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I
PAINT TECHNOLOGY
AND AIR POLLUTION:
SURVEY AND
C ASSESSMENT
ENTAL PROTECTION AGENCY
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950 R 72001
PAINT TECHNOLOGY
AND AIR POLLUTION: A SURVEY
AND ECONOMIC ASSESSMENT
J.W. Spence
and
F.H. Haynie
National Environmental Research Center
ENVIRONMENTAL PROTECTION AGENCY
Office of Air Programs
Research Triangle Park, North Carolina
February 1972
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C., 20402 - Price 35 cents
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The AP series of reports is issued by the Environmental Protection Agency to
report the results of scientific and engineering studies, and information of
general interest in the field of air pollution. Information presented in this series
includes coverage of intramural activities involving air pollution research and
control technology and of cooperative programs and studies conducted in
conjunction with state and local agencies, research institutes, and industrial
organizations. Copies of AP reports are available free of charge-as supplies
permit-from the Office of Technical Information and Publication, Office of
Air Programs, Environmental Protection Agency, Research Triangle Park,
North Carolina 27711.
Office of Air Programs Publication No. AP-103
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ACKNOWLEDGMENT
The authors wish to thank B. G. Brand, Senior Research Chemist, Battelle
Memorial Institute, for technical suggestions of value in preparing this
manuscript.
ill
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CONTENTS
Page
LIST OF FIGURES vi
LIST OF TABLES . vii
ABSTRACT .... ... . viii
INTRODUCTION .... .1
DEVELOPMENTS WITHIN THE PAINT INDUSTRY . . . . 3
Historical Developments ... . 3
Paint Formulation .... 7
Binders . 7
Pigments . 8
Water-Base Paints (Latex) 9
Application Techniques 11
Electrodeposition ..11
Coil Coating . .... 12
Electron-Beam Curing .... . 14
DETERIORATION OF EXTERIOR PAINT FILMS 17
Industrial Testing 17
Effects of Air Pollution on Exterior Paints . .22
Sulfur Dioxide ... 24
Hydrogen Sulfide . 25
Particulate Matter . 26
ECONOMIC ASSESSMENT OF AIR POLLUTION DAMAGE
TO EXTERIOR PAINTS . ... 31
AREAS FOR FUTURE INVESTIGATION 35
CONCLUSIONS 37
REFERENCES . 39
BIBLIOGRAPHY 43
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LIST OF FIGURES
Figure Page
1 Initial Creep of EM 7339 Second-Quality Emulsion-Base Paint,
Before and After 505-hr Exposure to Ozone at 60°C 21
2 Initial Creep of EM 7338 First-Quality Emulsion-Base Paint,
Before and After 505-hr Exposure to Ozone at 60°C 21
3 Relationship of Maintenance Frequency for Exterior Repainting
to Particulate Concentration 28
VI
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LIST OF TABLES
Table Page
1 History of Coatings Industry in the United States ... 4
2 1968 Trade and Industrial Paint Sales . .... 5
3 U. S. Shipments of Paints, Varnishes, and Lacquers . 6
4 Consumption of Resins by Coatings Industry, 1968 to 1975 . . 8
5 Pigment Consumed by Paint Industry, 1968 to 1975 9
6 Estimated Trade Sales of Latex Paints .... ... .10
7 Shipment of Coil-Coated Steel and Aluminum . . . .13
8 Coil-Coated Organic Resins . . 14
9 Types of Film Failure . .18
10 ASTM Test Methods for Exterior Paint Films . 19
11 Durability of Organic Resin Topcoats . . . .20
12 Mean Concentrations of Three Atmospheric Pollutants 1967 .22
13 Relative Pollution Damage to Materials and Availability of Useful
Information . . . . .23
14 Interval for Exterior Repainting as Function of Particulate
Concentration in Five U. S. Cities .27
15 Mean Annual Frequency for Exterior Wall Painting in Philadelphia
Area as a Function of Particulate Concentration . . .29
16 Economic Assessment of Chemical Deterioration of Exterior
Paints 32
Vll
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ABSTRACT
The objectives of this study are: (1) to survey the technical developments
occurring within the paint industry, (2) to identify the characteristics of
pollutant attacks on exterior paints, and (3) to estimate the annual cost of air
pollutant damage to such paints.
New paint formulations and new application techniques are emerging within
the paint industry. Factory-applied coatings (industrial finishes) appear to have
a bright future in the 1970's. Latex or water-base paints have captured
substantially more than 50 percent of the household painting market and are
spilling over into the industrial market.
The chemical attack of certain air pollutants on exterior finishes is
reviewed. Hydrogen sulfide, which is a localized pollutant, is known to attack
in-service exterior house paints. In laboratory studies ozone and sulfur dioxide
have also been shown to damage paints. There is evidence as well that sulfur
dioxide attacks certain pigments of exterior paints. Dose-response data for
these pollutants are lacking.
An economic assessment was made of the chemical damage of air pollutants
on four classes of exterior paints: (1) household, (2) automotive refinishing,
(3) coil coating, and (4) maintenance. The total estimated cost at the consumer
level is over $0.7 billion annually. Of the four types of exterior paints,
household paint sustains the most damage, representing over 75 percent of the
total dollar loss.
Key Words: material deterioration, exterior paints, pollutants, economic losses,
area surveys, costs.
vui
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PAINT TECHNOLOGY
AND AIR POLLUTION:
A SURVEY AND ECONOMIC
ASSESSMENT
INTRODUCTION
The purpose of this study is to provide the Environmental Protection
Agency and other scientific and lay readers with technical information
pertaining to the effects of air pollutants on exterior paints. The specific goals
of this report are: (1) to survey the technical developments within the paint
industry; (2) to identify the characteristics of pollutant attacks on exterior
paints; and (3) to estimate the annual cost of pollution damage to these paints.
This information will be used to set priorities in planning laboratory
investigations and future contract studies on the effects of air pollutants on
exterior paints.
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DEVELOPMENTS
WITHIN THE PAINT INDUSTRY
The paint industry is currently being confronted with structural materials
such as reinforced plastics, stainless steel, and laminated wood that require
little or no painting. The sales of such materials are cutting into the paint
industrial market. In order to compete, the paint industry is developing thinner
finishes with improved durability for metallic and wooden substrates. Paints
with new potential applications, such as fire retardants for household use and
coatings for plastic materials, are being developed by the industry. This section
discusses trends in the use of raw materials, new techniques emerging within
the industry, and outside factors, such as the continuing passage of air
pollution legislation, which are influencing these trends and techniques.
HISTORICAL DEVELOPMENTS
The paint industry has emerged in the 1970's as a scientific business; just 40
years ago the industry was largely an art. Paint formulation had its beginning
with natural resins and minerals; today the industry spends over $1.4 billion
annually for various synthetic resins, chemical additives, and containers.1 A
historical glimpse of the paint industry through 1962 is shown in Table I.2
The industry has grown to more than 1,600 companies with about 1,875
plants. Sherwin-Williams is the largest paint manufacturer, with about 10
percent of the total market. About 27 producers of paint account for 57
percent of the total sales, and fewer than 20 companies sell paints
nationwide.1'3 Paint manufacturing is one of the few remaining industries
within the United States that consists of small companies that specialize in a
limited product line to be marketed within a geographical region.
The paint industry does not invest heavily in the research and development
of raw materials. According to the National Paint, Varnish, and Lacquer
Association, the paint industry invests only about 2 percent of its sales in
research.3 The industry has been called a parasite because it depends upon the
technology generated within the rubber and plastics industry for new resins for
paint formulation, although the paint industry does pay for research indirectly
through the price of raw materials it purchases from the chemical industry. In
many respects this arrangement is advantageous to the small paint producer,
because new advances in materials are available to both small and large paint
companies.
The paint industry has two distinct markets, trade sales and industrial sales.
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Table 1. HISTORY OF COATINGS INDUSTRY IN THE UNITED STATES2
Year
Event
1804
1815
1865
1867
1910
1923
1924
1924
1927
1928
1929
1930
1930
1930
1933
1934
1937
1939
1939
1939
1939
1944
1948
1950
1950
1957
1962
First white lead production
First varnish production
First water paint patent (U. S. Patent 50,068 to D. P. Flinn)
Production of ready-mixed paints
Casein powder paints put on market
Nitrocellulose lacquer introduced
Titanium dioxide introduced
Modified phenolic resin made commercially available
Alkyd resins made commercially available
Oil-soluble phenolics introduced
Urea-formaldehyde resin used for modification of alkyd resin
Chlorinated rubber produced
Casein paste paints introduced
Molybdate orange introduced
Vinyl copolymer resins introduced
Oil-base emulsion paints put on market
Phthalocyanine blue introduced
Commercial production of dehydrated castor oil
Melanine-formaldehyde resins made available
Ethylcellulose introduced
Polyurethane resins introduced
Silicone resins made commercially available
Latex wall finishes based on styrene-butadiene put on market
Epoxy resins made commercially available
Polyvinyl acetate and acrylic copolymer latices made commer-
cially available
Latex house paints introduced
Electrodeposition of water-base paints used
Trade-sale paints are shelf products that are sold through retail stores to the
general public, professional painters, and builders. These products are largely
architectural coatings for interior and exterior surfaces of new and existing
structures. Industrial sales paints are products that are formulated and sold to
other manufacturers for factory application. Coatings for new automotive
vehicles, furniture, and appliances are industrial paints. The industrial market
also includes maintenance coatings, which are not factory applied but are
specially formulated for particular properties, such as chemical resistance, film
toughness, and resistance to high temperatures. Industrial plants and equip-
ment require such paints.
A breakdown of the 1968 paint market, according to use of the coatings is
shown in Table 2. The United States shipments of paints, varnishes, and
PAINT TECHNOLOGY AND AIR POLLUTION
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Table 2. 1968 TRADE AND INDUSTRIAL PAINT SALES1
Type of sale
Trade
Interior house paints:
Latex emulsion
Oil and alkyd
Primer, sealers, etc.
Miscellaneous
Exterior house paints:
Latex emulsion
Oil and alkyd
Enamels
Primers, sealers, etc.
Miscellaneous
Automotive refinishing
Traffic
Other
Industrial
Automotive, new
Marine
Railroad, aircraft, etc.
Coil coating
Prefinished wood
Industrial maintenance
Machinery and equipment
Miscellaneous
Sales
106 gal
424
145
45
10
25
55
40
15
10
20
30
25
4
419
55
20
15
20
15
45
30
219
$106
1,428
425
170
30
100
190
155
55
35
50
150
45
23
1,159
170
85
40
80
40
160
75
509
$/gal
2.93
3.78
3.00
3.88
3.66
3.50
5.00
1.80
3.09
4.25
2.67
4.00
2.67
3.56
2.50
lacquers for 1968 were 843 million gallons valued at $2,587 million.1 Latex or
water-base paints have captured about 50 percent of the architectural
trade-sales market. Paints produced for the industrial-sales market are primarily
oil- or solvent-formulated.
The shipments of the trade and industrial finishes through the last decade
and their projected growth into 1975 are shown in Table 3. Except for 1967,
the paint industry has maintained a steady growth during the 1960's with a
growth rate of 4.7 percent of the total annual dollar volume. In 1967 the
impact of high interest rates caused a drop in new construction and in overall
paint sales. It should be pointed out that an undetermined portion of this
dollar growth has resulted from continued inflation over this period. Thus a
better indication of growth of the paint industry is gallons sold. The average
Developments Within Paint Industry
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Table 3. U.S. SHIPMENTS OF PAINTS, VARNISHES,
AND LACQUERS1'4
Year
1961
1962
1963
1964
1965
1966
1967
1968
1969a
1975a
Trade
106 gal
329
337
373
395
411
416
398
424
439
540
$106
$1 ,038
1,078
1,125
1,173
1,247
1,312
1,329
1,428
1,480
2,050
Industrial
106 gal
294
306
305
330
365
421
383
419
435
600
$106
$ 712
755
765
829
922
1,052
1,019
1,159
1,213
1,860
Total
106 gal
623
643
678
725
776
837
781
843
874
1,140
$106
$1,750
1,833
1,890
2,002
2,169
2,364
2,348
2,587
2,693
3,910
a Estimated.
annual growth (gallonage) during the 1960's was projected to be about 3.3
percent.1
From 1962 through 1968, the dollar volume of industrial finishes increased
at an annual rate of 6.6 percent, compared with 4.4 percent for trade sales. The
rate of increase of industrial paint finish sales is likely to remain ahead of the
rate of growth of trade sales in the 1970's. Although construction is expected
to increase in the early 1970's and improve the sales of trade paints, the
demand for prefinished materials of construction will favor factory-applied
coatings at the expense of trade sales. The rising cost of labor for on-site
painting is another factor that is increasing the trend toward use of precoated
materials. The annual dollar sales of industrial finishes as projected into 1975
are not expected to exceed trade sales. The volume (gallonage) of industrial
finishes, however, is projected to take a commanding lead over trade sales by
1975.4
Air pollution legislation is also affecting developments within the paint
industry. Los Angeles County Rule No. 66, one of the legislative acts most
significant to the paint industry, recognizes paint as a source of hydrocarbon
emissions.3 It has been estimated by Los Angeles County officials that the
application of paint within the county contributes 20 percent of the total
organic emissions, or 360 tons of hydrocarbons per day.1 Certain hydro-
carbons that are used as solvents in paint formulation have been found to react
photochemically with nitric oxides to form smog. The damaging effects of
smog on materials are not completely understood; however, smog does cause
eye irritation and probably respiratory illness.
PAINT TECHNOLOGY AND AIR POLLUTION
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Los Angeles Rule No. 66, which went into effect July 1, 1967, regulates the
amount of daily hydrocarbon emissions and applies especially to all industrial-
coating manufacturing techniques as well as to the sale and utilization of
architectural coatings. Similar legislation is being considered by officials of
other cities because photochemical smog is rapidly becoming a problem in
cities across the United States. San Francisco has already adopted a law,
Regulation No. 3, that is very similar to Los Angeles Rule No. 66.
Through the National Paint, Varnish, and Lacquer Association, the paint
industry has financed the construction and operation of a smog chamber at
Battelle Memorial Institute, Columbus, Ohio.5 This chamber work should
provide additional data about the organic materials in paints that undergo
photochemical reactions and produce eye irritation. Rule No. 66 has focused
on the problem of hydrocarbon air pollution within the paint industry.
Consequently, it is very likely that new techniques, such as non-heat-curing
processes and paint formulations that avoid photochemically reactive solvents,
will be forthcoming within the industry. Water-base paints will probably find
increasing use in industrial painting processes.
PAINT FORMULATION
In general, the formula for paints—whether the paints be oil- or water-base
—consists of three basic components: (1) a binder, which forms the film and
consists of natural resins, drying oils, or synthetic polymers; (2) a solvent,
which is either water or an organic solvent; and (3) a pigment, which promotes
color and improves film properties.2 When the binder and solvent are
considered to be one component, they are referred to as the "vehicle" of the
paint formulation. Other ingredients are present, such as wetting agents and
fungicides, that aid in the processing, application, and protection of paint.
Oil- and water-base paint films are formed differently. Oil-base paint forms
a film through a combination of organic solvent evaporation and the catalytic
polymerization of the drying oil. Water-base paints form a continuous film
through evaporation of their water content and subsequent coalescence of the
synthetic polymer particles.
Binders
A major trend within the paint industry is the increasing formulation of
different resins as binders. The paint industry uses the term "resins" to mean
both natural and synthetic organic polymers that are used as binders in the
formulation of paints. The present and future consumption of resins by the
paint industry is shown in Table 4. This table represents the resins that are
consumed in both the trade and industrial markets. This report does not
elaborate on the numerous formulations and uses of these resins. The alkyd,
polyvinyl acetate, and acrylic resins are briefly discussed.
Alkyds are a group of polyester resins that are oil-modified for paint
formulations. These resins are the major binders used by the coatings industry.
Developments Within Paint Industry
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Their popularity stems from the fact that they are relatively low-cost, easily
applied resins and are compatible with other resins. Alkyd paints are used
primarily as industrial baking finishes; however, they still command about 50
percent of the exterior household paint market. Although the total volume of
alkyds consumed by the industry continues to grow, as shown in Table 4, their
share of the industry (gallonage) is declining with the use of more durable
synthetic resins.
Table 4. CONSUMPTION OF RESINS BY COATINGS INDUSTRY,
1968to19756
Resin
Alkyds
Polyvinyl acetate
Urea and melamine
Epoxy
Acrylics
Styrene butadiene
Phenolics
Polyester
Consumption, 106 Ib
1968
630.0
116.0
66.0
62.0
57.0
40.0
36.0
14.3
1969
673.8
142.6
72.0
72.9
63.6
37.8
38.0
10.5
1970
695.7
156.6
76.3
80.4
68.8
37.0
39.1
11.6
1975
828.0
248.5
103.5
127.1
101.2
29.7
47.2
18.2
The polyvinyl acetates are the second major group of resins and are perhaps
the fastest growing class. The consumption of these resins will probably double
by the end of the 1970's. Polyvinyl acetate resins, as well as blends of acrylic,
nitrocellulose, and hydroxyl-modified vinyl resin, are primarily used as interior
decorative and architectural coatings.
Acrylic resins provide coatings with excellent durability and chemical and
heat resistance. Resins with such properties are finding use as exterior
architectural finishes and in industrial finishes. Thermosetting-thermoplastic
lacquers and enamels of acrylic resins have been formulated for new
automotive topcoats and other industrial markets.
Pigments
The paint industry annually consumes millions of pounds of inorganic
oxides, sulfates, and carbonates for pigmentation of trade and industrial paints.
Both natural and synthetic pigments are used by the industry. Pigments are
used in paint formulations to obscure the substrate, to impart color for
PAINT TECHNOLOGY AND AIR POLLUTION
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aesthetic purposes, and to improve durability of the film. Materials such as
talcs, clays, and chalks are used to aid processing and to maintain formulation
stability. These materials are called extenders, fillers, and, more recently,
supplemental pigments.
White films are the most popular for exterior house paints. White pigments
are also utilized to formulate most tints and light hues. The quantity of white
pigments consumed by the paint industry in the past 3 years and the projected
consumption for 1975 are shown in Table 5.
Table 5. PIGMENT CONSUMED BY PAINT INDUSTRY,
1968to19756
Pigment
Titanium dioxide
Zinc oxide
Zinc dust
Lead, red, dry
Lead, white
Consumption, 106 Ib
1968
377.0
36.0
25.0
14.2
7.2
1969
396.2
32.3
27.4
14.4
6.9
1970
412.1
29.8
29.2
14.6
6.3
1975
516.0
13.2
41.9
15.8
2.6
White lead pigment was once used exclusively to formulate household
paints. Titanium dioxide is now being used increasingly in trade and industrial
finishes because of its superior hiding power and color retention. The
dwindling use of lead pigments can also be partially attributed to their toxicity.
Water-Base Paints (Latex)
The national concern over air pollution will certainly provide impetus
within the paint industry for the further development of water-base paints and
solvent-free coatings. Water-base paints or latex house paints probably
represent the most significant development in paint formulation since World
War II. The popularity and rapid growth in the use of water-base paints as
architectural trade coatings have been described as phenomenal. Certainly ease
of application and cleanup, as well as good performance, have contributed to
the popularity and success of water-base paints among weekend painters and
paint contractors.
It is quite evident that natural products have lost a significant portion of the
trade sales market to the newer synthetic resins. Linseed oil, the major natural
oil used by the paint industry, was once the principle oil used in exterior house
paints. The consumption of this oil, 245 million pounds in 1963, was only 150
million pounds in 1968. This decline can be attributed directly to the increased
Developments Within Paint Industry
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use of water-base paints for exterior coatings.1'6 As shown in Table 2,
water-base systems have largely captured the architectural interior market.
Latex exterior paints have also claimed more than 50 percent of the
architectural exterior market.
Projections indicate that latex paints will have about 70 percent of the
trade-sale exterior market in 1975. A breakdown of the gallonage of the major
latex paints is shown in Table 6.
Table 6. ESTIMATED TRADE SALES OF LATEX PAINTS1
Paint
Interior paints
Polyvinyl acetate
Vinyl acetate-acrylic
Styrene-butadiene
Acrylic
Exterior paints
Polyvinyl acetate
Vinyl acetate-acrylic
Acrylics
Sales, 106 gal
1966
45
7
29
12
11
11
21
1967
46
10
26
16
11
16
24
1970
48
22
18
24
9
28
30
1975
53
35
15
35
7
45
44
Acrylic binders and their various blends are predicted to capture the
architectural exterior paint market in the early 1970's. Acrylic resins make
possible the manufacture of paint with a superior film stability that will
withstand both ultraviolet light and weathering, two factors that must be
overcome for exterior durability. Straight acrylic resins are considerably higher
in price than other resins. This disadvantage can be overcome by
copolymerization with cheaper monomers, although this procedure does
sacrifice some film properties.
Water-base paints are just beginning to emerge within the industrial market.
Their adaptation to industrial application has been much slower than predicted
for two reasons: cost and formulation problems. Most of the industrial coatings
applied to consumer items require high-performance finishes with high gloss.
These properties have been difficult to obtain with water-formulated paints,
10
PAINT TECHNOLOGY AND AIR POLLUTION
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but semi-gloss latex paints are emerging on the market. As yet, however, their
properties do not compare with those of oil-base enamels. In addition, water is
more costly to evaporate from baking finishes than organic solvents, and the
rate of evaporation is difficult to control, which means that the industry must
face the cost of revamping equipment.
Nevertheless, several important reasons exist for eliminating organic solvents
from paint formulations. From a safety point of view, the use of water-base
systems minimizes the chance of fire and may make possible a reduction in
insurance premiums. Also, the solvent fumes, consisting of hydrocarbon
emissions that contribute to the formation of smog, would be virtually
eliminated.
APPLICATION TECHNIQUES
The efficiency with which a paint film protects the substrate depends on
the means by which it was applied and the type of coating. The trend emerging
within the industry is not only to develop improved coatings but also to
develop new techniques of application aimed at improving film durability.
Probably more paint has been applied by spraying techniques than by any
other method. Dipping is also a fast technique for applying coatings in a
continuous operation, but it is a difficult process because of the many variables
that must be closely controlled, such as viscosity and rate of withdrawal of the
object being coated. Flow coating is another means of applying paint that is
extensively used in industrial applications for automobile frames, appliance
primers, etc. Flow coating is actually a modified form of dipping except that it
has the advantage of not requiring a dip tank. Instead, the paint is sprayed on
the object as it moves on a conveyor line. The problems associated with both
dipping and spraying techniques include maintaining uniformity of the coatings
and controlling the emission of dangerous organic solvents during application
and drying of the finish. Improvements in these techniques, such as
electrostatic and airless spraying, are being explored by industrial painting
operations.
Other new techniques for applying and curing paints are being sought by
the industry. Application of paint by electrodeposition and coil coating, and
electron-beam curing of these coatings are discussed below, for they represent
new technology for applying and curing modern-day coatings.
Electrodeposition
The electrodeposition process of applying paint is not a new development.
A patent was obtained by Grosse and Blackwell in the 1930's for the anodic
deposition of an oleoresinous coating on cans.7 It was not until the 1950's,
however, that the Ford Motor Company began to experiment with the
electrodeposition of organic materials.8'9 The main reason for the lapse of
time was the slow development of suitable water-soluble paints. The Ford
Developments Within Paint Industry 11
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Motor Company began commercial operation of electrodeposition for
automobile primers in 1963. Presently the Ford Motor Company and General
Motors Corporation each have seven electrodeposition systems for priming
auto parts and bodies.3
The electrocoating process consists of three complex reactions: electrolysis,
electrophoresis, and electroosmosis, all of which are believed to occur
simultaneously.7'10'11 Basically, electrodeposition is analogous to
electroplating except that the metallic object to be coated is the anode and
deposited organic film acts as an insulator instead of a conductor. Because the
coatings act as an electrical barrier, only a single coating 1.0 to 1.5 mils thick
can be applied by this technique.3 The coating builds up uniformly over the
entire metallic surface and therefore presents a definite advantage over dipping
and spraying techniques. Furthermore, electrocoating uses paint solids very
efficiently, so that it requires 30 percent less paint than the dipping process.1 °
At present, PPG Industries and Glidden formulate about three-fourths of
the paint used in electrocoating. A wide range of polymers, including
maleinized drying oils, alkyds, epoxy esters, acrylate copolymers, and phenolic
modified oils, have been formulated into water systems for electrodeposition.3
The electrodeposition process presently consumes about $10 million of the
industrial paint market. About $3.5 to 4 million of paint is currently utilized in
automotive electrocoating tanks.3 This technique has not grown as rapidly as
expected, primarily for two reasons:
1. Although the process lends itself to assembly-line production and operating
costs are low, installation costs are high. Electrodeposition equipment for
priming automobile bodies can cost between $1.5 to 2.0 million.3
2. The industry needs coatings of greater durability or paints formulated with
conductive solids (pigments, etc.) to allow electrocoating topcoats over the
primer surface. Until such paints are available, a large number of industrial
painters will not consider installing electrodeposition equipment.10'11
Air pollution legislation regulating hydrocarbon emissions from industrial
processes could very well provide the major impetus for the electrodeposition
process in the 1970's, so that this technique of applying paint could
mushroom, becoming a primary coating process for automobiles, appliances,
electrical equipment, toys, and metal furniture. Many in the paint industry
believe that within the next 10 years electrocoating could constitute 50
percent of all industrial painting.9
Coil Coating
Two trends that are emerging within the paint industry are exemplified in
the coil-coating industry: (1) more coatings are being applied in the factory
than in the field, at the expense of trade-sale paints, mainly because labor for
on-site painting costs more; and (2) thinner and more uniform coatings (1 mil)
are being applied on a variety of substrates (wood and metal).12
12 PAINT TECHNOLOGY AND AIR POLLUTION
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Coil coating, which began with the coating of Venetian blind stock, is an
efficient process for continually coating and curing long, flat strips of metal. At
present there are about 45 large-scale coating lines utilizing industrial finishes
worth about $60 to 80 million.3 Shipments of coil-coated steel and aluminum
from 1962 through the first half of 1969 are shown in Table 7.1 3 Coil coating
of aluminum and steel enjoyed a growth rate in the 1960's of about 13 percent
per year. In 1968, more than a million tons of steel and about half a million
tons of aluminum were coil-coated. Coil-coated steel and aluminum used in
building and construction accounted for about half of the annual volume sales.
The mobile-home industry also uses precoated aluminum for exterior siding.14
Table 7. SHIPMENT OF COIL-COATED STEEL AND ALUMINUM '
Aluminum
Steel
Total
Shipments, 106 Ib
1962
343
585
928
1963
404
870
1,274
1964
463
1,135
1,598
1965
553
1,565
2,118
19B6
593
1,650
2,243
1967
111
1,721
2,448
1968
1,006
2,995
3,001
1969a
520
1,105
1,625
a First half of year.
Table 8 lists the durability and costs of some of the organic resins '5 that
are used to coat steel and aluminum in the coil-coating process. Coatings such
as siliconized alkyd have shown an exterior durability greater than that of
conventional coatings such as the alkyd amines. A new class of polymers called
fluorocarbons should find increasing use in the coil-coating industry. These
coatings have resisted degradation in accelerated weathering tests.3 Extensive
field testing on industrial structures and office buildings in varying
environments is currently being conducted. The use of fluorocarbons in the
coil-coating industry should open new markets in commercial construction;
such coatings will probably carry 15- to 20-year guarantees.3'16'17 Because
such coatings are organic-solvent-based rather than water-based, the process of
coil coating is plagued with the emission of hydrocarbons. Emissions could
possibly be controlled through recycling of organic solvents.
Coil coating is probably the cheapest method for applying paint to metallic
substrates. Operating costs are low and little paint is wasted. As with most new
techniques, there is a high initial installation cost: a high-speed line can amount
to $1 million. Currently, line speeds are rated at 200 to 300 feet per minute;
however, new installations are capable of 600 feet per minute. Normally such
high speeds cannot be maintained, primarily because the curing cycle requires
certain minimal periods. This technical problem could very well be solved by
electron-beam curing of the applied coating.3
Developments Within Paint Industry
13
-------
Table 8. COIL-COATED ORGANIC RESINS1
Resins
Amine alkyd
Polyester
Vinyl-alkyd
Solution-vinyl
Organosol
Plastisol
Straight epoxy
Epoxy-ester
Thermoset acrylic
Silicone alkyd
Polyvinyl fluoride
Polyvinylidene
fluoride
Polyvinyl fluoride
laminate
Polyvinyl chloride
laminate
Exterior durability
Pigment formula
Good
Good
Fair
Good
Excellent
Excellent
Poor
Poor
Good
Excellent
Excellent
Excellent
Excellent
Excellent
Clear film
formula
Fair
Fair
Fair
Poor
Poor
Poor
Poor
Poor
Good
Good
Excellent
Excellent
Fair
Poor
Unit finishing
cost range,
«2.50
>2.50
>2.50
>2.50
Electron-Beam Curing
Since the first application of paint on a production-line basis, the coating
industry has been in search of a rapid cure technique. Electron-beam curing,
(electrocure), which is not fully commercialized, presents an entirely new
concept of curing to the paint industry. This new technique uses an electron
beam to induce polymerization of specially formulated paint on a flat surface.
Curing by this process reportedly results in a firmer bond between the film and
substrate.3
Electrocuring has two advantages over conventional curing techniques: (1)
it cures 200 times faster than conventional methods; and (2) it cures at room
temperature. Electrocuring is best used on flat stock and is limited to curing
films 10 to 15 mils thick. Present paint formulations are not readily adapted to
electrocuting. Resins, however, such as polyester, acrylic, urethanes, and
epoxies, have been formulated with radiation-sensitive monomers or
pre-polymers. The electron beam induces the formation of free radicals that
react chemically with the resin to form a continuous film. These monomers or
14
PAINT TECHNOLOGY AND AIR POLLUTION
-------
pre-polymers can be looked upon as crosslinking reagents or curing agents.
Since virtually all of the coating is converted to protective film, hydrocarbon
emissions are not a problem as they are with coil coating and other bake-on
processes.3'17
The future of electron-beam curing certainly looks bright for application in
the coil-coating industry. Coil-coating line speeds could be doubled. To develop
the technique, Ford Motor Company is presently operating a pilot-scale
coil-coating unit in which conventional heat ovens have been replaced with
electrocuring units.3 Although there are technical problems associated with the
process and the equipment is expensive, electrocuring will probably find its
place in the paint industry within the 1970's.
Developments Within Paint Industry 15
-------
DETERIORATION
OF EXTERIOR PAINT FILMS
The paint industry is concerned about the overall performance of their
paints, whether they be applied by factory techniques or by the hands of
weekend painters. Consequently, the vast majority of finishes have undergone
extensive testing by the industry before they are commercialized. In the
following section, the testing of paint films by manufacturers is reviewed and
the damaging effects of gaseous pollutants and particulate matter on exterior
paints are discussed.
INDUSTRIAL TESTING
The test most widely used throughout the paint industry is the outdoor
exposure test, or "fence test." Such paint-test sites can be found across the
country; Florida, with its hot and humid climatic conditions, appears to be a
popular area for outdoor paint-test sites. Companies such as Sherwin-Williams,
DuPont, and Desoto conduct fence testing across the United States, but small
paint manufacturers must rely upon published information or must conduct
only limited fence tests in their own market areas.
During the actual outdoor exposure of paint films, the coating is observed
periodically and the extent of degradation is recorded. Paint films have been
observed to deteriorate or fail in a variety of ways, some of the more common
of which are presented in Table 9. One of these types, chalking of the exterior
coating, can be controlled by proper paint formulation that involves selected
pigments and binders; it may even be regarded as an added asset of the paint
film in some situations, because controlling the rate of chalking can produce a
self-cleaning effect in the exterior paint.
Paint producers have also established a variety of tests for determining the
extent of paint failure. In general, these tests involve visual observations and
measurements of adhesion and stress, weight loss, gloss, reflectance, and color
change of the film. Standard tests have been developed for determining the
durability or weatherability of exterior paint. The American Society for
Testing and Materials (ASTM) has established several such tests for evaluating
paint films; some of these are listed in Table 10.
The main concern of the paint industry is the development of exterior
paints that provide films of better durability under weathering. While
conducting exterior exposure studies for determining the weatherability
17
-------
Table9. TYPES OF FILM FAILURE1'
Failure
Description
Chalking
Cracking or checking
Alligatoring
Peeling
Color fading
Blistering
Rusting
Formation of powdery layer on surface of coating
that is being eroded away
Shrinkage of the coating resulting in film rupture
Film rupture resulting from the application of a
brittle film over a more flexible coating
Poor adhesion of the coat to substrate
Reaction of binder or pigment in presence of
sunlight or environment
Projections or pimples on film that result from
trapping of solvent or moisture between substrate
and film
Oxidation of metallic substrates such as iron or steel
when film permits moisture or chemicals to attack
substrates
potential of paints, the industry studies indirectly the effects of air pollutants
on exterior films; however, there has been little attempt to identify these
pollutant effects. At present the paint industry is more concerned over the
hydrocarbons emitted during the application of paints rather than over air
pollution damage to paint films.
With the earlier paints that were formulated with oleoresinous and alkyd
resins, film durability could be determined in a relatively short period of time
by outdoor exposure. As formulations and new techniques have improved,
paint films of greater durability have emerged on the market. Table 11 gives
the expected durability of various resins used as paint binders.
The biggest drawback to the outdoor testing of organic resin topcoats with
5-, 10-, or 20-year durability is obviously the time required to obtain valid
information. It seems impractical to conduct outdoor exposure studies of
paints with expected durability shown in Table II.17 In order, then, to obtain
information on the durability of such finishes, paint formulators are now using
accelerated-exposure chambers. These chambers, however, are not likely to
replace outdoor testing, which is regarded by the industry as the most reliable
method for testing actual film durability. This report will not review the
number of commercially available exposure chambers that are equipped with
18
PAINT TECHNOLOGY AND AIR POLLUTION
-------
Table 10. ASTM TEST METHODS FOR EXTERIOR PAINT FILMS1
Test no.
Test
D 659-44
D 660-44
D 661-44
D 662-44
D 772-47
D 1641-59
D 1543-63
D 1654-61
D 2197-68
D 2370-68
Evaluating degree of resistance to chalking of exterior
paints
Evaluating degree of resistance to checking of exterior
paints
Evaluating degree of resistance to cracking of exterior
paints
Evaluating degree of resistance to erosion of exterior
paints
Evaluating degree of resistance to flaking (scaling) of
exterior paints
Measuring exterior durability of varnishes
Measuring color change of white architectural enamels
Evaluating painted or coated specimens subjected to
corrosive environments
Measuring adhesion of organic coatings
Measuring elongation and tensile strength of free films
of paint, varnish, lacquer, and related products with
tensile testing apparatus.
different light sources and temperature-humidity programs; a literature survey
covering the period 1956 to 1966, "Accelerated Testing of Finishes for
Resistance to Weathering,"20 showed, however, that the durability potential of
paint is best predicted by the use of weatherometers equipped with
sunshine-arc or xenon light sources in addition to light-dark and hot-cold-wet
cycles The survey showed also that measurements of elongation and tensile
strength of the paint film are useful in predicting overall durability. Another
excellent review, conducted by Battelle Memorial Institute, covered the period
1921 to 1967.21
The paint industry is seeking accelerated test methods that predict
long-term weatherability or durability of paints. It must be pointed out that
"weatherability" in reference to chamber testing does not include resistance to
air pollutants as it does in reference to actual outdoor exposure tests. Although
Deterioration of Exterior Paints
19
-------
Table 11. DURABILITY OF ORGANIC RESIN TOPCOATS
17
Topcoat
Oleoresinous
Nitrocellulose lacquer
Alkyd, amine
Acrylic lacquer
Acrylic enamel
Vinyl solution
Epoxy ester
Urethanes
Silicone alkyds
Acrylics
Fluoropolymers
Durability, years3
1 to 2
2
5
8
8
8
2 to 5
2 to 10
8 to 15
8 to 15
20
Years of satisfactory exposure expected for quality white formulation.
pollutant chambers are commercially available, most accelerated tests of
coatings include only humidity, light, and dew cycles.
For the past several years, the National Paint, Varnish, and Lacquer
Association has supported a research project at the Illinois Institute of
Technology Research Institute to develop a laboratory test to be used in
predicting the performance of exterior paints.22 In this project a series of oil,
alkyd, and emulsion paint films with tensile loads of 4 to 7 pounds per square
inch were exposed to approximately 6 percent ozone at 35° and 60°C. The
deformation of the films was recorded during periods of 165 and 505 hours of
exposure to ozone. In general, for the 505-hour exposure, paints rated as
first-quality have less reduction in creep compliance than second-quality paints.
Figures 1 and 2 show the creep behavior of two emulsion paints: EM 7338,
first-quality, and EM 7339, second-quality. There is a definite reduction in
creep compliance as a result of exposure to ozone with both emulsion paints;
however, the extent of reduction is about three times greater for the
second-quality emulsion paint. The film of the first-quality paint was reported
to retain its flexibility better than that of the second-quality emulsion.
20
PAINT TECHNOLOGY AND AIR POLLUTION
-------
^40
X
03
30
20
10
LLJ n
CC 0
CJ
i—r
i—r
Ohr
505 hr
I
I
20
40
60
80 100
Till/IE, minute
120
140
160 180
Figure 1. Initial creep of EM 7339 second-quality emulsion-base
paint, before and after 505-hr exposure to ozone at 60°C.
20
40
60
80 100
TIME, minute
120 140
160
180
Figure 2. Initial creep of EM 7338 first-quality emulsion-base
paint, before and after 505-hr exposure to ozone at 60°C.
Deterioration of Exterior Paints
21
-------
Ozone was used in this investigation because it is known to degrade
materials by bond scission and crosslinking of the basic polymeric structure.2 3
High concentrations of ozone were selected to accelerate weathering of paint
films. Although films were observed to degrade in this environment, the extent
that this method will be used by the industry is questionable. Such high
concentrations of ozone pose a toxicity hazard in the laboratory. Also,
laboratory test methods in which only one parameter is accelerated-for
example, concentrations of ozone—are not likely to provide results that
correlate with actual outdoor conditions.
Although the IIT Research Institute study was not initiated to investigate
the effects of air pollutants on paint film, it can be looked upon as an initial
investigation of the effects of a common pollutant on paints. This work should
be expanded to include other gaseous pollutants, but at ambient concen-
trations.
EFFECTS OF AIR POLLUTION ON EXTERIOR PAINT
It has been estimated that over 213 million tons24 of air pollutants are
released annually over the United States. Primary gaseous pollutants produced
Table 12. MEAN CONCENTRATIONS OF THREE ATMOSPHERIC
POLLUTANTS, 1967
(«3/m3 )a
City
Chicago
Cincinnati
Denver
Philadelphia
St. Louis
Washington
S02
327.5
c
13.1
256.8
76.0
c
N02
90.0
52.6
69.6
80.8
45.1
80.8
Total oxidants
56.8
60.8
c
51.0
68.6
49.0
a Data furnished by EPA Air Surveillance Network and reported in ppm. 25
Conversion at 25°C, 760 mm Hg:
S02 : 1 ppm = 2620 fig/m3
NO2: 1 ppm= 1880Mg/m3
O3 : 1 ppm = 1960;ug/m3
Total oxidants computed as ozone.
cAverage not calculated; insufficient data.
22
PAINT TECHNOLOGY AND AIR POLLUTION
-------
by man are, by greatest weight, carbon monoxide, sulfur oxides, hydrocarbons,
and nitrogen oxides. Primary gaseous pollutants amount to 185 million tons
while the remaining 28 million tons consist of particulate matter. Not
represented in these figures are localized pollutants such as hydrogen sulfide
and fluoride, as well as secondary gaseous pollutants. Total amounts of the
secondary pollutants that are produced from photochemical reactions of
primary pollutants have been determined in certain localities but not on a
national scale.
To obtain concentration data for atmospheric pollutants, the Environ-
mental Protection Agency has placed continuous air monitoring stations in
several cities of the United States. The mean concentrations of sulfur dioxide,
nitrogen dioxide, and total oxidants in six cities during 1967 are shown in
Table 12. The concentrations of these gaseous pollutants were found to vary
considerably in each city. Of the six cities, Chicago was found to have the
highest mean concentration of sulfur dioxide and nitrogen dioxide, whereas St.
Louis had the highest concentration of total oxidants.
Midwest Research Institute2 6 recently conducted a program in which the
potential economic losses attributable to air pollution of 53 consumer
materials were ranked using a systems analysis approach. The 53 consumer
materials have been grouped by category in Table 13 to show the relative
orders of pollution damage and available information.
The potential economic loss for damaged paints was found to hold second
rank. Equally important is the fact that little has been published on the effects
of air pollutants on paint finishes. The 1-year study uncovered only 11 useful
references. From the Midwest Research Institute Report it is apparent that of
Table 13. RELATIVE POLLUTION DAMAGE TO MATERIALS
AND AVAI LABI LITY OF USEFUL INFORMATION
Materials
Metals
Paints
Textiles
Elastomers
Plastics
All others
Dollar loss, %
of total
39
32
9
5
3
12
References with
useful information,
% of total
54
7
14
12
9
4
the primary pollutants sulfur dioxide and particulate matter play an important
role in the chemical deterioration of modern- day exterior paints.
Deterioration of Exterior Paints
23
-------
Sulfur Dioxide
Sulfur dioxide has been shown to affect certain paint films at ambient
concentrations under laboratory conditions. Holbrow2 7 found that the drying
time of linseed, tung, and bodied dehydrated castor oil paint films increased by
50 to 100 percent at exposures of 1 to 2 ppm SO2. The touch and hard-dry
times of alkyd and oleoresinous paints with titanium dioxide pigments were
also reported to increase substantially. The time of exposure of the wet films
to SO2 was not reported. Analysis of the dried films indicated, however, that
S02 had chemically reacted with the drying oils, thereby altering the
oxidation-polymerization process. Based on these results, it was concluded that
concentrations of S02 encountered in fogs near industrial sites can increase the
drying and hardening times of certain kinds of paint systems.
There have been no studies reported on the effects of S02 on the drying of
latex paints, which have captured more than 50 percent of the present exterior
household market. At the time of application, S02 may interfere with the
evaporation of water and, therefore, the coalescence of the polymeric-pigment
particles. The equilibrium reaction of SO2 and water in the coating forms
sulfurous acid, which could cause instability of the protective colloid around
latex particles and, consequently, flocculation. Poor film formation would be
possible with resulting loss of aesthetic as well as protective value.
Holbrow also studied the effects of sulfur dioxide on the gloss of alkyd
paint film.27 In these experiments, paint films were allowed to dry, were
refrigerated, and then were desiccated for 15 minutes in an atmosphere
containing 1.2 percent sulfur dioxide. The paint films with condensed moisture
were finally placed in an accelerated-weathering chamber. Except for a
pentaerythritol alkyd paint, the gloss decreased significantly after 1 day in the
accelerated-weathering chamber. Without the accelerated weathering, the
actions of sulfur dioxide and moisture on the paint films produced only a slight
reduction in gloss. Microscopic examination of the accelerated-weathered paint
film revealed very fine wrinkles in the film. Holbrow concluded that the sulfur
dioxide had sensitized the film, which permitted water to be absorbed during
the weathering cycle. Control samples of paint, exposed for 1 hour of
accelerated weathering, showed no loss of gloss.
Sulfur dioxide has been reported to undergo oxidative reactions in the
atmosphere to produce acidic aerosols.28 Both photochemical and catalytic
reactions for this oxidization process have been investigated in many
laboratories. Although the exact mechanism is unknown, sulfuric acid has been
identified as a major product.29 The deposition of sulfuric acid on painted
surfaces may promote film deterioration through the reaction of the acid with
various paint ingredients such as pigments, fungicides, and the binder itself.
Furthermore, this acidic mist may also affect adhesion of the film on metallic
substrates by promoting the occurrence of electrochemical reactions at the
coating-substrate interface. As a result of these reactions, the service life of
exterior paint films could be drastically reduced from that of the manufac-
turer's warranty.
24 PAINT TECHNOLOGY AND AIR POLLUTION
-------
Holbrow did not attempt to correlate moisture and pollutant concentration,
or to obtain dose-response data. Although he used high levels of sulfur dioxide,
his experimentation does indicate that condensation and moisture evaporation
are critical in concentrating the pollutant on the surface of exterior paint films;
under these conditions, deterioration of the film occurs.
Hydrogen Sulfide
Any industrial operation that liberates sulfur dioxide can be a potential
source of hydrogen sulfide. Paper mills, petroleum refineries, and coke-pro-
cessing plants are likely sources of hydrogen sulfide. It can also be emitted
from sewage treatment plants by bacterial action on sulfur-containing organic
compounds.
Hydrogen sulfide is one pollutant that attacks in-service exterior house
paints. In one episode, which occurred in the southern portion of the San
Francisco Bay area, house-paint darkening ranged from various tones of
battleship gray to jet black. The discoloration occurred about doors and
windows, under eaves, or in locations that tended to remain moist. The most
severe episodes of discoloration occurred during the winter months, even
though the maximum 2-hour average air concentration of hydrogen sulfide was
twice as high in the summer months.30 This phenomenon tends to confirm the
finding that the presence of high humidity increases damage potentials.
The actual atmospheric concentration or threshold level of hydrogen sulfide
at which paint begins to darken is unknown. From the Bay Area episodes, it
appears that moisture on the paint films promotes the darkening effect.
Sensenbaugh and Hemeon3' and Sullivan32 report that under proper
conditions paint darkening is possible when the hydrogen sulfide concentration
is such that the gas can be smelled, which is approximately 70 to 140 ng/m3
In the laboratory studies conducted by G. B. Ward,33 it was concluded that
no blackening of the films by H2 S occurred unless the paint films were actually
wet with water. Unfortunately, no studies from which dose-response data can
be obtained were conducted on the effects of relative humidity and H2 S
interactions on paint film. The problem was traced to the formation of
dark-colored metal sulfide by the chemical reaction of H2 S on lead additives
and on organometallic driers and preservatives. A likely chemical reaction is:
o o
H20 "
H2S + R-C-OX >R-C-OH + XS
Hydrogen + Drier Acid + Dark salt
sulfide
Deterioration of Exterior Paints 25
-------
Mildewing of exterior paints has at times been confused with hydrogen
sulfide discoloration. Mildew has been reported as the darkening of paints
caused by a fungus, Pullularia pullulans.30 However, many different fungi,
such as Aspergillus niger and some species of Alternaria and Cladosporium,
have been identified on coatings.34 The fungi subsist on the organic matter or
resin in the paint film. Chemical tests and microscopic techniques have been
developed to differentiate between fungus attack and hydrogen sulfide
discoloration of paint.
Paint producers have formulated "fume-resistant paints" that contain
ingredients not susceptible to hydrogen sulfide attack. Such paints were
formulated by trial-and-error procedures involving laboratory and outdoor
exposures. Most exterior latex paints sold today are fume-resistant.
Particulate Matter
Exterior paints are soiled by liquids and solid particles that are composed of
soot, tarry acids, and other matter of varying chemical nature. Such an
agglomeration, called particulate matter, affects exterior paints in two ways:
(1) loss of aesthetic attractiveness, and (2) chemical degradation of the film.
In an investigation reported by Meller, fences were erected in various areas
of the United States.35 Paint applied to the clean fences became blackened at
most test sites by soot deposits. Examination of the coatings revealed that
tarry matter was imbedded in the film. Efforts to remove the soiling or to clean
the fence destroyed the paint film. Furthermore, Meller reported that the life
of two coats of paint used to cover the soiled paint was shortened, and
appearance of the paint was marred.
There have been numerous incidences of automotive paint damage near
industrial process plants. Airborne iron particles from a metal-grinding
operation were reported to cause pitting and staining of automobile paints.3 6
Another incident was reported in which automobile paints were severely
damaged by alkali mortar dust from demolition of brick buildings.37- The
vehicles in both situations had to be repainted.
Holbrow had conducted accelerated weathering tests in which various paints
were exposed to particulate matter.2 7 Severe staining of the paint films was
observed with 0.5 ppm copper and with 0.1 ppm of iron salts. Holbrow
concluded from his investigation that such staining could occur during natural
exposure inasmuch as these two metals have been identified in airborne
particulate matter found in United States cities and in rainwater.3 8
Data from case histories and experimental investigations show that
particulate matter has been found imbedded in the paint film. Imbedded
particulates can: (1) damage the coating in a physical sense; (2) provide
nucleation sites at which other pollutants can concentrate; or (3) undergo
chemical reactions with the paint film. In essence, particulate matter serves to
26 PAINT TECHNOLOGY AND AIR POLLUTION
-------
promote the chemical deterioration of exterior paints. Because there are many
materials classified as participate matter, their respective mechanisms of attack
on paints are too numerous to be discussed in this report.
A program was conducted by Michelson and Tourin to investigate the
frequency of house repainting as a function of suspended particulate
concentrations.39 Questionnaires were sent to residents of three suburbs of
Washington, D. C. (Suitland, Rockville, and Fairfax), and two cities (Steuben-
ville and Uniontown) in the Upper Ohio Valley. The intervals for exterior
repainting as a function of particulate concentrations for the five U. S. cities, as
compiled from the questionnaires, are shown in Table 14. The maintenance
intervals of the years between repaintings were observed to decrease as the
particulate concentrations increased. Repainting in Steubenville, which has
particulate concentrations as high as 235 jug/m3, was observed to occur about
every year. In Fairfax, with a concentration of 60 Mg/m3, repainting occurred
every 4 years.
Table 14. INTERVAL FOR EXTERIOR REPAINTING AS A FUNCTION
OF PARTICULATE CONCENTRATION IN FIVE U. S. CITIES39
Particulate
concentration, jug/m3
Maintenance interval, yr
Maintenance
frequency, number
per yra
Steubenville
235
0.88
1.14
Uniontown
115
1.89
0.53
Suitland
85
2.93
0.34
Rockville
75
3.62
0.28
Fairfax
60
3.90
0.26
a Reciprocal of maintenance interval in years.
The maintenance frequency (reciprocal of maintenance interval), as a
function of local particulate concentration, increases as particulate concen-
tration increases (Figure 3). The results of the Michelson investigation are
highly suggestive that a significant relationship exists between the frequency of
repainting and the particulate concentration. However, extrapolation of the
line indicates that repainting does not occur at zero particulate concentration
and that repainting frequency continues to increase as particulate concen-
tration increases. A leveling out of the line to form a plateau at the low and
high extremes of particulate concentration should be expected. It would
appear that additional maintenance data is needed, particularly for cities with
mean annual particulate concentrations greater than 150 Mg/m3, before
attempting to establish a more realistic relationship.
Deterioration of Exterior Paints
-------
o
cy
LU
a:
Ll_
LU
O
1.50
1.25
1.00
0.75
0.50
0.25
FAIRFAX
I
STEUBENVILLE i
IUNIONTOWN
ISUITLAND
ROCKVILLE
I
I
1
50 100 150 200
PARTICULATE CONCENTRATION, Jig/m3
250
Figure 3- Relationship of maintenance frequency for exterior
repainting to particulate concentration.
28
PAINT TECHNOLOGY AND AIR POLLUTION
-------
A study40 to determine maintenance frequencies at various particulate
concentration zones in the Philadelphia area was recently completed. In this
study, problems encountered in Michelson's study were minimized, such as
different characteristics in population, climate, and type of industry. The range
of mean annual particulate concentrations for the Philadelphia area was 46 to
151 Mg/m3. Maintenance frequencies for exterior wall painting were obtained
as shown in Table 15. This study, conducted by Booz, Allen, and Hamilton,
Inc., for EPA, also delineated socioeconomic factors by pollution zone. The
fact that the percentage of households with incomes of less than $6000
increased with pollution level is a factor that tends to counteract the effect of
suspended particulates on paint life and that partially explains why no
statistically significant difference in painting frequency as a function of
particulate level was detected.
Table 15. MEAN ANNUAL FREQUENCY FOR EXTERIOR WALL
PAINTING IN PHILADELPHIA AREA AS A FUNCTION
OF PARTICULATE CONCENTRATION
Particulate concentration
ranges, jUg/m3
<75
75 to 100
100 to 125
> 125
Exterior wall painting
Mean annual
frequency
0.28
0.35
0.35
0.29
Standard error
of mean
0.016
0.053
0.041
0.055
Deterioration of Exterior Paints
29
-------
ECONOMIC ASSESSMENT
OF AIR POLLUTION
DAMAGE TO EXTERIOR PAINTS
Previous estimates of the cost of pollutant damage to exterior paints have
been undertaken primarily by local government officials. Damage estimates
have been basically derived from questionnaires and interviews with the general
public and with paint contractors and other members of the paint industry.
Although such estimates are helpful, they seldom present effects data and
therefore represent an incomplete picture of the deterioration of paints caused
by air pollution.
An attempt was made to establish a reasonable estimate of the potential
annual consumer cost for repainting that can be attributed to pollutant damage
in urban areas. This estimate, which should rank market classes by damage
cost, will be used to select classes of paints for laboratory and field exposure
studies. The cost estimates of the pollutant damage to exterior paints in urban
areas are summarized in Table 16. The dollar volume of the 1968 paint market
for four classes of exterior paints was used.
The total value at the manufacturer's level for the four paint classes was
$775 million. This figure represents the dollar volume of paints used as exterior
finishes and amounts to more than 50 percent of the entire 1968 paint market
volume at the manufacturer's cost level. Since coil coating and maintenance
finishes are not entirely exposed to the environment, the dollar volume as
shown in the table is for exterior exposures only. Factory-applied automotive
paints, such as the thermoplastic-thermosetting acrylic paints, are reported to
protect the vehicle for the expected body life. Repainting would probably be
done to repair accidental damage or to increase resale value. Therefore, only
automotive refinishing paints are considered in this estimate. Of the four
classes, household paints that include water- and oil-base paints comprised the
largest dollar volume.
There has been no attempt to factor-out from the $775 million (column 2)
the dollar volume of exterior paints that are applied to new surfaces. This
damage estimate is based solely on the dollar volume of four classes of exterior
paints. Whether these paints were applied to new construction or used to
repaint existing structures was not considered.
In columns 3, 4, and 5 of Table 16, the expected service life and
maintenance frequencies are determined for rural and urban areas for each of
31
-------
Table 16. ECONOMIC ASSESSMENT OF AIR POLLUTION DETERIORATION OF EXTERIOR PAINTS
Column
1
Exterior paint
class
Coil coating
Automotive
refinishing
Maintenance
Household
Total
Column
2
Value at
manufacturer's
level.
$ million
40
150
100
485
775
Column
3
Area
Rural
Urban
Rural
Urban
Rural
Urban
Rural
Urban
—
Column
4
Expected
service
life.yr
20
15
5
4
5
4
6
3
—
Column
5
Maintenance
frequency.
number per yra
0.05
0.07
0.20
0.25
0.20
0.25
0.17
0.33
—
Column
6
Estimated
distribution
of paint,
% population
30
70
30
70
30
70
40
60
—
Column
7
Paint
consumed
in urban
areas,%
77
74
74
74
—
Column
8
Value of paint
exposed in
urban areas.
$ million
31
111
74
359
575
Column
g
Service
life,
%loss
25
20
20
Column
10
Loss at
manufacturer's
level, $ million
8
22
15
!
50 i 180
—
225
Column
11
Labor
factor
2
4
4
3
"
Column
12
Loss at
consumer's
level.
$ million
16
88
60
540
704
H
m
o
o
5
o
3
r
r
H
"Maintenance frequency is the reciprocal of expected service (Column 4).
-------
the tour paint classes. The average paniculate concentrations were 110 Mg/m3
in U. S. cities and 40 ng/m3 in rural areas.41 The Michelson linear relationship,
Figure 3, predicts service life of 8 and 2 years, respectively, for paint exposed
to 40 and 110 Mg/m3 of particulate matter. The Booz, Allen, and Hamilton,
Inc., study shows no difference in service life for paint exposed over this
concentration range, the average paint life being 3.14 years. Because neither
study was complete in its analysis, paint lives are estimated at 6 and 3 years,
respectively, for rural and urban areas. The expected service life and the
maintenance frequencies for coil coating, automotive refinishing, and
maintenance coatings for rural and urban areas are not published and can only
be estimated. Actual exposure data of paints exist within the paint industry,
but not in terms of rural and urban areas relative to type of pollution or
pollutant concentration.
Column 7 represents the amount of paint, expressed as the percentage, for
each exterior paint class that is consumed in urban areas. These percentages
were derived from data on maintenance frequency and estimated distribution.
An example of the calculation is shown for coil coating paints:
Maintenance frequency Estimated distribution
Rural area: 0.05 x 0.30 =0.015
Urban area: 0.07 x 0.70 = 0.049
0.064
Percentage of paint consumed in urban area:
0.049 100 = 77
0.064 x 1UU /7
As shown in column 8, paint equivalent to a total dollar volume of $575
million is exposed in urban areas. It is apparent that the major portion of this
dollar volume is related to household paints. Column 8 represents the dollar
volume of each paint class used annually in urban areas.
A total dollar volume of $225 million, as shown in column 10, was
determined as the damage loss at the manufacturer's cost level. This damage
was obtained as the product of the value of paint exposed in urban areas
(column 8) and the percentage service-life loss (column 9). The percentage
service-life loss attributed to air pollution was determined as the difference in
expected service life between rural and urban areas. The computation shown
for coil-coating, using a service life in rural areas of 20 years and a service life in
urban areas of 15 years, yields the percentage service life loss resulting from air
pollution:
2°--5x 100 = 25
Economics of Air Pollution Damage 33
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The values in column 10 represent the dollar loss at the manufacturer's level
rather than the retailer's. In general, the cost of paint is about one cent per
square foot, or about 5 to 10 percent of the paint cost. Thus, the cost of paint
represents a small portion of the total economic loss. As a conservative
estimate, the mark-up, including labor cost, is over three times the value lost at
the manufacturing level.42 Therefore, the value lost at the retail level, shown in
column 12 for the four classes, amounts to $704 million. Household paints,
with a value loss of $540 million, represent over 75 percent of the total. A
considerable portion of exterior painting, especially household, is accomplished
by weekend or non-professional painters. Since a labor factor for such painters
can not be determined, this dollar loss has been determined on the basis of
professional painting costs.
The magnitude of error for the dollar loss of over 0.7 billion can not be
determined. Before a more reliable economic assessment can be made,
dose-response and expected service-life data must be obtained. Such data can
only be compiled through laboratory and field studies that correlate pollutant
damage with loss of service life.
34 PAINT TECHNOLOGY AND AIR POLLUTION
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AREAS FOR FUTURE INVESTIGATION
One of the important purposes of this report is to identify areas of
inadequate information. The identification of information gaps will provide a
starting point for further laboratory and field investigations. In summary,
information is inadequate in the following areas:
1. Little information has been compiled concerning the degradation of
exterior finishes by air pollutants. Although new coatings are emerging
on the market at a fast pace, the following generic types of exterior
paints should be considered for laboratory and field exposure studies.
a. Household: water-base acrylic (latex) and oil-alkyd.
b. Coil coating: urea-alkyd-coated aluminum, steel, and galvanized steel.
c. Maintenance coating: alkyd on primed galvanized steel.
d. Automotive finishes: nitrocellulose/acrylic.
2. Numerous test methods currently exist for assessing the weatherability
of exterior paints. A program should be initiated, however, to establish
test methods that correlate detectable initial film damage with service
life. Such methods would greatly facilitate the study of air pollutant
effects on exterior paints.
3. Environmental studies should be conducted in the laboratory to
duplicate initial paint film deterioration observed in actual outdoor
exposure. These laboratory studies should include: (1) dew cycle, to
allow pollutants to collect and concentrate on film; (2) ultraviolet light
(<2800 A) for promoting chemical reactions; and (3) air pollutants such
as ozone, sulfur dioxide, and nitrogen oxides, and particulate matter at
ambient concentrations.
4. Surveys should be made of city residents and paint contractors to obtain
information about the frequency of cleaning and repainting, cost of
earlier repainting (labor), etc. Such information, together with effects or
dose-response data, is necessary before a more realistic economic
assessment of the problem can be made.
As part of an EPA effort to overcome the lack of essential information-
particularly the lack of effects and dose-response data-about air pollutant
damage to exterior paints, a research program for EPA was recently initiated
35
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with the Sherwin-Williams Company.42 This program is designed to determine
the best techniques for assessing initial degradation of exterior paints, which in
turn can be correlated with actual service life. The effects of ozone and sulfur
dioxide at ambient concentrations on selected exterior paints will be of
primary concern. Erosion, surface roughness, gloss, and tensile measurements
will be evaluated as possible methods for detecting film damage. The scanning
electron microscope will provide a visual record of topographical changes.
Techniques which are developed in this program will be used at EPA's
laboratory facilities at Research Triangle Park, North Carolina. Both commu-
nity and controlled environment studies are planned in our programs to
determine the effects of S02, N02, and ozone on consumer materials.
36 PAINT TECHNOLOGY AND AIR POLLUTION
-------
CONCLUSIONS
In order to compete with the industrial market demand for structural
materials that require little or no painting, the paint industry is beginning to
develop new paint formulations. Current technology is centered around the
development of synthetic resins and of new techniques for applying and curing
these paints. Since hydrocarbons are emitted during the use of some of these
new techniques, extant and proposed air pollution legislation that regulates
hydrocarbon emissions will affect this technology. Such legislation should give
impetus to the formulation and use of new water-base industrial paints or
paints formulated with hydrocarbon solvents that are not photochemically
reactive.
A review of literature on the chemical attack of certain air pollutants on
exterior finishes reveals that dose-response data for the effects of common air
pollutants on exterior paints are sadly lacking at this time. It is known,
however, that ozone, sulfur dioxide, hydrogen sulfide, and particulate matter
can cause damage to exterior paints. Only a few mechanisms of chemical attack
of pollutants on paints have as yet been elucidated and these are noted in this
report.
An economic assessment of the damage caused by air pollutants to exterior
paints reveals that the cost at the consumer level of such damage is more than
$0.7 billion annually. Of the four categories of exterior paints studied—house-
hold, automotive refmishing, coil coating, and maintenance—household paints
sustain damage representing over 75 percent of the total annual dollar loss.
Because dose-response data on the effects of common air pollutants on
exterior paints are lacking, future research should be directed toward
remedying this deficiency. Field and laboratory studies of the degradation of
exterior finishes by air pollutants should be conducted. In addition, test
methods should be developed for correlating paint film damage with service
life. Exposure-chamber studies should be conducted on the effects of common
air pollutants on paints. In addition to these studies, surveys of city residents
and paint contractors should be made to obtain information on maintenance
repainting. Only when survey and effects or dose-response data are available
can a realistic economic appraisal of the problem be made.
37
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39
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14. Walker, P. Steel Comeback Predicted in Cans and Mobile Homes.
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40 PAINT TECHNOLOGY AND AIR POLLUTION
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29. Gerhard, E. R. and G. F. Johnston, Photochemical Oxidation of
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References
41
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42. The Sherwin-Williams Company. Study to Evaluate Techniques for
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42 PAINT TECHNOLOGY AND AIR POLLUTION
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BIBLIOGRAPHY
TESTING OF PAINTS
1. Berg, C. J. et al. Performance of Polymers in Pigment Systems. J.
Paint Technol. 39(510):436453, July 1967.
2. Bigos, J. et al. Five Year Test Results: AISI Research Project on
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AIR POLLUTANTS AND PAINTS
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J. Appl. Chem. 8: 590-598, September 1958.
4. Hayakowa, K. Air Pollution and Protective Coatings. Japan Air
Cleaning Assoc. (Tokyo) 4(4):36-38, 1966.
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TRENDS IN THE PAINT INDUSTRY
1. Buttignol, V. J. et al. Protective Coatings. Ind. and Eng. Chem.
5
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