ASTM D5861-95

Standard Guide for Significance of Particle Size Measurements of Coating Powders

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

• Status: Historical
• Publication Date: 31-Dec-1994
• Technical Committee: D01 - Paint and Related Coatings, Materials, and Applications
• Drafting Committee: D01.51 - Powder Coatings

Standards Content (Sample)

ASTM D5BbL 95 - 0759510 0579338 45L m
AMERICAN SOCIETY FOR TESTING AND MATERIALS
Designation: D 5861 - 95
100 Barr Harbor Dr., West Conshohocken, PA 19428
RePrinW from the Annual Book of ASTM Standards. Copyright ASTM
If not listed !n the current combined index, will appear in the next edition.
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 (c) indicates an editorial change since the last revision or reapproval.
The distribution can be described by an actual plot of the
1. Scope
particle size distribution, or by numerical attributes of the
1.1 This guide covers the significance of referencing the
distribution, such as the calculated values of its mean,
techniques used whenever specifying the particle size distri-
median or mode. The mean represents the average particle
bution of a coating powder.
size (the sum of all the particle sizes divided by the number
of particles). The median represents a size such that half the
2. Referenced Documents
particles are larger than it and half the particles are smaller
2.1 ASTM Standards:
than it. The mode represents the most frequently occurring
D 192 1 Test Method for Particle Size (Sieve Analysis) of
particle size. For all coating powders these three figures are
Plastic Materials2
numerically different.
D 3451 Practices for Testing Polymeric Powders and
5.2 The particle size distribution is generally chosen by
Powder Coatings3
the coating powder manufacturer from knowledge of the
application technique, the required cured film thickness,
3. Terminology
surface appearance, and performance. Once the desired
3.1 Definitions: particle size distribution has been selected, it needs to be
3.1.1 coating powders-these are finely divided particles monitored to ensure consistency from batch to batch and,
of organic polymer that generally contain pigments, fillers,
indeed, within each batch. Occasionally the coating powder
and additives and that remain finely divided during storage
applicator may specify the particle size from knowledge of
under suitable conditions.
the specific application equipment or customer require-
3.1.2 powder coatings-these are coatings that are protec-
ments, or both.
tive, decorative, or both; and that are formed by the
5.3 It is important for all involved to understand that the
application of a coating powder to a substrate and fused into numerical data comprising a particle size distribution are
continuous films by the application of heat or radiant energy. significantly dependent on the technique used to obtain
them. It is, therefore, of little use to quote or specify a
4. Significance and Use
particle size distribution, and even less a single particle size,
without also defining the technique used to obtain that
4.1 This guide describes the need to specify the measuring
measurement, or, if a single size, whether it is, for example,
technique used whenever quoting the particle size distribu-
the mean, median or modal value.
tion of a coating powder.
4.2 This guide is for use by manufacturers of coating
6. Measurement of Particle Size
powders and by specifiers for process control and product
6.1 There are a wide variety of instruments currently
acceptance.
available for measuring the particle size distributions of
coating powders. Actual sieving, such as described in Test
5. Particle Size of Coating Powders
Method D 1921, where the percentage weight of coating
5.1 The size of the particles comprising a coating powder
powder retained on sieves of known mesh size is measured, is
plays a critical role in the fluidization, application, and
relatively inexpensive and direct. It is, however, significantly
reclamation of the powder, and in the final appearance of the
slower than indirect measurement techniques, such as laser
coated part. Coating powders are comprised of particles of
scattering and electrolytic conductivity, such as described in
widely differing sizes, from as low as about 1 pm to as high as
Practices D 345 1. With indirect measurement techniques, a
about 150 pm. Collectively, the individual particles form a
secondary effect, induced by the presence of the coating
size distribution, defined by the percentages of particles
powder particles, is measured, such as changes in light
present of a given size or within a given size range. There are
scattering or in the conductivity of an electrolyte. These
generally few particles at the low and high ends of the
effects are analyzed using a specific theoretical algorithm,
distribution, the majority being in the 25 to 65-pm range.
unique to the measurement technique, and the particle size
distribu
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