JP2015125158A - Development apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a development apparatus for preventing developer leakage occurring at a developer carrier end part and preventing carrier adhesion, development sleeve lock or the like due to the developer leakage.SOLUTION: An area having a magnet is made smaller than the area formed when the peripheral lengths of the outside of a magnet member 47 opposite to a developer carrier 44 end part in a non-contact manner are connected to each other, and the number of points where magnetic force is concentrated is increased, so that sealability is enhanced.

Description

  The present invention relates to an image forming apparatus that forms an image using an electrophotographic system, and more particularly, to an image forming apparatus such as a copying machine, a printer, a FAX, or a multifunction machine having a plurality of these functions.

  Recently, as a demand from the market for an electrophotographic image forming apparatus, color image forming apparatuses such as a color copying machine and a color printer are increasing. Even in a color image forming apparatus, an image forming speed comparable to that of a monochrome image forming apparatus, an image quality comparable to offset printing, and a reduction in the number of maintenance are required.

  With these demands, it has become an important issue to extend the life of parts, and some developing devices have achieved a life of 500,000 sheets or more than 1,000,000 sheets.

  The developing device 4 uses a two-component developer including non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. In particular, in color image forming apparatuses, it is not necessary to include a magnetic substance in the toner, so that it is widely used for reasons such as good color.

  The developing device 4 using a two-component developer is generally configured as shown in FIGS. The developing device 4 includes a developing container 41 that stores a developer. The developing container 41 is divided into a developing chamber (developer conveying path) 41a and an agitating chamber (developer conveying path) 41b by a partition wall 41c extending in the vertical direction. A first developer transport stirring member 42 and a second developer transport stirring member 43 are arranged in the developing chamber 41a and the stirring chamber 41b, respectively. In addition, delivery portions (developer transport paths) 41d and 41e that allow the developer to pass between the developing chamber 41a and the stirring chamber 41b are provided at the end in the longitudinal direction of the partition wall 41c. The first and second developer transport stirring members 42 and 43 transport the developer while stirring and circulate the developer container 41. A developing sleeve 44 as a developer carrying member is rotatably disposed at a position facing the photosensitive drum 1 of the developing container 41. The developing sleeve 44 incorporates a magnet 45 as a magnetic field generating means.

  In such a developing device 4, as shown in FIG. 2, the developer supplied from the developing chamber 41 a to the developing sleeve 44 develops toner on the photoreceptor 1 in the vicinity of the S1 pole of the magnet 45. Thereafter, the magnetic field is returned to the developing chamber 41a again between the N3 and N2 poles where the repulsive magnetic field created by the magnet 45 is formed. By adopting such a configuration, a toner having a low toner density developed on the photosensitive member 1 is once returned into the developing container 41, and the density reduction and longitudinal density unevenness that occur when the toner density becomes low are eliminated. It is preventing.

  Incidentally, the developer in the developing container 41 is transferred along the surface of the developing sleeve 44 to the end of the developing sleeve 44 shown in FIG. At this time, in particular, almost no magnetic force is generated between the N3 and N2 poles formed by the magnet 45 for returning the developer into the developing container 41, so that the sealability of the developer is likely to deteriorate. For this reason, the developer may leak or scatter from the end of the developing sleeve 44. With regard to such scattering from the end of the developing sleeve 44, there has been proposed a method in which an elastic seal member is attached to both ends of the developing sleeve 44 and sealing is performed so that toner does not leak from the end of the seal member. However, in this seal configuration, since the elastic seal member is pressed against the outer peripheral surface of the developing sleeve 44, there is a problem that the load on the developing sleeve 44 is large and the sealing performance is deteriorated due to deterioration of the elastic seal member. Therefore, in the developing device 4 that uses magnetically adsorbed toner or carrier, it is considered to magnetically seal with a magnetic force generating means (see, for example, Patent Document 1). As shown in FIG. 4B, a magnetic seal member MP that is magnetized on the opposing surface that maintains a predetermined distance from the surface of the developing sleeve 44 is provided, and the developer is magnetically attracted and held. This magnetic seal configuration is advantageous in that since the developing sleeve 44 and the magnetic seal member MP are not in contact with each other, the rotational load of the developing sleeve 44 is reduced, and deterioration due to wear or the like does not occur, resulting in a long life. . When a plate-like magnet is provided as a magnetic seal member MP so as to surround the developing sleeve 44 in a non-contact manner, a magnetic brush (magnetic brush) by a developer is provided between the magnet roller 45 in the developing sleeve 44 and the magnetic seal member MP. Is formed to prevent leakage. Furthermore, the magnetic poles on the surface of the magnetic seal member MP on the developing sleeve 44 side are set to the S poles and the different poles are opposed to N3 and N2 where the repulsive magnetic field created by the magnet 45 is formed. By carrying out like this, it is formed so that a magnetic force line may be connected between the magnet 45 and the magnetic seal member MP, and it can be set as the structure which improves a sealing performance more, and is suitable.

Japanese Patent Laid-Open No. 03-004266

  However, in the developing device 4 of Patent Document 1, as the durability increases, the developer leaks from the end of the developing sleeve 44 on the 41e side of the developing container 41 in order to achieve a long life. There was a case. According to the study by the inventors, when the developing sleeve 44 is removed after forming 500,000 images and the state of the magnetic seal member MP is observed, a large amount of developer is constrained on the outer periphery of the magnetic seal member MP. Almost no developer was seen in the central part of the MP. As shown in FIG. 6, the magnetic flux lines are concentrated on the end portion by making the magnetic pole on the surface of the magnetic seal member MP on the developing sleeve 44 side as a single unit. Since the magnetic flux lines are not dense in the center portion compared to the end portion, the above phenomenon occurs. As a result, the sealing performance at the end of the magnetic seal member MP is high, but there is almost no sealing performance at the central portion, and there is a concern of image failure and developing sleeve lock due to developer leakage.

  Further, in order to compensate for a decrease in sealing performance, it is conceivable to divide the magnetic seal member into a plurality of ends on one end side, but the mounting operation becomes complicated. In addition, the divided magnetic seals are attached in close proximity to each other, and at that time, the magnetic seals stick to each other due to their magnetic force. If the magnetic seals stick together, the shape becomes substantially like a single magnetic seal, and magnetic flux lines concentrate on the ends, making it difficult to improve the sealing performance.

  The present invention has been made in view of the above problems. The purpose of the developer is to provide a magnetic seal member with a magnetic seal member that is opposed to both ends of the developer carrier in a non-contact manner without complicating the process of attaching the magnetic seal. An object of the present invention is to provide a developing device that can be strengthened.

The above object is achieved by the developing device according to the present invention. In summary, the present invention
A developer carrying body that carries a developer having toner and a carrier, and that develops the electrostatic latent image at a position facing the image carrying body;
A magnetic field generating means included in the developer carrier and having a plurality of magnetic poles;
A development member including a magnet member provided at a position opposite to the image carrier so as to face the surface of the developer carrier in a non-contact manner and magnetically seals an end of the developer carrier. In the device
The magnet member is formed so that the width of the magnet member is different in the circumferential direction of the developer carrier.

  As described above, according to the present invention, in the developing device provided with the magnetic seal members facing each other in a non-contact manner at both ends of the developer carrying member, the magnetic seal is attached without complicating the magnetic seal attachment process. A developing device capable of enhancing the sealing performance of the seal can be provided.

1 is a diagram illustrating an image forming apparatus according to a first embodiment of the present invention. It is sectional drawing explaining the Example of this invention, and the conventional developing device. FIG. 6 is another cross-sectional view illustrating an embodiment of the present invention and a conventional developing device. It is a schematic diagram of the developing sleeve end part of Example 1 of the present invention. It is a figure which shows the positional relationship of the developing sleeve and magnetic seal member of a developing sleeve edge part. It is sectional drawing of the conventional magnetic seal member, and magnetic flux density distribution which a magnetic seal member produces. It is sectional drawing of the magnetic seal member of Example 1 of this invention, and magnetic flux density distribution which a magnetic seal member makes. It is sectional drawing of the shape of the other magnetic seal member of the Example of this invention. It is sectional drawing explaining the developing apparatus of the other Example of this invention. FIG. 6 is another cross-sectional view illustrating a developing device according to another embodiment of the present invention.

Example 1
Embodiments of the present invention will be described below in detail with reference to the drawings.

[Image forming apparatus]
First, the overall configuration and operation of the image forming apparatus of this embodiment will be described. FIG. 1 shows an image forming apparatus to which the present invention can be applied. The image forming apparatus shown in the figure is a four-color full-color electrophotographic image forming apparatus having four image forming units, and the figure is a longitudinal sectional view schematically showing the schematic configuration thereof. Note that this embodiment is one form to which the present invention can be applied, and is not limited to this. In the image forming apparatus shown in the figure, four image forming portions (image forming stations) are arranged from the upstream side to the downstream side along the rotation direction (arrow R7 direction) of the intermediate transfer belt 7 as an intermediate transfer member. ing. Each image forming section includes drum-type electrophotographic photosensitive members (hereinafter referred to as “photosensitive drums”) 1a, 1b, 1c, and 1d as image carriers, and in this order, yellow, magenta, cyan, and black. This is a photosensitive drum for forming toner images of respective colors. The photosensitive drums 1a, 1b, 1c, and 1d are each driven to rotate in the direction of arrow R1 (clockwise in FIG. 1). Around the photosensitive drums 1a, 1b, 1c, and 1d, the following configurations are arranged in order along the rotation direction. That is, chargers (charging means) 2a, 2b, 2c, 2d, exposure devices (latent image forming means) 3a, 3b, 3c, 3d, and developing devices (developing means) 4a, 4b, 4c, 4d are arranged. . Further, primary transfer rollers (primary transfer means) 5a, 5b, 5c, 5d and drum cleaners (cleaning devices) 6a, 6b, 6c, 6d are provided.

  An endless intermediate transfer belt 7 as an intermediate transfer member is stretched around the primary transfer rollers 5a, 5b, 5c, 5d and the secondary transfer counter roller 8 described above. The intermediate transfer belt 7 is pressed by the primary transfer rollers 5a, 5b, 5c, and 5d from the back side thereof, and the surface thereof is brought into contact with the photosensitive drums 1a, 1b, 1c, and 1d. The intermediate transfer belt 7 rotates in the direction of arrow R7 as the secondary transfer counter roller 8 also serving as a driving roller rotates in the direction of arrow R8. The rotation speed of the intermediate transfer belt 7 is set to be approximately the same as the rotation speed (process speed) of each of the photosensitive drums 1a, 1b, 1c, and 1d. A secondary transfer roller (secondary transfer means) 9 is disposed at a position corresponding to the secondary transfer counter roller 8 on the surface of the intermediate transfer belt 7. The secondary transfer roller 9 holds an intermediate transfer belt 7 between the secondary transfer counter roller 8 and a secondary transfer nip (secondary transfer) between the secondary transfer roller 9 and the intermediate transfer belt 7. A transfer portion) is formed. The transfer material P used for image formation is stored in a state of being stacked on the paper feed cassette 10. The transfer material P is supplied to the above-described secondary transfer nip portion by a feeding / conveying device (all not shown) having a paper feeding roller, a conveying roller, a registration roller, and the like. A fixing device 11 having a fixing roller 12 and a pressure roller 13 pressed against the fixing roller 12 is disposed on the downstream side of the secondary transfer nip portion along the conveyance direction of the transfer material P, and further fixing. A paper discharge tray is disposed on the downstream side of the apparatus 11.

  In the image forming apparatus configured as described above, a four-color full-color toner image is formed on the transfer material P as follows. First, the photosensitive drums 1a, 1b, 1c, and 1d are rotationally driven at a predetermined process speed in the direction of the arrow by a photosensitive drum driving motor (not shown), and are set to a predetermined polarity and potential by the chargers 2a, 2b, 2c, and 2d. Uniformly charged. The charged photosensitive drums 1a, 1b, 1c, and 1d are exposed based on image information by the exposure devices 3a to 3d, and the charge of the exposed portions is removed to form an electrostatic latent image for each color. These electrostatic latent images on the photosensitive drums 1a, 1b, 1c, and 1d are developed as toner images of respective colors of yellow, magenta, cyan, and black by the developing devices 4a, 4b, 4c, and 4d. These four color toner images are sequentially primary-transferred onto the intermediate transfer belt 7 by the primary transfer rollers 5a, 5b, 5c, and 5d in the primary transfer nip. Thus, the four color toner images are superimposed on the intermediate transfer belt 7. At the time of primary transfer, toner (residual toner) that is not transferred to the intermediate transfer belt 7 and remains on the photosensitive drums 1a, 1b, 1c, and 1c is removed by the drum cleaners 6a, 6b, 6c, and 6d. The photosensitive drums 1a, 1b, 1c, and 1d from which the residual toner has been removed are used for the next image formation. The four color toner images superimposed on the intermediate transfer belt 7 as described above are secondarily transferred to the transfer material P.

  The transfer material P conveyed from the paper feed cassette 10 by the feeding / conveying device is supplied to the secondary transfer nip T <b> 2 by the registration roller so as to be synchronized with the toner image on the intermediate transfer belt 7. To the supplied transfer material P, the four-color toner images on the intermediate transfer belt 7 are secondarily transferred collectively at the secondary transfer nip by the secondary transfer roller 9. The transfer material P onto which the four color toner images have been secondarily transferred is conveyed to the fixing device 13 where it is heated and pressed to fix the toner image on the surface. The transfer material P after the toner image is fixed is discharged onto a paper discharge tray. The four-color full-color image formation on one surface (front surface) of one transfer material P is thus completed.

[Developer]
Here, the developing device of this embodiment will be described in detail with reference to FIGS. Since each developing device used in the image forming apparatus main body of the present embodiment has the same configuration, only one developing device will be described. In the following description, the developing device 4 may refer to any of the developing devices 4a, 4b, 4c, and 4d. 2 and 3 are sectional views of the developing device 4 according to this embodiment.

  The developing device 4 according to the present embodiment includes a developing container 41 in which a two-component developer containing toner and a carrier is accommodated as a developer. Further, the developing sleeve 44 as a developer carrying member is rotatably supported by the developing container 41, and the developer is supplied from the developing container 41. In addition, a regulation blade 46 that regulates the ears of the developer carried on the development sleeve 44 is provided.

  In the present embodiment, the inside of the developing container 41 is partitioned into a developing chamber 41a and an agitating chamber 41b by a partition wall 41c whose substantially central portion extends in a direction perpendicular to the paper surface. It is accommodated in the chamber 41b. In the developing chamber 41a and the agitating chamber 41b, first and second conveying screws 42 and 43 are arranged as developer agitating / conveying means. The first conveying screw 42 is disposed substantially parallel to the bottom of the developing chamber 41a along the axial direction of the developing sleeve 44, and rotates in the direction of the arrow (clockwise direction) shown in FIG. The developer is conveyed in one direction along the axial direction. The reason for the clockwise rotation is that it is advantageous from the viewpoint of supplying the developer to the developing sleeve 44. The second conveying screw 43 is disposed at the bottom of the stirring chamber 41b substantially in parallel with the first conveying screw 42, and rotates in the opposite direction (counterclockwise) to the first conveying screw 42. The developer in 41b is transported in the direction opposite to the first transport screw 42. As described above, the developer is conveyed by the rotation of the first and second conveying screws 42 and 43, so that the developer passes through the openings (that is, the communicating portions) 41d and 41e at both ends of the partition wall 41c. Cycled between. Further, a toner supply port 49 for supplying toner is provided in a part of the stirring chamber 41b. In order to stir the toner and the carrier as much as possible until the developer is supplied from the developing chamber 41a to the developing sleeve 44 and stabilize the toner charge amount, the toner replenishing port 49 is generally provided in the stirring chamber 41b. It is.

  In the present embodiment, there is an opening at a position corresponding to the developing region of the developing container 41 facing the photosensitive drum 1, and the developing sleeve 44 is partially exposed in the direction of the photosensitive drum 1 at this opening. It is rotatably arranged.

  Here, the diameter of the developing sleeve 44 is 20 mm, the diameter of the photosensitive drum 1 is 80 mm, and the closest region between the developing sleeve 44 and the photosensitive drum 1 is a distance of about 300 μm. By doing so, it is set so that development can be performed in a state where the developer conveyed to the developing unit is in contact with the photosensitive drum 1. The developing sleeve 44 is made of a nonmagnetic material such as aluminum or stainless steel. A magnet roller 45 as a magnetic field generating means is included in the developing sleeve 44 and is fixedly installed in a non-rotating state. The magnet roller 45 includes a developing pole S1 disposed facing the photosensitive drum 1 in the developing unit, and a magnetic pole S2 disposed facing the regulating blade 46. Furthermore, a magnetic pole N1 disposed between the magnetic poles S1 and S2, a magnetic pole N2 disposed on the upstream side of the developing sleeve 44 in the rotation direction of the magnetic pole S2, and a magnetic pole N3 disposed on the downstream side of the developing sleeve 44 in the rotational direction of the magnetic pole S1. Have.

[Magnetic seal configuration]
Here, the configuration of the magnetic seal at the end of the developing sleeve 44 of this embodiment will be described in detail with reference to FIGS. In this embodiment, the end of the developing sleeve 44 is magnetically sealed at a position opposite to the side where the photosensitive drum 1 is disposed. First, in this embodiment, developer leakage is prevented by providing a magnetic plate 50 facing the outer surface of the developing sleeve 44 and magnetically sealing it. The magnetic plate 50 is arranged so as to be opposed to the magnet roller 45 in the developing sleeve 44, so that the magnetic plate 50 is magnetized by the magnetic force formed by the magnet roller 45, and a magnetic spike is formed between the developing sleeve 44 and the magnetic plate 50. Produces a sealing effect.

  However, in the magnetic plate 50, since there is almost no magnetic force of the magnet roller 45 between the repulsion poles of the magnet roller 45, the magnetic plate 50 is hardly magnetized and the sealing property between the repulsion poles cannot be expected.

  Therefore, a magnetic seal member 47 as a magnet member is disposed outside the magnetic plate 50 in the longitudinal direction.

  The magnetic seal member 47 is a plate-like magnet (magnet plate), and is disposed at both ends of the developing sleeve 44 on the opposite side to the photosensitive drum, and is disposed in a non-contact state along the circumferential direction of the developing sleeve 44. ing. The magnetic seal member 47 is disposed close to the developing sleeve 44 at a distance of about 1 mm. The magnetic seal member 47 cooperates with the magnetic plate 50 to magnetically seal the end of the developing sleeve 44. With this configuration, the developer leaking out between the magnetic plate and the developing sleeve 44 forms a magnetic spike by the developer between the magnet roller 45 in the developing sleeve 44 and the magnet 47 which is a magnetic seal member. Can prevent.

  Here, the magnetic seal member 47 uses a magnet plate whose one surface is an N pole and whose back surface is an S pole. The magnetic seal member 47 preferably has a surface on the side of the developing sleeve opposite to the poles (N2 and N3) that form the repulsive magnetic field of the magnet roller 45 inside the developing sleeve 44. In this case, lines of magnetic force extend between the magnet roller 45 in the developing sleeve 44 and the magnet that is the magnetic seal member 47, and magnetic spikes due to the developer are formed, thereby preventing leakage. However, the magnetization pattern is not limited to the above configuration. For example, the polarity may be changed between the front and back sides, and different polarities may be alternately arranged on one surface.

  In this embodiment, the magnetic flux density on the surface of the magnetic seal member 47 is set between 5 mT and 100 mT. In this example, the magnetic seal member 47 is disposed between the developing sleeve 44 and the magnetic seal member 47 between 0.3 mm and 2.0 mm.

[Magnetic seal member]
Next, the configuration of the magnetic seal member, which is a characteristic part of the present invention, will be described in more detail. FIG. 6 is a view showing a configuration of a conventional magnetic seal member 47. FIG. 6 shows, in order from the left, a side view in which the thickness direction of the magnetic seal member is arranged in the left-right direction, a front view in which the thickness direction is arranged perpendicular to the paper surface, and a magnetic flux density distribution as seen from the side view. As described in “Problems to be Solved by the Invention”, in the configuration of the conventional magnetic seal member 47, a rectangular plate-like magnet is arranged along the circumferential direction of the developing sleeve. In this configuration, as can be seen from FIG. 6, the magnetic flux lines are concentrated at the end of the magnetic seal member, so that the developer sealability is high at the end of the magnetic seal member in the circumferential direction of the developing sleeve. However, since the magnetic flux lines are sparse in the central portion of the magnetic seal member 47, the sealing performance is low, and there is a case where a sufficient sealing performance cannot be ensured as a whole.

  Therefore, in this embodiment, the magnetic seal member 47 provided at the end of the developing sleeve 44 is shaped as shown in FIG. 7 to increase the portion where the magnetic flux lines are concentrated. (FIG. 7 shows a side view, a front view, and a magnetic flux distribution in order from the left as in FIG. 6.) In this embodiment, by making a hole in the middle, the number of locations where magnetic flux lines are concentrated is increased and developed. The sealability of the agent is improved. That is, when the magnetic seal member 47 is attached, the width of the magnetic seal member is different in the circumferential direction of the developing sleeve 44. Therefore, like the conventional magnetic seal member 47, the magnetic flux lines are more likely to be concentrated in the central portion than in the case where the width of the magnetic seal member is constant in the circumferential direction of the developing sleeve 44.

  Then, a comparative experiment was conducted with the developing device 4 provided with the magnetic seal member 47 as in the conventional example shown in FIG. 6 and the magnetic seal member 47 employed in the present embodiment shown in FIG. 7 as follows. . That is, the weight ratio (T / D) of the toner in the developer is set to 8%, the conditions such as the image ratio are matched, and the end of each developing device after image formation is repeated 500,000 sheets on A4 paper. The presence or absence of developer leakage existing under the developing unit in the part was confirmed and compared. In addition, the area when the outer periphery of the magnetic seal member 47 is tied is made uniform, the hole is formed, only the area where the magnet exists is changed, and the magnetizing conditions and material of the magnetic seal member 47 are also made to form an image. went. According to this evaluation result, about 5 g of developer was present under the end of the developing device using the magnetic seal member 47 of the conventional example, whereas the magnetic seal member 47 employed in this embodiment was used. There was no developer under the end of the used developing device.

  Further, when image formation is repeated up to 1000000 sheets, the developing device 4 using the conventional magnetic seal member 47 causes carrier adhesion due to developer leakage in the process of going up to 1000000 sheets, and then the developing sleeve 44 I locked it. When the state of the developing device 4 when the developing sleeve is locked is confirmed, a large amount of developer exists in the bearing 51 provided outside the magnetic seal member 47 shown in FIG. Toner fusion occurred between the flanges at the ends of the sleeve 44. For this reason, it was found that the bearing 51 was locked.

  On the other hand, the developing device 4 using the magnetic seal member 47 employed in this example did not leak developer, and of course, neither carrier adhesion nor locking of the developing sleeve 44 due to developer leakage occurred.

  From the above evaluation results, it was found that by increasing the number of locations where the magnetic flux density is concentrated, the sealing performance of the end portion of the developing sleeve 44 can be improved, and carrier adhesion and developing sleeve locking due to developer leakage do not occur. .

  As described above, a developing device that prevents the carrier from adhering to the end due to the leakage of the agent and the locking of the developing sleeve by increasing the magnetic flux concentration of the magnetic sealing member and improving the sealing performance by the magnetic sealing member is provided. I was able to do it.

  Further, in the configuration of the present embodiment, since only the holes are formed, the sealing performance can be improved without increasing the number of magnets, and the attaching work can be performed only once, so that the mounting work can be prevented from becoming complicated.

  Further, in the case of the configuration of this embodiment, the following effects can be expected when the diameter of the developing sleeve is reduced. That is, for example, when the diameter of the developing sleeve 44 is reduced, the configuration of the conventional magnetic seal member 47 has a strong rigidity of the magnetic seal member 47 and may cause the magnetic seal member 47 to be peeled off from the developing device 4. . On the other hand, it was found that when the magnetic seal member 47 employed in this example was used, the rigidity of the magnetic seal member 47 itself was weakened, and the structure was better against peeling.

  Furthermore, the material of the photosensitive drum, the developer, the configuration of the image forming apparatus, and the like used in the image forming apparatus of the present embodiment are not limited to these, and the present invention can be applied to various developers and image forming apparatuses. Needless to say. Specifically, as shown in FIG. 8, the shape of the magnetic seal member and the shape of the hole are not limited to the present embodiment. A plurality of holes may be provided. Further, the magnetic flux density, the color and number of toners, the presence or absence of wax, the order in which each color toner is developed, the number of developer agitating / conveying members, etc. are not limited to this embodiment. However, the present invention is also applicable.

(Example 2)
Since the basic configuration of the image forming apparatus describing this embodiment is the same as that of the first embodiment, description of the entire image forming apparatus is omitted. The present embodiment relates to a so-called function-separated vertical stirring and developing device in which developer stirring and conveying members are arranged vertically. A feature of the functionally separated vertical stirring and developing apparatus is that the width in the horizontal direction can be reduced, so that the size can be reduced. Furthermore, since the place where the developer is supplied to the developing sleeve is different from the place where the developer is collected from the developing sleeve, the developer having a lowered toner concentration after the process of developing the toner on the photosensitive member is sufficiently used. After stirring, it can be supplied to the developing sleeve again. Therefore, it is effective for problems such as density reduction and longitudinal density unevenness.

  First, the developing device 4 of this embodiment will be described with reference to FIGS. The developer in the developing device 4 of this embodiment is circulated between the developing chamber 41a and the stirring chamber 41b through openings (that is, communication portions) 41d and 41e at both ends of the partition wall 41c. Further, the developer is supplied from the developing chamber 41a to the developing sleeve 44, and the developer conveyed by the developing sleeve 44 is taken in the stirring chamber 41b. At this time, as shown in FIG. 9, the amount of the developer present in the stirring chamber 41b increases toward the opening 41e through which the developer is pumped. This is because the developer that has passed through the developing sleeve 44 and the agent that has been conveyed from the opening 41d by the second developer agitating and conveying member 43 merge, and the developer conveying of the second developer agitating and conveying member 43 is performed. This is because the amount of developer increases as the position becomes downstream.

  According to the study by the inventors, on the pumping side where the developer is lifted by the opening 41e, the amount of the developer increases as it goes to the pumping side. For this reason, the pressure applied to the end of the developing sleeve 44 increases, and the amount of the developer flowing into the magnetic seal member 47 provided at the end of the developing sleeve 44 increases, so that the developer cannot be sealed, and the developer It has been found that leaks may occur.

  Therefore, in the present embodiment, as in the first embodiment, the magnetic seal member 47 provided at the end of the developing sleeve 44 is shaped as shown in FIG. 7 to increase the portion where the magnetic flux lines are concentrated. did. In this embodiment, by making a hole in the middle, the number of locations where the magnetic flux lines are concentrated is increased, and the sealability of the developer is enhanced. Then, a comparative experiment was conducted with the developing device 4 provided with the magnetic seal member 47 as in the conventional example shown in FIG. 6 and the magnetic seal member 47 employed in the present embodiment shown in FIG. 7 as follows. . The weight ratio (T / D) of the toner in the developer is set to 8%, the conditions such as the image ratio are matched, and after the image formation is repeated 500,000 sheets on the A4 paper, at the end of each developing device. The presence or absence of developer leakage existing under the developing unit was confirmed and compared. Further, the area when the outer periphery of the magnetic seal member 47 was connected was made uniform, only the area where the magnet was present was changed, and the magnetizing conditions and materials of the magnetic seal member 47 were also made to form an image. According to this evaluation result, carrier adhesion due to developer leakage occurred in the process of forming 500,000 sheets under the end of the developing apparatus using the magnetic seal member 47 of the conventional example, and the developing apparatus 4 after 500,000 sheets. As a result, about 10 g of developer was present. In contrast, no developer was present under the end of the developing device using the magnetic seal member 47 employed in this example.

  Further, when image formation was repeated repeatedly up to 1000000 sheets, the developing sleeve 44 locked in the process of the conventional developing device 4 using the magnetic seal member 47 reaching 1000000 sheets. When the state of the developing device 4 when the developing sleeve is locked is confirmed, a large amount of developer exists in the bearing 51 provided outside the magnetic seal member 47 shown in FIG. Toner fusion occurred between the flanges at the ends of the sleeve 44. For this reason, it was found that the bearing 51 was locked.

  On the other hand, the developing device 4 using the magnetic seal member 47 employed in this example did not leak developer, and of course, neither carrier adhesion nor locking of the developing sleeve 44 due to developer leakage occurred.

  From the above evaluation results, it was found that by increasing the number of locations where the magnetic flux density is concentrated, the sealing performance of the end portion of the developing sleeve 44 can be improved, and carrier adhesion and developing sleeve locking due to developer leakage do not occur. .

  As described above, even in the function-separated vertical stirring and developing device in which the developer stirring and conveying members are arranged up and down, by forming holes in the magnetic seal member, the magnetic flux concentration of the magnetic seal member is increased and the magnetic flux is concentrated. The sealing performance by the sealing member could be improved. Therefore, it was possible to provide a developing device that prevents carrier adhesion and development sleeve locking due to agent leakage from the end.

  Further, the material of the photosensitive drum, the developer, and the configuration of the image forming apparatus used in the image forming apparatus of the present embodiment are not limited to these, and the present invention can be applied to various developers and image forming apparatuses. Needless to say. Specifically, the color and number of toners, the presence or absence of wax, the order in which each color toner is developed, the number of developer agitating / conveying members, and the like are not limited to this example. More specifically, it goes without saying that the present invention is applicable even if the shape and magnetic flux density of the magnetic seal member 47 are changed as described in the first embodiment.

  Although the image forming apparatus of the present invention has been described by the above two embodiments, the present invention is not limited to the above-described configuration, and various configurations can be taken according to the proposal of the present invention.

  When a plurality of holes are formed in the magnetic seal member 47, a relatively large number of holes may be formed at a position where the magnetic sealability is particularly likely to deteriorate. And the structure which does not form a hole in a position with a comparatively favorable sealing property, or relatively reduces the number of holes may be sufficient. For example, the holes are concentrated in the region facing the region (between the N2N3 poles) where the repulsive magnetic field is formed as in the first embodiment to improve the sealing performance. On the other hand, since the sealing performance is relatively good between the S2 pole and the N2 pole of the magnet roller, no hole is formed, or the number of holes may be relatively reduced. By doing so, it is possible to suppress a decrease in the rigidity of the magnetic seal member.

100 Image forming apparatus 1 Photoconductor (photosensitive drum)
2 Charging device 3 Exposure device 4 Developing device 41a Developing chamber (developer transport path)
41b Stir chamber (developer transport path)
41c Bulkhead 41d, 41e Delivery section (developer transport path)
42 1st member (developer conveyance member)
43 Second member (developer transport member)
44 Development sleeve (developer carrier)
45 Magnet roll 46 Developer regulating member (regulating blade)
47 Magnetic seal member 48 Reservoir part 49 Supply port 50 Magnetic plate 51 Bearing

Claims (4)

A developer carrying body that carries a developer having toner and a carrier, and that develops the electrostatic latent image at a position facing the image carrying body;
A magnetic field generating means included in the developer carrier and having a plurality of magnetic poles;
A development member including a magnet member provided at a position opposite to the image carrier so as to face the surface of the developer carrier in a non-contact manner and magnetically seals an end of the developer carrier. In the device
The developing device according to claim 1, wherein the magnet member is formed so that the width of the magnet member is different in a circumferential direction of the developer carrier.   The developing device according to claim 1, wherein the magnet member has a hole.   The developing device according to claim 1, wherein the magnet member has a plurality of holes formed along a rotation direction of the developing sleeve.   The magnetic field generating means includes a region in the circumferential direction of the developer carrying member in which a magnetic field for carrying the developer is relatively small, and the magnet member has a relatively small magnetic field. The developing device according to claim 3, wherein the number of holes in the region is larger than that in the relatively large region.

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