1、Designation: D 7356 07Standard Test Method forAccelerated Acid Etch Weathering of Automotive ClearcoatsUsing a Xenon-Arc Exposure Device1This standard is issued under the fixed designation D 7356; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers an accelerated exposure testintended to simulate defects in automot
3、ive clearcoats caused byacid rain2that 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 12.7mm (0.5 in.) in diameter or larger acid-etched spots. The lattertype of defect is no
4、t produced in other acid-etch tests that onlyproduce pits that are smaller than 6.35 mm (0.25 in.) indiameter.3NOTE 1Digital images of the acid etch defects produced in outdooracid-rain exposures and in the accelerated test described in this testmethod are found in Appendix X1.1.2 The accelerated te
5、st described in this test method uses axenon-arc light source with daylight filter conforming to therequirements of Practice G 155. Specimens are sprayed with asimulated acid rain solution and requires the use of a horizon-tal, flat specimen array in order to allow the acid rain solutionto remain on
6、 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 thestandard. The values given in parentheses are for informationonly.1.5 This standard does not purport to address all of thesafety conc
7、erns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:4D 1293 Test Methods for pH of WaterD 45
8、17 Test Method for Low-Level Total Silica in High-Purity Water by Flameless Atomic Absorption Spectros-copyG113 Terminology Relating to Natural and ArtificialWeathering Tests of Nonmetallic MaterialsG 147 Practice for Conditioning and Handling of Nonme-tallic Materials for Natural and Artificial Wea
9、thering TestsG 151 Practice for Exposing Nonmetallic Materials in Ac-celerated Test Devices that Use Laboratory Light SourcesG 155 Practice for Operating Xenon Arc Light Apparatusfor Exposure of Non-Metallic Materials3. Terminology3.1 DefinitionsDefinitions applicable to this standard canbe found in
10、 Terminology G113.3.2 Definitions of Terms Specific to This Standard:3.2.1 acid rain, ncloud or rain droplets containing pollut-ants, such as oxides of sulfur and nitrogen, to make themacidic.3.2.2 acid rain spots, nspots are produced when the sunevaporates standing water on the vehicles surface.3.2
11、.2.1 DiscussionThey fall into two categories, mineraldeposits and acid-etched spots. Mineral deposits are whitecalcium spots or salt deposits left on the surface after waterevaporates. These deposits can be easily removed with apre-wax cleaner (polish) or a clay bar. Acid-etched spots aredepressions
12、 in the paint or clear coat, which cannot be easilyremoved.4. Summary of Test Method4.1 The Automotive Clearcoat coating being evaluated isapplied to an automotive basecoat (typically black) that has1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Mater
13、ials, and Applications and is the direct responsibility ofSubcommittee D01.27 on Accelerated Testing.Current edition approved June 1, 2007. Published June 2007.2The acid etch test method is covered by a patent. Interested parties are invitedto submit information regarding the identification of an al
14、ternative(s) to thispatented item to ASTM International Headquarters. Your comments will receivecareful considerations at a meeting of the responsible technical committee,1whichyou may attend.3Brennan, P. J, Marino, M., Boisseau, J. and Campbell, D., Accelerated AcidEtch, Part II: Refined Test Proce
15、dure to Reproduce Automotive Acid Etch ProvidesImproved Lab Practicality and Proven Correlation, FSCT, 2006 FutureCoat Pro-ceedings.4For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume inform
16、ation, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.been coated onto a steel panel.All edges of the panel are sealedto prevent corrosion. Coatings applied to other ty
17、pes of panelsmay also be used.4.2 Test specimens are placed in a xenon-arc deviceequipped with a horizontal exposure rack and are exposed toalternating periods of light, spray with acid rain solution, andspray with water. The evaporation of the water from the acidsolution on the test specimen surfac
18、e results in deposits withhigh acid concentration.4.3 After 400 hours of exposure, test specimens are evalu-ated and rated for etch.5. Significance and Use5.1 Acid etch damage is an important warranty claim itemfor automotive companies. As a result, acid etch resistance isan important parameter for
19、automotive exterior coatings. Themethod described in this test method has been shown tosimulate acid etch damage of automotive clearcoats that occurswhen such coatings are exposed from May through mid-August in Jacksonville, FL.3,5The accelerated test described inthis standard allows year-round test
20、ing as opposed to thelimited outdoor exposure time available for the Jacksonville,FL exposures.6. Apparatus6.1 Xenon-arc exposure device conforming to PracticeG 151 and Practice G 155 with the following additional re-quirements.6.1.1 Specimen rack that is within 63 degrees of horizontal.6.1.2 Means
21、to spray pure deionized water and acid rainsolutions independently, and without cross contamination,from one another.NOTE 2Use of dual spray systems, one for acid solution and the otherfor high purity water has been found to be effective for eliminating crosscontamination.6.1.2.1 The volume of spray
22、 water shall be sufficient toflood (with excess) the surface of the specimen within theone-minute spray time. A spray delivery rate of 3 litres perminute per square metre has been found suitable.6.1.3 Use of a single spray system has not been evaluated. Ifa single spray system is used, the following
23、 shall be includedwith the test report:6.1.3.1 If a single spray system is used for both the acidsolution and high purity water, data verifying that there is nocross contamination between the acid spray and the high puritywater spray.6.1.4 Xenon-arc apparatus shall be equipped with daylightfilters t
24、hat meet the requirements of Practice G 155.6.1.5 Xenon-arc apparatus shall be able to simultaneouslyand automatically control irradiance, black panel temperature,relative humidity and chamber air temperature.6.2 Xenon-arc apparatus shall be equipped with an uninsu-lated black panel complying with P
25、ractice G 151.6.3 pH meter capable of measuring to 60.2 units.7. Reagents and Materials7.1 0.02 N H2SO4Sulfuric Acid Volumetric Solution, (accu-rate to 61 part per 1000).7.2 0.3 % HNO3(Nitric Acid), by weight or v/v.7.3 0.02 N NaOH Sodium Hydroxide Volumetric Solution,(accurate to 6 1 part per 1000)
26、.7.4 0.01 M CaCl2, (Calcium Chloride Standard for waterhardness testing).7.5 0.01 M KCl (Potassium Chloride) Conductivity Solu-tion, calibration standard solution 1413 micro-ohms.8. Apparatus Setup8.1 Operate, maintain and calibrate the apparatus to manu-facturers specifications. The test should not
27、 be interruptedonce it has started (excluding daily panel reposition). Calibra-tions and maintenance should be completed before the teststarts or after the test has completed.8.2 Water used for spray and humidification shall have amaximum of 1 ppm total solids and a maximum of 0.2 ppmsilica. Unless
28、otherwise specified, determine silica levels inaccordance with Practice D 4517. A combination of deioniza-tion and reverse osmosis treatment can effectively producewater with the desired purity.8.3 Acid Rain SolutionThe composition for the acid rainsolution is as follows:8.3.1 Add 977.5 g of deioniz
29、ed water to a 1 litre flask andthen 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
30、 of 3.3to 3.5, which is similar to that of Jacksonville rain water.8.3.3 After the water has cooled to room temperature andstirred for 24 hours, measure the pH of the solution with a pHmeter following Practice D 1293. If the solution pH is notbetween 3.3 and 3.5 make a new solution.8.4 Expose the te
31、st specimens to the cycle shown in Table 1.8.4.1 Refer to Table X.3.2, Operational Fluctuations onExposure Conditions, in Practice G 155 for the maximumallowed fluctuations about the set points. If the operationalfluctuations are greater than the maximum allowed after theequipment has stabilized, di
32、scontinue the test and correct thecause 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 edgesof the test specimens. An air-dry primer or silicone sealant hasbeen found to be suitabl
33、e for sealing cut edges. The exposedsurface of all test specimens must be clean and free from fingerprints or other surface contaminants. All other procedures forspecimen handling and identification shall be in accordancewith Practice G 147.9.2 Place specimens in the xenon-arc exposure device andpro
34、gram the device to run the exposure cycle described inTable 1, starting at Step 1 (dark exposure with acid spray).5Boisseau, J. and Pattison, L., BASF Corporation, and Henderson, K. and Hunt,R., Bayer Material Science, “The Flaws in Accelerated Weathering of AutomotiveOEM Coatings,” Paint and Coatin
35、gs Industry, June 2006.D7356072Unless otherwise specified, set the device timer to provide a400 hour exposure. Refer to the device manufacturers instruc-tions for proper operation.9.2.1 Once the exposure has started, do not interrupt theexposure more than once per day. The single test interruptionsh
36、all be for 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 beexcessive, running off the panels. A spray volume of at least 3litres per min per square metre has been found accept
37、able.9.4 Periodic repositioning of specimens during the exposureperiod is required to ensure that each receives an equal amountof exposure to the acid solution and pure water spray. Repo-sition the panels daily during the light cycle. Follow themanufacturers guidelines for the repositioning pattern.
38、 See Fig.1 for an example of how samples are repositioned. Reposition-ing of specimens on the weekends is not required.9.5 Report the acid damage as agreed upon by contractualparties.10. Evaluation Report10.1 The evaluation of acid damage is performed visuallyand the test specimen is rated on a scal
39、e from 0 (best) to 10(worst). A summary of the rating scale is shown in Table 2 andTable 3. Other evaluations can be used if agreed up by partiesconcerned. Example of pictorial ratings are shown inAppendixX2.11. Exposure Report11.1 The exposure report is as agreed upon by contractualparties.11.2 The
40、 Exposure Control/Report form shall include thefollowing 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 method.11.2.5 Frequency of operation verification, for example,three or seven day interv
41、als.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.12. Precision and Bias12.1 The test results are a visual comparison to a pictorialstandard and the ranking of the test sets. The repeatabilitystandard deviation (Tabl
42、e 4) has been determined to be:TABLE 1 Accelerated Acid Etch Exposure 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 air temperat
43、ure; 80 % RHStep 3 12 hr Light exposure; 0.55 W/m2/nm at 340 nm; daylight filters; 65Cuninsulated B.P.; 50C chamber air temperature; 80 % RHStep 4 27 min Dark exposure; 40C uninsulated B.P. temperature (monitored notcontrolled); 40C chamber air temperature; 80 % RHStep 5 1 min Dark exposure; with pu
44、re water (DI) sprayStep 6 3 hr 50 min Dark exposure; 40C uninsulated B.P. temperature (monitored notcontrolled); 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 notcontrolled); 40C
45、 chamber air temperature; 80 % RHNoteChamber air temperature 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 specifi
46、ed.FIG. 1 Example of Repositioning PatternTABLE 2 Acid Etch Evaluation RatingsRating 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
47、 are severe enough that many vehicle owners wouldnotice and complainD7356073TABLE 4 Repeatability for Lab ACoating Set #1 Set #2 Set #3 Set #5 MeanStandardDeviationPaintA35464.51.29B66676205PaintC79988.5.96D1010101010012.1.1 The Spearman rank correlation coefficient was 1.0for all possible compariso
48、ns between the different sets. ThePearson linear correlation coefficients for comparisons of thedata in the different sets were as follows:Set 1 to Set 2 = 0.92Set 1 to Set 3 = 0.93Set 1 to Set 4 = 0.98Set 2 to Set 3 = 0.99Set 2 to Set 4 = 0.9412.2 The reproducibility of this test method is being de
49、ter-mined and will be available on or before 2012.13. Keywords13.1 accelerated weathering; acid etch; acid rain; automo-tive; clearcoats; Jacksonville; xenon-arcAPPENDIXES(Nonmandatory Information)X1. ACCELERATED WEATHERING XENON ACID ETCH TEST FOR AUTOMOTIVE CLEARCOATSX1.1 Acid etch images. See Figs. X1.1-X1.4.TABLE 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 o
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