ISO 14309:2019

INTERNATIONAL STANDARD
Deleted: /FDIS
ISO
Second edition
2019‐07
Rubber, vulcanized or thermoplastic — Determination of
volume and/or surface resistivity
Caoutchouc vulcanisé ou thermoplastique — Détermination de la résistivité transversale et/ou
superficielle
© ISO 2019 – All rights reserved i

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national
standards bodies (ISO member bodies). The work of preparing International Standards is normally
carried out through ISO technical committees. Each member body interested in a subject for which a
technical committee has been established has the right to be represented on that committee.
International organizations, governmental and non‐governmental, in liaison with ISO, also take part in
the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all
matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 45, Rubber and rubber products,
Subcommittee SC 2, Testing and analysis.
This second edition cancels and replaces the first edition (ISO 14309:2011), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— A detailed explanation on the requirement for the electrode gap for volume resistivity has been
added in 5.4.2.
— The typical dimension for D2 has been changed to (60 ± 0,5) mm in 5.4.2.
— To calculate the volume resistivity, the effective area of the main electrode is now derived from
D + B in 11.1, and the information on B has been newly included as Annex D.
1 g g
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
ii © ISO 2019 – All rights reserved

Introduction
Rubber materials are widely used in many industries, either as the major material or forming a part of
the product, because of their unique physical properties which can be tailored by compounding to
match the particular requirements of the product specification. Although rubbers are generally
regarded as insulating materials, they can be made electrically conductive or dissipative by
compounding with a certain amount of carbon black or ionizable ingredients. Hence, the range of
electrical resistance to be measured is very wide. It is difficult, however, to obtain high accuracy for
measurements in the high‐resistance range due to a number of factors.
In this document, the guarded‐electrode system is used to determine the resistivity of rubber test
pieces since it is considered a good compromise between minimizing the errors by shunting away stray
currents and using more unwieldy measurement instruments (see also IEC 62631‐3‐1).
ISO 1853, on the other hand, covers rubber materials with medium to low resistance, i.e. resistivities of
10 Ω⋅m or below. It specifies three methods for determining volume resistivity which minimize or
eliminate contact resistance.
The methods specified in this document were originally designed for the determination of both surface
and volume resistivity of insulating rubber materials, but their use can be extended to cover the range
from high to low resistivity.
It is known that the test results are sensitive to the test conditions, such as temperature and humidity,
and to heat and strain history.
© ISO 2019 – All rights reserved iii

Rubber, vulcanized or thermoplastic — Determination of volume
and/or surface resistivity
WARNING 1 — Persons using this document should be familiar with normal laboratory practice. This
document does not purport to address all of the safety problems, if any, associated with its use. It is the
responsibility of the user to establish appropriate safety and health practices and to determine the
applicability of any other restrictions.
WARNING 2 — Certain procedures specified in this document might involve the use or generation of
substances, or the generation of waste, that could constitute a local environmental hazard. Reference
should be made to appropriate documentation on safe handling and disposal after use.
1 Scope
This document specifies a method for the determination of the volume and the surface resistivity of
vulcanized or thermoplastic rubbers. The method can be applied to materials with a resistivity from
1 17
10 Ω⋅m to 10 Ω⋅m.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 1382, Rubber — Vocabulary
ISO 18899:2013, Rubber — Guide to the calibration of test equipment
ISO 23529, Rubber — General procedures for preparing and conditioning test pieces for physical test
methods
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1382 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
volume resistance
Rv
quotient of a direct‐current voltage applied between two electrodes in contact with opposite faces of a
test piece and the current between the electrodes, excluding current along the surface
Note 1 to entry: It is expressed in ohms (Ω).
3.2
surface resistance
© ISO 2019 – All rights reserved 1

R
s
quotient of a direct‐current voltage applied between two electrodes on the same surface of a test piece
and the current between the electrodes
Note 1 to entry: It is expressed in ohms (Ω).
3.3
volume resistivity
ρ
v
measured volume resistance calculated to apply to a cube of unit side
Note 1 to entry: It is expressed in ohm metres (Ω⋅m).
3.4
surface resistivity
ρ
s
measured surface resistance calculated to apply to a square
Note 1 to entry: It is expressed in ohms (Ω) and the size of the square is immaterial.
3.5
guarded-electrode system
electrode system composed of three electrodes, a guard, and a guarded and an unguarded electrode to
reduce measurement errors by protecting the current‐measuring electrode from the interfering
influences of voltages other than the test voltage, and of stray conductances
Note 1 to entry: Guarding depends on interposing, in all critical insulated parts, guard electrodes which intercept
all stray currents that might otherwise cause errors. The guard electrodes are connected together, constituting the
guard system and forming with the measurement terminals a three‐terminal network. When suitable connections
are made, stray currents from spurious external voltages are shunted away from the measurement circuit by the
guard system, the insulation resistance from either measurement terminal to the guard system shunts a circuit
element which should be of very much lower resistance, and the specimen resistance constitutes the only direct
path between the measurement terminals. By this technique, the probability of error is considerably reduced (see
5.3.2 of IEC 62631‐3‐1:2016 for more details).
4 Principle
The volume and surface resistances of a rubber test piece are determined, using a suitable arrangement
of electrodes, from the current flowing when a voltage is applied. The volume and surface resistivities
are calculated from the measured resistances, which include the contact resistance.
5 Apparatus
The test equipment consists of a power supply, current‐measuring equipment and electrodes:
5.1 Stabilized direct-current power supply, capable of applying a voltage of 1 V to 1 000 V to the
test piece.
5.2 Voltmeter, capable of measuring the applied voltage with an accuracy of ±2 %.
5.3 Ammeter or other current-measuring device, capable of measuring a current of 0,01 pA to
100 mA, depending on the resistivity of the test piece to be measured. The accuracy of the current‐
measuring device shall be better than 5 %.
5.4 Electrodes
2 © ISO 2019 – All rights reserved

5.4.1 Guarded-electrode system
Three electrodes shall be applied to the test piece:
— a main electrode (circular);
— a ring electrode (annular);
— an opposed electrode (circular).
5.4.2 Shapes and dimensions of electrodes
The main (smallest) electrode is circular and is surrounded by the ring electrode. The third electrode is
circular and placed on the opposite side of the test piece to the main electrode. The arrangement of the
electrodes is shown schematically in Figure 1.

A typical example
D1 (50 ± 0,5) mm
D (60 ± 0,5) mm
D (80 ± 0,5) mm
D (83 ± 2) mm
g 5 mm
h 2 mm
Key
1 main electrode
2 ring electrode
3 opposed electrode
4 test piece
© ISO 2019 – All rights reserved 3

Figure 1 — Arrangement of electrodes
The dimensions of the electrodes shall comply with following requirements:
— The diameter D1 of the main electrode shall be at least ten times the test piece thickness h.
— The gap g between the main electrode and the ring electrode shall be uniform in width. For the
measurement of volume resistivity, the gap needs to be such as to give a balance between fringing
and current leakage. Fringing is current flowing in a curved path near the electrode and is more
prevalent with a wide gap. Leakage current between the main and ring electrodes will be greater
with a narrow gap. Gaps between 1 mm and 15 mm have been used depending on the range of
resistivity to be measured.
For the measurement of surface resistivity, the gap g shall be at least twice the test piece thickness so
that the effect of the volume resistance can be ignored.
— The width of the ring electrode shall be greater than the test piece thickness h.
— The diameter D4 of the opposed electrode shall be greater than the outer diameter D3 of the ring
electrode.
NOTE The measured volume or surface resistance might depend strongly on the test piece and electrode
dimensions. For comparative determinations, the same size of test piece and electrodes need to be used.
5.4.3 Electrode materials
Electrodes shall be of a conducting material capable of being intimately applied to the test piece. If they
are applied before conditioning, the material shall be moisture‐permeable. Electrodes other than of
rigid metal shall be supplemented by rigid metal backing plates.
NOTE Suitable electrode materials are considered in Annex A.
5.4.4 Electrical circuits
Suitable circuits for testing are shown in Figures 2 and 3.
4 © ISO 2019 – All rights reserved

Key
1 guarded electrode (main electrode)
2 guard electrode (ring electrode)
3 test piece
4 unguarded electrode (opposed electrode)
5 direct‐current supply
6 switch
7 connection for short‐circuiting electrodes (to discharge test piece)
8 connection for measurement circuit
9 ammeter
10 earth
11 measurement current
12 guard current
Figure 2 — Circuit configuration for volume resistivity
© ISO 2019 – All rights reserved 5

Key
1 guarded electrode (main electrode)
2 unguarded electrode (ring electrode)
3 test piece
4 guard electrode (opposed electrode)
5 direct‐current supply
6 switch
7 connection for short‐circuiting electrodes (to discharge test piece)
8 connection for measurement circuit
9 ammeter
10 earth
11 measurement current
12 guard current
Figure 3 — Circuit configuration for surface resistivity
6 Calibration
The requirements for calibration of the test apparatus are given in Annex C.
7 Test pieces
7.1 Form
The test piece shall be a flat, smooth sheet of sufficient size that the annular electrode does not reach its
edges. The surfaces of the sheet shall not be buffed.
The nominal thickness of the test piece shall be in the range 0,5 mm to 5 mm. Recommended thickness
is 1 mm or 2 mm.
The thickness of the test piece shall be measured at several points distributed uniformly over the area
covered by the main electrode to the nearest 0,01 mm. The average value shall be used as the test piece
6 © ISO 2019 – All rights reserved

thickness. The variation in thickness within a given test piece shall not exceed 10 % of the mean value.
Test pieces used for comparative tests shall be, as nearly as practicable, of the same thickness.
7.2 Number of test pieces
Three test pieces shall be used.
8 Conditioning
The time interval between vulcanization and testing shall be in accordance with ISO 23529.
Samples and test pieces shall be stored in accordance with ISO 23529 during the interval between
vulcanization and testing.
The material shall be conditioned before testing for a minimum of 16 h at standard laboratory
temperature and humidity as specified in ISO 23529.
Metal foil, liquid and conductive elastomeric electrodes shall be applied after conditioning. This shall be
carried ou
...