Overview
ISO 3915:2022 specifies a laboratory method for measuring the resistivity of conductive plastics - polymers made conductive by conductive fillers or structural modification. The standard applies to materials with resistivity below 10^6 Ω·cm (10^4 Ω·m). It mandates the four‑terminal (four‑probe) method to obtain resistance values that are independent of contact resistance and gives detailed requirements for specimen preparation, conditioning, apparatus and test reporting.
Key topics and requirements
- Test principle: Four‑terminal measurement - a stable DC current is applied through end current electrodes and the voltage drop between two potentiometric electrodes is read by an electrometer. Resistance is R = ΔU / I and resistivity ρ = R·A / d (where A is cross‑sectional area and d the potential electrode separation).
- Specimen geometry: Preferably 10 mm wide, 70–150 mm long and typically 3–4 mm thick with ±5% thickness uniformity. Specimens must be cut to avoid distortion.
- Electrodes and instrumentation:
- Current electrodes that span specimen width (clamps/grips or conductive paint).
- Potentiometric electrode system with specified contact spacing (nominally 10 mm) and a prescribed contact force (mass ≈ 60 g).
- Electrometer and current measurement (milli-/microammeter) with required accuracy.
- Conditioning and procedure:
- Allow specimens to equilibrate at ambient conditions for ≥16 h after cutting.
- Optional oven conditioning to remove strain (e.g., 2 h at ~70 °C, then cool ≥1 h) followed by testing at ~23 °C and 50% RH - details may be set in material specifications.
- Test at least six specimens (three from two perpendicular directions) to assess anisotropy; report medians of nine measurements per direction.
- Reporting: Include specimen ID and dimensions, conditioning, electrode spacing, applied current, individual resistivity values and medians, deviations from procedure and any unusual observations.
Applications and users
ISO 3915 is essential for:
- Quality control and production testing of conductive and dissipative plastics (e.g., antistatic housings, EMI shielding parts).
- Materials R&D evaluating conductive filler loading and processing effects.
- Independent test laboratories performing standardized resistivity characterization.
- Designers and specifiers who require validated electrical property data for end‑use performance and safety.
Keywords: ISO 3915, conductive plastics, resistivity measurement, four‑terminal method, potentiometric electrodes, specimen conditioning, material testing.
Related standards
- ISO 1853 - measurement of resistivity for conducting/dissipative rubbers (related method and background).