ASTM D8331/D8331M-20

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D8331/D8331M − 20
Standard Test Method for
Measurement of Film Thickness of Thin-Film Coatings by
Non-Destructive Means Using Ruggedized Optical
Interference
This standard is issued under the fixed designation D8331/D8331M; 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 2.3 ruggedized optical interference (ROI), n—a term used to
distinguish this instrument that is suitable for use in an
1.1 This test method encompasses measuring the film thick-
industrial environment from other optical interference devices
ness of a coil coated organic coating layer. Operators can use
that are only suitable for use in a laboratory environment.
this method in process during the coating application or in a
laboratory setting. 2.4 supplier, n—the organization or person contracted to
supply the coil coated material who may or may not be the
1.2 This test method does not specify the expected film
producer (that is, coil coater, service center, or other seller).
thickness/test results for a coating, nor the specific “recipe” file
needed to measure a coating.
2.5 user, n—the person or organization that makes use of the
coil coated product.
1.3 The values stated in either SI units or inch-pound units
are to be regarded separately as standard. The values stated in
3. Summary of Test Method
each system are not necessarily exact equivalents; therefore, to
ensure conformance with the standard, each system shall be
3.1 An instrument is used to measure either a single paint
used independently of the other, and values from the two
layer, like a primer, or the total film thickness of a multi-layer
systems shall not be combined.
organic coil coating system through a non-contact, non-
destructive, ruggedized optical interference (ROI) method.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3.2 It is recommended that this system only be used to
responsibility of the user of this standard to establish appro-
determine total system thickness if the optical properties
priate safety, health, and environmental practices and deter-
between multiple layers are similar (for example, topcoat over
mine the applicability of regulatory limitations prior to use.
primer).Individuallayersmaybeabletobedistinguishedifthe
1.5 This international standard was developed in accor-
optical properties vary enough (for example, clear over pig-
dance with internationally recognized principles on standard-
mented layer).
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
4. Significance and Use
mendations issued by the World Trade Organization Technical
4.1 Coating film thickness plays a critical role in the
Barriers to Trade (TBT) Committee.
performance of the final product. This includes physical
2. Terminology
properties (abrasion/scratch resistance, color, gloss), chemical
2.1 producer, n—primary manufacturer of the coil coated properties (solvent resistance), corrosion resistance, and long-
material, that is, the coil coater, from which parts are fabri-
term durability (color change, chalk, fade).
cated.
4.2 The non-destructive measurement system based on rug-
2.2 recipe, n—a combination of specified settings in the
gedized optical interference transforms signal outputs in coat-
Ruggedized Optical Interference (ROI) measurement system
ing film thickness using digital formulas (or “recipes”) which
which is used by the instrument to interpret the reflectance
are reproducible from one instrument to another.
information gathered during a reading and provide an output in
4.3 TheROImeasurementunittakesasignificantnumberof
a specified unit of film thickness measurement.
measurements which can be read in a determined period of
time and each of these data points is recorded and reportable.
This test method is under the jurisdiction of ASTM Committee D01 on Paint
and Related Coatings, Materials, andApplications and is the direct responsibility of
4.4 Due to the number of variables that can affect film
Subcommittee D01.53 on Coil Coated Metal.
thickness during application and the number of variables that
Current edition approved Aug. 1, 2020. Published September 2020. DOI:
10.1520/D8331_D8331M-20. must be set in the measurement unit while determining a
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8331/D8331M − 20
recipe, it is important for the producer and the user to agree 8. Sampling, Test Specimens, and Test Units
upon recipe settings depending on the coating system.
8.1 For laboratory testing, obtain representative, coated, flat
panels, and cut the panels to an appropriate size for the test
5. Interferences
machine. It is recommended that sample panels be measured
5.1 Probe setup is one of the critical items needed for good
over an expanded surface area (minimum of 300 mm [0.5
measurement. The probes can be set at a certain height within
in. ]), rather than at one focused point in order to ensure a
the manufacturer’s specification from the sample. Once the
representative area of the product is measured and to ensure
height is established, the light will need to be focused at this
that the sample can be measured under the light source without
height. Changes to the height will require a refocusing of the
the beam moving off the sample. Note that the actual measure-
light.
ment area may vary by product and must be agreed upon by
producer and user.
5.2 Perpendicularity of the lens will affect accuracy of the
readings, as will the cleanliness of the lens. Refer to the
8.2 In-line measurements may be taken during the coating
instrument manufacturer’s instructions for proper alignment of
process on the wet film before curing or on the dried film after
the lens and cleaning procedures.
curing has occurred.
5.3 The sample has to be in motion during the scan time of
8.3 For products that may have varied coating thickness and
measurements. No measurements will be obtained if the
cure across the item (that is, across the width of a coated coil),
sample is not moved or if the movement is too slow (for
it is recommended that samples representing that variation be
example, less than 5.0 mm per second is too slow).
collected.
6. Apparatus
9. Preparation of Apparatus
6.1 ROI film measurement unit, with operator instructions.
9.1 Prepare in accordance with the manufacturer’s inst
...