Blown Film Extrusion An Introduction Kirk Cantor Hanser Publishers, Munich • Hanser Gardner Publications, Cincinnati Distributed in the USA and in Canada by Hanser Gardner Publications, Inc 6915 Valle.
Kirk Cantor Blown Film Extrusion An Introduction Hanser Publishers, Munich • Hanser Gardner Publications, Cincinnati The Author: Prof Kirk Cantor, Pennsylvania College of Technology, One College Avenue, Williamsport, PA 17701, USA Distributed in the USA and in Canada by Hanser Gardner Publications, Inc 6915 Valley Avenue, Cincinnati, Ohio 45244-3029, USA Fax: (513) 527-8801 Phone: (513) 527-8977 or 1-800-950-8977 www.hansergardner.com Distributed in all other countries by Carl Hanser Verlag Postfach 86 04 20, 81631 München, Germany Fax: +49 (89) 98 48 09 www.hanser.de The use of general descriptive names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone While the advice and information in this book are believed to be true and accurate at the date of going to press, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made The publisher makes no warranty, express or implied, with respect to the material contained herein Library of Congress Cataloging-in-Publication Data Cantor, Kirk Blown film extrusion : an introduction / Kirk Cantor p cm Includes bibliographical references and index ISBN-10: 1-56990-396-4 (hc) ISBN-13: 978-1-56990-396-4 (hc) Plastic films I Title TP1183.F5C36 2006 668.4‘95 dc22 2006000351 Bibliografische Information Der Deutschen Bibliothek Die Deutsche Bibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie; detaillierte bibliografische Daten sind im Internet über abrufbar ISBN-10: 3-446-22741-5 ISBN-13: 978-3-446-22741-5 All rights reserved No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying or by any information storage and retrieval system, without permission in writing from the publisher © Carl Hanser Verlag, Munich 2006 Production Management: Oswald Immel Typeset by Manuela Treindl, Laaber, Germany Coverconcept: Marc Müller-Bremer, Rebranding, München, Germany Coverdesign: MCP • Susanne Kraus GbR, Holzkirchen, Germany Printed by Kưsel, Krugzell, Germany Acknowledgements I am grateful for the many people that have supported my efforts to write this book and develop the software included Funding for these projects was provided through a grant to the Plastics Resources for Educators Program (PREP) by supporters at the National Science Foundation My colleagues at Pennsylvania College of Technology provided administrative support I am very thankful for my good friend and co-worker, Tim Weston, for his vision and leadership through PREP Other PREP colleagues for whom I am thankful are Alex Bierly, who masterfully created all of the graphics for the simulator, and our other very talented artists, Mike Fleck, Matt Byers, and Craig Reitz Many thanks go to another close friend and mentor, Chris Rauwendaal, for not only helping with the text of this book, but for teaching me so much about extrusion over the years I am thankful for the text review and insight given to me by Robert Krycki My friends at Hanser have been very helpful with the creation of the manuscript and artwork Thanks especially to Christine Strohm for her years of encouragement and assistance Finally, I am most thankful for the support of my devoted family and the opportunity given to me by God My lovely wife, Patsy, and my four beautiful daughters, Kristen, Caylee, Kelsey, and Shannon, have patiently endured my hours away and have even cheered me on to completion January 2006 Kirk Cantor Contents Acknowledgements V Introduction 1 Materials for Blown Film 1.1 Polymers 1.1.1 Polyethylene (PE) 1.1.2 Low-Density Polyethylene (LDPE) 1.1.3 High-Density Polyethylene (HDPE) 1.1.4 Linear Low-Density Polyethylene (LLDPE) 1.1.5 Metallocene Polyethylene (mPE) 10 1.1.6 Polypropylene (PP) 10 1.1.7 Polystyrene (PS) 11 1.1.8 Ethylene Vinyl Acetate (EVA) 12 1.1.9 Ethylene Vinyl Alcohol (EVOH) 12 1.1.10 Polyvinyl Chloride (PVC) 13 1.1.11 Polyamide (PA) 13 1.1.12 Polyurethane (PU) 13 1.2 Additives 14 1.2.1 Antiblocking Agents 15 1.2.2 Antioxidants 15 1.2.3 Antistatic Agents 15 1.2.4 Colorants 16 1.2.5 Lubricants 17 1.2.6 Reinforcements and Fillers 17 1.2.7 Stabilizers 19 1.2.8 Tackifiers 19 Extrusion Overview 21 2.1 Extruder Hardware Systems 21 2.1.2 Drive System 23 2.1.2.1 Motor 23 2.1.2.2 Speed Reducer 23 2.1.2.3 Thrust Bearing 24 2.1.3 Feed System 26 VIII Contents 2.1.4 2.2 Screw/Barrel System 28 2.1.4.1 Screw 28 2.1.4.2 Barrel 30 2.1.5 Head/Die System 31 2.1.5.1 Head Assembly 32 2.1.5.2 Adapter 32 2.1.5.3 Breaker Plate 32 2.1.5.4 Melt Filter 33 2.1.5.5 Die 35 2.1.6 Instrumentation and Control System 36 2.1.6.1 Temperature Control 37 2.1.6.2 Head Pressure 40 2.1.6.3 Motor Current 41 Extrusion Functional Zones 42 2.2.1 Solids Conveying 43 2.2.1.2 Gravity-Induced Region 43 2.2.1.3 Drag-Induced Region 44 2.2.2 Melting 45 2.2.3 Melt Pumping 47 2.2.4 Mixing 49 2.2.4.1 Distributive Mixing 49 2.2.4.2 Dispersive Mixing 50 2.2.4.3 Mixing Devices 51 2.2.5 Degassing 53 2.2.6 Die Forming 54 Hardware for Blown Film 59 3.1 Upstream Components 60 3.2 Grooved Feed Throat 62 3.3 Screws for Blown Film Extrusion 64 3.4 Blown Film Dies 65 3.5 Bubble Geometry 70 3.6 Bubble Cooling 73 3.7 Bubble Stabilization 78 3.8 Collapsing Frames 78 3.9 Haul-off 79 3.10 Winders 80 3.11 Film Treatment 82 3.12 Line Control 83 Contents IX Processing 89 4.1 Process Variables vs Bubble Geometry 90 4.2 Characteristic Bubble Ratios 92 4.3 Process/Structure/Property Relationships 94 Coextrusion 97 5.1 Dies 98 5.2 Interfacial Instabilities 100 Film Properties 103 6.1 Tensile Strength (ASTM D882) 105 6.2 Elongation (ASTM D882) 107 6.3 Tear Strength (ASTM D1004, ASTM D1922 and D1938) 107 6.4 Impact Resistance (ASTM D1709, D3420 and D4272) 109 6.5 Blocking Load (ASTM D3354) and Coefficient of Friction (ASTM D1894) 110 6.6 Gel (Fisheye) Count (ASTM D3351 and D3596) 111 6.7 Low Temperature Brittleness (ASTM D1790) 111 6.8 Gloss (ASTM D2457) 112 6.9 Transparency (ASTM D1746) 112 6.10 Haze (ASTM D1003) 113 6.11 Density (ASTM D1505) 113 6.12 Melt Index (ASTM D1238) 114 6.13 Viscosity by Capillary Rheometry (ASTM D3835) 116 Troubleshooting 119 7.1 Extruder Problems 120 7.1.1 Surging 120 7.1.2 High Melt Temperature 121 7.1.3 Excessive Cooling 123 7.1.4 Low Output 124 7.2 Film Problems 125 7.2.1 Melt Fracture 125 7.2.2 Thickness Variation 126 7.2.3 Die Lines 130 7.2.4 Gels 131 7.2.5 Low Mechanical Properties 132 7.2.6 Poor Optical Properties 133 X Contents Appendix A: The Blown Film Extrusion Simulator .135 A.1 Introduction 135 A.2 Installation 136 A.3 Running the Program 137 A.4 Worksheet 144 Appendix B: Useful Equations 147 References 155 Subject Index 159 Introduction Blown film extrusion is one of the most significant polymer processing methods Several billion pounds of polymer, mostly polyethylene, are processed annually by this technique While some applications for blown film are quite complex, such as scientific balloons (Fig 1), the majority of products manufactured on blown film equipment are used in commodity applications with low profit margins: grocery sacks, garbage bags, and flexible packaging (Fig 2) Consequently sophisticated hardware, materials, and processing methods have been developed to yield film at very high output rates with both low dimensional variation and consistent solid-state properties Figure A high altitude, scientific balloon being prepared for launch (National Aeronautics and Space Administration) Introduction Figure Blown film extrusion is used to produce very high volumes of commodity products such as grocery and produce bags Polymer chemistry and molecular structure are vital in establishing film properties, but bubble geometry resulting from processing conditions is also significant Molecular orientation and crystalline structure – controlled by bubble dimensions – affect properties such as tensile strength, impact toughness, and clarity As a manufacturing process, blown film is somewhat unique, even compared with other extrusion processes Molten polymer generally exits the die vertically in the form of a freely extruded bubble reaching heights of 50 feet (15 meters) or more (Fig 3) Guides surrounding the bubble may limit its mobility, but it is still quite exposed to dimensional variation compared to the fixed extrudate in most other extrusion processes, which use vacuum sizers, calibrators, rollers, or other techniques Depending on processing conditions, the blown film bubble has a shape freedom that allows almost any number of profiles within a designed range Operators must have a relatively high skill level to accurately obtain the required bubble geometry (i.e., the shape resulting in specified product dimensions and properties) The strong interdependence of process variables is another aspect of the process that requires a high level of operator skill and has led to extensive advancements in measurement and control techniques There are many process variables – screw speed, nip speed, internal bubble air volume, and cooling rate (frost-line height) – that influence bubble geometry and, as a result, film properties An adjustment to any one Index Terms Links die (Cont.) 130 133 148 149 125 130 133 127 128 130 133 swell 54 55 dispersed 17 dispersive mixing 49 distributed 17 distributive mixing 49 153 line 119 134 lip 50 51 50 51 44 45 18 downgauging drag-induced 43 draw down ratio 93 dried 13 14 drive 23 24 dryer 26 drying 11 dual lip 75 76 dye 16 17 104 107 E elongation elongational 51 energy 41 45 46 50 51 64 109 121 122 123 131 64 119 ethylene vinyl acetate 12 ethylene vinyl alcohol 12 excessive cooling 39 extensional 100 This page has been reformatted by Knovel to provide easier navigation 123 Index Terms Links extraction section 53 extraction zone 31 F falling dart feed 109 26 27 28 29 43 60 64 84 16 26 27 30 44 62 64 17 18 19 85 feeding 113 instability feed throat filler 120 60 106 film property filter 31 filtering 11 33 84 fisheye 33 104 111 flight 28 62 29 49 flood fed 27 43 flow-splitting device 99 fluff 43 tip regrind 60 131 122 61 83 26 fluffy 44 foaming 31 53 forming ratio 92 93 110 152 93 95 96 17 26 44 153 FR 92 152 friction This page has been reformatted by Knovel to provide easier navigation Index Terms Links friction (Cont.) 45 46 47 56 57 62 104 109 110 120 121 123 25 61 63 71 72 74 79 83 86 87 90 91 92 106 126 127 128 132 133 84 138 frictional 23 110 heat generation frost line 45 142 function 29 functional zone 42 funnel 44 flow 43 44 G gas 31 53 gauge 66 80 83 85 86 100 23 24 25 30 11 14 15 33 64 95 104 111 119 125 131 18 106 132 104 112 130 gear box 62 gel glass 18 fiber gloss This page has been reformatted by Knovel to provide easier navigation Index Terms Links gravity-induced 43 grooved feed throat guide 27 45 48 62 63 64 65 120 122 131 H haul-off 79 80 104 113 head assembly 31 32 head pressure 25 31 33 35 37 40 54 61 63 84 98 118 120 122 124 133 138 147 heat-seal ability 66 98 heater 30 haze band 45 46 47 123 130 heating unit heat seal 39 heat shrinkability 13 helix angle 46 high (or long) stalk 73 high-density polyethylene 73 75 113 homogeneous 21 28 65 83 hopper 26 27 42 43 44 60 61 138 15 74 75 humidity This page has been reformatted by Knovel to provide easier navigation Index Terms Links I IBC 76 86 128 impact resistance 104 109 110 132 impact strength 103 83 89 142 134 impact toughness infrared detector 38 instrumentation 36 insulator 75 interdependence 143 interface 100 interfacial instability 100 101 internal bubble cooling 76 128 interrelationship 90 isotropic 93 110 isotropy 93 96 L L/D ratio 29 layflat 71 72 80 83 86 89 93 133 142 149 150 154 width leakage 122 leakage flow 124 49 linear linearity linear low-density polyethylene 73 76 72 line control 83 line speed 36 55 125 150 This page has been reformatted by Knovel to provide easier navigation 79 Index Terms Links long stalk low-density polyethylene 73 132 138 17 75 113 56 57 125 89 108 109 120 126 130 151 153 mandrel 66 69 70 128 masterbatch 14 18 matrix 18 19 50 51 MD 89 91 92 93 95 105 106 126 132 151 lubricant M machine and transverse direction direction orientation melt 105 132 96 64 film fracture 46 47 17 54 55 56 101 119 125 114 115 116 134 index 104 117 pool 46 121 pumping 47 84 quality 30 65 66 83 11 13 14 64 65 84 speed strength 72 This page has been reformatted by Knovel to provide easier navigation Index Terms Links melt (Cont.) melting instability 73 138 29 41 42 43 44 45 46 47 49 83 84 120 121 122 120 121 43 48 147 mesh 33 metallocene 10 polyethylene 10 metering 28 mix 21 mixing 26 29 33 42 44 49 60 64 65 66 83 84 51 84 131 33 36 44 74 111 65 66 23 24 40 113 element moisture monolayer motor 53 41 138 current 37 41 power multilayer 13 66 N nanocomposite 18 nested mandrel 68 nip roller 15 37 72 74 78 79 91 138 This page has been reformatted by Knovel to provide easier navigation Index Terms nip speed Links 72 79 90 91 93 133 142 143 13 132 30 35 37 46 60 62 66 70 73 122 32 37 85 90 98 115 122 123 126 133 112 130 133 134 orange peel 55 125 orient 54 55 89 92 93 95 106 107 108 110 132 133 151 152 24 33 37 40 49 63 64 77 83 85 91 119 120 121 122 124 127 nylon O operation operator 135 optical orientation output ozone 82 P pancake 68 pellet 16 18 26 29 42 43 44 49 60 61 62 65 This page has been reformatted by Knovel to provide easier navigation Index Terms Links PID control 37 pigment 16 17 plug flow 26 44 72 73 10 12 13 17 54 63 64 70 74 82 107 111 113 120 132 82 pocket bubble 50 75 polarity 12 polishing 45 polyamide 13 polyethylene polyisobutylene 19 polypropylene 10 73 polystyrene 11 polyurethane 13 polyvinyl chloride 13 19 111 powder 16 26 27 43 power 23 39 51 52 21 24 28 29 30 32 34 35 41 47 48 49 51 54 64 65 84 98 120 40 41 41 103 12 13 14 12 18 consumption pressure transducer property 17 120 125 adhesive barrier This page has been reformatted by Knovel to provide easier navigation 98 Index Terms Links property (Cont.) dependence on processing 59 94 95 89 93 die 35 feed 60 63 10 11 14 15 17 18 19 64 93 95 98 100 119 132 133 10 11 14 95 100 119 133 134 89 29 42 51 65 122 124 regrind 44 120 reinforcement 17 106 132 reinforcing 18 mechanical optical solid state pumping 54 R property 18 reprocessed 60 83 85 132 residence time 49 69 70 98 121 131 133 ripple 55 rupture disk 30 40 S safe 36 safety 30 40 82 84 34 35 122 85 screen 124 changer 33 This page has been reformatted by Knovel to provide easier navigation Index Terms Links screen (Cont.) pack 32 33 34 40 23 24 25 27 28 29 30 32 41 42 43 44 63 64 65 83 122 123 122 screw 147 beat 120 channel 121 124 design 83 121 133 diameter 21 29 flight 120 122 speed 11 23 37 40 47 54 56 63 64 72 84 86 90 91 92 106 118 121 122 124 125 133 138 142 segregation shape freedom 44 60 shark skin 55 125 shear 51 100 heating rate 64 117 125 138 stress 55 100 117 shrinkage 95 side fed 65 66 This page has been reformatted by Knovel to provide easier navigation 125 Index Terms simulator Links 22 37 40 41 59 90 96 135 144 47 122 single lip 75 slide plate 122 solid 62 bed 42 46 124 breakup 41 121 43 84 specific heat 74 speed reducer 23 24 spider leg 66 spiral mandrel 65 66 68 stabilizer 19 60 78 stack 68 98 99 69 70 stalk 71 72 75 91 starve fed 27 static 15 18 44 81 33 49 51 83 120 conveying die mixer 120 84 pressure strain gage pressure transducer 74 41 41 surface winder 80 81 surging 46 63 119 121 126 127 This page has been reformatted by Knovel to provide easier navigation Index Terms Links T tackifier 19 take-up ratio 92 106 125 126 127 133 151 152 153 talc 18 TD 73 89 91 93 95 96 105 106 128 130 132 152 89 95 96 104 107 108 130 132 21 28 36 37 30 32 36 37 46 75 84 85 89 95 96 104 105 106 107 13 16 17 tear 89 strength temperature 40 control tensile strength 132 thermal stability 64 thermistor 38 thermocouple 38 39 37 55 66 70 71 72 78 79 80 83 85 89 90 91 93 100 119 120 125 126 130 133 142 thickness 153 This page has been reformatted by Knovel to provide easier navigation Index Terms Links throat 27 120 throughput 17 22 42 45 47 49 59 62 73 93 118 121 122 123 124 126 149 150 151 23 24 25 23 34 41 65 14 95 73 74 79 141 142 transfer pipe 32 69 70 transition 28 43 46 47 104 112 130 89 105 108 109 128 152 153 thrust bearing torque tough 32 89 toughness tower translucent transparency 80 112 16 134 transverse direction treatment troubleshooting TUR 82 119 147 92 93 95 133 151 152 turret winder 81 two-stage screw 31 53 U unmelt 65 This page has been reformatted by Knovel to provide easier navigation 96 Index Terms Links V valve 40 vented barrel 31 53 vent flow 31 54 viscosity 11 14 17 23 33 40 41 47 50 51 54 55 56 65 84 85 97 104 115 116 117 118 125 138 14 17 18 29 30 33 122 124 141 142 W wear weld line 66 winder 80 wood flour 18 This page has been reformatted by Knovel to provide easier navigation