Coating and Drying Defects: Troubleshooting Operating Problems, 2nd Edition
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
Preface to the First Edition.
About the Authors.
2. Troubleshooting or Problem Solving Procedure.
Basic Troubleshooting Principles.
Detect The Defect.
Define the Defect Or Problem.
Name the Defect.
Collect and Analyze Additional Data.
General Process Information.
Standard Operating Procedures.
Analyze the Data and Identify Potential Causes of Problem.
Eliminate the Problem.
Document the Results.
Use Results to Prevent Reoccurrence.
3. Coater and Defect Analytical Tools.
Overview of Analytical Tools.
Analytical Methods to Characterize Defects.
Defect Test Procedures.
Video Enhanced Microscopy.
Surface Characterization Techniques.
Coater Characterization Instruments.
The Coater Characterization Instruments.
On-Line Characterization Systems.
On‑Line Inspection Systems.
On-Line Coating Weight Measurement.
Data Analysis Techniques.
4. Problems Associated with Feed Preparation.
Dirt and Other Particulates.
Poor Cross-Web Uniformity.
Flow control for Down-Web Uniformity.
Feeding the Coating Liquid.
5. Problems Associated with Roll Coating and Related Processes.
Control of Coating Weight.
Ribbing in Forward Roll Coating.
Ribbing and Cascade (or Herringbone or Seashore) in Reverse Roll Coating.
Cascade, or Herringbone, or Seashore .
Streaks and Bands in Roll Coating.
Chatter in Roll Coating.
6. Problems in Slot, Extrusion, Slide, and Curtain Coating.
Description of Coating Method.
Limits of Coatability.
The Window of Coatability.
Vortices and Eddies.
Effect of Surface Roughness on the Limits of Coatability.
Instabilities in Pre-metered Coating.
Edge Beads and Heavy Edges.
Waves in Slide and in Curtain Coating.
Streaks and Bands in Pre-metered Coating.
7. Coating Problems Associated with Coating Die Design.
Corrections to Coating Die Internals.
Die Internal Pressures and Spreading.
Wall Shear Stress Control and Residence Time Control.
8. Surface-Tension-Driven Defects.
Surface Tension Effects in Coating.
9. Problems Associated with Static Electricity.
Formation of Charges.
Measurement of Static Charges.
Removal of Charges.
10. Problems Associated with Drying.
Dryer Control and Solvent Removal.
Dryer Condition Case History.
Air Bar Rubs.
Bubbles and Blisters.
Cockle or Wrinkling.
Dryer Contamination Spots.
Orange Peel and Crinkling.
The Role of Dryer Simulation in Troubleshooting.
The Role of Radiative Heating in Defect Reduction.
11. Problems Associated With Web Handling (Gerald I. Khebioan).
Web characteristics and Problems Associated with the Web.
Base web defects that cause wrinkling .
Causes of web defects.
Web cross-machine thickness profile variation.
Basis weight profile variation.
Surface of the web.
Web Transport Systems.
Reasons why operators must change tensions in order to successfully transport web.
When to use drive motors on an unwind stand.
Core Selection and Build-Down Ratios.
Draw Rolls, Pull Rolls, Capstans.
Web slippage and what slip affects.
Un-nipped rolls (elastomer rolls).
Suction aprons or tables.
Increasing the Reliability of Draw Roll Sections.
Driving Web-Carrying Rolls Within a Dryer.
Drives for Laminators.
When to drive both laminator rolls.
Coating Roll Drives.
Coating Defects - Sources and Some Solutions.
Backlash exists in timing belts, gearboxes, and geared couplings.
Chatter caused by the roll.
Non-concentric rolls .
Coating Roll Drive Systems.
Coating supply system.
Transmission of vibration through structural members to the coating stand.
Effects of Dryer Design on Coating Quality.
Troubleshooting ?Sudden? Coating Problems.
Monitoring Speeds and Tensions of Webs.
A speed monitoring system.
Monitoring the speed of idler rolls.
Monitoring for slip conditions on high speed coaters.
Tension monitoring systems.
Specifying the tension range.
Why is tension control needed.
Effects of wiring practices on tension control.
When do you use a pure speed control.
Equipment Lists Avoid Problems and Help Plant Personnel.
Frequency and Direction of a Speed Perturbation.
Problems that Occur After the Machine is in Production.
Types of Tension Control Systems.
Motor Current Regulation.
Dancer Roll Control.
Force Transducer Control.
Section Characteristics that Ensure Good Web Transport Control.
Master or Lead Section.
Sections with Limited Ability to Control Web Transport or Tension.
Drive Features that Give the Operator Additional Tools.
Tools that are Used for Troubleshooting Drive Problems.
Optical Alignment Tooling and Laser Technology.
12. The Role of Process Support Equipment.
Defect Support Equipment Interactions.
Support Equipment Effect on Defects.
Poor Physical Uniformity.
Low Overall Productivity.
Defects Due to Static Electricity.
Coating Weight Non-uniformity In Pre-metered Applicators.
Coating Weight Non-uniformity in Self Metered and Doctor Coaters.
Air Bar Rubs In A Floater Dryer.
Dry Point Variability.
Selection of Equipment.
13. Coating Defects Databases.
Need For Coating Defects Database.
Defects Database: Examples.
Aimcal Defects Lexicon: Guide to Web Coating Technology.
Description of Lexicon.
Defect Image Section.
14. Defect Prevention.
Define Product And Process Requirements.
Insure Availability Of Valid Analytical Techniques.
Insure Web Coating Process Meets Specifications.
Insure Web Coating Process Meets Specifications.
Develop And Implement Operational Procedures.
Quantify And Understand Defect Losses .
Use Structured Troubleshooting Protocol .
Computer Database To Store & Share Information.
Implement Improved Process Technology.
Use Statistical Process Control.
Develop Fundamental Process Understanding.
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.