JP5064163B2 - Developing device, image forming apparatus - Google Patents

Description

  The present invention relates to a developing device provided in an electrophotographic image forming apparatus.

  In an electrophotographic image forming process, a uniformly charged photoconductor is exposed according to image information to form an electrostatic latent image on the photoconductor, and the electrostatic latent image formed on the photoconductor. A developer is supplied to the image by a developing device to develop the electrostatic latent image.

  As a developing method, there are a one-component developing method using a magnetic one-component developer or a non-magnetic two-component developer and a two-component developing method using a two-component developer containing a toner and a magnetic carrier. In the two-component development method, the magnetic carrier and the toner are agitated and frictionally charged with each other in the developing tank, so that the toner adheres to the surface of the carrier. Then, the developer in the developing tank is attracted to the outer peripheral surface of the developing roller by a magnetic field generated from the inside of the developing roller, and the attracted developer is transferred from the developing roller to the electrostatic latent image on the photosensitive member for development. Such a two-component development method is a little more complicated than the one-component development method, but is frequently used because the potential setting of the toner is relatively easy and high-speed compatibility and stability are excellent. .

  Next, the configuration of a two-component developing type developing device will be described. The developing device includes a developing tank and a developing roller. The developing roller includes a rotatable developing sleeve and a magnetic member fixed non-rotatingly inside the developing sleeve. The developing sleeve rotates so that its outer peripheral surface alternately and repeatedly passes through the inside of the developing tank and the developing area outside the developing tank, and attracts the developer to the outer peripheral surface by a magnetic force inside the developing tank. The developer attracted to the toner is supplied to the photoconductor in the development area. When the developer is attracted to the surface of the developing sleeve, the developer is in the form of a magnetic brush (like a head) made of a carrier to which toner is attached.

  Further, the developer in the developing tank is in the developing tank and around the developing sleeve in order from the downstream to the upstream in the rotation direction of the developing sleeve with respect to the outer peripheral surface before passing through the developing region. An attracting region to be attracted and a separation region in which the developer remaining on the outer peripheral surface after passing through the developing region is separated from the outer peripheral surface are set.

  In the hollow portion inside the developing sleeve, the magnetic field for pulling the developer away from the outer peripheral surface and the first magnetic pole that forms the magnetic field for attracting the developer on the outer peripheral surface and the outer peripheral surface are drawn. A magnetic member having a second magnetic pole formed in the separation region is fixed in a non-rotating manner.

  As a result, the developing sleeve attracts the developer to the outer peripheral surface in the attracting region in the developing tank, and supplies the developer attracted to the outer peripheral surface to the photosensitive member in the developing region outside the developing tank. The developer remaining on the outer peripheral surface after passing through the region is separated from the outer peripheral surface in the separation region in the developing tank and returned to the developing tank. Then, the developer returned to the developing tank in the separation region is attracted again to the outer peripheral surface of the developing sleeve in the attraction region.

Patent Document 1 and Patent Document 2 below show typical configurations of a two-component developing system. 5 and 7 of Patent Document 1, the developing roller is shown. The P2 pole included in the developing roller corresponds to the first magnetic pole that forms a magnetic field in the attracting region. The P3 pole included in the roller corresponds to the second magnetic pole that forms a magnetic field in the separation region. Further, FIG. 2 and FIGS. 4 to 6 of Patent Document 2 also show a developing roller. The S2 pole included in the developing roller corresponds to the first magnetic pole that forms a magnetic field in the attracting region. The S3 pole included in the developing roller corresponds to the second magnetic pole that forms a magnetic field in the separation region.
JP 2004-219510 A (publication date: August 5, 2004) Patent 3276093 (issue date: April 22, 2002)

  By the way, in the conventional developing device, inside the developing sleeve included in the developing roller, the first magnetic pole and the second magnetic pole are adjacent to each other in this order from the downstream side in the rotation direction of the developing sleeve toward the upstream side. Arranged to fit. Therefore, in the developing tank and the outer periphery of the developing sleeve, the attraction area and the attraction area are adjacent to each other.

  Therefore, in the conventional developing device, as shown in FIG. 2 of Patent Document 2, the developer separated from the outer peripheral surface of the developing sleeve in the vicinity of the boundary between the pulling region and the attracting region is immediately attracted to the outer peripheral surface of the developing sleeve. Phenomenon occurs. Therefore, among the developers in the developer tank, only a part of the developer is continuously and repeatedly attracted to the developing sleeve, which causes a problem that the developer deteriorates immediately.

  The present invention has been made in view of the above problems, and an object thereof is to provide a developing device capable of suppressing the deterioration rate of a developer.

  In order to achieve the above object, the present invention provides a developing tank that stores a developer containing a magnetic carrier and toner, and an outer peripheral surface alternately passes through the inside of the developing tank and the developing area outside the developing tank. The developer is attracted to the outer peripheral surface by a magnetic force in the first region inside the developing tank, and development is performed in the developing region by the developer attracted to the outer peripheral surface. The developer remaining on the outer peripheral surface after passing through the developing region is separated by a magnetic force in a second region located inside the first region and upstream of the first region in the direction of rotation, and returned to the developing tank. A sleeve, a first magnetic pole fixed on the inner peripheral side of the developing sleeve, and forming a magnetic field in the first region for attracting the developer to the outer peripheral surface; and a magnetic field for separating the developer from the outer peripheral surface. Above In a developing device having a magnetic member including a second magnetic pole formed in two regions, a magnetic field that suppresses the developer from being attracted to the outer peripheral surface is located inside the developing tank and more than in the first region. The magnetic member includes a third magnetic pole formed in an intermediate region located upstream of the rotation direction and downstream of the second region in the rotation direction.

  According to the developing device of the present invention, in the developing tank, the first area, which is an area where the developer is attracted to the developing sleeve, and the second area, where the developer attracted to the developing sleeve is returned to the developing tank. An intermediate area, which is an area in which the developer in the developing tank is suppressed from being attracted to the developing sleeve, is disposed between the areas, and the second area and the first area are separated from each other. Therefore, the developer returned from the developing sleeve to the developing tank in the second region is not immediately attracted to the developing sleeve in the first region. Thereby, it is possible to suppress only a part of the developer from being repeatedly used, and it is possible to suppress the deterioration rate of the developer.

  On the other hand, in the conventional developing device, the separation region where the developer attracted to the developing sleeve is separated from the developing sleeve and falls to the developing tank, and the developer in the developing tank is attracted to the developing sleeve. Since the attracting area that is an area is adjacent, the developer that has dropped from the developing sleeve near the boundary between the separating area and the attracting area is attracted to the developing sleeve immediately after dropping, Only a part of the developer is repeatedly used, and only a part of the developer is deteriorated immediately.

  In addition, when the polarity of the second magnetic pole is the same as the polarity of the third magnetic pole, if the peak value of the magnetic flux density of the third magnetic pole is less than 10 mT, the influence of the first magnetic pole is applied to the second region. It is difficult to form a magnetic field that repels the developer from the outer peripheral surface in the second region. Further, when the peak value of the magnetic flux density of the third magnetic pole exceeds 30 mT, the developer is attracted to the developing sleeve by the magnetic field formed in the third magnetic pole, and the developer is attracted to the developing sleeve in the intermediate region. The inconvenience that it is attracted to. Therefore, in the developing device of the present invention, in addition to the above configuration, the polarity of the second magnetic pole is the same as the polarity of the third magnetic pole, and the peak value of the third magnetic pole is 10 mT or more and 30 mT or less. It is preferable that

  In addition, the said polarity means a N pole or a S pole. That is, the case where the polarity of the second magnetic pole is the same as the polarity of the third magnetic pole is the case where both the second magnetic pole and the third magnetic pole are N poles, or the case where the second magnetic pole and the third magnetic pole are Means the case where both are S poles.

  Further, the developing device of the present invention has a gap with respect to the outer peripheral surface of the developing sleeve on the upstream side in the rotational direction from the developing region and on the downstream side in the rotational direction from the first region. A blade member that is disposed and scrapes off a part of the developer attracted to the outer peripheral surface from the outer peripheral surface to the developing tank may be provided.

  If the peak value of the magnetic flux density of the first magnetic pole is less than 30 mT, a sufficient amount of developer cannot be attracted to the developing sleeve, and the amount of developer necessary for the developing process cannot be conveyed to the developing area. Therefore, it becomes impossible to obtain a good quality image. If the peak value of the magnetic flux density of the first magnetic pole exceeds 60 mT, too much developer is attracted to the developing sleeve in the first region, and the amount of developer scraped off by the blade member increases. Since the frequency of stress applied to the developer increases and the deterioration of the developer is promoted, the image quality is likely to deteriorate. Therefore, the peak value of the magnetic pole density of the first magnetic pole is preferably 30 mT or more and 60 mT or less.

  The blade member is preferably disposed in a region where the magnetic flux density of the magnetic flux along the tangential direction with respect to the outer peripheral surface is larger than the magnetic flux density of the magnetic flux along the normal direction with respect to the outer peripheral surface of the developing sleeve. . As a result, friction between the magnetic carrier and the magnetic carrier that occurs when the developer collides with the doctor blade is less likely to occur, and the deterioration rate of the developer can be suppressed.

  Further, it is preferable that the blade member is disposed in a region where the magnetic flux density of the magnetic flux along the tangential direction is higher on the downstream side than on the upstream side in the rotation direction. As a result, the friction between the magnetic carrier and the magnetic carrier generated when the developer collides with the blade member can be further reduced, and the deterioration rate of the developer can be further suppressed.

  The developing device of the present invention is provided in an image forming apparatus. The image forming apparatus means a printing apparatus such as an electrophotographic printer, a copier, a multifunction machine, a facsimile machine.

  As described above, in the developing device of the present invention, the magnetic field that suppresses the developer from being attracted to the outer peripheral surface of the developing sleeve is positioned inside the developing tank and the direction of the rotation is more than the first region. And a third magnetic pole formed in an intermediate region located downstream of the second region in the direction of rotation. Thereby, it is possible to suppress only a part of the developer from being repeatedly used, and it is possible to suppress the deterioration rate of the developer.

[Embodiment 1]
An image forming apparatus according to an embodiment of the present invention will be described. FIG. 1 is a diagram illustrating an internal configuration of the image forming apparatus according to the present exemplary embodiment.

  The image forming apparatus 100 is an electrophotographic printer, and a photosensitive drum 10 is disposed. Further, around the photosensitive drum 10, a charging device 11, an exposure device 12, a developing device 13, a transfer device 14, a cleaning device 15, and a static elimination device 16 are arranged in this order along the rotation direction of the photosensitive drum 10. Yes.

  As shown in FIG. 1, the photosensitive drum 10 includes a base material made of a metal drum such as aluminum, and an organic optical semiconductor (OPC) or amorphous silicon (a-Si) formed on the outer peripheral surface of the base material in a thin film shape. ) And the like.

  The charging device 11 is a device that uniformly charges the surface of the photosensitive drum 10. The charging device 11 may be a charging wire such as a tungsten wire, a corona charger made of a metal shield plate or grit plate, a charging roller, or a charging brush.

  The exposure device 12 scans light on the uniformly charged photosensitive drum 10 to write an electrostatic latent image on the photosensitive drum 10. The exposure apparatus 12 may be a laser scanning unit (LSU) or an LED (Light Emitting Diode) array.

  The developing device 13 visualizes (develops) the electrostatic latent image by supplying a developer to the electrostatic latent image written by the exposure device 12. The developing device 13 will be described in detail later.

  The transfer device 14 releases a transfer bias for transferring an image visualized on the photosensitive drum 10 onto a recording medium (paper). The transfer device 14 may be the transfer roller shown in FIG. 1, or a charging brush or a corona charger may be used as the transfer device 14.

  The cleaning device 15 removes the developer remaining on the photosensitive drum 10 after the transfer and enables a new image to be recorded on the photosensitive drum 10. The neutralizing device 16 is for neutralizing the surface of the photosensitive drum 10. The surface of the photosensitive drum 10 that has been neutralized by the static eliminator 16 is uniformly charged again by the charging device 11, and the above-described process is repeated.

  The recording medium on which the image is transferred by the transfer device 14 is conveyed to the fixing device 17. In the fixing device 17, the image on the recording medium is fixed by heat and pressure, whereby the image is printed on the recording medium.

  FIG. 2 shows a configuration example of a main part of the developing device 13. 2 is a view of the developing device 13 as viewed from the end side in the longitudinal direction (axial direction) of the developing roller 89. FIG. As shown in FIG. 2, the developing device 13 includes a developing roller 89 composed of a developing sleeve 20 and a magnetic member 21 that attracts the developer, a doctor blade 101 that regulates the amount of developer attracted by the developing sleeve 20, and a developer. A developing tank 19 to be housed, a first stirring / transporting member 28 and a second stirring / transporting member 29 for stirring and transporting the developer inside the developing tank 19, and a sensor 34 for detecting the amount of developer inside the developing tank 19. I have. Note that the developer of the present embodiment is a two-component developer composed of a magnetic carrier and toner. In this embodiment, toner having an average particle diameter of 6.2 μm and a magnetic carrier having an average particle diameter of 50 μm are used, but each average particle diameter is not limited to these values.

  The developing sleeve 20 rotates in the rotation direction indicated by reference numeral 102, that is, is a pumping developing system in which a portion exposed from the developing tank 19 rotates from below to above, and in a region facing the photosensitive drum 10. In a certain development area, the photosensitive drum 10 moves in the same direction (that is, the rotation direction is reverse). The developing device 13 of the present embodiment employs the pumping development method, but is not limited to this method. The developing sleeve 20 adsorbs the developer in the developing tank 19 to the outer peripheral surface by the magnetic force of the magnetic member 21, and forms a magnetic brush in which the developer is linked in a spike shape on the outer peripheral surface. That is, the developer is carried on the developing sleeve 20 in the form of a magnetic brush. Further, the developing sleeve 20 rotates to convey the developer adsorbed on the outer peripheral surface to the developing area. In the developing region, toner having a charge in the developer forming the magnetic brush is supplied from the developing sleeve 20 to the photosensitive drum 10 in accordance with a potential difference between the developing sleeve 20 and the photosensitive drum 10. As a result, the electrostatic latent image on the photosensitive drum 10 is developed and a toner image is formed. The configurations of the developing sleeve 20 and the magnetic member 21 will be described in detail later.

  The doctor blade (blade member) 101 is made of a nonmagnetic material. The doctor blade 101 is fixed to the developing tank 19 or a fixing metal plate (not shown) by screws or rivets. Here, the fixing plate is fixed to the fixing sheet metal or the like using a fixing screw, but it is not particularly limited. The doctor blade 101 is installed with a gap with respect to the outer peripheral surface of the developing sleeve 20. This interval is referred to as a doctor gap (hereinafter referred to as DG). In the developing device 13 of the present embodiment, DG is set to 0.5 mm, for example. The set value of DG may be adjusted as appropriate depending on the conditions of the developer, the conditions of the developing roller 89, and the like.

  FIG. 3 shows an internal configuration of the developing tank 19 shown in FIG. FIG. 3 is a view of the inside of the developing tank 19 as viewed from above. The developing tank 19 is made of, for example, hard synthetic resin, and is a housing whose longitudinal direction is the axial direction of the developing roller 89 as shown in FIG. The developing tank 19 has a length substantially corresponding to the axial length L1 of the developing roller 89, and the inside extends parallel to the longitudinal direction of the developing tank 19 (the same as the axial direction of the developing roller 89). It is partitioned into two tanks by a partition wall member 25 provided.

  One of the two tanks is a developing region tank 23 that stirs and conveys the developer and supplies the developer to the developing roller 89, and the other stirs toner supplied from the toner hopper 104 (see FIG. 2) with the developer. In addition, the stirring area tank 24 is conveyed and supplied to the developing area tank 23.

  Here, the partition wall member 25 divides the development area tank 23 and the agitation area tank 24, but does not partition the development area tank 23 and the agitation area tank 24 so as to be completely sealed. That is, the first passage 26 and the second passage 27 that connect the developing region tank 23 and the stirring region tank 24 are formed at two locations on the partition wall member 25 on both sides in the longitudinal direction of the developing tank 19.

  Thereby, a part of the developer stored in the developing tank 19 can be moved from the developing area tank 23 to the stirring area tank 24, and conversely, from the stirring area tank 24 to the developing area tank 23. It becomes possible to move.

  In the developing tank 19, the developing roller 89, the first agitating / conveying member 28 for agitating and conveying the developer, and the second agitating and conveying so that the rotation axis direction is parallel to the longitudinal direction of the developing tank 19. A member 29 is rotatably provided. Specifically, the developing roller 89 and the first stirring / conveying member 28 are provided in the developing region tank 23, and the second stirring / conveying member 29 is provided in the stirring region tank 24.

  In the present embodiment, the first agitation and conveyance member 28 and the second agitation and conveyance member 29 are so-called screw members, and agitate and convey the developer in the developing tank 19 by rotating.

  The first agitating / conveying member 28 supplies the developer in the direction of the arrow 35 (in the direction from one end A to the other end B of the developing tank 19) in the vicinity of the developing roller 89 in the developing area tank 23. Transport. The second agitating and conveying member 29 moves the developer conveyed to the vicinity of the end B of the developing tank 19 by the first agitating and conveying member 28 to the agitating region tank 24 through the first passage 26 and conveys it in the direction of arrow 36. At the same time, it is conveyed along the partition wall member 25 in the direction of arrow 37 (direction from the end B toward the end A).

  The developer passes through the second passage 27 in the vicinity of the end A and is conveyed in the direction of the arrow 38 and is moved again by the first agitation and conveyance member 28. Therefore, in the developing tank 19, a developer circulation flow indicated by the arrows 35, 36, 37, and 38 is formed by the first and second stirring and conveying members 28 and 29 and the partition wall member 25.

  The sensor 34 detects the amount of developer in the developing tank 19. As the sensor 34, a magnetic permeability sensor or a piezoelectric detection sensor can be used. According to these sensors, the toner amount in the developer, in other words, the toner concentration which is the blending ratio of the magnetic carrier and the toner can be detected as the developer amount.

  Further, as shown in FIGS. 2 and 3, the sensor 34 is provided in the developing region tank 23 on the downstream side in the developer agitating and conveying direction, that is, in the vicinity of the end B of the developing tank 19 and on the wall material of the developing region tank 23. It is installed. By attaching the sensor 34 at such a position, the sensor 34 can measure the toner concentration of the developer immediately after the toner is consumed by the developing roller 89.

  In the developing device 13, a control unit (not shown) operates the toner hopper 104 (FIG. 2) in accordance with the toner density detection output to replenish toner to the stirring area tank 24.

  In this manner, the developing device 13 can detect the toner concentration of the developer after being developed, and can control the toner concentration of the developer with high accuracy so as to obtain an appropriate toner concentration. The sensor 34 may be placed anywhere other than the above position as long as the toner density can be properly detected.

  Next, an outline of processing for supplying toner from the toner hopper 104 to the developing tank 19 will be described with reference to FIG. The toner hopper 104 is a container member made of, for example, hard synthetic resin. The toner hopper 104 stores toner in the internal space, drives the internal toner supply roller 49 in accordance with an operation command from a control unit (not shown), and replenishes the developing tank 19 with the toner 50.

  The toner replenishing roller 49 is provided directly above the stirring area tank 24 so that its outer periphery can rotate while being in sliding contact with the toner replenishing port 104a. The toner replenishing roller 49 is provided with a cylindrical porous elastic member such as urethane foam around a cored bar. The toner held by the toner supply roller 49 in the toner hopper 104 is dropped from the toner supply roller 49 by the friction between the toner supply port 104 a and the toner supply roller 49 and is supplied to the developing tank 19.

  The toner replenishing port 104 a of the toner hopper 104 is disposed above the second stirring / conveying member 29 in the stirring region tank 24. As a result, the toner 50 in the toner hopper 104 is replenished to the developing tank 19 so as to drop onto the second stirring and conveying member 29. In the stirring area tank 24, the developer replenished with the toner 50 is stirred according to the circulating flow (flow indicated by arrows 35 to 38) in the developing tank 19 described above.

  Next, details of the developing sleeve 20 and the magnetic member 21 included in the developing roller 89 will be described. As shown in FIG. 2, the developing sleeve 20 faces the photosensitive drum 10 and is arranged so that its axial direction is parallel to the axial direction of the photosensitive drum 10, and is supported by the frame of the developing tank 19. ing.

  The developing sleeve 20 is a member rotatably provided on the outer periphery of the magnetic member 21, and the magnetic member 21 is disposed non-rotatably in the hollow portion (inner peripheral side) of the developing sleeve 20 and a plurality of magnetic members 21 are provided. It is a cylindrical magnet roller formed from a magnet. Further, the magnetic member 21 is composed of, for example, a plurality of permanent magnets, and the permanent magnets are arranged so as to be aligned along the circumferential direction, and form a cylindrical shape as a whole.

  The developing sleeve 20 is a cylindrical member made of a nonmagnetic material. Examples of the nonmagnetic material include SUS302, SUS303, SUS304, SUS304Cu, SUS304L, SUS304N1, SUS304J3, SUS305, SUS305J1, SUS309S, SUS310S, SUS316, SUS316L, SUS316N, SUS316F, SUS3US17, SUS3US34 Stainless steel, aluminum, and copper can be used.

  The magnetic member 21 has an N1 pole arranged at a position facing the developing region, an S2 pole arranged adjacent to the N1 pole on the downstream side in the rotation direction 102 from the N1 pole, and a rotation more than the S2 pole. From the N3 pole disposed adjacent to the S2 pole on the downstream side in the direction 102, the N2 pole disposed adjacent to the N3 pole on the downstream side in the rotational direction 102 from the N3 pole, and the N1 pole And the S1 pole disposed upstream of the rotation direction 102 and downstream of the rotation direction 102 with respect to the N2 pole. The S1 pole and the S2 pole are each an S pole magnetic pole, and the N1 pole to the N3 pole are each an N pole magnetic pole.

  The S1 pole (first magnetic pole) is located in the developing tank 19 and the outer peripheral surface of the developing sleeve 20 removes the developer in the developing tank 19 with respect to the first area 40 located upstream of the developing area in the rotation direction 102. It has a function as an attracting pole (pumping pole) that forms a magnetic field for attracting (pumping).

  The N1 pole has a function as a developing pole that forms a magnetic field in the developing area so that the developer attracted to the outer circumferential face of the developing sleeve 20 by the S1 pole is kept on the outer circumferential face even in the developing area.

  The N3 pole (second magnetic pole) is located in the developing tank 19 and in the second region 41 located downstream of the developing region in the rotational direction 102 and upstream of the first region 40 in the rotational direction 102. It has a function as a separation pole (release pole) for forming a magnetic field for separating (releasing) the developer adhering to the outer peripheral surface of the developing sleeve 20 from the outer peripheral surface. As a result, the developer remaining on the outer peripheral surface of the developing sleeve 20 after passing through the developing region falls from the outer peripheral surface to the developing tank 19 in the second region 41. Therefore, the developer is almost removed from the outer peripheral surface of the developing sleeve 20 after passing through the second region 41.

  The N2 pole (third magnetic pole) is located in the developing tank 19 and in an intermediate area 42 located upstream of the first area 40 in the rotational direction 102 and downstream of the second area 41 in the rotational direction 102. The developer tank 19 has a function as an attracting restriction electrode (pumping restriction electrode) that forms a magnetic field for suppressing the developer from being attracted (pumped) to the outer peripheral surface of the developing sleeve 20. Accordingly, the developer in the developing tank 19 is not attracted to the outer peripheral surface of the developing sleeve 20 after passing through the second region 41 and before reaching the first region 40.

  In addition, around the developing sleeve 20, a doctor blade 101 is disposed upstream of the developing region in the rotational direction 102 and downstream of the first region 40 in the rotational direction 102.

  With such a configuration, the developer in the developing tank 19 is attracted to the outer peripheral surface of the developing sleeve 20 by the magnetic field formed in the S1 pole (attracting pole) in the first region 40. Then, the doctor blade 101 regulates the amount of developer attracted to the outer peripheral surface of the developing sleeve 20 by the S1 pole. As a result, the amount of developer conveyed to the development area is adjusted.

  Thereafter, toner contained in the developer attracted to the outer peripheral surface of the developing sleeve 20 is supplied to the photosensitive drum 10 in the developing region. Further, the developer remaining on the outer peripheral surface of the developing sleeve 20 after passing through the developing region is separated from the outer peripheral surface in the second region 41 by the magnetic field formed in the N3 pole (separation pole), and the developing tank. Fall to 19.

  Then, in the intermediate region 42 downstream of the second region 41 in the rotational direction 102 and upstream of the first region 40 in the rotational direction 102, a magnetic field formed at the N2 pole (attracting regulation pole) The developer in the developing tank 19 repels against the outer peripheral surface of the developing sleeve 20.

  That is, as shown in FIG. 2, the first region 40 where the developer in the developing tank 19 is attracted to the developing sleeve 20 and the region where the developer attracted to the developing sleeve 20 falls into the developing tank 19. Between the certain second area 41, an intermediate area 42, which is an area where the developer in the developing tank 19 repels against the developing sleeve 20, is disposed, and the second area 41 and the first area 40 are separated from each other. Will be. Therefore, the developer that has dropped from the developing sleeve 20 to the developing tank 19 in the second region 41 is not attracted to the developing sleeve 20 in the first region 40 immediately after dropping. Thereby, it is possible to suppress only a part of the developer from being repeatedly used, and it is possible to suppress the deterioration rate of the developer.

  On the other hand, in the conventional developing device, a separation area where the developer attracted to the developing sleeve is separated from the developing sleeve and falls to the developing tank, and an area where the developer in the developing tank is attracted to the developing sleeve. Since the attracting area is adjacent to each other, the developer that has fallen from the developing sleeve near the boundary between the falling area and the attracting area may be attracted to the developing sleeve immediately after dropping, Only one developer was repeatedly used, and only a part of the developer deteriorated immediately.

  In this embodiment, the S1 pole functions as the attracting pole, the N1 pole functions as the developing pole, the N3 pole functions as the separating pole, and the N2 pole functions as the attracting regulating pole. Therefore, the N pole with a magnetic flux density peak value of 125 mT is the N1 pole, the S pole with a magnetic flux density peak value of 45 mT is the S1 pole, the N pole with a magnetic flux density peak value of 20 mT is the N2 pole, and the magnetic flux The N pole with a density peak value of 42 mT was designated as the N3 pole, and the S pole with a magnetic flux density peak value of 80 mT was designated as the S2 pole.

  In order to cause the N3 pole to function as the separation pole and to cause the N2 pole adjacent to the N3 pole on the downstream side of the rotation direction 102 from the N3 pole to function as the attraction regulating pole, It is necessary that the peak value of the magnetic flux density of the N2 pole be 10 mT to 30 mT with the N2 pole as the magnetic pole having the same polarity.

  In this embodiment, the magnetic member 21 has five magnets. However, the magnetic member 21 includes the developing pole, the attracting pole, the separating pole, and the attracting restriction pole. If so, the number of magnets contained is not limited to five. The magnetic strength of each pole is adjusted by adjusting the thickness and width of each magnet contained in the magnetic member 21 and changing the conditions of the magnetization process for each magnet contained in the magnetic member 21. It is possible to adjust.

[Embodiment 2]
In order to continuously form a high-quality toner image on the photosensitive drum for a long period of time, it is important to stabilize the amount of developer transported to the development area by the developing roller. However, when the developer deteriorates, the developer becomes spent (the toner melts and a toner film is formed on the carrier), and the external additive (silica and titanium oxide) is peeled off from the toner and the external additive is added. A phenomenon occurs in which the agent is buried in the toner. As a result, the fluidity of the developer is deteriorated, the developer transport amount becomes unstable, and as a result, an image quality defect that white stripes occur when a solid image or the like is printed occurs.

  Then, since the factor which causes deterioration of a developer was examined, the examination content is demonstrated below. In the developer tank, the developer is agitated by the screw, the developer is attracted to the outer peripheral surface of the developing sleeve, the development in the developing region, and the developer is separated from the outer peripheral surface of the developing sleeve. I am stressed. Among them, significant stress is applied in the process of attracting the developer to the outer peripheral surface of the developing sleeve and in the process of regulating the amount of the developer attracted to the outer peripheral surface of the developing sleeve by the doctor blade. Deterioration will be significantly promoted.

  Further, since the deterioration of the developer due to the doctor blade has been examined in detail, the contents of this examination will be described below. The developer in the developing tank is attracted to the outer peripheral surface of the developing sleeve by the magnetic flux generated from the attracting pole and extending in the normal direction of the outer periphery of the developing sleeve, and adheres to the outer peripheral surface of the developing sleeve. Further, the developer becomes a brush-like magnetic brush that extends in the normal direction by the magnetic flux in the normal direction on the outer peripheral surface of the developing sleeve. The magnetic brush moves along the rotation direction of the developing sleeve (tangential direction of the outer periphery of the sleeve) by the rotation of the developing sleeve, and collides with the doctor blade 101 at DG (doctor gap). At this time, a restraining force in the normal direction acts on the magnetic brush by the magnetic flux in the normal direction, while an impact force due to the collision acts in the rotation direction. This causes friction between the carrier of the magnetic brush and the carrier, and this friction gives a large stress to the developer, and the developer deteriorates due to this stress.

  Considering the contents of the examination described above, it is considered that the magnetic flux in the normal direction and the doctor blade contribute to the deterioration of the developer. Therefore, the inventor of the present application studied to suppress the deterioration of the developer by adjusting the arrangement of the doctor blade. The contents of this examination will be described with reference to FIG.

  FIG. 4 is a view showing the distribution of the magnetic field formed around the developing sleeve 20 shown in the first embodiment. In FIG. 4, a region indicated by a one-dot chain line indicates a distribution of a magnetic field composed of magnetic flux extending in a tangential direction (direction of a tangent to the outer periphery of the developing sleeve), and a region indicated by a two-dot chain line indicates a normal direction (developing sleeve The distribution of a magnetic field consisting of magnetic flux extending in the direction of the normal to the outer periphery) is shown.

  In FIG. 4, the magnetic flux density (magnetic force) of the magnetic field 105 formed by the N1 pole (development pole) and made of a normal magnetic flux, and the magnetic field formed by the N1 pole and the S1 pole and made of a tangential magnetic flux. The magnetic flux density 106 becomes equal on the dotted line L1. Further, in FIG. 4, the magnetic flux density of the magnetic field 106 is equal to the magnetic flux density of the magnetic field 107 formed by the S1 pole (attracting pole, pumping pole) and consisting of the normal direction magnetic flux on the dotted line L2. In FIG. 4, in the region between the dotted line L <b> 1 and the dotted line L <b> 2, the magnetic flux density of the magnetic field 106 made of tangential magnetic flux is larger than the magnetic flux density of the magnetic field 105 made of normal magnetic flux.

  Here, as shown in FIG. 4, if the doctor blade 101 is arranged in a region between the dotted line L <b> 1 and the dotted line L <b> 2, when the magnetic brush formed on the outer peripheral surface of the developing sleeve 20 collides with the doctor blade 101. The frictional force acting on the magnetic brush is reduced, thereby reducing the stress applied to the developer and suppressing the deterioration rate of the developer. This is because, in the region between the dotted line L1 and the dotted line L2, the magnetic flux in the tangential direction becomes more prominent than the magnetic flux in the normal direction, and the restraining force in the normal direction acting on the magnetic brush becomes small. At the same time, the magnetic force in the tangential direction acts on the magnetic brush moving in the tangential direction (rotating direction of the developing sleeve 20), so that even if the magnetic brush moving in the tangential direction collides with the doctor blade, the carrier This is because friction is less likely to occur between the carrier and the carrier.

[Experimental example]
An experiment for examining an appropriate value of the magnetic flux density for each magnetic pole included in the developing roller was conducted, and this experiment will be described below.

  The experiment was performed on the developing device of Example 1 to the developing device of Example 8, and the developing device of Comparative Example 1 to the developing device of Comparative Example 6. In this experiment, while the developing sleeve is continuously rotated for 10 hours (rotation speed: 500 rpm), a constant development condition (charging, charging, and so on) is made at a certain time by a copying machine (trade name: MX-7000N, manufactured by Sharp Corporation). A solid image is printed under a certain condition (development, constant condition), and it is checked whether density unevenness or white streaks occur in the solid image. In this check, if there is no problem in the image, ○, if the image has obvious density unevenness or white streaks, ×, if the image is at a level where there is no problem but density unevenness is about to occur Δ. (1) The internal temperature of the developing tank is 25 ° C. and the internal humidity is 50%, (2) The internal temperature of the developing tank is 35 ° C. and the internal humidity is 50%, (3) The internal temperature of the developing tank is 45 ° C. and the internal humidity is 50%, The experiment was performed under each condition. The results of the experiment are shown in Table 1 below.

(A) About Examples 1-3 and Comparative Examples 1-2 In Example 1, in the developing device 13 of FIG. 2, the peak value of the magnetic flux density of the N1 pole is 125 mT, the peak value of the magnetic flux density of the S1 pole is 45 mT, The peak value of the magnetic flux density of the N2 pole is 20 mT, the peak value of the magnetic flux density of the N3 pole is 42 mT, and the peak value of the magnetic flux density of the S2 pole is 80 mT. Example 2 is the same as Example 1 except that the peak value of the magnetic flux density of the N2 pole is 10 mT. Example 3 is the same as Example 1 except that the peak value of the magnetic flux density of the N2 pole is set to 30 mT. Comparative Example 1 is the same as Example 1 except that the peak value of the magnetic flux density of the N2 pole is 5 mT. Comparative Example 2 is the same as Example 1 except that the peak value of the magnetic flux density of the N2 pole is 40 mT.

  As shown in Table 1, good images were obtained in Examples 1 to 3, whereas in Comparative Examples 1 and 2, white streaks occurred after 1 hour in each environment. In Comparative Example 1, since the magnetic force of the N2 pole is weak, the influence of the S1 pole is exerted on the second region 41 and the N3 pole, and in the second region 41, it should be separated from the outer peripheral surface of the developing sleeve 20 by the N3 pole. This is considered to be because the developer was not sufficiently separated and remained on the outer peripheral surface of the developing sleeve 20 and the same developer continued to be used, and the developer immediately deteriorated. Further, in Comparative Example 2, the magnetic force of the N2 pole is too strong compared to Example 1, so that the developer in the developing tank 19 is attracted to the developing sleeve 20 by the N2 pole in the intermediate region 42 as shown in FIG. When a situation occurs, the developer that has fallen from the developing sleeve 20 to the developing tank 19 in the second region 41 is attracted to the developing sleeve 20 in the intermediate region 42 immediately after dropping, and the same developer is repeatedly applied. This is considered to be because the developer deteriorated immediately after being used.

  Therefore, according to Examples 1 to 3 and Comparative Examples 1 and 2, it can be said that the peak value of the magnetic flux density of the N2 pole is preferably 10 mT to 30 mT.

(B) Examples 4 to 5 and Comparative Examples 3 to 4 Example 4 is the same as Example 1 except that the peak value of the magnetic flux density of the S1 pole is set to 30 mT. In Example 5, the same conditions as in Example 1 were used except that the peak value of the magnetic flux density of the S1 pole was set to 60 mT. Comparative Example 3 is the same as Example 1 except that the peak value of the magnetic flux density of the S1 pole is 20 mT. Comparative Example 4 is the same as Example 1 except that the peak value of the magnetic flux density of the S1 pole is 70 mT.

  As shown in Table 1, good images were obtained in Example 4 and Example 5, whereas in Comparative Example 3, density unevenness occurred in the solid image from the initial stage to the end of the experiment. White streaks occurred in the solid image from the middle of the experiment in the environment of ℃ and 45 ℃. In Comparative Example 3, since the magnetic force of the S1 pole is weak, a sufficient amount of developer cannot be attracted to the developing sleeve 20, and the amount of developer necessary for the development process cannot be conveyed to the development region. It is considered that a good quality image cannot be obtained. Further, in Comparative Example 4, since the magnetic force of the S1 pole is too strong, the amount of developer attracted to the developing sleeve 20 in the first region 40 becomes excessive, and the amount of developer scraped off by the doctor blade 101 increases. Since the frequency of stress applied to the developer is increased and the deterioration of the developer is promoted, it is considered that the image quality is deteriorated.

  Therefore, according to Examples 4 to 5 and Comparative Examples 3 to 4, it can be said that the peak value of the magnetic flux density of the S1 pole is preferably 30 mT to 60 mT.

(C) Examples 6 to 8 and Comparative Examples 5 to 6 Examples 6 to 8 and Comparative Examples 5 to 6 are developing devices having the developing roller 89a shown in FIG. As shown in FIG. 5, the developing roller 89a includes a developing sleeve 20 and a magnetic member 21a disposed inside the developing sleeve 20, and the magnetic member 21a includes seven magnets. In the magnetic member 21a, as shown in FIG. 5, the N11 pole, the S14 pole, the N13 pole, the S13 pole, the S12 pole, the N12 pole, and the S11 pole are arranged in this order along the rotation direction 102a of the developing sleeve 20. Arranged side by side. The S11 pole to S14 pole are each an S pole magnetic pole, and the N11 pole to N13 pole are each an N pole magnetic pole.

  Furthermore, in the magnetic member 21a of FIG. 5, the magnetic pole that functions as the developing pole is the N11 pole, and the magnetic pole that functions as the separation pole (release pole) is the S13 pole, which functions as an attracting restriction pole (pumping restriction pole). The magnetic pole to be operated is the S12 pole, and the magnetic pole functioning as the attracting pole (pumping pole) is the N12 pole. In the magnetic member 21a of FIG. 5, the peak value of the magnetic flux density of the N11 pole is 115 mT, the peak value of the magnetic flux density of the S11 pole is 65 mT, and the peak value of the magnetic flux density of the N12 pole is 40 mT. The peak value of the magnetic flux density of the S12 pole is 25 mT, the peak value of the magnetic flux density of the S13 pole is 25 mT, the peak value of the magnetic flux density of the N13 pole is 45 mT, and the peak value of the magnetic flux density of the S13 pole is 75 mT. is there.

  Further, in FIG. 5, the magnetic flux density (magnetic force) of the magnetic field 105a formed by the S11 pole and made of the normal direction magnetic flux, and the magnetic flux density of the magnetic field 106a made of the S11 pole and the N12 pole and made of the tangential magnetic flux. Are equal on the dotted line L1 ′. Further, in FIG. 5, the magnetic flux density of the magnetic field 106a is equal to the magnetic flux density of the magnetic field 107a formed by the N12 pole (attracting pole, pumping pole) and composed of the normal direction magnetic flux on the dotted line L2 ′.

  In the region between the dotted line L1 'and the dotted line L2', the magnetic flux density of the magnetic field 106a composed of magnetic flux in the tangential direction is higher than the magnetic flux density of the magnetic field 105a composed of magnetic flux in the normal direction, and the dotted line L1 'and dotted line L2 On the dotted line L3 ′ in the region between “′”, the magnetic flux density of the magnetic field 106a composed of magnetic flux in the tangential direction shows a peak.

  Further, in FIG. 5, the magnetic flux density of the magnetic field 105a shows a peak on the dotted line L4 ′, and the magnetic flux density of the magnetic field 107a shows a peak on the dotted line L5 ′. Here, in the region between the dotted line L4 ′ and the dotted line L1 ′, the magnetic flux density of the magnetic field 105a composed of the magnetic flux in the normal direction is larger than the magnetic flux density of the magnetic field 106a composed of the magnetic flux in the tangential direction. Further, in the region between the dotted line L2 ′ and the dotted line L5 ′, the magnetic flux density of the magnetic field 107a composed of the magnetic flux in the normal direction is larger than the magnetic flux density of the magnetic field 106a composed of the magnetic flux in the tangential direction.

  Although not shown, in the developing device of Example 6, a doctor blade is installed between the dotted line L1 ′ and the dotted line L3 ′ in FIG. In the developing device of Example 7, the doctor blade is disposed between the dotted line L2 ′ and the dotted line L3 ′ in FIG. Furthermore, in the developing device of Example 8, the doctor blade is disposed on the dotted line L3 ′ in FIG.

  Further, in the developing device of Comparative Example 5, the doctor blade is disposed between the dotted line L2 ′ and the dotted line L5 ′ in FIG. In the developing device of Comparative Example 6, a doctor blade is disposed between the dotted line L4 ′ and the dotted line L1 ′ in FIG.

  As shown in Table 1, in Comparative Example 5 and Comparative Example 6, white streaks occurred in the solid image from the middle of the experiment, and a good image was not obtained. The reason for this will be described below. In Comparative Example 5 and Comparative Example 6, since the doctor blade is disposed at a location where the normal magnetic flux is stronger than the tangential magnetic flux, the magnetic brush colliding with the doctor blade is magnetically generated by the normal magnetic flux. While the restraining force acts strongly, the impact force directed in the rotation direction of the developing sleeve due to the collision acts on the magnetic brush. These actions cause friction between the carrier of the magnetic brush and the carrier, and this friction gives a large stress to the developer. This stress promotes the deterioration of the developer and degrades the image quality of the printed image. it is conceivable that.

  In contrast, in Examples 6 to 8, good images were obtained in each environment. This is because, in Examples 6 to 8, since the doctor blade is disposed at a location where the magnetic flux in the normal direction is weak and the magnetic flux in the tangential direction is strong, the normal acting on the magnetic brush in the vicinity of the doctor blade. Since the magnetic force in the tangential direction acts on the magnetic brush, even if the magnetic brush moving in the tangential direction collides with the doctor blade, friction is generated between the carrier and the carrier. It is difficult to happen.

  In particular, in Example 7 and Example 8, the doctor blade 101 has a region (L2 ′) in which the magnetic flux density of the magnetic flux along the tangential direction is higher on the downstream side than on the upstream side in the rotation direction. However, with such an arrangement, the deterioration rate of the developer can be further reduced, and a better image can be obtained.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and the embodiments can be obtained by appropriately combining the respective technical means disclosed in the above-described embodiments. The form is also included in the technical scope of the present invention.

  The developing device of the present invention is suitable for an electrophotographic printing apparatus.

1 is a diagram illustrating an internal configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of a developing device according to an embodiment of the present invention. It is a figure which shows the inside of the developing tank in the developing device shown in FIG. FIG. 6 is a diagram showing a distribution of a magnetic field formed around a developing sleeve. It is the figure which showed distribution of the magnetic field formed in the circumference | surroundings of the developing roller containing seven magnets. FIG. 10 is a diagram illustrating a developing device of Comparative Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photosensitive drum 13 Developing apparatus 19 Developing tank 20 Developing sleeve 21 Magnetic member 40 1st area | region 41 2nd area | region 42 Intermediate area | region 89 Developing roller 100 Image forming apparatus 101 Doctor blade (blade member)
S1 pole Attracting pole (first magnetic pole)
N3 pole Separating pole (second magnetic pole)
N2 pole Pulling restriction pole (third pole)

Claims (4)

A developer tank containing a developer containing a magnetic carrier and toner;
The outer peripheral surface rotates so as to alternately pass through the inside of the developing tank and the developing area outside the developing tank, and attracts the developer to the outer peripheral surface by a magnetic force in the first area inside the developing tank, Development is performed in the development area by the developer attracted to the outer peripheral surface, and the development area is located in a second area located inside the development tank and upstream in the rotation direction from the first area. A developing sleeve that pulls away the developer remaining on the outer peripheral surface after passing by a magnetic force and returns the developer to the developing tank;
A first magnetic pole that is fixed on the inner peripheral side of the developing sleeve and that forms a magnetic field in the first region that attracts the developer to the outer peripheral surface, and a magnetic field that pulls the developer away from the outer peripheral surface. In a developing device having a magnetic member including a second magnetic pole formed in a region,
A magnetic field that suppresses the developer from being attracted to the outer peripheral surface is located inside the developing tank and is upstream of the first region in the direction of rotation and is more rotated than the second region. A third magnetic pole formed in an intermediate region located downstream in the direction is included in the magnetic member ;
The developing sleeve is arranged with a gap with respect to the outer peripheral surface of the developing sleeve at the upstream side in the rotation direction from the developing region and the downstream side in the rotational direction from the first region, and is attracted to the outer peripheral surface. A blade member that scrapes off a part of the developer from the outer peripheral surface to the developer tank,
The blade member is a region in which the magnetic flux density of the magnetic flux along the tangential direction with respect to the outer peripheral surface is larger than the magnetic flux density of the magnetic flux along the normal direction with respect to the outer peripheral surface of the developing sleeve, and is along the tangential direction. A developing device, wherein the developing device is disposed in a region where the magnetic flux density of the magnetic flux is higher on the downstream side than on the upstream side in the rotation direction . The polarity of the second magnetic pole and the polarity of the third magnetic pole are the same,
The developing device according to claim 1, wherein a peak value of the magnetic flux density of the third magnetic pole is 10 mT or more and 30 mT or less. The developing device according to claim 1 , wherein a peak value of the magnetic flux density of the first magnetic pole is 30 mT or more and 60 mT or less. Image forming apparatus including a developing device according to any one of claims 1 to 3.

Images