1、Designation: D 6988 08Standard Guide forDetermination of Thickness of Plastic Film Test Specimens1This standard is issued under the fixed designation D 6988; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 guide covers the determination of the thickness ofplastic films where the thickness is used directly in determiningthe result
3、s of tests for various properties. Use this practiceexcept as otherwise required in material specifications or inapplicable test standards.NOTE 1Films are defined as having thicknesses#0.250 mm #0.010in.NOTE 2Alternative methods are acceptable if they meet the require-ments of measurement precision
4、as noted in this guide.NOTE 3This guide is not intended to address the sampling techniquesor the measurement of film thickness for the commercial classification ofcommercial products or for quality control purposes.1.2 The values stated in SI units are to be regarded as thestandard.1.3 This standard
5、 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 requirements prior to use.NOTE 4This standard and ISO 459
6、3 address the same subject matterbut differ in technical content.2. Referenced Documents2.1 ASTM Standards:2D 618 Practice for Conditioning Plastics for TestingD 883 Terminology Relating to PlasticsD 4805 Terminology for Plastics Standards3D 5947 Test Methods for Physical Dimensions of SolidPlastics
7、 SpecimensD 6287 Practice for Cutting Film and Sheeting Test Speci-mens2.2 ISO Standard:ISO 472 PlasticsVocabulary43. Terminology3.1 DefinitionsSee Terminologies D 883 and D 4805, andISO 472 for definitions pertinent to this guide.3.2 Definitions of Terms Specific to This Standard:3.2.1 absolute unc
8、ertainty (of a measurement), nthesmallest division that can be read directly on the instrumentused for measurement.3.2.2 calibration, nthe set of operations that establishes,under specified conditions, the relationship between valuesmeasured or indicated by an instrument or system, and thecorrespond
9、ing reference standard or known values derivedfrom the appropriate reference standards.3.2.3 dead-weight micrometer, nan instrument capable ofmeasuring the thickness of thin films utilizing a weight to applyuniform pressure to the specimen.3.2.4 verification, nproof, with the use of calibratedstanda
10、rds or standard reference materials that the calibratedinstrument is operating within specified requirements.4. Summary of Methods4.1 This guide describes four different methods for thethickness measurement of plastic film specimens. The methods(identified as Methods A, B, C, and D) use different mi
11、crome-ters that actuate the weights in different manners or utilizedifferent means of reading the thickness.4.2 It is permissible to use other instruments, includingnon-contact instruments and instruments using alternativereadout systems in place of dials provided they meet or exceedthe precision re
12、quirements noted in this practice.5. Significance and Use5.1 This guide is intended to provide recommendations andsuggested good practices to determine precise dimensionswhen necessary for the calculation of properties expressed inphysical units. It is not intended to replace practical thickness1Thi
13、s guide is under the jurisdiction of ASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.19 on Film and Sheeting.Current edition approved Nov. 1, 2008. Published November 2008. Originallyapproved in 2003. Last previous edition approved in 2007 as D 6988 - 07.2For refer
14、enced 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.3Withdrawn.4Available from American National Standards Institute (ANSI)
15、, 25 W. 43rd St.,4th Floor, New York, NY 10036.1*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.measurements based on commercial portable tools, nor is itimplied that t
16、hickness measurements made by the procedureswill agree exactly.6. Apparatus6.1 The instruments described in this guide share manycommon features:6.1.1 A dead-weight gauge calibrated in accordance withthe guidelines described in Appendix X2 and consisting of thefollowing:NOTE 5Additional guidance for
17、 calibration and verification of gaugescan be found in Test Method D 5947.NOTE 6Since there is such a wide variety of instruments in use, therecan be significant differences in the accuracy of different instrument types.The values stated for each type of apparatus are intended to be typical ofthat t
18、ype of instrument.6.1.1.1 Apresser foot that moves in an axis perpendicular tothe anvil face;6.1.1.2 The surfaces of the presser foot and anvil (whichcontact the specimen) parallel to within 2.5 m;6.1.1.3 A spindle, vertically oriented if a dead-weight appa-ratus;6.1.1.4 An indicator essentially cap
19、able of repeatable read-ings within 6 0.001 mm at zero setting or within 60.001 mmwhen using a steel gauge block;6.1.1.5 A frame, housing the indicator, of such rigidity thata load of 15 N applied to the housing, out of contact with thepresser foot spindle (or any weight attached thereto), willprodu
20、ce a deflection of the frame not greater than the smallestscale division or digital count on the indicator;6.1.1.6 If employed, a dial diameter of at least 50 mm andgraduated continuously to read directly to the nearest 2.5 m.The dial can be equipped with a revolution counter thatdisplays the number
21、 of complete revolutions of the large hand,or6.1.1.7 An electronic instrument having a digital readout inplace of the dial indicator if that instrument meets all of theother requirements of this guide, and6.1.1.8 The force applied to the presser foot spindle and theforce necessary to register a chan
22、ge in the indicator readingshall be less than the force that will cause deformation of thespecimen. The force applied to the presser foot spindle and theforce necessary to just prevent a change in the indicator readingshall be more than the minimum permissible force specified fora specimen.6.2 Appar
23、atus AManually Operated Thickness Gauge:6.2.1 An instrument having a presser foot and spindle that ismanually lifted and lowered.6.3 Apparatus BAutomatically Operated ThicknessGauge:6.3.1 A pneumatic or motor-operated instrument having apresser foot spindle that is lifted and lowered either by apneu
24、matic cylinder or by a constant-speed motor through amechanical linkage such that the rate of descent (for a specifiedrange of distances between the presser foot surface and anvil)and dwell time on the specimen are within the limits specifiedfor the material being measured.6.3.2 A preferred drop rat
25、e between 0.750 and 1.500 mm/sbetween 0.625 and 0.025 mm on the dial and a capacity of atleast 0.775 mm.6.4 Apparatus CManually Operated Thickness Gaugewith Linear Optical Encoder:6.4.1 Similar to Apparatus A except it employs a digitaldevice with an electronic readout capable of repeatable read-ing
26、s to within 6 1 m at zero setting or on a steel gauge blockand a linear optical encoder using a scale of increments not lessthan 100 lines/mm and capable of reading within 0.5 m witha 10 mm range.6.5 Apparatus DAutomatically Operated ThicknessGauge with Digital Display:6.5.1 Similar toApparatus B ex
27、cept it employs an electronicdevice with a digital readout capable of a resolution not lessthan 0.5 m and repeatable readings to within 6 1 m at zerosetting or on a steel gauge block.6.5.2 A preferred drop rate between 0.750 and 1.500 mm/sbetween 0.625 and 0.025 mm on the dial and a capacity of atle
28、ast 0.775 mm.6.6 Other Instruments:6.6.1 Other instruments are commercially available thatutilize different methods of measuring thickness. These aregenerally non-contact devices employing ultrasonic response,electrical capacitance, or similar material properties that can becorrelated to thickness.
29、Some of these devices are also de-signed to provide a means of measuring discreet sections offilm in a continuous scanning mode. Instruments of this natureare acceptable provided they meet or exceed the precisionrequirements noted in this practice and the requirements of theapplicable material or pr
30、oduct specifications or applicable teststandards.7. Test Specimens7.1 The test specimens shall be prepared from plastic filmsthat have been cut to the required dimensions according toPractice D 6287.7.2 Allow specimens to equilibrate at 23 6 2C (73.4 63.6F) and 50 6 10 % relative humidity in accorda
31、nce withProcedure A of Practice D 618 unless otherwise specified byagreement or the relevant ASTM material specification.7.3 Unless otherwise specified, make all dimension mea-surements at the same conditions used for equilibration.7.4 For each specimen, take precautions to prevent damageor contamin
32、ation that will adversely affect the measurements.8. Procedure8.1 General Guidelines:NOTE 7In this section, the word “method” denotes a combination ofboth a specific apparatus and a procedure describing its use.8.1.1 The selection of a method for measurement of filmthickness is influenced by the cha
33、racteristics of the film formeasurement. Each material and, in some cases, film construc-tion in the case of multi-layer structures, will differ in itsresponse to test method parameters, which include, but are notlimited to, compressibility, rate of loading, ultimate load, dwelltime, and dimensions
34、of the presser foot and anvil. For aspecific plastic material or structure, these responses can, inD6988082some cases, cause measurements made using one method todiffer significantly from measurements made using anothermethod. The effects due to differences in elasticity are ad-dressed in Appendix X
35、1.TABLE 1 Instrument GuidelinesMethodDiameter of PresserFoot or Spindle, mmAPressure on Specimen,Approximate, kPaBA 3.2 to 12.7 160 to 185B 3.2 to 12.7 160 to 185C 3.2 to 12.7 160 to 185D 3.2 to 12.7 160 to 185AIt is known that the diameters of the pressure foot and spindle can influencethe results.
36、 Data obtained from instruments with different geometries may not becomparable.BThe total force applied to the specimen shall be less than the force that willcause permanent deformation or distortion of the specimen. For very thin ordeformable films, a practical pressure range of 5 to 70 kPa has bee
37、n found to besuitable.NOTE 8The pressure exerted by the gauge on the specimen beingmeasured shall not distort or deform the specimen. For thin films,#0.025mm 0.001 in., or films which exhibit visual deformation duringmeasurement, a maximum pressure of 70 kPa 10 psi is suggested. Forthicker or stiffe
38、r films, a pressure range between 160 and 185 kPa 23 and27 psi is suggested. See Table 1.NOTE 9An electronic gauge can be substituted for the dial gauge inMethod A or B if the presser foot and anvil meet the requirements of thatmethod.8.1.2 The presence of contaminating substances on thesurfaces of
39、the test specimens, presser foot, anvil, or spindlecan interfere with dimension measurements and result inerroneous readings. To help prevent this interference, selectonly clean specimens for testing, and keep them and thedimension measuring instrument covered until ready to makemeasurements. (Warni
40、ngCleaning the presser foot and anvilsurfaces as described in X2.1 can cause damage to digitalelectronic gauges resulting in very expensive repairs by theinstrument manufacturer. Obtain procedures for cleaning suchelectronic gauges from the instrument manufacturer to preventthese costs.)8.1.3 One th
41、ickness determination per specimen or theaverage thickness determined by a continuous scanning instru-ment is acceptable if it can be demonstrated that the overallthickness does not deviate 6 10 % from the average. This isespecially applicable if measurements are being made forreference, that is, to
42、 report nominal film thickness, and are notrequired for the determination of specific properties.8.1.4 Some instruments do not require calibration. For theseinstruments, periodic verification procedures should be con-ducted according to the recommendations of the instrumentsupplier.8.2 Method A:8.2.
43、1 Using Apparatus A and specimens in conformancewith Section 7, place the instrument on a solid, level, cleantable or bench that is free of excessive vibration. Confirm thatthe anvil and presser foot surfaces are clean. Adjust the zeropoint.8.2.2 Lower the presser foot on an area of the specimen for
44、measurement. Observe this reading.8.2.3 Raise the presser foot slightly.8.2.4 Move the specimen to the first measurement location,and lower the presser foot to a reading approximately 0.007 to0.010 mm higher than the initial reading of 8.2.2.8.2.5 Drop the foot onto the specimen (see Warning in8.1.2
45、).NOTE 10This procedure minimizes small errors present when thepressure foot is lowered slowly onto the specimen and does not allow thepresser foot to seat properly.8.2.6 Observe the reading. After correcting the observedindicated dimension, record the corrected dimension value. Amethod for developi
46、ng a calibration correction curve is de-scribed in X2.4.8.2.7 Move the specimen to another measurement position,and repeat the steps given in 8.2.3 through 8.2.6.8.2.8 Unless otherwise specified, make and record at leastthree dimension measurements on each specimen. The arith-metic mean of all dimen
47、sion values is the dimension of thespecimen.8.2.9 Recheck the instrument zero setting after measuringeach specimen. If a change is observed, this is usuallyindicative of contamination on the contact surfaces and willrequire cleaning. (See Warning in 8.1.2 and Note 9.)8.3 Method B:8.3.1 Using Apparat
48、us B and specimens in conformancewith Section 7, place the instrument on a solid, level, cleantable or bench that is free of excessive vibration. Confirm thatthe anvil and presser foot surfaces are clean.8.3.2 Apply power to the motor or air to the pneumatics, andallow the instrument to reach a ther
49、mal equilibrium with theambient. Equilibrium is attained when the zero point adjust-ment becomes negligible. Do not stop the motor or remove theair until all of the measurements are made. This will minimizeany tendency to disturb the thermal equilibrium between theinstrument and ambient during the dimension measurements.8.3.3 Insert and position a specimen for the first measure-ment when the opening between the presser foot and anvil isnear its maximum.8.3.4 Observe the dial reading while the presser foot is atrest on the specimen surface. After co
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