Week 7; Inkjet Printing PDF

MEC 454 Inkjet Printing – Lecture 1 Droplet Ejection Patrick J. Smith University of Sheffield England 11th November 2024 1 Three Lectures on Inkjet Printing Methods of Writing Droplet Behaviour Applications Inkjet Printing...

MEC 454 Inkjet Printing – Lecture 1 Droplet Ejection Patrick J. Smith University of Sheffield England 11th November 2024 1 Three Lectures on Inkjet Printing Methods of Writing Droplet Behaviour Applications Inkjet Printing & Control 1. Droplet ejection 2. Droplet behaviour 3. Applications  What today’s lecture covers ✴What is meant by direct writing ✴A little bit of inkjet history ✴ The various types of inkjet ✴ How droplets are generated in Drop-on-Demand inkjet ✴ A little bit of fluid mechanics ✴ Droplet volume ✴Influence of rheology ✴ Influence of voltage, pulse width and frequency ✴Factors affecting droplet production ✴Comments and references Methods of Writing  Direct write... ✴...is not new  Indirect Write... ✴...is just as old  Drawing a line ✴ Stamping/contact printing ✴Masking/stencilling ✴ Direct writing  Stamping/contact printing 1. Make the stamp 2. Apply the ink 3. Make the print Examples: Gutenberg’s printing press Micro-contact printing Advantages Stamp can be re-used (printing presses) Stamp defines final print Disadvantages Contamination from earlier prints Incomplete ink transfer One ink at a time Substrate might be sensitive to impacts Masking/stencilling 1. Make the stencil 2. Apply the ink Example: Screen printing Advantages Stencil can be re-used Stencil defines final print Disadvantages Contamination from earlier prints Incomplete ink transfer One ink at a time  Direct writing 1. Apply the ink Example: Inkjet printing Advantages Contamination minimised/removed Printhead Pattern storage is on hard-disk Layered manufacture More than one ink Reduced waste Cupboard Disadvantages Incomplete ink transfer A typical hard- Droplets can misbehave drive for a Hard-drive Screen printer Low loadings Inkjet Printing decreases the number of process steps needed to make a feature  Inkjet Printing... ✴...is a direct write technology ✴...jets ink and makes a print ✴...is widely used ✴...does not need masks ✴...can be scaled up ✴...has its problems, like all things ✴...has many advantages ✴...has some unique advantages ✴ …is a non-contact technique!  Origin of Inkjet In 1867, William Thomson (later Lord Kelvin) was granted a patent for his proposal to use electrostatic forces to control the release of ink drops onto paper. However, his proposal did not describe a way of controlling the pattern of the droplets. Lord Rayleigh - Fluid under pressure issues from an orifice and breaks into uniform droplets due to the amplification of induced capillary waves, which are usually due to an electromechanical device that causes pressure oscillations to propagate throughout the liquid This principle is employed in inkjet devices W. Thomson, “Improvements in Telegraphic Receiving and Recording Instruments,” GB Pat 2,147 (1867) Lord Rayleigh, Proc. London. Math. Soc.; 1878, 10, 4  Continuous Inkjet (CIJ) Droplets break off in the presence of an electrostatic field and acquire a charge Droplets may then be directed by another electrostatic field to land upon the substrate Advantages: Rapid droplet formation rate No waste due to droplet recycling Some CIJ Manufacturers Hitachi Disadvantages: Ink must be electrically conducting Domino Droplet recycling is a cause of contamination Chaudhary et al. J. Fluid Mech. 1979, 96, 257: Pimbley, IBM J. Res. Dev. 1984, 29, 148  Drop on Demand Inkjet Drop on Demand (DOD) Droplets are produced by pressure/velocity transients that are caused by volumetric changes, which are induced by a piezoelectric material Thermal Inkjet Printing (TIJ) Droplets can also be produced by thin film resistors instead of piezoelectric transducers Advantages: No contamination No waste since droplets only made when needed Wider range of inks can be used (more so for DOD than TIJ) Some DOD Manufacturers Disadvantages: Microdrop Lower droplet formation rate than CIJ Ink rheology imposes limitations MicroFab Fujifilm Dimatix Hansell, U.S. Patent 2,512,743, 1950 PixDro  Different Types of Drop-on-Demand Printheads Heater bubble droplet Thermal Inkjet Piezo Inkjet Drop ejection for DOD Voltage I - Piezo moves outwards II - Negative waves travel outwards III - Waves reflect and one reverses IV - Waves arrive at centre when piezo contracts V - Wave is magnified and drop ejected Shin, Grassia & Derby, J. Acoust. Soc. Am., (2003) 114, 1315  Wave forms Simple waveform generates droplets Complex waveform generates droplets Pressure waves propagate then dampens/removes acoustic after- Voltage effects (or Pulse Amplitude) Ink expands Ink contracts Time / μs (Pulse Width Residual oscillations cancelled Frequency = the number of times a waveform is repeated during a second  Ink Rheology Viscosity The acoustic waves which cause a droplet to be ejected are affected by ink viscosity. The more viscous an ink is, the more the acoustic waves will be dampened. If an ink’s viscosity is increased, then voltage has to be increased to eject a droplet. A benefit of a fairly viscous ink is a reduction in satellite formation. Ink with a viscosity value between 0.5 - 40 mPa.s can be jetted. (As a rule, 1 – 20 mPa.s is printable. Nb: water is 1 mPa.s)  Ink Rheology Density The main effect of density is on the acoustic speed, it does not affect droplet generation. Surface Tension An increase in surface tension will require an increase in voltage to generate a droplet. Low surface tension values can lead to bubbles forming inside the nozzle. Ink with a surface tension value between 20 - 70 mN.m-1 can be jetted. (Check with your printer vendor.) Inkjet Printing: Fluid Mechanics Gareth H. McKinley - Rheology Bulletin, July 2005 https://dspace.mit.edu/bitstream/1721.1/18086/1/05-P-05.pdf  Reynolds and Weber Numbers Re =  V L /  The Reynolds number is the ratio between viscosity and inertial force We =  V2 L /  The Weber number is the ratio between surface tension and inertial force  = density V = fluid velocity L = length  = viscosity  = surface tension  The Z number Fromm obtained an approximate solution to the Navier – Stokes equations to describe droplet formation: ρ = density γ = surface tension η = viscosity a = characteristic length Re/We = Z = Oh-1 (Ohnesorge number) Fromm: If Z > 2 then drop formation in drop-on-demand systems is possible Reis et al: If 1 < Z < 10 then drop formation is possible. Lower limit is controlled by viscosity, upper limit represents satellite formation Fromm, IBM J. Res. Dev. 1984, 28, 322 Reis, Derby J. Appl. Phys. 2005, 97, 094903 PAUSE 24  Effect of Z on Droplet Volume Droplet volume increases with Z as predicted by Fromm Droplet volume is normalised to the volume displaced by the actuator at different driving voltages Reis, Derby J. Appl. Phys. 2005, 97, 094903 By varying the ink’s rheology (viscosity or surface tension), we can vary the size of the ejected droplet  Influence of Voltage on Droplet Volume Applied voltage is proportional to droplet volume Increased Voltage = Increased Droplet Volume Molten paraffin wax Reis, Derby, J. Appl. Phys. 2005, 97, 094903 By varying voltage, we can vary the size of the ejected droplet Aqueous PEDOT solution  Influence of Pulse Width on Droplet Volume Pulse width has a complicated effect on droplet volume Molten paraffin wax Reis, Derby, J. Appl. Phys. 2005, 97, 094903 Aqueous PEDOT solution Influence of Frequency on Droplet Volume Sinusoidal behaviour similar to that of varying pulse width. Ainsley, Derby, J. Mater. Sci. 2002, 37, 3155  Thankfully… 1 mm If you see droplets, your ink is printable. Although, what goes on behind the nozzle is quite complicated the beauty of inkjet is that a simple visual check is all that is needed for most users - assuming your ink has the proper rheometry  Factors Affecting Droplet Production ✴Nozzle Clogging ✴Solutions are better than suspensions but have a lower solids content ✴Viscosity ✴Critical before ejection ✴If it is too high, no droplets ✴Surface Tension ✴Plays a part after ejection ✴Solution or Suspension ✴Suspensions decrease nozzle life-time due to abrasion  The advantage of Inkjet is... QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Reproducible Droplets Image taken by Steve Hoath, http://www.ifm.eng.cam.ac.uk/pp/inkjet/default.html How we build (print) with inkjet A row of over-lapping drops results in line (hopefully) An array of drops results in a film (hopefully) Dot-spacing The dot-spacing is the distance between the centres of two droplets The larger the dot-spacing, the less overlap. Large dot-spacings can give narrow lines (see later) but can also result in line breaks. Inkjet Printing... ✴...is a contactless (non-impact), direct-write technology for making films, structures and lines ✴...is an additive technology ✴...produces minimal/no waste ✴...reduces/removes contamination ✴...reduces the number of process steps ✴ therefore, cheapens production costs Comments on Inkjet Printing Inkjet printers are widely used, usually for small document printing runs but are increasingly being used for a wide variety of applications. Inkjet’s appeal lies in its ability to reproducibly generate uniform sized droplets. Three types of inkjet printing Continuous, thermal and piezo With ink, viscosity is important. At 40 mPa.s, and above, jetting becomes impossible. Droplets are generated by a voltage pulse. Typically, the larger the voltage, the larger the droplet.  References ✴Tekin, Smith & Schubert, Soft Matter, 2008, 4, 703 ✴MicroFab’s Tech-note 99-01 is useful ✴ It can be found at: http://www.microfab.com/equipment/technotes.html  MEC 454 Inkjet Printing – Lecture 2 Droplet Behaviour & Control Patrick J. Smith University of Sheffield England 11th & 12th November 2024  Outline of Droplets Section ✴ Droplet impact ✴ Behaviour of lines ✴ Droplet evaporation ✴ Coffee staining ✴ Preventing coffee staining The lifetime of a droplet from creation (ejection) to final dried feature! Droplet Impact - inkjet printed Water We = 30 Initial diameter = 85 µm Velocity = 5.1 m/s Contact angle = 35º Delay is 3 µs van Dam & Le Clerc, Phys. Fluids 2004, 16, 3403  Contact Angle basics Receding Angle angle formed by a retreating droplet and by drying droplets Vapour Liquid θ Solid GLV x Cos θ= GVS - GLS Advancing Angle angle formed by an advancing droplet and by forming/growing droplets  Why not reduce surface energy? Hydrophobic glass Contact angle >90 ° Hydrophilic glass Contact angle Fe3O4 +8NaCl …print silver/polyaniline hybrids …print silk 50 mm x 5 mm 3 inks (aniline, silver nitrate and ammonium persulphate) printed in turn to synthesise polyaniline/silver nanocomposite Modified silk in water initially printed, then ethanol was printed on top causing silk to precipitate Patrick J. Smith  Inkjet and Composites Carbon fibre composites – as strong as metals but much lighter – however, they’re brittle Using inkjet printing to deposit polymeric agents along predicted crack pathways. Why choose IJP? Polymer  Inkjet printing can deposit highly controllable droplets into various patterns  Minimum amount of polymer used Composite ply  Simple manufacturing process [email protected] Pattern – Hexagon dx dy hexagon Patrick J. Smith  Experimental Diameter Parameters of Group Composition of ink of pattern printhead Pattern Substrate Solute wt % Solvent / μm dx / μm dy / μm Ink 1 PEG1 50 DMF PU Ink 2 IPDI/BiNeo 74/1 DMF 60 Hexagon 0.4 0.2 CFRP P1+Water P1 5 Distilled water 60 Hexagon 0.4 0.2 CFRP P1+Ethanol P1 5 Ethanol 60 Hexagon 0.4 0.2 CFRP P2 P2 5 DMF 60 Hexagon 0.4 0.2 CFRP  PEG: poly(ethylene glycol) (Mn = 400)  DMF: N,N-Dimethylformamide  PU: polyurethane  IPDI: isophorone diisocyanate  P1 & P2 – polymers (sorry, I can’t be more specific)  BiNeo: Bismuth neodecanate  CFRP: carbon fibre reinforced plastic (Cycom 977-2) [email protected]  Image analysis Optical images of P2 droplets printed on glass slide 300 μm 300 μm 300 μm a. Before curing b. Heated to 100℃ 2hr c. After curing [email protected] Standard Mechanical Tests Loader Fibre-reinforced plastic Sample composites — Determination of apparent interlaminar shear Supporter strength by short-beam method. (BS EN ISO 14130:1998) Fibre-reinforced plastic Loader composites — Determination of mode I interlaminar fracture toughness, GIC, for unidirectionally reinforced materials. Loader (BS ISO 15024:2001) [email protected]  Interlaminar shear stress test 4.0 3.5 3.0 2.5 Load / 10 N 3 2.0 1.5 Δy 1 2 1.0 3 0.5 Δx 4 5 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 P1e P1w P2 Extension / mm Stiffness = Δy / Δx Samples containing printed polymeric agents have up to 33.84% increased stiffness compared to the virgin samples. P1e P1w P2 Note: error bar represents standard deviation, n = 5 Less than 1% additional weight (~0.25%) Patrick J. Smith  Mode I interlaminar fracture toughness (GIC) test The addition of P2 and P1w has greatly increased GIC P1e has delivered a slight increase 0.4 0.4 Before Healing Cycle Virgin After Healing Cycle Virgin PEGw P1w PEGw P1w PEGe P1e PEGe P1e 0.3 P2 PMMA 0.3 PMMA P2 2 2 Avg. GIC / kJ/m Avg. GIC / kJ/m 0.2 0.2 0.1 0.1 0.0 0.0 NL 5% / MAX PROP NL 5% / MAX PROP Note: error bar represents standard deviation, n = 5 Less than 1% additional weight (~0.25%) Paper to be submitted soon, patent first! Patrick J. Smith Summary ✴ Inkjet printing is a useful technique for the direct fabrication of a variety of devices ✴ The print is important - so a good understanding of what ink does on the substrate is vital ✴ Strategies exist for narrow, cheap and highly conductive interconnects ✴By controlling the coffee stain, OFETs based on TIPS- Pentacene/PS blends have mobilities as high as pure TIPS- Pentacene ✴Inkjet is being used to toughen Carbon fibre Composites