In offices the world over, heaps of printouts and
photocopies from laser printers get used once before being discarded, or tossed
on shelves to collect dust indefinitely. But what if they could be wiped clean
and used again?
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. It can delete
words and images printed on paper.
Toshiba of Japan already sells a
special laser printer/copier (video) 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.
Allwood and colleagues estimate it would cost Rs. 1,330,000/- to build a prototype unprinter but that the costs would come
down as technology improves and it is commercialized. They believe that
reducing the cost would make the device valuable in most offices by reducing
the need to buy paper. It could also be kinder to the environment by reducing
the need to use as many chemicals to recycle paper and cutting carbon emissions
savings of up to 79 percent, they noted.
