HOW DISAPPEARING INK CAN CUT PAPER WASTE

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How ‘disappearing ink’ can cut waste paper
Scientists have unveiled a new kind of ‘ink’ that disappears from a page 24 hours after printing, allowing paper to be re-used
Mission Impossible-style self-destructing messages may soon cross from the realm of fiction into the wilds of the nine-to-five office, according to scientists who have developed printer ink that vanishes after 24 hours.When a document is printed on the reusable paper, the text initially appears similar to normal printed text – only in a shade of dark purple, rather than black.Eight hours later, however, the image is a shadow of its former self and after a day – much like the McFly family photograph in Back to the Future – it is gone completely.The blank page can then be put back in the printer.It is hoped that the technique will reduce the trillion pages put in the recycling bin – or worse, thrown out – soon after being printed each year.

The ‘disappearing ink’ is not ink at all, but a temporary discolouration of light-sensitive molecules known as photochromes. The paper is coated with these molecules, which change colour when they are exposed to ultraviolet light. As soon as the printing is finished, the molecules begin reacting to the warmth in the surrounding air and gradually return to their natural state.Sheets of paper can be re-used before the ink has completely disappeared because the high temperatures inside a printer erase any remaining traces. As long as the paper is not creased, it can be used as many as 30 times.The unit which emits the ultraviolet light could feasibly be incorporated in an existing printer, the developers said, allowing computer users to select a special tray for ‘short lifespan’ documents.”Our studies were showing us that 45 per cent of all office printing is for ‘one-time use’, like reading an e-mail,” Paul Smith, a lab researcher at Xerox, who was demonstrating the technology in Grenoble, France, said. “Sometimes it can be a matter of minutes, then it goes straight in the recycling bin,” he said.The technology, which will not be commercially available for several years, will reduce the amount of energy required to print a single page by a factor of 200 – from just over 200kJ (which would power a 75W light bulb for an hour) to 1kJ (which would power the bulb for just 18 seconds), Mr Smith said. A recycled page uses about 110kJ of energy.

The paper itself is no more expensive than a regular page, costing about 0.5p per sheet.
Despite the proliferation of devices which display text on electronic screens, the market for printers is growing at 6 per cent per year, according to analysts, driving the likes of Xerox to make printing more cost-effective – and more green – for offices.Sophie Vandebroek, the company’s chief technology officer, said: “Green technologies are increasingly important, and re-usable paper, while it requires conscious participation from the user, is one way of reducing the impact of printed documents on the environment.”Sharon McNee, an analyst in Gartner’s printing group, said that despite being in its infancy, the technology had obvious commercial potential, but warned that there would be significant costs associated with switching over printers and paper supplies.A spokeswoman for Waste Watch, the environmental charity, said: “There is enormous potential for innovative new technology to reduce the amount we generate at work, as so many office documents are only used for a short time. We welcome any sustainable printing option.” 

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October 16, 2007 at 11:01 AM