ASTM_D_5861_-_07_2013.pdf

Designation:D586107(Reapproved 2013)Standard Guide forSignificance of Particle Size Measurements of CoatingPowders1This standard is issued under the fixed designation D5861;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 This guide covers the significance of referencing thetechniques used whenever specifying the particle size distribu-tion of a coating powder.2.Referenced Documents2.1 ASTM Standards:2D1921 Test Methods for Particle Size(Sieve Analysis)ofPlastic MaterialsD3451 Guide for Testing Coating Powders and PowderCoatings3.Terminology3.1 Definitions:3.1.1 coating powders,nthese are finely divided particlesof organic polymer that generally contain pigments,fillers,andadditives and that remain finely divided during storage undersuitable conditions.3.1.2 powder coatings,nthese are coatings that areprotective,decorative,or both;and that are formed by theapplication of a coating powder to a substrate and fused intocontinuous films by the application of heat or radiant energy.4.Significance and Use4.1 This guide describes the need to specify the measuringtechnique used whenever quoting the particle size distributionof a coating powder.4.2 This guide is for use by manufacturers of coatingpowders and by specifiers for process control and productacceptance.5.Particle Size of Coating Powders5.1 The size of the particles comprising a coating powderplays a critical role in the fluidization,application,and recla-mation of the powder,and in the final appearance of the coatedpart.Coating powders are comprised of particles of widelydiffering sizes,from as low as about 1 m to as high as about150 m.Collectively,the individual particles form a sizedistribution,defined by the percentages of particles present ofa given size or within a given size range.There are generallyfew particles at the low and high ends of the distribution,themajority being in the 25 to 65-m range.The distribution canbe described by an actual plot of the particle size distribution,or by numerical attributes of the distribution,such as thecalculated values of its mean,median,mode,and span.Themean represents the average particle size(the sum of all theparticle sizes divided by the number of particles).The medianrepresents a size such that half the particles are larger than itand half the particles are smaller than it.The mode representsthe most frequently occurring particle size.For all coatingpowders these three figures are numerically different.The spanis an indication of the width of the particle size distribution.Referring to Table A1.1,the span is calculated by subtractingthe d10 from the d90 and then dividing by the d50 or medianparticle size.5.2 The particle size distribution is generally chosen by thecoating powder manufacturer from knowledge of the applica-tion technique,the required cured film thickness,surfaceappearance,and performance.Once the desired particle sizedistribution has been selected,it needs to be monitored toensure consistency from batch to batch and,indeed,withineach batch.Occasionally the coating powder applicator mayspecify the particle size from knowledge of the specificapplication equipment or customer requirements,or both.5.3 It is important for all involved to understand that thenumerical data comprising a particle size distribution aresignificantly dependent on the technique used to obtain them.Itis,therefore,of little use to quote or specify a particle sizedistribution,and even less a single particle size,without alsodefining the technique used to obtain that measurement,or,ifa single size,whether it is,for example,the mean,median ormodal value.1This guide is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.51 on Powder Coatings.Current edition approved June 1,2013.Published July 2013.Originally approvedin 1995.Last previous edition approved in 2007 as D5861 07.DOI:10.1520/D5861-07R13.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.Measurement of Particle Size6.1 There are a wide variety of instruments currently avail-able for measuring the particle size distributions of coatingpowders.Actual sieving,such as described in Test MethodsD1921,where the percentage weight of coating powder re-tained on sieves of known mesh size is measured,is relativelyinexpensive and direct.It is,however,significantly slower thanindirect measurement techniques,such as laser scattering andelectr