Ink jet and flilament stretch

Ink jet rheology and filament stretching

In the 2000s a Cambridge based project on the science and technology of ink jet printing provided a welcome ten year period of funding and in the Chemical Engineering Department where our role was to characterise the complex and delicate behaviour of ink jet fluid rheology and formulation. From this work we developed our “Trimaster” family of filament stretching devices in order to capture the high speed extensional deformation and breakup behaviour of low viscosity fluids.

 

Ink jet processing is very sensitive to the formulation of the ink jet fluid and in particular  the rheology. Normally ink jet fluids have a  viscosity  below 5 mPas, close to that of normal solvents and water. Ink jet processing usually involves high jet speeds, typically 6 m/s and this results in high strain rate deformation with dominant extensional behaviour during drop formation outside the jet nozzle. Strain rates in excess of 1000 s-1 are often achieved. Ink jet fluids whilst generally being Newtonian in steady shear can be viscoelastic where the relaxation times involved can be very short, typically a millisecond or less. This takes rheology into an area of “extreme rheology” needing to characterise the viscoelasticity of “watery” fluids with short relaxation times. In addition nonlinear extensional behaviour of these low viscosity, viscoelastic fluids can be important.

 

2009. Monash Review presentation.

A summary of the ink jet rheology story is given below from a 2009 Seminar presentation at Monash University, Australia (Unfortunately some of the photographs and graphs have not come out in the reproduction).

 

 

More recent developments.

2018. Cambridge seminar. Fast filament stretching.

Over the past few years Dr Simon Butler and I have been working with a French Group (CEMEF) at Sophia Antipolis who have carried  out impressive modelling that provides insight on how viscosity, surface tension and yield stress influence high speed deformation and breakup of filaments and this presentation is a summary of that work.

Droplet deformation and breakup 

 

 

 

2019.  Fast filament stretching.

University  College London (UCL) seminar. 

This presentation is a concise follow up of the 2018 Cambridge seminar. Some movie clips are missing however hopefully the presentation conveys a simple message for the conditions required to form drops, threads and for “yield stress fluids”, a cusped conical section. There has also been much debate in the literature that “Carbopol” systems are the best preferred model yield stress fluid. This presentation shows that Nivea Cream gives a much sharper and cleaner Yield stress transition!

 

 

Papers relevant to Ink Jet Rheology and Processing