INDA, Association of the Nonwoven Fabrics Industry
1300 Crescent Green, Suite 135
Cary, NC 27512Copyright 2001, INDA
STANDARD TEST: IST 40.1 (01)Standard Test Method for
Surface Resistivity of Nonwoven Fabrics
A number in parenthes indicates the year of last revision.
1 Annual Book of ASTM Standards, Vol. 07.01
2 Annual Book of ASTM Standards, Vol. 10.01
3 National Fire Protection Association, 1 Batterymarch Park, PO Box 9101, Quincy, MA 02269-9101
4 General Services Administration, Building 197, Washington Navy Yard, Washington, DC 20407
1. Scope
1.1 This method determines the surface
electrical resistivity of fabrics, webs, films, or other sheet-like materials. The electrical resistivity
influences the accumulation of electrostatic charge on the surface of the material and its subquent dissipation.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parenthesis are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its u.It is the responsibility of the ur of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to u.
2. Referenced Documents
2.1 ASTM Standards :
D 123 Terminology Relating to Textiles 1
D 1776 Practice for Conditioning Textiles for Testing 1
2.2 Other Standards:
NFPA 99 (92) See 12 - 4.1.3.8 (f) (3)3
Federal Test Method No. 191 A-Method 5930 –Electrical Resistivity of Fabrics 4
D 257 DC Resistance or Conductance of Insulating Materials 2
3. Terminology
3.1 Definitions:
3.1.1 resistivity, n - the ratio of the potential gradient paralleling the current passing through the specimen.
3.1.1.1 Discussion – This is numerically
equivalent to the resistance between opposite faces of a unit cube. It is the reciprocal of conductivity.
3.1.2 resistivity surface, n – the surface resistance multiplied by that ratio of specimen
surface dimensions (width of electrodes defining the current path divided by the distance between
electrodes) which transforms the measured resistance to that obtained if the electrodes had formed the opposite sides of a square.
3.1.2.1 Discussion – Surface resistivity is popularly expresd in ohms, or ohms/square (the
size of the square is immaterial). Surface resistivity is the reciprocal of surface conductivity.
3.1.3 For definitions of other textile terms ud in this method, refer to the Standard for Terminology D 123.
4. Summary of the Method
4.1 Specimens, equilibrated to specific
temperature and humidity conditions, are tested for electrical resistance using an electrical resistance meter.
5. Significance and U
5.1 Fabrics, films or nonwovens that are ud in areas where flammable, combustible, or explosive atmospheres may be encountered, should not
accumulate static charges which may discharge with sufficient energy to cau ignition. Additionally,fabrics, films, or nonwovens that are handled in rapidly moving or automatic converting equipment should not accumulate excessive static charges.Surface electrical resisitivity measurements quantify the ea by which electrical charges may be dissipated from the fabrics.
5.2 This test method is considered satisfactory for quality control testing. It can be ud for acceptance testing of commercial shipments, but caution is advid becau of the abnce of reliable information on between-laboratory precision.
5.2.1 If there are differences of practical significance between reported test results for two laboratories (or more), comparative tests should be performed to determine if there is a statistical bia
s between them, using competent statistical assistance.As a minimum, test samples should be ud that are as homogeneous as possible, that are drawn from the material from which the disparate test results were obtained, and that are randomly assigned in equal numbers to each laboratory for testing. Other materials with established test values, such as
standard resistors, may be ud for this purpo. The test results from the two laboratories should be
compared using a statistical test for unpaired data, at a probability level chon prior to the testing ries.If a bias is found, either its cau must be found and corrected, or future test results must be adjusted in consideration of the know bias.
6. Apparatus1
6.1Electrical Resistance Meter
6.2Conditioning and Test Chamber
6.3 Standard Resistors – 1 x 1011 ohm, 1 x 1010 ohm, 1 x 109 ohm
6.4Radioactive Bar
6.5 Two rectangular flat metal surfaces of suitable size to rve as electrodes - e D 257
6.5.1 Alternatively, two concentric ring electrodes of spacing suitable to the materials being measured and the purpo of the results may be ud.
6.6 Gloves – Latex or cotton knit gloves to prevent contamination of fabric surfaces.
7.Hazards
7.1 The safety recommendations provided by the radioactive bar manufacturer should be followed.
7.2 The radioactive bar emits alpha radiation which is externally harmless to the human body. The radioactive isotope polonium 210 is toxic and precaution should be exercid to prevent ingestion or inhalation of the solid material. Do not take the radio active bar apart or touch the radioactive strip. If the strip is touched or handled, wash hands thoroughly at once. Return the device to the manufacturer when it los its effectiveness as a static eliminator or for disposal if u is to be discontinued. Do no discard as scrap.
8.Sampling and Test Specimens
8.1 Primary Sampling Unit – Consider rolls, bolts or pieces or fabric, or cartons of garments to be the primary unit, as applicable.
8.2 Laboratory Sampling Unit – As a laboratory sampling unit, take from the primary sampling unit at least one full-width piece of fabric that is 1 m (1 yd.) in length along the machine direction after first removing a 1 m (1 yd.) length. When applicable u an entire garment.
9.Preparation of Apparatus
9.1 The test unit should be installed in a conditioned environment identical to the environment ud to condition the specimens.
9.2 Calibrate the electrical resistance meter according to the manufacturer’s recommendations. This calibration should be done periodically in compliance with at total quality system.
9.3 Electrodes should be kept clean and not touched with ungloved hands.
10-Conditioning
10.1 Conditioning of samples is critical for the accurate execution of this test.
10.2 In fabrics where the end u requires antistatic treatments or the electrostatic propensity is critical, measurements at 20%R.H. may be required within an appropriate test chamber.
10.3 For Federal Test Method #5930 40% R.H. and 24°C are specified.
10.4 For NFPA-99 50% R.H. and 21°± 2°C are specified.
10.5 For textile or nonwoven measurements, standard conditions pre ASTM D 1776 may be ud.
10.6 Wherever possible methodology for exposing specimens to conditioning atmospheres should follow ASTM D 1776.
11. Preparation of Specimens
11.1 For testing with concentric ring electrodes, samples should be die or scissor cut to a size at least as large as the diameter of the outer ring.
11.2 For parallel electrodes one t of machine direction and one wet of cross direction specimens the size of the electrode ud should be obtained.
11.3 In all cas, the exact sample size depends on the construction of the particular equipment being ud.
12.Procedure
12.1 Optionally remove static charges using a radioactive bar.
12.1 Place the test specimen in firm contact with the electrodes. The contact should be such that when additional pressure is applied between the specimen and the electrodes the test results are not effected.
12.3 For parallel plate electrodes test both machine and cross direction. Report only the lower reading by direction.
12.4 For concentric ring electrodes the charge follows the path of least resistance automatically.
12.5 Measure the electrical resistance of the specimen according to the operating instructions and procedures for the particular resistance meter being ud. Allow the current to pass through the specimen for a minimum period of one minute until a constant reading is obtained. The criterion for constant electrical resistivity is a charge in the value of Log R of less than 0.1 units per minute. The
time to reach a constant reading may vary with the applied voltage and with the resistance of the test sample. High voltages for prolonged periods of time may damage the fabric.
12.6 For reference purpos, 80 – 100 volts at 1 in. electrode paration for one minute should be ud for the parallel plate configuration, and a similar voltage gradient for the concentric ring ca (e 10.6)
12.7 Avoid the u of any electrically conductive liquids on either the fabric test specimens or the apparatus.
13. Calculation
13.1 Compute the resistivity in ohms per square for each test specimen as follows:
For the parallel electrode ca:
Resistivity = Measured resistance (ohms) x Width of Specimen Distance between electrodes
For the concentric ring cas:
Resistivity = 2.73 x measured resistance (ohms)
Log outer electrode radius
Inner electrode radius
14.Report
14.1 Report the logarithm of the average of the three calculated resistivities in ohms per square of fabric, the relative humidity and the temperature employed, and the direction of measurement, lengthwi or widthwi. In the measurement of surface resistivity, the same numerical result is obtained regardless of the size of the square.
15.Precision and Bias
15.1P recision- The precision of this method has
not been determined.
15.2Bias- The accuracy of this test method is to
be determined.
16.Keywords
16.1r esistivity, electrostatic, surface resistivity
NOTES
1.Resistance meters ud in conjunction with
the electrode systems should be capable of
measuring values from 108 to 10 15 ohms.
2.Suitable concentric ring meters are available
from:
Keithly Instruments, Inc.
28775 Aurora Road
Cleveland, Ohio 44139
Hewlett-Packard Company
5301 Stevens Creek Blvd
Bldg. 51 L-SC
Santa Clara, CA 95052-8059
1-800-452-4844
Model 43339B
High Resistance Meter
Model 16008B Resistivity Cell 3.High Resistance meters 108 – 1013 are available
from:
Custom Scientific Instruments, Inc.
13 Wing Drive
Cedar Knolls, NJ 07927
Glen Rad
300 G Baker Avenue
Concord, MA 01442
4.Radioactive bar for removal of charges:
Staticmaster Ionizing Unit
Model 2 U 500
Nuclear Products Company
2519 North Merced Avenue
So. El Monte, CA 91734
