Practical Guide to Adhesive Bonding of Small Engineering Plastic and Rubber Parts

194 Pages·2010·5.13 MB·English

by  Goss

Practical Guide to
Adhesive Bonding of Small
Engineering Plastic and
Rubber Parts
Bob Goss
iSmithers – A Smithers Group Company
Shawbury, Shrewsbury, Shropshire, SY4 4NR, United Kingdom
Telephone: [phone] Fax: [phone]
http://www.ismithers.net
First Published in 2010 by
iSmithers
Shawbury, Shrewsbury, Shropshire, SY4 4NR, UK
©2010, Smithers Rapra
All rights reserved. Except as permitted under current legislation no part
of this publication may be photocopied, reproduced or distributed in any
form or by any means or stored in a database or retrieval system, without
the prior permission from the copyright holder.
A catalogue record for this book is available from the British Library.
Every effort has been made to contact copyright holders of any material reproduced
within the text and the authors and publishers apologise if
any have been overlooked.
ISBN: 978-1-84735-139-5 (hardback)
978-1-84735-138-8 (softback)
978-1-84735-140-1 (ebook)
Typeset by Integra Software Services Pvt. Ltd.
Printed and bound by Lightning Source Inc.
C
ontents
Preface .................................................................................................................vii
1. Introduction to Adhesives ..............................................................................1
1.1 Cyanoacrylates ....................................................................................1
1.1.1 Types of Cyanoacrylate ...........................................................3
1.2 UV-curing Adhesives ............................................................................9
1.2.1 The Curing Process .................................................................9
1.2.2 Health and Safety with UV ...................................................13
1.2.3 The Curing Equipment ..........................................................13
1.2.4 Curing Adhesive Tack-free ....................................................14
1.2.5 Types of UV Adhesives ..........................................................16
1.2.6 Benefi ts of UV Adhesives .......................................................17
1.3 Two-part Acrylics ..............................................................................17
1.4 Epoxies ..............................................................................................19
1.4.1 Advantages and Disadvantages of Epoxies ............................21
1.5 Flexible Adhesive Sealants .................................................................21
1.5.1 Silicone Adhesive Sealants .....................................................22
1.5.2 Polyurethane Adhesive Sealants ............................................23
1.5.3 Modifi ed Silane Adhesive Sealants ........................................24
1.6 Hot Melt Adhesives ...........................................................................25
1.6.1 Reactive Hot Melts ...............................................................25
2. Engineering Thermoplastics .........................................................................27
2.1 Introduction ......................................................................................27
2.2 Amorphous Thermoplastics ...............................................................27
2.3 Semi-crystalline Polymers ..................................................................29
2.4 Adhesive Performance on Thermoplastics ..........................................31
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Practical Guide to Adhesive Bonding of Small Engineering Plastic and Rubber Parts
2.4.1 ABS .......................................................................................32
2.4.2 LCP .......................................................................................32
2.4.3 Polyamide .............................................................................33
2.4.4 PBT .......................................................................................34
2.4.5 PC .........................................................................................36
2.4.6 PEEK ....................................................................................37
2.4.7 PES and PUS .........................................................................38
2.4.8 PE .........................................................................................39
2.4.9 PET .......................................................................................40
2.4.10 PMMA ..................................................................................40
2.4.11 POM .....................................................................................41
2.4.12 PPO ......................................................................................42
2.4.13 PPS ........................................................................................43
2.4.14 PP .........................................................................................43
2.4.15 PS ..........................................................................................45
2.4.16 PTFE .....................................................................................46
2.4.17 PVC ......................................................................................47
2.5 General Comments on Adhesive Bonding of Thermoplastics .............47
3. Engineering Thermoset Plastics ...................................................................51
3.1 Introduction ......................................................................................51
3.2 Adhesive Performance on Thermoset Plastics.....................................53
3.2.1 Diallyl Phthalate (DAP) .........................................................54
3.2.2 Epoxies .................................................................................55
3.2.3 Phenolics ...............................................................................55
3.2.4 Polyester (Thermoset) ...........................................................56
3.2.5 Polyurethanes ........................................................................57
3.2.6 Polyimides .............................................................................58
3.3 General Comments on Adhesive Bonding of Thermoset Plastics ........59
4. Elastomers and Thermoplastic Elastomers (TPE) .........................................61
4.1 Introduction ......................................................................................61
4.2 Adhesive Performance on Elastomers.................................................61
4.2.1 Butyl Rubber .........................................................................62
4.2.2 Copolyester TPE ...................................................................63
ii
Contents
4.2.3 Ethylene Acrylic (EEA) Rubber .............................................64
4.2.4 Ethylene Propylene Diene Monomer Rubber (EPDM) ..........64
4.2.5 Ethylene-Vinyl Acetate Co-polymer (EVA) ............................65
4.2.6 Fluorosilicone Rubber ...........................................................66
4.2.7 Natural Rubber .....................................................................66
4.2.8 Nitrile Rubber .......................................................................67
4.2.9 Neoprene Rubber ..................................................................68
4.2.10 Polyisoprene ..........................................................................68
4.2.11 Polyolefi n Elastomers ............................................................68
4.2.12 Silicone Rubber .....................................................................70
4.2.13 Styrene-Butadiene Rubber (SBR) ...........................................70
4.2.14 Styrenic TPE .........................................................................70
4.2.15 Thermoplastic Vulcanisates (TPV).........................................72
4.3 General Comments on Bonding of Elastomers ...................................72
5. Joint Design .................................................................................................75
5.1 Introduction ......................................................................................75
5.2 Lap Joint ...........................................................................................75
5.2.1 Joint Width versus Joint Overlap ..........................................76
5.2.2 Optimising Joints to Minimise Stress ....................................78
5.3 Double Lap Joint (Tongue and Groove) .............................................80
5.4 Cylindrical Joints ...............................................................................81
5.4.1 Design Details .......................................................................82
5.4.2 Cross Holes ...........................................................................84
5.4.3 Blind Holes ...........................................................................85
5.5 Butt Joint ...........................................................................................86
5.6 Bond Line Thickness ..........................................................................88
5.7 Thermal Effects .................................................................................89
5.8 Selecting the Viscosity of the Adhesive ...............................................89
5.9 Surface Preparation ...........................................................................91
6. Bonding of Low-energy Plastics and Rubbers ..............................................93
6.1 Surface Wetting ..................................................................................93
6.2 Measuring Surface Energy .................................................................97
6.3 Surface Treatments ............................................................................97
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Practical Guide to Adhesive Bonding of Small Engineering Plastic and Rubber Parts
6.3.1 Abrasion ...............................................................................98
6.3.2 Corona Discharge .................................................................98
6.3.3 Plasma Treatment..................................................................98
6.3.4 Flame Treatment ...................................................................98
6.3.5 Use of Primers .......................................................................99
6.4 Two-part Acrylics ..............................................................................99
7. Selecting the Adhesive ...............................................................................101
7.1 Introduction ....................................................................................101
7.2 Factors for Consideration ................................................................102
7.2.1 Selection of Materials ..........................................................102
7.2.2 Adhesive Performance .........................................................103
7.2.3 Durability and Long Term Performance and
Temperature Resistance .......................................................104
7.2.4 Surface Preparation .............................................................104
7.2.5 Ease of Application .............................................................105
7.2.6 Joint Design ........................................................................105
7.2.7 Viscosity ..............................................................................106
7.2.8 Cure Speed ..........................................................................107
7.2.9 Gap-fi lling Capability ..........................................................107
7.2.10 Sealing Capability ...............................................................107
7.2.11 Health and Safety (H&S) ....................................................108
7.2.12 Approvals ...........................................................................111
7.2.13 Recycling Adhesives ............................................................111
7.3 A Summary for Adhesive Selection ..................................................112
8. Dispensing Adhesives in Production ..........................................................115
8.1 Basic Principles ................................................................................115
8.1.1 Single- or Two-part Adhesive ..............................................115
8.1.2 Viscosity (see Section 5.8) ...................................................116
8.1.3 Cycle Time ..........................................................................118
8.1.4 Cure Method ......................................................................118
8.1.5 Dispense Quantity ...............................................................118
8.1.6 Open Time ..........................................................................120
8.1.7 Health and Safety ................................................................120
iv
Contents
8.1.8 Cost ....................................................................................121
8.2 Dispensing Systems ..........................................................................121
8.2.1 Manual Units ......................................................................122
8.2.2 Semi-automatic Dispensers ..................................................123
8.2.3 Syringe Dispensing ..............................................................123
8.2.4 Pressure Pot Dispensing ......................................................123
8.3 Automatic Systems ..........................................................................125
9. Durability and Environmental Testing .......................................................127
9.1 Introduction ....................................................................................127
9.1.1 Surface Finish and Surface Preparation ...............................127
9.1.2 Joint Design ........................................................................128
9.1.3 Substrate Bonded ................................................................129
9.2 Effect of Humidity and Water Absorption .......................................130
9.3 Durability of Cyanoacrylates ...........................................................130
9.3.1 Cyanoacrylates for Medical Applications ............................132
9.4 Durability of UV-curing Adhesives ...................................................132
9.4.1 UV Adhesives for Medical Applications ..............................133
9.5 Durability of Two-Part Acrylics .......................................................135
9.6 Durability of Epoxies .......................................................................135
9.7 Environmental Testing .....................................................................135
10. Troubleshooting ........................................................................................139
10.1 ‘No Glue’ – Inspecting for the Presence of Adhesive ........................139
10.1.1 ‘No Glue’ – Verifying the Adhesive Has Been Dispensed .....140
10.1.2 ‘No Glue’ – Air Bubbles and Voids ......................................141
10.1.3 ‘No Glue’– Destructive and Non-destructive Methods ........142
10.1.4 ‘No Glue’ – Other Factors ...................................................142
10.2 ‘No Cure’ ........................................................................................143
10.2.1 ‘No Cure’ – Odour ..............................................................143
10.2.2 ‘No Cure’ – Factors Inhibiting Cure ....................................143
10.2.3 ‘No Cure’ – Disturbing Partially Cured Adhesive ................144
10.2.4 ‘No Cure’ – Differential Scanning Calorimetry (DSC) .........144
10.2.5 ‘No Cure’ – Adhesive Curing Problems ...............................145
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Practical Guide to Adhesive Bonding of Small Engineering Plastic and Rubber Parts
10.2.6 Blooming of Cyanoacrylates ...............................................145
10.3 ‘No Stick’ ........................................................................................148
10.3.1 Theories of Adhesion ..........................................................148
10.3.2 Cohesive .............................................................................149
10.3.3 Adhesive Failure ..................................................................150
10.3.4 Substrate Failure .................................................................151
10.4 No Performance ..............................................................................152
10.4.1 Surface Analysis ..................................................................153
10.4.2 Defi ning the Failure Mode ..................................................153
Abbreviations ....................................................................................................155
Author Index .....................................................................................................157
Subject Index .....................................................................................................159
vi
P
reface
Plastics are an integral part of everyday life. There are huge numbers of manufacturing
processes that use plastics either for the complete build or for sub-components within
the assembly. Even components nominally composed entirely of metals may well
include a polymeric material to coat, seal or adhesively bond the various components.
There are countless different grades available and new trade names are introduced
every year. Plastic manufacturers are able to formulate grades to meet the performance
needs for almost any application.
Not only is there a limitless number of plastics available but also there is a vast
number of adhesives available. You only have to type the word ‘adhesives’ into an
internet search engine and you will receive a cascade of data on adhesives of all types.
This guide is written to help designers of plastic engineering components select an
adhesive that may be suitable for their intended application. It is not intended for
the packaging industry or for the bonding of composite materials and deliberately
no mention is given to mechanical clips, ultrasonic welding or other plastic joining
methods as these would be outside the scope of this guide. The adhesives discussed
in this guide are aimed primarily at ‘small part’ bonding – parts typically (but not
exclusively) smaller than an A4 pad.
There are chapters on the bonding of ‘diffi cult’ plastics, joint design and dispensing
systems but an adhesive cannot be selected for an application solely on the information
given in this guide as it is not possible to provide environmental data for every
combination of adhesive, plastic grade and joint confi guration and so it is always
recommended that adhesive manufacturers are consulted and trials are conducted.
The guide discusses 30 of the most commonly used generic families of both
thermoplastics and thermoset plastics and also includes a number of commonly used
rubbers and elastomers.
The fi nal chapter discusses methods of troubleshooting possible reasons for an
adhesive failure.
Bob Goss
vii