Deposition of Molten Ink Droplets on a Solid Surface

Abstract

An experimental study on the deposition of micro-size droplets (∼39 μm in diameter) of molten wax ink on an aluminum surface is presented. Effects of initial temperature of droplets, substrate temperature and distance from printhead to substrate on the deposited droplet shape and textures were investigated. Depending on impact conditions, droplets may have either smooth or irregular edges, and the final shape may be either regular or two tiered. Analysis was conducted to compare the time scales for solidification, viscous damping and oscillation. A simple heat transfer model was developed, and temperature dependences of viscosity and surface tension were taken into account. The Ohnesorge number of droplets was investigated as a function of time to compare the transient effects of viscous damping and oscillation of the droplets after impact. The number of oscillations completed before the Ohnesorge number reaches unity agrees with the number of tiers formed. The height of the first tier was related to the value of the Ohnesorge number during the first oscillation. The thermal capillary effect was evaluated by defining and examining two Marangoni numbers for the spreading and post-spreading phases of the droplet impact. Splashing of droplets occurred and produced fingers around the droplet peripheries, which was mainly determined by local solidification and spreading dynamics in the vicinity of contact line.