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MNL17-EB/Jun
...
K o l e s k e I
MIXING A PIGMENT WITH LINSEED OIL and m a k i n g a paste is a
p r e l i m i n a r y test a p p l i e d to p i g m e n t s that has been in use in a
systematic m a n n e r for a l m o s t a century a n d p e r h a p s even
longer in a less defined m a n n e r
...
If the test is c o n d u c t e d in a quantitative
m a n n e r , the a m o u n t of oil n e e d e d to m a k e a stiff paste is
obtained
...
F o r example, Mills [2] i n d i c a t e d that if equal volumes
of "oil a b s o r p t i o n paste" are m i x e d o r t h i n n e d with equal
volumes of thinners, the paints p r e p a r e d have equal resistance to flow, viscosity, or consistency
...
This test is also related to the p i g m e n t packing
factor (PPF) a n d critical p i g m e n t volume c o n c e n t r a t i o n
(CPVC)
...
More extended
discussions of oil a b s o r p t i o n t h e o r y a n d practice can be
f o u n d in the literature [6-10]
...


Gardner-Coleman M e t h o d
This classical m e t h o d or some variation of it [11] has been
in use for a b o u t three quarters of a century
...
In this test, a soft paste is f o r m e d from the
p i g m e n t by drop-wise a d d i t i o n of r a w linseed oil with an acid
n u m b e r of 3 _+ 1 from a b u r e t t e to the gently stirred pigment
...
The mixture is not vigorously r u b b e d as in the rubout method
...
The rate of oil a d d i t i o n is r e d u c e d as
the end p o i n t is reached
...
The end
p o i n t for paste f o r m a t i o n is t a k e n to be the p o i n t w h e n the
l u m p s of wet p i g m e n t form a single ball or w h e n an excess of
oil s m e a r s the wall of a c o n t a i n e r (Fig
...
This will take place
within one or two d r o p s of oil
...
'Mthough
the c u r r e n t test calls for use of a steel spatula with p a r t i c u l a r
d i m e n s i o n s a n d a glass flask for the test, variations of these
tools have been used [13,14]
...
The a m o u n t
of oil n e e d e d d e p e n d s on the specific p i g m e n t area, w h i c h is a
function of particle size, roughness, and porosity
...
As oil is a d d e d
b e y o n d the particle e n c a s e m e n t stage, the interstices b e t w e e n
the oil-encased particles b e c o m e filled with oil
...
Packing can range f r o m
r h o m b e h e d r a l to cubic
...
A g g l o m e r a t i o n is affected by the
n a t u r e of the oil, a n d linseed oil that meets ASTM D 234:
Specification for R a w Linseed Oil [5], except that it should

where M is the m L of oil used, P is the a m o u n t of p i g m e n t
used in grams, a n d 0
...
Test results by a single o p e r a t o r a n d
b e t w e e n o p e r a t o r s in different laboratories t h a t differ by
m o r e t h a n 9
...
3%, respectively, are suspect
...

1Senior consultant, Consolidated Research, Inc
...

252
Copyright9 1995 by ASTM International

www
...
org

CHAPTER 2 8 - - 0 I L ABSORPTION OF PIGMENTS
TABLE 1--Various non-ASTM methods for determination of oil
absorption values
...
See
text
...
Pore volume
of a compressed pigment wafer
is determined
...


8

British Standards
Institution

Method is similar to ASTM
D 281, but differs mainly in
acid value of oil, 7
...
5;
rubbing is done for 20-25 min
...
Can have void
volume errors associated with
it
...


18

Smith-Stead

Pigment is added to oil in this
method, and a mechanical
muller is used to better define
the rubbing effort
...


Azam M e t h o d
The Azam Method [15] is essentially the same test as ASTM
D 281 with the main difference being a more rigorously defined end point
...
Azam found that a complete paste absorbed no more oil when immerse in oil, but an "incomplete"
paste would absorb oil in an amount sufficient to make it a
"complete" paste
...


PLASTICIZER ABSORPTION BY PIGMENTS
Although linseed oil is used to obtain the oil absorption
values, it is obvious that a variety of liquids can be absorbed
by pigments
...


CRITICAL PIGMENT VOLUME

sorption values obtained by this method and the following
rub-out method are given in Table 2
...
It is approved for use by
agencies of the U
...
Department of Defense
...
It differs from the prior method in that
ASTM D 1483 requires only gentle folding and stirring,
whereas the rub-out test requires a thorough rubbing action
of the pigment and oil with a steel spatula
...
After the addition of each drop of
oil, the oil is incorporated into the pigment by working or
rubbing the two together with the spatula
...
Various stages in the spatula rub-out
test are described in Fig
...
The weight of oil is determined,
and the oil adsorption value is calculated as the grams of oil
used per 100 g of pigment
...
3 and 38
...
Oil ab-

For a long time, the paint industry formulated on a weight
basis
...
Not long after this,
Wolff [21,22] related optimum performance of exterior
paints to their critical oil contents, and simple graphical
methods for determining this parameter were devised [23]
...
Later Vannoy [25]
studied the matter and concluded that replacement of certain
pigments by others on a volume basis was the manner in
which formulating should be approached
...
It is a simple percentage calculated in
the following manner:
[
Pigment Volume
]
PVC = [Pigment Volu--m--ee~
Solids Volume_] [ 100%]
Studies such as these led to the critical pigment volume
concentration (CPVC) concept, and its importance to paint
formulation was established by Asbeck and Van Loo [26]
...
This is the point of commonality at which a
variety of properties show marked change
...

For example, it is readily understood that gloss decreases
as pigment volume increases, that permeability and rusting
are relatively constant until the pigment concentration
reaches relatively high values after which marked decreases

254

PAINT AND COATING TESTING MANUAL

FIG
...
Left photograph is the oil/
pigment mass just before the end point where the mass retains its rigidity
...


TABLE 2--Oil absorption values, grams of oil/100 g of pigment,
of some common pigments [1]
...
5
18
30
30
51
33
...

13
...
8
15
...
0

...
5

...
0

...
5
17
...
5

in performance takes place, and so on
...
When two vehicles--latex,
oil-base, etc
...
Predictably, the one with
a higher CPVC formulation should have better permeability
characteristics, such as stain and scrubbability, than the
other
...
The selection of which paint to modify by increasing
pigment or vehicle is made on the basis of additive economics
...
For
example, a ceiling paint does not need to have excellent
washability, and usually this paint type only requires low to
moderate gloss
...
In contrast, m a n y exterior paints that have a high gloss as well as glossy enamels are
formulated well below the CPVC, and it is PVC rather than
CPVC that has significance
...

The pigment volume is often expressed as bulk, which is
the volume occupied by a given weight of pigment
...
33 (1 kg/L)
...
0, its bulk can be calculated
as follows
[2
...
33 lb]BULK = L 1
...
661b 2
...
06 gal/lb (0
...
66 = 6
...
From this example, it is apparent that the higher the bulking value of a
pigment, the more advantageous it is from a cost standpoint
...


Asbeck-Van Loo M e t h o d o f D e t e r m i n i n g CPVC
The Asbeck-Van Loo [9,26] method of directly determining
the CPVC is based on the observation that the packing pattern
of a pigment in a paste persists when the dispersion is diluted
for sedimentation tests if nonpolar liquids are used for the
dilutions
...
Then, the cake
volume is subtracted from the actual volume of the pigment
calculated from density data
...


Pigment Packing Factor
Asbeck and coworkers [9] proposed the term "pigment
packing factor" (PPF) as a name for a pigment parameter that
replaces or supplements the oil absorption value
...
The investigators suggested a blend of 4 mL of
heat-bodied linseed oil and 50 mL of naphtha as the dispersing vehicle
...
To this, 6 mL of pigment (the weight in grams of pigment equal to the specific gravity times 6) are added
...


CHAPTER 2 8 - - 0 I L ABSORPTION OF PIGMENTS

255

FIG
...
Rub-Out A (top) is crumbly and
breaks up when an attempt is made to lift it with a spatula
...
Rub-Out C (lower
right) contains too much oil and does not roll
...
The bottom two photographs are additional examples of the mixture condition just before the end point is reached
...
If the PPF is to be compared with oil absorption
values, it must be converted to a weight basis, PPFweight, by
means of
F(100 - PPF)(specific gravity of oil)]
PPVweight = "[_( - - P P F - ) ( ~ y
~
_]" (100)

C o l e M e t h o d f o r CPVC
The CPVC depends on pigment particle packing or orientation [9,26], and Cole [27] noted that spherical particles may
pack similarly in both liquid and dry films
...
The method is based

on the fact that below the CPVC dry film volume, V, is a sum
of the pigment, Vv, and binder solids, Vb volumes

v=vp+vb
and that above the CPVC the volume of the voids must also be
considered with
V = PVp

where P is the relative pigment packing factor (the ratio of
bulk volume to true volume)
...

Pierce-Holsworth

M e t h o d f o r CPVC

This method [28] also used paint films, but it treated the
data in a different manner by introducing specific volume

256

PAINT AND COATING TESTING MANUAL

TABLE 3--Plasticizer absorption for some typical pigments [1]
...
6
179
...
2
26
...
4
145
...
5
19
...
0
80
...
0
65
...
4
106
...
3
31
...
0
28
...
2

24
...
0
39
...
2
50
...
5
24
...
0
72
...
6
126
...
5
32
...
0
47
...
0
55
...
2
34
...
0
106
...
0
14
...
2
41
...
0
7
...
9
53
...
0
50
...
0
51
...
5
35
...
6
14
...
7

line with the previously described straight line should occur
at a value of fv corresponding to the CPVC
...
The good agreement is apparent
...


CRITICAL PIGMENT VOLUME
CONCENTRATION AND OIL ABSORPTION
Oil absorption and CPVC are accepted to be interrelated

[29-31] a n d actually are two ways of stating the same concept: i
...
, CPVC is the c o n c e n t r a t i o n of p i g m e n t in a pigmentb i n d e r system that contains just sufficient b i n d e r (oil) to fill
the space between the p i g m e n t particles [1 ]
...
If OA is expressed as X v o l u m e s of oil
per Y volumes of pigment, then

concepts
...
Since
the s u m of fp a n d fb is unity, the expression can be arranged to

OA-

CPVC
1 - CPVC

and

1
I +OA

CPVC - - v = % , - v~)f,, + vb

I f v is plotted as a f u n c t i o n offp, a straight line of slope (vp Vb) a n d intercept of Vb should result
...
If both sides of this expression are
divided by W, the expression

V = Pvpfp
is obtained
...
The intersection of this

The PPF a n d OA values are compared in Table 5
...
Explanations
[1, 9] for the difference based o n conditions existing at the end
point are tabulated in Table 6
...
I n addition, the study indicated that r u b - o u t OA values are a good
indication of the CPVC
...


Paint System

Critical PigmentVolume Concentration
PierceTensile Elongation WaterVapor
Holsworth Strength
at Break
Permeability
Method
Method
Results
Results

Acrylic latex exterior House Paint A

47

47

42

46

Acrylic latex exterior House Paint B

41

42

4l

42

Poly(vinyl Acetate) latex masonry paint

44

44

44

45

Acrylic exterior masonry paint (from House
Paint A above)

48

47

44

48

CHAPTER 2 8 - - 0 I L ABSORPTION OF PIGMENTS
TABLE 5--Comparison of pigment packing factors, calculated

and experimentally determined oil absorption values [1]
...
It seems
that i n t e r p r e t a t i o n of the e n d p o i n t a n d not r e p r o d u c i b i l i t y is
the source of variation b e t w e e n o p e r a t o r s in these tests
...


CHARACTERIZATION OF D I S P E R S I O N S AT
T H E OIL A B S O R P T I O N P O I N T
E x a m i n a t i o n of the d i s p e r s i o n s (pastes) f o r m e d b e t w e e n
oil a n d p i g m e n t at the oil a b s o r p t i o n p o i n t is a source of
considerable information
...

Others are tough a n d short, others have a high gloss, others
have a dull a p p e a r a n c e , others are soft a n d easy to spread,
a n d still others are stiff a n d require a large p r e s s u r e s p r e a d or
flatten
...

Daniel a n d G o l d m a n [38] developed a s c h e m e for evaluating d i s p e r s i o n c h a r a c t e r b y using the p a s t e o b t a i n e d at the
end of the spatula r u b - o u t test
...
F r o m
this i n f o r m a t i o n a n d the types of flow exhibited by the pastes,
dispersions are classed as good, fair, or poor
...
The oil a b s o r p t i o n value is called the wet point
...

In well-dispersed systems, the flow p o i n t is the stage w h e r e a
substantial p o r t i o n of the paste flows from a vertically held
spatula w i t h o u t leaving jagged flow edges
...
Cases
i n t e r m e d i a t e to these two are difficult to define
...
If
a p a s t e does not flow after a d d i t i o n of 10 to 20% m o r e liquid
t h a n is r e q u i r e d for the wet point, a p o r t i o n of the diluted
paste is placed on the tip of a h o r i z o n t a l l y held spatula
...
The
t a p p i n g is gentle at first a n d t h e n m o r e vigorous
...


[1,9]
...


Electrokinetic equilibrium

Agglomeration is complete because
of high system fluidity,

Agglomeration is incomplete
Agglomeration is incomplete
because of low system fluidity
...


Pigment surface requirements

Satisfied

Not completely satisfied

Work of dispersion

Defined and very high (approaching Undefined but low
maximum)

Undefined but relatively high

Work of packing

Defined and very low (approaching
zero)

Undefined but relatively high

Undefined but low

Substantially satisfied

TABLE 7--Characteristics of pastes from oil absorption studies [1]
...


At flow point

Flows without tapping; offers
resistance to suddenly applied
pressure

Gap between wet and
flow points

Very small

Fair Dispersion

Poor Dispersion

Shines when sharply tapped

Remains dull even when sharply
tapped

Flows only on tapping;
occasionally has a resistance
to suddenly applied pressure

Rises on tapping; has no
resistance to suddenly applied
pressure; has a high yield value

Falls with elongation at
breaking line; no resistance
to suddenly applied pressure;
has visible thixotropy

Falls without elongation at
breaking line

-
...
Characteristics of pastes tested in
this m a n n e r are given in Table 7
...


REFERENCES
[1] "Oil Absorption of Pigments," Chapter 3
...
, G
...
Sward, Ed
...

[2] Mills, G
...
34, 1951, p
...

[3] Stieg, F
...
, Jr
...
38, 1956, p
...

[4] Long, J
...
, "Creative Imagination as it Applies to the Decorative
and Protective Industry," Official Digest, Federation of Paint and
Varnish Production Clubs, Vol
...
989
...
06
...

[6] Marsden, E
...
42, 1959, p
...

[7] Mill, C
...
and Bank, H
...
, "An Interpretation of the Oil Absorption of Pigments," Journal of the Oil and Colour Chemists'
Association, Vol
...
599,
[8] Bessey, G
...
and Lammiman, K
...
, "The Measurement and
Interpretation of Oil Absorption," Journal of the Oil and Colour
Chemists' Association, Vol
...
519
...
K
...
D
...
, "Oil Absorption and Critical Pigment Volume Concentration," Official Digest, Federation of Paint and Varnish Production Clubs, Vol
...
156
...
R
...
43, 1960, p
...

[ll] Gardner, H
...
and Coleman, R
...
, "Oil Absorption of Pigments," Scientific Section Circular, No
...

[12] Annual Book of ASTM Standards, Vol
...
02
...
A
...
D
...
29,
1923, p
...

[14] van Wullen-Scholton, W
...
344, 1929, p
...

[15] Azam, M
...
14, 1942, p
...

[16] British Standards Institution, Standard 3483, 1962, p
...

[17] Bessey, G
...
and Lammiman, K
...
, "Oil Absorption of Pigments and Extends," Journal of the Oil and Colour Chemists'
Association, Vol
...
411
...
TP-P-OA, National Lead Company, Titanium Division, New York, 10 April 1953
...
M
...
M
...
37, 1954, p
...


[20] Calbeck, J
...
, "Application of the Statistical Method in Testing
Paints for Durability," Industrial and Engineering Chemistry,
Vol
...
1220
...
, "Oil Absorption of Pigments," Farben Zeitung, Vol
...
2940
...
, "The Critical Oil Content of Paints," Farben Zeitung,
Vol
...
374
...
and Zeidler, G
...
12, No
...
7
...
C
...
26, 1934, p
...


[25] Vannoy, W
...
, "Extenders in Outside House Paints," Official
Digest, Federation of Paint and Varnish Production Clubs, Vol
...
1961, p
...


[26] Asbeck, W
...
and Van Loo, M
...
41, 1949,
p
...

[27] Cole, R
...
, "Determination of Critical Pigment Volume Concentration in Dry Surface Coating Films," Journal of the Oil and
Colour Chemists' Association, Vol
...
776
...
E
...
M
...
37, 1965, p
...

[29] Smith, A
...

[30] Philadelphia Paint and Varnish Production Club, "Determination of CPVC by Calculation," Official Digest, Federation of Paint
and Varnish Production Clubs, Vol
...
1437
...
31, 1959,
p
...

[32] Stieg, F
...
, Jr
...
45, No
...
41
...
B
...
, "A Complex Problem and a Simple Answer,"

Official Digest, Federation of Paint and Varnish Production Clubs,
Vol
...
695
...
B
...
, "Effects of Pigmentation on Modern Flat Wall
Paints," Official Digest, Federation of Paint and Varnish Production Clubs, Vol
...
81
...
, "Selective Polar Adsorption and Some Rheological Phenomena in Paint Systems," Journal of the Oil and
Colour Chemists' Association, Vol
...
25
...
B
...
, "Particle Size as a Formulating Parameter,"
Journal of Paint Technology, Vol
...
703
...
G
...
H
...
19, 1947, p
...


[38] Daniel, F
...
and Goldman, P
...
18, 1946, p
...




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