Overview
ISO 8781-2:1990 specifies a laboratory method to assess pigment and extender dispersibility by monitoring the change in fineness of grind during progressive dispersion. The method compares a test pigment against an agreed reference pigment by dispersing each in stages in a defined binder system, measuring fineness after each stage (per ISO 1524), and plotting fineness versus dispersion work (time, revolutions, etc.). From the plot, the work required to reach an agreed fineness is determined, giving a quantitative measure of pigment dispersibility.
Key topics and requirements
- Scope: Intended for comparing similar pigments (test vs reference) under agreed dispersion and binder conditions.
- Dispersion methods: Use one of the procedures in ISO 8780 (several parts cover different dispersers: high-speed turbine, bead mill, CI sessile machine, automatic disc mills, three-roll or tricuspid mills).
- Fineness measurement: Determined according to ISO 1524 using a grind gauge (groove depth typically 50 µm or 100 µm depending on pigment/filler and target fineness).
- Sampling protocol: Take portions of the mill base after each dispersion stage (at least four stages recommended, with intermediate stages in geometric progression).
- Data presentation: Plot fineness-of-grind values on log–log paper against dispersion work (time, number of revolutions, etc.), smooth the curve and interpolate to find the work needed for the target fineness.
- Reporting: Test report must include product ID, references to ISO 8781-2 and relevant ISO 8780 part, binder type, target fineness, reference pigment (if used), dispersion work and achieved fineness, graphical representation, deviations, and test dates.
- If target not reached: Record the maximum fineness actually achieved and the work applied.
Practical applications and users
- Provides a repeatable, quantitative method for assessing dispersion characteristics and ease of grind.
- Useful for:
- Pigment and extender manufacturers (quality control, batch comparisons).
- Paint, coating and ink formulators evaluating raw-material performance in a given binder.
- R&D labs optimizing milling processes and dispersion equipment.
- Third‑party testing and conformity assessment laboratories.
- Helps select pigments that deliver required optical and rheological properties with minimal milling energy, reducing production costs and improving product consistency.
Related standards
- ISO 1524 - Determination of fineness of grind (measurement procedure).
- ISO 8780 series - Methods of dispersion (various dispersing equipment: turbine, bead mill, CI machine, disc mill, three-roll, etc.).
- Other parts of ISO 8781 - Part 1 (assessment from change in tinting strength) and Part 3 (assessment from change in specular gloss).
Keywords: pigment dispersibility, fineness of grind, dispersion characteristics, ISO 8781-2, ISO 1524, grind gauge, pigment testing, mill base, binder system.