the handbook rubber bonding

The Handbook ofRubber Bonding

(Revised Edition)

Editor: Bryan Crowther

Rapra Technology Limited

Shawbury, Shrewsbury, Shropshire, SY4 4NR, United KingdomTelephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118

http://www.rapra.net

TECHNOLOGYrapra

First Published 2001 by

Rapra Technology LimitedShawbury, Shrewsbury, Shropshire, SY4 4NR, UK

©2001, Rapra Technology Limited

Revised and Reprinted 2003

All rights reserved. Except as permitted under current legislation no partof this publication may be photocopied, reproduced or distributed in anyform 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.

Cover photograph reproduced with permission from Rubber Chemistry and Technology,1994, 67, 4582. Copyright 1994, Rubber Division, American Chemical Society, Inc.

Typeset by Rapra Technology LimitedPrinted and bound by Rapra Technology Limited

ISBN: 1-85957-394-0

i

Contents

Introduction .......................................................................................................... 1

1 Substrate Preparation Methods ....................................................................... 3

1.1 Metal Preparation - General Techniques ................................................ 3

1.1.1 Structure of Metal Substrates - Metallography .......................... 3

1.1.2 Bonding ..................................................................................... 5

1.1.3 Rubber Component with Metal Support ................................... 5

1.1.4 Metal Pre-treatments ................................................................. 6

1.2 Pre-treatments of Plastics and Rubbers ................................................ 12

1.2.1 Introduction ............................................................................. 12

1.2.2 Studies of Pre-treatments for Plastics ....................................... 13

1.2.3 Hydrocarbon Rubbers with Little or No Unsaturation ............ 19

1.2.4 Unsaturated Hydrocarbon Rubbers ......................................... 20

1.2.5 Halogenated Rubbers .............................................................. 25

1.2.6 Miscellaneous Rubbers ............................................................ 26

1.2.7 Discussion ................................................................................ 27

1.2.8 Summary ................................................................................. 29

1.3 Bonding Rubbers to Plastic Substrates ................................................. 29

1.3.1 Introduction ............................................................................. 29

1.3.2 Plastics Substrate Preparation .................................................. 31

1.3.3 Degreasing and Solvent Cleaning ............................................. 35

1.3.4 Adhesive/Bonding Agent Choice .............................................. 36

1.4 Substrate Preparation for Bonding Using the Wet Blast Process ........... 42

1.4.1 Summary ................................................................................. 42

1.4.2 The Wet Blast Phosphating Plant ............................................. 42

The Handbook of Rubber Bonding

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1.4.3 Comparison Between Conventional and Wet Blast Phosphating .. 45

1.4.4 The Wet Blast Phosphating Plant ............................................. 46

1.4.5 Advantages of the Wet Blast Phosphating Plant ....................... 47

2 Rubber to Metal Bonding ............................................................................. 57

2.1 History................................................................................................. 57

2.2 Bond System Characteristics ................................................................ 62

2.2.1 Adhesive Characteristics .......................................................... 62

2.2.2 Compound Characteristics....................................................... 64

2.3 Adhesion .............................................................................................. 66

2.4 Effective Bond Formation .................................................................... 71

2.5 Post Vulcanisation Bonding ................................................................. 73

2.6 Factors Affecting Bond Integrity .......................................................... 73

2.7 Bond Failure Types .............................................................................. 74

2.8 Bond Test Procedures ........................................................................... 76

2.9 Summary.............................................................................................. 77

3 Rubber to Metal and Other Substrate Bonding ............................................. 81

3.1 Introduction ......................................................................................... 81

3.1.1 Foreword ................................................................................. 81

3.1.2 History .................................................................................... 81

3.1.3 Types of Bonding ..................................................................... 82

3.1.4 The Bonding Process - An Overview ........................................ 83

3.1.5 Development of Bonding ......................................................... 84

3.1.6 Bonding Agent Reliability ........................................................ 84

3.1.7 The Environment and Solvent Use ........................................... 86

3.1.8 Methods of Reduction in Solvent Emissions ............................ 87

3.2 Substrates and their Preparation .......................................................... 87

3.2.1 Mechanical Treatment of Metals ............................................. 88

iii

ContentsContents

3.2.2 The Abrasion Process ............................................................... 90

3.2.3 Levels of metal cleanliness ....................................................... 92

3.2.4 Time Window .......................................................................... 93

3.2.5 Chemical Preparation of Surfaces ............................................ 94

3.2.6 Future Developments ............................................................... 96

3.3 Bonding Agent Preparation .................................................................. 97

3.3.1 Solvent-borne Bonding Systems ............................................... 97

3.4 Bonding Agent Application and Use .................................................... 98

3.4.1 Application Methods ............................................................... 98

3.4.2 Waterborne Bonding Systems ................................................... 98

3.4.3 Bonding Agent Thickness......................................................... 99

3.5 Post Vulcanisation Bonding ............................................................... 100

3.5.1 Post Vulcanisation Bonding Applications............................... 100

3.5.2 Choice of Bonding Agent for Post Vulcanisation Bonding ..... 100

3.5.3 Rubber Substrate Preparation for PV Bonding....................... 101

3.5.4 Metal Substrate Preparation .................................................. 101

3.5.5 Methods of Application ......................................................... 101

3.6 Waterborne Bonding Systems ............................................................. 103

3.6.1 History .................................................................................. 103

3.6.2 Differences Between Solvent and Waterborne Bonding Agents .. 103

3.6.3 Suggested Spraying Equipment and Conditions ..................... 105

3.6.4 Application and Substrate Temperatures ............................... 105

3.6.5 Film Thickness ....................................................................... 106

3.6.6 Layover .................................................................................. 106

3.6.7 Progress in Performance......................................................... 106

3.7 Health and Safety in the Workplace ................................................... 109

3.7.1 The Safety Data Sheet ............................................................ 109

3.7.2 Perspective ............................................................................. 110

3.8 Bonding Agent Testing ....................................................................... 110


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3.9 Shelf Life Considerations ................................................................... 112

3.9.1 Shelf Life Categories .............................................................. 113

3.9.2 Procedures for Re-certification of Bonding Agents ................ 113

3.10 Troubleshooting ................................................................................. 115

3.11 Summary............................................................................................ 120

4 Bonding Rubber to Metals with Waterborne Adhesive Systems .................. 125

4.1 Introduction ....................................................................................... 125

4.1.1 Solvent Elimination by the Rubber Industry .......................... 126

4.1.2 Techniques Necessary in Bonding of Rubber to MeetLocal Environmental Pollution Limits ................................... 127

4.2 Waterborne Bonding Systems ............................................................. 127

4.2.1 Structure of Organic Solvent-based Bonding Systems ............ 127

4.2.2 Structure of Waterborne Bonding Systems ............................. 127

4.2.3 Fundamentals of Waterborne Bonding Agent Application ..... 128

4.2.4 Waterborne Bonding Systems in Factory Usage ..................... 128

4.2.5 Metal Preparation - For Waterborne Bonding Systems .......... 129

4.2.6 Waterborne Bonding Agent Application ................................ 129

4.2.7 Waterborne Bonding Agent Storage Stability ......................... 130

4.2.8 Non Bond Advantages of Waterborne Bonding Systems ........ 130

4.2.9 General Comments - Waterborne Bonding Agents ................. 130

4.3 Waterborne Bonding Agents - A Factory Experience ......................... 131

4.3.1 Thickness Effects ................................................................... 131

4.3.2 Pre-bake Resistance ............................................................... 133

4.3.3 Primers .................................................................................. 134

4.3.4 Polymer Range ....................................................................... 134

4.3.5 Product Range ....................................................................... 134

4.3.6 Current Disadvantages of Waterborne Bonding Agents ......... 134

5 Rubber to Rubber Bonding ......................................................................... 137

5.1 Bonding of Unvulcanised Rubbers ..................................................... 137

v

ContentsContents

5.1.1 Tack/Autohesion .................................................................... 137

5.1.2 Influence of Vulcanisation System.......................................... 139

5.1.3 Influence of Filler Type .......................................................... 140

5.1.4 Effects of Plasticisers/Process Oils .......................................... 141

5.1.5 Effects of Tackifiers ............................................................... 141

5.1.6 Effects of Other Ingredients ................................................... 142

5.1.7 Effects of Surface Modification .............................................. 142

5.1.8 Effects of Surface Roughness ................................................. 144

5.1.9 Influence of Contact Time/Pressure/Temperature ................... 144

5.1.10 Effects of Blooming................................................................ 145

5.1.11 Effects of Ageing .................................................................... 146

5.1.12 Testing of Tack/Autohesion Levels ......................................... 147

5.1.13 Adhesion Theories ................................................................. 148

5.2 Bonding of Vulcanised Rubbers to Unvulcanised Rubbers ................. 150

5.3 Bonding of Vulcanised Rubbers ......................................................... 152

5.3.1 Strip Bonding of Tyre Retreading Components ...................... 152

5.3.2 Effects of Strip Thickness ....................................................... 155

5.3.3 Effects of Surface Roughness ................................................. 156

5.3.4 Effects of Temperature on Bonding ........................................ 156

5.3.5 Effects of the Chemical Nature of Polymers/Polymeric Additives/Surface Roughness ................................. 156

5.3.6 Urethane Adhesive Systems .................................................... 158

5.3.7 Surface Treatments to Improve Bonding ................................ 158

5.3.8 Effects of Contact Time/Surface Bloom.................................. 159

5.4. The Mechanism of Adhesion of Fully Cured Rubbers........................ 159

6 Rubber-Brass Bonding ................................................................................. 163

6.1 Introduction ....................................................................................... 163

6.2 Mechanism of Rubber-Brass Bonding ................................................ 165

6.2.1 Reviews ................................................................................. 165

6.2.2 Recent Mechanistic Studies .................................................... 165


vi

6.2.3 Updated Rubber-Brass Adhesion Model ................................ 170

6.2.4 New Evidence for Ageing of the Interfacial Sulphide Film ..... 177

6.2.5 Compounding for Brass Adhesion ......................................... 180

6.2.6 Additives to Compounds for Brass Adhesion ......................... 181

6.2.7 Developments in Metal Pre-treatments .................................. 184

6.2.8 Developments of Novel Alloys for Bonding to Rubber .......... 189

6.2.9 Miscellaneous ........................................................................ 190

6.2.10 Summary ............................................................................... 190

7 Review of Tyre Cord Adhesion ................................................................... 197

7.1 Introduction ....................................................................................... 197

7.2 Accepted Mechanisms of Rubber-Brass Bonding ............................... 198

7.3 Ageing of the Rubber-Brass Bond ...................................................... 200

7.4 Metal Organic Cobalt Salts ................................................................ 201

7.5 The Role of Resins and Silica/Resin Systems ...................................... 205

7.6 Summary............................................................................................ 208

8 Rubber to Metal Bonding Using Metallic Coagents .................................... 213

8.1 Introduction ....................................................................................... 214

8.2 Metallic Coagents .............................................................................. 215

8.2.1 Scorch Safety ......................................................................... 217

8.2.2 Tensile Properties ................................................................... 219

8.2.3 Tear Strength ......................................................................... 220

8.3 Experimental ..................................................................................... 221

8.3.1 Materials ............................................................................... 221

8.4 Results and Discussion....................................................................... 229

8.4.1 Adhesion to Metals ................................................................ 229

8.4.2 Adhesion to Fibres and Fabrics .............................................. 235

8.5 Summary............................................................................................ 238

vii

Contents

9 Rubber to Fabric Bonding ........................................................................... 241

9.1 Introduction ....................................................................................... 241

9.2 Adhesive Systems ............................................................................... 241

9.2.1 Aqueous Fabric Treatments ................................................... 241

9.2.2 Solvent-Based Adhesive Systems ............................................ 248

9.2.3 In Situ Bonding Systems......................................................... 249

9.3 Mechanisms of Adhesion ................................................................... 250

9.3.1 Dip/rubber Interface .............................................................. 250

9.3.2 Dip/textile Interface ............................................................... 252

9.4 Other Factors Affecting Adhesion ...................................................... 253

9.4.1 Storage of Treated Textiles ..................................................... 253

9.4.2 Adhesion in Service ................................................................ 254

9.5 Environmental Aspects ...................................................................... 254

9.5.1 Storage and Handling ............................................................ 254

9.5.2 In Process ............................................................................... 255

9.5.3 Wastes and Disposal .............................................................. 255

10 Bonding Rubber with Cyanoacrylates ......................................................... 259

10.1 Introduction ....................................................................................... 259

10.2 Liquid Cyanoacrylates ....................................................................... 259

10.3 Curing of Cyanoacrylates .................................................................. 260

10.3.1 Factors Affecting Cure ........................................................... 261

10.3.2 Cure Speed ............................................................................. 263

10.4 Types of Cyanoacrylate ...................................................................... 263

10.4.1 Bonding to Acidic and Porous Substrates............................... 264

10.4.2 Toughened Cyanoacrylates .................................................... 265

10.4.3 Flexible Cyanoacrylates ......................................................... 266

10.4.4 UV Curing Systems ................................................................ 266

10.5 Design Considerations ....................................................................... 266


viii

10.5.1 Minimise Peel and Deavage Loads .................................... 267

10.5.2 Bond Line Thickness ......................................................... 268

10.5.3 Special Requirements for Bonding with Cyanoacrylates .... 269

10.5.4 Internal and External Mould Release Agents .................... 269

10.5.5 Successful Joint Design ...................................................... 269

10.6 Bonding to Silicone Rubber ............................................................. 270

10.7 Environmental Resistance ............................................................... 270

10.7.1 Glass Bonding ................................................................... 272

10.7.2 Hot Strength ..................................................................... 272

10.8 Activators........................................................................................ 274

10.9 Application Methods for Cyanoacrylates ........................................ 275

10.9.1 Pressure/Time Systems ....................................................... 275

10.9.2 Syringe Systems ................................................................. 276

10.10 Health and Safety and Handling Precautions .................................. 276

10.11 Typical Applications........................................................................ 277

10.11.1 Bonding Nitrile, Polychloroprene and Natural Rubbers .... 277

10.11.2 Bonding EPDM ................................................................. 277

10.11.3 Bonding Santoprene and Silicone Rubbers ........................ 279

10.11.4 Bonding Medical Devices .................................................. 279

10.12 Troubleshooting .............................................................................. 280

10.12.1 Blooming of Cyanoacrylates ............................................. 280

11 Bonding Silicone Rubber to Various Substrate ............................................ 285

11.1 Introduction .................................................................................... 285

11.2 Why Bond Silicone Rubber?............................................................ 286

11.3 Material Combinations of Interest - Examples ................................ 287

11.3.1 Silicone to Silicone Bonding (Soft and Soft) ...................... 287

11.3.2 Silicone to Plastic Bonding (Soft and Hard) ...................... 288

11.3.3 Silicone to Metal Bonding (Soft and Hard) ....................... 288

11.3.4 Why Use Silicone Rubber for Such Composites? ............... 288

ix

Contents

11.4 Some Applications of Silicone Rubber Composites ......................... 290

11.5 Bonding Concepts ........................................................................... 291

11.5.1 Undercuts .......................................................................... 291

11.5.2 Primers .............................................................................. 292

11.5.3 Self-adhesive Silicone Rubbers .......................................... 292

11.5.4 The Build-up of Adhesion ................................................. 292

11.6 Bonding of Liquid Rubber (LR) ...................................................... 293

11.6.1 Properties of Self-adhesive LR ........................................... 297

11.6.2 Limitations of Self-adhesive LR......................................... 298

11.7 Bonding of Solid Rubber (HTV) ..................................................... 299

11.7.1 Self-adhesive HTV Silicone Rubber Applications .............. 299

11.7.2 Applications for Self-adhesive HTV .................................. 301

11.7.3 HTV Used in Other Bonding Applications ........................ 303

11.8 Processing Techniques ..................................................................... 303

11.8.1 Liquid Rubbers in Inserted Parts Technology .................... 303

11.8.2 LR in Two-component Injection Moulding Technology(Two Colour Mould) ......................................................... 306

11.9 Silicone to Silicone Bonding (Soft and Soft) .................................... 308

11.10 Cable Industry ................................................................................ 309

11.11 Duration of Bonding Properties ...................................................... 309

11.11.1 Duration of Bonding - Chemically Bonded Composites .... 311

11.12 Alternatives to Injection Moulding ................................................. 313

11.12.1 Adhesives .......................................................................... 313

11.12.2 Welding ............................................................................. 313

11.12.3 Mechanical Bonding Techniques After Moulding.............. 314

11.13 Summary ......................................................................................... 314

12 Failures in Rubber Bonding to Substrates ................................................... 319

12.1.1 Introduction ...................................................................... 319

12.1.2 Incorrect Moulding Procedures ......................................... 328


x

12.1.3 Incorrect Production Quality Testing Procedures .............. 329

12.1.4 Corrosion in Service .......................................................... 330

12.1.5 Product Abuse ................................................................... 333

12.1.6 Other Failure Modes ......................................................... 333

12.1.7 Factors Affecting Adhesion of Rubbers ............................. 334

12.1.8 Topography of Substrate ................................................... 335

12.1.9 Surface Conditions of Adherend ....................................... 335

12.1.10 Classification of Rubber According to their Wettabilities .. 336

12.1.11 Bonding - Interphase or Interface Considerations ............. 337

12.1.12 Problems in Adhesion........................................................ 339

12.2 Rubber Bonding in Power Transmission Belting ............................. 339

12.2.1 Introduction ...................................................................... 339

12.2.2 Power Transmission Belt Failure Modes ............................ 340

12.2.3 Adhesion Systems in Power Transmission Belts ................. 346

12.2.4 Adhesion Testing in Power Transmission Belts .................. 347

12.3 Undesirable Adhesion Occuring Under Service Conditions (Fixing) .. 349

12.3.1 Factors Affecting ‘Fixing’ .................................................. 349

12.3.2 Prevention of ‘Fixing’ ........................................................ 351

12.3.3 Other Methods of Preventing ‘Fixing’ -Examined Experimentally ................................................. 351

Abbreviations and Acronyms............................................................................. 357

Author Index ..................................................................................................... 363

Company Index ................................................................................................. 371

Main Index ........................................................................................................ 373

Contributors

Derek BrewisLoughborough University, Institute of Surface Science and Technology, Department ofPhysics, Loughborough, Leicestershire, LE11 3TU, UK.

Richard CostinThe Sartomer Company, 502 Thomas Jones Way, Exton, PA 19341, USA.

Bryan Crowther49 The Avenue, Bengeo, Hertford, Hertfordshire, SG14 3DS, UK.

Kenneth DalgarnoSchool of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT, UK.

Steve FultonOMG Limited, Ashton New Road, Clayton, Manchester, M11 4AT, UK.

Robert GossHenkel Loctite Adhesives Limited, Watchmead, Welwyn Garden City, Hertfordshire,AL7 1JB, UK.

Jim HalladayLord Corporation, Chemical Products Division, 2000 West Grandview Boulevard, POBox 10038, Erie, PA 16514-0038, USA.

Richard Holcroft5 Brooklands Drive, Birmingham, West Midlands, B14 6EJ, UK.

Peter JerschowWacker-Chemie GmbH, Johannes-Hess Strasse 24, D-84489 Burghausen, Germany.

Rani JosephDepartment of Polymer Science and Rubber Technology, Cochin University of Scienceand Technology, Cochin 682022, Kerala, India.

Mike RookeHenkel Loctite Adhesives Limited, Watchmead, Welwyn Garden City, Hertfordshire,AL7 1JB, UK.


Commercial rubbers

Berndt StadelmannWacker-Chemie GmbH, Johannes-Hess Strasse 24, D-84489 Burghausen, Germany.

Walter StrassbergerWacker-Chemie GmbH, Johannes-Hess Strasse 24, D-84489 Burghausen, Germany.

Wim van OoijDepartment of Chemical and Materials Engineering, University of Cincinnati, Cincinnati,OH 45221-0012, USA.

Patrick WarrenLord Corporation, Chemical Products Division, 2000 West Grandview Boulevard, POBox 10038, Erie, PA 16514-0038, USA.

Ron Woodcock5 Lower Leicester Road, Lutterworth, Leicester, LE17 4NF, UK.

David Wootton95 Greenhill Road, Bury, Lancashire, BL8 2LL, UK

Keith WorthingtonChemical Innovations Limited (CIL), 217 Walton Summit Centre, Bamber Bridge, Preston,PR5 8AL, UK.

1

Introduction

Although many volumes of information have been published about the subject of adhesionof materials in general, it is some forty years since a publication has been devoted solelyto the subject of the bonding of rubbers to various substrates. Three very successfulRapra Technology, conferences on the subject of the bonding of rubber have shown thatthere is clearly a need for such a publication to be devoted to this topic of wide industrialsignificance. Although from time to time manufacturers of bonding agent systems publishpapers in trade journals there is generally a dearth of available information for the factorypractitioner to consult. The subject matter for this present volume has been selected tocover a wide range of interests, both in terms of products and applications.

Rubbers in many applications need the support of, or reinforcement by, a variety ofmaterials ranging from fibres to metals. To ensure optimisation of the properties fromthese composites it is necessary to ensure that the optimum adhesion levels are achieved,both initially and to be maintained throughout the service life of the products. Rubbersare bonded to a variety of substrates in many products, in numerous applications, tomeet the needs of the modern world.

The Rubber Bonding Handbook draws together the expertise of a number of worldauthorities engaged in improving the bonded product to meet the ever increasing demandsplaced on composites and components manufactured from rubbers bonded to metals,fabrics, fibres and plastic substrates.

The papers included in this volume have been written by experts in their fields, many ofwhom have world-renowned reputations. Thus the information they include in theirchapters can be considered to be the most up-to-date, state-of-the-art discussions of theirrespective areas of research and knowledge.

The topics range from in depth discussions of such fundamental topics as the mechanismsof bonding of rubbers to brass, bonding techniques for adhesion to fabrics through tomethods of preparation of substrates and the development of bonding agent systems foradhesion to metals and plastic substrates. Bonding with silicone rubbers and cyanoacrylateadhesives for post vulcanisation bonding are also included. A section dealing withinformation related to adhesion, failure and other adhesion related topics such as ‘fixing’and practical reasons for a variety of bond failures, either during production or serviceare also covered.


2

Although there is some discussion of relevant theory in various sections of text, theemphasis in this volume has been to concentrate on the practicalities of bonding ofrubbers, to themselves and substrates. It is considered that this type of information is ofimmediate interest to the practising technologist dealing with shop floor problems on adaily basis.

It is hoped that the publication of definitive papers on the subject of adhesion of rubberswill be of considerable value to the practitioner in factories engaged in the previouslyseldom discussed variety of bonding applications being carried out by the rubber industry.

Because of the legislation now in progress of being implemented by the rubber industryto eliminate sources of environmentally hazardous chemicals, there is information onthe development and applications of waterborne bonding systems.

Acknowledgements

I would like to express my appreciation of the help and assistance given to me in theediting of this publication. To Claire Griffiths (Editorial Assistant), Sandra Hall fortypesetting, to Steve Barnfield for the cover design, Rebecca Dolbey for editorial adviceand particularly to Frances Powers (Commissioning Editor), for her support, patienceand guidance on general editorial matters.

Bryan Crowther

November 2000

3

1 Substrate Preparation Methods

B. Crowther (Section 1.1)D. Brewis (Section 1.2)K. Worthington (Section 1.3)R. Holcroft (Section 1.4)

1.1 Metal Preparation – General Techniques

1.1.1 Structure of Metal Substrates – Metallography

There is little written about the subject of metallography with respect to the bondingcharacteristics of the various metals used within the hot bonding process carried out bythe general goods, rubber to metal bonding profession. Some work has been carried outin the field of adhesives for aeronautical applications [1]. In general only a few of themetals or adhesives described for this type of bonding have much application in therubber to metal bonding factory, except perhaps if one is post vulcanisation bonding.The lack of fundamental metallography studies in the hot bonding of rubbers to metalsis mainly due, no doubt, to the lack of influence which the bonding technologist has inthese matters. He is usually told the grade of metal to be used and proceeds to find thebest way, according to current factory processes, equipment, practices and experience,to deal with the problem. He can of course discuss the nature of his problem with hisbonding agent supplier, who can in turn consult his research department if the problemis really abstruse. Perhaps a better understanding of metallography would enable thefactory technologist to choose the best way to pre-treat his customer-dictated metal forhis factory processes, or to discuss his customer’s ‘real’ metal requirements.

To understand some of the problems associated with the achievement of good rubber tometal bonds it is worth considering some of the scenarios involving the atomic structureof metals at their surfaces.

A metal, or an alloy of metals, naturally assumes a crystalline structure and it is likely thatit will have a regular shape and lattice structure, with some voids in the interstices. As withrubber compounds, metals are formed by mixing a number of components together whichdisperse relative to each other, but never, except maybe in the case of pure metals, becomeone totally uniform uninterrupted phase. Most metals are used as some type of alloy, i.e.,


4

Commercial rubbers

steel consists of iron mixed with carbon in varying proportions to produce the differentgrades of commercial product. Also minor proportions of other metals are added to givedifferent processing and end use characteristics to the steel, e.g., chromium, manganese,molybdenum, nickel, tungsten. The finishing processes of steels can also seriously alter theability of adhesive to bond to them, due to the altered surface microstructure.

With a pure metal its strength will depend on the size of the crystals making up its structure.In general small crystals make strong metals, whilst metals with large crystals, such as zinc,are weaker. The strength of a metal is also affected by the amount of impurity which maybe present, as the impurities tend to arrange themselves at the interfaces between the crystals,thus preventing perfect crystal contact.

In most metal alloys, as with rubber alloys or blends, the individual metals remain indiscrete, but dispersed domains within the metal alloy structure. In an alloy the metalcrystals involved, during cooling, have different shrinkage values and thus tend to moveapart, allowing either voids to occur or when chemically hardened, other metals to infiltrateinto these voids or interstices, at or near the surface. The individual crystals of the metalsduring cooling and shrinkage can join together to form chain structures, giving interlockingof the various metallic crystals. In some metal mixtures there is a mutual solubility and inthese cases all crystals of the metal are the same.

Although as a rubber to metal bonder one is not very interested in the metals structure withinthe mass of the metal, one must consider what is happening in and on its surface layers.

Most metals form oxide layers on their surfaces, some of which, like iron are porous andthus continual oxygen ingress enables the oxide layer continually to increase whilst inaerobic conditions. Other metals such as aluminium form a dense oxide film which doesnot permit oxygen ingress and thus protects the metal underneath from further oxidation.Both metals types are being oxidised, albeit at different rates and this oxidation can betermed as a form of corrosion. Although the rubber to metal bonder must take theprecautions necessary to prevent this type of corrosion continuing under his processingconditions, once the bonding agent has been applied, the condition at the metal interfacebecomes anaerobic and thus further oxidative corrosion is prevented (see Sections 12.1.2.2and 12.1.5).

There are a great variety and complexity of steel microstructures available to the componentspecifier, which complicate any cleaning procedure carried out prior to bonding. Incorrectchemical cleaning of low carbon and stainless steels, for example, can result in iron oxide‘smutting’ of the surface leaving a deposit difficult to remove entirely [1] during metalcleaning. These deposits may subsequently give an extremely weak bonding surface and,as a result a bonded product which fails easily under low working stresses in service.

5

Substrate Preparation Methods

However, as far the rubber to metal bonder is concerned he must avoid situations whichcan cause galvanic corrosion, a far more serious condition, which can propagate under thebonding system to cause eventual degradation of the bond and inevitable failure. Galvaniccorrosion [2] is caused by the formation of an electrolytic cell between the different metalcrystals within a structure in the presence of such agents as acids and salt water. Acids canbe generated from degeneration of compounding materials or cleaning and degreasingfluids (see also Section 12.1.4).

Certain metals are manufactured for their ability to prevent corrosion, e.g., stainless steel,and they contain chromium to enhance their corrosion resistance. If the level of chromiumused in the metal’s makeup is high, then the very tough layer of chromium oxide, whichforms on the metal’s surface as the anti-corrosion layer, is also exceedingly difficult tobond to rubbers. Wherever possible therefore stainless steels to be used in conjunctionwith bonding systems for rubbers should contain as low a chromium level as possible.

1.1.2 Bonding

The bonding mechanisms of the multiphase systems involved in making a rubber to metalcomponent are complex and the chemistry of the reactions involved not totally disclosedor understood. In the region of the metal contact the interactions are deemed to be acombination of mechanical and chemisorption processes. From the patent literature andsome of the more recent reviews of rubber to metal bonding [3, 4], it can be seen that theprimers contain a variety of halogenated rubbers and resins, which are known to have ahigh ability to wet out metal surfaces, thus ensuring the greatest degree of interface contact.In addition these rubbers and resins act as barriers to the migration of external corrosioncatalysts of the metal surface. The resins and rubbers probably form an interpenetratingnetwork of polymer chains within the adhesive system, thus giving strength and structureto the primer and rubber bonding coats.

Bond quality depends to a large extent on the ability of all interfaces to freely exchangechemical entities. Any contamination of surfaces will upset the surface chemistry at thatpoint and will reduce the bond strength.

1.1.3 Rubber Component with Metal Support

Engineering products for a wide range of applications are made by the use of rubbersbonded to metals during the vulcanisation of the rubber. The quality of bond achievedduring the manufacture of this type of component must be of sufficient integrity, notonly to be stronger than the rubber itself, but also to outlast the active life of therubber constituent of the components. To this end, the design of the component and


6

metal part must be carefully considered to ensure that no undue stress concentrationsare created in the area of the bond between the rubber and the metal. Componentsconsisting of moulded rubber bonded to metal, carried out during high temperaturevulcanisation, can have inherent stresses simply due to shrinkage of the rubber whencooling from the vulcanisation temperature and the coefficient of thermal expansionrelationship of the rubber/metal combination. The ‘shrinkage’ of the rubber in thesystem will be different for each type of rubber being used and is dependent also uponthe compound hardness, or degree of filler present. Allowances for the rubber shrinkagemust be made in determining the shape of the mould cavity and hence the component’sfinal shape.

The environment in which the component is to work will also affect the stresses towhich the rubber-metal bond will be subjected. Some oil and solvent environmentswill penetrate a bond at the interface and thus may weaken or destroy the integrity ofthe bond until the stress becomes relieved by failure.

Corrosion of the metal component of the bonded unit by salt environments can also bea major problem and thus due concern and allowance must be made for the serviceconditions in which the rubber to metal component will be resident. Corrosion of thebonded metal under the bonding system can also occur if the metal pre-preparation iscarried out with acidic degreasing fluids. Care must be taken that degreasing fluids areand remain, neutral in pH throughout their use in the application. Recovery of usedsolvents and redistillation can significantly change the pH of a solvent. This can be aparticular problem with chlorinated solvents, where after redistillation the distillatecan be acidic in nature.

To effect good long-lasting bonds between rubber and metals it is essential that bothmaterials presented to the interface be clean and free from detritus. The presence ofoils and the possibility that compounding ingredients can exude or bloom from therubber surface, before or after moulding, or during the service life of the componentmust also be taken into consideration and remedied.

1.1.4 Metal Pre-treatments

Metals must be suitably pre-treated for satisfactory bonds to be achieved with rubbers.Two basic methods of preparation are used:

• Mechanical,

• Chemical.

7

1.1.4.1 Mechanical Methods

Metals, especially the more common iron and steel types, come from the foundry andmetal plate stamping shop, coated with oil, grease and most often with a generous layerof oxide and rolling mill scale formed on the exposed surfaces. Oxide films can alsodevelop further during storage prior to use by the bonding shop. All these materials mustbe removed from the surfaces and from the voids in the metal, to ensure that the oils andgreases which otherwise may be trapped unseen cannot exude under the increasedtemperature of vulcanisation, when they become more mobile or volatile. Surface oxidesmust be removed for they are often only loosely structured in their attachment at themetal substrate and will rupture and detach themselves under duress, causing the metal/adhesive bond to fail. Once the original oxide layer has been removed, the freshly exposedmetal will immediately start to build a new oxide film which must be minimised by rapiddegreasing and application of primer/adhesive coat.

• Initial degreasing

Metals must be degreased as the first step in any metal preparation process, otherwise oiland grease contamination of blasting media, chemical treatments and machinery canresult in severe factory quality problems and unreliable and variable bonding.

Traditionally the most usual method of grease and oil removal from the metal surfacehas been by degreasing in the vapour of a chlorinated solvent such as trichloroethyleneor 1,1,1-trichloroethane or perchloroethylene. The chlorinated solvent used must have aneutral pH, otherwise the acidic condition can cause the initiation of underbond corrosion.Re-distilled chlorinated solvents, especially if recovery is carried out in-house, must beadequately checked for neutrality. The metal parts must dwell in the solvent vapour untilsuch time as the metal reaches the temperature of the vapour and condensation hasceased. The solvent will have had the best opportunity to work at its most efficient ingrease removal under these conditions. Direct contact with the degreasing solvent is notan efficient way of removing greases from metal surfaces, always leaving a molecularlayer at least, still lying on the ‘cleaned’ surface. This cleaning method should not beused for metals to be used in bonding.

All air lines in the bonding shop must have oil/water filters connected to them to removethe possibility of oil/water emulsion being sprayed onto the metal surfaces before, afteror during bonding agent application. Air compressors are notorious for allowing oilseepage into the pressure vessel, together with an amount of water, which then usuallycauses an oil/water emulsion to be formed. This emulsion in contact with cleaned metalsurfaces will give corrosion or reduce bond formation to a minimum level through thedeposit of a film of oil.



8

The current legislation trend and environmental pressure for the industry is to movetowards the use of alternative means of removal of contaminants from the metal surfaces(see Section 1.4). Equipment is available which uses water and detergents to removethese oils and thus present a more environmentally favourable working atmosphere.The action of the detergent can be supplemented by the use of ultrasonic agitation toremove oxide flakes. These systems being water-based require efficient drying of themetals, especially in the areas between contacting metals, otherwise further oxidationof the cleaned metal will rapidly take place. Careful choice of the detergent is alsonecessary otherwise its residues can detract from the bond strength achievable. Thewater quality being used in the degreasing system final wash process will have to bedetermined to prevent deposit of any salts or metallic ions. The ideal final wash is withde-ionised water.

Alternative solvents, if used in a vapour degreasing system must have a similar evaporationrate to that of the presently used chlorinated solvents. Otherwise too rapid evaporationof the condensed solvent on withdrawal of the metals from the solvent vapour will resultin rapid surface cooling of the metal, with resultant condensation of water, especially inconditions of high humidity.

• Alkaline removal of oils and greases

An alternative method of removal of the metal preparation oils and greases is to usean alkaline cleaning method. The alkaline solution is used either in dip tanks ortumbler spray units (see Section 4.1). The strength of alkaline, the temperature usedand the necessary dwell time in the solution to remove the amount of greaseencountered will be determined in individual factories. The length of time requiredfor oil and grease removal can be anything up to two hours. The alkaline tanks haveto be followed by water rinse tanks to remove the alkaline dip from the metals,followed by drying.

• Solvent dip methods for large scale removal of greases

Solvent dip methods are generally expensive to run and do not usually, unless a numberof dip tanks are used, completely remove oils and greases from the metal surfaces.Contaminants are easily carried from tank to tank and it is difficult to ascertain whetherthe metal surface is completely cleaned after its passage through the tank series. Thismethod would not normally be used for anything other than small scale operations. Fastdrying solvents such as methylene chloride and acetone evaporate so quickly that theylower the temperature of the metal surface and water condenses.

9

• Removal of surface oxides

Metals, after degreasing, have to be blasted with a sufficiently abrasive material toremove the surface oxidation layer. The usual medium used for ferrous substrates issteel or chilled-iron grit to BS EN ISO 11124-4 grades G12 to G24 [5] (see also Section4.2.2). Alumina or other non-ferrous grits such as quartz sand and carborundum maybe used on ferrous metals, but their use on non-ferrous metals is essential to preventthe possible formation of galvanic cells. Initially impingement of the metal surfacewith abrasive grit has the effect of gouging the surface of the steel to give a largersurface area for bonding, but with use the grit wears and its efficiency decreases. Thetype of grit used must be coupled to the type of metal being treated. Incorrect grit/metal combinations can lead to formation of galvanic cells remaining on the surface ofthe blasted metals and the commencement of underbond corrosion. Grits larger thanabout 30-50 mesh diameter soon lose their irregularities and grittiness, effectively turninginto shot at which stage they must be discarded. The hardness of the steel grits shouldbe a Rockwell C hardness of 60 – 65.

Iron or steel shot should not be used as these tend to give cavitation of the blastedmetal surfaces, followed by peaning over of the sharp metal pinnacles, often trappingloose shot, blasted material, etc., in the peaned over cavities. These cavitations andtheir contents cause weaknesses and possible underbond corrosion sites, resulting inultimate failure in service.

The service life of the blasting media should be established for efficiency and quality ofsurface finish. Grit in use should be cleaned of dust resulting from removed oxide scale andits own degradation products and be downgraded or discarded if it becomes too worn.

Revolving drum blast machines give the best production efficiency for metals which arestout enough to resist damage from the tumbling action involved. The metal parts aretumbled on a rubber belt inside a revolving drum whilst being bombarded with theabrasive medium.

Once the metal surface has been adequately cleaned of oxide contamination, dusted offand once more degreased, it is vital that the application of a bonding agent primer coatbe carried out as quickly as possible to ensure that the re-oxidation of the metal surfaceis kept to a minimum. Ambient temperature, humidity and dust must all be controlled ifthe optimum bond strength is to be achieved. To consistently ensure optimum bondquality, metal components, whether unprimed or primed, should be kept in enclosedcabinets. At no time should cleaned and degreased metals be handled with bare hands.Human skin, however clean it may appear, always carries a surface layer of oils and fats,which are bond killers. Neither should metals, whether in the ‘just cleaned’ state, or



10

treated with bonding agent, be handled with ‘press gloves’. Press gloves are usually heavilycontaminated with a variety of materials, from oil, to mould release agents and sweat.Clean, frequently discarded cotton gloves are the best protection for handling metals.They should not be allowed to become dirty and sweat ridden.

1.1.4.2 Chemical Methods

The alternative metal pre-treatment processes to grit blasting use a variety of differentchemical routes. It is sufficient to say here that these can be very efficient, but do occupyrather large factory floor areas and can, if not controlled correctly give variable qualityof prepared surface. The usual chemical pre-treatment systems consist of acid etching ofthe surface followed by several water dips and subsequent phosphate or in somecircumstances cadmium plating and passivating (render inert). Many of these treatmentswill have been carried out by the metal processor and are not the rubber bonder’s processes.

• Treatments for stainless steels (see also Section 3.3)

There are various systems for the pre-treatment of stainless steels which consist of treatingthe metal surface with strong acids to attack crystal grain boundaries in the alloys andchromium poor regions around chromium carbide particles. All the methods give surfaceroughness to the stainless steel which enhances the bond to the adhesive. Mixtures ofnitric, hydrofluoric, sulphuric or chromic acid are suggested as most suitable. However,the nature of the substrate alloy and the heat treatment experienced all have a bearing onthe bondability of the metal.

• Phosphate coating (see also Sections 1.2, 3.3 and 4.2.5)

Steel is often phosphate coated for use within the engineering and decorative laminateindustries to reduce corrosion. Iron or zinc phosphate can be used. However, althoughused for some years as a corrosion protection technique for rubber to steel bonding, it canbe difficult to control the process, with a resultant variable thickness of phosphate depositof varying crystalline structure. If too thick a phosphate layer is obtained it becomes toofriable and lacking in the cohesive integrity required to maintain a rubber to metal bondunder load during service. If only a moderate phosphate coat is produced it is often necessaryto ‘passivate’ the areas of steel, only minimally covered or lacking in a coating of phosphate,by treating with chromic acid to form chromium oxide to prevent corrosion. However,chromium oxide does not readily react with a bonding agent (see Section 3.1). Chromicacid is a restricted material and alternative materials can be recommended by bondingagent suppliers for the passivation or sealing of the phosphate coating.

11

The nature of the phosphate deposited on the surface of the steel depends to a largeextent upon the nature of the microstructure of the steels and the orientation of itsunderlying crystal lattice. Hardened steels having a martensite structured surface(consisting of interlacing rectilinear fibrous elements arranged in a triangular shape)support a fine flake phosphate structure. Cold-rolled steel can, having acquired a differentsurface orientation structure during the rolling process, acquire a lumpy large flakephosphate structure, which is easily broken apart under service stress.

Any water going to drain from these processes is a potential pollution hazard and mustbe tested for zinc content, as this is a hazardous material. Any zinc present must beremoved or limited to 1 – 2 parts per million.

• Zinc coating or galvanising

To be effective the zinc coating must be hot dipped onto the freshly cleaned metal, togive a ‘galvanised’ finish. Bonding to this finish is not easy, but sometimes demanded bythe component specifier. The crystalline structure of the galvanised zinc and its dippedcoating thickness, can result in the flaking off, under stress, of some of the coating,resulting in bond failure (see also Section 1.1.1). The recommended treatment [6] forcleaning a galvanised finish is

a) degrease metal part

b) abrade the galvanised surface with grit

c) degrease then apply adhesive as soon as possible

or

a) immerse in a solution of 20 parts by weight concentrated hydrochloric acid with80 parts by weight de-ionised water, for 2 – 4 minutes at 25 °C

b) rinse thoroughly in cold, running de-ionised water

c) dry for 20 – 30 minutes in 70 °C oven

d) apply adhesive as soon as possible

The second method of zinc coating is more widely used.

• Zinc sheradising

A method used to give what is in effect a fused zinc surface to a steel component can bespecified which gives very good environmental protection for the steel component.



12

The steel part to be bonded is baked whilst being tumbled in zinc dust. The process is notgenerally suitable for delicate metal parts and causes problems with zinc build-up inscrew threaded components (the latter must be protected by a sleeve or require a dierunning down the thread to clear it). After treatment exposed zinc surfaces do of courseoxidise if stored incorrectly, but this is not usually a problem. The oxide forms after bothmethods of zinc coating.

• Aluminium - anodising

Aluminium is usually electrolytically anodised, in the presence of an acid, either sulphuric,chromic or phosphoric, to give a tough resistant oxide film, which usually forms good bondswith the usual bonding systems. The anodising must be carried out with care and with amind to the type of crystalline structure being formed on the aluminium surface. A uniformreticulated structure is desired, not a microscopically fragmented rippled surface, sometimescalled ‘ice flows’ [7], which are unstable, easily fractured, and therefore too unstable tomaintain good adhesive quality. If anodising is to be carried out by a custom plater he willneed to be informed of the type of anodised structure desired.

N.B. The final stages of any ‘wet’ metal preparation process for metals to be bonded torubber is to ensure that all chemicals used in the processes have been removed in the finalwater rinse tank, and then to ensure that all faces of the metal parts are fully dried prior tobonding agent application. All warehouse metal storage areas must be held at least 5 – 10 °Cabove the dew-point and ideally as near to ambient temperature in the bonding agentapplication shop which should be in the region of 18 – 22 °C minimum.

• Metal preparation - for waterborne bonding systems

Although the general principles used for solvent-based adhesives apply, the cleaning of metalsfor the application of waterborne bonding systems becomes much more critical. Scrupulouslyclean metals are vital, to ensure maximum wettability of the prepared metal bonding surface.Lord Corporation [8] suggest that calcium modified phosphating of metals is preferable toconventional grit blasting with its potential for ‘re-infecting’ the metal surface after initialdegreasing by using contaminated grit. Proper housekeeping should eliminate such problems.

1.2 Pre-treatments of Plastics and Rubbers

1.2.1 Introduction

In many cases, rubbers are joined to other materials during the process of vulcanisation.However, in other cases, rubbers are joined to other materials after vulcanisation. With this

13

second group, it is often necessary to pre-treat the rubbers before bonding. Pre-treatmentsrange from physical methods such as a solvent wipe or abrasion to chemical methodssuch as treatment with trichloroisocyanuric acid (TCICA). Physical methods may removecohesively weak layers from the polymer. This is essential to good bonding unless theselayers can be absorbed by the adhesive. However, physical methods will only be effectiveif the underlying rubber possesses suitable groups which can interact strongly with theadhesive. Chemical methods may also remove weak layers or chemically modify them sothat they are more compatible with the adhesive; in addition chemical methods mayroughen a surface. However, an effective chemical method will also modify the chemistryof the rubber so that the interaction with the adhesive is increased.

In general, rubbers contain a greater variety and quantity of additives than plastics;fifteen components in a particular formulation is quite common. These additives orcompounding ingredients as they are often called, may well create a cohesively weaklayer on the rubber surface. On the other hand, plastics usually contain a small numberof additives and usually in relatively low concentration.

Over the last 50 years many methods have been developed to pre-treat plastics andrubbers. Partly because of the much simpler formulations, pre-treatments for plasticshave been the subject of much greater scientific interest. Our understanding of pre-treatments for plastics is therefore much greater than that for rubbers. Some of the keystudies on pre-treatments of plastics will therefore be outlined in Section 1.2.2.

Pre-treatments for rubbers have been developed on an empirical basis but some scientificstudies of successful pre-treatments have been undertaken. Methods for different rubberswill be reviewed in Section 1.2.3. Rubbers will be considered in groups, namelyhydrocarbons that possess little unsaturation, unsaturated hydrocarbons, halogenatedrubbers and miscellaneous materials.

1.2.2 Studies of Pre-treatments for Plastics

These studies may seem out of context in a book concerned with bonding of rubber butthe great deal of work carried out with plastics can be used to understand the problemsof rubbers.

Some of the most important pre-treatments for plastics were developed in the 1950s.These include the corona and flame treatments for polyolefins [9, 10, 11, 12, 13] and theuse of sodium complexes for fluorinated polymers [14 – 17]. The plasma treatment wasdeveloped somewhat later [18, 19], as was halogenation [20, 21].

It was suspected that these treatments were chemically modifying the surfaces of the plasticsbut there was little direct evidence as the analytical methods available at the time were not



14

sufficiently surface-sensitive. However, in the 1970s a new method for studying surfacechemistry became available, namely X-ray photoelectron spectroscopy (XPS) which is alsoknown as electron spectroscopy for chemical analysis (ESCA). This method is able tocharacterise and quantify the chemical changes caused by pre-treatments. XPS analyses thefirst few atomic layers of a material. This is important as some pre-treatments only modify afew nanometers of a polymer. Reflection infrared techniques in the 1970s were often unableto detect changes to the surface chemistry of polymers caused by the pre-treatments.

Three of the earliest pre-treatment studies were by Dwight [15], Collins [22] and Briggs[23]. Dwight treated polytetrafluoroethylene (PTFE) and fluorinated ethylene-propylenecopolymer (FEP) with sodium in liquid ammonia and sodium naphthalenide intetrahydrofuran (THF). X-ray photoelectron spectroscopy showed extensivedefluorination of the polymers together with formation of carbon–carbon double bondsand various oxygen-containing groups. Collins treated PTFE with ammonia and airplasmas. Again, XPS showed extensive defluorination and in the case of the ammoniaplasma, nitrogen containing groups were introduced. Briggs [23] was the first to quantifythe chemical modification caused by a pre-treatment. Briggs studied the changes causedby chromic acid etching of low density polyethylene and polypropylene. Some of theresults are given in Table 1.1. Angular variation studies, i.e., the angle of incidence of theX-ray beam was varied, showed that in the case of polypropylene, the depth of thechemically modified layer was only a few nanometers.

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A given pre-treatment may result in the introduction of several different chemicalgroups. There are two methods by which these groups may be quantified and bothinvolve XPS. The first method involves derivatisation reactions and the second methodthe use of high resolution spectra. The basic idea behind the derivatisation method isto use several reagents each of which will react with only one of the groups introducedby the pre-treatment. There are two other requirements. Each reagent should introducean atom, e.g., fluorine, that is not already present in the surface and each reactionshould proceed to 100% conversion. The method is illustrated by the work of Gerenser[24] where some corona treated polyethylene was derivatised. The reagents andderivatisation reactions are shown in Figure 1.1 and the results of the experimentsare shown in Table 1.2.


Figure 1.1 Derivatisation reactions to identify functional groups introduced by pre-treatments; a) peroxide groups reacting with sulphur dioxide, b) alcohol group

reacting with hexafluoroacetic anhydride, c) carbonyl group reacting with hydrazine,d) epoxide group reacting with hydrogen chloride, e) carboxylic acid group reacting

with tertiary amine.

(Reprinted from L. J. Gerenser, J. F. Elman, M. G. Mason and J. M. Pochan, Polymer,1985, 26, 8, 1162. ©1985, with permission from Elsevier Science)


16

The second method to quantify the chemical groups introduced by a pre-treatment involvesobtaining a high resolution spectrum of the photoelectrons from the C1s core level andresolving this into the various contributions. This approach is illustrated by Beamson[25] who examined a rubber-modified polypropylene which had been subjected to acorona discharge treatment. The high resolution C1s spectrum is given in Figure 1.2 and

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17

Substrate Preparation MethodsCorona treatment after derivatisation

the information on the groups introduced is given in Table 1.3. This method is muchquicker than the derivatisation approach but requires an instrument with very goodenergy resolution and great care in attribution of the various peaks.

Figure 1.2 High resolution C1s spectrum of corona treated polypropylene [25]

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18

Strobel [12] compared the effectiveness of various gas-phase reactions for polypropylene,by determining how much oxygen was introduced into the polymer surface (the O:Catomic ratio) in a given time. These results are summarised in Table 1.4.

It can be seen that to achieve a given level of chemical modification, flame, corona andplasma require much shorter treatment times than ozone or UV or a combination of UVplus ozone.

The pre-treatments described above represent just a few of the many studies relating tothe mechanisms of pre-treatments for plastics. However, it is clear that much is knownabout pre-treatments of plastics relating to:

• Quantification of the chemical changes caused by pre-treatments,

• The depth of the chemical modification,

• Identification and quantification of chemical groups,

• The rate of chemical modification.

In contrast, much less work has been done relating to the mechanisms of pre-treatmentsfor rubbers.

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Surface analysis

1.2.3 Hydrocarbon Rubbers with Little or No Unsaturation

1.2.3.1 Ethylene-Propylene Rubbers

Ethylene-propylene rubbers (EP) have low total surface energies with small polarcomponents. As would be expected, the adhesion of paints and adhesives to untreatedEP is poor. To achieve good adhesion to EP, the introduction of suitable functional groupsis necessary unless a diffusion mechanism can operate. Bragole [26] found that UVtreatment of EPDM coated with a thin layer of benzophenone resulted in large increasesin the adhesion of acrylic, epoxy and urethane paints to the polymer.

Ellul [27] subjected EPDM/polypropylene and natural rubber/polypropylene blends tovarious halogenation treatments, namely fluorine/carbon dioxide, sodium hypochlorite/acetic acid and bromine water. With the natural rubber blend, there was a substantialuptake of fluorine, chlorine and bromine in the surface regions as indicated by energydispersive X-ray analysis and with all three pre-treatments the adhesion to an acrylic tapewas greatly enhanced. In contrast, with the EPDM blend, fluorine was the only reagentwhich reacted with the rubbers and only this treatment resulted in a significant increase inadhesion to the acrylic tape. The above results can be explained in terms of the differentconcentrations of carbon–carbon double bonds in the two blends. Substantial incorporationof chlorine and bromine could occur with the natural rubber-polypropylene blend but notwith the EPDM blend. However, fluorine gas will react readily with saturated hydrocarbons[28, 29] and therefore the incorporation of fluorine into the EPDM blend is not surprising.

Lawson [30] using X-ray photoelectron spectroscopy (XPS) found that trichloroisocyanuricacid (TCICA) in ethyl acetate did not chemically modify EPDM.

Lawson [31] also found that a corona treatment improved the wettability of EPDM asindicated by glycerol contact angles and the use of a series of formamide/2-ethoxyethanolmixtures (ASTM D2578 [32]). However, the contact angles increased significantly overa period of one hour, indicating molecular rearrangement with the polar groups introducedby the pre-treatment tending to move to the bulk of the rubber. No improvement in apeel test involving a polyurethane coating was observed.

Minagawa [33] treated an EP rubber with UV and sputter etching. Large increases inadhesion were reported. However, the treatment times were long, being 10 minutes forion etching and one hour for the UV treatment. Scanning electron microscopy (SEM)indicated the two methods caused considerable roughening of the surface. XPS and Fouriertransform infrared analysis (FTIR) indicated the introduction of substantial quantitiesof oxygen-containing functional groups. Kondyurin [34] noted only modest improvements,at best, after treating EPDM with UV, despite clear infrared evidence for the formationof hydroxyl and carbonyl groups after treatment.


20

1.2.3.2 Butyl Rubber

Butyl rubber consists of ≥95% of isobutylene units with a small quantity of isoprene whichpermits crosslinking via sulphur vulcanisation. Butyl rubber has a low surface energy andin addition organic components with a low cohesive strength may exist on the surface. Inone study [35] butyl rubber was subjected to several treatments which normally causesubstantial chemical modification to polymer surfaces. The treatments included chromicacid etching, corona discharges, flames, bromination, UV radiation and potassiumpermanganate. Most of the treatments had little effect on the adhesion to an epoxide. Itwas concluded that much chain scission occurred with the result that suitable functionalgroups were not introduced in sufficient quantity into long polymer chains. Such chemicalmodification is necessary for good adhesion unless a diffusion mechanism is operating.

1.2.4 Unsaturated Hydrocarbon Rubbers

1.2.4.1 Natural Rubber

Natural rubber (NR), being essentially a hydrocarbon, has a low surface energy. Some ofthe components in a formulated rubber, such as zinc oxide and carbon black, maysubstantially increase the surface energy, whereas organic additives such as extender oiland antioxidants may migrate to the surface and create a potentially weak boundary layer.

Pettit and Carter [36] found that chlorine gas, acidic sodium hypochlorite and an organicchlorine donor in a organic solvent all much improved the peel strengths of joints involvingNR and a polyurethane adhesive. Oldfield and Symes [37, 38] found that aqueous ororganic-based chlorination gave much higher joint strengths than a solvent-wipe, abrasionor cyclisation (see Table 1.5).

Oldfield and Symes used X-ray fluorescence, infrared analysis and contact anglemeasurement to study the TCICA treatment. X-ray fluorescence showed the amount ofchlorine introduced into the polymer increased with the TCICA concentration; with a3% TCICA solution, they estimated the chlorine content in the treated NR was 16.7%w/w. Reflection infrared analysis indicated that chlorine substituted at the allylic positionin the polymer backbone. Substantial improvements in wettability were achieved especiallyif the concentration of TCICA was at least 0.8%.

Lawson [30] pre-treated various rubbers, including NR, with a 3% w/v solution of TCICAin ethyl acetate and used XPS to study the chemical changes caused by the pre-treatment.In agreement with Oldfield, they concluded that the chemical modification was mainlysubstitution rather than addition at the carbon–carbon double bond.

21

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Peel strengths

Extrand [39] treated NR surfaces in an acidified sodium hypochlorite solution and usedcontact angle measurements and reflection FTIR to study the changes caused by thechlorination. They studied ‘pure’ NR, a peroxide cured formulation and a conventionallycured formulation. Contact angles of glycerol on the rubber surfaces reduced afterchlorination as shown in Table 1.6.

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22

With regard to the infrared study, bands at 660, 750 and 1260 cm-1 were assigned to theeffects of chlorination. In addition, bands at 780, 916 and 1410 cm-1 were almost certainlydue to chlorination.

Kusano [40] found that neither corona nor plasma treatments improved peel strengthwith a polyurethane adhesive despite improved wettability as indicated by water contactangles. FTIR indicated substantial oxidation after the corona treatment but only minoroxidation after the plasma treatment.

1.2.4.2 Styrene-Butadiene Copolymers

Styrene-butadiene rubber has a low surface energy, but this may be considerably increasedby the incorporation of various components. Organic additives such as antioxidants willtend to migrate to the surface thus creating a potential weak boundary layer.

Pettit [36] found that treatment of SBR with chlorine gas, acidified sodium hypochloriteor an organic chlorine donor in an organic solvent resulted in large increases in peelstrength for SBR-polyurethane-SBR joints.

Oldfield [37] found that physical treatments were inferior to three chemical pre-treatments(see Table 1.7).

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23

Using X-ray fluorescence, they estimated the chlorine concentration in the first few micronsof the SBR after treatment with TCICA at various concentrations. With a 3% solution,the resulting chlorine concentration was 16.1% w/w.

Pastor-Blas [41] found that physical treatments such as abrasion did not result in significantincreases in the peel strengths obtained with a polyurethane adhesive. On the other hand,treatment with TCICA in ethyl acetate resulted in large increases in peel strength.

On the basis of the relative amounts of chlorine and nitrogen introduced into SBR,Lawson [30] concluded that both substitution and addition reactions were significantwhen this rubber was treated with TCICA in ethyl acetate. Similar results were obtainedwith polybutadiene.

Pastor-Blas [42] studied the effect of TCICA concentration in ethyl acetate. For solutions upto 2% w/w mainly chlorinated hydrocarbon and C–O species were reported. At between 2and 5% w/w an excess of unreacted TCICA was indicated while above 5% w/w there was adetrimental effect on adhesion due to a weak boundary layer consisting of isocyanuric acid.

Pastor-Blas [43] treated an SBR formulation with TCICA solutions in ethyl acetate havingconcentrations ranging from 0.5 – 7% by weight. The chemical changes caused by thepre-treatments are shown in Table 1.8.

Rubber strips were bonded with a solvent-based polyurethane (PU) and the joint strengthsdetermined in a T-peel test. After peeling, the test pieces were examined using a varietyof techniques; XPS and FTIR confirmed that the treatment introduced various chemicalgroups. The peel strengths were obtained after treatments with 0.5, 2 and 7% w/w. Thehighest peel strength was obtained with the 2% solution.


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24

In a related publication, treatments with fumaric acid in a butan-2-ol/ethanol mixtureand TCICA in butan-2-ol were compared [44]. In general, the TCICA was more effectiveat enhancing the peel strength achieved with a solvent-based PU adhesive. Infrared analysisindicated the treatments were probably effective by removing zinc stearate (reduction inpeak at 1540 cm-1) and the introduction of carbon-oxide functionalities (1704 cm-1 and1670 cm-1 for the TCICA and fumaric acid, respectively). With TCICA, C–Cl bondswere also observed.

Pastor-Sempere [45] treated two styrene-butadiene rubbers with fumaric acid in a butan-2-ol/ethanol mixture. This resulted in improved adhesion in both cases, but theimprovement with one formulation was significantly greater than the other. The lowerpeel strength was attributed to the presence of paraffin wax and zinc stearate. Rougheningprior to treatment with fumaric acid resulted in additional improvements with bothrubbers. Infrared analysis indicated that the fumaric acid was effective by introducingC=O bonds and by reducing the concentration of zinc stearate. In addition, the fumaricacid caused a roughening of both rubbers.

Later Pastor-Blas [46] demonstrated that high concentrations of TCICA could lead tothe formation of weak boundary layers. Treatment of two SBR materials with a 7 wt%solution of TCICA in ethyl acetate resulted in poor peel strengths unless the treatedsurfaces were vacuum dried for one hour at 1.34 Pa.

Other methods have been shown to considerably improve the bondability of SBR materials.Aqueous solutions of an organic chlorine donor or the use of an electrochemical methodresulted in large increases in peel strength with a water-based PU adhesive [47]. Kusano[40] found that corona and plasma treatments resulted in large increases in peel strengthwith a PU adhesive. Lawson [31] reported that a 10 second corona treatment improvedthe water wettability of an SBR. He also reported cracking of the rubber which he ascribedto the ozone generated in the discharge.

Styrene-butadiene block copolymers SBS thermoplastic rubbers have a low surface energy.Therefore, to achieve good adhesion to SBS a chemical pre-treatment may be necessary.A complicating factor is that migratory organic additives may lead to a weak layer. Pettit[36] found that treatment of SBS with chlorine gas, acidified sodium hypochlorite or anorganic donor in an organic solvent resulted in large increases in peel strength with apolyurethane adhesive.

As with SBR, aqueous solutions of an organic chlorine donor and an electrochemicalmethod were also effective with SBS [47].

Pastor-Blas [48] treated SBS with TCICA solutions (0.5, 2 or 7 wt%) in ethyl acetate. TheSBS was bonded with a PU and the joint strengths determined in a T-peel test. The failedsurfaces, after peeling, were examined by a variety of techniques including XPS and FTIR.

25

It was concluded that the highest strength (3.3 N mm-1) was obtained with the 0.5%solution. It was concluded that the stronger solutions weakened the surface regions. FTIRand XPS showed that the treatment introduced chlorine and oxygen functionalities.

1.2.5 Halogenated Rubbers

Introduction of bromine and chlorine atoms in hydrocarbon polymers will enhanceadhesion. In the case of PE, introduction of bromine to a Br:C ratio of 0.05:1 resulted inhigh adhesion to an epoxide adhesive [49]. However, the quantity of halogen in bromo-and chloro-butyl rubbers is low and poor adhesion to these polymers is not unexpectedespecially if organic additives are present on the surfaces. Oldfield [37] only obtainedmodest adhesion to untreated bromobutyl rubber (see Table 1.9). Of the treatments theyinvestigated only TCICA in ethyl acetate resulted in very high peel strengths, althoughaqueous chlorination gave a substantial improvement.

Using X-ray fluorescence, Oldfield and Symes found that the uptake of chlorine intobromobutyl rubber was very much less than that observed with NR, SBR and nitrilerubber, as would be expected from the relative number of carbon–carbon double bondsusing XPS. Lawson [30] found chlorobutyl rubber did not take up any measurable amountof chlorine in treatment with TCICA in ethyl acetate. The reason for the large improvementin bondability with bromobutyl observed by Oldfield is unclear. It may be that the TCICAwas acting as an oxidising agent rather than a chlorinating agent. However, Lawson didnot observe any introduction of oxygen-containing groups with chlorobutyl rubber.


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Polychloroprene (CR) has much more chlorine than the chlorobutyl rubber examined byLawson and good adhesion to untreated CR would be expected provided there was noweak layer was on the surface. If such layers exist a suitable solvent treatment or abrasionshould result in good adhesion. Cyclisation has been recommended as a pre-treatment[50, 51]. Lawson noted a large uptake of chlorine, nitrogen and oxygen on treatment ofpolychloroprene with TCICA, indicating addition across the carbon–carbon double bond.

Lawson [31] reported that a corona discharge treatment of CR increased its surfaceenergy, but did not improve the peel strength with a polyurethane coating. Minagawa[32] reported large increases in adhesion with CR after UV irradiation or sputter ionetching. However, the treatment times were long, being 10 minutes with ion sputteringand one hour with the UV treatment. SEM indicates that the two methods causedconsiderable roughening of the surface. XPS and FTIR indicated the introduction ofsubstantial quantities of oxygen-containing groups.

1.2.6 Miscellaneous Rubbers

1.2.6.1 Silicone Rubber (see also Chapter 12)

Adhesion to untreated silicone rubber is difficult. The poor adhesion may be due to alow surface energy (approximately 24 mJ m-2) or a layer of low cohesive strength or acombination of these two factors. Plasma treatment has been shown to substantiallyimprove the wettability of silicone rubber [50-57]. Peel strengths were measured in onestudy and found to be much increased by plasma treatment [53]. Swanson [58] foundthat coating a silicone rubber with photoactive reagents and then exposing the surface toUV resulted in a large increase in joint strengths obtained with a cyanoacrylate adhesive.

Combette [59] reported that microwave or radio frequency plasma treatment of siliconerubber with a gas rich in oxygen gave high peel strengths with an epoxide adhesive.

1.2.6.2 Nitrile Rubber

Nitrile rubber is moderately polar and good adhesion would be expected between apolar adhesive like an epoxide and the untreated polymer provided no weak boundarylayers were present. This was found to be the case by Oldfield [37] as can be seen inTable 1.10. High adhesion values were obtained with a solvent wipe.

Cyclisation and TCICA treatments resulted in large increases in adhesion. X-rayfluorescence indicated substantial uptake of chlorine in the latter case [37].

Peel strengths

27

1.2.6.3 Polyurethanes

Polyurethanes (PU) have relatively high surface energies. Adhesion problems with PUsubstrates are, therefore, likely to be due to cohesively weak material, such as mouldrelease agents on the surface. Abrasion is one of the main methods recommended as apre-treatment [50]; such a pre-treatment can remove cohesively weak material and exposestrong material of relatively high surface energy. Cryoblasting, in which carbon dioxideparticles are fired at a substrate, has been shown to be capable of removing siliconerelease agents from PUs and thus giving large improvements in adhesion [47].

1.2.7 Discussion

As noted in Section 1.2.1, there have been many detailed studies relating to the pre-treatment of plastics. Much is now known about these pre-treatments including thechemical groups introduced, their concentrations and the depth of chemical modification.In contrast, the number of studies involving rubbers is much lower and in general thestudies have been much less informative. One of the reasons for this is that rubbersusually contain several additives, often in relatively high concentrations. These additivesmake an understanding of the pre-treatments much more difficult. Because of the widerange of formulations for a particular rubber, it is also more difficult to generalise aboutpre-treatments than it is with plastics. For example, it is known that some formulationsof SBR are considerably easier to pre-treat than others.


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The four groups of rubbers considered above will now be discussed. Conclusions aboutpre-treatments for rubbers will then be presented.

Hydrocarbon materials with few carbon–carbon double bonds will be considered first.The most important examples in this group are ethylene-propylene rubbers which maybe crosslinked with peroxides or sulphur systems in which case small quantities of dimersare polymerised with ethylene and propylene (EPDM). As EP rubbers contain no polargroups it will normally be necessary to chemically modify the polymers to enable themto interact strongly with polar adhesives such as epoxides and polyurethanes. In the caseof plastics such as polyethylene and polypropylene, large increases in adhesion can beachieved by treating with a flame [9, 10], corona [11, 13], plasma [18, 19], or etchingsolution [23]. It would be expected that EP rubbers would respond in the same way tothese pre-treatments. However, this is not always the case. Thus, Lawson [31], foundthat a corona treatment of an EPDM did not improve the peel strength to a polyurethanecoating. It is probable that the reason for the poor adhesion is a layer of low molecularweight material on the EPDM. During corona treatment this layer, rather than theunderlying polymer, would be oxidised. Hence, the polyurethane coating would not beable to interact strongly with the EPDM. Even if the EPDM was oxidised by the coronatreatment, there would still be a cohesively weak layer on its surface.

Many rubbers possess carbon–carbon double bonds. In such cases there is the possibilitythat pre-treatment may be effective by addition or substitution reactions. Thus somereagents may be effective with unsaturated hydrocarbons such as SBR and SBS but notwith EP rubbers. This is demonstrated by the work of Lawson [30] who found thattreatment with TCICA in ethyl acetate resulted in the introduction of substantial quantitiesof chlorine into SBR, polybutadiene and NR, but not into EPDM.

Several methods have been shown to be effective at pre-treating unsaturated hydrocarbonrubbers. These include treatment with concentrated sulphuric acid, acidified sodiumhypochlorite and TCICA in ethyl acetate. The last method is the most commonly usedcommercially but in many countries legislation is being introduced to reduce the use oforganic solvents. Promising results have been obtained with new solvent-free methods,namely an electrochemical method involving a highly reactive complex ion, and a methodinvolving a water-soluble organic chlorine donor [47].

Like hydrocarbon rubbers, silicones have low surface energies and interactions withpolar adhesives will be low unless the surface chemistry is modified. Plasma treatmentsimprove the wettability [52, 53, 54, 55, 56, 57] or bondability [58, 59] of silicones.

It is generally accepted that the introduction of a wide range of functional groups makesa polymer much more bondable. The effect of introducing individual chemical groupsinto polyethylene was demonstrated by Chew [60]. Thus, bromine, carbonyl, hydroxyl

Peel strengths

29

and carboxylic acid groups were all shown to greatly increase the bondability ofpolyethylene to an epoxide adhesive. This is in line with the general experience thatpolymers possessing halogens or oxygen-containing groups are much easier to bondthan polyolefins. Whether rubbers containing such groups are easy to bond dependsvery much on whether the bonding surface is covered by low molecular weight (MW)additives or contaminants. On the one hand, Oldfield [37] achieved high peel strengthswith chemically unmodified nitrile rubber whereas Brewis [47] obtained low peel strengthswith an as-received polyurethane. However, after the removal of a silicone release agentby cryoblasting, much higher peel strengths were obtained [47].

1.2.8 Summary

• Methods are available to pre-treat all rubbers but additives or processing aids maymake successful pre-treatment much more difficult.

• TCICA in various organic solvents is very effective with those rubbers possessingcarbon-carbon double bonds. However, legislation restricting the use of organicsolvents is being introduced in many countries. Promising new pre-treatments includethe use of water-soluble organic chlorine donors and an electrochemical method inwhich a highly active complex ion is generated.

• With some polymers containing suitable chemical groups, e.g., PU, simply removingcohesively weak material from the surface may be all that is necessary to achievegood adhesion.

1.3 Bonding Rubbers to Plastic Substrates

1.3.1 Introduction

This section is based mainly on first hand personal experience and is not intended to bean overview of bonding. It covers the basic practical principles of bonding rubbers to avariety of plastics materials.

It is typical to find that those who are skilled in the art of moulding and bonding rubbershave little affinity to plastics materials and vice versa. As for polyurethanes; these aresomething else altogether.

This chapter will concentrate on those plastics and rubbers which are likely to have usesin the manufacture of composite materials (see Appendix 1.1).



30

1.3.1.1 Why Use Plastics?

• Cost,

• Weight saving,

• Technically superior,

• Environmentally more acceptable,

• Fashion/style.

1.3.1.2 What Form Does the Plastics Material Come In?

• Moulded components,

• Cast components,

• Sheet or film,

• Tube/pipe or rod.

Fabric, fibres and filaments are obviously important forms and uses of plastics materials.Although the basic principles of bonding plastics apply to fibres and fabrics, the other factorsinvolved in bonding them are a subject in themselves and will not be discussed further.

In the bonding of rubbers it is assumed that the plastics component is an item which hasbeen preformed and it is this which will be treated with a bonding agent. In most casesthe rubber will be moulded onto the primed surface, by techniques including the following:

• Injection moulding,

• Reaction injection moulding (RIM),

• Compression moulding,

• Transfer moulding,

• Extrusion blow moulding,

• Lamination, which could involve post vulcanisation bonding,

• Autoclave vulcanisation - rollers, pipes, hoses, stators,

• Casting at zero or low pressure - casting of PU.

The basic principles should apply to any form of plastics material and to any method ofmoulding.

31

Of course there is always the potential to mould the plastics material onto the vulcanisedrubber, but this is rare. In practice, this type of moulding is an example of postvulcanisation bonding.

1.3.2 Plastics Substrate Preparation

In preparing metals for bonding, steel in particular, the idea is to produce a surfacewhich is free of contamination, is easy to wet, has a ‘sharp’ irregular surface to promotea mechanical key and controlled oxidation (see Figure 1.3).


Figure 1.3 Metal surface sites for bond

Fortunately for the commonly used metals this ‘controlled’ oxidation occurs naturallyafter grit blasting or acid etching. In the case of plastics, no such convenient oxidationprocess takes place. However, each material will have a unique surface layer containingpotential sites for bonding:

• Polyamides

The polar group NH-C=O is capable of hydrogen bonding through the activated C=Ogroup and via the N-H group. The N-H leaves a reactive site for chemical reaction withsilanes, epoxies, isocyanates and any chemical adducts, which can release such species orany other species, which can react with an active hydrogen. Of course the amide groupneeds to be on the surface to be able to undergo hydrogen bonding or chemical reactionand steric hindrance will reduce the capability of such groups to partake in bonding,which is especially so in the case of aromatic polyamides.


32

• Polyesters

The C(=O)O, ester group will partake in hydrogen bonding through both oxygen atoms,especially the activated carbonyl group. Some polyesters will be less easy to bond if sterichindrance is likely. Even PBT proves difficult to bond and often requires further treatment.

• Polyurethanes

In theory PU should be very active towards bonding, with an activated N-H and a carbonylgroup, as described for polyamides. However PUs are never that easy to bond and couldbe due to surface oxidation and/or surface hydrolysis, it is normal to remove the surface,degrease and prime before the surface is too old.

• Polyureas

The sites for hydrogen bonding and chemical reaction are significant and polyureas aregenerally easy to bond. Being more oxidation resistant and hydrolysis resistant than theurethane group is significant.

• Polycarbonates

A regular repeating stable carbonyl group is available for polar attraction and hydrogen bonding.

• PPS (and PPO)

33

As for polycarbonates, a regular repeating stable polar sulphur (oxygen) atom allows forpolar attraction and hydrogen bonding.

However, in the case of the polyolefines, there are no obvious adhesion sites:

• Polyethylene

• Polypropylene

For the bonding of these an oxidation process is essential.

When one looks at the surface of metals and plastics under an electron microscope thedisruption in that surface explains why bonding is never straightforward.

The surface is often described as a weak surface layer and in the case of plastics one caninclude the surface stresses, general contamination, the presence of abhesive ingredients,i.e., process aids which have migrated to the surface. Some high temperature mouldingprocesses may lead to variable and unwanted oxidation and/or reversion (crosslinkdegradation) at the surface.

Therefore, one can accept the general opinion that the surfaces of plastics do need someform of abrasive or chemical treatment to remove the weak surface layer, or at least reduceit to an adequate level, as shown by the number of publications on the subject [61-69].

Putting it in simple terms the level of surface preparation depends on the performancerequirements of the bond.

To apply a pressure sensitive decal, no surface treatment is a feasible option, but to makea suspension mount then the plastics surface will require controlled treatments.

Most engineering plastics can be treated with alumina or steel grit as for metals. However,in the real world it is quite normal to find that grit blasting is impractical for manyreasons, including:

• Loss of shape, especially in thin sections,

• The reduction in dimensions is not reproducible,



34

• Surface damage, such as fibrillation and plastic flow,

• Trapped (embedded) grinding media and other contaminants.

The harder and the thicker the surface to be bonded the better it is for grit blasting.Similarly, the more highly filled plastics respond much better to blasting than unfilledplastics, and thermosets, especially glass-filled thermosets, are usually very successfullyprepared by blasting.

If a standard grit blasting process gives problems then the use of a finer grit in anystandard grit blasting machine should be thoroughly tested to determine if there is aneffective optimum grit size.

Abrasive and chemical techniques include the following:

• Treatment with abrasive belts,

• Hydrosonic/ultrasonic cleaning,

• High pressure water/detergent cleaning,

• Acid etching, but effluent control means that this is not feasible for anything otherthan high priced specialities and for long running applications,

• The satinisation process for POM is an example of acid etching and involves a slurrycontaining p-toluene sulphonic acid,

• Phenol treatments of polyamides. This includes RFL treatments,

• Alkali etching. As for acid etching, the action is mild surface hydrolysis and looseningof ‘debris’ on the surface,

• Oxidation with relatively mild oxidising agents. Hydrogen peroxide and sodiumhypochlorite are often cited, but a low hazard system worthy of testing out isammonium persulphate,

• Powerful oxidising agents, such as sulphuric dichromate etching,

• Abrasion in an aqueous abrasive slurry. Since this involves effluent waste, it is seldomused on a large scale, but is an effective laboratory method, especially when combinedwith a mild acid, alkali or oxidising agent,

• Direct oxidation by flame, or hot air. Normally only applicable to simple shapes, likeextruded film, tube and rod,

35

• UV treatments. Again this has restricted use, mainly films,

• Plasma treatments. Yet to become a mainstream treatment for rubber to plastics bonding,

• Corona discharge,

• Chlorination.

1.3.3 Degreasing and Solvent Cleaning

Degreasing has always been considered an integral part of ideal surface preparation, butunder current environmental pressures, it is quite normal to find it has been partlyeliminated or even totally eliminated. The need for thorough degreasing becomes morerelevant where the environmental resistance of the bond is important and especiallywhere an abrasive technique has left a contaminated surface.

Degreasing of plastics with solvents can cause problems:

• Stress cracking of the surface, where the effect can remain undetected,

• Absorption and even adsorption of a solvent of a similar solubility parameter to theplastics material. This can be a very serious problem, since retained solvent within thebond line could well act as a release agent.

If solvent degreasing/cleaning is going to be employed, then a fast drying solvent which hasa relatively low solvating power towards the plastics being degreased needs to be used.

Aqueous degreasing can be effective, especially when fully automated. However, anyaqueous process can leave a surface which requires desorption of water, which addsanother process.

Unfortunately, for low pressure moulding and casting in particular, the ultimate bondsare often only achieved if desorption of the adsorbed water and gases is specified. This ismost evident with polyamides, some polyesters, PU, melamine and urea resins and someepoxy resins.

However, in the majority of high pressure moulding processes adsorbed water and gasesdo not appear to affect bonding, but long term environmental tests may show up a problem.

A general guide to reduce the effects of water adsorption is to dry the plastic’s surface,prime with the bonding agent, dry the primed surface and give the component a pre-bake (the coated dried surface is heated, prior to the moulding process). Pre-bakes can



36

be as little as 10 minutes at 70 – 90 °C, which could be part of the drying process, up to30 minutes at 150 °C, which would be an additional process (see Table 1.11). For plasticsgroup definitions see Appendix 1.1

1.3.4 Adhesive/Bonding Agent Choice

1.3.4.1 Post Vulcanisation Bonding

This includes adhesive bonding and bonding with vulcanising bonding agents under theinfluence of heat and pressure, in those cases where the plastics component needs to beadhered to the preformed vulcanised rubber.

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This may be the only method of manufacture for some products and there is a host ofadhesives available for plastics, some of which are described in the literature [63 – 69]for example.

The main adhesives for bonding plastics to rubbers include cyanoacrylates, two-parturethanes, two-part epoxies, hot melt reactive urethane prepolymers, heat reactive contactcements and silane treatments.

Many adhesive bonding applications require a unique answer and it is difficult to makegeneralised recommendations, as you can within limits, with vulcanisation bonding.

1.3.4.2 Vulcanisation Bonding

This is bonding the rubber during the vulcanisation process. The ideal situation is whereno bonding agent is required, but in the real world it is rare to find situations where nobonding agent, whether an internal bonding agent (added to the rubber) or a conventional(external) agent is necessary.

• Primers for the Plastics Substrate for Vulcanisation Bonding

In theory the primer should match the polarity of the plastics substrate, but this couldinfer the need for a range of primers depending on the polarity of the plastics to bebonded. In practice, bonding agent primers contain curable polar resins and less polarrubbery polymers, which may or may not be crosslinkable. This gives some versatility inthe bonding of a range of polar plastics.

An ideal primer would contain highly polar curable resins and speciality polymers.The speciality polymers would vary in their polarity along the polymer chains, givingit variable polarity, a positive attribute in the bonding of a range of plastics. Thepolymer could be produced by grafting a polar monomer (or monomers) onto anunsaturated polymer such as NR, IR, BR or even NBR, which leads to a polymerwhich has certain properties:

1. It still contains unsaturation and segments of the original main chain polymer. Thismeans it can crosslink and intermix with the rubber being moulded.

2. Any polar groups on the ungrafted polymer (for example C–N groups in NBR) takepart in polar bonding to the plastics substrate.

3. The grafted monomer(s), being polar, can also partake in polar bonding.


Degrease Grit blasting Chemical treatments


38

4. If the grafted monomer retains reactivity it can take part in chemical bonding. Suchreactivity could include isocyanates, silanes, epoxides, or even heat reactive adducts,such as blocked isocyanates.

5. If the grafted monomer results in a large and highly polar site, it is possible for thismoiety to behave in a way which appears similar to solvent welding (surface softening),but in this case the ‘solvent’ is the polar moiety. This phenomenon is a particularfeature of one type of speciality one coat technology, because this ‘welding’ not onlyapplies to the plastics surface, but also to the rubber surface, whether the rubber is inan uncured state or cured state. Though it has been compared to solvent welding thephenomenon described above shows no thermoplasticity, in fact heat and solventresistance are the big features of this type of technology, along with the capability ofpost vulcanisation bonding.

6. The ability of the polymer and resin in the primer to react with each other generallyimproves the environmental resistance of both the bond and the bonding agent.

7. For improved heat resistance, aliphatic chlorine should be avoided in the polymers.

For general purpose vulcanisation bonding, conventional primers are available from theestablished suppliers of bonding agents and all such suppliers can cite many examples ofrubber to plastics bonding (see Table 1.12).

For improved adhesion and improved environmental resistance the more reactive primerscan exhibit advantages, such that in some tough applications, they are the only choice.

• Cover coat/top coat

If one is required it should be chosen only with regard to the rubber/rubber being moulded,just as for rubber to metal bonding. (See Table 1.12.)

Summary

With attention to detail, most plastics can be bonded to rubbers, provided one acceptsthe limitations of the rubbers, the plastics and the adhesive system chosen to bond them.It is the aim of those who recommend the adhesives/bonding agents to ensure the bondsare fit for purpose, but it is normal to find that the component manufacturer wants tosee no failure attributable to the adhesive.

39


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40

APPENDIX 1.1

Plastics are divided into groups, loosely based on factors such as surface preparation andbonding characteristics:

Group A1 Plastics

Engineering Thermoplastics

Acrylics

POM - Acetals

Polyesters - PET, PBT

Polycarbonate, PC

PES

PPO

PPS

Polyamides - Nylon 6, 66, 11, 12

Aramids

PEEK

Group A2 Plastics - Thermosets

Epoxies

Unsaturated polyesters, FRP/GRP

Phenolics, including RF resins

Polyamides

Group B Plastics - Other Thermoplastics

TPOs

Group C Plastics - Miscellaneous

ABS

SEBS

41


Polystyrene

Cellulosics

UF, MF

Group D Plastics - Miscellaneous

PU

PVC, PVDC

PTFE, PVF

Rubbers

Conventional Rubbers

NR

SBR

IR

BR

CR

CSM

ACM, VAMAC

NBR, XNBR, HNBR

EPDM

IIR

ECO

EVM

CPE

Millable PU

Others

PUs - TPU and castable PU

Thermoplastic rubbers

VMQ

FKM

Polyolefins


42

1.4 Substrate Preparation for Bonding Using the Wet Blast Process

1.4.1 Summary

Abrasive Developments have, in conjunction with their Japanese licensee, developed awet blast phosphating plant that raises the quality standard within the industry. Thesolution achieved delivers high quality components from an automatic machine thatcombines both the cleaning and phosphating processes. The cleaning section benefitsfrom the unique degreasing and surface treatment properties of the VAQUA process.

Wet blast phosphating was first developed some 15 years ago in co-operation with theYamashita Rubber Company, who make anti-vibration rubber and bond it to supportingmetal parts exclusively for the Honda Motor Company.

Yamashita had two main objectives to achieve from the development of a wet blastphosphating plant:

• To increase the strength of adhesive bonding between the anti-vibration rubber andthe metal parts,

• To improve the corrosion resistance of the metal parts and hence their useful lifeunder any weather conditions.

In addition to these objectives, the demand from the automotive industry as a whole forthis type of component was increasing, and the requirement was for it to be phosphatedprior to bonding whilst still keeping the cost at an acceptable level. To achieve the improvedquality and reduced cost requirements the wet blast phosphating plant had to operatecontinuously and automatically process the metal parts for phosphating.

1.4.2 The Wet Blast Phosphating Plant

The plant has two major processing sections, the wet blast section and the phosphatetreatment section.

1.4.2.1 The Wet Blast Process

The wet blast process is one of the world’s most versatile, efficient and economicalprocesses for metal cleaning and finishing, replacing costly chemicals and the need tosandblast. It saves hours of messy cleaning and eliminates health and environmentalhazards associated with strong chemicals and dust from conventional blasting methods.

43

1.4.2.2 How is Wet Blasting Done?

The component surfaces are bombarded by a recirculating high volume flow of waterborne particles (normally abrasive or glass beads) contained within the cabinet.

The specially developed VAQUA pump pulls the concentrated slurry of media and water,inhibitors and degreasing agents, from the cabinet sump and pushes it at constant highvolume to the process gun. The VAQUA pumps have been developed to minimise thefriction wear from the blast media as it is accelerated round the system by the blast pumpitself. Before reaching the process gun a proportion of the water and media is diverteddown the bypass to provide agitation in the sump, this ensures a stable concentration ofmedia and water. To accelerate the flow of media particles onto the surface of the workpiece and therefore achieve the cleaning and surface finishing effects, a controlled flowof compressed air is introduced into the blast gun. The water within the system lubricates,washes, carries mild inhibitors/degreasers and eliminates dust formation.

At the rinse stage, elements of the blasting media will be carried over and need to beremoved and recirculated, this is done by cyclones. There is a two-stage cyclone system,with the first stage separating the media and water by centrifugation which removeshigh concentration slurry, returning it to blast tank from the pipe arrangements locatedat the bottom of the cyclone. Low concentration slurry is transferred to the second cyclonewhere the process is repeated and the media further separated from the water. The waterseparated here is used for subsequent rinse stages and the separated broken down mediais transferred to the klarti separator. This is a form of oil and grease settling tank wherethe broken down abrasive is separated from the water to allow for subsequent removalof the used media.

1.4.2.3 The Wet Blast Section

It is important that a certain type of surface finish is produced on the metal componentsto enable effective phosphating and bonding. The optimal surface roughness for bondingis 5 – 10 µm, this can be best achieved by wet blasting. The machine is equipped with aspecially designed barrel in which the components are held, and large capacity processguns, through which the media, water and air combination is delivered. This set upallows metal parts with complicated shapes to be effectively and thoroughly processedgiving a uniform and fine satin finish on all of the metal parts.

By adding a degreasing agent to the blasting slurry, any oil and grease on the metal part’ssurface is completely removed thus providing a clean component for presentation to thephosphating section.



44

Wet blasting removes the oxide film covering the metal parts and exposes the pure metalunder the film offering an ideal condition for the phosphate treatment which follows.The process is so efficient that even cast components, if wet blasted, can be treated withphosphate which was impossible using traditional methods.

Figure 1.4 The VAQUA pump

45

1.4.2.4 The Phosphate Treatment Section

In the phosphate treatment section, metal parts go through multiple vessels containingphosphate, rinse water, and a specially designed barrel in each vessel oscillates to keepthe metal parts in continuous motion thus preventing bubbles forming or liquid stayinginside the parts that have openings within them.

The barrel oscillation also ensures that the metal parts are always exposed to freshphosphate which is essential for a uniform and stable phosphate film to be created.

To avoid cross contamination of the phosphating chemicals, the barrel containing themetal parts does not travel through the individual vessels but stays in a particular vessel.When the processing of the metal parts in the barrel is complete they are automaticallydumped into the next barrel for the subsequent process. During their transfer from onevessel to the next, the metal parts are only exposed to the air for a short time whichavoids the possibility of them rusting in the future.

By automatically transferring products from one vessel to another this also minimisesthe contamination of chemicals from one vessel to the next.

1.4.3 Comparison Between Conventional and Wet Blast Phosphating

The conventional process stages are:

1. Dip in trichloroethane for degreasing,

2. Dry shot blasting,

3. Treat with triethane vapour for degreasing,

4. Water rinse,

5. Phosphate treatment,

6. Water rinse,

7. Hot water rinse,

8. Drying.

By comparison the wet blast phosphating stages are:

1. Wet blast,

2. Degrease – detergent system,

3. Water rinse,



46

4. Phosphate treatment,

5. Water rinse,

6. Hot water rinse,

7. Drying.

1.4.4 The Wet Blast Phosphating Plant

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47

1.4.5 Advantages of the Wet Blast Phosphating Plant

1.4.5.1 Product Quality

High quality phosphate film. The plant produces high quality phosphate film for a numberof reasons as listed below:

• The quality of the phosphating achieved is very dependent upon the surface finish ofthe component prior to phosphating. The surface finish achieved through wet blastingis ideal for the phosphating process, hence the high quality film.

• The wet blast section connects with the phosphate treatment plant and therefore themetal work pieces are treated with phosphate immediately after blasting.

• During transit from the wet blast section to the phosphating plant the work pieces arecovered with water so eliminating the possibility of oxidation of the components. Arust inhibitor in the blast system also prevents the oxidation of the components.

1.4.5.2 Clean Components Prior to Phosphating

The powerful wash available from the wet blast process removes any kind of oil and greasewithout any adjustment of the system. The wet blast media physically removes oil andgrease from the surface of the components and prevents it from sticking to the surface.

This is achieved through the repeated blasting of the water media slurry, in a 7:1 ratio,against the work piece. The media particles in a slurry can reach speeds in excess of sonicspeeds so imparting large energy to the component and assisting in the cleaning.

1.4.5.3 High and Uniform Quality Products Made Continuously

The wet blast phosphating plant is fully automated which means that once the initial setup is complete, the repeatability of the process ensures a consistent quality of componentafter phosphating. In an alternative system where a barrel transfers components from oneprocess to the next the inconsistency of time in each stage means that there could be someinconsistency in the end result, which is not the case with the wet blast phosphating plant.

In chemical processes involving pre-treatment and processing, the concentration ofchemicals may alter depending upon the condition of the work pieces such as the type ofoil or grease on them. With wet blast phosphating the type of oil or grease is irrelevant,the process continues to give the same high quality cleaning and phosphating of thework pieces regardless of the type of oil and grease.



48

1.4.5.4 The Wet Blast Phosphating Plant Can Process Any Type of Material

The wet blast process physically removes the surface oxide film and does not rely on achemical reaction, therefore the range of materials that can be processed can be anythingfrom common steel and steel alloy to special steels. This physical ‘scraping off’ of theoxide layer means the process is consistent for each work piece and also does not requirechange of chemicals between different types of component metals. The universal natureof the wet blast process can significantly reduce process times if alternative processesrequire chemical or other changes between different types of components.

1.4.5.5 Ease of Machine Operation

Two factors assist in the efficient operation of this machine, these are:

• Automatic operation,

• Footprint of the machine.

The automatic nature of the wet blast phosphating plant means that once loaded themachine will complete the process automatically allowing the operator to carry out othertasks at the same time. This may even be operating more than one wet blast phosphatingplant because the small footprint of this machine will allow two of these machines to belocated in the area normally allocated to a conventional process.

The reason it is possible to obtain such a small footprint is that there is no requirementfor conveyors between the cleaning and phosphating plants as they are incorporated inthe same machine.

In addition to these operational benefits, the plant is of a single floor type, thus making itsimple to install and easy to locate related machinery nearby. It is worth noting that onlythree days are required for installation before the plant is ready for operation. There is alsono ancillary pipe work required for the machine apart from the primary supply piping.

The ability to locate related machinery nearby has enabled some users to incorporateautomatic load and unload facilities to their plants thus increasing the automation of themachine and hence reducing the labour costs further.

1.4.5.6 Work Pieces of Any Shape Can be Processed

Any shape of component can be processed through the wet blast phosphating plant withoutthe possibility of any liquid remaining inside the component. The barrel in the machine has

49

been designed to prevent the components slipping inside the barrel whilst the barrel oscillates.Components such as tubes, struts and flat washers are all being successfully processed withthe wet blast phosphating plant.

1.4.5.7 Environmental Issues

Each country or region has its own laws relating to the safe and environmentally friendly useof chemicals. Cleaning and degreasing is possible without using chemicals which damage theenvironment. Wet blasting is a physical cleaning method that does not rely upon chemicals.The reduction in the use of chemicals can also reduce the taxes or disposal charges requiredfor some chemicals.

1.4.5.8 The Work Environment

Traditional blasting processes have in some cases been associated with high dust levels andtherefore a poor work environment, this is not true for the wet blast process. Dust generatedby the physical cleaning is absorbed into the liquid supporting the cleaning media andsubsequently extracted through the filtration and/or the oil separation system. The wet blastprocess is a completely dust free cleaning system.

As the equipment is essentially self-contained, the clean work environment also benefits fromthe absence of piping on the floor thus making it easy to clean the area around the machine.

1.4.5.9 Enclosed Phosphate Treatment Plant

The design of the phosphating plant is such that any vapour generated is not allowed toescape. The specially designed transfer system allows the phosphate treatment section to befully enclosed. The transfer system of a conventional machine is such that the barrels themselveshave to travel through each process, meaning the enclosure has to be large enough to enclosethe whole machine. On the contrary with the wet blast phosphating plant, just each vessel isenclosed and the mechanical devices are outside the enclosure.

1.4.5.10 Additional Benefits

With the wet blast phosphating plant, only the work pieces and not the barrels transfer, thusreducing the amount of rinse water consumed. The volume of the rinse water consumed isproportional to the amount of chemical liquid brought into the rinse water vessel. For thesame reason, that only the work pieces are transferred, the amount of chemical liquid consumedis relatively small.



50

1.4.5.11 Maintenance

Maintenance is significantly reduced, with the wet blast phosphating machine not requiringall barrels to be regularly maintained but only the phosphating vessels and the followingwater rinse vessel. If the maintenance is not sufficient in conventional machines, sludgecan be transported into the drying section giving poor quality components with sludgesticking to them.

1.4.5.12 The Wet Blast Phosphating Process

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51

References

1. H. M. Clearfield, J. Thomas, D. K. McNamarra and G. D. Davis in AdhesiveBonding, Ed., L-H. Lee, Plenum Press, New York, 1991.

2. J. S. Thornton, R. E. Montgomery and J. F. Cartier, Presented at the ACSDivision of Polymeric Materials: Science and Engineering, Chicago, IL, Fall 1985,53, 465.

3. T. Symes and D. Oldfield, in Treatise on Adhesion and Adhesives, Volume 7, Ed.,J. D. Minford, Marcel Dekker, Inc., New York, 1991, Chapter 2.

4. F. H. Sexsmith, in Rubber Products Manufacturing Technology, Eds., A. K.Bhowmick, M. M. Hall and H. A. Benarey, Marcel Dekker, Inc., New York,1994, Chapter 11.

5. BS EN ISO 11124-4Preparation of steel substrates before application of paints and related products -specifications for metallic blast-cleaning abrasives - low-carbon cast-steel shot, 1997.

6. C. L. Mahoney, in Handbook of Adhesives, 3rd Edition, Ed., I. Skeist, VanNostrand Rheinhold, New York, 1990, p.74-93.

7. L. Setiawan, D. Schoenherr and J. Weihe, International Polymer Science andTechnology, 1993, 20, 9, T13.

8. K. M. Bond and D. H. Mowrey, Presented at the 141st ACS Rubber DivisionMeeting, Louisville, KY, Spring 1992, Paper No.57.

9. R. L. Ayres and D. L. Shofner, SPE Journal, 1972, 28, 51.

10. D. Briggs, D. M. Brewis and M. B. Konieczko, Journal of Materials Science,1979, 14, 6 ,1344.

11. D. Briggs, C. R. Kendall, A. R. Blythe and A. B. Wootton, Polymer, 1983, 24,1, 47.

12. M. Strobel, M. J. Walzak, J. M. Hill, A. Lin, E. Karbashewski and C. S. Lyons, inPolymer Surface Modification, Ed., K. L. Mittal, VSP, Utrecht, 1996, 233.

13. R. Krüger and H. Potente, Journal of Adhesion, 1980, 11, 2, 113.

14. H. Brecht, F. Mayer and H. Binder, Die Angewandte Makromolekulare Chemie,1973, 33, 89.



52

15. D. W. Dwight and W. M. Riggs, Journal of Colloid Interface and Science, 1974,47, 3, 650.

16. I. Mathieson, D. M. Brewis, I. Sutherland and R. A. Cayless, Journal ofAdhesion, 1994, 46, 1/4, 49.

17. E. R. Nelson, T. J. Kilduff and A. A. Benderly, Industrial Engineering Chemistry1958, 6, 221.

18. H. Schonhorn and R. H. Hansen, Journal of Applied Polymer Science, 1967, 11,8, 1461.

19. C. A. L. Westerdahl, J. R. Hall, E. C. Schramm and D. W. Levi, Journal ofColloid and Interface and Science, 1974, 47, 3, 610.

20. H. Schonhorn and R. H. Hansen, Journal of Applied Polymer Science, 1968, 12,5, 1231.

21. A. Chew, R. H. Dahm, D. M. Brewis, D. Briggs and D. G. Rance, Journal ofColloid and Interface Science, 1986, 110, 88.

22. G. C. S. Collins, A. C. Lowe and D. Nicholas, European Polymer Journal, 1973,9, 11, 1173.

23. D. Briggs, D. M. Brewis and M. B. Konieczko, Journal of Materials Science,1976, 11, 7, 1270.

24. L. J. Gerenser, J. F. Elman, M. G. Mason and J. M. Pochan, Polymer, 1985, 26,8, 1162.

25. G. Beamson, D. M. Brewis and J. F. Watts, unpublished work.

26. R. A. Bragole, The Journal of Rubbers and Plastics, 1974, 6, 3, 213.

27. M. D. Ellul and D. R. Hazleton, Rubber Chemistry and Technology, 1994, 67,4, 582.

28. I. Brass, D. M. Brewis, I. Sutherland and R. Wiktorowicz, International Journalof Adhesion and Adhesives, 1991, 11, 5, 150.

29. G. Kranz, R. Lüschen, T. Gesang, V. Schlett, O. D. Hennemann and W. D.Stohrer, International Journal of Adhesion and Adhesives, 1994, 14, 4, 243.

30. D. F. Lawson, K. J. Kim and T. L. Fritz, Rubber Chemistry and Technology,1996, 69, 2, 245.

53

31. D. F. Lawson, Rubber Chemistry and Technology, 1987, 60, 1, 102.

32. ASTM D2578-99aStandard Test Method for Wetting Tension of Polyethylene and Polypropylene Films

33. M. Minagawa, T. Saito, Y. Fujikura, T. Watanabe, H. Iwabuchi, F. Yoshi and T.Sasaki, Journal of Applied Polymer Science, 1997, 63, 12, 1625.

34. A. Kondyurin and Y. Klyachtin, Journal of Applied Polymer Science, 1996, 62, 1, 1.

35. B. C. Cope, D. M. Brewis, J. Comyn, K. R. Nangreave and R. J. P. Carne,Adhesion 10, Ed., K. W. Allen, Elsevier Applied Science Publishers, London,1986, 178.

36. D. Pettit and A. R. Carter, Journal of Adhesion, 1973, 5, 4, 333.

37. D. Oldfield and T. E. F. Symes, Journal of Adhesion, 1983, 16, 2, 77.

38. D. Oldfield and T. E. F. Symes, Journal of Adhesion, 1992, 39, 2-3, 91.

39. C. W. Extrand and A. N. Gent, Rubber Chemistry and Technology, 1988, 61,4, 688.

40. Y. Kusano, T. Noguchi, M. Yoshikawa, N. Kato and K. Naito, Presented at KobeInternational Rubber Conference (IRC 95), 1995, Kobe, Japan, 432.

41. M. M. Pastor-Blas, M. S. Sánchez-Adsuar and J. M. Martín-Martínez in PolymerSurface Modification Ed., K. L. Mittal, VSP, Utrecht, 1996, 379.

42. M. M. Pastor-Blas, J. M. Martín-Martínez and J. G. Dillard, Journal ofAdhesion, 1997, 63, 1/3, 121.

43. M. M. Pastor-Blas, J. M. Martín-Martínez and J. G. Dillard, Journal ofAdhesion, 1997, 62, 1/4, 23.

44. A. Torró-Palau, J. C. Fernández-García, A. C. Orgilés-Barceló and J. M. Martín-Martínez, Journal of Adhesion, 1996, 57, 1/4, 203.

45. N. Pastor-Sempere, J. C. Fernández-García, A. C. Orgilés-Barceló, R. Torregrosa-Maciá and J. M. Martín-Martínez, Journal of Adhesion, 1995, 50, 1, 25.

46. M. M. Pastor-Blas, J. M. Martín-Martínez and J. G. Dillard, Journal of AdhesionScience and Technology, 1997, 11, 4, 447.



54

47. D. M. Brewis and I. Mathieson, Presented at the 22nd Annual Meeting of theAdhesion Society, Panama City Beach, USA, 1999, 4.

48. M. M. Pastor-Blas, R. Torregrosa-Maciá, J. M. Martín-Martínez and J. G.Dillard, International Journal of Adhesion and Adhesives, 1997, 17, 2, 133.

49. A. Chew, R. H. Dahm, D. M. Brewis, D. Briggs and D. G. Rance, Journal ofColloid and Interface Science, 1986, 110, 1, 88.

50. J. Shields, Adhesives Handbook, 3rd Edition, Butterworth, London, 1984, 87.

51. R. F. Wegman, Surface Preparation Techniques for Adhesive Bonding, NoyesPublications, New Jersey, 1989, 127.

52. R. R. Sowell, N. J. DeLollis, H. J. Gregory and O. Montoya, Journal ofAdhesion, 1972, 4, 1, 15.

53. J. Y. Lai, Y. Y. Lin, Y. L. Denq, S. S. Shyu and J. K. Chen, Journal of AdhesionScience and Technology, 1996, 10, 3, 231.

54. E. P. Everaert, H. C. van der Mei, J. de Vries and H. J. Busscher, Polymer SurfaceModification, Ed., K. L. Mittal, VSP, Utrecht, 1996, 33.

55. M. Hudis and L. E. Prescott, Journal of Applied Polymer Science, 1975, 19,2, 451.

56. J. R. Hollahan and G. L. Carlson, Journal of Applied Polymer Science, 1970, 14,10, 2499.

57. J. L. Fritz and M. J. Owen, Journal of Adhesion, 1995, 54, 1/4, 33.

58. M. J. Swanson and G. W. Opperman, Journal of Adhesion Science andTechnology, 1995, 9, 3, 385.

59. C. Combette, D. Hivert, J. Maucourt, W. Brunat, T. M. Duc, G. Michel, P. LePrince and G. Legeay, Presented at Euradh 94, Mulhouse, France, 1994, 416.

60. A. Chew, D. M. Brewis, D. Briggs and R. H. Dahm in Adhesion 8, Ed., K. W.Allen, Elsevier Applied Science Publishers, London, 1984, 97.

61. Handbook of Plastics Joining, A Practical Guide, Plastics Design Library,Norwich, NY, 1997.

62. K. W. Allen, Joining of Plastics, Rapra Review Report No.57, Rapra,Shrewsbury, UK, 1992.

55

63. D. G. Brandon and W. D. Kaplan, Joining Processes, An Introduction, Wiley,Chichester, 1997.

64. F. Garbassi, M. Morra and E. Occhiello, Polymer Surfaces from Physics toTechnology, Wiley, Chichester, 1998.

65. J. Shields, Adhesives Handbook, 3rd Edition (Revised), Butterworths,London, 1985.

66. Handbook of Adhesives, 3rd Edition, Ed., I. Skeist, Van Nostrand Reinhold, NewYork, 1990.

67. Treatise on Adhesion and Adhesives, Volume 5, Ed., R. L. Patrick, MarcelDekker Inc., New York, 1981.

68. A. H. Landrock, Adhesives Technology Handbook, Noyes Publications,Parkridge, NJ, 1985.

69. R. C. Snogren, Handbook of Surface Preparation, Palmerton, New York, 1974.



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the handbook rubber bonding

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