ASTM D7541-09
(Practice)Standard Practice for Estimating Critical Surface Tensions
Standard Practice for Estimating Critical Surface Tensions
SIGNIFICANCE AND USE
Knowledge of the critical surface tension of substrates, primers and other coatings is useful for explaining or predicting wettability by paints and other coatings applied to those surrfaces. Surfaces with low critical surface tensions usually are prone to suffer defects such as crawling, picture framing, cratering and loss of adhesion when painted. Low or irregular values, or both, often are indicative of contamination that could reduce adhesion. Surfaces with high critical surface tensions are easy to wet and usually provide an excellent platform for painting.
The swab, marking pen and draw-down tests all simulate the application of a film
The swab and marking pen techniques are simple and rapid and are particularly useful for testing in the field or on curved, irregular or porous surfaces where contact angles cannot be measured. The drop test does not work well on such surfaces and the draw-down method requires a flat specimen that is relatively large.
The estimation of critical surface tension has been useful in characterizing surfaces before and after cleaning processes such as power washes and solvent wipes in order to evaluate the efficiency of the cleaning.
One or more of these techniques could be the basis of a go/no-go quality control test where if a certain liquid wets, the surface is acceptable for painting, but if that liquid retracts and crawls, the surface is not acceptable.
Another go/no go test is possible where the test liquid is a paint and the surface is a substrate, primer or basecoat. A form of this test has been used for coatings for plastics.
SCOPE
1.1 This practice covers procedures for estimating values of the critical surface tension of surfaces by observing the wetting and dewetting of a series of liquids (usually organic solvents) applied to the surface in question.
1.2 Another technique, measurement of the contact angles, θ, of a series of test liquids and plotting cos θ versus surface tension (Zisman plots), provides data that allow the determination of more exact values for critical surface tension.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D7541–09
Standard Practice for
Estimating Critical Surface Tensions
This standard is issued under the fixed designation D7541; 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 drops, narrow strips, or spots. Drops may be applied using a
dropper, syringe or other device capable of producing indi-
1.1 This practice covers procedures for estimating values of
vidualdrops.Liquidstripsorspotsareappliedtothesurfaceby
the critical surface tension of surfaces by observing the wetting
swabbing with saturated cotton swabs or by another type of
and dewetting of a series of liquids (usually organic solvents)
applicator, such as one that is similar to a marker pen. In the
applied to the surface in question.
case of the drop, the observer determines whether the drop
1.2 Another technique, measurement of the contact angles,
stays in place or spreads. In the case of the liquid strip or spot,
u, of a series of test liquids and plotting cos u versus surface
the question is whether the liquid stays in place or dewets and
tension (Zisman plots), provides data that allow the determi-
crawls. In each case, the break point between wetting and
nation of more exact values for critical surface tension.
dewetting provides the critical surface tension.
1.3 The values stated in SI units are to be regarded as the
standard. The values given in parentheses are for information
5. Significance and Use
only.
5.1 Knowledge of the critical surface tension of substrates,
1.4 This standard does not purport to address all of the
primers and other coatings is useful for explaining or predict-
safety concerns, if any, associated with its use. It is the
ing wettability by paints and other coatings applied to those
responsibility of the user of this standard to establish appro-
surrfaces. Surfaces with low critical surface tensions usually
priate safety and health practices and determine the applica-
are prone to suffer defects such as crawling, picture framing,
bility of regulatory limitations prior to use.
cratering and loss of adhesion when painted. Low or irregular
2. Referenced Documents values,orboth,oftenareindicativeofcontaminationthatcould
reduce adhesion. Surfaces with high critical surface tensions
2.1 ASTM Standards:
are easy to wet and usually provide an excellent platform for
D2578 Test Method for Wetting Tension of Polyethylene
painting.
and Polypropylene Films
5.2 The swab, marking pen and draw-down tests all simu-
3. Terminology late the application of a film
5.3 The swab and marking pen techniques are simple and
3.1 Definitions:
rapid and are particularly useful for testing in the field or on
3.1.1 critical surface tension, n—the surface tension of a
curved, irregular or porous surfaces where contact angles
hypothetical liquid that would just spontaneously spread if
cannot be measured. The drop test does not work well on such
applied as a drop to the surface in question; any liquid with a
surfaces and the draw-down method requires a flat specimen
surface tension lower than the critical surface tension will
that is relatively large.
spread spontaneously.
5.4 The estimation of critical surface tension has been
4. Summary of Practice
useful in characterizing surfaces before and after cleaning
processes such as power washes and solvent wipes in order to
4.1 In this practice, a series of liquids of gradually increas-
evaluate the efficiency of the cleaning.
ing surface tension are applied to a surface in the form of
5.5 One or more of these techniques could be the basis of a
go/no-go quality control test where if a certain liquid wets, the
This practice is under the jurisdiction of ASTM Committee D01 on Paint and
surface is acceptable for painting, but if that liquid retracts and
Related Coatings, Materials, and Applications and is the direct responsibility of
crawls, the surface is not acceptable.
Subcommittee D01.23 on Physical Properties of Applied Paint Films.
Current edition approved June 1, 2009. Published August 2009. DOI: 10.1520/ 5.6 Another go/no go test is possible where the test liquid is
D7541-09.
a paint and the surface is a substrate, primer or basecoat. A
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
form of this test has been used for coatings for plastics.
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 ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7541–09
TABLE 1 Test Liquids and Their Surface Tensions
6. Interferences
Surfact Tension
6.1 The specimen must be clean in order for results to be
Liquid
mN/m (= dynes/cm)
meaningful. The surface must not be touched or rubbed.
Acetone 23.7
6.2 The surface tensions of test liquids, especially those that
Dimethyl formamide 35.2
are mixtures, are subject to change with time. Test liquid
2-pyrollidone 37.6
N-methyl-2-pyrollidone 39.0
surface tensions should be confirmed before they are first used,
Dimethyl sulfoxide 43.0
measured periodically after that and whenever change is
Ethylene cyanohydrin 44.4
suspected.
Formamide 56.0
Water 72.8
6.3 Test liquids may become contaminated, in which case
results with them will be meaningless. Test liquid surface
tensions should be confirmed before they are first used,
considering how the process may alter the surface. Cleaning
measuredperiodicallyafterthatandwhenevercontaminationis
must be clearly indicated in the report.
suspected.
6.4 High ambient temperature may cause rapid evaporation
10. Procedure–Cotton Swab
of test liquids and make it difficult to determine whether
10.1 Beginning with the lowest surface tension liquid in the
retraction has occurred or shrinkage is due to evaporation.
test series, saturate the cotton ball at the end of the stick and
apply three uniform strips 0.5 to 1 cm wide and 2 to 5 cm long
7. Apparatus
to the test specimen.
7.1 Several of one of the following types of applicators:
10.2 Observe whether the liquid remains as an intact film,
7.1.1 Cotton swab(smallballofcottonattheendofastick).
retracts (crawls) or completely beads up. Allow 3 seconds for
7.1.2 Marker pen type applicator.
retraction or beading to occur. Longer times may be used, but
7.1.3 Dropper or syringe.
evaporation of the liquid may cause retraction that appears to
7.1.4 Other device with the ability to apply a drop, strip, or
be dewetting, but is not.
spot.
10.3 If the liquid strip does not retract or bead up within 3
7.2 Dra
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