Overview - ISO 12644:1996 (Falling Rod Viscometer)
ISO 12644:1996 is an International Standard from ISO/TC 130 (Graphic technology) that specifies a test method for determining the rheological properties - principally apparent viscosity and yield stress - of paste inks and vehicles that are unreactive at normal room conditions. The method uses a falling rod viscometer and is applicable to inks in the apparent viscosity range 2 Pa·s to 200 Pa·s. Results are reported at a reference temperature of 25 °C with defined procedures for calibration, temperature correction and reporting.
Key topics and technical requirements
- Test principle: Measure fall time of a vertical rod moving through a sample-filled aperture; different load weights produce different shear rates.
- Apparatus: Falling rod viscometer assembly (rod ≈ 132 ± 1 g recommended for steel rods), aperture ring with tight dimensional tolerances, levelling device, timing sensor, temperature control (water jacket or cabinet).
- Load weights: Predefined sets (e.g., 5 000, 4 000, 3 000 g … down to 0 g) with mass tolerances ±0.2 g; choose set so highest-load fall time is typically 4–10 s.
- Calibration: Use at least two standard viscosity oils traceable to standards institutions; determine device factors a and p, and a correction factor for each rod/aperture set.
- Flow models: Data may be interpreted with Casson, Bingham, or Power Law models; linear regressions on measured shear stress vs shear rate (or their transforms) yield viscosity, yield stress, k and n parameters.
- Temperature control & corrections: Test temperature averaged before/after run; reference 25 °C. If needed, correct fall times using a temperature gradient factor (typical β = 0.1 °C⁻¹ for viscosity; β = 0.05 °C⁻¹ for pseudo yield stress).
- Quality criteria: Minimum data points (≥4 fall times), correlation coefficients for regressions should be ≥ 0.999 for reliable results. Maximum allowable fall time 60 s.
- Reporting: Viscosity at reference temp, sample ID, test temp, flow model used, viscometer model, rod material, deviations, date, operator.
Applications and users
ISO 12644 is practical for:
- Ink manufacturers (formulation, QC and batch release)
- Printing houses and prepress labs (ink performance verification)
- R&D and materials labs evaluating rheology of paste inks and vehicles
- Instrument manufacturers of falling rod viscometers (calibration and compliance)
The standard supports consistent viscosity/yield stress measurement for process control, troubleshooting (set-off, transfer properties), and specification of printable paste inks.
Related standards
- Other ISO graphic technology standards developed by ISO/TC 130 (for print testing, ink properties and related measurements).
- General rheology and viscometry standards (consult ISO catalogs or national standards bodies for complementary methods and interlaboratory guidance).
Keywords: ISO 12644:1996, falling rod viscometer, paste inks, viscosity testing, yield stress, Casson model, Bingham, Power Law, graphic technology, ink rheology.
