120 innovations

Laser 'unprinter' wipes documents in a flash

An engineering team at the University of Cambridge in the UK has figured out how to erase pages by vaporising common toners using a laser-based technique that doesn't damage the underlying paper.

Toshiba of Japan already sells

a special laser printer/copier

 (that uses a blue toner which can be almost completely erased with heat treatment. David Leal-Ayala and his colleagues at Cambridge have taken the idea a step further, though, with a method that can recover the paper from any laser printed or photocopied document. After testing and ruling out toner removal processes that use mechanical abrasion and chemical solvents, they focused on the most promising method: laser pulses which vaporise toner particles in thin layers until they are no more.

"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," Leal-Ayala told New Scientist.  

Source: newscientist.comAdded: 20 June 2012