ASTM F1921F1921M-12(2018) Standard Test Methods for Hot Seal Strength (Hot Tack) of Thermoplastic Polymers and Blends Comprising the Sealing Surfaces of Flexible Webs.pdf

1、Designation: F1921/F1921M 12 (Reapproved 2018)Standard Test Methods forHot Seal Strength (Hot Tack) of Thermoplastic Polymers andBlends Comprising the Sealing Surfaces of Flexible Webs1This standard is issued under the fixed designation F1921/F1921M; the number immediately following the designation

2、indicates the yearof original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 These two test methods cover laborator

3、y measurementof the strength of heatseals formed between thermoplasticsurfaces of flexible webs, immediately after a seal has beenmade and before it cools to ambient temperature (hot tackstrength).1.2 These test methods are restricted to instrumented hottack testing, requiring a testing machine that

4、 automaticallyheatseals a specimen and immediately determines strength ofthe hot seal at a precisely measured time after conclusion of thesealing cycle. An additional prerequisite is that the operatorshall have no influence on the test after the sealing sequencehas begun. These test methods do not c

5、over non-instrumentedmanual procedures employing springs, levers, pulleys andweights, where test results can be influenced by operatortechnique.1.3 Two variations of the instrumented hot tack test aredescribed in these test methods, differing primarily in tworespects: (a) rate of grip separation dur

6、ing testing of the sealedspecimen, and (b) whether the testing machine generates thecooling curve of the material under test, or instead makes ameasurement of the maximum force observed following a setdelay time. Both test methods may be used to test all materialswithin the scope of these test metho

7、ds and within the range andcapacity of the machine employed. They are described inSection 4.1.4 SI units are preferred and shall be used in refereedecisions. Values stated herein in inch-pound units are to beregarded separately and may not be exact equivalents to SIunits. Therefore, each system shal

8、l be used independently ofthe other. Combining values from the two systems may resultin non-conformance with the standard.1.5 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-

9、priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.The operator of the equipment is to be aware of pinch points asthe seal jaws come together to make a seal, hot surfaces of thejaws, and sharp instruments used to cut specimens.

10、It isrecommended that the operator review safety precautions fromthe equipment supplier.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,

11、 Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D882 Test Method for Tensile Properties of Thin PlasticSheetingE171 Practice for Conditioning and Testing Flexible BarrierPackagingE691 Practice f

12、or Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodF88 Test Method for Seal Strength of Flexible BarrierMaterialsF2029 Practices for Making Laboratory Heat Seals forDetermination of Heat Sealability of Flexible BarrierMaterials as Measured by Seal Strength3. Terminology

13、3.1 Definitions:3.1.1 adhesive failure, na failure mode in which the sealfails at the original interface between the surfaces being sealed.3.1.2 breadth, ntemperature range over which peel forceof a seal is (relatively) constant.3.1.3 burnthrough, na state or condition of a heatsealcharacterized by

14、melted holes and thermal distortion.1These test methods are under the jurisdiction of ASTM Committee F02 onPrimary Barrier Packaging and are the direct responsibility of subcommittee F02.20on Physical Properties.Current edition approved Jan. 1, 2018. Published February 2018. Originallyapproved in 19

15、98. Last previous edition approved in 2012 as F1921/F1921M121.DOI: 10.1520/F1921-12R18.2For 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 Summar

16、y page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles f

17、or theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.3.1 DiscussionBurnthrough indicates that the sealingconditions (time or temperature, or both) were too high toproduce an acceptable seal.3.

18、1.4 cohesive failure, na failure mode where either orboth of the sealed webs fails by splitting approximately parallelto the seal, and the seal itself remains intact.3.1.4.1 DiscussionRefer to Fig. 1. The term may bedefined somewhat differently when applied to sealing systemsinvolving an adhesive ma

19、terial as a separate component.3.1.5 cooling curve, nthe graphical depiction of the in-crease in strength of the seal with time, as it cools during theperiod immediately following conclusion of the sealing cycle(for example, see Fig. 2).3.1.5.1 DiscussionThe cooling curve is a plot of hot sealstreng

20、th versus cooling time. The portion of the cooling curveof greatest practical significance is the first 1000 ms followingopening of the heatseal jaws.3.1.6 cooling time, ntime in the instrument cycle betweenthe opening of the seal jaws and the termination of the peelforce measurement.3.1.7 cycle, nt

21、he combination of instrument mechanicaland electrical operations automatically performed from initia-tion of sealing through peeling apart a seal and measuring thehot tack strength. The cycle can be broken down into fourphases: sealing, delay, withdrawal, and peel.3.1.8 delay time, nthe time interva

22、l from when the heat-seal jaws open after sealing two film surfaces, to the point atwhich withdrawal of the sample from between the jaws isinitiated.3.1.9 dwell time, nthe time interval during the seal phasewhen the sealing jaws are in contact with, and exertingpressure on, the material being sealed

23、.3.1.10 failure mode, na visual determination of the man-ner in which the test strip fails during grip separation.3.1.11 hot tack strength, nforce per unit width of a sealneeded to peel apart a hot seal measured at a specified timeinterval after sealing but prior to the seal cooling to ambienttemper

24、ature.3.1.11.1 DiscussionThe desired outcome of the test is topeel apart the seal formed by the test instrument. Other types offilm failure in the tensile phase of the instrument test cycle maynot represent hot tack strength.3.1.12 hot-tack curve, na plot of measured hot-tackstrength versus sealing

25、temperature at fixed dwell time andsealing pressure (for example, see Fig. 3).3.1.12.1 DiscussionThis is the basic curve used for com-paring materials for their hot tack performance. It shows notonly the maximum hot seal strength achievable by eachmaterial and the sealing temperature required, but a

26、lso thebreadth of the sealing temperature range at any specified levelof hot tack. The portion of the curve at higher sealingtemperatures may be affected by failure of the substrate ratherthan the seal and may not be an accurate representation of hottack strength.3.1.13 seal initiation temperature,

27、nsealing temperature atwhich a heatseal of minimum measureable strength is pro-duced.3.1.14 sealing pressure, nforce required, with transfer ofheat, to fuse two surfaces together to form a seal. Pressuresettings may be different than the actual applied pressure andshould be verified as part of instr

28、ument calibration.3.1.15 sealing temperature, nmaximum temperaturereached at the interface between the two web surfaces beingsealed during the dwell time of the sealing cycle.3.1.15.1 DiscussionSealing temperature will equal jawtemperature (both jaws at same temperature) if the dwell timeis long eno

29、ugh for the interface to reach equilibrium with thejaws. At this point, seal strength will no longer rise withincreasing dwell time.3.1.16 withdrawal time, nthe time interval from the end ofthe delay phase to the beginning of the peel of the hot seal.4. Summary of Test Method4.1 Two sample strips ar

30、e sealed by applying pressure fromseal jaws under defined conditions of temperature, contact timeand pressure. The strips may be either the same film ordissimilar films. Some instrument designs allow the use of asingle strip of film which is cut during the sealing phase toform two strips. Either one

31、 or both of the seal jaws may beheated. The jaw faces may either be smooth or textured andmay be covered with a material to promote release from the hotfilm.4.2 When the jaws of the sealing unit open, the sealed stripis automatically withdrawn from between the jaws by retrac-tion of the grips holdin

32、g the unsealed ends of the strips.4.3 As the grips move apart at a set speed and the sealedsample is peeled to eventual failure, the force required to peelopen the seal is measured by the testing machine.4.4 In Method A (machines of the Fixed Delay type) themachine measures and plots hot tack streng

33、th versus time afterjaw opening, starting after a manufacturer-set delay andwithdrawal period, which is part of the cooling curve for thematerial. The computer then measures the force at varioususer-selectable times (minimum of two), and reports the forceas hot-tack strength at those cooling times.4

34、.5 In Method B (machines of the Variable Delay type) thecomputer plots maximum hot tack strength versus time aftercompletion of a user-selected delay time. The maximum forceencountered during grip travel is determined from that plot andreported as hot-tack strength for the delay time employed inthat

35、 test.F1921/F1921M 12 (2018)2NOTE 1Schematic representation of seal failure modes for seals between two webs. No diagram is included for systems including an adhesive as athird component.FIG. 1 Test Strip Failure ModesF1921/F1921M 12 (2018)34.6 In both methods the operator cannot influence the testo

36、nce the sealing cycle is initiated.4.7 Hot-tack strength at various sealing temperatures isplotted as the hot-tack curve of the material tested (see Fig. 3).4.8 The type of seal failure is noted for each determination.5. Significance and Use5.1 In form-fill operations, sealed areas of packages arefr

37、equently subject to disruptive forces while still hot. If the hotseals have inadequate resistance to these forces, breakage canoccur during the packaging process. These test methodsmeasure hot seal strength and can be used to characterize andrank materials in their ability to perform in commercialap

38、plications where this quality is critical.6. Apparatus6.1 Specimen CutterSized to cut specimens to a width ofeither 25 mm (0.984 in.), 15 mm (0.591 in.), or 1.00 in. (25.4mm). Tolerance shall be 60.5 %. Cutter shall conform torequirements specified in Test Method D882.6.2 Testing Machine3An automate

39、d sealing and tensiletesting instrument having the following minimum capabilities:6.2.1 Equipped with two heated jaws for making seals,6.2.2 User-selectable and precise control of jawtemperatures, dwell time and pressure,6.2.3 User-selectable constant rate of grip separation,6.2.4 Automatic activati

40、on of the withdrawal and pullcycles when seal jaws open,6.2.5 Measures the force required to cause failure in thesealed specimen, and6.2.6 Displays measurements in SI, inch-pound, or mixedunits.7. Instrument Calibration7.1 Calibration of the hot tack tester should be in accor-dance with manufacturer

41、s instructions and should include, asa minimum, seal bar temperature, seal bar pressure, phasetimes, transducer, and withdrawal rate.7.2 The interval between calibrations may be determinedlocally based on frequency of use and stability of calibration.8. Test Specimen8.1 Conditioning of samples or sp

42、ecimens prior to hot-tacktesting is commonly omitted. The atmospheric conditions ofSpecification E171 are recommended when it is desired toprecondition materials to be tested.8.2 The number of test specimens shall be chosen to permitan adequate determination of representative performance.When hot ta

43、ck strength is being measured at a series of sealingtemperatures, a minimum of three replicates shall be used to3For further information on machines, users of these test methods are referred tointernet web sites of the various manufacturers.FIG. 2 Cooling CurveFIG. 3 Hot Tack CurveF1921/F1921M 12 (2

44、018)4determine the mean value at each temperature. When themeasurements are not part of a series where an identifiabletrend is expected, a minimum of five replicates shall beemployed.8.3 Specimens may be prepared by cutting test material ineither the machine direction (MD) or the transverse directio

45、n(TD). If the direction of seal stress is of concern, the directionin which the samples are cut should be noted in the final report.8.4 Specimen width may be either 25 mm, 15 mm, or 1.00in. Test results shall identify the width used. Specimen lengthmust be adequate for the testing machine (range of

46、25 to 35 cm;10 to 14 in.).8.5 Atypical hot tack curve may require 25 to 50 specimensof each material.8.6 Specimens that fail at some obvious film flaw such as anick or a gel shall be discarded and a resample measurementmade.9. Procedure9.1 Sealing ConditionsEnter values of sealing parametersinto mac

47、hine controller. Sealing conditions for hot tack testingshall be the same for all makes and types of testing machines.9.1.1 TemperatureSet both sealing jaws to the sametemperature, which will vary depending on the properties ofthe material under test. In running a hot tack curve, temperatureis set i

48、nitially to a low temperature and typically increased in5C to 10C intervals, although to locate maxima or otherfeatures of the curve smaller steps may be desirable locally.The first temperature point of the curve is typically at about theseal initiation temperature.9.1.2 Dwell TimeMust be long enoug

49、h for the sealinginterface to come to the known temperature of the jaws, whichdepends on the thickness and construction of the material.Typical minimum dwell times:Films25 (1 mil) and thinner: dwell time, 500 ms (0.5 s).Films25 to 64 (1 to 2.5 mil): dwell time, 1000 ms (1 s).9.1.3 Sealing PressureSet pressure in the range of 15 to30 N/cm2 (22 to 44 psi).49.2 Clamp the strip to be tested in the machine grips,observing alignment precautions and proper orientation of theheatseal side in accordance with the manufacturers i