JPH01172880A - Developing device - Google Patents

Abstract

PURPOSE:To prevent the generation of surface contamination and color mixture on an image by providing a magnet roller for drawing a developer which is going to a developing sleeve side, between the developing sleeve and a developer stirring, carrying and drawing member. CONSTITUTION:A magnet roller 20 for delivering a developer as relaying to a developing sleeve 12 from a developer stirring, carrying and drawing member 5, at the time of supplying a two component compound developer in which at least a part thereof consists of a magnetic material, to the developing sleeve 12, and drawing the developer which is going to the developing sleeve 12 side, at the time of cutting off its supply is provided between the developing sleeve 12 and the developer stirring, carrying and drawing member 6. Accordingly, it is prevented that the developer adheres to the developing sleeve 12, and its bristle cutting effect can be raised greatly. In such a way, the generation of surface contamination and color mixture on an image is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic copying apparatus.

Some types of image forming devices, such as electrophotographic copying devices, form an electrostatic latent image on a latent image carrier such as a photoreceptor, and develop this electrostatic latent image using a powder developer. It is visualized. FIG. 4 shows a conventional example of a dry type developing device that achieves this function.

In the developing device of this example, a two-component developer containing carrier in addition to toner is stored in the developer container 1, and a toner concentration detection sensor 2 detects a decrease in the toner concentration of the developer. At this time, toner is supplied from the toner replenishing section 3 to the developer in the container 1 via the toner replenishing roller 4. The developer replenished with toner in this manner is agitated immediately below the replenishment by the rotation of the agitator 5. At least a portion 1 of the developer, for example only the carrier, or both the carrier and the toner, is made of a magnetic material.

A developer stirring, transporting and pumping member 6 is provided in the developing container 1 adjacent to the agitator 5, and the developer stirring, transporting and pumping member 6 shown as an example in the figure is connected to a return auger 8. Paddle9. It is composed of a supply auger 10, etc. Of these, the return auger 8 and paddle 9 rotate in the direction of the arrow as a pair, with the return auger 8 transporting the developer from the back side to the front side in the figure, and the paddle 9 transporting the developer around the circumference. Pump up and transport in the direction. On the other hand, the supply auger 10 at the center rotates in the direction of the arrow to convey the developer from the front side to the back side.

In this way, the developer agitation conveyance pumping member 6 agitates the developer while conveying it in this axial direction, and also agitates the developer in a direction perpendicular to the axial direction while pumping up the developer with the paddle 9. During this bidirectional stirring, the carrier and toner are triboelectrically charged to opposite polarities. The developer agitation conveyance pumping member 6 stirs the developer in two directions: vertical direction (axial direction) and horizontal direction (direction perpendicular to the axial direction), and is also called a dual cross mixer. It also achieves the developer dispersion function of crushing the supplied toner and mixing it into the developer.

A developing sleeve 12 is provided adjacent to the developer stirring, conveying and pumping member 6, and has five fixed magnets P1. Pz-Pz-P4. The magnetic poles S and N of these magnets on the side facing the sleeve 12 are set as illustrated in the figure. Further, a magnetic shield plate 13 made of a magnetic material such as iron is provided inside the developing sleeve 12, and this can be moved between the solid line and the imaginary line position, and when the developing device performs development, it is moved to the solid line position It is located in

Magnet P1~. Hereinafter referred to as P pole, P pole faces the developer agitation conveyance pumping member 6, and magnetically transfers the developer drawn up by the developer agitation conveyance pumping member 6. Then, pull it toward the developing sleeve 12 side. The developer thus received on the developing sleeve 12 is carried on the circumferential surface of the developing sleeve 12 as a magnetic brush and rotates in the same direction as the direction of rotation of the sleeve as the developing sleeve 12 is driven to rotate in the direction of the arrow. 6 When the developer is carried on the developing sleeve and reaches the part of the doctor blade 14 located between the P4 pole and the P pole, the excess developer is scraped off, and the developer on the sleeve is removed from the developing sleeve. The thickness is set to suit. In this state, the developer on the sleeve comes into contact with a latent image carrier, for example, a drum-shaped photoreceptor 15 rotating in the direction of the arrow as shown in the figure, and the electrostatic latent image formed on the surface of the photoreceptor is transferred to the developer. Visualized by toner.

Next, when the developer on the developing sleeve 12 reaches the P2 pole, the developer on the sleeve reaches the magnetic shield plate 1.
Since the magnetic field of the P2 pole is shielded by the action of 3, the developer is released from the magnetic field, moves away from the sleeve, and is carried toward the developer stirring, conveying, and pumping member 6.

Here, when the supply of developer to the developing sleeve 12 is cut off, the magnetic shield plate 13 receives the developer on the sleeve surface and pumps the developer toward the doctor blade 14.
It is arranged to be displaced to a virtual line position covering the P4 pole.

When the magnetic shield plate 13 is displaced to such a virtual line position, the magnetic fields of the P, pole, and P4 poles are shielded,
This prevents magnetic adsorption of the developer.
The developer on the developing sleeve 12 runs out. In other words, the development sleeve 12 is subjected to ear cutting.

However, although such panicle cutting is performed, if the magnetic field of the magnetic poles p, . If the magnetic force of the magnet that attracts the sleeve 12 is particularly strong, this kind of problem will be further exacerbated. Therefore, the magnetic shield plate 13 may be large enough to completely cover the P pole and the P4 pole, but if it is done this way, when it is at the solid line position, for example, the magnetic shield plate 13 will be deep enough to cover the P pole. This causes a problem in the developer supply area.

For this reason, there are restrictions on the size and setting position of the magnetic shield plate, and the developer ends up adhering to the developing sleeve side in spots.

Further, when the toner concentration in the developer container 1 increases and the volume of the developer increases, and the height becomes higher than the developer agitation conveyance pumping member 6, the effect of cutting off the ears becomes worse, and the developer is If the developer adheres to the toner, the toner will inadvertently adhere to the photoreceptor even during non-development, resulting in background stains and the like on one image.

Further, as shown in FIG. 5, the developing devices 100A and 100B are arranged in pairs with respect to the photoreceptor 15, and these are configured to develop with different color toners, and one of the developing devices performs development. When performing the development, if the developing configuration is such that the magnetic shield plate 13 of the developing device is placed at the solid line position in FIG. 4, and the magnetic shield plate 13 of the other developing device is placed at the phantom line position in the same figure, If the cutting effect on the developing sleeve of the device is poor, color mixing may occur.

For example, if the developing device 100B on the downstream side performs development with respect to the rotational direction of the photoreceptor 15, and the developing sleeve of the upstream developing device 100A is poorly cut, the toner on the developing sleeve will be transferred to the photoreceptor. may be inadvertently attached to the
If this attached portion is a latent image portion, it will be developed, and color mixture will occur on the image after development is performed in the next developing device 100B.

(2) An object of the present invention is to provide a developing device that can enhance the effect of cutting off the ears of the developing sleeve during non-developing.

In order to achieve the above object, the present invention provides a developer container that accommodates a developer, a developer agitation conveyance pumping member that agitates and pumps up the developer in the developer container, and an internal circumference. A developing sleeve for electrostatic latent image development, in which a plurality of fixed magnets are arranged in a direction, receives the pumped up developer, carries the developer on a surface as a magnetic brush, and conveys the developer, and an inside of the developing sleeve. and a magnetic shield plate that can be moved to a position on the circumferential surface of the developing sleeve to cover the fixed magnet on the side that receives and pumps up the developer when the supply of developer to the developing sleeve is cut off. When supplying developer to the developing sleeve, the developer is transferred from the developer agitation conveyance pumping member to the developing sleeve, and when the supply is cut off, the magnetic roller that pulls the developer that is about to head towards the developing sleeve is moved to the developing sleeve. and the developer agitation conveyance pumping member.

The present invention will be explained below based on one embodiment. In this description, the same reference numerals are used for the members that achieve the same functions as those in the conventional example for convenience.

FIG. 1 shows an embodiment of the present invention, and the feature of this embodiment is that when a two-component developer, at least a part of which is made of a magnetic material, is supplied to the developing sleeve 12, the developer is stirred, conveyed, and pumped. When the developer is relayed from the member 6 to the developing sleeve 12 and the supply is cut off, the developing sleeve 12
A magnetic roller 20 that attracts the developer that is heading toward the side is provided between the developing sleeve 12 and the developer agitation conveyance pumping member 6.

This magnet roller 20 has the same structure as the developing sleeve 12, and includes four fixed magnets p, p7. It is an array of p,, p,. The magnetic poles S and N of each magnet ps-p on the side facing the sleeve 21 are as illustrated in FIG. below,
Magnets P6-9 are called P6-9 poles.

In order to perform development using the developing device, the developing sleeve 1
When supplying developer to the second magnetic shield plate 13, the magnetic shield plate 13
As shown in the figure, the P2 pole and the P2 pole are placed so as to cover the etched portions (corners) of the poles. Note that this etched portion is where lines of magnetic force enter and exit.

The developer on the sleeve 21 of the magnet roller 20, which has been supplied with developer from the developer agitation conveyance pumping member 6 (FIG. 1), is carried along the peripheral surface portion where the P, pole, and P9 poles are located. It is transferred to the developing sleeve 12. In order for this transfer to take place, the P3 pole and the P and P poles have different polarities.Next, this transferred developer flows over the circumferential surface of the sleeve 12 to the P3 pole, the P4 pole, and the Ps pole. After being transported in this order and subjected to development, as it approaches the P2 pole,
Due to the action of the magnetic shield plate 13, it moves away from the developing sleeve 12 and toward the magnet roller 20.

When the supply of developer to the developing sleeve 12 is cut off after the development by the developing device is completed, the magnetic shield plate 13 is displaced to the position shown in FIG. 3, covering the P3 pole and the P4 pole. It is designed to stop at this position.

Then, the magnetic field of the four poles P and IP is blocked, and the supply of developer to the developing sleeve 12 is interrupted. In this case, in the conventional developing device, the magnetic shield plate 13
The developer adheres to the sleeve 12 due to leakage of magnetic lines of force from the ends of the sleeve 12 . In other words, the ears become difficult to cut.

A P9 pole and a P pole are located at positions facing the displaced magnetic shield plate 13, and even if the developer tries to move toward the sleeve 12, it will not be affected by the magnetic field of these magnetic poles. The developer is magnetically attracted to the magnetic roller 20 side, and the sleeve 2 of the magnetic roller 20
It remains held on the circumferential surface of 1. That is, the developer is prevented from adhering to the developing sleeve 12, and the effect of breaking the ears can be greatly enhanced.

After a predetermined period of time has elapsed after the magnetic shield plate 13 has been brought to the position shown in FIG. You can leave it there.

As described above, toner is prevented from accidentally adhering to the photoreceptor during non-development, and the occurrence of background stains on the image is avoided. Further, when a plurality of developing devices are provided and each of these is used for developing with toner of a different color, the above-mentioned color mixture can be prevented from occurring.

Note that a developing sleeve 12 with grooves (in the axial direction) carved at a predetermined pitch on the circumferential surface may be used, but instead of using such a sleeve, a developing sleeve with a smooth surface without grooves may be used. The use of a sleeve can partially enhance the ear cutting effect.

As described above, according to the present invention, since the effect of cutting off the developing sleeve during non-development is enhanced, it is possible to effectively prevent the occurrence of background stains, color mixing, etc. on the image.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of one embodiment of the present invention, Figure 2 is a diagram showing how the developer is relayed by a magnetic roller during development, and Figure 3 is a diagram showing how the developer is conveyed as a relay to the developing sleeve. FIG. 4 is a sectional view of a conventional example, and FIG. 5 is a diagram for explaining a problem in an example in which a pair of developing devices are provided. 1...Developing container 6...Developer stirring conveyance pumping member 12...Developing sleeve 13...Magnetic shield plate 20...Magnetic roller

Claims (1)

[Claims] A developer container that accommodates developer, a developer agitation conveyance pumping member that conveys, stirs, and pumps up the developer in the developer container, and a plurality of fixed magnets arranged in the circumferential direction inside the developer container; A developing sleeve for developing an electrostatic latent image that receives the pumped up developer and carries this developer as a magnetic brush on its peripheral surface, and a developing sleeve that is provided inside the developing sleeve and that carries the developer onto the developing sleeve. A magnetic shield plate is provided which is movable to a position on the circumferential surface of the developing sleeve that covers the fixed magnet on the side that receives and pumps up the developer when the supply of the developer is cut off, and when the developer is supplied to the developing sleeve. When the developer is transferred from the developer agitation conveyance pumping member to the developing sleeve and the supply is cut off, the magnetic roller that pulls the developer that is about to go toward the development sleeve side is moved between the developing sleeve and the developer agitation conveyance pumping member. A developing device characterized by being provided between.