Carrier, two-component developer, and image forming method

A two-component developer comprising a toner containing at least a binder resin and a colorant and a carrier comprising carrier particles;

• each carrier particle comprising at least a carrier core and a coat layer for coating the carrier core, wherein;
• said carrier core has a ferrite component, and the ferrite component contains i) a metal oxide having at least one metallic element selected from the group consisting of Mg, Li and Ca, where the total-sum content of the metal oxide having at least one of the metallic elements Mg, Li and Ca is from 15 to 30 mole % based on the whole ferrite component, and ii) a metal oxide having at least one metallic element selected from the group consisting of Mn, Cu, Cr and Zn, where the total-sum content of the metal oxide having at least one of the metallic elements Mn, Cu, Cr and Zn is from 50 to 4,000 ppm on mass basis based on the whole ferrite component;
• said carrier has a volume distribution based 50% particle diameter (D50) of from 15.0 μm to 55.0 μm;
• said carrier has a degree of surface unevenness of from 1.05 to 1.30;
• and
• said coat layer contains particles, and the particles have a number-average primary particle diameter of from 10 nm to 500 nm.

An image forming method comprising:

• a charging step of charging the surface of a photosensitive member electrostatically;
• a latent-image forming step of forming an electrostatic latent image on the photosensitive member surface thus charged;
• a developing step of feeding a toner to the electrostatic latent image by the action of an electric field formed between i) a two-component developer held in a developing unit and ii) the photosensitive member to render the electrostatic latent image visible to form a toner image;
• a transfer step of transferring the toner image onto a transfer material via, or not via, an intermediate transfer member;
• and
• a fixing step of making the transfer material pass a nip formed by a fixing member and a pressure member pressed against the fixing member, to fix the toner image to the transfer material with heating and in pressure contact;
• said steps being repeated to perform image formation;
• said charging step being carried out after a charge quantity control step has been carried out in which a transfer residual toner having remained on the photosensitive member surface after the transfer step is charged to a regular polarity;
• and the transfer residual toner being collected in said developing step;
• and
• said two-component developer having a toner containing at least a binder resin and a colorant and a carrier comprising carrier particles;
• each carrier particle comprising at least a carrier core and a coat layer for coating the carrier core, wherein;
• said carrier core has a ferrite component, and the ferrite component contains i) a metal oxide having at least one metallic element selected from the group consisting of Mg, Li and Ca, where the total-sum content of the metal oxide having at least one of the metallic elements Mg, Li and Ca is from 15 to 30 mole % based on the whole ferrite component, and ii) a metal oxide having at least one metallic element selected from the group consisting of Mn, Cu, Cr and Zn, where the total-sum content of the metal oxide having at least one of the metallic elements Mn, Cu, Cr and Zn is from 50 to 4,000 ppm on mass basis based on the whole ferrite component;
• said carrier has a volume distribution based 50% particle diameter (D50) of from 15.0 μm to 55.0 μm;
• said carrier has a degree of surface unevenness of from 1.05 to 1.30;
• and
• said coat layer contains particles, and the particles have a number-average primary particle diameter of from 10 nm to 500 nm.

An image forming method comprising forming an electrostatic latent image on an electrostatic latent image bearing member, forming a magnetic brush out of a toner and a carrier on a developer carrying member internally provided with a magnetic-field generating means, and developing the electrostatic latent image by means of the magnetic brush formed on the developer carrying member, to form a toner image on the electrostatic latent image bearing member;

• said magnetic brush having the toner in an amount of from 2 parts by weight to 20 parts by weight based on 100 parts by weight of the carrier;
• a replenishing developer being fed to a developing assembly, and the carrier that has become excess in the interior of the developing assembly being discharged out of the developing assembly;
• and the replenishing developer being a two-component developer having a toner containing at least a binder resin and a colorant and a carrier comprising carrier particles;
• each carrier particle comprising at least a carrier core and a coat layer for coating the carrier core, wherein;
• said carrier core has a ferrite component, and the ferrite component contains i) a metal oxide having at least one metallic element selected from the group consisting of Mg, Li and Ca, where the total-sum content of the metal oxide having at least one of the metallic elements Mg, Li and Ca is from 15 to 30 mole % based on the whole ferrite component, and ii) a metal oxide having at least one metallic element selected from the group consisting of Mn, Cu, Cr and Zn, where the total-sum content of the metal oxide having at least one of the metallic elements Mn, Cu, Cr and Zn is from 50 to 4,000 ppm on mass basis based on the whole ferrite component;
• said carrier has a volume distribution based 50% particle diameter (D50) of from 15.0 μm to 55.0 μm;
• said carrier has a degree of surface unevenness of from 1.05 to 1.30;
• and
• said coat layer contains particles, and the particles have a number-average primary particle diameter of from 10 to 500 nm.