Visualization of drop-on-demand inkjet: Drop formation and deposition

Abstract

An apparatus developed for visualizing drop-on-demand (DOD) drop formation and impaction on substrates is described. Using a pulsed laser, a low-speed charge coupled device camera, and signal generators, an imaging system based on flash photography is shown to be able to obtain sharp images with a temporal resolution of 200ns and a spatial resolution of 0.81μm∕pixel. Several steps are taken to minimize the “first drop problem” so that excellent reproducibility is achieved; drop formation is reproducible with a positional variation of 1μm. The visualization system coupled with a motorized stage allows imaging of the impaction of micron-size drops on surfaces. A wave form generator and an amplifier are used to produce the required wave form for a given printhead and ejected liquid. Demonstration of the system for study of DOD micron-size drop formation and impaction on a substrate is presented. The effects of signal wave form on DOD drop formation are demonstrated using a Trident printhead driven by four different signal wave forms. The effect of surface wettability on micron-size drop impaction is shown using hydrophilic and hydrophobic surfaces.

A mechanism of the penetration limit for producing holes in poly(4-vinyl phenol) films by inkjet etching

“…The first drop problem is a well-known issue in inkjet printing and is the inconsistency of the first few drops ejected by a nozzle after it has been sitting idle for some time and is caused by evaporation of the ink at the orifice [34]. This evaporation shifts the physical and chemical properties of the ink away from those required and causes problems with proper jetting, especially after prolonged idle times.…”

Dynamic nozzles for drop generators

“…The parametric space of this or any other droplet generator is wide and includes variables such as the liquid properties, the dynamical response of the fluid, the mechanical response of the actuator, the waveform characteristics, and the nozzle dynamics. 5,13 Inkjet manufacturers explore this space as to find the best or desired conditions of jetting. FIG.…”

“…In commercial drop on demand systems great efforts are taken on the engineering of the waveform (this is often a try and error process) to find jetting conditions free of satellites. 13 Waveforms commonly have several parameters, such as multiple pulses with different amplitudes and widths. The experiments shown in this article demonstrate that both the timing of the nozzle closure and its extent can be used to achieve satellite free conditions.…”

“…In a micrometre commercial system (with 50 m nozzles), a droplet formation event normally last ≈30 µs. 13,19 Scaling down this technology would mean that the nozzle closing action (total or partial) should be carried out within a fraction of that total time in order to be effective. The reset time of the system presented in this work is limited by the responses the of stepper motor and the actuator, yet there are existing technologies that can be miniaturized and operated in the microsecond range, i.e., magneto-electro mechanical actuators, thermally actuated flexures, or piezoelectric actuators.…”

“…Electric signals deform these walls causing a large pressure increase that is used to jet the droplets. 13 In DoD, at the start of the jetting process, the liquid emerging from the nozzle quickly begins to form what will become the main droplet. As the jet continues to emerge, a filament forms between the drop and the nozzle, connecting the fluid of the main drop and the fluid left at the reservoir.…”