Novel rewritable paper that doesn't need ink

Researchers have developed a novel rewritable paper that can be written on and erased 20 times with no significant loss in contrast or resolution.
The paper developed by chemists at the University of California, Riverside is based on the colour switching property of commercial chemicals called redox dyes.
The dye forms the imaging layer of the paper. Printing is achieved by using ultraviolet light to photobleach the dye, except the portions that constitute the text on the paper.
The new rewritable paper can be erased and written on more than 20 times with no significant loss in contrast or resolution, researchers said.

"This rewritable paper does not require additional inks for printing, making it both economically and environmentally viable," said Yadong Yin, a professor of chemistry, whose lab led the research.
"It represents an attractive alternative to regular paper in meeting the increasing global needs for sustainability and environmental conservation," said Yin.

The rewritable paper is essentially rewritable media in the form of glass or plastic film to which letters and patterns can be repeatedly printed, retained for days, and then erased by simple heating.
The paper comes in three primary colours: blue, red and green, produced by using the commercial redox dyes methylene blue, neutral red and acid green, respectively.

Included in the dye are titania nanocrystals which serve as catalysts and the thickening agent hydrogen cellulose (HEC).
The combination of the dye, catalysts and HEC lends high reversibility and repeatability to the film.
During the writing phase, ultraviolet light reduces the dye to its colourless state. During the erasing phase, re-oxidation of the reduced dye recovers the original colour; that is, the imaging material recovers its original colour by reacting with ambient oxygen.
Heating at 115 degrees Celsius can speed up the reaction so that the erasing process is often completed in less than 10 minutes.
"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," Yin added.
His lab is currently working on a paper version of the rewritable paper and on increasing the cycling number (the number of times the paper can be printed and erased), with a target of 100, to reduce overall cost.
The research team is exploring ways to extend the legibility of the printed texts or images for more than three days to expand their potential uses.
The study was published in the journal Nature Communications.