JP2017026937A - Development device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a development device in which it is possible to suppress developer leakage and suppress toner leakage by a simple configuration.SOLUTION: A magnet roller 9 is provided in such a way that ends of a pair of adjacent magnetic poles of the same polarity are overlapped on a magnetic seal member 12 in a development container, while ends of the other magnetic poles are not overlapped on the magnetic seal member 12. The magnetic roller 9 is formed so that there is a difference in level between ends of a pair of adjacent magnetic poles of the same polarity and ends of the other magnetic poles. This facilitates the movement of a developer that forms a magnetic brush generated between a development sleeve 8 and the magnetic seal member 12, and in no case does the same developer suffer continuous friction. Furthermore, since the developer hardly stay stagnant in a place where the developer is collected in the developer container, developer leakage hardly occurs. Thus, it is possible to suppress developer leakage and suppress toner leakage by a simple configuration.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a developing device applicable to an image forming apparatus that forms a toner image on a recording material using an electrophotographic system or the like.

  Conventionally, a two-component developer containing a non-magnetic toner and a magnetic carrier (hereinafter referred to as a developer) is carried on a rotating developing sleeve, and the toner is supplied from the developing sleeve to the photosensitive drum, thereby forming the photosensitive drum. A developing device that develops the electrostatic latent image formed is known. As a developing device, a magnetic plate is provided in a non-contact manner along the circumferential surface of the sleeve in the developing container so that a part of the developer carried on the developing sleeve does not leak from the end of the sleeve to the outside of the developing container. (Patent Document 1).

  In the apparatus described in Patent Document 1, the magnetic plate is magnetized by the magnetic force of the magnet roller provided in the developing sleeve, and a magnetic field (magnetic force) is generated between the magnetic plate and the developing sleeve. Then, a magnetic brush is formed between the magnetic plate and the developing sleeve by the developer moving on the sleeve surface from the central portion of the sleeve to the sleeve end portion, and this magnetic brush forms a gap between the magnetic plate and the developing sleeve. As a result, the developer leakage is suppressed. However, a region where the magnetic field is weak is generated between the magnetic plate and the developing sleeve, and the developer is likely to leak from there. Therefore, a magnetic seal member having a plurality of magnetic poles is provided on the outer side (sleeve bearing side) of the sleeve end portion further than the magnetic plate. In this case, even if the developer leaks from the magnetic plate, the developer is restrained by the magnetic field generated between the magnetic seal member and the developing sleeve, so that it is difficult to leak out of the developing container.

Japanese Patent Laid-Open No. 9-218583

  As described above, a magnetic spike is formed between the magnetic plate or the magnetic seal member and the developing sleeve and the leakage of the developer is suppressed by this magnetic spike, but the amount of developer that can be held as a magnetic spike is There is a limit, and beyond that, developer leakage will occur. Therefore, conventionally, the magnet roller protrudes not only to the magnetic plate but also to the magnetic seal member over the entire circumference and overlaps the magnetic seal member, thereby increasing the area of the opposing surface between the magnetic seal member and the developing sleeve. (Magnetic force) was made stronger. This increases the developer that can be held as magnetic spikes.

  However, when the magnetic field generated between the magnetic seal member and the developing sleeve becomes strong, not only the developer moving to the end of the sleeve but also the developer collected in the developing container as the developing sleeve rotates. Can be taken in as. For this reason, the developer collected in the developing container is dammed up at the end of the sleeve and is likely to stay. As a result, the developer is likely to leak out of the developing container, and the magnetic spike flutters and the developer is likely to be scattered out of the developing container.

  On the other hand, when the magnet roller does not protrude to the magnetic seal member over the entire circumference and does not overlap the magnetic seal member, developer leakage is suppressed. However, in this case, the developer that forms the magnetic spikes is held almost without being replaced. For this reason, the magnetic brush is divided into a developer that is repeatedly rubbed against the developing sleeve and a developer that is not rubbed, and the carrier and toner can be liberated by natural discharge. Since the toner is non-magnetic, the released toner can leak out of the developing container without being restricted by the magnetic field generated between the magnetic seal member and the developing sleeve (this is called toner leakage). Toner leakage causes image defects and needs to be suppressed.

  The main cause of developer leakage is that the magnetic roller overlaps with the magnetic seal member over the entire circumference, and the magnetic field generated between the magnetic seal member and the developing sleeve becomes stronger. However, if the magnet roller does not overlap with the magnetic seal member, toner leakage may occur. Thus, in the conventional apparatus, suppression of developer leakage and suppression of toner leakage are in a trade-off relationship, and it has been difficult to achieve both of them.

  The present invention has been made in view of the above problems, and an object thereof is to provide a developing device capable of realizing both suppression of developer leakage and suppression of toner leakage with a simple configuration.

  A developing device according to the present invention includes a developing container that contains a developer containing non-magnetic toner and a magnetic carrier, a developing sleeve that is disposed so as to be partially exposed from the developing container, and that rotates inside the developing sleeve. A magnetic field generating means provided in a non-rotating manner and having a plurality of magnetic poles arranged in the circumferential direction for carrying the developer in a developer carrying area formed on the surface of the developing sleeve; and the development outside the developer carrying area The end of the sleeve in the rotation axis direction is provided so as to oppose at least a part of the peripheral surface on the non-exposed portion side of the developing sleeve, and the developer is disposed between the end and the opposing peripheral surface. A magnet member capable of forming magnetic spikes, a conveying member that is disposed opposite to the developing sleeve at a position where the developer is collected from the developing sleeve, and conveys the developer in the rotational axis direction of the developing sleeve; The magnetic field generating means includes a pair of repelling magnetic poles arranged side by side in the circumferential direction of the developing sleeve and having the same polarity, and the pair of repelling magnetic poles, in order to form a repelling magnetic field on the peripheral surface of the developing sleeve An upstream magnetic pole disposed upstream of the developing sleeve in the rotational direction of the developing sleeve, and the magnetic field generating means includes at least an end of the pair of repulsive magnetic poles at an end of the transporting member downstream in the transport direction. The magnetic member protrudes to the outside on the end side of the developing sleeve from the inner end edge on the developer carrying region side of the magnet member, and the end of the upstream magnetic pole is inside the inner end edge outside the developer carrying region. It is characterized by protruding.

  A developing device according to the present invention includes a developing container that contains a developer containing non-magnetic toner and a magnetic carrier, a first developing sleeve that is disposed and rotated so as to be partially exposed from the developing container, and the first A second developing sleeve arranged in parallel with the developing sleeve so as to be partially exposed from the developing container, and a developer carried on the first developing sleeve is delivered to the inside of the first developing sleeve A first magnetic field generating means arranged in a circumferential direction with a plurality of magnetic poles for carrying developer on a first developer carrying region formed on the surface of the first developing sleeve; and A second magnetic field generating means provided in a non-rotating manner inside and having a plurality of magnetic poles arranged in a circumferential direction to carry a developer in a second developer carrying region formed on a surface of the second developing sleeve; One developer An end of the first developing sleeve outside the area in the rotational axis direction is provided so as to be opposed along at least a part of the circumferential surface on the non-exposed portion side of the first developing sleeve, and the end of the first developing sleeve A first magnet member capable of forming a magnetic spike of the developer between the opposed peripheral surfaces of the first portion and the end of the second developing sleeve outside the second developer carrying region in the rotational axis direction; Provided along the circumferential surface of at least a part of the non-exposed part side of the two developing sleeves, and can form a developer magnetic brush between the opposing circumferential surfaces of the end parts of the second developing sleeve A second magnet member and a conveying member that is disposed opposite to the second developing sleeve at a position where the developer is collected from the second developing sleeve and conveys the developer in the rotation axis direction of the second developing sleeve. And the second magnetic field generating means includes a front In order to form a repelling magnetic field on the peripheral surface of the second developing sleeve, a pair of repelling magnetic poles arranged side by side in the circumferential direction of the second developing sleeve and having the same polarity, and the second repelling magnetic pole than the pair of repelling magnetic poles. An upstream magnetic pole disposed on the upstream side of the developing sleeve rotation direction, and the second magnetic field generating means includes at least an end portion of the pair of repulsive magnetic poles at an end portion on the downstream side in the transport direction of the transport member. The second magnet member protrudes to the outside on the end side of the second developing sleeve from the inner end edge on the second developer carrying region side, and the end of the upstream magnetic pole is outside the second developer carrying region. It protrudes inward rather than the inner end edge of the second magnet member.

  According to the present invention, both suppression of developer leakage from the end portion of the developing sleeve and suppression of toner leakage can be realized with a simple configuration.

1 is a schematic diagram illustrating a configuration of an image forming apparatus to which a developing device according to a first embodiment is applied. FIG. 3 is a cross-sectional view illustrating a configuration of the developing device according to the first embodiment. Sectional drawing which shows the structure in the longitudinal cross-section of the longitudinal direction of a developing container. It is the schematic which shows the magnet roller and magnetic seal structure of 1st Embodiment, (a) is the figure seen from the conveyance screw side, (b) is the figure seen from the photosensitive drum side. The perspective view which shows the structure of the magnet roller of 1st Embodiment. Schematic which shows the magnet roller and magnetic seal structure of 2nd Embodiment. Sectional drawing which shows the structure of the developing device of 3rd Embodiment. Schematic which shows the magnet roller and magnetic seal structure of 3rd Embodiment. Sectional drawing which shows the structure of the developing device of 4th Embodiment. It is the schematic which shows the magnet roller and magnetic seal structure of 4th Embodiment, (a) is upstream and downstream developing sleeve both ends, (b) is downstream developing sleeve both ends, (c) is upstream and downstream developing sleeve one end, (D) shows the case where the downstream developing sleeve is overlapped at one end.

<First Embodiment>
A first embodiment will be described with reference to FIGS. 1 to 5. First, a schematic configuration of an image forming apparatus to which the developing device of the first embodiment is applied will be described with reference to FIG.

[Image forming apparatus]
The image forming apparatus shown in FIG. 1 is a tandem direct transfer type full-color printer in which image forming units PY, PM, PC, and PK are arranged along a transfer material conveyance belt 24. In the image forming unit PY, a yellow toner image is formed on the photosensitive drum 10Y and transferred to a recording material 27 (sheet, sheet material such as an OHP sheet) conveyed to the transfer material conveyance belt 24. In the image forming unit PM, a magenta toner image is formed on the photosensitive drum 10 </ b> M and transferred to the recording material 27 conveyed to the transfer material conveying belt 24. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 10C and 10K, respectively, and transferred to the recording material 27 conveyed to the transfer material conveying belt 24.

  The recording material 27 onto which the four color toner images have been transferred is sent to the fixing device 25 with the curvature being separated from the transfer material conveying belt 24. The recording material 27 is heated and pressurized by the fixing device 25 to fix the toner image on the surface, and then is discharged to the outside of the machine body.

  The image forming units PY, PM, PC, and PK are configured the same except that the colors of toner used in the developing devices 1Y, 1M, 1C, and 1K are different from yellow, magenta, cyan, and black. Therefore, hereinafter, the image forming unit PY will be described in detail, and the image forming units PM, PC, and PK will be described by replacing Y at the end of the symbol with M, C, and K.

  The image forming unit PY surrounds the photosensitive drum 10Y and includes a primary charger 21Y, an exposure device 22Y, a developing device 1Y, a transfer charger 23Y, and a drum cleaning device 26Y. The photosensitive drum 10Y as an image carrier has a photosensitive layer formed on the outer peripheral surface, and rotates in the direction of arrow R1 in the drawing at a predetermined process speed.

  The primary charger 21Y irradiates charged particles accompanying corona discharge, for example, to charge the photosensitive drum 10Y to a uniform negative polarity dark portion potential. The exposure device 22Y scans the scanning line image data obtained by developing the separation color image of each color with a rotating mirror, and writes an electrostatic latent image of the image on the surface of the charged photosensitive drum 10Y. The developing device 1Y supplies toner to the photosensitive drum 10Y to develop the electrostatic latent image into a toner image.

  The transfer charger 23Y has a transfer blade, and presses the transfer blade against the transfer material transport belt 24 to form a toner image transfer portion between the photosensitive drum 10Y and the transfer material transport belt 24Y. By applying a DC voltage having a polarity opposite to the charging polarity of the toner to the transfer blade, the toner image carried on the photosensitive drum 10Y is transferred to the recording material 27 on the transfer material conveying belt 24Y. The so-called transfer residual toner remaining on the photosensitive drum 10Y after the transfer is removed by the drum cleaning device 26Y.

  Here, the method of directly transferring from the photosensitive drum 10Y to the recording material 27 conveyed to the transfer material conveying belt 24 has been described, but the present invention is not limited to this. For example, an intermediate transfer member is provided in place of the transfer material transport belt 24, and after the primary transfer of each color toner image from the photosensitive drum 10Y of each color to the intermediate transfer member, the composite toner images of each color are collectively put on the recording material 27. The present invention is also applied to an image forming apparatus configured to perform secondary transfer.

[Two-component developer]
In the developing device 1Y, a two-component developer including a non-magnetic toner having a negative charging characteristic and a magnetic carrier having a positive charging characteristic is used. The two-component developer will be described.

  The toner is a binder resin such as a styrene resin or a polyester resin, a colorant such as carbon black, a dye, or a pigment, and further colored resin particles containing other additives as necessary, and a colloidal silica fine powder. And externally added colored particles. In the present embodiment, a toner having a negative charge characteristic polyester-based resin and a volume average particle diameter of 7.0 μm is used.

As the carrier, for example, metal such as surface-oxidized or unoxidized iron, nickel, cobalt, manganese, chromium, rare earth, alloys thereof, or oxide ferrite can be preferably used. The method for producing these magnetic particles is not particularly limited. In this embodiment, for example, the volume average particle diameter of the carrier is 20 to 60 μm, preferably 30 to 50 μm. Further, the resistivity of the carrier is 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more.

[Developer]
Next, the developing device 1Y will be described. A developing device 1Y shown in FIG. 2 is a vertical stirring type developing device. The developing device 1 </ b> Y includes a developing container 2, a developing sleeve 8 as a developer carrier, and a regulating blade 20. The developing container 2 contains a two-component developer. The developing container 2 is partitioned into an upper developing chamber 3 and a lower agitating chamber 4 by a partition wall 7 extending in a direction perpendicular to the paper surface at a substantially central portion. The developing chamber 3 serving as the first chamber and the stirring chamber 4 serving as the second chamber communicate with each other vertically at both ends to form a developer circulation path.

  In the developing chamber 3 and the agitating chamber 4, a developing screw 5 as a first conveying means (conveying member) and an agitating screw 6 as a second conveying means (conveying member) are rotatably disposed, respectively. As the developing screw 5 and the agitating screw 6 rotate, the developer T is circulated and conveyed in the developing container 2 while being agitated. As the developer T is agitated, the toner is negatively charged and the carrier is positively charged.

  The developing screw 5 is arranged substantially in parallel along the rotation axis of the developing sleeve 8 in the developing chamber 3 (first chamber). The stirring screw 6 is disposed substantially in parallel with the developing screw 5 in the stirring chamber 4 (second chamber). As shown in FIG. 3, when the developing screw 5 rotates, the developer T in the developing chamber 3 is conveyed in one direction from the left to the right in FIG. 3 along the rotation axis of the developing screw 5. On the other hand, when the stirring screw 6 rotates, the developer T in the stirring chamber 4 moves in one direction from the right to the left in FIG. 3 along the rotation axis of the stirring screw 6, that is, with the developer T in the developing chamber 3. Are conveyed in the opposite direction. The developer T conveyed by the developing screw 5 and the agitating screw 6 passes through the open communication portions 71 and 72 provided at both ends of the partition wall 7, and in the direction indicated by the arrow R3 in the drawing, the developing chamber 3 and the agitating chamber. Cycle between 4.

  The developing screw 5 and the stirring screw 6 have a screw structure in which stirring blades made of a nonmagnetic material are provided in a spiral shape around the rotation axis. In this embodiment, for example, the screw diameter is 20 mm and the screw pitch is 30 mm. Further, the rotation speed when the developer T is conveyed is set to, for example, 800 rpm.

  Returning to FIG. 2, the developing sleeve 8 is partially exposed from the opening of the developing container 2 provided at a position facing the photosensitive drum 10 </ b> Y, and is rotatably disposed in the developing container 2. The distance (SD gap) between the positions where the developing sleeve 8 and the photosensitive drum 10Y are closest to each other is set to about 250 μm, for example. Accordingly, the toner image can be developed with the developer carried and conveyed by the developing sleeve 8 in contact with the photosensitive drum 10Y. The developing sleeve 8 is formed in a cylindrical shape with a non-magnetic material such as aluminum or stainless steel, and a magnet roller 9 as a magnetic field generating means forms a gap with a certain interval from the inner peripheral surface of the developing sleeve 8. It is fixed and non-rotating. That is, the magnet roller 9 cannot rotate.

  The magnet roller 9 disposed in the developing sleeve 8 has a developing pole N2 and a plurality of magnetic poles S1, S2, N1, and N3 for transporting the developer on the surface thereof. Here, in the developing area A, the developing pole N2 is disposed to face the photosensitive drum 10Y, and the magnetic pole S1 is disposed to face the regulating blade 20. A magnetic pole S2 is arranged downstream of the magnetic pole N2 in the developing sleeve rotation direction, and a magnetic pole N3 is arranged downstream of the magnetic pole S2 in the developing sleeve rotation direction. A magnetic pole N1 is disposed upstream of the magnetic pole S1 in the developing sleeve rotation direction. The adjacent magnetic poles N1 and N3 having the same polarity are repulsive magnetic poles, the magnetic pole N3 is a developer intake pole, and the magnetic pole N1 is a developer pumping pole.

Due to the magnetic force of the magnet roller 9, magnetic spikes of the developer are formed on the surface of the developing sleeve 8 (hereinafter referred to as the sleeve surface). The developer in the developing container 2 is pumped up by the action of the magnetic pole N1 and the magnetic pole S1, and magnetic spikes are formed on the surface of the rotating developing sleeve 8. The magnetic spike formed by the magnetic force of the magnetic pole N1 and the magnetic pole S1 is sent to the development area A with the layer thickness regulated by the regulating blade 20. The regulating blade 20 is a plate-like member made of a nonmagnetic material such as aluminum, and is disposed along the rotation axis direction (longitudinal direction) of the developing sleeve 8 on the upstream side of the developing sleeve rotating direction from the photosensitive drum 10Y. Has been. By adjusting the gap (gap) between the tip of the regulating blade 20 and the sleeve surface, the amount of magnetic spikes formed on the sleeve surface is regulated, and the amount of developer conveyed to the development area A is adjusted. The The regulating blade 20 regulates, for example, 30 mg / cm ² of the coating amount per unit area in the coated area (developer carrying area) on the sleeve surface where the roughening treatment has been performed.

  The developing sleeve 8 rotates in the same direction as the opposing photosensitive drum 10Y (in the direction of arrow R2 in the figure) while carrying the developer whose layer thickness is regulated by the cutting of the magnetic spikes by the regulating blade 20, and the carried development. The agent is conveyed to the development area A. The peripheral speed ratio of the developing sleeve 8 to the photosensitive drum 10Y is set to 170%, for example. In the development area A, the tip of the magnetic spike rubs against the photosensitive drum 10Y, supplies toner to the electrostatic latent image formed on the photosensitive drum 10Y, and develops the electrostatic latent image into a toner image. At this time, a developing bias voltage is applied to the developing sleeve 8 from a power source (not shown).

  The developing sleeve 8 conveys the developer remaining on the surface of the sleeve past the developing area A into the developing container 2. Since the magnetic pole N1 and the magnetic pole N3 having the same polarity are disposed in the developing container 2 at positions adjacent to each other, a repulsive magnetic field is formed between these poles. In the developing container 2, the developer is peeled from the sleeve surface by the repulsive magnetic field, and the peeled developer falls into the stirring chamber 4 and is collected. That is, the stirring chamber 4 forms a recovery path for recovering the developer carried on the sleeve surface without passing through the developing chamber 3.

[Magnetic seal configuration]
The developer in the developing container 2 is easily transferred along the sleeve surface from the central portion of the sleeve to the end portion (sleeve end portion) in the rotation axis direction of the developing sleeve 8 by the circulating movement in the container. For this reason, the developer enters the bearing of the developing sleeve 8 and accumulates in the bearing to impede its function, obstruct the smooth rotation of the developing sleeve 8, or the developer passes through the bearing and the developing container. May leak or splash outside. In order to prevent this, the end of the developing sleeve 8 is sealed. In the present embodiment, as a configuration for sealing the end portion of the developing sleeve 8, a magnetic seal configuration that magnetically blocks the outside and the inside of the developing container 2 is used. The magnetic seal configuration will be described with reference to FIGS. 4 (a) and 4 (b).

  As shown in FIGS. 4A and 4B, the magnetic seal configuration is such that the magnetic plate 11 and the magnetic seal member 12 are arranged on the sleeve end side outside the coat region. The magnetic plate 11 as a magnetic member is formed in a plate shape using a magnetic material, and develops in a non-contact manner along the outer periphery of the developing sleeve 8 on the non-exposed portion side (the side opposite to the photosensitive drum) in the developing container 2. The sleeve 8 is provided so as to cover a partial range. The magnetic plate 11 is magnetized by the magnet roller 9. Since a magnetic field is generated between the magnetic plate 11 and the developing sleeve 8, the developer that has entered between the magnetic plate 11 and the developing sleeve 8 forms a magnetic spike. This magnetic spike closes the gap between the magnetic plate 11 and the developing sleeve 8, so that developer leakage from the sleeve end can be suppressed.

  However, if there is a weak magnetic field (magnetic force) region in a part of the circumferential direction of the magnet roller 9, the magnetic field lines generated between the magnetic roller 11 and the magnetic plate 11 become sparse in this region, and the region is magnetic compared to other regions. Since the ears are not formed densely, the developer leaks easily. In particular, in the places where the magnetic poles N1 and N3 of the same polarity are arranged adjacent to each other (see FIG. 2), it is difficult for magnetic lines of force to be generated between the magnetic poles N1 and N3. Therefore, even though the magnetic plate 11 is provided, the developer is likely to leak from the region between the magnetic poles N1 and N3. That is, at the center position of the repulsive magnetic field region between the magnetic poles N1 and N3, the magnetic field between the magnetic poles is weak and the outside of the magnetic plate 11 is reversed to the reverse polarity (S pole). On the inside of the magnetic plate 11, the magnetic flux density at the location facing the sleeve surface is almost zero. Therefore, it is difficult to form magnetic spikes of the developer between the magnetic plate 11 and the developing sleeve 8 near the center position of the repulsive magnetic field region, and the developer is likely to leak from there. Further, in the repulsive magnetic field region other than the center position, for example, at the magnetic pole N3, a magnetic spike is formed between the magnetic plate 11 and the developing sleeve 8, but the reverse polarity (outside the end of the sleeve from the magnetic pole N3) (S pole) magnetic force was generated, and the developer sometimes leaked therefrom.

  In order to restrain the developer leaking from the magnetic plate 11, as already described, a magnetic seal is provided on the outer side (bearing side) of the sleeve end further than the magnetic plate 11 on the non-exposed portion side in the developing container 2. A member 12 is provided. The magnetic seal member 12 as a magnet member is composed of, for example, a sheet-like magnet, and is opposed to the both ends of the developing sleeve 8 in a non-contact manner along at least a part of the peripheral surface of the developing container 2 on the non-exposed portion side. Is provided. The magnetic seal member 12 has magnetic poles arranged on the inner peripheral surface so that the magnetic poles having different polarities face the magnetic poles of the magnet roller 9. In the case of this embodiment, the magnetic seal member 12 has an inner peripheral surface facing the developing sleeve 8 as an S pole and an outer peripheral surface as an N pole.

  As described above, since the magnetic seal member 12 and the magnet roller 9 are provided with magnetic poles having different polarities, a magnetic force is generated between the magnetic seal member 12 and the magnet roller 9. . Therefore, when the developer enters the gap between the magnetic seal member 12 and the developing sleeve 8, the entering developer forms a magnetic spike. The magnetic spike closes the gap between the magnetic seal member 12 and the developing sleeve 8 at the end of the sleeve and restrains the developer leaking from the magnetic plate 11. As described above, also in this embodiment, by providing the magnetic seal member 12 capable of forming magnetic spikes in addition to the magnetic plate 11, developer leakage from the sleeve end portion can be further suppressed.

  However, in the above-described magnetic seal configuration, there is a limit to the amount of developer that the magnetic plate 11 and the magnetic seal member 12 can constrain as magnetic spikes, and the developer can no longer be constrained as it continues to be used. In addition, the magnetic seal configuration using magnetic spikes cannot seal the developing container 2, and developer leakage may inevitably occur. For example, when pressure is applied to the magnetic spike formed between the magnetic plate 11 or the magnetic seal member 12 and the developing sleeve 8 with a force stronger than the magnetic force of the magnet roller 9, the developer is pushed out of the magnetic spike and leaks. (So-called peeling leakage). The conventional magnet roller is not provided with a step as described later at the roller end. Therefore, when the magnet roller overlaps with the magnetic seal member 12 over the entire circumference, as described above, developer leakage is remarkable.

  Therefore, it can be considered that the magnetic seal member 12 is provided at a relative position not including the magnet roller at the end of the sleeve so that the magnet roller does not overlap the magnetic seal member 12 over the entire circumference. In this case, since the magnetic flux density at the edge portion of the magnet roller is increased, the magnetic sealability between the edge portion of the magnet roller and the edge portion of the magnetic seal member 12 is improved, and developer leakage hardly occurs. However, as already described, toner leakage tends to occur in this case. The magnet roller 9 overlaps the magnetic seal member 12 when the magnet roller end 901 is closer to the developing sleeve end 81 than the inner end edge 121 of the magnetic seal member 12 on the coat region side (developer carrying region side). The state which protrudes outside is pointed out (refer to Drawing 4 (a)). On the other hand, when the magnet roller 9 does not overlap the magnetic seal member 12, the magnet roller end 901 protrudes inward from the inner end edge 121 of the magnetic seal member 12 outside the coat region (outside the developer carrying region). (Refer to FIG. 4B).

  In view of the above points, in the present embodiment, the length of the magnet pieces of the magnetic poles N1 and N3 and the length of the magnet pieces of the magnetic poles N2, S1, and S2 of the magnet roller 9 are different from each other. A step is provided. Hereinafter, a description will be given with reference to FIGS.

[Magnet roller]
As shown in FIG. 5, a round shaft support shaft 61 is provided at the center of the magnet roller 9. The support shaft 61 is formed using a rigid material such as a metal such as stainless steel. The magnet roller 9 is formed by radially bonding a fan-shaped cross-sectional magnet piece 92 to a support shaft 61 with an adhesive or the like. In this embodiment, since there are five magnetic poles, a pair of magnetic poles N1 and N3 as repulsive magnetic poles and magnetic poles S1, N2 and S2 other than the repulsive magnetic poles are formed around the support shaft 61. The five magnet pieces 92 are bonded together. The magnet piece 92 is formed of a known magnet such as a resin magnet or a sintered magnet based on resin, rubber, or the like. In the present embodiment, the magnetic pole S2 disposed on the upstream side in the developing sleeve rotation direction with respect to the magnetic poles N1 and N3 corresponds to at least the upstream magnetic pole.

  The magnet piece 92 is arranged in the circumferential direction so that magnetic poles having different polarities form a magnetic field pattern. In the present embodiment, the magnet pieces 92B of the magnetic poles S1, N2, and S2 are formed so that the sleeve rotation axis direction length is shorter than the sleeve rotation axis direction length of the magnet pieces 92A of the magnetic poles N1 and N3. A step is created at the end. Note that the number of magnetic poles need not be five. Further, the number of magnet pieces 92 is not limited to five. Furthermore, the magnet roller 9 is not limited to the one formed by bonding the magnet piece 92 together. In the present embodiment, the end of the magnet piece 92 forms the end of the magnet roller 9.

  As shown in FIG. 4A, the magnet roller 9 and the magnetic seal member 12 are arranged on the developing container side (in the developing container, on the front side in the drawing) of the sleeve circumferential direction. The end portion (roller end 901) is provided so as to overlap. As shown in FIG. 4B, the magnet roller 9 and the magnetic seal member 12 are arranged on the photosensitive drum side (outside the developing container, on the front side in the drawing) of the sleeve circumferential direction. The end (roller end 901) is provided so as not to overlap. In other words, the magnet roller 9 and the magnetic seal member 12 are relatively arranged so that the overlap mode of the magnet roller 9 and the magnetic seal member 12 is different inside and outside the developing container (in the circumferential direction of the sleeve). The magnet piece 92B is formed shorter than the magnet piece 92A so that the overlap mode differs between inside and outside the developing container. The length in the sleeve rotation axis direction of each piece 92A, 92B satisfies the following relationship. (Coat area length) <(Magnet piece 92B) <(Coat area length + Coat area end to magnetic seal member inner end) <(Magnet piece 92A) <(Coat area length + Coat area end to magnetic seal member outer end) Meet. The length of the magnetic seal member 12 in the sleeve rotation axis direction may be a predetermined length.

[Comparative Example 1]
The inventors of the present application conducted an experiment to verify the occurrence of developer leakage and toner leakage from the sleeve end. In the experiment, a durability test was performed in which an image was continuously formed on 100,000 recording materials in terms of A4 in an operating environment where the temperature was 30 ° C. and the humidity was 80%. At that time, developer leakage and toner leakage occurred. The presence or absence of was compared. The experimental results are shown in Table 1. In Table 1, a circle mark represents that no leakage occurred, and a cross mark represents that leakage occurred.

  Conventional Example 1 is a case where a conventional magnet roller having no step overlaps with the magnetic seal member 12 over the entire circumference (with all pole overlap). In Conventional Example 1, toner leakage did not occur, but developer leakage occurred. The reason for this is as already described. On the other hand, Comparative Example 1 is a case where a conventional magnet roller without a step does not overlap with the magnetic seal member 12 over the entire circumference (no overlap between all poles). In Comparative Example 1, developer leakage did not occur, but toner leakage occurred. The reason for this is as already described.

  Compared to Conventional Example 1 and Comparative Example 1, neither developer leakage nor toner leakage occurs in the first embodiment described above (Embodiment 1 in Table 1, only some poles have overlap). This is presumably because the developer that forms the magnetic spike is delivered. Of the magnet roller 9, the length is changed between the magnetic poles N 1 and N 3 of the same polarity arranged in the developing container 2 and the other magnetic poles N 2, S 1 and S 2 arranged outside the developing container 2 in the circumferential direction of the sleeve. When a step is formed at the end, a part of the developer can be circulated at the end of the sleeve. In other words, at the end of the sleeve, when a part of the developer forming the magnetic spike between the magnet piece 92A and the magnetic seal member 12 reaches the dividing point with the magnet piece 92B, it moves to the magnet piece 92B side. And it is carried on the sleeve surface by the magnet piece 92B. After that, a part of the developer carried on the sleeve surface moves to the magnet piece 92A side when reaching the junction with the magnet piece 92A. In this way, a part of the developer forming the magnetic spike generated between the magnetic seal member 12 and the developing sleeve 8 is circulated so that the developer forming the magnetic spike does not continue to be rubbed. , The toner is not released. That is, toner leakage is less likely to occur. Further, since the magnet piece 92B is shorter than the magnet piece 92A, when the developer is collected in the developing container 2, the development collected on the end side of the magnet piece 92A outside the end of the magnet piece 92B. The amount of the agent is small compared to the conventional amount. For this reason, the developer collected in the developing container 2 is not blocked and stays at the end of the sleeve, and as a result, developer leakage hardly occurs.

  Further, in the case of the first embodiment described above, neither developer leakage nor toner leakage occurred even if the magnetic plate 11 was not provided. Example 1 in Table 1 shows the experimental results in that case. From this result, in the present embodiment, the presence or absence of the magnetic plate 11 is not particularly limited, but it is better to provide the magnetic plate 11 from the viewpoint of increasing the developer that can be held as magnetic spikes.

  Thus, the end portions (92A) of the adjacent magnetic poles N1, N3 having the weakest magnetic field in the circumferential direction between the magnetic poles are overlapped with the magnetic seal member 12, and the end portions (92B) of the magnetic poles S1, S2, N3 are magnetized. The magnet roller 9 is provided without overlapping the seal member 12. In order to do so, the magnet roller 9 has a step formed between the ends of a pair of magnetic poles N1, N3 having the same polarity and the ends of the other magnetic poles S1, S2, N3. By doing so, a part of the developer forming the magnetic spike generated between the sleeve surface and the magnetic seal member 12 is easily moved, so that the same developer does not continue to be rubbed. Further, since the developer is less likely to stay at the place where the developer is collected in the developing container 2, the developer leakage is less likely to occur. Therefore, in the developing device of the present embodiment, it is possible to realize both the suppression of developer leakage and the suppression of toner leakage with a simple configuration.

Second Embodiment
Both ends may be provided at the end of the magnet roller 9 as described above, or only one end may be provided. When a step is provided only at one end of the magnet roller 9, it is preferable that a step be generated on the downstream side of the stirring screw 6 in the developer conveyance direction (downstream side of the stirring screw). FIG. 6 shows a magnet roller according to the second embodiment.

  In the first embodiment described above, a step is generated at both ends of the magnet roller 9 regardless of the developer circulation direction. Thereby, the overlap mode of the magnet roller 9 and the magnetic seal member 12 is made different between the inside and outside of the developing container at both ends of the developing sleeve 8. However, the ease of developer leakage from the developing sleeve 8 differs between the upstream side and the downstream side in the developer transport direction. In the case of the vertical stirring type developing device shown in FIG. 1, the developer is fed from the stirring chamber 4 to the developing chamber 3 from the side of the communicating portion 72 where the developer falls from the developing chamber 3 to the stirring chamber 4 in the developing container 2. Developer leakage is likely to occur from the side of the communicating portion 71 that is flipped up (see FIG. 3).

  As already described, the magnet roller 9 is formed by bonding a plurality of magnet pieces 92 to the support shaft 61 (see FIG. 5). A surface to which the magnet piece 92 is attached is formed in advance on the support shaft 61, and it is necessary to attach the end face of the magnet piece 92 to the attaching surface. That is, since it is easier to generate a step at one end of the magnet roller 9 than to generate a step at both ends, it is preferable to generate a step only at one end of the magnet roller 9.

  Therefore, in the second embodiment shown in FIG. 6, the overlap mode between the magnet roller 9 and the magnetic seal member 12 is different between the inside and outside of the developing container only on the downstream side of the stirring screw. That is, on the downstream side of the stirring screw, the magnet piece 92A having a long length in the sleeve rotation axis direction is overlapped with the magnetic seal member 12, and the magnet piece 92B having a short length in the sleeve rotation axis direction is not overlapped with the magnetic seal member 12. On the other hand, on the upstream side of the stirring screw, both the magnet piece 92A and the magnet piece 92B overlap the magnetic seal member 12.

[Comparative Example 2]
The inventors of the present application conducted an endurance test under the same conditions as in the first embodiment in order to verify the occurrence of developer leakage and toner leakage from the sleeve end also in the developing device of the second embodiment. The experimental results are shown in Table 2. In Table 2, a circle mark represents that no leakage occurred, and a cross mark represents that leakage occurred.

  Comparative Example 2 is a case where a step is provided only at one end of the magnet roller 9 and the end provided with the step is disposed on the upstream side of the stirring screw (only some poles are overlapped). In this case, on the upstream side of the stirring screw, as described above, the overlap mode of the magnet roller 9 and the magnetic seal member 12 is different between inside and outside the developing container. On the downstream side of the stirring screw, the magnet roller 9 is overlapped with the magnetic seal member 12 over the entire circumference (that is, the overlap mode of the magnet roller 9 and the magnetic seal member 12 is not different between inside and outside the developing container). Therefore, the developer tends to stay on the downstream side of the stirring screw because the developer is transferred from the stirring chamber 4 to the developing chamber 3. In this case, the amount of the developer taken into the stirring chamber 4 from the developing sleeve 8 tends to increase even on the downstream side of the stirring screw. From the above, it is considered that in Comparative Example 2, developer leakage occurred on the downstream side of the stirring screw.

  On the other hand, in the second embodiment, neither developer leakage nor toner leakage occurs on the upstream side and the downstream side of the stirring screw (Embodiment 2 in Table 2). In the second embodiment, although the magnet roller 9 is overlapped with the magnetic seal member 12 over the entire circumference on the upstream side of the stirring screw, there is room in the space of the developing container 2 on the upstream side of the stirring screw. The taken-in developer is conveyed by the stirring screw 6 to the downstream side of the stirring screw in the stirring chamber 4. Therefore, the developer taken into the stirring chamber 4 from the developing sleeve 8 does not stay on the upstream side of the stirring screw, so that the developer is difficult to leak. On the downstream side of the stirring screw, as in the case of the first embodiment described above, neither developer leakage nor toner leakage is likely to occur. Thus, the same effects as those of the first embodiment can be obtained in the developing device of the second embodiment.

<Third Embodiment>
A third embodiment will be described with reference to FIGS. FIG. 7 is a cross-sectional view illustrating a configuration of the developing device according to the third embodiment. The developing device 100A shown in FIG. 7 is different from the developing device 1Y according to the first embodiment shown in FIG. 2 only in having a conveying screw 15, and the others are the same. Therefore, the same components as those of the developing device shown in FIG.

  In the case of the developing device 1Y shown in FIG. 2, the developer tends to stay on the downstream side of the stirring screw, and when the amount of the developer increases or the fluidity of the developer decreases, the developer starts from the downstream side of the stirring screw. There was a leak. As a countermeasure, in the developing device 100A shown in FIG. 7, a conveying screw 15 as a third conveying means (conveying member) is provided in the agitating chamber 4 on the side (near) closer to the developing sleeve 8 than the agitating screw 6. ing. The conveying screw 15 conveys the developer in the opposite direction to the stirring screw 6 (same direction as the developing screw 5). By providing the conveying screw 15, a part of the developer staying on the downstream side of the stirring screw can be moved to the upstream side of the stirring screw, so that the developer surface in the stirring chamber 4 is made uniform and the stirring effect of the developer is obtained. Can be increased. Further, the developer recovered in the developing container 2 is less likely to stay on the downstream side of the stirring screw.

  In the developing device 100A shown in FIG. 7, the conveying screw 15 provided in the vicinity of the developing sleeve 8 has the most influence on the developer leakage among the three screws. Therefore, in the developing device 100A, a step is provided only at one end of the magnet roller 9, and the side on which the step is provided is disposed on the downstream side of the conveying screw. As shown in FIG. 8, on the downstream side of the conveying screw, a magnet piece 92 </ b> A having a long sleeve rotation axis direction length is overlapped with the magnetic seal member 12, and a magnet piece 92 </ b> B having a short sleeve rotation axis direction length is a magnetic seal member 12. And do not overlap. On the other hand, on the upstream side of the conveying screw, the magnet roller 9 is overlapped with the magnetic seal member 12 over the entire circumference. That is, both the magnet piece 92A and the magnet piece 92B overlap the magnetic seal member 12.

[Comparative Example 3]
The inventors of the present application conducted an endurance test under the same conditions as in the first embodiment in order to verify the occurrence of developer leakage and toner leakage from the sleeve end also in the developing device of the third embodiment. The experimental results are shown in Table 3. In Table 3, “◯” indicates that no leakage occurred, and “X” indicates that leakage occurred.

  Comparative Example 3 is a case where a step is provided only at one end of the magnet roller 9, and the side where the step is provided is disposed on the upstream side of the conveying screw (only some of the poles overlap). In this case, on the downstream side of the conveying screw, the magnet roller 9 is overlapped with the magnetic seal member 12 over the entire circumference (with all pole overlap). On the upstream side of the conveying screw, the overlap mode of the magnet roller 9 and the magnetic seal member 12 is different between inside and outside the developing container (only some poles have overlap). In this case, the developer retained on the downstream side of the stirring screw is transported to the downstream side of the transport screw. In addition, the magnet roller 9 is overlapped with the magnetic seal member 12 over the entire circumference on the downstream side of the conveying screw. Therefore, in Comparative Example 3, it is considered that developer leakage occurred on the downstream side of the conveying screw.

  In contrast, in the third embodiment, neither developer leakage nor toner leakage occurs in the upstream and downstream of the conveying screw (Embodiment 3 in Table 3). In the third embodiment, although the magnet roller 9 is overlapped with the magnetic seal member 12 over the entire circumference on the upstream side of the conveying screw, there is a margin in the space on the upstream side of the conveying screw, so that the incorporated developer is difficult to leak. . Then, the taken-in developer is transported to the downstream side of the transport screw by the transport screw 15. From the above, no developer leakage occurred. The toner leakage is the same as in the first embodiment. Thus, the same effects as those of the first embodiment can be obtained in the developing device of the third embodiment.

<Fourth embodiment>
A fourth embodiment will be described with reference to FIGS. 9 to 10 (d). First, a developing device according to a fourth embodiment will be described with reference to FIG. A developing device 100B shown in FIG. 9 is a developing device provided with a plurality (here, two) of developing sleeves 8A and 8B. Here, the same reference numerals are given to portions overlapping the description of the developing device 100A shown in FIG. 7, and the description thereof is omitted.

  The developing device 100B shown in FIG. 9 includes a developing container 2, an upstream developing sleeve 8A as a first developing sleeve, a downstream developing sleeve 8B as a second developing sleeve, a regulating blade 20, a developing screw 5, and a stirring screw. 6 and a conveying screw 15. The conveying screw 15 is provided in the stirring chamber 4 on the side (near) closer to the downstream developing sleeve 8 </ b> B than the stirring screw 6.

<Upstream developing sleeve>
The upstream developing sleeve 8A is partially exposed from the opening of the developing container 2 provided at a position facing the photosensitive drum 10Y, and is disposed in the developing container 2 so as to be rotatable in the direction of arrow R2 in the drawing. The upstream developing sleeve 8A is formed by coating a resin film on the surface of a cylindrical body made of a nonmagnetic material such as aluminum or stainless steel, and the sleeve surface is subjected to a roughening treatment (first developer carrying). Area). The upstream developing sleeve 8A is formed with a diameter of 20 mm, for example, and is rotated at a peripheral speed of, for example, 750 mm / s.

<Upstream magnet roller>
Inside the upstream developing sleeve 8A, an upstream magnet roller 9A as a first magnetic field generating means is fixedly disposed with a gap of a certain distance from the inner peripheral surface of the upstream developing sleeve 8A. In the upstream magnet roller 9A, magnetic poles having different polarities are alternately arranged in the circumferential direction so as to form a magnetic field pattern (see N1, S1, N3, N2, and S2 in the figure). Here, in the developing area A, the developing pole S1 is disposed to face the photosensitive drum 10Y, and the magnetic pole N2 is disposed to face the regulating blade 20. A magnetic pole N3 having the same polarity is disposed adjacent to the magnetic pole N2 upstream of the developing sleeve 8A in the rotation direction so as to form a repulsive magnetic field. Of these repulsive magnetic poles, the magnetic pole N3 is a developer delivery pole, and the magnetic pole N2 is a developer pumping pole. In the upstream magnet roller 9A, the magnetic pole S1 disposed on the upstream side in the upstream developing sleeve rotation direction (the upstream side in the first developing sleeve rotation direction) with respect to the magnetic poles N2 and N3 corresponds to at least the upstream magnetic pole.

<Downstream development sleeve>
The downstream developing sleeve 8B is parallel to the lower side of the upstream developing sleeve 8A and faces both the upstream developing sleeve 8A and the photosensitive drum 10Y, and is rotatable in the same direction as the upstream developing sleeve 8A (in the direction of arrow R2 in the figure). The developer container 2 is disposed. The distance between the positions where the upstream developing sleeve 8A and the downstream developing sleeve 8B are closest to each other (the closest position) may be 1 mm or less, for example, set to about 420 μm. The downstream developing sleeve 8B is formed by coating a resin film on the surface of a cylindrical body made of a nonmagnetic material like the upstream developing sleeve 8A, and can develop the electrostatic latent image formed on the photosensitive drum 10Y on the sleeve surface. A coating region (second developer carrying region) subjected to a roughening treatment. The downstream developing sleeve 8B is formed to have a diameter of 20 mm, for example, and is rotated at a peripheral speed of, for example, 750 mm / s.

<Downstream magnet roller>
Inside the downstream developing sleeve 8B, a downstream magnet roller 9B as a second magnetic field generating means is fixedly disposed with a gap of a certain distance from the inner peripheral surface of the downstream developing sleeve 8B. On the downstream magnet roller 9B, magnetic poles having different polarities are alternately arranged in the circumferential direction so as to form a magnetic field pattern (see N4, S4, N5, S5, and S3 in the figure). Here, in the developing region B, the developing pole N4 is disposed to face the photosensitive drum 10Y, and the magnetic pole S3 is disposed to face the upstream developing sleeve 8A (more specifically, the magnetic pole N3). In the downstream magnet roller 9B, the magnetic poles S3 and S5 having the same polarity are disposed adjacent to each other, and a repulsive magnetic field is formed between these poles. Of these repulsive magnetic poles, the magnetic pole S3 is a developer delivery pole, and the magnetic pole S5 is a developer pumping pole. Note that the magnetic pole N3 and the magnetic pole S3, which are developer transfer poles, do not need to be opposed to each other, and may be substantially opposed to each other within a range of, for example, 45 ° from the opposed position of the upstream developing sleeve 8A and the downstream developing sleeve 8B. . In the downstream magnet roller 9B, the magnetic pole N5 disposed on the upstream side in the downstream developing sleeve rotation direction (the upstream side in the second developing sleeve rotation direction) with respect to the magnetic poles S3 and S5 corresponds to at least the upstream magnetic pole.

  The flow of the developer in the developing device 100B will be described with reference to FIG. The developer in the developing container 2 is supplied to the upstream developing sleeve 8 </ b> A while being stirred by the developing screw 5 and the stirring screw 6. Then, magnetic spikes are formed on the surface of the upstream developing sleeve 8A by the magnetic force of the upstream magnet roller 9A. That is, the developer is carried on the upstream developing sleeve 8A. The developer carried on the upstream developing sleeve 8A is sent to the developing area A with the layer thickness regulated by the regulating blade 20. By adjusting the gap (gap) between the tip of the regulating blade 20 and the surface of the upstream developing sleeve 8A, the amount of magnetic spikes formed on the surface of the upstream developing sleeve 8A is regulated and conveyed to the developing region A. The developer amount is adjusted. When the upstream developing sleeve 8A conveys the developer to the developing area A, the upstream developing sleeve 8A performs the first development on the electrostatic latent image formed on the photosensitive drum 10Y. At this time, a developing bias voltage is applied to the upstream developing sleeve 8A from a power source (not shown).

  The developer remaining on the surface of the upstream developing sleeve 8A past the developing region A is peeled off from the surface of the upstream developing sleeve 8A by a repulsive magnetic field formed by the magnetic pole N3 and the magnetic pole N2. The peeled developer moves to the downstream developing sleeve 8B side according to the magnetic field formed between the magnetic pole N3 and the magnetic pole S3, and is carried on the downstream developing sleeve 8B. The developer carried on the downstream developing sleeve 8B is sent to the developing area B. When the downstream developing sleeve 8B transports the developer to the developing area B, the downstream developing sleeve 8B performs the second development on the electrostatic latent image formed on the photosensitive drum 10Y. At this time, a developing bias voltage is applied to the downstream developing sleeve 8B from a power source (not shown). Of the developer carried on the downstream developing sleeve 8B, the developer that has not been used for image formation is peeled off from the sleeve surface by the repulsive magnetic field formed by the magnetic pole S5 and the magnetic pole S3. Returned.

<Magnetic seal configuration>
As shown in FIGS. 9 to 10 (d), the magnetic seal configuration of the present embodiment is such that the magnetic plates 11A and 11B and the magnetic seal members 12A and 12B are sleeves outside the coat region for the developing sleeves 8A and 8B, respectively. It is arranged at the end. Since the magnetic plates 11A and 11B are the same as the magnetic plate 11 described above (see, for example, FIG. 4A), description thereof is omitted here.

  As shown in FIGS. 9 and 10 (a), an upstream magnetic seal member 12A as a first magnet member and a downstream magnetic seal member 12B as a second magnet member are provided at the end portions of the developing sleeves 8A and 8B. Each is provided. These magnetic seal members 12A and 12B are composed of magnets, and magnetically shut off the outside and the inside of the developing container 2 at both ends of the developing sleeves 8A and 8B in the rotation axis direction of the developing sleeves 8A and 8B. The magnetic seal members 12A and 12B have at least a part of the end of the developing sleeves 8A and 8B on the developing container 2 side (the opposite side to the photosensitive drum) with respect to the rotation axis direction of the developing sleeves 8A and 8B. It is provided so as to face non-contact along the surface. In these magnetic seal members 12A and 12B, magnetic poles having different polarities from the magnetic poles in the opposing magnet rollers 9A and 9B are arranged in the circumferential direction. The magnetic seal members 12A and 12B are formed so that the inner peripheral surface facing the developing sleeves 8A and 8B is an S pole and the outer peripheral surface is an N pole.

  Since the magnetic seal members 12A and 12B and the magnet rollers 9A and 9B are provided with a plurality of magnetic poles having different polarities at the opposed positions, the magnetic seal members 12A and 12B and the magnet rollers 9A and 9B are disposed between the magnetic seal members 12A and 12B and the magnet rollers 9A and 9B. Magnetic force is generated. Therefore, when the developer enters the gap between the magnetic seal members 12A and 12B and the developing sleeves 8A and 8B, the entering developer forms a magnetic spike. The magnetic brush closes the gap between the magnetic seal members 12A and 12B and the developing sleeves 8A and 8B at the ends of the developing sleeves 8A and 8B, and moves the developing sleeves 8A and 8B to the sleeve end side. Capture developer. As described above, also in this embodiment, the magnetic seal members 12A and 12B are provided at the end portions of the developing sleeves 8A and 8B, thereby suppressing the developer leakage from the sleeve end portions.

  The magnet rollers 9A and 9B described above are also formed by radially bonding fan-shaped magnet pieces 92 to the support shaft 61 with an adhesive or the like (see FIG. 5). Although not shown, regarding the magnet roller 9A, the magnet pieces of the magnetic poles S2, N1, and S1 are formed so that the length in the sleeve rotational axis direction is shorter than the length of the magnetic pieces N3 and N2 in the sleeve rotational axis direction. A step is created at the end. However, the length of the magnet piece of the magnet roller 9A in the sleeve rotation axis direction satisfies the following relationship. (Coating region length) <(Length of magnet piece of magnetic poles S2, N1, S1 in the sleeve rotation axis direction) <(Coating region length + Coating region to inner end of magnetic seal member) <(Magnetic piece of magnetic poles N3, N2) Sleeve rotation axis direction length) <(Coating region length + Coating region to magnetic seal member outer end). On the other hand, with respect to the magnet roller 9B, the magnet pieces of the magnetic poles N4, S4, N5 are formed so that the length in the sleeve rotation axis direction is shorter than the length of the magnetic pieces S5, S3 in the sleeve rotation axis direction. A step is generated in the part. However, the length of the magnet piece of the magnet roller 9B in the sleeve rotation axis direction satisfies the following relationship. (Coating area length) <(Magnetic piece sleeve magnetic axis length of magnetic poles N4, S4, N5) <(Coating area length + Coating area to magnetic seal member inner end) <(Magnetic piece sleeve of magnetic poles S3, S5) (Rotation axis direction length) <(Coat region length + Coating region to magnetic seal member outer end).

  In the present embodiment, the magnet rollers 9A and 9B and the magnetic seal members 12A and 12B include the end portions of the magnet pieces on the developing container side (inside the developing container) with respect to the rotation direction of the developing sleeve. Are relatively positioned. That is, the magnet rollers 9A and 9B are overlapped with the magnetic seal members 12A and 12B when viewed from the direction orthogonal to the developing sleeve rotation axis direction on the non-exposed portion side in the developing container 2. On the other hand, the magnet rollers 9A and 9B and the magnetic seal members 12A and 12B are relatively positioned on the photosensitive drum side (outside the developing container) so that the magnetic seal members 12A and 12B do not include the end of the magnet piece. . That is, on the photosensitive drum side (outside the developing container), the magnet rollers 9A and 9B are not overlapped with the magnetic seal members 12A and 12B when viewed from the direction orthogonal to the developing sleeve rotation axis direction. As described above, the overlap between the magnet rollers 9A and 9B and the magnetic seal members 12A and 12B differs between the inside and outside of the developing container with respect to the developing sleeve rotation direction. That is, as shown in FIG. 10A, on the non-exposed portion side in the developer container 2, the magnet roller end 901A is on the coat region side (first developer carrying region side, second developer carrying portion) of the magnetic seal member 12. It protrudes to the outside on the developing sleeve end portion 81 side from the inner end edge 121 on the region side). On the other hand, on the photosensitive drum side (outside the developing container), the magnet roller end 901B is outside the coat area (outside the first developer carrying area and outside the second developer carrying area) and inside the inner edge 121 of the magnetic seal member 12. Protruding.

  The inventors of the present application conducted an endurance test under the same conditions as in the first embodiment in order to verify the occurrence of developer leakage and toner leakage from the sleeve end also in the developing device of the fourth embodiment. The experimental results are shown in Table 4. The circles in Table 4 indicate that no leakage occurred.

  In the case of the configuration shown in FIG. 10A described above, neither developer leakage nor toner leakage occurred (Embodiment 4-1 in Table 4). This is because the developer is delivered to the individual developing sleeves 8A and 8B in the same manner as in the first embodiment described above. Therefore, the developer does not become excessive on the magnetic seal members 12A and 12B, so that the developer leakage hardly occurs. Further, since the magnetic spikes generated between the magnetic seal members 12A and 12B and the developing sleeves 8A and 8B are not continuously rubbed, the toner is not released. Therefore, toner leakage does not occur.

  Embodiment 4-2 is the experimental result of the structure shown in FIG.10 (b). Compared with the configuration shown in FIG. 10A, the configuration shown in FIG. 10B has a conventional magnet roller 90 that does not cause a step at the end portions of the upstream developing sleeve 8A. The difference is that it overlaps the seal member 12A. In Embodiment 4-2, neither developer leakage nor toner leakage occurs. In this case, the developer leakage is likely to occur in the upstream developing sleeve 8A as in Conventional Example 1 of Table 1 described above. However, in the case of the developing device 100B including the two developing sleeves 8A and 8B, as described above, the developer is transferred from the upstream developing sleeve 8A to the downstream developing sleeve 8B. Therefore, it is difficult for the developer to leak from the end portion in the upstream developing sleeve 8A. On the other hand, in the downstream developing sleeve 8B, since the relationship between the magnetic seal member 12B and the magnet roller 9B is the same as that in the first embodiment described above, neither developer leakage nor toner leakage occurs.

  Embodiment 4-3 is the experimental result of the structure shown in FIG.10 (c). The configuration shown in FIG. 10C is different from the configuration shown in FIG. 10A in that the developing sleeves 8A and 8B are provided with a step only at one end of the magnet rollers 9A and 9B, and the side provided with the step is developed. The difference is that they are arranged on the downstream side of the screw 5 and the downstream side of the conveying screw 15, respectively. In this case, since the upstream developing sleeve 8A is the same as the developing device of the second embodiment described above, neither developer leakage nor toner leakage occurs (see Embodiment 2 in Table 2). Since the downstream developing sleeve 8B is the same as the developing device of the third embodiment described above, neither developer leakage nor toner leakage occurs (see Embodiment 3 in Table 3).

  Embodiment 4-4 is the experimental result of the structure shown in FIG.10 (d). Compared with the configuration shown in FIG. 10B, the configuration shown in FIG. 10D is provided with a step at only one end of the magnet roller 9B in the downstream developing sleeve 8B, and the side where the step is provided is downstream of the conveying screw 15. It is different in the points placed on the side. In this case, the upstream developing sleeve 8A is the same as the configuration of FIG. 10B described above, and the downstream developing sleeve 8B is the same as the developing device of the third embodiment described above. Will not occur.

  As described above, in the developing device including the plurality of developing sleeves 8A and 8B, a step is provided at the end of the magnet roller 9B at least on the downstream side of the conveying screw, and the overlapping manner of the magnet roller 9B and the magnetic seal member 12 is developed. Different inside and outside the container. Thereby, also in the developing device of the fourth embodiment, as in the first embodiment described above, both the suppression of developer leakage and the suppression of toner leakage can be realized with a simple configuration.

  There is a developing device provided with a plurality of developing sleeves 8A and 8B in which the conveying screw 15 is not provided. In that case, a step may be provided at the end of the magnet roller 9B at least on the downstream side of the stirring screw.

<Other embodiments>
In general, a magnetic brush is formed by making the magnetic pole of the magnetic seal member 12 different from the repulsion pole to prevent end leakage. However, in a developing device having a plurality of developing sleeves, downstream development is performed. There is also a configuration in which the magnetic seal member 12 facing the sleeve 8B has the same polarity as the repulsion pole. The present invention is effective even in such a configuration.

  The developing device of each of the embodiments described above is applied to an image forming apparatus described below, but is not limited to this, and can be applied to other image forming apparatuses. That is, the image forming apparatus can be implemented without distinction between a tandem type / 1 drum type and an intermediate transfer type / direct transfer type. Further, the present invention can be carried out without distinction between two-component developer / one-component developer. In this embodiment, only main parts related to toner image formation / transfer will be described. However, in the present invention, a printer, various printing machines, a copier, a FAX, It can be implemented in various applications such as a multifunction machine.

  In each of the above-described embodiments, the vertical stirring type developing device in which the developing container 2 is partitioned in the vertical direction into the developing chamber 3 and the stirring chamber 4 has been described as an example, but the present invention is not limited to this configuration. That is, the present invention can also be applied to a lateral stirring type developing device in which the developing container 2 is partitioned into the developing chamber 3 and the stirring chamber 4 in the horizontal direction. In this embodiment, the supply and recovery of the developer to the developing sleeve are divided into the developing chamber 3 and the stirring chamber 4. However, for example, the supply and recovery may be performed in the developing chamber 3.

  In the above-described embodiment, a pair of magnetic poles (repulsive poles) having the same polarity are arranged next to each other (N1 and N2 in FIG. 2) to form a repulsive magnetic field (magnetic flux density of 50 gauss or less). Or S5 and S3 in FIG. 9). However, when the repulsive magnetic field is formed, there may be a case where a different polarity is generated between the pair of magnetic poles having the same polarity, and the magnetic flux density is extremely small (the magnetic flux density is 50 gauss or less). Alternatively, there may be a case where a magnetic pole having a different polarity with a very small magnetic flux density is provided between the repulsive poles. For example, a very small S pole may be disposed between the repulsive poles N1 and N2. In the present invention, including those cases, the repulsive poles N1 and N2 are called a pair of magnetic poles having the same polarity and arranged adjacent to each other. That is, even when the magnetic pole S having a different polarity from the repulsive pole having a very small magnetic force is disposed between the repelling poles N1 and N2, the repelling poles N1 and N2 are paired with a pair of adjacent magnetic poles. I'm calling.

2 ... developing container, 3 ... first chamber (developing chamber), 4 ... second chamber (stirring chamber), 5 ... first conveying means (developing screw), 6 ... second conveying means (stirring screw), 8 ... developing Sleeve, 8A ... First developing sleeve (upstream developing sleeve), 8B ... Second developing sleeve (downstream developing sleeve), 9 ... Magnetic field generating means (magnet roller), 9A ... First magnetic field generating means (upstream magnet roller), 9B ... Second magnetic field generating means (downstream magnet roller), 10Y (10M to 10K) ... image carrier (photosensitive drum), 11 ... magnetic member (magnetic plate), 12 ... magnet member (magnetic seal member), 12A ... first Magnet member (upstream magnetic seal member), 12B ... second magnet member (downstream magnetic seal member), 15 ... third transfer means (transfer screw)

Claims (10)

A developer container containing a developer containing a non-magnetic toner and a magnetic carrier;
A developing sleeve which is arranged to be partially exposed from the developing container and rotates;
A magnetic field generating means provided in a non-rotating manner inside the developing sleeve and having a plurality of magnetic poles arranged in the circumferential direction for carrying the developer in a developer carrying region formed on the surface of the developing sleeve;
The end of the developing sleeve in the rotational axis direction outside the developer carrying region is provided so as to face along the peripheral surface of at least a part of the developing sleeve on the non-exposed portion side, and the end faces the end. A magnet member capable of forming magnetic spikes of developer between the peripheral surface,
A conveying member that is disposed to face the developing sleeve at a position for collecting the developer from the developing sleeve and conveys the developer in the rotation axis direction of the developing sleeve;
The magnetic field generating means is arranged side by side in the circumferential direction of the developing sleeve so as to form a repelling magnetic field on the peripheral surface of the developing sleeve, and a pair of repelling magnetic poles having the same polarity and a pair of repelling magnetic poles An upstream magnetic pole disposed on the upstream side in the rotation direction of the developing sleeve,
The magnetic field generating means is configured such that at least the end of the pair of repulsive magnetic poles at the end of the transport member on the downstream side in the transport direction has an end edge of the developing sleeve that is closer to the developer carrying region side of the magnet member. Protruding to the outside on the end side, and the end of the upstream magnetic pole protrudes to the inside of the inner end edge outside the developer carrying region,
A developing device. The developer container forms a circulation path through which the developer is circulated in communication with the first chamber and a first chamber that supplies the developer to the developer sleeve, and delivers the developer to and from the first chamber. And a second chamber for collecting the developer carried on the developing sleeve without passing through the first chamber,
A first conveying means provided in the first chamber for conveying the developer in the first chamber in one direction,
The transport member is a second transport unit that is provided in the second chamber and transports the developer in the second chamber in a direction opposite to the first transport unit.
Of the end portions of the magnetic field generating means, at least on the downstream side in the developer transport direction of the second transport means, the end portions of the pair of repulsive magnetic poles are from the inner edge of the magnet member on the developer carrying region side. Projecting outward on the end side of the developing sleeve, and the end of the upstream magnetic pole projects inward from the inner end edge outside the developer carrying region,
The developing device according to claim 1. The developer container forms a circulation path through which the developer is circulated in communication with the first chamber and a first chamber that supplies the developer to the developer sleeve, and delivers the developer to and from the first chamber. And a second chamber that forms a recovery path for recovering the developer carried on the developing sleeve without passing through the first chamber,
A first conveying means provided in the first chamber for conveying the developer in the first chamber in one direction;
A second conveying means provided in the second chamber for conveying the developer in the second chamber in a direction opposite to the first conveying means,
The transport member is provided in the second chamber on a side closer to the developing sleeve than the second transport unit, and transports the developer in the second chamber in a direction opposite to the second transport unit. And
Out of the end portions of the magnetic field generating means, at least on the downstream side in the developer transport direction of the third transport means, the end portions of the pair of repulsive magnetic poles are from the inner edge of the magnet member on the developer carrying region side. Projecting outward on the end side of the developing sleeve, and the end of the upstream magnetic pole projects inward from the inner end edge outside the developer carrying region,
The developing device according to claim 1, wherein Opposite to the magnetic field generating means via the developing sleeve, it is provided between the developer carrying region and the inner edge of the magnet member, and a magnetic spike of the developer can be formed between the developing sleeve. Equipped with a magnetic member,
The developing device according to claim 1, wherein Both end portions of the pair of repulsive magnetic poles project toward the end portion side of the developing sleeve from the inner end edge of the magnet member on the developer carrying region side with respect to the rotation axis direction of the developing sleeve, and both ends of the upstream magnetic pole Part protrudes inward from the inner edge outside the developer carrying region,
The developing device according to claim 1, wherein A developer container containing a developer containing a non-magnetic toner and a magnetic carrier;
A first developing sleeve that is arranged to be partially exposed from the developing container and rotates;
A second developing sleeve arranged in parallel with the first developing sleeve so as to be partially exposed from the developing container and to which a developer carried on the first developing sleeve is delivered;
A first magnetic field that is provided non-rotatingly inside the first developing sleeve and has a plurality of magnetic poles arranged in the circumferential direction for carrying the developer in a first developer carrying region formed on the surface of the first developing sleeve. Generating means;
A second magnetic field in which a plurality of magnetic poles, which are provided non-rotatingly inside the second developing sleeve and carry a developer in a second developer carrying region formed on the surface of the second developing sleeve, are arranged in the circumferential direction. Generating means;
The end of the first developing sleeve outside the first developer carrying region in the rotational axis direction is provided so as to face along the peripheral surface of at least a part of the first developing sleeve on the non-exposed portion side, A first magnet member capable of forming magnetic spikes of developer between the opposing peripheral surfaces of the end portions of the first developing sleeve;
The end of the second developing sleeve outside the second developer carrying region in the rotational axis direction is provided so as to face along the circumferential surface of at least a part of the non-exposed portion side of the second developing sleeve, A second magnet member capable of forming magnetic spikes of developer between the opposing peripheral surfaces of the end portions of the second developing sleeve;
A conveying member that is disposed opposite to the second developing sleeve at a position for collecting the developer from the second developing sleeve and conveys the developer in the rotation axis direction of the second developing sleeve;
The second magnetic field generating means is arranged side by side in the circumferential direction of the second developing sleeve to form a repelling magnetic field on the peripheral surface of the second developing sleeve, and a pair of repelling magnetic poles having the same polarity, An upstream magnetic pole disposed upstream of the pair of repelling magnetic poles in the second developing sleeve rotation direction;
In the second magnetic field generating means, at least the end of the transport member downstream in the transport direction, the ends of the pair of repulsive magnetic poles are the inner edges of the second magnet member on the second developer carrying region side. More than the end of the second developing sleeve, and the end of the upstream magnetic pole protrudes inward of the inner edge of the second magnet member outside the second developer carrying region.
A developing device. The developer container forms a circulation path that communicates with the first chamber and circulates the developer in a first chamber that supplies the developer to the second developing sleeve, and supplies the developer between the first chamber and the first chamber. And having a second chamber for collecting the developer carried on the first developing sleeve without passing through the first chamber,
A first conveying means provided in the first chamber for conveying the developer in the first chamber in one direction;
A second conveying means provided in the second chamber for conveying the developer in the second chamber in a direction opposite to the first chamber;
The conveying member is provided in the second chamber closer to the first developing sleeve than the second conveying means, and conveys the developer in the second chamber in the opposite direction to the second conveying means. Transport means,
Among the end portions of the second magnetic field generating means, at least on the downstream side in the developer transport direction of the third transport means, the end portions of the pair of repulsive magnetic poles are the second developer carrying region of the second magnet member. Projecting to the outside on the end side of the second developing sleeve from the inner end edge on the side, and projecting the end of the upstream magnetic pole to the inside of the inner end edge outside the second developer carrying region,
The developing device according to claim 6. The first magnetic field generating means is arranged side by side in the circumferential direction of the first developing sleeve to form a repelling magnetic field on the peripheral surface of the first developing sleeve, and a pair of repelling magnetic poles having the same polarity, An upstream magnetic pole of the first magnetic field generating means arranged upstream of the pair of repulsive magnetic poles in the first developing sleeve rotation direction,
The first magnetic field generating means has at least one end of the pair of repulsive magnetic poles of the first magnetic field generating means on the downstream side in the transport direction of the transport member. It protrudes to the outside on the end side of the first developing sleeve from the inner end edge on the region side, and the end of the upstream magnetic pole of the first magnetic field generating means is outside the first developer carrying region of the first magnet member. Projecting inward from the inner edge,
The developing device according to claim 6, wherein: A rotating image carrier provided opposite to the first developing sleeve and the second developing sleeve that are partially exposed from the developing container;
The first developing sleeve is provided downstream of the second developing sleeve in the rotation direction of the image carrier.
The developing device according to claim 6, wherein The first magnet member is provided at both ends of the first developing sleeve,
The second magnet member is provided at both ends of the second developing sleeve,
The developing device according to any one of claims 6 to 9, wherein the developing device.

Images