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FLEXOGRAPHY:
Principles & Practices
VOLUME
4
5th Edition
CHAPTER 1
Printing
Plates
CHAPTER 2
Mounting
And
Proofing
FLEXOGRAPHY: PRINCIPLES & PRACTICES
Flexography: Principles And Practices
Foundation of Flexographic Technical Association, Inc.
900 Marconi Avenue, Ronkonkoma NY 11772
TEL 631-737-6020 FAX 631-737-6813
Find us on the World Wide Web at:
http://www.fta-ffta.org
Copyright
©
1999 by the Flexographic Technical Association, Inc.
and the Foundation of Flexographic Technical Association, Inc.
Fifth Edition
Notice of Liability:
All rights reserved. No portion of this publication may be reproduced or transmitted in
any form or by any means, electronic, mechanical, photocopying, recording, or other-
wise, without the prior written permission of the publisher.
Notice of Liability:
The information in this book is distributed on an “as is” basis, without warranty.
While every precaution has been taken in the preparation of this book, neither the authors
nor the publisher shall have any liability to any person or entity with respects to any loss,
liability or damage caused or alleged to be caused, directly or indirectly by the informa-
tion presented in this book.
Published by the
Foundation of Flexographic Technical Association, Inc.
Printed in the United States of America
VOLUME 4
PLATES
INTRODUCTION 3
PLATE CLASSES 5
Hand-engraved Rubber Plates...............................................5
Molded-rubber Plates..............................................................6
Photopolymer Plates...............................................................6
Plates for Process Printing..............................................7
Liquid and Sheet Photopolymers Compared.................7
Film Negative Requirements..................................................7
Direct-imaged Plates...............................................................8
Laser-engraved Plates.......................................................8
MOLDED-RUBBER PLATES 10
The Master Pattern................................................................10
Metal Masters ..................................................................10
Photopolymer Masters...................................................12
The Molding Press.................................................................12
Auxiliary Equipment.......................................................13
The Matrix Mold....................................................................13
Making the Thermosetting Mold or Matrix.................14
Molding a Matrix.............................................................16
Molding the Printing Plate....................................................17
Determining Molded Plate Thickness..........................18
Accurate Plate Molding..................................................19
Inspection and Finishing................................................20
Troubleshooting Rubber-molding Problems......................21
Rubber Plate Compounds and Properties..........................21
Thickness.........................................................................21
Storage..............................................................................21
Types of Molded Plates.........................................................22
Special Considerations for Process Plates..................22
PHOTOPOLYMER PLATES 24
Characteristics.......................................................................24
Durometer........................................................................24
Plate Construction..........................................................25
Special Plate Construction ............................................25
Photopolymer Plates: An Overview..............................25
Housekeeping.........................................................................26
Physical Hazard of UV Radiation..................................26
Film Negative Preparation and Handling...........................27
Table of Contents
FLEXOGRAPHY: PRINCIPLES & PRACTICES
Principles of Photopolymer Plate Exposures....................27
Back Exposure................................................................28
Back-exposure Test ........................................................28
Face or Image Exposure................................................28
Face- or Image-exposure Test.......................................29
Post-exposure or Light Finishing..................................29
Light Intensity..................................................................29
Liquid Photopolymer Platemaking......................................29
Equipment........................................................................30
The Liquid Platemaking Sequence......................................30
Casting the Plate.............................................................30
Back Exposure................................................................30
Face Exposure.................................................................31
Exposure-control Guides...............................................31
Reclaim.............................................................................31
Plate Washout..................................................................32
Post-exposure/Plate Drying...........................................32
Light Finishing.................................................................32
Special Liquid Platemaking Techniques.............................32
Prepress Makeready.......................................................32
Capping.............................................................................32
Image-positioned Plates.................................................32
Sheet Photopolymer Platemaking.......................................33
Equipment........................................................................34
Sheet Platemaking Sequence...............................................34
Material Preparation.......................................................34
Back Exposure................................................................34
Main Exposure ................................................................35
Face-test Exposures.......................................................35
Plate Processing..............................................................35
Preliminary Inspection...................................................35
Plate Drying.....................................................................35
Light Finishing and Post-exposure...............................36
Troubleshooting.....................................................................36
DIRECT-IMAGED PLATES 37
Laser-engraved Plates ...........................................................37
Laser Ablation of Liquid Photopolymers............................37
Design Rolls............................................................................37
Preparing the Roll...........................................................38
Vulcanized Rubber Selection...................................39
Compound Application ............................................39
Vulcanizing.................................................................39
Photopolymer Application.......................................39
Grinding and Polishing.............................................40
Polyurethane Covering.............................................40
Preparing Artwork for Design Rolls.............................40
Engraving the Cylinder...................................................40
Proofing and Inspection.................................................40
Special Care Consideration...........................................41
Direct-to-Plate Imaging.........................................................41
Integral Mask Technology..............................................42
Ink-jet Mask Technology................................................43
Exposure and Processing of Direct-imaged Plates....44
PLATE CONSIDERATIONS 45
Measuring Plate Thickness ..................................................45
Checking Plate Hardness......................................................46
Care and Handling of Plates ................................................47
Plate Mounting.......................................................................47
Plate Washup..........................................................................48
Plate Storage..........................................................................49
Ink and Solvent Compatibility.............................................50
Wrap Distortion .....................................................................51
Surface Tension...............................................................53
APPENDIX 55
A: Matrix-molding Problems and Corrective Actions.....55
B: Common Plate-molding Problems
and Corrective Actions...................................................57
C: Common Photopolymer Problems
and Corrective Actions...................................................59
MOUNTING AND PROOFING
INTRODUCTION 63
Development of Mounting and Proofing Equipment........63
The Purpose of Mounting and Proofing.............................64
PREPARING FOR MOUNTING AND PROOFING 66
Equipment Calibration..........................................................66
Leveling the Machine......................................................66
Impression Cylinder Concentricity...............................66
Condition of Plate Cylinders.........................................66
Plate Cylinder to Impression Cylinder Relationship..67
Condition of Gears..........................................................67
Care of Equipment ................................................................68
Understanding the Mounting Instructions.........................68
Tools Needed..........................................................................69
MOUNTING AND PROOFING A COMPLETE LINE JOB 70
Plate-mounting Procedures..................................................70
Impression Cylinder Layout
for Corrugated Postprint..............................................73
Cleaning the Plates and Cylinders................................73
Trimming and Preparing the Plate Edge......................74
Applying Stickyback.......................................................74
Zoning...............................................................................75
Framing and Priming......................................................75
Matching Plate Thickness .............................................75
Mounting the First Set of Plates..........................................76
Mounting for Corrugated Post-print ...................................77
Proofing the First Set of Plates ...........................................77
Proofing for Printability........................................................78
VOLUME 4 5
FLEXOGRAPHY: PRINCIPLES AND PRACTICES
Steps to Proofing for Profitability ................................78
Prepress Makeready..............................................................80
Lowering High Areas......................................................80
Building -up Low Areas..................................................81
Composite Proof.............................................................82
Edge Sealing ....................................................................82
Cleaning............................................................................82
Wrapping Mounted Cylinders........................................82
Additional Off-line Time Savers...........................................83
Web-edge Guide Marks...................................................83
Web-trim Mark.................................................................83
Slitter-knife Marks...........................................................83
Bag-folds, Former-guide Marks.....................................83
RECENT INTRODUCTIONS IN MOUNTING EQUIPMENT SYSTEMS 84
Computerized Mounting and Proofing System..................84
Pin-register Mounting System I ..........................................85
Operating Principles.......................................................85
System Components.......................................................85
Preparation for Pin Mounting........................................85
Procedure for Pin Mounting..........................................85
Advantages of Pin Mounting..........................................85
Pin-register Mounting System II..........................................88
System Components.......................................................88
Procedure for Punching Negatives...............................88
Procedure for Punching Printing Plates......................90
Procedure for Plate Mounting ......................................91
Advantages of the System..............................................91
Plate Mounting to Pins in the Plate Cylinder.....................91
Digital Pin Registration for Corrugated Postprint............92
Video-mounting Systems................................................93
Sleeve Mounting Systems.....................................................94
Types of Sleeves..............................................................95
Mounting Procedures.....................................................97
Sleeve Storage.................................................................97
AN OFF-LINE, NONPRODUCTION FLEXO PROOFING PRESS 98
Mounting the Proof ...............................................................98
Inking the Printing Plate.......................................................99
PLATE MOUNTING WITHOUT A
MOUNTING AND PROOFING MACHINE 101
MISCELLANEOUS PROCEDURES 103
Removing Plates from the Cylinder..................................103
Using Release Agents...................................................103
Mounting Metal-backed Plates ..........................................103
Plate Staggering.............................................................104
APPENDIX
A: Tools for Mounting and Proofing ................................105
CHAPTER 1
Flexographic Printing Plates
2 FLEXOGRAPHY: PRINCIPLES & PRACTICES
ACKNOWLEDGEMENTS
Author/Editor: Yvonne Dykes, MacDermid, Inc.
Contributors: Dan Rosen, Polyfibron Technologies, Inc.
Mark Mazur, DuPont
Harvey Schwartz, MacDermid, Inc.
John Shreve, Midwest Rubber Plate Co.
PLATES 3
T
he manufacture of flexographic
printing plates has been revolu-
tionized in recent years. In the
past, hand-cut and molded rub-
ber was the only choice for
flexo printers. These plates
were labor intensive, operator-skill-depen-
dent, imprecise and time consuming to man-
ufacture. Mounting was also imperfect.
Often, plates had to be repositioned on the
press because of inaccuracies in the mount-
ing devices or methods. With rubber plates,
this could be a problem because they were
not dimensionally stable and could stretch
unevenly if pulled off a mount.
Today, technology has been adopted from
the offset and gravure industries. Images are
stepped and repeated multiple times on one
plate. These plates may be positioned me-
chanically onto a printing cylinder by a vari-
ety of techniques: pins, micro dot and
microvideo registration systems. Plate
mounting now takes minutes, not hours, pro-
duces accurately mounted plates and elimi-
nates the need for special skills.
With the advent of dimensionally stable
rubber compounds and polyester-backed
photopolymer, images on the printing plate
are now of predictable size with no distor-
tion across the cylinder. These plates last
longer and can be registered accurately.
They are also more environmentally safe to
manufacture, and can be made in larger
sizes with multiple images on one plate.
Chemical changes in ink formulation have
resulted in photopolymer printing plates
gaining wide popularity, becoming the stan-
dard quality plate of choice.
Rubber plates are still used in some mar-
ket segments of flexo, but their stronghold
on the industry has been relinquished to
photopolymer. Many printers have typically
chosen rubber because of its ink-transfer
characteristics. With new photopolymer
technologies that emulate these properties,
this point is moot.
Large-format platemaking systems have
also become popular. One-piece photopoly-
mer plates are now being manufactured in
sizes up to 52" x 110". Images that are
stepped and repeated multiple times on one
plate are larger than ever before. This step-
ping of multiple images, combined with the
need for large, one-piece, corrugated plates
and pin register, has led to rapid acceptance
of these large-format platemaking systems.
Large platemaking systems are computer-
controlled, ensuring predictable and consis-
tent plate quality.
Halftone process-printing plates are made
from electronically imaged films, computer-
compensated for dot gain and other printing
characteristics. These films are output for
each individual press, based on press char-
acterization data. In an effort to further
enhance quality, modern suppliers produce
all their printing plates using statistical
process control.
Artwork for the manufacture of flexogra-
phic printing plates is also computer-gener-
ated, with all copyart and masks output to
exact specifications, including print-length
distortion. Artwork is designed by using
electronic design software that is accurate,
quick and capable. Logos, bar codes, register
marks, tone reproduction targets and other
frequently used items can be stored elec-
tronically and called up for any job required.
Introduction
4 FLEXOGRAPHY: PRINCIPLES & PRACTICES
There are not many general manufacturing
areas that have seen as many changes in the
past few years as the techniques for making
quality-controlled flexographic printing
plates. This chapter will cover these new
techniques, as well as the traditional ones,
used for the manufacture of the many types
of flexographic plates.