1、Designation: D 6441 05Standard Test Methods forMeasuring the Hiding Power of Powder Coatings1This standard is issued under the fixed designation D 6441; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods determine and report the hidingpower of a powder coating with respect to two parameters:1.1.1 Test Method AContrast
3、Ratio at a given film thick-ness1.1.2 Test Method BFilm thickness at 0.98 (98 %) con-trast ratio.NOTE 1The measured parameters follow powder coating industrypractice by measuring hiding power in relation to film thickness, ratherthan the “Spreading Rate” function employed in Test Methods D 344 andD
4、2805 and other hiding power test methods.NOTE 2Hiding power is photometrically defined as the spreading rateat 0.98 contrast ratio. See definitions of spreading rate and hiding powerin Terminology D16, D 2805, and the Paint and Coatings TestingManual.NOTE 3The contrast ratio 0.98 is conventionally a
5、ccepted in thecoatings industry as representing “complete” hiding for reflectometrichiding power measurements. But visually, as well as photometrically, it isslightly less than complete.1.2 These test methods cover the determination of thehiding power of powder coatings applied by electrostaticspray
6、ing.1.3 These test methods determine hiding power by means ofreflectometric and thickness gage measurements. They arelimited to coatings having a minimum CIE-Y reflectance of15 %.1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationo
7、nly.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices, and to determine in advancethe applicability of regulatory limitations prior to us
8、e.2. Referenced Documents2.1 ASTM Standards:2D16 Terminology for Paint, Related Coatings, Materials,and ApplicationsD 344 Test Method for Relative Hiding Power of Paints bythe Visual Evaluation of BrushoutsD 2805 Test Method for Hiding Power of Paints by Reflec-tometryD 3451 Practices for Testing Co
9、ating Powders and PowderCoatingsE 284 Terminology of AppearanceE 1331 Test Method for Reflectance Factor and Color bySpectrophotometry Using Hemispherical GeometryE 1347 Test Method for Color and Color Difference Mea-surement by Tristimulus (Filter) ColorimetryE 1349 Test Method for Reflectance Fact
10、or and Color bySpectophotometry Using Bidirectional Geometry2.2 Other Standard:1-GP-71, Method 14.7, Hiding Power, Contrast RatioMethod, October 198233. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 reflectanceterm of wide applicability, referringherein to the luminous reflecta
11、nce factor as defined in Termi-nology E 284, and equivalent to the CIE Tristimulus value Ymeasured in accordance with Test Methods E 1331, E 1347 orTest Method E 1349 with specular reflection excluded. It isexpressed as a percentage in this standard.3.1.2 white substrateFor purposes of this test, a
12、substrateof neutral shade with a minimum reflectance of 78 %.3.1.3 black substrateA substrate with a maximum reflec-tance of 1 %, which is effectively zero for the purpose ofmeasuring hiding power.3.1.4 white reflectance (RW)Reflectance of the appliedtest film over a white substrate of reflectance W
13、.1These test methods are under the jurisdiction of ASTM Committee D01 onPaint and Related Coatings, Materials, andApplications and the direct responsibilityof Subcommittee D01.51 on Powder Coatings.Current edition approved Jan. 1, 2005. Published February 2005. Originallyapproved in 1999. Last previ
14、ous edition approved in 1999 as D 6441 99ae1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Canadian Genera
15、l Standards Board, (CGSB), 222 Queen St., Ottawa, Ont.,Canada K1A 1G6.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.5 black reflectance (Ro)Reflectance of the applied testfilm over a black substrate.3.1.6 reflectivity (R)The re
16、flectance of a coating appliedthickly enough to be completely opaque, as evidenced by equalreflectance over the black and a white test substrate.3.1.7 contrast ratio (CW)(1) The ratio of the reflectanceof a film applied on a black substrate to a film of equalthickness applied on a white substrate. (
17、2) An instrumentalmeasure of film opacity.3.1.7.1 DiscussionContrast ratio can be expressed as adecimal fraction (RO/RW) or as a percentage (100RO/RW), thelatter being preferred for the general concept of hiding oropacity, and employed in these test methods.3.1.8 opacityThe degree to which a coating
18、 film hides ablack and white substrate, as perceived visually or as measuredinstrumentally, (see contrast ratio defined in 3.1.7).3.1.9 wedge of coatingAfilm of coating having a range offilm thickness giving a corresponding range of opacities on ablack and white substrate. (see Fig. 1).3.2 Definitio
19、ns of Symbols Used in Calculations Specific toThis Standard:3.2.1 Tthe specified or measured thickness of the testcoating on the substrate.3.2.2 tothe amount by which the black substrate exceedsthe white substrate in thickness.3.2.3 T8T + to; the thickness reading corresponding to Tover the black su
20、bstrate when measured with the gage cali-brated to the white substrate as zero.3.3 For additional definitions applicable to these test meth-ods see Terminology E 284.4. Summary of Test Method4.1 Test Method AContrast Ratio (CW) at a Specified FilmThickness:4.1.1 The coating is applied as a “wedge” o
21、n a specified testpanel.4.1.2 Several pairs of points are encircled over the black andwhite substrate at the specified coating thickness, their reflec-tances ROand RWare measured, and their contrast ratios (CW= 100 RO/RW) calculated.4.1.3 The mean contrast ratio for the panel is calculated.NOTE 1Sho
22、ws black and white substrate areas exposed after removal of masking tape.FIG. 1 “Wedge” Film ApplicationD64410524.2 Test Method BFilm Thickness (T98) at a ContrastRatio of 98 %:4.2.1 The coating is applied as a “wedge” on the specifiedtest panel.4.2.2 Several equal thickness pairs of black and white
23、substrate points, at varying thicknesses, are located and theircontrast ratios determined.4.2.3 Contrast ratio versus film thickness is plotted onsuitable graph paper, and the thickness at T98determined fromthe graph.5. Significance and Use5.1 Contrast ratio at a specified film thickness is a useful
24、hiding power parameter for production control and purchasingspecifications.5.2 The greater the hiding power, the less coating is requiredper unit area to obtain adequate hiding. Knowledge of hidingpower is therefore important in regard to coating costs and forcomparing coating value.6. Apparatus and
25、 Material6.1 Reflectometer, that measures the luminous reflectancefactor, (specular reflection excluded) using CIE standard illu-minant C and the CIE 1931 (2) standard observer, in accor-dance with Test Method E 1331, E 1347 or E 1349. Theinstrument shall be capable of viewing a diameter of at least
26、 3to5mm(18 to316 in.).NOTE 4Other observer-illuminant combinations and apertures may beused by agreement.6.2 Test Panels: Smooth, glossy, pre-painted steel panels,thickness approximately 0.28 mm (0.011 in.), divided equallyinto black and white areas by a straight boundary. The blackarea shall have a
27、 maximum reflectance of 1 % and the whitearea a minimum reflectance of 78 %. The white area shall notyellow or darken appreciably when subjected to a normalpowder coating baking schedule.4(see Fig. 2 for commerciallyavailable sizes.)NOTE 5Some test panels require a pre-bake before using, to expelres
28、idual volatiles that can create pinholes in the subsequently appliedpowder coating. When necessary pre-bake for 10 min at 180C (350F) toeliminate this problem.6.3 Suitable equipment for applying and baking the testcoatings.6.4 Electronic Gage, adequately sensitive for measuringcoating film thickness
29、.6.5 Heat-Resistant Tape, 20-mm (34-in.) wide, easily re-moved after baking, leaving no discoloration or adhesiveresidue.56.6 Permanent Marker, extra fine point.6.7 Suitable Graph Paper.7. MeasurementsGeneral Rules7.1 For each powder and test method, fill out an individualwork sheet in the form of a
30、 table (see Fig. 3 for Test MethodA, Fig. 4 for Test Method B), into which all test data andcalculated values are entered in the indicated locations.7.2 Measure reflectance as a percentage to two decimalplaces. Calculate (or measure) contrast ratio (CW) as a percent-age (100RB/RW) to two decimal pla
31、ces, and report final resultsto one decimal place.7.3 The circles drawn to locate measurement points must beat least larger than the measurement opening of the reflecto-meter.7.4 Measure thickness as accurately as possible, reporting tonearest 1.3 micrometers (0.05 mils), or closer if possible.8. Ca
32、libration and Panel Preparation8.1 Select a panel and pre-bake if necessary, as discussed inNote 5.8.2 Locate and encircle a point of mean thickness in thewhite and in the black areas about 20-mm (34 in.) from thepanel edge, and mask each point with a short length of thespecified tape, extending ove
33、r the edge.4The sole source of supply of panels known to the committee at this time is theLeneta Company, 15 Whitney Rd., Mahwah, NJ 07430. If you are aware ofalternative suppliers, please provide this Information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at
34、 a meeting of theresponsible technical committee,1which you may attend.5The sole source of supply of the tape, Product No. 8902 known to thecommittee at this time is 3M industrial Tape Division; 3M Center 220-8E-04; St.Paul, MN 55144. If you are aware of alternative suppliers, please provide thisInf
35、ormation to ASTM International Headquarters. Your comments will receivecareful consideration at a meeting of the responsible technical committee,1whichyou may attend.FIG. 2 Examples of Commercially Available Test PanelsD64410538.3 With the panel thus prepared, apply the test coating as athickness “w
36、edge,” cure at the specified schedule, then removethe tapes to expose the uncoated white and black substratepoints (see Fig. 1).8.4 Recalibrate the film thickness gage to zero on thewhite-substrate points, measure the thickness of the blacksubstrate point and record as t0in the indicated location of
37、 therelevant work sheet in the form of a table (see 7.1).NOTE 6The black substrate is always thicker than the white by anamount t0that is determined for each panel.NOTE 7With thickness gages capable of dual calibration, calibratealso to zero on the black substrate point and store both the white and
38、blackcalibrations.8.5 Measure the coating reflectance of one panel for eachtest coating, at a location of visually complete opacity. Recordthis value as the reflectivity Rof the coating, in the indicatedlocation of the work table.9. Procedure and CalculationsTest Method A, PercentContrast Ratio (CW)
39、 at a Given Film Thickness9.1 Use Fig. 3 for entries in this test method.9.2 Record the thickness (T) for which the contrast ratio isto be determined.NOTE 8For significance and adequate sensitivity, the thickness shouldbe such that the mean contrast ratio is not much over 98 % and preferablyless.9.3
40、 Enter the value T8 as the reading on the black substratecorresponding to the coating thickness T.(T8 =T+t0).9.4 Find and encircle five pairs of points over the black andthe white substrates, where the powder coating is at thespecified thickness T.9.5 Measure the reflectances of each pair of points
41、and enterin the ROand RWcolumns of the table, then calculate thecontrast ratio (CW= 100 RO/RW) for each pair.NOTE 9Some reflectance instruments can measure the contrast ratiodirectly. In that case, pair the equal-thickness points randomly for contrastratio measurements and record values.9.6 Calculat
42、e and record the mean contrast ratio CWforeach panel, and then the grand mean for all panels.10. Procedure and CalculationsTest Method B, FilmThickness (T98) at 98 % Contrast Ratio10.1 Use Fig. 4 for entries in this test method.10.2 Encircle five points in the coated black-substrate areaat locations
43、 where the contrast ratio varies up to about 98 % asFIG. 3 Work Table for Test Method AD6441054recognized visually by familiarity with past results, or bycomparison with a previously prepared visual standard.10.3 Measure the thickness value T8 of each of the fiveencircled points, and subtract t0from
44、 each value to obtain thetrue thickness T of the powder coating at those points.10.4 For each of the points located in 10.3, locate andencircle a point of equal powder coating thickness in thewhite-substrate area.NOTE 10Since the gage is calibrated to zero on the white substrate,the gage reading her
45、e needs no correction.10.5 For each pair of equal thickness points, measure andrecord the reflectances R0and RW, then calculate and recordCW= 100 R0/RW. Do not search for 98 % contrast ratio pairs.NOTE 11With instruments that can measure the contrast ratio directly,reflectances need not be measured.
46、10.6 Plot CWversus film thickness (T) on suitable graphpaper, (see Fig. 5) then draw the best-fit straight line, and selectthe best graph-point for T98.NOTE 12Do not plot graph-points outside the contrast ratio range of96.5 to 98.5 %. If the plotted points do not give an adequate indication ofT98, l
47、ocate and plot additional equal thickness pairs.10.7 Enter into the table the T98value for each panel, andthe grand mean for all panels.11. Report11.1 Report the following information:11.1.1 The identity of the subject coating,11.1.2 The cure conditions employed for the test panels,11.1.3 Test Metho
48、d A: Contrast ratio _% at film thick-ness of _micrometers (_mils),11.1.4 Test Method B: Film thickness (T98) at 98 % Con-trast Ratio _micrometers (_mils),11.1.5 Reflectivity (R) of the coating _%,11.1.6 General color and gloss description (for example,light green semi-gloss), and11.1.7 Reflectometer
49、 Descriptionmanufacturer, model,aperture size, and shape, bidirectional or spherical, and anyother measurement parameters deemed significant.12. Precision and Bias12.1 PrecisionIn an inter-laboratory study of Test Meth-ods A and B, operators in 5 different laboratories measured 3test coatings differing in color and reflectivity. The coatingswere applied in quadruplicate in accordance with the specifiedapplication procedure common to both methods, whereby eachof the resultant 12 coated test panels presented a range
