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Nano Silver Ink Creates Wiring Diagrams Invisible to the Naked Eye

Electrical wiring diagrams, whose conductive tracks are thinner than 20 micrometers and thus invisible to the naked eye, can now be produced using new BayInk® nanoparticulate silver inks. The aqueous nano dispersions were developed by Bayer MaterialScience AG in cooperation with Bayer Technology Services. They are about to be released for commercial sale and are tailor-made for a new generation of ink jet printers that can be used to produce wiring diagrams cost effectively with a high level of productivity - even on an industrial scale. "Our nano inks achieve ten percent of the specific conductivity of elemental silver with only a relatively low percentage of silver by weight. At the same time, they adhere very well to a wide variety of substrates, such as polycarbonate, polyethylene terephthalate, thermoplastic polyurethane and glass," explains Dr. Stefan Bahnmüller, nanotechnology expert in the New Technologies group at Bayer MaterialScience.

The curing temperatures of the new nano inks are well below 130 °C - much lower than those of most commercially available silver inks. Therefore, BayInk® can be printed on a variety of plastics that would otherwise not be able to withstand the thermal load during the curing process. In addition, the printed conductive tracks are very flexible and extensible. "This is, for example, particularly important for plastic films that are shaped using the film insert molding process after the wiring diagram has been printed, and are then back-injected," says Bahnmüller.

Printing wiring diagrams using an ink jet printer is an attractive option because the process is very straightforward and precise. What’s more, unlike chemical etching processes, it is also ecologically safe. In the past, silver inks in ink jet printers often caused problems when used on an industrial scale because the printers’ spray nozzles would clog easily, causing high reject rates and uneconomical production. "In contrast, the size and distribution of the particulates in our nano inks are perfectly matched to the process, which means that the nozzles don’t clog, thus enabling continuous high-quality production without interruption," observes Bahnmüller.

Bahnmüller envisages great potential for BayInk® - which incidentally can also be used in screen printing - in the field of printed electronics, for instance with sensors, actuators and radio frequency identification systems (RFID). Conductive tracks of photovoltaic cells could also be produced using nano silver inks. In the automotive industry, wiring diagrams produced using BayInk® are ideal as an alternative to cable harnesses, for example in instrument panels. Very thin filaments based on nano inks, which are invisible to the naked eye, could be used in rear windows or headlamp lenses to prevent them from steaming up or icing over.

At present, Bayer MaterialScience is working with the Universities of Jena and Marburg to reduce the width of conductive tracks made of BayInk® still further.

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