Tiny Bubbles

Inkjet printers that commit electronic words and images to paper inhabit most computer-equipped homes and offices. Costing as little as $100, the machines form a multibillion-dollar industry. But the road to that market required some twists and turns, including a serendipitous lab accident.

In the late 1970s, Canon was one of several companies pursuing inkjet technology to create text and pictures at resolutions much higher than dot-matrix printers could achieve. Like its competitors, the Canon team was trying to use pressure to push tiny, controlled amounts of ink out of nozzles. Their initial plan was to fabricate the nozzles out of a piezoelectric material; electronic signal pulses would deform the nozzle so that it would first suck ink into a chamber, then force it out. But that approach was abandoned in 1977 shortly after a carelessly placed soldering iron touched the tip of an ink-filled syringe-and changed the direction of their research. The hot tool boiled the ink, and as the bubbles expanded, they forced the ink out of the syringe. Canon’s Ichiro Endo realized that heat might lead to a better approach. (A Hewlett-Packard team independently hit on the same idea in 1978.)

Canon demonstrated the prototype “bubble jet” printer in 1981; a commercial version debuted in 1985. Other companies, including Lexmark and Xerox, adapted and enhanced the technology. Epson went on to develop inkjet printers using piezoelectric technology. In today’s thermal inkjet printers, tiny heating elements reach temperatures of 500 C, vaporizing minute amounts of ink for a few millionths of a second. As bubbles form and expand, nozzles like those shown above eject droplets of ink as small as four trillionths of a liter. Print heads containing 300 to 600 such nozzles squirt thousands of drops per second as they scan back and forth across a sheet of paper.

Researchers are now using inkjet printers to spray more than just ink. Last May, Sandia National Laboratories used an HP printer to deposit self-assembling nanostructures that could one day form ready-to-use sensor arrays or photonic circuits. Even PC circuits might be printed using piezoelectric inkjets if research at MIT’s Media Lab pans out (see “Print Your Next PC,” TR November/December 2000).