DLC-engineered flat gravure surface: enabling sustainable fabrication to replace chrome for printing conductive line electrodes in flexible electronics

Abstract

In this research we compare conductive fine line electrodes printed from a flat gravure surface fabricated with diamond-like carbon (DLC) with prints from a chromium/chrome (Cr) surface. The study of DLC as gravure surface is important because it has durable surface. The DLC fabrication process does not produce toxic waste, while the Cr fabrication process results in toxic wastewater. Cr is deemed a hazardous material and a substance of high concern (SHC), while DLC is environmentally friendly. In this study, eight experimental trials were conducted to assess the quality of print reproduction. Combinations of ink, substrate, and doctor blade are used as printing conditions to test print reproduction from the chrome and the standard DLC gravure surfaces. These tests demonstrated the effect of print conditions on the reproduction of fine lines and an observable trend in studies with both surfaces. Experimental data show that under various printing conditions, the prints of electrode grids reproduced from standard DLC had increased line widths for 20 and 30 μm lines compared to chrome. Comparing the print samples from trial to trial that used the same gravure surface and print condition-associated factors such as higher total surface free energy (SFE) and its polar component of the PET (Polyethylene terephthalate) substrate, the viscosity and contact angle of the deposited ink, and various other factors influenced ink transfer to the substrate. Under different trial printing conditions, chrome-printed samples displayed a noticeable trend in terms of line width, electrical resistance and transparency. Interestingly, standard DLC-printed samples also displayed a similar trend to chrome-printed samples. However standard DLC-printed samples also demonstrated improved surface wetting, ink doctoring on the surface and ink transfer capability from line engravings. These differences resulted in increased line gain and low electrical resistance for DLC-printed surfaces when compared to chrome-printed surfaces. Additionally, a statistical t-test analysis indicated that standard DLC-printed surfaces provided significantly higher mean line width, likely as a results of improved ink release and transfer characteristics.