Coatings Technology Handbook 2010 Part 2 doc

4-6 Coatings Technology Handbook, Third Edition
(4.13)
where G
e
is given by Equation 4.11 and f
e
is a probability factor for trapped entanglements.
In the case of network imperfections, Equation 4.12 is modified.
14,15
The quantity f
e
can be calculated
if the reaction parameters for network formation are known.
14,16,17
4.3.3 Other Properties
Several other properties of dried films influence performance characteristics. Examples are the coefficient
of thermal expansion, ultimate mechanical properties, stress relaxation and creep, and dielectric prop-
erties. However, correlation of these properties with structure for polymeric films is not well established;
some of the more successful attempts are treated in Refs. 2 and 3.
References
1. R. B. Bird, R. C. Armstrong, and O. Hassager, Dynamics of Polymeric Fluids, Vol. 2. New York:
Wiley-Interscience, 1987.
2. J. D. Ferry, Viscoelastic Properties of Polymers. New York: Wiley, 1980.
3. D. W. Van Krevelen, Properties of Polymers. New York: Elsevier, 1976.
4.
5. J. W. Berge and J. D. Ferry, J. Colloid Sci., 12, 400 (1957).
6. G. Pezzin and N. Gligo, J. Appl. Polym. Sci., 10, 1 (1966).
7. Ref. 2, p. 510.
8. T. Matsumoto, O. Yamamoto, and S. Onogi, J. Rheol., 24, 279 (1980).
9. D. W. Meitz, Ph.D. thesis, Carnegie-Mellon University, December 1984.

10. Ref. 3, p. 383.
11. F. Bueche, Physical Properties of Polymers. New York: Wiley, 1962.
12. Ref. 3, p. 384.
13. Ref. 3, p. 266.
14. E. M. Valles and C. W. Macosko, Macromolecules, 12, 673 (1979).
15. P. J. Flory, Principles of Polymer Chemistry. Ithaca, NY: Cornell University Press, 1953, p. 458.
16. M. Gottlieb, C. W. Macosko, G. S. Benjamin, K. O. Meyers, and E. W. Merill, Macromolecules, 14,
1039 (1981).
17. D. S. Pearson and W. W. Graessley, Macromolecules, 13, 1001 (1980).
G
M
fG
RT
c
ee

ρ
+
DK4036_C004.fm Page 6 Thursday, May 12, 2005 9:39 AM
© 2006 by Taylor & Francis Group, LLC
Ref. 2, see discussion in Chapter 17.

5

-1

5

The Theory of Adhesion

5.1 Contact Angle Equilibrium

5-

1
5.2 Forces of Attraction

5-

3
5.3 Real and Ideal Adhesive Bond Strengths

5-

8
References

5-

9
When pressure-sensitive adhesive is applied to a smooth surface, it sticks immediately. The application
pressure can be very slight, not more than the pressure due to the weight of the tape itself. The adhesive
is said to “wet” the surface, and, indeed, if the tape is applied to clear glass and one views the attached
area through the glass, it is found that in certain areas the adhesive–glass interface looks like a liquid–glass
interface. From this one would infer that a pressure-sensitive adhesive, even though it is a soft, highly
compliant solid, also has liquidlike characteristics. Some knowledge of the interaction between liquids
and solids is beneficial to the understanding of adhesion.

5.1 Contact Angle Equilibrium

When a drop of liquid is placed on a surface of a solid that is smooth, planar, and level, the liquid either
spreads out to a thin surface film, or it forms a sessile droplet on the surface. The droplet has a finite
between the solid and the liquid and the surface tension of the liquid. The contact angle equilibrium has
received a great deal of attention, principally because it is perhaps the simplest direct experimental
approach to the thermodynamic work of adhesion.
Many years ago Young

1

proposed that the contact angle represents the vectorial balance of three tensors,
the surface tension of the solid in air (

γ

sa

), the surface tension of the liquid in equilibrium with the vapor
(

γ

lv

), and the interfacial tension between the solid and the liquid (

γ

sl

), The force balance can be written

γ

sa

=

γ

lv

cos ++

γ

sl

(5.1)
Young’s equation has come under criticism on the grounds that the surface tension of a solid is ill
defined, but most surface chemists find his equation acceptable on theoretical grounds.
The equation can be written as a force equilibrium or as an energy equilibrium, because the surface
tension, expressed as a force per unit of length, will require an energy expenditure of the same numerical
value when it acts to generate a unit area of new surface.
Harkins and Livingston

2

recognized that Young’s equation must be corrected when the exposed surface
of the solid carries an adsorbed film of the liquid’s vapor. The solid–“air-plus-vapor” tensor,

γ

sv

, is less
than the solid–air tensor,

γ

sa

. Harkins and Livingston introduced a term,

π

e

, to indicate the reduction thus:

γ

sv

=

γ

sa

−



π

e

(5.2)

Carl A. Dahlquist

3M Company

DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
angle of contact (Figure 5.1). The magnitude of the contact angle depends on the force of attraction

5

-4

Coatings Technology Handbook, Third Edition

where

r

is the center-to-center distance between the dipoles.

If the rotational energy is less than the thermal energy of the system, then
where

k

is Boltzmann’s constant (0.0821 1·atm/mol deg), and

T

is absolute temperature (K).
There may be dipole-induced dipoles, where the potential energy of interaction is given by
where

α

2

and

α

1

are the molecular polarizabilities.
There may be acid–base interactions

7,8

across the interface that can lead to strong bonding. Examples
are hydrogen bonding, Lewis acid–base interactions, and Brønsted-type acid–base interactions.

Covalent bonding between adhesive and adherend, if achievable either by chemical reactions or by
high energy radiation, can lead to very strong bonds.
Interdiffusion, usually not achievable except between selected polymers, can also lead to high adhesion.
The force of attraction between planar surfaces has been derived from quantum mechanical consid-
erations by Casimir, Polder,

9

and Lifshitz.

10

Lifshitz calculated the attractive forces between nonmetallic solids at distances of separation sufficiently
large that the phase lag due to the finite velocity of electromagnetic waves becomes a factor. He obtained
the following relationship between the attractive force and the known physical constants:
where

F

is the attractive force per unit of area,

h

is Planck’s constant,

C

is the velocity of light,

d

is the
distance of separation,

e

o

is the dielectric constant, and

φ

(

e

o

) is a multiplying factor that depends on the
dielectric constant as follows:
Strictly speaking, the dielectric constant in this expression should be measured at electron orbital
frequency, about 10

15

Hz. However, if we assume handbook values of the dielectric constant at 10

6

Hz,

which for nylon, polyethylene, and polytetrafluoroethylene, are 3.5, 2.3, and 2.0, respectively, the corre-
sponding

φ

(

e

o

) values are 0.37, 0.36, and 0.35. The force values then stand in the ratios 0.11 to 0.056 to
0.039. When normalized to

F

(nylon)

=

1.0, they fall to the following ratios:

F

(nylon), = 1.00;

F

(PE), 0.51;

F

(PTFE), 0.35
When the

γ

c

values (dynes/cm) of these three materials are similarly normalized to the

γ

c

values for
nylon, the values fall in remarkedly similar ratios.
1/

e

o

:00.025 0.10 0.25 0.50 1

φ

(

e

o

): 1 0.53 0.41 0.37 0.35 0.35
Nylon PE PTFE

γ

c

γ

c

(norm)
56
1.00
31
0.55
18.5
0.33
U
r
nt
P
=
−2
12
3
µµ

U
kTr
K
==
−
Keesom potential
2
3
1
2
1
2
6
µµ
U
r
1
1
2
22
2
1
6
=
−+µα µα
F
hc e e
de
oo
o

=
−
+
πφ
2
4
1
240 1
()[()]
()

DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC

The Theory of Adhesion

5

-5

In the Lifshitz equation, the force of attraction is shown to decrease as the inverse fourth power of the
distance of separation. However, when the separation becomes so small that the phase lag in the inter-
action no longer is significant (it is of the order of 6

°

at a separation of 50 Å), the attractive force varies
as the inverse third power of the distance of separation. This has been verified experimentally,

11

although
the direct measurement is extremely difficult (Figure 5.4). The forces existing at separations greater than
50 Å contribute very little to adhesion.
Some 30 years ago Good and Girifalco reexamined the interfacial tensions between dissimilar liquids
and developed a theory of adhesion.

12

They found that the work of adhesion, given by
could be approximated quite well by the geometric mean of the works of cohesion of the two liquids
when the only attractive forces of cohesion are dispersion forces:
However, in some liquid pairs (e.g., water and hydrocarbons), this did not hold, and they coined an
“interaction parameter,”

Φ

, given by
Thus,

FIGURE 5.4

Attraction between ideally planar solids.
Separation in Angstrom Units
250
200
100
50
20
110

100
1000
Force Constant
D
4.07
1
F∝
D
2.94
1
F∝
W
aLL LL
=+−γγγ
1212
W
aLL
= 2
12
12
()
/
γγ
Φ=
+−γγγ
γγ
LL LL
LL
1212
12

2
12
()
/
W
aLL
= 2
12
12
Φ()
/
γγ

DK4036_book.fm Page 5 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC

5

-6

Coatings Technology Handbook, Third Edition

For water on a paraffinic hydrocarbon, where the contact angle is 108

°

,

Φ

would have a value of about
0.55. For hexadecane on polyethylene,

Φ

is very near unity. Good and his associates

11,12

have provided
directions for calculating

Φ

, and they give experimental and calculated values for several combinations
of water and organic liquids.
Fowkes

13

approached the problem from a different point of view. He reasoned that the only forces
operable at the interface between water and an aliphatic hydrocarbon molecule contain no hydrogen
bonding groups and no fixed dipoles.
Fowkes also assumed that the work of adhesion would be given by twice the geometric mean of the
surface energies of the two liquids on either side of the interface but now taking into consideration only
the dispersion force components of the surface energies. For the work of adhesion between water (L
1
)
and n-octane (L
2

), we have
where the superscript D stands for the dispersion energy component of the total surface energy. Accepted
values for the surface energies and interfacial energies are as follows:
If these values are substituted into the equation above to solve for we get 22.0 ergs/cm
2
. Fowkes
evaluated several water-aliphatic hydrocarbon systems and found that they all yielded essentially the same
value for the dispersion energy component of the surface energy of water, 21.8 ± 0.7 ergs/cm
2
.
Tur ning now to the work of adhesion and the interfacial energy between mercury and aliphatic
hydrocarbon, Fowkes calculated the dispersion energy component of the surface energy of mercury. Using
n-octane as the hydrocarbon liquid having a surface energy of 21.8 ergs/cm
2
(all of it attributed to
dispersion forces), the surface energy of mercury, 484 ergs/cm
2
, and the interfacial energy, 375 ergs/cm
2
,
we have
The average for a series of mercury–aliphatic hydrocarbon systems yielded 200 ± 7 ergs/cm
2
for
the dispersion energy component of the surface energy of mercury.
Since the remaining forces that contribute to the surface energy of mercury are metallic forces, the
only interacting forces at the water–mercury interface are the dispersion forces, and the work of adhesion
is given by
from which
This compares very favorably with the measured value of 426 ergs/cm

2
.
W
aL
D
L
D
LLL
==−2
12 1 12
12
()
/
γγ γ γ
γγγγ
LLL
D
L
122
72 8 21 8
2
===.; .;ergs/cm ergs/cm
2
112
50 8
L
= .ergs/cm
2
γ
HO

2
D
,
W
a
D
n
D
Hg n Hg n
==+−
−−−
2
12
()
/
(,
γγ γ γ γ
Hg oct oct oct)
WW
a
D
D
=× =+−
=
2218484 21 8 375
196 2
12
(.) .
.
/

γ
γ
Hg
Hg
γ
Hg
D
W
aHHO
g
=× =+−2 200 21 8 484 72 8
12
2
(.) .
/
(, )
γ
γ
(, )
.
HHO
g 2
424 7= ergs/cm
2
DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
The Theory of Adhesion 5-7
The work of adhesion due to dispersion forces is numerically small in work or energy units. For
example, the work of adhesion of methylene iodide on polyethylene is 82 ergs/cm
2

(θ = 52°). This
small value is not, however, indicative of a small force of attraction across the interface. Keep in mind
that the work is the product of force and displacement, and that the attractive force, at separation
distances less than 50 Å (5 × 10
−7
cm) increases as the inverse of displacement raised to the third
The molecules at the interface are at an equilibrium distance of separation where attractive forces and
repulsive forces balance. The variation in the repulsive forces with distance of separation has a dependence
several orders of magnitude higher than the attractive forces (of the order of 10
12
for atom pairs and 10
8
for repulsion forces across a hypothetical plane). We can calculate the maximum force of attraction by
equating the work of adhesion to the work of separation.
Let F
a
indicate the attractive force, F
r
the repulsive force, x the distance separation, and d the equilibrium
distance. We cannot measure d directly, but we can estimate it from calculations of the distance between
molecular centers in a liquid of known specific gravity and molecular weight. In the case of methylene
iodide (sp g 3.325, mol 267.9), we calculate the separation to be about 5 × 10
−8
cm between the centers
of adjacent molecules.
If we take 5 × 10
−8
cm as a reasonable distance of separation across the interface between methylene
iodide and polyethylene, and we accept the force versus distance relationships for attraction (a) and
repulsion (r), we can write:

where the subscript e stands for “equilibrium.” At equilibrium we have the condition that (F
a
)
e
= (F
r
)
e
.
We can then express the work of adhesion as
The solution is
For methylene iodide on polyethylene, W
a
is 82 ergs/cm
2
. Taking d as 5 × 10
−8
cm, F
e
= F = F
r
= 4.92
× 10
9
dynes/cm
2
.
The maximum attractive force is encountered where the difference between the attractive forces and
the repulsive forces maximizes as separation proceeds. This occurs where (d/x)
3

− (d/x)
8
maximizes, at
about x = 1.22d.
At this displacement, F = 0.347F
e
, or, in the case of methylene iodide and polyethylene, at 1.71 × 10
9
dynes/cm
2
(about 25,000 psi). This would be the maximum attractive force experienced when separation
of the materials is attempted; it far exceeds the average stresses that are typically observed when adhesive
bonds are broken.
Others have calculated theoretical forces of adhesion by other approaches. All yield results that predict
breaking strength far exceeding the measured breaking strengths.
FF
d
x
FF
d
x
aae
rre
=







=






()
()
3
8
WF
d
x
dx F
d
x
dx
ae e
dd
=






−







∞∞
∫∫
() ()
38
WF
dd
ae
=−






27
DK4036_book.fm Page 7 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
power (Figure 5.4).

6

-1

6

Adhesion Testing

6.1 Fundamentals of Adhesion

6-

1

6.2 Standardization of Adhesion Tests

6-

3

6.3 Delamination Procedures

6-

4

6.4 Local Debonding Systems

6-

7

6.5 Flaw Detection Methods

6-

10

6.6 Outlook

6-

12
References

6-

13

6.1 Fundamentals of Adhesion

Without sufficient adhesion, a coating of otherwise excellent properties in terms of resistance to weather,
chemicals, scratches, or impact would be rather worthless. It is therefore necessary to provide for good
adhesion features when paint materials are formulated. There must also be adequate means for controlling
the level of adhesion strength after the coating has been spread and cured on the substrate. Moreover,
methods should be available that allow for the detection of any failure in the case of the dissolution of
the bond between coating and substrate, under any circumstances whatsoever.

6.1.1 Components at the Interface

In chemical terms, there is a considerable similarity between paints on one side and adhesives or glues
in this chapter to concentrate on the behavior of paint materials. Adhesion is the property requested in
either case, though perhaps with different emphasis on its intensity, according to the intended use.
Such a coating is, in essence, a polymer consisting of more or less cross-linked macromolecules and
a certain amount of pigments and fillers. Metals, woods, plastics, paper, leather, concrete, or masonry,
to name only the most important materials, can form the substrate for the coating.
It is important, however, to keep in mind that these substrate materials may inhibit a rigidity higher

than that of the coating. Under such conditions, fracture will occur within the coating, if the system
experiences external force of sufficient intensity. Cohesive failure will be the consequence, however, if the
adhesion at the interface surpasses the cohesion of the paint layer. Otherwise, adhesive failure is obtained,
indicating a definite separation between coating and substrate.

Ulrich Zorll

Forschungsinstitut für Pigmente and
Lacke

DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
Components at the Interface • Causes of Failure • Measures of
Cross-Cut Test • Tensile Methods
Adhesion
Scratch Technique • Indentation Debonding • Impact Tests
Ultrasonic Pulse-Echo System • Acoustic Emission Analysis •
Knife-Cutting Method • Peel Test • Blister Method
Thermographic Detection of Defects
on the other (Figure 6.1). Both materials appear in the form of organic coatings; thus, it is appropriate

7

-1

7

Coating Calculations

7.1 Introduction

7-

1
7.2 Resins

7-

1
7.3 Pigments

7-

2
7.4 Solvents

7-

2
7.5 Additives

7-

2
7.6

7.7 Calculations

7-

2

7.8 Converting to a 100 Gallon Formulation

7-

4
7.9 Cost

7-

4
7.10 Coverage

7-

5
7.11 Computer Use

7-

5
Bibliography

7-

5

7.1 Introduction

Coatings are defined as mixtures of various materials. The questions arise as to how much of which
materials, and how do these things relate. The materials fall into four general categories, as follows:
•Resins
• Pigments
•Solvents
•Additives

7.2 Resins

These are the generally solid, sticky materials that hold the system together. They are also called binders,
and when in a solvent, they are the vehicles for the system. They may come as a “single-package” or “two-
package” system. Single package is just the liquid resin or the resin in solvent. Two package means that
an “A” part was blended with a “B” part to cause a chemical reaction. In both systems, we need to know
the amount of solid resin present. This dry material divided by the total of the dry plus the solvent is
frequently called a “resin solid.” With the two-package systems, we need to know not only the solids but
also the ratio of these solids to form the desired film. This ratio may be designated as a simple ratio of
1 to 1. Or it may be based on 1 or 100, as 0.3 to 1, or 30 parts per hundred, or a total of 100 as 43 to
57. These ratios determine the film properties. We will also need to know the density (weight per unit
volume, usually as pounds per gallon) of the resin or vehicle to help calculate volume.

Arthur A. Tracton

Consultant

DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
Formulation Weight • Formulation Volume • Formulation
Density • Formulation of “Nonvolatile by Weight” •
Ratio (Weight) • Pigment Volume Content (Volume)
Conventions

7-2
Formulation “Nonvolatile by Volume” • Pigment to Binder

Coating Calculations

7

-3

TA B LE 7.1

Paint Formulation Calculations

No.

Constants

Calculations
Material lb/gal gal/lb %NV Cost, $/lb Weight Volume Dry Weight Dry Volume #/100 gal gal/100 gal Cost/gal

1Titanium Dioxide 34.99 0.029 100 $1.15 100 2.86 100 2.86 196.00 5.6 2.25
2 Phthalocyanine Blue 12.99 0.077 100 $10.55
50 3.85 50 3.85 98.00 7.5 10.34
3Acrylic Resin Solution 9.05 0.11 50 $1.09 300 33.15 150 16.58 588.00 65.0 6.41
4Toluene 7.55 0.132 0 $0.28 20 2.65
0
0.0 39.20 5.2 0.11
5Butoxyethanol 7.51 0.133 0 $0.75 30 3.99
0 0
.0 58.80 7.8 0.44

6Methyl Ethyl Ketone 6.71 0.149 0 $0.55 30 4.47 0 0
.0 58.80 8.8 0.32
7
8
9
10
Total X X X X 530 50.97 300 23.29 1038.8 99.9 19.88
Factor = 1.96
On Total Formulation
a% Nonvolatile Weight 56.60
b% Nonvolatile Volume
45.69
c Pigment/Binder Ratio
2 to 3
d Pigment Volume Content
28.81
eDensity, lb/gal
10.4
fsquare feet/gal @ 1 mil dry
733

DK4036_book.fm Page 3 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC

7

-6

Coatings Technology Handbook, Third Edition

TA B LE 7.2

Paint Formulation

Constants

Calculations
No.Material lb/gal gal/lb %NV
%
Solvent
%
Water
Cost,
$/lb Weight Gallons Dry Wt Dry Vol #/100 gal gal/100#
Cost/
100 gal Water Solvent

1 Gloss Varnish 8.43 0.118623962 1 0 0 $0.00 75 8.896797153 75.00 8.896797153 347.76 41.25 $0.00 0 0
2Resin @ 40% in BCarbAc 8.71 0.114810563 0.4 0.6 0 $0.00 25 2.870264064 10.00 1.148105626
115.92 13.31 $0.00 0 69.55284525
3Titanium Dioxide 10.5 0.095238095 1 0 0 $0.00 95 9.047619048 95.00 9.047619048
440.50 41.95 $0.00 0 0
4Antiskin Agent 13 0.076923077 1 0 0 $0.00 0.1 0.007692308
0.10 0.007692308 0.46 0.04 $0.00 0 0
5Butyl Carbitol Acetate 10.8 0.092592593 0 1 0 $0.00 7.4 0.685185185 0.00 0 34.31 3.18 $0.00 0 34.31273699
6Cobalt Drier, 6% 17.83 0.05608525 0.5 0.5 0 $0.00 0.253 0.014189568 0.13 0.007094784
1.17 0.07 $0.00 0 0.586562328
7Lead Drier, 12% 8.5 0.117647059 0.5 0.5 0 $0.00 0.379 0.044588235
0.19 0.022294118 1.76 0.21 $0.00 0 0.878684278
8

0.00 0 0.00 $0.00 0 0
9
0.00 0 0.00 $0.00 0 0
10
0.00 0 0.00 $0.00 0 0
Total X X X X X 203.132 21.56633556 180.42 19.12960304 941.89 100.00 $0.00 0 105.3308289
Total Formulation
factor = 4.63685635 cost/gal
lb/gal 9.42
$0.00
% Nonvolatile weight
88.817
% Nonvolatile volume
88.701 for loss $@95$
Pigment/Binder Ratio 0.51
$0.00
wt pigment 95
wt binder 90
Pigment Volume Content 0.22
vol pigment 2.87
vol binder 10.05
vol pigment + binder
% Water 0.00 VOC = 1.05 lbs/gal
% Solvent 11.18

DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC

8

-1

8

Infrared Spectroscopy

of Coatings

8.1 Introduction

8-

1
8.2 Principles

8-

1
8.3

8.4 Data Collection

8-

3

8.5 Data Interpretation

8-

5
8.6 Applications

8-

6
References

8-

7

8.1 Introduction

Infrared (IR) spectroscopy is a most useful technique for characterizing coatings, a very cost-effective
and efficient means of gathering information. If not the final answer, IR studies can point the way to
other information or techniques needed to solve a problem. Ease of sample preparation is one advantage
of IR. There are numerous ways of presenting the coating sample to the infrared spectrometer. The wide
variety of sampling accessories or attachments, which can easily be swapped in and out of most spec-
trometers, enables the study of liquids and solids under a wide range of conditions. There is large body
of literature on infrared methodology,

1,2,3

and there are extensive collections of reference spectra available.
Almost all components of coatings can be identified by IR; it is especially useful for polymers. IR
spectroscopy can monitor changes, such as drying, curing, and degradation, which occur to coatings.
Quality control of raw materials and process monitoring during coating synthesis and formulation can
be done by IR spectroscopy.
Most important to the identification of coatings and the study of their properties is the skill of the

analytical scientist. This factor is often overlooked because the trend in analytical instrumentation in recent
years has been increasing computer control and automation. Even when these systems are at hand, they
have little value without a well-trained and experienced analytical scientist behind them. The individual
with a coatings problem or application is well advised to seek the services of an experienced spectroscopist.

8.2 Principles

The atoms of any molecule are continuously vibrating and rotating. The frequencies of these molecular
motions are of the same order of magnitude (10

13

to 10

14

cycles per second) as those of IR radiation.
When the frequency of molecular motion is the same as that of the IR radiation impinging on that

Douglas S. Kendall

National Enforcement
Investigations Center, U.S.
Environmental Protection Agency

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© 2006 by Taylor & Francis Group, LLC
Infrared Microscopy • Imaging
Separation • Transmission Spectra • Attenuated Total
Depth Profiling • Other Sampling Methods

Instrumentation
8-2
Reflectance (ATR) • Infrared Photoacoustic Spectroscopy and
8-8 Coatings Technology Handbook, Third Edition
38. D. Lin-Vien, N. B. Colthup, W. G. Fateley, and J. G. Grasselli, The Handbook of Infrared and Raman
Characteristic Frequencies of Organic Molecules. New York: Academic Press, 1991.
39. B. J. Kip, T. Berghmans, P. Palmen, A. van der Pol, M. Huys, H. Hartwig, M. Scheepers, and D.
Wienke, Vib. Spectrosc., 24, 75 (2000).
40. J. R. Ferraro and K. Krishnan, Eds., Practical Fourier Transform Infrared Spectroscopy: Industrial
and Laboratory Chemical Analysis. New York: Academic Press, 1989.
41. B. Schrader and D. Bougeard, Eds., Infrared and Raman Spectroscopy: Methods and Applications.
Weinheim, Germany: VCH Publishers, 1995.
42. W. Sueteka and J. T. Yates, Surface Infrared and Raman Spectroscopy: Methods and Applications.
New York: Plenum Press, 1995.
43. A. M. Millon and J. M. Julian, in ASTM Spec. Tech. Publ., Anal. Paints Relat. Mater., STP 1119, 173
(1992).
44. J. K. Haken and P. I. Iddamalgoda, Prog. Org. Coat., 19, 193 (1991).
45. S. V. Compton, J. R. Powell, and D. A. C. Compton, Prog. Org. Coat., 21, 297 (1993).
46. R. L. De Rosa and R. A. Condrate, Glass Researcher, 9, 8 (1999).
47. A. R. Cassista and P. M. L. Sandercock, J. Can. Soc. Forensic Sci., 27, 209 (1994).
48. J. A. Payne, L. F. Francis, and A. V. McCormick, J. Appl. Polym. Sci., 66, 1267 (1997).
49. G. A. George, G. A. Cash, and L. Rintoul, Polym. Int., 41, 162 (1996).
50. J. L. Gerlock, C. A. Smith, E. M. Nunez, V. A. Cooper, P. Liscombe, D. R. Cummings, and T. G.
Dusibiber, Adv. Chem. Ser., 249, 335 (1996).
51. A. A. Dias, H. Hartwig, and J. F. G. A. Jansen, Surf. Coat. Int., 83, 382 (2000).
52. R. J. Dick, K. J. Heater, V. D. McGinniss, W. F. McDonald, and R. E. Russell, J. Coat. Technol., 66,
23 (1994).
53. M. W. Urban, C. L. Allison, G. L. Johnson, and F. Di Stefano, Appl. Spectrosc., 53, 1520 (1999).
54. D. J. Skrovanek, J. Coat. Technol., 61, 31 (1989).
55. M. L. Mittleman, D. Johnson, and C. A. Wilke, Trends Polym. Sci., 2, 391 (1994).

56. M. Irigoyen, P. Bartolomeo, F. X. Perrin, E. Aragon, and J. L. Vernet, Polym. Degradation and
Stability, 74, 59 (2001).
57. H. Kim and M. W. Urban, Polymeric Mater. Sci. and Eng., 82, 404 (2000).
58. B. W. Johnson and R. McIntyre, Prog. Org. Coat., 27, 95 (1996).
59. M. R. Adams, K. Ha, J. Marchesi, J. Yang, and A. Garton, Adv. Chem. Ser., 236, 33 (1993).
60. L. J. Fina, Appl. Spectrosc. Rev, 29, 309 (1994).
61. T. Buffeteau, B. Besbat, and D. Eyquem, Vib. Spectrosc., 11, 29 (1996).
62. N. Dupuy, L. Duponchel, B. Amram, J. P. Huvenne, and P. Legrand, J. Chemom, 8, 333 (1994).
63. M. W. C. Wahls, E. Kentta, and J. C. Leyte, Appl. Spectrosc., 43, 214 (2000).
64. J. E. Dietz, B. J. Elliott, and N. A. Peppas, Macromolecules, 28, 5163 (1995).
65. T. A. Thorstenson, J. B. Huang, M. W. Urban, and K. Haubennestal, Prog. Org. Coat., 24, 341 (1994).
66. B. W. Ludwig and M. W. Urban, J. Coat. Technol., 68, 93 (1996).
67. E. Kientz and Y. Holl, Polym. Mater. Sci. Eng., 71, 152 (1994).
68. G. C. Pandey and A. Kumar, Polym. Test., 14, 309 (1995).
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9

-1

9

Thermal Analysis
for Coatings

Characterizations

9.1 Introduction

9-

1
9.2 Characteristics

9-

1
9.3 Techniques

9-

1
9.4 Applications

9-

2
Bibliography

9-

3

9.1 Introduction

The evaluation of substances and finished materials by thermal analysis will be discussed as a tool that
the paint chemist can use to help evaluate coating properties. These properties are those that change as
a function of temperature.

9.2 Characteristics

Substances change in a characteristic manner as they are heated. Thermal analysis (TA) monitors these
changes. TA procedures are generally used to characterize various substances and materials that change
chemically or physically as they are heated. These changes in properties as a function of temperature
have been used to help characterize the interrelationship of a coating’s composition and performance.
TA methods or techniques measure changes in properties of materials as they are heated or at times cooled.
A TA evaluation entails subjecting a small sample of from a few milligrams to 100 mg to a programmed
change in temperature. The resulting change in property is detected, attenuated, plotted, and measured
by a recording device.
The instrumentation consists of an analysis module, a heating or cooling source, a measuring device,
and a system for reporting the results, usually as an

X

–

Y

plot. A computer is used to program and control
the procedure and analyze and store the results.

9.3 Techniques

The techniques of prime importance in coatings’ characterization and analysis include differential scan-
ning calorimetry (DSC), differential thermal analysis (DTA), thermogravimetric analysis (TGA), ther-
momechanical analysis (TMA), and dynamic mechanical analysis (DMA). Each of these will be discussed,
with examples of the information derivable from each procedure.

William S. Gilman

Gilman & Associates

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-4

Coatings Technology Handbook, Third Edition

Colborn, Robert,

Modern Science and Technology

. Princeton, NJ: Van Nostrand, 1965.
Foreman, Jon, “Dynamic mechanical analysis of polymers,”

American Laboratory,

January 1997, p. 21.
Hassel, Robert L., “Evaluation of polymer flammability by thermal analysis,”

American Laboratory,

January
1997

.

Hassel, Robert L.,

Using Temperature to Control Quality,

Second Quarter 1991 P1 Quality. Hitchcock,
1991

.

Hassel, Robert L., “Thermomechanical analysis instrumentation for characterization of materials,”

Amer-
ican Laboratory,

January 1991.
Kelsey, Mark, et al., “Complete thermogravimetric analysis,”

American Laboratory,

January 1997, p. 17.
Neag, C. Michael,

Coatings Characterizations by Thermal Analyses

. ASTM Manual 17. West Consho-
hocken, PA: American Society for Testing and Materials, 1995.
Park, Chang-Hwan, et al., “Syntheses and characterizations of two component polyurethane flame retar-
dant coatings using 2,4dichlor modified polyester,”

J. Coat. Technol.,

December 1997, p. 21.
Reading, Micheal, et al., “Thermal analysis for the 21

st

century,”

American Laboratory,

January 1998, p. 13.
Riesen, Rudolf, “Maximum resolution in TGA by rate adjustment,”

American Laboratory,

January 1998,
p. 18.
TA Instruments Company, Thermal Analysis Application briefs available from TA Instruments Company,
New Castle, Delaware: TA-8A, Thermal Solutions — Long Term Stability Testing of Printing Inks
by DSC; TA-73, A Review of DSC Kinetics Methods; TA-75, Decomposition Kinetics Using TGA;
TA-121, Oxidation Stability of Polyethylene Terephthalate; TA-123, Determination of Polymer
Crystallinity by DSC; TA-125, Estimation of Polymer Lifetime by TGA Decomposition Kinetics;
TA-134, Kinetics of Drying by TGA; and TA-135, Use of TGA to Distinguish Flame-Retardant
Polymers from Standard Polymers.

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10

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10

Color Measurement for

the Coatings Industry

Color is the most important appearance of coatings for their formulation, application, or inspection.
Color is also the most subjective parameter to characterize visually, and characterization is often
attempted under uncontrolled conditions that result in poor color judgement. Proper viewing conditions
require controlled lighting in a viewing booth where the different types of light, such as simulated daylight,
tungsten, and fluorescent light sources, can be used for evaluation. Visual evaluation always requires a
physical standard for comparison because the “color memory” of the brain is quite poor without one,
but very good when two samples are compared beside each other. Even when proper viewing conditions
are used, it is often difficult to determine the direction and intensity of color difference between two
samples. This process requires a trained colorist to make the evaluation.
A more accurate and consistent approach to evaluate color difference is the use of a color measurement
instrument. The two types of instruments that can be used for this purpose are colorimeters and
spectrophotometers. A colorimeter uses optical filters to simulate the color response of the eye, and a
spectrophotometer breaks the visible spectrum into intervals that mathematically simulate the color
response of the eye. The advantage of using spectrophotometers to determine color difference is in their
accuracy, stability, and ability to simulate various light sources. Spectrophotometer cost and complexity
of operation are greatly reduced on new versions of the instruments.
There are three different technologies that are used in modern industrial spectrophotometers: inter-
ference filters, gratings, and light-emitting diodes (LEDs). Interference filters require a filter for each
wavelength measured and usually have 16 or 31 filters depending on the resolution required. Grating-
based instruments have diode arrays of 20 to 256 elements to provide higher resolution for applications
that require it. The advantage of interference filters is in their simplicity of operation and mechanical

ruggedness. However, they are difficult to make consistent and deteriorate over time. High-performance
instruments usually have gratings that give more resolution and better consistency, but they are usually
more expensive and complex to build and calibrate. A new market entrant for spectrophotometers is
based on LEDs of different illumination colors. Up to nine separate color LEDs are now available to cover
most of the visible spectrum. The instruments operate by illuminating one LED at a time while measuring
the reflected light. The advantage is that they can be made very small and cost less to manufacture. The
disadvantages are reduced accuracy and stability, but the technology is improving with the advent of
newer LEDs with better methods for compensation.
There are several different measurement geometries: sphere, 45/0, and multiangle. A sphere instrument
illuminates a sample from all directions and views the sample at near normal or perpendicular. The 45/
0 illuminates the sample at 45 degrees from all directions and views the sample normal. It is also possible
to illuminate at 0 and view at 45. The multiangle approach illuminates at multiple angles and views at
a fixed angle. It is also possible to illuminate at a fixed angle and view at multiple angles.

Harold Van Aken

GretagMacbeth

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Bibliography 10-2

11

-1

11

The Use of X-ray
Fluorescence for Coat

Weight Determinations

11.1 Introduction

11-

1
11.2 Technique

11-

1
11.3 Method

11-

2
11.4 Accuracy

11-

3
11.5 Repeatability and Reproducibility

11-

3
11.6 Conclusion

11-

5

11.1 Introduction

The technique of elemental analysis by x-ray fluorescence (XRF) has been applied to the quality control
of coating weights at the plant level. Measurements by nonlaboratory personnel provide precise and rapid
analytical data on the amount and uniformity of the applied coating. XRF has proved to be an effective
means of determining silicone coating weights on paper and film, titanium dioxide loading in paper, and
silver on film.

11.2 Technique

XRF is a rapid, nondestructive, and comparative technique for the quantitative determination of elements
in a variety of matrices. XRF units come in a variety of packages; however, the type of unit most prevalent
in the coating industry is described in this chapter.
The XRF benchtop analyzer makes use of a low level radioisotope placed in close proximity to the
sample. The primary x-rays emitted from the excitation source strike the sample, and fluorescence of
secondary x-rays occurs. These secondary x-rays have specific energies that are characteristic of the
elements in the sample and are independent of chemical or physical state. These x-rays are detected in
a gas-filled counter that outputs a series of pulses, the amplitudes of which are proportional to the energy
of the incident radiation. The number of pulses from silicon x-rays, for example is proportional to the
silicone coat weight of the sample. Because the technique is nondestructive, the sample is reusable for
further analysis at any time.
To ensure optimum excitation, alternate radioisotopes may be necessary for different applications. For
silicone coatings and titanium dioxide in paper, an iron-55 (Fe-55) source is used. Fe-55 x-rays are soft
(low energy) and do not penetrate far into a sample. For silver on film, a more energetic americanum-
241 source has been used.

Wayne E. Mozer

Oxford Analytical, Inc.

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11

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Coatings Technology Handbook, Third Edition

FIGURE 11.2

Differences in sensitivities in products from different suppliers of silicone.

FIGURE 11.3

Differences in paper backings.
X-Ray CPS
200
150
100
50
.25 .50 .75 1.00
Concentration g/m
2
Vendor A
Vendor B

Vendor C
X-Ray CPS
200
150
100
50
.25 .50 .75 1.00
Concentration g/m
2

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12

-1

12

Sunlight, Ultraviolet,
and Accelerated

Weathering

12.1 Introduction

12-

1
12.2 Sunlight

12-

1

Va riability of Sunlight

12.3 Accelerated Light Sources Compared to Sunlight

12-

2

The Importance of Short-Wavelength Cutoff

12.4 Arc-Type Light Sources

12-

4

12.5 Fluorescent UV Lamps

12-

7

12.6 Conclusions

12-

9
Acknowledgments

12-

9
References

12-

10

12.1 Introduction

Sunlight is an important cause of damage to coatings. Short-wavelength ultraviolet (UV) light has long
been recognized as being responsible for most of this damage.

1

Accelerated weathering testers use a wide variety of light sources to simulate sunlight and the damage
that it causes. Comparative spectroradiometric measurements of sunlight and laboratory testers of various
types show a wide variety of UV spectra. These measurements highlight the advantages and disadvantages
of the commonly used accelerated light sources: enclosed carbon arc, sunshine carbon arc, xenon arc,
and fluorescent UV. The measurements suggest recommendations for the use of different light sources
for different applications.

12.2 Sunlight

The electromagnetic energy from sunlight is normally divided into ultraviolet light, visible light, and

Infrared energy (not shown) consists of wavelengths longer than the visible red wavelengths and starts
above 760 nanometers (nm). Visible light is defined as radiation between 400 and 760 nm. Ultraviolet
light consists of radiation below 400 nm. The International Commission of illumination (CIE) further

Patrick Brennan

Q-Panel Lab Products

Carol Fedor

Q-Panel Lab Products

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Enclosed Carbon Arc (ASTM G 153) • Sunshine Carbon Arc
(Open Flame Carbon Arc: ASTM G 152) • Xenon Arc (ASTM
FS-40 Lamps (F40-UVB) (ASTM G 154) • UVB-313 Lamp
G 155)
(ASTM G 154) • UVA-340 Lamp (ASTM G 154)
infrared energy. Figure 12.1 shows the spectral energy distribution (SED) of noon midsummer sunlight.