Fundamentals of Inkjet Printing

List of Contributors Preface xxi 1 Introductory Remarks 1 Ian M. Hutchings, Graham D. Martin, and Stephen D. Hoath 1.1 Introduction 1 1.2 Drop Formation: Continuous Inkjet and Drop-on-Demand 2 1.3 Surface Tension and Viscosity 6 1.4 Dimensionless Groups in Inkjet Printing 8 1.5 Length and Time Scales in Inkjet Printing 9 1.6 The Structure of This Book 11 1.7 Symbols Used 11 References 12 2 Fluid Mechanics for Inkjet Printing 13 Edward P. Furlani 2.1 Introduction 13 2.2 Fluid Mechanics 13 2.3 Dimensions and Units 14 2.4 Fluid Properties 15 2.4.1 Density 15 2.4.2 Viscosity 16 2.4.2.1 Newtonian Fluids 17 2.4.2.2 Non-Newtonian Fluids 17 2.4.3 Surface Tension 18 2.5 Force, Pressure, Velocity 19 2.6 Fluid Dynamics 20 2.6.1 Equations of Fluid Dynamics 20 2.6.1.1 Conservation of Mass 21 2.6.1.2 Conservation of Momentum 21 2.6.1.3 Conservation of Energy 22 2.6.2 Solving the Equations of Fluid Dynamics 24 2.7 Computational Fluid Dynamics 25 2.7.1 Preprocessor 26 2.7.2 Solver 28 2.7.3 Postprocessor 28 2.8 Inkjet Systems 29 2.8.1 Inkjet Modeling Challenges 31 2.8.1.1 Free-Surface Analysis 32 2.8.1.2 Fluid–Structure Interaction 35 2.8.1.3 Phase Change Analysis 35 2.8.1.4 Ink–Media Interaction 35 2.8.1.5 Non-Newtonian Fluids 35 2.8.2 Inkjet Processes 36 2.8.2.1 DOD Droplet Generation 36 2.8.2.2 CIJ Droplet Generation 43 2.8.2.3 Crosstalk 45 2.8.2.4 Aerodynamic Effects 47 2.8.2.5 Ink–Media Interactions 48 Summary 52 Acknowledgments 53 References 53 3 Inkjet Printheads 57 Naoki Morita, Amol A. Khalate, Arend M. van Buul, and Herman Wijshoff 3.1 Thermal versus Piezoelectric Inkjet Printing 57 3.2 Thermal Inkjet 58 3.2.1 Boiling Mechanism 58 3.2.1.1 Theoretical Model 58 3.2.1.2 Observation of Boiling Bubble Behavior 59 3.2.2 Printhead Structure 63 3.2.3 Jetting Characteristics of TIJs 64 3.2.3.1 Input Power Characteristics and Heat Control of TIJs 64 3.2.3.2 Frequency Response and Crosstalk Control 65 3.2.4 Problems Associated with Pressure and Heat Generated in TIJs 66 3.2.4.1 Cavitation Damage on the Heater Surface 66 3.2.4.2 Ink Residue Scorching (Kogation) on the Heater Surface 67 3.2.5 Evaporation of Water in Aqueous Ink 69 3.2.5.1 Approaches to Compensate for Condensed Ink through Evaporation 69 3.2.5.2 Measurement of Physical Properties of Flying Droplets 70 3.3 Future Prospects for Inkjets 72 3.3.1 Printing Speed Limit Estimated by Drop Behavior 72 3.3.2 Control of Bleeding Caused by High-Speed Drying 72 3.4 Continuous Inkjet (CIJ) 74 3.5 Examples and Problems (TIJ) 76 3.5.1 Example 76 3.5.2 Problem 76 3.6 Piezo Inkjet Printhead 78 3.6.1 Introduction 78 3.6.2 Working Principle 79 3.6.3 Ink Channel Behavior 82 3.6.3.1 Residual Oscillations 82 3.6.4 Control of Inkjet Printhead 84 3.6.4.1 Constrained Actuation Pulse Design 84 3.6.4.2 Complex Actuation Pulse Design: Feedforward Control Approach 86 3.6.5 Industrial Applications 88 References 89 4 Drop Formation in Inkjet Printing 93 Theo Driessen and Roger Jeurissen 4.1 Introduction 93 4.1.1 Continuous Inkjet Printing 93 4.1.2 Drop-on-Demand Inkjet Printing 94 4.2 Drop Formation in Continuous Inkjet Printing 95 4.2.1 Rayleigh–Plateau Instability 96 4.2.2 Satellite Formation 99 4.2.3 Final Droplet Velocity 99 4.2.3.1 Capillary Deceleration 99 4.2.3.2 Acceleration due to Advection 101 4.3 Analysis of Droplet Formation in Drop-on-Demand Inkjet Printing 102 4.3.1 The Scenario of the Analyzed Droplet Formation 102 4.3.1.1 Head Droplet Formation 103 4.3.1.2 Tail Formation 105 4.3.1.3 Pinch-Off and Tail Breakup 108 4.4 Worked Examples 111 4.4.1 Tail Formation for the Purely Inertial Case 111 4.4.2 Dispersion Relation of the Rayleigh–Plateau Instability 112 Acknowledgment 114 References 114 5 Polymers in Inkjet Printing 117 Joseph S.R. Wheeler and Stephen G. Yeates 5.1 Introduction 117 5.2 Polymer Definition 117 5.3 Source- and Architecture-Based Polymer Classification 118 5.4 Molecular Weight and Size 118 5.5 Polymer Solutions 122 5.6 Effect of Structure and Physical Form on Inkjet Formulation Properties 124 5.7 Zimm Interpretation for Polymers in High Shear Environments 125 5.8 Printability of Polymer-Containing Inkjet Fluids 126 5.9 Simulation of the Inkjet Printing of High-Molecular-Weight Polymers 129 5.10 Molecular Weight Stability of Polymers during DOD Inkjet Printing 130 5.11 Molecular Weight Stability of Polymers during CIJ Printing 132 5.12 Molecular Weight Stability of Associating Polymers During DOD Inkjet Printing 134 5.13 Case Studies of Polymers in Inkjet Formulation 135 5.13.1 Role of Polymer Architecture 135 5.13.2 Inkjet Printing of PEDOT:PSS 136 5.13.3 Inkjet Printing of Polymer–Graphene and CNT Composites 136 References 137 6 Colloid Particles in Ink Formulations 141 Mohmed A. Mulla, Huai Nyin Yow, Huagui Zhang, Olivier J. Cayre, and Simon Biggs 6.1 Introduction 141 6.1.1 Colloids 141 6.1.2 Inkjet (Complex) Fluids 141 6.2 Dyes versus Pigment Inks 142 6.3 Stability of Colloids 143 6.3.1 DLVO Theory 144 6.3.2 van der Waals Attractive Force 144 6.3.3 Electrostatic Repulsive Force 145 6.3.4 Stabilization of Colloidal Systems 146 6.4 Particle–Polymer Interactions 149 6.4.1 Steric Stabilization 149 6.4.2 Bridging Flocculation 150 6.4.3 Depletion Flocculation 151 6.5 Effect of Other Ink Components on Colloidal Interactions 152 6.5.1 Surfactants 152 6.5.2 Viscosity Modifiers 153 6.5.3 Humectants 153 6.5.4 Glycol Ethers 154 6.5.5 Storage – Buffers and Biocides 154 6.5.6 Other Additives 155 6.6 Characterization of Colloidal Dispersions 155 6.6.1 Dynamic Light Scattering (DLS) 155 6.6.2 Electrophoretic Mobility (Zeta Potential) 156 6.6.3 Rheology 157 6.6.4 Bulk Colloidal Dispersion 157 6.6.5 Jetting 159 6.7 Sedimentation/Settling 160 6.7.1 Sedimentation Characterization Techniques 162 6.8 Conclusions/Outlook 165 References 166 7 Jetting Simulations 169 Neil F. Morrison, Claire McIlroy, and Oliver G. Harlen 7.1 Introduction 169 7.2 Key Considerations for Modelling 172 7.3 One-Dimensional Modelling 177 7.3.1 The Long-Wavelength Approximation 177 7.3.2 A Simple CIJ Model 178 7.3.3 Error Analysis for Simple Jetting 180 7.3.4 Validation of the Model by Rayleigh’s Theory 180 7.3.5 Exploring the Parameter Space 183 7.3.6 A Numerical Experiment 184 7.4 Axisymmetric Modelling 185 7.4.1 Continuous Inkjet 186 7.4.2 Drop-on-Demand 189 7.5 Three-Dimensional Simulation 194 References 196 8 Drops on Substrates 199 Sungjune Jung, Hyung Ju Hwang, and Seok Hyun Hong 8.1 Introduction 199 8.2 Experimental Observation of Newtonian Drop Impact on Wettable Surface 201 8.2.1 Effect of Initial Speed on Drop Impact and Spreading 202 8.2.2 Effect of Surface Wettability on Drop Impact and Spreading 206 8.2.3 Effect of Fluid Properties on Drop Impact and Spreading 208 8.3 Dimensional Analysis: The Buckingham Pi Theorem 209 8.4 Drop Impact Dynamics: The Maximum Spreading Diameter 211 8.4.1 Viscous Dissipation Dominates Surface Tension 213 8.4.2 The Flattened-Pancake Model 214 8.4.3 The Kinetic Energy Transfers Completely into Surface Energy 215 8.4.3.1 Evaporation: A Scaling Exponent of the Radius 216 References 218 9 Coalescence and Line Formation 219 Wen-Kai Hsiao and Eleanor S. Betton 9.1 Implication of Drop Coalescence on Printed Image Formation 219 9.2 Implication of Drop Coalescence on Functional and 3D Printing 220 9.3 Coalescence of Inkjet-Printed Drops 222 9.3.1 Coalescence of a Pair of Liquid Drops on Surface 222 9.3.2 Coalescence with Drop Impact 226 9.3.3 Coalescence of a Pair of Inkjet-Printed Drops 229 9.3.3.1 Experimental Setup 230 9.3.3.2 Necking Stage Dynamics 230 9.3.3.3 Discussion 234 9.3.3.4 Summary 234 9.4 2D Features and Line Printing 235 9.4.1 Model of Drop–Bead Coalescence 236 9.4.2 Experiment and Observations 237 9.4.2.1 Effect of Drop Spacing 238 9.4.2.2 Effect of Drop Deposition Interval 242 9.4.3 Stability Regimes and Discussion 244 9.4.4 Summary 246 9.5 Summary and Concluding Remarks 247 9.6 Working Questions 248 References 249 10 Droplets Drying on Surfaces 251 Emma Talbot, Colin Bain, Raf De Dier, Wouter Sempels, and Jan Vermant 10.1 Overview 251 10.2 Evaporation of Single Solvents 252 10.3 Evaporation of Mixed Solvents 259 10.3.1 Marangoni Flows 260 10.3.1.1 Thermal Marangoni Flows 260 10.3.1.2 Solutal Marangoni Flows 262 10.4 Particle Transport in Drying Droplets 263 10.4.1 The “Coffee Ring Effect” 263 10.4.1.1 Disadvantages to the Ring-Shaped Pattern 265 10.4.1.2 Exploiting the Coffee Ring Effect 266 10.4.1.3 Avoiding the Coffee Ring Effect 267 10.4.2 Particle Migration 268 10.5 Drying of Complex Fluids 268 10.5.1 Contact Line Motion 269 10.5.2 Particle Character 269 10.5.3 Segregation of Solids 272 10.5.4 Local Environment 273 10.5.5 Substrate Patterning 273 10.5.6 Destabilization of Colloids during Drying 274 10.6 Problems 274 References 275 11 Simulation of Drops on Surfaces 281 Mark C T Wilson and Krzysztof J Kubiak 11.1 Introduction 281 11.2 Continuum-Based Modeling of Drop Dynamics 282 11.2.1 Finite Element Analysis 282 11.2.2 Finite Element Boundary Conditions for Free Surfaces 283 11.2.3 The Moving Contact-Line Problem 284 11.2.3.1 The Contact Angle as a Boundary Condition 285 11.2.3.2 An Interface Formation Model 285 11.2.4 The Volume of Fluid Method 286 11.3 Challenging Contact Angle Phenomena 288 11.3.1 Apparent Contact Angles 288 11.3.2 Contact Angle Hysteresis 289 11.3.3 Dynamic Contact Angles 291 11.3.4 Dynamic Contact Angles in Numerical Simulations 292 11.3.5 Resting Time Effect 293 11.4 Diffuse-Interface Models 294 11.5 Lattice Boltzmann Simulations of Drop Dynamics 296 11.5.1 Background and Advantages of the Method 296 11.5.2 Multiphase Flow and Wetting 299 11.5.3 Capturing Contact Angle Hysteresis 301 11.5.4 Rough Surfaces 305 11.5.5 Chemically Inhomogeneous Surfaces 306 11.6 Conclusion and Outlook 307 Acknowledgment 309 References 309 12 Visualization and Measurement 313 Kye Si Kwon, Lisong Yang, Graham D. Martin, Rafael Castrejón-Garcia, Alfonso A. Castrejón-Pita, and J. Rafael Castrejón-Pita 12.1 Introduction 313 12.2 Basic Imaging of Droplets and Jets 314 12.3 Strobe Illumination 317 12.4 Holographic Methods 320 12.5 Confocal Microscopy 325 12.6 Image Analysis 330 12.6.1 Binary Image Analysis Method 330 12.6.1.1 Edge Detection Method (Droplet Volume Calculation Using LabVIEW) 331 12.6.1.2 Edge Detection Method (Threshold Detection Using MATLAB) 335 References 336 13 Inkjet Fluid Characterization 339 Malcolm R. Mackley, Damien C. Vadillo, and Tri R. Tuladhar 13.1 Introduction 339 13.2 The Influence of Ink Properties on Printhead and Jetting 340 13.3 The Rheology of Inkjet Fluids 341 13.3.1 Base Viscosity 342 13.3.2 Viscoelasticity (LVE) 344 13.4 The Measurement of Linear Viscoelasticity for Inkjet Fluids 347 13.5 The Measurement of Extensional Behavior for Inkjet Fluids 351 13.6 Linking Inkjet Rheology to Printhead Performance 356 13.7 Conclusions 361 Acknowledgments 362 References 362 14 Surface Characterization 365 Ronan Daly 14.1 Introduction 365 14.1.1 Understanding Surface Characterization Requirements 366 14.2 Process Map to Define Characterization Needs 367 14.2.1 Prejetting Surface Quality 367 14.2.1.1 Example 1: Graphical Printing 367 14.2.1.2 Example 2: Printed Electronics 370 14.2.1.3 Summary 373 14.2.2 Drop Impact Behavior 373 14.2.2.1 Example 1: 3D Printing 374 14.2.2.2 Example 2: Reactive Inkjet Printing and High-Throughput Screening 375 14.2.2.3 Summary 376 14.2.3 Delivery of Function 376 14.2.3.1 Example 1: Graphical Printing 377 14.2.3.2 Example 2: Advanced Functional Materials 378 14.2.4 The Final Functionalized Surface 379 14.2.5 Long-Term Behavior 380 14.2.5.1 Example 1: Paper 380 14.2.5.2 Example 2: Protein Printing 380 14.2.5.3 Example 3: Cured Ink Adhesion 381 14.3 Surface Characterization Techniques 381 14.3.1 Chemical Analysis of Surfaces 381 14.3.1.1 Surface Tension and Wettability Studies 381 14.3.1.2 Liquid Drops on Solid Surfaces 382 14.3.1.3 Example of Contact Angle Measurement 385 14.3.1.4 Liquid Drops on Liquid Surfaces 385 14.3.1.5 Role of Surface Chemistry on Imbibition 386 14.3.2 Mechanical Testing of Surfaces 387 14.3.2.1 Atomic Force Microscopy (AFM) 388 14.3.2.2 Nanoindentation 388 14.3.3 Electrical Analysis of Surfaces 389 14.3.4 Optical Analysis 390 14.3.5 Biological Analysis 393 14.4 Conclusion 394 14.5 Questions to Consider 394 References 395 15 Applications in Inkjet Printing 397 Patrick J. Smith and Jonathan Stringer 15.1 Introduction 397 15.2 Graphics 398 15.3 Inkjet Printing for Three-Dimensional Applications 399 15.4 Inorganic Materials 404 15.4.1 Metallic Inks for Contacts and Interconnects 404 15.4.2 Ceramic Inks 405 15.4.3 Quantum Dots 406 15.5 Organic Materials 407 15.6 Biological Materials 410 15.6.1 Biomacromolecules for Analysis and Sensing 411 15.6.2 Tissue Engineering 412 References 414 16 Inkjet Technology: What Next? 419 Graham D. Martin and Mike Willis 16.1 Achievements So Far 419 16.2 The Inkjet Print-Head as a Delivery Device 420 16.3 Limitations of Inkjet Technology 421 16.3.1 Jetting Fluid Constraints 421 16.3.2 Control of Drop Volume 421 16.3.3 Variations in Drop Volume 422 16.3.4 Jet Directionality and Drop Placement Errors 423 16.3.5 Aerodynamic Effects 424 16.3.6 Impact and Surface Wetting Effects 424 16.4 Today’s Dominant Technologies and Limitations 424 16.4.1 Thermal Drop-on-Demand Inkjet 425 16.4.2 Piezoelectric Drop-on-Demand Inkjet 427 16.5 Other Current Technologies 428 16.5.1 Continuous Inkjet 428 16.5.2 Electrostatic Drop-on-Demand 429 16.5.3 Acoustic Drop Ejection 429 16.6 Emerging Technologies and Techniques 431 16.6.1 Stream 431 16.6.2 Print-Head Manufacturing Techniques 431 16.6.3 Flextensional 434 16.6.4 Tonejet 435 16.6.5 Ink Recirculation 435 16.6.6 Indirect Inkjet Printing 436 16.6.7 Wide Format Printing 438 16.6.8 Failure Detection 438 16.7 Future Trends for Print-Head Manufacturing 439 16.8 Future Requirements and Directions 440 16.8.1 Customization of Print-Heads for Nongraphics Applications 440 16.8.2 Reduce Sensitivity of Jetting to Ink Characteristics 440 16.8.3 Higher Viscosities 441 16.8.4 Higher Stability and Reliability 441 16.8.5 Drop Volume Requirements 442 16.8.6 Lower Costs 442 16.9 Summary of Status of Inkjet Technology 443 References 444 Index 445