ISO 8780-3:1990

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.