1、Designation: D7356 07D7356/D7356M 13Standard Test Method forAccelerated Acid Etch Weathering of Automotive ClearcoatsUsing a Xenon-Arc Exposure Device1This standard is issued under the fixed designation D7356;D7356/D7356M; the number immediately following the designation indicatesthe year of origina
2、l adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope Scope*1.1 This test method covers an accelerated exposure test intend
3、ed to simulate defects in automotive clearcoats caused by acidrain2 that occur at the Jacksonville, Florida exposure site. Exterior exposures at an acid rain test location in Jacksonville, Floridaproduce etch defects that range from small pits to 12.7 mm (0.5 in.)0.5 in. in diameter or larger acid-e
4、tched spots. The latter typeof defect is not produced in other acid-etch tests that only produce pits that are smaller than 6.35 mm (0.25 in.)0.25 in. indiameter.3NOTE 1Digital images of the acid etch defects produced in outdoor acid-rain exposures and in the accelerated test described in this test
5、method arefound in Appendix X1.1.2 The accelerated test described in this test method uses a xenon-arc light source with daylight filter conforming to therequirements of Practice G155. Specimens are sprayed with a simulated acid rain solution and requires the use of a horizontal, flatspecimen array
6、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 either SI units or inch-pound units are to be regarded separately as standard. The values given inparentheses are
7、for information only.stated in each system may not be exact equivalents; therefore, each system shall be usedindependently of the other. Combining values from the two systems may result in non-conformance with the standard.1.5 This standard does not purport to address all of the safety concerns, if
8、any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:4D1293 Test Methods for pH of WaterD4517 Test Method
9、 for Low-Level Total Silica in High-Purity Water by Flameless Atomic Absorption SpectroscopyG113 Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic MaterialsG147 Practice for Conditioning and Handling of Nonmetallic Materials for Natural and Artificial Weathering TestsG15
10、1 Practice for Exposing Nonmetallic Materials in Accelerated Test Devices that Use Laboratory Light SourcesG155 Practice for Operating Xenon Arc Light Apparatus for Exposure of Non-Metallic Materials3. Terminology3.1 DefinitionsDefinitions applicable to this standard can be found in Terminology G113
11、.3.2 Definitions of Terms Specific to This Standard:3.2.1 acid rain, ncloud or rain droplets containing pollutants, such as oxides of sulfur and nitrogen, to make them acidic.1 This test method is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications
12、 and is the direct responsibility ofSubcommittee D01.27 on Accelerated Testing.Current edition approved June 1, 2007June 1, 2013. Published June 2007September 2013. Originally approved in 2007. Last previous edition approved in 2007 as D7359 07. DOI: 10.1520/D7356-07. 10.1520/D7356_D7356M-13.2 The a
13、cid etch test method is covered by a patent. Interested parties are invited to submit information regarding the identification of an alternative(s) to this patented itemto ASTM International Headquarters. Your comments will receive careful considerations at a meeting of the responsible technical com
14、mittee,1 which you may attend.3 Brennan, P. J, Marino, M., Boisseau, J. and Campbell, D.,AcceleratedAcid Etch, Part II: Refined Test Procedure to ReproduceAutomotiveAcid Etch Provides ImprovedLab Practicality and Proven Correlation, FSCT, 2006 FutureCoat Proceedings.4 For referencedASTM standards, v
15、isit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM stan
16、dard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by AST
17、M is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.2 acid rain spots, nspots are produced when the sun evaporates standing w
18、ater on the vehicles surface.3.2.2.1 DiscussionThey fall into two categories, mineral deposits and acid-etched spots. Mineral deposits are white calcium spots or salt deposits lefton the surface after water evaporates. These deposits can be easily removed with a pre-wax cleaner (polish) or a clay ba
19、r.Acid-etched spots are depressions in the paint or clear coat, which cannot be easily removed.4. Summary of Test Method4.1 The Automotive Clearcoat coating being evaluated is applied to an automotive basecoat (typically black) that has beencoated onto a steel panel.All edges of the panel are sealed
20、 to prevent corrosion. Coatings applied to other types of panels may alsobe used.4.2 Test specimens are placed in a xenon-arc device equipped with a horizontal exposure rack and are exposed to alternatingperiods of light, spray with acid rain solution, and spray with water. The evaporation of the wa
21、ter from the acid solution on thetest specimen surface results in deposits with high acid concentration.4.3 After 400 hours of exposure, test specimens are evaluated and rated for etch.5. Significance and Use5.1 Acid etch damage is an important warranty claim item for automotive companies. As a resu
22、lt, acid etch resistance is animportant parameter for automotive exterior coatings. The method described in this test method has been shown to simulate acidetch damage of automotive clearcoats that occurs when such coatings are exposed from May through mid-August in Jacksonville,FL.3,5 The accelerat
23、ed test described in this standard allows year-round testing as opposed to the limited outdoor exposure timeavailable for the Jacksonville, FL exposures.6. Apparatus6.1 Xenon-arc exposure device conforming to Practice G151 and Practice G155 with the following additional requirements.6.1.1 Specimen r
24、ack that is within 63 degrees of horizontal.6.1.2 Means to spray pure deionized water and acid rain solutions independently, and without cross contamination, from oneanother.NOTE 2Use of dual spray systems, one for acid solution and the other for high purity water has been found to be effective for
25、eliminating crosscontamination.6.1.2.1 The volume of spray water shall be sufficient to flood (with excess) the surface of the specimen within the one-minutespray time. A spray delivery rate of 3 litres per minute per square metre has been found suitable.6.1.3 Use of a single spray system has not be
26、en evaluated. If a single spray system is used, the following shall be included withthe test report:6.1.3.1 If a single spray system is used for both the acid solution and high purity water, data verifying that there is no crosscontamination between the acid spray and the high purity water spray.6.1
27、.4 Xenon-arc apparatus shall be equipped with daylight filters that meet the requirements of Practice G155.6.1.5 Xenon-arc apparatus shall be able to simultaneously and automatically control irradiance, black panel temperature,relative humidity and chamber air temperature.6.2 Xenon-arc apparatus sha
28、ll be equipped with an uninsulated black panel complying with Practice G151.6.3 pH meter capable of measuring to 60.2 units.7. Reagents and Materials7.1 0.02 N H2SO4 Sulfuric Acid Volumetric Solution, (accurate to 61 part per 1000).7.2 0.3 % HNO3 (Nitric Acid), by weight or v/v.7.3 0.02 N NaOH Sodiu
29、m Hydroxide Volumetric Solution, (accurate to 6 1 part per 1000).7.4 0.01 M CaCl2, (Calcium Chloride Standard for water hardness testing).7.5 0.01 M KCl (Potassium Chloride) Conductivity Solution, calibration standard solution 1413 micro-ohms.5 Boisseau, J. and Pattison, L., BASF Corporation, and He
30、nderson, K. and Hunt, R., Bayer Material Science, “The Flaws in Accelerated Weathering of Automotive OEMCoatings,” Paint and Coatings Industry, June 2006.D7356/D7356M 1328. Apparatus Setup8.1 Operate, maintain and calibrate the apparatus to manufacturers specifications. The test should not be interr
31、upted once it hasstarted (excluding daily panel reposition). Calibrations and maintenance should be completed before the test starts or after the testhas completed.8.2 Water used for spray and humidification shall have a maximum of 1 ppm total solids and a maximum of 0.2 ppm silica.Unless otherwise
32、specified, determine silica levels in accordance with Practice D4517. A combination of deionization and reverseosmosis treatment can effectively produce water with the desired purity.8.3 Acid Rain SolutionThe composition for the acid rain solution is as follows:8.3.1 Add 977.5 g of deionized water t
33、o a 1 litre flask and then add the following:15.0 grams 0.02 N H2SO4 (Sulphuric Acid)2.2 grams 0.3 % HNO3 (Nitric Acid)2.5 grams 0.02 N NaOH (Sodium Hydroxide)1.8 grams 0.01 M CaCl2 (Calcium Chloride)1.0 grams 0.01 M KCl (Potassium Chloride)8.3.2 This provides a 1000 g (1 L) solution with a pH of 3.
34、3 to 3.5, which is similar to that of Jacksonville rain water.8.3.3 After the water has cooled to room temperature and stirred for 24 hours, measure the pH of the solution with a pH meterfollowing Practice D1293. If the solution pH is not between 3.3 and 3.5 make a new solution.8.4 Expose the test s
35、pecimens to the cycle shown in Table 1.8.4.1 Refer to Table X.3.2, Operational Fluctuations on Exposure Conditions, in Practice G155 for the maximum allowedfluctuations about the set points. If the operational fluctuations are greater than the maximum allowed after the equipment hasstabilized, disco
36、ntinue the test and correct the cause of the problem before continuing.9. Test Procedure9.1 Apply coating to be evaluated to the desired substrate. After coating is applied and dried or cured, seal any cut edges of thetest specimens. An air-dry primer or silicone sealant has been found to be suitabl
37、e for sealing cut edges. The exposed surface ofall test specimens must be clean and free from finger prints or other surface contaminants. All other procedures for specimenhandling and identification shall be in accordance with Practice G147.9.2 Place specimens in the xenon-arc exposure device and p
38、rogram the device to run the exposure cycle described in Table 1,starting at Step 1 (dark exposure with acid spray). Unless otherwise specified, set the device timer to provide a 400 hour exposure.Refer to the device manufacturers instructions for proper operation.9.2.1 Once the exposure has started
39、, do not interrupt the exposure more than once per day. The single test interruption shall befor specimen repositioning and placement or removal. Additional interruptions may increase variability of test results.9.3 The volume of water and acid spray for the test must be excessive, running off the p
40、anels.Aspray volume of at least 3 litresper min per square metre has been found acceptable.9.4 Periodic repositioning of specimens during the exposure period is required to ensure that each receives an equal amount ofexposure to the acid solution and pure water spray. Reposition the panels daily dur
41、ing the light cycle. Follow the manufacturersguidelines for the repositioning pattern. See Fig. 1 for an example of how samples are repositioned. Repositioning of specimenson the weekends is not required.9.5 Report the acid damage as agreed upon by contractual parties.TABLE 1 Accelerated Acid Etch E
42、xposure Cycle SequenceAccelerated Acid Test Exposure CycleStep 1 1 min Dark exposure; with acid rain sprayStep 2 3 hr 50 min Dark exposure; 40C uninsulated black panel (B.P.) temperature (monitored not controlled); 40C chamber airtemperature; 80 % RHStep 3 12 hr Light exposure; 0.55 W/m2/nm at 340 n
43、m; daylight filters; 65C uninsulated B.P.; 50C chamber air temperature; 80 %RHStep 4 27 min Dark exposure; 40C uninsulated B.P. temperature (monitored not controlled); 40C chamber air temperature; 80 % RHStep 5 1 min Dark exposure; with pure water (DI) sprayStep 6 3 hr 50 min Dark exposure; 40C unin
44、sulated B.P. temperature (monitored not controlled); 40C chamber air temperature; 80 % RHStep 7 1 min Dark exposure; with pure water (DI) sprayStep 8 3 hr 50 min Dark exposure; 40C uninsulated B.P. temperature (monitored not controlled); 40C chamber air temperature; 80 % RHNoteChamber air temperatur
45、e and black panel temperature are controlled during the light period. Chamber air is controlled during the dark steps and the uninsulatedblack panel temperature is monitored. The % RH is controlled during light and dark periods where specified.D7356/D7356M 13310. Evaluation Report10.1 The evaluation
46、 of acid damage is performed visually and the test specimen is rated on a scale from 0 (best) to 10 (worst).A summary of the rating scale is shown in Table 2 and Table 3. Other evaluations can be used if agreed up by parties concerned.Example of pictorial ratings are shown in Appendix X2.11. Exposur
47、e Report11.1 The exposure report is as agreed upon by contractual parties.11.2 The Exposure Control/Report form shall include the following additional information:11.2.1 Laboratory Name.11.2.2 Type and serial number of exposure equipment.11.2.3 Month and Year of equipment operation.11.2.4 Test metho
48、d.11.2.5 Frequency of operation verification, for example, three or seven day intervals.11.2.6 Daily record of black panel temperature (BPT).11.2.7 Daily record of chamber temperature.11.2.8 Daily record of irradiance.FIG. 1 Example of Repositioning PatternTABLE 2 Acid Etch Evaluation RatingsRating
49、Description0 to 3 The etch spots are very faint and only noticed by a trained observer4 to 6 The etch spots are slight to moderate and in some cases noted by avehicle owner (untrained observer)7 to 10 The etch spots are severe enough that many vehicle owners wouldnotice and complainTABLE 3 Detailed Acid Etch RatingsRating Description Skill Level0 No damage N/A1 Slight pitting damage, no acid etch spots trained observer2 Moderate pitting no acid etch spots trained observer3 Few full or partial acid etch spots start trained observer4 Full acid e
