1、Designation:D748811(Reapproved 2016)Standard Test Method forOpen Time of Latex Paints1This standard is issued under the fixed designation D7488;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 par
2、entheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers a procedure to determine thelength of time a latex paint remains“wet”or“open”enough toallow for brush-in and repair.1.2 This sta
3、ndard 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
4、 Standards:2D3924 Specification for Environment for Conditioning andTesting Paint,Varnish,Lacquer,and Related MaterialsD5068 Practice for Preparation of Paint Brushes for Evalu-ationD5301 Practice for Physical Characterization of PaintBrushesE177 Practice for Use of the Terms Precision and Bias inAS
5、TM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 Definitions:3.1.1 open time,nthe length of time a coating remains wetor open enough to allow for brush-in without the edges of thefirst coat becoming visible and allowing f
6、or repair within thepreviously painted area.4.Summary of Test Method4.1 Since environmental conditions such as temperature,humidity and air flow can result in variable results,it isrecommended that this test method be performed in a constanttemperature/humidity room(23 6 2C(73.5 6 3.5F)/506 5%relati
7、ve humidity.Test paints are applied to the center ofa sealed chart with a 76 microns(3 mil)wet film thickness.Xmarks are made immediately.The number of X marks willdepend on how many can fit on one drawdown(see Fig.1).Thetest paint is then applied in perpendicular sections,brushingeach section acros
8、s the initial painted section.The perpendicu-lar sections are repeated at agreed upon time intervals.Afterdrying,wet edge is recorded as the last time the test paint couldbe brushed into the initial painted section without the edges ofthe first coat being visible.The time at which the X marksbecome
9、visible is also noted.5.Significance and Use5.1 Latex paints dry very quickly which often causesdifficulty in final appearance of painted areas,especially paintsformulated below 100g/L VOC where lower amounts ofsolvents are in the formulated latex paint.This method is ameans of determining the time
10、available before a test paintcannot be worked into a previously painted area.6.Apparatus6.1 Constant Temperature/Humidity Room(23 6 2C(73.56 3.5F)/50 6 5%relative humidity in accordance withSpecification D3924.6.2 Contrasting Sealed Chart(that is,black sealed chart forwhite paints or white sealed ch
11、art for tinted paints),typically30 by 60 cm(1 by 2 ft.).6.3 Glass Plate,30 by 60 cm(1 by 2 ft.)or vacuum plate.6.3.1 If using a glass plate,tape to secure sealed chart toglass plate.6.4 Good Quality Brush,50 mm(2 in.)wide with straightedge,polyester bristles in accordance with Practice D5301.6.5 Tim
12、er or Clock to record time intervals.6.6 Film Applicator,capable of applying a film with a widthof 7.5 cm(3 in.)and approximate wet film thickness of 75microns(3 mil).7.Procedure7.1 Condition the brush in with the test paint accordancewith Practice D5068.1This test method is under the jurisdiction o
13、f ASTM Committee D01 on Paintand Related Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.42 on Architectural Coatings.Current edition approved April 1,2016.Published April 2016.Originallyapproved in 2010.Last previous edition approved in 2011 as D7488 11.DOI:1
14、0.1520/D7488-11R16.2For 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.Copyright ASTM International,100 Barr Harbor Dr
15、ive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.2 Tape the edges of the chart to a smooth glass plate or usea vacuum plate.7.3 Along the length of the panel,drawdown 76 microns(3mil)wet film thickness of the test paint(see Fig.1).Thedrawdown must be free of ridges,craters,or other i
16、mperfec-tions.7.4 Start the timer or record the time.7.5 Immediately make X marks approximately in 4 cm(112in.)wide and 4 cm(112in.)long in four to five different areason the drawdown,as shown in Fig.1.NOTE1The wide curved end of a wooden tongue blade/paint brush orthe end of a tongue depressor/metal spatula has been found suitable forthis purpose.3Depending on the type of instrument used to make the Xmark,ensure that the X marks are consistent in size down the chart andthroughout your testing.7
