ASTM D5861-07(2013)
(Guide)Standard Guide for Significance of Particle Size Measurements of Coating Powders
Standard Guide for Significance of Particle Size Measurements of Coating Powders
SIGNIFICANCE AND USE
4.1 This guide describes the need to specify the measuring technique used whenever quoting the particle size distribution of a coating powder.
4.2 This guide is for use by manufacturers of coating powders and by specifiers for process control and product acceptance.
SCOPE
1.1 This guide covers the significance of referencing the techniques used whenever specifying the particle size distribution of a coating powder.
General Information
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Standards Content (Sample)
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Designation:D5861 −07 (Reapproved 2013)
Standard Guide for
Significance of Particle Size Measurements of Coating
Powders
This standard is issued under the fixed designation D5861; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 5. Particle Size of Coating Powders
1.1 This guide covers the significance of referencing the
5.1 The size of the particles comprising a coating powder
techniques used whenever specifying the particle size distribu-
plays a critical role in the fluidization, application, and recla-
tion of a coating powder.
mation of the powder, and in the final appearance of the coated
part. Coating powders are comprised of particles of widely
2. Referenced Documents
differing sizes, from as low as about 1 µm to as high as about
150 µm. Collectively, the individual particles form a size
2.1 ASTM Standards:
distribution, defined by the percentages of particles present of
D1921 Test Methods for Particle Size (Sieve Analysis) of
a given size or within a given size range. There are generally
Plastic Materials
few particles at the low and high ends of the distribution, the
D3451 Guide for Testing Coating Powders and Powder
majority being in the 25 to 65-µm range. The distribution can
Coatings
be described by an actual plot of the particle size distribution,
or by numerical attributes of the distribution, such as the
3. Terminology
calculated values of its mean, median, mode, and span. The
3.1 Definitions:
mean represents the average particle size (the sum of all the
3.1.1 coating powders, n—these are finely divided particles
particle sizes divided by the number of particles). The median
of organic polymer that generally contain pigments, fillers, and
represents a size such that half the particles are larger than it
additives and that remain finely divided during storage under
and half the particles are smaller than it. The mode represents
suitable conditions.
the most frequently occurring particle size. For all coating
3.1.2 powder coatings, n—these are coatings that are
powders these three figures are numerically different. The span
protective, decorative, or both; and that are formed by the
is an indication of the width of the particle size distribution.
application of a coating powder to a substrate and fused into
Referring to Table A1.1, the span is calculated by subtracting
continuous films by the application of heat or radiant energy.
the d10 from the d90 and then dividing by the d50 or median
particle size.
4. Significance and Use
5.2 The particle size distribution is generally chosen by the
4.1 This guide describes the need to specify the measuring
coating powder manufacturer from knowledge of the applica-
technique used whenever quoting the particle size distribution
tion technique, the required cured film thickness, surface
of a coating powder.
appearance, and performance. Once the desired particle size
distribution has been selected, it needs to be monitored to
4.2 This guide is for use by manufacturers of coating
ensure consistency from batch to batch and, indeed, within
powders and by specifiers for process control and product
each batch. Occasionally the coating powder applicator may
acceptance.
specify the particle size from knowledge of the specific
application equipment or customer requirements, or both.
This guide is under the jurisdiction of ASTM Committee D01 on Paint and 5.3 It is important for all involved to understand that the
Related Coatings, Materials, and Applications and is the direct responsibility of
numerical data comprising a particle size distribution are
Subcommittee D01.51 on Powder Coatings.
significantlydependentonthetechniqueusedtoobtainthem.It
CurrenteditionapprovedJune1,2013.PublishedJuly2013.Originallyapproved
is, therefore, of little use to quote or specify a particle size
in 1995. Last previous edition approved in 2007 as D5861 – 07. DOI: 10.1520/
D5861-07R13.
distribution, and even less a single particle size, without also
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
defining the technique used to obtain that measurement, or, if
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
a single size, whether it is, for example, the mean, median or
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. modal value.
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D5861−07 (2013)
6. Measurement of Particle Size 7.2 The data obtained can be found in AnnexA1 and Annex
A2. They have been transposed into two respective standard
6.1 There are a wide variety of instruments currently avail-
formats for ease of comparison. Where possible, additional
able for measuring the particle size distributions of coating
numerical data were extracted from the original plots of
powders. Actual sieving, such as described in Test Methods
particle size distribution. In these instances, such figures are
D1921, where the percentage weight of coating powder re-
enclosed in parentheses in Annex A1 (see Figs. A1.1-A1.14).
tained on sieves of known mesh size is measured, is relatively
Some of the original plots of particle size distribution were
inexpensive and direct. It is, however, significantly slower than
replotted for clarity, with a consistent ordinate and abscissa, of
indirect measurement techniques, such as laser scattering and
“percentage of particles in a given range” and “log (particle
electrolytic conductivity, such as described in Guide D3451.
size in µm)” respectively. These standardized distributions
With indirect measurement techniques, a secondary effect,
constitute Figs. A1.1-A1.14.
induced by the presence of the coating powder particles, is
measured, such as changes in light scattering or in the
7.3 It can be seen that there are distinct differences between
conductivity of an electrolyte. These effects are analyzed using
the data acquired by different techniques, and by the same
a specific theoretical algorithm, unique to the measurement
technique when the machine manufacturer or model is
technique, and the particle size distribution calculated that
changed.There are even differences when instruments with the
would cause the measured changes. Various other statistical
same model number are used in different laboratories.
data on the distributions, such as the mean, the median, the
7.4 It must be emphasized that these data are not presented
mode, and the span are also often automatically calculated.
in order to recommend one measurement technique over
6.2 Secondary measurement techniques make assumptions
another, or one participating piece of equipment over another
such as the measured particles being spherical, and do not
nonparticipating piece of equipment, but rather to clearly
acknowledge the fractured, randomized shapes the particles
illustrate the necessity of defining how a size measurement is
actuallypossess.Othersrequirethepreparationofasuspension
obtained when quoting any numerical value regarding particle
of the particles in a liquid, which could alter the physical state
size.
of particle agglomerates present in the dry state. Even the
required processing for dry powder measurement techniques
8. Measurement Techniques Used
could mechanically break up larger particles or agglomerates
8.1 Agitated Sieving, Dry Sampling
into smaller ones, or both.
8.2 Electrolyte Conductivity, Wet Sampling
6.3 Thus not only can the theoretical algorithms for the
measuring
...
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