Fluid Dynamics & Acoustics

How inkjet printing really works

COURSE FOCUS

Inkjet printing is a process of depositing small droplets with a specified volume onto a precise location on a substrate. During the course we follow the ink through the printhead, into droplet formation and onto landing on the substrate.

The course mainly covers piezo-driven printheads jetting Newtonian inks, although the issue of viscoelastic inks will be discussed. A piezo-driven printhead is modelled as a set of acoustic cavities, the characteristics of which will be presented in the time (response to waveforms) and frequency domain.

The course is based on precise descriptions of the physical phenomena involved and the derivation of the mathematical framework needed to solve the governing equations. Where possible the outcomes will be compared with experimental findings. Different mathematical methods will be presented to calculate the responses of different systems in the frequency and time domain. To describe correctly the behaviour of a printhead with a large number of narrow pitched nozzles, the long duct theory will be presented.

The aim of this course is to couple the characteristics of droplet formation and landing, spreading and permeation to the acoustics and microfluidics of the printhead. The knowledge conveyed during the course will enable the participants to analyse the behaviour of a wide variety of existing printheads and to support the development of new printheads and inks from a physics point of view.

Session 1

General introduction

  • Introduction on physics & mathematics

  • Basic concepts (single degree of freedom system)

    • Waveforms

    • Fluid dynamics

    • Mathematics

Different piezo designs

  • Helmholtz theory and waveforms (two and five degree of freedom systems)

    • Single nozzle printheads

    • Multi-nozzle devices

Session 2

Theoretical considerations

  • Long duct theory

  • Droplet formation

  • Speed of sound

  • Damping

  • Refilling

Session 3

Further considerations

  • Maximum jetting frequency

  • Drag on droplets

  • Droplet impact and spreading

  • Jetting of viscoelastic inks

  • Examples: polyLED display printing, printing of biomolecules (co-authored by Dr Anke Pierik, Philips Research)

Course Leader

Prof Dr J. Frits Dijksman
University of Twente, Faculty of Science and Technology, Netherlands

Prof Frits Dijksman is professor of biomedical applications of inkjet technology at the University of Twente, Netherlands. He has worked with Philips Research for more than 30 years and his main area of interest has been inkjet technology for consumer and non-consumer applications, such as PolyLED display manufacturing and the printing of biomolecules.

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