Pigment Dispersion Equipment — From Agglomerate to a Stable Sub-Micron Dispersion
If the fineness is right out of the mill and wrong by morning, you do not have a grinding problem. Here is how to tell which of the three steps is failing.
The real challenge: it is not grinding, it is de-agglomeration plus stabilisation
A carbon black pigment may have a primary particle size of 20 – 50 nm. By the time it reaches your plant, it exists as agglomerates of 10 – 100 µm. You are not making particles smaller. You are breaking clumps apart, and then keeping them apart.
That is three distinct steps, and only the second one is a grinding problem:
- Wetting — displacing air and moisture from the pigment surface with resin/solvent. If wetting is incomplete, no amount of grinding will fix the result.
- De-agglomeration — mechanical breakdown of agglomerates. This is where the bead mill does its work.
- Stabilisation — keeping the separated particles from re-clumping. This is a formulation problem, solved with the right dispersant at the right loading.
The most common failure we see: a customer hits target fineness in the mill and loses it in the let-down tank. That is a stabilisation failure, not a grinding failure — and buying a bigger mill will not fix it.
Organic vs. inorganic: different strategies
| Organic (phthalocyanine blue, azo red, quinacridone) | Inorganic (titanium dioxide, iron oxide, carbon black) | |
|---|---|---|
| Primary particle | Very fine, 20 – 100 nm | Coarser, 200 – 500 nm |
| Agglomeration | Severe — hard, tightly bound aggregates | Moderate — softer agglomerates |
| Energy required | High | Moderate to high (carbon black excepted) |
| Heat sensitivity | High — many organic pigments degrade or shift shade above 60 – 70 °C | Low |
| Typical target | D90 200 nm – 1 µm | D90 1 – 15 µm |
| Key risk | Over-grinding reduces colour strength and shifts shade | Under-dispersion causes haze, poor gloss, low tint strength |
Carbon black deserves a special note. It has an extremely high surface area and forms very strong agglomerates. It typically needs two or three passes and more energy per unit than any other common pigment. If you are running carbon black, tell us up front — it changes the media, the separator and the cooling specification.
Recommended equipment by production scale
| Scale | Throughput | Recommended | Notes |
|---|---|---|---|
| R&D / formulation | 0.5 – 5 L batch | PM-L lab mill, or basket mill for screening | Basket mill is ideal for screening many formulations quickly |
| Pilot / small production | 10 – 100 L/h | PM-N5 / PM-N15 | Same media and tip speed as production — so results scale |
| Production | 100 – 800 L/h | PM-N30 / PM-N60 / PM-N150 | Continuous, with recirculation for tighter distribution |
| Pre-dispersion | Batch | High-shear disperser | Do the rough work first — it roughly halves the load on the mill |
A practical point: the cheapest way to increase mill throughput is usually a better pre-dispersion step, not a bigger mill.
Target fineness by application
| Application | Typical D90 target | Why |
|---|---|---|
| Automotive basecoat | < 1 µm | Gloss, DOI, colour travel |
| Industrial / general coatings | < 10 – 15 µm | Hiding power without over-grinding |
| Gravure and flexo ink | < 5 µm | Printability, no nozzle or doctor blade wear |
| Inkjet pigment concentrate | < 200 nm | Nozzle diameter, jetting reliability |
| Plastic masterbatch | < 2 – 5 µm | Dispersion in the carrier resin |
| Transparent iron oxide | < 100 nm | Transparency depends on staying below the visible threshold |
Common problems and what actually causes them
This is the table most people come to this page for. If it helps, it also tells you what kind of supplier you are talking to.
| Symptom | Most likely cause | Fix |
|---|---|---|
| Fineness is fine in the mill, coarser next morning | Stabilisation failure — dispersant type or loading | Reformulate; do not increase grinding energy |
| Colour strength drops as you grind finer | Over-grinding — particle size below optimum for that pigment | Reduce passes / increase feed rate; target is not "as fine as possible" |
| Shade shifts during grinding | Temperature too high, or over-grinding | Improve cooling; reduce tip speed |
| Viscosity climbs during the pass | Temperature rise, or solvent loss | Check cooling; check chamber pressure |
| Separator blocks | Media fracture, or media too large for the gap | Replace media; check fill rate and wear |
| Batch-to-batch variation | Inconsistent media charge, or inconsistent pre-dispersion | Weigh media charge; standardise the pre-mix step |
Process parameters that actually matter
| Parameter | Typical range | What goes wrong |
|---|---|---|
| Media size | 0.1 – 1.0 mm | Too large → cannot reach target; too small → slow, hot, expensive |
| Tip speed | 8 – 15 m/s | Too low → no energy transfer; too high → heat, media wear, shade shift |
| Media fill | 70 – 85% | Too low → poor contact; too high → heat build-up |
| Product temperature | < 60 °C for organics | Overheating → degradation, shade shift, viscosity change |
| Number of passes | 1 – 4 | Single pass gives broader distribution than recirculation |
| Dispersant loading | Formula-specific | Under-dosed → re-agglomeration; over-dosed → cost, foaming |
Tell us what you are dispersing — we'll recommend a setup within 24 hours.
Send 1 kg of your mill base and we will run it, measure it, and return the D10 / D50 / D90 report plus our recommendation on media and number of passes.