Dispersion quality describes how easily a pigment powder breaks down into fine particles in your ink, paint or plastic, and how well those particles stay apart. A pigment that disperses well gives full colour strength, gloss and clean results with less milling energy.
Poor dispersion shows up as specks, streaks, weak colour, low gloss, blocked filters or broken fibres. Two pigments with the same Colour Index name can differ widely here, because dispersion depends on how the maker finished the pigment.
Dispersion is also a cost question, even if it never shows on the invoice. A pigment that needs extra passes through a mill, more dispersant or a slower extruder costs you time and energy on every batch you make.
Why it varies
Pigment particles are made very small, but they stick together during drying into aggregates and agglomerates. Your process has to wet the particles, break the agglomerates apart and then stabilise them so they do not clump again.
Makers control this through crystal growth, particle size, drying method and surface treatment with resins or additives. A cheap finishing step can save the maker time while costing you milling hours or rejected goods.
How it is tested
- Fineness of grind, measured with a grindometer or Hegman gauge under ISO 1524, shows the size of the largest particles left in a paint or ink after milling.
- Colour strength development compares strength after short and long dispersion times; a pigment that reaches full strength quickly disperses easily.
- Rub-out and flocculation tests in paint show whether particles re-cluster after dispersion.
- For plastics, the filter pressure value test in EN 13900-5 pushes coloured melt through a fine screen and measures the pressure rise caused by undispersed particles.
- Film or sheet tests look for specks under a microscope or by eye in a thin film or blown film, counted per unit area.
How to buy for good dispersion
Tell the supplier your system and equipment, such as a bead mill for solvent ink or a twin-screw extruder for masterbatch. Ask for the grade designed for it. Ask for test results in your system, then repeat the test in your own lab beside your current pigment, at the same loading.
Write the agreed tests and limits into your specification. Agree how much variation you will accept between lots. Ask for at least one dispersion result on each lot's COA, especially for plastics and fibre uses where specks cause rejects. For plastics, also check heat stability. For a wider view, read what organic pigments are used for.
Next step
We find pigment makers whose grades suit your process, compare samples in your system and have lots tested before loading. To begin, book a free sourcing review.