Overview
ISO 8780-3:1990 describes a laboratory method for dispersing pigments and extenders using a high-speed impeller mill. It is intended for mill bases of moderately high viscosity (due to high binder and/or pigment concentration) and is written to be used in conjunction with the assessment methods in ISO 8781. The procedure provides a reproducible way to evaluate dispersibility and dispersion characteristics for coatings, inks and related mill-base development.
Key Topics
- Scope and use: Restricted to moderately high-viscosity mill bases; not intended as a direct scale-up recipe for full-scale factory milling. Can be used as a preliminary dispersion step prior to bead mills or attritors.
- Apparatus: A cylindrical vessel with a horizontal disc (impeller). Important parameters include disc geometry and vessel/disc relationships:
- Diameter of vessel: approximately 1.3 d to 3 d (d = disc diameter)
- Clearance between disc plane and vessel base: 0.25 d to 0.5 d
- Depth of mill base: 0.5 d to 2 d
- Peripheral disc speed adjustable between 5 m/s and 20 m/s
- Drive unit power and adjustable rotational frequency to achieve agreed peripheral speed
- Binder system: The binder, solvent and concentration must be agreed and reported; rheological properties (e.g., viscosity) should be noted. Use the same binder batch across a test series.
- Procedure essentials:
- Sample according to ISO 842
- Pre-mix at reduced speed, add pigment gradually until a toroid (doughnut) flow pattern forms
- Adjust pigment/binder ratio to obtain the toroid flow pattern
- Take test portions after agreed stirring times (example series: 4, 8, 16, 32 min) and measure temperature between intervals
- Stabilize or de-aerate test portions if required
Applications
- Comparative assessment of dispersibility for pigments and extenders in coatings and inks
- Laboratory pre-dispersion before transfer to bead mills or other high-energy equipment
- Development and quality control of mill-base formulations where high shear and viscosity are key factors
Practical tips: use a double-walled vessel for temperature control, note the type and serration direction of the disc, and record all agreed parameters (speed, vessel/disc geometry, stirring times) to ensure reproducibility.
Related Standards
- ISO 8780-1 - Introduction to methods of dispersion for assessment
- ISO 8780-2, -4, -5, -6 - Other dispersion methods (oscillatory shaker, bead mill, automatic muller, triple-roll mill)
- ISO 8781 (Parts 1–3) - Methods of assessment of dispersion characteristics (tinting strength, fineness of grind, gloss changes)
- ISO 842 - Sampling of raw materials for paints and varnishes
Required supplementary information (Annex A) includes: impeller mill details, binder system, mill-base composition and temperature, stirring times, stabilization and de-aeration procedures. Include these in the test report for traceability and comparability.
Open preview (PDF)Pigments and extenders — Methods of dispersion for assessment of dispersion characteristics — Part 3: Dispersion using a high-speed impeller mill