Developing method for an image forming apparatus and developing device using the same

A method of developing a latent image formed on an image carrier having a photoconductive layer on a surface thereof with a developer including toner grains and magnetic carrier grains, said method comprising:

• providing a developer carrier including a magnet, said developer carrier facing said image carrier to form a developing zone;
• causing the developer to deposit on said developer carrier and move through said developing zone;
• causing the carrier grains to gather and rise along magnetic lines of force of said magnet in a form of brush chains;
• causing the brush chains rising along the magnetic lines of force to contact said image carrier, the brush chains rising to cause the toner grains to part from the carrier grains in a form of free toner grains;
• and
• scattering the free toner grains onto said image carrier to develop the latent image,
• wherein h is a height of the developer on the developer carrier at a zero point at which the magnetic force exerted on the developer by the magnet is zero, L is a distance between the zero point and the image carrier, and L/h is at least 1.5.

A method of developing a latent image formed on an image carrier having a photoconductive layer on a surface thereof with a developer including toner grains and magnetic carrier grains, said method comprising:

• providing a developer carrier including a magnet, said developer carrier facing said image carrier to form a developing zone;
• causing the developer to deposit on said developer carrier and move through said developing zone;
• causing the carrier grains to gather and rise along magnetic lines of force of said magnet in a form of brush chains;
• causing the brush chains to move with tips thereof contacting said image carrier;
• developing an image portion forming the latent image by an electric field formed between said image carrier and said developer carrier and an electric field formed between said image carrier and the carrier grains;
• and
• returning the toner grains present on a non-image portion of said image carrier toward the carrier grains forming the brush chains,
• wherein h is a height of the developer on the developer carrier at a zero point at which the magnetic force exerted on the developer by the magnet is zero, L is a distance between the zero point and the image carrier, and L/h is at least 1.5.

A method of developing a latent image formed on a drum-shaped image carrier having a photoconductive layer on a surface thereof to produce a corresponding toner image, said method comprising:

• providing a drum-shaped developer carrier including a magnet, said developer carrier facing said image carrier to form a developing zone between curved surfaces of the developer carrier and the image carrier that are facing each other, wherein said developing zone includes a middle portion including a position where said developer carrier and said image carrier are closest to each other, a fore portion upstream of said middle portion in a direction of movement of said image carrier, and a hind portion downstream of said middle portion in said direction;
• depositing a developer including toner grains and magnetic carrier grains retaining said toner grains thereon on said developer carrier;
• causing said developer carrier to be in rotation to convey said developer via said developing zone;
• causing the developer to gather along magnetic lines of force of said magnet in a form of brush chains in said developing zone;
• when the carrier grains gathering with the toner grains deposited thereon start rising in said fore portion along the magnetic lines of force, causing said toner grains to part from said carrier grains in accordance with relative displacement of said carrier grains and become free toner grains for developing the latent image;
• contacting the brush chains risen in said fore portion with said image carrier in said middle portion, the brush chains releasing the toner grains, resulting in free toner grains being sprayed onto said image carrier for developing the latent image;
• developing, at least in said hind portion, an image portion of the latent image by an electric field formed between said image carrier and said developer carrier and an electric field formed between said image carrier and the carrier grains;
• and
• returning, at least in said hind portion, the toner grains present in a non-image portion of said image carrier toward said carrier grains forming the brush chains;
• wherein h is a height of the developer on the developer carrier at a zero point at which the magnetic force exerted on the developer by the magnet is zero, L is a distance between the zero point and the image carrier, and L/h is at least 1.5.

A developing device configured to develop a latent image formed on a drum-shaped image carrier having a photoconductive layer on a surface thereof to produce a corresponding toner image, comprising:

• a drum-shaped developer carrier including a magnet, said developer carrier facing said image carrier to form a developing zone between curved surfaces of the developer carrier and the image carrier that are facing each other, said developer carrier configured to be deposited thereon with a developer including toner grains and magnetic carrier grains retaining said toner grains thereon, configured to be caused to be in rotation to convey said developer via said developing zone, and configured to cause the developer to gather along magnetic lines of force of said magnet in a form of brush chains in said developing zone,
• wherein said developing zone includes a middle portion including a position where said developer carrier and said image carrier are closest to each other, a fore portion upstream of said middle portion in a direction of movement of said image carrier, and a hind portion downstream of said middle portion in said direction,
• wherein when the carrier grains gathering with the toner grains deposited thereon start rising in said fore portion along the magnetic lines of force, said toner grains part from said carrier grains in accordance with relative displacement of said carrier grains and become free toner grains for developing the latent image,
• wherein the brush chains risen in said fore portion contact said image carrier in said middle portion, the brush chains release the toner grains, and resulting free toner grains are sprayed onto said image carrier for developing the latent image,
• wherein at least in said hind portion, an image portion of the latent image is developed by an electric field formed between said image carrier and said developer carrier and an electric field formed between said image carrier and the carrier grains, and the toner grains present in a non-image portion of said image carrier are turned toward said carrier grains forming the brush chains, and
• wherein h is a height of the developer on the developer carrier at a zero point at which the magnetic force exerted on the developer by the magnet is zero, L is a distance between the zero point and the image carrier, and L/h is at least 1.5.

An image forming apparatus comprising:

• a drum-shaped image carrier having a photoconductive layer on a surface thereof
• a developing device configured to develop a latent image formed on said image carrier with a developer including toner grains and magnetic carrier grains retaining said toner grains thereon to form a toner image, said developing device including:
• a drum-shaped developer carrier including a magnet and facing said image carrier to form a developing zone between curved surfaces of the developer carrier and the image carrier that are facing each other, said developer carrier configured to be deposited thereon with said developer, configured to be caused to be in rotation to convey said developer via said developing zone, and configured to cause the developer to gather along magnetic lines of force of said magnet in a form of brush chains in said developing zone;
• a transfer device configured to transfer said toner image to a recording medium;
• and
• a fixing device configured to fix said toner image on said recording medium,
• wherein said developing zone includes a middle portion including a position where said developer carrier and said image carrier are closest to each other, a fore portion upstream of said middle portion in a direction of movement of said image carrier, and a hind portion downstream of said middle portion in said direction,
• wherein when the carrier grains gathering with the toner grains deposited thereon start rising in said fore portion along the magnetic lines of force, said toner grains part from said carrier grains in accordance with relative displacement of said carrier grains and become free toner grains for developing the latent image,
• wherein the brush chains risen in said fore portion strongly contact said image carrier in said middle portion, the brush chains release the toner grains, and resulting free toner grains are sprayed onto said image carrier for developing the latent image,
• wherein at least in said hind portion, an image portion of the latent image is developed by an electric field formed between said image carrier and said developer carrier and an electric field formed between said image carrier and the carrier grains, and the toner grains present in a non-image portion of said image carrier are turned toward said carrier grains forming the brush chains, and
• wherein h is a height of the developer on the developer carrier at a zero point at which the magnetic force exerted on the developer by the magnet is zero, L is a distance between the zero point and the image carrier, and L/h is at least 1.5.