ISO 1853:2018 導電性および散逸性ゴム、加硫または熱可塑性—抵抗率の測定 | ページ 2

Foreword

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This document was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee SC 2, Testing and analysis.

This fourth edition cancels and replaces the third edition (ISO 1853:2011), which has been technically revised. The main changes compared to the previous edition are as follows:

• Clause 3, terms have been newly defined;
• 4.3, the length of the test piece has been changed from 70 mm to 95 mm;
• Annex A, information on the solid-state electrometer manufacturer has been updated;
• Annex B, a calibration schedule has been added.

Introduction

Rubber is normally regarded as a material of high electrical resistivity; consequently, it is widely used as an insulator. However, the incorporation of various materials, in particular certain forms of carbon black, greatly reduces the electrical resistance so that volume resistivities between 10¹³ Ω⋅m and 0,01 Ω⋅m are obtainable.

There are various technical and industrial purposes for which rubber with a reduced resistivity is a useful material, the most frequent application being for the dissipation of static charges. In certain circumstances, a lower limit of resistance is specified on a product with this latter application, as a safety precaution to prevent its ignition or to prevent severe shock to a person in contact with it, in the event of faulty insulation or nearby electrical equipment.

Products which, while conducting away static charges, are sufficiently insulating to fulfil the safety requirements above are termed “dissipative rubbers” (the description antistatic rubber is also used). Products which do not fulfil the safety requirements are termed “conducting” rubbers. Since the dimensions of the product are involved, it is not possible to define a suitable range of volume resistivity for either of these classes, but only a range of resistance values between defined points. However, conductive materials are generally considered to have a resistivity below 10⁶ Ω⋅m and dissipative materials to have a resistivity between 10⁵ Ω⋅m and 10¹⁰ Ω⋅m.

The principal hazard, apart from static electricity, in most buildings and with most electrical equipment is from leakage currents from normal voltage supply mains. To guard against these hazards, it is recommended that the lower limit of resistance for a dissipative rubber product be 5 ⋅ 10⁴ Ω for 250 V mains supplies, which is a maximum current of 5 mA. The limit can be proportionally less for lower voltages.

The maximum resistance which will permit the dissipation of static charges depends on the rate of generation of charge required to produce the minimum voltage which can be regarded as a hazard in a particular application.

Effect of temperature changes and strain on conducting and dissipative rubbers

The resistance of rubber and plastics made conductive by the addition of carbon black is very sensitive to strain and temperature history, since resistance depends on the structural configuration of the carbon particles in the matrix.

Under normal conditions of service with varying temperature and strain history, the resistance of a sample of a given material can vary considerably, for example by a hundred or more times, between freshly strained materials at room temperatures and material which has remained unstrained for a short period at 100 °C.

To make valid comparisons on test pieces, a conditioning treatment is specified so that the measurements are made on test pieces brought close to a condition of zero strain.

Electrode systems

Certain types of electrode, when applied to these rubbers, have a contact resistance which can be many thousands of times greater than the intrinsic resistance of the test piece. Dry contacts under light pressure or point contacts are particularly poor.

The definition of a suitable electrode system is therefore an important part of this document and, in order to satisfy the various practical requirements for tests on laboratory-prepared test pieces, several electrode systems have been selected and are described in Clauses 4, 5 and 6.

1 Scope

This document specifies the requirements for the laboratory testing of the volume resistivity of specially prepared test pieces of vulcanized or thermoplastic rubber compounds rendered conducting or dissipative by the inclusion of carbon black or ionizable materials. The tests are suitable for materials with a resistivity of less than about 10⁸ Ω⋅m.

Method 1 is the preferred method when test pieces with bonded electrodes are not available.

Method 2 is the preferred method when test pieces are moulded with the inclusion of bonded electrodes.

Method 3 is another method that can be used if the apparatus for method 1 or 2 is not available, but it has lower accuracy.

If a reference to this document is made without specifying the method, method 1 is used.

2 Normative reference

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.

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 14309 apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses: