JP2000155467A - Two-component developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the density irregularity of an image and the load fluctuation of a latent image carrier from occurring by perfectly obstructing the accompanying rotation of the developer with a developer carrier. SOLUTION: Two developer carriers 24 and 25 having a magnet inside are arranged in the moving direction of the photoreceptor (latent image carrier) 12. Besides, a developer scraping member 30 is arranged at the position of a developer separation pole P12 between the carriers 24 and 25. The scraping member 30 is constituted by sticking an elastic plate 32 to an aluminum extrusion bar 31. Then, both ends of the bar 31 are supported by a developing case. Besides, one end of the plate 32 is made to abut on the circumferential surface of the upper carrier 24 and the other end of the plate 32 is made to abut on the circumferential surface of the lower carrier 25 in a counter direction with respect to the respective moving directions. Thus, the developer left on the carriers 24 and 25 after the toner is attached to the photoreceptor 12 is scraped by the scraping member 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of transferring an image formed on a latent image carrier using an electrophotographic method, such as a copying machine, a printer, a facsimile, or a multifunction machine using a laser. The present invention relates to an image forming apparatus that performs recording on a sheet-like transfer material such as a sheet. Specifically, using a two-component developer composed of a toner and a carrier, a developer carrier having a magnet inside is rotated, and the developer is attached to the latent image carrier by the developer carrier, and the latent image carrier is used. The present invention relates to a two-component developing device that visualizes an electrostatic latent image formed on the surface of a developing device.

[0002]

2. Description of the Related Art Conventionally, in a known image forming apparatus, a developing device supplies toner to a latent image formed on a moving latent image carrier and visualizes the latent image. In some cases, a toner image formed by transfer is transferred to record an image on a transfer material.

In a developing device used in such an image forming apparatus, a two-component developer in which a magnetic carrier and a magnetic or non-magnetic toner are mixed is used. There is one that is supplied to a developer carrier.

[0004] The developer supplied to the developer carrier is carried by a magnet provided inside the developer carrier with a magnetic brush formed on the surface of the developer carrier and formed on the latent image carrier. The electrostatic latent image is electrostatically attracted and image-processed.

Incidentally, in such a developing device, there is a case where only one developer carrier is provided. However, in this case, since the developing area (developing nip) for the latent image carrier is relatively narrow, it is not possible to supply a sufficient amount of developer. Therefore, it is necessary to set the linear velocity of the developer carrier to, for example, three times or more the linear velocity of the latent image carrier to compensate for the shortage of developer supply.

However, when such a linear velocity is set, the developer carrier is rotated at a high speed, so that toner scatters and contaminates the inside of the image forming apparatus. Also,
When the developer pulls back the toner at the rear end of the solid image that has been visualized on the latent image carrier, there is a possibility that a defect called a solid rear end white spot may occur.

Therefore, in order to solve such a problem,
There has been proposed a configuration in which a plurality of the above-described developer carriers are provided in the moving direction of the latent image carrier to lengthen the development area. However, when a plurality of developer carrying members are provided, a part of the developer carried on the surface of the developer carrying member passes through a portion where the developer carrying members are closest to each other as the developer carrying member rotates. In other words, a so-called entrainment may occur, and the proper delivery of the developer between the adjacent developer carrying members may not be performed.

In the prior art example shown in FIG. 4, developer carriers A and B are arranged vertically along the moving direction of the latent image carrier C, and, for example, are stirred and mixed with the lower developer carrier B. And transports the developer from the lower developer carrier B to the upper developer carrier A, while the upper developer carrier A transfers the lower developer carrier B to the lower developer carrier B. The developer is transferred along a development area which is a portion facing the latent image carrier C toward. This example will be specifically described. In FIG. 4, symbols P11 to P15 and P21 to P23 indicate magnetic poles, respectively.

As indicated by an arrow C1, a part of the developer supplied to the upper developer carrier A is not transferred to the lower developer carrier B, and the developer carriers A and B In some cases, the paper may be conveyed to the side opposite to the development area through the closest point between them.

When a part of the developer discharged from the paddle wheel or the like reaches the lower developer carrier B, as shown by arrow C2, the lower developer carrier B
Attracted by the magnetic force of the magnets inside the developer carrier A and B
In some cases, the developer may be conveyed directly to the portion of the lower developer carrier B facing the latent image carrier C, passing through the closest portion between the two.

Here, as shown by the arrow C1, the carrier carried on the upper developer carrying member A rotates along with it, and as shown by the arrow C2, the carrier carried on the lower developer carrier B carries the carrier. Turning around is called under rotation.

When the upward rotation occurs, the delivery amount of the developer to the lower developer carrier B becomes insufficient, so that
Since the amount of the developer carried on the lower developer carrier B decreases, causing a decrease in image density, or the amount of developer between the latent image carrier C and the developer carrier B decreases, so that There is a possibility that toner may be scattered due to lack of the sealing property of the agent itself, thereby contaminating the inside of the image forming apparatus main body.

Further, when the downward rotation occurs, the amount of the developer carried on the developer carrier B becomes excessive, and when the developer is brought into contact with the latent image carrier C, the latent image carrier C is The rotational load of the image forming apparatus fluctuates in speed, causing band-like density unevenness in the image, or an excessive amount of the carried amount collides with a part of the housing of the developing device to be broken down and fall down. There was a risk of contaminating the body.

Therefore, in order to solve such a problem, the magnetic poles related to the transfer of the developer between the developer carriers A and B are made to have different polarities, and the magnetic flux density difference between the respective magnetic poles is ± 10%.
There has been proposed a configuration in which the magnetic flux density of a magnetic pole for transferring the developer of the lower developer carrier B is set to 70 mT or more (see Japanese Patent Application Laid-Open No. 9-80919).

According to this configuration, the developer from the upper developer carrier A can be used to reduce the developer from the upper developer carrier B by setting the magnetic flux density difference between the transfer carriers between the developer carriers to ± 10 mT or less. In addition to preventing the developer from being swung up and down, the magnetic flux density of the magnetic poles associated with the transfer of the developer of the developer carrier B on the downstream side is set to 70 mT or more, so that the high speed can be achieved. It is possible to prevent over-rotation caused by an increase in the kinetic energy of the developer of the machine, thereby magnetically preventing the developer from passing between the developer carriers A and B.

[0016]

However, in such a configuration, in order to favorably pump up and down the developer in the vicinity of the closest point between the developer carrying members A and B, the magnets must be connected to each other. It is necessary to considerably increase the accuracy of the strength and arrangement of the magnetic force, the size of the magnet, and the like, which may increase the manufacturing cost and the management cost during use.

Further, even if the precision is increased, it is not possible to completely prevent vertical rotation, such as when the upper and lower limits of the magnetic force strength and the magnetic pole angle tolerance of the developer carrier are combined.

SUMMARY OF THE INVENTION It is an object of the present invention to completely prevent the rotation of the developer in the developer carrier, thereby preventing the occurrence of uneven image density and fluctuations in the load of the latent image carrier.

[0019]

According to the first aspect of the present invention, a plurality of developer carriers having magnets therein are provided in the moving direction of the latent image carrier, and the developer carriers are rotated. In a two-component developing device for attaching toner to the latent image carrier and visualizing the electrostatic latent image formed on the surface of the latent image carrier, the toner is adhered to the latent image carrier, and then developed. A scraping member for scraping off the developer remaining on the developer carrier is provided between the developer carriers.

According to a second aspect of the present invention, in the two-component developing apparatus according to the first aspect, the scraping member is provided at a position where the developer is separated between the developer carriers. .

According to a third aspect of the present invention, in the two-component developing device according to the first or second aspect, the scraping member is brought into contact with the developer carrier in a counter direction with respect to the rotation direction thereof. It is characterized by that.

According to a fourth aspect of the present invention, a developer carrying member having a magnet therein is rotated so that toner adheres to the latent image carrying member with the developer carrying member, and is formed on the surface of the latent image carrying member. In a two-component developing device that visualizes the electrostatic latent image
After the toner is attached to the latent image carrier, a cleaning unit for removing the developer remaining on the developer carrier is provided.

According to a fifth aspect of the present invention, in the two-component developing device of the fourth aspect, the cleaning means is provided at a position of a developer separating pole around the developer carrier.

According to a sixth aspect of the present invention, in the two-component developing device according to the fourth or fifth aspect, the cleaning means is constituted by a flexible member that presses the tip against the developer carrier. It is characterized by the following.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an overall schematic configuration of a two-component developing apparatus according to the present invention. In the figure, reference numeral 10 denotes a two-component developing device, and reference numeral 12 denotes a drum-shaped photosensitive member serving as a latent image carrier. The photoreceptor 10 rotates clockwise in the figure.

The developing device 10 comprises a developing container 20 and a toner replenishing device 40 mounted thereon.

The developing container 20 has a stirring roller 22 and a paddle wheel 23 in a developing case 21.
The two sleeve-shaped developer carriers 24 and 25 facing the opening 21a of the developing case 21 facing the
Up and down along the direction of rotation.

The two developer carriers 24 and 25 are both made of a non-magnetic material such as aluminum or stainless steel, and each can be rotated counterclockwise in the drawing by a driving force from the outside. In each of the developer carrying members 24 and 25,
Mag rollers 26 and 27 made of ferrite magnets / rubber magnets or magnets formed by kneading nylon powder and ferrite powder are fixed.

As shown by a dashed line in FIG. 2, the developing roller P11 (N-pole) for developing the electrostatic latent image on the photoconductor 12 is provided on the mag roller 26 in the upper developer carrier 24 in the circumferential direction.
A developer release pole P12 (S pole) for transferring the developer to the lower developer carrier 25, a pumping pole P13 (S pole) for pumping the developer supplied by the paddle wheel 23, and conveying the pumped developer. The transport pole P14 (N pole) and the developer uniformed by the doctor blade 34 described later
There are provided five magnetic poles of a transport pole P15 (S-pole) for transporting to 11

Mag roller 2 in lower developer carrier 25
Reference numeral 7 denotes a developing pole P21 (S pole) for developing an electrostatic latent image facing the photoconductor 10 in the circumferential direction, and a developer release for transporting the developer after completion of development to the developing device 10. Pole P22
(N-pole), and three magnetic poles P23 (N-pole) for receiving the developer delivered from the upper developer carrier 24 are provided.

The upper mag roller 26 forms magnetic poles P12 and P13, both of which are S poles, where the upper and lower developer carriers 24 and 25 are closest to each other. Then, a repulsive magnetic field is formed between the magnetic poles P12 and P13 by the same poles.

In the illustrated example, the toner remaining on the developer carriers 24 and 25 after the toner is adhered to the photoconductor 12 is located at the position where the upper and lower developer carriers 24 and 25 are closest to each other. A developer scraping member 30 for scraping is provided. The developer scraping member 30 is formed by bonding an elastic plate 32 made of polyurethane rubber having a thickness of 0.2 to 0.3 mm to a non-magnetic aluminum push rod 31.

Then, both ends of the push rod 31 are supported by the developing case 21 described above, and one end of the elastic plate 32 is provided on the peripheral surface of the upper developer carrier 24 and the other end is provided on the lower developer carrier 2.
5 in the counter direction with respect to the rotation direction.

As shown in FIG. 1, a doctor blade 34 supported by the developing case 21 is pressed against the upper developer carrier 24 from above. In the developing container 20, one side of the doctor blade 3 is placed on the paddle wheel 23.
A separator 35 is provided near the front end of No. 4 and the other side is positioned on the stirring roller 22. A transport screw 36 is provided on the stirring roller 22 side on the separator 35.

On the other hand, the toner replenishing device 40 is provided with a toner replenishing roller 37 for replenishing the toner contained therein to the developing container 20 and an agitator 38 for stirring and transporting the toner to the roller.

Then, a two-component developer comprising a magnetic carrier and a magnetic or non-magnetic toner is stored in the developing case 21. Thus, when the image forming apparatus is driven, when the density of the toner supplied to the photoconductor 12 decreases,
By rotating the toner supply roller 37, the toner is fed from the toner supply device 40 toward the stirring roller 22.

The stirring roller 22 frictionally charges the developer in the developing case 21 while stirring and mixing the same.
Send to 3. The paddle wheel 23 pumps up the developer by centrifugal force, and a part of the developer is discharged directly to the upper developer carrier 24 as shown by an arrow a in FIG. The released developer is carried on the upper developer carrier 24.

Another part of the developer pumped up by the paddle wheel 23 is repelled by hitting the lower developer carrier 25 and is carried on the surface by the magnetic force of the upper developer carrier 24. Is done.

As described above, in order to supply the developer to the upper developer carrier 24 from the lower developer carrier 25 as well, In order to increase the lifting amount, it is necessary to relatively increase the rotation speed of the paddle wheel 23 and increase the centrifugal force.

The developer carried on the upper developer carrier 24 reaches the developing area facing the photoconductor 12 with its rotation. Then, the photosensitive member 12 is
The electrostatic latent image formed on the surface of the photoconductor 12 is visualized. When it reaches the developer release pole P12 at which the action of the magnetic force is weakened after passing through the developing area, the developer is separated from the upper developer carrier 24 by the rotation of the lower developer carrier 25 and the magnetic force of the mag roller 27, and the lower developer carrier 25 is rotated. The developer carrier 25 and the photoreceptor 12 are transported toward a development area facing each other.

In other words, the order of transport of the developer is determined by P
13-P14-P15-P11-P12-P23-P2
1-P22. Then, it falls to the bottom of the developing container 20 at a position where the magnetic force of the lower mag roller 27 stops working, and is again stirred by the paddle wheel 23.

The developer scraped off by the doctor blade 34 is guided by the separator 35 toward the transport screw 36 and is shaken off onto the stirring roller 22 by the transport screw 36. Therefore, although not shown, a slit for dropping the developer is formed in the separator 35 at a position facing the stirring roller 22.

However, if the distance between the magnetic poles P12 and P13 is too large or too small, the inertia force of the developer due to the high rotation of the developer carriers 24 and 25, and the natural force generated between the magnetic poles. The generated pole P12.5 generates leakage magnetic lines of force from the magnetic pole for forming the repulsive magnetic field, and the repulsive magnetic field is weakened, and the magnetic force of the repulsive magnetic field and the range (nip) for forming the repulsive magnetic field are narrowed. In some cases,
If the inertial force of the developer generated by the moving force of the developer exceeds the strength of the repulsive magnetic field, the developer is moved through the range in which the repulsive magnetic field is formed, that is, the gap between the developer carriers 24 and 25 being closest to each other. May pass through, that is, a rotation of the developer may occur.

Therefore, in the present invention, the developer which could not be controlled by the repulsive magnetic field is removed from the developer scraping member 30.
Is completely forcibly dropped in the direction in which the transport direction is toward the lower developer carrier 25, and the lower developer carrier is rotated by the lower developer carrier 25 and the magnetic force of the magnetic pole P23. It will be delivered to the carrier 25.

In the developer scraping member 30, a part of the developer pumped up from the paddle wheel 23 is sucked by the magnetic force of the magnetic pole P23 of the developer scraping member 30, and the developer carrying members 24 and 25 are removed. It will also completely prevent them from entering while they are closest.

In the illustrated example, the developer scraping member 30
An elastic plate 32 made of polyurethane rubber is provided with one end on the peripheral surface of the upper developer carrier 24 and the other end on the peripheral surface of the lower developer carrier 25 in counter directions with respect to the rotation direction. Make contact. This is because, if the contact direction is the trailing direction, when the magnetic force of the developer carrying members 24 and 25 is extremely high, or when the high speed rotation is performed, poor scraping occurs, and the surface of the developer carrying members 24 and 25 This is because the upper developer cannot be completely scraped off.

Therefore, the developer transported by the upper developer carrier 24 has a weak repulsive magnetic field due to the same poles located at the positions where the developer carriers 24 and 25 are closest to each other. Even if the nip becomes narrow or the nip becomes narrow, the developer that could not be controlled by the repulsive magnetic field is mechanically scraped off by the developer scraping member 30.

Further, since the developer pumped from the paddle wheel 23 can be prevented from entering, the management of the magnetic force setting (magnetic pole angle and magnetic strength) and the size of the magnet can be facilitated. The design can be given a margin.

In the example shown in the figure, the scraping member 30 for mechanically scraping the developer which could not be controlled by the repulsive magnetic field is provided between the developer carrying members 24 and 25, that is, at the position of the developer transfer pole, so that the developing performance is improved. The agent carriers 24 and 25 can be prevented from entering the location where they are closest to each other.

In the illustrated example, two developer carriers 24 and 25 each having a magnet therein are provided in the moving direction of the photosensitive member 12 as a latent image carrier, but the invention is not limited to two.
The same applies to the case where three or more developer carriers are provided.

FIG. 3 shows another embodiment of the present invention. In this example, a partition plate 50 is provided between the lower developer carrier 25 and the paddle wheel 23 instead of the developer scraping member 30 between the developer carriers 24 and 25. A seal member 51 as a cleaning member is attached to the partition plate 50 by pressing the leading end of the lower developer carrier 25 over the entire area in the axial direction. The seal member 51 is an elastic flexible plate member made of, for example, polyurethane rubber having a thickness of 0.2 to 0.3 mm. The lower magnetic roller 27 is provided at a position of a magnetic pole P22 which is a developer separating pole.

After the toner adheres to the photoconductor 10, the developer remaining on the lower developer carrier 25 is mechanically scraped off by the seal member 51 and removed. This allows
Even if the magnetic pole P22.5 is generated between the magnetic poles P22 and P23, the magnetic pole P22.5 can block the developer and prevent the developer from being pumped up by the magnetic pole P22.5.

[0053]

Thus, according to the first to third aspects of the present invention, the toner is adhered to the developer carrier by the scraping member provided between the developer carriers, and then remains on the developer carrier. Since the developer is scraped off, the vertical rotation of the developer on the developer carrier is completely prevented, and the developer is reliably prevented from passing between the developer carriers. And the load fluctuation of the latent image carrier can be prevented.

Further, it is possible to easily manage the setting conditions such as the strength and arrangement position of the magnetic force and the size of the magnet, to improve the yield, and to provide a low-cost developer carrier. .

According to the second aspect of the present invention, since the scraping member is provided at the position of the developer separation between the developer carriers, the above-mentioned effect can be achieved more effectively.

According to the third aspect of the present invention, the scraping member is brought into contact with the developer carrier in the counter direction with respect to the rotation direction. It is possible to completely prevent poor scraping occurring at the time of rotation or the like, and it is possible to reliably prevent the developer from rotating vertically.

According to the invention described in claims 4 to 6,
After attaching the toner to the developer carrier by the cleaning means,
Since the developer remaining on the developer carrier is scraped off,
The vertical rotation of the developer in the developer carrier is completely prevented, and problems such as low image density, uneven density, and black streak are prevented, and good image formation can always be ensured.

According to the fifth aspect of the present invention, since the cleaning means is provided at the developer separation pole position around the developer carrier, the above-mentioned effect can be achieved more effectively.

According to the sixth aspect of the present invention, since the cleaning means is constituted by the flexible member which presses the tip against the developer carrier, it can be easily manufactured and inexpensive.

[Brief description of the drawings]

FIG. 1 is an overall schematic configuration diagram of a two-component developing device according to the present invention.

FIG. 2 is a partially enlarged view of the developer carrier.

FIG. 3 is a partially enlarged view of a developer carrier of another example.

FIG. 4 is a partially enlarged view of a conventional developer carrier.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 two-component developing device 12 photoconductor (image carrier) 20 developing container 21 developing case 22 stirring roller 23 paddle wheel 24 upper developer carrier 25 lower developer carrier 26 upper mag roller (magnet) 27 lower Mag roller (magnet) 30 Developer scraping member 31 Push rod 32 Elastic plate 34 Doctor blade 35 Separator 36 Conveying screw 37 Toner supply roller 38 Agitator 40 Toner supply device 50 Partition plate 51 Seal member (cleaning member) P11 Developing pole P12 Developing Discharge pole P13 Pumping pole P14 Transport pole P15 Transport pole P21 Development pole P22 Developer release pole P23 Receiving pole

Claims (6)

[Claims] A plurality of developer carrying members each having a magnet therein are provided in a moving direction of the latent image carrying member, and the developer carrying members are rotated to attach toner to the latent image carrying member. In a two-component developing device for visualizing an electrostatic latent image formed on the surface of an image carrier, a toner remaining on the developer carrier after toner is attached to the latent image carrier is removed. A scraping member for scraping is provided between the developer carrying members,
Two-component developing device. 2. The two-component developing device according to claim 1, wherein said scraping member is provided at a position of a developer separating pole between said developer carrying members. 3. The two-component developing device according to claim 1, wherein the scraping member is in contact with the developer carrier in a counter direction with respect to a rotation direction of the developer carrier. 4. A developer carrier having a magnet therein is rotated, and toner is attached to the latent image carrier by the developer carrier.
In a two-component developing device for visualizing an electrostatic latent image formed on the surface of the latent image carrier, a toner remaining on the developer carrier after toner is attached to the latent image carrier A two-component developing device comprising a cleaning means for removing an agent. 5. The cleaning device according to claim 4, wherein said cleaning means is provided at a developer separation pole position around said developer carrier.
2. The two-component developing device according to claim 1. 6. The two-component developing device according to claim 4, wherein said cleaning means is constituted by a flexible member whose tip is pressed against said developer carrier.