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Radiation Curing Science and Technology
TOPICS IN APPLIED CHEMISTRY Series Editors: Alan R. Katritzky, FRS
Kenan Professor of Chemistry University of Florida, Gainesville, Florida
Gebran J. Sabongi Laboratory Manager, Encapsulation Technology Center 3M, St. Paul, Minnesota
BIOCATALYSTS FOR INDUSTRY Edited by Jonathan S. Dordick
CHEMICAL TRIGGERING Reactions of Potential Utility in Industrial Processes Gebran J. Sabongi
THE CHEMISTRY AND APPLICATION OF DYES Edited by David R. Waring and Geoffrey Hallas
HIGH-TECHNOLOGY APPLICATIONS OF ORGANIC COLORANTS Peter Gregory
INFRARED ABSORBING DYES Edited by Masaru Matsuoka
RADIATION CURING Science and Technology Edited by S. Peter Pappas
STRUCTURAL ADHESIVES Edited by S. R. Hartshorn
TARGET SITES FOR HERBICIDE ACTION Edited by Ralph C. Kirkwood
A Continuation Order Plan is available for this series. A continuation order will bring delivery of each new volume immediately upon publication. Volumes are billed only upon actual shipment. For further information please contact the publisher.
Radiation Curing Science and Technology
Edited by
S. Peter Pappas Polychrome Corporation Corporate Research Laboratories Carlstadt, New Jersey
Springer Science+Business Media, LLC
Library of Congress Cataloging-in-Publication Data
Radiation curing : science and technology / S. Peter Pappas.p. cm. — (Topics in applied chemistry)
Includes bibliographical references and index.
1. Radiation curing. I. Pappas, S. Peter (Socrates Peter), 1936-II. Series.
TP156.C8R344 1992660'.age—dc20 92-9589
CIP
ISBN 978-1-4899-0714-1 ISBN 978-1-4899-0712-7 (eBook)DOI 10.1007/978-1-4899-0712-7
© Springer Science+Business Media New York 1992Originally published by Plenum Press, New York in 1992Softcover reprint of the hardcover 1st edition 1992
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmittedin any form or by any means, electronic, mechanical, photocopying, microfilming,recording, or otherwise, without written permission from the Publisher
Contributors
Anthony J. Bean • Sun Chemical Corporation, Carlstadt, New Jersey 07072
Christian Decker • Laboratoire de Photochimie Generale (CNRS), Ecole Nationale Superieure de Chimie, 68200 Mulhouse, France
Charles E. Hoyle • Department of Polymer Science, University of Southern Mississippi, Hattiesburg, Mississippi 39406-0076
Anthony F. Jacobine • Chemical and Materials Science Group, Loctite Corporation, Newington, Connecticut 06111
Charles Kutal • Department of Chemistry, University of Georgia, Athens, Georgia 30602
Stephen C. Lapin • Research and Technology, Allied Signal, Inc., Des Plaines, Illinois 60017-5016; present address: New Ventures Group, DSM Desotech, Inc., Elgin, Illinois 60120
Bruce M. Monroe • Du Pont Electronics, E. I. du Pont de Nemours and Company, Inc., Wilmington, Delaware 19880-0021
Steven T. Nakos • Chemical and Materials Science Group, Loctite Corporation, Newington, Connecticut 06111
S. Peter Pappas • Polychrome Corporation, Corporate Research Laboratories, Carlstadt, New Jersey 07072
Howard R. Ragin • General Printing Ink Division, Sun Chemical Corporation, Northlake, Illinois 60164
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vi CODtrilluton
John G. Woods • Research and Development Department, Loctite (Ireland) Ltd., Tallaght, Dublin 24, Ireland; present address: Chemical and Materials Science Group, Loctite Corporation, Newington, Connecticut 06111
D. Billy Yang • Chemical and Materials Science Group, Loctite Corporation, Newington, Connecticut 06111
Preface
The science and technology of radiation curing have progressed substantially within the last 20 years. In a recent marketing report (Skeist, Radiation Curing III, 1991), the volume of radiation-curable coatings, inks, and adhesives in the United States was estimated at 50 million pounds, with a value of $275 million. The annual volume growth was estimated at 9 %, which is well above the average for these markets as a whole. In Western Europe, the current volume is estimated at 46 million pounds, which is expected to double by 1995. Nevertheless, radiation-curable compositions typically command relatively small shares in many of their competitive markets. This situation signifies that potential advantages of radiation curing are not generally perceived to overcome their limitations.
An important objective of this book is to address this issue, within the scope of the subjects offered, by providing the present state of knowledge and by identifying the directions and challenges for future studies. Within this context we have also attempted to achieve a balance of science and technology and to integrate the fundamental and practical aspects as opposed to the more common (and more readily accomplished) practice of treating them independently. An important criterion in the selection of subjects was to complement earlier volumes in the field. This objective is reflected in the high proportion of chapters that constitute the first comprehensive accounts of their subject.
The first chapter introduces radiation curing and attempts to highlight the important aspects from the standpoint of a personal perspective. Although organic photoinitiators, discussed in Chapter 1, currently dominate the field of UV curing, inorganic and organometallic photoinitiators are becoming increasingly important. Therefore, it is timely that Chapter 2 offers the first systematic presentation of these versatile photoinitiators, as well as a tutorial on their photochemistry.
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Preface
Advances in photocuring have resulted in large measure from the development of analytical techniques, of which photocalorimetry and, more recently, real-time infrared spectroscopy (RTIR) have made major contributions. These important techniques are presented, comprehensively, in Chapters 3 and 4, respectively. A general conclusion that emerges is the danger of relying on anyone technique for analysis of photocurable compositions, a caution that applies broadly to complicated systems.
Recent advances in resin technology are offered in Chapters 5 and 6, which constitute the first comprehensive accounts of (meth)acrylated silicones and vinyl ethers, respectively. Discussion of UV-curable (meth)acrylated silicones includes the uniquely broad range of film properties attainable as well as compositions with auxiliary dark cure processes to overcome some of the inherent limitations of UV cure alone. The striking versatility of vinyl ether-functional resins is exemplified by their capability of undergoing both UV - and EB-induced cationic polymerization, free radical copolymerization with maleate/fumarate resins, and concurrent free radical-cationic polymerization with acrylated resins.
Radiation-curable coatings, printing inks, and adhesives are discussed in Chapters 7-9, respectively. Compositions and formulation strategies are provided throughout these chapters. Dual UV -curable adhesives with auxiliary dark cure processes, including thermal, moisture, aerobic, and anaerobic cure, are also considered in Chapter 9, which is unsurpassed in the scope and depth of its coverage.
Chapter 10 offers a timely exposure to photopolymer imaging systems. As the chapter title signifies, these imaging systems fall within the scope of radiation curing. Yet there are unique aspects of polymer imaging that set this field apart from curing per se and that offer the potential for inspiring new insights that often arise from one's delving within the borders of a related discipline.
As is often the case with complex systems wherein science does not keep pace with technology and practical know-how, there is "general wisdom" that frequently traces back to someone's speculation. When properly identified, such speculation can accelerate the process of transforming today's challenges into tomorrow's technology by stimulating experimental verification. With this intent, we have not avoided the interjection of speculation throughout this volume. Indeed, a measure of its worth may be the rapidity with which this transformation occurs, a kind of built-in obsolescence.
While proud of the accomplishment that this volume represents, we recognize that many aspects of radiation curing are not treated adequately herein and, therefore, welcome comments and criticisms as well as suggestions of topics for subsequent volumes in this field.
Polychrome Corporation Carlstadt, New Jersey
S. Peter Pappas
Contents
1. Radiation Curing-A Personal Perspective
S. Peter Pappas
1.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2. Characteristic Features of Radiation Curing ..................... 2
1.2.1. Free Radical Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2.2. Cationic Polymerization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. UV Curing-Photoinitiated Polymerization ..................... 5 1.3.1. Interrelationships of Photoinitiator Concentration,
Film Thickness, and Light Intensity . . . . . . . . . . . . . . . . . . . . . . . 6 1.3.2. Air Inhibition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.3.3. Organic Photoinitiators for Free Radical Polymerization . . . .. 11 1.3.4. Organic Photoinitiators for Cationic Polymerization ........ 12
1.4. EB Curing-General Principles ............................ ,. .. 16 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18
2. Inorganic and Organometallic Photoinitiators
D. Billy Yang and Charles Kutal
2.1. Introduction................................................ 21 2.1.1. Structural and Bonding Features of Coordination Complexes 22 2.1.2. Some Important Terminology.. . . .... . .. . . .. . . . .. . .. . . . .. 24
2.2. Excited States of Transition Metal Complexes ................... 25 2.2.1. Ligand Field Excited States . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 26
ix
x Contents
2.2.2. Charge Transfer Excited States ........................... 27 2.2.3. Metal-Metal Bonded Excited States ...................... 27
2.3. Survey of Inorganic and Organometallic Photoinitiators . . . . . . . . . .. 28 2.3.1. Carbonyl Complexes.. . . . .. . . .. . . . .. . .. . . . . . . . . .. . .. . . .. 28 2.3.2. Alkyl and Aryl Complexes .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 34 2.3.3. p-Diketonate, Alkoxide, and Oxalate Complexes. . .. . .. . . . .. 38 2.3.4. Halide Complexes ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 40 2.3.5. Cyclopentadienyl Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 42 2.3.6. Solvated Ions and Ion Pairs ............................. 44 2.3.7. Am(m)ine Complexes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 46 2.3.8. Miscellaneous Photoinitiator Systems ..................... 48
2.4. Concluding Remarks. .. . . . . .. . . .. . . . .. . . . .. . .. . . . . . . . . .. . . . .. 51 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 52
3. Calorimetric Analysis of Photopolymerization
Charles E. Hoyle
3.1. Introduction................................................ 57 3.2. Heat Evolution in Polymerization Processes . . . . . . . . . . . . . . . . . . . .. 58 3.3. Basic Instrumentation for Photocalorimetry ..................... 61
3.3.1. Light Delivery System .................................. 62 3.3.2. Calorimeter ........................................... 63 3.3.3. Recording System ...................................... 68
3.4. Sample Preparation and Analysis .............................. 69 3.5. Basic Features of Exotherm Curves ............................ 70 3.6. Exotherm Literature Review .................................. 74
3.6.1. Photoinitiator Type and Concentration. . . .. . . .. . . .. . . . ... 74 3.6.2. Inhibitors ............................................ 82 3.6.3. Monomer Structural Effects. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 83 3.6.4. Kinetics and Temperature .............................. 88 3.6.5. Photocalorimetry of Cationic Polymerization. . . . . . . . . . . . .. 104 3.6.6. Thermal/Mechanical Properties of Photocured Films ....... 109 3.6.7. Monomer Mixtures .................................... 114 3.6.8. Oxygen Inhibition ..................................... 115 3.6.9. Liquid-Crystalline Monomers ........................... 123
3.6.10. Other Monomer Systems ............................... 125 3.6.11. Laser-Initiated Polymerization .......................... 126
3.7. Summary ................................................... 129 References ...................................................... 130
Contents xi
4. Kinetic Analysis and Performance of UV -Curable Coatings
Christian Decker
4.1. Introduction ................................................ 135 4.2. Analysis ofthe Cure Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 136
4.2.1. Basic Principles ........................................ 136 4.2.2. Kinetic Analysis by Discrete Measurements ................ 139 4.2.3. Real-Time Analysis ..................................... 145 4.2.4. Real-Time Infrared Spectroscopy ......................... 151
4.3. Performance of UV-Cured Coatings ............................ 162 4.3.1. Characteristics of UV-Cured Polymers .................... 162 4.3.2. Properties of UV-Cured Polymers ........................ 168
4.4. Conclusions ................................................ 174 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 175
5. Photopolymerizable Silicone Monomers, Oligomers, and Resins
Anthony F. Jacobine and Steven T. Nakos
5.1. Introduction ............................................. _ ... 181 5.2. General Background ......................................... 182 5.3. General Silicone Terminology and Chemistry .................... 183 5.4. Nonphotoinitiated Siloxane Cure Chemistry . . . . . . . . . . . . . . . . . . . .. 187
5.4.1. Moisture-Curable Siloxanes .............................. 187 5.4.2. Peroxide-Initiated Vinylsiloxane Polymerization ............ 188 5.4.3. Platinum-Catalyzed Silane Addition Curing ................ 189 5.4.4. Electron Beam-Cured Silicones . . . . . . . . . . . . . . . . . . . . . . . . . .. 191
5.5. Fillers, Treatments, and Formulation Considerations ............. 192 5.5.1. Fillers and Treatments .................................. 192 5.5.2. Effects of Fillers on Elastomer Properties .................. 194
5.6. Photocurable Siloxane Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 195 5.6.1. Polymerization Additives ................................ 195 5.6.2. Photoinitiated Cationic Polymerization. . . . . . . . . . . . . . . . . . .. 197 5.6.3. Thiol-Ene Silicones ..................................... 198 5.6.4. Acrylated Silicones ..................................... 200 5.6.5. Preparations .......................................... 200 5.6.6. Silicones with Multiple Cure Mechanisms .................. 214
5.7. Applications of Photocured Silicones ........................... 220 5.7.1. Ophthalmic Devices .................................... 220 5.7.2. Medical Applications ................................... 224 5.7.3. Gasketing and Sealing .................................. 224 5.7.4. Optical Fiber Coatings .................................. 225
xii Contents
5.7.5. Electronic Circuit Encapsulation ......................... 227 5.7.6. Coatings: General Applications. '" ....................... 228 5.7.7. Gas or Fluid Separation Membranes ...................... 230 5.7.8. Release Applications ........ " .......................... 232 5.7.9. Pressure-Sensitive Adhesives ............................. 234
5.8. Authors Note ............................................... 234 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 235
6. Radiation-Induced Cationic Curing of Vinyl Ethers
Stephen C. Lapin
6.1. Background ................................................ 241 6.2. Preparation of Vinyl Ethers ................................... 243
6.2.1. Acetylene Chemistry .................................... 243 6.2.2. Nonacetylene Routes to Vinyl Ethers ....... '" ............ 245
6.3. Vinyl Ether-Functional Monomers and Oligomers ................ 246 6.3.1. Vinyl Ether-Terminated Esters ........................... 246 6.3.2. Vinyl Ether-Terminated Urethanes ........................ 248 6.3.3. Vinyl Ether-Terminated Ethers . . . . . . . . . . . . . . . . . . . . . . . . . .. 249 6.3.4. Vinyl Ether-Functional Siloxanes ......................... 250
6.4. Radiation-Induced Cationic Polymerization of Vinyl Ethers ........ 250 6.4.1. UV-Induced Polymerization ............................. 252 6.4.2. Electron Beam-Induced Polymerization. . . . . . . . . . . . . . . . . . .. 253 6.4.3. Vinyl Ether Reactivity .................................. 254
6.5. Coating Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 262 6.5.1. Vinyl Ether-Based Systems .............................. 262 6.5.2. Hybrid Coating Systems ................................ 265 6.5.3. Related Systems ........................................ 268
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 270
7. Radiation-Curable Coatings with Emphasis on the Graphic Arts
Howard R. Ragin
7.1. General Overview ........................................... 273 7.2. Radiation-Cured Coatings in Graphic Arts ...................... 276
7.2.1. Examination of Industry Demands and Requirements ....... 276 7.2.2. Which Energy Source: UV or EB? ..... ~ .................. 279 7.2.3. Processing ............................................ 282 7.2.4. Application/Deposition Methods ......................... 285
Contents xiii
7.2.5. Formulating Strategies .................................. 292 7.2.6. Curing Equipment ..................................... 297
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 299
8. Radiation Curing of Printing Inks
Anthony J. Bean
8.1. Introduction ............................................... 301 8.2. Radiation Curing Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 302 8.3. Printing Processes .......................................... 304
8.3.1. Letterpress ........................................... 304 8.3.2. Offset Lithography .................................... 306 8.3.3. Gravure ............................................. 306 8.3.4. Silk Screen ........................................... 307 8.3.5. Flexography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 307 8.3.6. Letterset ............................................. 307 8.3.7. Miscellaneous ........................................ 308
8.4. UV and EB Considerations .................................. 308 8.5. UV Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 308 8.6. Ink Chemistry ............................................. 314 8.7. Photoinitiators ............................................. 320 8.8. Formulating UV Inks ....................................... 322
8.8.1. Letterpress ........................................... 323 8.8.2. Lithography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 324 8.8.3. Flexography and Gravure .............................. 325 8.8.4. Screen .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 326 8.8.5. Metal Decorating ..................................... 327
8.9. Formulating EB Inks ....................................... 327 8.10. Manufacturing ............................................. 328 8.11. Safety ..................................................... 330 References ...................................................... 332
9. Radiation-Curable Adhesives
John G. Woods
9.1. Introduction ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 333 9.2. Evaluation and Performance of Radiation-Curable Adhesives ...... 335
9.2.1. Adhesion and Adhesive Strength .......................... 335 9.2.2. Radiation-Curable Structural Adhesives ................... 336
xiv Contents
9.2.3. Pressure-Sensitive and Hot-Melt Adhesives ................ 362 9.2.4. Photocurable Dental Composites and Sealants ............. 367
9.3. Composition and Chemistry .................................. 369 9.3.1. Functional Oligomer Structure and Chemistry .............. 369 9.3.2. Radiation-Curable Adhesives with Auxiliary Cure Systems ... 380
9.4. Equipment for Radiation-Curable Adhesives ..................... 388 9.4.1. Radiation Sources ...................................... 388 9.4.2. Application and Dispensing Equipment. . . . . . . . . . . . . . . . . . .. 389
9.5. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 390 References ...................................................... 391
10. Photopolymers: Radiation-Curable Imaging Systems
Bruce M. Monroe
10.1. Introduction ............................................... 399 10.1.1. Polymer Imaging Systems ............................. 399 10.1.2. Scope of the Chapter ................................. 400
10.2. Components of Photopolymerizable Compositions .............. 401 to.2.1. Photo initiator Systems ................................ 401 10.2.2. Monomers .......................................... 414 10.2.3. Binders ............................................. 416 10.2.4. Other Ingredients .................................... 417
10.3. Photopolymer Technology ................................... 423 10.3.1. Composition ........................................ 423 10.3.2. Manufacture ........................................ 423 10.3.3. Microstructure ....................................... 424 10.3.4. Exposure ........................................... 425 10.3.5. Photographic Properties .............................. 425
10.4. Applications ............................................... 426 10.4.1. Physical Property Changes ............................ 426 10.4.2. Solubility ........................................... 427 10.4.3. Tackiness ........................................... 429 10.4.4. Adhesion and Cohesion ............................... 429 10.4.5. Electrical Conductivity ................................ 430 10.4.6. Refractive Index ..................................... 431
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 434
Index .......................................................... 441
