1、Designation: D 7488 10Standard Test Method forOpen Time of Latex Paints1This standard is issued under the fixed designation D 7488; 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
2、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 stan
3、dard 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 A
4、STM 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 Bia
5、s 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 al
6、lowing 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,
8、 brushingeach 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 t
9、ime 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
10、is 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 seal
11、ed 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, polyest
12、er 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 accordance with Practice D5068.7.2 Ta
13、pe 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 imperfec-tions.1This test method is under the jurisdiction of
14、ASTM Committee D01 on Paintand Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.42 on Architectural Coatings.Current edition approved Dec. 1, 2010. Published February 2011. DOI: 10.1520/D748810.2For referenced ASTM standards, visit the ASTM website, w
15、ww.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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7.4
16、 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 wide curved end of a wooden tongue blade/paint brush orthe end of a tongue depressor/metal spatula
17、 has been found suitable forthis purpose.7.6 Re-wet the 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.
18、7.7 At agreed upon time intervals between each X mark,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 slig
19、htlyless than the width of the chart and moving across 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 interval
20、s from 8 to 14 minutes.)7.9 Dry the chart in a horizontal 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
21、 of the first coatbecome visible.8.2 The time elapsed when the X marks become visible.8.3 Any deviations from this test method.9. Precision and Bias39.1 The precision of this test method is based on aninterlaboratory study conducted in 2006/2007. Each of 15laboratories tested four commercial paints
22、for time elapsedwhen edges of first coat become visible (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 formul
23、ations vary in open time,precision will also vary. This 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 theydiff
24、er by more than the “r” value for that material; “r”istheinterval 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 Tab
25、le 2.9.2.2 Reproducibility Limit (R)Two test results shall bejudged not equivalent if they differ by more than the “R” valuefor that material; “R” is the interval representing the critical3Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Re
26、port RR:D01-1154.FIG. 1 IllustrationTABLE 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 3.02 1.77 3.87 1.28AThe average of
27、 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 l
28、aboratories calculated averages.D7488102difference between two test results for the same material,obtained by different operators using different equipment indifferent laboratories.9.2.2.1 Reproducibility limits are listed in Table 1 and Table2. At times in this data you will see that the reproducib
29、ilitylimit is higher than average Xbar. Variable environmentalconditions from lab to lab with this test method can influencereproducibility data.9.2.3 The above terms (repeatability limit and reproducibil-ity limit) are used as specified in Practice E177.9.2.4 Any judgement in accordance with statem
30、ents 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, therefore no statement on bias can be made.9.4 MaterialsThe paints tested in this study were
31、commercially-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 corresponding paint labels are as follows:Paint A 150 g/LPaintB0g/LPaintC0g/LPaint D 250 g/L10. Ke
32、ywords10.1 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 andif not revised, either reapproved or withdrawn. Your comments are invited either for rev
33、ision 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, which you may attend. If you feel that your comments have not received a fair hearing you
34、 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 19428-2959,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 standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D7488103
