1、Designation: D7488 11Standard 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 parentheses in
2、dicates 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 standa
3、rd 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 AST
4、M 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
5、inASTM 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 allo
6、wing for 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)
7、/ 506 5 % relative 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, b
8、rushingeach section across 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 tim
9、e at which the X marksbecome 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
10、 ameans of determining the time 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
11、 chart forwhite paints or white sealed chart 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
12、 bristles in accordance with Practice D5301.6.5 Timer 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 Prac
13、tice D5068.7.2 Tape the edges of the chart to a smooth glass plate or usea vacuum plate.1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.42 on Architectural Coatings.Current
14、 edition approved July 1, 2011. Published August 2011. Originallyapproved in 2010. Last previous edition approved in 2010 as D7488 - 10. DOI:10.1520/D748811.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of AS
15、TMStandards volume information, 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.7.3 Along the length of the panel, drawdown 76 microns (3mil) wet film thickness of the t
16、est paint (see Fig. 1). Thedrawdown must be free of ridges, craters, or other imperfec-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 (112 in.) long in four to five different areason the drawdown, as shown in Fig. 1.NOTE 1The wi
17、de 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.7.6 Re-wet th
18、e brush by dipping it into the test paint.Remove excess paint by lightly scraping both sides of the brushacross the top edge of the can.NOTE 2The objective is to keep the brush wet; but not to addsignificantly more paint to the area being tested.7.7 At agreed upon time intervals between each X mark,
19、start brushing the first X mark in perpendicular direction to theinitial drawdown using ten strokes back and forth (1 stroke =1 back and forth motion) to work the brush-applied paint intothe drawdown area. The length of the strokes should be slightlyless than the width of the chart and moving across
20、 and pass theinitial drawdown to determine the time elapsed when the edgesof the first coat become visible.7.8 Repeat 7.6 and 7.7 by moving sequentially down thechart to each X mark at the agreed upon time interval. (Forexample, 2 minute intervals from 8 to 14 minutes.)7.9 Dry the chart in a horizon
21、tal position overnight.7.10 After drying overnight, observe each panel to deter-mine the time elapsed when the edges of the first coat becomevisible and the time elapsed when the X marks become visible.8. Report8.1 The time elapsed when the edges of the first coatbecome visible.8.2 The time elapsed
22、when the X marks become visible.8.3 Any deviations from this test method.9. Precision and Bias49.1 The precision of this test method is based on aninterlaboratory study conducted in 2006/2007. Each of 15laboratories tested four commercial paints for time elapsedwhen edges of first coat become visibl
23、e (min) and time elapsedwhen the X marks become visible (min) to determine preci-sion. Practice E691 was followed for the design and analysis ofthe data; the details are given in ASTM Research Report No.D01-1154.9.2 Because different paint formulations vary in open time,precision will also vary. Thi
24、s interlaboratory study includedsamples from four different commercial paints each resulting indifferent open time measurements.9.2.1 Repeatability Limit (r)Two test results obtainedwithin one laboratory shall be judged not equivalent if theydiffer by more than the “r” value for that material; “r”is
25、theinterval representing the critical difference between two testresults for the same material, obtained by the same operatorusing the same equipment on the same day in the samelaboratory.9.2.1.1 Repeatability limits are listed in Table 1 and Table 2.9.2.2 Reproducibility Limit (R)Two test results s
26、hall bejudged not equivalent if they differ by more than the “R” valuefor that material; “R” is the interval representing the criticaldifference between two test results for the same material,obtained by different operators using different equipment indifferent laboratories.9.2.2.1 Reproducibility l
27、imits are listed in Table 1 and Table2. At times in this data you will see that the reproducibilitylimit is higher than average Xbar. Variable environmentalconditions from lab to lab with this test method can influencereproducibility data.3It is suggested that you wrap the brush in a disposable plas
28、tic wrap betweentimed intervals to prevent the paint from drying on the brush.4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D01-1154.FIG. 1 IllustrationD7488 1129.2.3 The above terms (repeatability limit and reproducibil-ity l
29、imit) are used as specified in Practice E177.9.2.4 Any judgement in accordance with statements 9.2.1and 9.2.2 would have an approximate 95 % probability ofbeing correct.9.3 BiasAt the time of the study, there was no acceptedreference material suitable for determining the bias for this testmethod, th
30、erefore no statement on bias can be made.9.4 MaterialsThe paints tested in this study werecommercially-purchased white semi-gloss architectural paints.The paints were selected because of the variation in claimedvolatile content (VOC) levels. VOC levels as indicated by themanufacturer on the correspo
31、nding paint labels are as follows:Paint A 150 g/LPaintB0g/LPaintC0g/LPaint D 250 g/L10. Keywords10.1 coatings; lapping; latex; open time; overlap; paint;waterborne; wet edgeThis standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years a
32、ndif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,
33、 which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-29
34、59,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standar
35、d may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).TABLE 1 Time Elapsed When Edges of First Coat BecomeVisible (minutes)AverageARepeatabilityLimitReproducibilityLimitMaterial Xbar r R R / XbarPaint A 2.33 1.50 2.71 1.16Paint B 2.18 0.83 1.64 0.75Paint C 2.04 0.83 0.83 0.41Paint D
36、3.02 1.77 3.87 1.28AThe average of the laboratories calculated averages.TABLE 2 Time Elapsed When the X Marks Become Visible(minutes)AverageARepeatabilityLimitReproducibilityLimitMaterial Xbar r R R / XbarPaint A 4.51 2.64 5.95 1.32Paint B 3.02 2.04 3.40 1.12Paint C 3.11 1.45 3.96 1.27Paint D 6.33 3.04 8.44 1.33AThe average of the laboratories calculated averages.D7488 113
