Versatile carbon-loaded shellac ink for disposable printed electronics

Abstract

Emerging technologies such as smart packaging are shifting the requirements on electronic components, notably regarding service life, which counts in days instead of years. As a result, standard materials are often not adapted due to economic, environmental or manufacturing considerations. For instance, the use of metal conductive tracks in disposable electronics is a waste of valuable resources and their accumulation in landfills is an environmental concern. In this work, we report a conductive ink made of carbon particles dispersed in a solution of shellac. This natural and water-insoluble resin works as a binder, favourably replacing petroleum-derived polymers. The carbon particles provide electrical conductivity and act as a rheology modifier, creating a printable shear-thinning gel. The ink’s conductivity and sheet resistance are 1000 S m ⁻¹ and 15 Ω sq ⁻¹, respectively, and remain stable towards moisture. We show that the ink is compatible with several industry-relevant patterning methods such as screen-printing and robocasting, and demonstrate a minimum feature size of 200 μm. As a proof-of-concept, a resistor and a capacitor are printed and used as deformation and proximity sensors, respectively.