Radiation Curing: Science and Technology PDF
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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 1992 660'.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 1992 Originally published by Plenum Press, New York in 1992 Softcover reprint of the hardcover 1st edition 1992 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in 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 Labo ratories, Carlstadt, New Jersey 07072 Howard R. Ragin • General Printing Ink Division, Sun Chemical Corpora tion, Northlake, Illinois 60164 v 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 Corpora tion, 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 com mand relatively small shares in many of their competitive markets. This situa tion 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. vii 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 contribu tions. These important techniques are presented, comprehensively, in Chap ters 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 polymer ization 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 radia tion 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. S. Peter Pappas Polychrome Corporation Carlstadt, New Jersey 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
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