Development magnet roller, development device, process cartridge and image forming apparatus

A development device of an electrophotographic image forming apparatus, comprising:

• a development sleeve configured to bear a developer on a surface thereof;
• and
• a development magnet roller fixedly arranged in the development sleeve and having a development pole configured to form a magnetic field causing the developer on the surface of the development sleeve to rise in a form of a series of ears in a development area of the image forming apparatus where the development sleeve opposes an image bearing member, wherein
• (a) in a magnetic flux density distribution in a normal line direction of the development pole,
• a peak magnetic flux density is 120mT or greater,
• a zero gauss region width is 70° or greater, and
• a half-width region width is 40° or smaller;
• and
• (b) said zero gauss region width is measured on the surface of the development sleeve.

A development device of an electrophotographic image forming apparatus, comprising:

• an image bearing member;
• a plurality of development rollers;
• an image forming area where the plurality of development rollers oppose said image bearing member;
• and
• a development case housing the plurality of development rollers to be partially exposed, wherein
• said plurality of development rollers each include a development sleeve and a development roller located at a downstream side in a direction in which a developer is conveyed in said development area, said development roller including,
• a development magnet roller having a development pole configured to form a magnetic field causing a developer on a surface of the development sleeve of the development roller to rise in a form of a series of ears in the development area, wherein
• (a) in a magnetic flux density distribution in a normal line direction of the development pole,
• a peak magnetic flux density is 120 mT or greater,
• a zero gauss region width is 70° or greater
• a half-value region width is 40° or smaller
• (b) said zero gauss region width is measured on the surface of the development sleeve.

A process cartridge of an electrophotographic image forming apparatus, comprising:

• a development device including a development roller having a development magnet roller and a development sleeve;
• and
• a process device,
• wherein
• (a) the development magnet roller has a development pole configured to form a magnetic field causing a developer on a surface of the development sleeve of the development roller to rise in a form of a series of ears in a development area of the image forming apparatus where the development roller opposes an image bearing member,
• (b) in a magnetic flux density distribution in a normal line direction of the development pole,
• a peak magnetic flux density is 120 mT or greater,
• a zero gauss region width is 70° or greater and
• a half-value region width is 40° or smaller;
• and
• (c) said zero gauss region width is measured on the surface of the development sleeve.

An image forming apparatus of electrophotography, comprising:

• an image bearing member;
• and
• a development device including a development roller having a development magnet roller and a development sleeve, wherein
• (a) the development magnet roller has a development pole configured to form a magnetic field causing a developer on a surface of the development sleeve of the development roller to rise in a form of a series of ears in a development area where the development roller opposes the image bearing member,
• (b)in a magnetic flux density distribution in a normal line direction of the development pole,
• a peak magnetic flux density is 120 mT or greater,
• a zero gauss region width is 70° or greater, and
• a half-value region width is 40° or smaller;
• and
• (c) said zero gauss region width is measured on the surface of the development sleeve.