From droplet formation to final applications, this practical book presents the subject in a comprehensive and clear form, using only content derived from the latest published results.
Starting at the very beginning, the topic of fluid mechanics is explained, allowing for a suitable regime for printing inks to subsequently be selected. There then follows a discussion on different print-head types and how to form droplets, covering the behavior of droplets in flight and upon impact with the substrate, as well as the droplet's wetting and drying behavior at the substrate. Commonly observed effects, such as the coffee ring effect, are included as well as printing in the third dimension. The book concludes with a look at what the future holds. As a unique feature, worked examples both at the practical and simulation level, as well as case studies are included.
As a result, students and engineers in R&D will come to fully understand the complete process of inkjet printing.

Dr. Stephen D. Hoath works in the Inkjet Research Centre of the Department of Engineering at Cambridge University, UK. After obtaining his academic degrees from Oxford University, UK, he was a Lecturer in Physics at Birmingham University and then held various positions in the UK industry. He took up his full time research appointment at Cambridge in 2005. He is a Chartered Engineer, Scientist and Physicist; with over 50 scientific publications, he is a Fellow of the Institute of Physics, and is a Governing Body Fellow and the Director of Studies in Engineering at Wolfson College Cambridge.

List of Contributors XV

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 ofWater 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 MolecularWeight Stability of Polymers during DOD Inkjet Printing 130

5.11 MolecularWeight Stability of Polymers during CIJ Printing 132

5.12 MolecularWeight 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 DLVOTheory 144

6.3.2 van derWaals 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 onWettable Surface 201

8.2.1 Effect of Initial Speed on Drop Impact and Spreading 202

8.2.2 Effect of SurfaceWettability 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 PiTheorem 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 TWilson 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 FluidMethod 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 andWetting 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 andWettability 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 SurfaceWetting 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

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Fundamentals of Inkjet Printing The Science of Inkjet and Droplets

9783527337859

3527337857

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