ASTM D7394-08
(Practice)Standard Practice for Rheological Characterization of Architectural Coatings using Three Rotational Bench Viscometers
Standard Practice for Rheological Characterization of Architectural Coatings using Three Rotational Bench Viscometers
SIGNIFICANCE AND USE
A significant feature of this practice is the ability to obtain a semblance of coating rheology over a broad range of shear rates with the same bench viscometers and test protocol that paint formulators and paint QC analysts routinely use. By using this procedure, an approximation of the shear rheology of a coating is possible without using a rheometer, and performance predictions can be made based on those measurements.
Low-Shear Viscosity (LSV)—The determination of low-shear viscosity in this practice can be used to predict the relative “in-can” performance of coatings for their ability to suspend pigment or prevent syneresis, or both. The LSV can also predict relative performance for leveling and sag resistance after application by roll, brush or spray. Fig. 1 shows the predictive low-shear viscosity relationships for several coatings properties.
5.3 Mid-Shear Viscosity (MSV)—The determination of MSV (coating consistency) in this practice is often the first viscosity obtained. This viscosity reflects the coatings resistance to flow on mixing, pouring, pumping, or hand stirring. Architectural coatings nearly always have a target specification for mid-shear viscosity, which is usually obtained by adjusting the level of thickener in the coating. Consequently, mid-shear viscosity is ideally a constant for a given series of coatings being tested to provide meaningful comparisons of low-shear and high-shear viscosity. With viscosities at the same KU value, MSV can also be used to obtain the relative Mid-Shear Thickener Efficiency (MSTE) of different thickeners in the same coating expressed as lb thickener/100 gal wet coating or g thickener/L wet coating.
5.4 High-Shear Viscosity (HSV)—High-shear viscosity in this practice is a measure of the coatings resistance to flow on application by brush or roller, which is often referred to as brush-drag or rolling resistance respectively. This viscosity relates to the coatings ability to provide one-coat hiding, its ease o...
SCOPE
1.1 This practice covers a popular industry protocol for the rheological characterization of waterborne architectural coatings using three commonly used rotational bench viscometers. Each viscometer operates in a different shear rate regime for determination of coating viscosity at low shear rate, mid shear rate, and at high shear rate respectively as defined herein. General guidelines are provided for predicting some coating performance properties from the viscosity measurements made. With appropriate correlations and subsequent modification of the performance guidelines, this practice has potential for characterization of other types of aqueous and non-aqueous coatings.
1.2 The values stated in SI units are to be regarded as standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D7394 − 08
StandardPractice for
Rheological Characterization of Architectural Coatings
using Three Rotational Bench Viscometers
This standard is issued under the fixed designation D7394; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D2805 Test Method for Hiding Power of Paints by Reflec-
tometry
1.1 This practice covers a popular industry protocol for the
D4040 Test Method for Rheological Properties of Paste
rheological characterization of waterborne architectural coat-
Printing and Vehicles by the Falling-Rod Viscometer
ings using three commonly used rotational bench viscometers.
D4062 Test Method for Leveling of Paints by Draw-Down
Each viscometer operates in a different shear rate regime for
Method
determination of coating viscosity at low shear rate, mid shear
D4287 Test Method for High-Shear Viscosity Using a Cone/
rate, and at high shear rate respectively as defined herein.
Plate Viscometer
General guidelines are provided for predicting some coating
D4400 Test Method for Sag Resistance of Paints Using a
performance properties from the viscosity measurements
made. With appropriate correlations and subsequent modifica- Multinotch Applicator
tion of the performance guidelines, this practice has potential D4414 Practice for Measurement of Wet Film Thickness by
for characterization of other types of aqueous and non-aqueous
Notch Gages
coatings. D4958 Test Method for Comparison of the Brush Drag of
Latex Paints
1.2 The values stated in SI units are to be regarded as
standard.
3. Terminology
1.3 This standard does not purport to address all of the
3.1 Definitions:
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.1.1 coating rheology, n—the viscosity profile obtained for
priate safety and health practices and determine the applica-
a fluid coating over a range of shear rates.
bility of regulatory limitations prior to use.
3.1.2 high-shear viscosity (HSV), n—the viscosity of a fluid
coating at high shear rate (typically measured at 10,000 or
2. Referenced Documents
-1
12,000 sec ), and for architectural coatings, it is often referred
2.1 ASTM Standards:
to as the “ICI” or “brush-drag” viscosity.
D562 Test Method for Consistency of Paints Measuring
KrebsUnit(KU)ViscosityUsingaStormer-TypeViscom-
3.1.3 leveling, n—the ability of a wet coating to flow out to
eter
a smooth dry film after application, thereby minimizing or
D869 TestMethodforEvaluatingDegreeofSettlingofPaint
eliminating coating surface irregularities that occur during
D1005 Test Method for Measurement of Dry-Film Thick-
brushing, rolling or spraying (see also Test Method D4062).
ness of Organic Coatings Using Micrometers
3.1.4 low-shear viscosity (LSV), n—the viscosity of a coat-
D1200 Test Method for Viscosity by Ford Viscosity Cup
ing fluid at low shear rate (typically in the range of 0.001 to
D2196 Test Methods for Rheological Properties of Non-
-1
1s ), often referred to as the “leveling viscosity” or inversely
Newtonian Materials by Rotational (Brookfield type)
as the “suspension viscosity.”
Viscometer
3.1.5 mid-shear thickener effıciency (MSTE), n—the weight
of active thickener per unit volume of wet coating required to
This practice is under the jurisdiction of ASTM Committee D01 on Paint and
give the target MSV, commonly expressed as lb active
Related Coatings, Materials, and Applications and is the direct responsibility of
Subcommittee D01.24 on Physical Properties of Liquid Paints & Paint Materials.
thickener/100 gal wet coating (or in g/L units).
Current edition approved Nov. 1, 2008. Published December 2008. DOI:
10.1520/D7394-08.
3.1.6 mid-shear viscosity (MSV), n—the viscosity of a
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
coating fluid at medium shear rate (typically in the range of 10
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
-1
to 1000 s ), often referred to as the “consistency” or the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. “mixing viscosity.”
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7394 − 08
3.1.7 newtonian, n—a rheological term describing a fluid viscosity constant, meaningful comparisons between coatings
that maintains constant viscosity over a range of shear rates can then be made in the extreme shear rate regimes for LSV
(see also Test Method D1200 and Test Method D4040). and HSV where many coatings properties are affected.
3.1.8 rheometer, n—an instrument capable of continuously
5. Significance and Use
measuring fluid viscosity over a range of shear rates or shear
stresses, often capable of other types of rheological determi- 5.1 A significant feature of this practice is the ability to
nations, and ideally suited for research and well-defined
obtain a semblance of coating rheology over a broad range of
characterization of fluid rheology. shear rates with the same bench viscometers and test protocol
that paint formulators and paint QC analysts routinely use. By
3.1.9 rotational viscometer, n—an instrument that uses one
usingthisprocedure,anapproximationoftheshearrheologyof
or more turning surfaces in contact with a fluid to measure the
a coating is possible without using a rheometer, and perfor-
fluid’s viscosity, is capable of operating at one or more
mance predictions can be made based on those measurements.
rotational speeds to provide different shear rates, is typically
limited to one speed per measurement, is relatively simple to
5.2 Low-Shear Viscosity (LSV)—The determination of low-
operate and ideally suited for quality control or routine lab
shear viscosity in this practice can be used to predict the
determinations.
relative “in-can” performance of coatings for their ability to
suspend pigment or prevent syneresis, or both. The LSV can
3.1.10 settling, n—the gradual sedimentation of pigment or
also predict relative performance for leveling and sag resis-
other disperse phase particles, or both, that may occur during
tance after application by roll, brush or spray. Fig. 1 shows the
storage of a coating (see also Test Method D869).
predictive low-shear viscosity relationships for several coat-
3.1.11 shear rate, n—the change in velocity of a fluid per
ings properties.
unit gap between shearing surfaces.
5.3 Mid-Shear Viscosity (MSV)—The determination of
3.1.12 suspension, n—as defined in this practice, a coating
MSV (coating consistency) in this practice is often the first
formulation’s ability to suspend pigment and other disperse
viscosity obtained. This viscosity reflects the coatings resis-
phase particles, thereby inhibiting or preventing settling or
tance to flow on mixing, pouring, pumping, or hand stirring.
syneresis, or both.
Architectural coatings nearly always have a target specification
3.1.13 syneresis, n—the separation of a clear liquid layer at
for mid-shear viscosity, which is usually obtained by adjusting
the top of coating in a container that may occur during storage.
the level of thickener in the coating. Consequently, mid-shear
3.1.14 thixotropy, n—a rheological term describing a non-
viscosity is ideally a constant for a given series of coatings
newtonian fluid that decreases in viscosity with time at a given
being tested to provide meaningful comparisons of low-shear
shear rate, and then rebuilds viscosity with time when the
and high-shear viscosity. With viscosities at the same KU
shearing stops (see also Test Methods D2196).
value, MSV can also be used to obtain the relative Mid-Shear
Thickener Efficiency (MSTE) of different thickeners in the
4. Summary of Practice
same coating expressed as lb thickener/100 gal wet coating or
4.1 This practice involves characterization of architectural
g thickener/L wet coating.
coating rheology by measuring viscosity with three rotational
5.4 High-Shear Viscosity (HSV)—High-shear viscosity in
bench viscometers to obtain low-shear viscosity (LSV), mid-
this practice is a measure of the coatings resistance to flow on
shear viscosity (MSV) and high-shear viscosity (HSV), respec-
application by brush or roller, which is often referred to as
tively. LSV is obtained with a Brookfield-type spindle viscom-
brush-drag or rolling resistance respectively. This viscosity
eteroperatingatitslowestspeed(ateither0.5orpreferably0.3
relates to the coatings ability to provide one-coat hiding, its
rpm). The applicable shear rate for this viscometer/speed
ease of application (brushing or rolling resistance), and its
-1
combination is in the range of 0.01 to 1 s . The MSV or
spread rate. Fig. 2 shows high-shear viscosity relationship
coating consistency is obtained using an analog or digital
predictions for relative coating performance.
rotational paddle-type viscometer that measures viscosity in
KrebsUnits(KU).Theapplicableshearrateforthisinstrument
6. Reagents
-1
isintherangeof10to200s formostarchitecturalpaints.The
high-shear viscosity is obtained using a cone/plate-type vis-
-1
cometer with a fixed shear rate of either 10,000 or 12,000 s .
If coatings are to be characterized without any viscosity
adjustments being made, measurements with the three viscom-
eters can be conducted in any order. However, if a series of
paints is being compared where it is desirable to have one of
the three viscosities a constant, viscosity adjustments may be
needed to achieve that. For example, it is quite common to
have a specification for the Krebs Unit viscosity in architec-
tural coatings. In this case, MSV would be the first viscosity
measurement made, and any coatings out of specification
would be adjusted (usually with the amount of thickener) to
obtain the same or similar Krebs viscosity. With the Krebs FIG. 1 Low Shear Viscosity (LSV)
D7394 − 08
brieflyintheASTMPaintandCoatingsTestingManual andin
more detail in the Handbook of CoatingsAdditives. Although
controlled shear rate and controlled shear stress rheometers do
provide more complete coating rheology profiles, have well
defined shear rates and shear stresses, are often more accurate
in their measurements, and can provide other rheological
information such as elastic properties etc., many routine
decisions about relative coating rheology performance predic-
tions are made using the test protocol of this practice.
8.1.2 The mid-shear Krebs Unit viscosity is a primary
FIG. 2 High Shear Viscosity (HSV)
specificationfornearlyallarchitecturalcoatings.Consequently
this is usually the first viscosity measurement made. If the
Krebs Unit viscosity is not on target, a common practice is to
6.1 Viscosity Standards—optional, for checking the accu-
adjust thickener level to bring the coating into the correct KU
racy of each of the three viscometers used in this practice.
specification range. Krebs Unit viscosity specifications for
architectural coatings can range from about 70 to 120 KU 6 3
7. Apparatus and Equipment
KU, depending on the type of coating and application. For a
7.1 Spatula or Lab Stirrer—optional, for mixing coating
typical house paint with a midpoint specification of 100 KU
samples prior to viscosity measurements.
viscosity, the specification range would be 63 %. Since MSV
is often a primary specification, a series of coatings being
7.2 Brookfield-Type Viscometer—to measure the low-shear
compared for rheology will often have the same or similar KU
viscosity of a coating at the lowest instrument rpm (Brookfield
viscosity, and this is actually advantageous and important for
LVT at 0.3 rpm is standard, LVT at 0.5 rpm is optional).
meaningful comparisons of LSV and HSV. The reason for this
7.3 Paddle-Type Rotational Viscometer— digital or analog
is that an increase in MSV for a coating will result in a
instrument to measure the mid-shear viscosity of the coating in
corresponding increase in its LSV and HSV. If the coatings do
Krebs Units (KU).
not have the same MSV, viscosity comparisons at low and high
7.4 Cone/Plate-Type Viscometer—tomeasurethehigh-shear
shear cannot be made on an equal basis.
viscosityofthecoatingatafixedshearrateof10,000or12,000 8.1.3 In some protocols, LSV or HSV can be a primary
-1
s .
specification for a coating with MSV having secondary prior-
ity. In those instances, LSV or HSV are adjusted to constant
7.5 Thermometer (ASTM 49C or equivalent of 0.1C accu-
value with thickeners or rheology modifiers, or both, and the
racy per Test MethodD562 or Test MethodsD2196)—torecord
other two viscosities are then determined for comparison
and adjust the coating sample temperature.
8.2 Adjustment of the Mid-Shear Rate Krebs Unit Viscosity:
7.6 Leveling Draw-Down Blade—optional, to determine the
8.2.1 A first step based on the preferred test protocol
relative leveling of coatings for comparison and correlation
outlinedaboveinthispracticeisthedeterminationoftheKrebs
with low-shear viscosity measurements.
viscosity (or just KU viscosity) of the coating using a paddle-
7.7 Sag Bar—optional, to determine the sag resistance of
type analog or digital viscometer that measures viscosity in
coatings for comparison and correlation with low-shear viscos-
Krebs Units. Test Method D562 is the test method recom-
ity measurements.
mended for this determination. All setup and operational
7.8 Paint Brush—optional, for brushing out paints for rela- criteria should be followed. As some paints are thixotropic, it
tive brush drag, wet film thickness, hiding power, and leveling is a good practice to pre-stir the paint with a spatula or lab
of brush marks for comparison and correlation with low-shear mixer to break up any structure prior to making a viscosity
and high-shear viscosity measurements. measurement. If the mid-shear Krebs viscosity is a specifica-
tion or is a fixed value for the paints being tested, the Krebs
7.9 Paint Roller—optional, for rolling out paints for relative
viscosity of each paint should be measured followed by
rolling resistance and for measuring wet film thickness, hiding
appropriate thickener adjustments to obtain the same or similar
power, and leveling of roller tracking marks for comparison
KU before proceeding to obtain LSV or HSV. Sometimes
and correlation with low-shear and high-shear viscosity mea-
paints have to be remade if the thickener amount is too high.
surements.
Adjustment of the paints being tested to the same Stormer
viscosity is optional, but it is highly recommended for mean-
8. Procedure
ingful comparison of the effects of coat
...
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