Inkjet printing of silver and carbon conductive functional coatings

Abstract

The direct inkjet printing of conductive silver and/or carbon suspension inks on flexible substrates is a promising route for the direct manufacture of printed and functional electronics. In this thesis silver flake inks designed for flexography were modified for inkjet printing. The effect of the printing parameters on the properties of the printed silver layers was examined using a Taguchi design of experiments which allowed for the electrical conductivity to be optimised. It was shown that dynamics of the inkjet deposition had a strong influence on the compaction of the silver flakes in the printed layers. The compaction observed led to conductivities which were only 1/100 of the conductivity of bulk silver. The impact of the deposition dynamics on the compaction in the silver layers was modelled and was found to be dominated by the properties of the ink droplet. The model was found to be in agreement with my previous measurements and it allows for the prediction of the compaction behaviour as a function of the drop size, rheology and the volume loading of the ink. Carbon nanoform powders from the plasma splitting of natural gas were tailored by pyrolysis to improve their electrical conductivity and porosity. These powders were formulated into a water based ink suitable for inkjet printing, on printing conductive layers were formed with only printed layer without any further thermal treatment. The resistance of the coatings was demonstrated to decrease as the number of printed layers was increased.