1、Designation: D 2838 08Standard Test Method forShrink Tension and Orientation Release Stress of PlasticFilm and Thin Sheeting1This standard is issued under the fixed designation D 2838; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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. Scope*1.1 This test method covers the determination of the shrinktension and related characteristics, that is, sh
3、rink force andorientation release stress, of heat-shrinkable plastic film andsheeting of less than 1.0 mm (0.04 in.) thickness. Twoprocedures are described that permit the measurement of shrinkforces at predetermined temperatures. They are as follows:1.1.1 Procedure A is designed to measure the maxi
4、mumforce exerted by a specimen that is totally restrained fromshrinking as it is heated rapidly to a specific temperature.1.1.2 Procedure B is designed to measure the maximumforce exerted by a specimen that is permitted to shrink apredetermined amount prior to restraint while being heatedrapidly to
5、a specific temperature.1.2 Orientation release stress can be determined from thedata obtained using Procedure A.1.3 The values stated in SI units are to be regarded as thestandard. The values in parentheses are for information only.NOTE 1There is no known ISO equivalent to this test method.1.4 This
6、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 practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2
7、.1 ASTM Standards:2D 618 Practice for Conditioning Plastics for TestingD 883 Terminology Relating to PlasticsD 4000 Classification System for Specifying Plastic Mate-rialsD 5947 Test Methods for Physical Dimensions of SolidPlastics SpecimensD 6287 Practice for Cutting Film and Sheeting Test Speci-me
8、nsD 6988 Guide for Determination of Thickness of PlasticFilm Test SpecimensE 2251 Specification for Liquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision Liquids3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 orientation release stress, nthe maximum shrinktension develo
9、ped by a film in a specified direction throughoutits range of shrink temperatures while totally restrained fromshrinking.3.1.2 shrink force, nthe force per original unit widthdeveloped by a film in a specified direction and at a specifiedtemperature in its attempt to shrink while under restraint.3.1
10、.3 shrink tension, nthe force per original averagecross-sectional area developed by a film in a specified directionand at a specified temperature in its attempt to shrink whileunder restraint.3.2 Definitions:3.2.1 For definitions of terms used in this test method, referto Terminology D 883.4. Summar
11、y of Test Method4.1 A 25.4-mm (1-in.) wide strip of film or sheeting isclamped in the arms of a shrink tension holder (see Fig. 1), onearm of which contains a strain gage. The holder is immersed ina hot bath and the force exerted by the film is measured by thestrain gage. The data is collected by a
12、data acquisition device.The tests may be carried out with or without free shrinkage ofthe material before restraint.5. Significance and Use5.1 As a result of the manufacturing process, internalstresses are locked into the film and these can be released byheating. For any given type of film or sheeti
13、ng, the tempera-tures at which shrinkage will begin are related to processing1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.19 on Film and Sheeting.Current edition approved Nov. 1, 2008. Published November 2008. Origi
14、nallyapproved in 1969. Last previous edition approved in 2007 as D 2838 - 07.2For 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 ont
15、he ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.techniques employed to manufacture the film and also may berelated to a phase transition in the base re
16、sin.5.2 Shrink tension affects the appearance and performanceof a film in a shrink-packaging application. It may also be usedto determine the degree and direction of orientation. Theorientation exerts a great influence upon important physicalcharacteristics such as tensile strength, stiffness, tear
17、resis-tance, and impact strength.5.3 Data from Procedure A are most useful for determiningthe degree and direction of orientation, orientation releasestress, and the maximum force that the film can exert at a giventemperature.5.4 Since, in actual applications, film is seldom, if ever,totally restrai
18、ned, data from Procedure B are useful in estimat-ing the force an item to be packaged will actually receive andin predicting the appearance of packaged items.5.5 The characterization of shrink tension as a function oftemperature, and the resultant determination of orientationrelease stress and its c
19、orresponding temperature, is usuallycarried out only for a particular material of specified thicknessfor a defined fabrication process. For product developmentpurposes, quality control and determination of conformity tospecification limits, the measurement of shrink tension at onlyone or two specifi
20、ed temperatures is normally sufficient.5.6 Before proceeding with this test method, reference shallbe made to the specification of the material being tested. Anytest specimen preparation, conditioning, dimensions, or testingparameters, or combination thereof, covered in the relevantASTM material spe
21、cification shall take precedence over thosementioned in this test method. If there are no relevant ASTMmaterial specifications, then the default conditions apply. Table1 of Classification Systems D 4000 lists the ASTM materialspecifications that currently exist6. Apparatus6.1 Shrink Tension Holder3A
22、 suggested design is por-trayed in Fig. 1 and Fig. 2.6.2 Strain Gage Conditioner, four-arm bridge, preferable.6.3 Data Acquisition Device Electronic, digital or chartrecorder pen having a response of no more than 30 ms from 10to 90 % of full-scale deflection, chart width of at least 100 mmis prefera
23、ble.6.4 Specimen Cutter For the apparatus and techniques forcutting film and sheeting used in this test method, refer toPractice D 6287.3The sole source of supply of the Shrink Tension Holder known to the committeeat this time is Standard Scientific Supply Company, 105 West Butternut Road,Hellertown
24、, PA180555, ph: 610-8387500. If you are aware of alternative suppliers,please provide this information to ASTM International Headquarters. Your com-ments will receive careful consideration at a meeting of the responsible technicalcommittee,1which you may attend.FIG. 1 Design for Shrink Tension Holde
25、rD28380826.5 Constant-Temperature Liquid Bath, capable of control-ling accurately to 60.5C and covering the range of interest,usually from 50 to 175C.6.6 Thermometer, covering the range of interest and con-forming to the requirement of Specification E 2251.6.7 Liquid Bath, which will not plasticize
26、or react withspecimens. Polyethylene glycol, glycerin, and water have beenfound to have wide applicability. Silicone oils are useful forsamples requiring temperatures above 175C.6.8 ThicknessAmicrometer as prescribed in Test MethodsD 5947 or D 6988, or a method of an equivalent measuringdevice, read
27、ing to 0.0025 mm (0.0001 in.) or less. The pressureexerted by the gage on the specimen being measured shall notdistort or deform the specimen. For thin films, # 0.0025 mm(0.001 in.), or films which exhibit visual deformation duringmeasurement, a maximum pressure of 70 kPa (10 psi) isrecommended. For
28、 thicker or stiffer films, the pressure shall bebetween 160 and 185 kPa (23 and 27 psi).7. Test Specimens7.1 The test specimens shall consist of strips of uniformwidth and thickness. The width of the specimens shall be 25.46 0.2 mm (1.0 6 0.01 in.).7.2 Length of Test Specimens:7.2.1 Specimens for Pr
29、ocedureAshall be at least 127 mm (5in.) in length.7.2.2 Length of specimens for Procedure B is dependentupon the amount of shrink desired prior to restraint. At least 50mm shall be allowed for clamping. The remaining lengthrequired can be calculated by solving for L in the followingequation:L 5 d/10
30、0 2 s! 3 100 (1)where:L = specimen length required between clamps, mm or in.,d = distance between clamps, mm or in., ands = percent shrink desired prior to restraint.Measure a distance equivalent to L, leaving at least 25.4 mm(1 in.) at either end of the strip for clamping and mark thebeginning and
31、termination of the distance with a line perpen-dicular to the edge and across the width of the strip.7.3 Measure the thickness of the specimen to the nearest0.0025 mm (0.0001 in.) at a minimum of four positions, but atleast at each 25.4 mm (1 in.) along the length of the specimenthat will be between
32、 the clamps. Record the thicknesses.Calculate and record their average.7.4 For each measurement of shrink tension at a giventemperature, test at least four specimens from each direction,machine and transverse, of the test sample.8. Preparation of Apparatus8.1 Set up constant-temperature bath and equ
33、ilibrate at thetemperature chosen for the test. Shrink tension will normallybe observed near the softening temperature of polymericmaterial.8.2 Balance and set the data acquisition device at zero inaccordance with the manufacturers instructions.9. Calibration9.1 Zero shrink holder with no load on sh
34、rink arm.9.2 Place a weight (normally 4.45 N, 454 gf, 1 lbf) equal tothe chosen full-scale value for the measurements to be made onthe shrink arm. Adjust the data acquisition device to full scalein accordance with the manufacturers instructions.9.3 Check linearity by placing weights of less mass on
35、thearm. If the response is non-linear, have the equipment repairedto make response linear.9.4 Re-check the zero of the shrink holder with no load onthe shrink arm.FIG. 2 Circuit Diagram for Shrink, Tension HolderD283808310. Conditioning10.1 ConditioningCondition the test specimens at 23 62C (73.4 6
36、3.6F) and 50 6 10 % relative humidity for notless than 40 h prior to test in accordance with Procedure A ofPractice D 618, unless otherwise specified by agreement or therelevant ASTM material specification. In cases of disagree-ment, the tolerances shall be 61C (61.8F) and 65%relative humidity.11. P
37、rocedure ATotally Restrained11.1 Clamp the first specimen in the holder under theminimum positive loading force achievable. Under no circum-stances shall it exceed the maximum force observed afterimmersion of the specimen. The holder must be at ambienttemperature.11.2 Initiate data collection before
38、 immersing holder intobath. Immerse the shrink holder and specimen into the bath,taking special care to lower it in such a manner that thespecimen remains in a horizontal position. Immerse smoothlyand quickly without bumping or jerking the holder. Keep thespecimen in the bath long enough to reach a
39、peak or plateauand 2 to 3 s thereafter.NOTE 2Slight variations from the horizontal will generally produce anegligible error. The error, however, will increase in significance as theshrink force approaches zero. A jig may be used to aid in maintaining theproper alignment of the holder while immersing
40、 the specimen.11.3 Stop data collection and immerse the holder in a beakerof cold water until it returns to ambient temperature. Thenremove the specimen.11.4 Repeat 11.1-11.3 for each specimen in the set.11.5 Repeat 11.1-11.4 for temperature increments of nomore than 10C through the shrink temperatu
41、re range of thefilm or sheeting under test. This is usually the softeningtemperature range of the material.12. Procedure BPredetermined Shrink BeforeRestraint12.1 Clamp the specimen in the holder so that the linesmarked in 7.2.2 coincide with the inside edges of the clamps.12.2 Follow the instructio
42、ns given in 11.1-11.5.13. Calculation13.1 Record the maximum force (peak or plateau whicheveris greater) to the nearest 0.045 N (0.01 lbf or 4.5 gf).13.2 Shrink ForceDivide the maximum force by thespecimen width to obtain shrink force. Express shrink force ineither newtons per metre or pounds-force
43、per inch.13.3 Shrink TensionDivide the maximum force in new-tons (or pounds force) by the product of the average thicknessin millimetres (inches) and the specimen width in millimetres(inches) to obtain the shrink tension in pascals.14. Orientation Release Stress14.1 Prepare graphs of shrink tension
44、as a function oftemperature for each film direction of interest, using dataobtained by Procedure A.14.2 The maximum shrink tension developed for eachdirection of interest, as determined by the graphs prepared in14.1, is the orientation release stress.15. Report15.1 Report the following information:1
45、5.1.1 Complete sample identification,15.1.2 Procedure used,15.1.3 Percent shrink prior to restraint,15.1.4 Test temperature,15.1.5 Film direction (longitudinal, transverse),15.1.6 Number of specimens tested,15.1.7 Average thickness of each specimen,15.1.8 Shrink force of each specimen,15.1.9 Shrink
46、tension of each specimen,15.1.10 Average results, standard deviation, and confidencelimits where applicable, and15.1.11 Orientation release stress, film direction, and tem-perature where it occurs, plus plots used to obtain it.16. Precision and Bias16.1 RepeatabilityThe standard deviation of measure
47、-ments of shrink force within a laboratory is usually a functionof the magnitude of the measurement between the limits of 9.8N/m (0.056 lbf/in.) and 175 N/m (1.0 lbf/in.). The standarddeviation will increase with the magnitude of the measurement.The percent coefficient of variation (s/X3 100) will g
48、enerallynot exceed 10 %.16.2 ReproducibilityThe standard deviation of averagesof shrink force obtained by different laboratories is relativelyconstant for measurements between the limits of 9.8 N/m(0.056 lbf/in.) and 175 N/m (1.0 lbf/in.) and generally will notexceed 5.8 N/m (0.034 lbf/in.).16.3 Bia
49、sThe bias of this test method cannot be assessedsince applicable accepted reference materials are not available.17. Keywords17.1 film; orientation release stress; shrink force; shrinktension; thin sheetingD2838084SUMMARY OF CHANGESCommittee D20 has identified the location of selected changes to this standard since the last issue(D 2838 - 07) that may impact the use of this standard. (November 1, 2008)(1) Revised Section 10.Committee D20 has identified the location of selected changes to this standard since the last issue(D 2838 - 02) that may impact th
