ASTM_D_6441_-_05_2016.pdf

Designation:D644105(Reapproved 2016)Standard Test Methods forMeasuring the Hiding Power of Powder Coatings1This standard is issued under the fixed designation D6441;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 parentheses indicates the year of last reapproval.Asuperscript epsilon()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 Ratio at a given film thick-ness1.1.2 Test Method BFilm thickness at 0.98(98%)con-trast ratio.NOTE1The measured parameters follow powder coating industrypractice by measuring hiding power in relation to film thickness,ratherthan the“Spreading Rate”function employed in Test Methods D344 andD2805 and other hiding power test methods.NOTE2Hiding power is photometrically defined as the spreading rateat 0.98 contrast ratio.See definitions of spreading rate and hiding powerin Terminology D16,D2805,and the Paint and Coatings Testing Manual.NOTE3The contrast ratio 0.98 is conventionally accepted 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 electrostaticspraying.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 informationonly.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 use.2.Referenced Documents2.1 ASTM Standards:2D16 Terminology for Paint,Related Coatings,Materials,andApplicationsD344 Test Method for Relative Hiding Power of Paints bythe Visual Evaluation of BrushoutsD2805 Test Method for Hiding Power of Paints by Reflec-tometryD3451 Guide for Testing Coating Powders and PowderCoatingsE284 Terminology of AppearanceE1331 Test Method for Reflectance Factor and Color bySpectrophotometry 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)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 reflectance,nterm of wide applicability,referringherein to the luminous reflectance factor as defined in Termi-nology E284,and equivalent to the CIE Tristimulus value Ymeasured in accordance with Test Methods E1331,E1347 orTest Method E1349 with specular reflection excluded.It isexpressed as a percentage in this standard.3.1.2 white substrate,nFor purposes of this test,a sub-strate of neutral shade with a minimum reflectance of 78%.1These test methods are under the jurisdiction of ASTM Committee D01 onPaint and Related Coatings,Materials,and Applications and are the directresponsibility of Subcommittee D01.51 on Powder Coatings.Current edition approved April 1,2016.Published April 2016.Originallyapproved in 1999.Last previous edition approved in 2010 as D6441 10.DOI:10.1520/D6441-05R16.2For 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 General Standards Board,(CGSB),222 Queen St.,Ottawa,Ont.,Canada K1A 1G6.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.3 black substrate,nA substrate with a maximumreflectance of 1%,which is effectively zero for the purpose ofmeasuring hiding power.3.1.4 white reflectance(RW),nReflectance of the appliedtest film over a white substrate of reflectance W.3.1.5 black reflectance(Ro),nReflectance of the appliedtest film over a black substrate.3.1.6 reflectivity(R),nThe reflectance of a coating ap-plied thickly enough to be completely opaque,as evidenced byequal reflectance over the black and a white test substrate.3.1.7 contrast ratio(CW),n(1)The ratio of the reflectanceof a film applied on a black substrate to a film of equalthickness applied on a white substrate.(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 thes