ASTM_D_7541_-_11_2015.pdf

Designation:D754111(Reapproved 2015)Standard Practice forEstimating Critical Surface Tensions1This standard is issued under the fixed designation D7541;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()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers procedures for estimating values ofthe critical surface tension of surfaces by observing the wettingand dewetting of a series of liquids(usually organic solvents)applied to the surface in question.1.2 Another technique,measurement of the contact angles,of a series of test liquids and plotting cos versus surfacetension(Zisman plots),provides data that allow the determi-nation of more exact values for critical surface tension.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.4 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:2D2578 Test Method for Wetting Tension of Polyethylene andPolypropylene Films2.2 Nordtest Standards:3NT poly 176 Spreading Surface Tension by the AppliedDroplet Method.3.Terminology3.1 Definitions:3.1.1 critical surface tension,nthe surface tension of ahypothetical liquid that would just spontaneously spread ifapplied as a drop to the surface in question;any liquid with asurface tension lower than the critical surface tension willspread spontaneously.4.Summary of Practice4.1 In this practice,a series of liquids of gradually increas-ing surface tension are applied to a surface in the form ofdrops,narrow strips,or spots.Drops may be applied using adropper,syringe or other device capable of producing indi-vidual drops.Liquid strips or spots are applied to the surface byswabbing with saturated cotton swabs or by another type ofapplicator,such as one that is similar to a marker pen.In thecase of the drop,the observer determines whether the dropstays in place or spreads.In the case of the liquid strip or spot,the question is whether the liquid stays in place or dewets andcrawls.In each case,the break point between wetting anddewetting provides the critical surface tension.5.Significance and Use5.1 Knowledge of the critical surface tension of substrates,primers and other coatings is useful for explaining or predict-ing wettability by paints and other coatings applied to thosesurrfaces.Surfaces with low critical surface tensions usuallyare prone to suffer defects such as crawling,picture framing,cratering and loss of adhesion when painted.Low or irregularvalues,or both,often are indicative of contamination that couldreduce adhesion.Surfaces with high critical surface tensionsare easy to wet and usually provide an excellent platform forpainting.5.2 The swab,marking pen and draw-down tests all simu-late the application of a film5.3 The swab and marking pen techniques are simple andrapid and are particularly useful for testing in the field or oncurved,irregular or porous surfaces where contact anglescannot be measured.The drop test does not work well on suchsurfaces and the draw-down method requires a flat specimenthat is relatively large.5.4 The estimation of critical surface tension has beenuseful in characterizing surfaces before and after cleaningprocesses such as power washes and solvent wipes in order toevaluate the efficiency of the cleaning.5.5 One or more of these techniques could be the basis of ago/no-go quality control test where if a certain liquid wets,the1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.23 on Physical Properties of Applied Paint Films.Current edition approved June 1,2015.Published June 2015.Originallyapproved in 2009.Last previous edition approved in 2011 as D7541 11.DOI:10.1520/D7541-11R15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3For Nordtest standards,see or contactNordtest,Tekniikantie 12,FIN-02150 Espoo,Finland.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 surface is acceptable for painting,but if that liquid retracts andcrawls,the surface is not acceptable.5.6 Another go/no go test is possible where the test liquid isa paint and the surface is a substrate,primer or basecoat.Aform of this test has been used for coatings for plastics.6.Interferences6.1 The specimen must be clean in order