Masterclass on Inkjet Rheology

PROGRAM

This course covers all aspects of rheology relevant to inkjet printing and at timescales relevant to inkjet printing. We discuss shear (low, mid and high), high frequency, and extensional rheology. We also look at the influence of ink components on ink rheology and its influence on jetting behavior. We explore ways to optimise the rheological properties of inks to control misting, satellites, and achieve reliable jetting.

BACKGROUND

Rheology is the study of the deformation and flow of matter under the influence of an applied stress/strain. Flow/deformation behavior of complex fluids like ink cannot be simply described by classical fluid mechanics or elasticity, which is why they are termed non-Newtonian fluids. Recent innovative ideas and technological breakthroughs in printhead design and ink formulation have extended inkjet technology to newly emerging markets and applications, such as display fabrication, control-release drug delivery, anti-counterfeit and 3D printing. A fundamental understanding of ink chemistry, formulations, and the influence of individual components and ink as a whole on dynamic flow behavior in-channel, in the nozzle, in-flight and on-substrate during printing is vital to adequately control print quality (drop ejection characteristic, reliability) and to increase the capabilities of inkjet technology.

ADVANCED RHEOLOGY

The Advanced Rheology course is aimed at ink formulators and chemists. The course provides insight into the (i) flow behavior of Newtonian and non-Newtonian fluids and (ii) rheometry tools to characterize high shear as well as extensional and high frequency rheology of low viscosity fluids. In this Masterclass we do an overview of inkjet inks, and how and where individual ink components influence jetting behavior during printing.

Physical properties alone are no guide to ink performance. Small variations in ink viscoelasticity influence upstream flow dynamics and jet break-up mechanisms downstream. We will present techniquesfor quantifying the complex fluid rheology of low viscosity inkjet inks at conditions similar to those during printing.These techniques have not been possible until recently.

We will discuss and demonstrate that jetting behaviour of weak viscoelastic inkjet fluids during printing can be linked with appropriate measurement of inkjet fluid rheology. Bulk viscosity alone is no guide to print performance. The size of the main drop, ligament length and jetting speed can be correlated with other rheological properties. These techniques, used prior to filling print heads, would provide useful tools to differentiate between identical inks that have similar bulk properties but show different jetting behaviour during printing. This is often the case, as ink batch variations may result in different jetting behavior and issues with ink printability. These tools will aid ink formulators to quickly shortlist their inks.