Abstract
Screen-printable carbon-based inks are available in a range of carbon morphologies and concentrations, resulting in various rheological profiles. There are challenges in obtaining a good print when high loading and elasticity functional inks are used, with a trade-off often required between functionality and printability. There is a limited understanding of how ink rheology influences the ink deposition mechanism during screen-printing, which then affects the print topography and therefore electrical performance. High speed imaging was used with a screen-printing simulation apparatus to investigate the effect of viscosity of a graphite and carbon-black ink at various levels of solvent dilution on the deposition mechanisms occurring during screen-printing. With little dilution, the greater relative volume of carbon in the ink resulted in a greater tendency towards elastic behavior than at higher dilutions. During the screen-printing process this led to the ink splitting into filaments while remaining in contact with both the mesh and substrate simultaneously over a greater horizonal length. The location of separating filaments corresponded with localized film thickness increases in the print, which led to a higher surface roughness (Sz). This method could be used to make appropriate adjustments to ink rheology to overcome print defects related to poor ink separation.
Highlights
Conductive carbon-based inks are used in several printed electronics applications due to their electrical properties and relative low cost when compared with alternative functional materials such as silver
This cannot be predicted with shear rheological analyses alone, this method provides a way of relating the rheological profile of the ink with the ink separation mechanisms during printing which influence the print profile. This can enable the ink to be modified to reduce the elasticity and observe and quantify the presence of filaments and their effect on the print profile without the need for large print runs. These studies have used high-speed imaging to identify the effect of altering the carbon concentrations of carbon-based screen-printing inks on the deposition and separation mechanisms in screen-printing
With the higher viscosity inks (
Summary
Conductive carbon-based inks are used in several printed electronics applications due to their electrical properties and relative low cost when compared with alternative functional materials such as silver. They are widely used in applications including resistive heaters [1,2], electrochemical sensors [3,4], printed batteries [5,6] and perovskite photovoltaics [7,8]. The binders used are typically determined by the curing temperature, substrate material and compatibility with the particular application [14] These different combinations produce a wide range of rheological profiles of screen-printing carbon-based inks, each requiring different press settings for optimal performance
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