We have been scribbling and printing on paper for centuries and so it seemed inevitable that the paperless office we were promised decades ago would be a long time coming. Now, chemists at the University of California, Riverside, USA, have developed a new material, which is essentially rewritable paper. It exploits the color-switching properties of redox dyes embedded in an imaging layer of the rewriteable paper. Printing is carried out using ultraviolet light to photobleach the dye layer except those areas making up the text or graphics to be "printed" on the paper. The developers say it can be used more than twenty times without degradation of contrast or resolution.
"This rewritable paper does not require additional inks for printing, making it both economically and environmentally viable," explains team leader Yadong Yin. "It represents an attractive alternative to regular paper in meeting the increasing global needs for sustainability and environmental conservation." The text is "erased" by heating the paper to 115 Celsius and takes about ten minutes for the bleached areas to return to their original color. Of course, this is useful provided one doesn't need to keep a printed copy of a document indefinitely Yin et al (2014) Nature Commun DOI: 10.1038/ncomms6459.
The team explains that their paper comes in three colors: blue, red and green, made using the commercially available redox dyes methylene blue, neutral red and acid green, respectively. They also embed titania nanocrystals as a photocatalyst and a thickening agent hydrogen cellulose (HEC). During the writing phase, ultraviolet light reduces the dye to its colorless state. During the erasing phase, re-oxidation of the reduced dye recovers the original color; that is, the imaging material recovers its original color by reacting with atmospheric oxygen.
"The printed letters remain legible with high resolution at ambient conditions for more than three days - long enough for practical applications such as reading newspapers," Yin said. "Better still, our rewritable paper is simple to make, has low production cost, low toxicity and low energy consumption." The team is now working on a converting the film form into an actual paper form and increasing the number of cycles that a given sheet can take before it degrades. Their target is 100 rewrites. They are also investigating how to make the printing last longer than three days to expand potential applications and to find a way to do color printing.
"Our short term goal in the next step is to increase the number of rewrites of the system and the life time of the printed images," Yin told Materials Today. "We are also trying to build a laser printer that can print arbitrary text and patterns directly on the rewritable paper in a way similar to current laser printing so that we do not need to rely on photomasks."
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".