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Last December a few people occasionally broke from the hordes of dark-suited salarymen passing through Tokyo Station to examine a bizarre sculpture of interlocking plexiglass panels. Suspended in the panels, a half dozen translucent signs the size of a sheet of notebook paper displayed weather forecasts, ads for TVs and other gizmos, and a news story about a sumo star from Bulgaria.



Anyone who didn't linger could be forgiven for dismissing it as irrelevant. But those who took a closer look might have noticed that the information changed every few minutes thanks to a wireless feed from a nearby computer.



Developed by Hitachi (HIT), the signs offered a sneak peek at a new e-paper technology set to reach the market soon. Although they seem a far cry from the paper of books and billboards, these superthin screens -- no thicker than a weekly magazine -- run on so little energy they might one day mean big changes for the advertising and publishing industries.



Hitachi execs say they're targeting Japan's $2.5 billion ad market and are wagering that businesses will come knocking when they hear about the potential cost savings. "We can get rid of the printing and pasting up of leaflets and posters with wireless, real-time e-paper," says Kazunori Fujiwara, Hitachi's senior vice-president in charge of e-paper research.



PAPER JAM.

It's an idea that has been a long time in coming. PCs and other machines were supposed to let us store records in digital files that would eliminate the paper clutter. E-books would make your old paperbacks obsolete. Flat-screen TVs would replace posters.



But the fact is, paper hasn't gone away. The spread of the Internet and the rise of the PC have made information ever more accessible, leading not to the death of paper but to its proliferation. In 2004, worldwide paper production was roughly 400 million tons, compared with about 300 million in 1995, according to Japan Pulp & Paper statistics.



One reason e-paper hasn't ousted the dead-tree variety is that nobody has found a way of making a flat display that can be as easily shuffled or written on as paper. It's also tough to beat the low cost of printing sheets in bulk on a press.



COMPETING TECHNOLOGIES.

But recent advances in flat-panel technology for TVs and portable gadgets have given a push to e-paper research. Fuji Xerox is collaborating with Oji Paper on flexible black-and-white plastic panels the size of notebooks.



These are designed to help factory and office workers keep records on lightweight tablets, and ultimately they may cut down on printouts. Others are planning to make bendable color panels, hoping to sell them to advertisers for posters.



Still others, such as a joint venture between Japanese mobile operator NTT DoCoMo (DCM) and British startup Plastic Logic, want to wirelessly deliver news, e-mail, and other digital content to floppy paper-like viewers. And watchmaker Citizen has unveiled a low-energy wall clock with a digital readout developed by E Ink, the same company that supplies technology for Sony's (SNE) digital books.



E-paper encompasses a gamut of technologies. One is based on the liquid-crystal displays, or LCDs, commonly used for TVs and laptop screens. These crystals sandwiched between two panels appear ready for prime time.



Another is a technology commonly found in cell-phone screens, called organic electro-luminescent displays, or OLEDs. Despite their differences, LCDs and OLEDs share two important traits: They can quickly change what they display and dont need a backlight, so the only time they use power is when text or images change.



FUTURE WORLD.

Despite all the hoopla over the years about e-books, commercial uses are likely to lead the way when e-paper is rolled out. Shop owners, for instance, could avoid the trouble of printing out price tags for every shipment of merchandise -- they could simply reprogram e-paper tags instead.



Billboard owners wouldn't have to pay a printer to run off new ads and then dispatch crews to paste them up -- they could change the display on e-billboards with the click of a button. Such applications could help the market for e-paper surge to nearly $900 million by 2011, from $2 million last year, according to Tokyo-based market watcher Techno System Research.



Those concepts are already being tested. In January, Mitsukoshi department store, Fujitsu (FJTSY), and Cisco Systems (CSCO) teamed up in Tokyo to present a model for the store of the future, in which shelves were labeled with e-paper, and radio ID tags on merchandise let consumers check the availability of certain items at special terminals.



The next wave of e-paper could go a step further. Fujitsu has a technology that blends the colors of three separate LCD layers each no thicker than a strand of hair.



Conventional LCDs are inflexible because they have an outer shell of glass. But Fujitsu has substituted a conductive plastic for the glass so the panel can bend, and tinkered with the crystal structure to keep images from getting wiped out by pressure or extreme temperatures.



POP ART.

At just three one-hundredths of an inch thick, Fujitsu's product is nearly as thin as paper, and there's no problem rolling it up. The company hopes to begin pitching its e-paper to railway operators and other businesses by yearend.



"If you look at how paper is used globally, ads make up more than 30% of the market," says Tomohisa Shingai, who heads Fujitsu's e-paper research team. "This is the biggest sector of the paper market, and where a color display would have the broadest application."



A more far-fetched idea is being hatched at Tokyo-based DaiNippon Printing. There, researchers have spent the past eight years experimenting with OLEDs. The film itself radiates light, so it could offer brighter, more attention-grabbing images than any of the LCD-type e-paper offerings.



If researchers can find a way to keep moisture and air from contaminating the film, they could create soft-drink labels with neon-like text and ordinary book covers with glowing, scrolling banners sometime in the next two years.



"We want to be able to print them in bulk on our presses," says Daigo Aoki, head of DNP's project. "Eventually we might be able to show video images or scrolling text that would be eye-catching."



BETA TEST.

Futuristic as Hitachi's e-paper seemed when shown at Tokyo Station two months ago, it's probably destined to be an interim technology. Its biggest assets -- the memory chip and wireless antenna that allowed content to be served up from afar -- were also a drawback, since they add weight and cost.



At just over a pound per panel, it's heavier than most rivals' offerings and still costs over $100 -- issues Hitachi hopes to resolve when it releases a color version next year. Still, it could be just enough to show people that e-paper can indeed replace printed pages, and might also become a powerful new digital medium on its own.