Innovations made laser printers durable and affordable
Chemists Damodar Pai, John Yanus and Milan Stolka of Webster, N.Y., will be honored on August 20 by the world's largest scientific society for innovations that made laser printers more durable and affordable for home as well as office use. As a team, they will be designated one of 12 Heroes of Chemistry by the American Chemical Society at its 220th national meeting, in Washington, D.C.
"The heart of electrophotography -- that's what we call laser printing -- is similar to what was invented in 1938," said Pai, a senior research fellow at Xerox Corp. "What Xerox wanted our group to do was to make the process lower cost, more efficient, flexible, environmentally sound, and useful over and over and over again."
The key to rapid, high-print-quality laser printers is the "photoconductor," a device that converts patterns of light and dark into a template of electrical charges. Particles of toner cling to the charges and transfer the pattern to paper.
Chester Carlson discovered the effect more than 60 years ago. But the typical drum-shaped photoconductor was brittle and expensive, as well as relatively inefficient at producing electrical charges. So Xerox decided to develop a new device, one based on tough but flexible organic compounds.
The Xerox team discovered a class of small molecules they could dissolve in polycarbonate, a readily available polymer, and layer on a mylar belt. The molecules, called biphenyl diamines, turn photons of light into an electrically charged template in less than 50 milliseconds and with near-perfect efficiency.
"The challenge was that we needed extraordinarily high purity," said Yanus, an organic chemist who with Stolka (now retired) studied methods to make the diamines. "We're sending billions of electrical charges through them, and any impurities would quickly show up in the prints."
Designing the diamine photoconductor "was the enabling advance that led to practical commercial devices" for home as well as office use, wrote Xerox manager Merlin Scharfe to nominate the researchers for the award.
The Heroes of Chemistry program, started in 1996, honors industrial chemists and chemical engineers who create commercially successful products that improve the quality of life.
A nonprofit organization with a membership of 161,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals and databases, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.