Inkjet Printing on Hydrophobic Surface: Practical Implementation of Stacked Coin Strategy

While inkjet printing on many hydrophilic surfaces can be achieved through control of drop spacing and droplet deposition delay alone, the same for hydrophobic substrates prove to be challenging. The low surface energies of hydrophobic surfaces lead to dewetting, unwanted coalescence of wet drops, and bulging, preventing intact and uniform lines of low‐viscosity ink to form. In this paper, we have adapted the stacked coin strategy, a well‐established and successful technique for hydrophilic surfaces, for use on hydrophobic surfaces. Stacked coin morphology occurs when the time taken to deposit a subsequent overlapping droplet in a pattern is longer than the evaporation time of the prior droplet. On hydrophobic surfaces, it is considerably more challenging and the parameter window for successful printing is smaller than on hydrophilic surfaces, thus requiring in‐depth study to implement this methodology on hydrophobic surfaces. We conducted experiments using a custom‐built inkjet printer with variable stage speed and stage temperature, where silver nanoparticle ink was used to print on Teflon‐AF substrates. Our study identified the following regimes: isolated droplets, isolated multi‐droplets, broken line, true stacked coin, and delamination. The relationship between substrate temperature, drop spacing and droplet deposition delay controls the printability window of true stacked coin morphology and its surrounding regimes. The key to the success of this strategy on hydrophobic surfaces is rapid drying of individual droplets to minimize movement due to hydrophilic coalescence of overlapping dried and wet droplets. Our study identified 180⁰C as the critical temperature for instantaneous drying of the studied ink, and a maximum drop spacing of 20µm.This article is protected by copyright. All rights reserved.