Surface Application of Paper Chemicals

Transcription

1 Surface Application of Paper Chemicals

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3 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

4 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, Weinheim, Germany Chapman & Hall USA, 115 Fifth Avenue, New York NY 10003, USA Chapman & Hall Japan, ITP-Japan, Kyowa Building, 3F, 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 , India First edition Chapman & Hall Softcover reprint of the hardcover 1st edition 1997 Typeset in 1OI12pt Times by Cambrian Typesetters, Frimley, Surrey ISBN-13: e-isbn-13: DOl: / 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: ~ Printed on permanent acid-free text paper, manufactured in accordance with ANSIINISO Z (Permanence of Paper).

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6 Contents List of contributors Preface Introduction J. BRANDER and I. THORN Background Technology of on-machine application Chemicals for surface application Paper products and surface treatment xv xvii IOn-machine surface treatment of paper and board with the blade coater K. STRANGER 1.1 The origins of on-machine surface treatment 1.2 The blade-coating system today 1.3 Advantages and disadvantages of on-machine surface treatment 1.4 Paper and board grades utilizing on-machine surface treatment 1.5 Designing the surface treatment line Webrun Web-threading 1.6 Examples Folding boxboard Graphic board Low-coat-weight papers On-machine coated wood-free papers Speciality papers Conclusions On-machine surface treatment of paper and board with the film press R. RANTANEN 2.1 Introduction Review of surface sizing equipment up to the 1980s Metered size press technology Quality and runnability aspects of different surface sizing processes Two-roll size press Gate-roll size press/coater Blade surface sizing New generation film presses Coat-weight development and metering-element-related phenomena 25 21

7 viii CONTENTS Grooved-rod metering Smooth-rod metering Large-diameter grooved-rod metering Blade metering 2.5 Film transfer at film-press nip Surface sizing Coating 2.6 Precalendering 2.7 Control of paper quality 2.8 Nip mechanics and roll covers 2.9 Quality differences between film-press and blade coated sheets 2.10 The SymSizer film press Process designs Applications and production experiences Synthetic latex binders for paper manufacture G. BACQUET and I.-c. ISOARD 3.1 Introduction From molecule to particle: latex synthesis Radical emulsion polymerization The monomers Finishing and final characteristics From particles to dispersion: latex stability The importance of controlling stability Stability control The viscosity of latices and coating colors: the novel contribution of the particle state Novelty of emulsion polymerlatices The impact of the particle state and the chemistry of the latex on its viscosity From particle to film: latex coalescence Howtoobtainahomogeneousfilm Wetting latex particles on pigments Preventing film formation From latex to coated paper: the role of polymers in a paper coating Binding power The latex polymer: an elastic material Polymer chemistry as a modifier of paper surface energy Porosity and ink setting in coated papers Conclusions Starches N.-O. BERGH 4.1 Introduction 4.2 Principles of starch technology Chemical principles Physical properties of starch 4.3 Starch modification Physical modification Chemical modification 4.4 Surface application methods

8 CONTENTS IX Size press Apron size press Foam-coat size press Gate-roll coater Metered size press TWIN-HSM Liquid application system Starch properties required for size-press application Influence of viscosity Influence of solids content Penetration Influence of papermachine parameters Starch properties required for metered size-press application Starch properties required for blade application and as a coating colour binder Blade application of starch solutions Starch as a coating binder Starch properties required when applied by liquid application system Size-press starch application to waste-based packaging paper One-sided size-press operation Rheology modifiers and pigment dispersants LB. CLARKE 5.1 Introduction 5.2 General principles of viscosity and rheology 5.3 Flow types encountered in paper surface treatment Newtonianflow Pseudoplasticflow Dilatantflow Thixotropicflow Plastic flow 5.4 Variation of shear stress during surface application 5.5 Waterretention 5.6 Types of rheology modifier Natural products Synthetic polymers Hydrophobic modification of synthetic polymers 5.7 Pigment dispersants What is dispersion? Electrostatic repulsion theory Chemical types used as dispersants Molecular weight effects 5.8 Interactions Effect of pigment particle size distribution Effect of multivalent cations Effect oflatex formulation Pigments for on-line surface treatment I. ATIRUP and S. HANSEN 6.1 Introduction 6.2 The pigments 6.3 Application Pigment choice

9 x CONTENTS 6.4 General paper improvement De-inked-pulp-based paper Porosity 6.5 Conclusions Surface sizing J. ANDERSON 7.1 Definition and overview 7.2 Chemicals applied at the surface Types of chemicals Wet-end sizes applied at the surface Synthetic polymeric surface sizes Miscellaneous specialities 7.3 Function of the products Solution polymers Acrylic emulsion polymers Polyurethane microdispersions 7.4 End-use properties Typical end-use properties Plain fine paper Coated paper and specialities Recycled grades 7.5 Interactions and possible problems Chemical compatibility at the size press Foam Contamination in closed systems Size-press pick-up Fixation and distribution of the size Influence of post-treatment Balancedsizing 8 Surface brightening of paper H. WEAVER 8.1 Introduction 8.2 Spectra of different iiiuminants 8.3 The quantification of the effectiveness of fluorescent brightening agents Quantum efficiency Shade build curves 8.4 The chemical nature of fluorescent brightening agents Disulpho brighteners Tetrasulpho brighteners Hexasulpho brighteners Buffered brighteners Tetrasulpho/hexasulpho mixtures Other brightener types 8.5 Application of fluorescent brightening agents to paper Surface application Film-press versus size-press application Brightener addition levels 8.6 Impairment of fluorescent brightening agents: greening and quenching

10 CONTENTS Xl Concentration of fluorescent brightening agents Acidity Starch temperature Cationicity Other interfering substances 8.7 Lightfastness Lightfastness of brighteners in solution Lightfastness of brightened paper 8.8 Recycling Charge considerations Residual fluorescence 8.9 Monitoring and control of surface brightened paper Instrument specification Appropriate illumination Stability Geometry Calibration Cleanliness Measurement Control 8.10 Toxicology and ecotoxicity of fluorescent brightening agents 8.11 Summary of the effects and influences on surface addition of fluorescent brightening agents to paper Acknowledgements On-machine surface coloration A.S. TINDAL 9.1 Introduction 9.2 Size-press dyeing Selection of dyes and pigments Practicalities of size-press dyeing Promoters for size-press dyeing Advantages and disadvantages of size-press dyeing Split addition Colour recipe match prediction When should size-press dyeing be considered? 9.3 Dyes used in on-machine coating Dye and pigment classes 9.4 Calender stack dyeing 9.5 Spraying 9.6 Broke treatment 9.7 Survey of surface dyeing 9.8 Conclusions Acknowledgements Further reading The surface treatment of fine business papers M. WATSON 10.1 Introduction 10.2 Non-impact printing Laser printing Ink-jet printing

11 xii CONTENTS 10.3 The chemical natures of non-impact printing image-forming materials Laser printer toner Ink-jet inks 10.4 Paperrequirements fornon-impact printing Laser printers Ink-jet printers 10.5 Surface treatment for non-impact printing papers Polymeric surface sizing agents Coated ink-jet papers 10.6 Surface application methods Size press Film press 10.7 Summary Acknowledgement Further reading 11 Barrier dispersion coating of paper and board T. KIMPIMAKI and A.V. SAVOLAINEN 11.1 Dispersion coating in general Dispersion coating methods Typically used barrier dispersions 11.2 Film formation Film formation theories Rheology 11.3 Commonly measured film properties Water vapour transmission rate Cobb value Other properties 11.4 Heat sealing, blocking and gluing 11.5 Products 11.6 Disposal of dispersion coated papers Recycling Composting 12 Recycling surface treated paper products D. GUEST 12.1 Introduction Surface treated paper in context Solid-waste management policies Design for recycling The influence of fibres on paper recycling 12.2 Recycling surface treated paper products The influence of separate particles The influence of additives that remain attached to the fibres The influence of additives that form colloids Additives that are soluble Summary of effects of surface applied chemicals on papermaking 12.3 Stock preparation and the impact of surface treatment chemicals Repulping and ink detachment

12 CONTENTS Xlll Index De-inking and de-ashing Dispersion Co\ourstripping Water treatment 12.4 Summary of the effects of surface treated papers on recycling

13 Contributors J. Anderson Eka Chemicals Ltd, 304 Worle Parkway, Summer Lane, Worle, Weston-super-Mare, Somerset BS22 OWA, UK I. Attrup Faxe Kalk, Frederiksholms Kanal 16, PO Box 2183, DK-1017 Copenhagen K, Denmark G. Bacquet Rhone Poulenc Recherches, Centre de Recherches d'aubervilliers, 52 Rue de la Haie-Coq, F Aubervilliers, France N.-O. Bergh Cerestar Euro Centre Paper, Diisseldorfer StraBe 191, D-4150 Krefeld 12, Germany J. Brander Arjo Wiggins Ltd, Research & Development, Butler's Court, Wattleton Road, Beaconsfield, Buckinghamshire HP9 lrt, UK J.B. Clarke Allied Colloids Ltd, PO Box 38, Low Moor, Bradford, Yorkshire BD12 OJZ, UK D. Guest Director of Technology, Masonite International Paper Co., John M. Coates Technical Center, 1955 Powis Road, West Chicago, IL 60185, USA S. Hansen Faxe Kalk, Frederiksholms Kanal 16, PO Box 2183, DK-I017, Copenhagen K, Denmark J.-C.Isoard Rhone Poulenc Recherches, Centre de Recherches d'aubervilliers, 52 Rue de la Haie-Coq, F Aubervilliers, France T. Kimpimaki Paper Converting Institute, Tampere University of Technology, PO Box 541, SF Tampere, Finland R. Rantanen Valmet Corporation, PO Box 587, SF Jyvaskyla, Finland A.V. Savolainen Paper Converting Institute, Tampere University of Technology, PO Box 541, SF Tampere, Finland K. Stranger Jagenberg Papiertechnik GmbH, JagenbergerstraBe 1, D Neuss, Germany

14 xvi I. Thorn A.S. Tindal M. Watson H. Weaver CONTRIBUTORS Eka Chemicals Ltd, 304 Parkway, Summer Lane, Worle, Weston-super-Mare, Somerset BS22 OWA, UK Clariant UK Ltd, Calverley Lane, Horsforth, Leeds LS18 4RP, UK Arjo Wiggins Ltd, Research & Development, Butler's Court, Wattleton Road, Beaconsfield, Buckinghamshire HP9 lrt, UK Renaissance Chemicals, Holly House, Brayton Lane, Brayton, Selby, Yorkshire Y08 9DZ, UK

15 Preface With the exception of a slight hiccup during the height of the recent environmental movement (during the early 1990s), when for a year or two consumers were prepared to pay a price premium for lower quality recycled paper than for the virgin product, the inexorable improvement in the quality demanded of paper products continues. This demand for quality covers not only the aesthetics ofthe product but also its performance. Moreover, it is becoming increasingly the case that papers designed for a particular use must, as it were incidentally, also perform well in alternative applications. An example is that of office and printing papers, which are expected to perform as well in copier machines as in all the various forms of impact and non-impact printers. But even greater demands are made in other product areas, where board designed for dry foods can also be expected to protect moist and fatty materials and be made of 100% recycled fibre. The need to isolate foodstuffs from some of the contaminants that can affect recycled board is a serious challenge. Thus, papermakers are constantly striving to meet a broadening spectrum of demands on their products; often while accepting declining quality of raw materials. The product design philosophy that has arisen in response to this is increasingly to isolate the bulk of a paper from its uses: to engineer the needed performance characteristics into the paper surfaces while more or less ignoring what happens inside. Thus surface application and treatment has assumed greater and greater importance, and a need for knowledge of the technologies and chemicals used has spread throughout all sectors of the industry. A great deal of surface treatment is still performed in separate offmachine coating operations, using tolerably-well-understood technologies such as blade or roll applicators. However, the cost of such activities is obviously high, both in investment and in operational terms, and there is a constant search for ways to carry out larger proportions of the overall manufacture in a single operation. Hence, interest in the paper industry and its suppliers in on-machine surface application technologies and chemicals is intense. Special attention is being given to finding binders, rheology modifiers and barrier polymers less susceptible to the film-splitting arising from the low-shear metering

16 xviii PREFACE used in on-machine application systems; and in developing simply applied surface treatments adequately receptive to the dyes used in ink-jet inks. Alongside these development efforts, on-machine surface treatment has an important role even when the final surface properties are provided offmachine. Paper and board containing a high proportion of recycled fibre simply can't be treated directly in high-shear metering systems such as blade coaters (which give the best results both for printing papers and for barrier films). It is simply too dirty; some form of pretreatment must be applied first. On-machine application of simple starch is ideal for this. Happily, too, many of the surface treatments being applied, especially to food board, are replacing quite complex composite materials, including aluminium and polythene as well as paper. This means that the new, onmachine surface treated boards are actually easier to recycle than the materials they replace. This is important, as our supplies of virgin fibre are not going to increase as rapidly as our demand for paper and board in the coming decades. This book describes some of the recent achievements in this field. James Brander Beaconsfield, Bucks May, 1997