2 Rheology of Pressure-Sensitive Adhesives

761 Pages·2004·4.8 MB·English

Pressure-Sensitive Adhesives
and Applications
Second Edition, Revised and Expanded
Istvan Benedek
Wuppertal, Germany
MARCEL -
MARCELD EKKERIN, C. NEWY ORK BASEL
DEKKER
The first edition of this book was published as Pressure-Sensitive Adhesives
Technology, Istva´nBenedekand LucJ. Heymans(Marcel Dekker, Inc., 1996).
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Preface to the Second Edition
The growing interest in the advances described in this book have called for
this second edition of this book. In the past few years pressure-sensitive
products have reached a maturity that warrants a detailed and critical
examination of their science and technology. This is a vast domain, and I
havetriedtocoversomeofitsspecialaspectsinseparateworks.Thevolume
Development and Manufacture of Pressure-Sensitive Products (Marcel
Dekker, 1998) describes the whole domain of self-adhesive products;
Pressure-SensitiveFormulation(VSP,Utrecht)givesadetaileddiscussionof
a special, practical segment of pressure sensitivity. However, Pressure-
Sensitive Adhesives Technology (Marcel Dekker, 1996), the first of these
books, constitutes the main step on the way to understanding adhesive-
based pressure-sensitive products.
In the past decade advances in contact physics and mechanics have
allowed us to correlate the macroscopic aspects of adhesive bonding
and debonding with the macromolecular basis of the viscoelastomers. The
mostimportantelementsofthisprogressaredescribedinaseparatesection
oftherevisedbook.Developmentsinthepracticalexaminationandquality
assurance of pressure-sensitive products required an enlarged discussion
and reformulation of Chapter 10, ‘‘Test Methods.’’ Environmental
considerations made necessary the discussion of recycling methods, and
biodegradability of raw materials, product components, and pressure-
sensitive products. Other scientific and industrial advances (i.e., new raw
materials and improved coating technology) are also included in the
second edition. Thus, after undergoing a major revision, the second edition
of this book remains a comprehensive and convenient up-to-date source of
iii
iv Prefaceto theSecond Edition
information for users in industry and academia. So far as I am aware,
this is the first single-author book on general aspects of pressure-sensitive
adhesive technology, and it has been my pleasure to assist in its success.
Istva´n Benedek
Preface to the First Edition
Sincetheirintroductionhalfacenturyago,pressure-sensitiveadhesiveshave
been successfully applied in many fields. They are used in self-adhesive
labels, and tapes and protective films, as well as in dermal dosage systems
for pharmaceutical applications, the assembly of automotive parts, toys,
andelectroniccircuitsandkeyboards.Theyhaveexperiencedanastonishing
growth rate, and the installed manufacturing and converting capacity has
also sharply increased. A specific engineering technology for pressure-
sensitive adhesives, surprisingly a special science, appears to be lacking.
Very few books deal with intrinsic features of pressure-sensitive adhesives.
The application of pressure-sensitive adhesives requires a thorough
knowledge of basic rheological and viscoelastic phenomena. Adhesive and
polymer scientists, however, are not very often employed as industrial
managersormachineoperators.Thereforetheneedarisestoinvestigateand
summarize the most important features of pressure-sensitive adhesive
technology and to explain the phenomena scientifically. This book covers
allthefieldsofmanufacturing,conversion,andapplicationandend-usesof
pressure-sensitive adhesives.
The classical approach would be to compile a treatise based on the
work of various experts, theoreticians, chemists, and engineers, thereby
coming upwithabook consistingofaseriesofpaperswithacommon title
only. We have, however, chosen a different approach. Based on our
experience as engineers (in both scientific activity and industrial areas) and
using the available technical literature, we have addressed all aspects of
pressure-sensitive adhesives. We have included the scientific basis of
suitability for specific applications (i.e., chemical and physical, rheology),
therawmaterials,themanufacture(formulation)oftheadhesiveandofthe
labelstock (converting the adhesive). We have selected self-adhesive labels
as the most complex self-adhesive laminate; we mainly discuss labels, but,
v
vi Prefaceto theFirst Edition
wheneverpossible,acomparisonwithandextensiontootherapplicationsis
included. In order to illustrate the different topics and issues discussed, we
have referred to a number of commercially available products. Itshould be
kept in mind that these products are only mentioned in order to clarify the
discussion and in no way does it constitute any judgment about inherent
performance characteristics or their suitability for specific applications or
end-uses.
It is not the aim of this book to establish or complete the science of
pressure-sensitiveadhesives,nordoesitconstituteaseriesofrecipes.Rather
itservesasapracticalaidtoconvertersandthoseinvolvedinthedesignand
use of pressure-sensitive adhesives.
Istva´n Benedek
Luc J. Heymans
Contents
Preface to the Second Edition iii
Preface to the First Edition v
1. Introduction 1
References 3
2. Rheology of Pressure-Sensitive Adhesives 5
1 Rheology of Uncoated PSAs 5
1.1 Properties of PSAs 6
1.2 Influence of Viscoelastic Properties on the
Adhesive Properties of PSAs 11
1.3 Influence of Viscoelastic Properties on the
Converting Properties of PSAs and PSA Laminates 25
1.4 Influence of Viscoelastic Properties on
End-Use Properties of PSAs 26
1.5 Factors Influencing Viscoelastic Properties of PSAs 31
2 Rheology of PSA Solutions and Dispersions 40
2.1 Rheology of PSA Solutions 41
2.2 Rheology of PSA Dispersions 44
3 Rheology of the Pressure-Sensitive Laminate 52
3.1 Influence of the Liquid Components of
the Laminate 54
3.2 Influence of the Solid Components of
the Laminate 58
3.3 Influence of the Composite Structure 81
References 82
vii
viii Contents
3. Physical Basis for the Viscoelastic Behavior of
Pressure-Sensitive Adhesives 89
1 The Role of the T in Characterizing PSAs 90
g
1.1 Values of T for Adhesives 91
g
1.2 Factors Influencing T 92
g
1.3 Adjustment of T 104
g
1.4 Correlation Between the Main Adhesive, End-Use,
and Converting Properties of PSAs and T 107
g
2 Role of the Modulus in Characterizing PSAs 110
2.1 Factors Influencing the Modulus 113
2.2 Adjustment of the Modulus 124
2.3 Modulus Values 126
3. Contact Physics 129
3.1 Contact Mechanics for Elastic Materials 129
3.2 Contact Mechanics for Viscoelastic Materials 130
3.3 Micromechanical Considerations 132
4 The Role of Other Physical Parameters in
Characterizing PSAs 137
References 138
4. Comparison of PSAs 147
1 Comparison of PSAs with Thermoplastics and Rubber 147
1.1 Cold Flow 148
1.2 Relaxation Phenomena 155
1.3 Mechanical Resistance 156
2 Comparison Between PSAs and Other Adhesives 158
References 159
5. Chemical Composition of PSAs 161
1 Raw Materials 162
1.1 Elastomers 163
1.2 Viscoelastomers 176
1.3 Viscous Components 187
1.4 Components for In-line Synthesis 189
1.5 Components for Special Pressure-Sensitive
Formulations 197
1.6 Other Components 198
1.7 Release Coatings 199
2 Factors Influencing the Chemical Composition 205
2.1 Synthesis 205
2.2 Formulation 210
Contents ix
2.3 Physical State of PSAs 211
2.4 End-Use 216
2.5 Coating Method 220
2.6 Solid State Components of the Laminate 221
2.7 Product Build-Up 222
2.8 Environment Related Considerations 223
References 224
6. Adhesive Performance Characteristics 235
1 Adhesion-Cohesion Balance 235
1.1 Tack 235
1.2 Peel Adhesion 261
1.3 Shear Resistance (Cohesion) 307
2 Influence of Adhesive Properties on Other
Characteristics of PSAs 320
2.1 Influence of Adhesive Properties
on the Converting Properties 320
2.2 Influence of Adhesive Properties on End-Use
Properties 320
2.3 Influence of Peel Adhesion 320
2.4 Influence of Shear 321
3 Comparison of PSAs on Different Chemical Bases 321
3.1 Rubber-Based Versus Acrylic-Based PSAs 321
3.2 Acrylics and Other Synthetic Polymer-Based
Elastomers 322
References 341
7. Converting Properties of PSAs 353
1 Convertability of the Adhesive 353
1.1 Convertability of Adhesive as a Function of
the Physical State 353
1.2 Convertability of Adhesive as a Function of
Adhesive Properties 361
1.3 Convertability of Adhesive as a Function of the
Solid State Components of the Laminate 361
1.4 Convertability of Adhesive as a Function of
Coating Technology 361
1.5 Convertability of Adhesive as a Function of
End-Use Properties 362
2 Converting Properties of the Laminate 362
2.1 Definition and Construction of the Pressure-Sensitive
Laminate 363