Surface Treatment Application FAQ

There is no universal figure. Dosage is set per powder, from its specific surface area and from what you want the treatment to do.

The rule is straightforward: the higher the specific surface area, the more agent is needed to reach the same coverage. Fine and porous grades — high-absorption silica, nano TiO2 — therefore carry noticeably more agent than coarse, low-area fillers at the same weight percentage.

Coverage can be estimated as agent loading divided by (specific surface area × area per molecule), but treat that as an order-of-magnitude check, not a specification. It assumes a uniform monolayer, and a real treatment self-aggregates and covers unevenly.

What actually sets the number is performance: oil absorption should fall, dispersion in the target oil phase should improve, water repellence should shift, and stability should hold. Ask the supplier for the agent loading and for the process — dry or wet — because two grades both labelled "SI treated" can behave differently.

Usually a clear drop, and the size of it depends on agent type and coverage. For most formulas that drop is the main reason to pay for treatment.

The mechanism: the agent occupies active sites on the surface and lowers surface energy, so oil no longer wicks into pores and surface crevices. On porous powders it is most pronounced, because pore mouths are partly sealed.

Three consequences follow. Viscosity falls, so the same solids load handles thinner. You can push in more powder — pigment or UV filter — without it turning to paste. And skin feel improves, with less dryness and drag.

The catch is the same property working against you. If oil control is the product's function, as in an oil-control loose powder, a treated grade can weaken it, and the untreated version may be the better choice. Measure oil absorption on your own samples before and after, using the standard method, rather than relying on the datasheet figure.

Yes, and the direction depends on the agent and the loading. It cannot be assumed either way — it has to be measured.

Two mechanisms act at once. Better dispersion means the particles sit more evenly through the film, which usually raises UV shielding efficiency. The treatment layer itself can absorb in the UV range or alter refraction at the particle surface, which can nudge efficiency down or up.

The same particle size in different treatments can therefore give different SPF. Our grades include N15E (alumina plus stearic acid), N23M (silica plus triethoxycaprylylsilane), Z-45 AS (triethoxycaprylylsilane) and Z-45 DSG (disodium stearoyl glutamate) at comparable sizes.

When you change treatment spec, re-run in-vitro SPF on the same formula and do not carry the old data over. Test UVA as well — PA or critical wavelength — because treatment need not affect UVA and UVB the same way. If the product is already notified, a change of treatment is a change of raw material and may require re-assessment.

Slightly, and mostly through gloss, transparency and saturation rather than hue. Pale and bright shades are the sensitive ones.

The layer changes refractive index and scattering at the surface, so what you see is a shift in gloss, a small loss of transparency, and a small hue drift. Deep and matte shades usually hide it; light, high-chroma shades show it.

Measure it rather than argue about it: colorimeter ΔE plus a visual check against an untreated control, on the same base. Above ΔE 1–2 you will need to adjust pigment loading.

There is a second, indirect effect. Better dispersion raises effective tinting strength — fewer agglomerates, more even coverage — so the batch reads more saturated and deeper. That is dispersion, not hue, and the answer is to cut the loading.

Keep a standard drawdown of both the untreated and treated grade. When a batch or a spec changes, compare panels; it is faster and more reliable than reading numbers alone.

Three-roll milling, bead milling, high-shear homogenising, and long hot emulsification. All four apply shear and heat together, which is what a treatment layer tolerates least.

When the layer fails you tend to see the same two symptoms: the batch thickens as it is milled, and it coarsens on standing. Dispersion and water repellence both regress, so the properties you paid for disappear during processing rather than in storage.

Our SI grades are specified as a chemically bound, shear-resistant coating with a wide temperature window, which is the design intent for exactly these processes. Physically adsorbed treatments, some fatty-acid types among them, desorb more readily under the same conditions.

To find out where you stand, measure fineness of grind, viscosity and oil absorption before and after the process step. If they move, the layer is not surviving your line. Then either move to a chemically bound treatment, add the treated powder later at lower shear, or shorten the hot hold.

No — not if the treatment is a silicone. This is the most common place a "silicone-free" claim fails.

"SI" is a family label, not an ingredient. The agent may be dimethicone, a polymethylsiloxane or a combination. AS is triethoxycaprylylsilane, DSG is disodium stearoyl glutamate, ITT is isopropyl titanium triisostearate. Each has a different regulatory standing, and some carry concentration or use limits.

Ask for three things with every treated grade: the full INCI names with content ranges, the permitted-use basis in the target market, and a COA for the treated powder as a whole.

Two places this bites. The agent content counts toward the formula total, so a limited ingredient can be pushed over its cap by the powder rather than by a direct addition. And combination treatments — ITT over SI, for instance — multiply the number of ingredients to clear one by one. A claim like silicone-free, oil-free or PEG-free has to be checked against the treatment, never assumed to sit outside it.

Six items minimum: dispersion, viscosity, stability, skin feel, colour where a pigment is involved, and whatever functional claim the product makes.

Dispersion and viscosity move first, because the agent sets how the powder wets into the system. Expect the process window — shear time, temperature — to need adjustment as much as the formula.

Stability is not optional: 40°C for one to three months, freeze-thaw cycling, and a centrifuge test. Incompatibility between the new layer and the system shows up as oil separation, layering or coarsening during storage, not on day one.

Skin feel and colour are sensory and optical, so they need actual panels and actual drawdowns. Functional testing follows the product: in-vitro SPF and PA for sunscreen, oil absorption and sebum control for an oil-control product.

The step most often skipped is regulatory. A different treatment changes the INCI list, and on a notified product that may mean a variation. Treat a treatment change as a raw-material change and run the full change-control route.

It helps, but it cannot change the physics. Settling is a density and particle-size problem; treatment only changes surface compatibility.

What treatment does: better compatibility with the continuous phase means fewer agglomerates, and smaller effective particles settle more slowly. The layer can also add a little steric hindrance, which slows flocculation.

What it cannot do: if the powder is much denser than the phase — TiO2 in a light oil — the density difference is unchanged, and a long undisturbed shelf life will still produce sediment.

So the practical answer is a combination: a treated grade to slow it, a suspending agent such as an organically modified clay or fumed silica to give the system a yield value, and particle-size control to keep the coarse tail out.

Test with a centrifuge for a fast read, then sit a sample at ambient for one to three months and watch sediment height and how easily it redisperses. Redispersibility matters more than height: a visible sediment that shakes back in is fine, while a small hard cake is the worse outcome.

Yes, usually — and yes, expect to cut the loading when you move from an untreated to a treated pigment.

The gain is a dispersion effect, not a stronger pigment. Fewer agglomerates mean more effective colouring area, so the same weight reads more saturated and deeper.

Opacity can move the other way. The layer narrows the refractive index difference between pigment and base, so scattering drops slightly, and a thick layer shows it more. In most cases the improved uniformity from better dispersion offsets the loss.

In practice a straight swap at equal loading comes out too deep. Cut by roughly 5–15% depending on how light the shade is, then bring it back to target.

Verify with equal-loading drawdowns, reading L/a/b and contrast ratio, then adjust. Deep shades tolerate the shift; pale and bright ones — pinks, oranges — need re-matching every time.

Four layers, in this order: surface properties, dispersion state, formula performance, then stability. Skipping to the last one is why treatments get blamed for problems they did not cause.

Surface first, because it is cheap and direct. Contact angle of a water drop on a pressed disc should rise clearly on a hydrophobic treatment. Oil absorption should fall. FTIR shows the agent's characteristic peaks if you need proof of identity rather than effect.

Then dispersion: put the powder into the target oil phase, read fineness of grind, look for agglomerates under a microscope, and watch sediment and redispersibility on standing.

Then the real formula: viscosity, yield value, sensory panel, and the functional claim — SPF, oil control, wear. Finally stability: 40°C, freeze-thaw, centrifuge, checking for layering, coarsening and oil separation.

What makes all of it meaningful is the control. Every test needs an untreated sample of the same base powder alongside it, otherwise you cannot separate the effect of the treatment from the effect of the formula. Fix a short list of these tests and run the same list for every supplier and every batch.