Method and device for developing a latent image and image forming apparatus using the same

In a method of developing a latent image formed on an image carrier by using a sleeve, which accommodates magnetic field forming means having a plurality of magnetic poles and faces said image carrier, and causing said sleeve to rotate and convey a developer made up of toner grains and magnetic carrier grains and deposited thereon to a developing zone for thereby feeding said toner grains from a magnet brush formed by said developer to said latent image, when said developing zone is divided into an upstream region, a center region and a downstream region and when said upstream region, said center region and said downstream region are seen from an image carrier side, there holds following relations at tips of said magnet brush:

• 0<α1.p1.q1+α2.p2.q2+α3.p3.q3<5α1+α2+α3=1
• where p1 denotes a ratio of a total area of voids present in said upstream region to a total area of said upstream region, p2 denotes a ratio of a total area of voids present in said center region to a total area of said center region, p1 denotes a ratio of a total area of voids present in said downstream region to a total area of said downstream region, q1 denotes a ratio of voids present in said upstream region and having an area of 17,500 μm2 or above to the total area of the voids present in said upstream region, q2 denotes a ratio of voids present in said center region and having an area of 4,000 μm2 or above to the total area of the voids present in said center region, q3 denotes a ratio of voids present in said downstream region and having an area of 17,500 μm2 or above to the total area of the voids present in said downstream region, α1 denotes a weighting coefficient, which is a constant of 0.375, assigned to said upstream region, α2 denotes a weighting coefficient, which is a constant of 0.25, assigned to said center region, and α3 denotes a weighting coefficient, which is a constant, assigned to said downstream region.

A developing device for developing a latent image formed on an image carrier with a developer made up of toner grains and magnetic carrier grains, said developing device comprising:

• a rotatable sleeve facing the image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is seen from an image carrier side, a ratio of a total area of voids present at tips of the magnet brush to a total area of said developing zone is 25% or less.

A developing device for developing a latent image formed on an image carrier with a developer made up of toner grains and magnetic carrier grains, said developing device comprising:

• a rotatable sleeve facing the image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said center region is seen from an image carrier side, a ratio of a total area of voids present at tips of the magnet brush in said center region to a total area of said center region is 25% or less.

A developing device for developing a latent image formed on an image carrier with a developer made up of toner grains and magnetic carrier grains, said developing device comprising:

• a rotatable sleeve facing the image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said center region is seen from an image carrier side, a distribution of voids present at tips of the magnet brush in said center region satisfies a relation:
• S1/S2>0.4
• where S1 denotes a total area of, among individual voids present in said center region, voids smaller in size than a mean size, and S2 denotes a total area of voids present in said center region.

A developing device for developing a latent image formed on an image carrier with a developer made up of toner grains and magnetic carrier grains, said developing device comprising:

• a rotatable sleeve facing the image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said upstream region, said center region and said downstream region are seen from an image carrier side, a mean area of individual voids present at tips of the magnet brush is 7,500 μm2 or below, 5,000 μm2 or below and 7,500 μm2 or below, respectively.

A developing device for developing a latent image formed on an image carrier with a developer made up of toner grains and magnetic carrier grains, said developing device comprising:

• a rotatable sleeve facing the image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said center region is seen from an image carrier side, a mean size of individual voids present at tips of the magnet brush in said center portion is 7 μm or below in an axial direction of said sleeve and 200 μm or below in a direction of rotation of said sleeve.

A developing device for developing a latent image formed on an image carrier with a developer made up of toner grains and magnetic carrier grains, said developing device comprising:

• a rotatable sleeve facing the image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said upstream region, said center region and said downstream region are seen from an image carrier side, there holds following relations at tips of the magnet brush:
• 0<α1.p1.q1+α2.p2.q2+α3.p3.q3<5α1+α2+α3=1
• where p1 denotes a ratio of a total area of voids present in said upstream region to a total area of said upstream region, p2 denotes a ratio of a total area of voids present in said center region to a total area of said center region, p1 denotes a ratio of a total area of voids present in said downstream region to a total area of said downstream region, q1 denotes a ratio of voids present in said upstream region and having an area of 17,500 μm2 or above to the total area of the voids present in said upstream region, q2 denotes a ratio of voids present in said center region and having an area of 4,000 μm2 or above to the total area of the voids present in said center region, q3 denotes a ratio of voids present in said downstream region and having an area of 17,500 μm2 or above to the total area of the voids present in said downstream region, α1 denotes a weighting coefficient, which is a constant of 0.375, assigned to said upstream region, α2 denotes a weighting coefficient, which is a constant of 0.25, assigned to said center region, and α3 denotes a weighting coefficient, which is a constant, assigned to said downstream region.

An image forming apparatus comprising:

• an image carrier configured to carry a latent image thereon;
• and
• a developing device configured to develop the latent image with a developer made up of toner grains and magnetic carrier grains;
• said developing device comprising:
• a rotatable sleeve facing said image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is seen from an image carrier side, a ratio of a total area of voids present at tips of the magnet brush to a total area of said developing zone is 25% or less.

An image forming apparatus comprising:

• an image carrier configured to carry a latent image thereon;
• and
• a developing device configured to develop the latent image with a developer made up of toner grains and magnetic carrier grains;
• said developing device comprising:
• a rotatable sleeve facing said image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said center region is seen from an image carrier side, a ratio of a total area of voids present at tips of the magnet brush in said center region to a total area of said center region is 25% or less.

An image forming apparatus comprising:

• an image carrier configured to carry a latent image thereon;
• and
• a developing device configured to develop the latent image with a developer made up of toner grains and magnetic carrier grains;
• said developing device comprising:
• a rotatable sleeve facing said image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said center region is seen from an image carrier side, a distribution of voids present at tips of the magnet brush in said center region satisfies a relation:
• S1/S2>0.4
• where S1 denotes a total area of, among individual voids present in said center region, voids smaller in size than a mean size, and S2 denotes a total area of voids present in said center region.

An image forming apparatus comprising:

• an image carrier configured to carry a latent image thereon;
• and
• a developing device configured to develop the latent image with a developer made up of toner grains and magnetic carrier grains;
• said developing device comprising:
• a rotatable sleeve facing said image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said upstream region, said center region and said downstream region are seen from an image carrier side, a mean area of individual voids present at tips of the magnet brush is 7,500 μm2 or below, 5,000 μm2 or below and 7,500 μm2 or below, respectively.

An image forming apparatus comprising:

• an image carrier configured to carry a latent image thereon;
• and
• a developing device configured to develop the latent image with a developer made up of toner grains and magnetic carrier grains;
• said developing device comprising:
• a rotatable sleeve facing said image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said center region is seen from an image carrier side, a mean size of individual voids present at tips of the magnet brush in said center portion is 7 μm or below in an axial direction of said sleeve and 200 μm or below in a direction of rotation of said sleeve.

An image forming apparatus comprising:

• an image carrier configured to carry a latent image thereon;
• and
• a developing device configured to develop the latent image with a developer made up of toner grains and magnetic carrier grains;
• said developing device comprising:
• a rotatable sleeve facing said image carrier;
• and
• magnetic field forming means having a plurality of magnetic poles and held stationary inside said sleeve;
• said sleeve being rotated to convey the developer deposited thereon to a developing zone for thereby feeding the toner grains from a magnet brush formed by said developer to the latent image;
• wherein when the developing zone is divided into an upstream region, a center region and a downstream region and when said upstream region, said center region and said downstream region are seen from an image carrier side, there holds following relations at tips of the magnet brush:
• 0<α1.p1.q1+α2.p2.q2+α3.p3.q3<5α1+α2+α3=1
• where p1 denotes a ratio of a total area of voids present in said upstream region to a total area of said upstream region, p2 denotes a ratio of a total area of voids present in said center region to a total area of said center region, p1 denotes a ratio of a total area of voids present in said downstream region to a total area of said downstream region, q1 denotes a ratio of voids present in said upstream region and having an area of 17,500 μm2 or above to the total area of the voids present in said upstream region, q2 denotes a ratio of voids present in said center region and having an area of 4,000 μm2 or above to the total area of the voids present in said center region, q3 denotes a ratio of voids present in said downstream region and having an area of 17,500 μm2 or above to the total area of the voids present in said downstream region, α1 denotes a weighting coefficient, which is a constant of 0.375, assigned to said upstream region, α2 denotes a weighting coefficient, which is a constant of 0.25, assigned to said center region, and α3 denotes a weighting coefficient, which is a constant, assigned to said downstream region.