ASTM D4470-97(2004)
(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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An American National Standard
Designation: D4470 – 97 (Reapproved 2004)
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 conductingmaterial(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—Theterm“conductingmaterial”isusu-
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
3.1.3 excess electrostatic charge, n—the algebraic sum of
elimination or reduction of unwanted electrostatic charge.
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-
3.1.5 resistivity, surface—the surface resistance multiplied
priate safety and health practices and determine the applica-
by that ratio of specimen surface dimensions (width of elec-
bility of regulatory limitations prior to use.
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.
D618 Practice for Conditioning Plastics for Testing
3.1.5.1 Discussion—Surface resistivity is expressed in
D5032 Practice for Maintaining Constant Relative Humid-
ohms.Itispopularlyexpressedalsoasohms/square(thesizeof
ity by Means of Aqueous Glycerin Solutions
thesquareisimmaterial).Surfaceresistivityisthereciprocalof
E104 Practice 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 apparentcontactarea,n—theareaofcontactbetween
two flat bodies.
3.1 Definitions:
3.2.1.1 Discussion—It is the area one would calculate by
measuringthelengthandwidthoftherectangularmacroscopic
This test method is under the jurisdiction of ASTM Committee D09 on
contact region.
Electrical and Electronic Insulating Materials and is the direct responsibility of
3.2.2 dissipative material, n—a material with a volume
Subcommittee D09.12 on Electrical Tests.
Current edition approved March 1, 2004. Published March 2004. Originally
resistivitygreaterthan10 ohm-cmandlessthan10 ohm-cm,
approved in 1985. Last previous edition approved in 1997 as D4470–97. DOI:
a resistivity range between conductive and insulating material
10.1520/D4470-97R04.
as defined in this test method.
Vosteen, R. E., and Bartnikas, R., Chapter 5, “Electrostatic Charge Measure-
ments,” Engineering Dielectrics, Vol. IIB, Electrical Properties of Solid Insulating 3.2.3 real contact area, n—the regions of contact between
Materials, Measurement Techniques , R. Bartnikas, Editor, ASTM STP 926,ASTM,
two bodies through which mechanical actions or reactions are
Philadelphia, 1987.
transferred.
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. 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 (2004)
3.2.3.1 Discussion—Since real bodies are never perfectly sliding down chutes, by vacuum platens, and by pinch rollers.
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
3.2.4 triboelectric charge generation—theformation,with the charge generated. Pinch rollers are usually a high pressure,
or without rubbing, of electrostatic charges by separation of smallapparentareaofcontact,leadingtoarelativelylargereal
contacting materials. area of contact between the sheet and rollers. Sliding serves to
multiply the real area of contact over that which would be
4. Significance and Use
obtained with a contact without sliding.
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
be found on these materials if at least one of the materials is a measurement while Fig. 2 shows a schematic diagram.
5.2.1 Faraday Cage—The Faraday cage consists of two
good insulator. This excess charge gives rise to electric fields
which can exert forces on other objects. If these fields exceed conducting enclosures, one enclosed and insulated from the
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 Shunt Capacitors—Shunt capacitors may be neces-
todayhaveverygoodinsulatingqualities,itisdifficulttoavoid
sary to reduce the measured voltage to a range where it can be
generation of static electricity. Since it depends on many
readbytheelectrometer.Suchshuntcapacitorsmusthavevery
parameters, it is difficult to generate static electricity reliably
low leakage insulation relatively unaffected by relative humid-
and reproducibly.
ity 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,
100TVorhigher)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 WebsTransportedOverRollers—Contactbetweenthe
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
Shashoua, V. E., “Static Electricity in Polymers: Theory and Measurement,” FIG. 1 Block Diagram of Apparatus for Measurement of
Journal of Polymer Science, Vol XXXIII, 1958, pp 65–85. Electrostatic Charge
D4470 – 97 (2004)
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 Display Unit—The display unit may contain the
andtheelectrometermustbehighlyinsulatedandwellshielded
power switch, circuits to process the signal (amplifiers, recti-
from external electric fields.They should be stable in time and
fiers, 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
6.1 Staticelectrificationdependsuponmanyparameters.To
calculating or measuring the capacitance of the input system,
obtain reproducible results apparatus must be constructed to
unless using an electrometer with negative feedback.
control all the measurable parameters and to keep all the
5.2.5.2 Connections to Display Unit—No special connect-
unmeasurable parameters constant. The known parameters are
ing wires are normally necessary between the electrometer
as follows:
output and the display unit. Manufacturer’s recommendations
shouldbefollowedwhenconnectinganexternaldisplayunitto 6.1.1 Cleanliness of Material Surfaces—Static electrifica-
tionofcontactingmaterialsisasurfacephenomenon.Thus,the
the electrometer output.
5.3 Electric Field Strength Measurements—The diagram of surfaces must be kept in an uncontaminated state. Since
contamination is very difficult to measure, efforts should be
Fig. 3 illustrates the major parts of a commercially available
rotating vane fieldmeter. A commercially available vibrating made to keep the surfaces clean. Storing samples under
constant ambient conditions, such as temperature and relative
plate fieldmeter is illustrated in Fig. 4. The setup required for
calibration of a fieldmeter is shown in Fig. 5. humidity, is a must. Introduction of different gases into the air
wheretheycanbeadsorbedonthesurfaceshasbeenknownto
5.3.1 Rotating Vane Fieldmeter—In Fig. 1 an electrostati-
cally charged material placed at a known distance from the change the results of an electrification test. Dirt particles
settling on one or more surfaces can alter the results. Even
sensing unit will induce electrostatic charge in the face of the
sensing unit, the rotating vane, and the fixed sensor plate. contact to another surface during a test can alter a surface and
givenonreproducibleresultsinsubsequenttests.Sometimes,it
When the rotating vane covers the sensor plate, the induced
charge in the sensor is small.When the opening in the rotating is better to use new samples from a sufficiently uniform
material than to re-use samples. “Cleaning” of a surface with
vane is opposite the sensor, the induced charge in the sensor is
a maximum. Thus the rotating vane produces a periodically solvents rarely cleans the surface. It probably produces
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