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Transparent touch panel is non-breakable

Film-on-plastic replaces film-on-glass

By David Bak, Editor-in-Chief, Global Design News -- Design News, May 20, 2002

Osaka, Japan — Osaka, Japan—Transparent touch panels used in PDAs (personal digital assistants), pocket PCs, and other consumer electronics products are evolving. Replacing traditional glass substrates with plastic results in touch panels offering greater shock resistance, higher light transmission, and lower reflection. In addition, end products weigh less and present a slimmer profile.

Until now, glass has been the common substrate for transparent touch panels. Conductive layers of indium tin oxide (ITO), applied by high-temperature sputtering technology and separated by micro-dot spacers, form the electrodes. Because glass is impervious to the high-temperature coating process, it maintains a flat, non-bending surface for application of the rigid ITO. A protective layer of PET completes the package.

Recently introduced film/film/plastic configurations improve the technology. For example, engineers at Matsushita Electronic Components Co. apply a second film of PET over a plastic, rather than glass, substrate. This bottom PET layer protects the plastic from the high-temperatures required by the ITO sputtering process, for a distortion-free, flat face during production. In addition, application of two anti-reflection layers ensures better visibility.

Even more recently, Matsushita Electronic Components Co. has developed a single film/plastic panel. By substituting a proprietary ITO print technology for high-temperature sputtering (see Global Design News, November 2001, p. 38), company engineers can coat the plastic substrate directly, eliminating the need for a bottom layer of PET film. The printing process, unlike sputtering which results in a rigid ITO film susceptible to cracking or diminished performance if bent, allows a thinner, more flexible touch panel. Elimination of the air gap between the bottom PET layer of the touch panel and the LCD module, furthermore, permits higher light transmission.

Ultimately, predicts Hirofumi Komiya, team leader of product development and engineering, electro-mechanical components, both film/film/plastic and film/plastic panels will be replaced by film/film no-substrate panels. These will be even thinner and more bendable, with superior light transmission. The challenge, he explains, is to work with LCD manufacturers to set up compensation solutions to negate damage due to bending. Komiya reports the technology is presently under development.

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