A close-up image of a sheet of "unphotocopied"
paper reveals most of the toner has been removed
The process involves using short laser pulses to erase words and images by heating the printed material to the point that they vaporise. The researchers say it works with commonly used papers and toner inks and is more eco-friendly than recycling. However, they add that more research is needed to bring a product to market.
"When you fire the laser, it hits the thin toner layer and heats it up until the point that you vaporise it," the team's lead author, David Leal-Ayala
"Toner is mostly composed of carbon and a plastic polymer. It's the polymer in the toner that is vaporised."
In their study, published in the Proceedings of The Royal Society A journal and reported by New Scientist, the engineers acknowledge that they are not the first to have thought of the idea.
But they say that others who have tried to solve the problem have found that they damaged and/or discoloured the paper in the process, or required specially formulated toner. Toshiba already markets a laser printer which can erase ink, but notes that the machine is dependent on its own "e-blue" ink to function.
Mr Leal-Ayala and his colleagues tested a range of ultraviolet, infra-red and visible lasers at different speeds. They eventually found that the best setting was green laser pulses, lasting just four billionths of a second in duration, which removed all but a hint of the print.
Tests reveal only a faint outline
of erased text were left behind
They say that curling, bending and accelerated-ageing tests carried out on the resulting "unprinted" paper suggested it had not sustained significant damage and was "comparable to blank unlasered paper". A gas extraction system was used to capture nanoparticles and "mostly harmless" gases produced by the process.
Having demonstrated the technique in a lab setting, the engineers now plan to develop a prototype device suitable for an office.
They concede that most businesses would still find recycled paper a more cost-effective solution, but add that the price should fall if it went into production thanks to economies of scale.
"When you recycle paper you use a lot of resources," Mr Leal-Ayala said.
"You use electricity, water and chemicals, and to be honest when you print something the only reason that you don't re-use the paper is because there is print on it.
"The paper is still in good condition and there is no point in going through all the heavy industrial process if the paper is still perfectly fine."