A Method for Production of Binder-Free Graphite Thin Films on Polyimide for Flexible Electronics

Polyimide (PI) is extensively used in flexible electronic devices. In general, conductive interconnects are made on these substrates using electrically conductive inks with different additives. In this study, we optimized the interaction between graphite and polyimide to develop an adhesive thin film of graphite on DuPont Kapton (PI). The ink was produced from highly purified Sri Lankan vein-type graphite mixed with deionized water to form a thick film paste. The graphite films were fabricated on the PI substrate using the blading method and cured gradually in an oven. The hardness and adhesion properties of the thin films were evaluated according to the ASTM D3363 pencil hardness test and the ASTM D3359-78 crosshatch adhesion test. The results obtained through these tests indicated HB hardness and 5B standard with superior adherent graphite thin film on PI, respectively. The developed binder-free thin graphite films show a low sheet resistance in comparison with the reported values for similar tests on thin films in the presence of binders. This low-cost and scalable method of coating graphite on the surface of Polyimide can be applied in the commercially viable production of flexible electronic devices.