Developing device including a developer container with toner particles and magnetic carrier particles (Rz=0.5−3.0 gm) and a developer bearing member (Rz=10−30 gm), and an image forming apparatus and process cartridge containing the same

An image forming apparatus, comprising:

• an electrostatic latent image bearing member;
• an electrostatic latent image forming device adapted to form an electrostatic latent image on the electrostatic latent image bearing member;
• a developing device adapted to develop the electrostatic latent image into a toner image with a two-component developer, the developing device including:
• a developer container, the developer container containing a two-component developer, the two-component developer comprising toner particles and magnetic carrier particles, the magnetic carrier particles having a ten-point average surface roughness Rz of 0.5 to 3.0 μm;
• and
• a developer bearing member, the developer bearing member being a cylindrical member containing a magnetic field generator having multiple magnetic poles, the developer bearing member being adapted to bear the two-component developer on a surface thereof and to convey the two-component developer as the surface rotates, the developer bearing member having a ten-point average surface roughness Rz of 10 to 30 μm,
• wherein the multiple magnetic poles include three developer bearing poles each adapted to generate a magnetic field having a strength enough for retaining the two-component developer on a surface of the developer bearing member, and the three developer bearing poles consist of a developing pole, a pre-developing pole, and a post-developing pole,
• wherein the developing pole is adapted to generate a first magnetic field in a developing area in which the developer bearing member faces the electrostatic latent image bearing member,
• wherein the pre-developing pole is adapted to generate a second magnetic field, the second magnetic field supplying the two-component developer from the developer container to a surface of the developer bearing member and conveying the two-component developer to the developing area, the second and first magnetic fields retaining the two-component developer on a surface of the developer bearing member between a position where the two-component developer is supplied thereto and the developing area, and
• wherein the post-developing pole is adapted to generate a third magnetic field, the third magnetic field separating the two-component developer from the developer bearing member at a downstream side from the developing area and an upstream side from the developing pole relative to a direction of rotation of the developer bearing member, the first and third magnetic fields retaining the two-component developer on a surface of the developer bearing member between the developing area and a position where the two-component developer is separated therefrom;
• and
• a transfer device adapted to transfer the toner image onto a recording medium;
• and
• a fixing device adapted to fix the toner image on the recording medium.

A process cartridge detachably attachable to image forming apparatus, comprising:

• an electrostatic latent image bearing member;
• and
• a developing device adapted to develop the electrostatic latent image into a toner image with a two-component developer, the developing device including:
• a developer container, the developer container containing a two-component developer, the two-component developer comprising toner particles and magnetic carrier particles, the magnetic carrier particles having a ten-point average surface roughness Rz of 0.5 to 3.0 μm;
• and
• a developer bearing member, the developer bearing member being a cylindrical member containing a magnetic field generator having multiple magnetic poles, the developer bearing member being adapted to bear the two-component developer on a surface thereof and to convey the two-component developer as the surface rotates, the developer bearing member having a ten-point average surface roughness Rz of 10 to 30 μm,
• wherein the multiple magnetic poles include three developer bearing poles each adapted to generate a magnetic field having a strength enough for retaining the two-component developer on a surface of the developer bearing member, and the three developer bearing poles consist of a developing pole, a pre-developing pole, and a post-developing pole,
• wherein the developing pole is adapted to generate a first magnetic field in a developing area in which the developer bearing member faces the electrostatic latent image bearing member,
• wherein the pre-developing pole is adapted to generate a second magnetic field, the second magnetic field supplying the two-component developer from the developer container to a surface of the developer bearing member and conveying the two-component developer to the developing area, the second and first magnetic fields retaining the two-component developer on a surface of the developer bearing member between a position where the two-component developer is supplied thereto and the developing area, and
• wherein the post-developing pole is adapted to generate a third magnetic field, the third magnetic field separating the two-component developer from the developer bearing member at a downstream side from the developing area and an upstream side from the developing pole relative to a direction of rotation of the developer bearing member, the first and third magnetic fields retaining the two-component developer on a surface of the developer bearing member between the developing area and a position where the two-component developer is separated therefrom.