Handbook of Plastics, Elastomers and Composites Part 10 pot

360 Chapter Six
whose choice of such a coating is based on properties of the generic resin, can be greatly
disappointed. Instead, selections must be made on the basis of performance data for spe-
cific coatings or finish systems. Performance data are generated by the paint and product
manufacturing industries when conducting standard paint evaluation tests. Test methods
for coating material evaluation are listed in Table 6.7.
6.4.4 Selection by Electrical Properties
Electrical properties of organic coatings and finishes vary by resin (also referred to as
polymer) type. When selecting insulating varnishes, insulating enamels, and magnet wire
enamels, the electrical properties and physical properties determine the choice.
Table 6.8 shows electric strengths, Table 6.9 shows volume resistivities, Table 6.10
shows dielectric constants, and Table 6.11 shows dissipation factors for coatings using
most of the available resins. Magnet wire insulation is an important use for organic coat-
ings. National Electrical Manufacturer’s Association (NEMA) standards and manufactur-
ers’ trade names for various wire enamels are shown in Table 6.12. This information can
be used to guide the selection of coatings. However, it is important to remember the afore-
mentioned warnings about blends of various resins and the effects on performance proper-
ties.
6.5 Coating and Finishing Materials
Since it is the resin in the coating’s vehicle that determines its performance properties,
coatings and finishes can be classified by their resin types. The most widely used resins for
manufacturing modern coatings and finishes are acrylics, alkyds, epoxies, polyesters,
polyurethanes, and vinyls.
3
In the following section, the resins used in coatings and fin-
ishes are described.
6.5.1 Common Coating Resins
6.5.1.1 Acrylics. Acrylics are noted for color and gloss retention in outdoor exposure.
Acrylics are supplied as solvent-containing, high-solids, waterborne, and powder coatings.
They are formulated as lacquers, enamels, and emulsions. Lacquers and baking enamels
are used as automotive and appliance finishes. Both these industries use acrylics as top-

coats for multicoat finish systems. Thermosetting acrylics have replaced alkyds in applica-
tions requiring greater mar resistance such as appliance finishes. Acrylic lacquers are
brittle and therefore have poor impact resistance, but their outstanding weather resistance
allowed them to replace nitrocellulose lacquers in automotive finishes for many years.
Acrylic and modified acrylic emulsions have been used as architectural coatings and fin-
ishes and also on industrial products. These medium-priced resins can be formulated to
have excellent hardness, adhesion, abrasion, chemical, and mar resistance. When acrylic
resins are used to modify other resins, their properties are often imparted to the resultant
resin system.
Uses. Acrylics, both lacquers and enamels, were the topcoats of choice for the auto-
motive industry from the early 1960s to the mid 1980s. Thermosetting acrylics are still
used by the major appliance industry. Acrylics are used in electrodeposition and have
largely replaced alkyds. The chemistry of acrylic-based resins allows them to be used in
radiation curing applications alone or as monomeric modifiers for other resins. Acrylic-
modified polyurethane coatings and finishes have excellent exterior durability.
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364 Chapter Six
6.5.1.2 Alkyds. Alkyd resin-based coatings and finishes were introduced in the 1930s
as replacements for nitrocellulose lacquers and oleoresinous coatings. They offer the ad-
vantage of good durability at relatively low cost. These low- to medium-priced coatings
and finishes are still used for finishing a wide variety of products, either alone or modified
with oils or other resins. The degree and type of modification determine their performance
properties. They were used extensively by the automotive and appliance industries through
the 1960s. Although alkyds are used in outdoor applications, they are not as durable in
long-term exposure, and their color and gloss retention is inferior to that of acrylics.
Uses. Once the mainstay of organic coatings and finishes, alkyds are still used for fin-
ishing metal and wood products. Their durability in interior exposures is generally good,
but their exterior durability is only fair. Alkyd resins are used in fillers, sealers, and caulks
for wood finishing because of their formulating flexibility. Alkyds have also been used in
electrodeposition as replacements for the oleoresinous vehicles. They are still used for fin-
ishing by the machine tool and other industries. Alkyds have also been widely used in ar-
chitectural and trade sales coatings. Alkyd-modified acrylic latex paints are excellent
architectural finishes.
6.5.1.3 Epoxies. Epoxy resins can be formulated with a wide range of properties.
These medium- to high-priced resins are noted for their adhesion, make excellent primers,
and are used widely in the appliance and automotive industries. Their heat resistance per-
mits them to be used for electrical insulation. When epoxy topcoats are used outdoors,
they tend to chalk and discolor because of inherently poor ultraviolet light resistance.
Other resins modified with epoxies are used for outdoor exposure as topcoats, and proper-
ties of many other resins can be improved by their addition. Two-component epoxy coat-
ings and finishes are used in environments with extreme corrosion and chemical
conditions. Flexibility in formulating two-component epoxy resin-based coatings and fin-

ishes results in a wide range of physical properties.
Uses. Owing to their excellent adhesion, they are used extensively as primers for
most coatings and finishes over most substrates. Epoxy coatings and finishes provide ex-
cellent chemical and corrosion resistance. They are used as electrical insulating coatings
and finishes because of their high electric strength at elevated temperatures. Some of the
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370 Chapter Six
original work with powder coating was done using epoxy resins, and they are still applied
using this method. Many of the primers used for coil coating are epoxy resin-based.
6.5.1.4 Polyesters. Polyesters are used alone or modified with other resins to formu-
late coatings and finishes ranging from clear furniture finishes (replacing lacquers) to indus-
trial finishes (replacing alkyds). These moderately priced finishes permit the same
formulating flexibility as alkyds but are tougher and more weather resistant. There are basi-
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Plastics in Coatings and Finishes 371
cally two types of polyesters: two-component and single-package. Two-component polyes-
ters are cured using peroxides, which initiate free-radical polymerization, while single-
package polyesters, sometimes called oil-free alkyds, are self-curing, usually at elevated
temperatures. It is important to realize that, in both cases, the resin formulator can adjust
properties to meet most exposure conditions. Polyesters are also applied as powder coatings.
Uses. Two-component polyesters are well known as gel coats for glass-reinforced
plastic bathtubs, lavatories, boats, and automobiles. Figure 6.2 shows tub and shower units
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372 Chapter Six
using a polyester gel coat. High-quality one-package polyester finishes are used on furni-
ture, appliances, automobiles, magnet wire, and industrial products. Polyester powder

coatings are used as high-quality finishes in indoor and outdoor applications for anything
from tables to trucks. They are also used as coil coatings.
6.5.1.5 Polyurethanes. Polyurethane resin-based coatings and finishes are extremely
versatile. They are higher in price than alkyds but lower than epoxies. Polyurethane resins
are available as oil-modified, moisture-curing, blocked, two-component, and lacquers. Ta-
ble 6.13. is a selection guide for polyurethane coatings. Two-component polyurethanes
can be formulated in a wide range of hardnesses. They can be abrasion resistant, flexible,
resilient, tough, chemical resistant, and weather resistant. Abrasion resistance of organic
coatings is shown in Table 6.14. Polyurethanes can be combined with other resins to rein-
force or adopt their properties. Urethane-modified acrylics have excellent outdoor weath-
ering properties. They can also be applied as air-drying, forced-dried, and baking liquid
finishes as well as powder coatings.
Uses. Polyurethanes have become very important finishes in the transportation indus-
try, which includes aircraft, automobiles, railroads, trucks, and ships. Owing to their
chemical resistance and ease of decontamination from chemical, biological, and radiolog-
ical warfare agents, they are widely used for painting military land vehicles, ships, and air-
craft. They are used on automobiles as coatings and finishes for plastic parts and as clear
topcoats in the basecoat-clearcoat finish systems. Low-temperature baking polyurethanes
are used as mar-resistant finishes for products that must be packaged while still warm.
Figure 6.2 Polyester gel coats are used to give a decorative and protective surface to tub
shower units that are made out of glass fiber-reinforced plastics. (Courtesy of Owens-Corning
Fiberglas Corporation)
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373
TABLE 6.13 Guide to Selecting Polyurethane Coatings
One-component
Property Urethane Oil Moisture Blocked

Two-
component Lacquer
Abrasion resistance Fair–good Excellent
Good–excellent Excellent Fair
Hardness Medium Medium–hard Medium–hard Soft–very hard Soft–medium
Flexibility Fair–good Good–excellent Good Good–excellent Excellent
Impact resistance Good Excellent Good–excellent Excellent Excellent
Solvent resistance Fair Poor–fair Good Excellent Poor
Chemical resistance Fair Fair Good Excellent Fair–good
Corrosion resistance Fair Fair Good Excellent Good–Excellent
Adhesion Good Fair–good Fair Excellent Fair–good
Toughness Good Excellent Good Excellent Excellent
Elongation Poor Poor Poor Excellent Excellent
Tensile Fair Good Fair–good Good–excellent Excellent
Weatherability:
Aliphatic Good Poor–fair Good–excellent Good
Conventional Poor–fair Poor–fair Poor–fair Poor–fair Poor
Pigmented gloss High High High High Medium
Cure rate Slow Slow Fast Fast None 150–225°F
Cure temperature Room temperature Room temperature
300–390°F 212°F 225°F
Work life Infinite 1 y 6 months 1–24 hr Infinite
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374 Chapter Six
Polyurethanes are used in an increasing number of applications. They are also used in ra-
diation curable coatings.
6.5.1.6 Polyvinyl chloride. Polyvinyl chloride (PVC) coatings, commonly called vi-

nyls, are noted for their toughness, chemical resistance, and durability. They are available
as solutions, dispersions, and lattices. Properties of vinyl coatings are listed in Table 6.15.
They are applied as lacquers, plastisols, organisols, and lattices. PVC coating powders
have essentially the same properties as liquids. PVC organisol, plastisol, and powder coat-
ings have limited adhesion and require primers.
Uses. Vinyls have been used in various applications, including beverage and other
can linings, automobile interiors, and office machine exteriors. They are also used as thick
film liquids and as powder coatings for electrical insulation. Owing to their excellent
chemical resistance, they are used as tank linings and as rack coatings in electroplating
shops. Typical applications for vinyl coatings are shown in Fig. 6.3. Vinyl-modified acrylic
TABLE 6.14 Abrasion Resistance of Coatings
Coating
Taber ware index,
mg/1000 rev.
Polyurethane type 1
Polyurethane type 2 (clear)
Polyurethane type 2 (pigmented)
Polyurethane type 5
Urethane oil varnish
Alkyd
Vinyl
Epoxy-amine-cured varnish
Epoxy-polyamide enamel
Epoxy-ester enamel
Epoxy-polyamide coating (1:1)
Phenolic spar varnish
Clear nitrocellulose lacquer
Chlorinated rubber
Silicone, white enamel
Catalyzed epoxy, air-cured (PT-401)

Catalyzed epoxy, Teflon-filled (PT-401)
Catalyzed epoxy, bake-Teflon-filled (PT-201)
Parylene N
Parylene C
Parylene D
Polyamide
Polyethylene
Alkyd TT-E-508 enamel (cured for 45 min at 250°F)
Alkyd TTLE-508 (cured for 24 hr at room temperature)
55–67
8–24
31–35
60
155
147
85–106
38
95
196
50
172
96
200–220
113
208
122
136
9.7
44
305

290–310
360
51
70
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376 Chapter Six
latex trade sale paints are used as trim enamels for exterior applications and as semigloss
wall enamels for interior applications.
6.5.2 Other Coating Resins
In addition to the aforementioned materials, there are a number of other important resins
used in formulating coatings. These materials, used alone or as modifiers for other resins,
provide coating vehicles with diverse properties.
6.5.2.1 Aminos. Resins of this type, such as urea formaldehyde and melamine, are
used in modifying other resins to increase their durability. Notable among these modified
resins are the super alkyds used in automotive and appliance finishes.
Uses. Melamine and urea formaldehyde resins are used as modifiers for alkyds and
other resins to increase hardness and accelerate cure.
6.5.2.2 Cellulosics. Nitrocellulose lacquers are the most important of the cellulosics.
They were introduced in the 1920s and used as fast-drying finishes for a number of manu-
factured products. Applied at low solids using expensive solvents, they will not meet air-
quality standards. By modifying nitrocellulose with other resins such as alkyds and ureas,
the VOC content can be lowered, and performance properties can be increased. Other im-

portant cellulosic resins are cellulose acetate butyrate and ethyl cellulose.
Uses. Although no longer used extensively by the automotive industry, nitrocellulose
lacquers are still used by the furniture industry because of their fast-drying and hand-rub-
bing properties. Cellulose acetate butyrate has been used for coating metal in numerous
applications. In 1959, one of the first conveyorized powder coating lines in the United
States coated distribution transformer lids and hand-hole covers with a cellulose acetate
butyrate powder coating.
Figure 6.3 Vinyl plastisols and organisols are used extensively for dip coating of wire products. The
coatings can be varied from very hard to very soft. (Courtesy of M & T Chemicals)
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Plastics in Coatings and Finishes 377
6.5.2.3 Chlorinated rubber. Chlorinated rubber coatings and finishes are used as
swimming pool paints and traffic paints.
6.5.2.4 Fluorocarbons. These high-priced coatings and finishes require high pro-
cessing temperatures and therefore are limited in their usage. They are noted for their lu-
bricity or nonstick properties due to low coefficients of friction, and also for
weatherability. Table 6.16. gives the coefficients of friction of typical coatings.
Uses. Fluorocarbons are used as chemical-resistant coatings and finishes for process-
ing equipment. They are also used as nonstick coatings and finishes for cookware, friction-
reducing coatings and finishes for tools, and as dry lubricated surfaces in many other con-
sumer and industrial products, as shown in Fig. 6.4. Table 6.17 compares the properties of
four fluorocarbons.
6.5.2.5 Oleoresinous. Oleoresinous coatings, based on drying oils such as soybean
and linseed, are slow curing. For many years prior to the introduction of synthetic resins,
TABLE 6.16 Coefficients of Friction of Typical Coatings
Coating
Coefficient of

friction, µ Information source
Polyvinyl chloride
Polystyrene
Polymethyl methacrylate
Nylon
Polyethylene
Polytetrafluoroethylene (Teflon)
Catalyzed epoxy air-dry coating with Teflon filler
Parylene N
Parylene C
Parylene D
Polyimide (Pyre–ML)
Graphite
Graphite–molybdenum sulfide:
Dry-film lubricant
Steel on steel
Brass on steel
Babbitt on mild steel
Glass on glass
Steel on steel with SAE no. 20 oil
Polymethyl methacrylate to self
Polymethyl methacrylate to steel
0.4–0.5
0.4–0.5
0.4–0.5
0.3
0.6–0.8
0.05–0.1
0.15
0.25

0.29
0.31–0.33
0.17
0.18
0.02–0.06
0.45–0.60
0.44
0.33
0.4
0.044
0.8 (static)
0.4–0.5 (static)
a
a
a
a
a
a
b
c
c
c
d
d
e
e
e
e
e
e

e
e
a
R.P. Bowder, Endeavor, Vol. 16, No. 61, l957, p. 5.
b
Product Techniques Incorporated, Bulletin on PT–401 TE, October l7, l961.
c
Union Carbide data.
d
DuPont Technical Bulletin 19, Pyre–ML Wire Enamel, August l967.
e
Electrofilm, Inc. data.
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378
TABLE 6.17 Properties of Four Fluorocarbons
Property
Polyvinyl fluoride
(PVF) (CH
2
–CHF)
n
Polyvinyl-idene fluoride
(CH
2
–CF
2
)

n
Polytrifluorochloroethylene
(PTFC1)
(CC1F–CF
2
)
n
Polytetrafluoroethylene
(PTFE)
(CF
2
–CF
2
)
n
Physical properties:
Density
Fusing temperature, °F
Maximum continuous service and temperature, °F
Coefficient of friction
Flammability
Mechanical properties:
Tensile strength, lb/in
2
Elongation, %
Izod impact, ft-lb/in
Durometer hardness
Yield strength at 77°F, lb/in
2
Heat-distortion temperature at 66 lb/in

2
°F
Coefficient of linear expansion
Modulus (tension) × 10
5
lb/in
2
Electrical properties:
Dielectric strength, V/mil
Short time, V/mil (in)
Dielectric constant, 10
3
Hz
Arc resistance (77°F) ASTM D 495
Volume resistivity Ω-cm at 50% RH, 77°F
Dissipation factor, 100 Hz
1.4
300
225
0.16
Burns
7000
115–250
6000
NA
2.8 × 10
5
2.5–3.7
3400 (0.002)
8.5

NA
10
12
1.6
1.76
460
300
0.16
Nonflammable
7000
300
3.8
80
5500
300
8.5 × 10
5
1.2
260 (0.125)
7.72
60
10
14
0.05
2.104
500
400
0.15
Nonflammable
5000

250
5
74–78
4500
265
15 × 10
5
1.9
500 (0.063)
2.6
300
10
16
0.022
2.17–2.21
750
550
0.1
Nonflammable
2500–3500
200–400
3
50–65
1300
250
8 × 10
5
0.6
600 (0.060)
2.1

300
10
18
0.0003
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Plastics in Coatings and Finishes 379
they were used as the vehicles in most coatings. They still find application alone or as
modifiers to other resins.
Uses. Oleoresinous vehicles are used in low-cost primers and enamels for structural,
marine, architectural, and, to a limited extent, industrial product finishing.
6.5.2.6 Phenolics. Introduced in the early 1900s, phenolics were the first commer-
cial synthetic resins. They are available as 100 percent phenolic baking resins, oil-modi-
fied, and phenolic dispersions. Phenolic resins, used as modifiers, will improve the heat
and chemical resistance of other resins. Baked phenolic resin-based coatings and finishes
are well known for their corrosion, chemical, moisture, and heat resistance.
Uses. Phenolic coatings and finishes are used on heavy-duty air-handling equipment,
on chemical equipment, and as insulating varnishes. Phenolic resins are also used as bind-
ers for electrical and decorative laminated plastics.
6.5.2.7 Polyamides. One of the more notable polyamide resins is nylon, which is
tough, wear resistant, and has a relatively low coefficient of friction. It can be applied as a
powder coating by fluidized bed, electrostatic spray, or flame spray. Table 6.18 compares
the properties of three types of nylon polymers used in coatings. Nylon coatings and fin-
ishes generally require a primer. Polyamide resins are also used as curing agents for two-
component epoxy resin coatings. Film properties can be varied widely by polyamide se-
lection.
Uses. Applied as a powder coating, nylon provides a high degree of toughness and
mechanical durability to office furniture. Other polyamide resins are used as curing agents

in two-component epoxy resin-based primers and topcoats, adhesives, and sealants.
Figure 6.4 Nonstick feature of fluorocarbon finishes makes
them useful for products such as saws, fan and blower blades,
door-lock parts, sliding- and folding-door hardware, skis, and
snow shovels. (Courtesy of E. I. DuPont de Nemours & Com-
p
any)
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6.5.2.8 Polyolefins. These coatings, which can be applied by flame spraying, hot
melt, or powder coating methods, have limited usage.
Uses. Polyethylene is used for impregnating or coating packaging materials such as
paper and aluminum foil. Certain polyethylene-coated composite packaging materials are
virtually moisture proof. Table 6.19 compares the moisture vapor transmission rates of
various coatings and films. Polyethylene powder coatings are used on chemical processing
and food-handling equipment.
6.5.2.9 Polyimides. Polyimide coatings and finishes have excellent long-term ther-
mal stability, wear, mar and moisture resistance, and electrical properties. They are high in
price.
Uses. Polyimide coatings and finishes are used in electrical applications as insulating
varnishes and magnet wire enamels in high-temperature, high-reliability applications.
They are also used as alternatives to fluorocarbon coatings and finishes on cookware, as
shown in Fig. 6.5.
6.5.2.10 Silicones. Silicone resins are high in price and are used alone or as modifi-
ers to upgrade other resins. They are noted for their high-temperature resistance, moisture
resistance, and weatherability. They can be hard or elastomeric, baking, or room tempera-
ture curing.

Uses. Silicones are used in high-temperature coatings and finishes for exhaust stacks,
ovens, and space heaters. Figure 6.6 shows silicone coatings and finishes on fireplace
equipment. They are also used as conformal coatings for printed wiring boards, moisture
repellents for masonry, weather-resistant finishes for outdoors, and thermal control coat-
ings for space vehicles. The thermal conductivities of coatings are listed in Table 6.20.
TABLE 6.18 Properties of Nylon Coatings
Nylon 11 Nylon 6/6 Nylon 6
Elongation (73°F), % 120 90 50–200
Tensile strength (73°F), lb/in
2
8,500 10,500 10,500
Modulus of elasticity (73°F), lb/in
2
178,000 400,000 350,000
Rockwell hardness R 100.5 R 118 R 112–118
Specific gravity 1.04 1.14 1.14
Moisture absorption, ASTM D 570 0.4 1.5 1.6–2.3
Thermal conductivity, Btu/(ft
2
) (h × °F/in) 1.5 1.7 1.2–1.3
Dielectric strength (short time), V/mil 430 385 440
Dielectric constant (10 Hz) 3.5 4 4.8
Effect of:
Weak acids
Strong acids
Strong alkalies
Alcohols
Esters
Hydrocarbons
None

Attack
None
None
None
None
None
Attack
None
None
None
None
None
Attack
None
None
None
None
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Plastics in Coatings and Finishes 381
6.6 Application Methods
The selection of an application method is as important as the selection of the coating itself.
Basically, the application methods for industrial liquid coatings and finishes are dipping,
flow coating, and spraying, although some are applied by brushing, rolling, printing, and
silk screening. The application methods for powder coatings and finishes are fluidized
beds, electrostatic fluidized beds, and electrostatic spray outfits. In these times of environ-
mental awareness, regulation, and compliance, it is mandatory that coatings and finishes
be applied in the most efficient manner.

3
Not only will this help meet the air-quality stan-
dards, it will also reduce material costs. The advantages and disadvantages of various coat-
ing application methods are given in Table 6.21.
TABLE 6.19 Moisture-Vapor Transmission Rates per 24-hr Period of Coatings and
Films in g/(mil) (in
2
)
Coating or Film MVTR
Information Source
Epoxy-anhydride 2.38 Autonetics data (25°C)
Epoxy-aromatic amine 1.79 Autonetics data (25°C)
Neoprene 15.5 Baer (39°C)
Polyurethane (Magna X–500) 2.4 Autonetics data (25°C)
Polyurethane (isocyanate-polyester) 8.72 Autonetics data (25°C)
Olefane,
*
polypropylene 0.70 Avisum data
Cellophane (type PVD uncoated film) 134 DuPont
Cellulose acetate (film) 219 DuPont
Polycarbonate 10 FMC data
Mylar
†
1.9
1.8
Baer (39°C)
DuPont data
Polystyrene 8.6
9.6
Baer (39°C)

Dow data
Polyethylene film 0.97 Dow data (1-mil film)
Saran resin (F120) 0.097–0.45 Baer (39°C)
Polyvinylidene chloride 0.15 Baer (2-mil sample, 40°C)
Polytetrafluoroethylene (PTFE) 0.32 Baer (2-mil sample 40°C)
PTFE, dispersion cast 0.2 DuPont data
Fluorinated ethylene propylene (FEP) 0.46 Baer (40°C)
Polyvinyl fluoride 2.97 Baer (40°C)
Teslar 2.7 DuPont data
Parylene N 14 Union Carbide data (2-mil sample)
Parylene C 1 Union Carbide data (2-mil sample)
Silicone (RTV 521) 120.78 Autonetics data
Methyl phenyl silicone 38.31 Autonetics data
Polyurethane (ABO130–002) 4.33 Autonetics data
Phenoxy 3.5 Lee, Stoffey, and Neville
Alkyd-silicone (DC–1377) 6.47 Autonetics data
Alkyd-silicone (DC–1400) 4.45 Autonetics data
Alkyd-silicone 6.16–7.9 Autonetics data
Polyvinyl fluoride (PT–207) 0.7 Product Techniques Incorporated
*Trademark of Avisun Corporation, Philadelphia, PA
†Trademark of E.I. DuPont de Nemours & Company, Wilmington, DE
Plastics in Coatings and Finishes
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382 Chapter Six
Figure 6.5 Polyimide coating is used as a protective finish on the inside of
aluminum, stainless steel, and other cookware. (Courtesy of Mirro Aluminum
Company)
Figure 6.6 Silicone coatings are used as heat-stable finishes

for severe high-temperature applications such as fireplace
equipment, exhaust stacks, thermal control coatings for
spacecraft, and wall and space heaters. (Courtesy of Copper
D
evelopment Assn.)
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383
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384
Plastics in Coatings and Finishes
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