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.