Drop-on-demand inkjet deposition of complex fluid on textiles

The objective of the research was to develop fundamental understanding of the process of deposition of complex mixtures by the inkjet method. Motivation for this work resulted from the requirement that "inks" in a growing number of textile applications contain solid particles, typically also requiring additives including dispersants. Such inks are likely to be highly solids-laden and non-Newtonian, and predictions of behavior based on existing understanding of drop formation from Newtonian liquids may be unsatisfactory. The formulation of high performance/high value-added treatments in the form of inks for textiles greatly affects deposition and ink-substrate interaction. Characterization of the effects of the various components of the solids-laden inks on drop formation and substrate interaction is crucial to utilization.;In the first part of the research, the rheological properties and DOD drop formation dynamics of carbon black pigmented inkjet inks were investigated. It was found that the suspension microstructure responds to bulk motions, leading to shear rate and time dependent shear viscosity. However, DOD drop formation dynamics of highly pigmented inkjet ink and pure Newtonian fluid was similar even though shear rate up to 2x105 s -1 exists during inkjet jetting process. A proposed explanation for these observations is that the shearing time during DOD drop ejection is insufficient for changing and stabilizing the microstructure of the suspension.;The second part of the research contributes to the understanding of DOD drop formation dynamics of pure Newtonian fluids and builds on the work done previously in our group. The focus was on the effects of signal amplitude and jetting frequency on DOD drop formation dynamics. Higher signal amplitude led to higher speeds of primary drop and satellites and larger liquid volume ejected. The reproducibility of evolution of the secondary liquid thread was very low once voltage amplitude was increased to a level where the wave-like instability breakup occurred. Jetting frequency was found to affect the volume and speed of ejected liquid body when it is sufficiently high. When the nozzle went from idle to jetting, the drop triggered by the first pulse was found to be identical and independent of jetting frequency. However, at sufficiently high jetting frequency, DOD drop formation varied over the first four pulses after idle. A modulating pulse added before the first pulse eliminated the variation in drop formation at the higher jetting frequencies.;The last part of the thesis was a qualitative investigation of DOD drop impaction and post-impaction on inkjet paper and textiles. Dynamics of DOD drop accumulation and spreading on the substrates and final ink distribution show drastic differences between these two substrates. The final ink distributions on inkjet paper resembled irregular circles, with their size increasing as the number of drops increased. The final ink distribution on fabric was greatly affected by the fabric structure, that is, the yarn direction and intersections. The ink tended to stay on one yarn as drops accumulated until excess ink moved to neighboring yarns. As the number of drops increased, the primary change in the ink distribution on the cotton fabric was the increasing distance over which the ink spread along the yarns. Fibers protrude from the surface of the cotton yarns, creating a "hairy" fabric. These fibers can affect the distribution of ink on the fabric.