JP3109931B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image using a two-component developer containing a toner and a magnetic carrier.

[0002]

2. Description of the Related Art Since toner density unevenness occurs in a two-component developer layer after an electrostatic latent image has been developed in a developing section, a fixed magnet provided in the developing sleeve is rotated more in the direction of rotation of the developing sleeve than in the developing section. On the downstream side, first and second magnetic poles of the same polarity adjacent to each other are provided, the developer is removed from the developing sleeve by a repulsive magnetic field formed by the two magnetic poles, and a rotary stirring member arranged in the repulsive magnetic field Thus, the removed developer is agitated to make the toner concentration uniform, and the developer having made the toner concentration uniform is supplied to the developing sleeve on the second magnetic pole side by the rotary stirring member. .

[0003] This prevents the occurrence of density unevenness due to the development history in the developed image.

[0004]

However, depending on the repulsive magnetic field, the developer cannot be completely removed from the developing sleeve, and the developer moves from the first magnetic pole side to the second magnetic pole side while adhering to the developing sleeve. There are also agents.

In particular, when the toner is a small particle size toner having a volume average particle size of about 4 to 10 μm, or the magnetic carrier is a small particle size carrier having a volume average particle size of about 20 to 50 μm, , The frictional charge per unit weight becomes relatively large, the electrostatic adhesion to the developing sleeve becomes strong, and the developer cannot be sufficiently removed from the developing sleeve even by the repulsive magnetic field.

In any case, when the developer that has passed through the developing section arrives at the developing section again without being removed from the developing sleeve, the density of the developed image becomes uneven, and a high-definition image cannot be obtained.

Further, if the developing device is operated for a long period of time without sufficiently removing the developer from the developing sleeve, the deterioration of the developer is promoted, and there is a problem that the density of a developed image is reduced and fogging occurs.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a developing device in which a developer after development is easily removed from a developing sleeve by a repulsive magnetic field, and the removed developer is easily supplied to a rotary stirring member. .

[0009]

The main object of the present invention is to provide a developing container containing a developer having a toner and a magnetic carrier;
A developer carrying member for carrying a developer in the developing container and transporting the developer to a developing section for developing an electrostatic latent image; a first magnetic pole provided in the developer carrying member; A magnet having a second magnetic pole having the same polarity as the first magnetic pole, which is provided adjacent to the downstream side of the first magnetic pole with respect to the rotation direction, and separated from the developer carrier on the first magnetic pole side A stirring member for receiving the developer and supplying the developer to the developer carrier on the second magnetic pole side,
With respect to the rotation direction of the developer carrier, the first magnetic pole is positioned between the first magnetic pole and a position where the magnetic flux density between the first magnetic pole and the second magnetic pole is minimized. A magnetic member to be magnetized is provided in non-contact with the inner wall of the developing container,
A developing device, wherein a developer brush for removing a developer from the developer carrier is formed between the first magnetic pole and the magnetic member.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a cross section of a developing device 2 disposed on the side of an electrophotographic photosensitive drum 1. The developing device 2 is a two-component developing device comprising a carrier of magnetic particles and a toner of non-magnetic particles. The developer 15 is used, and the latent image on the photosensitive drum 1 is developed by the magnetic brush developing method.

The developing device 2 rotates in the direction of arrow A while adsorbing the developer to the outer peripheral portion by the action of a magnetic force, and serves as a developer carrier for supplying the toner in the developer toward the photosensitive drum 1. A cylindrical non-magnetic developing sleeve 20; a magnet 21 fixedly disposed within the developing sleeve 20 and having predetermined magnetic poles S1, S2, N1, N2, and N3 formed outwardly; It has a developer layer thickness regulating blade 22 that regulates the layer thickness of the developer adsorbed on the sleeve 20 and conveyed to the developing section D that develops the electrostatic latent image.

After the development of the latent image in the developing section D, the developer layer is carried by the sleeve 20 and returns into the developing container 10.

As described above, two magnetic poles N ₁ and N ₂ adjacent to each other are arranged on the downstream side of the developing section D in the sleeve rotation direction A. These two magnetic poles N ₁ and N ₂ are magnetic poles of the same polarity, and
The magnetic pole N ₁ contributes to transport the developer that has passed through the developing unit D into the container 10, while the second magnetic pole N ₂ on the downstream side in the rotation direction A is agitated and transported by the screw 23 described later. It contributes to pumping the agent onto the sleeve 20 by magnetic force.

Further, since the first and second magnetic poles N ₁ and N ₂ have the same polarity as described above, a repulsive magnetic field is formed between the two magnetic poles. By forming a repulsive magnetic field in this way, even without pressing a sleeve or the like against the sleeve,
The developer is separated from the sleeve 20 by a magnetic force.

That is, a position P where the magnetic flux density is minimum exists on the peripheral surface of the sleeve between the first magnetic pole N ₁ and the second magnetic pole N _2, and the developer is located between the position of the magnetic pole N ₁ and the position P. With sleeve 2
It is peeled off from 0.

(In this specification, the position of the magnetic pole is referred to as
The position on the sleeve peripheral surface where the magnetic flux density on the sleeve peripheral surface due to the magnetic pole becomes a peak, and the magnetic flux density means the magnetic flux density component in the normal direction to the sleeve peripheral surface. I do. )

A first screw 23 is disposed opposite the sleeve 20 in the repelling magnetic field. Screw 2
3 is closest to the sleeve 20 at a position between the _two magnetic poles N ₁ and N ₂ . The first screw 23 rotates in the direction of the arrow, and conveys the developer along the longitudinal direction of the sleeve 20 while stirring the developer.

On the other hand, another screw 24 is arranged with the partition wall 14 interposed therebetween. The screw 24 conveys the developer in the direction opposite to that of the screw 23 while stirring the developer.

Openings are respectively provided on the front side and the rear side of the partition wall 14 in the drawing, and the developer conveyed by the screw 23 is passed to the screw 24 through one opening, and the developer conveyed by the screw 24 is It is passed to the screw 23 through the other opening.

An amount of toner corresponding to the amount of toner consumed by the developing unit D is supplied to the screw 24 through the opening 18 so that the toner concentration of the developer is kept constant.

A magnetic body 51 is disposed between the position of the magnetic pole N ₁ and the position P and between the sleeve 20 and the screw 23 so as to face the sleeve 20. The magnetic body 51 is a round or square rod-shaped iron or nickel having a diameter of about 0.5 to 3 mm.
0 and an interval of about 0.5 to 2 mm
And are arranged in parallel.

The magnetic material 51 is magnetized by the magnetic pole N ₁ , and forms a magnetic brush of developer between the sleeve 20 and the magnetic material 51.

As described above, since a repulsive magnetic field is formed, the force for transporting the developer from the magnetic pole N ₁ to the magnetic pole N ₂ is originally weak, and the developer is formed into a sleeve by the formation of the magnetic brush. The developer substantially completely removed from 20 and removed by the magnetic material 51 falls on the screw 23 as shown by the arrow 11 and is taken into the screw 23.
That is, the magnetic body 51 also has a function of mediating the transfer of the developer from the sleeve 20 to the screw 23.

The magnetic material 51 is connected to the sleeve 20 and the screw 23 so that the developer once removed from the sleeve by the magnetic material 51 is not again pumped into the sleeve by the magnetic pole N ₂ before being sufficiently stirred by the screw 23. It is preferable that the position is located on the upstream side in the sleeve rotation direction with respect to the closest contact point.

The developer sufficiently stirred by the screw 23 is pumped up again into the sleeve 20 by the magnetic force of the magnetic pole N ₂ , as shown by the arrow 12. The developer pumping point Q on the sleeve is downstream of the position P in the sleeve rotation direction.

The developer pumped up again into the sleeve 20 is regulated in layer thickness by the blade 22 and is conveyed to the developing section D.

[0028]

According to the present invention, the developer can be sufficiently removed from the developer carrier by the repulsive magnetic field, and the removed developer can be satisfactorily taken into the stirring member. Unevenness and deterioration of the developer can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

[Explanation of symbols]

20 first agitating screw 51 magnetic developing sleeve 21 magnet 23 N ₁ first magnetic pole N ₂ second pole

Claims (1)

(57) [Claims] A developing container for storing a developer having a toner and a magnetic carrier; a developer carrying member for carrying the developer in the developing container and transporting the developer to a developing section for developing an electrostatic latent image;
A first magnetic pole provided in the developer carrier, and a second magnetic pole having the same polarity as the first magnetic pole, which is provided adjacent to and downstream of the first magnetic pole with respect to the rotational direction of the developer carrier. And a stirring member that receives the developer separated from the developer carrier on the first magnetic pole side and supplies the developer to the developer carrier on the second magnetic pole side. In the developing device, the first magnetic pole and the position where the magnetic flux density between the first magnetic pole and the second magnetic pole is minimized with respect to the rotation direction of the developer carrying member, A magnetic member magnetized by one magnetic pole is provided in non-contact with the inner wall of the developing container,
A developing device, wherein a developer brush for removing a developer from the developer carrier is formed between the first magnetic pole and the magnetic member.