ASTM D5861-95(2002)

Designation: D 5861 – 95 (Reapproved 2002)
Standard Guide for
Significance of Particle Size Measurements of Coating
Powders
This standard is issued under the fixed designation D 5861; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 150 μm. Collectively, the individual particles form a size
distribution, defined by the percentages of particles present of
1.1 This guide covers the significance of referencing the
a given size or within a given size range. There are generally
techniques used whenever specifying the particle size distribu-
few particles at the low and high ends of the distribution, the
tion of a coating powder.
majority being in the 25 to 65-μm range. The distribution can
2. Referenced Documents be described by an actual plot of the particle size distribution,
or by numerical attributes of the distribution, such as the
2.1 ASTM Standards:
calculated values of its mean, median or mode. The mean
D 1921 Test Methods for Particle Size (Sieve Analysis) of
represents the average particle size (the sum of all the particle
Plastic Materials
sizes divided by the number of particles). The median repre-
D 3451 Guide for Testing Coating Powders and Powder
sents a size such that half the particles are larger than it and half
Coatings
the particles are smaller than it. The mode represents the most
3. Terminology
frequently occurring particle size. For all coating powders
these three figures are numerically different.
3.1 Definitions:
5.2 The particle size distribution is generally chosen by the
3.1.1 coating powders—these are finely divided particles of
coating powder manufacturer from knowledge of the applica-
organic polymer that generally contain pigments, fillers, and
tion technique, the required cured film thickness, surface
additives and that remain finely divided during storage under
appearance, and performance. Once the desired particle size
suitable conditions.
distribution has been selected, it needs to be monitored to
3.1.2 powder coatings—these are coatings that are protec-
ensure consistency from batch to batch and, indeed, within
tive, decorative, or both; and that are formed by the application
each batch. Occasionally the coating powder applicator may
of a coating powder to a substrate and fused into continuous
specify the particle size from knowledge of the specific
films by the application of heat or radiant energy.
application equipment or customer requirements, or both.
4. Significance and Use
5.3 It is important for all involved to understand that the
numerical data comprising a particle size distribution are
4.1 This guide describes the need to specify the measuring
significantly dependent on the technique used to obtain them. It
technique used whenever quoting the particle size distribution
is, therefore, of little use to quote or specify a particle size
of a coating powder.
distribution, and even less a single particle size, without also
4.2 This guide is for use by manufacturers of coating
defining the technique used to obtain that measurement, or, if
powders and by specifiers for process control and product
a single size, whether it is, for example, the mean, median or
acceptance.
modal value.
5. Particle Size of Coating Powders
6. Measurement of Particle Size
5.1 The size of the particles comprising a coating powder
6.1 There are a wide variety of instruments currently avail-
plays a critical role in the fluidization, application, and recla-
able for measuring the particle size distributions of coating
mation of the powder, and in the final appearance of the coated
powders. Actual sieving, such as described in Test Methods
part. Coating powders are comprised of particles of widely
D 1921, where the percentage weight of coating powder
differing sizes, from as low as about 1 μm to as high as about
retained on sieves of known mesh size is measured, is
relatively inexpensive and direct. It is, however, significantly
This guide is under the jurisdiction of ASTM Committee D01 on Paint, and
slower than indirect measurement techniques, such as laser
Related Coatings, Materials, and Applications and is the direct responsibility of
scattering and electrolytic conductivity, such as described in
Subcommittee D01.51 on Powder Coatings.
Current edition approved Nov. 10, 1995. Published January 1996.
Guide D 3451. With indirect measurement techniques, a sec-
Annual Book of ASTM Standards, Vol 08.01.
ondary effect, induced by the presence of the coating powder
Annual Book of ASTM Standards, Vol 06.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5861
particles, is measured, such as changes in light scattering or in 7.3 It can be seen that there are distinct differences between
the conductivity of an electrolyte. These effects are analyzed the data acquired by different techniques, and by the same
using a specific theoretical algorithm, unique to the measure- technique when the machine manufacturer or model is
ment technique, and the particle size distribution calculated changed. There are even differences when instruments with the
that would cause the measured changes. Various other statisti- same model number are used in different laboratories.
cal data on the distributions, such as the mean, the median, and 7.4 It must be emphasized that these data are not presented
the mode 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
actually possess. Others require the preparation of a suspension 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
8. Measurement Techniques Used
required processing for dry powder measurement techniques
8.1 Agitated Sieving, Dry Sampling
could mechanically break up larger particles or agglomerates
8.2 Electrolyte Conductivity, Wet Sampling
into smaller ones, or both.
8.3 Laser Scattering, Dry Sampling
6.3 Thus not only can the theoretical algorithms for the
8.4 Laser Scattering, Wet Sampling
measuring techniques be quite different, but each measurement
8.5 Sedimentation/X-Ray Absorption, Wet Sampling
technique can cause the particle size distribution to change
8.6 Mercury Porosimetry, Dry Sampling
during sample preparation or the measurement process itself,
8.7 Note that some of the instruments were used indepen-
or both. This simply serves to emphasize that once a measure-
dently of each other, and by more than one participant.
ment technique has been selected, there is still need for
consistency in all aspects of its operation.
9. Keywords
9.1 coating powder; electroconductivity; laser scattering;
7. Effect of Using Different Measurement Techniques
mercury porosimetry; particle size analysis; powder coating;
7.1 To illustrate the numerical differences in measured
sedimentation; sieve analysis; X-ray
particle size that can be found when different measurement
techniques are used, the same coating powder was provided to
Jet sieve available from Alpine American Corporation, 5, Michigan Drive,
a number of participants, who measured the particle size of the
Natick, MA 01760, and Sonic Sifter Separator Model L3P available from ATMt
Corporation, 645 S94th Place, Milwaukee, WI 53214 have been found suitable for
sample, usually in triplicate, using their own preferred tech-
this purpose.
nique. Participants included coating powder manu
...