JP4944629B2 - Development device - Google Patents

Description

The present invention relates to a developing equipment for developing an electrostatic image formed by an electrophotographic method or an electrostatic recording method.

  In an image forming apparatus such as an electrophotographic copying machine, conventionally, developing devices applied to these image forming apparatuses are known by a powder cloud method, a cascade method, a magnetic brush method, or the like. Of these, in the case of the magnetic brush method of the two-component development method, the two-component developer containing a mixture of magnetic carrier, toner, etc. is adsorbed to the magnetic field generating means, and the developer is spiked in the magnetic pole portion. The image is developed by rubbing the electrostatic image on the photosensitive drum. At this time, since the magnetic carrier itself in the developer acts as a soft developing electrode, the toner can be attached in proportion to the charge density of the electrostatic image, that is, suitable for reproduction of a gradation image. . Further, the developing device itself can be made compact.

  As this two-component developing type magnetic brush developing device, a magnetic brush developing method using a developing sleeve which is a developer carrying member is generalized. This includes a magnetic carrier such as a magnetic powder, for example, ferrite, and a toner in which a pigment is dispersed in a resin in order to achieve the purpose of efficiently developing an electrostatic image on the photosensitive drum. The two-component developer is mixed with stirring. Then, while the toner retains electric charge by frictional charging due to these mutual friction, the developer is applied to a developing sleeve which is a hollow cylindrical developer carrier made of a nonmagnetic material having a magnetic pole inside. Hold. Then, the developing sleeve transports the developer from the developer container to the developing region facing the photosensitive drum by the developing sleeve, and the developer is sprinkled by the action of the magnetic field in this developing region to rub the surface of the photosensitive drum. Thus, the electrostatic image formed on the photosensitive drum is developed.

  The two-component magnetic brush developing method using the developing sleeve is used in many products, mainly black-and-white digital copying machines and full-color copying machines that require high image quality.

  In the developing device, the developer in the developer container is moved to the bearing 51 portion of the developing sleeve 50 along the surface of the developing sleeve 50 shown in FIG. 12 by circulating movement in the developer container. Be transported. For this reason, the developer may enter the portion of the bearing 51 to inhibit the smooth rotation of the developing sleeve 50, or the developer may pass through the portion of the bearing 51 and leak out of the developing container.

  For this reason, conventionally, with respect to the developer leakage from the end portion of the developing sleeve, there has been proposed a method of attaching an elastic seal member to both end portions of the developing sleeve and sealing the toner member so that the toner does not leak. ing. However, since the elastic seal member is press-fitted on the outer peripheral surface of the developing sleeve in the above-described seal configuration, there is a problem that the load on the developing sleeve is large and the sealing performance is deteriorated due to the deterioration of the elastic seal member.

  Therefore, in a developing device using 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. 12, this is a configuration in which a magnetic seal member 52 magnetized is provided on the facing surface facing the surface of the developing sleeve 50 while maintaining a predetermined distance, and the developer is magnetically attracted and held.

  The magnetic seal configuration has an advantage that the developing sleeve 50 and the magnetic seal member 52 are not in contact with each other, so that the rotation load of the developing sleeve 50 is reduced and the deterioration due to wear or the like does not occur, resulting in a long life.

  When a plate-shaped magnet is attached as the magnetic seal member 52 so as to surround the developing sleeve 50 in a non-contact manner, a magnetic spike is formed between the magnet roller 53 and the magnet in the developing sleeve 50 to prevent leakage. it can. At this time, when a magnet plate having one surface with N pole and the back surface with S pole is used as the magnet, the pole is different from the pole (for example, S and S) that forms the repulsive magnetic field of the magnet roller 53 inside the developing sleeve. If this surface is not the surface on the developing sleeve side, toner leakage is likely to occur.

  This is because when the magnetic pole of the magnet roller 53 and the magnetic seal member 52 face each other with the same polarity, a repulsive magnetic field is also formed between the magnet roller 53 and the magnetic seal member 52. For this reason, as shown in FIG. 13a, the magnetic lines of force of the magnetic seal member 52 are bent and extended toward the outside in the longitudinal direction of the developing sleeve 50. At this time, as shown in FIG. 13b, the developer is arranged along the lines of magnetic force, so that the developer extends toward the end portion of the developing sleeve, and the developer easily escapes in the end portion direction.

  Further, FIG. 13 c schematically shows the force applied to the magnetic carrier in the region surrounded by the magnetic seal member 52 and the developing sleeve 50. The arrow indicates the direction of the force at that position, and the length of the arrow indicates the magnitude of the force. When magnets are facing each other with the same polarity, there should be a continuous area between the magnets that has almost no magnetic force acting on the magnetic carrier (a region where the direction of the force acting on the magnet is reversed). It becomes. In FIG. 13c, a region where the magnetic force acting on the magnetic carrier is small and hardly present is indicated by a circle. As shown in this figure, a region having almost no force acting on the magnetic carrier continuously exists between the magnetic seal member and the developing sleeve. In that case, there is a risk that the magnetic carrier leaks in accordance with the flow shown by the dotted arrow shown in FIG. 13c without being pulled by the magnetic seal member or the magnet roller. As a result, the developer easily flows out to the outside of the developer region, and good sealing performance cannot be exhibited.

  Therefore, a configuration has been proposed in which the repulsive magnetic field and the magnetic seal member are opposed to each other with different polarities. When facing each other with different polarities, the magnetic lines of force of the magnetic seal member 52 extend in the direction of the developing sleeve 50 as shown in FIG. For this reason, it becomes difficult for the developer to escape in the direction toward the end of the developing sleeve. At this time, as shown in FIG. 14 b, the developer extends in the direction of the developing sleeve 50, and a magnetic spike is formed between the developing sleeve 50 and the magnetic seal member 52. The magnetic ears serve to seal the developer that tends to escape toward the end portion, and are more difficult to leak.

  FIG. 14c schematically shows the force applied to the magnetic carrier in the region surrounded by the magnetic seal member 52 and the developing sleeve 50, as in FIG. 13c. When the magnets are opposed to each other with different polarities, there is a region between the magnets where there is almost no magnetic force acting on the magnetic carrier (indicated by a circle), but there is no continuous presence between the magnets. Therefore, the magnetic carrier in the region surrounded by the magnetic seal member and the developing sleeve is always pulled by the magnetic seal member 52 and the magnet roller 53 in the process of moving toward the end of the developing sleeve, and as a result, outside the developing region. It becomes difficult for the developer to flow out and good sealing performance can be exhibited.

  In addition, a configuration using a magnet with NS poles magnetized in multiple magnetic poles on its inner peripheral surface as a magnetic seal member has also been proposed. In such a configuration, since the magnetic lines of force extend between the multiple magnetic poles of the magnetic seal member, it is difficult for the magnetic lines of force to extend outward in the longitudinal direction of the developing sleeve, and good sealing performance can be exhibited.

Japanese Patent Laid-Open No. 11-133750

  By the way, in recent high-speed copying machines, the rotational speed of the photosensitive drum has been increased, and the circumferential rotational speed of the developing sleeve has been increased in order to obtain sufficient development efficiency for the photosensitive drum rotating at high speed. As a result, toner scattering is likely to occur.

  Here, the developing sleeve 50 is subjected to blasting on the peripheral surface of the image forming area. On the other hand, as shown in FIG. 15, both end portions in the longitudinal direction where the magnetic seal 52 is provided have non-blast regions 54 that are not subjected to blasting.

  The non-blast region 54 is applied with a developing bias Vdc, and the end of the image carrier 55 facing the non-blast region 54 is charged to Vd. For this reason, force is applied to the scattered toner in the direction of arrow c in FIG. Therefore, in the developing sleeve 50 that rotates at a high speed, the non-blast region 54 is easily contaminated with scattered toner.

  On the other hand, in the developing sleeve that rotates at a high speed, as shown in FIG. 16, the sliding between the magnetic brush of the developer extending from the magnetic seal member 52 toward the developing sleeve 50 and the developing sleeve 50 that rotates at a high speed becomes large. Therefore, there is a possibility that the toner adhering to the non-blasted area is liberated in the area 56 in the drawing due to rubbing and contaminates the image forming apparatus main body.

Things present invention has been made in view of the above points, and its object is to prevent the contamination with the developer of the longitudinal ends of the developer carrying member, to provide a developing equipment to prevent toner contamination in the apparatus It is.

A typical means in the present invention for solving the above-described problem is that in the developing device for developing the electrostatic image formed on the image carrier by carrying the magnetic developer on the rotating developer carrier, the developer The carrier has a blast region that is blasted in the longitudinal direction and a non-blast region that is not blasted at both ends thereof, and a boundary position between the blast region and the non-blast region with respect to the longitudinal direction of the developer carrier. A magnet member disposed on the outer side and spaced apart from the boundary position and disposed in contact with the developer carrying member in a non-contact manner to prevent developer leakage, and the same polarity as the developer In the longitudinal direction of the developer carrier, the insulating member is electrically charged to a position outside the opposed region where the magnet member and the developer carrier face each other. Ku and so as to cover, and having an insulating member, provided on the entire developer carrier circumferential direction.

  In the above configuration, since the insulating member is charged with the same polarity as the developer by rubbing against the developer, the developer hardly adheres to the insulating member. For this reason, it is possible to prevent the developer from being contaminated at the end in the longitudinal direction of the developer carrying member magnetically sealed by the magnetic member, and to prevent contamination in the apparatus.

  Next, a developing device according to an embodiment of the present invention will be described with reference to the drawings together with an image forming apparatus including the developing device.

[Overall configuration of image forming apparatus and developing apparatus]
FIG. 1 is a schematic explanatory view of an image forming apparatus provided with a developing device according to the present embodiment. The overall configuration of the image forming apparatus and the developing device will be described together with the image forming operation.

  As shown in FIG. 1, the image forming apparatus A of the present embodiment is provided with a photosensitive drum 1 that is an image bearing member so as to be freely rotatable, and the photosensitive drum 1 is uniformly charged by a primary charger 2, and laser The image signal is exposed by the light emitting element 3 to form an electrostatic image. This electrostatic image is developed by the developing device B to be visualized.

  Next, the visualized developer image is transferred onto a sheet 6 conveyed by a conveying belt 5 by a transfer charger 4, and further fixed by a fixing unit 7, and then discharged outside the apparatus. Further, the transfer residual developer on the photosensitive drum 1 is removed by the cleaning device 8.

  The developing device B of the present embodiment is a two-component developer having toner and a carrier, and develops using a magnetic developer having magnetism. As shown in FIG. 2, the developing device B includes a developer container 11, and screws 12 and 13 are disposed in the developer container 11. The developer 14 is reciprocated in the developer container 11 by the screws 12 and 13.

  Further, the developing device B transfers the developer 14 in the developer container 11 to the photosensitive drum 1 in order to develop the electrostatic image formed on the photosensitive drum 1 rotating in the direction of arrow a in FIG. A developer carrier 15 is provided for conveyance. As shown in FIG. 2, the developer carrier 15 of the present embodiment is fixed to a magnetized fixed magnet roller 16 and is rotatably mounted around the magnet roller 16 in the direction of arrow b in FIG. It comprises a cylindrical developing sleeve 17 for conveying 14 to the photosensitive drum 1.

  During image formation, a developer is sent along the peripheral surface of the developing sleeve 17 that is rotated by the magnetic force of the magnet roller 16, and this developer is formed on the photosensitive drum 1 by applying a developing bias to the developing sleeve 17. Development is performed by adhering according to the image.

  During development, the patch electrostatic image formed corresponding to the predetermined density is developed with toner by the developing device B, and the density of the patch image is detected by the density detection sensor without being transferred. By supplying an appropriate amount of toner into the developing device based on this detected density, the ratio of toner to carrier is kept constant.

[Development sleeve end seal configuration]
Next, an end seal configuration of the developing sleeve 17 in the developing device of the present embodiment will be described. FIG. 3 is a schematic explanatory view of the end seal structure of the developing sleeve. 3 shows only one end in the longitudinal direction of the developing sleeve, the same applies to the other end.

  The developing sleeve 17 is rotatably supported by bearings 18 at both ends in the longitudinal direction. When the developing sleeve 17 is rotated and developed, the developer circulates along the surface of the developing sleeve 17 by the circulating movement of the developer in the developer container 11 as described above, and the portion of the bearing 18 of the developing sleeve 17 It is transferred to. At this time, it is necessary to prevent developer leakage from the longitudinal end of the developing sleeve 17 and rotation failure of the developing sleeve 17 due to the intrusion of the developer into the bearing 18. Therefore, in this embodiment, a magnetic seal member 19 that is a magnetic member that is magnetized on an opposing surface that maintains a predetermined distance (non-contact) with the surface of the developing sleeve 17 is provided.

  As shown in FIG. 4, the magnetic poles of the magnetic seal member 19 are configured such that the N poles that are different from the repulsive magnetic fields S2 and S3 of the opposing magnet roller 16 are opposed to each other. In this way, by opposing the repulsive magnetic field with a different polarity, the magnetic lines of force of the magnetic seal member 19 extend in the direction of the developing sleeve 17 as described above, and magnetic spikes of the developer are formed along the magnetic lines of force. Leakage from the end is prevented.

  Further, the peripheral surface of the developing sleeve 17 of the present embodiment is formed with a blast region that is blasted in the longitudinal direction and a non-blast region that is not blasted at both ends. That is, the developer carrying region of the developing sleeve 17 is blasted, and both ends in the longitudinal direction where the magnetic seal member 19 is disposed are not blasted.

[Insulating material]
As described above, the magnetic seal property is enhanced by making the magnetic pole of the magnetic seal member different from the magnetic pole of the opposing magnet roller 16. However, as described above, when the circumferential rotation speed of the developing sleeve 17 is increased, the scattering of the developer increases, and the non-blast region that is easily contaminated by the scattered developer and the magnetic brush formed by the magnetic seal member 19 are rubbed. There is a possibility that the developer is liberated and the inside of the image forming apparatus is contaminated.

  Therefore, as shown in FIG. 3, the insulating member 20 that is charged to the same polarity as the developer is provided on the entire circumferential direction at the end portion in the longitudinal direction of the developing sleeve 17 and facing the magnetic seal member 19. .

  In the present embodiment, an insulating tape is used as the insulating member, and the insulating tape 20 is attached to the non-blast region. More specifically, as shown in FIG. 5, the insulating tape 20 having a width of 13 mm, which is negatively charged in the same manner as the polarity of the developer, is longer in the longitudinal direction of the developing sleeve 17 than the magnetic seal member 19 having a magnetic force of 500 gauss and a width of 5 mm. Affixed from 2mm.

  At this time, as shown in FIG. 5, the region where the insulating tape 20 is attached is charged to −600V. This is because the insulating tape 20 has a property of being negatively frictionally charged by rubbing with the magnetic spikes, so that the developing bias of −400V is further charged by −200V.

  Therefore, the region where the insulating tape 20 is attached has the same potential with respect to the photosensitive drum 1. For this reason, the scattered developer is not attracted, and the developer charged negatively because of the lower potential than the blast region is attracted to the blast region. As a result, the non-blasted region to which the insulating tape 20 is attached is not soiled by the developer, and the developer is not released even by rubbing against the magnetic spikes.

[Experimental result]
Here, in the developing device of this embodiment, the result of examining the relationship between the position where the insulating tape 20 is applied and how the non-blast region of the developing sleeve 17 is stained is shown.

  When a magnetic seal member 19 having a magnetic force of 500 gauss and a width of 5 mm is provided with an end portion of 2 mm outward from the boundary between the blast region and the non-blast region, as shown in FIG. 20 was pasted as follows.

  (1) Affix with reference to a position 2 mm inside the magnetic seal member.

  (2) Paste the inner end of the magnetic seal member as a reference.

  (3) Affix with the outer end of the magnetic seal member as a reference.

  As described above, the insulating tape 20 was attached to the three positions, and the end of the developing sleeve 17 was examined for contamination.

  As a result, when the insulating tape was affixed at the position (1), the developer contamination in the non-blast area did not occur.

  On the other hand, when the insulating tape 20 is affixed to the position (2), developer contamination occurs in the non-blast area (width 2 mm) where the insulating tape 20 is not affixed. In addition, the insulating tape 20 and the non-blast area At the boundary, a free developer was confirmed (see FIG. 7). This is because the friction between the magnetic brush extending from the magnetic seal member 19 and the non-blast region is stronger as it is closer to the magnetic seal member 19.

  In addition, when the insulating tape 20 is applied at the position (3), the developer stains occur in the non-blasted area (width 7 mm) where the insulating tape 20 is not applied, and the entire area of the exposed non-blasted area is magnetic. The developer was liberated by rubbing with the ears (see FIG. 8).

  Therefore, in the present embodiment, it can be seen that the attaching position of the insulating tape 20 is preferably attached with reference to the inside from the inner end of the magnetic seal member 19. Therefore, it is desirable to provide the insulating tape 20 in a region wider than the region facing the magnetic seal member 19 in the longitudinal direction of the developing sleeve 17, and more preferably to cover the entire non-blast region.

  Next, the length of the insulating tape 20 was changed to examine how the non-blast region of the developing sleeve 17 was stained.

  When a magnetic seal member 19 having a magnetic force of 500 gauss and a width of 5 mm is provided on the basis of a position of 2 mm outward from the boundary between the blast region and the non-blast region, the boundary between the blast region and the non-blast region as shown in FIG. As a reference, the following insulating tape was attached.

  (4) Affix 5mm wide insulating tape.

  (5) Affix an insulating tape with a width of 7 mm.

  (6) Affix an insulating tape with a width of 13 mm.

  As described above, the insulating tape 20 having three kinds of widths was attached, and the end of the developing sleeve 17 was examined for contamination.

  As a result, when the insulating tape 20 having a width of 5 mm (4) was applied, the developer was stained in the non-blast region (8 mm width) where the insulating tape 20 was not applied. Further, the release of the developer occurred in a region where the friction between the magnetic brush extending from the magnetic seal member 19 and the exposed non-blasted region was strong (see FIG. 10).

  On the other hand, when (7) a 7 mm wide insulating tape is applied, developer contamination occurs in the non-blasted area (6 mm wide) where no insulating tape is applied, and the boundary between the insulating tape and the non-blasted area. In Fig. 11, free developer was confirmed.

  Furthermore, when the insulating tape having a width of 13 mm of (6) is attached, the developer contamination in the non-blast area does not occur as in the case of the examination (1). The developer was not liberated by strong rubbing.

  Therefore, in the present embodiment, the width of the insulating tape is preferably longer than the width of the magnetic seal member and the developing sleeve facing each other.

1 is a schematic explanatory diagram of an image forming apparatus to which the embodiment can be applied. It is a figure which shows the example of the developing device of a magnetic brush developing system. It is explanatory drawing of a structure of the image development sleeve edge part of this embodiment. It is a figure which shows the mode of the magnetic seal member vicinity of this embodiment. It is a figure explaining the electric potential of the image development sleeve edge part in this embodiment. It is explanatory drawing which investigates the optimal insulating tape position in this embodiment. It is explanatory drawing which investigates the optimal insulating tape position in this embodiment. It is explanatory drawing which investigates the optimal insulating tape position in this embodiment. It is explanatory drawing which investigates the optimal insulating tape width in this embodiment. It is explanatory drawing which investigates the optimal insulating tape width in this embodiment. It is explanatory drawing which investigates the optimal insulating tape width in this embodiment. It is a figure showing the structure of the image development sleeve edge part of the conventional image development apparatus. It is a figure showing the direction of a magnetic force line when using the edge part magnetic seal member of the same polarity as a repulsion pole. It is a figure showing the mode of a magnetic spike when using the end magnetic seal member of the same polarity as a repulsion pole. It is a figure showing the magnitude | size of a magnetic force when using the edge part magnetic seal member of the same polarity as a repulsion pole. It is a figure showing the direction of a magnetic force line when using the end part magnetic seal member of a repulsion pole and a different pole. It is a figure showing the mode of a magnetic spike when using the end magnetic seal member of a repulsion pole and a different pole. It is a figure showing the magnitude | size of a magnetic force when an end part magnetic seal member of a repulsion pole and a different pole is used. It is a figure for demonstrating the subject which generate | occur | produces with the conventional developing device. It is a figure for demonstrating the subject which generate | occur | produces with the conventional developing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS A ... Image forming apparatus B ... Developing apparatus 1 ... Photoconductor drum 2 ... Primary charger 3 ... Laser light emitting element 4 ... Transfer charger 5 ... Conveying belt 6 ... Sheet 7 ... Fixing device 8 ... Cleaning device
11… Developer container
12, 13 ... screw
14 ... Developer
15 ... Developer carrier
16… Magnet roller
17… Development sleeve
18… Bearing
19… Magnetic seal member
20… Insulating tape

Claims (3)

In a developing device for developing an electrostatic image formed on an image carrier by carrying a magnetic developer on a rotating developer carrier,
The developer carrier has a blast region that is blasted in the longitudinal direction, and a non-blast region that is not blasted at both ends thereof,
With respect to the longitudinal direction of the developer carrier, the developer carrier is disposed outside the boundary position between the blast region and the non-blast region and spaced from the boundary position to prevent developer leakage. A magnet member arranged in a non-contact manner with the body;
An insulating member charged to the same polarity as the developer, from the boundary position to a position outside a facing region where the magnet member and the developer carrier face each other with respect to the longitudinal direction of the developer carrier. An insulating member provided over the entire circumferential direction of the developer carrier so as to cover at least
A developing device comprising:   The developing device according to claim 1, wherein the insulating member is charged with the same polarity as the developer so as to reduce a difference between a non-image portion potential of the image carrier and a potential of the developer carrier. The magnetic brush formed of the magnetic developer by the magnetic force of the magnet member is in contact with the non-blast region between the magnet member and the blast region with respect to the longitudinal direction of the developer carrier. The developing device according to claim 1 or 2, characterized in that

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