Magnetic particles and magnetic carrier for electrophotographic developer

Magnetic particles having an average particle size of 10 to 200 μm, comprising:

• magnetic core particles;
• and
• a coating layer formed on each surface of said magnetic core particles, consisting essentially of:
• (1) a silicone resin,
• (2) at least one metal alkoxide selected from the group consisting of aluminum-tri-n-butoxide, aluminum-tri-ethoxide, aluminum-tri-sec-butoxide, aluminum-tri-isopropoxide, titanium-tetra-n-butoxide, titanium-tetraethoxide and titanium-tetra-iso-propoxide, in an amount of 0.05 to 0.3% by weight based on the weight of said silicone resin (solid content), and
• (3) at least one silane-based coupling agent selected from the group consisting of an amino-containing silane coupling agent, an epoxy-containing silane coupling agent, a mercapto-containing silane coupling agent, and a halogen-containing silane-based coupling agent, in an amount of 0.1 to 20.0% by weight based on the weight of said silicone resin (solid content).

Magnetic particles having an average particle size of 10 to 200 μm, comprising:

• magnetic core particles;
• and
• a coating layer formed on each surface of said magnetic core particles, consisting essentially of:
• (1) a silicone resin,
• (2) at least one metal alkoxide selected from the group consisting of aluminum-tri-n-butoxide, aluminum-tri-ethoxide, aluminum-tri-sec-butoxide, aluminum-tri-isopropoxide, titanium-tetra-n-butoxide, titanium-tetraethoxide and titanium-tetra-iso-propoxide, in an amount of 0.05 to 0.3% by weight based on the weight of said silicone resin (solid content), and
• (3) at least one silane-based coupling agent selected from the group consisting γ-aminopropyl trimethoxysilane, N-β-aminoethyl-γ-aminopropyl trimethoxysilane, N-β-aminoethyl-γ-aminopropylmethyl dimethoxysilane, N-phenyl-γ-aminopropyl trimethoxysilane, β-glycidoxypropylmethyl diethoxysilane, β-3,4-epoxycyclohexyl trimethoxysilane, β-glycidoxypropyl trimethoxysilane, dimethyl dichlorosilane, methyl trichlorosilane, allyl dimethyl chlorosilane, allyl phenyl dichlorosilane, benzyl dimethyl chlorosilane, bromomethyl dimethyl chlorosilane, α-chloroethyl trichlorosilane, β-chloroethyl trichlorosilane, and γ-mercaptopropyl trimethoxysilane in an amount of 0.1 to 20.0% by weight based on the weight of said silicone resin (solid content).

A method of making magnetic particles having an average particle size of 10 to 200 μm, comprising applying a coating layer formed on each surface of magnetic core particles, said coating laver consisting essentially of:

• (1) a silicone resin, (2) at least one metal alkoxide, and (3) at least one silane-based coupling agent selected from the group consisting of an amino-containing silane coupling agent, an epoxy-containing silane coupling agent, a mercapto-containing silane coupling agent, a halogen-containing silane coupling agent, in an amount of 0.1 to 20.0% by weight based on the weight of said silicone resin (solid content),
• wherein brittleness of the coating is avoided by using a non-tin containing metal alkoxide represented by the general formula (I):
• (RO)nM (I)
• wherein R is a C1 to C16 alkyl group;
• M is Al, Ti, Na, K, Ca, Zn or Fe;
• and n is an integer of 1 to 4, in an amount of 0.05 to 0.3% by weight based on the weight of said silicone resin (solid content).