ASTM D6441-99ae1

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Designation:D6441–99a
Standard Test Methods for
Measuring the Hiding Power of Powder Coatings
This standard is issued under the fixed designation D 6441; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Last line of Table 1 editorially corrected in February 2000.
1. Scope D 16 Terminology for Paint, and Related Coatings, Materi-
als, and Applications
1.1 These test methods determine and report the hiding
D 344 Test Method for Relative Hiding Power of Paints by
power of a powder coating with respect to two parameters:
the Visual Evaluation of Brushouts
1.1.1 Test Method A—Contrast Ratio at a given film thick-
D 2805 Test Method for Hiding Power of Paints by Reflec-
ness
tometry
1.1.2 Test Method B—Film thickness at 0.98 (98 %) con-
D 3451 Practices for Testing Polymeric Powders and Pow-
trast ratio.
der Coatings
NOTE 1—The measured parameters conform to powder coating indus- 2
E 284 Terminology Relating to Appearance
trypracticebymeasuringhidingpowerinrelationtofilmthickness,rather
E 1331 Test Method for Reflectance Factor and Color by
than the more conventional “Spreading Rate” function employed in Test
Spectrophotometry Using Hemispherical Geometry
Methods D 344 and D 2805 and other hiding power test methods.
E 1347 Test Method for Color and Color Difference Mea-
NOTE 2—Hiding power is photometrically defined as the spreading rate
at 0.98 contrast ratio. See definitions of spreading rate and hiding power surement by Tristimulus (Filter) Colorimetry
in Terminology D 16, D 2805, and the Paint and Coatings Testing
E 1349 Test Method for Reflectance Factor and Color by
Manual.
Spectophotometry Using Bidirectional Geometry
NOTE 3—The contrast ratio 0.98 is conventionally accepted in the
2.2 Other Standard:
coatings industry as representing “complete” hiding for reflectometric
1-GP-71, Method 14.7, Hiding Power, Contrast Ratio
hiding power measurements. But visually, as well as photometrically, it is
Method, October 1982
slightly less than complete.
2.3 Paint & Coatings Testing Manual (Gardner-Sward
1.2 These test methods cover the determination of the
Handbook), 14th Edition, Chapter 42, Hiding Power
hiding power of powder coatings applied by electrostatic
spraying.
1.3 Thesetestmethodsdeterminehidingpowerbymeansof
3. Terminology
reflectometric and thickness gage measurements. They are
3.1 Definitions of Terms Specific to This Standard:
limited to coatings having a minimum CIE-Y reflectance of
3.1.1 reflectance—term of wide applicability, referring
15 %.
herein to the luminous reflectance factor as defined in Termi-
1.4 The values stated in SI units are to be regarded as the
nology E 284, and equivalent to the CIE Tristimulus value Y
standard. The values given in parentheses are for information
measured in accordance with Test Methods E 1331, E 1347 or
only.
Test Method E 1349 with specular reflection excluded. It is
1.5 This standard does not purport to address all of the
expressed as a percentage in this standard.
safety concerns, if any, associated with its use. It is the
3.1.2 white substrate—For purposes of this test, a substrate
responsibility of the user of this standard to establish appro-
of neutral shade with a minimum reflectance of 78 %.
priate safety and health practices, and to determine in advance
3.1.3 black substrate—A substrate with a maximum reflec-
the applicability of regulatory limitations prior to use.
tance of 1 %, which is effectively zero for the purpose of
measuring hiding power.
2. Referenced Documents
3.1.4 white reflectance (R )—Reflectance of the applied
W
2.1 ASTM Standards:
test film over a white substrate of reflectance W.
1 2
ThesetestmethodsareunderthejurisdictionofASTMCommitteeD-1onPaint Annual Book of ASTM Standards, Vol 06.01.
and Related Coatings, Materials, and Applications and the direct responsibility of Annual Book of ASTM Standards, Vol 06.02.
Subcommittee D01.51 on Powder Coatings. Canadian General Standards Board, (CGSB), 222 Queen St., Ottawa, Ont.,
Current edition approved Dec. 10, 1999. Published February 2000. Originally Canada K1A 1G6.
published as D 6441 – 99. Last previous edition D 6441 – 99. Paint & Coatings Testing Manual, MNL 17, ASTM, 1995.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D6441–99a
NOTE 1—Shows black and white substrate areas exposed after removal of masking tape.
FIG. 1 “Wedge” Film Application
3.1.5 black reflectance (R )—Reflectance of the applied test 3.2.1 T—the specified or measured thickness of the test
o
film over a black substrate. coating on the substrate.
3.2.2 t —the amount by which the black substrate exceeds
3.1.6 reflectivity (R )—The reflectance of a coating applied
o
`
the white substrate in thickness.
thicklyenoughtobecompletelyopaque,asevidencedbyequal
reflectance over the black and a white test substrate. 3.2.3 T8—T + t ; the thickness reading corresponding to T
o
over the black substrate when measured with the gage cali-
3.1.7 contrast ratio (C )—(1) The ratio of the reflectance
W
brated to the white substrate as zero.
of a film applied on a black substrate to a film of equal
3.3 For additional definitions applicable to these test meth-
thickness applied on a white substrate. (2) An instrumental
ods see Terminology E 284.
measure of film opacity.
3.1.7.1 Discussion—Contrast ratio can be expressed as a
4. Summary of Test Method
decimal fraction (R /R ) or as a percentage (100R /R ), the
O W O W
latter being preferred for the general concept of hiding or
4.1 Test MethodA—Contrast Ratio (C ) at a Specified Film
W
opacity, and employed in these test methods.
Thickness:
3.1.8 opacity—The degree to which a coating film hides a
4.1.1 The coating is applied as a “wedge” on a specified test
black and white substrate, as perceived visually or as measured
panel.
instrumentally, (see contrast ratio defined in 3.1.7).
4.1.2 Severalpairsofpointsareencircledovertheblackand
3.1.9 wedge of coating—Afilmofcoatinghavingarangeof white substrate at the specified coating thickness, their reflec-
film thickness giving a corresponding range of opacities on a
tances R and R are measured, and their contrast ratios (C
O W W
black and white substrate. (see Fig. 1). = 100 R /R ) calculated.
O W
3.2 Symbols: 4.1.3 The mean contrast ratio for the panel is calculated.
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D6441–99a
FIG. 2 Examples of Commercially Available Test Panels
NOTE 5—Some test panels require a pre-bake before using, to expell
4.2 Test Method B—Film Thickness (T ) at a Contrast
residual volatiles that can create pinholes in the subsequently applied
Ratio of 98 %:
powder coating.When necessary pre-bake for 10 min at 180°C (350°F) to
4.2.1 The coating is applied as a “wedge” on the specified
eliminate this problem.
test panel.
6.3 Suitable equipment for applying and baking the test
4.2.2 Several equal thickness pairs of black and white
coatings.
substrate points, at varying thicknesses, are located and their
6.4 Electronic Gage, adequately sensitive for measuring
contrast ratios determined.
coating film thickness.
4.2.3 Contrast ratio versus film thickness is plotted on
6.5 Heat-Resistant Tape, 20-mm ( ⁄4-in.) wide, easily re-
suitable graph paper, and the thickness at T determined from
moved after baking, leaving no discoloration or adhesive
the graph.
residue.
5. Significance and Use
6.6 Permanent Marker, extra fine point.
6.7 Suitable Graph Paper.
5.1 Contrast ratio at a specified film thickness is a useful
hiding power parameter for production control and purchasing
specifications. 7. Measurements—General Rules
5.2 Thegreaterthehidingpower,thelesscoatingisrequired
7.1 For each powder and test method, fill out an individual
per unit area to obtain adequate hiding. Knowledge of hiding
work sheet in the form of a table (see Fig. 3 for Test Method
power is therefore important in regard to coating costs and for
A, Fig. 4 for Test Method B), into which all test data and
comparing coating value.
calculated values are entered in the indicated locations.
7.2 Measure reflectance as a percentage to two decimal
6. Apparatus and Material
places. Calculate (or measure) contrast ratio (C ) as a percent-
W
6.1 Reflectometer, that measures the luminous reflectance
age (100R /R ) to two decimal places, and report final results
B W
factor, (specular reflection excluded) using CIE standard illu-
to one decimal place.
minant C and the CIE 1931 (2°) standard observer, in accor-
7.3 The circles drawn to locate measurement points must be
dance with Test Method E 1331, E 1347 or E 1349. The
at least larger than the measurement opening of the reflecto-
instrument shall be capable of viewing a diameter of at least 3
meter.
1 3
to5mm( ⁄8 to ⁄16in.).
7.4 Measurethicknessasaccuratelyaspossible,reportingto
nearest 1.3 µm (0.05 mils), or closer if possible.
NOTE 4—Otherobserver-illuminantcombinationsandaperturesmaybe
used by agreement.
8. Calibration and Panel Preparation
6.2 TestPanels: Smooth,glossy,paintedsteelpanels,thick-
ness approximately 0.28 mm (0.011 in.), divided equally into 8.1 Select a panel and pre-bake if necessary, as discussed in
Note 5.
black and white areas by a straight boundary. The black area
shall have a maximum reflectance of 1 % and the white area a 8.2 Locate and encircle a point of mean thickness in the
white and in the black areas about 20-mm ( ⁄4 in.) from the
minimum reflectance of 78 %. The white area shall not yellow
or darken appreciably when subjected to a normal powder panel edge, and mask each point with a short length of the
specified tape, extending over the edge.
coating baking schedule. (see Fig. 2 for commercially avail-
able sizes.)
6 7
The sole source of supply of panels known to the committee at this time is the The sole source of supply of the tape, Product No. 8902 known to the
Leneta Company, 15 Whitney Rd., Mahwah, NJ 07430. If you are aware of committee at this time is 3M industrial Tape Division; 3M Center 220-8E-04; St.
alternative suppliers, please provide this Information to ASTM Headquarters. Your Paul, MN 55144. If you are aware of alternative suppliers, please provide this
comments will receive careful consideration at a meeting of the responsible Information to ASTM Headquarters. Your comments will receive careful consider-
1 1
technical committee, which you may attend. ation at a meeting of the responsible techni
...