JPH0468378A - Developing device - Google Patents

Abstract

PURPOSE:To obtain an image of good quality by specifying the quantity of developer carried over an outer periphery surface of a most upstream side developing sleeve and then returned. CONSTITUTION:The quantity of developer fed and carried to the developing sleeve 11 positioned in the most upstream side in the moving direction of the developer carried on a side facing a latent image carrier 1 of the developing sleeves 11 and 12 is considered 100%. Then, when the developer quantity which is carried over the outer periphery surface of the most upstream side developing sleeve 11 and then returned without being fed to the adjacent developing sleeve 12 against the before mentioned developer quantity is considered Q%, and the carried quantity of the developer is fixed so that this Q is below 20. Therefore, sufficient quantity of the developer is carried to the downstream side developing sleeve 12 from the upstream side developing sleeve 11. Thus, lowering of the image density, image density uneveness, ground soiling, and toner scattering can be prevented from being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-stage developing device having a plurality of developing sleeves.

[Prior Art and Problems to be Solved by the Invention] In image forming apparatuses such as copiers, printers, and facsimile machines, so-called electrophotographic ones that form an electrostatic latent image on a latent image carrier are dry type. Development devices are widely used.

In such a developing device, the developer is magnetically supported and conveyed around a developing sleeve that has a magnet inside, and the electrostatic potential of the latent image carrier is absorbed by the developer that is carried and conveyed. A magnetic brush type developing device that visualizes an image is known.

Among such developing devices, in order to prevent the occurrence of abnormal images such as white spots at the trailing edge of the image and to improve the reproducibility of horizontal lines, a developing device is equipped with not one but multiple developing sleeves. While the developer is transferred between adjacent developing sleeves on the side facing the latent image carrier, the developer is magnetically carried and conveyed on each developing sleeve, and the developer is carried and conveyed.

Multistage developing devices that visualize the same electrostatic latent image have recently come to be used in image forming apparatuses of the above type.

In such a developing device, the amount of developer conveyed on this developing sleeve with respect to the most upstream developing sleeve in the moving direction of the developer conveyed on the side of the developing sleeve opposite to the latent image carrier. The doctor blades are arranged close to each other in order to control the latent image. A magnet for forming a repulsive magnetic field is provided inside the developing sleeve on the side opposite to the carrier.

When such a magnet is provided, 100% of the developer delivered to each developing sleeve is transferred to the adjacent developing sleeve on the side facing the latent image carrier due to the magnetic force. Instead of being delivered to the other side, some of them end up being conveyed on the circumferential surface of the developing sleeve and returned.

When such a returning amount increases, the amount of developer transferred to the next developing sleeve decreases, resulting in uneven image density. Further, there are cases where a large amount of developer that is not delivered remains carried on the developing sleeve, and in such a case, it becomes difficult to supply new developer, resulting in an image with insufficient density. Furthermore, when the developer on the most downstream side of the developer sleeve is rubbed against the developer casing to achieve a sealing function, it becomes difficult to achieve this function, and the inside of the developer casing becomes difficult to achieve. The pressure causes the developer to scatter outside the developer casing, staining the outside of the machine.

An object of the present invention is to prevent a decrease in image density or unevenness in image density in a developing device in which developer is transferred between developing sleeves, thereby producing an image of much better quality. The object of the present invention is to prevent the above-mentioned developer from scattering.

[Means to solve the problem]

In order to achieve the above object, the present invention arranges a plurality of developing sleeves each having a magnet inside thereof, and arranges a plurality of developing sleeves adjacent to each other on a latent image carrier, and transfers developer between the adjacent developing sleeves. , a developing device that magnetically carries and conveys a developer on each developing sleeve and visualizes the same electrostatic latent image formed on a latent image carrier with the carried and conveyed developer; The amount of developer supplied and carried by the developing sleeve located on the most upstream side in the moving direction of the developer conveyed on the side facing the latent image carrier of the developing sleeve is defined as 100%, and this amount of developer is defined as 100%. In contrast, the amount of developer that is not transferred to adjacent developing sleeves but is transported on the circumferential surface of the most upstream developing sleeve and returns as is is Q%.
It is characterized in that the amount of developer carried is determined so that Q is 20 or less.

〔Example〕

The present invention will be explained below based on one embodiment.

In FIG. 1, reference numeral 1 denotes a drum-shaped photoreceptor, which is an example of a latent image carrier. This photoreceptor 1 is rotatably driven in the direction of the arrow in the figure, and its surface is charged with electricity before development. , exposure, etc. are performed to form an electrostatic latent image.

A developing device 10 according to an embodiment of the present invention is placed opposite to the photoreceptor 1 . A two-component developer (not shown) having carrier and toner is stored in the developing goo sink 2 of this developing device, and when the concentration of toner in this developer decreases, a toner replenishing section 3 supplies the toner to the toner replenishing roller 4. Toner (not shown) is replenished via the toner. The developer supplied with toner is stirred by the rotation of the developer stirring member 5 and is sent toward the paddle wheel 6.

The developer sent to the paddle wheel 6 is further stirred here and sent toward the adjacent paddle wheel 7, and the developer is also stirred by the paddle wheel 7 here.

The photoreceptor 1 has two developing sleeves 1 made of non-magnetic material.
1.12 are placed adjacent to each other. A plurality of magnets are arranged in the circumferential direction inside the developing sleeve 11 . In this example, as shown in FIG. 2, magnets P□ to P6 are provided, and these are kept in a fixed state while maintaining the positions shown in the figure. Hereinafter, for convenience, such magnets will be referred to as P0 pole and P2 pole.
P1 pole is N pole, P2 pole is S pole, P3 pole is N pole, P4 pole is S pole, P5 pole is N pole, etc.
The P6 pole is the S pole.

On the other hand, inside the developing sleeve 12, as shown in FIG. is N pole, P
The 3' pole is the north pole, and the P4' pole is the north pole. The developing sleeves 11 and 12 are each driven to rotate in the direction of the arrow with respect to such a fixed magnetic pole. In FIG. 2, what is indicated by the symbol A is the magnetic force waveform of the P□ pole, and what is shown other than this is also the magnetic force waveform corresponding to each magnetic pole.

Here, in FIGS. 1 and 2, the most upstream developing sleeve 11 in the rotational direction of the photoreceptor 1 is referred to as a first developing sleeve, and the adjacent developing sleeve 12 on the downstream side is referred to as a second developing sleeve. As the first and second developing sleeves 11 and 12 rotate in the directions of the arrows, the two-component developer is conveyed while being magnetically supported on the circumferential surface of each developing sleeve. . In other words, it becomes a magnetic brush and is carried in the direction of rotation of each developing sleeve.

The second developing sleeve 12 is supplied with developer that has been stirred and drawn up by the paddle wheel 7 . The p, , p, poles of the first developing sleeve 11 and the P'3 poles of the second developing sleeve 12 transport the developer supplied from the paddle wheel 7 to the doctor blade 8 by magnetic force. As a result, the developer on the second developing sleeve 12 is transferred to the first developing sleeve 11 at the location opposite to the photoreceptor 1 and is drawn up to the doctor blade 8 location.

The developer that has been conveyed to the doctor blade 8 is scraped off at that portion. The scraped developer is
The developer is guided to the separator 13 and the developer transport screw 14, where it is laterally agitated and collected by both paddle wheels 6.7. On the other hand, the developer whose amount is regulated by passing through the doctor blade 8 is attracted by the magnetic force of the P5 pole and is further moved to the developing sleeve 11.
conveyed in the direction of rotation.

After this, the developer is carried over the developing sleeve while being attracted by the magnetic force of the PG pole and P1 pole, and the toner in the developer is electrostatically transferred toward the photoreceptor 1 at the P1 pole. , the electrostatic latent image on the photoreceptor 1 is visualized.

After that, the developer is attracted by the magnetic force of the P2 pole and is transported toward the same pole, and from this part to the second developing sleeve 12.
It is attracted by the magnetic force of the P,' pole and is delivered onto the developing sleeve where this pole is located.

Next, the developer is attracted by the magnetic force of the P-pole and is conveyed to the peripheral surface of the developing sleeve with the same polarity, where the same latent image carrier becomes a visible image due to the toner in the developer. be converted into That is, development is performed twice. By performing development twice or more times in this manner, white spots at the rear end of the image are less likely to occur, and the reproducibility of horizontal lines is also improved, resulting in improved image quality.

Note that when development is performed three times, three similarly configured developing sleeves are arranged, and even in the case of 29 or more, the same number of developing sleeves as the number of times of development are arranged.

The developer after development is attracted by the magnetic force of the P2' pole and is carried onto the developing sleeve where this pole is located, at which point the developer collides with the inner wall of the developing casing 2, as shown in FIG. Due to the impact at this time, the developer is transferred to the developing sleeve 12.
It flies away from the developer in the direction of the arrow and is collected into the developer casing. This recovered developer is then transferred to the paddle wheel 7.
The sample is then stirred again by a method such as the like, and subjected to development again.

FIG. 3 shows the flow of developer, with P,
The / pole is for magnetically attracting and pumping up the developer that has been pumped up and flying by the rotation of the paddle wheel 7. This magnetic pole and the P3 pole mutually form a repulsive magnetic field, and this magnetic field causes the above-mentioned pumping up. The developed developer is delivered to the first developing sleeve 11.

For example, as shown in FIG. 10, without providing the P3 pole or the P,' pole, the developer from the paddle wheel 7' is transferred to the relay plate 1.
5 to the first developing sleeve 11 and pumped up to the doctor blade 8, but with such a configuration, the relay plate 15 is required and the number of parts increases. become. Furthermore, the paddle wheel 7' also needs to be made larger because the developer must be directly supplied to the first developing sleeve 11 without going through the second developing sleeve 12.
The developing device itself inevitably becomes a big deal. From this point of view, it is advantageous to draw the developer up to the doctor blade 8 via the two developer sleeves 11, 12.

Returning to FIGS. 1 and 2, for the above reasons, for example, P for the first developing sleeve 11.

If a pole is provided, a part of the developer to be transferred from the P2 pole to the P4' pole is attracted by the magnetic force of the P pole and is not transferred to the adjacent second developing sleeve 12. Then, it is transported on the circumferential surface of the developing sleeve 11 and returned as it is.

In other words, "trailing" of the developer occurs.

Now, assuming that the amount of developer supplied and carried by the first developing sleeve 11 is 100%, some percentage of this amount will be carried around. now.

Monobinding in which this amount of drift is Q (<100)%,
If this percentage increases, the amount of developer delivered to the second developing sleeve 12 will decrease, resulting in uneven image density. Further, the developer that is not delivered is transferred to the first developing sleeve 11.
In some cases, a large amount of developer remains carried on the surface, and in this case, it becomes difficult to supply new developer, which may result in an image with insufficient density.

In addition to this, if the amount of delivered developer decreases, the developer will not be sufficiently transported to the P-pole and P2' pole of the second developing sleeve 12, and the developer will The developer may no longer be able to come into contact with the developer casing 2. If this happens, the sealing function of the agent within the developing casing may deteriorate, or the sealing function may not work at all.

By the way, inside the developer casing, the developer stirring member 5, both paddle wheels 6.7, and the developer conveying screw 1 are
The pressure inside the developing casing tends to increase due to the agitation of the agent by the rotation of the developer casing 4 and the replenishment of toner from the toner replenishing section 3. The pressure distribution inside the developing casing is as shown in FIG. Incidentally, Φ is a location where positive pressure is generated, and e is a location where negative pressure is generated.

Due to this increased internal pressure and pressure distribution, as shown in FIG. 7, airflow flows from the gap G between the second developing sleeve 12 and the developing casing 2 toward the outside of the developing casing as shown by the broken line. The developer inside the developer casing flies out on this airflow and stains the outside of the machine. Furthermore, if the toner in the developer that has flown out adheres to the photoreceptor 1, background stains may occur on the image.

Here, FIG. 8 shows the correlation between the trailing amount of the developer on the first developing sleeve 11 and the amount of toner scattering, and when the trailing amount Q mentioned above increases.

The amount of toner scattered from the gap G also increases. In particular, when the drag amount Q exceeds 20%, the amount of toner scattering increases rapidly.

Here, the inventor conducted the following experiment.

That is, in FIG. 1, there is no developer in the developing casing 2, and the first developing sleeve 11
1 g of developer was placed on top of the sleeve, and the developing sleeve was slowly turned once by hand to check the amount of developer that returned to its original position.

If this is 0.1g, Q will be 10%.

While changing the amount of such return by changing the magnetic force of P2 pole and P4' pole, etc., for 2 minutes each.

The image forming apparatus was put into operation, and the number of fine toner particles adhering to the photoreceptor 1 was checked at measurement point B shown in FIG. At this time, a developer having a toner concentration of 5% by weight was used.

The characteristic curve shown in FIG. 8 is plotted based on such an experiment, and the amount of toner scattering is approximately 3000 pieces/2 minutes at a 20% drag amount, and when it exceeds that percentage, the toner The amount of scattering also tends to increase rapidly. Therefore, it is sufficient to suppress the amount of drag Q to 20% or less. Note that FIG. 9 shows the correlation between the toner concentration of the developer and the amount of toner scattering, and when the toner concentration of the developer becomes 5% by weight or more, the amount of scattering also increases.

This example is characterized by a plurality of developing sleeves 11.
The developing sleeve is located on the most upstream side with respect to the moving direction of the developer conveyed on the side facing the photoconductor 1 of 12, and in this example, the first developing sleeve is located on the most upstream side with respect to the rotational direction of the photoconductor 1.
The amount of developer carried on the developing sleeve 11 is determined so that the amount of developer carried on the sleeve is 20% or less. By changing the rotation speed of the developing sleeve 11 and the magnetic force of the magnets in the first and second developing sleeves 11.12, the first developing sleeve 11 can be made into a developing sleeve that can carry such a developer amount. I can do it. In particular, it is relatively easy to reduce the amount of entanglement to 20% or less by changing the strength of the magnetic force of the P2 and P4' poles that transfer the developer. In addition, the amount of gap between the photoreceptor 1 and the second developing sleeve 12 may be changed, or
Even by changing the gap G (Fig. 7), the first developing sleeve 1
It is possible to determine the amount of developer carried on the substrate 1.

From the above, from the first developing sleeve 11 to the second developing sleeve 11,
Since the amount of developer delivered to the developing sleeve 12 is prevented from decreasing, development is also performed satisfactorily by the second developing sleeve, and unevenness in image density is avoided. or.

Since a large amount of undelivered developer is prevented from remaining on the first developing sleeve 11, a sufficient amount of new developer is supplied, and images without insufficient density can be obtained. can.

Furthermore, since more developer is delivered to the second developing sleeve 12, as shown in FIG. 6, the developer at the P2' pole comes into good contact with the inner wall of the developer casing 2. The developer will be blown away into the developing casing with great force. Therefore, recovery of the developer from the second developing sleeve 12 after development can be performed satisfactorily.

In addition to this, the sealing function of the developer casing is also improved, making it difficult for developer to scatter from the developer casing, resulting in contamination caused by developer outside the machine and background smudges on images. The occurrence of this can be prevented or reduced.

〔Effect of the invention〕

As described above, according to the present invention, in a developing device in which developer is transferred between developing sleeves, a sufficient amount of developer is conveyed from the upstream developing sleeve to the downstream developing sleeve. It is possible to suppress the occurrence of a decrease in image density, uneven image density, background smudge, toner scattering, etc. caused by insufficient feeding of the toner.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an embodiment of the present invention, Fig. 2 is a diagram showing the magnetic force distribution of the first and second developing sleeves, etc., and Fig. 3 is a diagram showing how the developer is distributed between the first and second developing sleeves. FIG. 4 is a diagram showing how the developer is blown away between the second developing sleeve and the developing casing. FIG. 5 is a diagram showing the pressure distribution inside the developing device. Figure 6 shows how the sealing function of the developer casing is achieved, Figure 7 shows how the developer scatters outside the developer casing, and Figure 8 shows how the developer on the first developer sleeve is scattered. Figure 9 shows the correlation between the amount of drift and the amount of toner scattering.
FIG. 0 is a schematic configuration diagram of a conventional example. 1...Drum-shaped photoreceptor 11.12 as a latent image carrier
...Development sleeve P-P6...Magnet P1'-p, /...Magnet agent Patent attorney Nori Hoshino Fuo δ Zugarasu

Claims (1)

[Claims] A plurality of developing sleeves each having a magnet inside are placed adjacent to each other on the latent image carrier, and while the developer is transferred between the adjacent developing sleeves, the developer is transferred magnetically onto each developing sleeve. In a developing device that carries and conveys the same electrostatic latent image formed on a latent image carrier with the carried and conveyed developer, the plurality of developing sleeves are opposed to the latent image carrier. The amount of developer supplied and carried by the developing sleeve located on the most upstream side in the moving direction of the developer transported on the side where the developer is conveyed is assumed to be 100%, and the amount of developer carried on the adjacent developing sleeve is 100%. When the amount of developer that is not delivered and is transported on the circumferential surface of the most upstream developing sleeve and returns as is is Q%, the amount of developer carried is determined so that this Q is 20 or less. A developing device characterized by: