At Nanotech, the world's leading nanotechnology trade fair in Tokyo, Bayer MaterialScience is showcasing the two conductive inks BayInk TP S and BayInk TP CNT, which have been developed primarily for use in the growing "printed electronics" market.
These new inks boast excellent adhesion to plastic films, other flexible substrates, glass, silicon and indium tin oxide (ITO), where they form highly stable structures. "This makes them ideal in supporting the concept of flexible, inexpensive electronics. They also have the potential for use in conventional electronic components, where they can replace metallization with its complex process technology," says Dr. Daniel Rudhardt, global head of research and development for conductive materials for printable electronic applications at Bayer MaterialScience.
To date, there are only a few examples of applications for producing electronic circuits using printable inks. The technology is deployed in manufacturing RFID chips and certain film displays, for instance. But experts believe printed electronics offers significant market potential and expect to see it expand rapidly. Future areas of application could include e-books or rollable screens but also electrically conductive structures in vehicles, such as integrated receiving antennae for navigation systems. "We are open to development partnerships at all stages of the value-added chain," comments Rudhardt.
The excellent properties of the new aqueous products are the result of adding nanoparticles. BayInk TP CNT contains Baytubes carbon nanotubes (CNTs). This eco-friendly ink enables production of switches and other electronic elements using virtually all current printing processes - from inkjet and gravure printing to screen printing - with conductivities up to 5,000 S/m. This completely removes the need for resintering, which not only means energy savings but is also a key benefit for use in temperature-sensitive substrates.
Bayer MaterialScience is working closely with other industrial companies and research institutes in developing CNT-based printing inks as part of the "CarboInk" alliance on innovations with carbon nanotubes (Inno.CNT). "We aim to support the production of printable, thin and cost-effective conductor tracks using printable CNT-based inks," explains Rudhardt, who is also head of this project sponsored by the BMBF (German Federal Ministry of Education and Research).
BayInk TP S is based on silver nanoparticles. The dispersion can be used to produce conductor tracks and circuits using inkjet technology, for example. The resintering this requires can be performed at temperatures below 140 °C. This results in outstanding conductivity amounting to up to 35 percent of that of solid silver, depending on the sintering conditions.
The fact that the silver particles in BayInk TP S lie in the nanometer range makes it easier for them to melt during sintering, thus enabling this ink to be used at low temperatures to create more conductive structures than are possible with conventional screen printing pastes containing silver. BayInk TP S can also even be used to achieve a print resolution well below 50 micrometers, with the resolution being determined only by the printing process and not by the ink itself.
The experts from Bayer MaterialScience were helped in developing the conductive inks by the fact that they have now amassed wide-ranging expertise in nanoparticle dispersion in aqueous media. The challenge is to stabilize particles with relatively small quantities of additives. A high proportion of emulsifiers would greatly reduce the conductivity of the printed electronics. The processes developed also allow production of these nano inks in larger volumes while maintaining the same quality.