Development device and image forming apparatus therewith

A development device developing an electrostatic latent image formed on an image carrying member into a toner image, comprising:

• a developer container including a first conveyance chamber and a second conveyance chamber disposed above the first conveyance chamber across a partition portion, the developer container storing two-component developer containing carrier and toner;
• a first stirring-conveyance member rotatably supported in the first conveyance chamber, the first stirring-conveyance member conveying, while stirring, developer in the first conveyance chamber in a first direction;
• a second stirring-conveyance member rotatably supported in the second conveyance chamber parallel to the first stirring-conveyance member, the second stirring-conveyance member conveying, while stirring, developer in the second conveyance chamber in a second direction opposite to the first direction;
• a developer carrying member rotatably supported on the developer container, the developer carrying member carrying on a surface thereof the developer in the second conveyance chamber;
• and
• a regulation blade disposed opposite the developer carrying member, the regulation blade regulating a layer thickness of the developer on the developer carrying member,
• wherein
• the first conveyance chamber is isolated from the developer carrying member by a separating wall extending downward from the partition portion,
• feeding of the developer to the developer carrying member and collection of the developer from the developer carrying member are carried out in the second conveyance chamber,
• the developer carrying member includes:
• a development sleeve rotatable and in a cylindrical shape;
• and
• a magnetic member fixed inside the development sleeve so as not to be rotatable, the magnetic member having, along a rotation direction of the development sleeve, a plurality of magnetic poles including a regulation pole opposite the regulation blade, a main pole opposite the image carrying member, a release pole releasing the developer carried on the developer carrying member, and an attracting pole attracting the developer onto the developer carrying member, and
• a release start position at which a magnetic flux density of the release pole becomes 5 [mT] or less is below a straight line L1 horizontally passing through a center of a rotation shaft of the second stirring-conveyance member and, when a central angle of a developer releasing region where a magnetic flux density between the release pole and the attracting pole is 5 [mT] or less is represented by X [° ] and a peak magnetic flux density of the attracting pole is represented by Y [mT], formula (1) below is satisfied:
• Y
• ≤
• 2.1
• X
• -
• 3
• ⁢
• 2.7
• .
• (
• 1
• )