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

While inkjet printing on many hydrophilic surfaces is achieved through control of drop spacing and droplet deposition delay, the same for hydrophobic substrates proves challenging. Low surface energies of hydrophobic surfaces prevents intact and uniform lines of low-viscosity ink to form. In this article, the stacked coin printing strategy used for hydrophilic surfaces, is adapted for hydrophobic surfaces. Stacked coin morphology is seen when droplet deposition time between two sequentially deposited droplets is longer than the evaporation time of the first droplet. On hydrophobic surfaces, the parameter window for successful printing is smaller than on hydrophilic surfaces, thus an investigation is needed to implement this methodology. Experiments were conducted using an inkjet printer with variable stage speed and stage temperature. Silver nanoparticle ink was used to print on Teflon–AF substrates. We 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 occurence of each regime. In this study, 180 °C was identified as the critical temperature for instantaneous drying of the studied ink, and a maximum drop spacing of 20 μm to print continuous lines.