Surface Application of Paper Chemicals VISIT OUR FINE CHEMISTRY SITE ON THE WEB http://www.finechemistry.com e-mail orders: [email protected] Surface Application of Paper Chemicals Edited by JAMES BRANDER Head of Exploratory Research Arjo-Wiggins Limited Beaconsfield Buckinghamshire, UK and IAN THORN European Business Development Manager Eka Chemicals Weston-super-Mare Somerset, UK BLACKIE ACADEMIC & PROFESSIONAL An Imprint of Chapman & Hall London· Weinheim . New York· Tokyo· Melbourne· Madras Published by Blackie Academic and Professional, an imprint of Chapman & Hall, 2-6 Boundary Row, London SEt 8HN Chapman & Hall, 2--6 Boundary Row, London SE1 8HN, UK Chapman & Hall GmbH, Pappelallee 3, 69469 Weinheim, Germany Chapman & Hall USA, 115 Fifth Avenue, New York NY 10003, USA Chapman & Hall Japan, ITP-Japan, Kyowa Building, 3F, 2-2-1 Hirakawacho, Chiyoda-ku, Tokyo 102, Japan DA Book (Aust.) Pty Ltd, 648 Whitehorse Road, Mitcham 3132, Victoria, Australia Chapman & Hall India, R. Seshadri, 32 Second Main Road, CIT East, Madras 600 035, India First edition 1997 © 1997 Chapman & Hall Softcover reprint of the hardcover 1st edition 1997 Typeset in 1OI12pt Times by Cambrian Typesetters, Frimley, Surrey ISBN-13: 978-94-010-7151-2 e-ISBN-13: 978-94-009-1457-5 DOl: 10.1007/978-94-009-1457-5 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library Library of Congress Catalog Card Number: 97-73236 ~ Printed on permanent acid-free text paper, manufactured in accordance with ANSIINISO Z39.48-1992 (Permanence of Paper). For our families Contents List of contributors xv Preface xvii Introduction 1 J. BRANDER and I. THORN Background 1 Technology of on-machine application 2 Chemicals for surface application 4 Paper products and surface treatment 6 IOn-machine surface treatment of paper and board with the blade coater 9 K. STRANGER 1.1 The origins of on-machine surface treatment 9 1.2 The blade-coating system today 9 1.3 Advantages and disadvantages of on-machine surface treatment 12 1.4 Paper and board grades utilizing on-machine surface treatment 13 1.5 Designing the surface treatment line 14 1.5.1 Webrun 14 1.5.2 Web-threading 15 1.6 Examples 15 1.6.1 Folding boxboard 16 1.6.2 Graphic board 16 1.6.3 Low-coat-weight papers 17 1.6.4 On-machine coated wood-free papers 18 1.6.5 Speciality papers 18 1.6.6 Conclusions 20 2 On-machine surface treatment of paper and board with the film press 21 R. RANTANEN 2.1 Introduction 21 2.1.1 Review of surface sizing equipment up to the 1980s 21 2.1.2 Metered size press technology 22 2.2 Quality and runnability aspects of different surface sizing processes 23 2.2.1 Two-roll size press 23 2.2.2 Gate-roll size press/coater 23 2.2.3 Blade surface sizing 24 2.3 New generation film presses 24 2.4 Coat-weight development and metering-element-related phenomena 25 viii CONTENTS 2.4.1 Grooved-rod metering 25 2.4.2 Smooth-rod metering 28 2.4.3 Large-diameter grooved-rod metering 30 2.4.4 Blade metering 31 2.5 Film transfer at film-press nip 31 2.5.1 Surface sizing 31 2.5.2 Coating 33 2.6 Precalendering 39 2.7 Control of paper quality 39 2.8 Nip mechanics and roll covers 40 2.9 Quality differences between film-press and blade coated sheets 42 2.10 The SymSizer film press 42 2.10.1 Process designs 42 2.10.2 Applications and production experiences 44 References 46 3 Synthetic latex binders for paper manufacture 48 G. BACQUET and I.-c. ISOARD 3.1 Introduction 48 3.2 From molecule to particle: latex synthesis 49 3.2.1 Radical emulsion polymerization 49 3.2.2 The monomers 51 3.2.3 Finishing and final characteristics 52 3.3 From particles to dispersion: latex stability 52 3.3.1 The importance of controlling stability 52 3.3.2 Stability control 54 3.4 The viscosity of latices and coating colors: the novel contribution of the particle state 55 3.4.1 Novelty of emulsion polymerlatices 55 3.4.2 The impact of the particle state and the chemistry of the latex on its viscosity 56 3.5 From particle to film: latex coalescence 58 3.5.1 Howtoobtainahomogeneousfilm 58 3.5.2 Wetting latex particles on pigments 60 3.5.3 Preventing film formation 61 3.6 From latex to coated paper: the role of polymers in a paper coating 62 3.6.1 Binding power 62 3.6.2 The latex polymer: an elastic material 63 3.6.3 Polymer chemistry as a modifier of paper surface energy 65 3.6.4 Porosity and ink setting in coated papers 66 3.7 Conclusions 67 References 68 4 Starches 69 N.-O. BERGH 4.1 Introduction 69 4.2 Principles of starch technology 69 4.2.1 Chemical principles 69 4.2.2 Physical properties of starch 72 4.3 Starch modification 76 4.3.1 Physical modification 76 4.3.2 Chemical modification 76 4.4 Surface application methods 82 CONTENTS IX 4.4.1 Size press 82 4.4.2 Apron size press 84 4.4.3 Foam-coat size press 84 4.4.4 Gate-roll coater 84 4.4.5 Metered size press 85 4.4.6 TWIN-HSM 86 4.4.7 Liquid application system 88 4.5 Starch properties required for size-press application 89 4.5.1 Influence of viscosity 90 4.5.2 Influence of solids content 93 4.5.3 Penetration 94 4.5.4 Influence of papermachine parameters 96 4.6 Starch properties required for metered size-press application 96 4.7 Starch properties required for blade application and as a coating colour binder 99 4.7.1 Blade application of starch solutions 99 4.7.2 Starch as a coating binder 102 4.8 Starch properties required when applied by liquid application system 105 4.9 Size-press starch application to waste-based packaging paper 105 4.9.1 One-sided size-press operation 106 5 Rheology modifiers and pigment dispersants 109 LB. CLARKE 5.1 Introduction 109 5.2 General principles of viscosity and rheology 109 5.3 Flow types encountered in paper surface treatment 111 5.3.1 Newtonianflow 111 5.3.2 Pseudoplasticflow 112 5.3.3 Dilatantflow 112 5.3.4 Thixotropicflow 113 5.3.5 Plastic flow 113 5.4 Variation of shear stress during surface application 114 5.5 Waterretention 115 5.6 Types of rheology modifier 116 5.6.1 Natural products 116 5.6.2 Synthetic polymers 117 5.6.3 Hydrophobic modification of synthetic polymers 119 5.7 Pigment dispersants 120 5.7.1 What is dispersion? 120 5.7.2 Electrostatic repulsion theory 122 5.7.3 Chemical types used as dispersants 122 5.7.4 Molecular weight effects 124 5.8 Interactions 126 5.8.1 Effect of pigment particle size distribution 127 5.8.2 Effect of multivalent cations 127 5.8.3 Effect oflatex formulation 127 References 128 6 Pigments for on-line surface treatment 129 I. ATIRUP and S. HANSEN 6.1 Introduction 129 6.2 The pigments 130 6.3 Application 132 6.3.1 Pigment choice 133 x CONTENTS 6.4 General paper improvement 133 6.4.1 De-inked-pulp-based paper 135 6.4.2 Porosity 135 6.5 Conclusions 137 References 137 7 Surface sizing 138 J. ANDERSON 7.1 Definition and overview 138 7.2 Chemicals applied at the surface 139 7.2.1 Types of chemicals 139 7.2.2 Wet-end sizes applied at the surface 140 7.2.3 Synthetic polymeric surface sizes 141 7.2.4 Miscellaneous specialities 142 7.3 Function of the products 143 7.3.1 Solution polymers 143 7.3.2 Acrylic emulsion polymers 144 7.3.3 Polyurethane microdispersions 144 7.4 End-use properties 145 7.4.1 Typical end-use properties 145 7.4.2 Plain fine paper 146 7.4.3 Coated paper and specialities 150 7.4.4 Recycled grades 150 7.5 Interactions and possible problems 151 7.5.1 Chemical compatibility at the size press 151 7.5.2 Foam 152 7.5.3 Contamination in closed systems 152 7.5.4 Size-press pick-up 153 7.5.5 Fixation and distribution of the size 153 7.5.6 Influence of post-treatment 153 7.5.7 Balancedsizing 154 References 155 8 Surface brightening of paper 156 H. WEAVER 8.1 Introduction 156 8.2 Spectra of different iIIuminants 156 8.3 The quantification of the effectiveness of fluorescent brightening agents 158 8.3.1 Quantum efficiency 158 8.3.2 Shade build curves 158 8.4 The chemical nature of fluorescent brightening agents 158 8.4.1 Disulpho brighteners 160 8.4.2 Tetrasulpho brighteners 161 8.4.3 Hexasulpho brighteners 162 8.4.4 Buffered brighteners 162 8.4.5 Tetrasulpho/hexasulpho mixtures 163 8.4.6 Other brightener types 163 8.5 Application of fluorescent brightening agents to paper 163 8.5.1 Surface application 164 8.5.2 Film-press versus size-press application 165 8.5.3 Brightener addition levels 165 8.6 Impairment of fluorescent brightening agents: greening and quenching 166 CONTENTS Xl 8.6.1 Concentration of fluorescent brightening agents 167 8.6.2 Acidity 167 8.6.3 Starch temperature 167 8.6.4 Cationicity 167 8.6.5 Other interfering substances 168 8.7 Lightfastness 169 8.7.1 Lightfastness of brighteners in solution 169 8.7.2 Lightfastness of brightened paper 169 8.8 Recycling 170 8.8.1 Charge considerations 170 8.8.2 Residual fluorescence 170 8.9 Monitoring and control of surface brightened paper 171 8.9.1 Instrument specification 171 8.9.2 Appropriate illumination 171 8.9.3 Stability 172 8.9.4 Geometry 172 8.9.5 Calibration 172 8.9.6 Cleanliness 172 8.9.7 Measurement 172 8.9.8 Control 173 8.10 Toxicology and ecotoxicity of fluorescent brightening agents 173 8.11 Summary of the effects and influences on surface addition of fluorescent brightening agents to paper 173 Acknowledgements 174 References 174 9 On-machine surface coloration 175 A.S.