Overview
EN ISO 3915:2022 - Plastics: Measurement of resistivity of conductive plastics specifies a laboratory method for measuring the electrical resistivity of plastics rendered conductive by conductive fillers or structural modification. The standard applies to materials with relatively low resistivity (given in the standard) and uses the four‑terminal (potentiometric) testing principle so that contact resistances do not bias the result. It notes that measured values are not strictly volume resistivity because surface conduction can contribute, although this effect is generally negligible.
Key Topics and Requirements
- Test principle: Mandatory four‑terminal (Kelvin) method - a stable DC current is passed along a strip and the voltage drop between internal potential electrodes is measured with an electrometer to compute resistance and resistivity.
- Specimen preparation: Preferred strip width 10 mm; length typically 70–150 mm; normal thickness 3–4 mm with ±5% uniformity tolerance. Specimens are cut along two perpendicular directions (to assess anisotropy) and conditioned (left at ambient temperature/humidity for at least 16 hours).
- Electrodes and contacts: Current electrodes (metal clamps or conductive paint) and a potentiometric electrode assembly (approx. 60 g mass, ~0.6 N contact force). Potentiometric contact spacing is normally (10 ± 0.2) mm (can be increased up to 70 mm for special purposes) with specified contact geometry.
- Apparatus: Requires a stable DC current source, milli/microammeter or series sense resistor, electrometer for voltage measurement, insulating support sheet, and optionally an oven for thermal conditioning. The standard includes minimum insulation and instrument performance notes.
- Sensitivity factors: The document highlights sensitivity of conductive plastics to temperature‑history and strain‑history, and gives procedures to reduce these influences (e.g., specimen conditioning and careful cutting/handling). Cleaning procedures (e.g., Fuller’s earth and distilled water) are described to avoid surface contamination.
Applications and Users
- Who uses this standard: Polymer test laboratories, material development and R&D teams, quality control engineers, conductive‑composite manufacturers, and safety/compliance testing bodies.
- Practical uses: Characterizing conductive polymer batches, comparing conductive filler formulations, verifying product compliance, evaluating anisotropy from processing, and supporting selection of materials for electrostatic discharge (ESD) control, shielding, sensors, or conductive components.
Related Standards
- ISO 1853 (rubber resistivity testing) - method similarities and differences are discussed in the ISO 3915 introduction.
- Other electrical and materials test standards for ESD and conductivity may be referenced depending on application.
Keywords: EN ISO 3915, ISO 3915:2022, conductive plastics, resistivity measurement, four‑terminal method, potentiometric electrodes, polymer testing, conductive fillers.