ASTM D7356-07
(Test Method)Standard Test Method for Accelerated Acid Etch Weathering of Automotive Clearcoats Using a Xenon-Arc Exposure Device
Standard Test Method for Accelerated Acid Etch Weathering of Automotive Clearcoats Using a Xenon-Arc Exposure Device
SIGNIFICANCE AND USE
Acid etch damage is an important warranty claim item for automotive companies. As a result, acid etch resistance is an important parameter for automotive exterior coatings. The method described in this test method has been shown to simulate acid etch damage of automotive clearcoats that occurs when such coatings are exposed from May through mid-August in Jacksonville, FL.3 ,5 The accelerated test described in this standard allows year-round testing as opposed to the limited outdoor exposure time available for the Jacksonville, FL exposures.
SCOPE
1.1 This test method covers an accelerated exposure test intended to simulate defects in automotive clearcoats caused by acid rain that occur at the Jacksonville, Florida exposure site. Exterior exposures at an acid rain test location in Jacksonville, Florida produce etch defects that range from small pits to 12.7 mm (0.5 in.) in diameter or larger acid-etched spots. The latter type of defect is not produced in other acid-etch tests that only produce pits that are smaller than 6.35 mm (0.25 in.) in diameter.Note 1
Digital images of the acid etch defects produced in outdoor acid-rain exposures and in the accelerated test described in this test method are found in Appendix X1.
1.2 The accelerated test described in this test method uses a xenon-arc light source with daylight filter conforming to the requirements of Practice G 155. Specimens are sprayed with a simulated acid rain solution and requires the use of a horizontal, flat specimen array in order to allow the acid rain solution to remain on the test specimens for an extended period of time.
1.3 There is no known ISO equivalent to this test method.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D7356 − 07
StandardTest Method for
Accelerated Acid Etch Weathering of Automotive Clearcoats
Using a Xenon-Arc Exposure Device
This standard is issued under the fixed designation D7356; 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. Referenced Documents
1.1 This test method covers an accelerated exposure test
2.1 ASTM Standards:
intendedtosimulatedefectsinautomotiveclearcoatscausedby
D1293 Test Methods for pH of Water
acid rain that occur at the Jacksonville, Florida exposure site.
D4517 Test Method for Low-Level Total Silica in High-
Exterior exposures at an acid rain test location in Jacksonville,
Purity Water by Flameless Atomic Absorption Spectros-
Florida produce etch defects that range from small pits to 12.7
copy
mm (0.5 in.) in diameter or larger acid-etched spots. The latter
G113 Terminology Relating to Natural andArtificial Weath-
type of defect is not produced in other acid-etch tests that only
ering Tests of Nonmetallic Materials
produce pits that are smaller than 6.35 mm (0.25 in.) in
G147 Practice for Conditioning and Handling of Nonmetal-
diameter.
lic Materials for Natural and Artificial Weathering Tests
NOTE 1—Digital images of the acid etch defects produced in outdoor
G151 Practice for Exposing Nonmetallic Materials inAccel-
acid-rain exposures and in the accelerated test described in this test
erated Test Devices that Use Laboratory Light Sources
method are found in Appendix X1.
G155 Practice for Operating XenonArc LightApparatus for
1.2 The accelerated test described in this test method uses a
Exposure of Non-Metallic Materials
xenon-arc light source with daylight filter conforming to the
requirements of Practice G155. Specimens are sprayed with a
3. Terminology
simulated acid rain solution and requires the use of a
3.1 Definitions—Definitions applicable to this standard can
horizontal, flat specimen array in order to allow the acid rain
be found in Terminology G113.
solutiontoremainonthetestspecimensforanextendedperiod
of time.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 acid rain, n—cloud or rain droplets containing
1.3 There is no known ISO equivalent to this test method.
pollutants, such as oxides of sulfur and nitrogen, to make them
1.4 The values stated in SI units are to be regarded as
acidic.
standard. The values given in parentheses are for information
3.2.2 acid rain spots, n—spots are produced when the sun
only.
evaporates standing water on the vehicle’s surface.
1.5 This standard does not purport to address all of the
3.2.2.1 Discussion—They fall into two categories, mineral
safety concerns, if any, associated with its use. It is the
deposits and acid-etched spots. Mineral deposits are white
responsibility of the user of this standard to establish appro-
calcium spots or salt deposits left on the surface after water
priate safety and health practices and determine the applica-
evaporates. These deposits can be easily removed with a
bility of regulatory limitations prior to use.
pre-wax cleaner (polish) or a clay bar. Acid-etched spots are
depressions in the paint or clear coat, which cannot be easily
This test method is under the jurisdiction of ASTM Committee D01 on Paint removed.
and Related Coatings, Materials, andApplications and is the direct responsibility of
Subcommittee D01.27 on Accelerated Testing.
4. Summary of Test Method
Current edition approved June 1, 2007. Published June 2007. DOI: 10.1520/
D7356-07.
4.1 The Automotive Clearcoat coating being evaluated is
The acid etch test method is covered by a patent. Interested parties are invited
applied to an automotive basecoat (typically black) that has
to submit information regarding the identification of an alternative(s) to this
patented item to ASTM International Headquarters. Your comments will receive
careful considerations at a meeting of the responsible technical committee, which
you may attend.
3 4
Brennan, P. J, Marino, M., Boisseau, J. and Campbell, D., Accelerated Acid For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Etch, Part II: Refined Test Procedure to ReproduceAutomotiveAcid Etch Provides contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Improved Lab Practicality and Proven Correlation, FSCT, 2006 FutureCoat Pro- Standards volumeinformation,refertothestandard’sDocumentSummarypageon
ceedings. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7356 − 07
beencoatedontoasteelpanel.Alledgesofthepanelaresealed 6.3 pH meter capable of measuring to 60.2 units.
to prevent corrosion. Coatings applied to other types of panels
may also be used.
7. Reagents and Materials
4.2 Test specimens are placed in a xenon-arc device
7.1 0.02 N H SO Sulfuric Acid Volumetric Solution, (accu-
2 4
equipped with a horizontal exposure rack and are exposed to
rate to 61 part per 1000).
alternating periods of light, spray with acid rain solution, and
7.2 0.3 % HNO (Nitric Acid), by weight or v/v.
spray with water. The evaporation of the water from the acid
solution on the test specimen surface results in deposits with 7.3 0.02 N NaOH Sodium Hydroxide Volumetric Solution,
high acid concentration. (accurate to 6 1 part per 1000).
4.3 After 400 hours of exposure, test specimens are evalu-
7.4 0.01 M CaCl , (Calcium Chloride Standard for water
ated and rated for etch.
hardness testing).
7.5 0.01 M KCl (Potassium Chloride) Conductivity
5. Significance and Use
Solution, calibration standard solution 1413 micro-ohms.
5.1 Acid etch damage is an important warranty claim item
for automotive companies. As a result, acid etch resistance is
8. Apparatus Setup
an important parameter for automotive exterior coatings. The
8.1 Operate, maintain and calibrate the apparatus to manu-
method described in this test method has been shown to
facturer’s specifications. The test should not be interrupted
simulate acid etch damage of automotive clearcoats that occurs
once it has started (excluding daily panel reposition). Calibra-
when such coatings are exposed from May through mid-
3,5
tions and maintenance should be completed before the test
August in Jacksonville, FL. The accelerated test described in
starts or after the test has completed.
this standard allows year-round testing as opposed to the
limited outdoor exposure time available for the Jacksonville,
8.2 Water used for spray and humidification shall have a
FL exposures.
maximum of 1 ppm total solids and a maximum of 0.2 ppm
silica. Unless otherwise specified, determine silica levels in
6. Apparatus
accordance with Practice D4517. A combination of deioniza-
6.1 Xenon-arc exposure device conforming to Practice
tion and reverse osmosis treatment can effectively produce
G151 and Practice G155 with the following additional require-
water with the desired purity.
ments.
8.3 Acid Rain Solution—The composition for the acid rain
6.1.1 Specimenrackthatiswithin 63degreesofhorizontal.
solution is as follows:
6.1.2 Means to spray pure deionized water and acid rain
8.3.1 Add 977.5 g of deionized water to a 1 litre flask and
solutions independently, and without cross contamination,
then add the following:
from one another.
15.0 grams – 0.02 N H SO (Sulphuric Acid)
2 4
NOTE 2—Use of dual spray systems, one for acid solution and the other
2.2 grams – 0.3 % HNO (Nitric Acid)
for high purity water has been found to be effective for eliminating cross
2.5 grams – 0.02 N NaOH (Sodium Hydroxide)
contamination.
1.8 grams – 0.01 M CaCl (Calcium Chloride)
6.1.2.1 The volume of spray water shall be sufficient to
1.0 grams – 0.01 M KCl (Potassium Chloride)
flood (with excess) the surface of the specimen within the
8.3.2 This provides a 1000 g (1 L) solution with a pH of 3.3
one-minute spray time. A spray delivery rate of 3 litres per
to 3.5, which is similar to that of Jacksonville rain water.
minute per square metre has been found suitable.
8.3.3 After the water has cooled to room temperature and
6.1.3 Useofasinglespraysystemhasnotbeenevaluated.If
stirred for 24 hours, measure the pH of the solution with a pH
a single spray system is used, the following shall be included
meter following Practice D1293. If the solution pH is not
with the test report:
between 3.3 and 3.5 make a new solution.
6.1.3.1 If a single spray system is used for both the acid
8.4 ExposethetestspecimenstothecycleshowninTable1.
solution and high purity water, data verifying that there is no
cross contamination between the acid spray and the high purity
8.4.1 Refer to Table X.3.2, Operational Fluctuations on
water spray. Exposure Conditions, in Practice G155 for the maximum
6.1.4 Xenon-arc apparatus shall be equipped with daylight
allowed fluctuations about the set points. If the operational
filters that meet the requirements of Practice G155. fluctuations are greater than the maximum allowed after the
6.1.5 Xenon-arc apparatus shall be able to simultaneously
equipment has stabilized, discontinue the test and correct the
a
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.