ASTM D4470-97(2010)
(Test Method)Standard Test Method for Static Electrification
Standard Test Method for Static Electrification
SIGNIFICANCE AND USE
Whenever two dissimilar materials are contacted and separated, excess electrostatic charge (triboelectric charge) will be found on these materials if at least one of the materials is a good insulator. This excess charge gives rise to electric fields which can exert forces on other objects. If these fields exceed the breakdown strength of the surrounding gas, a disruptive discharge (spark) may occur. The heat from this discharge may ignite explosive atmospheres, the light may fog photosensitized materials, and the current flowing in a static discharge may cause catastrophic failure of solid state devices. Electric forces may be used beneficially, as in electrostatic copying, spray painting and beneficiation of ores. They may be detrimental as when they attract dirt to a surface or when they cause sheets to stick together. Since most plastic materials in use today have very good insulating qualities, it is difficult to avoid generation of static electricity. Since it depends on many parameters, it is difficult to generate static electricity reliably and reproducibly.
SCOPE
1.1 This test method covers the generation of electrostatic charge, the measurement of this charge and its associated electric field, and the test conditions which must be controlled in order to obtain reproducible results. This test method is applicable to both solids and liquids. This test method is not applicable to gases, since a transfer of a gas with no solid impurities in it does not generate an electrostatic charge. This test method also does not cover the beneficial uses of static electrification, its associated problems or hazards, or the elimination or reduction of unwanted electrostatic charge.
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 limitations prior to use.
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Standards Content (Sample)
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Designation:D4470 −97 (Reapproved 2010)
Standard Test Method for
Static Electrification
This standard is issued under the fixed designation D4470; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 conducting material (conductor), n—amaterialwithin
which an electric current is produced by application of a
1.1 This test method covers the generation of electrostatic
voltage between points on or within the material.
charge, the measurement of this charge and its associated
3.1.1.1 Discussion—The term “conducting material” is usu-
electric field, and the test conditions which must be controlled
ally applied only to those materials in which a relatively small
in order to obtain reproducible results. This test method is
potentialdifferenceresultsinarelativelylargecurrentsinceall
applicable to both solids and liquids. This test method is not
materials appear to permit some conduction current. Metals
applicable to gases, since a transfer of a gas with no solid
and strong electrolytes are examples of conducting materials.
impurities in it does not generate an electrostatic charge. This
3.1.2 electric field strength, n—the magnitude of the vector
test method also does not cover the beneficial uses of static
force on a point charge of unit value and positive polarity.
electrification, its associated problems or hazards, or the
elimination or reduction of unwanted electrostatic charge.
3.1.3 excess electrostatic charge, n—the algebraic sum of
all positive and negative electric charges on the surface of, or
1.2 The values stated in SI units are to be regarded as the
in, a specific volume.
standard.
3.1.4 insulatingmaterial(insulator),n—amaterialinwhich
1.3 This standard does not purport to address all of the
a voltage applied between two points on or within the material
safety concerns, if any, associated with its use. It is the
produces a small and sometimes negligible current.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3.1.5 resistivity, surface—the surface resistance multiplied
bility of regulatory limitations prior to use.
by that ratio of specimen surface dimensions (width of elec-
trodes defining the current path divided by the distance
2. Referenced Documents between electrodes) which transforms the measured resistance
to that obtained if the electrodes formed the opposite sides of
2.1 ASTM Standards:
a square.
D618Practice for Conditioning Plastics for Testing
3.1.5.1 Discussion—Surface resistivity is expressed in
D5032PracticeforMaintainingConstantRelativeHumidity
ohms.Itispopularlyexpressedalsoasohms/square(thesizeof
by Means of Aqueous Glycerin Solutions
thesquareisimmaterial).Surfaceresistivityisthereciprocalof
E104Practice for Maintaining Constant Relative Humidity
surface conductivity.
by Means of Aqueous Solutions
3.2 Definitions of Terms Specific to This Standard:
3. Terminology 3.2.1 apparent contact area, n—the area of contact between
two flat bodies.
3.1 Definitions:
3.2.1.1 Discussion—It is the area one would calculate by
measuringthelengthandwidthoftherectangularmacroscopic
contact region.
This test method is under the jurisdiction of ASTM Committee D09 on
3.2.2 dissipative material, n—a material with a volume
Electrical and Electronic Insulating Materials and is the direct responsibility of
4 12
Subcommittee D09.12 on Electrical Tests. resistivitygreaterthan10 ohm-cmandlessthan10 ohm-cm,
Current edition approved Oct. 1, 2010. Published October 2010. Originally
a resistivity range between conductive and insulating material
approved in 1985. Last previous edition approved in 2004 as D4470–97(2004).
as defined in this test method.
DOI: 10.1520/D4470-97R10.
Vosteen, R. E., and Bartnikas, R., Chapter 5, “Electrostatic Charge
3.2.3 real contact area, n—the regions of contact between
Measurements,” Engineering Dielectrics, Vol. IIB, Electrical Properties of Solid
two bodies through which mechanical actions or reactions are
Insulating Materials, Measurement Techniques, R. Bartnikas, Editor, ASTM STP
transferred.
926, ASTM, Philadelphia, 1987.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 3.2.3.1 Discussion—Since real bodies are never perfectly
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. Annual Book of ASTM Standards, Vol 11.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4470−97 (2010)
smooth,atleastonamicroscopicscale,therealcontactareaof Of these types of transport, pinch rollers and sliding down
apparently flat materials is always less than the apparent chutes generate the largest amount of charge. Generally, the
contact area. better the contact (larger real contact area), the greater will be
the charge generated. Pinch rollers are usually a high pressure,
3.2.4 triboelectric charge generation—theformation,with
smallapparentareaofcontact,leadingtoarelativelylargereal
or without rubbing, of electrostatic charges by separation of
area of contact between the sheet and rollers. Sliding serves to
contacting materials.
multiply the real area of contact over that which would be
obtained with a contact without sliding.
4. Significance and Use
5.2 Electrostatic Charge Measurements—Fig. 1 shows a
4.1 Whenever two dissimilar materials are contacted and
block diagram of the typical components necessary for this
separated,excesselectrostaticcharge(triboelectriccharge)will
measurement while Fig. 2 shows a schematic diagram.
be found on these materials if at least one of the materials is a
5.2.1 Faraday Cage—The Faraday cage consists of two
good insulator. This excess charge gives rise to electric fields
conducting enclosures, one enclosed and insulated from the
which can exert forces on other objects. If these fields exceed
other.Theinnerenclosureiselectricallyconnectedtotheshunt
the breakdown strength of the surrounding gas, a disruptive
capacitors and the electrometer input. It is insulated from the
discharge(spark)mayoccur.Theheatfromthisdischargemay
outerenclosurebyrigid,veryhighresistance,insulatorswhich
ignite explosive atmospheres, the light may fog photosensi-
haveresistancepracticallyindependentofrelativehumidity(an
tized materials, and the current flowing in a static discharge
example is polytetrafluoroethylene (PFTE). The inner enclo-
may cause catastrophic failure of solid state devices. Electric
sure should be of such construction that the test specimen can
forces may be used beneficially, as in electrostatic copying,
be substantially surrounded by it. The outer enclosure is
spray painting and beneficiation of ores. They may be detri-
connected to ground and serves to shield the inner enclosure
mentalaswhentheyattractdirttoasurfaceorwhentheycause
from external fields which could affect the measurement.
sheets to stick together. Since most plastic materials in use
5.2.2 ShuntCapacitors—Shuntcapacitorsmaybenecessary
todayhaveverygoodinsulatingqualities,itisdifficulttoavoid
to reduce the measured voltage to a range where it can be read
generation of static electricity. Since it depends on many
by the electrometer. Such shunt capacitors must have very low
parameters, it is difficult to generate static electricity reliably
leakage insulation relatively unaffected by relative humidity
and reproducibly.
changes (for example, polystyrene). They should be kept
5. Apparatus
short-circuited when not in use and should be protected from
high relative humidity.
5.1 Charging Mechanisms—The charging mechanisms can
5.2.3 Electrometer—The electrometer voltmeter measures
be constructed in a variety of ways, and should preferably be
the voltage developed on the Faraday cage and shunt capaci-
made as analagous to the particular application as possible.
tors. The electrometer must have a high impedence (such as
Someexamplesofchargingmechanismsaredescribedin5.1.1,
100TΩorhigher)andalowdriftrateconcordantwiththetime
5.1.2, and 5.1.3.
of measurement. Electrometers are available with built-in
5.1.1 Powder or Liquids Transported Through Tubes or
shunt capacitors selected by a range switch. Electrometers are
DownTroughs—Contactbetweenthespecimenandwallofthe
also available with negative feedback circuits which minimize
tube will charge the specimen or the tube, or both. Either the
the effect of input capacity. These circuits reduce the input
specimenorthetubemustbeinsulating,orpartiallyinsulating.
voltagedroptonearlyzerominimizingtheeffectsofleakageof
When the specimen is separated from the tube, electrostatic
charge to ground and polarization of insulators.
charge will be generated. This charge may be measured by
5.2.4 Display Unit—The display unit indicates the voltage
catching a known amount of the specimen in a Faraday cage,
developed on the electrometer. If the input capacitance is
orthechargeremainingonthetubemaybemeasured.Atrough
known and does not vary, or if negative feedback is used, the
may be substituted for the tube and gravity used to effect the
display unit may be calibrated to measure the charge on the
movement of the specimen along the trough.
Faraday cage directly. The unit may be a meter showing the
5.1.2 Webs Transported Over Rollers—Contact between the
instantaneous value or it may be more complicated equipment,
web and the roller surface will charge the web if it is an
such as a strip chart recorder giving a reading as a function of
insulator or partial insulator. If the rollers are insulators or
time. The electrometer and display unit may be combined in
partial insulators they will become charged thus lowering, or
one instrument.
eliminating, the charge transfer to the web after a period of
time. The electric field on the web may be measured with a
fieldmeter, or the charge on the web can be measured with a
cylindrical Faraday cage if the width of the web is not too
large.
5.1.3 Transport of Insulating or Partially Insulating Sheet
Material—Sheetmaterialsmaybetransportedonairlayers,by
sliding down chutes, by vacuum platens, and by pinch rollers.
Shashoua, V. E., “Static Electricity in Polymers: Theory and Measurement,” FIG. 1 Block Diagram of Apparatus for Measurement of Electro-
Journal of Polymer Science, Vol XXXIII, 1958, pp 65–85. static Charge
D4470−97 (2010)
adequately shield the sensor and associated circuits from noise
generated by the motor driving the rotating vane.
5.3.2 Vibrating Plate Fieldmeter—In Fig. 2 a vibrating
sensor plate is enclosed in a sensing unit. A charged material
placed in front of the sensing unit induces a charge in the face
plate and in the sensor. As the sensor moves away from the
charged material, less charge is induced on the sensor. As it
moves toward the charged material, more charge is induced on
the sensor. This produces a periodically varying electrical
FIG. 2 Schematic Diagram signal on the sensor plate. This signal is amplified, processed,
and read on a suitable display unit. Charge polarity is deter-
mined by phase detection circuits. Again, the sensor and
5.2.5 Electrical Connnections:
associated circuits must be adequately shielded from noise
5.2.5.1 Connections to Faraday Cage—Connections from
generated by the driving mechanism.
the inner enclosure of the Faraday cage to the shunt capacitors
5.3.3 DisplayUnit—Thedisplayunitmaycontainthepower
andtheelectrometermustbehighlyinsulatedandwellshielded
switch, circuits to process the signal (amplifiers, rectifiers,
from external electric fields.They should be stable in time and
phase detectors, and the like), and a meter showing the
in the different ambient conditions in which measurements are
instantaneous value of the electric field. Alternatively, a strip
made.Preferably,theyshouldberigid,althoughshieldedcable
chart recorder giving a reading as a function of time may be
may be used if it is low noise cable where flexing will not lead
used.
to the generation of static charge between the shield and the
insulation of the cable.When using cable or rigid connections,
6. Test Conditions
the capacitance of these must be taken into account when
calculating or measuring the capacitance of the input system,
6.1 Staticelectrificationdependsuponmanyparameters.To
unless using an electrometer with negative feedback.
obtain reproducible results apparatus must be constructed to
5.2.5.2 Connections to Display Unit—No special connect-
control all the measurable parameters and to keep all the
ing wires are normally necessary between the electrometer
unmeasurable parameters constant. The known parameters are
output and the display unit. Manufacturer’s recommendations
as follows:
shouldbefollowedwhenconnectinganexternaldisplayunitto
6.1.1 Cleanliness of Material Surfaces—Static electrifica-
the electrometer output.
tionofcontactingmaterialsisasurfacephenomenon.Thus,the
surfaces must be kept in an uncontaminated state. Since
5.3 Electric Field Strength Measurements—The diagram of
contamination is very difficult to measure, efforts should be
Fig. 3 illustrates the major parts of a commercially available
made to keep the surfaces clean. Storing samples under
rotating vane fieldmeter. A commercially available vibrating
constant ambient conditions, such as temperature and relative
plate fieldmeter is illustrated in Fig. 4. The setup required for
humidity, is a must. Introduction of different gases into the air
calibration of a fieldmeter is shown in Fig. 5.
wheretheycanbeadsorbedonthesurfaceshasbeenknownto
5.3.1 Rotating Vane Fieldmeter—In Fig. 1 an electrostati-
change the results of an electrification test. Dirt particles
cally charged material placed at a known distance from the
settling on one or more surfaces can alter the results. Even
sensing unit will induce electrostatic charge in the face of the
contact to another surface during a test can alter a surface and
sensing unit, the rotating vane, and the fixed sensor plate.
givenonreproducibleresultsinsubsequenttests.Sometimes,it
When the rotating vane covers the sensor plate, the induced
is better to use new samples from a sufficiently uniform
charge in the sensor is small.When the opening in the rotating
material than to re-use samples. “Cleaning” of a surface with
vane is opposite the sensor, the induced charge in the sensor is
solvents rarely cleans the surface. It probably produces a
a maximum. Thus the rotating vane produces a periodically
uniform, reproducible, sta
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