Technology for Waterborne Coatings

311 Pages·1997·28.225 MB·English

by  J. Edward Glass (Eds.)

A CS S Y M P O S I UM SERIES 663
Technology for Waterborne
Coatings
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66 J. Edward Glass, EDITOR
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American Chemical Society, Washington, DC
In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
TP 934 .T43 1997 Copy 1
Technology for waterborne
coatings
Library of Congress Cataloging-in-Publication Data
Technology for waterborne coatings / J. Edward Glass, editor.
p. cm—(ACS symposium series, ISSN 0097-6156; 663)
"Developed froma symposium sponsored by the Division of Polymeric
Materials: Science and Engineering, Inc., at the 210th National Meeting
of the American Chemical Society, Chicago, Illinois, August 20-25,
1995."
01 Includes bibliographical references and indexes.
0
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3.f ISBN 0-8412-3501-5
6
6
7-0 1. Emulsion paint—Congresses.
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19 I. Glass, J. E. (J. Edward), 1937- . II. American Chemical Society.
k- Division of Polymeric Materials: Science and Engineering. III. American
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1/ Chemical Society. Meeting (210th: 1995: Chicago, Ill.) IV. Series.
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0.1 TP934.T43 1997
1 667'.9—dc20 97-5741
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p://pubs.April 1, This book is printed on acid-free, recycled paper.
2 | httDate: Copyright © 1997 American Chemical Society
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PRINTED IN THE UNITED STATES OF AMERICA
In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Advisory Board
ACS Symposium Series
Robert J. Alaimo Cynthia A. Maryanoff
Procter & Gamble Pharmaceuticals R. W. Johnson Pharmaceutical
Research Institute
Mark Arnold
University of Iowa Roger A. Minear
University of Illinois
1 David Baker at Urbana-Champaign
0
w0 University of Tennessee
3.f Omkaram Nalamasu
6
6 Arindam Bose AT&T Bell Laboratories
0
7- Pfizer Central Research
9
19 Vincent Pecoraro
bk- Robert F. Brady, Jr. University of Michigan
21/ Naval Research Laboratory
0
0.1 George W. Roberts
org 7 | doi: 1 MChaermy EEd.i tC Caosmteplalnioyn NJoohrtnh RC.a rSohlinaap lSetya te University
acs.199 Margaret A. Cavanaugh University of Illinois
bs.1, National Science Foundation at Urbana-Champaign
2 | http://puDate: April AUnritvheursr itBy .o Ef Wllisis consin at Madison DCoonucgurlaresn At T. eSchmniotlho gies Corporation
ust 17, 201ublication UGnuinvedras itIy. oGf Keoarngsa s LD.u SPoonmt asundaram
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Au Madeleine M. Joullie Michael D. Taylor

University of Pennsylvania Parke-Davis Pharmaceutical Research
Lawrence P. Klemann William C. Walker
Nabisco Foods Group DuPont
Douglas R. Lloyd Peter Willett
The University of Texas at Austin University of Sheffield (England)
In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Foreword
THE ACS SYMPOSIUM SERIES was first published in 1974 to
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0. This anonymous review process is supervised by the organiz
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oi: er^) of the symposium, who become the editor(s) of the book.
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cs.99 mendations of both the reviewers and the editors, prepare
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ust 17, 201ublication AtioCnSs BoOf OprKeSv ioDuEsPlyA pRuTbMliEshNeTd papers are not accepted.
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In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Preface
MANY INDUSTRIAL SUPPLIERS in the mid-1960s, even those supplying
solvent to the coating industry, were actively engaged in research in zero
volatile organic component (VOC) UV and powder coatings. For most
suppliers, this effort declined significantly or was terminated by the early
1970s because growth in these areas was slow and demanded new equip
ment. However, even with growth, the number of surfaces to which LTV
1 and powder coatings can be applied is limited. Much of the research in
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pr the 1970s and 1980s was devoted to the high-solids area. Some of this
3.
6 research suggested that elimination of the solvent in high-solids formula
6
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7- tions was achievable by replacing the solvent with nonpolluting supercriti
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9 cal fluids such as carbon dioxide. After a short time, it was concluded
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bk- that nearly half of the solvent used in high solids had to be added back in
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2 the critical fluid approach. In the 1990s, the emphasis in coatings
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0. research has turned strongly to the waterborne area.
1
oi: In accordance with the rapid changes in technology, the Polymeric
org 7 | d Materials: Science and Engineering, Inc. (PMSE), division of the Ameri
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used in architectural, photographic, and paper coatings, and aqueous
epoxy and polyurethane dispersions used in original equipment manufac
turer coatings. Topics include their synthesis from the view of their
chain-growth or step-growth mechanism, the type of stabilizer employed
in the production of the disperse phase, and the compositional influences
of the resin particle on their interfacial energies and morphology.
Chapters are also included on the radiation curing of applied aqueous
dispersions, on the curing of films through carbodiimide chemistry, and
on polyurethane films formed from nonisocyanate precursors. The
dispersions and film properties of the different resin types are discussed,
as well as surfactant orientations at the film substrate and air interfaces.
The prior art of particle coalescence and film formation of latex
vii
In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
particles is reviewed, and recent studies on the particle coalescence of
step-growth oligomer dispersions (polyurethanes and epoxies) are dis
cussed The phenomenon of film formation is presented from uniquely
different perspectives in the chapters on waterborne alkyd dispersions and
high-clay-content paper coatings.
Drying is an important part in the film formation process, and a
chapter devoted to this subject is included in this text. Chapters devoted
to the interactions of dispersions and dispersion rheology and to the spray
application of waterborne coatings are also included.
Acknowledgments
Funding for support of the symposium speakers was provided by the
1 PMSE division of the ACS; the S. C. Johnson, Aqualon division of Her
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pr0 cules, Inc.; Union Carbide Corporation; and Rohm and Haas Company.
63. Their support is gratefully acknowledged. Appreciation is also expressed
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7-0 to the reviewers for their comments and contributions to this book.
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ugust 17, 201 Publication
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viii
In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Chapter 1
Waterborne Coatings with an Emphasis
on Synthetic Aspects: An Overview
Melissa A. Grunlan, Lin-Lin Xing, and J. Edward Glass1
Department of Polymers and Coatings, North Dakota State University,
Fargo, ND 58105
01 This chapter provides an overview of water-borne coatings to
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ch complement the chapters that follow. It provides the basic chemical
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6 reactions that many outside the field will not be familiar with, and
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7- general principles that those practicing in the field may have forgotten.
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9 The most active areas in water-borne coatings are in the synthesis of
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21/ mechanism and water-borne polyurethane, polyester, and epoxy resins
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0.1 synthesized by step-growth polymerizations. Water-borne epoxy resins
oi: 1 are discussed in detail in chapter 5. The other resin families are
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2 | http://pubs.Date: April 1, film properties.
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A application of a coating the concentration of the polymeric resin was necessarily low,
and the organic solvent emitted to the atmosphere (VOC, Volatile Organic
Component) was high. As society changed and environmental concerns were
emphasized, coating technology has advanced in several directions. Two areas
considered VOC free are UV cure(i) and powder(2) coatings. UV curing of solvent-
free formulations is restricted, with only a few exceptions, to flat surfaces, with film
thickness and pigmentation limitations. Powder coatings are subject to Faraday effects
and can not be applied to many surfaces.
The effort to produce synthetic rubber during World War II led to the
development of an emulsion polymerization process, and with it, water-bome coatings
1Corresponding author
© 1997 American Chemical Society
In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
2 TECHNOLOGY FOR WATERBORNE COATINGS
as they are designed in the architectural and paper coatings area. Such an emulsion
polymerization recipe employs a surfactant, a monomer with low solubility in water,
and a redox free radical initiator in the aqueous phase (recipe given in Table I in
chapter 2). When a monomer with low solubility in the aqueous phase (e.g., styrene
and butadiene) is employed, the emulsion polymerization occurs by a micellar process.
After the initiator has reacted with the monomer in the aqueous phase, the monomer
propagates to an oligomeric form and then enters a micelle, formed by the aggregation
of excess of surfactant used in the polymerization recipe. The chain growth
polymerization (chapter 3 in reference 3) of the olefinic monomer then occurs in the
micelle. When the chain growth polymerization of olefinic monomers occurs in bulk or
solvent, the free-radical concentration of the propagating species should be kept below
10"8 molar to miriimize termination reactions. Polymerization in a micellar
environment isolates the propagating species and permits higher concentrations of
propagating radicals. Thus, higher rates of polymerization (Rp) with simultaneous
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3.
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and
N = k(R/i)2/5(aS)3/5 (3)
it s
where: k = constant
|i = rate of volume increase of a polymer particle
as = interfacial surface area occupied by a surfactant molecule
S = total concentration of surfactant in the system
A more developed description of the process is given in chapter 2 by a major
contributor to this technology, John Gardon. The high rates of polymerization, with
In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
1. GRUNLAN ET AL. Overview with an Emphasis on Synthetic Aspects 3
ease of removal of the heats of polymerization in an aqueous environment and the ease
in handling of a low glass transition temperature particle, are major assets of the
emulsion polymerization process.
As the market was developed in the sixties, the compositions of the latices
varied from styrene/butadiene, to methylmethacrylate/acrylic esters (for their exterior
durability), to low cost vinyl esters. With the transition in latex compositions to vinyl
acetate, the oligomers became more hydrophilic and participated less in the micellar
polymerization process. They continued to polymerize in the aqueous phase and then
aggregate into a polymer colloid. Consequently, the rate for an emulsion
polymerization of vinyl acetate is not dependent on the surfactant concentrations as
cited for styrene in equations 1 and 3. For a more detailed treatment of the nonmicellar
emulsion polymerization where there is essentially no polymerization in micelles, (i.e.,
the Hansen, Ugelstad, Fitch, Tsai theory) the reader is referred to references 4 and 5.
For a discussion of the influence of monomer and surfactant hydrophilicity on the
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3.
66 The use of seeding techniques to produce latices for more specialty applications
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7- is discussed in chapter 2. Compositional influences on interfacial tensions and how this
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19 affects the latex's morphology are discussed in chapter 3. What follows below in this
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b chapter relates more to commodity latex production for use in architectural and paper
1/
2 coating markets.
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A semi-continuous process. The acids polymerize in sequence runs of acrylic or

methacrylic acid, not possible in the step-growth synthesis of polyester and
polyurethane disperse phases, discussed in the later section of this chapter. The
repeating acid segments position near or on the surface of the latex and expand to
provide electrosteric stabilization of the particle when neutralized. The parameters that
influence the positioning of the acid surface stabilizers near the water/latex interface
are the hydrophilicity of the copolymer and the latex's glass transition temperature^).
Thus, for a methyl methacrylate latex having equivalent glass transition temperatures,
the surface acid content and its extent of swelling (reflected by sedimentation
coefficients in Figures 2 and 3) will be greater in a copolymer composition having a
In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
4 TECHNOLOGY FOR WATERBORNE COATINGS
more hydrophilic acrylate comonomer (where more is required of ethyl acetate than of
butyl acrylate to achieve a given glass transition temperature, Figure 2). With the more
hydrophobic acrylate comonomer, more of the 2 wt.% methacrylic acid charged is
retained within the latex particle. The importance of the hydrophilicity of the latex
composition also is evident in styrene and methyl methacrylate latices (not illustrated),
both containing 50 % ethyl acrylate. The methacrylic acid segments are buried within
the more hydrophobic styrene latex synthesized by a conventional batch process. In
other compositions having a constant hydrophobicity but varying glass transition
temperature, the importance of the glass transition temperature is evident (Figure 3).
Such stabilizers have been important in small particle (100 nm) latices used in
formulations containing a variety of pigments, because of their high pigment binding
power. The importance of the oligomeric surface stabilizers in photographic processes
are discussed in chapter 12. The theoretical treatment of the parameters influencing the
stability of this type of latex particle and for those discussed in the next paragraph
1
0 containing only nonionic grafted segments are treated in chapter 6 by Professor
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Figure 1. Electrosteric and Steric Stabilized Latices
While oligomeric surface acid stabilizers are used in vinyl acetate latices in
the paper coatings area, where water sensitivity is not a factor in formulations
containing high clay contents, and in methacrylic and styrene based latices in
architectural latex coatings, vinyl acetate latices in low pigment volume concentration
architectural coatings are water sensitive and surface acids are not the method of
In Technology for Waterborne Coatings; Glass, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.