Overview
ISO 12058-1:2018 specifies the inclined‑tube falling‑ball viscometer method for determining the viscosity of plastics - specifically polymers and resins in the liquid, emulsified or dispersed state. The standard covers measurements over a wide dynamic viscosity range (0.6 mPa·s to 250 000 mPa·s) and temperatures from −20 °C to +120 °C, and is intended for liquids that exhibit Newtonian behaviour (viscosity independent of shear rate).
Keywords: ISO 12058-1, falling-ball viscometer, inclined-tube method, viscosity of plastics, dynamic viscosity, Newtonian behaviour.
Key topics and technical requirements
- Scope & applicability: For polymers and resins in liquid, emulsified or dispersed form where shear stress and shear rate are proportional (Newtonian response).
- Measurement range: 0.6 mPa·s to 250 000 mPa·s; temperature −20 °C to +120 °C.
- Apparatus: Inclined measurement tube (typically 10° ± 1° to vertical), tubular thermal jacket, calibrated precision balls (six sizes, diameters ≈ 11.0–15.81 mm), plugs with capillary to avoid pressure variations, and a stand with levelling. The Hoeppler-type viscometer is a common example.
- Supporting equipment: High-precision thermometer (≤ ±0.03 K), timer or electronic/automatic timing device, and thermostat capable of maintaining ±0.03 K (10–80 °C) or ±0.05 K outside that range.
- Procedure essentials: Clean apparatus, fill tube, introduce ball, equilibrate sample at test temperature (minimum 15 min, longer for viscous samples), roll ball to mix, measure fall time between two marks at least three times.
- Calculation & reporting: Dynamic viscosity is calculated using the instrument calibration constant (K), ball and liquid densities, and the measured fall time (formula in clause 10). Results are averaged and reported to three significant figures. Test reports must include sample identification, temperature, average viscosity, deviations and operator information.
- Precision: Repeatability and reproducibility limits are given by ball number (e.g., Ball 1 repeatability ≈1.0%, reproducibility ≈2%; Balls 2–4 finer limits).
Applications and users
- Quality control and acceptance testing of polymer resins, emulsions and dispersions.
- R&D and material characterization in plastics manufacturing and processing.
- Laboratories benchmarking viscosity for formulation, processability, and rheological specification.
- Useful where Newtonian viscosity data are needed across a wide temperature/viscosity range.
Related standards
- ISO 2811-1 for density determination (pycnometer method) - referenced for liquid density measurements used in calculations.
- Historical reference: DIN 53015 (Hoeppler viscometer) - example instrument type.
ISO 12058-1 is essential for laboratories and manufacturers seeking standardized, reproducible viscosity data for plastics using the inclined‑tube falling‑ball viscometer method.