ASTM D7027-05
(Test Method)Standard Test Method for Evaluation of Scratch Resistance of Polymeric Coatings and Plastics Using an Instrumented Scratch Machine
Standard Test Method for Evaluation of Scratch Resistance of Polymeric Coatings and Plastics Using an Instrumented Scratch Machine
SIGNIFICANCE AND USE
Scratch tests are performed on specimens:
(1) to evaluate the scratch or mar resistance of a particular material,
(2) to rank the relative scratch resistance of different materials, or
(3) to determine the scratching coefficient of friction of materials.
Since polymers exhibit mechanical properties that are strongly dependent on temperature, the test method prescribed herein is designed to yield reproducible results when users perform tests under the similar testing environment and on specimens of the same material and surface texture that are subjected to the same conditioning procedures.
Certain polymers are self-healing (recoverable) when subjected to scratches and other physical deformations because of their viscoelastic and relaxation properties. It is important to note the difference between the instantaneous (if readily measurable) and the post-scratch damages and appropriately compare results to ensure reproducibility.
“Whitening” of the scratched surface is a key damage mechanism that has prompted much concern in automotive and other applications where surface aestheticism is important. This type of damage is undesirable because it is evident to human eyes. The critical normal load at which this phenomenon appears serves as a benchmark in ranking material performance.
For polymers that do not exhibit whitening, a scratch groove from severe ploughing is still highly noticeable. In such cases, the normal load required to achieve a certain scratch width shall be reported to characterize scratch visibility and scratch resistance. The critical scratch width shall be decided by users in accordance with the specific material and remains the same throughout a set of tests for a consistent comparison. The variation of the scratch width as a function of the applied load shall also be plotted for comparison purposes.
SCOPE
1.1 This test method describes a laboratory procedure using an instrumented scratch machine to produce and quantify surface damage under controlled conditions. This test method is able to characterize the mar and scratch resistance of polymers by measuring many significant material parameters. The scratch-inducing and data acquisition process is automated to avoid user-influenced effects that may affect the results.
1.2 The values stated in SI units are to be regarded as 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 limitations prior to use.
Note 1—FLTM BN 108-13, ISO 1518 and ISO 12137-2 are related to this test method; the contents are significantly different from this method.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D7027–05
Standard Test Method for
Evaluation of Scratch Resistance of Polymeric Coatings and
Plastics Using an Instrumented Scratch Machine
This standard is issued under the fixed designation D 7027; 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 ISO1518 MethodsofTestforPaints—PartE2:ScratchTest
ISO 12137-2 Methods of Test for Paints—Part E18: Deter-
1.1 This test method describes a laboratory procedure using
mination of Mar Resistance using a Pointed Stylus
an instrumented scratch machine to produce and quantify
ISO 3290 Rolling Bearings: Balls—Dimensions and Toler-
surface damage under controlled conditions. This test method
ances
is able to characterize the mar and scratch resistance of
2.3 Other Standards:
polymers by measuring many significant material parameters.
FLTM BN 108-13 Resistance to Scratching
Thescratch-inducinganddataacquisitionprocessisautomated
to avoid user-influenced effects that may affect the results.
3. Terminology
1.2 The values stated in SI units are to be regarded as
3.1 Definitions:
standard.
3.1.1 critical normal load, n—the normal load at which
1.3 This standard does not purport to address all of the
whitening(see3.1.10)ofthematerialwithinthescratchgroove
safety concerns, if any, associated with its use. It is the
first occurs.
responsibility of the user of this standard to establish appro-
3.1.2 friction force, n—the tangential force present at the
priate safety and health practices and determine the applica-
interfacebetweentwobodieswhenonebodymovesortendsto
bility of regulatory limitations prior to use.
moverelativetotheother,undertheactionofanexternalforce.
NOTE 1—FLTM BN 108-13, ISO 1518 and ISO 12137-2 are related to
Depending on the penetration of the indenter into the test
this test method; the contents are significantly different from this method.
surface,frictionforcecanbecausedbysliding(relativelysmall
displacement of material) or ploughing (gross removal/
2. Referenced Documents
displacement of materials).
2.1 ASTM Standards:
3.1.3 mar resistance, n—ability to resist surface damage
D 618 Practice for Conditioning Plastics for Testing
from the light abrasion by small objects. Quantitatively, it can
D 638 Test Method for Tensile Properties of Plastics
be characterized by the loss in gloss, increase in haze, or slight
D 1894 Test Method for Static and Kinetic Coefficients of
shift in gray level.
Friction of Plastic Film and Sheeting
3.1.4 normal load, n—a load acted onto the scratch stylus
E 177 Practice for Use of the Terms Precision and Bias in
that is imposed in a vertically downward direction while
ASTM Test Methods
maintaining its perpendicularity with the direction of scratch.
F 2215 Specification for Balls, Bearings, Ferrous and Non-
3.1.5 scratch depth, n—the vertical distance to be measured
ferrous for Use in Bearings, Valves, and Bearing Applica-
from the trough of the scratch groove to (a) its peak or (b) to
tions
the undisturbed specimen surface.
G99 Test Method for Wear Testing with a Pin-On-Disk
3.1.6 scratch resistance, n—ability to withstand damage
Apparatus
that is accompanied by the gross deformation typically asso-
G 171 TestMethodforScratchHardnessofMaterialsUsing
ciated with sharp objects that may involve compressing,
a Diamond Stylus
ploughing, and shearing off of material. Quantification can be
2.2 ISO Standards:
accomplished through the measurement of scratch depth
(3.1.5), scratch width (3.1.7) and other geometric characteris-
This test method is under the jurisdiction ofASTM Committee D20 on Plastics tics of the scratch.
and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
3.1.7 scratch width, n—the horizontal distance between the
Current edition approved June 1, 2005. Published June 2005.
two peaks on both sides of the scratch groove.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
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
the ASTM website.
3 4
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St., Available from Ford Motor Company, Central Laboratories, 15000 Century
4th Floor, New York, NY 10036. Drive, Dearborn, MI 48120.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7027–05
3.1.8 scratching, v—mechanical removal, or displacement, herein is designed to yield reproducible results when users
or both of material from a surface by the action of abrasive perform tests under the similar testing environment and on
particles, or protuberances, or both sliding across the surfaces. specimens of the same material and surface texture that are
3.1.9 scratching coeffıcient of friction, n—the ratio of the subjected to the same conditioning procedures.
frictionforce(3.1.2)tothenormalload(3.1.4).Thiscoefficient 5.3 Certain polymers are self-healing (recoverable) when
is a measure of the resistance of a material to scratching. For subjected to scratches and other physical deformations because
tests conducted under constant load, two distinct quantities of their viscoelastic and relaxation properties. It is important to
may be characterized, the static and kinetic coefficients. The note the difference between the instantaneous (if readily
static coefficient is related to the friction force measured prior measurable) and the post-scratch damages and appropriately
to the movement of the scratch stylus while the kinetic compare results to ensure reproducibility.
coefficient is related to the constant friction force measured in 5.4 “Whitening” of the scratched surface is a key damage
sustainingthismovement.Thisquantityisnotequivalenttothe mechanismthathaspromptedmuchconcerninautomotiveand
coefficient of friction, which is obtained in accordance with other applications where surface aestheticism is important.
TestMethodD 1894andissimilartothestylusdragcoefficient This type of damage is undesirable because it is evident to
as defined in Test Method G 171. human eyes. The critical normal load at which this phenom-
3.1.10 whitening, n—the visible damage along the scratch enon appears serves as a benchmark in ranking material
groove of the surface caused by microcracking, voiding, performance.
crazing, and debonding. 5.5 For polymers that do not exhibit whitening, a scratch
groovefromsevereploughingisstillhighlynoticeable.Insuch
4. Summary of Test Method
cases, the normal load required to achieve a certain scratch
4.1 This test method utilizes an automated scratch machine
width shall be reported to characterize scratch visibility and
to administer controlled scratch tests on polymeric specimens. scratch resistance. The critical scratch width shall be decided
Two basic test modes (Test Modes A and B) are presented.
by users in accordance with the specific material and remains
4.1.1 Test Mode A—A scratch is applied onto the specimen
the same throughout a set of tests for a consistent comparison.
surface under an increasing load from 2 to 50 N 6 0.1 N over
The variation of the scratch width as a function of the applied
a distance of 0.1 m 6 0.0005 m at a constant rate of 0.1 m/s 6
load shall also be plotted for comparison purposes.
0.0005 m/s - average. This test mode is intended to determine
6. Apparatus
the critical normal load at which whitening will occur for a
material system. For materials that do not show any whitening,
6.1 General Description—The instrumented scratch ma-
the normal load at which a predetermined scratch width exists
chine described here has been developed at Texas A&M
will be used as a basis for comparison. To compare and rank
University under the auspices of the Scratch Behavior Consor-
different materials, the normal load shall be plotted as a
tium; a schematic of the scratch machine is shown in Fig. 1.
function of the scratch width.
The instrument consists of a sample stage, clamping devices, a
4.1.2 Test Mode B—A scratch is applied onto the specimen
spring-load/dead-load system, and a horizontal motion servo
surface under a constant load of 30 N 6 0.1 N over a distance
system. Optional systems such as load and position sensing
of0.1m 60.0005mataconstantrateof0.1m/s 60.0005m/s
system, data acquisition and computer systems can be included
- average. This test mode is intended to evaluate the homoge-
when position and load data are required. An environmental
neous response of the material and establish the scratching
chamber can also be added for non room-temperature (23 6
coefficient of friction.
2°C) tests. For post-scratch study, evaluation instruments like
4.2 Scratched surface can be visually inspected or by using
optical microscopes, flatbed scanners and image capturing
evaluationtoolstostudythesurfacedamage.ForTestModeA,
tools can separately be used.
the critical normal load is determined by the onset of the
6.2 Spring-Load Mechanism—The instrument is a stylus-
whitening of the material due to scratch. Measurement of the
type scratcher in which a 1-mm-diameter spherical tip is used
scratch widths, or depths, or both shall also be taken to aid the
to scratch the surface of a flat specimen. It consists of a sample
quantification of scratch resistance.
stage with dimensions of 305 by 305 mm on which test
4.3 Scratching coefficient of friction as defined in 3.1.9 can
specimens can be anchored. The spring-load driven mecha-
be computed for material characterization using the friction
nism,capableofgenerating0to75Nofnormalload,exertsthe
force and normal load data recorded during tests.
force onto the scratch stylus, either at a constant magnitude or
increasingly to a desired magnitude.
5. Significance and Use
6.3 Dead-Load Mechanism—The dead-load mechanism, as
5.1 Scratch tests are performed on specimens:
presented in Fig. 1, is similar to the setup of the spring-load
(1) to evaluate the scratch or mar resistance of a particular
mechanism as in 6.2, except that it uses dead weights for the
material,
(2) to rank the relative scratch resistance of different
materials, or
The sole source of supply of the apparatus known to the committee at this time
is Surface Machine Systems, LLC, 2151 Harvey Mitchell Parkway, Suite 223,
(3) to determine the scratching coefficient of friction of
College Station,TX 77840. If you are aware of alternative suppliers, please provide
materials.
this information to ASTM International Headquarters. Your comments will receive
5.2 Since polymers exhibit mechanical properties that are
careful consideration at a meeting of the responsible technical committee , which
strongly dependent on temperature, the test method prescribed you may attend.
D7027–05
FIG. 1 Schematic of the Instrumented Scratch Machine
normalloadduringscratch.ThissetupcanalsobeusedforTest tip in their material and geometry. The material of the scratch
Mode B, where a constant load is required. stylustipshallbestainlesssteelanditsshapeshallbespherical
6.4 Horizontal Motion Servo System—Ahigh-precisionmo- with a diameter of 1 mm. Surface quality of the tip shall be of
tor controlled via microprocessor, actuates the scratch stylus. Grade 10 or better, in accordance with Specification F 2215 or
The horizontal speed of the scratch stylus can be set at a ISO 3290.
constant rate between 0 to 400 mm/s or with a constant
NOTE 2—Other materials for the stylus tip are acceptable so long as
acceleration from 0 to 400 mm/s .
they have higher indentation hardness than the test material. If the relative
6.5 Load and Position Sensing System (optional)—If re-
hardness of the materials is significantly different from the stainless steel,
quired, the instrument can be incorporated with devices to
the resulting scratch test data will be dissimilar as those yielded by a
monitor the normal load, friction force, instantaneous scratch
stainless steel spherical tip. Using a tip of other geometry is optional but
their results shall not supersede those from the spherical tip tests.
depth and horizontal position. The friction force acting on the
stylus shall be measured with an accuracy of 0.1 N. The data
7. Hazards
acquired for depth, horizontal position and velocity of the
stylus shall have accuracy of 0.5 µm, 5 µm and 0.0005 m/s
7.1 The scratch carriage could suddenly accelerate to 400
(average), respectively.
mm/s; precaution shall be taken to avoid having hands, fingers,
6.6 Data Acquisition and Computer Systems (optional)—
and loose clothing pinched by the moving part.
Connections from the sensing system to the computer system
7.2 When performing tests at extreme temperatures, ensure
must be insulated against electromagnetic interference to
thatthermallyinsulatedglovesareusedinhandlingspecimens.
ensure clean and reliable data.The computer system shall have
the capability to collect the force and position data. The
8. Test Specimens and Sample Preparation
minimumsamplingrateforthedataacquisitionsystemshallbe
8.1 Materials—The test method can be applied to a variety
kept at 1000 data points per second for reliable and accurate
of polymeric and coating materials.The materials must be able
data.
to be prepared to the desired dimensions and able to withstand
6.7 Environmental Chamber (optional)—An environmental
thestressesimposedduringthetestwithoutfailureorexcessive
chamber with heating and cooling controls allows experiments
fracture. The materials being tested shall be described by
to be performed from –50 to 100°C.
dimensions, surface finish, material type, form, composition,
6.8 Evaluation Instruments—Other than visual inspection,
processing treatment and, when appropriate, indentation hard-
the scratch grooves can be further examined with optical
ness (see Test MethodG99).
microscopes, flatbed scanners, or interferometers, or a combi-
nation of the three, for measuring scratch widths and depths. 8.2 Tensile Specimens—Injection-molded tensile bars as
Sincethecapabilityandsensitivityofeachdevicearedifferent, specified in Test Method D 638 (Test specimen I-III) are
itisrequiredthattheadoptedmethodofevaluationbereported. acceptable for use with this test. Typical thickness shall be
For the purpose of quantifying whitening, other instruments between 3 and 10 mm. Since the scratch length for different
that are capable of measuring reflected light intensity in the testmodesistakentobe100mm,thespecimenshallbeatleast
scratch groove can be used. The basic requirement for any 140 mm in leng
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.