1、Designation: F1921 12Standard 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; the number immediately following the designation indicates the year oforiginal ad
2、option 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 These two test methods cover laboratory measurementof the strength of
3、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 automaticallyheatseals a specim
4、en 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 cover non-instrumentedmanual proc
5、edures 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 during testing of the sealedspecime
6、n, 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 methods and within the range andcapac
7、ity 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 shall be used independently ofthe ot
8、her. 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-priate safety and health practic
9、es and determine the applica-bility of regulatory limitations prior to use. The operator of theequipment is to be aware of pinch points as the seal jaws cometogether to make a seal, hot surfaces of the jaws, and sharpinstruments used to cut specimens. It is recommended that theoperator review safety
10、 precautions from the equipment sup-plier.2. Referenced Documents2.1 ASTM Standards:2D882 Test Method for Tensile Properties of Thin PlasticSheetingE171 Practice for Conditioning and Testing Flexible BarrierPackagingE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a
11、 Test MethodF88 Test Method for Seal Strength of Flexible BarrierMaterialsF2029 Practices for Making Heatseals for Determination ofHeatsealability of Flexible Webs as Measured by SealStrength3. Terminology3.1 Definitions:3.1.1 adhesive failure, na failure mode in which the sealfails at the original
12、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 melted holes and thermal distortion.3.1.3.1 DiscussionBurnthrough indicates that the sealingcon
13、ditions (time or temperature, or both) were too high toproduce an acceptable seal.3.1.4 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 be
14、defined somewhat differently when applied to sealing systemsinvolving an adhesive material as a separate component.1These test methods are under the jurisdiction of ASTM Committee F02 onFlexible Barrier Packaging and are the direct responsibility of subcommittee F02.20on Physical Properties.Current
15、edition approved July 1, 2012. Published August 2012. Originallyapproved in 1998. Last previous edition approved in 2004 as F1921-98(2004). DOI:10.1520/F1921-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book o
16、f 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.NOTE 1Schematic representation of seal failure modes for seals between two webs. No d
17、iagram is included for systems including an adhesive as athird component.FIG. 1 Test Strip Failure ModesF1921 1223.1.5 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 ex
18、ample, see Fig. 2).3.1.5.1 DiscussionThe cooling curve is a plot of hot sealstrength 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
19、 of the seal jaws and the termination of the peelforce measurement.3.1.7 cycle, nthe 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 fo
20、urphases: sealing, delay, withdrawal, and peel.3.1.8 delay time, nthe time interval 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 se
21、aling jaws are in contact with, and exertingpressure on, the material being sealed.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 s
22、pecified timeinterval after sealing but prior to the seal cooling to ambienttemperature.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 st
23、rength.3.1.12 hot-tack curve, na plot of measured hot-tackstrength versus sealing 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 se
24、al strength achievable by eachmaterial and the sealing temperature required, but also 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 a
25、n accurate representation of hottack strength.3.1.13 seal initiation temperature, nsealing temperatureat which a heatseal of minimum measureable strength isproduced.3.1.14 sealing pressure, nforce required, with transfer ofheat, to fuse two surfaces together to form a seal. Pressuresettings may be d
26、ifferent than the actual applied pressure andshould be verified as part of instrument 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 e
27、qual jawtemperature (both jaws at same temperature) if the dwell timeis long enough 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 endof the delay phase to the beginni
28、ng of the peel of the hot seal.4. Summary of Test Method4.1 Two sample strips are 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 s
29、trip of film which is cut during the sealing phase toform two strips. Either one 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.FIG. 2 Cooling CurveF1921 1234.2 When the jaws of the sealing u
30、nit open, the sealed stripis automatically withdrawn from between the jaws by retrac-tion of the grips holding 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 tes
31、ting machine.4.4 In Method A (machines of the Fixed Delay type) themachine measures and plots hot tack strength 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 vari
32、oususer-selectable times (minimum of two), and reports the forceas hot-tack strength at those cooling times.4.5 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
33、 grip travel is determined from that plot andreported as hot-tack strength for the delay time employed inthat test.4.6 In both methods the operator cannot influence the testonce the sealing cycle is initiated.4.7 Hot-tack strength at various sealing temperatures isplotted as the hot-tack curve of th
34、e 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 arefrequently subject to disruptive forces while still hot. If the hotseals have inadequate resistance to these forces, breakage ca
35、noccur during the packaging process. These test methodsmeasure hot seal strength and can be used to characterize andrank materials in their ability to perform in commercialapplications where this quality is critical.6. Apparatus6.1 Specimen CutterSized to cut specimens to a width ofeither 25 mm (0.9
36、84 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 automated sealing and tensiletesting instrument having the following minimum capabilities:6.2.1 Equipped with two heated jaws for maki
37、ng seals,6.2.2 User-selectable and precise control of jaw tempera-tures, dwell time and pressure,6.2.3 User-selectable constant rate of grip separation,6.2.4 Automatic activation of the withdrawal and pullcycles when seal jaws open,6.2.5 Measures the force required to cause failure in thesealed spec
38、imen, 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 manufacturers instructions and should include, asa minimum, seal bar temperature, seal bar pressure, phasetimes, transducer, and withdra
39、wal 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 specimens prior to hot-tacktesting is commonly omitted. The atmospheric conditions ofSpecification E171 are recommended when i
40、t 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 tack strength is being measured at a series of sealingtemperatures, a minimum of three replicates shall be used todetermine th
41、e 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 direction(TD). If the dir
42、ection 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 25 to 35 cm;10 to
43、 14 in.).8.5 Atypical hot tack curve may require 25 to 50 specimensof each material.3For further information on machines, users of these test methods are referred tointernet web sites of the various manufacturers.FIG. 3 Hot Tack CurveF1921 1248.6 Specimens that fail at some obvious film flaw such as
44、 anick or a gel shall be discarded and a resample measurementmade.9. Procedure9.1 Sealing ConditionsEnter values of sealing parametersinto machine 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 t
45、o the sametemperature, which will vary depending on the properties ofthe material under test. In running a hot tack curve, temperatureis set initially to a low temperature and typically increased in5C to 10C intervals, although to locate maxima or otherfeatures of the curve smaller steps may be desi
46、rable locally.The first temperature point of the curve is typically at about theseal initiation temperature.9.1.2 Dwell TimeMust be long enough for the sealinginterface to come to the known temperature of the jaws, whichdepends on the thickness and construction of the material.Typical minimum dwell
47、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 orie
48、ntation of theheatseal side in accordance with the manufacturers instruc-tions.9.3 Measurement of Hot Tack StrengthEnter the desiredinstrument cycle parameters into the machine controller. Thefollowing parameters are commonly used for routine hot-tacktesting, but may be varied over the ranges provid
49、ed by eachmachine manufacturer, depending on the intended applicationof the data. Values of all instrument cycle parameters must beincluded in the report.9.3.1 Method A (Fixed Delay)Typical test parameters:Cooling times for hot tack measure-ments:Minimum of two settings,in msClamp separation rate: 200 cm/min9.3.2 Method B (Variable Delay)Typical test parameters:Delay time (user-selectable): 100 msClamp separation rate: 1200 cm/min9.4 Start the machine. It will progress through the seal,delay, withdrawal, and hot tack strength-testing pha
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