JP5945947B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device used in an image forming apparatus such as a printer, a facsimile machine, and a copying machine, and an image forming apparatus provided with the developing device.

  As an image forming apparatus such as an electrophotographic copying apparatus, an electrostatic recording apparatus, and a magnetic recording apparatus, a two-component developer (hereinafter simply referred to as “developer”) is used for a latent image formed on a latent image carrier. A device using a two-component developing type developing device that performs development processing is known. In this development processing, the developer is conveyed while being magnetically supported on the surface of a developer carrier that is rotatably attached to a developing device housing or the like, and the developer carrier and the latent image carrier face each other. In the development area, a magnetic force is applied to the developer to make it stand up. Then, the magnetic brush formed by the spikes is rubbed against the surface of the latent image carrier to attach toner to the latent image on the surface of the latent image carrier to visualize the latent image.

  Such development processing generally requires magnetic field generating means such as a magnet having a plurality of magnetic poles arranged inside the developer carrier. Examples of the magnetic pole generated by the magnetic field generating means include a pumping magnetic pole for generating a magnetic force for pumping up the developer onto the developer carrier. In addition, the developer carried on the surface of the developer carrying member passes through a regulation gap for regulating the amount of the developer conveyed to the development region, so that the developer can be spiked. There is also a restriction magnetic pole that generates a restriction magnetic force. In addition, a developing magnetic pole that generates a developing magnetic force for causing the developer on the developer carrying member to rise in the developing region is also exemplified.

  Such a two-component developing system developing device is disclosed in, for example, Japanese Patent Application Laid-Open No. H10-228707. The developing device disclosed in this document includes a developer circulation path including a developer supply transport path that transports the developer supplied onto the surface of the developer support along the direction of the rotation axis of the developer support by a developer supply transport member. The developer in the developing device is circulated along the line. The developer supply conveyance path is disposed adjacent to the surface of the developer carrier, and the developer being conveyed exceeds the upper end of the side wall on the developer carrier side of the developer supply conveyance path and draws up the magnetic force. By the action, it is attracted to the surface of the developer carrier and is carried on the surface of the developer carrier.

  The developer thus carried on the developer carrier is conveyed in the direction of rotation of the developer carrier as the developer carrier is rotated, and the surface of the developer carrier and the developer regulating member face each other. Pass the regulatory gap. During this passage, the developer carried at a distance close to the surface of the developer carrying body can pass through the regulation gap, but the developer carried at a distance far from the surface of the developer carrying body does not pass through the developer regulating member. It is blocked and cannot pass through the regulatory gap. As a result, the amount of developer carried on the developer carrying body is regulated. The developer that has passed through the regulation gap is transported to the development region as the developer carrying member rotates, and the developer that has been blocked from passing through the regulation gap by the developer regulation member returns to the developer supply transport path side and is developed. It is collected in the agent supply / conveyance path and is pumped up again to the developer carrier.

  In general, characteristics such as developer fluidity change due to deterioration of the developer or environmental change due to use over time. Then, the amount of developer that passes through the regulation gap fluctuates, and a fixed amount of developer cannot be transported to the development region, resulting in a problem that the developing ability cannot be stably maintained. For such a problem, it is possible to reduce the problem by providing a restriction magnetic pole that generates a restriction magnetic force, and causing the developer passing through the restriction gap to act with the restriction magnetic force. Are known.

  However, when such a regulation magnetic pole is arranged, the regulation magnetic force acts on the developer blocked from passing through the regulation gap, and the space on the downstream side of the developer carrying member rotation direction of the developer regulation member (hereinafter referred to as “regulation”). A situation where the developer is retained in the “retaining space”. The developer staying in the restricted stay space (hereinafter referred to as “restricted stay developer”) rotates in the restricted stay space in the direction opposite to the direction of rotation of the developer carrier due to the surface movement of the developer carrier. It stays in the restricted stay space while (circulating movement). The regulated staying developer is rubbed and charged while circulating in the regulated staying space while receiving the restraining force of the regulated magnetic force, and compared with other developers circulating in the developing device, The toner charge amount is high. Therefore, there is a difference in developing ability (amount of toner attached per unit area that adheres to the latent image during development) between the regulated staying developer and other developers.

  Even with such developers with different development capabilities, if they are uniformly dispersed and mixed with each other, even if they are used for development, image density unevenness that can be recognized by humans will occur. There is no. However, if the developer is used in development in an insufficiently mixed state, image density unevenness that is recognizable by humans is generated and image quality is deteriorated. The conventional developing device as described in Patent Document 1 is used for development in a state where the regulated staying developer having an abnormally high toner charge amount is insufficiently mixed with other developer having a normal toner charge amount. There has been a problem that image density unevenness occurs and image quality is deteriorated.

  More specifically, the regulated staying developer that has escaped the restraint of the regulated magnetic force during the circulation movement is sequentially collected into the developer supply conveyance path. If the developer is collected in the developer supply conveyance path, the regulated staying developer is sufficiently mixed with the other developer and then pumped up again, and the above-described image quality deterioration problem does not occur. However, when a pumping magnetic pole having a polarity opposite to that of the regulating magnetic pole is arranged adjacent to the upstream side in the rotation direction of the developer carrier, the magnetic lines of force connecting the regulating magnetic pole and the pumping magnetic pole are A magnetic field is formed so as to pass through the staying restricted staying space. In such a magnetic field, a part of the regulated staying developer, specifically, the part of the regulated staying developer that is closest to the pumping magnetic pole moves to the pumping magnetic pole side along the magnetic field line, and the surface of the developer carrier Be drawn to As a result, a part of the regulated staying developer is carried on the surface of the developer carrying member without being collected in the developer supply conveyance path.

  When the regulated staying developer attracted by the pumping magnetic force is carried on the surface of the developer carrier, the developer from the developer supply transport path has already been pumped onto the surface of the developer carrier. In locations where the amount of developer pumped from the developer supply transport path to the surface of the developer carrier is sufficient, the regulated staying developer attracted by the pumping magnetic force is placed on the developer from the developer supply transport path. It is carried in a region far from the surface of the developer carrying member so as to overlap. In this way, the regulated staying developer carried in the region far from the surface of the developer carrying member cannot pass through the regulation gap by the developer regulating member and stays again in the regulated residence space without being transported to the development region. It will be. Therefore, a developer layer in an insufficiently mixed state between a regulated staying developer with an abnormally high toner charge amount and another developer having a normal toner charge amount is not sent to the development region, resulting in uneven image density. It does not occur and image quality degradation does not occur.

  However, the regulated staying developer attracted by the pumping magnetic force hinders the pumping of the developer from the developer supply transport path to the surface of the developer carrier, and the amount of the developer pumped from the developer supply transport path is locally May cause a shortage. In particular, in a configuration in which the developer in the developer supply conveyance path is conveyed in the direction of the rotation axis by a conveyance screw having a blade portion provided in a screw shape on the rotation shaft, the developer is moved toward the developer carrier by the blade portion. Is not uniform in the direction of the rotation axis.

  For this reason, at locations where the force to feed the developer to the developer carrier side is weak, pumping of the developer from the developer supply conveyance path is hindered by the regulated staying developer attracted by the pumping magnetic force, and the developer supply conveyance path Insufficient amount of developer to be pumped. In locations where the amount of developer pumped up from the developer supply / conveyance path is locally insufficient, the regulated staying developer attracted by the pumping magnetic force is carried in a region close to the surface of the developer carrier, and the regulation gap is increased. It passes through and is transported to the development area. As a result, a developer layer in an insufficiently mixed state between a regulated staying developer with an abnormally high toner charge amount and another developer having a normal toner charge amount is fed into the development region, resulting in uneven image density. Causing image quality degradation.

  In order to solve such a problem, the present applicant has proposed a developing device described in Japanese Patent Application No. 2011-121747 (hereinafter referred to as “prior application”). The developing device described in the prior application lowers the height of the partition wall by lowering the upper end position of the partition wall than the conventional developing device. In addition, a blocking member is provided that prevents the regulated staying developer, which has been blocked from passing through the regulation gap by the developer regulating member, from moving toward the surface of the developer carrying member along the magnetic force lines of the regulating magnetic force. The blocking member is provided while ensuring a supply passage between the upper end of the partition wall for allowing the developer in the developer supply conveyance path to pass to the developer carrier side at least over the entire width of the development region.

  By providing such a blocking member, the regulated staying developer attracted by the pumping magnetic force of the pumping magnetic pole does not hinder the pumping of the developer from the developer supply conveyance path. Further, since the supply passage is formed between the upper end of the partition wall and the blocking member, even if the blocking member is provided, the operation of pumping up the developer in the developer supply transport path to the surface of the developer carrier is performed. There is no inhibition. Therefore, it is difficult to generate a location where the amount of developer pumped up from the developer supply conveyance path is locally insufficient, and the surface of the developer carrier that allows the regulated staying developer attracted by the pumping magnetic force to pass through the regulation gap. It becomes difficult to carry in the region close to. Therefore, it is possible to suppress the occurrence of a situation where a developer layer in an insufficiently mixed state between a regulated staying developer having an abnormally high toner charge amount and a developer having a normal toner charge amount is sent to the development region. Image quality deterioration due to density unevenness is suppressed.

  On the other hand, in the developing device using the two-component developer, density unevenness may occur in the developed image due to “developer carrier surface contamination” in which toner directly adheres to the surface of the developer carrier. there were.

  The developer on the surface of the photosensitive member is in contact with the developer on the developer carrying member and the surface of the photosensitive member, even in a non-image area such as a space between images where an image to be transferred to the paper is not formed. There is toner that is transferred from the carrier to the surface of the photosensitive member or adhered due to other causes. Usually, the surface potential of the developer carrying member is formed so that an electric field is generated to move the toner from the non-image region on the photosensitive member surface to the developer carrying member so that the non-image region on the photosensitive member surface is not stained with toner. And a potential difference between the surface potential of the non-image area on the surface of the photoreceptor. As a result, the toner adhering to the non-image area on the surface of the photoconductor is attracted to the surface of the developer carrying member, so that the non-image area on the surface of the photoconductor is prevented from being stained with toner.

  However, the toner attracted to the surface of the developer carrying member from the non-image area on the surface of the photoreceptor is contaminated with the toner. If the surface of the developer carrying member becomes soiled with toner in this way, density unevenness occurs in the developed image when the image to be developed is longer than one round of the developer carrying member.

  The toner adhering to the surface of the developer carrying member in the non-image region is used when developing the latent image formed in the image region on the surface of the photosensitive member together with the toner in the developer spiked on the developer carrying member. Used on the first round of the developer carrier. As a result, more toner is delivered to the latent image on the photoreceptor on the first round of the developer carrier than when only the toner in the developer spiked on the developer carrier is used for development. As a result, the toner density of the developed image increases. Therefore, between the image after the second round of the developer carrier after the toner attached to the surface of the developer carrier in the non-image region is used for development and the image of the first round of the developer carrier, A density difference will occur.

  The present invention has been made in view of the above problems, and an object thereof is to provide a developing device capable of reducing image density unevenness and suppressing image quality deterioration, and an image forming apparatus including the developing device. .

  In order to achieve the above object, the invention of claim 1 is provided with magnetic field generating means inside, and a developer containing toner and magnetic carrier is carried on the surface by the magnetic force generated by the magnetic field generating means. The developer carrying member that conveys the developer to the developing region facing the surface of the latent image carrying member by rotating, and the developer carried on the surface of the developer carrying member passes to the developing region. A developer regulating member for forming a regulating gap for regulating the amount of developer conveyed between the developer carrying member and the surface of the developer carrying member; The developer supplied on the surface of the developer carrier is conveyed by the developer supply and conveyance member along the direction of the rotation axis of the developer carrier, and the developer whose passage through the regulation gap is blocked by the developer regulation member Recovering developer And the magnetic field generating means passes the developer in the developer supply / conveyance path beyond the upper end of the side wall on the developer support / conveyance path in the developer supply / conveyance path. A pumping magnetic pole for generating a pumping magnetic force to draw the developer on the surface of the developer carrying member and a regulation magnetic pole for generating a regulation magnetic force for causing the developer to pass through the regulation gap. In the developing device, the pumping magnetic pole and the regulation magnetic pole are adjacent to each other in the rotation direction of the developer carrier and have opposite polarities, and between the upper end of the side wall of the developer supply conveyance path. In addition, while securing a supply passage for passing the developer in the developer supply transport path to the developer carrier side over at least the entire area of the developer carrier rotation axis of the development region, A blocking member made of a metal material that blocks the developer blocked by the developer blocking member from moving toward the surface of the developer carrying member along the magnetic force line of the blocking magnetic force. And a bias is applied to the blocking member so that the toner moves from the surface of the developer carrying member to the blocking member.

In the present invention, by providing the blocking member, it is possible to suppress the occurrence of a situation where the developer layer that is not sufficiently mixed as described above is sent to the development region, and image quality deterioration due to image density unevenness is prevented. It is suppressed.
In the present invention, a bias is applied to the blocking member made of a metal material so that the toner moves from the surface of the developer carrying member to the blocking member. Thereby, the toner adhering to the surface of the developer carrying member can be moved to the blocking member, the surface of the developer carrying member can be cleaned, and toner contamination on the surface of the developer carrying member can be reduced. Therefore, it is possible to reduce the density difference between the image on the first round of the developer carrier and the subsequent image due to the toner stain on the surface of the developer carrier, and to reduce image density unevenness. Can do.

  As described above, according to the present invention, there is an excellent effect that image density unevenness can be reduced and image quality deterioration can be suppressed.

FIG. 6 is a diagram illustrating toner movement by a background potential X [V] and a developing sleeve cleaning potential Y [V] in the developing device. 1 is a schematic configuration diagram illustrating a main part of a printer according to an embodiment. FIG. 3 is an explanatory diagram illustrating a schematic configuration of a developing unit in a printer. Explanatory drawing which shows an example of the conventional image development unit in which the shielding wall is not provided. FIG. 4 is an explanatory diagram showing a relationship between a slit width and a maximum image forming area width in a developing unit. The figure which shows the abnormal image actually printed with an image image. FIG. 4 is a diagram illustrating how toner is smeared by an image pattern on a developing sleeve. The figure which shows the image of the state by which the developing sleeve was cleaned. The figure which shows the image of the image actually printed with the case where an image image and an Example are employ | adopted.

  Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic color laser printer (hereinafter simply referred to as “printer”) will be described. FIG. 2 is a schematic configuration diagram illustrating a main part of the printer according to the present embodiment.

  This printer includes four toner image forming units 1M, 1C, 1Y, and 1K for forming toner images of respective colors of magenta, cyan, yellow, and black (hereinafter referred to as M, C, Y, and K). ing. Further, a transfer unit 50 is provided on the side of the toner image forming portions 1M, 1C, 1Y, and 1K arranged in the vertical direction.

  The toner image forming units 1M, 1C, 1Y, and 1K have substantially the same configuration except that the color of the toner used is different. The M toner image forming unit 1M for forming an M toner image will be described. The toner image forming unit 1M includes a process unit 2M, an optical writing unit 10M, and a developing unit 20M.

  The process unit 2M for M includes a charging device 4M, a drum cleaning device 5M, a charge removal lamp 6M, and the like around a drum-shaped photoreceptor 3M that is driven to rotate counterclockwise in the drawing. These are held by a common casing and are integrally attached to and detached from the printer main body. The photoreceptor 3M as a latent image carrier is obtained by coating an organic photosensitive layer on a base tube made of aluminum or the like.

  The charging device 4M uniformly charges the surface of the photosensitive member 3M, which is driven to rotate counterclockwise in the drawing, to a negative polarity, for example, by corona charging.

  The optical writing unit 10M includes a light source composed of a laser diode or the like, a regular hexahedral polygon mirror, a polygon motor for rotationally driving the mirror, an fθ lens, a lens, a reflection mirror, and the like. A laser beam Lm emitted from a light source driven based on image information sent from a personal computer (not shown) is reflected on the polygon mirror surface and deflected with the rotation of the polygon mirror, while being photoreceptor 3M. To reach. As a result, the surface of the photoreceptor 3M is optically scanned, and a latent image for M is formed on the surface of the photoreceptor 3M.

  The developing unit 20M for M, which is a developing device, has a developing roll 21M that exposes a part of the peripheral surface from an opening provided in the casing. The developing roll 21M includes a developing sleeve as a developer carrying member made of a non-magnetic pipe that is driven to rotate by a driving unit (not shown), and a magnet roller as a magnetic field generating unit (not shown) that is included so as not to rotate. have.

  In the developing unit 20M, an M developer (not shown) including M toner having a normal charging polarity of negative polarity and a magnetic carrier is included. The M developer is agitated and conveyed by three conveying screws described later, and frictional charging of the M toner is promoted, and the magnetic force of the magnet roller in the developing roll 21M is applied to the surface of the developing sleeve rotated by the developing roll 21M. Adsorbed and pumped up. Then, with the rotation of the developing sleeve, the layer thickness is regulated when passing through the position facing the doctor blade 25M as the regulating member, and then the sheet is conveyed to the developing position facing the photoreceptor 3M.

  At this developing position, negative M toner is transferred from the developing sleeve side to the latent image side between the developing sleeve to which a negative developing bias output from a power source (not shown) is applied and the latent image on the photoreceptor 3M. The development potential for electrostatic movement acts on the surface. In addition, a non-developing potential for electrostatically moving the negative M toner from the background portion side to the developing sleeve side acts between the developing sleeve and the uniformly charged portion (background portion) of the photoreceptor 3M. The M toner in the M developer on the developing sleeve is transferred onto the latent image on the photoreceptor 3M by the action of the developing potential. By this transfer, the latent image on the photoreceptor 3M is developed into an M toner image.

  The M developer that has consumed M toner by development is returned to the casing as the developing sleeve rotates. Further, the M toner image on the photoreceptor 3M is intermediately transferred onto an intermediate transfer belt 51 of a transfer unit 50 described later.

  Further, the developing unit 20M has a toner concentration sensor (not shown) composed of a magnetic permeability sensor. The toner concentration sensor outputs a voltage having a value corresponding to the magnetic permeability of the M developer accommodated in a developer collection and conveyance path (described later) of the developing unit 20M. Since the magnetic permeability of the developer shows a good correlation with the toner concentration of the developer, the toner concentration sensor outputs a voltage having a value corresponding to the toner concentration. The value of the output voltage is sent to a toner supply control unit (not shown).

  The toner replenishment control unit includes storage means such as a RAM. In this storage means, M Vtref, which is a target value of the output voltage from the M toner density sensor, and C, which are target values of the output voltage from the toner density sensor mounted in another developing unit. Vtref data for Y and M are stored.

  For the M developing unit 20M, the output voltage value from the M toner density sensor is compared with the M Vtref, and an M toner density replenishing device (not shown) is driven for a time corresponding to the comparison result. As a result, M toner for replenishment is replenished into the developer collection transport path of the developing unit 20M. By controlling the driving of the M toner replenishing device in this way (toner replenishment control), an appropriate amount of M toner is replenished to the M developer whose M toner density has been reduced along with development, and the inside of the developing unit 20M. The M toner concentration of the M developer is maintained within a predetermined range.

  The same toner replenishment control is performed for the developing units 20C, 20Y, and 20K.

  The M toner image developed on the photoreceptor 3M is transferred to the front surface of an intermediate transfer belt 51 described later. The untransferred toner that has not been transferred onto the intermediate transfer belt 51 adheres to the surface of the photoreceptor 3M that has undergone the transfer process. This transfer residual toner is removed by the drum cleaning device 5M. The surface of the photoreceptor 3M from which the transfer residual toner has been removed in this manner is discharged by the discharging lamp 6M and then charged again by the charging device 4M.

  The toner image forming unit 1M for M has been described in detail. However, in the toner image forming units 1C, 1Y, and 1K for other colors, C, Y, and K toners are formed on the surfaces of the photoreceptors 3C, 3Y, and 3K by the same process. An image is formed.

  A transfer unit 50 is disposed on the right side of the toner image forming units 1M, 1C, 1Y, and 1K that are arranged in the vertical direction. The transfer unit 50 includes a driving roller 52, a tension roller 53, and a driven roller 54 inside a loop of an endless intermediate transfer belt 51. Then, while the intermediate transfer belt 51 is stretched by these three rollers, it is moved endlessly in the clockwise direction in the drawing by the rotational drive of the drive roller 52. The intermediate transfer belt 51 moved endlessly in this way has its front surface on the left side of the drawing in contact with the M, C, Y, and K photoconductors 3M, 3C, 3Y, and 3K, respectively. This forms primary transfer nips for M, C, Y, and K.

  In addition to the three rollers described above, four transfer chargers 55M, 55C, 55Y, and 55K are disposed inside the loop of the intermediate transfer belt 51. These transfer chargers 55M, 55C, 55Y, and 55K are arranged on the back side of the primary transfer nip for M, C, Y, and K so as to apply charges to the back surface of the intermediate transfer belt 51. By applying this electric charge, the toner is transferred in the primary transfer nip for M, C, Y, and K in such a direction that the toner is electrostatically moved from the photoreceptor 3M, 3C, 3Y, 3K side to the belt front surface side. An electric field is formed. A transfer roller to which a transfer bias is applied may be used instead of the corona charge type transfer charger.

  The M, C, Y, and K toner images formed on the photoreceptors 3M, 3C, 3Y, and 3K of the respective colors are put on the belt from the photoreceptor side by the influence of the nip pressure and the transfer electric field in the primary transfer nip of each color. The image is moved to the surface side and transferred onto the intermediate transfer belt 51 in a superimposed manner. As a result, a four-color superimposed toner image (hereinafter referred to as “four-color toner image”) is formed on the intermediate transfer belt 51.

  A secondary transfer bias roller 56 is in contact with the driving roller 52 on the intermediate transfer belt 51 from the belt front surface side, thereby forming a secondary transfer nip. A secondary transfer bias is applied to the secondary transfer bias roller 56 by a voltage applying means including a power source and wiring (not shown). As a result, a secondary transfer electric field is formed between the secondary transfer bias roller 56 and the grounded driving roller 52. The four-color toner image formed on the intermediate transfer belt 51 enters the secondary transfer nip as the intermediate transfer belt 51 moves endlessly.

  The printer includes a paper feed cassette (not shown), and accommodates a recording paper bundle in which a plurality of recording papers P are stacked therein. Then, the uppermost recording paper P is sent out to the paper feed path at a predetermined timing. The fed recording paper P is sandwiched between the rollers of the registration roller pair 60 disposed at the end of the paper feed path.

  The registration roller pair 60 rotates both rollers in order to sandwich the recording paper P sent from the paper feed cassette between the rollers. However, as soon as the leading edge of the recording paper P is sandwiched, both rollers rotate. Stop. Then, the recording paper P is sent toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 51.

  In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 51 are collectively transferred onto the recording paper P by the action of the secondary transfer electric field and the nip pressure. A full color image is formed in combination with the white color of the recording paper P. The recording paper P on which the full-color image is formed in this manner is discharged from the secondary transfer nip, and then sent to a fixing device (not shown) to fix the full-color image.

  The secondary transfer residual toner adhering to the surface of the intermediate transfer belt 51 after passing through the secondary transfer nip is removed from the belt surface by the belt cleaning device 57 that sandwiches the intermediate transfer belt 51 with the driven roller 54. Removed.

FIG. 3 is an explanatory diagram showing a schematic configuration of the developing unit 20 of the toner image forming unit 1.
In the figure, the graph of the magnetic flux density in the normal direction on the outer peripheral surface of the magnet roller 23 is displayed in an overlapping manner. In the following description, description of color-coded codes M, C, Y, and K is omitted.

  In the figure, the drum-shaped photoconductor 3 is disposed in such a posture that its axial direction extends in a direction perpendicular to the drawing sheet. Inside the developing unit 20, a developer supply transport path 27 and a developer recovery transport path 28 are provided, and a developer is accommodated in these. Further, a supply screw 32 as a developer supply / conveyance member is rotatably accommodated in the developer supply / conveyance path 27. Further, a collecting screw 35 as a developer collecting and conveying member is rotatably accommodated in the developer collecting and conveying path 28.

  The developing roll 21 is disposed so that a part of the peripheral surface of the developing sleeve 22 is exposed from an opening formed in the casing on the side facing the photoreceptor 3. On the opposite side of the developing sleeve 22 from the side facing the photoreceptor 3, the developer supply / conveyance path 27 and the developer recovery / conveyance path 28 face each other over almost the entire area in the axial direction. The developer collection / conveyance path 28 is disposed below the developing roll 21, and the developer supply / conveyance path 27 is disposed at a position slightly shifted downward from the side of the developing roll 21.

  The supply screw 32 accommodated in the developer supply / conveying path 27 has a posture extending in the horizontal direction, like the photoreceptor 3 and the developing roll 21. Then, the rod-shaped rotating shaft member 33 and the screw blade 34 erected in a spiral shape on the peripheral surface thereof are integrated in a counterclockwise direction in the figure by driving means such as a motor or a drive transmission system (not shown). Is driven to rotate.

  The recovery screw 35 accommodated in the developer recovery conveyance path 28 also has a posture extending in the horizontal direction, like the photoconductor 3, the developing roll 21, and the supply screw 32. Then, the rotating shaft member 36 and the screw blade 37 are integrally rotated in the clockwise direction in the drawing by a driving means (not shown).

  The developer supply transport path 27 and the developer recovery transport path 28 are partitioned by a partition wall 43 that forms a side wall on the developing roll side of the developer supply transport path 27. The partition wall 43 has openings at both ends in the developing roll axial direction, and the developer supply transport path 27 and the developer recovery transport path 28 communicate with each other through the openings.

  In the developer supply conveyance path 27, the developer G1 held in the screw blades 34 of the supply screw 32 moves from the front side to the back side in the direction orthogonal to the drawing surface as the supply screw 32 rotates. Be transported. In the course of this conveyance, as indicated by a thick solid arrow in the figure, the developer G1 is sequentially supplied to the developing sleeve 22 side over the upper end of the partition wall 43, and the magnetic force pumped up by the magnet roller 23 in the developing sleeve 22 is supplied. Is pumped up to the surface of the developing sleeve 22. The developer G1 transported to the vicinity of the downstream end of the developer supply transport path 27 in the developer transport direction (near the rear end in the figure) without being drawn up by the developing sleeve 22 is developed through the opening of the partition wall 43. It falls into the agent recovery conveyance path 28.

  With the rotation of the developing sleeve 22, the developer G <b> 2 that has been transported to the developing region and contributed to the development is then transported to a position facing the developer recovery transport path 28 with the rotation of the developing sleeve 22. Then, it is peeled off from the sleeve surface due to the influence of the repulsive magnetic field formed by the magnet roller 23 and falls into the developer collecting and conveying path 28 as shown by a one-dot chain line arrow in the figure.

  In the developer collection conveyance path 28, the developer G2 held in the blades of the collection screw 35 is conveyed from the back side to the front side in the direction orthogonal to the drawing sheet as the collection screw 35 rotates. . In this conveyance process, toner is supplied by the above-described toner supply device. Further, in the vicinity of the upstream end of the developer recovery transport path 28 in the developer transport direction (near the rear end in the figure), the development falling from the developer supply transport path 27 through the opening of the partition wall 43. Take in the agent. The developer transported to the vicinity of the downstream end in the developer transport direction by the recovery screw 35 (near the front end in the figure) passes through the opening of the partition wall 43 and supplies the developer. It is lifted to the conveyance path 27.

  As shown in FIG. 3, the magnet roller 23 in the present embodiment has a configuration in which five magnetic poles N1, S1, N2, S2, and S3 are arranged along the developing sleeve rotation direction.

  The magnetic pole N1 is a developing magnetic pole that generates a developing magnetic force for causing the developer carried on the surface of the developing sleeve 22 to rise in the developing region. The magnetic pole S <b> 1 is a transport magnetic pole that generates a magnetic force for transporting the developer carried on the surface of the developing sleeve 22 to the developing region. The magnetic pole N2 is a regulation magnetic pole that generates a regulation magnetic force for causing the developer to rise when passing through a regulation gap formed between the surface of the developing sleeve 22 and a doctor blade 25 as a developer regulation member. is there. Examples of the magnetic pole S2 include a pumping magnetic pole that generates a magnetic force for pumping up the developer on the surface of the developing sleeve 22. The magnetic pole S3 is a magnetic pole that forms the above-described repulsive magnetic field together with the magnetic pole S2, peels off the developer from the surface of the developing sleeve 22, and recovers it to the developer recovery conveyance path.

Next, the developing unit in the conventional image forming apparatus will be described.
FIG. 4 is an explanatory view showing an example of a conventional developing unit 120.
Compared with the developing unit 20 of the present embodiment shown in FIG. 3, the conventional developing unit 120 has a higher upper end position of the partition wall 143, and is a shielding member that will be described later provided in the developing unit 20 of the present embodiment. The wall 44 is not provided.

  In the conventional developing unit 120 having such a configuration, the restriction magnetic force by the restriction magnetic pole N2 acts on the developer G3 blocked from passing through the restriction gap, and the restriction adjacent to the downstream side in the rotation direction of the developing sleeve of the doctor blade 25. This causes a situation in which the developer G3 is retained in the retention space. The restricted stay developer G3 staying in the restricted stay space rotates in the opposite direction to the rotation direction of the developing sleeve 22 in the restricted stay space by the surface movement of the developing sleeve 22 as indicated by the dotted arrow in the figure ( It stays in the restricted stay space while circulating).

  The regulated staying developer G3 may also take in the developer G1 that has been splashed up by the supply screw 32.

  The regulated staying developer G3 is rubbed and charged while being circulated and moved in the regulated staying space while receiving the restraining force of the regulated magnetic force. The amount is abnormally high. Therefore, a difference occurs in the developing ability between the regulated staying developer G3 and the developer G1 in the developer supply conveyance path 27. Even with the developers G1 and G3 having different developing capabilities, even if they are in a state of being uniformly dispersed and mixed with each other, even if they are used for development, image density unevenness that can be recognized by human beings. Will not occur. However, if the developer G1 and G3 are used in development in a state where mixing of the developers G1 and G3 is insufficient, image density unevenness that can be recognized by humans is generated and image quality is deteriorated.

  In the conventional developing unit 120 shown in FIG. 4, the restricted staying developer G <b> 3 that has escaped the restriction of the restricting magnetic force during the circulating movement is collected into the developer supply conveyance path 27. If collected in the developer supply conveyance path 27, the regulated staying developer G3 is sufficiently mixed with the developer G1 and then pumped up again, so that the above-described image quality degradation problem does not occur.

  However, a pumping magnetic pole S2 having a polarity opposite to that of the regulation magnetic pole N2 is disposed adjacent to the upstream side in the developing sleeve rotation direction. For this reason, in the conventional developing unit 120 shown in FIG. 4, a magnetic field is formed such that the magnetic lines of force that emerge from the regulation magnetic pole N2 are drawn up through the regulation retention space to the magnetic pole S2. In such a magnetic field, the restricted staying developer portion that is closest to the pumping magnetic pole S2 of the restricted staying developer G3 (the portion that is close to the upper end of the partition wall 143) is drawn along the line of magnetic force S2 side. To the surface of the developing sleeve 22. As a result, a part of the restricted staying developer G3 is carried on the surface of the developing sleeve 22 without being collected in the developer supply conveyance path 27.

  At this time, if the developer G1 from the developer supply / conveying path 27 is sufficiently pumped on the surface of the developing sleeve 22, the regulated staying developer G3 attracted by the pumping magnetic force is placed on the developer G1. It is carried on the surface of the developing sleeve 22 so as to overlap. In this case, since the regulated staying developer G3 is carried in a region far from the surface of the developing sleeve, passage of the regulating gap is blocked by the doctor blade 25, and a developer layer composed only of the developer G1 is conveyed to the developing region. . Therefore, in this case, image density unevenness does not occur and image quality deterioration does not occur.

  However, in the conventional developing unit 120 shown in FIG. 4, the restricted staying developer G <b> 3 attracted by the pumping magnetic force obstructs the pumping of the developer G <b> 1 from the developer supply conveyance path 27. In particular, the portion of the developer G1 supplied to the developing sleeve side where the feeding force to the developing sleeve side by the screw blade 34 of the supply screw 32 is weak is pumped up by the regulated staying developer G3 attracted by the pumping magnetic force. Be inhibited. Note that examples of the location where the feeding force is weak include a location where the outer peripheral end portion of the screw blade 34 does not pass through the vicinity of the developing sleeve 22.

  As a result of the pumping being inhibited as described above, the restricted staying developer G3 attracted by the pumping magnetic force is carried in a region near the surface of the developing sleeve 22 in such a place, and passes through the restriction gap. It will be transported to the development area. Therefore, in the conventional developing unit shown in FIG. 4, there is a developer layer in a state where mixing of the regulated stay developer G3 having an abnormally high toner charge amount with the developer G1 having a normal toner charge amount is insufficient. The image is sent to the development area, causing image density unevenness and image quality degradation.

  In particular, the conventional developing unit 120 shown in FIG. 4 is of a supply / recovery separation type in which the developer on the developing sleeve 22 that has passed through the developing region is recovered to a developer recovery / conveyance path 28 different from the developer supply / conveyance path 27. Development unit. In such a developing unit, the developer G1 in the developer supply transport path 27 is transported to the downstream end portion in the developer transport direction while being pumped up to the surface of the developing sleeve 22. Accordingly, the amount of the developer G1 flowing in the developer supply transport path 27 is smaller toward the downstream side in the developer transport direction, and therefore, the developer supply transport path 27 at the downstream end of the developer supply transport path 27 in the developer transport direction. From this, the amount of the developer G1 supplied to the developing sleeve 22 side tends to be insufficient. For this reason, at the downstream end of the developer supply conveyance path 27 in the developer conveyance direction, pumping of the developer G1 is easily hindered by the regulated staying developer G3 attracted by the pumping magnetic force, and image quality deterioration due to image density unevenness occurs. It's easy to do.

  Therefore, in the developing unit 20 of the present embodiment, in order to suppress the image quality deterioration, the height of the partition wall 43 is lowered by lowering the upper end position of the partition wall 43 than the conventional developing unit 120, and as a blocking member. The shielding wall 44 made of a metal material is provided. The shielding wall 44 is disposed at a position that prevents the regulated staying developer G3, which has been prevented from passing through the regulation gap by the doctor blade 25, from moving to the surface side of the developing sleeve 22 along the lines of magnetic force of the regulation magnetic force. ing.

  By providing such a shielding wall 44, the regulated staying developer G3 attracted by the pumping magnetic force does not hinder the pumping of the developer G1 from the developer supply conveyance path 27. Therefore, it is difficult to generate a portion where the amount of the developer G1 pumped up from the developer supply conveyance path 27 is locally insufficient, and the development stay sleeve G3 attracted by the pumping magnetic force can pass through the regulation gap. It becomes difficult to carry in a region close to the surface.

  Therefore, it is possible to suppress the occurrence of a situation where a developer layer in an insufficiently mixed state between the regulated stay developer G3 having an abnormally high toner charge amount and the developer G1 having a normal toner charge amount is sent to the development region. Thus, image quality deterioration due to image density unevenness is suppressed.

  Further, the shielding wall 44 of the present embodiment includes a slit 45 that is a supply passage for allowing the developer G1 in the developer supply conveyance path 27 to pass to the developing sleeve 22 side over at least the entire area of the developing sleeve in the developing sleeve axial direction. It is formed between the upper end of the partition wall 43. Therefore, even if such a shielding wall 44 is provided, the operation of pumping up the developer G1 in the developer supply transport path 27 to the surface of the developing sleeve 22 is not hindered.

  In particular, in the present embodiment, the slit 45 is disposed at a position where the straight line L connecting the rotation center position of the development sleeve 22 and the rotation center position of the supply screw 32 passes through the slit 45 as viewed from the axial direction of the development sleeve. Has been. Therefore, the developer G1 in the developer supply conveyance path 27 can be supplied to the surface of the developing sleeve 22 at the shortest distance.

  Further, the length of the slit 45 in the axial direction of the developing sleeve in this embodiment is set to be larger than the width of the maximum image forming area as shown in FIG.

  When the length of the slit 45 in the developing sleeve axial direction is narrower than the maximum image forming region, the surface of the developing sleeve 22 corresponding to both end portions in the developing sleeve axial direction of the maximum image forming region passes through the slit 45 and the developing sleeve shaft. The developer G1 moved so as to wrap around in the direction is carried. Therefore, the amount of the developer G1 carried on the surface portion of the developing sleeve 22 corresponding to both end portions in the axial direction of the developing sleeve in the maximum image forming region tends to be insufficient. Therefore, in the surface portion of the developing sleeve 22, the shortage is compensated for by the restricted stay developer G <b> 3 in the restricted stay space. As a result, when image formation is performed using the entire maximum image forming region, image density unevenness occurs between the central portion and both end portions in the axial direction of the developing sleeve, causing image quality degradation.

  In this embodiment, since the length of the slit 45 in the axial direction of the developing sleeve is set to be larger than the width of the maximum image forming area, such image quality deterioration does not occur.

  The opening width of the slit 45 (the length in the developing sleeve rotation direction) is preferably 2 [mm] or more.

  If it is less than 2 [mm], it becomes difficult for the developer G1 to smoothly pass through the slit 45 by the action of the pumping magnetic force when a carrier having a volume average particle size of about 50 [μm] is used. If the developer G1 cannot smoothly pass through the slit 45, the amount of the developer G1 pumped up on the surface of the developing sleeve 22 is insufficient, and the regulated staying developer G3 is replenished in the insufficient portion and developed through the regulated gap. It will be transported to the area. In this case, the image quality may be deteriorated due to uneven image density.

  On the other hand, if it is 2 [mm] or more, the developer G1 can be smoothly passed through the slit 45 even when a carrier having a volume average particle diameter of about 50 [μm] is used. Thereby, if it is a developer using the small particle size carrier of recent years in which the carrier particle size has been reduced, the developer G1 can pass through the slit 45 smoothly and smoothly. Therefore, it is possible to avoid the deterioration of the image quality due to the image density unevenness because the developer G1 cannot pass through the slit 45 smoothly.

  In addition, since fluctuations in the amount of developer conveyed to the development area have a great influence on the development capability, a specified amount of developer is stably sent to the development area by the regulation gap between the doctor blade 25 and the surface of the development sleeve 22. Is set to

  Here, when the shielding wall gap between the shielding wall 44 and the surface of the developing sleeve 22 (gap between the closest portions) is narrower than the regulation gap, the developer carried on the surface of the developing sleeve 22 and passing through the shielding wall gap. The amount will be less than the amount that passes through the regulatory gap. Therefore, even when the developer passing through the shielding wall gap includes only the developer G1 pumped up from the developer supply conveyance path 27 and does not include the regulated staying developer G3, the developer is regulated on the developer G1. The developer layer on which the staying developer G3 overlaps passes through the regulation gap. Even in this case, as long as the regulated staying developer G3 is uniformly dispersed in the developer layer passing through the regulation gap, the image quality deterioration due to the image density unevenness as described above does not occur.

  However, as a result of the developer layer containing a large amount of regulated staying developer having an abnormally high toner charge amount contributing to the development in the development region, there is a problem that a normal image density cannot be obtained.

  Therefore, in the present embodiment, the shielding wall gap between the shielding wall 44 and the surface of the developing sleeve 22 is set to be the same as the regulation gap or wider than the regulation gap. As a result, the developer layer passing through the regulation gap is the developer layer passing through the shielding wall gap, that is, the developer layer consisting only of the developer G1 having a normal toner charge pumped up from the developer supply conveyance path 27. It becomes. Therefore, the above-described problem that a normal image density cannot be obtained can be solved.

  In order to effectively prevent the regulated staying developer G3 from entering the slit 45 around the shielding wall 44, at least the position of the end (lower end) of the shielding wall 44 facing the slit 45 is It is necessary to set as follows. That is, it is necessary to set the end portion to be located upstream of the straight line L2 connecting the inflection point between the pumping magnetic pole S2 and the regulating magnetic pole N2 and the rotation center of the developing sleeve 22 in the developing sleeve rotation direction. is there.

  Further, in the present embodiment, as shown in FIG. 3, the shielding wall 44 has the shielding wall 44 so that the developer G4 is pumped and carried by the action of the magnetic force on the surface of the shielding wall 44 on the developer supply conveyance path 27 side. The shape and arrangement, the configuration of the magnet roller 23, and the like are adjusted.

  With such a configuration, the developer G4 raised on the shielding wall 44 by the pumping magnetic force becomes a wall, and the movement of the regulated staying developer G3 attracted to the slit 45 side by the pumping magnetic force is prevented. Can do. As a result, it is possible to prevent a situation where the regulated staying developer G3 passes around the shielding wall 44 and passes through the slit 45. As a result, there is a possibility that a developer layer in an insufficiently mixed state between the regulated stay developer G3 having an abnormally high toner charge amount and the developer G1 having a normal toner charge amount is sent to the development region. Further, image quality deterioration due to image density unevenness is further suppressed.

  Even if the shape of the shielding wall 44 is changed in design and the same function as the wall of the developer G4 raised on the shielding wall 44 is realized by the shielding wall 44 itself, the same effect as described above can be obtained. can get.

  However, in this case, the size of the shielding wall 44 becomes large, and it is required to arrange the shielding wall 44 having such a large size in a narrow space between the developing sleeve 22 and the supply screw 32. Therefore, high accuracy is required for the component accuracy and assembly accuracy of the shielding wall 44, resulting in an increase in cost. Therefore, in terms of cost, it is more advantageous to form the wall with the developer G4 that is raised on the shielding wall 44 as in the present embodiment.

  Further, as described above, at the downstream end of the developer supply transport path 27 in the developer transport direction, the amount of the developer G1 is small, and the developer G1 supplied from the developer supply transport path 27 to the developing sleeve 22 side. The amount of is easy to run out.

  However, in this embodiment, the height of the partition wall 43 is made lower than that of the conventional developing unit 120 shown in FIG. Therefore, in the conventional developing unit 120, even if the developer G1 is present in the developer supply / conveyance path 27 so that the developer supply amount to the developing sleeve 22 is insufficient, the development of the present embodiment is performed. If the unit 20 is used, it is possible to avoid a shortage of the developer supply amount. As a result, even at the downstream end of the developer supply transport path 27 in the developer transport direction, the mixing state of the regulated stay developer G3 having an abnormally high toner charge amount and the developer G1 having a normal toner charge amount is insufficient. Occurrence of a situation in which a developer layer in an unsatisfactory state is sent to the development area is suppressed. Therefore, image quality deterioration due to image density unevenness can be suppressed.

  The height of the partition wall 43 needs to be such that the developed developer G2 can be prevented from moving to the developer supply transport path 27 side. For this purpose, the upper end position of the partition wall 43 is positioned downstream of the peeling direction of the developing sleeve relative to the peeling region where the peeling magnetic force for peeling the developed developer G2 from the surface of the developing sleeve 22 acts. Set. Specifically, for example, it is set so as to be located downstream of the straight line L1 connecting the inflection point between the pumping magnetic pole S2 and the magnetic pole S3 and the rotation center of the developing sleeve in the developing sleeve rotation direction.

  In the present embodiment, the pumping magnetic pole S2 and the regulating magnetic pole N2 are disposed adjacent to each other in the developing sleeve rotation direction. That is, there is no other magnetic pole between the pumping magnetic pole S2 and the regulating magnetic pole N2.

  With such a configuration, the developer carried on the surface of the developing sleeve 22 between the pumping magnetic pole S2 and the regulation magnetic pole N2 is in a state of lying along the magnetic field lines between the pumping magnetic pole S2 and the regulation magnetic pole N2. When the developer lies down, the developer is in a dense state. Therefore, even if the regulated staying developer G3 is attracted to the surface of the developing sleeve 22 with a strong force between the pumping magnetic pole S2 and the regulating magnetic pole N2, it only gets onto the developer G1 already carried on the surface of the developing sleeve. It is. Therefore, the regulated staying developer G3 does not push the developer G1 away and enter the vicinity of the surface of the developing sleeve. Therefore, the restricted stay developer G3 is prevented from being mixed into the developer passing through the restriction gap, and the development process can be performed only with the developer G1 having a normal toner charge amount.

  Here, even if the surface of the photoconductor is a non-image area such as a space between sheets, the developer on the developing sleeve 22 and the surface of the photoconductor are in mechanical contact with each other, so that the developing sleeve 22 contacts the surface of the photoconductor. There is toner that has been transferred or adhered due to other causes.

  Usually, the surface potential of the developing sleeve 22 is formed so that an electric field is formed so as to move the toner from the non-image area on the photosensitive member surface to the developing sleeve 22 so that the non-image area on the photosensitive member surface is not stained with toner. A potential difference is provided between the surface potential of the non-image area on the surface of the photoreceptor.

  In addition, the image area on the surface of the photoconductor is irradiated with laser light Lm, Lc, Ly, and Lk from the optical writing unit 10 according to an image pattern to be imaged, and an latent image is formed. There are non-image areas that do not form an image. Then, the surface of the developing sleeve 22 is formed so that an electric field is generated to move the toner from the non-image portion on the surface of the photosensitive member to the developing sleeve 22 so that the non-image portion of the image area on the surface of the photosensitive member is not stained with toner. A potential difference is provided between the potential and the surface potential of the non-image area on the surface of the photoreceptor.

  Since the surface of the photoconductor is uniformly charged by the charging device 4, the surface potential of the non-image forming area on the surface of the photoconductor where no latent image is formed and the surface potential of the non-image portion of the image area are the same potential. . In this embodiment, the potential difference (B−A) [V] between the surface potential A [V] of the developing sleeve 22 and the surface potential B [V] of the non-image area and the non-image portion on the surface of the photoreceptor is The background potential is X [V].

  Specifically, when the toner having a normal charging polarity of minus polarity is used and the surface potential A [V] of the developing sleeve 22 is set to −500 [V], the surface potential of the non-image area and the non-image portion on the surface of the photoreceptor. B [V] is set to -650 [V]. Further, the background potential X [V] at this time is −150 [V].

  As a result, the toner adhering to the non-image area or non-image portion on the surface of the photoconductor is attracted to the surface of the developing sleeve 22 to prevent the non-image area or non-image portion on the surface of the photoconductor from being stained with toner. be able to.

  However, by applying the background potential X [V], toner is attracted to the surface of the developing sleeve 22 instead of causing non-image areas or non-image areas on the surface of the photosensitive member to be stained. Becomes dirty with toner.

  That is, the toner attracted to the surface of the developing sleeve 22 from the non-image area on the surface of the photosensitive member is contaminated with the toner. If the surface of the developing sleeve 22 is contaminated with toner from the non-image area as described above, density unevenness occurs in the developed image when the image to be developed is longer than the circumference of the developing sleeve.

  The toner adhering to the surface of the developing sleeve 22 from the non-image area on the surface of the photoconductor develops the latent image formed in the image area on the surface of the photoconductor together with the toner in the developer spiked on the developing sleeve 22. Used in the first round of the developing sleeve. As a result, more toner is transferred to the latent image on the photoreceptor 3 in the first round of the developing sleeve than when only the toner in the developer spiked on the developing sleeve 22 is used for development. The toner density of the developed image increases. Therefore, the density between the image after the second round of the developing sleeve after the toner attached to the surface of the developing sleeve 22 from the non-image area on the surface of the photosensitive member is used for development and the image of the first round of the developing sleeve There will be a difference.

  Further, on the surface of the developing sleeve 22, a portion where toner contamination corresponding to a non-image portion of the image area on the surface of the photosensitive member occurs, and a portion where toner contamination corresponding to the image portion of the image region on the surface of the photosensitive member does not occur, Will be mixed. When a black image is printed on the entire surface in such a mixed state, the toner in the developer acting on the development is divided into a portion where the toner stain is generated on the surface of the developing sleeve 22 and a portion where the toner stain is not generated. Make a difference in quantity. For this reason, the amount of toner developed on the photoconductor 3 is different, resulting in a difference in image density.

  FIG. 6 shows an image image and an abnormal image that is actually printed. FIG. 6A shows an image image to be created, and FIG. 6B shows an actually printed image.

  FIG. 7 is a diagram for explaining how the surface of the developing sleeve 22 is smeared with toner. FIG. 7A is a diagram illustrating how the developing sleeve 22 is smeared with toner adhering to the surface of the developing sleeve 22 from the non-image area of the photoreceptor surface. Shows the direction.

  FIG. 7B shows how the developing sleeve is stained by the image pattern formed in the image area on the surface of the photoconductor in the image image shown in FIG. That is, it shows how the developing sleeve 22 is stained after the first round of the developing sleeve by the toner adhering to the surface of the developing sleeve 22 from the non-image portion on the surface of the photoreceptor corresponding to the first round of the developing sleeve. In the non-image portion, toner is not used for development in the first round of the developing sleeve. Therefore, the surface of the developing sleeve 22 corresponding to the non-image portion is caused by toner adhering from the non-image region on the surface of the photoreceptor. Is also dirty.

  FIG. 7C shows a state in which the toner stain on the developing sleeve 22 formed by the image pattern as shown in FIG. 7B is eliminated when the entire black image is printed in the second round of the developing sleeve. .

  Due to the difference in how the developing sleeve 22 is smeared with toner as shown in FIGS. 7A, 7B, and 7C, the image of the first developing sleeve and the image of the second developing sleeve are different. Or a difference in density occurs in the image on the second round of the developing sleeve. For this reason, an abnormal image as shown in FIG. 6B is generated with respect to the image of FIG.

  Since it is impossible to prevent the surface of the developing sleeve 22 from being stained with toner due to the ground potential X [V], the toner adhering to the developing sleeve 22 is removed from the surface of the developing sleeve 22 with another force. is necessary.

  Therefore, in the developing unit 20 of the present embodiment, a bias having a potential at which an electric field is generated so that the toner moves from the surface of the developing sleeve 22 to the shielding wall 44 is applied to the shielding wall 44 formed of a metal material. Since the shielding wall 44 is disposed at a position facing the surface of the developing sleeve 22, the electric field is applied to the toner on the surface of the developing sleeve 22 by applying a bias having the above-described potential to the shielding wall 44. Can contribute.

  When the surface potential A [V] of the developing sleeve 22 is -500 [V], the surface potential X is assumed when the surface potential B [V] of the non-image area and the non-image portion of the photoreceptor 3 is -650 [V]. [V] is -150 [V]. The distance between the shielding wall 44 and the developing sleeve 22 is the same as the distance between the photosensitive member 3 and the developing sleeve 22. In this case, by applying a bias of −350 [V] or less to the shielding wall 44, the toner on the surface of the developing sleeve 22 can be attracted to the shielding wall 44 to clean the surface of the developing sleeve 22.

  In order to generate the same potential at a certain point, when the distance is increased, it is necessary to increase the applied voltage in inverse proportion to the square of the distance.

  For example, the distance between the surface of the photoreceptor 3 and the surface of the developing sleeve 22 is 0.3 [mm], the distance between the surface of the developing sleeve 22 and the shielding wall 44 is 1 [mm], and the background potential X [V]. Is −150 [V]. Further, the potential difference (C−A) [V] between the surface potential A [V] of the developing sleeve 22 and the applied potential C [V] to the shielding wall 44 is expressed by the toner from the surface of the developing sleeve 22 to the shielding wall 44. A developing sleeve cleaning potential Y [V] for cleaning the surface of the developing sleeve is moved. At this time, the developing sleeve cleaning potential Y [V] can be obtained from the following equation (1).

  From the relationship of Equation 1, when the developing sleeve cleaning potential Y [V] is about 1670 [V] or higher and the surface potential of the developing sleeve 22 is −500 [V], a bias of 1170 [V] or higher is applied to the shielding wall 44. What is necessary is just to apply. As a result, an electric field that moves toner from the surface of the developing sleeve 22 to the shielding wall 44 is formed between the surface of the developing sleeve 22 and the shielding wall 44, and the developing sleeve 22 can be cleaned.

  In this cleaning operation, the toner moves and adheres to the shielding wall 44 from the surface of the developing sleeve 22. In the developing unit 20 of the present embodiment, as the developing sleeve 22 rotates, the shielding wall 44 is rubbed by the developer carried on the developing sleeve 22 and the toner attached to the shielding wall 44 is removed. As described above, since the cleaning operation of the shielding wall 44 by the developer carried on the developing sleeve 22 is performed, it is possible to prevent toner from accumulating on the shielding wall 44.

  In the developing unit 20 of the present embodiment, as shown in FIG. 1, the toner is applied to the developing sleeve 22 from the non-image area on the surface of the photoreceptor or the non-image portion of the image area by the background potential X [V] in the direction of arrow T1 in the figure. Move to. In addition, by applying a bias for cleaning the surface of the developing sleeve 22 to the shielding wall 44, the toner attached to the surface of the developing sleeve 22 from the surface of the developing sleeve 22 by the developing sleeve cleaning potential Y [V]. It moves to the shielding wall 44 in the direction of arrow T2 in the figure.

FIG. 8 shows an image diagram in a state where the developing sleeve 22 is cleaned.
FIG. 8A shows a state in which the developing sleeve is soiled by toner adhering to the surface of the developing sleeve 22 from the non-image area on the surface of the photoreceptor.

  FIG. 8B shows how the developing sleeve is stained by the image pattern formed in the image area on the surface of the photoconductor in the image image shown in FIG. That is, the state of the toner stain on the developing sleeve 22 after the developing sleeve 22 has made one turn due to the toner adhering to the surface of the developing sleeve 22 from the non-image portion on the surface of the photoreceptor corresponding to the first round of the developing sleeve is shown. Yes. In the non-image portion, toner is not used for development in the first round of the developing sleeve. Therefore, the surface of the developing sleeve 22 corresponding to the non-image portion is caused by toner adhering from the non-image region on the surface of the photoreceptor. Is also dirty.

  FIG. 8C shows a state in which the toner stain on the developing sleeve 22 due to the image pattern is cleaned by the developing sleeve cleaning potential Y [V].

  In FIG. 8C, the toner contamination of the developing sleeve 22 due to the image pattern is caused by the developing sleeve cleaning potential Y [V] generated between the surface of the developing sleeve 22 and the shielding wall 44. Is cleaned, and the toner contamination of the developing sleeve 22 is reduced.

  FIG. 9A is an image, and FIG. 9B is an image printed using the developing unit 20 of the present embodiment. Compared with the print image shown in FIG. 9B and the print image shown in FIG. 6B, the image density unevenness of the print image is reduced by printing using the developing unit 20 of the present embodiment. It can be seen that the abnormal image is improved.

  Although the developing sleeve 22 can be cleaned depending on the condition of the developing sleeve cleaning potential Y [V], an electric field of the developing sleeve cleaning potential Y [V] is formed between the surface of the developing sleeve 22 and the shielding wall 44. The cleaning effect varies depending on the time for cleaning the surface of the developing sleeve 22. That is, a sufficient cleaning effect appears by applying the developing sleeve cleaning potential Y [V] for a longer time than the time when the developing sleeve 22 is soiled with the background potential X [V].

  In order for a sufficient cleaning effect of the developing sleeve 22 to appear when the developing sleeve cleaning potential Y [V] is applied between the surface of the developing sleeve 22 and the shielding wall 44, the following relationship is satisfied. You can do that. That is, the relationship between the application time Tx of the background potential X [V] and the application time Ty of the developing sleeve cleaning potential Y [V] is made to satisfy the relationship of Equation 2.

  Thereby, a sufficient cleaning effect of the developing sleeve 22 can be obtained. Conversely, if the time is shorter than this, the developing sleeve 22 cannot be sufficiently cleaned, and the cleaning effect becomes insufficient. The toner stain on the top is detected as an image.

  The rotating shaft member 33 of the supply screw 32 provided in the developing unit 20 of the present embodiment is formed of a nonmagnetic metal. Thereby, the flow of the developer can be made smooth by not having a magnetic field in the vicinity of the developing sleeve 22 and having a strength higher than that when the rotary shaft member 33 is formed of resin or the like.

  Further, since a bias is applied to the shielding wall 44 in the developing unit 20, if there is a metal member near the shielding wall 44, the bias may leak from the shielding wall 44 to the metal. Therefore, in the developing unit 20 of this embodiment, the portion of the rotating shaft member 33 formed of a nonmagnetic metal material that touches the developer is covered with resin, and a bias leaks from the shielding wall 44 to the rotating shaft member 33. Can be suppressed.

  In addition, if there is a metal member in the portion closest to the shielding wall 44, the bias applied to the shielding wall 44 may leak to the metal member. For this reason, in the developing unit 20 of the present embodiment, the screw blade 34 that is the portion closest to the shielding wall 44 of the supply screw 32 is formed of resin, thereby suppressing bias from leaking from the shielding wall 44 to the screw blade 34. doing.

  The developing unit 20 of the present embodiment includes an input path for applying a bias to the shielding wall 44 from a power source provided outside the developing unit 20 and in the printer. As this input path, there is a method in which a terminal that communicates with the shielding wall 44 is brought out of the developing unit 20 and power is supplied from a power source provided in the printer.

  Since the bias applied to the shielding wall 44 is large, an insulation process is performed so that the bias does not leak around the shielding wall 44 and the input path, or a metal member is not arranged around the terminal of the input path. Good to do.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A magnetic field generating unit such as a magnet roller 23 is provided inside, and a developer including toner and a magnetic carrier is carried on the surface by a magnetic force generated by the magnetic field generating unit and rotated to rotate the latent image of the photosensitive member 3 or the like. A developer carrying member such as a developing roll 21 that conveys the developer to a developing region facing the surface of the image carrying member, and the developer carried on the surface of the developer carrying member pass to the developing region. A developer regulating member such as a doctor blade 25 that forms a regulating gap for regulating the amount of developer conveyed between the developer carrying member and the surface of the developer carrying member. The developer that is disposed and is supplied onto the surface of the developer carrier is conveyed along the developer carrier rotation axis by a developer supply and conveyance member such as a supply screw 32, and the restriction gap A developer supply transport path such as a developer supply transport path 27 that collects the developer that has been blocked by the developer regulating member, and the magnetic field generating means includes at least the developer supply transport path in the developer supply transport path. A pumping magnetic force for pulling the developer in the developer supply / conveyance path beyond the upper end of the side wall such as the partition wall 43 on the developer carrier side toward the developer carrier and pumping it up to the surface of the developer carrier is provided. A developing device such as a developing unit 20 including a pumping magnetic pole such as a pumping magnetic pole S2 to be generated and a regulation magnetic pole such as a regulation magnetic pole N2 that generates a regulation magnetic force for causing the developer passing through the regulation gap to rise. In the above, the pumping magnetic pole and the regulating magnetic pole are adjacent to each other in the rotation direction of the developer carrier and have opposite polarities, and the developer supply / transport A supply passage such as a slit 45 for passing the developer in the developer supply / conveyance path to the developer carrier side at least over the entire region of the developer carrier rotation axis in the development region between the upper end of the side wall of the path. A metal material that prevents the developer blocked from passing through the restriction gap by the developer restricting member from moving to the surface side of the developer carrying member along the magnetic force lines of the restricting magnetic force. A blocking member such as the shielding wall 44 formed in step 1 is provided, and a potential is applied to the blocking member so that the toner moves from the surface of the developer carrying member to the blocking member. According to this, as described in the above embodiment, image density unevenness can be reduced and image quality deterioration can be suppressed.
(Aspect B)
In (Aspect A), the potential difference (B−A) [V] between the surface potential A [V] of the developer carrying member and the surface potential B [V] of the non-image area and non-image area of the image area on the surface of the photoreceptor. ] Is the background potential X [V], which is a potential at which an electric field is generated so as to move the toner from the non-image area and the non-image area of the image area on the surface of the photoreceptor to the developer carrier. The potential difference (C−A) [V] between the surface potential A [V] of the carrier and the bias potential C [V] applied to the blocking member causes the toner to move from the surface of the developer carrier to the blocking member. The developer carrying member cleaning potential Y [V] is a potential at which such an electric field is formed. According to this, as described in the above embodiment, the non-image area on the surface of the photoreceptor and the non-image area are prevented from being soiled, and the toner adhering to the surface of the developer carrying member is moved to the blocking member. Thus, the surface of the developer carrying member can be cleaned.
(Aspect C)
In (Aspect B), when the distance between the surface of the photoreceptor and the surface of the developer carrying member is a and the distance between the surface of the developer carrying member and the blocking member is b, the background potential X [V] And the developer carrying member cleaning potential Y [V] satisfy | X / a ² | ≦ | Y / b ² |. According to this, as described in the above embodiment, the potential suitable for cleaning the surface of the developer carrying member can be set according to the distance between the members.
(Aspect D)
In (Aspect B) or (Aspect C), the application time Tx of the background potential X [V] and the application time Ty of the developer carrier cleaning potential Y [V] satisfy the relationship of Tx ≦ Ty. According to this, as described in the above embodiment, the developer carrying member cannot be sufficiently cleaned, and the cleaning effect is insufficient, and the occurrence of toner contamination on the developer carrying member as an image is suppressed. be able to.
(Aspect E)
In (Aspect A), (Aspect B), (Aspect C) or (Aspect D), the developer supply / conveyance member has a screw-like blade portion such as a screw blade 34 on a rotation shaft such as the rotation shaft member 33. A conveyance screw that conveys the developer in the developer supply conveyance path in a direction along the rotation axis, and the rotation axis of the conveyance screw is formed of a nonmagnetic metal material, and the rotation axis The portion that touches the developer is coated with resin. According to this, as described in the above embodiment, the flow of the developer can be smoothed and applied to the blocking member by having a strength and not generating a magnetic field in the vicinity of the developer carrier. It is possible to suppress leakage of the bias to the rotating shaft.
(Aspect F)
In (Embodiment E), the blade portion of the conveying screw is formed of resin. According to this, as described in the above embodiment, the bias applied to the blocking member can be prevented from leaking to the blade portion.
(Aspect G)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D), (Aspect E) or (Aspect F), an external input path for applying a voltage from the outside to the blocking member is provided. According to this, as described in the above embodiment, it is possible to apply a voltage to the blocking member from the outside.
(Aspect H)
A latent image carrier such as the photosensitive member 3; a latent image forming unit such as an optical writing unit 10 that forms a latent image on the latent image carrier; and a developer containing toner and carrier. Developing means such as a developing unit 20 for developing the image, and the toner image formed on the latent image carrier by the developing means is finally transferred to a recording material such as recording paper P, and the In an image forming apparatus such as a printer that forms an image, as the developing unit, (Aspect A), (Aspect B), (Aspect C), (Aspect D), (Aspect E), (Aspect F) or (Aspect G) ) Developing device was used. According to this, as described in the above embodiment, it is possible to reduce the image density unevenness and suppress the deterioration of the image quality, and to perform a good image formation.

DESCRIPTION OF SYMBOLS 1 Toner image formation part 2 Process unit 3 Photoconductor 4 Charging apparatus 5 Drum cleaning apparatus 6 Static elimination lamp 10 Optical writing unit 20 Developing unit 21 Developing roll 22 Developing sleeve 23 Magnet roller 25 Doctor blade 27 Developer supply conveyance path 28 Developer Recovery conveyance path 32 Supply screw 33 Rotating shaft member 34 Screw blade 35 Recovery screw 36 Rotating shaft member 37 Screw blade 43 Partition wall 44 Shielding wall 45 Slit 50 Transfer unit 51 Intermediate transfer belt 52 Drive roller 53 Tension roller 54 Drive roller 55 Transfer charger 56 Secondary transfer bias roller 57 Belt cleaning device 60 Registration roller pair 120 Development unit 143 Partition wall

JP 2008-256813 A

Claims (8)

A developing region having a magnetic field generating means therein and facing the surface of the latent image carrier by rotating the developer containing toner and magnetic carrier on the surface by the magnetic force generated by the magnetic field generating means. A developer carrier for conveying the developer to
A regulation gap is formed between the surface of the developer carrying body and the surface of the developer carrying body to regulate the amount of the developer conveyed to the development area by passing the developer carried on the surface of the developer carrying body. A developer regulating member that
The developer disposed adjacent to the surface of the developer carrying member and conveyed on the surface of the developer carrying member is conveyed along the direction of the rotation of the developer carrying member by the developer supply conveying member. A developer supply transport path for collecting the developer that has been blocked by the developer regulating member through the regulation gap;
The magnetic field generating means draws the developer in the developer supply / conveying path toward the developer carrying body, at least beyond the upper end of the side wall of the developer carrying / conveying path in the developer supply / conveying path. In a developing device comprising a pumping magnetic pole for generating a pumping magnetic force for pumping to the surface of the head and a regulation magnetic pole for generating a regulation magnetic force for causing the developer to pass through the regulation gap,
The pumping magnetic pole and the regulating magnetic pole are adjacent to each other in the rotation direction of the developer carrier and are of opposite polarities to each other,
Supply for allowing the developer in the developer supply / conveyance path to pass to the developer carrier side over at least the entire area of the developer carrier rotating shaft in the developing region between the upper end of the side wall of the developer supply / conveyance path. A metal that prevents passage of the developer blocked by the developer restricting member to the surface side of the developer carrying member along the magnetic lines of force of the restricting magnetic force while securing a passage. A blocking member made of material is provided,
A developing device, wherein a bias is applied to the blocking member such that toner moves from the surface of the developer carrying member to the blocking member. The developing device according to claim 1.
The potential difference (B−A) [V] between the surface potential A [V] of the developer carrying member and the surface potential B [V] of the non-image portion and the non-image region of the image area on the surface of the photoreceptor is the photosensitivity. The background potential X [V], which is a potential at which an electric field that moves toner from the non-image area and the non-image area of the image area on the body surface to the developer carrying member is formed,
The potential difference (CA) [V] between the surface potential A [V] of the developer carrying member and the potential C [V] of the bias applied to the blocking member is determined from the surface of the developer carrying member to the blocking member. And a developer carrying member cleaning potential Y [V], which is a potential at which an electric field that causes toner to move is formed. The developing device according to claim 2.
When the distance between the surface of the photoreceptor and the surface of the developer carrying member is a, and the distance between the surface of the developer carrying member and the blocking member is b, the background potential X [V] and the developer A developing device characterized in that the relationship with the carrier cleaning potential Y [V] satisfies | X / a ² | ≦ | Y / b ² |. The developing device according to claim 2 or 3,
The developing device, wherein the application time Tx of the background potential X [V] and the application time Ty of the developer carrier cleaning potential Y [V] satisfy a relationship of Tx ≦ Ty. The developing device according to claim 1, 2, 3 or 4,
The developer supply transport member is a transport screw that is provided with a blade portion on a rotating shaft in a screw shape and transports the developer in the developer supply transport path in a direction along the rotating shaft.
2. A developing device according to claim 1, wherein a rotating shaft of the conveying screw is made of a nonmagnetic metal material, and a portion of the rotating shaft that contacts the developer is coated with a resin. The developing device according to claim 5.
The developing device according to claim 1, wherein the blade portion of the conveying screw is made of resin. The developing device according to claim 1, 2, 3, 4, 5 or 6.
A developing device comprising an external input path for applying a voltage from the outside to the blocking member. A latent image carrier;
Latent image forming means for forming a latent image on the latent image carrier;
Developing means for developing the latent image on the latent image carrier with a developer containing toner and carrier,
In the image forming apparatus for finally transferring the toner image formed on the latent image carrier by the developing unit to a recording material and forming an image on the recording material,
An image forming apparatus using the developing device according to claim 1, as the developing unit.