Coatings Technology Handbook Episode 3 Part 5 doc

101

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Coatings Technology Handbook, Third Edition

zinc oxide surface as the zinc layer becomes thinner. The white zinc oxide has substantial water solubility
and washes away in rain. The zinc surface is often painted to give protection against these losses.

101.1.1.2 Flame/Plasma Spray

Although all the flame and plasma spray processes project liquid metal droplets through the air to the
substrate, each starts with a solid metal wire or solid molten powder. The solid is taken into a device
which heats it to the molten state, breaks it into microscopic droplets, and propels the droplets at the
substrate. Longo edited a reference book on this topic.

1

The “flame” or “thermal” spray uses a modified oxyacetylene torch as the heat source. After the flame
has been adjusted to its hottest, additional compressed air is blown into the flame. The wire or powder
is then fed in via a funnel, and the blast of liquid metal particles is pointed at the substrate. The “plasma”
spray uses an electric arc as the heat source to melt the wire or feed powder into the compressed airstream.
The distance between the molten metal’s origin and the substrate will determine the type of coating
obtained. The close approach of the nozzle means that most particles will hit the substrate surface as a
liquid. Many will stick, and transfer their heat to the substrate, but some particles will bounce off. If the
nozzle is further away, the smaller liquid particles will solidify and bounce off the substrate, while the
larger particles will still stick. If the nozzle is too far from the substrate, none of the particles will stick
because they will have cooled too much. Losses from bounce-off or from premature cooling will be on
the order of 25% of the weight of the metal sprayed.

The metals most commonly sprayed include copper, zinc, iron, and aluminum. Alloys and even metal
oxides can also be sprayed, provided there is enough heat in the flame to make the particle soften. Since
the sprayed metal is of lower density than the solid metal, there is occluded air, and even porosity.
However, adhesion to most substrates is good, and is often assured by cleaning and roughening the
surface (e.g., sandblasting). The inorganic coating may be built up enough to be machined, and may be
strong enough to be a bearing surface.

101.1.1.3 Other Liquid Metal Coatings

Any solid can be dipped into a molten metal.

101.1.2 Solid Metal Processes

101.1.2.1 Sherrodizing

An item of steel or iron is put in a drum with powdered zinc and steel balls, and the drum is rotated.
The zinc powder is essentially hammered onto the surface of the steel/iron item as individual spots. The
length of time in the rotating drum, the amount of zinc powder, the number of steel balls, and the
number of items to be treated all govern the actual amount of zinc that ends up on the surface of the
item to be treated. The zinc coating on the iron/steel acts as a corrosion (rust) inhibitive protection for
the item.

101.1.2.2 “Detaclad” Process

The construction of metal laminates, such as the coinage products now used by the U.S. Treasury, is a
simple process involving a layer of metal applied to another metal surface by the force of an explosion
on one surface. If silver is needed as an outer surface over copper, the explosive is on the side away from

101.1.3 Vapor Processes

101.1.3.1 Vacuum Evaporation

The simplest of the vapor processes is vacuum evaporation. The items to be coated are put on racks that
circle a central set of trays formed from electrical resistance heaters. A bell jar is lowered over the whole
array, and sealed to be pumped down to 1 mm Hg of vacuum. The resistance heaters are fired off to
evaporate the metal powder or slug in the tray, and the individual atoms of metal fly off in a straight

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the copper in the setup, as shown in Figure 101.1.

101

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Coatings Technology Handbook, Third Edition

101.1.4 Plating

101.1.4.1 Electroplating

A good place to start the investigation of plating processes is an annual handbook supplied by a trade
magazine publisher.

16

Plating on plastics has been reviewed by Saubestre

17

and by Muller and associ-
ates.

18

Springer and associates

19

described details of polymer treatments

20,21

and morphology

22

as impor-
tant in electroplating polymer surfaces. Safrenek

23

detailed the properties of electroplated metals and
alloys. A zinc–nickel alloy electroplated onto steel is reputed to have better corrosion properties than
galvanized steel.

24

101.1.4.2 Electroless Plating

The handbook cited earlier is a good reference for electroless plating as well.

16

The idea is simply to put
a metal solution on a surface, and let it deposit the zero valent metal on the surface because of an added
chemical. It turns out not to be quite so simple, because addition of the reducing agent to a solution
does not guarantee that the metal will deposit on the surface, and it does not mean that the deposit will
adhere if deposited. Hence, there are sequences of “washes” and “activators” that prepare the substrate
to accept the final plating formulation. In the case of plating on plastics, several oxidative techniques
(chromic acid solutions, plasma etching, nitric acid washes, etc.) are used to prepare a surface. One
process uses three deposition steps, with clean water rinses between, to end up with copper on plastic.
The three solutions are tin chloride, palladium chloride, and a formulated copper solution that has
reducing agent along with rate modifier and surface modifier chemicals as well. Rigorous rinsing between
the metal solutions is needed to assure that the last solution does not become a slurry of colloidal copper,
because of “dragout” or contamination by preceding metal ions. The electroless plating deposits are
continuous, conductive, and bright, but are thin — micrometers in thickness.

101.2 Coating on Metals

Coatings for metals may be divided into two classes by main function: those that are decorative, and
those that are protective. That is not to say that a protective coating cannot be decorative, but that the
coating’s main function is protective, while it is chosen to be decorative as an additional option.

101.2.1 Decoration

The decorative aspect of coatings lies in several features that are dealt with elsewhere in this book. Among
those aspects are color, gloss/flatness, and texture. Each entails specific approaches the formulator uses
to attain the desired appearance, mainly involving choices of vehicle (the adhesive that sticks the pigment
particles together and then to a substrate), pigments, the ratio of pigments to vehicle, and (occasionally)

the additive that confers a certain property when pigment or vehicle cannot.
Ye t another aspect of decoration is pattern. If and when there are multiple colors on a surface, the
shape described at the color interfaces can be important. The camouflage paints strive to have what
appear to be random splotches, because a regular geometric pattern (especially a straight line) attracts

smears, and lines simulating natural mineral or rock formation surfaces. And the pattern is a main point
in signage or artwork.

101.2.2 Protection

The metal substrate is generally thermodynamically unstable and is easily converted to the more ther-
modynamically stable oxide. However, the protection provided to the metal substrate is often designed
to guard against sorts of attack other than chemical oxidation. Mechanical damage may aid the oxidation,
by providing sites for the oxidant to work. Electrical exposure or damage can ease the chemical degra-
dation. So, work on protecting a metal substrate must include consideration of the insults or attacks to

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the eye to a potential target. The multicolor paints (described in Chapter 87) have the dots, splotches,

Metal Coatings

101

-5

be expected. In the instance of corrosion, the protection may aim to prohibit contact of the coating with
oxygen or water — each a necessary element of the corrosion reaction. The aim may also be to prohibit
contact with corrosion catalysts — salts, acids or alkalis. Schweitzer

25

reviewed corrosion and protective
schemes, and one unit of the educational booklets from the Federation of Societies for Coating Technology
deals with corrosion protection

26a

while another covers corrosion and surface protection for painting.

26b

Wilmhurst

22

described aqueous maintenance paints for corrosion protection in Australia, while Campbell
and Flynn

27

did so for the United States and Poluzzi

28

for Italy. A Golden Gate Society for Coatings
Te c hnology Technical Committee study

29

showed the waterborne systems have come to equal the solvent-
borne coatings for corrosion protection in aggressive environments (i.e., the Golden Gate Bridge).
At the National Coatings Center, we divide a “pitchfork” diagram (Figure 101.2) to describe the three
major corrosion protection schemes. The main emphasis was on improving ways to give corrosion
protection through combinations of some of the corrosion protection schemes.
Examples of the barrier coatings are fairly straightforward. As noted earlier, the zinc in galvanizing is
initially a barrier, and any impervious coating is a barrier, be it wax, asphalt, coal tar, polyethylene, or
whatever. There are selective barriers that aim to protect against corrosion by blocking a specific corrosive
element. The wax, polyethylene, coal tar, or asphalt is specifically aimed at prevention of water permeation
to the metal surface, as water is a specific corrosive substance. Other coatings (PVDC, Barex-type nitriles,
etc.) aim to prohibit oxygen permeation. In both cases, the coatings are diffusion barriers, and the key
is to have a coating that dissolves as little as possible of the permeant within the coating, and also inhibits
permeation. A highly polar coating material is always more water permeable than the nonpolar material,
because water dissolves so well in the polar material that the polar material acts as a pipeline rather than
a barrier. It is a chuckle to hear of silicones or acrylates described as waterproofings, but you have to
understand the implied statement that they protect against liquid water, while water vapor goes through
them 100 to 1000 times faster than it would go through a hydrocarbon barrier. Munger

30

reviewed
protective coatings for corrosion prevention.
The electrochemical protection schemes are bound up in converting the iron or steel into a cathode,
since the corrosion reaction is an anodic oxidation of the zero-valent iron metal to ionic forms (usually
ferrous). The easiest way is to simply contact the metal with something that is oxidized more easily (zinc,
magnesium, aluminum, etc.) and let the iron be the cathode while the other metal is corroded as the
sacrificial anode. Indeed, there is a substantial market in bars of magnesium or zinc that are attached to
iron (pipelines, underground tankage) to act as sacrificial anodes. We already noted that galvanized iron
with the zinc surface damaged to penetrate to the iron is still electrochemically protecting the iron. The
“zinc-rich” paints (having about 85% by weight of zinc metal powder and 15% binder) are also cathodic

protectors of steel. But the sacrificial anode does send its corrosion products into the surroundings. In
a tidal area, the sacrificial anode specified by some regulatory agencies feeds metal ions into the under-
ground water while it is protecting the underground storage tank.

FIGURE 101.2

Corrosion protection schemes.
Corrosion Protection
Barrier
Chemical
Inhibition
Electrochemical
Inhibition

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Coatings Technology Handbook, Third Edition

An alternative in cathodic protection is to impress a current onto the potentially corroding metal to
make it cathodic. Here a battery, or a step-down transformer is used with another power source. This
technique is used on shipboard for iron hulled vessels, and the battery can be recharged when needed.
Some pipelines are cathodically protected with impressed current. The advantage is that there are no
ions lost to the surroundings, hence subsequent contamination of water.
The chemical inhibitors are many and varied items of commerce and may work in many ways. Most
are sold because they have been shown to work, though no mechanism is proposed. Some of the

surfactant-type materials (oleyl sarcosine, for instance) may only add a physical barrier by adsorbing to
the surface and blocking approach of oxygen, water, or catalytic ion. Other materials may adsorb on the
metal and act as a pH modifier or buffer, as an amine would inhibit acid-catalyzed attack. Some inhibitors
modify the electromotive potential at which corrosion occurs and are said to have “passivated” the surface.
Most of the chemical inhibitors are low molecular weight compounds and can be washed away or
otherwise rendered ineffective by chemical attacks or reactions. They are effective over short periods of
time, and can be stabilized against erosions by formulation to some degree. For instance, there are oils
into which corrosion inhibitors are formulated.
There are corrosion-inhibitive pigments. Seldom is there discussion of the mechanism by which these
chemical inhibitive pigments work, and such characterization could extend their utility. It has been shown
and corrosion studies by the technical committees of the Northwest, New England, and Golden Gate
Societies for Coatings Technology). Indeed, Nadim Ghanem (American University of Cairo) told of a
basic lead carbonate formulation study in which the solvent-borne vinyl binder gave no corrosion
protection, while a waterborne vinyl gave excellent protection. His hypothesis was that the coating needs
to be permeable to water to get the lead ions to migrate to where they need to be to act as corrosion
protectors. That may have also been the message in the Los Angeles Society for Coatings Technology
work with aminosilane-treated talcs in latex formulations. Though many demonstrations of the effec-
tiveness of the corrosion-inhibitive pigments exist, the mechanisms should be more thoroughly described
to aid the formulator.

References

1. F. N. Longo, Ed.,

Thermal Spray Coatings: New Materials, Processes and Applications

, American
Society for Metals Conference Book. Metals Park, OH: ASM, 1985.
2. R. T. Sorg,

Prod. Finish.,

July, 72 (1978).
3. Anon.,

Ind. Finish.,

January, 24 (1978).
4. British Patent 1,369,056;

Chem. Abstr., 83,

116382u.
5. M. Rogers,

Plast. Technol.,

November, 20 (1982).
6. R. H. Hochman et al., Eds.,

Ion Implantation and Plasma Assisted Processes

, American Society for
Metals Conference Book. Metals Park, OH: ASM, 1988.
7. Fujitsu Ltd., Japanese Patent 8,089,833 December 28, 1978;

Chem. Abstr. 5.

39579m.
8. A. K. Sharma et al.,

J. Appl. Polym. Sci., 26,

2197 (1981).
9. R. Athey et al.,

J. Coatings Technol., 57

(726), 71 (July 1985).
10. A. Morikana and Y. Asano,

J. Appl. Polym. Sci., 27

, 2139 (1982).
11. C. Arnold, Jr., et al.,

J. Appl. Polym. Sci., 27

, 821 (1982).
12. M. R. Havens et al.,

J. Appl. Polym. Sci. 22

(10), 2793 (1978).
13. D. T. Clark and M. Z. Abraham,

J. Polym. Sci., Polym. Chem. Ed. 19

, 2129 (1981).
14. N. Inagaki et al.,

J. Polym. Sci., Polym. Lett. Ed., 19,

335 (1981).
15. H. A. Beale,

Ind. Res. Dev.,

July, 135 (1981).
16. M. Murphy, Ed.,

Metal Finishing Handbook,

Hackensack, NJ.
17. E. B. Saubestre, in

Modern Electroplating

,



3rd ed., F. Lowenheim, Ed. New York; Wiley-Interscience,
Chapter 28, 1974.
18. G. Muller et al.,

Plating on Plastics

. Surrey, England: Portcullis Press.

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that nominally corrosion-inhibitive pigments do not work in some formulations (see SSPC literature

Metal Coatings

101

-7

19. J. Springer et al.,

Angew. Makromol. Chem., 89,

81 (1980).
20. J. Springer et al.,

Angew. Makromol. Chem., 89,

81 (1980).
21. J. Springer et al.,

Angew. Makromol. Chem.,



89,

81 (1980).
22. A. G. Wilmhurst,

Aust. Oil Colour Chem. Assoc.,

November, 12 (1978).
23. W. H. Safranek,

The Properties of Electrodeposited Metals and Alloys

. American Electroplaters and
Surface Finishers Society, 1986.
24. S. A. Watson,

Nickel. 4

(1), 8 (September 1988).
25. P. A. Schweitzer, Ed.,

Corrosion and Corrosion Protection Handbook

. New York, Dekker, 1983.
26. (a) Unit 27,

Anticorrosive Barriers and Inhibitive Primers

. Philadelphia: Federation of Societies for
Coating Technology, 1979. (b) Unit 26,

Corrosion and the Preparation of Metallic Surfaces for
Painting

. Philadelphia: FSCT, 1979.
27. D. Campbell and R. W. Flynn,

Am. Paint Coatings J.,

March 6, 55 (1978).
28. A. Poluzzi,

14th Annual FATIPEC Congress Proceedings

, 1978, p. 61.
29. R. Athey et al.,

J. Coatings Technol., 57

(726), 71 (July 1985).
30. C. H. Munger,

Corrosion Prevention by Protective Coatings

. National Association Engineering, 1984.

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102

-1

102

Corrosion and Its

Control by Coatings

102.1 Introduction

102-

1

102.2 Coatings

102-

6

References

102-

9

102.1 Introduction

102.1.1 Energy Transfer

The metallic state is in most metals an unstable condition resulting from the smelting operation, in which
energy is imported by the ore as the metal is derived. After extraction, most metals undergo a slow
deterioration process during which they shed this energy and return to a more stable condition in which

they are combined with some element of their environment, such as an oxide, a sulfide, or some other
corrosion product. This energy conversion process is known as corrosion.

102.1.2 The Electrochemical Nature of Corrosion

Corrosion is most usually driven by some electrochemical inhomogeneity in the metal or its environment.
In this process, different areas of the metal, having different levels of free energy and therefore different
corrosion potentials, become the electrodes of an electrochemical cell in contact with a common electro-
lyte.

1

−

5

The electrochemical couples are set up with areas of more active electrochemical potential acting
the anodes as metal dissolves into the electrolyte as ions, so releasing electrons, which pass through the
metal to the adjacent cathode areas where they react with the environment. This flow of electricity, the
electron passage from anode to cathode, and the accompanying charge transfer back through the elec-
trolyte from cathode to anode, make up the corrosion current. The rate of the current flow, i.e., the
magnitude of the corrosion current (

I

) that develops, is a measure of the amount of degradation and is
related to the potential difference (

V

) between the anodic and cathodic sites by Ohm’s law:
(102.1)
where

R

is the total resistance of the cell.
I
V
R
=

Clive H. Hare

Coating System Design, Inc.

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© 2006 by Taylor & Francis Group, LLC
Energy Transfer • The Electrochemical Nature of Corrosion
Depassivation • Area Effects
Corrosion Control by Coatings • Barrier Coatings • Inhibitive
• Electrode Reactions • Polarization • Electrode Film
Breakdown and Depolarization • Passivation and
Coatings • Zinc-Rich Coatings
as anodes of the cell, while more passive areas act as cathodes (Figure 102.1). Corrosion takes place at

Corrosion and Its Control by Coatings

102

-3

M

=

M

n+



+



ne

(102.4)
where

n

is the valency of the metal.
In the case of iron, this equation becomes
Fe

→

Fe

2+



+

2e (102.5)
The exact nature of the reaction at the surface of the cathode (in which electrons released in anodic
dissolution are, in turn, consumed) depends upon the nature of the environment. Under neutral and
alkaline conditions, the reaction involves oxygen and proceeds
2H

2

O

+

O

2



+

4e

=

4OH

–

(102.6)
Under acidic conditions, if oxygen is present, the reaction may proceed
O

2



+

4H

+



+

4e

=

2H

2

O (102.7)
Where oxygen is not available, hydrogen gas may form under acidic conditions:
2H

+



+

2e

=

H

2

(102.8)
Migration of the oxidative product (M

n+

) from the anode and the reduction product (OH

–

) from the
cathode occurs until they combine to form the oxide, which precipitates. In the case of steel this may be

Fe(OH)

2

, ferrous hydroxide, or, depending upon the nature of the environment, one of several precursor
products, such as ferrous hydroxy chloride in salt water. Ferrous products are readily soluble, and this
favors migration, so that oxide formations are not intimately associated with the anode but are loosely
adherent and porous. Given sufficient oxygen, a second oxidation reaction will occur in steel corrosion,
which converts the divalent ion to the trivalent ferric state,
Fe

2+



→

Fe

3+



+

e (102.9)
The solubility of the trivalent corrosion product is much less than that of the ferrous product. Under
normal circumstances, however, where the secondary oxidative process occurs gradually after the ferrous
ions have migrated away from the anode, the corrosion product is no more tightly adherent than is the
ferrous product from which it is formed, and films of rust, hydrated ferric oxide (Fe

2

O

3

× Η

2

Ο)

, are
usually loose and crumbly.

TA BLE 102.1

Electrode Potentials

Electrode Reaction Potential (volts)

Active
Na

⇔

Na

+

+

e –2.71
Mg

⇔

Mg

+2



+

2e –2.38
Al

⇔

Al

+3



+

3e –1.66
Zn

⇔

Zn

+2



+

2e –0.76
Fe

⇔

Fe

+2



+

2e –0.44
Pb

⇔

Pb

+2



+

2e –0.13
H

⇔

H

+



+

e 0.00
Cu

⇔

Cu

+2



+

2e 0.34
Ag

⇔

Ag

+



+

e 0.80
Pt

⇔

Pt

+2

+

e 1.2
Au

⇔

Au

+3



+

3e 1.4
Noble (Passive)

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103

-1

103

Marine Coatings

Industry

Bibliography

103-

2
Marine coatings are special-purpose coatings that are supplied to the shipbuilding and repair, offshore,
and pleasure craft markets. The products used are diverse and unique and are formulated for severe
climatic and immersion conditions.
As a result of these conditions, the coatings used must have maximum resistance properties to salt
spray, constant seawater, and in the case of tankers, a broad range of chemicals. For these reasons, a
substantial volume of products sold today are two-component epoxy primers, intermediate high builds,
and tank linings.
Above-the-waterline finishes are still predominantly single-package alkyds or acrylics on commercial
ships and offshore platforms. This is due to the subsequent ease of maintenance required. Similarly,
single-pack alkyds, urethane-alkyds, and silicone-alkyds are predominant in the pleasure craft market,
at least for hulls up to the 30- to 35-foot class.
Larger pleasure crafts are still painted with the single-pack finishes, but many such craft (yachts) are
coated today with two-part aliphatic polyurethanes to achieve the best in gloss and gloss retention,
abrasion resistance, and long-term durability.
The use of two-component products, whether applied to a ship’s tanks or a yacht’s topside, requires
more professional applicators to achieve the best result. Such applicators must be familiar with multiple
spray application equipment from the simple siphon cup to the sophisticated twin-feed heated airless spray.
Whether coating deep-sea ships, offshore platforms, or pleasure craft, one unique characteristic of the
marine coatings industry is the need to protect the underwater surfaces from the attachment and growth
of marine fouling organisms. These are living animals, algae or slime, that will adhere, colonize, and
grow rapidly if not controlled through the use of antifouling coatings.
Antifouling paints are unique to this industry and make up approximately 50% of the total volume
of coatings used. By their nature, in order to mitigate fouling attachment, antifouling paints contain
biocides, which are registered with the U.S. Environmental Protection Agency (EPA) as pesticides under
the Federal Insecticide, Fungicide and Rodenticide Act.
Subsequently, all antifouling paints must be both federally registered with the EPA and registered with

the state EPA in which they are sold.
This unique class of product is expensive to develop, test, and register and thus is expensive for the
customer. Most antifouling paints contain rosin (gum or wood) as part of the vehicle and a copper
compound

−

cuprous oxide being the most common — as the biocide.
Some antifoulings are based on organotin-copolymer resins, which are biocidally active polymers along
with a copper compound. These are generally the best-in-class for complete fouling control.

Jack Hickey

International Paint Company

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104

-1

104

Decorative Surface

Protection Products

104.1 Introduction

104-

1
104.2 History

104-

1
104.3 Products

104-

2

104.4 Process of Manufacturing

104-

5

104.5 Applications

104-

7
References

104-

8

104.1 Introduction

Decorative surface protection products, as the term suggests, are products that provide both decoration
and protection to a wide variety of surfaces. These products are available to consumers in a variety of
colors, decorative designs, and surface finishes. They are attractive, durable, washable, waterproof, and
resistant to stains from food, beverages, and common household items. They must be conformable to a
wide variety of surfaces, requiring no tools, water, or paste to be applied to any plain surface.
In most cases, they have informative and instructional carriers traditionally known as printed release
liners, which are affixed by a flexible pressure-sensitive adhesive to a base sheet, also known as a primary
substrate or a face stock. In some cases, the release liner has been eliminated by using an embossed
primary substrate. Alternatively, the primary substrate may have been coated on one side with a release
coating and on the other side with a low tack adhesive.

1

These products are known as self-wound adhesive
coated decorative sheets. They are made in solid colors, decorative prints, and textured woodgrains.

104.2 History

Pressure-sensitive adhesive usage in making decorative surface protection products goes back to the early
1950s. Similar types of vinyl film were used by consumers on products such as printed and laminated
tablecloths and printed draperies. The idea of printed film led to the making of decorative surface
protection products by a low tack, pressure-sensitive adhesive on printed film.

Jaykumar (Jay) J. Shah

Decora

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© 2006 by Taylor & Francis Group, LLC
Primary Substrate or Base Sheet • Pigmented Coating for
Pressure-Sensitive Adhesives
Application of Release Coatings • Adhesive Coating
Decorative Printing • Release Paper • Release Coatings •
Application Process • Finishing
The construction of decorative products is shown in Figure 104.1.

105

-1

105

Coated Fabrics for

Protective Clothing

105.1 Introduction

105-

1
105.2 Protection from What?

105-

1
105.3 Coating Materials

105-

2

105.4 Markets and Standards

105-

4
Bibliography

105-

4

105.1 Introduction

Our need for protection from the environment in which we live or work is becoming ever more complex
and demanding. We can travel easily to any part of the earth, even to the vacuum of space, and we expect
to be able to live more or less normal and active lives no matter where we are or what we may wish to
do. We have become more conscious of the potential dangers that surround us at home and at work,
and we expect some protection from hazards that only a short time ago were thought of as risks that
our way of life required us to accept without question. Consequently, we have recently seen advances in
the design of a wide range of protective clothing of ever higher levels of sophistication, made possible
by the continuing development of new materials capable of providing improved protection from many
threats to our well-being.
Protective clothing is commonly designed to isolate the body from its surroundings through the use
of an assembly that includes as one of its components a continuous film, either in the form of a coating
or a lamination. This is essential whenever resistance to absorption or penetration of a liquid is required,

and is often used also for gases, though these can sometimes be adsorbed or chemically modified in a
layer that may not be totally impermeable. Often a structure designed to provide protection from a
nonfluid threat — cold, for example — will function effectively only if it remains dry. Some degree of
resistance to wetting may be provided by giving the fibers a water-repellent treatment. But totally effective
resistance to the penetration of water into the structure requires that a film be added to the assembly,
which provides improved wind resistance but otherwise plays only a secondary role in providing protec-
tion from cold.
Coating or laminating, then, is widely used in protective clothing, and the properties of the films, as
well as how they are incorporated into the clothing assembly, are of prime importance to the production
of an acceptable garment.

105.2 Protection from What?

Perhaps our most universal need is for protection from rain and cold. Other needs are more specialized,
and generally apply only to that segment of the population whose livelihood exposes them to annoyances

N. J. Abbott

Albany International Research
Company

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Coating Types • Method of Application • Properties