1、Designation: F 2029 08Standard Practices forMaking Heatseals for Determination of Heatsealability ofFlexible Webs as Measured by Seal Strength1This standard is issued under the fixed designation F 2029; the number immediately following the designation indicates the year oforiginal adoption or, in th
2、e 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 practices cover laboratory preparation of heat-seals and the treatment and eval
3、uation of heatseal strength datafor the purpose of determining heatsealability of flexiblebarrier materials. It does not cover the required validationprocedure for the materials and production equipment.1.2 Testing strength or other properties of the heatsealsformed by these practices is not include
4、d in this standard. Referto Test Method F88for testing heatseal strength.1.3 The practices of this standard are restricted to sealingwith a machine employing hot-bar jaw(s). Impulse, high-frequency, and ultrasonic heating methods are not included.1.4 These practices apply primarily to webs intended
5、to beused on commercial machines employing reciprocating sealingjaws, such as most form-fill-seal packaging machines, platenheatsealers, and so forth. Conditions of dwell time and sealingpressure on machines of this type typically are different fromthose on rotary machines.1.5 The procedure of this
6、practice with respect to choice ofheatsealing conditions apply to ultimate seal strength or hottack measurement.1.6 Seals may be made between webs of the same ordissimilar materials. The individual webs may be homoge-neous in structure or multilayered (coextruded, coated, lami-nated, and so forth).1
7、.7 Strength of the heatseal as measured by Test MethodF88is the criterion for judging heatsealability employed inthese practices.1.8 Determination of heatsealability as judged by seal con-tinuity, typically measured by air-leak, dye penetration, visualexamination, microorganism penetration, or other
8、 techniques,are not covered by these practices.1.9 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.10 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibili
9、ty 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 ASTM Standards:2F88 Test Method for Seal Strength of Flexible BarrierMaterialsF 1921 Test Methods for Hot Seal Stre
10、ngth (Hot Tack) ofThermoplastic Polymers and Blends Comprising the Seal-ing Surfaces of Flexible WebsD 4332 Practice for Conditioning Containers, Packages, orPackaging Components for Testing3. Terminology3.1 Definitions:3.1.1 dwell time, nthe time interval when the sealing jawsare in contact with, a
11、nd exerting pressure on, the material beingsealed.3.1.2 heatseal curve, na plot of measured seal strengthversus sealing temperature when dwell and pressure are fixed.3.1.2.1 DiscussionThis is the basic curve for comparingsealability of materials. It plots the force required to extend asealed test st
12、rip to failure, as a function of sealing temperaturewhen dwell and pressure are fixed. The portion of the curve athigher sealing temperatures may be affected by failure of thesubstrate and may not be an accurate representation of sealstrength.3.1.3 heatseal strength, nforce required to peel the seal
13、apart, per unit width of seal.3.1.3.1 DiscussionIn many tests of seal strength ,it is notthe seal that fails, it is the substrate or a layer. In those tests, thetrue heatseal strength may be somewhat higher than themeasured force that caused the specimen to fail. Some mate-rials are intentionally de
14、signed to fail in a layers not at the seal1These practices are under the jurisdiction ofASTM Committee F02 on FlexibleBarrier Packaging and are the direct responsibility of Subcommittee F02.20 onPhysical Properties.Current edition approved April 1, 2008. Published May 2008. Originallyapproved in 200
15、0. Last previous edition approved in 2000 as F 2029 00.2For 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 Summary page onthe ASTM website.1Copyr
16、ight ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.interface in order to gain other attributes such as transferappearance. In this case, this failure is the desired outcome.Homogeneous materials with fusion seals, for example, com-monly break
17、 along a line immediately adjacent to the seal,while the seal itself remains intact.3.1.4 heatsealability, nthe property of thermoplastic poly-mers and blends, when comprising a surface of a flexible web,that defines how well the material bonds to itself or a dissimilarmaterial when sealed by the ap
18、plication of pressure, heat, anddwell (time).3.1.4.1 DiscussionHow well the material bonds is ex-pressed quantitatively as seal strength as a function of thesealing conditions of temperature, time, and pressure. Sincestrength of a heatseal can be measured either while the seal isstill hot (hot tack)
19、 or after cooling and stabilizing (ultimatestrength), a complete evaluation of heatsealability of a materialmay include both tests.3.1.5 hot tack, nstrength of a hot seal measured at aspecified time interval after completion of the sealing cycle butprior to the temperature of the seal reaching ambie
20、nt. Refer toTest Methods F 1921.3.1.6 seal initiation temperature, nthe sealing tempera-ture at which a heatseal of significant strength (typically 0.5N/cm; 125 g/25 mm; 0.3 lb/in.) is produced.3.1.7 sealing interface, nthe interface of the two websurfaces being sealed.3.1.8 sealing pressure, nthe f
21、orce per unit area of sealapplied to the material by the sealing jaws during the sealingprocess.3.1.8.1 DiscussionDuring the dwell time, the sealingpressure pulse rises from zero usually to a plateau level andthen drops to zero. Frequently, there is an initial spike. Veryshort dwell times may not ha
22、ve a plateau. Two parameters canbe used to characterize the pressure variable. One is a calcu-lated average pressure, that excludes the initial rise, as well as,the terminal fall of pressure, and the other is the maximumvalue reached either during any initial impact spike or later.NOTE 1A common err
23、or is to report air pressure in the cylinderapplying the force as the sealing pressure.3.1.9 sealing temperature, nthe setpoint in degrees ofeach temperature controlled sealing jaw. The actual surfacetemperature of the sealing jaws making contact with thematerials. The Set Point Temperature is the c
24、ontroller settingwhich will produce the desired surface temperature. Often, thesetpoint temperature will be numerically higher that the surfacetemperature.3.1.10 ultimate seal strength, nthe final value of strengththat is reached after the heatseal has both cooled to ambienttemperature and achieved
25、stability in strength.3.1.10.1 DiscussionSome materials, when cooling from amelt, continue to change in strength over extended periods oftime after reaching ambient temperature.4. Significance and Use4.1 This practice allows determination of the heatsealabilityof a surface or sealant layer. While it
26、 is necessary to have aheatseal surface layer that has adequate seal strength for theapplication, other material properties, such as the specificconstruction and total thickness, both chosen to satisfy require-ments other than heatsealability, will impact the sealing prop-erties of the material. Thi
27、s practice allows the impact ofchanges in material properties on heatsealability to be mea-sured.5. Apparatus5.1 Laboratory Heatsealer:5.1.1 Sealing JawsHeat controlled jaw or jaws withappropriate sealing surfaces to provide a flat seal. If only oneheated jaw is used, the unheated jaw should be cove
28、red with agasket material such as a silicone rubber of known durometer.5.1.1.1 Jaw Temperature ControlEach jaw should haveindependent temperature control and the precision of thecontrolling unit should be known and calibrated. The tempera-ture should be verified periodically using a calibrated pyrom
29、-eter adequate for the range of use.5.1.1.2 Heated Jaw Coatings or CoveringsAnti-stick orcompressible jaw coatings or coverings, such as TFE-fluorocarbon, TFE-fluorocarbon/glass cloth, or oriented PETfilm are often used to prevent the test specimen from adheringto the sealing jaws. Thick or heat flo
30、w-resistance materials willimpact the rate of heat transfer from jaws to sealing surface. Itis important to inspect the quality of these materials periodi-cally to prevent loss of properties causing unwanted tempera-ture fluctuations in the sealing process.(1) Unheated Jaw Coating or CoveringsSilico
31、ne or otherheat resistant rubbers of known durometer may be used. Therubber may be covered TFE-fluorocarbon, TFE-fluorocarbon/glass cloth, or oriented PET film. It is important to inspect thequality of these materials periodically to prevent loss ofproperties causing unwanted temperature fluctuation
32、s in thesealing process.5.1.1.3 Jaw Sealing Surfaces, must be capable of beingaligned for parallelism.(1) The uniformity of pressure across the sealing jaws canbe checked using pressure indicating materials or devices byactuating the sealing jaws while at ambient temperature.(2) Temperature applied
33、to sealing jaws may affect thealignment and parallelism of the jaw sealing surfaces as a resultof thermal expansion.5.1.2 Dwell TimeVariable control and readout of dwelltime, with minimum range of 100 to 10 000 milliseconds.5.1.2.1 Time of jaw closure should be measured directly (asby force sensor o
34、utput, micro switch, optically, and so forth).5.1.2.2 Precision of dwell time control should be 610 ms orbetter.5.1.3 Pressure, variable control, with readout of sealingpressure.5.1.3.1 The sealing pressure for machines that have only anair pressure gauge on the air supply line and whose cylindersiz
35、e is known can be calculated using the formula below:Pseal5SAlineAjawDPline Pw(1)where:Pseal= pressure of the sealing jaw,Pline= pressure of the incoming air line,F2029082Ajaw= area of the sealing jaw,Aline= cross-sectional area of the incoming air line, andPw= pressure loss due to mechanical work w
36、hich isfrequently difficult to calculate with any precision.5.1.3.2 When materials are being sealed under pressure thesilicone rubber on the unheated jaw will compress. When thinmaterials being sealed are less than the full length of thesealing jaw, the compression can be significant enough tochange
37、 the contact to the full area of the jaw. As a result, thepressure is then distributed across the entire surface and thisarea is what should be used in the pressure calculation. Whensealing thick materials, only the area of the seal should be usedto calculate the sealing pressure since contact is li
38、mited to thesurface of the thicker materials.5.1.3.3 Machines that have only an air pressure gage indi-cating the air supply pressure, should have a table relatingsealing and supply pressure.6. Test Specimen6.1 The number of test specimens shall be chosen to permitan adequate determination of repres
39、entative performance basedon a statistical rationale. When heatseal strength will bemeasured at a series of sealing temperatures, an adequate oragreed upon number of replicates shall be used to determinethe mean value for each material at each temperature. When themeasurements will not be part of a
40、series where an identifiabletrend is expected, a separate determination of the number ofreplicates should be made.6.2 Mark the transverse direction and the seal side of eachpiece. Superimpose the two pieces to be sealed, with thetransverse directions parallel and the seal surfaces facing eachother.
41、Seal each specimen with the jaws parallel to either themachine or transverse direction noting the orientation of thesample. Perform the heatseal process at the same locationrelative to the sealing jaws.Astrip for seal-strength testing willsubsequently be cut perpendicular to the seal at its center,
42、andthe seal will be peeled by pulling the strip.NOTE 2The seal must be located on the specimen so the legs of thestrip on each side of the seal will be long enough to span the distancebetween the grips of the testing machine.6.3 Alternatively to sealing a wide spectrum and thencutting a strip for st
43、rength testing, strips of the width forstrength testing may be cut in the machine direction and sealed,either to strips of similar material or to dissimilar strips. Thesealed strip may then be tested for strength without furtherpreparation. Comparisons should be made only among speci-mens sealed by
44、the same procedure.6.4 Common strip widths are 25 mm (1.00 in.) and 15 mm(0.59 in.).7. Procedure7.1 Calibration and AlignmentPrior to starting testing,ensure that the heatsealer is in proper calibration and that thejaws have been aligned for parallelism.7.2 Sealing Conditions, for heatsealability te
45、sting, eitherultimate seal strength or hot tack, shall be within the rangesspecified below for all makes and types of heatsealers.7.2.1 Dwell TimeThe dwell time must be long enough forthe sealing interface to come to the known temperature of thejaws. This depends on the thickness and construction of
46、 theweb, as well as on jaw configuration factors. Typical minimumdwell times (without anti-stick jaw covering):Films: 1 mil (25) and under: dwell time, 500 ms (0.5 s)Films: 1 to 2.5 mil (64): dwell time, 1000 ms (1 s)7.2.1.1 The minimum required dwell time can be deter-mined from a few trial sealing
47、 cycles. Refer to A2.1. Thisprocedure usually will be necessary for thicker films, structurescontaining paper or foil, or when anti-stick jaw coverings areused.7.2.2 Sealing PressureSet pressure in the range of 138 to413 kPa (20 to 60 psi). See Appendix X1 for discussion ofeffect of pressure on heat
48、seal strength.7.2.3 Web Sealability:7.2.3.1 TemperatureChoice of temperature setting of eachjaw (including unheated) is dependent on application of thedata. In the absence of reasons to the contrary, it is recom-mended both jaws be set to the same temperature.7.2.3.2 Dwell TimeSet the dwell time to
49、the desiredperiod.(1) If the dwell time is set sufficiently long that the heatflow through the webs is at steady-state, the seal strength of thematerial can be measured independently of dwell time, as longas the dwell time is above the equilibrium dwell time.7.2.3.3 Sealing PressureSet pressure in the range of 138to 413 kPa (20 to 60 psi), or at other level depending onspecific application. See Appendix X1 for discussion of effectof pressure on heatseal strength.7.2.3.4 Jaw ConfigurationThe coatings or coverings ap-plied to the sealing jaws should be ne
