1、Designation: D2805 11Standard Test Method forHiding Power of Paints by Reflectometry1This standard is issued under the fixed designation D2805; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in
2、parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.INTRODUCTIONUsing equations derived from Kubelka-Munk turbid media theory (1
3、-4)2(see Annex A1), thereflectance of a coating can be predicted for any film thickness from measurements made at only one.On this basis several rapid and accurate test methods (5, 6) have been developed for determininghiding power. In the past such test methods have been considered difficult due to
4、 complexities,apparent and actual, in the treatment of data. The present test method has been simplified in thisrespect, primarily by adapting it fully for computer calculations.Although the use of broad-band reflectometry makes this test method theoretically valid only fornonchromatic (white or gra
5、y) colors, good agreement has been obtained with chromatic paints as well.This is undoubtedly because the experimental measurements are made fairly close to the hiding powerend point so that the Kubelka-Munk extrapolation and thus any associated error is relatively small.This test method is therefor
6、e recommended without restriction as to color.1. Scope1.1 This test method covers the determination, withoutreference to a material paint standard, of the hiding power ofair dry coatings with Y tristimulus values greater than 15 %.With appropriate modification, it can also be used to testbaking fini
7、shes.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 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
8、 appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D344 Test Method for Relative Hiding Power of Paints bythe Visual Evaluation of BrushoutsD1475 Test Method For Density of Liquid Coatings, Inks
9、,and Related ProductsD3924 Specification for Environment for Conditioning andTesting Paint, Varnish, Lacquer, and Related MaterialsE284 Terminology of AppearanceE1247 Practice for Detecting Fluorescence in Object-ColorSpecimens by SpectrophotometryE1331 Test Method for Reflectance Factor and Color b
10、ySpectrophotometry Using Hemispherical GeometryE1347 Test Method for Color and Color-Difference Mea-surement by Tristimulus ColorimetryE1349 Test Method for Reflectance Factor and Color bySpectrophotometry Using Bidirectional (45:0 or 0:45)Geometry3. Terminology3.1 DefinitionsFor definitions used in
11、 this test method,see Terminology E284.3.2 Definitions of Terms Specific to This Standard:3.2.1 contrast ratio, nthe ratio of the reflectance of a filmon a black substrate to that of an identical film on a whitesubstrate.1This test method is under the jurisdiction of ASTM Committee D01 on Paintand R
12、elated Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.26 on Optical Properties.Current edition approved June 1, 2011. Published June 2011. Originallyapproved in 1969. Last previous edition approved in 2003 as D2805 96a (2003).DOI: 10.1520/D2805-11.2The bold
13、face numbers in parentheses refer to the list of references at the end ofthis standard.3For 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 Summar
14、y page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.1.1 CW,nthe contrast ratio with a white substrate ofreflectance W.Thus: CW5 R0/RW3.2.1.2 C, nthe contrast ratio with a white substrate forwhich W = 0.80.Th
15、us: C 5 R0/R0.803.2.2 reflectance, nthe daylight luminous diffuse reflec-tance factor (specular reflection excluded). Also referred to inthis test method as the Y-tristimulus value. This value may beexpressed as a percent or a decimal fraction, the latter beingpreferred and usually required for math
16、ematical calculations.3.2.2.1 reflectivity, R,nthe reflectance of film thickenough to have the same reflectance over both a black and awhite substrate.3.2.2.2 R0,nthe reflectance of a film on a black surfacewith a reflectance of 1 % or less, which is effectively zero forthe purpose of this test.3.2.
17、2.3 W, nthe reflectance of a white substrate.3.2.2.4 RW,nthe reflectance of a film applied on a whitesubstrate of reflectance W.3.2.2.5 R0.80,nthe reflectance of a film applied on asubstrate having a reflectance of 80 %, which is the standardwhite-substrate reflectance in paint technology.3.2.3 scat
18、tering coeffcient, S, nthe ability of a material tointernally scatter and thereby reflect light; expressed in this testmethod in the same units as spreading rate.3.2.4 spreading rate, H, nfilm area per unit volume ofcoating, in this test method expressed in square metres per litre(m2/L).3.2.4.1 spre
19、ading rate, HX,nan experimentally deter-mined value of H.3.2.4.2 spreading rate, HC,nvalue of H at a specifiedcontrast ratio C.3.2.4.3 hiding power, H0.98,nthe spreading rate at thecontrast ratio C = 0.98.NOTE 1It should be emphasized that a contrast ratio of 0.98 does notrepresent visually complete
20、 hiding, nor does it indicate that the samecontrast ratio holds at every wavelength.4. Summary of Test Method4.1 The reflectivity Rof the coating is determined fromreflectance measurements on black and white hiding powercharts.4.2 The scattering coefficient S of the coating is determinedfrom R, and
21、the reflectance R0and spreading rate HXof a filmapplied on black glass.4.3 The hiding power, H0.98of the coating is calculatedfrom the reflectivity Rand the scattering coefficient S.4.4 As an optional procedure the contrast ratio C at aspecified spreading rate HCis calculated from Rand S.5. Signific
22、ance and Use5.1 This is a precise instrumental method giving resultshaving an absolute physical significance without reference to acomparison paint. It should be used when maximum precisionand minimum subjectivity are required, as in testing specifica-tion coatings or evaluating the hiding efficienc
23、y of pigments.5.2 Hiding power Test Method D344 is visual instead ofinstrumental, and gives results that are relative to a materialstandard instead of absolute. It is less precise than Test MethodD2805 but more closely aligned with practical painting proce-dures.6. Apparatus and Materials6.1 Substra
24、tes:6.1.1 Black Glass Panels, minimum size 200 by 200 mm,and approximately 6-mm thick.6.1.2 Black and White Paper ChartsThe surface shall besmooth and level, and impervious to paint liquids. The blackarea shall have a maximum reflectance of 1 % and the whitearea a minimum reflectance of 78 %. The wh
25、ite area shall benon-fluorescent, as observed visually under ultra-violet illumi-nation, or determined in accordance with Practice E1247.6.2 Balance, accurate to 0.1 mg.6.3 Glass SlidesRound or square plates of thicknesssimilar to that used for microscope specimen slides, with aminimum area of 40 cm
26、2.6.4 Reflectance-Measuring Instrument4One that allowsonly diffusely reflected, radiant flux to be incident upon themeasuring element. It shall employ a photometric system,including source, filters, and receptor, that provides a responseclosely similar to the product of the spectral luminous effi-ci
27、ency function of the CIE standard observer and source C.Itshall provide readings to at least the third decimal place andpermit estimation to the fourth.6.5 Template,5with a film area approximately 100 cm2determined to the nearest tenth. Record the exact value on LineC of the worksheet shown in Fig.
28、1.6.6 Doctor Blade Film Applicators, width 150 mm, clear-ances 50, 75, 100, 125, 150, 175, and 200 m.6.7 Computer and Software, for solving the relevantKubelka-Munk equations.7. Procedure7.1 General Instructions:7.1.1 Film ApplicationMake drawdowns manually with asmooth uniform motion, at the rate o
29、f about 6 cm/s. Hold papercharts flat by a vacuum plate or other suitable device whilemaking drawdowns.7.1.2 Reflectance MeasurementsMeasure the reflectanceof each test area at a minimum of three locations, reading orestimating to four decimal places and calculating mean valuesto the same. Place cha
30、rts over a white surface and black glassover a black surface while measurements are being made.4Conforming with Test Methods E1331, E1347,orE1349. Other methods formeasuring the CIE-Y tristimulus value (specular reflection excluded) are permis-sible.5The sole source of supply of the template known t
31、o the committee at this timeis Paul Gardner Co., 316 N. E. First St., Pompano Beach, FL33061. If you are awareof alternative suppliers, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committ
32、ee,1which you may attend.D2805 1127.1.3 Record KeepingRecord all data on a copy of theworksheet form specified in Fig. 1. Typical data entries areshown in Fig. 2.7.1.4 Weight MeasurementsMake all weighings to 0.1 mgon the analytical balance.7.2 Paint density, DDetermine the density in g/mL to fourde
33、cimal places in accordance with Test Method D1475 andrecord on Line A of the worksheet (Fig. 1).7.3 Nonvolatile Content, NSandwich 0.3 mL of paint(dispensed with a 1-mL syringe) between two previouslyweighed slides, squeezing them together so that the paintspreads to a diameter of about 45 mm. Rewei
34、gh to obtain theweight of paint sample. Separate the slides, allow the films todry, and weigh a third time to determine the dry weight. Thencalculate the nonvolatile content of the paint as a decimalfraction to four places. Run in duplicate and report the meanvalue to three decimal places on Line B
35、of the worksheet (Fig.1).7.4 Applicator SelectionMake trial drawdowns on blackand white charts at clearances of 100, 150, and 200 m. Allowthem to dry overnight and measure their contrast ratios. Basedon the results select the best applicator for a contrast ratio of0.97 6 0.01, which may be one of th
36、e trial applicators or oneof intermediate clearance. If it seems necessary, make anadditional trial drawdown to confirm the correct applicator.7.5 Drawdowns on Glass and Charts Using the applicatorselected from 7.4, make four drawdowns each on black glassand on black and white charts in accordance w
37、ith 7.1.1. Leaveenough of the white area of each chart uncoated to permitmeasurement of the reflectance W.7.6 Drying of the FilmsImmediately after applicationplace each drawdown horizontally in a well-ventilated dust-free location, with all drawdowns in close proximity to oneanother to assure identi
38、cal drying conditions, and allow to drya minimum of 40 h before testing. Drying conditions for filmFIG. 1 Work Sheet FormD2805 113applications and nonvolatile determinations shall be the same,and in accordance with Specification D3924.7.7 Reflectance MeasurementsOn the second or third dayafter appli
39、cation measure the reflectances on all of the draw-downs within as brief a time span as possible, alternating themeasurements between charts and glass rather than doing firstall one and then the other. Enter the values of R0, RW, and W forcharts into Section D of the worksheet, and the values of R0f
40、orglass into Section E.7.8 Weight of Dry Film, MAfter all of the reflectances aremeasured, position the template on the glass panels, each in itsturn, and scrape off the surplus paint with a razor blade, toleave film areas defined by the template. If the template area isnot already specified, measur
41、e one of the resultant filmscarefully to determine its area in square centimeters to thenearest tenth. Record this value on Line C of the worksheet(Fig. 1) as the characteristic area of the template. Then scrapeoff each paint film carefully into a weighing dish, weigh to 0.1mg, and record the weight
42、s M in Section E of the worksheet,entering each weight adjacent to the value of R0for the sameglass panel.8. Calculation8.1 In general, make the calculations and record to foursignificant figures and final report values to three. Entercalculated results in the worksheet (Fig. 1). Typical entries are
43、shown in Fig. 2.8.2 Contrast Ratio CWand Reflectivity RFrom the dataentered in Section D of the worksheet calculate CWand Rforeach of the four charts, thus:CW5 R0/RW(1)R5 fR0, RW, W!Enter the values, as they are calculated, in the appropriatecolumns of Section D, then calculate and likewise enter th
44、eirmeans.FIG. 2 Typical Work SheetD2805 1148.3 Spreading Rate HXFrom the data recorded in theworksheet on Lines A, B, and C and in Section E, calculate thespreading rate Hxfor each of the four glass panels, thus:HX5A 3 N 3 D10Mwhere:HX= spreading rate, m2/L,A = template area, cm2,N = nonvolatile con
45、tent of the paint,D = density of the paint, g/mL, andM = dry film weight, g.and enter the values in the appropriate column of Section E.8.4 Scattering Coeffcient S and Hiding Power H0.98Continuing on Section E of the worksheet (see Fig. 1), andusing the mean value of Rfrom Section D, calculate for e
46、achof the glass panels, first S and then H0.98in square millimetresper litre as follows:S 5 fR0, R, HX! (2)H0.985 fS, C, R! given C 5 0.98 (3)Enter the values as they are calculated in the appropriatecolumns of Section E, then calculate and likewise enter theirmeans.8.5 Contrast Ratio C at a Specifi
47、ed Spreading Rate HIfdesired, calculate the contrast ratio at a specified spreading rateusing the mean values of Rand S from worktable Sections Dand E, of the worksheet (Fig. 1), thus:C 5 fS, H, R! (4)9. Report9.1 Enter the following information on the indicated line inFig. 1, Section G:9.1.1 Hiding
48、 Power, H0.98Enter the mean value of H0.98from Section E, rounded to the second decimal place, onto LineG (1). If desired, multiply this value by 40.746 to obtain thevalue in square feet per gallon to the nearest whole number andenter it on the same line.9.1.2 Reflectivity, REnter the mean value of
49、RfromSection D, rounded to three significant figures, onto Line G (2).9.1.3 Scattering Coeffcient, SEnter the mean value of Sfrom Section E, rounded to three significant figures, onto LineG (3).9.1.4 Applicator ClearanceOn Line G (4) enter the clear-ance of the applicator, expressed in m and if desired also inmils.9.1.5 Contrast Ratio, CW Enter the mean value of CWfrom Section D, rounded to the third decimal place, onto LineG (5).9.1.6 On Line G (6) enter the identification and briefdescription of the coating.9.
