A developer mix used in a dual component development (DCD) system is a mixture of toner particles and magnetic carrier particles, wherein the magnetic carrier particle is surface treated with a hydrophobized titania particle. The surface treatment with a hydrophobized titania particle may be selected from either a spherical, disk, or spindle shaped. Tribocharge of the toner and the toner charge stability across cartridge life or environments may be suitably modified by selecting a preferred size and shape of the hydrophobized titania.

A developer includes a toner including toner particles and a carrier including carrier particles. The carrier particles each include a carrier core and a carrier coating layer covering the carrier core. The carrier coating layer contains a fluorine-containing resin. The toner particles each include a toner mother particle and resin particles located on a surface of the toner mother particle. The resin particles have a number average primary particle diameter of at least 70 nm and no greater than 200 nm. A dispersion obtained by dispersing 0.1 g of the resin particles in 100 mL of distilled water has an electrical conductivity of at least 2.5 S/m and no greater than 6.0 S/m. A degree of aggregation Y.sub.160 of the resin particles represented by expression (1) Y.sub.160=100M.sub.160A/M.sub.160B is at least 15% by mass and no greater than 40% by mass.

A magnetic carrier comprising: a magnetic material-dispersed resin carrier core material; and a resin coating layer on the surface of the magnetic material-dispersed resin carrier core material, wherein the magnetic material-dispersed resin carrier core material contains a core material particle containing a magnetic material and a binder resin, and a primer compound having an amino group, the resin coating layer contains a coating resin A, which is a polymer of monomers including at least a (meth)acrylic acid ester having an alicyclic hydrocarbon group, and the content of the primer compound in the magnetic material-dispersed resin carrier core material and the content of the resin coating layer are in specific range.

The present invention relates to a magnetic carrier for an electrophotographic developer comprising spherical magnetic composite particles comprising a phenol resin as a binder and ferromagnetic iron oxide particles bonded to each other through the phenol resin, wherein the spherical magnetic composite particles have a ten-point mean roughness Rz of 0.3 to 2.0 m. The magnetic carrier for an electrophotographic developer according to the present invention exhibits an excellent durability against peeling-off and abrasion of coating resins formed thereon and a high stability to mechanical stress exerted onto the carrier, is free from occurrence of spent toner, can be stably held over a long period of time without occurrence of fogging and unevenness in density of toner images, and can keep high-quality images with an excellent gradation for a long period of time.

An electrostatic charge image developing carrier contains a core particle and a resin coat layer on a surface of the core particle, wherein the core particle has a BET specific surface area of from 0.05 m.sup.2/g to 0.10 m.sup.2/g, and the resin coat layer contains a nitrogen-containing (meth)acrylate resin.

The present invention relates to a magnetic carrier for an electrophotographic developer comprising spherical magnetic composite particles comprising a phenol resin as a binder and ferromagnetic iron oxide particles bonded to each other through the phenol resin, wherein the spherical magnetic composite particles have a ten-point mean roughness Rz of 0.3 to 2.0 m. The magnetic carrier for an electrophotographic developer according to the present invention exhibits an excellent durability against peeling-off and abrasion of coating resins formed thereon and a high stability to mechanical stress exerted onto the carrier, is free from occurrence of spent toner, can be stably held over a long period of time without occurrence of fogging and unevenness in density of toner images, and can keep high-quality images with an excellent gradation for a long period of time.

A developer mix used in a dual component development (DCD) system is a mixture of toner particles and magnetic carrier particles, wherein the magnetic carrier particle is surface treated with a hydrophobized titania particle. The surface treatment with a hydrophobized titania particle may be selected from either a spherical, disk, or spindle shaped. Tribocharge of the toner and the toner charge stability across cartridge life or environments may be suitably modified by selecting a preferred size and shape of the hydrophobized titania.

A method for providing a developer mix having tribocharge uniformity across varying temperature and humidity conditions is provided. Tribocharge uniformity is achieved in the developer mix by performing the step of treating the surface of the polymer coated magnetic carrier particles with hydrophobized titania surface additives before the polymer coated magnetic carrier particles are mixed with the toner particles. The surface treatment with the hydrophobized titania surface additives can be either a spherical, disk, or spindle shaped.

The present invention is a magnetic carrier that has a magnetic carrier core and a resin coat layer, wherein the resin coat layer contains a coat resin A and a coat resin B, the coat resin A is a polymer obtained by polymerization of a (meth)acrylate ester monomer that has an alicyclic hydrocarbon group, the coat resin B is a polymer obtained by polymerization of (meth)acrylic monomer and has a polar group and an acid value of 4.0 to 50.0 mg KOH/g, the content of the coat resin A is 10 to 90 mass %, the content of the coat resin B is 10 to 90 mass %, and an acid value of the resin component in the resin coat layer is 1.0 to 10.0 mg KOH/g.

A method for providing a developer mix having tribocharge uniformity across varying temperature and humidity conditions is provided. A developer mix used in a dual component development (DCD) system typically is a mixture of toner particles and magnetic carrier particles. Tribocharge uniformity is achieved in the developer mix by performing the step of treating the surface of the magnetic carrier particles with surface additives before the magnetic carrier particles are mixed with the toner particles. Surface additives include but are not limited to silica, titania and alumina.