1、Designation: D 4470 97 (Reapproved 2004)An American National StandardStandard Test Method forStatic Electrification1This standard is issued under the fixed designation D 4470; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the generation of electrostaticcharge, the measurement of this charge and its associated
3、electric field, and the test conditions which must be controlledin order to obtain reproducible results. This test method isapplicable to both solids and liquids. This test method is notapplicable to gases, since a transfer of a gas with no solidimpurities in it does not generate an electrostatic ch
4、arge. Thistest method also does not cover the beneficial uses of staticelectrification, its associated problems or hazards, or theelimination or reduction of unwanted electrostatic charge.21.2 The values stated in SI units are to be regarded as thestandard.1.3 This standard does not purport to addre
5、ss all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D 618 Practice
6、for Conditioning Plastics for TestingD 5032 Practice for Maintaining Constant Relative Humid-ity by Means of Aqueous Glycerin SolutionsE 104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous Solutions3. Terminology3.1 Definitions:3.1.1 conducting material (conductor), na materia
7、l withinwhich an electric current is produced by application of avoltage between points on or within the material.3.1.1.1 DiscussionThe term “conducting material” is usu-ally applied only to those materials in which a relatively smallpotential difference results in a relatively large current since a
8、llmaterials appear to permit some conduction current. Metalsand strong electrolytes are examples of conducting materials.3.1.2 electric field strength, nthe magnitude of the vectorforce on a point charge of unit value and positive polarity.3.1.3 excess electrostatic charge, nthe algebraic sum ofall
9、positive and negative electric charges on the surface of, orin, a specific volume.3.1.4 insulating material (insulator), na material in whicha voltage applied between two points on or within the materialproduces a small and sometimes negligible current.3.1.5 resistivity, surfacethe surface resistanc
10、e multipliedby that ratio of specimen surface dimensions (width of elec-trodes defining the current path divided by the distancebetween electrodes) which transforms the measured resistanceto that obtained if the electrodes formed the opposite sides ofa square.3.1.5.1 DiscussionSurface resistivity is
11、 expressed inohms. It is popularly expressed also as ohms/square (the size ofthe square is immaterial). Surface resistivity is the reciprocal ofsurface conductivity.3.2 Definitions of Terms Specific to This Standard:3.2.1 apparent contact area, nthe area of contact betweentwo flat bodies.3.2.1.1 Dis
12、cussionIt is the area one would calculate bymeasuring the length and width of the rectangular macroscopiccontact region.3.2.2 dissipative material, na material with a volumeresistivity greater than 104ohm-cm and less than 1012ohm-cm,a resistivity range between conductive and insulating materialas de
13、fined in this test method.3.2.3 real contact area, nthe regions of contact betweentwo bodies through which mechanical actions or reactions aretransferred.1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibilit
14、y ofSubcommittee D09.12 on Electrical Tests.Current edition approved March 1, 2004. Published March 2004. Originallyapproved in 1985. Last previous edition approved in 1997 as D 4470 97.2Vosteen, R. E., and Bartnikas, R., Chapter 5, “Electrostatic Charge Measure-ments,” Engineering Dielectrics, Vol.
15、 IIB, Electrical Properties of Solid InsulatingMaterials, Measurement Techniques , R. Bartnikas, Editor, ASTM STP 926, ASTM,Philadelphia, 1987.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vo
16、lume information, refer to the standards Document Summary page onthe ASTM website.4Annual Book of ASTM Standards, Vol 11.03.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.3.1 DiscussionSince real bodies are never perfectlysmooth
17、, at least on a microscopic scale, the real contact area ofapparently flat materials is always less than the apparentcontact area.3.2.4 triboelectric charge generationthe formation, withor without rubbing, of electrostatic charges by separation ofcontacting materials.54. Significance and Use4.1 When
18、ever two dissimilar materials are contacted andseparated, excess electrostatic charge (triboelectric charge) willbe found on these materials if at least one of the materials is agood insulator. This excess charge gives rise to electric fieldswhich can exert forces on other objects. If these fields e
19、xceedthe breakdown strength of the surrounding gas, a disruptivedischarge (spark) may occur. The heat from this discharge mayignite explosive atmospheres, the light may fog photosensi-tized materials, and the current flowing in a static dischargemay cause catastrophic failure of solid state devices.
20、 Electricforces may be used beneficially, as in electrostatic copying,spray painting and beneficiation of ores. They may be detri-mental as when they attract dirt to a surface or when they causesheets to stick together. Since most plastic materials in usetoday have very good insulating qualities, it
21、 is difficult to avoidgeneration of static electricity. Since it depends on manyparameters, it is difficult to generate static electricity reliablyand reproducibly.5. Apparatus5.1 Charging MechanismsThe charging mechanisms canbe constructed in a variety of ways, and should preferably bemade as anala
22、gous to the particular application as possible.Some examples of charging mechanisms are described in 5.1.1,5.1.2, and 5.1.3.5.1.1 Powder or Liquids Transported Through Tubes orDown TroughsContact between the specimen and wall of thetube will charge the specimen or the tube, or both. Either thespecim
23、en or the tube must be insulating, or partially insulating.When the specimen is separated from the tube, electrostaticcharge will be generated. This charge may be measured bycatching a known amount of the specimen in a Faraday cage,or the charge remaining on the tube may be measured.Atroughmay be su
24、bstituted for the tube and gravity used to effect themovement of the specimen along the trough.5.1.2 Webs Transported Over RollersContact between theweb and the roller surface will charge the web if it is aninsulator or partial insulator. If the rollers are insulators orpartial insulators they will
25、become charged thus lowering, oreliminating, the charge transfer to the web after a period oftime. The electric field on the web may be measured with afieldmeter, or the charge on the web can be measured with acylindrical Faraday cage if the width of the web is not toolarge.5.1.3 Transport of Insula
26、ting or Partially Insulating SheetMaterialSheet materials may be transported on air layers, bysliding down chutes, by vacuum platens, and by pinch rollers.Of these types of transport, pinch rollers and sliding downchutes generate the largest amount of charge. Generally, thebetter the contact (larger
27、 real contact area), the greater will bethe charge generated. Pinch rollers are usually a high pressure,small apparent area of contact, leading to a relatively large realarea of contact between the sheet and rollers. Sliding serves tomultiply the real area of contact over that which would beobtained
28、 with a contact without sliding.5.2 Electrostatic Charge MeasurementsFig. 1 shows ablock diagram of the typical components necessary for thismeasurement while Fig. 2 shows a schematic diagram.5.2.1 Faraday CageThe Faraday cage consists of twoconducting enclosures, one enclosed and insulated from the
29、other. The inner enclosure is electrically connected to the shuntcapacitors and the electrometer input. It is insulated from theouter enclosure by rigid, very high resistance, insulators whichhave resistance practically independent of relative humidity (anexample is polytetrafluoroethylene (PFTE). T
30、he inner enclo-sure should be of such construction that the test specimen canbe substantially surrounded by it. The outer enclosure isconnected to ground and serves to shield the inner enclosurefrom external fields which could affect the measurement.5.2.2 Shunt CapacitorsShunt capacitors may be nece
31、s-sary to reduce the measured voltage to a range where it can beread by the electrometer. Such shunt capacitors must have verylow leakage insulation relatively unaffected by relative humid-ity changes (for example, polystyrene). They should be keptshort-circuited when not in use and should be protec
32、ted fromhigh relative humidity.5.2.3 ElectrometerThe electrometer voltmeter measuresthe voltage developed on the Faraday cage and shunt capaci-tors. The electrometer must have a high impedence (such as100 TV or higher) and a low drift rate concordant with the timeof measurement. Electrometers are av
33、ailable with built-inshunt capacitors selected by a range switch. Electrometers arealso available with negative feedback circuits which minimizethe effect of input capacity. These circuits reduce the inputvoltage drop to nearly zero minimizing the effects of leakage ofcharge to ground and polarizati
34、on of insulators.5.2.4 Display UnitThe display unit indicates the voltagedeveloped on the electrometer. If the input capacitance isknown and does not vary, or if negative feedback is used, thedisplay unit may be calibrated to measure the charge on theFaraday cage directly. The unit may be a meter sh
35、owing theinstantaneous value or it may be more complicated equipment,such as a strip chart recorder giving a reading as a function oftime. The electrometer and display unit may be combined inone instrument.5Shashoua, V. E., “Static Electricity in Polymers: Theory and Measurement,”Journal of Polymer
36、Science, Vol XXXIII, 1958, pp 6585.FIG. 1 Block Diagram of Apparatus for Measurement ofElectrostatic ChargeD 4470 97 (2004)25.2.5 Electrical Connnections:5.2.5.1 Connections to Faraday CageConnections fromthe inner enclosure of the Faraday cage to the shunt capacitorsand the electrometer must be hig
37、hly insulated and well shieldedfrom external electric fields. They should be stable in time andin the different ambient conditions in which measurements aremade. Preferably, they should be rigid, although shielded cablemay be used if it is low noise cable where flexing will not leadto the generation
38、 of static charge between the shield and theinsulation of the cable. When using cable or rigid connections,the capacitance of these must be taken into account whencalculating or measuring the capacitance of the input system,unless using an electrometer with negative feedback.5.2.5.2 Connections to D
39、isplay UnitNo special connect-ing wires are normally necessary between the electrometeroutput and the display unit. Manufacturers recommendationsshould be followed when connecting an external display unit tothe electrometer output.5.3 Electric Field Strength MeasurementsThe diagram ofFig. 3 illustra
40、tes the major parts of a commercially availablerotating vane fieldmeter. A commercially available vibratingplate fieldmeter is illustrated in Fig. 4. The setup required forcalibration of a fieldmeter is shown in Fig. 5.5.3.1 Rotating Vane FieldmeterIn Fig. 1 an electrostati-cally charged material pl
41、aced at a known distance from thesensing unit will induce electrostatic charge in the face of thesensing unit, the rotating vane, and the fixed sensor plate.When the rotating vane covers the sensor plate, the inducedcharge in the sensor is small. When the opening in the rotatingvane is opposite the
42、sensor, the induced charge in the sensor isa maximum. Thus the rotating vane produces a periodicallyvarying electrical signal on the sensor plate. This signal isamplified, processed, and read on a suitable display unit. Thesefieldmeters can be made polarity-sensitive by inducing acharge of known pol
43、arity on the sensor with an internal sourceor by phase detection circuitry. Efforts must be made toadequately shield the sensor and associated circuits from noisegenerated by the motor driving the rotating vane.5.3.2 Vibrating Plate FieldmeterIn Fig. 2 a vibratingsensor plate is enclosed in a sensin
44、g unit. A charged materialplaced in front of the sensing unit induces a charge in the faceplate and in the sensor. As the sensor moves away from thecharged material, less charge is induced on the sensor. As itmoves toward the charged material, more charge is induced onthe sensor. This produces a per
45、iodically varying electricalsignal 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 andassociated circuits must be adequately shielded from noisegenerated by the driving mechani
46、sm.5.3.3 Display UnitThe display unit may contain thepower switch, circuits to process the signal (amplifiers, recti-fiers, phase detectors, and the like), and a meter showing theinstantaneous value of the electric field. Alternatively, a stripchart recorder giving a reading as a function of time ma
47、y beused.6. Test Conditions6.1 Static electrification depends upon many parameters. Toobtain reproducible results apparatus must be constructed tocontrol all the measurable parameters and to keep all theunmeasurable parameters constant. The known parameters areas follows:6.1.1 Cleanliness of Materia
48、l SurfacesStatic electrifica-tion of contacting materials is a surface phenomenon. Thus, thesurfaces must be kept in an uncontaminated state. Sincecontamination is very difficult to measure, efforts should bemade to keep the surfaces clean. Storing samples underconstant ambient conditions, such as t
49、emperature and relativehumidity, is a must. Introduction of different gases into the airwhere they can be adsorbed on the surfaces has been known tochange the results of an electrification test. Dirt particlessettling on one or more surfaces can alter the results. Evencontact to another surface during a test can alter a surface andgive nonreproducible results in subsequent tests. Sometimes, itis better to use new samples from a sufficiently uniformmaterial than to re-use samples. “Cleaning” of a surface withsolvents rarely cleans the surface. It probabl
