Developing method and apparatus using two-ingredient developer with prescribed coating of particles and resin

An image forming apparatus comprising:

• a developing unit configured to develop a latent image formed on an image carrier with a developer carrier, the developing unit including,
• a rotatable, nonmagnetic sleeve,
• a magnetic unit configured to cause a two-ingredient type developer including magnetic carrier grains and toner grains to deposit on a surface of said developer carrier, the magnetic unit disposed in or circumscribed by said sleeve, and
• a rigid metering member configured to meter an amount of said developer deposited on said surface of said developer carrier, wherein
• a gap between the sleeve and the image carrier is 0.4 mm or below,
• the carrier grains each are covered with a coating layer including at least binder resin and coating grains,
• a ratio of a diameter D of an individual coating grain included in said coating layer to a thickness h of a layer of the binder resin lies in a range of 5<D/h<10.

An image forming method using a developing unit configured to develop a latent image formed on an image carrier with a developer carrier, the developing unit including,

• a rotatable, nonmagnetic sleeve,
• a magnetic unit configured to cause a two-ingredient type developer including magnetic carrier grains and toner grains to deposit on a surface of said developer carrier the magnetic unit disposed in or circumscribed by said sleeve, and
• a rigid metering member configured to meter an amount of said developer deposited on said surface of said developer carrier, wherein
• a gap between the sleeve and the image carrier is 0.4 mm or below,
• the carrier grains each are covered with a coating layer including at least binder resin and coating grains,
• a ratio of a diameter D of an individual coating grain included in said coating layer to a thickness h of a layer of the binder resin lies in a range of 5<D/h<10.

An image forming apparatus comprising:

• a developing unit configured to develop a latent image formed on an image carrier with a developer carrier, the developing unit including,
• a rotatable, nonmagnetic sleeve,
• a magnetic unit configured to cause a two-ingredient type developer including magnetic carrier grains and toner grains to deposit on a surface of said developer carrier, the magnetic unit disposed in or circumscribed by said sleeve, and
• a rigid metering member configured to meter an amount of said developer deposited on said surface of said developer carrier, wherein
• the sleeve has a surface roughness Rz ranging from 5 μm to 20 μm,
• the carrier grains each are covered with a coating layer including at least binder resin and coating grains,
• a ratio of a diameter D of an individual coating grain included in said coating layer to a thickness h of a layer of the binder resin lies in a range of 5<D/h<10,
• the carrier grains have a weight-mean grain size d ranging from 20 μm to 60 μm, and
• even after 60,000 images of size A4 are developed by said developing unit, said amount of said developer deposited on said developer carrier decreases by less than 30%.

An image forming apparatus comprising:

• a developing unit configured to develop latent images formed on an image carrier with a developer carrier, the developing unit including,
• a rotatable, nonmagnetic sleeve,
• a magnetic unit configured to cause a two-ingredient type developer including magnetic carrier grains and toner grains to deposit on a surface of said developer carrier, the magnetic unit disposed in or circumscribed by said sleeve, and
• a rigid metering member configured to meter an amount of said developer deposited on said surface of said developer carrier, wherein
• a gap between the sleeve and the image carrier is 0.4 mm or below,
• the carrier grains each are covered with a coating layer including at least binder resin and coating grains,
• a ratio of a diameter D of an individual coating grain included in said coating layer to a thickness h of a layer of the binder resin lies in a range of 5<D/h<10, and
• even after 200,000 images of size A4 are developed by the developing unit, brush marks do not appear in said latent images.

An image forming apparatus comprising:

• a developing unit configured to develop a latent image formed on an image carrier with a developer carrier, the developing unit including,
• a rotatable, nonmagnetic sleeve,
• a magnetic unit configured to cause a two-ingredient type developer including magnetic carrier grains and toner grains to deposit on a surface of said developer carrier, the magnetic unit disposed in or circumscribed by said sleeve, and
• a rigid metering member configured to meter an amount of said developer deposited on said surface of said developer carrier, wherein
• a gap between the sleeve and the image carrier is 0.4 mm or below,
• the carrier grains each are covered with a coating layer including at least binder resin and coating grains,
• a ratio of a diameter D of an individual coating grain included in said coating layer to a thickness h of a layer of the binder resin lies in a range of 5<D/h<10, and
• even after 200,000 images of size A4 are developed by said developing unit, said amount of said developer deposited on said developer carrier decreases by about 5 mg/cm2 or less.