Overview
ISO 23900-3:2015 - "Pigments and extenders - Methods of dispersion and assessment of dispersibility in plastics - Part 3" - specifies a laboratory method for assessing the colouristic properties and ease of dispersion of black and coloured pigments in polyethylene (PE) using a two-roll mill. The standard quantifies dispersibility as DH_PE, the percentage increase in colour strength achieved when pigments are further milled at a narrower roll gap. Photometric measurement and colour strength calculations follow ISO 18314-1 and ISO 787-24.
Key topics and requirements
- Scope and purpose
- Measures colouristic properties of a test pigment relative to a standard and evaluates ease of dispersion (DH_PE) in polyethylene.
- Two complementary procedures: Method A (powders and flakes, e.g., organic pigments, carbon black, many inorganic powders) and Method B (granules and masterbatches, suitable for inorganic pigments in any form).
- Sample preparation
- Typical pre-blend: 100 parts PE + 1.0 part TiO2 (or 5.0 parts for carbon black) plus specified test pigment additions; antioxidant optional for HDPE.
- Dispersion procedure (two-roll milling)
- Two-roll mill with roll diameter 80–200 mm; peripheral speed ratio ≈ 1:1.1.
- Initial milling to form sheet at 0.4–0.5 mm gap (140–160 °C typical), cutting and folding every 30 s for a defined number of roll revolutions.
- Further milling at reduced gap (0.3 mm) to evaluate improved dispersion.
- Specimen handling and measurement
- Press sheets between high-gloss chrome steel plates (spacer ~1 mm) at up to 160–170 °C, cool rapidly.
- Measure colour strength and colourimetric properties with photometer per ISO 18314-1; compute DH_PE as percentage increase in colour strength (0.3 mm vs 0.5 mm).
- Precision and reporting
- Test report must identify product, method, materials, mill conditions, and measured DH_PE. Results are valid for the specified equipment and conditions.
Applications and users
- Useful for pigment manufacturers, additive suppliers, plastics compounders, and quality control / testing laboratories to:
- Compare dispersibility of pigments in PE formulations.
- Optimize pigment form (powder vs granule vs masterbatch) and processing conditions.
- Support product specifications, troubleshooting dispersion-related defects (mottling, poor colour strength), and R&D screening.
- Particularly relevant where pigment reagglomeration or handling form influences dispersion (e.g., carbon black, organic powders).
Related standards
- ISO 23900 series (Parts 1, 2, 4–6) for broader dispersion assessment methods in plastics.
- ISO 18314-1 (analytical colorimetry) and ISO 787-24 (tinting strength / photometric methods) referenced for measurement and calculation.
Keywords: ISO 23900-3:2015, pigments, dispersibility, polyethylene, two-roll milling, colouristic properties, ease of dispersion, DH_PE.