ASTM D7490-13(2022)
(Test Method)Standard Test Method for Measurement of the Surface Tension of Solid Coatings, Substrates and Pigments using Contact Angle Measurements
Standard Test Method for Measurement of the Surface Tension of Solid Coatings, Substrates and Pigments using Contact Angle Measurements
SIGNIFICANCE AND USE
5.1 The method described in this standard is based on the concept that the total free energy at a surface is the sum of contributions from different intermolecular forces, such as dispersion, polar and hydrogen bonding. There are other techniques that employ three components (dispersion, polar and hydrogen bonding). These methods are further complicated by needing three to five test liquids and are not practical for routine testing. This method uses contact angles of two liquids to provide data for the calculation of two components, dispersion, γsd, and polar, γsp.
5.2 Dispersion and polar component data, along with the total solid surface tension, are useful for explaining or predicting wetting or adhesion, or both, of coatings on pretreatments, substrates and other coatings. Low solid surface tension values often are a sign of contamination and portend potential wetting problems. High polar components may signal polar contamination. There is evidence in the literature that matching of polar components of topcoats and primers gives better adhesion.4
5.3 Solid surface tensions of pigments, particularly the polar components, may be useful in understanding dispersion problems or to provide signals for the composition of dispersants and mill bases. However, comparison of pigments may be difficult if there are differences in the roughness or porosity, or both, of the disks prepared from them.
5.4 Although this technique is very useful in characterizing surfaces, evaluating surface active additives and explaining problems, it is not designed to be a quality control or specification test.
SCOPE
1.1 This test method describes a procedure for the measurement of contact angles of two liquids, one polar and the other nonpolar, of known surface tension on a substrate, pigment (in the form of a disk), or cured or air dried coating in order to calculate the surface properties (surface tension and its dispersion and polar components) of the solid.
1.2 The total solid surface tension range that can be determined using this method is approximately 20 to 60 dyn/cm.
1.3 The values stated in CGS units (dyn/cm) are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D7490 − 13 (Reapproved 2022)
Standard Test Method for
Measurement of the Surface Tension of Solid Coatings,
Substrates and Pigments using Contact Angle
Measurements
This standard is issued under the fixed designation D7490; 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 Tester (Withdrawn 2010)
D7334 Practice for Surface Wettability of Coatings, Sub-
1.1 This test method describes a procedure for the measure-
strates and Pigments by Advancing Contact Angle Mea-
ment of contact angles of two liquids, one polar and the other
surement
nonpolar, of known surface tension on a substrate, pigment (in
the form of a disk), or cured or air dried coating in order to
3. Terminology
calculate the surface properties (surface tension and its disper-
3.1 Definitions:
sion and polar components) of the solid.
3.1.1 contact angle, n—the interior angle that a drop makes
1.2 The total solid surface tension range that can be deter-
between the substrate and a tangent drawn at the intersection
mined using this method is approximately 20 to 60 dyn/cm.
between the drop and the substrate as shown in Fig. 1; this is
the angle formed by a liquid at the three phase boundary where
1.3 The values stated in CGS units (dyn/cm) are to be
a liquid, gas (air) and solid intersect.
regarded as standard. No other units of measurement are
included in this standard. 3.1.2 dispersion component, n—the component of solid
surface tension that is related to intermolecular attraction
1.4 This standard does not purport to address all of the
caused by nonpolar dispersion forces.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 3.1.3 polar component, n—the component of solid surface
priate safety, health, and environmental practices and deter- tension that is related to polar forces, such as hydrogen
mine the applicability of regulatory limitations prior to use. bonding and ion-dipole forces.
1.5 This international standard was developed in accor-
3.1.4 solid surface tension, n—the surface tension of a solid
dance with internationally recognized principles on standard-
surface; this parameter cannot be measured directly, but must
ization established in the Decision on Principles for the
be determined by extrapolation of polymer melt or solution
Development of International Standards, Guides and Recom-
datato100 %solidsorbycontactangleswithliquidsofknown
mendations issued by the World Trade Organization Technical
surface tension.
Barriers to Trade (TBT) Committee.
3.1.5 surface energy, n—excess free energy of surface
molecules compared to those of the bulk material; arises from
2. Referenced Documents
unbalanced molecular cohesive forces at a surface that cause
2.1 ASTM Standards: the surface to contract and behave like a film or membrane
(units are energy/unit areas such as joules/cm ).
D1193 Specification for Reagent Water
D5725 Test Method for Surface Wettability andAbsorbency
3.1.6 surface tension, n—the force necessary to break the
of Sheeted Materials Using an Automated Contact Angle
surface of a film of a given length (units are force/length, such
as dyn/cm or newtons/m); the same numerically as surface
energy, but different units.
This test method is under the jurisdiction of ASTM Committee D01 on Paint
4. Summary of Test Method
and Related Coatings, Materials, andApplications and is the direct responsibility of
Subcommittee D01.23 on Physical Properties of Applied Paint Films.
4.1 Contact angles of drops of distilled water and di-
Current edition approved Jan. 1, 2022. Published January 2022. Originally
iodomethane (methylene iodide) are measured on the surface
approved in 2008. Last previous edition approved in 2013 as D7490 – 13. DOI:
10.1520/D7490-13R22. of interest. The two values are then substituted into two
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7490 − 13 (2022)
6.1.2 A rough or porous test surface such that drops sink in
rapidly.Suchsurfacesaremostlikelyfoundwithpigmentdisks
or sanded coatings.
6.1.3 A curved test surface such that angles are difficult or
impossible to measure.
6.1.4 Low humidity (<40 % RH) when water is the test
liquid such that the contact angle changes rapidly.
A = contact angle
7. Apparatus
D=dropofliquid
P = specimen
7.1 Goniometer—An instrument consisting of a controlled
T = tangent at specimen surface
light source, a stage to hold the test specimen, and a micro-
FIG. 1 Measuring Angle of Contact
scope or camera for viewing of the drop on the specimen is
required. An automated instrument for measuring angle of
contact and a method for using it can be found in Test Method
separate expressions of the Owens-Wendt-Kaelble equation
(one for each liquid). This results in two equations in two D5725.
unknowns, which are then solved for the dispersion and polar
7.2 Hypodermic Syringe—A syringe, such as a 1-mL
components of surface tension. The sum of the components is
hypodermic, equipped with a No. 27 stainless steel needle,
the surface tension of the solid.
capable of providing 100 to 200 drops from 1 mL, is suitable
for use with water-like liquids. More viscous liquids may
5. Significance and Use
require a needle of different size.
5.1 The method described in this standard is based on the
concept that the total free energy at a surface is the sum of
8. Reagents and Materials
contributions from different intermolecular forces, such as
8.1 Water—Type II reagent water (distilled) in accordance
dispersion, polar and hydrogen bonding. There are other
with Specification D1193.
techniques that employ three components (dispersion, polar
and hydrogen bonding). These methods are further compli-
8.2 Diiodomethane—reagent grade or better.
cated by needing three to five test liquids and are not practical
for routine testing. This method uses contact angles of two
9. Preparation of Specimens
liquids to provide data for the calculation of two components,
9.1 If the part or panel of interest is too large to fit on the
d p
dispersion, γ , and polar, γ .
s s
stage, then test specimens should be cut to a size appropriate
5.2 Dispersion and polar component data, along with the
for the instrument being used. They shall be cut in such a way
total solid surface tension, are useful for explaining or predict-
as to be thoroughly representative of the sample.
ing wetting or adhesion, or both, of coatings on pretreatments,
9.2 The areas tested shall not contain visible blemishes or
substrates and other coatings. Low solid surface tension values
defects and shall not be touched with the fingers or contami-
often are a sign of contamination and portend potential wetting
nated in any other way.
problems. High polar components may signal polar contami-
9.3 If contamination or improper handling is suspected, the
nation.Thereisevidenceintheliteraturethatmatchingofpolar
specimen may be rinsed with water or washed with laboratory
components of topcoats and primers gives better adhesion.
detergent and water. However, cleaning may affect the results
5.3 Solidsurfacetensionsofpigments,particularlythepolar
and must be noted on the report.
components, may be useful in understanding dispersion prob-
lems or to provide signals for the composition of dispersants 9.4 Pigment specimens shall be in the form of disks pre-
pared in a press such as those used to prepare KBr disks for
and mill bases. However, comparison of pigments may be
difficult if there are differences in the roughness or porosity, or infrared analysis.
both, of the disks prepared from them.
10. Procedure
5.4 Although this technique is very useful in characterizing
surfaces, evaluating surface active additives and explaining 10.1 Test the specimens at a standard temperature of 23 6
problems, it is not designed to be a quality control or 2 °C and at a relative humidity ≥50 %, unless otherwise agreed
specification test. upon.
10.2 Set up the goniometer and level the stage according to
6. Interferences
the manufacturer’s instructions.
6.1 The
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