocopied paper, with no need for special toner that’s more expensive. It works by tracing the outline of the toner and then flash-frying it off using the device’s laser. “The key idea was to find a laser energy level that is high enough to ablate – or vaporise – the toner that at the same time is lower than the destruction threshold of the paper substrate. It turns out the best wavelength is 532 nanometres – that’s green visible light – with a pulse length of 4 nanoseconds, which is quite long,” said team member David Leal-Ayala.
The team demonstrated the technique by wiping a standard sheet of A4 three times without appreciable damage. They did warn that using the system too much could result in damage to the paper which could result in a yellowing effect. They have found some papers hardier than others, and are continuing experiments while considering whether to file patents or commercialize the technology.
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