Rewritable paper which can be written & erased on more than 20 times

Despite
society’s move toward a fully digital world, a good deal of business is still
transacted on paper. In some estimates, it’s as high as 90 percent, with a
great deal of printed paper discarded after just one-time use. That waste comes
at a cost, not only for the paper but also for the ink. We shouldn’t forget the
environmental effect due to cutting of trees and chemical pollution to air (to
satisfy the paper requirement).


Rewritable
paper that does not use ink but instead uses dyes that respond to ultraviolet
light has been developed by US scientists. The dyed paper may be a solution to
growing environmental problems associated with the use of regular paper.
Chemists at the University of California, Riverside have now fabricated in the
lab just such novel rewritable paper, one that 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. “This rewritable paper does not
require additional inks for printing, making it both economically and
environmentally viable,” said Yadong Yin, whose lab led the research. “It
represents an attractive alternative to regular paper in meeting the increasing
global needs for sustainability and environmental conservation.” The rewritable
paper is essentially rewritable media in the form of glass or plastic firm to
which letters and patterns can be repeatedly printed, retained for days, and
then erased by simple heating. The study results appear online in Nature Communications.

Let’s
understand the working principle of rewritable paper. 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 nanocristals (these serve as catalysts) and the thickening
agent hydroxyethyl 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 recovers the original colour; that is,
the imaging material recovers its original colour by reacting with ambient
oxygen. Heating at 115C 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.”

His lab is
currently working on a paper version of the rewritable paper. “Even for this
kind of paper, heating to 115C poses no problem,” Yin said. “In conventional
printers, paper is already heated to 200C in order to get toner particles to
bond to the paper.” His lab also is working on increasing the cycling number
(the number of times the rewritable paper can be printed and erased), with a
target of 100, to reduce the overall cost.

Given the
number of different solutions now in the game for solidly readable rewritable
digital text, it remains to be seen what this new development has to offer that
is truly unique, but it certainly looks good and interesting, and the
commercial possibilities are obvious – if no one else gets there first.

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