Drop Speeds from Drop-on-Demand Ink-Jet Print Heads

Hoath, Stephen D.; Hsiao, Wen‐Kai; Jung, Sungjune; Martin, Graham D.; Hutchings, I.M.; Morrison, N. A.; Harlen, Oliver G.

doi:10.2352/j.imagingsci.technol.2013.57.1.010503

Cited by 30 publications

(22 citation statements)

References 27 publications

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“…It has been shown to behave particularly well in drop-on-demand (DoD) inkjet printing [4] in comparison with Newtonian fluids exposed to the same conditions. [5] Typical shear rates are >10 5 s À1 within the small nozzles (with diameter ca. 40 lm) employed in DoD printing, for jet velocities of the order of 5 m s À1 , well beyond the range of measurement of conventional rheometers.…”

Section: Introductionmentioning

confidence: 99%

Oscillations of aqueous PEDOT:PSS fluid droplets and the properties of complex fluids in drop-on-demand inkjet printing

Hoath

Hsiao

Martin

et al. 2015

Journal of Non-Newtonian Fluid Mechanics

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a b s t r a c tShear-thinning aqueous poly(3,4-ethylenedioxythiophene): poly(styrene sulphonate) (PEDOT:PSS) fluids were studied under the conditions of drop-on-demand inkjet printing. Ligament retraction caused oscillation of the resulting drops, from which values of surface tension and viscosity were derived. Effective viscosities of <4 mPa s at drop oscillation frequencies of 13-33 kHz were consistent with conventional high-frequency rheometry, with only a small possible contribution from viscoelasticity with a relaxation time of about 6 ls. Strong evidence was found that the viscosity, reduced by shear-thinning in the printhead nozzle, recovered as the drop formed. The low viscosity values measured for the drops in flight were associated with the strong oscillation induced by ligament retraction, while for a weakly perturbed drop the viscosity remained high. Surface tension values in the presence of surfactant were significantly higher than the equilibrium values, and consistent with the surface age of the drops.

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Section: Introductionmentioning

confidence: 99%

Oscillations of aqueous PEDOT:PSS fluid droplets and the properties of complex fluids in drop-on-demand inkjet printing

Hoath

Hsiao

Martin

et al. 2015

Journal of Non-Newtonian Fluid Mechanics

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“…The slope is 1.1 m s −1 V −1 and is independent of fluid properties, while the V o threshold increases linearly with Oh as discussed earlier. The linear dependence of droplet speed on V o appears to be general, as it has also been found for paraffin waxes jetted by a tubular transducer (Reis, Ainsley & Derby 2005) and for polymer solutions jetted by several microfabricated transducers and a tubular transducer (Hoath et al 2012). This arises simply from the linear dependence of the pressure and displacement amplitudes on V o .…”

Section: Resultsmentioning

confidence: 87%

“…Several examples are shown in figure 6 for different fluids for V o,min < V o < V o,max . At short times, the speed of the leading edge of the projected fluid column decreases sharply because of conversion of kinetic to surface and viscous energies (Wijshoff 2010;Hoath et al 2012). After a certain elapsed time, which here we call the final-state time t f , the tail has pinched off to give the final spherical droplet in free flight.…”

Section: Resultsmentioning

confidence: 99%

Jettable fluid space and jetting characteristics of a microprint head

Wong

Lim

et al. 2012

J. Fluid Mech.

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The influence of fluid droplet properties on the droplet-on-demand jetting of a Newtonian model fluid (water-isopropanol-ethylene glycol ternary system) has been studied. The composition of the fluid was adjusted to investigate how the Ohnesorge number (Oh) influences droplet formation (morphology and speed) by a microfabricated short-channel shear-mode piezoelectric transducer. The fluid space for satellite-free single droplet formation was indeed found to be bound by upper and lower Oh limits, but these shift approximately linearly with the piezo pulse voltage amplitude V o , which has a stronger influence on jetting characteristics than pulse length. Therefore the jettable fluid space can be depicted on a V o -Oh diagram. Satellite-free droplets of the model fluid can be jetted over a wide Oh range, at least 0.025 to 0.5 (corresponding to Z = Oh −1 of 40 to 2), by adjusting V o appropriately. Air drag was found to dominate droplet flight, as may be expected. This can be accurately modelled to yield droplet formation time, which turned out to be 20-30 µs under a wide range of jetting conditions. The corresponding initial droplet speed was found to vary linearly with V o , with a fluid-dependent threshold but a fluid-independent slope, and a minimum speed of about 2 m s −1 . This suggests the existence of isovelocity lines that run substantially parallel to the lower jetting boundary in the V o -Oh diagram.

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“…The speed-drive curve for the jetted solvent has a gradient that seems representative of weakly elastic polymer solutions, shear thinning fluids and colloidal suspensions, and which also appears to be relatively insensitive to the effective jetting viscosity of complex fluids. 7 Increased particle content can disproportionately increase the drive voltage required to jet the fluid. Suspension viscosity η( ) increases nonlinearly with increasing (or vol.…”

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confidence: 99%

Jetted mixtures of particle suspensions and resins

et al. 2014

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Drop-on-demand (DoD) ink-jetting of hard particle suspensions with volume fraction ∼ 0.25 has been surveyed using 1000 ultra-high speed videos as a function of particle size (d 90 = 0.8-3.6 μm), with added 2 wt. % acrylic (250 kDa) or 0.5 wt. % cellulose (370 kDa) resin, and also compared with Newtonian analogues. Jet breakoff times from 80 μm diameter nozzles were insensitive (120 ± 10 μs) to particle size, and resin jet break-off times were not significantly altered by >30 wt. % added particles. Different particle size grades can be jetted equally well in practice, while resin content effectively controls DoD break-off times. C 2014 AIP Publishing LLC.Many materials applications are being implemented using additive manufacturing, in particular, using digital processes such as drop-on-demand (DoD) inkjet printing. Reliable inkjet printing of colloids, and hard particle suspensions such as inorganic pigments, is desirable for modern manufacturing processes. There has been much prior effort to understand ceramic inkjet printing, 1 but perhaps surprisingly, there are still many unresolved aspects of complex fluid behaviour under jetting conditions although recent progress has been reported 2 for the understanding of polymeric fluid jetting.The deposition of hard particles is of increasing interest for larger scale decorative applications, but is currently restricted to relatively small particle (d 90 ∼1 μm) sizes. Close packed spheres have a maximum occupied volume of ∼64 vol. %. The rheology for model suspensions of spherical polystyrene particles is well-described 3 by the Zarraga model 4 η(ϕ) = η 0 exp(-2.34 ϕ)/(1 -ϕ/ϕ m ) 3 where η 0 is the base fluid viscosity (200 mPa s) and the maximum volume fraction is ϕ m = 0.62. However, in DoD inkjet applications the base fluid viscosity is typically 5 mPa s, very much lower than that used in liquid bridge and dripping experiments with particles, and jetted particle loadings are limited to 35 wt. %, for which the corresponding volume fraction is typically 0.20-0.30 (but still well beyond the Einstein regime). Recent numerical modelling of liquid bridges 5 and experimental work on the dripping of liquids containing particles 3, 6 suggest that DoD break-off times could be significantly lowered (by typically >10%) for particle loadings with > 0.20.We report here the DoD jetting of complex liquids containing particles and/or resins observed using ultra-high speed imaging techniques. A Shimadzu HPV-1 ultra-high speed camera and 500 W flash lamp recorded single jets in a 312 × 260 pixel frame at a rate of 500 000 frames per second for 102 frames of 0.5 μs exposure time in conventional shadowgraph mode at typically 1.7 μm/pixel image. Off-line analyses determined the jet and drop speeds, while jet break-off times (±3 μs) were deduced from the video image counter.Jets and drops in DoD inkjet printing have speeds and volumes that appear to vary almost linearly with print head drive voltage above a threshold value of drive voltage that depends on viscosity. The DoD jetting thresh...

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Drop Speeds from Drop-on-Demand Ink-Jet Print Heads

Abstract: Recent results from a number of UK academic inkjet research studies advance the understanding of complex fluid jetting behaviour and may be of interest to the wider digital fabrication community for the enhancement of inkjet printing applications.

Cited by 30 publications

References 27 publications

Oscillations of aqueous PEDOT:PSS fluid droplets and the properties of complex fluids in drop-on-demand inkjet printing

Oscillations of aqueous PEDOT:PSS fluid droplets and the properties of complex fluids in drop-on-demand inkjet printing

Jettable fluid space and jetting characteristics of a microprint head

Jetted mixtures of particle suspensions and resins

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