ASTM D6988-03
(Guide)Standard Guide for Determination of Thickness of Plastic Film Test Specimens
Standard Guide for Determination of Thickness of Plastic Film Test Specimens
SCOPE
1.1 This guide covers the determination of the thickness of plastic films where the thickness is used directly in determining the results of tests for various properties. Use this practice except as otherwise required in material specifications or in applicable test standards.
Note 1—Films are defined as having thicknesses 0.250 mm [ 0.010 in.].
Note 2—Alternative methods are acceptable if they meet the requirements of measurement precision as noted in this guide.
Note 3—This guide is not intended to address the sampling techniques or the measurement of film thickness for the commercial classification of commercial products or for quality control purposes.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.
Note 4—ISO 4593 is similar but differs in technical content and scope.
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Designation:D6988–03
Standard Guide for
Determination of Thickness of Plastic Film Test Specimens
This standard is issued under the fixed designation D 6988; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This guide covers the determination of the thickness of 3.1 Definitions—See Terminologies D 883 and D 4805, and
plasticfilmswherethethicknessisuseddirectlyindetermining ISO 472 for definitions pertinent to this guide.
the results of tests for various properties. Use this practice 3.2 Definitions of Terms Specific to This Standard:
except as otherwise required in material specifications or in 3.2.1 absolute uncertainty (of a measurement), n—the
applicable test standards. smallest division that can be read directly on the instrument
used for measurement.
NOTE 1—Films are defined as having thicknesses # 0.250 mm [#
3.2.2 calibration, n—the set of operations that establishes,
0.010 in.].
under specified conditions, the relationship between values
NOTE 2—Alternative methods are acceptable if they meet the require-
measured or indicated by an instrument or system, and the
ments of measurement precision as noted in this guide.
NOTE 3—This guide is not intended to address the sampling techniques
corresponding reference standard or known values derived
or the measurement of film thickness for the commercial classification of
from the appropriate reference standards.
commercial products or for quality control purposes.
3.2.3 dead-weight micrometer, n—an instrument capable of
1.2 The values stated in SI units are to be regarded as the measuringthethicknessofthinfilmsutilizingaweighttoapply
standard.
uniform pressure to the specimen.
1.3 This standard does not purport to address all of the 3.2.4 verification, n—proof, with the use of calibrated
safety concerns, if any, associated with its use. It is the
standards or standard reference materials that the calibrated
responsibility of the user of this standard to establish appro- instrument is operating within specified requirements.
priate safety and health practices and determine the applica-
4. Summary of Methods
bility of regulatory requirements prior to use.
4.1 This guide describes four different methods for the
NOTE 4—ISO 4593 is similar but differs in technical content and scope.
thickness measurement of plastic film specimens.The methods
(identified as MethodsA, B, C, and D) use different microme-
2. Referenced Documents
ters that actuate the weights in different manners or utilize
2.1 ASTM Standards:
different means of reading the thickness.
D 618 Practice for Conditioning Plastics Material for Test-
4.2 It is permissible to use other instruments, including
ing
non-contact instruments and instruments using alternative
D 883 Terminology Relating to Plastics
readout systems in place of dials provided they meet or exceed
D 4805 Terminology for Plastics Standards
the precision requirements noted in this practice.
D 5947 Test Methods for Physical Dimensions of Solid
Plastics Specimens
5. Significance and Use
D 6287 Practice for Cutting Film and Sheeting Test Speci-
5.1 This guide shall be followed where precise dimensions
mens
are necessary for the calculation of properties expressed in
2.2 ISO Standard:
3 physical units. It is not intended to replace practical thickness
ISO 472 Plastics—Vocabulary
measurements based on commercial portable tools, nor is it
implied that thickness measurements made by the procedures
will agree exactly.
This guide is under the jurisdiction of ASTM Committee D20 on Plastics and
is the direct responsibility of Subcommittee D20.19 on Films and Sheeting.
Current edition approved Dec. 1, 2003. Published January 2004.
6. Apparatus
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
6.1 The instruments described in this guide share many
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on common features:
the ASTM website.
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6988–03
6.1.1 Adead-weight gage calibrated in accordance with the andalinearopticalencoderusingascaleofincrementsnotless
guidelines described in Appendix X2 and consisting of the than 100 lines/mm and capable of reading within 0.5 µm with
following: a 10 mm range.
6.5 Apparatus D—Automatically Operated Thickness Gage
NOTE 5—Additional guidance for calibration and verification of gages
with Digital Display:
can be found in Test Methods D 5947.
6.5.1 SimilartoApparatusBexceptitemploysanelectronic
NOTE 6—Since there is such a wide variety of instruments in use, there
device with a digital readout capable of a resolution not less
canbesignificantdifferencesintheaccuracyofdifferentinstrumenttypes.
than 0.5 µm and repeatable readings to within 6 1 µm at zero
The values stated for each type of apparatus are intended to be typical of
setting or on a steel gage block.
that type of instrument.
6.5.2 A preferred drop rate between 0.750 and 1.500 mm/s
6.1.1.1 Apresser foot that moves in an axis perpendicular to
between 0.625 and 0.025 mm on the dial and a capacity of at
the anvil face;
least 0.775 mm.
6.1.1.2 The surfaces of the presser foot and anvil (which
6.6 Other Instruments:
contact the specimen) parallel to within 2.5 µm;
6.6.1 Other instruments are commercially available that
6.1.1.3 Aspindle, vertically oriented if a dead-weight appa-
utilize different methods of measuring thickness. These are
ratus;
generally non-contact devices employing ultrasonic response,
6.1.1.4 An indicator essentially capable of repeatable read-
electricalcapacitance,orsimilarmaterialpropertiesthatcanbe
ings within 6 0.001 mm at zero setting, or on a steel gage
correlated to thickness. Some of these devices are also de-
block;
signed to provide a means of measuring discreet sections of
6.1.1.5 A frame, housing the indicator, of such rigidity that
film in a continuous scanning mode. Instruments of this nature
a load of 15 N applied to the housing, out of contact with the
are acceptable provided they meet or exceed the precision
presser foot spindle (or any weight attached thereto), will
requirements noted in this practice and the requirements of the
produce a deflection of the frame not greater than the smallest
applicable material or product specifications or applicable test
scale division or digital count on the indicator;
standards.
6.1.1.6 If employed, a dial diameter of at least 50 mm and
7. Test Specimens
graduated continuously to read directly to the nearest 2.5 µm.
The dial can be equipped with a revolution counter that 7.1 The test specimens shall be prepared from plastic films
displays the number of complete revolutions of the large hand, that have been cut to the required dimensions according to
or
Practice D 6287.
7.2 Prepare and condition each specimen in equilibrium
6.1.1.7 An electronic instrument having a digital readout in
with the appropriate standard laboratory test conditions or in
place of the dial indicator if that instrument meets all of the
accordance with the conditions specified in the test method
other requirements of this guide, and
applicable to the specific material for test.
6.1.1.8 The force applied to the presser foot spindle and the
7.3 For each specimen, take precautions to prevent damage
force necessary to register a change in the indicator reading
or contamination that will adversely affect the measurements.
shall be less than the force that will cause deformation of the
7.4 Unless otherwise specified, make all dimension mea-
specimen. The force applied to the presser foot spindle and the
surements at the standard laboratory atmosphere in accordance
forcenecessarytojustpreventachangeintheindicatorreading
with Practice D 618.
shallbemorethantheminimumpermissibleforcespecifiedfor
a specimen.
8. Procedure
6.2 Apparatus A—Manually Operated Thickness Gage:
8.1 General Guidelines:
6.2.1 Aninstrumenthavingapresserfootandspindlethatis
manually lifted and lowered.
NOTE 7—In this section, the word “method” denotes a combination of
both a specific apparatus and a procedure describing its use.
6.3 Apparatus B—Automatically Operated Thickness Gage:
6.3.1 A pneumatic or motor-operated instrument having a
8.1.1 The selection of a method for measurement of film
presser foot spindle that is lifted and lowered either by a
thickness is influenced by the characteristics of the film for
pneumatic cylinder or by a constant-speed motor through a
measurement. Each material and, in some cases, film construc-
mechanicallinkagesuchthattherateofdescent(foraspecified
tion in the case of multi-layer structures, will differ in its
range of distances between the presser foot surface and anvil)
response to test method parameters, which include, but are not
and dwell time on the specimen are within the limits specified
limited to, compressibility, rate of loading, ultimate load, dwell
for the material being measured.
time, and dimensions of the presser foot and anvil. For a
6.3.2 A preferred drop rate between 0.750 and 1.500 mm/s specific plastic material or structure, these responses can, in
between 0.625 and 0.025 mm on the dial and a capacity of at some cases, cause measurements made using one method to
least 0.775 mm. differ significantly from measurements made using another
method. The procedures that follow are categorized according
6.4 Apparatus C—Manually Operated Thickness Gage with
to the materials to which each applies. See Appendix X1.
Linear Optical Encoder:
6.4.1 Similar to Apparatus A except it employs a digital
NOTE 8—The pressure exerted by the gage on the specimen being
device with an electronic readout capable of repeatable read-
measuredshallnotdistortordeformthespecimen.Forthinfilms,#0.025
ings to within 6 1 µm at zero setting or on a steel gage block mm [0.001 in.], or films which exhibit visual deformation during
D6988–03
measurement, a maximum pressure of 70 kPa [10 psi] is suggested. For
8.2.6 Observe the reading. After correcting the observed
thicker or stiffer films, a pressure range between 160 and 185 kPa [23 and
indicated dimension, record the corrected dimension value. A
27 psi] is suggested. See Table 1.
method for developing a calibration correction curve is de-
NOTE 9—An electronic gage can be substituted for the dial gage in
scribed in X2.4.
MethodAor B if the presser foot and anvil meet the requirements of that
8.2.7 Move the specimen to another measurement position,
method.
and repeat the steps given in 8.2.3 through 8.2.6.
8.1.2 The presence of contaminating substances on the
8.2.8 Unless otherwise specified, make and record at least
surfaces of the test specimens, presser foot, anvil, or spindle
three dimension measurements on each specimen. The arith-
can interfere with dimension measurements and result in
metic mean of all dimension values is the dimension of the
erroneous readings. To help prevent this interference, select
specimen.
only clean specimens for testing, and keep them and the
8.2.9 Recheck the instrument zero setting after measuring
dimension measuring instrument covered until ready to make
each specimen. If a change is observed, this is usually
measurements. Warning—Cleaning the presser foot and anvil
indicative of contamination on the contact surfaces and will
surfaces as described in X2.1 can cause damage to digital
require cleaning. (See Warning in 8.1.2 and Note 9.)
electronic gages resulting in very expensive repairs by the
instrument manufacturer. Obtain procedures for cleaning such 8.3 Method B:
electronic gages from the instrument manufacturer to prevent 8.3.1 Using Apparatus B and specimens in conformance
these costs.
with Section 7, place the instrument on a solid, level, clean
8.1.3 One thickness determination per specimen or the table or bench that is free of excessive vibration. Confirm that
average thickness determined by a continuous scanning instru-
the anvil and presser foot surfaces are clean.
ment is acceptable if it can be demonstrated that the overall
8.3.2 Applypowertothemotororairtothepneumatics,and
thickness does not deviate > 6 10 % from the average. This is
allow the instrument to reach a thermal equilibrium with the
especially applicable if measurements are being made for
ambient. Equilibrium is attained when the zero point adjust-
reference, that is, to report nominal film thickness, and are not
ment becomes negligible. Do not stop the motor or remove the
required for the determination of specific properties.
air until all of the measurements are made. This will minimize
8.1.4 Some instruments do not require calibration. For these
any tendency to disturb the thermal equilibrium between the
instruments, periodic verification procedures should be con-
instrument and ambient during the dimension measurements.
ducted according to the recommendations of the instrument
8.3.3 Insert and position a specimen for the first measure-
supplier.
ment when the opening between the presser foot and anvil is
8.2 Method A:
near its maximum.
8.2.1 Using Apparatus A and specimens in conformance
8.3.4 Observe the dial reading while the presser foot is at
with Section 7, place the instrument on a solid, level, clean
rest on the specimen surface. After correcting the observed
table or bench that is free of excessive vibration. Confirm that
indicated dimension, record the corrected dimension value. A
the anvil and presser foot surfaces are clean. Adjust the zero
method for developing a calibration correction curve is de-
point.
scribed in X2.4.
8.2.2 Lower the presser foot on an area of the specimen for
8.3.5 While the presser foot is near its maximum lift, move
measurement. Observe this reading.
the specimen to another measurement position, and repeat the
8.2.3 Raise the presser foot slightly.
steps given in 8.3.3 and 8.3.4.
8.2.4 Move the specimen to the first measurement location,
8.3.6 Unless otherwise specified, make and record at least
and lower the presser foot to a reading approximately 0.007 to
three thickness measurements on each specimen. The arith-
0.010 mm higher than the initial reading of 8.2.2.
metic mean of all dimension values is the thickness of the
8.2.5 Drop the foot onto the specimen (see Warning in
specimen.
8.1.2).
8.3.7 Recheck the instrument zero setting after measuring
NOTE 10—This procedure minimizes small error
...
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