1、Designation: F 1921 98 (Reapproved 2004)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 F 1921; the number immediately following the designation indicates th
2、e year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover laboratory measurement o
3、f thestrength of heatseals formed between thermoplastic surfaces offlexible webs, immediately after a seal has been made andbefore it cools to ambient temperature.1.2 These test methods are restricted to instrumented hottack testing, requiring a testing machine that automaticallyheatseals a specimen
4、 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 proced
5、ures 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 sealedspecimen,
6、 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 andcapacit
7、y of the machine employed. They are described inSection 4.1.4 SI units are preferred and shall be used in refereedecisions.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
8、-priate safety and health practices 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 recommend
9、ed that theoperator review safety precautions from the equipment sup-plier.2. Referenced Documents2.1 ASTM Standards:2D 882 Test Method for Tensile Properties of Thin PlasticSheetingE 171 Specification for Atmospheres for Conditioning andTesting Flexible Barrier Materials3. Terminology3.1 Definition
10、s:3.1.1 adhesive failure, na failure mode in which the sealfails at the original interface between the surfaces being sealed.3.1.2 burnthrough, na state or condition of a heatsealcharacterized by melted holes and thermal distortion.3.1.2.1 DiscussionBurnthrough indicates that the sealingconditions (
11、time or temperature, or both) were too high for anacceptable seal.3.1.3 cohesive failure, na failure mode where either orboth of the sealed webs fails by splitting, approximatelyparallel to the seal, and the seal itself remains intact.3.1.3.1 DiscussionRefer to Fig. 1. The term may bedefined somewha
12、t differently when applied to sealing systemsinvolving an adhesive material as a separate component.3.1.4 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(see Fig. 2).3.1.4.1
13、 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.3.1.5 cooling time, nthe time interval from when theheatseal jaws open at conclusion of the se
14、aling cycle, to thepoint at which the hot-tack force is determined.3.1.6 delay time, nthe time interval from when the heat-seal jaws open at conclusion of the sealing cycle, to the pointat which withdrawal of the sample from between the jaws isinitiated.1These test methods are under the jurisdiction
15、 of ASTM Committee F02 onFlexible Barrier Materials and are the direct responsibility of subcommittee F02.20on Physical Properties.Current edition approved Oct. 10, 1998. Published February 1999.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at
16、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.3.1.7 dwell time, nthe time interval during the hea
17、tsealingcycle when the sealing jaws are in contact with, and exertingpressure on, the material being sealed.3.1.8 failure mode, na visual determination of the mannerin which the test strip fails during grip separation.3.1.9 hot tack, nstrength of a hot seal measured at aspecified time interval after
18、 completion of the sealing cycle butprior to the temperature of the seal reaching ambient.3.1.10 hot-tack curve, na plot of hot-tack strength versussealing temperature (see Fig. 3).FIG. 1 Test Strip Failure ModesF 1921 98 (2004)23.1.10.1 DiscussionThis is the basic curve used for com-paring material
19、s for their hot tack performance. It shows notonly the maximum hot seal strength achievable by eachmaterial and the sealing temperature required, but also thebreadth of the sealing temperature range at any specified levelof hot tack.3.1.11 sealing temperature, nmaximum temperaturereached at the inte
20、rface between the two web surfaces beingsealed, during the dwell time of the sealing cycle.3.1.11.1 DiscussionSealing temperature will equal jawtemperature (both jaws at same temperature) if the dwell timeis long enough for the interface to reach equilibrium with thejaws. At this point, seal strengt
21、h will no longer rise withincreasing dwell time.3.1.12 withdrawal time, nthe time interval from whenwithdrawal is initiated, to the point in time when all slack hasbeen removed from the test strip between the seal and the grips,so that measurement of the strength of the seal can commence.4. Summary
22、of Test Method4.1 A sample strip is sealed by applying pressure from twoflat heated jaws under defined conditions of temperature,contact time and pressure.4.2 When the jaws of the sealing unit open, the sealed stripis automatically withdrawn from between the jaws at conclu-sion of a set delay time (
23、which may be zero), by retraction ofthe grips.4.3 As the grips move apart at a set speed and the sealedsample is elongated to eventual failure, the force required ismeasured by the testing machine.4.4 In Method A (machines of the Theller type) the machinemeasures and plots strength versus time after
24、 jaw opening,starting after a withdrawal period of 100 to 150 ms, which isthe cooling curve for the material. The computer then deter-mines the force coordinates of the curve at various times, andreports the values as hot-tack strength at those cooling times.The machine is factory-set to start withd
25、rawal within 10 msafter jaw opening.4.5 In Method B (machines of the DTC andJ10 to 14 in.)7.5 A typical hot tack curve may require 25 to 50 specimensof each material.7.6 Specimens that fail at some obvious flaw shall bediscarded and a resample measurement made.8. Procedure8.1 Sealing ConditionsEnter
26、 values of sealing parametersinto machine controller. Sealing conditions for hot tack testingshall be the same for all makes and types of testing machines.8.1.1 TemperatureBoth jaws must be set at same tempera-ture, which will vary depending on the properties of thematerial under test. In running a
27、hot tack curve, temperature istypically varied in 5 to 10 intervals, although to locatemaxima or other features of the curve smaller steps may bedesirable locally. The first temperature point of the curve istypically at about the seal initiation temperature.8.1.2 Dwell TimeMust be long enough for th
28、e sealinginterface to come to the known temperature of the jaws, whichdepends on the thickness and construction of the material.Typical minimum dwell times:Films251(mil)andunder: dwell time, 500 ms (0.5 s).Films25 to 64 (1 to 2.5 mil): dwell time, 1000 ms (1 s).8.1.3 Sealing PressureSet pressure in
29、the range of 15 to30 N/cm2(22 to 44 psi).48.2 Clamp the strip to be tested in the machine grips,observing alignment precautions and proper orientation of theheatseal side.8.3 Measurement of Hot Seal Strength Enter the desiredtest parameters into the machine controller. The followingparameters are co
30、mmonly used for routine hot-tack testing, butmay be varied over the ranges provided by each machinemanufacturer, depending on the intended application of thedata. Values of all test parameters must be included in thereport.8.3.1 Method A (Testing machine: Theller type)Test pa-rameters:Cooling times
31、for hot tack measurements: ms5Clamp separation rate: 200 cm/minAir: 5.068.3.2 Method B (Testing machine: DTC andJ peelCohesive failure of the materialDelamination of surface layer (s) from substrateBreak of material at seal edgeBreak or tear of material remote from sealElongation of materialFrequent
32、ly, more than one mode will occur in the course offailure of an individual strip. Record all modes observed.8.6 After three or more replicates have been run, thecomputer calculates, displays and records the average andstandard deviation values when so programmed.3For further information on machines,
33、 users of these test methods are referred tointernet web sites of the various manufacturers.4Force per unit area of seal.5The machine automatically measures and displays the seal strength at twooperator-selectable cooling times.6See manufacturers description and recommendation. Air circulation can b
34、evaried or turned off entirely.F 1921 98 (2004)48.7 After all specimens have been tested at the currenttemperature level, set the machine to the next temperature andproceed with testing to develop data for the hot tack curve.Leave all other variables constant.8.8 The end point of the hot tack curve
35、is when increasingtemperature levels cause a progressive decrease in the force tofailure. In this region of the curve, the specimen fails byexcessive stretch, breaking, tearing, distortion, shrinkage,burnthrough, etc.9. Calculation9.1 Computer-controlled versions of the testing machinespreviously li
36、sted do all required calculations automatically.Other versions may require statistical calculations by theoperator.9.2 For each series of tests, the arithmetic mean of all testvalues shall be calculated to three significant figures when theforce value is, respectively, 1.00 lb, 1.00 N, or 100 g or a
37、bove,and to two significant figures when the force value is belowthose levels.9.3 The standard deviation (estimated) shall be calculated asdescribed in Test Method D 882 and reported to two significantfigures.10. Report10.1 Report the following information, with values in SIunits:10.1.1 General Info
38、rmation:10.1.1.1 Date of testing,10.1.1.2 Operator,10.1.1.3 Machinetype and model, and10.1.1.4 Laboratory ambient temperature and humidity.10.1.2 Materials tested; complete ID as appropriate. Includetest strip parameters.10.1.3 Test Parameters.10.1.4 Hot Tack Strength Results:10.1.4.1 Average force
39、and standard deviation, and10.1.4.2 Hot tack curve.10.1.5 Failure modes.10.1.6 Observations and comments.11. Precision and Bias11.1 PrecisionInterlaboratory tests are in progress.11.2 BiasThe procedures in these test methods have nobias because the values of hot tack are defined in terms of themetho
40、ds.12. Keywords12.1 heatseal; heatsealability; hot tack; seal strengthAPPENDIX(Nonmandatory Information)X1. COMPARISION OF METHODSX1.1 Timing of Data AcquisitionA basic principle of hottack testing is to measure the strength of the hot seal as soon aspossible after the sealing jaws open, since the s
41、eal starts to coolimmediately, and as it cools it gains strength. But before thestrength can be measured, the seal must be withdrawn from thejaws and the slack must be removed from the test strip. Asecond principlethat is a fundamental difference between theinstrumented methods of these test methods
42、 and non-instrumented methodsis to control or measure the time spanbetween jaw opening and the point in time when hot tackreadings are taken. Since Methods A and B approach thesepoints differently, the differences that affect timing are com-pared as follows:X1.1.1 Method AMachine type: Theller.X1.1.
43、1.1 TimingThe machine is set to start withdrawal ofthe seal 5 to 10 ms after the jaws open.X1.1.1.2 Withdrawal DeviceAir cylinders.X1.1.1.3 Withdrawal Time75 ms.7X1.1.1.4 Measurement Cycle, Motive DeviceMotor andscrew.X1.1.1.5 Time When Seal Strength Measurement Starts100 to 125 ms.7,8X1.1.1.6 Time
44、When Hot Tack Readings are Taken250 ms6 1 ms.8Time of second reading is set by operator.X1.1.2 Method BMachine type: DTC andJ higher for other models.8Time after jaws open.9Early models of DTC employ air cylinders.F 1921 98 (2004)5the peel rate is 50 % of the grip separation rate.X1.4 As the grips o
45、f the testing machine separate, anystretch, delamination, or other elongation of the test stripexcept for peel of the heatseal, results in a decrease in peel rate.Peel rate is then no longer determined directly by the set rateof grip separation. This reduction in peel rate affects peel force.ASTM In
46、ternational takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entire
47、ly their own responsibility.This 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 revision of this standard or for additional standardsand s
48、hould 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 shouldmake your views known to the ASTM Committee on S
49、tandards, 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).F 1921 98 (2004)6
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