1. Introduction

The final quality of a color paste is set not only by the dispersant chemistry, but also by dosage and milling process. This article optimizes polymeric dispersant dosage and sand-milling parameters using four key parameters: dispersant dosage, bead size, agitator tip speed, and temperature. Related literature is in the DENSON Literature and DENSON website.

2. Mechanism

Dispersion proceeds in three steps: wetting, deagglomeration and stabilization. The dispersant must cover new surfaces quickly; insufficient dosage leaves bare particles that re-flocculate, while excess dosage raises cost and can weaken the film. Optimum dosage is read from the millbase viscosity minimum.

3. Optimizing Dispersant Dosage

A dosage curve is run from 0.5% to 4.0% on pigment. Viscosity drops to a minimum then rises again. The optimum is at the minimum; for carbon black the optimum was ~2.0%, and for titanium dioxide ~1.2%. Zeta potential should reach |z|≥30 mV (ISO 13099).

Fig.1 Rotational viscometer for viscosity curve

4. Bead Size and Tip Speed

Smaller beads give finer grinding but lower energy efficiency. For sub-10 µm carbon black paste, 0.6-0.8 mm yttrium-stabilized zirconia beads and a tip speed of 10-12 m/s are typical. Too high speed raises temperature above 50 °C and degrades the dispersant; control at 30-40 °C.

Fig.2 Horizontal nano sand mill

5. Process Parameters and Scale-up

On scale-up, keep bead load 70-80%, fill level stable, and check fineness at intervals (GB/T 6753.1 Hegman gauge). A large production line validated the lab recipe with consistent &le;10 &micro;m fineness and batch-to-batch viscosity variation <5%.

Fig.3 Large-scale nano milling line

6. Key Selection Parameters

7. Conclusion

Optimize dispersant dosage at the viscosity minimum, match bead size to target fineness, and control tip speed and temperature; this gives reproducible, low-viscosity, fine color paste.

8. FAQ

Q1. How do I find the right dispersant dosage?
Run a dosage series and take the viscosity minimum; check fineness and storage stability at each point.

Q2. Why does viscosity rise again at high dosage?
Excess free dispersant can bridge particles and increase continuous-phase viscosity; it may also reduce film performance.

Q3. How to avoid overheating during milling?
Use cooling, limit tip speed, and keep temperature 30-40 &deg;C so the polymer dispersant does not degrade.

Q4. Is lab fineness repeatable at production scale?
It is repeatable if bead size, load, tip speed and temperature are kept the same and fineness is checked by the same gauge.