ASTM D2838-95
(Test Method)Standard Test Method for Shrink Tension and Orientation Release Stress of Plastic Film and Thin Sheeting
Standard Test Method for Shrink Tension and Orientation Release Stress of Plastic Film and Thin Sheeting
SCOPE
1.1 This test method covers the determination of the shrink tension and related characteristics, that is, shrink force and orientation release stress, of heat-shrinkable plastic film and sheeting of less than 1.0 mm (0.04 in.) thickness. Two procedures are described that permit the measurement of shrink forces at predetermined temperatures. They are as follows:
1.1.1 Procedure A is designed to measure the maximum force exerted by a specimen that is totally restrained from shrinking as it is heated rapidly to a specific temperature.
1.1.2 Procedure B is designed to measure the maximum force exerted by a specimen that is permitted to shrink a predetermined amount prior to restraint while being heated rapidly to a specific temperature.
1.2 Orientation release stress can be determined from the data obtained using Procedure A.
1.3 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.
Note 1—There is no equivalent ISO test method.
1.4 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 limitations prior to use.
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Designation: D 2838 – 95
Standard Test Method for
Shrink Tension and Orientation Release Stress of Plastic
Film and Thin Sheeting
This standard is issued under the fixed designation D 2838; 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 E 1 Specification for ASTM Thermometers
1.1 This test method covers the determination of the shrink
3. Terminology
tension and related characteristics, that is, shrink force and
3.1 Definitions of Terms Specific to This Standard:
orientation release stress, of heat-shrinkable plastic film and
3.1.1 orientation release stress—the maximum shrink ten-
sheeting of less than 0.8 mm (0.03 in.) thickness. Two
sion developed by a film in a specified direction throughout its
procedures are described that permit the measurement of shrink
range of shrink temperatures while totally restrained from
forces at predetermined temperatures. They are as follows:
shrinking.
1.1.1 Procedure A is designed to measure the maximum
3.1.2 sheeting—as defined for this test method, material
force exerted by a specimen that is totally restrained from
having a maximum thickness of 0.8 mm (0.03 in.).
shrinking as it is heated rapidly to a specific temperature.
3.1.3 shrink force—the force per original unit width devel-
1.1.2 Procedure B is designed to measure the maximum
oped by a film in a specified direction and at a specified
force exerted by a specimen that is permitted to shrink a
temperature in its attempt to shrink while under restraint.
predetermined amount prior to restraint while being heated
3.1.4 shrink tension—the force per original average cross-
rapidly to a specific temperature.
sectional area developed by a film in a specified direction and
1.2 Orientation release stress can be determined from the
at a specified temperature in its attempt to shrink while under
data obtained using Procedure A.
restraint.
1.3 The values stated in SI units are to be regarded as the
standard. The values in parentheses are for information only.
4. Summary of Test Method
NOTE 1—There is no equivalent ISO test method.
4.1 The ends of a 25.4-mm (1-in.) wide strip of film or
sheeting are clamped in the arms of a shrink tension holder (see
1.4 This standard does not purport to address all of the
Fig. 1), one arm of which contains strain gages. The holder is
safety concerns, if any, associated with its use. It is the
immersed in a hot bath and the force exerted by the film is
responsibility of the user of this standard to establish appro-
detected by strain gages attached to one arm and recorded by
priate safety and health practices and determine the applica-
a fast action strip chart recorder. The tests may be carried out
bility of regulatory limitations prior to use.
with or without free shrinkage of the material before restraint.
2. Referenced Documents
Other properties may be calculated from the measured forces,
sample parameters, and temperatures used.
2.1 ASTM Standards:
D 374 Test Methods for Thickness of Solid Electrical Insu-
2 5. Significance and Use
lation
5.1 As a result of the manufacturing process, internal
D 618 Practice for Conditioning Plastics and Electrical
stresses are locked into the film and these can be released by
Insulating Materials for Testing
heating. For any given type of film or sheeting, the tempera-
D 1898 Practice for Sampling of Plastics
tures at which shrinkage will begin are related to processing
techniques employed to manufacture the film and also may be
related to a phase transition in the base resin.
5.2 Shrink tension affects the appearance and performance
This test method is under the jurisdiction of ASTM Committee D-20 on Plastics
and is the direct responsibility of Subcommittee D20.19 on Film and Sheeting.
of a film in a shrink-packaging application. It may also be used
Current edition approved Nov. 10, 1995. Published January 1996. Originally
to determine the degree and direction of orientation. The
e1
published as D 2838 – 69. Last previous edition D 2838 – 83 (1989) .
orientation exerts a great influence upon important physical
The latest version of this document differs only from the previous document in
that Keywords and an ISO equivalency statement have been added.
Annual Book of ASTM Standards, Vol 10.01.
3 4
Annual Book of ASTM Standards, Vol 08.01. Annual Book of ASTM Standards, Vol 14.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 2838
FIG. 1 Design for Shrink Tension Holder
characteristics such as tensile strength, stiffness, tear resis- 6.2 Strain Gage Conditioner, applicable to a 120-V four-
tance, and impact strength. arm bridge.
5.3 Data from Procedure A are most useful for determining 6.3 Recorder, having a pen response of no more than 30 ms
the degree and direction of orientation, orientation release from 10 to 90 % of full-scale deflection. A chart width of at
stress, and the maximum force that the film can exert at a given least 100 mm is preferable.
temperature. 6.4 Sample Cutter, capable of cutting 25.4 6 0.2-mm (1 6
5.4 Since, in actual applications, film is seldom, if ever, 0.01-in.) wide strips of at least 127 mm (5 in.) in length.
totally restrained, data from Procedure B are useful in estimat- 6.5 Constant-Temperature Liquid Bath, capable of control-
ing the force an item to be packaged will actually receive and ling accurately to 60.5°C and covering the range of interest,
in predicting appearance of packaged items. usually from 50 to 175°C.
5.5 The characterization of shrink tension as a function of 6.6 Thermometer, covering the range of interest and con-
temperature, and the resultant determination of orientation forming to the requirement of Specification E 1.
release stress and its corresponding temperature, is usually 6.7 Liquid Bath, which will not plasticize or react with
carried out only on an audit basis for a particular material of specimens. Polyethylene glycol, glycerin, and water have been
specified thickness for a defined fabrication process. For found to have wide applicability. Silicone oils are useful for
purposes of quality control and of determining conformity to samples requiring temperatures above 175°C.
specification limits, the measurement of shrink tension at only 6.8 Thickness Gage, capable of measuring the thickness of
one or two specified temperatures is normally sufficient. samples in compliance with Test Methods D 374.
7. Sampling
6. Apparatus
7.1 Sampling must be performed in a manner that ensures
6.1 Shrink Tension Holder —A suggested design is por-
trayed in Fig. 1 and Fig. 2.
The following systems have been found satisfactory: Daytronics Model 9005
Mainframe equipped with a Model 9178 strain gage conditioner, a Model 9259
Model CS-205 Shrink Tension Holder, supplied by Custom Scientific Instru- peak-track-hold unit, and a Model 9530 digital indicator interfaced to an appropriate
ments, 13 Wing Drive, Whippany, NJ 07981, has been found satisfactory for this recorder. Honeywell Model 1858 Recorder equipped with a Model 1885A strain
purpose. gage control module. Other systems may function equally well.
D 2838
FIG. 2 Circuit Diagram for Shrink, Tension Holder
that the kind of information desired will be obtained. No single 9. Preparation of Apparatus
procedure for all situations can be given, but Practice D 1898
9.1 Set up constant-temperature bath and equilibrate at the
provides guidelines for use in planning sampling procedures.
temperature chosen for the test. Shrink tension will normally
be observed near the softening temperature of polymeric
8. Test Specimens
material.
8.1 The test specimens shall consist of strips of uniform
9.2 Connect shrink-tension holder to recorder. Balance and
width and thickness. The width of the specimens shall be 25.4
set at zero in accordance with the manufacturer’s instructions.
6 0.2 mm (1.0 6 0.01 in.).
10. Calibration
8.2 Length of Test Specimens:
8.2.1 Specimens for Procedure A shall be at least 127 mm (5
10.1 Place the shrink holder vertically on a solid level
in.) in length.
tabletop with the handle pointing down toward the floor and set
8.2.2 Length of specimens for Procedure B is dependent
t
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