In A Nutshell
Chemists at the University of California have invented rewritable paper that can be written on and erased over 20 times before you have to throw it away. This paper uses ultraviolet light and redox dyes to create printed letters and images on glass or plastic film. With so much conventional paper discarded after one use, rewritable paper may help us get closer to the reality of a paperless office.
The Whole Bushel
Even within new Internet companies, the promise of a paperless society from a move to digital communications and media has not been realized. It’s been estimated that businesses still keep up to 90 percent of their information on conventional paper. In addition to being a waste of paper and ink, it hurts our forests and adds to pollution.
Now, chemists at the University of California believe they have a solution: rewritable paper. It may not eliminate the problem entirely or immediately, but chemistry professor Yadong Yin and his associates believe their invention will reduce our need for conventional paper.
Rewritable paper can be written on and erased over 20 times before you have to throw it away. You don’t need ink, just ultraviolet light and commercially available redox dyes to create printed letters and images on glass or plastic film.
Here’s how it works. The paper is a thin plastic film or glass on which a color-switching chemical, the redox dye, is applied only once. To write on this type of paper, you place a photomasked template, a layer of glass etched with words and patterns, over the film with the redox dye. Using ultraviolet light, the letters and patterns from the template are stained onto the paper while the rest of the dye gets photo-bleached to its colorless state. When it’s done, you have printed text and images on the rewritable paper.
Currently, the paper is available in three colors: red, blue, and green, which corresponds to the redox dye colors of neutral red, methylene blue, and acid green. “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 told UCR Today. “Better still, our rewritable paper is simple to make, has low production cost, low toxicity and low energy consumption.”
When you want to reuse this paper, you simply heat it to 115 degrees Celsius (239 °F) to return the film to its original color by reoxidizing the dye. The paper can be erased in less than 10 minutes. Although the temperature required to do this sounds high, it’s actually less than that of a laser printer, which heats paper to about 200 degrees Celsius (392 °F) to bind toner particles to it. After erasing rewritable paper, you can print on it again using the same process but without additional ink.
The chemists are working on a cellulose-based rewritable paper that’s more like conventional paper. To increase the ways it can be used, the scientists want to extend the time that text is readable, increase the number of reuses to 100, and develop a multicolored version of the paper.