JP6237602B2 - Developing device and image forming apparatus including the same - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine and a developing device used therefor, and more particularly, to a method for preventing leakage of developer from a developing device using a magnetic developer.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, and a facsimile, a powder developer is mainly used, and an electrostatic latent image formed on an image carrier such as a photosensitive drum is used as a developer. A general process is to perform a fixing process after visualizing and transferring the toner image onto a recording medium.

  Developers are broadly divided into two-component developers composed of toner and a magnetic carrier (hereinafter also simply referred to as carrier) and one-component developers composed only of magnetic toner, and a regulating blade (developer regulating member). Thus, triboelectric charging of the developer carried on the developing roller (developer carrying member) is promoted. As the regulating blade, there are known a configuration constituted by only a magnetic member, and a configuration in which a magnetic member is arranged in a portion (developer regulating portion) facing a developing roller based on a non-magnetic member.

  In such a developing device using a regulating blade, a part of the developer supplied to the developer regulating unit with the rotation of the developing roller passes through the regulating blade and forms a thin developer layer on the developing roller. However, most of the remaining developer rides on the regulating blade and is returned to the developing device. At this time, the developer returned into the developing device tends to go to both ends in the longitudinal direction of the developing roller and the regulating blade. Accordingly, it is necessary to prevent leakage of the developer from the developing device in this portion.

  Conventionally, there has been proposed a method for preventing leakage of a developer by providing magnetic seal members at both ends in the longitudinal direction of a developing device. This is because a magnetic brush is formed in the gap between the magnetic seal member and the developing roller by a magnetic field between the fixed magnet body arranged in the developing roller and the magnetic seal member, and the gap is closed with the formed magnetic brush. It prevents the leakage of the agent.

  For example, Patent Document 1 discloses a developing device provided with a magnetic seal member in which NS poles are magnetized in multiple magnetic poles in the circumferential direction of the developing roller. Further, in Patent Document 2, a plurality of N poles and S poles are alternately magnetized on the inner peripheral surface of the magnetic seal member, and the arrangement direction of the magnetic poles is parallel to the longitudinal direction of the developing roller. A developing device is disclosed. Furthermore, Patent Document 3 discloses a developing device in which the magnetic poles of the magnetic seal member are arranged so that the same (same polarity) magnetic poles face the magnetic poles of the fixed magnet body arranged inside the developing roller. Yes.

Japanese Patent Laid-Open No. 11-133750 Japanese Patent No. 4231091 JP 2006-317564 A

  With recent increases in image formation speed and finer developer particles to improve image quality, it is required to more reliably leak the developer from the end of the developing roller.

  Here, as in Patent Document 3, when the same magnetic pole of the magnetic seal member is arranged to face the magnetic pole of the fixed magnet body, between the magnetic poles of the magnetic seal member facing the position between the poles of the fixed magnet body. The magnetic field of the sealing member is most reduced.

  In view of the above problems, an object of the present invention is to provide a developing device that can improve the sealing performance of a magnetic seal member easily and at low cost, and an image forming apparatus including the developing device.

  In order to achieve the above object, a first configuration of the present invention is a developing device including a housing, a developer carrier, a magnet member, and a magnetic seal member. The housing stores a magnetic developer. The developer carrier is rotatably supported by the casing and carries the developer on the outer peripheral surface. The magnet member is fixed inside the developer carrier and has a plurality of developer carrier-side magnetic poles along the circumferential direction of the developer carrier. The magnetic seal member is disposed at a predetermined interval along the outer peripheral surface of both end portions in the longitudinal direction of the developer carrier, and a plurality of magnetic seal side magnetic poles are disposed on the surface facing the developer carrier. The magnetic seal-side magnetic pole is disposed on the magnetic seal member so that the same pole is opposed to the developer carrier-side magnetic pole, and between the adjacent magnetic seal-side magnetic poles facing the position between the poles of the developer carrier-side magnetic pole. A gap is provided.

  According to the first configuration of the present invention, since the decrease in the magnetic field of the magnetic seal member can be suppressed between the magnetic poles of the magnetic seal member facing the position between the poles of the developer carrier side magnetic pole, the magnetic seal member is disposed on the magnetic seal member. A strong magnetic force is not required for the magnetic seal side magnetic pole, and good sealing performance can be maintained using a magnet magnetized to a relatively small magnetic flux density. Further, it is possible to effectively suppress the leakage of the developer accompanying the increase in the image forming speed and the finer development of the developer.

1 is a schematic cross-sectional view of an image forming apparatus 100 including a developing device 4 according to an embodiment of the present invention. The top view and front view of the developing device 4 of the first embodiment of the present invention. Side surface sectional drawing of the image development apparatus 4 of 1st Embodiment. Enlarged view around the developing roller 25 in FIG. Enlarged view of the magnetic seal member 33a in FIG. 4 is a perspective view of the periphery of the magnetic seal member 33a in FIG. The perspective view which looked at the magnetic seal member 33a periphery of the developing device 4 of 2nd Embodiment of this invention from the inner side of the developing device 4. FIG. The front view which looked at the magnetic seal member 33a periphery of the developing device 4 of 2nd Embodiment from the direction perpendicular | vertical to the axial direction of the developing roller 25. The graph which shows the relationship between the presence or absence of the clearance gap 43 between the magnetic poles of the magnetic seal side magnetic poles 40a and 40b and the magnetic flux density in Example 1. The graph which shows the relationship between the presence or absence of the clearance gap 43 between the magnetic poles of the magnetic seal side magnetic poles 40a and 40b and the magnetic flux density in Example 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 including a developing device 4 according to an embodiment of the present invention. In the image forming apparatus (for example, a monochrome printer) 100, when a copying operation is performed, an electrostatic latent image is formed based on document image data transmitted from a personal computer (PC) (not shown) in the image forming unit 9 in the apparatus main body. Then, the developing device 4 attaches toner to the electrostatic latent image to form a toner image. The toner is supplied to the developing device 4 from the toner container 5. In the image forming apparatus 100, an image forming process is performed on the photosensitive drum 1 while rotating the photosensitive drum 1 clockwise in FIG.

  The image forming unit 9 includes a charging device 2, an exposure unit 3, a developing device 4, a transfer roller 6, a cleaning device 7, and a charge eliminating device (not shown) along the rotation direction (clockwise direction) of the photosensitive drum 1. ) Is arranged. The photosensitive drum 1 is formed, for example, by laminating a photosensitive layer on an aluminum drum, and the charging device 2 uniformly charges the surface. Then, an electrostatic latent image with attenuated charging is formed on the surface that has received a laser beam from the exposure unit 3 described later. The photosensitive layer is not particularly limited, but for example, amorphous silicon (a-Si) having excellent durability is preferable.

  The charging device 2 uniformly charges the surface of the photosensitive drum 1. For example, the charging device 2 is a corona discharge device that discharges by applying a high voltage using a thin wire or the like as an electrode. Instead of the corona discharge device, a contact-type charging device that applies a voltage in a state where a charging member typified by a charging roller is in contact with the surface of the photoreceptor may be used. The exposure unit 3 irradiates the photosensitive drum 1 with a light beam (for example, a laser beam) based on the image data, and forms an electrostatic latent image on the surface of the photosensitive drum 1.

  The developing device 4 forms toner images by attaching toner to the electrostatic latent image on the photosensitive drum 1. In the present embodiment, a magnetic one-component developer (hereinafter also referred to as developer or toner) made of magnetic toner is accommodated in the developing device 4. Details of the developing device 4 will be described later. The cleaning device 7 includes a cleaning roller, a cleaning blade, and the like that are in line contact with the longitudinal direction of the photosensitive drum 1 (a direction perpendicular to the paper surface in FIG. 1). After the toner image is transferred (transferred) to the paper, The toner remaining on the surface of the photosensitive drum 1 (residual toner) is removed.

  A sheet is conveyed from the sheet storage unit 10 to the image forming unit 9 at a predetermined timing via the sheet conveyance path 11 and the resist roller pair 13 toward the photosensitive drum 1 on which the toner image is formed as described above. . The transfer roller 6 shifts (transfers) to the sheet conveyed through the sheet conveyance path 11 without disturbing the toner image formed on the surface of the photosensitive drum 1. Thereafter, in preparation for the subsequent formation of a new electrostatic latent image, residual toner on the surface of the photosensitive drum 1 is removed by the cleaning device 7, and the residual charge is canceled by the static eliminator.

  Then, the sheet on which the toner image is transferred is separated from the photosensitive drum 1, conveyed to the fixing device 8, and heated and pressed to fix the toner image on the sheet. The paper that has passed through the fixing device 8 passes through the discharge roller pair 14 and is discharged to the paper discharge unit 15.

  2A and 2B are a plan view and a front view of the developing device 4 according to the first embodiment of the present invention, and FIG. 3 is a side sectional view of the developing device 4 according to the first embodiment. In FIG. 2A, for the sake of convenience, a state in which the top cover is removed and the inside can be seen is represented. As shown in FIGS. 2 and 3, the inside of the housing 20 is partitioned into a first storage chamber 21 and a second storage chamber 22 by a partition wall 20 a formed integrally with the housing 20. A first stirring screw 23 is disposed in the first storage chamber 21, and a second stirring screw 24 is disposed in the second storage chamber 22.

  Each of the first stirring screw 23 and the second stirring screw 24 has a configuration in which spiral blades are provided around a supporting shaft (rotating shaft), and is rotatably supported by the housing 20 in a state of being parallel to each other. . In addition, as shown to Fig.2 (a), the partition wall 20a does not exist in the both ends of the longitudinal direction of the housing 20 which is the axial direction of the 1st stirring screw 23 and the 2nd stirring screw 24, and the 1st stirring screw 23, the toner can be transferred between the second stirring screws 24. As a result, the first stirring screw 23 transports the developer in the first storage chamber 21 in the direction of arrow P while stirring the developer, and transports it to the second storage chamber 22. The developer conveyed to the chamber 22 is conveyed in the direction of arrow Q while being agitated and supplied to the developing roller 25.

  The developing roller 25 rotates in accordance with the rotation of the photosensitive drum 1 (see FIG. 1), thereby supplying the developer to the photosensitive layer of the photosensitive drum 1. A fixed magnet body 27 made of a permanent magnet having a plurality of magnetic poles is fixed inside the developing roller 25. A magnetic brush is formed by attaching (carrying) developer to the surface of the developing roller 25 by the magnetic force of the fixed magnet body 27. The developing roller 25 is rotatably supported by the housing 20 in a state parallel to the first stirring screw 23 and the second stirring screw 24. The first stirring screw 23, the second stirring screw 24, and the developing roller 25 are rotationally driven by a motor (not shown).

  The regulating blade 29 is formed such that its longitudinal direction (left-right direction in FIG. 2) is larger than the maximum developing width, and is supplied to the photosensitive drum 1 by being arranged at a predetermined interval from the developing roller 25. A restricting portion 30 for restricting the developer amount is formed. As the material of the regulating blade 29, magnetic SUS (stainless steel) or the like is used.

  A developer amount detection sensor (not shown) for detecting the amount of developer stored in the housing 20 is provided on the bottom surface of the second storage chamber 22 facing the second stirring screw 24. In accordance with the detection result of the developer amount detection sensor, the developer stored in the container 5 (see FIG. 1) is supplied into the housing 20 through the developer supply port 20b provided in the upper portion of the housing 20. .

  DS rollers 31 a and 31 b are rotatably inserted on the rotation shaft of the developing roller 25. The DS rollers 31 a and 31 b strictly regulate the distance between the developing roller 25 and the photosensitive drum 1 by contacting both end portions of the outer peripheral surface of the photosensitive drum 1. The DS rollers 31a and 31b have built-in bearings, and the drum surface can be prevented from being worn by being rotated by being driven by the photosensitive drum 1. Further, magnetic seal members 33a and 33b for preventing the leakage of the developer from the gap between the housing 20 and the developing roller 25 are disposed at both ends of the developing roller 25.

  FIG. 4 is an enlarged view around the developing roller 25 in FIG. A method for regulating the amount of developer on the developing roller 25 will be described in detail with reference to FIG. As shown in FIG. 4, the fixed magnet body 27 has four magnetic poles 27a to 27d including S poles 27a and 27c and N poles 27b and 27d. A blade side magnet 35 is attached near the tip of the regulating blade 29. As shown in FIG. 2, the blade-side magnet 35 is attached over substantially the entire region in the longitudinal direction (left-right direction in FIG. 2) of the regulating blade 29 between the magnetic seal members 33 a and 33 b. The blade-side magnet 35 is in contact with the regulating blade 29 with the south pole facing downward, and the north pole is induced at the tip of the regulating blade 29. As a result, a magnetic field is generated in a direction attracting the restriction portion 30 between the fixed magnet body 27 and the south pole (regulation pole) 27a.

  By this magnetic field, a magnetic brush in which a developer is connected is formed between the regulating blade 29 and the developing roller 25, and the layer is regulated to a desired height when the magnetic brush passes through the regulating unit 30. On the other hand, the developer not used for forming the magnetic brush stays along the upstream (right) side surface of the regulating blade 29. After that, when the developing roller 25 rotates counterclockwise and the magnetic brush moves to a region (developing region) facing the photosensitive drum 1, a magnetic field is applied by the N pole (main pole) 27b. Contacts the surface of the photosensitive drum 1 to develop the electrostatic latent image.

  Further, when the developing roller 25 rotates counterclockwise, a magnetic field in the direction along the outer peripheral surface of the developing roller 25 is applied by the south pole (conveying pole) 27c, and is not used together with the magnetic brush for forming a toner image. The developed developer is collected on the developing roller 25. Further, the magnetic brush is detached from the developing roller 25 and dropped into the housing 20 at the defect portion 27e. Then, after being stirred and conveyed by the second stirring screw 24, a magnetic brush is formed again on the developing roller 25 by the magnetic field of the N pole (pump upper pole) 27d.

  Magnetic seal members 33a and 33b are disposed on the housing 20 surrounding both ends of the developing roller 25, respectively. In FIG. 4, only the magnetic seal member 33a is shown. As shown in FIG. 4, the magnetic seal members 33 a and 33 b are not in contact with the developing roller 25, i.e., are separated from the outer peripheral surface of the developing roller 25 by a predetermined distance (gap). It is arranged. The magnetic seal members 33a and 33b are disposed on the opposite side of the photosensitive drum 1 with the developing roller 25 interposed therebetween. Hereinafter, the magnetic seal member 33a will be described in detail, but the same applies to the magnetic seal member 33b.

  FIG. 5 is an enlarged view around the magnetic seal member 33a in FIG. In FIG. 5, illustration of the developing roller 25 and the fixed magnet body 27 is omitted. As shown in FIG. 5, the magnetic seal member 33a is formed by arranging magnetic seal side magnetic poles 40a, 40b with the N pole or S pole facing the inner peripheral surface side with a predetermined pitch width, and the magnetic field lines generated by the magnetic pole pattern. The developer sealability is improved by forming a magnetic brush along the surface. As the material of the magnetic seal side magnetic poles 40a and 40b, for example, anisotropic rubber magnets magnetized to a predetermined magnetic flux density or neodymium magnets are used. In FIG. 4, only the poles (S pole and N pole) on the inner peripheral surface side of the magnetic seal side magnetic poles 40a and 40b are shown.

  In the present embodiment, the magnetic seal side magnetic poles 40a and 40b of the magnetic seal member 33a are arranged to face the magnetic poles of the fixed magnet body 27 in the developing roller 25, and the magnetic poles of the fixed magnet body 27 facing each other. The (S pole 27a, N pole 27d) and the poles on the inner peripheral surface side of the magnetic seal side magnetic poles 40a, 40b of the magnetic seal member 33a are opposite to each other.

  As a result, the magnetic field lines run from the N pole 27d to the S pole 27a in the fixed magnet body 27, and the magnetic seal side magnetic pole 40b (N pole) to 40a (S pole) also in the magnetic seal member 33a. ) And the lines of magnetic force repel each other in the gap between the magnetic seal member 33a and the developing roller 25.

  In the space where the magnetic lines of force repel each other at the same polarity, a force for rejecting fine particles having a predetermined charge is formed. Accordingly, the positively charged developer is discharged by the removal force of the magnetic lines of force, and this prevents the developer from moving from the peripheral surface of the developing roller 25 toward both ends. The leakage of the developer from is effectively suppressed.

  In FIG. 4, the upper end portion of the magnetic seal member 33 a is in contact with the restriction blade 29 and the lower end portion of the magnetic seal member 33 a is a fixed magnet in order to preferentially suppress toner leakage near the restriction blade 29. It extends halfway through the N pole 27d of the body 27. Not limited to the configuration of FIG. 4, the lower end of the magnetic seal member 33 a may extend to the lower end of the N pole 27 d.

  By the way, the developer amount (magnetic brush amount) held on the magnetic seal member 33a is not only the magnetic field generated by the magnetic seal side magnetic poles 40a and 40b disposed on the magnetic seal member 33a, but also the fixed magnet body 27 and the magnetic field. It is affected by the magnetic field generated between the seal member 33a and the seal member 33a. When the same magnetic poles (magnetic seal side magnetic poles 40a, 40b) of the magnetic seal member 33a are arranged to face the magnetic poles (S pole 27a, N pole 27d) of the fixed magnet body 27, the fixed magnet body 27 It is known that the magnetic field of the magnetic seal member 33a is most reduced between the magnetic poles of the magnetic seal member 33a facing the inter-pole position.

  Therefore, in the present invention, the gap 43 is provided between the magnetic seal side magnetic poles 40a and 40b facing the position between the poles of the fixed magnet body 27 (the boundary between the S pole 27a and the N pole 27d in FIG. 4). With this configuration, end faces (free edges) are formed between the magnetic seal-side magnetic poles 40a and 40b. Since the magnetic brush is formed by concentrating the magnetic field on the end faces of the magnetic seal side magnetic poles 40a and 40b, the developing roller 25 and the magnetic seal member 33a are also formed between the magnetic seal side magnetic poles 40a and 40b where the magnetic field is most reduced. The gap can be filled with a magnetic brush.

  Therefore, a strong magnetic force is not required for the magnetic seal side magnetic poles 40a and 40b arranged on the magnetic seal member 33a, and a good sealing performance can be maintained using a rubber magnet or the like magnetized with a relatively small magnetic flux density. . Further, it is possible to effectively suppress the leakage of the developer even when the linear velocity of the developing roller 25 is increased in accordance with the increase in the image forming speed or when the developer is finely divided for improving the image quality. Can do.

  When the gap G of the gap 43 is too narrow, the magnetic field is not sufficiently concentrated on the end faces of the magnetic seal side magnetic poles 40a and 40b, and the sealing effect by the magnetic brush is reduced. On the other hand, when the gap G of the gap 43 is too wide, a gap is generated between the magnetic brushes formed on the end surfaces of the magnetic seal side magnetic poles 40a and 40b, and the developer leaks through the gap of the magnetic brush. Therefore, the gap G is preferably 1 mm or more and 2 mm or less where the magnetic brushes formed on the end faces of the magnetic seal side magnetic poles 40a and 40b overlap.

  When the interval between the developing roller 25 and the magnetic seal member 33a is wide, the developer is likely to leak from the gap between the developer held on the magnetic seal member 33a and the developing roller 25. On the other hand, when the distance between the developing roller 25 and the magnetic seal member 33a is narrow, the developer held on the magnetic seal member 33a fills the gap, so that the developer is difficult to leak. Therefore, the leakage of the developer can be more effectively suppressed by narrowing the interval between the developing roller 25 and the magnetic seal member 33a. However, if the gap is too narrow, the outer peripheral surface of the developing roller 25 may come into contact with the inner surface of the magnetic seal member 33a. Therefore, the distance between the developing roller 25 and the magnetic seal member 33a is preferably set to 0.1 mm or more and 0.5 mm or less.

  When the distance between the fixed magnet body 27 and the magnetic seal member 33a in the axial direction (left and right direction in FIG. 2) is large, the magnetic field between the fixed magnet body 27 and the magnetic seal member 33a becomes weak, so that the magnetic brush is held. The width is reduced, and the developer easily leaks from the gap between the developing roller 25 and the magnetic seal members 33a and 33b. On the other hand, when the axial distance is small, the developer holding amount increases and the holding width of the magnetic brush increases, so that the developer is difficult to leak.

  Therefore, the leakage of the developer can be more effectively prevented by narrowing the axial distance between the fixed magnet body 27 and the magnetic seal member 33a. Specifically, although it depends on the gap 43 between the magnetic seal side magnetic poles 40a and 40b and the strength of the magnetic flux density, the distance is preferably 1 mm or less.

  Further, by overlapping the magnetic seal member 33a and the fixed magnet body 27 in the axial direction, the magnetic brushes from the magnetic poles 27a to 27d of the fixed magnet body 27 are straightly formed in the radial direction of the fixed magnet body 27. Further, the movement of the developer carried on the developing roller 25 to both ends of the developing roller 25 can be more effectively regulated by extracting the magnetic force of the magnetic brush to the maximum. However, when the magnetic seal member 33a overlaps the developing area of the developing roller 25, the formation of the toner thin layer on the developing roller 25 is affected. Therefore, the magnetic seal member 33a and the fixed magnet body 27 are overlapped in the axial direction. The magnetic seal member 33a needs to be arranged in a range that does not cover the development area. Specifically, the overlap width is preferably 0.5 mm or less.

  6 is a perspective view of the periphery of the magnetic seal member 33a in FIG. 4 as viewed from the inside of the developing device 4 (right side in FIG. 4). In the present embodiment, as shown in FIG. 6, the magnetic seal side magnetic pole 40 a that is closest (uppermost) to the regulating blade 29 is disposed at a distance from the blade side magnet 35. This is because the layer thickness regulation of the magnetic brush on the developing roller 25 by the regulation blade 29 is prioritized over the sealing performance by the magnetic seal member 33a. That is, the blade side magnet 35 is extended to the end of the regulating blade 29 in order to reliably regulate the layer thickness of the magnetic brush at both ends of the developing roller 25, and the magnetic seal side magnetic pole 40a. This is to prevent the blade-side magnet 35 and the magnetic seal-side magnetic pole 40a from interfering with each other even when there is a dimensional tolerance or a positional deviation when the magnetic seal-side magnetic pole 40a is attached to the magnetic seal member 33a.

  7 is a perspective view of the periphery of the magnetic seal member 33a of the developing device 4 according to the second embodiment of the present invention as viewed from the inside of the developing device 4 (right side of FIG. 4), and FIG. 8 is a developing device of the second embodiment. 4 is a front view of the periphery of the magnetic seal member 33a of No. 4 as viewed from a direction perpendicular to the axial direction of the developing roller 25. FIG. In the present embodiment, the magnetic seal-side magnetic poles 40a and 40b are first magnetic poles 45a and 45b that contact the magnetic seal member 33a, respectively, and second magnetic poles 47a and 47b stacked on the surfaces of the first magnetic poles 45a and 45b. It is configured. Since the structure of the other part of the developing device 4 is the same as that of the first embodiment, description thereof is omitted. In FIG. 8, only the poles on the outer peripheral surface side of the first magnetic poles 45a and 45b and the second magnetic poles 47a and 47b constituting the magnetic seal side magnetic poles 40a and 40b are displayed.

  As shown in FIG. 7, the first magnetic pole 45a of the magnetic seal side magnetic pole 40a has the same polarity as the magnetic seal side magnetic pole 40a (see FIG. 6) of the first embodiment, and the inner peripheral surface side is the S pole and the outer peripheral surface side is the same. N pole. That is, the same polarity of the S pole 27a of the fixed magnet body 27 and the pole on the inner peripheral surface side of the first magnetic pole 45a are opposed to each other. The second magnetic pole 47a has a different polarity from the first magnetic pole 45a, and the inner peripheral surface side is an N pole and the outer peripheral surface side is an S pole.

  On the other hand, the first magnetic pole 45b of the magnetic seal side magnetic pole 40b has the same polarity as the magnetic seal side magnetic pole 40b (see FIG. 6) of the first embodiment, and the inner peripheral surface side is the N pole and the outer peripheral surface side is the S pole. That is, the N pole 27d of the fixed magnet body 27 and the pole on the inner peripheral surface side of the first magnetic pole 45b are opposite to each other. The second magnetic pole 47b has a different polarity from the first magnetic pole 45b, and has an S pole on the inner peripheral surface side and an N pole on the outer peripheral surface side.

  According to the configuration of the present embodiment, as in the first embodiment, by providing the gap 43 between the magnetic seal side magnetic poles 40a and 40b, the end face (free edge) is provided between the magnetic seal side magnetic poles 40a and 40b. ) Is formed. Since the magnetic brush is formed by concentrating the magnetic field on the end faces of the magnetic seal side magnetic poles 40a and 40b, the developing roller 25 and the magnetic seal member 33a are also formed between the magnetic seal side magnetic poles 40a and 40b where the magnetic field is most reduced. Can be filled with a magnetic brush, and good sealing performance can be maintained using a rubber magnet or the like magnetized with a relatively small magnetic flux density.

  Further, the magnetic field lines from the N pole 27d to the S pole 27a of the fixed magnet body 27 and the first magnetic pole of the magnetic seal side magnetic pole 40a from the magnetic pole (N pole) on the inner peripheral surface side of the first magnetic pole 45b of the magnetic seal side magnetic pole 40b. The magnetic lines of force directed to the magnetic pole (S pole) on the inner peripheral surface side of 45a are repelled from each other, and the positively charged developer is discharged by the rejecting force of the magnetic lines.

  Further, in the present embodiment, second magnetic poles 47a and 47b having different polarities are stacked on the first magnetic poles 45a and 45b, respectively. Therefore, as shown in FIG. 8, the first magnetic pole 45a and the second magnetic pole 47a During this time, a magnetic line of force (broken arrow) occurs between the first magnetic pole 45b and the second magnetic pole 47b. The wraparound of the magnetic field lines makes it easier for the magnetic field to concentrate on the end surfaces of the magnetic seal side magnetic poles 40a and 40b. Therefore, the developing roller 25 and the magnetic seal member 33a are also between the magnetic seal side magnetic poles 40a and 40b. Can be sufficiently filled with a magnetic brush.

  Therefore, since the movement of the developer from the peripheral surface of the developing roller 25 toward both ends is more reliably prevented as compared with the first embodiment, the leakage of the developer from the end of the developing roller 25 is more effectively performed. Can be suppressed. The preferred range of the gap G, the gap between the developing roller 25 and the magnetic seal member 33a, and the overlap width between the magnetic seal member 33a and the fixed magnet body 27 are the same as in the first embodiment.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiments, as shown in FIGS. 4 and 7, two pairs of magnetic poles face each other between the magnetic seal member 33 a and the fixed magnet body 27. The uppermost magnetic seal side magnetic pole 40a of the magnetic seal member 33a (the first magnetic pole 45a in the second embodiment) and the regulation pole 27a of the fixed magnet body 27 facing this are arranged so that the S poles face each other. The N poles of the magnetic seal side magnetic pole 40b (first magnetic pole 45b in the second embodiment) of the magnetic seal member 33a and the pumping pole 27d of the fixed magnet body 27 opposed to the magnetic seal side magnetic pole 33b are opposed to each other. However, the present invention is not limited to two pairs of magnetic poles facing each other, and may be three or more pairs depending on the situation.

  In addition, the present invention is not limited to a developing device that uses a magnetic one-component developer, but can be applied to a seal structure of a developing device that uses a two-component developer including a toner and a magnetic carrier. Furthermore, as a developing device using a two-component developer, a magnetic roller (developer carrier) and a developing roller (toner carrier) are provided, and only the toner is transferred onto the developing roller while leaving the carrier on the magnetic roller. The present invention can be applied in exactly the same manner to a sealing structure at both ends of a magnetic roller in a developing device in which a toner thin layer is formed and toner is attached to an electrostatic latent image on a photoreceptor by an alternating electric field. Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

  The relationship between the presence or absence of the gap 43 between the magnetic seal side magnetic poles 40a and 40b and the magnetic flux density was investigated. The test method is the same as the developing device 4 (present invention 1) of the first embodiment using magnetic seal members 33a and 33b arranged with a gap 43 between the magnetic seal side magnetic poles 40a and 40b as shown in FIG. The developing device 4 (comparative example) using the magnetic seal members 33a and 33b arranged in contact with the magnetic seal side magnetic poles 40a and 40b was produced, and the magnetic flux densities in the circumferential direction of the magnetic seal members 33a and 33b were measured, respectively. . And the fall degree of the magnetic flux density of the location facing the position between the poles 27a and 27d of the drawing pole 27d of the fixed magnet body 27 was compared. The results are shown in FIG.

  As shown in FIG. 9, in the developing device 4 (data series of ◆) of the present invention 1 in which the gap 43 is provided between the magnetic seal side magnetic poles 40a and 40b, the magnetic field of the magnetic seal member 33a is reduced between the magnetic poles (circumference). A magnetic flux density of 20 mT was also secured at the direction position 80 deg).

  On the other hand, in the developing device 4 of the comparative example in which the gap 43 is not provided between the magnetic seal side magnetic poles 40a and 40b (data series of ○), the magnetic flux is between the magnetic poles (circumferential position 80 deg) where the magnetic field of the magnetic seal member 33a is most reduced. The density decreased to about 10 mT.

  Therefore, when the gap 43 is provided between the magnetic seal side magnetic poles 40a and 40b, the developer leakage is more effective than when the magnetic seal side magnetic poles 40a and 40b are arranged in contact with each other without providing the gap 43. It can be seen that it can be suppressed.

  A gap 43 is provided between the magnetic seal side magnetic poles 40a and 40b using the two-layer magnetic seal side magnetic poles 40a and 40b composed of the first magnetic poles 45a and 45b and the second magnetic poles 47a and 47b as shown in FIG. The developing device 4 of the second embodiment using the magnetic seal members 33a and 33b (present invention 2) and the magnetic seal-side magnetic poles 40a and 40b having a single-layer structure similar to those of the first embodiment are placed in contact with each other. The developing device 4 (comparative example) using the magnetic seal members 33a and 33b was produced, and the magnetic flux density in the circumferential direction of the magnetic seal members 33a and 33b was measured. And the fall degree of the magnetic flux density of the location facing the position between the poles 27a and 27d of the drawing pole 27d of the fixed magnet body 27 was compared. The results are shown in FIG.

  As shown in FIG. 10, magnetic seal side magnetic poles 40a and 40b in which second magnetic poles 47a and 47b having different polarities are stacked on the surfaces of the first magnetic poles 45a and 45b are used, and a gap 43 is formed between the magnetic seal side magnetic poles 40a and 40b. In the provided developing device 4 of the present invention 2 (data series of ◆), a magnetic flux density of 30 mT or more is ensured even between the magnetic poles where the magnetic field of the magnetic seal member 33a is most reduced (circumferential position 80 deg), and the magnetic seal side magnetic pole The magnetic flux density was increased by 20 mT or more as compared with the developing device 4 of the comparative example in which the gap 43 was not provided between 40a and 40b (data series of ○).

  Accordingly, the magnetic seal side magnetic poles 40a and 40b having a two-layer structure in which the second magnetic poles 47a and 47b having different polarities are stacked on the surfaces of the first magnetic poles 45a and 45b are used, and the gap 43 is provided between the magnetic seal side magnetic poles 40a and 40b. According to the second aspect of the present invention, the developer leakage can be suppressed more effectively than in the first aspect of the present invention using the single-layer magnetic seal side magnetic poles 40a and 40b.

  The present invention can be used for a seal mechanism of a developing device using a magnetic developer. By utilizing the present invention, a developing device capable of effectively suppressing leakage of developer using a magnetic seal member magnetized to a relatively small magnetic flux density even when a carrier having a high degree of circularity is used. Can be provided.

4 Developing device 9 Image forming unit 20 Housing (housing)
23 1st stirring screw 24 2nd stirring screw 25 Developing roller (developer carrier)
27 Fixed magnet body (magnet member)
27a to 27d Magnetic pole (developer carrier side magnetic pole)
27e Deficient portion 29 Regulating blade 33a, 33b Magnetic seal member 35 Blade side magnet 40a, 40b Magnetic seal side magnetic pole 43 Clearance 45a, 45b First magnetic pole 47a, 47b Second magnetic pole 100 Image forming apparatus

Claims (9)

A housing for storing a magnetic developer;
A developer carrying member rotatably supported by the housing and carrying a developer on the outer peripheral surface;
A magnet member fixed inside the developer carrier and having a plurality of developer carrier-side magnetic poles along a circumferential direction of the developer carrier;
A magnetic seal member that is disposed at predetermined intervals along the outer peripheral surface of both ends in the longitudinal direction of the developer carrier, and a plurality of magnetic seal side magnetic poles are disposed on a surface facing the developer carrier;
In a developing device comprising:
The magnetic seal-side magnetic pole is disposed on the magnetic seal member so that the same pole is opposed to the developer-carrying-side magnetic pole, and the magnetic pole adjacent to the magnetic pole adjacent to the position between the poles of the developer-carrying-side magnetic pole. A developing device characterized in that a gap is provided between seal-side magnetic poles.   The magnetic seal-side magnetic pole is composed of a first magnetic pole opposite to the developer carrier-side magnetic pole, and a second magnetic pole having a different polarity from the first magnetic pole laminated on the surface of the first magnetic pole. The developing device according to claim 1. The developing device according to claim 1, wherein a gap between the magnetic seal side magnetic poles is 1 mm or more and 2 mm or less.   The developing device according to claim 1, further comprising a regulating blade formed of a magnetic material disposed at a predetermined interval with respect to the developer carrying member.   The regulation blade is provided with a blade-side magnet, and the blade-side magnet is arranged with the same pole as the developer carrier-side magnetic pole facing the regulation blade facing the tip end of the regulation blade. The developing device according to claim 4.   The developing device according to claim 5, wherein the blade-side magnet and the magnetic seal-side magnetic pole closest to the regulating blade are arranged at a predetermined interval. The developing device according to claim 1, wherein a distance between the magnetic seal member and an outer peripheral surface of the developer carrying member is 0.1 mm or more and 0.5 mm or less.   The developing device according to claim 1, wherein an overlap width between the magnetic seal member and the magnet member in the axial direction of the developer carrier is 0.5 mm or less.   An image forming apparatus comprising the developing device according to claim 1.

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