ISO 15091:2019

Overview - ISO 15091:2019 (Paints and varnishes - electrical conductivity and resistance)

ISO 15091:2019 specifies a laboratory method for measuring the electrical conductivity, electrical resistance, and, where required, resistivity of coating materials (paints and varnishes). The standard covers measurement apparatus, sampling and preparation, test conditions, calibration, result expression and reporting. It is primarily intended for low‑conductivity products (conductivity < 5 µS/cm, corresponding to resistivity > 200 kΩ·cm) and addresses both water‑borne and solvent‑borne systems. Conductivity is typically measured for water‑borne (including electrodeposition) coatings; resistance is typically measured for solvent‑borne coatings.

Key topics and technical requirements

• Scope and applicability: Method for coatings with conductivity < 5 µS/cm (resistivity > 200 kΩ·cm).
• Measurement principles: Direct current (V/I), AC two‑ or four‑electrode techniques, and bridge comparisons (Wheatstone bridge).
• Avoiding artifacts: Use alternating current to minimise electrolysis and polarization; frequencies should be as low as practical to limit capacitive reactance.
• Measuring cell and cell constant: Cells must have known cell constant (geometric factor) and inert, cleanable electrodes (stainless steel, platinum, graphite, titanium). Cell geometry should minimise contamination.
• Calibration: Instruments must be calibrated per Annex A; temperature dependence is covered in Annex B.
• Test conditions and procedure:
  • Standard test temperature (25 ± 1) °C unless agreed otherwise.
  • Samples prepared/examined per ISO 1513 and sampled per ISO 15528.
  • Maintain viscosity representative of ready‑to‑use product; dilute only by agreement.
  • Minimum of three determinations; use mean for reporting.
  • Wait times: DC measurements - read after ~10 s; continuous instruments - read only when value is stable for >20 s.
  • Clean cell after each test.
• Data and reporting: Report product ID, test temperature, solvent/dilution, instrument and cell details, results (conductivity/resistance/resistivity), and reference to ISO 15091:2019.

Practical applications and who uses it

• Coating formulators and R&D: to characterise conductivity/resistivity effects on application and drying.
• Electrodeposition & electrostatic process engineers: to assess processibility and control deposition uniformity.
• Quality control / testing laboratories: routine QC of water‑borne and solvent‑borne coatings to ensure batch consistency.
• Suppliers and compliance officers: include electrical properties in technical data sheets and regulatory/test reports.

Related standards (normative references)

• ISO 1513 - sample preparation and examination
• ISO 15528 - sampling of paints, varnishes and raw materials
• ISO 4618 - terms and definitions for paints and varnishes
• ISO 3696 - laboratory water quality

Keywords: ISO 15091, electrical conductivity, electrical resistance, resistivity, paints and varnishes, electrodeposition, measuring cell, cell constant, calibration, coating testing, electrostatic processing.