Binder-free conductive graphite coatings on polyimide substrates for applications in flexible electronics

The production of graphite/graphene derivative inks, incorporating different solvents, binders, and stabilizers is a focused research area for the development of printed electronic circuits on flexible substrates. Within the scope of the present study, a facile methodology was employed to produce a water-based graphite paste, devoid of binders and stabilizers, serving as a conductive paste while preserving the unique properties of graphite. A superior adhesive graphite thin film, attaining a 5B standard according to the ASTM D3359 crosshatch adhesion test, was successfully developed on a polyimide substrate (PI). This graphite coating on polyimide (Gr/PI) was characterized using mechanical reliability tests and four-probe resistance measurements. The adhesive Gr/PI exhibited an optimal sheet resistance value of 114 +/- 12 Omega/sq/mil. The shifts in the FTIR of Gr/PI, compared to the spectrum of PI indicate significant pi-pi interactions between the graphite and polyimide structure of the flexible substrate, elucidating the mechanism of graphite ink adhesion. The results obtained from ASTM mechanical reliability tests encompassing hardness, crease, and bending tests underscore the viability of employing Gr/PI in the manufacturing of conductive interconnects and electrodes for flexible electronic applications.