JP5983282B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus. More specifically, the present invention relates to an image forming apparatus including a developing device that develops and visualizes an electrostatic latent image formed on an image carrier using a two-component developer including a toner and a carrier.

  In an electrophotographic image forming apparatus applied to a copying machine, a facsimile machine, a laser beam printer, etc., after charging a photosensitive member as an image carrier, electrostatic discharge is performed by exposing a document image or writing light according to an image signal. A latent image is formed, and the electrostatic latent image formed on the photosensitive member is visualized by developing it with a developing device using a two-component developer in which toner and carrier are frictionally charged. A visual image (toner image) is transferred onto a transfer material (also referred to as recording paper, recording medium, or paper) by a transfer means, and the toner image on the transfer material is fixed by fixing with a fixing device using pressure, heat, or the like. It has gained.

  As a developing device of this image forming apparatus, one having a carrier recovery roller that recovers a magnetic carrier adhering to a photosensitive member with a magnetic force or an electrostatic force is known.

  For example, in Patent Document 1, a carrier recovery roller is provided at a position close to the developing sleeve, a rotatable magnetic roller is accommodated inside the carrier recovery roller, and the magnetic roller in the carrier recovery roller is connected to the developing sleeve side. A developing device that rotates synchronously with the magnetic force of a magnetic roller is disclosed. Further, in this developing device, the carrier captured on the outer peripheral surface of the carrier recovery roller is conveyed by the synchronous rotation of the magnetic roller. In addition, the carrier conveyed on the outer peripheral surface of the carrier recovery roller is scraped off by bringing the tip of the scraper into pressure contact with the outer peripheral surface of the carrier recovery roller.

  Further, Patent Document 2 discloses a developing device including a carrier recovery roller in which a groove is formed so as to be along a direction orthogonal to the rotation direction of the surface.

  Further, Patent Document 3 discloses that when the static charge level of the carrier collecting member that is initially in an insulated state is less than a predetermined value, the carrier collecting member is electrically insulated and collected on the carrier collecting member. When the static charge level exceeds a predetermined value due to the increase in the amount of collection, the carrier collection ability can be recovered by electrostatic force by providing a self-discharge means that self-discharges the charged charge on the carrier collection member. An image forming apparatus is disclosed.

  Further, Patent Document 4 discloses that a carrier recovery roller has a carrier recovery sleeve that can rotate while supporting the carrier on the surface, and a carrier recovery magnet roller that is fixedly disposed so as to be included in the carrier recovery sleeve and has a plurality of magnetic poles. The carrier recovery magnet roller has no magnetic pole at the portion facing the developing sleeve, and the surface movement direction of the developing sleeve and the surface movement of the carrier collecting sleeve at a position where the developing sleeve and the carrier carrier collecting sleeve face each other. A developing device having directions opposite to each other is disclosed.

  In recent years, the speed of the image forming apparatus has been increased, and the developing roller of the developing apparatus has been driven at a high speed, or the carrier has been made smaller in size to improve the image quality. There is a problem to do.

  In order to cope with this problem, it is conceivable to increase the electrostatic force or the magnetic force in order to recover the carrier attached to the photosensitive member by the carrier recovery roller. However, when the electrostatic force for collecting the carrier with the conventional carrier collecting roller is increased, there arises a problem that the toner image on the photosensitive member is disturbed.

  Further, in the configuration in which a rotatable magnetic roller is housed inside the carrier recovery roller as in the developing device of Patent Document 1, when the magnetic force of the carrier recovery magnetic pole in the carrier recovery roller is increased, the carrier recovery roller There is a problem in that the collected carrier cannot be conveyed, and the toner image on the photosensitive member is rubbed with the collected carrier to be rubbed. This is a phenomenon that occurs because the carrier slips and accumulates when the surface of the carrier recovery roller is smooth and the magnetic force of the carrier recovery magnetic pole is high.

  Further, in the developing device described in Patent Document 2, since a groove is formed on the surface of the carrier recovery roller, a scraper that scrapes off the carrier on the surface of the carrier recovery roller cannot be used. For this reason, it is difficult to completely peel off the carrier on the carrier recovery roller, and the rubbing image may be generated.

  Further, in the image forming apparatus of Patent Document 3, when the charge relaxation time of the deposit on the surface of the carrier collecting member, which is a factor that changes the charge level, is long, the carrier collecting ability remains reduced during that period. There is a possibility of causing a problem in the image forming apparatus.

  According to the developing device of Patent Document 4 described above, the carrier recovery rate can be improved by setting the conditions of the magnetic force generation means included in the carrier recovery roller to an appropriate condition, but depending on the operating state of the image forming apparatus. In this case, the chargeability of the toner changes significantly, and in some cases the ratio of positively charged toner to the developer in the developing device may increase significantly. It is desirable to recover it.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of recovering a carrier adhering to a photoconductor regardless of an operation state of the image forming apparatus.

  In order to achieve such an object, an image forming apparatus according to the present invention includes a developer support unit that can rotate by supporting a two-component developer including toner and a carrier to be supplied to an image carrier on the surface, and the development. A developer carrying member having a first magnetic field generating means having a plurality of magnetic poles contained in the agent supporting means, and provided on the downstream side of the developer carrying member in the surface movement direction of the image carrier, and the image carrier A carrier supporting means having a carrier supporting means which can be rotated by carrying the carrier attached to the surface, and a carrier collecting means having a second magnetic field generating means having a plurality of magnetic poles fixedly disposed so as to be included in the carrier supporting means; And a developing device that is rotatably provided so that a plurality of magnetic poles sequentially pass through a position facing the carrier support means, and the key. And a bias applying means for applying a bias to the rear support means, said biasing means is configured to change the bias applied to the carrier support means at a predetermined timing.

  According to the present invention, the carrier adhering to the photoconductor can be collected regardless of the operation state of the image forming apparatus.

1 is a schematic configuration diagram of a copier according to an embodiment of the present invention. It is an enlarged block diagram (1) which shows the developing device and photoconductor which concern on this embodiment. It is an enlarged block diagram (2) which shows the developing device and photoconductor which concern on this embodiment. FIG. 4 is a partial perspective view of the developing device showing the flow of the developer in the developer conveyance path. FIG. 6 is an external perspective view illustrating a position where toner is supplied from a developing device. It is the elements on larger scale of the principal part which the developing roller and the carrier collection | recovery roller are facing. It is explanatory drawing which shows the magnetic flux density waveform on the carrier collection | recovery sleeve which used the block magnet as the rare earth bond magnet. It is explanatory drawing which shows the magnetic flux density waveform on the carrier collection | recovery sleeve which used the block magnet as the rare earth sintered magnet. It is a schematic block diagram which shows one structural example of the drive part of a carrier collection | recovery roller. It is a schematic block diagram for demonstrating the toner removal from a carrier collection | recovery roller. FIG. 6 is an explanatory diagram illustrating a relationship between potentials of respective units during a normal printing operation and a toner removal mode. 6 is a graph showing a charge amount distribution when a positively charged toner ratio is increased. 6 is a graph showing a relationship between a potential difference and a toner adhesion amount on a photoreceptor. 6 is a graph showing a relationship between a bias setting value applied to a carrier recovery roller and a toner recovery rate on the carrier recovery roller in a state where positively charged toner adheres to the surface of the carrier recovery roller. 6 is a graph showing a relationship between a toner density and a carrier adhesion number when no bias is applied to a carrier recovery roller. 6 is a graph showing a charge amount distribution when a toner replenishment amount varies per unit driving time.

  Hereinafter, a configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

[First Embodiment]
The image forming apparatus (copier 500) according to the present embodiment has a developer support unit that can rotate by carrying a two-component developer including toner and a carrier supplied to an image carrier (photosensitive member 1) on the surface. (Development sleeve 81), a developer carrier (development roller 5) having first magnetic field generation means (magnet roller 82) included in the developer support means and having a plurality of magnetic poles, and surface movement of the image carrier Carrier support means (carrier recovery sleeve 90) that is provided on the downstream side of the developer carrier in the direction and is capable of carrying the carrier adhering to the image carrier on the surface and rotating, and to be included in the carrier support means And at least a carrier recovery means (carrier recovery roller 13) having a second magnetic field generation means (carrier recovery magnet roller 91) having a plurality of magnetic poles. The first magnetic field generating means includes a developing device (developing device 4) rotatably provided so that a plurality of magnetic poles sequentially pass through a position facing the carrier supporting means, and bias application for applying a bias to the carrier supporting means. And a bias applying means for changing a bias applied to the carrier supporting means at a predetermined timing. In addition, the code | symbol in embodiment and the example of application are shown in a parenthesis.

  An embodiment in which the present invention is applied to an electrophotographic full-color image forming apparatus (hereinafter referred to as “copier 500”) will be described below.

(Configuration of image forming apparatus)
FIG. 1 is a schematic configuration diagram of a copying machine 500 according to the present embodiment. In FIG. 1, a copying machine 500 is fixed on a printer unit 100 as an image forming unit, a paper feeding device 200 as a recording medium supply unit that supplies transfer paper as a recording medium to the printer unit 100, and a printer unit 100. A scanner 300 as image reading means. An automatic document feeder 400 is fixed on the scanner 300.

  The printer unit 100 includes an image forming unit including four sets of process cartridges 18Y, 18M, 18C, and 18K for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). 20 is provided. Y, M, C, and K added after the numerals of the respective symbols indicate members for yellow, magenta, cyan, and black (the same applies hereinafter). In addition to the process cartridges 18Y, 18M, 18C, and 18K, the printer unit 100 includes an optical writing unit 21 as a latent image writing unit, an intermediate transfer unit 17, a secondary transfer device 22, a registration roller pair 49, a belt fixing system. The fixing device 25 is provided.

  The optical writing unit 21 includes a light source (not shown), a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates a laser beam onto the surface of the photoreceptor 1 described later based on image data.

  The process cartridges 18Y, 18M, 18C, and 18K develop a latent image formed on the photosensitive member 1, a drum-shaped photosensitive member 1 as an image carrier, a charging device as a charging unit that charges the surface of the photosensitive member 1. The image forming apparatus includes a developing device 4 as a developing unit, a drum cleaning device as an image carrier cleaning unit that cleans the surface of the photoreceptor 1, and a static eliminator as a neutralizing unit that neutralizes the surface of the photoreceptor 1. Since the process cartridges 18Y, 18M, 18C, and 18K have the same configuration, the process cartridge 18Y for yellow will be described below.

  The surface of the photoreceptor 1Y is uniformly charged by the charging device. The surface of the photoreceptor 1Y that has been subjected to the charging process is irradiated with laser light that is modulated and deflected by the optical writing unit (exposure device) 21. Thereby, the potential of the surface of the photoreceptor 1Y of the irradiation part (exposure part) is attenuated. Due to the attenuation of the surface potential, an electrostatic latent image for Y is formed on the surface of the photoreceptor 1Y.

  The formed electrostatic latent image for Y is developed by the developing device 4Y to become a Y toner image. The Y toner image formed on the Y photoconductor 1Y is primarily transferred to an intermediate transfer belt 110 as an intermediate transfer member described later. The surface of the photoreceptor 1Y after the primary transfer is cleaned of the transfer residual toner by a drum cleaning device. Further, in the Y process cartridge 18Y, the photoreceptor 1Y cleaned by the drum cleaning device is discharged by the charge eliminator. Then, it is uniformly charged by the charging device and returns to the initial state. The series of processes as described above is the same for the other process cartridges 18M, 18C, and 18K.

  Next, the intermediate transfer unit 17 will be described. The intermediate transfer unit 17 includes an intermediate transfer belt 110 as an intermediate transfer member, a belt cleaning device 60 as an intermediate transfer member cleaning unit that cleans the surface of the intermediate transfer belt 110, and the like. The intermediate transfer unit 17 also includes a stretching roller 14, a drive roller 15, a secondary transfer backup roller 16, four primary transfer bias rollers 62Y, M, C, and K.

  The intermediate transfer belt 110 is tensioned by a plurality of rollers including the tension roller 14 so as to have a predetermined tension. The intermediate transfer belt 110 moves endlessly in the clockwise direction in the drawing by the rotation of the driving roller 15 driven by a belt driving motor (not shown).

  The primary transfer bias rollers 62Y, 62M, 62C, and 62K are disposed so as to be in contact with the inner peripheral surface side of the intermediate transfer belt 110, and receive a primary transfer bias from a power source (not shown).

  Further, the intermediate transfer belt 110 is pressed toward the photoreceptors 1Y, 1M, 1C, and 1K from the inner peripheral surface side to form primary transfer nips. In each primary transfer nip, a primary transfer electric field is formed between the photoreceptor 1 and the primary transfer bias roller 62 due to the influence of the primary transfer bias.

  The Y toner image formed on the Y photoconductor 1Y is primarily transferred onto the intermediate transfer belt 110 by the influence of the primary transfer electric field and nip pressure. On the Y toner image, the M, C, K toner images formed on the M, C, K photoconductors 1M, C, K are sequentially superposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as “four-color toner image”) as a multiple toner image is formed on the intermediate transfer belt 110.

  The four-color toner image superimposed and transferred onto the intermediate transfer belt 110 is secondarily transferred onto a transfer sheet (not shown) as a recording medium at a secondary transfer nip described later. Transfer residual toner remaining on the surface of the intermediate transfer belt 110 after passing through the secondary transfer nip is cleaned by a belt cleaning device 60 that sandwiches the belt with the driving roller 15 on the left side in the drawing.

  Next, the secondary transfer device 22 will be described. Below the intermediate transfer unit 17 in the figure, a secondary transfer device 22 is disposed in which a paper conveying belt 24 is stretched by two stretching rollers 23. The paper transport belt 24 moves endlessly in the counterclockwise direction in the drawing in accordance with the rotational drive of at least one of the stretching rollers 23. Of the two stretching rollers 23, one stretching roller 23 disposed on the right side in the drawing, that is, the upstream stretching roller 23 disposed on the upstream side in the transfer sheet conveying direction is the intermediate transfer unit 17. The intermediate transfer belt 110 and the paper transport belt 24 are sandwiched between the secondary transfer backup roller 16.

  By this sandwiching, a secondary transfer nip is formed in which the intermediate transfer belt 110 of the intermediate transfer unit 17 and the paper transport belt 24 of the secondary transfer device 22 are in contact with each other. A secondary transfer bias having a polarity opposite to that of the toner is applied to the one (upstream side) stretching roller 23 by a power source (not shown).

  By applying the secondary transfer bias, the four-color toner image on the intermediate transfer belt 110 of the intermediate transfer unit 17 is applied from the belt side to the one (upstream) stretching roller 23 side in the secondary transfer nip. A secondary transfer electric field to be electrostatically moved is formed. The transfer paper fed into the secondary transfer nip so as to synchronize with the four-color toner image on the intermediate transfer belt 110 by a registration roller pair 49 described later has four colors affected by the secondary transfer electric field and nip pressure. The toner image is secondarily transferred. Instead of the secondary transfer method in which the secondary transfer bias is applied to the one (upstream side) stretching roller 23, a charger for charging the transfer paper in a non-contact manner may be provided.

  In the paper feeding device 200 provided at the lower part of the copying machine 500 main body, a plurality of paper feeding cassettes 44 in which a plurality of transfer sheets can be stacked and stored in a bundle of sheets are arranged so as to overlap each other in the vertical direction. It is installed. Each paper feed cassette 44 presses the paper feed roller 42 against the uppermost transfer paper in the paper bundle. Then, by rotating the paper feed roller 42, the uppermost transfer paper is sent out toward the paper feed path 48.

  The paper feed paths 46 and 48 that receive the transfer paper delivered from the paper feed cassette 44 have a plurality of conveying roller pairs 47 and a registration roller pair 49 provided near the end in the paper feed path 48. . Then, the transfer paper is conveyed toward the registration roller pair 49. The transfer sheet conveyed toward the registration roller pair 49 is sandwiched between the rollers of the registration roller pair 49. On the other hand, in the intermediate transfer unit 17, the four-color toner image formed on the intermediate transfer belt 110 enters the secondary transfer nip as the belt moves endlessly. The registration roller pair 49 sends out the transfer paper sandwiched between the rollers at a timing at which the transfer paper can be brought into close contact with the four-color toner image at the secondary transfer nip. Thereby, in the secondary transfer nip, the four-color toner image on the intermediate transfer belt 110 is in close contact with the transfer paper. Then, it is secondarily transferred onto the transfer paper and becomes a full color image on the white transfer paper. The transfer paper on which the full-color image is formed in this manner exits the secondary transfer nip as the paper transport belt 24 moves endlessly, and then is sent from the paper transport belt 24 to the fixing device 25.

  The fixing device 25 includes a belt unit that stretches the fixing belt 26 by two rollers and moves endlessly, and a pressure roller 27 that is pressed toward one roller of the belt unit. The fixing belt 26 and the pressure roller 27 are in contact with each other to form a fixing nip, and the transfer paper received from the paper transport belt 24 is sandwiched therebetween. Of the two rollers in the belt unit, the roller that is pressed from the pressure roller 27 has a heat source (not shown) inside, and heats the fixing belt 26 by the heat generated by the heat source. The heated fixing belt 26 heats the transfer paper sandwiched in the fixing nip. The full color image is fixed on the transfer paper by the influence of the heating and the nip pressure.

  The transfer paper subjected to the fixing process in the fixing device 25 is stacked on the stack portion 57 provided outside the left side plate in the drawing of the printer housing, or forms a toner image on the other surface. Any one of the transport modes to be returned to the secondary transfer nip is selected.

  When a document (not shown) is copied, for example, a bundle of sheet documents is set on the document table 30 of the automatic document feeder 400. However, when the original is a single-sided original that is closed in a main form, it is set on the contact glass 32. Prior to this setting, the automatic document feeder 400 is opened with respect to the copying machine main body, and the contact glass 32 of the scanner 300 is exposed. Thereafter, the single-bound original is pressed by the closed automatic document feeder 400.

  When a copy start switch (not shown) is pressed after the document is set in this way, the document reading operation by the scanner 300 starts. On the other hand, when a sheet document is set on the automatic document feeder 400, the automatic document feeder 400 automatically moves the sheet document to the contact glass 32 prior to the document reading operation. In the document reading operation, first, the first traveling body 33 and the second traveling body 34 start traveling together, and light is emitted from a light source provided in the first traveling body 33.

  Then, the reflected light from the document surface is reflected by a mirror provided in the second traveling body 34, passes through the imaging lens 35, and then enters the reading sensor 36. The reading sensor 36 constructs image information based on the incident light.

  In parallel with such document reading operation, each device in each of the process cartridges 18Y, 18M, 18C, 18K, the intermediate transfer unit 17, the secondary transfer device 22, and the fixing device 25 starts driving. Then, based on the image information constructed by the reading sensor 36, the optical writing unit (exposure device) 21 is driven and controlled, and Y, M, C, and K toner images on the respective photoreceptors 1Y, 1M, 1C, and 1K. Is formed. These toner images become four-color toner images superimposed and transferred on the intermediate transfer belt 110.

  Further, almost simultaneously with the start of the document reading operation, the paper feeding operation is started in the paper feeding device 200. In this paper feeding operation, one of the paper feeding rollers 42 is selectively rotated, and the transfer paper is sent out from one of the paper feeding cassettes 44 accommodated in the paper bank 43 in multiple stages. The fed transfer paper is separated one by one by the separation roller 45 and enters the paper feed path 46, and is then transported toward the secondary transfer nip by the transport roller pair 47. In some cases, paper feeding from the manual feed tray 51 is performed instead of such paper feeding from the paper feeding cassette 44.

  In this case, after the manual feed roller 50 is selectively rotated and the transfer paper on the manual feed tray 51 is sent out, the separation roller 52 separates the transfer paper one by one and feeds it to the manual feed path 53 of the printer unit 100. To do.

  In the case of forming a multicolor image composed of two or more colors of toner, the copying machine 500 stretches the intermediate transfer belt 110 so that the upper stretched surface is almost horizontal, and all the upper stretched surface is placed on the upper stretched surface. Photoconductors 1Y, 1M, 1C, and 1K are brought into contact. On the other hand, when forming a monochrome image consisting of only K toner, the intermediate transfer belt 110 is tilted to the lower left in the drawing by a mechanism (not shown) and the upper stretched surface is set to Y, M, C. The photoconductors 1Y, 1M, and 1C are separated.

  Of the four photoconductors 1Y, 1M, 1C, and 1K, only the K photoconductor 1K is rotated counterclockwise in the drawing to form only the K toner image. At this time, for Y, M, and C, not only the photosensitive member 1 but also the developing device 4 is stopped, and each member of the photosensitive member 1 and the developing device 4 and the toner and magnetic carrier (hereinafter referred to as the developing device 4). And a two-component developer (hereinafter referred to as “developer”).

  The copier 500 includes a control unit as a control unit (not shown) configured by a CPU that controls each device in the copier 500, an operation display unit (not illustrated) configured by a liquid crystal display, various key buttons, and the like. It has. The operator sends a command to the control unit by a key input operation on the operation display unit, so that the single-sided printing mode, which is a mode for forming an image only on one side of the transfer paper, can be selected from, for example, three modes. One can be selected. The three single-sided printing modes include a direct discharge mode, a reverse discharge mode, and a reverse decal discharge mode.

  Further, as will be described later, the control unit applies a bias to the carrier recovery sleeve 90 of the developing device 4 at a predetermined timing, an image ratio counting unit that counts an image ratio printed by the copier 500, and development. It functions as a replenishing toner amount / driving time counting means for counting the amount of toner replenished to the device 4 and the driving time of the developing device 4.

(Configuration of developing device)
FIG. 2 is an enlarged configuration diagram showing the developing device 4 and the photosensitive member 1 respectively installed in the process cartridges 18Y, 18M, 18C, and 18K installed in the copier 500 according to the present embodiment. Since the four process cartridges 18Y, 18M, 18C, and 18K have substantially the same configuration except that the colors of the toners to be handled are different from each other, Y, M, C, and the like denoted by “4” in FIG. The subscript K is omitted.

  As shown in FIG. 2, the process cartridge 18 includes a photosensitive drum 1 as an image carrier, a charging unit (not shown), a developing device 4 (developing unit), and a photosensitive member cleaning unit (not shown). In addition, a premix development method (development method in which carrier is replenished / discharged as appropriate) is employed.

  The photosensitive drum 1 as an image carrier is a negatively charged organic photosensitive member, and is rotationally driven counterclockwise by a rotation driving mechanism (not shown).

  Here, the developing device 4 in the present embodiment is of a premix developing system, and a new carrier C (developer G) is appropriately supplied from the agent cartridge into the developing device 4 and deteriorated. The developer G is discharged toward a not-shown agent storage container installed outside the developing device 4. The developer cartridge contains developer G (toner T and carrier C) to be supplied into the developing device 4 therein.

  The agent cartridge functions as a toner cartridge that supplies new toner T to the developing device 4, and also functions as a supply unit that supplies new carrier C to the developing device 4. In this embodiment, the mixing ratio (toner concentration) of the toner T with respect to the carrier C in the developer G of the agent cartridge is set to be relatively high.

  As shown in FIG. 2, the surface of the photosensitive member 1 is charged by a charging device (not shown) while rotating in the direction of arrow G in the drawing. An electrostatic latent image is formed on the surface of the charged photoreceptor 1 by laser light emitted from an optical writing unit (exposure device) (not shown), and toner is supplied to the electrostatic latent image from the developing device 4. A toner image is formed.

  The developing device 4 stores a developer containing toner and a carrier, and supplies the toner to the latent image on the surface of the photosensitive member 1 while developing the developer in the direction of arrow I in the drawing as a developer carrying member. The developing roller 5 is provided. The developing roller 5 includes a developing sleeve 81 as a developer support means that can rotate, and includes a magnet roller 82 as a first magnetic field generating means that is composed of a plurality of magnetic poles and that can rotate in the direction of arrow A in the figure. .

  Further, a carrier recovery roller 13 as a carrier recovery means is provided below the developing roller 5 and at a position close to the developing roller 5 and the photosensitive member 1 on the downstream side in the surface movement direction of the photosensitive member 1. . Similarly to the developing roller 5, the carrier recovery roller 13 also includes a carrier recovery sleeve 90 as a rotatable carrier support means, and a carrier as second magnetic field generation means (carrier recovery magnetic field generation means) composed of a plurality of fixed magnetic poles. A collection magnet roller 91 is included. The carrier adhering to the photoreceptor 1 is collected by the carrier collection roller 13 and returned to the developing device 4 by the magnetic force of the carrier collection magnet roller 91 and the rotation of the carrier collection sleeve 90.

  Further, the developing device 4 supplies the developer to the developing roller 5 along the axial direction of the developing roller 5 with respect to the back side of the paper surface shown in FIG. It has a supply screw 8 as a supply conveyance member that conveys the developer toward the rear side.

  A doctor blade 12 serving as a developer regulating means for regulating the developer supplied to the developing roller 5 to a thickness suitable for development is provided downstream of the developing roller 5 facing the supply screw 8 in the developer transport direction. I have. Further, on the downstream side in the developer transport direction with respect to the developing region that is the portion of the developing roller 5 facing the photoreceptor 1, the developer that collects the developed developer that has passed through the developing region and separated from the surface of the developing roller 5 is collected. The conveyance path 7 faces the developing roller 5.

  The collection conveyance path 7 is a collection conveyance member that conveys the collected developer collected in the same direction as the supply screw 8 along the axial direction of the developing roller 5. I have. A supply conveyance path 9 having a supply screw 8 is arranged in parallel above the developing roller 5, and a collection conveyance path 7 having a collection screw 6 is arranged in parallel below the development roller 5.

  Further, the developing device 4 is provided with an agitation transport path 10 in parallel with the supply transport path 9 and the recovery transport path 7. The stirring conveyance path 10 is inclined so as to be substantially the same height as the supply conveyance path 9 on the rear side and on the front side of the collection conveyance path 7.

  Further, the agitating / conveying path 10 is in the direction opposite to the supply screw 8 while stirring the developer along the axial direction of the developing roller 5, that is, on the front side of the paper shown in FIG. As a stirring / conveying member that conveys in the direction of (in some cases), a helical stirring screw 11 is provided that is inclined in the axial direction.

  The supply conveyance path 9 and the stirring conveyance path 10 are partitioned by a first partition wall 133 as a partition wall. The supply conveyance path 9 and the agitation conveyance path 10 of the first partition wall 133 have an opening on the front side in the figure, and the supply conveyance path 9 and the agitation conveyance path 10 communicate with each other. Further, the supply conveyance path 9 and the collection conveyance path 7 are partitioned by a second partition wall 134. The supply conveyance path 9 and the collection conveyance path 7 of the second partition wall 134 have an opening on the back side in the drawing, and the supply conveyance path 9 and the collection conveyance path 7 communicate with each other. In addition, the two developer conveyance paths of the agitation conveyance path 10 and the recovery conveyance path 7 are partitioned by a third partition wall 135 as a partition member. The third partition wall 135 has an opening on the back side in the figure, and the stirring conveyance path 10 and the collection conveyance path 7 communicate with each other.

  Further, as shown in FIG. 3, it is also preferable to provide a developer discharge port shutter 136 on a part of the outer wall in the longitudinal direction facing the stirring screw 11. In the discharge mode, the developer discharge shutter 136 is capable of discharging the developer G from below the screw 11 by rotating as shown in the figure. For the operation of the developer outlet shutter 136, for example, a solenoid (not shown) can be used. The solenoid can be opened and closed at any time by turning the solenoid on / off. In the example shown in FIG. 3, the shutter is opened when the solenoid is on, and the developer G containing the toner T having the reverse charging characteristic is discharged by opening the shutter when the toner removal mode on the surface of the carrier recovery roller is on. The

  The supply screw 8, the recovery screw 6 and the stirring screw 11, which are developer conveying members, are made of resin or metal screws. The diameters of the screws are 26 (mm) for the supply screw 8 and the recovery screw 6, and the stirring screw 11 is φ30 (mm). The supply screw 8 is a double winding with a screw pitch of 54 (mm), the recovery screw 6 is a double winding with a screw pitch of 36 (mm), and the stirring screw 11 has a screw pitch of 54 (mm). It is a double roll. The number of rotations of each screw is set to about 600 (rpm).

  The developer carried on the developing roller 5 is thinned by a doctor blade 12 made of stainless steel, and then transported to a developing region that is a portion facing the photosensitive member 1, so that the latent image on the photosensitive member 1 is developed. Done. The diameter of the developing roller 5 is φ40 (mm), and the gap between the doctor blade 12 and the photoreceptor 1 is about 0.3 (mm).

The developer after development is collected in the collection conveyance path 7, conveyed to the back side in FIG. 2, and developed to the agitation conveyance path 10 at the opening of the third partition wall 135 provided in the non-image area portion. The agent is transferred.
In addition, in the vicinity of the opening of the second partition wall 134 on the downstream side in the developer conveyance direction in the supply conveyance path 9, there is a supply conveyance path from a toner replenishing port 95, which will be described later, above the supply conveyance path 9. Toner 9 is supplied.

(Developer circulation)
Next, the circulation of the developer in the three developer conveyance paths will be described. FIG. 4 is a partial perspective view of the developing device 4 for explaining the flow of the developer in the developer transport path. Each arrow in the figure indicates the moving direction of the developer.

  In FIG. 4, in the supply conveyance path 9 that receives the supply of the developer from the stirring conveyance path 10, the developer is supplied in contact with the developing roller 5 while moving. The surplus developer that has moved to the downstream end in the transport direction of the supply transport path 9 without being supplied to the developing roller 5 is supplied to the recovery transport path 7 from the surplus opening of the second partition wall 134 (arrow in FIG. 4). E).

  On the other hand, the developer supplied to the developing roller 5 is used for development in the developing region, and then separated from the developing roller 5 and separated from the developing roller 5 and is delivered to the collection conveyance path 7. The collected developer that has been transferred from the developing roller 5 to the collection conveyance path 7 and conveyed to the downstream end in the conveyance direction of the collection conveyance path 7 by the collection screw 6 passes through the collection opening of the third partition wall 135 to the stirring conveyance path 10. Supplied (arrow F in FIG. 4).

  In the agitating / conveying path 10, the excess developer supplied from the supply / conveying path 9, the collected developer collected in the collecting / conveying path 7, and the toner replenished from a toner replenishing port 95 (see FIG. 5) described later 4 arrow t) is stirred. The agitated developer is conveyed downstream in the conveying direction of the agitating screw 11 and upstream in the conveying direction of the supply screw 8, and is supplied to the supply conveying path 9 from the supply opening of the first partition wall 133. (Arrow D in FIG. 4).

  A toner concentration sensor (not shown) as a toner detection means including a magnetic permeability sensor is provided below the stirring and conveying path 10 and a toner supply control device (not shown) is operated based on the output of the toner concentration sensor. The toner is replenished from a developer cartridge (not shown).

  In the developing device 4 shown in FIG. 4, a supply conveyance path 9 and a collection conveyance path 7 are provided, and developer supply and collection are performed in different developer conveyance paths, so that the developed developer is supplied to the supply conveyance path 9. There is no contamination. For this reason, it is possible to suppress a decrease in the toner concentration of the developer supplied to the developing roller 5 toward the downstream side of the supply conveyance path 9 in the conveyance direction. Further, since the recovery conveyance path 7 and the agitation conveyance path 10 are provided and the developer recovery and agitation are performed in different developer conveyance paths, the developed developer does not fall during the agitation.

  Thereby, since the sufficiently stirred developer is supplied to the supply conveyance path 9, it is possible to suppress the developer supplied to the supply conveyance path 9 from being insufficiently stirred. In this way, the toner density of the developer in the supply conveyance path 9 can be suppressed from decreasing, and the developer in the supply conveyance path 9 can be prevented from being insufficiently stirred, so the image density during development can be reduced. Can be constant.

(Toner supply)
FIG. 5 is an external perspective view for explaining the toner replenishing position of the developing device 4. As shown in FIG. 5, the replenishment port 95 for replenishing the developer is provided above the downstream end in the transport direction of the supply transport path 9 including the supply screw 8. The developer replenishing port 95 is located above the surplus opening (arrow E in FIG. 4) of the second partition wall 134, so that the replenished developer is easily mixed with the surplus developer and the collected developer. The developer can be more efficiently stirred by replenishing with.

(Development roller)
Next, the configuration of the developing roller 5 and the carrier recovery roller 13 in the developing device 4 of the copying machine 500 having the above-described configuration and the surroundings will be described. FIG. 6 is a partially enlarged view of a main part where the developing roller 5 and the carrier recovery roller 13 face each other. In FIG. 6, a developing roller 5 is a developing sleeve 81 as a cylindrical developer supporting means for carrying the developer, and a first magnetic field generating means that is contained in the developing sleeve 81 and attracts the developer by magnetic force. And a magnet roller 82.

The developing sleeve 81 is made of a nonmagnetic and conductive material such as aluminum, austenitic stainless steel, or magnesium. The surface of the developing sleeve 81 may be smooth, but in a high speed machine, any of the following roughening treatments / processings (A) to (C) may be performed to suppress developer slip.
(A) Groove extrusion processing such as V-groove or U-groove, machining of various concave shapes or laser processing or edging processing (B) Blast treatment (C) Thermal spray treatment of metal or ceramic

  The magnet roller 82 is rotatably provided in the arrow A direction opposite to the developer transport direction (moving direction of the developing sleeve surface) I. The magnet roller 82 has an even number (16 in the configuration example of FIG. 6) of magnets 83 arranged at equal intervals in the circumferential direction. The polarities of the magnets 83 are opposite to each other so as to attract each other between adjacent magnets.

  Further, in the present embodiment, the driving relationship between the magnet roller 82 and the developing sleeve 81 is configured so that either the same or relative rotational direction can be selected. The rotational relationship is set on the condition that the number of times the developer carried on the surface of the developing sleeve 81 and the magnet 83 on the magnet roller 82 side face each other is increased.

  Due to the increase in the number of times the developer is opposed to the magnet of the magnet roller 82 obtained by setting the drive relationship described above, a spike is formed when the developer is opposed to the magnetic pole, and the spike is broken when the developer is separated from the magnetic pole. This increases the number of times the phenomenon is repeated, thereby increasing the chance of frictional contact between the toner and the carrier, thereby improving the charging characteristics of the toner.

  In this case, the increase in the number of facings can be obtained by setting the rotational direction of the magnet roller 82 and the developing sleeve 81, setting the speed difference, or the like as described above. That is, when both rotate in the same direction, the number of times the developer faces the magnet 83 can be increased by setting a speed difference between them, and the opposite direction without setting the speed difference. In this case, the number of times the developer faces the magnet 83 can be increased in the same manner.

  As for the above-described magnet 83, a conventional inexpensive ferrite magnet can be used, but a stronger rare earth magnet such as a samarium cobalt magnet or a neodymium magnet can also be used for downsizing and speeding up. The magnet 83 may be supported on the magnet holder 84 by adhesion, and the outer periphery thereof may be protected by a heat shrinkable tube or the like (not shown).

  If the magnet holder 84 is made of a magnetic material, the magnetic force of the magnet 83 can be slightly improved. However, since the cost is high and magnetic materials mainly composed of iron are generally high in specific gravity, the moment of inertia increases at the time of high-speed rotation, which may cause a problem in the durability of the drive unit. Therefore, although the magnetic force of the magnet 83 is slightly reduced, nonmagnetic and light specific gravity aluminum or magnesium may be used as a material.

  In the present embodiment, as shown in FIG. 6, the rotation center P ′ of the magnet roller 82 is eccentrically positioned at a position away from the rotation center P of the developing sleeve 81 by a distance (T). The direction of eccentricity is set in the vicinity of the developer carried on the surface of the developing roller 5 moving to the photosensitive member 1, and the amount of eccentricity corresponding to the distance indicated by the symbol T is the carrier in the developing region. The amount that can be suppressed by the magnetic force from the magnetic pole.

  As a result, the developer transferred to the photosensitive member 1 can be contacted in a state in which the rising is ensured upon contact with the photosensitive member, and carrier transfer is prevented by the magnetic force from the approaching magnetic pole so that only the toner is transferred to the photosensitive member. It moves so that it may be supplied to the latent image. On the other hand, the magnetic force can be kept low on the side opposite to the eccentric direction. For this reason, the developer carried on the surface of the developing sleeve 81 can be easily peeled off. By providing such an eccentric structure, the developer can be easily peeled off without using external mechanical external force.

  Next, the transfer of the developer in the developing device 4 of the present embodiment will be described based on FIG. The developer supplied to the flange 9 ′ by the supply screw 8 is attracted onto the developing sleeve 81 by the magnetic force of the magnet roller 82, conveyed by the rotation of the developing sleeve 81, and the amount of developer when passing through the doctor blade 12. Is regulated to a certain level. The developer that has passed through the doctor blade 12 is arranged along the magnetic field lines. In other words, magnetic spikes are generated on the magnet 83 as indicated by reference numeral B1, and the magnetic spikes fall between the magnets 83 as indicated by reference numeral B2.

  When the rotation direction of the magnet roller 82 is the opposite direction (the direction of the arrow A in the figure) to the rotation direction of the developing sleeve 81 (the direction of the arrow I in the figure), while the magnet roller 82 rotates, The magnetic spike rotates in a so-called flip flap shape and proceeds in the direction of arrow F opposite to the direction indicated by arrow A, which is the direction of rotation of the magnet roller 82. At this time, the developing sleeve 81 may be supplementarily rotated in the direction of arrow I at a relatively low speed.

  As the developer that passes through the doctor blade 12 continues to rotate, the attraction force to the developing sleeve 81 gradually increases due to the eccentricity of the magnet roller 82, and the carrier is prevented from moving to the photoreceptor 1. As the magnet roller 82 rotates more rapidly, the developer is vigorously stirred at the opposite portion of the photoconductor 1, so that the toner can be transferred efficiently according to the latent image of the photoconductor 1. Since it increases in proportion to the square of the number of rotations, carrier adhesion to the photoreceptor 1 also increases.

  As the developer continues to rotate, the attracting force to the developing sleeve 81 gradually decreases due to the eccentricity of the magnet roller 82, and is separated from the developing sleeve 81 by its own weight in the supply conveyance path 7 (directions of arrows K and L in FIG. 6). ).

(Carrier collection roller)
The carrier recovery roller 13 includes a carrier recovery sleeve 90 as a rotatable carrier support means, and includes a carrier recovery magnet roller 91 as second magnetic field generation means (carrier recovery magnetic field generation means) composed of a plurality of fixed magnetic poles. ing. The carrier recovery magnet roller 91 can be configured by attaching a composite magnet 93 and a block magnet 94 to a shaft 92 made of a nonmagnetic material such as aluminum, austenitic stainless steel, magnesium, or various resin materials.

  The composite magnet 93 uses Sr ferrite or Ba ferrite as magnet powder, and PA (polyamide) material such as 6PA or 12PA as a polymer compound, EEA (ethylene / ethyl copolymer) or EVA (ethylene / vinyl copolymer). ) And the like, chlorine-based materials such as CPE (chlorinated polyethylene), and rubber materials such as NBR. Using these materials, the composite magnet 93 can be obtained by forming the magnetic poles P22, P23, and P24 by magnetization so that the shape in a cross section perpendicular to the axial direction is a half-moon shape. it can. The notch portion of the composite magnet 93 is disposed on the developing roller 5 side, and does not have a magnetic pole on the side facing the developing roller 5.

  The block magnet 94 requires a high magnetic force in a volume smaller than that of the composite magnet 93 in order to collect the carrier attached to the photoreceptor 1, and uses a material of Br (residual magnetic flux density)> 0.5T (Tesla). Most of them are Nd-based (Nd-Fe-B, etc.) or Sm-based (Sm-Co, Sm-Fe-N, etc.) rare earth sintered magnets, or rare earth bonds in which these magnet powders are mixed with a polymer compound. A magnet can be used.

  In addition, rare earth magnet powders include isotropic and anisotropic magnet powders, and anisotropic magnet powders can provide higher magnetic force, but whichever type is used depending on the desired magnetic properties. It doesn't matter. Then, the block magnet 94 can be obtained by performing sintering, extrusion molding / injection molding, or in-mold compression molding of magnetic powder and a binder on the above materials and magnetizing the magnetic pole P21.

  The shape in the cross section orthogonal to the longitudinal direction (axial direction) of the block magnet 94 is, for example, a square as shown in FIG. The dimension of the block magnet 94 in the cross section is, for example, 3 (mm) in width, which is the circumferential dimension of the carrier recovery roller 13, and 3 mm in thickness, which is the radial dimension of the carrier recovery roller 13, for example. ). The length of the block magnet 94 in the longitudinal direction is, for example, 346 (mm), and is about 10 (mm) longer than the magnet roller 82 so that the carrier can be reliably collected to the end.

  FIG. 7 is an explanatory diagram showing a magnetic flux density waveform on a carrier recovery sleeve in which the block magnet 94 is a rare earth bonded magnet. A high magnetic flux density of 150 (mT) was obtained on the carrier recovery sleeve facing the magnetic pole P21 of the block magnet 94. The magnetic flux density due to the magnetic pole P21 of the block magnet 94 was 140 (mT) on the photosensitive member 1 separated by 0.5 (mm). The magnetic flux density formed on the carrier recovery sleeve by the transport poles P22, P23, and P24, which are other magnetic poles, is 100 (mT) for the magnetic pole P22, 70 (mT) for the magnetic pole P23, and the magnetic pole P24. On the other hand, it was 40 (mT).

  FIG. 8 is an explanatory diagram showing a magnetic flux density waveform on the carrier recovery sleeve 90 in which the block magnet 94 is a rare earth sintered magnet. In this example, a higher magnetic flux density of 230 (mT) was obtained on the carrier recovery sleeve facing the magnetic pole P21 of the block magnet 94. The magnetic flux density by the magnetic pole P21 of the block magnet 94 was 200 (mT) on the photosensitive member 1 separated by 0.5 (mm). The magnetic flux density formed on the carrier recovery sleeve by the transport poles P22, P23, and P24, which are other magnetic poles, is 110 (mT) for the magnetic pole P22, 70 (mT) for the magnetic pole P23, and the magnetic pole P24. On the other hand, it was set to 40 (mT).

The carrier recovery sleeve 90 is made of a nonmagnetic and conductive material such as aluminum, austenitic stainless steel, or magnesium. Further, as described above, in order to transport the carrier adsorbed on the magnetic pole P21 having a high magnetic flux density to the magnetic pole P22 having a relatively low magnetic flux density without slipping, the following (A) to (A It is necessary to perform any roughening treatment / processing of C).
(A) Groove extrusion processing such as V-groove or U-groove, machining of various concave shapes or laser processing or edging processing (B) Blast treatment (C) Thermal spray treatment of metal or ceramic

  For the processing of (A) above, the depth of the groove or recess is about 0.05 (mm) to 0.5 (mm), and the shape, number, etc. thereof can be set, for example, in the same manner as in the known art. Is possible. About the process of said (B), the roughness has the preferable range of Rz7 (micrometer)-Rz50 (micrometer). The roughness range is a range that can be manufactured in the above (B), and a range in which carrier slip can be prevented. About the process of said (C), the roughness has the preferable range of Rz40 (micrometer)-Rz90 (micrometer). This roughness range is a range that can be manufactured in the above (C), and is a range that can prevent carrier slip.

  Further, by setting the gap between the carrier recovery roller 13 and the photoconductor 1 as narrow as 0.5 (mm), for example, the magnetic flux density on the photoconductor 1 is 10 to 30 (from the magnetic flux density on the carrier recovery sleeve 90). mT). By setting the gap between the carrier recovery roller 13 and the developing roller 5 as narrow as 2 (mm), the spikes of the developing roller 5 can be brought into contact with the carrier recovery roller 13.

  Further, as shown in FIG. 6, a casing 96 is provided on the opposite side of the carrier recovery roller 13 from the developing roller 5 (below the carrier recovery roller 13 in FIG. 6). By setting the gap between the carrier recovery roller 13 and the casing 96 to be as narrow as 1.5 (mm), for example, the spikes at the magnetic pole P24 can be brought into contact with the casing 96.

(Developer etc.)
In addition, as a developer used in this embodiment, a developer having the following configuration can be used. The toner used in this embodiment contains at least a binder resin and a colorant, and if necessary, a release agent, a charge control agent, and other components. In addition to the above-mentioned additives, a fluidity improver and other components are added as necessary. For these materials, all known materials are possible.

  Examples of the binder resin include styrene, parachlorostyrene, vinyl toluene, vinyl chloride, vinyl acetate, vinyl propionate, methyl (meth) acrylate, ethyl (meth) tacrylate, propyl (meth) acrylate, (meth ) N-butyl acrylate, isobutyl (meth) acrylate, dodecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) Hydroxypropyl acrylate, 2-chloroethyl (meth) acrylate, (meth) acrylonitrile acid, (meth) acrylamide, (meth) acrylic acid, vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether. Examples include a weight body of monomers such as vinyl methyl ketone, N-vinyl pyrrolidone, N-vinyl pyridine and butadiene, a copolymer composed of two or more of these monomers, or a mixture thereof. In addition, polyester resin, polyol resin, polyurethane resin, polyamide resin, epoxy resin, rosin, modified rosin, terbene resin, phenol resin, hydrogenated petroleum resin, ionomer resin, silicone resin, ketone resin, xylene resin, etc. alone or in combination Can be used.

  As the colorant, all known dyes and pigments can be used. For example, carbon black, nigrosine dye, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, ocher, Yellow lead, Titanium yellow, Polyazo yellow, Oil yellow, Hansa yellow (GR, A, RN, R), Pigment yellow L, Benzidine yellow (G, GR), Permanent yellow (NCG), Vulcan fast yellow (5G, R) ), Tartrazine Lake, Quinoline Yellow Lake, Anthrazan Yellow BGL, Isoindolinone Yellow, Bengala, Red Dan, Lead Zhu, Cadmium Red, Cadmium Mercury Red, Antimon Zhu, Permanent Red 4R, Para Red, Phi Se Red, Parachlor Ortonito Aniline Red, Resol Fast Scarlet G, Brilliant Fast Scarlet, Brilliant Carmin Min BS, Permanent Red (F2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Belkan Fast Rubin B, Brilliant Scarlet G, Resol Rubin GX, Permanent Red F5R, Brilliant Carmine 6B, Pigment Scarlet 3B, Bordeaux 5B, Tolujing Maroon, Permanent Bordeaux F2K, Helio Bordeaux BL, Bordeaux 10B, Bon Maroon Light, Bon Maroon Medium, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake , Thioindigo red B, thioindigo maroon, oil red, quinacridone red, pyrazolone red, Riazo Red, Chrome Vermillion, Benzidine Orange, Perinone Orange, Oil Orange, Cobalt Blue, Cerulean Blue, Alkaline Blue Lake, Peacock Blue Lake, Victoria Blue Lake, Metal Free Phthalocyanine Blue, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue (RS, BC), indigo, ultramarine blue, bitumen, anthraquinone blue, fast violet B, methyl violet lake, cobalt purple, manganese purple, dioxane violet, anthraquinone violet, chrome green, zinc green, chromium oxide, pyridian, emerald green, pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake, Malachite Green Lake, Phthalo Cyanine green, anthraquinone green, titanium oxide, zinc white, litbon and mixtures thereof can be used. The amount used is generally 0.1 to 50 parts by weight per 100 parts by weight of the binder resin.

  Examples of the charge control agent include nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxy amines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts). .), Alkylamide, phosphorus simple substance or compound, tungsten simple substance or compound, fluorine-based activator, salicylic acid metal salt, metal salt of salicylic acid derivative, and the like. The amount of charge control agent used is determined by the type of binder resin, the presence or absence of additives used as necessary, and the toner production method including the dispersion method, and is not uniquely limited. Preferably, it is used in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin. The range of 2 to 5 parts by weight is preferable. If the amount is less than 0.1 parts by weight, the toner is not practically negatively charged. When the amount exceeds 10 parts by weight, the chargeability of the toner is too high, and the electrostatic attraction force with the carrier increases, leading to a decrease in developer fluidity and a decrease in image density.

  Examples of release agents include low molecular weight polyolefin waxes such as low molecular weight polyethylene and low molecular weight polypropylene, synthetic hydrocarbon waxes such as Fischer-Tropsch wax, beeswax, carnauba wax, candelilla wax, rice wax, and montan wax. Natural waxes such as paraffin wax, petroleum wax such as microcrystalline wax, higher fatty acids such as stearic acid, palmitic acid, myristic acid, metal salts of higher fatty acids, higher fatty acid amides, and various modified waxes thereof. Can be mentioned.

  These may be used alone or in combination of two or more, but it is preferable to use those having a melting point in the range of 70 to 125 (° C). By setting the melting point to 70 (° C) or higher, it is possible to obtain a toner having excellent transferability and durability. By setting the melting point to 125 ° C or lower, the toner melts quickly at the time of fixing and exhibits a reliable release effect. it can. The amount of these release agents used is preferably 1 to 15 (% by mass) based on the toner. If it is less than 1 (mass%), the effect of preventing offset is insufficient, and if it is 15 (mass%) or more, the transferability and durability are lowered.

  As an additive (external additive), fine particles having a volume average particle size of 50 to 500 (nm) and a bulk density of 0.3 (g / cm 3) or more are added. The amount of external addition is preferably 0.2 to 3 (% by mass) with respect to the toner base. If the amount is less than this range, the effect of forming an appropriate gap between the toners or between the toner and the others is not exhibited. On the other hand, when the amount is large, the fluidity is inhibited or the amount of desorption increases, so that an aggregate of external additives is formed, and the image quality is deteriorated. In addition to the above-mentioned additives, additives outside this range can be added, and it is preferable to add fine particles having a small volume average particle diameter for the purpose of improving fluidity.

In the additive in the present embodiment, as the inorganic _{compound, SiO 2, TiO 2, Al} 2 O 3, MgO, CuO, ZnO, SnO 2, CeO 2, Fe 2 O 3, BaO, CaO, K 2 O, Examples include Na ₂ O, ZrO ₂ , CaO · SiO ₂ , K ₂ O (TiO ₂ ) n, Al ₂ O ₃ · 2SO ₂ , CaCO ₃ , MgCO ₃ , BaSO ₄ , MgSO ₄ , SrTiO _{3 and the} like. Of these, SiO ₂ , TiO ₂ , and Al ₂ O ₃ are preferable. In particular, these inorganic compounds may be hydrophobized with various coupling agents, hexamethyldisilazane, dimethyldichlorosilane, octyltrimethoxysilane, and the like. Further, the organic compound additive may be a thermoplastic resin or a thermosetting resin, for example, vinyl resin, polyurethane resin, epoxy resin, polyester resin, polyamide resin, polyimide resin, silicon resin, phenol resin, melamine resin. , Urea resin, aniline resin, ionomer resin, polycarbonate resin and the like. As the resin fine particles, two or more of the above resins may be used in combination. Of these, vinyl resins, polyurethane resins, epoxy resins, polyester resins, and combinations thereof are preferred because an aqueous dispersion of fine spherical resin particles is easily obtained.

  Specific examples of vinyl resins include polymers obtained by homopolymerization or copolymerization of vinyl monomers, such as styrene- (meth) acrylic acid ester copolymers, styrene-butadiene copolymers, (meth) acrylic acid. -Acrylic ester copolymer, styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, styrene- (meth) acrylic acid copolymer, and the like.

  The additive (fine particles) in this embodiment is excellent as a toner for a developer in the developing device. That is, the contact area with the toner particles, the photoconductor drum, and the charge imparting member is very small and contacts evenly, so the effect of reducing adhesion is great and effective in improving development / transfer efficiency.

  Furthermore, since it acts as a roller, it is buried in the toner particles even when cleaning the cleaning drum and the photosensitive drum under high stress (high load, high speed, etc.) without wearing or damaging the photosensitive drum. It is difficult to remove or return even after being buried a little, so that stable characteristics can be obtained over a long period of time. Further, the toner is moderately detached from the surface of the toner and accumulated at the tip of the cleaning blade, and the so-called dam effect has an effect of preventing a phenomenon that the toner passes from the blade.

  As a method for producing the toner in the present embodiment, a method obtained by melting and kneading a toner constituent material and then pulverizing and classifying is generally used as a conventional method, but is not limited to this method. A method is possible. As the polymerization method, a suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method, and the like are possible. Although different from the polymerization method, in addition to a dissolution suspension method, a polymer suspension method, etc., an extension reaction method or the like can be used. . Other than the conventional method is preferable in that the toner having the above-described particle size range and circularity can be easily obtained. Further, the circularity may be adjusted by subjecting the toner after pulverization and classification to heat treatment.

  The method for adding the additive in the present embodiment is not particularly limited, and a method in which the toner base particles and the additive are mechanically mixed and adhered using various known mixing devices, or a toner base in a liquid phase. There is a method in which particles and additives are uniformly dispersed with a surfactant and the like, followed by an adhesion treatment and then drying.

  The particle size distribution of the toner described above can be measured by using a toner particle size distribution measuring apparatus by the Coulter counter method. Examples of these devices include Coulter Counter TA-II and Coulter Multisizer II (both manufactured by Coulter).

  The measurement method is described below. First, 0.1 to 5 (ml) of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 (ml) of the aqueous electrolytic solution. Here, the electrolytic solution is prepared by preparing about 1 (%) NaCl aqueous solution using primary sodium chloride, and for example, ISOTON-II (manufactured by Coulter) can be used. Here, 2-20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the weight and number of toner particles or toner are determined by using the 100 (μm) aperture as the aperture by the above-described measuring apparatus. Measure and calculate weight distribution and number distribution. From the obtained distribution, the weight average particle diameter (D4) and the number average particle diameter (D1) of the toner can be obtained.

  As a channel, it is less than 2.00-2.52 (micrometer); 2.52-3.17 (micrometer); 3.17-4.00 (micrometer); 4.00-5.04 (micrometer) Less than 5.04 to 6.35 (μm); 6.35 to less than 8.00 (μm); 8.00 to less than 10.08 (μm); 10.08 to less than 12.70 (μm); 12.70 to less than 16.00 (μm); 16.00 to less than 20.20 (μm); 20.20 to less than 25.40 (μm); 25.40 to less than 32.00 (μm); Using 13 channels of 00 to less than 40.30 (μm), particles having a particle size of 2.00 (μm) or more and less than 40.30 (μm) are targeted.

The circularity of the toner described above is a value obtained by the following equation (1).
Circularity = (peripheral length of a circle having the same area as the projected area of the particle) / (peripheral length of the projected particle image) Formula (1)

  The circularity is an index of the degree of unevenness of the toner particles, and indicates 1.00 when the toner is a perfect sphere. The more complicated the surface shape, the smaller the circularity. The circularity can be measured using, for example, a flow particle image analyzer FPIA-1000 manufactured by Toa Medical Electronics. As a specific measuring method, a surfactant, preferably an alkylbenzene sulfonate, is added in an amount of 0.1 to 0.5 (as a dispersant) in 100 to 150 (ml) of water from which impure solids have been previously removed. ml) and about 0.1 to 0.5 (g) of a measurement sample. The suspension in which the sample is dispersed is subjected to dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the concentration of the dispersion is set to 3000 to 10,000 (pieces / μl), and the shape of the toner is measured with the above-described apparatus.

  Hereinafter, the carrier used in this embodiment will be described supplementarily. The carrier used in the present embodiment is formed so that the weight average particle diameter is 20 to 60 (μm) (preferably 20 to 45 (μm)). This particle size range is also excellent as a carrier for the developer in the developing device. When the average particle diameter of the carrier is less than 20 (μm), the fine particles are increased in the distribution of the carrier particles, and the magnetization per particle may be lowered to cause carrier scattering. On the other hand, if the average particle diameter of the carrier exceeds 45 (μm), the carrier spikes during the development process become rough, and the uniformity of solid and halftone may be inferior (particularly, the average particle diameter is It becomes remarkable when it exceeds 60 (μm)). In addition, since the specific surface area is reduced, toner scattering may occur in a small particle size toner.

  The carrier is not particularly limited except for the particle diameter, and can be appropriately selected according to the purpose. However, a carrier having a core material and a resin layer covering the core material is preferable. There is no restriction | limiting in particular as a material of a core material, It can select suitably from well-known things, For example, 50-90 (emu / g) manganese-strontium (Mn-Sr) type material, manganese-magnesium ( Mn—Mg) -based materials and the like are preferable, and highly magnetized materials such as iron powder (100 (emu / g) or more) and magnetite (75 to 120 (emu / g)) are preferable in terms of securing image density. Also, copper-zinc (Cu-Zn) type (30 to 80 (emu / g)) or the like is advantageous in that it can weaken the contact with the photosensitive drum in which the toner is in a spiked state and is advantageous for high image quality. The weakly magnetized material is preferred. These may be used alone or in combination of two or more.

  The material for the resin layer of the carrier is not particularly limited and can be appropriately selected from known resins according to the purpose. Examples thereof include amino resins, polyvinyl resins, polystyrene resins, and halogenated olefin resins. Polyester resin, polycarbonate resin, polyethylene resin, polyvinyl fluoride resin, polyvinylidene fluoride resin, polytrifluoroethylene resin, polyhexafluoropropylene resin, copolymer of vinylidene fluoride and acrylic monomer, fluoride Examples thereof include a copolymer of vinylidene and vinyl fluoride, a fluoroterpolymer such as a terpolymer of tetrafluoroethylene, vinylidene fluoride, and a non-fluorinated monomer, and a silicone resin. These may be used individually by 1 type and may use 2 or more types together.

  The resin layer may contain conductive powder or the like as necessary. Examples of the conductive powder include metal powder, carbon black, titanium oxide, tin oxide, and zinc oxide. The average particle diameter of these conductive powders is preferably 1 (μm) or less. When the average particle diameter exceeds 1 (μm), it may be difficult to control electric resistance.

  For example, the resin layer of the carrier is prepared by dissolving a silicone resin or the like in a solvent to prepare a coating solution, and then uniformly coating the coating solution on the surface of the core material by a known coating method, followed by drying and baking. Can be formed. Examples of the application method include a dipping method, a spray method, and a brush coating method.

The amount of the resin layer in the carrier is preferably 0.01 to 5.0 (% by mass). If the amount of the resin layer is less than 0.01 (% by mass), a uniform resin layer may not be formed on the surface of the core material. If the amount exceeds 5.0 (% by mass), the resin layer Becomes too thick and granulation of carriers occurs, and uniform carrier particles may not be obtained.

  The developer (initial agent) stored in advance in the developing device is also a mixture of the above-described toner and carrier. There is no restriction | limiting in particular as content (carrier density | concentration) of the carrier in a developing agent, According to the objective, it can select suitably. For example, 90-98 (mass%) is preferable and 93-97 (mass%) is more preferable.

(Drive carrier recovery roller)
Next, a method for driving the carrier recovery roller 13 will be described. FIG. 9 is a schematic configuration diagram illustrating a configuration example of the drive unit of the carrier recovery roller 13. In FIG. 9, the end of the recovery screw 6 on the front side of the developing device 4 is provided with an eccentric cam 97. The eccentric cam 97 is fitted in the elongated hole of the cam follower 98 in a rotatable state. A one-way clutch 99 is press-fitted into the opposite end portion of the cam follower 98, and a drive shaft of the carrier recovery roller 13 is inserted into the inner diameter portion of the one-way clutch 99.

In FIG. 9, when the eccentric cam 97 rotates in the P direction by the rotation of the recovery screw 6, the cam follower 98 swings in the Q direction and the R direction. The one-way clutch 99 is locked only when operating in the Q direction and is idled when operating in the R direction.
3 is driven intermittently in the J direction. By setting the swing angle of the cam follower 98 to 7.2 (°), for example, when the recovery screw 6 rotates 50 times, the carrier recovery roller 13 rotates 360 (°), that is, once. Since the collection screw 6 rotates at about 600 (rpm), the carrier collection roller 13 rotates intermittently at an extremely low speed of about 12 (rpm).

  The drive unit shown in FIG. 9 can obtain a large reduction ratio with a simple configuration. However, the drive system of the carrier recovery roller 13 is not limited to this configuration. It is also possible to select a method such as installation.

  In the developing device 4 configured as described above, the developing sleeve 81 and the carrier recovery sleeve 90 are rotated in the I and J directions, that is, in the same direction in FIG. That is, at the position where the developing roller 5 and the carrier recovery roller 13 face each other, the developing sleeve 81 and the carrier recovery sleeve 90 are moved so that the surface of the developing sleeve 81 and the surface of the carrier recovery sleeve 90 move in directions opposite to each other. It is rotating.

(Developer movement and carrier recovery operation)
Hereinafter, the movement of the developer and the recovery operation of the carrier at this time will be described with reference to FIG.

  In FIG. 6, the carrier adhering to the photosensitive member 1 in the developing region reaches the carrier recovery roller 13 by the rotation of the photosensitive member 1, and is attracted and recovered by the magnetic pole P21 having a high magnetic flux density. In the present embodiment, since the surface of the carrier recovery sleeve 90 is roughened, the magnetic pole P21 has a high magnetic flux density, but the carrier on the carrier recovery roller 13 is conveyed without slipping, and the magnetic pole P24 is Then, it falls to the collection conveyance path 7 by gravity at the end of the casing 96 (arrow M in FIG. 6).

  However, the carrier that has not fallen due to the residual magnetic flux density between the magnetic pole P24 and the magnetic pole P21 or has entered the concave portion of the roughening process tends to be brought along with the carrier recovery sleeve 90. Here, at the facing portion between the carrier recovery roller 13 and the developing roller 5, the surface of the developing sleeve 81 and the surface of the carrier recovery sleeve 90 move in opposite directions. Therefore, the carrier on the carrier recovery roller 13 is rubbed violently by the spikes on the developing roller 5. Further, since there is no magnetic pole on the side of the carrier recovery roller 13 facing the developing roller 5, it is completely recovered to the developing roller 5 by the magnet 83 in the developing roller 5 (arrow N in FIG. 6).

  On the other hand, even if a part of the developer on the developing roller 5 is scattered by the centrifugal force or gravity of the developing roller 5 after passing through the developing region, the carrier is recovered after falling on the carrier collecting roller 13. Since it is collected by the magnetic pole P21 in the roller 13, there is no problem (arrow O in FIG. 6). Further, the heading by the magnetic pole P24 is always in contact with the casing 96 to form a magnetic seal. Therefore, even if there is no contact of the scraper as the carrier removing means, there is no problem that the developer dropped by the arrow K falls from the gap between the carrier recovery roller 13 and the casing 96. Further, since the carrier recovery roller 13 rotates intermittently at an extremely low speed, there is no problem that the recovered carrier is scattered by centrifugal force.

  In order to sequentially convey the carriers adsorbed on the magnetic pole P21 having a high magnetic flux density without roughing the carrier recovery sleeve 90 to the facing portions of the magnetic poles P22, P23, and P24 without slipping, the magnetic poles P22˜ It is also conceivable to set P23 to a high magnetic flux density. However, if a plurality of expensive high magnetic flux density magnets are used, the cost is extremely increased. Therefore, it is preferable that the magnetic poles P22 to P23 are conventional magnets and the carrier recovery sleeve 90 is subjected to the aforementioned roughening treatment and processing.

  There is already known a developing device that efficiently rotates the magnet roller in the developing roller and efficiently stirs and charges the developer. However, in this type of developing device, the magnetic roller vibrates strongly on the developing roller due to the rotation of the magnet roller. As the carrier rotates, the carrier is scattered by the centrifugal force, and the carrier adhering to the photosensitive member is a more serious problem.

  On the other hand, when the carrier recovery roller is arranged in the vicinity of the photosensitive member and the developing roller in order to recover the carrier on the photosensitive member, the alternating magnetic field of the magnet roller in the developing roller and the magnetic field of the magnet roller in the carrier recovery roller are There has been a problem that interference and repetitive suction and repulsion between the magnet rollers generate a great deal of vibration. This vibration propagates to the photoconductor and the optical writing unit (exposure device) to form a banding image, noise is generated, and the life of the developing device is reduced. Further, the developer may overflow due to the interference of the magnetic field.

  Although it is conceivable to reduce the magnetic field of the carrier recovery roller in order to prevent the image quality deterioration due to the vibration, the noise, the life of the developing device, the overflow of the developer, and the like, the carrier recovery efficiency is lowered. Although it is conceivable to arrange the carrier recovery roller at a position sufficiently away from the developing roller without lowering the magnetic field of the carrier recovery roller, the image forming apparatus is enlarged or the recovered carrier is returned to the developing apparatus. There is a problem that a complicated mechanism is required, and there is a problem that the number of carriers in the developing device gradually decreases when the collected carriers are not collected in the carrier reservoir and returned to the developing device.

  Therefore, in order to solve the problems such as vibration, the carrier recovery magnet roller 91 as the second magnetic field generation unit is configured so as not to have a magnetic pole in a portion facing the developing sleeve 81 as described above. ing. More specifically, the shape of the cross section perpendicular to the axial direction of the composite magnet 93 constituting the carrier recovery magnet roller 91 is formed in a half-moon shape, and the notch portion without the magnetic pole of the composite magnet 93 is formed on the developing roller. It is arranged on the 5 side.

  In the case where the surface of the carrier recovery sleeve 90 of the carrier recovery roller 13 is roughened, if a large amount of toner adheres to the carrier recovery roller 13, the unevenness of the roughening process is filled with the adhered toner, and the carrier is transported. There is a risk of toner adhesion causing defects. In the prior art, the scraper is brought into contact with the carrier recovery roller 13 and the toner is peeled off at the same time as the carrier. However, in this embodiment, the scraper is not used. Toner adhesion is prevented.

(Toner removal from carrier recovery roller)
FIG. 10 is a schematic configuration diagram for explaining toner removal from the carrier recovery roller 13. In the example shown in FIG. 10, the photosensitive member 1 is charged to about −600 (V) by a charging device (not shown) (background portion), and is neutralized to about −100 (V) by an optical writing unit (exposure device) (not shown). (Image part). The process is a negative-positive process that uses a developer in which the toner is negatively charged and the carrier is positively charged. A developing bias of about −500 (V) is applied to the developing sleeve 81. In such a negative-positive process, the potential of the carrier recovery sleeve 90 is set to about −700 (V), so that the surface potential of the photoreceptor 1 and the developing bias of the developing sleeve 81 are set lower.

  In FIG. 10, large particles are positive polarity carriers and small particles are negative polarity toners. The potential difference of the carrier recovery sleeve 90 viewed from the photoreceptor 1 is at least −100 (V). As a result, an electrostatic force directed toward the carrier recovery sleeve 90 acts on the positive polarity carrier, but an electrostatic force directed toward the photoreceptor 1 acts on the contrary to the negative polarity toner, so that the toner is not attracted to the carrier recovery sleeve 90.

  However, the floating toner may adhere to the carrier recovery sleeve 90, although it is not aggressive. However, the potential difference of the developing sleeve 81 as viewed from the carrier recovery sleeve 90 is +200 (V). The toner adhering to the carrier recovery sleeve 90 is conveyed to the opposite portion of the developing sleeve 81 by the rotation of the carrier recovery sleeve 90, and is rubbed with a magnetic brush and simultaneously attracted to the developing sleeve 81 with a potential difference of +200 (V). It is taken into the developer. As a result, toner contamination on the surface of the carrier recovery roller 13 is prevented.

  By setting the potential conditions shown in FIG. 10 for each member of the developing device 4, it is possible to collect the carrier from the photoreceptor 1 while suppressing toner adhesion on the surface of the carrier collecting roller 13 during the normal printing operation. It becomes.

  However, depending on the operating state of the image forming apparatus, the chargeability of the toner may change significantly, and in some cases, the ratio of positively charged toner in the developer in the developing apparatus may increase significantly.

  In such a case, since the developing device 4 seals the gap between the developing roller 5 and the carrier recovery roller 13 with the developer on the developing roller 5, the carrier from the developing roller 5 under the potential condition shown in FIG. The positively charged toner moves to the collection roller 13. Then, the negatively charged toner adheres to and accumulates on the surface of the carrier recovery roller 13, whereby the surface potential of the carrier recovery roller 13 decreases in the reverse polarity direction from the set potential of −700 V. For example, when negatively charged toner adheres to the carrier recovery roller 13, the bias of about -150V is raised, and the effective bias becomes -850V.

  As a result, the ability to collect the carrier adhering to the photoconductor 1 is reduced, and if the image forming apparatus continues to operate, the carrier on the photoconductor 1 is not collected and the carrier of hard particles is transferred to the device disposed downstream of the rotation. Will be entered, and there is a risk of failure occurring in downstream devices.

  As described above, when electrostatic force is used, depending on the use state of the image forming apparatus, the toner charging polarity in the developer may be charged either positively or negatively. The toner may adhere to the carrier recovery roller 13, and the effective bias applied to the carrier recovery roller 13 may differ from a desired value depending on the charge level of the attached toner.

  Therefore, in the present embodiment, by changing the bias applied to the carrier recovery sleeve 90 at a predetermined timing, the toner adhering to the surface of the carrier recovery roller is removed, and a bias is applied to the carrier recovery roller 13 to thereby improve the carrier recovery rate. By improving the above, the collection effect is surely obtained.

  For example, when the image forming apparatus is operated in a mode in which positively charged toner is increased, the image forming apparatus is stopped and the toner attached to the carrier recovery roller 13 is removed at a timing when only the developing device 4 is driven. The mode is shifted to the toner removal mode. The situation in which the positively charged toner increases includes, for example, operation under a low humidity environment, leaving for a long time, continuous output with a high printing area, and the like, and a combination of these.

  In this toner removal mode (also referred to as a collection mode), for example, the bias applied to the developing roller 5 is set to −100 V and the potential of the carrier collection roller 13 is set to 0 V (ground) when shifting to the toner removal mode. By setting such a potential condition, the positively charged toner adhering to the carrier recovery roller 13 is recovered into a developer that seals between the developing roller 5 and the carrier recovery roller 13.

  The execution time of the toner removal mode can be, for example, a time equivalent to three rotations of the toner collection roller 13.

Table 1 shows the results of confirmation of the carrier recovery rate depending on the presence / absence of the toner removal mode when the amount of positively charged toner is increased. Evaluation condition 1 is bias application of the carrier recovery roller 13 and toner removal mode “none”, evaluation condition 2 is bias application of the carrier recovery roller 13 “present”, toner removal mode “no”, and evaluation condition 3 is the carrier recovery roller 13 A bias application and toner removal mode “present” is shown.

  In Table 1, “carrier recovery rate” indicates the number of carriers attached per unit area on the photoreceptor 1 after the development process and before the transfer process, and the number of attachments without the carrier recovery roller is 100%. The ratio of the number of adhered carriers during operation of the carrier recovery roller was taken as the carrier recovery rate. The gap between the carrier recovery roller 13 and the photoreceptor 1 is set to 0.5 (mm).

  In addition, the magnetic flux density on the surface of the photoreceptor 1 located opposite to the carrier recovery roller 13 was 100 mT. As shown in Table 1, a comparison with the presence / absence of the toner removal mode (evaluation conditions 2 and 3) and the execution of the toner removal mode achieve a carrier recovery rate of no problem.

  Further, since the evaluation condition 1 does not depend on the bias condition of the carrier recovery roller 13, the increase in the recovery rate by applying a bias to the carrier recovery roller 13 can be confirmed by comparing the evaluation conditions 1 and 3.

  Here, when the toner removal mode is carried out, the positively charged toner is mixed in the developer in the developing device 4, so that the charged state is not suitable for the electrophotographic process. In this embodiment, a premix development method is employed. Therefore, as shown in FIG. 3, as a developer discharge port arranged in the developing device 4, it is arranged on the screw side wall between the longitudinal direction of the recovery screw 6 and the upstream side of the supply screw 89 from the longitudinal direction. It is preferable to provide a shutter (developer outlet shutter 136) that can be opened and closed at timing.

  When the toner removal mode in which the developer is mixed in the toner bottle is executed, the developer discharge port shutter 136 is opened and the developer is forcibly discharged, whereby the developer containing positively charged toner recovered from the carrier recovery roller 13 is used. The occurrence of defects can be prevented. In this way, it is possible to maintain the effect of removing the carrier adhering to the image carrier by reliably removing the reverse polarity toner adhering to the carrier recovery roller 13 from the inside of the developing device.

[Second Embodiment]
Hereinafter, other embodiments of the image forming apparatus according to the present invention will be described. In addition, the description about the same point as the said embodiment is abbreviate | omitted.

  The timing for changing the bias applied to the carrier recovery sleeve 90 is preferably during non-image area printing. The bias applied to the carrier recovery sleeve 90 is smaller than the bias applied to the developing roller 5, and the potential difference between the surface potential of the carrier recovery sleeve 90 and the surface potential of the developer roller 5 is the image carrier dark portion potential. It is preferable that the potential difference is smaller than the potential of the developer carrying member. FIG. 11 is a schematic diagram showing the relationship between the potentials of the respective parts during the normal printing operation and the toner removal mode in the present embodiment. Hereinafter, the bias application control in this embodiment will be described with reference to FIG.

  In the second embodiment, in a non-image area between print pages at a predetermined timing (for example, every 100 pages), for example, a bias (carrier recovery roller potential) applied to the carrier recovery roller 13 is from −700V. The voltage is changed to -450 V, the bias applied simultaneously with the end of the non-image area is changed from -450 V to -700 V, and the normal printing operation is continued.

  Here, it is mainly reverse (positive) charged toner that is desired to be removed from the carrier recovery roller 13, the toner charge amount level is very small, and these are attached to the carrier recovery roller 13 during normal printing under the surrounding potential condition. The electrostatic force consisting of is dominant.

  Therefore, by applying a relatively low reverse bias condition (smaller than the bias for developing the normally charged toner to the photoreceptor 1), the positively charged toner attached to the carrier recovery roller 13 is peeled off from the carrier recovery roller 13.

  Also, although the case where the ratio of the positively charged toner is not in an increasing state is performed, the negatively charged toner having the normal charging polarity is positively changed from the developing roller 5 to the carrier recovery roller if the potential difference is in the vicinity of the development start voltage. The amount of toner that moves (develops) to 13 is very small.

  However, when a potential difference (background potential) between the photosensitive member dark portion potential and the developer carrying member potential set in the image forming apparatus is given or more, the carrier recovery roller is similar to the case where background contamination occurs on the photosensitive member 1. There is a risk that the regular charged toner will also adhere to the surface 13.

  Therefore, in this embodiment, negatively charged toner is applied by applying to the carrier recovery roller 13 −450 V, which is less than −500 V, which is an applied bias (developing bias) of the developing roller 5, and a potential difference that is smaller than 100 V of the background potential. It is possible to collect the positively charged toner from the carrier collecting roller 13 while minimizing the adhesion of the toner, and it is possible to maintain the collection rate of the carrier adhered to the photoreceptor 1.

  FIG. 12 shows the charge amount distribution when the positively charged toner ratio increases. The charge amount Q (fC) of the toner and the particle size d (μm) of the toner, and changes in the distribution before and after the increase are indicated by arrows. Even if the positively charged toner ratio increases in this way, the distribution does not reverse from negative to positive, and there is a peak of non-normally charged toner where the charge amount is slightly located on the positively charged side. In general, the force acting between the toner and the sleeve (metal) has a mirror image force, and the contribution of the toner charge amount is large. Therefore, a relatively weak mirror image force and the carrier recovery roller are generated between the positively charged toner and the carrier recovery roller. An electrostatic force due to a potential difference between 13 and the developing roller 5 acts.

  FIG. 13 shows the relationship between the potential difference and the toner adhesion amount on the photoreceptor. In this embodiment, the development start voltage of the negatively charged toner is about +50 to +100 V, and even if a potential difference of at least equal to or less than that is applied between the carrier recovery roller 13 and the development roller 5, the negatively charged toner is a normally charged toner. The movement of the charged toner from the developing roller 5 to the carrier recovery roller 13 can be minimized. As described above, the situation in which the positively charged toner is increased is, for example, a situation in which operation is performed in a low humidity environment, left for a long time, continuous output with a high printing area, and the like.

  With the positively charged toner adhering to the surface of the carrier recovery roller 13, the applied bias setting value of the carrier recovery roller 13 and the toner recovery rate on the carrier recovery roller 13 were confirmed. The confirmation result is shown in FIG.

  As shown in FIG. 14, the positively charged toner adhering to the carrier recovery roller 13 is removed in the direction in which the bias applied to the carrier recovery roller 13 is reduced, but it can be seen that the toner recovery rate decreases as the toner is further lowered. This is considered because the negatively charged toner has moved from the developer on the developing roller 5 to the carrier recovery roller 13, and as a result, the recovery rate has decreased. Therefore, by appropriately setting the bias applied to the carrier recovery roller 13, it becomes possible to effectively recover the positively charged toner. As a result, the appropriate carrier recovery roller bias is applied during normal printing. The carrier recovery capability can be maintained.

[Third Embodiment]
As described above, the developing device 4 has a toner concentration sensor (not shown) including a magnetic permeability sensor below the stirring and conveying path 10 and detects the toner concentration in the developer.

  Although it is important to reliably remove the carrier adhering to the photoconductor 1, it has been found that the carrier adhering to the photoconductor 1 occurs when the toner density is relatively low.

  FIG. 15 shows the relationship between the toner density and the number of adhered carriers when no bias is applied to the carrier recovery roller 13. The limit of the number of carriers attached was 100 / A4. From this result, when the toner concentration is 7 wt% or more, the limit of the number of adhered carriers (100) is not exceeded without applying a bias, so that the effective toner is applied to the carrier recovery roller 13 due to the adhesion of positively charged toner. Even if the bias is lowered, there is no problem with the image forming apparatus.

  Therefore, in this embodiment, whether or not to change the bias applied to the carrier recovery roller 13 is determined based on the detection result of the toner density sensor. Accordingly, it is possible to reduce the frequency of execution of the toner removal mode, maintain the carrier removal effect without stopping the printing operation of the image forming apparatus and reduce the printing speed, and provide a defect-free image.

  Further, the toner attached to the carrier recovery roller 13 is effectively removed without the risk of adhesion of negatively charged toner due to the change in the bias applied to the carrier recovery roller 13, and the carrier attached on the image carrier is removed. A good image can be provided.

[Fourth Embodiment]
In addition, when the image area ratio is relatively high (for example, 20% or more), toner replenishment is frequently performed, so the average toner charge amount in the developer is, for example, as shown in FIG. It tends to decline. At this time, the toner charge amount in the developer has a relatively wide distribution and shifts to the low charge side as a whole, so that the proportion of toner having weak to reverse charge characteristics also increases. In such a state, there is a concern about the reversely charged toner adhering to the carrier recovery roller 13, and therefore it is necessary to execute the toner removal mode or to recover the positively charged toner by changing the carrier recovery roller bias.

  Therefore, the image forming apparatus includes an image ratio counting unit that counts an image ratio to be printed, and determines whether or not to apply a bias to the carrier recovery roller 13 based on a counting result of the image ratio counting unit. preferable.

  Accordingly, it is possible to reduce the frequency of execution of the toner removal mode, maintain the carrier removal effect without stopping the printing operation of the image forming apparatus and reduce the printing speed, and provide a defect-free image.

  Further, the toner attached to the carrier recovery roller 13 is effectively removed without the risk of adhesion of negatively charged toner due to the change in the bias applied to the carrier recovery roller 13, and the carrier attached on the image carrier is removed. A good image can be provided.

[Fifth Embodiment]
In addition, the image forming apparatus includes a humidity detecting unit (humidity sensor) that detects humidity around the image forming apparatus, and determines whether to change the bias applied to the carrier recovery roller 13 based on the detection result of the humidity detecting unit. It is also preferable to do. Thus, it is also effective to determine the toner removal mode frequency on the carrier recovery roller 13 or the bias change control frequency based on the installation environment of the image forming apparatus.

  For example, when the humidity is 50% or more, the overall toner charge amount decreases, so the ratio of toner having weak to reverse charge characteristics tends to increase. Therefore, the toner removal mode on the carrier recovery roller 13 is not executed at 50% or less, and the toner removal mode is executed every 2000 pages when the other adjustment mode is executed under a high humidity environment. is there.

  In a high-humidity environment, the developer charge amount is low, so the counter charge remaining on the carrier is relatively small, and the carrier adhesion margin on the photosensitive member 1 is also improved. Even if the bias is reduced, if it is about 2000 pages, there is little damage on the image forming apparatus, and a high-quality image can be provided.

  Accordingly, it is possible to reduce the frequency of execution of the toner removal mode, maintain the carrier removal effect without stopping the printing operation of the image forming apparatus and reduce the printing speed, and provide a defect-free image.

  Further, the toner attached to the carrier recovery roller 13 is effectively removed without the risk of adhesion of negatively charged toner due to the change in the bias applied to the carrier recovery roller 13, and the carrier attached on the image carrier is removed. A good image can be provided.

[Sixth Embodiment]
The image forming apparatus also includes a replenished toner amount / driving time counting unit that counts the toner amount replenished to the developing device 4 and the driving time of the developing device, and is based on the detection result of the replenishing toner amount / driving time counting unit. It is also preferable to determine whether or not the bias applied to the carrier recovery roller 13 can be changed.

  FIG. 16 shows the charge amount distribution when the toner replenishment amount varies per unit drive time. As shown in FIG. 16, the ratio of weak to reversely charged toner is remarkably generated at the timing of switching from low image area printing with low toner consumption / replenishment to high image area printing with high toner consumption / replenishment.

  This is mainly due to the fact that a part of the toner in the developer is in a vigorous stirring state when the toner consumption is low and the charge amount is increased. Therefore, in the present embodiment, there is provided means for counting the average value of the toner replenishment amount per unit driving time of the past 100 pages, and when the counted value exceeds a specific value, the toner removal on the carrier recovery roller 13 is removed. Transition to mode. In this embodiment, for example, when the average value of the toner replenishment amount changes at 10 mg / min or less, the image forming apparatus is stopped when the average value of toner replenishment amount is 50 mg / min or more, and the mode is shifted to the toner removal mode. If the average value is 10 mg / min or more, even if the toner consumption / replenishment increases thereafter, the ratio of the weakly charged toner to the reversely charged toner hardly rises, so that the toner adheres on the carrier recovery roller 13 under the normal printing potential conditions. Never do.

  Therefore, by determining whether or not the toner removal mode can be executed based on the toner replenishment amount per unit driving time, it is possible to effectively suppress toner adhesion on the carrier recovery roller.

  Accordingly, it is possible to reduce the frequency of execution of the toner removal mode, maintain the carrier removal effect without stopping the printing operation of the image forming apparatus and reduce the printing speed, and provide a defect-free image.

  Further, the toner attached to the carrier recovery roller 13 is effectively removed without the risk of adhesion of negatively charged toner due to the change in the bias applied to the carrier recovery roller 13, and the carrier attached on the image carrier is removed. A good image can be provided.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

1, 1Y, M, C, K Photosensitive member 4, 4Y, M, C, K Developing device 5 Developing roller 6 Recovery screw 7 Recovery conveyance path 8 Supply screw 9 Supply conveyance path 9 '樋 10 Agitation conveyance path 11 Agitation screw 12 Doctor blade 13 Carrier recovery roller 14 Tension roller 15 Drive roller 16 Secondary transfer backup roller 17 Intermediate transfer unit 18, 18Y, M, C, K Process cartridge 20 Image forming unit 21 Optical writing unit 22 Secondary transfer device 23 Tension Roller roller 24 Paper transport belt 25 Fixing device 26 Fixing belt 27 Pressure roller 30 Document base 32 Contact glass 33 First traveling body 34 Second traveling body 35 Imaging lens 36 Reading sensor 42 Paper feed roller 43 Paper bank 44 Paper feed cassette 45 Separating rollers 46 and 48 Paper feed path 47 Conveying roller pair 49 Registrho 50 Manual feed roller 51 Manual feed tray 52 Separating roller 53 Manual feed path 57 Stack unit 60 Belt cleaning device 62Y, M, C, K Primary transfer bias roller 81 Developing sleeve 82 Magnet roller 83 Magnet 84 Magnet holder 90 Carrier recovery sleeve 91 Carrier recovery magnet roller 92 Shaft 93 Composite magnet 94 Block magnet 95 Toner supply port 96 Casing 97 Eccentric cam 98 Cam follower 99 One-way clutch 100 Printer unit 110 Intermediate transfer belt 133 First partition wall 134 Second partition wall 135 Third partition wall 136 Developer outlet shutter 200 Paper feeder 300 Scanner 400 Automatic document feeder 500 Copier G Developer T Toner C Carrier

JP-A-62-83767 JP-A-11-311903 JP 2006-154103 A JP 2012-113044 A

Claims (9)

A developer support means which can carry a two-component developer including a toner and a carrier to be supplied to the image carrier on the surface and can rotate, and a first magnetic field generation which has a plurality of magnetic poles contained in the developer support means A developer carrier having means;
Carrier support means provided on the downstream side of the developer carrier in the surface movement direction of the image carrier and capable of carrying and rotating the carrier attached to the image carrier on the surface, and the carrier support means And at least a carrier recovery means having a second magnetic field generating means fixedly arranged and having a plurality of magnetic poles,
The first magnetic field generating means includes a developing device rotatably provided so that a plurality of magnetic poles sequentially pass through a position facing the carrier supporting means;
Bias applying means for applying a bias to the carrier supporting means,
The image forming apparatus, wherein the bias applying unit changes a bias applied to the carrier support unit at a predetermined timing.   The image forming apparatus according to claim 1, wherein the predetermined timing is a timing at which the image forming apparatus stops and the developing device is driven.   The image forming apparatus according to claim 1, wherein the predetermined timing is when a non-image area is printed by the image forming apparatus.   The bias applied to the carrier support means is smaller than the bias applied to the developer carrier, and the potential difference between the surface potential of the carrier support means and the surface potential of the developer carrier is an image carrier dark portion potential. The image forming apparatus according to claim 3, wherein the image forming apparatus is smaller than a potential difference between the toner and the developer carrying member potential. The developing device has a developer outlet that can be opened and closed,
5. The image according to claim 1, wherein opening and closing of the developer discharge port is controlled based on a bias applied to the carrier support means and a bias applied to the developer carrying member. Forming equipment. A toner detecting means for detecting the toner concentration in the developer in the developing device;
6. The image forming apparatus according to claim 1, wherein whether or not the applied bias can be changed by the bias applying unit is determined based on a detection result of the toner detecting unit. An image ratio counting unit for counting an image ratio printed by the image forming apparatus;
6. The image forming apparatus according to claim 1, wherein whether or not the bias applied by the bias applying unit can be changed is determined based on a counting result of the image ratio counting unit. Humidity detection means for detecting the humidity around the image forming apparatus,
6. The image forming apparatus according to claim 1, wherein whether or not the applied bias can be changed by the bias applying unit is determined based on a detection result of the humidity detecting unit. A replenishing toner amount / driving time counting means for counting the amount of toner replenished to the developing device and the driving time of the developing device;
6. The image forming apparatus according to claim 1, wherein whether the applied bias can be changed by the bias applying unit is determined based on a detection result of the replenishing toner amount / driving time counting unit.