Overview
EN ISO 8781-3:1995 specifies a reproducible, gloss-based method to assess the dispersion characteristics of pigments and extenders. The method compares a test pigment with an agreed reference by preparing staged dispersions in an agreed binder system, producing dried films from portions of the mill base, and measuring specular gloss. Gloss development is used as an objective indicator of dispersibility and of the work required to reach a target specular reflection value.
The approach provides a practical route for manufacturers and laboratories to quantify how easily a pigment disperses and to detect differences in formulation or milling efficiency.
Key Topics
- Principle: Prepare incremental dispersions, make films from each stage, measure specular gloss and plot gloss versus dispersion stage to determine the work required to reach a target gloss.
- Measurement: Specular gloss measurement is performed in accordance with ISO 2813 (commonly at 20°, 60° or 85° depending on substrate and application).
- Dispersion methods: Dispersions are prepared using any of the methods described in ISO 8780 (e.g., impeller mills, bead mills, muller or triple-roll mills); the chosen dispersion method and sequence must be agreed between parties.
- Apparatus (typical): substrate (glass panels or art paper), applicator (spray gun, film applicator or proofing press), glossmeter compliant with ISO 2813, ventilated oven for drying or stoving.
- Data treatment: Plot mean gloss values against dispersion stage (time, revolutions, passes). From the gloss-development curve, interpolate the dispersion work (milling time, revolutions) required to obtain the agreed specular gloss.
- Stability indication: Ease of attaining the ultimate gloss can also indicate pigment/binder stability (resistance to flocculation or rewetting).
Applications
- Quality control (QC) for batch-to-batch consistency of pigments and extenders.
- Comparative testing of a new or test pigment against an agreed reference pigment.
- Evaluation of the effectiveness of milling equipment or process changes (e.g., mill type, energy input, formulation adjustments).
- Supporting formulation decisions where final appearance (specular gloss) is critical, for paints, varnishes and printing inks.
Related Standards
- ISO 2813 - Determination of specular gloss of non-metallic paint films (measurement method referenced in this part).
- ISO 8780 (Parts 1–6) - Methods of dispersion for assessment of dispersion characteristics; these parts define the dispersion procedures to be used before gloss assessment.
Notes: Annex A of EN ISO 8781-3 lists the supplementary information required to run the test (dispersion method, binder type and ratio, substrate/application/drying conditions, and a target gloss level). Test reports should record identification, procedure references, gloss-development graphs and the dispersion work needed to reach the target gloss.
