Toner additives comprising composite particles

1. A method of making a composite particle, comprising:

providing an aqueous dispersion comprising metal oxide particles;

adding a first hydrophobizing agent to the aqueous dispersion to form an emulsion, wherein a mass ratio of the first hydrophobizing agent to the metal oxide particles in the emulsion is at least 1.5;

incubating the emulsion for one to three hours at a temperature from 25 to 60° C., wherein the first hydrophobizing agent becomes chemically attached to the metal oxide particles;

following incubating, adding a polymerization initiator to the aqueous dispersion to form metal oxide-polymer composite particles comprising a polymer matrix and a plurality of metal oxide particles, wherein at least a portion of the plurality of metal oxide particles project into and out from the polymer matrix; and

treating available surfaces of the plurality of metal oxide particles with a second hydrophobizing agent selected from the group consisting of silazane compounds, siloxane compounds, silane compounds, and silicone fluids having a number average molecular weight of at most 500, wherein the treating is performed after formation of the metal oxide-polymer composite particles.

2. The method of making a composite particle of claim 1 , further comprising drying the metal oxide-polymer composite particles, wherein the drying may be performed before or after the treating.

3. The method of claim 1 , wherein the initiator is an on-soluble initiator.

4. The method of claim 1 , wherein the first hydrophobizing agent has the formula [R 3 3-x (OR 1 ) x ]SiR 2 Q, where x is 1, 2, or 3, R 1 is methyl or ethyl, R 2 is an alkyl linker with the general formula C n H 2n , where n=1-10, R 3 is methyl or ethyl and Q is a substituted or unsubstituted vinyl, acrylate ester, or methacrylate ester group, with the proviso that when Q is substituted or unsubstituted vinyl, n is 2-10.

5. The method of claim 1 , further comprising drying the metal oxide-polymer composite particles to form a powder.

6. Metal oxide-polymer composite particles produced by the method of claim 1 .

7. The method of claim 1 , wherein the metal oxide particles comprise silica or titanic.