Overview
EN ISO 8780-6:1995 specifies a laboratory method for dispersing pigments and extenders using a triple-roll mill to assess dispersion characteristics. The procedure is intended to be used with agreed high-viscosity mill bases and the assessment methods described in ISO 8781. Results permit conclusions about behaviour when processed on corresponding production machinery and support correlation between laboratory and production dispersing equipment.
Key Topics
- Equipment and control: triple-roll mill with temperature control and mixing unit. Typical roll diameter is about 150 mm and roll length 200–300 mm; transmission (friction) ratios and take-off speeds (150–200 r/min) are specified for reproducible results.
- Operating parameters: roll contact (line) pressure is expressed per millimetre of roll length; mill designs should allow reproducible settings up to a line pressure equivalent to the machine capability (up to 80 cN/mm is given as a reference). Temperature control of heating/cooling fluid is specified to ±1 °C in the 20 °C to 60 °C range.
- Mill base and binder system: use an agreed binder, solvent and concentration with rheological data (viscosity) supplied. The method is restricted to high-viscosity, sticky mill bases; pigment concentrations are adjusted according to binder demand.
- Procedure notes: pre-mixing of pigment and binder (typically about 50 g minimum for the apparatus described) until homogeneous; pre-heating rolls; establishing friction between rolls to create thin uniform coatings; passes are defined and material from roll aprons is collected and mixed for assessment.
- Reproducibility controls: pre-mixing time guidance (approximately 2 minutes for 50 g mill base), stabilization procedures where required, and recommendation to perform test and reference pigment dispersions at the same temperature.
Applications
This standard is used by:
- Quality control laboratories evaluating dispersibility of pigments and extenders.
- Formulation and process development teams correlating lab dispersion behaviour with production-scale triple-roll or similar mills.
- Suppliers and purchasers agreeing binder systems and mill-base compositions for comparative testing.
Practical benefits include ease of handling, ability to prepare adequate mill-base quantities, straightforward cleaning and improved correlation with production machinery when agreed parameters are followed.
Related Standards
- ISO 8781 (Parts 1–3): methods of assessment (tinting strength, fineness of grind, gloss change) used in conjunction with this method.
- ISO 787-24: reference for white pigment paste and photometric methods.
- ISO 842: sampling of raw materials for paints and varnishes.
For complete implementation, provide the items of supplementary information listed in Annex A (machine details, binder system, mill base composition and temperature, pre-mixing and dispersion conditions, and any stabilization procedures).