A practical guide for ensuring a defect-free coating and drying process

For professionals in the coating and drying industry, the world is a demanding place. New, technically complex products such as fuel cell membranes, thin film batteries, solar cells, and RFID chips require coatings of extreme precision. With the bar raised so high, understanding how to troubleshoot and eliminate defects on a coating line is an essential skill for all personnel.

Coating and Drying Defects, Second Edition provides manufacturing and quality control personnel, equipment operators and supervisors, and plant engineers and scientists with the full complement of proven tools and techniques for detecting, defining, and eliminating coating defects and operating problems, and for ensuring that they do not recur.

Updating the valuable contents of the first edition, this practical Second Edition:

• Describes all major processes for coating and drying of continuous film on sheets or webs
• Covers technologies that have been recently developed to prevent defect formation and improve operating procedures
• Provides a rational framework within which to assess and analyze virtually any defect that may arise
• Offers step-by-step guidelines for conducting every phase of the troubleshooting process, including defect prevention

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.

For professionals in the coating and drying industry, the world is a demanding place. New, technically complex products such as fuel cell membranes, thin film batteries, solar cells, and RFID chips require coatings of extreme precision. With the bar raised so high, understanding how to troubleshoot and eliminate defects on a coating line is an essential skill for all personnel.

Coating and Drying Defects, Second Edition provides manufacturing and quality control personnel, equipment operators and supervisors, and plant engineers and scientists with the full complement of proven tools and techniques for detecting, defining, and eliminating coating defects and operating problems, and for ensuring that they do not recur.

Updating the valuable contents of the first edition, this practical Second Edition:

• Describes all major processes for coating and drying of continuous film on sheets or webs
• Covers technologies that have been recently developed to prevent defect formation and improve operating procedures
• Provides a rational framework within which to assess and analyze virtually any defect that may arise
• Offers step-by-step guidelines for conducting every phase of the troubleshooting process, including defect prevention

Going beyond simply describing a disparate set of troubleshooting techniques, this unique guide arms readers with a systematic, nonmathematical methodology encompassing the entire coating operation, becoming an indispensable resource for manufacturing and quality-control personnel as well as plant engineers, polymer scientists, surface scientists, organic chemists, and coating scientists.

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

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