Google – AFP, 28 January 2014
 |
Water drops
are seen in Honduras on March 4, 2010 (AFP/File, Orlando Sierra)
|
Paris —
Like any ordinary printer, this machine ingests a blank page and spits it out
covered in print.
But instead
of ink, it uses only water, and the used paper fades back to white within a
day, enabling it to be reused.
A team of
chemists claims their "water-jet" technology allows each page to be
reprinted dozens of times -- a money- and tree-saving option in a digital world
that still relies heavily on hard copy.
"Several
international statistics indicate that about 40 percent of office prints (are)
taken to the waste paper basket after a single reading," said Sean Xiao-An
Zhang, a chemistry professor at Jilin University in China, who oversaw work on
the innovation.
The trick
lies in the paper, which is treated with an invisible dye that colours when
exposed to water, then disappears.
The print
fades away within about 22 hours at temperatures below 35 degrees Celsius (95
deg Fahrenheit) as the water evaporates -- quicker if exposed to high heat,
Zhang and a team wrote in a paper describing their invention in the journal
Nature Communications.
The print
is clear, claim the designers, and the technology cheap.
"Based
on 50 times of rewriting, the cost is only about one percent of the inkjet
prints," Zhang said in a video on the Nature website.
Even if
each page was re-used only a dozen times, the cost would still be about
one-seventeenth of the inkjet version.
Sean said
dye-treating the paper, of the type generally used for printing, added about
five percent to its price, but this is more than compensated for by the saving
on ink.
Crucially,
the new method does not require a change of printer but merely replacing the
ink in the cartridge with water, using a syringe.
"Water
is a renewable resource and obviously poses no risk to the environment,"
said the study.
Previous
work in the quest for a disappearing ink has tended to yield a low-contrast
print, often at a high cost, and sometimes using hazardous chemicals.
Zhang and
his team used a previously little-studied dye compound called oxazolidine,
which yielded a clear, blue print in less than a second after water was
applied.
They have
managed to create four water-printed colours so far -- blue, magenta, gold and
purple -- but can only print in one hue at a time, for now.
The next
step is to improve both the resolution and the duration of the print.
They are
also working on a machine that will heat pre-printed sheets of paper as they
are fed into the machine, fading the pages instantaneously for re-printing.
At 70 C
(158 F), the colour disappears within about 30 seconds.
Zhang said
the dyed paper was "very safe" but toxicity tests are underway on
mice to be sure.
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