Metallic Pigments in Polymers Ian Wheeler Rapra Technology Limited Shawbury, Shrewsbury, Shropshire SY4 4NR, United Kingdom Telephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118 http://www.rapra.net 1MP Title Page etc 1 27/11/01, 12:08 pm First Published 1999 by Rapra Technology Limited Shawbury, Shrewsbury, Shropshire, SY4 4NR, UK ©1999, Rapra Technology Limited The right of Ian Wheeler to be recognised as author of this Work has been asserted by him in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1998. All rights reserved. Except as permitted under current legislation no part of this publication may be photocopied, reproduced or distributed in any form or by any means or stored in a database or retrieval system, without the prior permission from the copyright holder. A catalogue record for this book is available from the British Library. ISBN: 1-85957-166-2 Typeset by Rapra Technology Limited Printed and bound by Polestar Scientifica, Exeter, UK 1MP Title Page etc 2 27/11/01, 12:08 pm Contents 1 Introduction and History ................................................................................3 1.1 Introduction...........................................................................................3 1.2 Origins and history................................................................................4 2 Metal Pigment Types.......................................................................................7 2.1 Aluminium.............................................................................................7 2.2 Gold bronze...........................................................................................8 2.3 Copper...................................................................................................8 2.4 Nickel ....................................................................................................8 2.5 Stainless steel .........................................................................................9 2.6 Zinc .......................................................................................................9 2.7 Iron........................................................................................................9 2.8 Tin.......................................................................................................10 2.9 Silver....................................................................................................10 2.10 Gold.....................................................................................................10 2.11 Other metals........................................................................................10 3 Manufacture .................................................................................................11 3.1 Dry milling...........................................................................................11 3.1.1 Aluminium...............................................................................12 3.1.2 Gold bronze.............................................................................12 3.2 Continuous dry milling........................................................................13 3.2.1 Aluminium...............................................................................13 3.2.2 Gold bronze.............................................................................13 i 2MP CONTENTS 1 27/11/01, 12:08 pm Metallic Pigments in Polymers 3.3 Wet milling ..........................................................................................14 3.3.1 Aluminium...............................................................................14 3.3.2 Gold bronze.............................................................................19 3.3.3 Silver........................................................................................19 3.3.4 Nickel......................................................................................20 3.3.5 Stainless steel ...........................................................................21 3.3.6 Zinc.........................................................................................22 3.4 Continuous wet milling........................................................................22 3.5 Spherical metal pigments .....................................................................22 3.6 Rapidly solidified flakes.......................................................................23 3.7 Vacuum deposition ..............................................................................24 3.8 Cut foil glitters.....................................................................................25 3.9 Flakes with coloured surfaces ..............................................................25 3.9.1 Chemical modification of metal surfaces .................................26 3.9.2 Colour formation in situ..........................................................27 3.9.3 Attachment of pre-formed colorants........................................28 3.10 Metal coatings on non-metallic substrates ...........................................29 3.11 Other methods.....................................................................................30 References.....................................................................................................31 4 Pigment Characteristics.................................................................................35 4.1 Morphology.........................................................................................35 4.1.1 Particle size..............................................................................35 4.1.2 Particle shape...........................................................................38 4.1.3 Aspect ratio .............................................................................39 4.1.4 Surface uniformity ...................................................................41 4.2 Physical properties...............................................................................41 4.2.1 Specific gravity.........................................................................41 4.2.2 Water covering area.................................................................41 ii 2MP CONTENTS 2 27/11/01, 12:08 pm CCoonntteennttss 4.2.3 Specific surface area.................................................................42 4.2.4 Heat and lightfastness..............................................................42 4.2.5 Chemical resistance..................................................................43 4.2.6 Magnetism...............................................................................43 4.3 Visual properties..................................................................................43 4.3.1 Colour and brightness..............................................................44 4.3.2 Opacity....................................................................................45 4.3.3 Flop .........................................................................................45 4.3.4 Leafing and non-leafing...........................................................47 4.3.5 Sparkle.....................................................................................50 4.3.6 Distinctiveness of image...........................................................50 4.4 Glitter flakes........................................................................................52 References.....................................................................................................53 5 Delivery Forms..............................................................................................55 5.1 Dry powder..........................................................................................55 5.2 Paste ....................................................................................................55 5.3 Dispersion in resin and solvent ............................................................56 5.4 Plasticiser dispersions...........................................................................56 5.5 Granules ..............................................................................................57 5.6 Dry masterbatch ..................................................................................59 5.7 Liquid masterbatch..............................................................................59 5.8 Compound...........................................................................................60 References.....................................................................................................61 6 Comparison of Mass Pigmentation and Coating...........................................63 6.1 Advantages of coating..........................................................................63 6.1.1 Brightness ................................................................................63 6.1.2 Colour uniformity....................................................................64 iii 2MP CONTENTS 3 27/11/01, 12:08 pm Metallic Pigments in Polymers 6.1.3 Flop .........................................................................................64 6.1.4 Application temperature..........................................................65 6.1.5 Vacuum metallisation ..............................................................65 6.2 Mass pigmentation advantages............................................................65 6.2.1 Depth of coloration .................................................................65 6.2.2 Single stage versus multistage processing.................................66 6.2.3 Environmental and legislative pressures...................................66 6.2.4 Cost.........................................................................................67 References.....................................................................................................67 7 Mass Pigmentation Application Characteristics ............................................69 7.1 Colour .................................................................................................69 7.2 Dispersibility........................................................................................69 7.3 Opacity and tint strength.....................................................................70 7.4 Orientation..........................................................................................71 7.5 Mechanical properties..........................................................................71 7.6 Cost .....................................................................................................75 7.7 Interrelationships.................................................................................76 7.8 Compatibility.......................................................................................77 7.9 Spherical metal pigments .....................................................................78 7.10 Metal flake pigments with coloured surfaces .......................................78 7.11 ‘Glitter’ flakes......................................................................................79 8 Flow and Weld Lines in Mass Pigmented Applications .................................81 8.1 Description and origins........................................................................81 8.2 Tool design for injection moulding ......................................................85 8.3 Orientation in multiphase and glass filled polymers ............................87 8.4 Orientation of metal pigments.............................................................89 iv 2MP CONTENTS 4 27/11/01, 12:08 pm CCoonntteennttss 8.5 Mould tool design for metal pigments .................................................92 8.6 Gates, sprues and runners....................................................................92 8.7 Tool texturing......................................................................................94 8.8 Additional cavity .................................................................................94 8.9 Dynamic melt techniques.....................................................................94 8.9.1 SCORTEC ...............................................................................94 8.9.2 Other techniques......................................................................97 8.10 Localised mould heating ......................................................................98 8.11 Other techniques..................................................................................99 References.....................................................................................................99 9 Formulation of Mass Pigmented Polymers..................................................105 9.1 General techniques.............................................................................105 9.2 Optimising the formulation ...............................................................105 9.2.1 Flake size ...............................................................................106 9.2.2 Flake concentration ...............................................................106 9.2.3 Polymer transparency ............................................................107 9.2.4 Polymer viscosity ...................................................................107 9.2.5 Metallic/organic pigment combinations.................................108 9.2.6 Deep shades...........................................................................108 9.2.7 Spherical pigments.................................................................108 9.3 Incorporation in polymers .................................................................109 9.3.1 Low shear forces....................................................................109 9.3.2 Improvement of flake orientation ..........................................110 9.4 Increasing pigment quality.................................................................110 9.5 Summary............................................................................................111 References...................................................................................................112 10 Conversion Processes ..................................................................................113 v 2MP CONTENTS 5 27/11/01, 12:08 pm Metallic Pigments in Polymers 10.1 Injection moulding.............................................................................114 10.2 Blow moulding ..................................................................................115 10.2.1 Blown film.............................................................................115 10.2.2 Blown containers ...................................................................116 10.3 Extrusion...........................................................................................117 10.4 Co-extrusion......................................................................................117 10.5 Paint-less film moulding.....................................................................117 10.6 In-mould decoration ..........................................................................118 10.7 Vacuum forming and thermoforming.................................................118 10.8 Rotational moulding..........................................................................118 10.9 Glass reinforced plastic......................................................................119 10.10Thermosetting polymers ....................................................................120 References...................................................................................................121 11 Applications of Mass Pigmented Systems....................................................123 11.1 Household goods...............................................................................123 11.2 Sports goods ......................................................................................124 11.3 Agricultural film ................................................................................125 11.4 Sacks and bags...................................................................................125 11.5 Containers .........................................................................................126 11.6 Automotive........................................................................................126 11.7 Pearl simulants...................................................................................127 11.8 Mineral simulants..............................................................................128 11.9 Fibres and textiles..............................................................................128 References...................................................................................................129 12 Metal Pigmented Coatings ..........................................................................131 vi 2MP CONTENTS 6 27/11/01, 12:08 pm CCoonntteennttss 12.1 Substrate preparation.........................................................................131 12.2 Coating formulation and properties...................................................132 12.2.1 Pigment particle size ..............................................................132 12.2.2 Concentration........................................................................132 12.2.3 Leafing and non-leafing.........................................................133 12.3 Dispersion and incorporation ............................................................133 12.4 Application to the substrate...............................................................134 12.5 Solvent based systems ........................................................................134 12.6 Water-based systems ..........................................................................135 12.7 UV/EB cured coatings ........................................................................139 References...................................................................................................140 13 Applications of Metal Pigmented Coatings .................................................145 13.1 Painting..............................................................................................145 13.1.1 Solvent-based paints ..............................................................146 13.1.2 Water-based paints.................................................................148 13.1.3 In-mould coating ...................................................................152 13.1.4 Miscellaneous paints..............................................................153 13.2 Printing..............................................................................................153 13.2.1 Solvent-based inks .................................................................154 13.2.2 Paste inks...............................................................................154 13.2.3 Water-based inks....................................................................156 13.2.4 Laminates ..............................................................................157 13.2.5 Security Inks ..........................................................................157 13.2.6 Bronze replacement................................................................158 13.3 UV cured coatings..............................................................................161 13.4 PVC Plastisols....................................................................................162 13.5 Anticorrosive and barrier coatings.....................................................162 13.6 Other applications .............................................................................163 vii 2MP CONTENTS 7 27/11/01, 12:08 pm Metallic Pigments in Polymers 14 Powder Coatings.........................................................................................167 14.1 Material types and properties ............................................................168 14.2 Manufacture......................................................................................168 14.2.1 Dry blend...............................................................................169 14.2.2 Bonding .................................................................................169 14.2.3 Co-extrusion..........................................................................171 14.2.4 Coated flakes.........................................................................172 14.2.5 Other technologies.................................................................172 14.3 Formulation, application techniques and markets..............................173 14.4 Safety and handling ...........................................................................175 References...................................................................................................176 15 Non-colouristic Applications ......................................................................179 15.1 Mechanical reinforcement..................................................................179 15.2 Microwave heating ............................................................................180 15.3 Electrical conductivity........................................................................183 15.3.1 Product forms........................................................................183 15.4 EMI shielding ....................................................................................184 15.4.1 Origin and measurement........................................................185 15.4.2 Legislative requirements.........................................................185 15.4.3 Shielding principles and techniques........................................185 15.4.4 Shielding of polymers.............................................................186 15.4.5 Coating techniques ................................................................187 15.4.6 Mass pigmentation techniques...............................................191 15.5 Light exclusion ..................................................................................192 15.6 Heat and light reflection....................................................................193 15.7 Thermal conductivity.........................................................................194 15.8 Lubrication and wear reduction.........................................................196 15.9 Gas and moisture barrier ...................................................................196 viii 2MP CONTENTS 8 27/11/01, 12:08 pm