ASTM_D_2620_-_87_1995e1.pdf

Designation:D 2620 87(Reapproved 1995)e1Standard Test Method forLight Stability of Clear Coatings1This standard is issued under the fixed designation D 2620;the number immediately following the designation indicates the year oforiginal adoption or,in the case 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.e1NOTEKeywords and unit of measurement statement were added editorially in May 1995.1.Scope1.1 This test method covers the determination of the discol-oration of clear coatings by sunlight through glass.1.2 The values stated in inch-pound units are to be regardedas the standard.The values given in parentheses are forinformation only.1.3 This standard does not purport to address all of thesafety concerns,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:D 1729 Practice for Visual Evaluation of Color Differencesof Opaque Materials2D 1925 Test Method for Yellowness Index of Plastics3G 24 Practice for Conducting Exposures to Daylight Fil-tered Through Glass43.Summary of Test Method3.1 The effect of sunlight on discoloration of clear coatingsis determined by exposing under glass,coated panels maskedat one end,to natural sunlight for a specified time.At the endof the exposure,the mask is removed and the panels evaluatedfor degree of discoloration.4.Significance and Use4.1 Color change,particularly yellowing,is not generallyacceptable to users of coatings when it is readily noticeable.Indesigning clear coating systems for interior use on varioussubstrates,it is of interest to know how well the clear coats willresist color change caused by ambient light.This test methodpermits the evaluation of the effect of natural indoor light onthe color stability of clear coatings.5.Apparatus5.1 Exposure Cabinet as described in Practice G 24.6.Test Specimens6.1 For each clear coating under test,use one test panelapproximately 3 by 5 in.(75 by 125 mm)of white carrara glassor other specified substrate material.NOTE1Other materials that may be considered for this purposeinclude:(1)White ceramic tile.(2)Awhite pigmented,light-stable coatingwhich would not be lifted by the clear topcoat.(A baking enamel with thecomposition of 30%melamine formaldehyde resin and 70%of thephthalic anhydride/coconut alkyd resin with 3 lb/gal(1.36 kg/L)oftitanium dioxide per gallon has been found satisfactory.)(3)The substrateintended for use with the clear coating.The light stability of the substratemay be determined by including an extra test panel without a cleartopcoat.6.2 Prepare specimens of the test materials by applying thecoatings on the test panels to a dry film thickness of 2 6 0.2mil(50 6 5 m).6.3 Prepare a reference specimen,representing a material ofknown performance in this test,with each set of test specimens.6.4 Record the panel preparation details:method of coatingapplication,baking conditions,film thickness,etc.These de-tails will be established by mutual agreement between pur-chaser and seller in accordance with the type of product and itsintended use.7.Conditioning7.1 Unless otherwise specified,condition the coated panelsat 73.5 6 3.5F(23 6 2C)and 50 6 5%relative humidity for48 h if baked,or 7 days if air dried.8.Procedure8.1 Prior to exposure,mask one-half of each test panel withaluminum foil to exclude sunlight from the other half of thecoating.NOTE2The tape used to attach the mask to the panel should notextend over the edge of the mask but should extend beyond the ends of themask and stick to the rear of the panel,thereby holding the mask inposition.This will prevent contact between the tape and the finish andeliminate the possibility of staining from the tape.8.2 Mount the test specimens in the glass-covered exposurecabinet continuously 24 h a day for the specified period of1This test method is under the jurisdiction of ASTM Committee D-1 on Paintand Related Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.55 on Factory-Applied Coatings on Preformed Products.Cur-rent edition approved May 29,1987.Published July 1987.Originally published asD 2620 67.Last previous edition D 2620 68(1981)e1.2Annual Book of ASTM Standards,Vol 06.01.3Annual Book of ASTM Standards,Vol 08.01.4Annual Book of ASTM Standards,Vol 14.02.1AMERICAN SOCIETY FOR TESTING AND MATERIALS100 Barr Harbor Dr.,West Conshohocken,PA 19428Reprinted from the Annual Book of ASTM Standards.Copyright ASTMexposure.It is recommended this period should be approxi-mately 5 weeks,since longer periods of exposure do notsignificantly change the results.NOTE3In cooperative tests,exposure of nitrocellulose lacquers,cellulose acetate butyrate lacquer,and low-bake alkyd enamel for 22weeks did not show significa