Coatings Technology Handbook Episode 1 Part 1 docx

COATINGS
TECHNOLOGY
HANDBOOK
Third
Edition
© 2006 by Taylor & Francis Group, LLC
A CRC title, part of the Taylor & Francis imprint, a member of the
Taylor & Francis Group, the academic division of T&F Informa plc.
COATINGS
TECHNOLOGY
HANDBOOK
Third
Edition
Edited by
Arthur A. Tracton
Boca Raton London New York Singapore
© 2006 by Taylor & Francis Group, LLC

Published in 2006 by
CRC Press
Taylor & Francis Group
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Boca Raton, FL 33487-2742
© 2006 by Taylor & Francis Group, LLC
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10987654321
International Standard Book Number-10: 1-57444-649-5 (Hardcover)
International Standard Book Number-13: 978-1-57444-649-4 (Hardcover)
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v

Preface to Third Edition

The world of coatings is very broad. The application techniques are many, and the uses are numerous.
Technical people need to be aware of many things. One study said that a coating chemist must be proficient
in 27 different disciplines. This book is directed at supplying a broad cross-index of some of the different
aspects to help the technical person. It is not meant to be an in-depth treatise on any subject. It is meant
to give insight into the various subjects covered. The chapter authors or the editor may be contacted for
more information or direction on the subjects.
To aid the person involved in coatings, inks, or adhesives, be they chemists, engineers, technicians,
researchers, or manufacturers, chapters are given in the areas of fundamentals and testing, coating and
processing, techniques and materials, and surface coatings. Each section contains information to expand
the awareness and knowledge of someone practicing in the field. The objective is to help people solve
problems and increase their level of technology. With time, technology increases, as shown by the chapter
on statistical design of experiments, and the chapter on using equipment to determine ultraviolet (UV)
resistance. Newer materials such as fluorocarbon resins, polyurethane thickeners, and high-temperature
pigments are included as well as older materials such as alkyds, clays, and driers.
To accomplish the presentation of technology, this book has been expanded to 118 chapters by adding
new material and updating other material. Hopefully, the reader will expand his or her knowledge and
further push the envelope of technology.
The editor gratefully acknowledges the many contributions of the chapter authors and the publishers
who have made this book possible.

Arthur A. Tracton

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vii

Contributors

N. J. Abbott

Albany International Research
Company
Dedham, Massachusetts

Harold Van Aken

GretagMacbeth
New Windsor, New York

Walter Alina

General Magnaplate
Corporation
Linden, New Jersey

Mark J. Anderson

Stat-Ease, Inc.
Minneapolis, Minnesota

Robert D. Athey, Jr.

Athey Technologies
El Cerrito, California

Brian E. Aufderheide

W. H. Brady Company
Milwaukee, Wisconsin

Bruce R. Baxter

Specialty Products, Inc.
Lakewood, Washington

William F. Beach

Bridgeport, New Jersey

Edward A. Bernheim

Exxene Corporation
Corpus Christi, Texas

Deepak G. Bhat

GTE Valenite Corporation
Troy, Michigan

Thomas P. Blomstrom

Monsanto Chemical Company
Springfield, Massachusetts

Kenneth Bourlier

Union Carbide Corporation
Bound Brook, New Jersey

J. David Bower

Hoechst Celanese Corporation
Somerville, New Jersey

Donald L. Brebner

E. I. du Pont de Nemours &
Company
Wilmington, Delaware

Patrick Brennan

Q-Panel Lab Products
Cleveland, Ohio

George E. F. Brewer

George E. F. Brewer Coating
Consultants
Birmingham, Michigan

Lisa A. Burmeister

Aqualon Company
Wilmington, Delaware

Peter A. Callais

Pennwalt Corporation
Buffalo, New York

Naomi Luft Cameron

Datek Information Services
Newtonville, Massachusetts

Robert W. Carpenter

Windsor Plastics, Inc.
Evansville, Indiana

Chi-Ming Chan

Raychem Corporation
Menlo Park, California

Gary W. Cleary

Cygnus Research Corporation
Redwood City, California

Carl A. Dahlquist

3M Company
St. Paul, Minnesota

B. Davis

ABM Chemicals Limited
Stockport, Cheshire, England

Richey M. Davis

Hercules Incorporated
Wilmington, Delaware

David R. Day

Micromet Instruments, Inc.
Cambridge, Massachusetts

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viii

Marcel Dery

Chemical Fabrics Corporation
Merrimack, New Hampshire

Arnold H. Deutchman

BeamAlloy Corporation
Dublin, Ohio

John W Du

BYK-Chemie USA
Wallingford, Connecticut

Richard P. Eckberg

General Electric Company
Schenectady, New York

Jesse Edenbaum

Consultant
Cranston, Rhode Island

Eric T. Everett

Q-Panel Lab Products
Cleveland, Ohio

Carol Fedor

Q-Panel Lab Products
Cleveland, Ohio

William C. Feist

Consultant
Middleton, Wisconsin

R. H. Foster

Eval Company of America
Lisle, Illinois

James D. Gasper

ICI Resins US
Wilmington, Massachusetts

Sam Gilbert

Sun Chemical Corporation
Cincinnati, Ohio

K. B. Gilleo

Sheldahl, Inc.
Northfield, Minnesota

William S. Gilman

Gilman & Associates
South Plainfield, New Jersey

F. A. Goossens

Stork Brabant
Boxmeer, The Netherlands

Joseph Green

FMC Corporation
Princeton, New Jersey

Douglas Grossman

Q-Panel Lab Products
Cleveland, Ohio

Clive H. Hare

Coating System Design, Inc.
Lakeville, Massachusetts

William F. Harrington,
Jr.

Uniroyal Adhesives and Sealants
Company, Inc.
Mishawaka, Indiana

J. Rufford Harrison

E. I. du Pont de Nemours &
Company
Wilmington, Delaware

Helen Hatcher

Johnson Matthey Pigments &
Dispersions
Kidsgrove, Stoke-on-Trent,
Staffs, United Kingdom

Jack Hickey

International Paint Company
Union, New Jersey

Herman Hockmeyer

Hockmeyer Equipment
Corporation
Elizabeth City, North Carolina

Krister Holmberg

Chalmers University of
Technology
Göteborg, Sweden

Albert G. Hoyle

Hoyle Associates
Lowell, Massachusetts

H. F. Huber

Hüls Troisdorf AG

Troisdorf/Marl, Germany

Michael Iskowitz

Kop-Coat Marine Group
Rockaway, New Jersey

Joseph L. Johnson

Aqualon Company
Wilmington, Delaware

Stephen L. Kaplan

Plasma Science, Inc.
Belmont, California

Douglas S. Kendall

National Enforcement
Investigations Center
U.S. Environmental Protection
Agency
Denver Federal Center
Denver, Colorado

Ashok Khokhani

Engelhard Corporation
Iselin, New Jersey

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ix

Carol D. Klein

Spectra Colors Corporation
Kearny, New Jersey

Lisa C. Klein

Ceramic and Materials
Engineering
Rutgers — The State University
of New Jersey
Piscataway, New Jersey

Joseph V. Koleske

Charleston, West Virginia

Alan Lambuth

Boise Cascade
Boise, Idaho

Kenneth Lawson

DeSoto, Inc.
Des Plaines, Illinois

B. H. Lee

Ciba-Geigy Corporation
Ardsley, New York

Peter A. Lewis

Sun Chemical Corporation
Cincinnati, Ohio

Raimond Liepins

Los Alamos National Laboratory
Los Alamos, New Mexico

H. Thomas Lindland

Flynn Burner Corporation
New Rochelle, New York

Harry G. Lippert

Extrusion Dies, Inc.
Chippewa Falls, Wisconsin

Ronald A. Lombardi

ICI Resins US
Wilmington, Massachusetts

Donald M. MacLeod

Industry Tech
Oldsmar, Florida

Algirdas Matukonis

Kaunas Technical University
Kaunas, Lithuania

John A. McClenathan

IMD Corporation
Birmingham, Alabama

Christopher W.
McGlinchey

The Metropolitan Museum of
Art
New York, New York

Frederic S. McIntyre

Acumeter Laboratories, Inc.
Marlborough, Massachusetts

Timothy B. McSweeney

Screen Printing Association
International
Fairfax, Virginia

R. Milker

Lohmann GmbH
Neuwied, Germany

Samuel P. Morell

S. P. Morell and Company
Armonk, New York

Wayne E. Mozer

Oxford Analytical, Inc.
Andover, Massachusetts

Helmut W. J. Müller

BASF AG
Ludwigshafen/Rhein, Germany

Richard Neumann

Windmöller & Hölscher
Lengerich/Westfalen, Germany

Robert E. Norland

Norland Products, Inc.
North Brunswick, New Jersey

Milton Nowak

Troy Chemical
Newark, New Jersey

Michael O’Mary

The Armoloy Corporation
DeKalb, Illinois

Robert J. Partyka

BeamAlloy Corporation
Dublin, Ohio

John A. Pasquale III

Liberty Machine Company
Paterson, New Jersey

Patrick Patton

Q-Panel Lab Products
Cleveland, Ohio

Detlef van Peij

Solventborne Coatings —
Europe
Elementis GmbH
Cologne, Germany

Kim S. Percell

Witco Corporation
Memphis, Tennessee

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x

Edwin P. Plueddemann

Dow Corning Corporation
Midland, Michigan

Liudas Pranevicius

Vytautas Magnus University
Kaunas, Lithuania

Charles P. Rader

Advanced Elastomer Systems,
L.P.
Akron, Ohio

Valentinas Rajeckas

Kaunas Polytechnic University
Kaunas, Lithuania

H. Randhawa

Vac-Tec Systems, Inc.
Boulder, Colorado

Richard Rathmell

Londonderry, New Hampshire

Donald A. Reinke

Oliver Products Company
(Retired)
Grand Rapids, Michigan

Peter W. Rose

Plasma Science, Inc.
Belmont, California

D. Satas

Satas & Associates
Warwick, Rhode Island

Milton C. Schmit

Plymouth Printing Company,
Inc.
Cranford, New Jersey

Jaykumar (Jay) J. Shah

Decora
Fort Edward, New York

Douglas N. Smith

Waterborne Coatings — Global
Elementis GmbH
Cologne, Germany

Steve Stalker

ITW Industrial Finishing
Glendale Heights, Illinois

Henry R. Stoner

Henry R. Stoner Associates
North Plainfield, New Jersey

D. Stoye

Hüls Troisdorf AG
Troisdorf/Marl, Germany

Larry S. Timm

Findley Adhesives, Inc.
Wauwatosa, Wisconsin

Harry H. Tomlinson

Witco Corporation
Memphis, Tennessee
Arthur A. Tracton
Consultant
Bridgewater, New Jersey
George D. Vaughn
Surface Specialties Melamines
Springfield, Massachusetts
A. Vaˇskelis
Lithuanian Academy of Sciences
Vilnius, Lithuania
Subbu Venkatraman
Raychem Corporation
Menlo Park, California
Theodore G.
Vernardakis
BCM Inks USA, Inc.

Cincinnati, Ohio
Lawrence R. Waelde
Troy Corporation
Florham Park, New Jersey
Leonard E. Walp
Witco Corporation
Memphis, Tennessee
Patrick J. Whitcomb
Stat-Ease, Inc.
Minneapolis, Minnesota
K. Winkowski
ISP Corporation
Piscataway, New Jersey
Kurt A. Wood
Arkema, Inc.
King of Prussia, Pennsylvania
Daniel M. Zavisza
Hercules Incorporated
Wilmington, Delaware
Randall W. Zempel
Dow Chemical Company
Midland, Michigan
Ulrich Zorll
Forschungsinstitut fur Pigmente
and Lacke
Stuttgart, Germany
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xi

Contents

I

Fundamentals and Testing

1 Rheology and Surface Chemistry 1-1

K. B. Gilleo

2 Coating Rheology 2-1

Chi-Ming Chan and Subbu Venkatraman

3 Leveling 3-1

D. Satas*

4 Structure–Property Relationships in Polymers 4-1

Subbu Venkatraman

5 The Theory of Adhesion 5-1

Carl A. Dahlquist

6 Adhesion Testing 6-1

Ulrich Zorll

7 Coating Calculations 7-1

Arthur A. Tracton

8 Infrared Spectroscopy of Coatings 8-1

Douglas S. Kendall

9 Thermal Analysis for Coatings Characterizations 9-1

William S. Gilman

10 Color Measurement for the Coatings Industry 10-1

Harold Van Aken

11 The Use of X-ray Fluorescence for Coat Weight Determinations 11-1

Wayne E. Mozer

12 Sunlight, Ultraviolet, and Accelerated Weathering 12-1

Patrick Brennan and Carol Fedor

13 Cure Monitoring: Microdielectric Techniques 13-1

David R. Day

14 Test Panels 14-1

Douglas Grossman and Patrick Patton

*Deceased.

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xii

15 Design of Experiments for Coatings 15-1

Mark J. Anderson and Patrick J. Whitcomb

16 Top 10 Reasons Not to Base Service Life Predictions upon Accelerated Lab
Light Stability Tests 16-1

Eric T. Everett

17 Under What Regulation? 17-1

Arthur A. Tracton

II

Coating and Processing Techniques

18 Wire-Wound Rod Coating 18-1

Donald M. MacLeod

19 Slot Die Coating for Low Viscosity Fluids 19-1

Harry G. Lippert

20 Extrusion Coating with Acid Copolymers and Lonomers 20-1

Donald L. Brebner

21 Porous Roll Coater 21-1

Frederic S. McIntyre

22 Rotary Screen Coating 22-1

F. A. Goossens

23 Screen Printing 23-1

Timothy B. McSweeney

24 Flexography 24-1

Richard Neumann

25 Ink-Jet Printing 25-1

Naomi Luft Cameron

26 Electrodeposition of Polymers 26-1

George E. F. Brewer

27 Electroless Plating 27-1

A. Vakelis

28 The Electrolizing Thin, Dense, Chromium Process 28-1

Michael O’Mary

29 The Armoloy Chromium Process 29-1

Michael O’Mary

30 Sputtered Thin Film Coatings 30-1

Brian E. Aufderheide

31 Vapor Deposition Coating Technologies 31-1

Lindas Pranevicius

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xiii

32 Cathodic Arc Plasma Deposition 32-1

H. Randhawa

33 Industrial Diamond and Diamondlike Films 33-1

Arnold H. Deutchman and Robert J. Partyka

34 Tribological Synergistic Coatings 34-1

Walter Alina

35 Chemical Vapor Deposition 35-1

Deepak G. Bhat

36 Solvent Vapor Emission Control 36-1

Richard Rathmell

37 Surface Treatment of Plastics 37-1

William F. Harrington, Jr.

38 Flame Surface Treatment 38-1

H. Thomas Lindland

39 Plasma Surface Treatment 39-1

Stephen L. Kaplan and Peter W. Rose

40 Surface Pretreatment of Polymer Webs by Fluorine 40-1

R. Milker and Artur Koch

41 Calendering of Magnetic Media 41-1

John A. McClenathan

42 Embossing 42-1

John A. Pasquale III

43 In-Mold Finishing 43-1

Robert W. Carpenter

44 HVLP: The Science of High-Volume, Low-Pressure Finishing 44-1

Steve Stalker

45 A Practical Guide to High-Speed Dispersion 45-1

Herman Hockmeyer

III

Materials

46 Acrylic Polymers 46-1

Ronald A. Lombardi and James D. Gasper

47 Vinyl Ether Polymers 47-1

Helmut W. J. Müller

48 Poly(Styrene-Butadiene) 48-1

Randall W. Zempel

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xiv

49 Liquid Polymers for Coatings 49-1

Robert D. Athey, Jr.

50 Polyesters 50-1

H. F. Huber and D. Stoye

51 Alkyd Resins 51-1

Krister Holmberg

52 The Polyurea Revolution: Protective Coatings for the 21st Century 52-1

Bruce R. Baxter

53 Phenolic Resins 53-1

Kenneth Bourlier

54 Coal Tar and Asphalt Coatings 54-1

Henry R. Stoner

55 Vulcanizate Thermoplastic Elastomers 55-1

Charles P. Rader

56 Olefinic Thermoplastic Elastomers 56-1

Jesse Edenbaum

57 Ethylene Vinyl Alcohol Copolymer (EVOH) Resins 57-1

R. H. Foster

58 Elastomeric Alloy Thermoplastic Elastomers 58-1

Charles P. Rader

59 Polyvinyl Chloride and Its Copolymers in Plastisol Coatings 59-1

Jesse Edenbaum

60 Polyvinyl Acetal Resins 60-1

Thomas P. Blomstrom

61 Polyimides 61-1

B. H. Lee

62 Parylene Coating 62-1

William F. Beach

63 Nitrocellulose 63-1

Daniel M. Zavisza

64 Soybean, Blood, and Casein Glues 64-1

Alan Lambuth

65 Fish Gelatin and Fish Glue 65-1

Robert E. Norland

66 Waxes 66-1

J. David Bower

67 Carboxymethylcellulose 67-1

Richey M. Davis

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xv

68 Hydroxyethylcellulose 68-1

Lisa A. Burmeister

69 Antistatic and Conductive Additives 69-1

B. Davis

70 Silane Adhesion Promoters 70-1

Edwin P. Plueddemann

71 Chromium Complexes 71-1

J. Rufford Harrison

72 Nonmetallic Fatty Chemicals as Internal Mold Release Agents in Polymers 72-1

Kim S. Percell, Harry H. Tomlinson, and Leonard E. Walp

73 Organic Peroxides 73-1

Peter A. Callais

74 Surfactants for Waterborne Coatings Applications 74-1

Samuel P. Morell

75 Surfactants, Dispersants, and Defoamers for the Coatings, Inks, and
Adhesives Industries 75-1

John W Du

76 Pigment Dispersion 76-1

Theodore G. Vernardakis

77 Colored Inorganic Pigments 77-1

Peter A. Lewis

78 Organic Pigments 78-1

Peter A. Lewis

79 Amino Resins 79-1

George D. Vaughn

80 Driers 80-1

Milton Nowak

81 Biocides for the Coatings Industry 81-1

K. Winkowski

82 Clays 82-1

Ashok Khokhani

83 Fluorocarbon Resins for Coatings and Inks 83-1

Kurt A. Wood

84 High Temperature Pigments 84-1

Helen Hatcher

85 Polyurethane Associative Thickeners for Waterborne Coatings 85-1

Douglas N. Smith and Detlef van Peij

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xvi

IV

Surface Coatings

86 Flexographic Inks 86-1

Sam Gilbert

87 Multicolor Coatings 87-1

Robert D. Athey, Jr.

88 Paintings Conservation Varnish 88-1

Christopher W. McGlinchey

89 Thermoset Powder Coatings 89-1

Lawrence R. Waelde

90 Peelable Medical Coatings 90-1

Donald A. Reinke

91 Conductive Coatings 91-1

Raimond Liepins

92 Silicone Release Coatings 92-1

Richard P. Eckberg

93 Silicone Hard Coatings 93-1

Edward A. Bernheim

94 Pressure-Sensitive Adhesives and Adhesive Products 94-1

D. Satas*

95 Self-Seal Adhesives 95-1

Larry S. Timm

96 Solgel Coatings 96-1

Lisa C. Klein

97 Radiation-Cured Coatings 97-1

Joseph V. Koleske

98 Nonwoven Fabric Binders 98-1

Albert G. Hoyle

99 Fire-Retardant/Fire-Resistive Coatings 99-1

Joseph Green

100 Leather Coatings 100-1

Valentinas Rajeckas

101 Metal Coatings 101-1

Robert D. Athey, Jr.

102 Corrosion and Its Control by Coatings 102-1

Clive H. Hare

103 Marine Coatings Industry 103-1

Jack Hickey

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xvii

104 Decorative Surface Protection Products 104-1

Jaykumar (Jay) J. Shah

105 Coated Fabrics for Protective Clothing 105-1

N. J. Abbott

106 Coated Fabrics for Apparel Use: The Problem of Comfort 106-1

N. J. Abbott

107 Architectural Fabrics 107-1

Marcel Dery

108 Gummed Tape 108-1

Milton C. Schmit

109 Transdermal Drug Delivery Systems 109-1

Gary W. Cleary

110 Optical Fiber Coatings 110-1

Kenneth Lawson

111 Exterior Wood Finishes 111-1

William C. Feist

112 Pharmaceutical Tablet Coating 112-1

Joseph L. Johnson

113 Textiles for Coating 113-1

Algirdas Matukonis

114 Nonwovens as Coating and Laminating Substrates 114-1

Albert G. Hoyle

115 General Use of Inks and the Dyes Used to Make Them 115-1

Carol D. Klein

116 Gravure Inks 116-1

Sam Gilbert

117 Artist’s Paints: Their Composition and History 117-1

Michael Iskowitz

118 Fade Resistance of Lithographic Inks — A New Path Forward: Real World
Exposures in Florida and Arizona Compared to Accelerated Xenon Arc
Exposures 118-1

Eric T. Everett, John Lind, and John Stack

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I

-1

I

Fundamentals and

Testing

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1

-1

1

Rheology and Surface

Chemistry

1.1 Introduction

1-

1
1.2 Rheology

1-

2

1.4 Summary

1-

12
References

1-

12
Bibliography

1-

12

1.1 Introduction

A basic understanding of rheology and surface chemistry, two primary sciences of liquid flow and
solid–liquid interaction, is necessary for understanding coating and printing processes and materials. A
generally qualitative treatment of these subjects will suffice to provide the insight needed to use and apply
coatings and inks and to help solve the problems associated with their use.
Rheology, in the broadest sense, is the study of the physical behavior of all materials when placed under
stress. Four general categories are recognized: elasticity, plasticity, rigidity, and viscosity. Our concern here
is with liquids and pastes. The scope of rheology of fluids encompasses the changes in the shape of a
liquid as physical force is applied and removed. Viscosity is a key rheological property of coatings and
inks. Viscosity is simply the resistance of the ink to flow — the ratio of shear stress to shear rate.
Throughout coating and printing processes, mechanical forces of various types and quantities are
exerted. The amount of shear force directly affects the viscosity value for non-Newtonian fluids. Most
coatings undergo some degree of “shear thinning” phenomenon when worked by mixing or running on
a coater. Heavy inks are especially prone to shear thinning. As shear rate is increased, the viscosity drops,
in some cases, dramatically.
This seems simple enough except for two other effects. One is called the yield point. This is the shear
rate required to cause flow. Ketchup often refuses to flow until a little extra shear force is applied. Then
it often flows too freely. Once the yield point has been exceeded the solidlike behavior vanishes. The
loose network structure is broken up. Inks also display this yield point property, but to a lesser degree.

Yield point is one of the most important ink properties.
Yield value, an important, but often ignored attribute of liquids, will also be discussed. We must
examine rheology as a dynamic variable and explore how it changes throughout the coating process. The
mutual interaction, in which the coating process alters viscosity and rheology affects the process, will be
a key concept in our discussions of coating technology.

K. B. Gilleo

Sheldahl, Inc.

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Types of Viscosity Behavior • Temperature Effects • Solvent
Surfactants • Leveling
1.3 Surface Chemistry 1-8
Effects • Viscosity Measurement • Yield Value
Surface Tension • Measuring Surface Tension • Wetting •

1

-4

Coatings Technology Handbook, Third Edition

1.1 shows the shear stress–shear rate curve and the yield point. Although plastic behavior is of questionable
value to ketchup, it has some benefit in inks and paints. Actually, it is the yield point phenomenon that
is of practical value. No-drip paints are an excellent example of the usefulness of yield point. After the
brush stroke force has been removed, the paint’s viscosity builds quickly until flow stops. Dripping is
prevented because the yield point exceeds the force of gravity.
Ink bleed in a printing ink, the tendency to flow beyond the printed boundaries, is controlled by yield

point. Inks with a high yield point will not bleed, but their flow out may be poor. A very low yield point
will provide excellent flow out, but bleed may be excessive. Just the right yield point provides the needed
flow out and leveling without excessive bleed. Both polymer binders and fillers can account for the yield
point phenomenon. At rest, polymer chains are randomly oriented and offer more resistance to flow.
Application of shear force straightens the chains in the direction of flow, reducing resistance. Solid fillers
can form loose molecular attraction structures, which break down quickly under shear.

1.2.1.2 Pseudoplasticity

Like plastic-behaving materials, pseudoplastic liquids drop in viscosity as force is applied. There is no
yield point, however. The more energy applied, the greater the thinning. When shear rate is reduced, the
viscosity increases at the same rate by which the force is diminished. There is no hysteresis; the shear
pseudoplastic behavior using viscosity–shear rate curves.
Many coatings exhibit this kind of behavior, but with time dependency. There is a pronounced delay
in viscosity increase after force has been removed. This form of pseudoplasticity with a hysteresis loop
is called thixotropy. Pseudoplasticity is generally a useful property for coatings and inks. However,
thixotropy is even more useful.

1.2.1.2.1 Thixotropy

Thixotropy is a special case of pseudoplasticity. The material undergoes “shear thinning”; but as shear
forces are reduced, viscosity increases at a lesser rate to produce a hysteresis loop. Thixotropy is very
common and very useful. Dripless house paints owe their driplessness to thixotropy. The paint begins
as a moderately viscous material that stays on the brush. It quickly drops in viscosity under the shear
stress of brushing for easy, smooth application. A return to higher viscosity, when shearing action stops,
prevents dripping and sagging.
Screen printing inks also benefit from thixotropy. The relatively high viscosity screen ink drops abruptly
in viscosity under the high shear stress associated with being forced through a fine mesh screen. The

FIGURE 1.1

Shear stress–shear rate curves.
Rate (sec.
−1
)
Yield
Point
Shear Stress
Plastic
Pseudoplastic
Dilatant
Newtonian

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© 2006 by Taylor & Francis Group, LLC
stress–shear rate curve is the same in both directions as was seen in Figure 1.1. Figure 1.2 compares

Rheology and Surface Chemistry

1

-9

high viscosity materials. The intermolecular (solid–liquid) attraction is greater in this case. The surface
energy of the solid is higher than the liquid’s surface tension.
Measuring the contact angle is a simple technique for determining the relative difference between the
two surface tensions. A high contact angle signifies a large departure, while a small angle suggests that
the two values are close, but not equal.

TA B LE 1.3

Surface Tension of Liquids

Liquid
Surface Tension
(dynes/cm)

SF

6

5.6
Tr ifluoroacetic acid 15.6
Heptane 22.1
Methanol 24.0
Acetone 26.3
Dimethylformamide (DMF) 36.8
Dimethyl sulfoxide (DMSO) 43.5
Ethylene glycol 48.4
Formamide 59.1
Glycerol 63.1
Diiodomethane 70.2
Water 72.8
Mercury, metal 490.6

Source:

From Dean, J., Ed.,

Lange’s Handbook

of Chemistry,

13th ed., McGraw-Hill, New York,
1985

.

4

TA B LE 1.4

Surface Tension of Polymers

Polymer
Surface Tension
(dynes/cm)

Polyperfluoropropylene 16
Polytetrafluoroethylene (Teflon) 18.5
Polydimethyliloxane 24
Polyethylene 31
Polystyrene 34
Polymethylmethacrylate (acrylic) 39
Polyvinyl chloride (PVC) 40
Polyethylene terephthalate (polyester) 43
Polyhexamethylene adipate (nylon) 46

Source

: From Bikales, N.M.,

Adhesion and

Bonding,
Wiley-Interscience, New York, 1971

.

5

FIGURE 1.4

Contact angle.
Liquid
θ

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© 2006 by Taylor & Francis Group, LLC

2

-1

2

Coating Rheology

2.1 Introduction

2-

1
2.2 Definitions and Measurement Techniques

2-

1

2.3 Rheological Phenomena in Coating

2-

5

Acknowledgments

2-

13
References

2-

13

2.1 Introduction

Depending on the nature of the starting material, coatings can be broadly classified into solvent-borne
and powder coatings. The solvent-borne coatings include both solutions (high and low solid contents)
and suspensions or dispersions. Methods of application and the markets for these coatings are listed in

2.2 Definitions and Measurement Techniques

2.2.1 Surface Tension

Surface tension is defined as the excess force per unit length at the surface; it is reckoned as positive if it
acts in such a direction as to contract the surface.

1,6

The tendency of a system to decrease its surface area
is the result of the excess surface energy, because the surface atoms are subjected to a different environment
as compared to those in the bulk. Surface tension of liquids and polymer melts can be measured by
methods such as capillary tube,

1

Du Nuoy ring,

2,7

Wilhelmy plate,

3,8

and pendent drop.

4,5

We shall focus

our discussion on two methods: the capillary-height and pendant-drop methods.
The capillary-height method is the most suitable for low viscosity liquids because the system takes a
long time to reach equilibrium for high viscosity liquids. It is reported that as many as 4 days are needed

5

At equilibrium, the force exerted on the meniscus periphery due to the surface tension must be balanced
by the weight of the liquid column. Neglecting the weight of the liquid above the meniscus, an approx-
imate equation can be written as follows:
(2.1)
where

∆ρ

is the density difference between the liquid and air,

g

is the gravitational constant,

h

is the
height of the liquid column,

γ

is the surface tension,

θ

is the contact angle, and

r

is the radius of the
∆ρ γ
θ
gh
r
= 2
cos

Chi-Ming Chan

Raychem Corporation

Subbu Venkatraman

Raychem Corporation

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© 2006 by Taylor & Francis Group, LLC
Surface Tension • Viscosity • Thixotropy • Dilatancy • Yield
Stress • Elasticity
We tting • Coalescence • Sagging and Slumping • Leveling •
Depressions: Bernard Cells and Craters
Viscosity Changes after Application • Edge and Corner Effects •
Ta ble 2.1.
to attain equilibrium for a polystyrene melt at 200°C. Figure 2.1 illustrates the capillary-height method.