EDGAR B. GUTOFF, SCD, is a consultant in coating and drying. He coedited Modern Coating and Drying Technology (Wiley) and coauthored The Application of Statistical Process Control to Roll Products as well as the first edition of this book. He was the first secretary of the International Society of Coating Science and Technology and served until 2002. He is a Fellow of the AIChE and of the Society for Imaging Science and Technology and an adjunct professor at Northeastern University.

EDWARD D. COHEN, PhD, is a technical consultant in all aspects of the web coating process. He recently retired from DuPont Central Research and Development as a DuPont Fellow. Dr. Cohen is coeditor of Modern Coating and Drying Technology(Wiley) and coauthor of the first edition of this book.

GERALD I. KHEBOIAN (Chapter 11 author) is a consultant on web transport systems. He has over thirty-five years' experience applying web handling systems, electrical drives, tension controls, and machine controls. He is past chairman of the national TAPPI Electrical Engineering Committee and of the TAPPI Drive Seminar Series.

Preface xv Preface to the First Edition xvii About the Authors xxi 1 Introduction 1 2 Troubleshooting or Problem-Solving Procedure 5 Basic Troubleshooting Principles 6 Detect the Defect 8 Define the Defect or Problem 9 Name the Defect 11 Problem Statement 15 Collect and Analyze Additional Data 16 Process Information 16 General Process Information 17 Analytical Data 19 Standard Operating Procedures 19 Analyze the Data and Identify Potential Causes of Problem 19 Eliminate the Problem 25 Document the Results 25 Use Results to Prevent Reoccurrence 27 References 27 3 Coater and Defect Analytical Tools 29 Overview of Analytical Tools 30 Analytical Methods to Characterize Defects 30 Defect Test Procedures 31 Video Enhanced Microscopy 31 Surface Characterization Techniques 33 Coater Characterization Instruments 38 Data Loggers 42 Rheological Measurements 44 Surface Properties 49 On-Line Characterization Systems 50 On-Line Inspection Systems 50 On-Line Coating Weight Measurement 52 On-Line Viscosity 54 Data Analysis Techniques 55 Keeping Current 56 References 61 4 Problems Associated with Feed Preparation 63 Dirt and Other Particulates 63 Filtration 64 Agglomerates 66 Bubbles 68 Poor Cross-Web Uniformity 69 In-Line Mixers 70 Temperature Control 70 Flow Control for Down-Web Uniformity 70 Feeding the Coating Liquid 70 Flow Control 72 Magnetic Flow Meters 72 Ultrasonic Meters 73 Coriolis Meters 73 References 74 5 Problems Associated with Roll Coating and Related Processes 75 Coating Methods 75 Control of Coating Weight 82 Ribbing 86 Ribbing in Forward Roll Coating 87 Ribbing and Cascade (or Herringbone or Seashore) in Reverse Roll Coating 89 Gravure Coating 92 Streaks and Bands in Roll Coating 92 Chatter in Roll Coating 94 Sagging 94 References 95 6 Problems in Slot Extrusion Slide and Curtain Coating 97 Description of Coating Methods 97 Limits of Coatability 107 The Window of Coatability 107 Slide Coating 109 Vortices and Eddies 110 Slot Coating 117 Extrusion Coating 124 Curtain Coating 126 Effect of Surface Roughness on the Limits of Coatability 128 Instabilities in Premetered Coating 131 Chatter 131 Ribbing 131 Neck-in 133 Scalloped Edges 133 Edge Beads and Heavy Edges 133 Waves in Slide and in Curtain Coating 135 Streaks and Bands in Premetered Coating 137 References 141 7 Coating Problems Associated with Coating Die Design 143 Cross-Web Uniformity 143 Temperature Control 148 Corrections to the Coating Die Internals 149 Die Internal Pressures and Spreading 150 Extrusion Dies 151 Wall Shear Stress Control and Residence Time Control 153 References 155 8 Surface Tension Driven Defects 157 Surfactants 158 Surface Tension Effects in Coating 159 Surface Tension Driven Defects 162 Convection or Bénard Cells 162 Craters 163 Fat Edges or Picture Framing 164 Nonuniform Edges in Multilayer Coatings 165 Dewetting and Crawling 166 Adhesive Failure and Delamination 167 Nonuniform Base Surface Energies 168 References 168 9 Problems Associated with Static Electricity 169 Formation of Charges 171 Electrostatic Fields 173 Surface Resistivity 174 Measurement of Static Charges 177 Removal of Charges 180 Free Charges 180 Bound Charges 182 References 183 10 Problems Associated with Drying 185 Dryer Control and Solvent Removal 189 Drying Condition Case History 195 Drying Defects 198 Air Bar Rubs 199 Blushing 199 Bubbles and Blisters 200 Cockle or Wrinkling 201 Curl 201 Mud Cracking 204 Delamination 204 Dryer Bands 205 Dryer Remelt 206 Dryer Contamination Spots 207 Dryer Condensation Spots 208 Haze 208 Mottle 208 Orange Peel and Crinkling 209 Overspray 209 Reticulation 209 Surface Blow-Around 211 Microscopic Defects 211 Starry Night 211 Pinholes 212 The Role of Dryer Simulation in Troubleshooting 212 The Role of Radiative Heating in Defect Reduction 214 References 215 11 Problems Associated with Web Handling 217by Gerald I. Kheboian Web 218 Web Characteristics and Problems Associated with the Web 219 Base Web Defects that Cause Wrinkling 219 Causes of Web Defects 221 Web Attributes 221 Web Camber 221 Web Cross-Machine Thickness Profile Variation 223 Basis Weight Profile Variation 225 Surface of the Web 225 Plastic Web 227 Web Transport Systems 228 Tension 230 Reasons Why Operators Must Change Tensions in Order to Successfully Transport Web 231 Unwind Stand 231 When to Use Drive Motors on an Unwind Stand 233 Web Control 234 Core Selection and Build-Down Ratio 235 Draw Rolls Pull Rolls Capstans 235 Web Slippage and What Slip Affects 235 Nip Rolls 236 Unnipped Rolls (Elastomer Rolls) 237 Suction Rolls 241 Suction Aprons or Tables 242 Increasing the Reliability of Draw Roll Sections 243 Tension Isolation 243 Differential Tension 244 Driving Web-Carrying Rolls Within a Dryer 245 The Rewinder 246 Use of Accumulators at the Rewind and Unwind 246 Surface/Center Rewinds 247 Center-Driven Winders 248 Drives for Laminators 248 When to Drive Both Laminator Rolls 249 Coating Roll Drives 249 Coating Defects-Sources and Some Solutions 249 Backlash Exists in Timing Belts Gearboxes and Geared Couplings 250 Chatter Caused by the Roll 251 Roll Unbalance 251 Nonconcentric Rolls 252 Coating Roll Drive Systems 252 Feedback Devices 254 Coating Supply System 254 Transmission of Vibration Through Structural Members to the Coating Stand 254 Effect of Dryer Design on Coating Quality 255 Troubleshooting ''Sudden'' Coating Problems 255 Monitoring Speeds and Tensions of Web 257 A Speed Monitoring System 257 Monitoring the Speed of Idler Rolls 257 Monitoring for Slip Conditions on High-Speed Coaters 258 Tension Monitoring Systems 258 Specifying the Tension Range 259 Why Is Tension Control Needed? 259 Effects of Wiring Practices on Tension Control 260 When Do You Use a Pure Speed Control? 261 Equipment Lists Avoid Problems and Help Plant Personnel 264 Frequency and Direction of a Speed Perturbation 265 Problems that Occur After the Machine Is in Production 266 Types of Tension Control Systems 266 Motor Current Regulation 268 Dancer Roll Control 268 Example of the Use of a Dancer in Close Proximity to an Air Roll 270 Using Air Roll Air Gap Control as a Dancer in the Dryer 270 Force Transducer Control 272 Sizing Strain Gauge Load Cells 274 Section Characteristics that Ensure Good Web Transport Control 274 Master or Lead Section 274 Using Load Cell Control in Close Proximity to an Air Roll 275 Defects that Occur When the Master Section Slips 275 Sections with Limited Ability to Control Web Transport or Tension 275 Dealing with Sections that Have Limited Ability to Control Tension 276 Sections that Always Slip or Almost Always Slip 277 Drive Features that Give the Operator Additional Tools 278 Tools that Are Used for Troubleshooting Drive Problems 278 Optical Alignment Tooling and Laser Technology 278 Machine Alignment: Avoiding Many Web Handling Problems 278 Experience: Dryers Installed with the Dryer Centerline Skewed from the Machine Centerline 279 Alignment Problems Due to Building Location in a Swamp or Tidal River 279 The Alignment Process 280 The Baseline 281 Checking the Alignment of a Size Press (Roll Coater) on a Paper Web 282 Knowing How Your Machine Operates Can Avoid Problems in the Future 283 Summary 284 References and Bibliography 284 12 The Role of Process Support Equipment 287 Introduction 287 Definitions 288 Defect Support Equipment Interactions 291 Support Equipment Effect on Defects 291 Mechanical Chatter 291 Serpentine Chatter 292 Poor Physical Uniformity 294 Ribbing 294 Bubbles 294 Contamination Spots 294 Low Overall Productivity 295 Defects Due to Static Electricity 295 Scratches 295 Streaks 296 Mottle 296 Coating Weight Nonuniformity in Premetered Applicators 297 Coating Weight Nonuniformity in Self-Metered and Doctor Coaters 297 Air Bar Rubs in a Floater Dryer 297 Dry Point Variability 298 Selection of Equipment 298 13 Coating Defects Database 299 Need for Coating Defects Database 299 Defects Database: Examples 302 Base Flake 303 Roll Repeats 303 Bubbles 303 Bacteria Bubbles 306 Aimcal Defects Lexicon: Guide to Web Coating Technology 306 Description of Lexicon 306 Need for Lexicon 306 Lexicon Overview 308 Lexicon Sections 308 Glossary 308 Troubleshooting Guide 309 Defect Image Section 310 Search Capability 310 Availability 312 References 314 14 Defect Prevention 315 Introduction 315 Define Product and Process Requirements 316 Ensure Availability of Valid Analytical Techniques 319 Ensure Web Coating Process Meets Specifications 319 Use Appropriate Coating Method 320 Develop and Implement Operational Procedures 321 Quantify and Understand Defect Losses 321 Use Structured Troubleshooting Protocol 325 Use Computer Database to Store and Share Information 325 Implement Improved Process Technology 327 Use Statistical Process Control 327 Develop Fundamental Process Understanding 328 Index 331