Electrically conductive inks: the role of graphitic materials

Electrically conductive inks are the foundations of printed electronics as they allow to print circuits on different surfaces. In wearable applications, the surface is often fabric and therefore circuits have to undergo elastic deformations due to body movements without losing their functional performances, i.e. they have to be bendable and stretchable. Two industrial-grade conductive, stretchable, screen-printable inks have been produced starting from some simple formulas developed at a lab scale which rely on a technology that helps the filler dispersion into the polymeric matrix. One ink is based on carbon black only and the other one is based on carbon black and graphite. Samples obtained using the so-called transfer printing technique (very common in the textile industry) have been subjected to progressive elongations and to cyclic elongations while electrical resistance data were recorded by a multimeter. The effective contribution of the graphitic portion is clear in lowering the static resistance value, in the entity of conductivity regained after stretching to 100% and in stabilizing the cyclic elongation performance. This positive effect can be probably explained considering graphite lamellas as bridges connecting carbon black clusters and ensuring a more continuous electric path