Method for preparing particles comprising metal oxide coating and particles with metal oxide coating

A process for coating solid benzoyl peroxide consisting of:

• (a) contacting, in an aqueous medium, the solid benzoyl peroxide with a cationic surfactant to obtain a dispersion of solid benzoyl peroxide having positive charges on its surface;
• (b) adding an aqueous solution of a metal oxide salt to said dispersion, under conditions wherein said metal oxide salt precipitates onto the benzoyl peroxide, and acidifying to thereby form benzoyl peroxide that has a metal oxide layer coated thereon;
• (b1) contacting, in an aqueous medium, the benzoyl peroxide coated with a metal oxide layer of the preceding step with a surface adhering additive being one or both of (i) a cationic polymer additive and (ii) a non-ionic additive, to obtain a dispersion of said coated solid benzoyl peroxide having an adhering additive on the surface thereof;
• (b2) bringing the dispersion obtained in step (b1) into contact with an aqueous solution of a metal oxide salt, under conditions wherein said metal oxide salt precipitates onto the surface of said coated solid benzoyl peroxide, and acidifying to thereby form a solid benzoyl peroxide that has a further metal oxide layer coated thereon;
• (c) repeating steps (b1) and (b2) at least 3 more times;
• (d) after completion of step (c), aging the metal oxide coating at a temperature ranging between 4° C. and 90° C. and at a pH of 3-9 to form a coated solid benzoyl peroxide, wherein no aging step is conducted between repeated coating steps, but only after completion of step c;
• and, optionally,
• (e) separating the coated, solid benzoyl peroxide from the aqueous medium and optionally rinsing and re-dispersing the coated, solid benzoyl peroxide in an aqueous medium.