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Effects of Fluid Viscosity on Drop-on-Demand Ink-Jet Break-Off

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Simulations of the jetting of Newtonian fluids from drop-ondemand print heads show that the radial jet pinch-off region, which may lie inside the nozzle, is strongly affected by the fluid viscosity over the range of values that are commonly used. Jet profiles beyond the nozzle exit predicted in these simulations match previously published high resolution images very well and validate the code used. The simulations show that the radial velocity at the minimum radius in the pinch-off region falls exponentially soon after neck formation but then approaches a speed near that predicted theoretically for filament rupture.

The overall jet length is primarily controlled by the slow speed of radial pinch-off. Towards the final break-off time, competition between the original radial minimum and a developing second radial minimum can alter the flow conditions towards symmetry. The simulations also explain why visible jets are shaped like truncated cones. Pinch-off occurs typically within one nozzle radius of the nozzle exit, and while it may be located within the nozzle region, another radial minimum also forms outside the nozzle, close to the exit for low viscosity fluids but well beyond it for higher viscosity fluid. The radial collapse follows a power law with time, with the power-law index n varying between the value of n=2/3 expected for an inviscid fluid and n=1 law expected for a viscous fluid. The transition in behavior occurs at a viscosity of ∼20 mPa s, which is within the range of ∼10–40 mPa s typical of most DoD inks formulations.

Document Type: Research Article

Publication date: January 1, 2010

More about this publication?
  • For more than 25 years, NIP has been the leading forum for discussion of advances and new directions in non-impact and digital printing technologies. A comprehensive, industry-wide conference, this meeting includes all aspects of the hardware, materials, software, images, and applications associated with digital printing systems, including drop-on-demand ink jet, wide format ink jet, desktop and continuous ink jet, toner-based electrophotographic printers, production digital printing systems, and thermal printing systems, as well as the engineering capability, optimization, and science involved in these fields.

    Since 2005, NIP has been held in conjunction with the Digital Fabrication Conference.

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