JP2005189754A - Developing device and image forming apparatus with the device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device in which a toner thin layer can steadily be formed on the surface of a developing roller and image deterioration can be prevented and to provide an image forming apparatus with the developing device. <P>SOLUTION: Magnetic sealing members 29 are disposed at the ends of a developing sleeve 26 in its lengthwise direction X. The internal edge 29a of each of the magnetic sealing members 29 facing the peripheral face of the developing sleeve 26 is formed in the shape of a curved face. Since magnetic force is weakened at the internal edge 29a formed in the shape of the curved face, magnetic force from a fixed magnet roller 25 does not concentrate on the internal edge 29a. In addition, each of the effective magnetized ends 25b of the fixed magnet roller 25 is located inside the internal edge 29a of the corresponding magnetic sealing member 29 in the lengthwise direction X of the developing sleeve 26. Since magnetic brush resulting from the napping of the magnetic toner T is formed inside the internal edge 29a of the corresponding magnetic sealing member 29, the thickness of a toner layer on the peripheral face of the developing sleeve 26 does not increase. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a developing device that performs development by electrophotographic development using a magnetic developer (or magnetic toner), and in particular, magnetic toner leaks from a longitudinal end portion of a developing sleeve containing a fixed magnet roller. The present invention relates to a developing device using a magnetic seal member for preventing the occurrence of the trouble and an image forming apparatus having the same.

  In general, in an image forming apparatus such as an electrophotographic developing printer, a facsimile, or a copying machine, a magnetic toner is used to form a toner image on the surface of a photoconductor on which an electrostatic latent image based on image data of an original is formed. There is provided a developing device that accommodates a one-component magnetic developer composed of a two-component magnetic developer formed by mixing a magnetic carrier and a toner.

  Further, as a developing device for developing using a one-component magnetic developer, electrostatic toner on the latent image carrier is caused by friction between magnetic toner particles and friction between a developing sleeve as a developer carrier and magnetic toner particles. A charge opposite in polarity to the image charge and the development reference potential is applied to the magnetic toner, and this magnetic toner is applied very thinly on the developing sleeve, so that the image bearing member and the developing sleeve are opposed to the developing region. The magnetic toner is transported and the magnetic toner flies and adheres to the electrostatic latent image on the surface of the photoreceptor due to the potential difference between the surface of the photoreceptor and the developing bias applied between the developing roller and the photoreceptor in the development area. It is generally known to develop and visualize an electrostatic latent image as a toner image.

  Conventionally, in such a developing device, a seal member for preventing the toner from flowing out of the developing area is provided. As the seal member, for example, an elastic body such as felt or foam rubber is used. A configured elastic seal member is used. This elastic seal member is attached to both ends in the longitudinal direction outside the developing region of the developing roller composed of a developing sleeve containing a fixed magnet, and presses the elastic sealing member against the outer peripheral surface of the developing roller. This prevents the toner from flowing out.

  However, in the developing device having such a configuration, as described above, since the elastic seal member is in pressure contact with the outer peripheral surface of the developing roller, a large load is applied to the motor that rotates the developing roller during development. Therefore, rotation unevenness occurs in the developing roller, which may adversely affect image formation. In addition, there is a problem that the elastic seal member deteriorates due to contact with the developing roller, and the sealing performance deteriorates.

  Therefore, in order to solve these problems, it is a common practice to prevent the toner from flowing out by disposing magnetic seal members made of a magnetic material at regular intervals at both ends in the longitudinal direction of the developing roller. Yes. In this case, the magnetic toner carried on the developing sleeve by the magnetic force of the fixed magnet is restrained by the magnetic field formed in the gap between the end of the fixed magnet and the magnetic seal member, and the developing sleeve and the magnetic seal member By forming a magnetic brush due to the rising of magnetic toner in the gap, the magnetic toner that is about to flow out is blocked and a sealing action is performed.

  However, when using a magnetic seal member, it is necessary to increase the magnetic flux density in the gap between the end of the fixed magnet and the magnetic seal member in order to improve the sealing performance. In the case of a cartridge type that is detachable, toner leakage is likely to occur due to vibration or impact during the detachment operation. Therefore, it is necessary to reinforce the magnetic force of the magnet magnetized on the magnetic seal member, which has been a factor in increasing costs.

Therefore, in order to solve the above problems, a developing device is proposed in which magnetic seal members are arranged at regular intervals at both ends in the longitudinal direction of the developing roller, and the arrangement of the magnetized end portions of the fixed magnet is devised. Has been. As shown in FIG. 9, the developing device has a magnetized end portion 100 a of the fixed magnet 100 and an inner end edge 103 a of the magnetic seal member 103 and an outer side in the longitudinal direction of the developing sleeve 101 (the direction of the arrow in the figure). By disposing it between the end edges 103b, in the vicinity of the magnetized end portion 100a of the fixed magnet 100, the toner constrained region due to the magnetic force of the fixed magnet 100 and the toner constrained region due to the magnetic force of the magnetic seal member 103 are superimposed and fixed. By strengthening the toner binding force in the vicinity of the magnetized end portion 100a of the magnet 100, toner leakage is reduced without increasing the magnetic force of the magnetic seal member 103, and an increase in the cost of the magnetic seal member 103 is avoided. (For example, refer to Patent Document 1).
JP 10-39629 A (page 3-4, FIG. 1-3)

  However, in the conventional developing device, although the cost increase of the magnetic seal member 103 can be suppressed, the developing sleeve 101 is formed on the inner end edge 103a of the magnetic seal member 103 facing the outer peripheral surface of the developing sleeve 101. Since the magnetic force from the fixed magnet 100 included in the toner is particularly concentrated, the toner T easily adheres to the outer peripheral surface of the developing sleeve 101 facing the inner end edge 103a of the magnetic seal member 103. Therefore, when the developing operation is repeated, the toner layer on the outer peripheral surface of the developing sleeve 101 facing the inner end edge 103a of the magnetic seal member 103 becomes thick as shown in FIG. Therefore, it is difficult to form a stable toner thin layer over a long period of time, and image defects are likely to occur. Further, as the toner layer thickness increases, the toner is easily transported to the outside, which makes it difficult to exhibit stable sealing performance for a long time.

  Accordingly, the present invention has been made in view of the above problems, and a developing device that can effectively prevent image defects and can exhibit stable sealing performance over a long period of time, and an image forming apparatus including the developing device. The purpose is to provide.

  In order to achieve the above object, the present invention includes a developing sleeve that includes a fixed magnet having a plurality of magnetic poles and that is rotatably supported to guide the stored magnetic toner onto the surface of the photoreceptor. In order to prevent the magnetic toner from leaking from the longitudinal end portion of the sleeve, a magnetic seal member disposed at a distance from the outer peripheral surface of the developing sleeve at the longitudinal end portion of the developing sleeve. In the developing device, the inner edge of the magnetic seal member facing the outer peripheral surface of the developing sleeve is formed in a curved surface.

  Here, the magnetic seal member has an arc-shaped portion facing the outer peripheral surface of the developing sleeve, and the interval between the outer peripheral surface of the developing sleeve and the arc-shaped portion is 0.3 to 0.7 mm. be able to.

  In addition, the effective magnetization end portion of the fixed magnet may be disposed further inside than the inner edge of the magnetic seal member in the longitudinal direction of the developing sleeve.

  Further, in the longitudinal direction of the developing sleeve, the distance between the inner edge and the effective magnetization edge can be 0 to 3 mm.

  Further, it is preferable that the magnetic seal member is disposed on the opposite side of the photoconductor via the developing sleeve.

  In addition, the present invention can be an image forming apparatus including the developing device according to any one of claims 1 to 5.

  According to the present invention, since the inner edge of the magnetic seal member facing the outer peripheral surface of the developing sleeve is formed in a curved shape, the outer surface of the developing sleeve facing the inner edge of the magnetic seal member is formed. Therefore, even when the developing operation is repeated, it is possible to avoid an increase in the thickness of the toner layer on the outer peripheral surface of the developing sleeve and generation of agglomerated toner. Accordingly, it is possible to form a stable toner thin layer over a long period of time and to prevent occurrence of image defects. In addition, since it is possible to avoid the conveyance of the toner to the outside, a stable sealing performance can be exhibited over a long period of time.

  According to the present invention, the magnetic seal member has an arc-shaped portion facing the outer peripheral surface of the developing sleeve, and a distance between the outer peripheral surface of the developing sleeve and the arc-shaped portion is 0.3 to 0.7 mm. Therefore, the magnetic restraint force is sufficiently exerted in the gap between the outer peripheral surface of the developing sleeve and the surface of the magnetic seal member, and clogging of magnetic toner and the temperature increase of the developing sleeve can be avoided. At the same time, stable sealing performance can be exhibited.

  Further, according to the present invention, since the effective magnetized end of the fixed magnet is arranged further inside than the inner edge of the magnetic seal member in the longitudinal direction of the developing sleeve, A magnetic brush by standing is formed further inward than the inner edge of the magnetic seal member, and the toner on the outer peripheral surface of the developing sleeve is magnetically compressed by the magnetic force between the magnetic seal member and the fixed magnet roller. It is possible to avoid an increase in the thickness of the layer and to prevent the generation of agglomerated toner. Further, since it is possible to avoid the conveyance of the magnetic toner to the outside, a stable sealing performance can be exhibited over a long period of time.

  Further, according to the present invention, since the distance between the inner edge and the effective magnetization end is set to 0 to 3 mm in the longitudinal direction of the developing sleeve, the outer peripheral surface of the developing sleeve and the surface of the magnetic seal member In this gap, the magnetic restraining force is sufficiently exerted, and stable sealing performance can be exhibited.

Further, according to the present invention, since the image forming apparatus including the developing device according to any one of claims 1 to 5 is configured, the image forming device according to any one of claims 1 to 5 described above is configured. The same effect as the developing device can be obtained.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the image forming apparatus 1 includes a sheet feeding unit 2 disposed at a lower portion of the main body of the image forming apparatus 1, and a sheet conveying unit disposed on the side and above the sheet feeding unit 2. 3, an image forming unit 4 disposed above the sheet conveying unit 3, a fixing unit 5 disposed on the discharge side of the image forming unit 4, the image forming unit 4, and a fixing device 5 is provided with an image reading unit 6 disposed above 5.

  The paper feed unit 2 includes a plurality (four in this embodiment) of paper feed cassettes 7 in which paper 9 is stored. The paper 9 is sent from the selected paper feed cassette 7 to the paper transport unit 3, and the paper 9 is surely fed to the paper transport unit 3 one by one. These four paper feed cassettes 7 are configured to be detachable from the image forming apparatus main body 1.

  The paper 9 fed to the paper transport unit 3 is transported toward the image forming unit 4 via the paper supply path 10. The image forming unit 4 forms a predetermined toner image on the paper 9 by an electrophotographic process, and is an image end holder that is rotatably supported in a predetermined direction (the arrow direction in the figure). A photoconductor 11, and a charging device 12, an exposure device 13, a developing device 14, a transfer device 15, a cleaning device 16, and a charge removal device 17 are provided around the photoconductor 11 along the rotation direction.

  The charging device 12 includes a charging wire to which a high voltage is applied. By applying a predetermined potential to the surface of the photoconductor 11 by corona discharge from the charging wire, the surface of the photoconductor 11 is uniformly charged. It is done. The exposure device 13 irradiates the photoconductor 11 with light based on the image data of the original read by the image reading unit 6, whereby the surface potential of the photoconductor 11 is selectively attenuated, and this photosensitivity is detected. An electrostatic latent image is formed on the surface of the body 11. Next, the developing device 14 attaches toner to the electrostatic latent image to form a toner image on the surface of the photoconductor 11, and the transfer device 15 transfers the toner image on the surface of the photoconductor 11 to the photoconductor 11. The image is transferred to a sheet 9 supplied between the apparatus 15 and the apparatus 15.

  The sheet 9 on which the toner image is transferred is conveyed from the image forming unit 4 toward the fixing unit 5. The fixing unit 5 is disposed on the downstream side of the image forming unit 4 in the sheet conveying direction, and the sheet 9 on which the toner image is transferred in the image forming unit 4 includes a heating roller 18 provided in the fixing unit 5, and The toner image is fixed on the sheet 9 by being sandwiched and heated by the pressure roller 19 pressed against the heating roller 18. Next, the sheet 9 on which the image is formed in the fixing device 5 from the image forming unit 4 is discharged onto the discharge tray 21 by the discharge roller pair 20. On the other hand, after the transfer, the toner remaining on the surface of the photoconductor 11 is removed by the cleaning device 16, and the residual charge on the surface of the photoconductor 11 is removed by the static eliminator 17. Then, the photoreceptor 11 is charged again by the charging device 12, and image formation is performed in the same manner.

  Next, the developing device will be described with reference to the drawings. FIG. 2 is a cross-sectional view showing a developing device in the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a front view of the developing roller provided in the developing device shown in FIG. FIG. 4 is a diagram showing the magnetic pole arrangement of the fixed magnet roller. As shown in FIG. 2, the developing device 14 according to this embodiment includes a developing container 22 that stores a magnetic one-component developer, a pair of mixers 23 and 24 disposed in the developing container 22, and a developing container 22. A fixed magnet roller 25 disposed on the drum opening side and having a plurality of magnetic poles, and enclosing the fixed magnet roller 25, and for guiding the stored magnetic developer (magnetic toner) onto the surface of the photoreceptor 11. It is composed of a developing roller (or toner carrying roller) 27 comprising a nonmagnetic developing sleeve 26 rotatably supported by a shaft and a plate-like magnetic body, and hangs down from above the developing roller 27 toward the upper surface of the developing roller 27. The magnetic blade 28, the magnetic seal member 29 disposed at the end of the developing sleeve 26 in the longitudinal direction (the direction of the arrow X shown in FIG. 3), and between the developing roller 27 and the photosensitive member 11. And a developing bias 30 applied.

  A toner replenishing hole H is opened on the upper surface of the developing container 22 above the mixer 23 so that toner from a toner cartridge (not shown) can be input. The charged toner is sufficiently stirred by the pair of mixers 23 and 24 and guided to the developing sleeve 26. The magnetic toner guided to the developing sleeve 26 is carried on the developing sleeve 26 using the magnetic force of the fixed magnet roller 25, and the magnetic toner is disposed above the developing roller 27 and serves as a toner layer thickness regulating member. The thickness is regulated by the acting magnetic blade 28. Thereafter, the magnetic toner carried on the developing sleeve 26 is guided to a developing position, that is, on the surface of the photoreceptor 11 by the developing roller 27.

  The developing sleeve 26 is set to a predetermined peripheral speed, and the developing sleeve 26 is set to rotate in the same direction between the drum and the sleeve with respect to the rotation direction of the photosensitive member 11 (see FIG. 2). . The developing sleeve 26 is disposed at a predetermined distance from the photoconductor 11. The developing bias 30 is applied with a low electric field developing bias in which a direct current component DC and an alternating current component AC are superimposed, and image density adjustment is performed by controlling the oscillation frequency of the AC. At the time of non-development, the DC component DC is cut off and only the AC component AC is applied to remove the reverse polarity toner.

  As shown in FIG. 4, the arrangement of the magnetic poles of the fixed magnet roller 25 is as follows: a developing pole S1 having an S pole near the developing position; Are arranged adjacent to the transport pole S2, the pumping pole N2 adjacent to the transport pole S2, and the blade pole S3 adjacent to the pumping pole N2.

  Here, the developing pole S1 is a pole for developing the magnetic toner on the photoconductor 11, and the lead-in pole N1 is a pole for returning the magnetic toner scattered from the developing area into the developing container 22. The transport pole S2 is a pole provided for improving the sealing performance, and the pumping pole N2 is a pole for pumping up the magnetic toner accommodated in the developing container 22. The blade pole S3 compresses magnetic toner between the magnetic blade 28 and the developing sleeve 27 by a magnetic field generated between the magnetic blade 28 and the magnetic force due to friction between the compressed magnetic toner and the developing sleeve 27. The pole for giving electric charge to the toner, and the scattering prevention pole N3 are poles for preventing the toner scattering.

  The magnetic seal member 29 is for preventing the magnetic toner from leaking from the longitudinal end portion of the developing sleeve 26. As shown in FIG. The developing sleeve 26 is disposed at a constant interval with respect to the outer peripheral surface. The magnetic seal member 29 is formed of a magnetic material (magnet), and the magnetic toner that moves so as to flow outward from the end of the developing sleeve 26 is between the fixed magnet roller 25 and the magnetic seal member 29. A magnetic brush is formed by the rising of magnetic toner along each magnetic field line that is constrained by the magnetic field formed in the gap and formed by the magnetic pole of the fixed magnet roller 25 and the magnetic pole of the magnetic seal member 29. By filling a gap between the outer peripheral surface of the developing sleeve 26 and the surface of the magnetic seal member 29, the toner is prevented from flowing out of the developing region. The magnetic seal member 29 is disposed on the opposite side of the photoconductor 11 via the developing sleeve 26 as shown in FIGS.

  In this configuration, the present embodiment is characterized by the shape of the magnetic seal member and the positional relationship between the fixed magnet and the magnetic seal member. This will be described in detail below with reference to the drawings. FIG. 5 is a cross-sectional view for explaining the positional relationship between the fixed magnet and the magnetic seal member in the developing device according to the embodiment of the present invention, and FIG. 6 is a magnetic body in the developing device according to the embodiment of the present invention. It is a perspective view of a sealing member.

  In the present embodiment, as shown in FIG. 5, in the longitudinal direction X of the developing sleeve 26, the magnetized end portion 25a of the fixed magnet roller 25 is formed between the inner end edge 29a and the outer end edge 29b of the magnetic seal member 29. 5 and FIG. 6, the inner edge 29a of the magnetic seal member 29 facing the outer peripheral surface of the developing sleeve 26 is formed in a curved shape. As described above, the inner end edge 29a has such a shape when the magnetized end portion 25a of the fixed magnet roller 25 is disposed between the inner end edge 29a and the outer end edge 29b of the magnetic seal portion 29. This is because the magnetic force from the fixed magnet roller 25 contained in the developing sleeve 26 is particularly concentrated on the inner end edge 29a of the magnetic seal member 29 facing the outer peripheral surface of the developing sleeve 26, so that the magnetic force is weakened.

  That is, by forming the inner end edge 29a of the magnetic seal member 29 facing the outer peripheral surface of the developing sleeve 26 into a curved surface, the magnetic force of the fixed magnet roller 25 is increased along the inner end edge 29a. Therefore, the magnetic force of the fixed magnet roller 25 can be prevented from concentrating on the inner edge 29a. Accordingly, the magnetic force generated by the spikes of the magnetic toner T is formed in the gap between the outer peripheral surface of the developing sleeve 26 and the magnetic seal member 29 along each magnetic force line formed by the magnetic poles of the fixed magnet roller 25 and the magnetic seal member 29. Although a brush is formed, it is possible to prevent toner T from adhering to the outer peripheral surface of the developing sleeve 26 facing the inner edge 29a of the magnetic seal member 29 (see FIG. 9), and the developing operation is repeated. Even in this case, it is possible to avoid an increase in the thickness of the toner layer on the outer peripheral surface of the developing sleeve 26 and generation of agglomerated toner. Accordingly, it is possible to form a stable toner thin layer over a long period of time and to prevent occurrence of image defects. Further, since the toner T can be prevented from being conveyed to the outside, a stable sealing performance can be exhibited over a long period of time.

  In the present embodiment, as shown in FIG. 5, the end portion (hereinafter referred to as the effective magnetization end portion) 25 b of the effective magnetization width Z (see FIG. 3) of the fixed magnet roller 25 is In the longitudinal direction X, the magnetic seal member 29 is positioned further inside than the inner end edge 29a. Here, as shown in FIG. 7, the effective magnetization width Z is a width set within a range of plus or minus 50 G (Gauss) with respect to the magnetic force G1 in the axial center portion of the fixed magnet roller 25. In the figure, W, which is the difference between the magnetic force G1 and the magnetic force G2, is 50G (that is, G1-G2 = W = 50G), and the effective magnetization width Z is set based on the magnetic force G2. . 3 and 7, the width Y indicates the magnetization width of the fixed magnet roller 25.

  In this effective magnetization width Z, the magnetic toner T is held on the developing sleeve 26 by the magnetic force generated by the fixed magnet roller 25 which is a magnetic field generating means. The head of the magnetic toner T formed in the gap between the outer peripheral surface of the developing sleeve 26 and the surface of the magnetic seal member 29 by being disposed further inside than the inner end edge 29 a of the magnetic seal member 29 in the direction X. Since the magnetic brush by standing is formed further toward the inner side than the inner end edge 29a of the magnetic seal member 29, the above-described development is performed by magnetic compression by the magnetic force between the magnetic seal member 29 and the fixed magnet roller 25. An increase in the thickness of the toner layer on the outer peripheral surface of the sleeve 26 can be avoided, and the generation of aggregated toner can be prevented. . Further, since the magnetic brush is formed further toward the inner side than the inner edge 29a of the magnetic seal member 29, it is possible to avoid the magnetic toner T from being conveyed to the outside, and a stable sealing performance can be achieved for a long time. It will be able to demonstrate over.

  That is, in the conventional developing device, the effective magnetization end portion is not mentioned at all. However, in the present embodiment, the effective magnetization end portion 25b is connected to the magnetic seal member in the longitudinal direction X of the developing sleeve 26. By disposing it further inside than the inner end edge 29a of 29, it becomes possible to obtain a sufficient sealing performance without being affected by the position of the magnetized end portion 25a.

  In the longitudinal direction X of the developing sleeve 26, when the effective magnetization end portion 25 b is disposed outside the inner end edge 29 a of the magnetic seal member 29, the outer peripheral surface of the developing sleeve 26 and the surface of the magnetic seal member 29 are The magnetic brush formed by the rising of the magnetic toner T formed in the gap is formed outward from the inner end edge 29a of the magnetic seal member 29, and the effective magnetization end portion 25b is sealed with the magnetic seal. Even when the member 29 is disposed further inside than the inner edge 29a, the distance S between the inner edge 29a and the effective magnetization end 25b in the longitudinal direction X of the developing sleeve 26 (see FIG. 5) is too large. As a result, the magnetic restraining force in the gap between the fixed magnet roller 25 and the magnetic seal member 29 becomes poor, and the sealing performance deteriorates. Therefore, in the present embodiment, the effective magnetization end portion 25b is disposed further inside than the inner end edge 29a of the magnetic seal member 29, and the interval S is set to 0 to 3 mm. By setting the interval S within this range, the above inconvenience can be avoided and stable sealing performance can be exhibited.

  In addition, it has been described that the magnetic seal member 29 is disposed at both ends in the longitudinal direction X of the developing sleeve 26 with a certain distance from the outer peripheral surface of the developing sleeve 26. FIGS. 8 and the arcuate portion 29c of the magnetic seal member 29 shown in FIG. 8 which is a cross-sectional view taken along the line AA of FIG. 5 (that is, the portion facing the outer peripheral surface of the developing sleeve 26 and formed in a curved shape) If the distance C between the outer peripheral surface of the developing sleeve 26 and the outer peripheral surface of the developing sleeve 26 is too small, the magnetic toner T is clogged in the gap between the magnetic seal member 29 and the developing sleeve 26 and the rotating developing is performed. The friction between the sleeve 26 and the magnetic toner T causes an increase in the temperature of the developing sleeve 26, resulting in a decrease in sealing performance. On the other hand, if the distance C is too large, the magnetic restraining force in the gap between the outer peripheral surface of the developing sleeve 26 and the magnetic seal member 29 becomes poor, and the sealing performance is deteriorated. Therefore, in this embodiment, the interval C is set to 0.3 to 0.7 mm. By setting the interval C within this range, the above inconvenience can be avoided and stable sealing performance can be exhibited.

  First, preconditions will be described. As the magnetic seal member 29, a SPCC material, which is a steel material, having a width of 4 mm obtained by electroless nickel plating was used. The photosensitive member 11 was a drum-shaped member made of amorphous silicon having a diameter of 80 mm, and was rotated at a speed of 440 mm / s. The developing sleeve 26 was made of stainless steel and rotated at a speed of 704 mm / s. The magnetic pole arrangement of the fixed magnet roller 25 contained in the developing sleeve 26 is such that the developing pole S1 is arranged at the developing position facing the photoconductor 11, and the drawing pole N1 is 50 downstream of the developing sleeve 26 with respect to the developing pole S1. The conveying pole S2 is arranged at an angle of about 95 ° downstream of the developing sleeve 26 with respect to the developing pole S1, and the pumping pole N2 is arranged with reference to the developing pole S1. The blade pole S3 is arranged with a declination of about 261 ° on the downstream side of the developing sleeve 26 with the developing pole S1 as a reference. Further, the anti-scattering pole N3 is arranged with a declination of about 50 ° upstream of the developing sleeve 26 with respect to the developing pole S1. The magnetic flux density of each magnetic pole was set to 900G for the developing pole S1, 910G for the blade pole S3, and 850G for the lead-in pole N1, the pumping pole N2, the scattering prevention pole N3, and the transport pole S2. Further, the effective magnetized end 25b of the fixed magnet roller 25 is set 2 mm inside the magnetized end 25a. Further, the magnetic blade 28 was disposed with a spacing of 0.3 mm with respect to the developing sleeve 26, and the developing sleeve 26 was disposed with a spacing of 0.32 mm with respect to the photoreceptor 11. The developing bias 30 was set such that the DC component DC was 250 V, the AC component AC was 1.6 kV, and the oscillation frequency was 2.5 kHz.

  Under the above preconditions, the distance C between the developing sleeve 26 and the arc-shaped portion 29c of the magnetic seal member 29 is set to 0.5 mm, and the effective magnetization end portion 25b of the fixed magnet roller 25 and the magnetic seal member are set. 29, the interval S between the inner end edges 29a is -2 to +5 mm (minus indicates that the effective magnetization end 25b is located outside the inner end edge 29a, and plus indicates that the effective magnetization end 25b is on the inner side. In this case, the original magnet having a black ratio of 6% is copied to the A4 size at a copy speed of 80 sheets / min. The sealing performance in the gap with the magnetic seal member 29 was evaluated. The results are shown in Table 1.

  As shown in Table 1, when the effective magnetization end portion 25b is arranged outside the inner end edge 29a (that is, when the interval S is -2 mm or -1 mm), the magnetic brush becomes the magnetic seal member 29. It was formed toward the outer side of the inner end edge 29a, and stable sealing performance could not be exhibited for a long time. Further, when the effective magnetization end portion 25b is gradually arranged inward from the inner end edge 29a of the magnetic seal member 29, good sealing performance is recognized in the range where the interval S is 0 to +3 mm. However, when the distance S exceeds +4 mm, the magnetic restraint force in the gap between the fixed magnet roller 25 and the magnetic seal member 29 becomes poor, and a decrease in sealing performance is recognized. From the above, it can be seen that stable sealing performance can be exhibited by setting the interval S in the range of 0 to 3 mm.

  Under exactly the same preconditions as described in the first embodiment, the interval S between the effective magnetization end portion 25b and the inner end edge 29a is set to +1 mm, and the arc-shaped portion of the developing sleeve 26 and the magnetic seal member 29 is set. Fixed magnet roller by setting the distance C to 29c every 0.1mm in the range of 0.2mm to 0.9mm, and copying the original with black ratio 6% to A4 size at the copy speed of 80 sheets / min The sealing performance in the gap between the magnetic seal member 29 and the magnetic seal member 29 was evaluated. The results are shown in Table 2.

  As shown in Table 2, when the interval C was set to 0.9 mm, the magnetic toner T did not leak to the end of the developing sleeve 26 at the end of copying 5000 sheets. As a result, toner leakage from the end of the developing sleeve 26 was confirmed. When the interval C was set to 0.2 mm or 0.8 mm, no leakage of the magnetic toner T to the end of the developing sleeve 26 was observed at the end of the 10000 copy, but further copying. As a result, toner leakage from the end of the developing sleeve 26 was confirmed. On the other hand, when the interval C was set to 0.3 to 0.7 mm, the leakage of the magnetic toner T to the end of the developing sleeve 26 was not recognized even when 15,000 copies were completed. As described above, by setting the distance C between the outer peripheral surface of the developing sleeve 26 and the arc-shaped portion 29c of the magnetic seal member 29 facing the outer peripheral surface of the developing sleeve 26 to a range of 0.3 to 0.7 mm, It can be seen that stable sealing performance can be exhibited.

  In addition, the said embodiment is only an explanatory example, The scope of the present invention is not limited to the said embodiment, Based on the meaning of this invention, the shape, dimension, material, etc. of each structural article are changed. It is possible that they are not excluded from the scope of the present invention.

  Examples of utilization of the present invention include a developing device that can effectively prevent image defects and can exhibit stable sealing performance over a long period of time, and an image forming apparatus including the developing device.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a developing device in an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a front view when a developing roller provided in the developing device shown in FIG. 2 is viewed from the photosensitive member side. It is a figure which shows the magnetic pole arrangement | positioning of the fixed magnet roller shown in FIG. FIG. 5 is a cross-sectional view for explaining the positional relationship between a fixed magnet and a magnetic seal member in the developing device according to the embodiment of the present invention. FIG. 5 is a perspective view of a magnetic seal member in the developing device according to the embodiment of the present invention. It is a figure for demonstrating the effective magnetization width of a fixed magnet roller. It is AA sectional drawing of FIG. It is sectional drawing for demonstrating the positional relationship of the fixed magnet and magnetic body sealing member in the conventional image development apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Paper feed part 3 Paper conveyance part 4 Image forming part 5 Fixing part 6 Image reading part 11 Photoconductor 14 Developing apparatus 25 Fixed magnet roller 25a Magnetization end part of fixed magnet roller 25b Effective magnetization of fixed magnet roller End 26 Developing sleeve 27 Developing roller 28 Magnetic blade 29 Magnetic seal member 29a Inner edge 29b of magnetic seal member Outer edge 29c of magnetic seal member Arc-shaped portion of magnetic seal member

Claims (6)

A developing sleeve that includes a fixed magnet having a plurality of magnetic poles and is rotatably supported to guide the stored magnetic toner onto the surface of the photosensitive member, and the magnetic toner from the longitudinal end of the developing sleeve. In order to prevent leakage, a developing device comprising a magnetic seal member disposed at a distance from an outer peripheral surface of the developing sleeve at a longitudinal end portion of the developing sleeve,
2. A developing device according to claim 1, wherein an inner edge of the magnetic seal member facing the outer peripheral surface of the developing sleeve is formed in a curved shape. The magnetic seal member has an arc-shaped portion facing the outer peripheral surface of the developing sleeve, and a distance between the outer peripheral surface of the developing sleeve and the arc-shaped portion is 0.3 to 0.7 mm. The developing device according to claim 1, wherein: The effective magnetization end portion of the fixed magnet is disposed further inside than the inner end edge of the magnetic seal member in the longitudinal direction of the developing sleeve. The developing device described. The developing device according to claim 3, wherein a distance between the inner end edge and the effective magnetization end portion is 0 to 3 mm in a longitudinal direction of the developing sleeve. 5. The developing device according to claim 1, wherein the magnetic seal member is disposed on a side opposite to the photoconductor via the developing sleeve. 6. An image forming apparatus comprising the developing device according to claim 1.

Images