Which processes break down a treatment layer?

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.