JP5618930B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using a cleaning blade for cleaning the surface of an image carrier such as a photosensitive drum, and more particularly to a method for reducing friction between a cleaning blade and the surface of an image carrier during setup of the image forming apparatus. Is.

  Conventionally, in an image forming apparatus using an electrophotographic process, a powdered developer is mainly used, and an electrostatic latent image formed on an image carrier such as a photosensitive drum is visualized using the developing apparatus, A process in which the visible image (toner image) is transferred onto a recording medium and then a fixing process is performed is common. The toner remaining on the surface of the photosensitive drum is removed by a cleaning device having a cleaning blade pressed against the image carrier, and a new toner image is formed.

  Here, since the cleaning blade is formed of hard rubber or the like, the friction resistance with the surface of the image carrier is high at the start of use of the image forming apparatus, the drive torque of the photosensitive member is increased, and the stick-slip motion of the cleaning blade There is a possibility that problems such as generation of blade vibration noise due to increase in amplitude, turning-up (rolling up) of the cleaning blade, and jitter may occur.

  Also, as the cumulative number of printed sheets from the time of setting up the image forming apparatus increases, the external additive gradually adheres to the edge portion of the cleaning blade, but the external additive is uniform on the edge portion of the cleaning blade. A portion where the external additive is attached and a portion where the external additive is not attached are formed. As a result, the portion where the external additive is not attached has high frictional resistance with the surface of the image carrier, and the toner remaining on the surface of the image carrier cannot be scraped off, resulting in streak noise on the surface of the image carrier. When the noise is remarkable, it may appear as a streak image.

  Therefore, as disclosed in Patent Document 1, the frictional resistance between the photosensitive drum and the cleaning blade is reduced by bringing the cleaning blade into contact with the surface of the photosensitive drum on which the toner is adhered and applying the toner to the cleaning blade. There is a way to reduce it.

Japanese Patent Laid-Open No. 9-244389

  However, depending on the material of the cleaning blade and the photosensitive drum, it may not be sufficient to simply apply toner to the cleaning blade as described above, causing streaky noise on the photosensitive drum or turning the cleaning blade over. May occur.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image forming apparatus capable of obtaining a good image immediately after setup by suppressing generation of streaky noise on the surface of the image carrier and the cleaning blade immediately after setup. For the purpose.

  In order to achieve the above object, the present invention provides an image carrier having a photosensitive layer formed on the surface, a charging means for uniformly charging the surface of the image carrier, and the image carrier charged by the charging means. An exposure unit for exposing the surface of the body to form an electrostatic latent image; and a toner carrier that is disposed to face the image carrier in a non-contact manner and carries toner including toner base particles and an external additive. An electrostatic latent image on the image carrier is formed by applying a developing device, a cleaning blade pressed against the surface of the image carrier at a predetermined pressure, and a bias composed of a direct current component and an alternating current component to the toner carrier. An image forming apparatus comprising: a voltage applying unit for attaching toner; and at the time of setting up the image forming apparatus, the charging unit is used to uniformly charge the surface of the image carrier, and the voltage applying unit is used. Statue An external additive attaching step for attaching the external additive to the edge portion of the cleaning blade by applying a bias to the toner carrier so that the external additive moves preferentially on the holder; And a toner discharge step of forcibly discharging the toner remaining on the toner carrier to the image carrier side following the step.

  According to the present invention, in the image forming apparatus configured as described above, the DC component of the bias applied to the toner carrier when the external additive attaching step is performed is made smaller than the DC component of the bias applied during image formation. It is a feature.

  In the image forming apparatus having the above-described configuration, the peak-to-peak value of the alternating current component of the bias applied to the toner carrier during the execution of the external additive attaching step can be expressed as the alternating current component of the bias applied during the image formation. It is characterized by being larger than the peak-to-peak value.

  According to the present invention, in the image forming apparatus having the above-described configuration, the developing device is disposed to face the toner carrier, and a developer carrier that supplies toner to the toner carrier using a magnetic brush formed on a surface thereof. And the voltage application means is capable of applying a bias comprising a direct current component and an alternating current component to the developer carrier, and a direct current component of the bias to be applied to the developer carrier during the execution of the external additive attaching step. Is the same voltage as the DC component of the bias applied during image formation.

  According to the first configuration of the present invention, the external additive can be selectively moved to the surface of the image carrier and adhered to the edge portion of the cleaning blade while leaving the toner base particles on the toner carrier as much as possible. it can. As a result, a uniform external additive layer is formed on the edge portion of the cleaning blade, which improves the cleaning performance of the surface of the image carrier immediately after the setup of the image forming apparatus. Frictional resistance can be reduced. Accordingly, it is possible to effectively suppress problems such as an increase in driving torque of the image carrier, vibration noise and turning of the cleaning blade, and jitter due to vibration of the image carrier. Further, since the deteriorated toner with a small amount of the external additive remaining on the toner carrier is forcibly consumed, the occurrence of uneven image density can be suppressed.

  Further, according to the second configuration of the present invention, in the image forming apparatus having the first configuration, a bias DC component applied to the toner carrier when the external additive attaching step is executed is applied to the bias applied during the image formation. Since the potential difference between the image carrier and the toner carrier increases, the external additive alone can be efficiently moved toward the image carrier.

  According to the third configuration of the present invention, in the image forming apparatus having the second configuration, the peak-to-peak value of the alternating current component of the bias applied to the toner carrier when the external additive attaching step is executed is By making it larger than the peak-to-peak value of the AC component of the developing bias applied during formation, the electric field strength on the surface of the toner carrier increases, and not only the external additive released from the toner base particles but also the toner base particles The external additive adhering to the surface of the toner can also be peeled off and allowed to fly to the image carrier side.

  According to the fourth configuration of the present invention, in the image forming apparatus having the second or third configuration, the toner is carried on the toner carrier using a magnetic brush that is disposed opposite to the toner carrier and formed on the surface. In the case of a developing device equipped with a developer carrying body that supplies the DC, the DC component of the bias applied to the developer carrying body when the external additive attaching step is executed is set to the same voltage as the DC component of the bias applied during image formation. As a result, the potential difference between the developer carrier and the toner carrier increases. Therefore, a large amount of toner can be supplied from the developer carrying member to the toner carrying member, and the amount of the external additive that can fly to the image carrying member side can also be increased.

1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus according to a first embodiment of the present invention. Partial enlarged view of the periphery of the image forming portion Pa in FIG. Side surface sectional drawing which shows the structure of the image development apparatus mounted in the image forming apparatus of 1st Embodiment. The figure which shows an example of the bias waveform applied to a developing roller and a magnetic roller 1 is a block diagram showing a control path of an image forming apparatus according to a first embodiment. Schematic showing a state in which the image forming portion Pa is in the external additive attaching step Schematic diagram showing a state in which the image forming unit Pa is in the toner discharge process Schematic cross-sectional view showing the overall configuration of an image forming apparatus according to a second embodiment of the present invention Side surface sectional drawing which shows the structure of the image development apparatus mounted in the image forming apparatus of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. Here, a tandem color printer is illustrated. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (magenta, cyan, yellow, and black), and magenta, cyan, and yellow are respectively subjected to charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  These image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d which carry visible images (toner images) of the respective colors, and are further illustrated by a driving means (not shown). In FIG. 1, an intermediate transfer belt 8 that rotates clockwise is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a transfer sheet S as an example of a recording medium, and further fixed on the transfer sheet S in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer sheet S on which the toner image is transferred is accommodated in a sheet cassette 16 at the lower part of the apparatus, and drives a secondary transfer roller 9 and an intermediate transfer belt 8 described later via a paper feed roller 12a and a registration roller pair 12b. It is conveyed to the nip portion with the roller 11. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. A blade-shaped belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9 in the rotation direction of the intermediate transfer belt 8.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning devices 5a, 5b, 5c and 5d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated according to the image data by the exposure device 4. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer containing toner of each color of magenta, cyan, yellow, and black. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d is less than a predetermined value due to the formation of a toner image described later, four toner containers filled with toner of each color ( The toner is supplied to each of the developing devices 3a to 3d from a not-shown). The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically attached to the electrostatic latent image formed by exposure from the exposure device 4. A toner image is formed.

  The primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and magenta, cyan, yellow, and yellow on the photosensitive drums 1a to 1d. A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning devices 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream transport roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer sheet S is conveyed from the registration roller pair 12b to the nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. Then, the full color image on the intermediate transfer belt 8 is transferred onto the transfer paper S. The transfer sheet S on which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer sheet S conveyed to the fixing unit 7 is heated and pressurized by the fixing roller pair 13 to fix the toner image on the surface of the transfer sheet S, thereby forming a predetermined full color image. The transfer sheet S on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper S, the image is directly discharged onto the discharge tray 17 by the discharge roller pair 15.

  On the other hand, when images are formed on both sides of the transfer sheet S, a part of the transfer sheet S that has passed through the fixing unit 7 is once protruded from the discharge roller pair 15 to the outside of the apparatus. Thereafter, the transfer sheet S is distributed to the reverse conveyance path 18 by the branching portion 14 by rotating the discharge roller pair 15 in the reverse direction, and is re-conveyed to the secondary transfer nip portion with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred by the secondary transfer roller 9 to the surface of the transfer paper S where the image is not formed, and conveyed to the fixing unit 7 and the toner image is fixed. The paper is discharged to the discharge tray 17 by the discharge roller pair 15.

  FIG. 2 is an enlarged view of the vicinity of the image forming portion Pa in FIG. Since the image forming units Pb to Pd have basically the same configuration, description thereof is omitted. Around the photosensitive drum 1a, a charger 2a, a developing device 3a, a cleaning device 5a, and a charge eliminating lamp 20 are disposed along the drum rotation direction (counterclockwise direction in FIG. 2). A primary transfer roller 6a is disposed between the rollers.

  The charger 2 a includes a charging roller 21 that contacts the photosensitive drum 1 a and applies a charging bias to the drum surface, and a charging cleaning roller 23 for cleaning the charging roller 21.

  The developing device 3a is a two-component developing type having two stirring screws 25a and 25b, a magnetic roller 27, and a developing roller 29, and uses a magnetic brush that stands on the surface of the magnetic roller 27 to apply toner to the developing roller 29. A thin layer is formed, and a developing bias having the same polarity (positive) as that of the toner is applied to the developing roller 29 to cause the toner to fly on the drum surface.

  Further, the developing device 3a can execute a toner discharge step of supplying (discharging) the toner on the developing roller 29 to the photosensitive drum 1a side. As a result, the deteriorated toner (overcharged toner) on the developing roller 29 is discharged to the photosensitive drum 1a side to prevent image defects such as fogging, and to the toner supplied to the photosensitive drum 1a side, the photosensitive drum 1a. Foreign matter such as surface moisture, paper powder, and toner external additive aggregates can be adsorbed and removed together with the toner.

  This toner discharge process is periodically executed at a predetermined timing, for example, after a predetermined number of prints, after a predetermined drive time has elapsed, or at the end of a continuous printing operation, or at the time of setting up an image forming apparatus as will be described later. This is performed following the external additive attaching step. The toner supplied to the photosensitive drum 1a is scraped off by the cleaning blade 31 of the cleaning device 5a.

  The cleaning device 5 a includes a cleaning blade 31 and a recovery screw 32. The cleaning blade 31 is fixed in contact with the surface of the photosensitive drum 1a with a predetermined pressure. As the cleaning blade 31, for example, a polyurethane rubber blade having a JIS hardness of 78 ° is used, and is attached at a predetermined angle with respect to the tangential direction of the photosensitive member at the contact point. The material, hardness, dimensions, the amount of biting into the photosensitive drum 1a, the pressure contact force, and the like of the cleaning blade 31 are appropriately set according to the specifications of the photosensitive drum 1a. Residual toner removed from the surface of the photosensitive drum 1 a by the cleaning blade 31 is discharged to the outside of the cleaning device 5 a as the recovery screw 32 rotates.

  A neutralizing lamp 20 is disposed between the cleaning device 5a and the charger 2a. The neutralization lamp 20 removes residual charges on the surface of the drum by irradiating the surface of the photosensitive drum 1a with light.

  FIG. 3 is a side sectional view showing a configuration example of the developing device installed in the color printer 100 of the present embodiment. Here, the developing device 3a disposed in the image forming unit Pa of FIGS. 1 and 2 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same. Since there is, explanation is omitted.

  As shown in FIG. 3, the developing device 3a includes a developing container 33 in which a two-component developer (hereinafter also simply referred to as a developer) is accommodated. The developing container 33 is divided into a first wall and a second wall by a partition wall 33a. The first and second agitating chambers 33b and 33c are divided into agitating chambers 33b and 33c, and toner (positively charged toner) supplied from a toner container (not shown) is mixed with a carrier and agitated and charged. The first stirring screw 25a and the second stirring screw 25b are rotatably arranged.

  Then, the developer is conveyed in the axial direction while being stirred by the first stirring screw 25a and the second stirring screw 25b, and the first and second are passed through the developer passage (not shown) formed in the partition wall 33a. It circulates between the stirring chambers 33b and 33c. In the example shown in the drawing, the developing container 33 extends obliquely upward to the left, the magnetic roller 27 is disposed above the second stirring screw 25b in the developing container 33, and the developing is performed obliquely upward to the left of the magnetic roller 27. Rollers 29 are arranged opposite to each other. The developing roller 29 faces the photosensitive drum 1a on the opening side (the left side in FIG. 3) of the developing container 33, and the magnetic roller 27 and the developing roller 29 rotate clockwise in the drawing.

  A toner concentration sensor (not shown) is arranged in the developing container 33 so as to face the first agitating screw 25a, and the toner container supplies a toner replenishing port according to the toner concentration detected by the toner concentration sensor. The toner is supplied into the developing container 33 through 33d.

  The magnetic roller 27 includes a non-magnetic rotating sleeve 27a and a fixed magnet body 27b having a plurality of magnetic poles contained in the rotating sleeve. In the present embodiment, the magnetic poles of the fixed magnet body 27 b have a five-pole configuration including a main pole 35, a regulation pole (head cutting pole) 36, a transport pole 37, a separation pole 38, and a pumping pole 39.

  Further, a regulating blade 34 is attached to the developing container 33 along the longitudinal direction of the magnetic roller 27 (front and back direction in FIG. 3), and the regulating blade 34 is rotated in the rotational direction of the magnetic roller 27 (clockwise in FIG. 3). In the direction), the developing roller 29 and the magnetic roller 27 are positioned on the upstream side. A slight gap (gap) is formed between the tip of the regulating blade 34 and the surface of the magnetic roller 27.

  The developing roller 29 includes a cylindrical developing sleeve 29a and a magnet member 29b fixed in the developing sleeve 29a. The magnetic roller 27 and the developing roller 29 have a predetermined gap at the facing position (opposite position). Are facing each other. The magnet member 29b has a different polarity from the opposing magnetic pole (main pole) 35 of the fixed magnet body 27b.

  A developing bias power source 43 (both see FIG. 5) is connected to the magnetic roller 27 and the developing roller 29 via a bias control circuit 41, and a direct current voltage (hereinafter referred to as Vslv (DC)) is connected to the developing roller 29. And an AC voltage (hereinafter referred to as Vslv (AC)) is applied, and a DC voltage (hereinafter referred to as Vmag (DC)) and an AC voltage (hereinafter referred to as Vmag (AC)) are applied to the magnetic roller 27.

  As described above, the first stirring screw 25a and the second stirring screw 25b circulate in the developing container 33 while the developer is being stirred to charge the toner, and the second stirring screw 25b causes the developer to reach the magnetic roller 27. Be transported. Since the regulation pole 36 of the fixed magnet body 27b faces the regulation blade 34, a nonmagnetic material or a magnetic material is used as the regulation blade 34, so that a magnetic field in a direction attracting the gap between the tip of the regulation blade 34 and the rotary sleeve 27a. Occurs.

  Due to this magnetic field, a magnetic brush is formed between the regulating blade 34 and the rotating sleeve 27a. When the thickness of the magnetic brush on the magnetic roller 27 is regulated by the regulating blade 34 and then moves to a position facing the developing roller 29, a magnetic field attracted by the main pole 35 of the fixed magnet body 27b and the developing roller side magnetic pole 23b is generated. Since the magnetic brush is applied, the magnetic brush contacts the surface of the developing roller 29. Then, a toner thin layer is formed on the developing roller 29 by a potential difference ΔV between Vmag (DC) applied to the magnetic roller 27 and Vslv (DC) applied to the developing roller 29 and a magnetic field.

  The toner layer thickness on the developing roller 29 varies depending on the resistance of the developer and the difference in rotational speed between the magnetic roller 27 and the developing roller 29, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 29 is thickened, and when ΔV is decreased, the toner layer is thinned. The range of ΔV at the time of development is generally about 100V to 350V.

  FIG. 4 is a diagram illustrating an example of a bias waveform applied to the developing roller 29 and the magnetic roller 27. As shown in FIG. 4A, the developing roller 29 has a composite bias Vslv (solid line) obtained by superimposing a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 on Vslv (DC). Is applied via the bias control circuit 41. The magnetic roller 27 has a composite waveform Vmag (broken line) obtained by superimposing a rectangular wave Vmag (AC) having a peak-to-peak value of Vpp2 and a phase different from Vslv (AC) on Vmag (DC). Applied from the power supply 43 via the bias control circuit 41.

  Therefore, the voltage applied between the magnetic roller 27 and the developing roller 29 (hereinafter referred to as between the MSs) is a composite waveform Vmag− having Vpp (max) and Vpp (min) as shown in FIG. Vslv. Note that Vmag (AC) is set so that the duty ratio is larger than Vslv (AC). Actually, an AC voltage having a partially distorted shape is applied instead of a complete rectangular wave as shown in FIG.

  The toner thin layer formed on the developing roller 29 by the magnetic brush is conveyed to the opposite portion between the photosensitive drum 1a and the developing roller 29 by the rotation of the developing sleeve 29a. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 29, the toner flies due to a potential difference between the developing roller 29 and the photosensitive drum 1a (hereinafter referred to as SD), and the photosensitive drum The electrostatic latent image on 1a is developed.

  When the rotating sleeve 27a further rotates in the clockwise direction, the magnetic brush is pulled away from the surface of the developing roller 29 by the horizontal (roller circumferential direction) magnetic field generated by the different polarity peeling pole 38 adjacent to the main pole 35. The toner remaining without being used for development is collected from the developing roller 29 onto the rotating sleeve 27a. When the rotating sleeve 27a further rotates, a repulsive magnetic field is applied by the peeling pole 38 of the fixed magnet body 27b and the scooping pole 39 of the same polarity, so that the toner separates from the rotating sleeve 27a in the developing container 33. Then, after being stirred and conveyed by the second agitating screw 25b, a magnetic brush is again formed on the rotating sleeve 27a by the scooping pole 39 as a two-component developer that is uniformly charged again with an appropriate toner concentration, and the regulating blade 34 It is conveyed to.

  Next, the control path of the color printer 100 of this embodiment will be described. FIG. 5 is a block diagram illustrating an example of a control path used in the image forming apparatus according to the first embodiment. In addition, since various controls of each part of the apparatus are performed when the color printer 100 is used, the control path of the entire color printer 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a read / write storage unit, A plurality of (two in this case) that transmit control signals to and receive input signals from the operation unit 50, such as a temporary storage unit 94 for storing image data and the like, a counter 95, and each device in the color printer 100. At least an I / F (interface) 96 is provided. Further, the control unit 90 can be arranged at an arbitrary location inside the apparatus main body.

  The ROM 92 stores a program for controlling the color printer 100, numerical values necessary for control, and the like that are not changed during use of the color printer 100. The RAM 93 stores necessary data generated during control of the color printer 100, data temporarily required for control of the color printer 100, and the like. The ROM 92 (or RAM 93) stores an execution time of an external additive attaching step and a toner discharge step, which will be described later, a development bias value at the time of execution, a bias application time, and the like. The counter 95 adds up the number of printed sheets and counts it. Note that the number of times may be stored in the RAM 93, for example, without providing the counter 95 separately.

  The control unit 90 transmits a control signal from the CPU 91 to the respective units and devices in the color printer 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. Examples of each part and device controlled by the control unit 90 include the image forming units Pa to Pd, the exposure device 4, the fixing unit 7, the paper cassette 16, the image input unit 40, the bias control circuit 41, and the operation unit 50. It is done.

  The image input unit 40 is a receiving unit that receives image data transmitted to the color printer 100 from a personal computer or the like. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

  The bias control circuit 41 is connected to the charging bias power source 42, the developing bias power source 43, and the transfer bias power source 44, and operates each of these power sources according to an output signal from the control unit 90. These power sources are bias controlled. In accordance with a control signal from the circuit 41, the charging bias power source 42 is supplied to the charging roller 21 in the chargers 2a to 2d, and the developing bias power source 43 is transferred to the magnetic roller 27 and the developing roller 29 in the developing devices 3a to 3d. Applies a predetermined bias to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively.

  The operation unit 50 is provided with a liquid crystal display unit 51 and an LED 52. The liquid crystal display unit 51 and the LED 52 indicate the state of the color printer 100, and display the image forming status and the number of copies to be printed. Yes. Various settings of the color printer 100 are performed from a printer driver of a personal computer.

  In addition, the operation unit 50 includes a start button for instructing the user to start image formation, a stop / clear button used for stopping image formation, and various settings of the color printer 100 when making the default settings. A reset button or the like to be used is provided.

  Next, the two-component developer used in the color printer 100 of this embodiment will be described. The two-component developer contains a toner and a carrier. The weight ratio (T / C) between the toner and the carrier in the two-component developer is preferably 5 to 20 parts by weight, more preferably 8 to 15 parts by weight with respect to 100 parts by weight of the carrier.

  The toner is obtained by adding an external additive to toner base particles. The toner base particles contain a binder resin and a colorant. The toner base particles may contain a release agent, a charge control agent, magnetic powder and the like as necessary. The weight average particle diameter of the toner base particles is preferably 5 to 12 μm, and more preferably 6 to 10 μm. The weight average particle diameter of the toner base particles is measured by a particle size distribution measuring device (for example, Multisizer II type manufactured by Coulter, Inc.). The toner base particles are produced by a known method such as a pulverization classification method, a melt granulation method, a spray granulation method, or a polymerization method.

  As the external additive, silica or titanium oxide is used. However, in the present invention, silica that accumulates at the edge portion of the cleaning blade 31 and easily forms the external additive layer is preferably used, and the surface of the toner base particle is physically or statically. Used with electrical attachment. The addition amount of the external additive is usually 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner base particles.

  As the carrier, magnetic particles or resin particles in which a magnetic material is dispersed in a binder resin are used. Examples of magnetic materials include magnetic metals such as iron, nickel, cobalt, alloys thereof, alloys containing rare earths, hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium Examples thereof include soft ferrites such as ferrite and lithium ferrite, iron-based oxides such as copper-zinc ferrite, and mixtures thereof.

  Examples of the binder resin include vinyl resins, polyester resins, epoxy resins, phenol resins, urea resins, polyurethane resins, polyimide resins, cellulose resins, polyether resins, and mixtures thereof. Magnetic particles are produced by a known method such as a sintering method or an atomizing method. The carrier may have a coating layer made of a coating resin on its surface.

  In the color printer 100 of the present embodiment, when the toner arrives at the place of use (when the image forming apparatus is set up), the toner mother particles remain on the developing roller 29 in the developing devices 3a to 3d as much as possible, and the outside of the silica or the like. A process in which the additive is preferentially moved to the photosensitive drums 1a to 1d to adhere to the edge portion of the cleaning blade 31 (hereinafter referred to as an external additive attaching process), and the toner remaining on the developing roller 29 is removed from the photoreceptor. The toner discharge process for moving the drums 1a to 1d to the drums 1a to 1d can be executed sequentially.

  As a method for preferentially moving the external additive toward the photosensitive drums 1a to 1d, a method in which the chargeability of the toner base particles and the external additive is opposite in polarity can be mentioned. When a charging bias and a developing bias are applied under the same conditions as in image formation, the photosensitive drums 1a to 1d are charged with the same polarity as the toner base particles (opposite polarity with respect to the external additive). It can be selectively moved to the 1a-1d side.

  In addition, when an external additive having the same polarity as the toner base particles is used, an external additive having a smaller chargeability (charge amount per unit weight) than that of the toner base particles is used. A bias smaller than the bias is applied to the developing roller 29. This preferentially moves the external additive to the photosensitive drums 1a to 1d charged with the same polarity as the toner base particles and the external additive under the same conditions as the image formation, without moving the toner base particles as much as possible. Can be made.

  The chargeability of the toner base particles can be adjusted by the type and amount of charge control agent (CCA). That is, when positive toner base particles are used, positively charged CCA may be used, and when negative toner base particles are used, negatively charged CCA may be used. In addition, the magnitude of the chargeability may be adjusted by increasing or decreasing the amount of CCA added.

  When an external additive having a reverse polarity to the toner base particles is used, a bias having a reverse polarity (same polarity as the external additive) is applied to the developing roller 29 to sensitize the external additive. It can also be moved to the body drums 1a to 1d.

  In this specification, “chargeability is reverse polarity” means that the charge characteristics are different in electrical polarity like positive charge and negative charge, and “chargeability is the same polarity” means that the charge characteristics are It means that the electric polarities are the same as between positively charged or negatively charged.

  FIG. 6 is a schematic view schematically showing a state in which the image forming portion Pa is in the external additive attaching step. Here, the case where the positively charged toner base particles T and the external additive G made of negatively charged silica are used is described. Actually, the external additive G adheres to the surface of the toner base particles T. However, for convenience of explanation, the toner base particles T are indicated by black circles and the external additive G is indicated by white circles. Further, the image forming portion Pa only shows the photosensitive drum 1a, the primary transfer roller 6a, the intermediate transfer belt 8, the developing roller 29, and the cleaning blade 31, and the same applies to the other image forming portions Pb to Pd. Since there is, explanation is omitted.

  FIG. 6A shows a state in which the external additive G is supplied from the developing roller 29 onto the photosensitive drum 1a. In this step, the surface potential (positive potential) of the photosensitive drum 1 a is higher than that of the developing roller 29 by applying a charging bias to the photosensitive drum 1 a and applying the developing bias to the developing roller 29 as in the image formation. Become higher. As a result, the negatively charged external additive G is selectively moved (flyed) to the surface of the photosensitive drum 1a with the positively charged toner mother particles T remaining on the developing roller 29.

  FIG. 6B shows a state in which the external additive G supplied to the surface of the photosensitive drum 1 a has reached the cleaning blade 31. In this step, the external additive G is adhered to the edge portion of the cleaning blade 31 to form a layer of the external additive G. During the supply of the external additive G to the cleaning blade 31, the primary transfer roller 6a is biased to the same polarity (negative) as the external additive G so that the external additive G does not adhere to the intermediate transfer belt 8. Is applied.

  FIG. 6C shows a state where the supply of the external additive G is stopped by turning off the bias application to the developing roller 29. Even after the supply of the external additive G from the developing roller 29 is stopped, the photosensitive drum 1a continues to rotate for a while.

  By performing the external additive attaching step shown in FIG. 6 for a preset time, the external additive can be selectively supplied to the surfaces of the photosensitive drums 1a to 1d. The external additive wraps around the back side, and a layer of the external additive is formed over the entire edge portion. By this external additive layer, the adhesion between the surfaces of the photosensitive drums 1a to 1d and the edge portion of the cleaning blade 31 is improved, and the frictional force is reduced.

  As a result, the uneven cleaning of the surfaces of the photosensitive drums 1a to 1d immediately after the setup of the image forming apparatus is eliminated, and the generation of streak images can be suppressed. Further, since the frictional resistance with the surfaces of the photosensitive drums 1a to 1d is reduced, the driving torque of the photosensitive drums 1a to 1d is increased, the vibration sound of the cleaning blade 31 is turned up (rolled up), and the photosensitive drums 1a to 1d. Problems such as jitter due to 1d vibration are also effectively suppressed. The execution time of the external additive attaching step is appropriately set according to the configuration of the photosensitive layer to be used, the material of the cleaning blade 31, and the like.

  The DC component (Vslv (DC)) of the developing bias applied to the developing roller 29 is set to be smaller than Vslv (DC) applied at the time of image formation, so that the photosensitive drums 1a to 1d and the developing roller 29 The potential difference can be increased. As a result, an external additive having a polarity opposite to that of the toner mother particles, or the same polarity as the toner mother particles and having a small chargeability, can more easily fly to the surface of the photosensitive drums 1a to 1d. Since it is difficult to fly to the surfaces 1a to 1d, only the external additive can be efficiently moved to the photosensitive drums 1a to 1d.

  Furthermore, the peak-to-peak value of the AC component (Vslv (AC)) of the developing bias applied to the developing roller 29 is preferably set larger than Vslv (AC) applied during image formation. Thereby, the electric field strength on the surface of the developing roller 29 is increased, and not only the external additive released from the toner base particles but also the external additive attached to the surface of the toner base particles can be peeled off. Therefore, it is possible to fly the external additive to the photosensitive drums 1a to 1d more efficiently.

  When Vslv (DC) applied to the developing roller 29 is set to be smaller than Vslv (DC) applied at the time of image formation, the direct current component (Vmag (DC)) of the bias applied to the magnetic roller 27 is used for image formation. It is preferable to set it to the same voltage as Vmag (DC) sometimes applied. Normally, toner is supplied from the magnetic roller 27 to the developing roller 29 by applying Vmag (DC) higher than Vslv (DC) to the magnetic roller 27, but Vmag (DC) is applied in the external additive attaching step. By reducing only Vslv (DC) without changing from the potential at the time of image formation, the potential difference between the magnetic roller 27 and the developing roller 29 increases. Accordingly, a large amount of toner can be supplied to the developing roller 29, and the amount of the external additive that is allowed to fly toward the photosensitive drums 1a to 1d can be increased.

  By the way, since the toner is normally in contact with the developing roller 29 and the carrier via the external additive attached to the surface, the contact area between the toner mother particle and the developing roller 29 or the toner mother particle and the carrier is reduced. It is easy to detach from the developing roller 29 and the carrier. However, when the external additive attaching step is executed, the toner in which the external additive is reduced (the ratio of the toner base particles is high) remains on the developing roller 29.

  When the external additive adhering to the toner surface decreases, the contact area between the toner base particles and the developing roller 29 or the carrier increases, so that the adhesion force of the toner increases and the flying property to the photosensitive drums 1a to 1d increases. descend. Further, since the toner having increased adhesion is held on the developing roller 29 to which the developing bias is applied for a long time, the toner deteriorates due to overcharging (charge-up). When the deteriorated toner is used for image formation, image defects such as a decrease in image density and pitch unevenness occur.

  Therefore, by executing the toner discharge process subsequent to the external additive attaching process, the deteriorated toner whose external additive is reduced is forcibly discharged to the photosensitive drums 1a to 1d and consumed. Thereby, it is possible to prevent image defects such as a decrease in image density and pitch unevenness. In order to completely consume the toner on the developing roller 29, a toner discharge pattern having a printing length that is larger than the outer peripheral area of the developing roller 29, that is, the outer peripheral length of the developing roller 29, is formed on the photosensitive drums 1a to 1d. It ’s fine.

  FIG. 7 is a schematic diagram illustrating a state in which the image forming unit Pa is in the toner discharge process. Here, only the image forming portion Pa will be described in the same manner as in FIG. 6, and the other image forming portions Pb to Pd are completely the same, and the description thereof will be omitted.

  FIG. 7A shows a state in which toner discharge from the developing roller 29 onto the photosensitive drum 1a is started. When a predetermined area of the photosensitive drum 1a is exposed by the exposure device 4 (see FIG. 1), toner (toner base particles T and external additive G) is selected in the exposed area of the photosensitive drum 1a having a reduced surface potential. Move (fly).

  FIG. 7B shows a state in which the toner discharged on the surface of the photosensitive drum 1 a has reached the cleaning blade 31. In this step, the toner on the surface of the photosensitive drum 1 a is removed by the cleaning blade 31. While the toner is discharged onto the surface of the photosensitive drum 1a, a bias voltage having the same polarity (positive) as that of the toner is applied to the primary transfer roller 6a so that the toner does not adhere to the intermediate transfer belt 8.

  FIG. 7C shows a state in which the bias application to the developing roller 29 is turned off and the toner discharge is stopped. Even after the toner discharge from the developing roller 29 is stopped, the photosensitive drum 1a continues to rotate for a while until the toner on the photosensitive drum 1a is completely recovered.

  FIG. 8 is a schematic configuration diagram illustrating the overall configuration of the image forming apparatus according to the second embodiment of the present invention, and the right side is illustrated as the front side of the image forming apparatus. Portions common to those in FIG. 1 are denoted by the same reference numerals. As shown in FIG. 8, a sheet cassette 16 that accommodates the stacked transfer sheets is disposed at the bottom of the main body of the monochrome printer 101. Above the paper cassette 16, a paper conveyance path is formed that extends substantially horizontally from the front of the main body to the rear of the main body and further extends upward to the discharge tray 17 formed on the upper surface of the main body. A paper feed roller 12a, a registration roller pair 12b, an image forming unit P, a fixing unit 7 and a discharge roller pair 15 are arranged in this order from the upstream side.

  The image forming unit P includes a photosensitive drum 1 pivotally supported in a clockwise direction in FIG. 8, a scorotron charger 2, a developing device 3, and a cleaning device disposed around the photosensitive drum 1. 5 is composed of a transfer roller 6 disposed so as to face the photosensitive drum 1 across the paper conveyance path and an exposure device 4 disposed above the photosensitive drum 1. A toner container 30 for supplying toner to the developing device 3 is disposed.

  By applying a predetermined voltage to the charger 2, the surface of the photosensitive drum 1 is uniformly charged. Next, an electrostatic latent image based on the image data input on the photosensitive drum 1 is formed by light irradiation from the exposure device 4, and toner is attached to the electrostatic latent image by the developing device 3, so that the photosensitive drum 1. A toner image is formed on the surface. Then, the transfer paper is supplied from the registration roller pair 12b to the nip portion (transfer position) between the photosensitive drum 1 and the transfer roller 6 at a predetermined timing, and the toner image on the surface of the photosensitive drum 1 is transferred onto the transfer paper by the transfer roller 6. Is transcribed.

  The transfer paper onto which the toner image has been transferred is separated from the photosensitive drum 1 and conveyed toward the fixing unit 7. The transfer paper on which the toner image is transferred in the image forming unit P is heated and pressed by a fixing roller pair 13a including a heating roller provided in the fixing unit 7 and a pressure roller pressed against the heating roller, and is applied to the transfer paper. The transferred toner image is fixed.

  The transfer paper on which the image is formed in the image forming unit P and the fixing unit 7 is discharged to the discharge tray 17 by the discharge roller pair 15. On the other hand, the toner remaining on the surface of the photosensitive drum 1 after the transfer is removed by the cleaning device 5. The photosensitive drum 1 is charged again by the charger 2, and image formation is performed in the same manner. The control path of the monochrome printer 101 is basically the same as the control path of the color printer 100 shown in FIG.

  FIG. 9 is a side sectional view showing an example of a developing device mounted on the image forming apparatus of the second embodiment. Portions common to FIG. 2 of the first embodiment are denoted by the same reference numerals. As shown in FIG. 9, the developing device 3 includes a first agitating screw 25 a, a second agitating screw 25 b, a developing roller 29, and a regulating blade 34 in a developing container 33 that stores a two-component developer. .

  The inside of the developing container 33 is partitioned into a first stirring chamber 33b and a second stirring chamber 33c by a partition wall 33a extending in the longitudinal direction (the front and back direction in FIG. 9). The first stirring screw 25a is disposed in the second stirring chamber 33c, and the second stirring screw 25b is disposed in the second stirring chamber 33c. Further, the partition wall 33a is not provided at both ends in the longitudinal direction of the developing container 33, and this portion is a passage (developer delivery portion) through which the toner moves between the first stirring chamber 33b and the second stirring chamber 33c. It has become.

  The developing roller 29 includes a metal developing sleeve 29a and a magnet member 29b having a plurality of magnetic poles (three poles here) fixed inside the developing sleeve 29a. It is rotatably supported in the first stirring chamber 33b so as to be substantially parallel to the stirring screw 25b. A developing bias power supply 43 (see FIG. 5) for applying Vslv (DC) and Vslv (AC) is connected to the developing roller 29 via a bias control circuit 41 (see FIG. 5).

  When the developing sleeve 29a rotates in accordance with the rotation of the photosensitive drum 1, a magnetic brush in which carrier particles and toner are connected is formed on the surface of the developing sleeve 29a by the magnetic force of the magnet member 29b. The magnetic brush formed on the developing sleeve 29 a contacts the surface of the photosensitive drum 1 at the developing nip where the developing roller 29 and the photosensitive drum 1 face each other, and the surface potential of the photosensitive drum 1 and the developing roller 29 are contacted. Only the toner particles move to the photosensitive drum 1 due to the potential difference from the developing bias applied to the photosensitive drum 1 and adhere to the photosensitive layer, and a toner image is formed on the surface of the photosensitive drum 1.

  The regulating blade 34 regulates the amount of toner supplied to the photosensitive drum 1, that is, the amount of toner attached to the developing roller 29. For example, a magnetic material such as SUS (stainless steel) is used. The regulating blade 34 is disposed so that a predetermined gap (0.2 to 0.3 mm) is formed between the tip of the regulating blade 34 and the developing roller 29. The amount of toner adhering to the developing roller 29 is regulated by the magnetic field generated in the gap and the gap, and a thin toner layer of several tens of microns is formed on the surface of the developing roller 29. Since the configuration of other parts is the same as that of the first embodiment, description thereof is omitted.

  Also in the present embodiment, as in the first embodiment, by controlling the polarity (chargeability) of the external additive and toner base particles and the bias applied to the developing roller 29, the external additive is set up during the monochrome printer 101 setup. The adhesion process and the toner discharge process can be executed sequentially. As a result, the cleaning performance of the surface of the photosensitive drum 1 immediately after the setup of the monochrome printer 101 can be improved. In addition, problems such as an increase in driving torque of the photosensitive drum 1, vibration noise and turning (rolling up) of the cleaning blade 31, and jitter due to vibration of the photosensitive drum 1 are also effectively suppressed.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the second embodiment, an example using a two-component developer has been described. However, a one-component developer made of only magnetic toner can be used in the developing device of the second embodiment shown in FIG. In this case, a toner layer is formed by adhering (carrying) magnetic toner on the developing sleeve 29a, and the photosensitive member is caused by the potential difference between the surface potential of the photosensitive drum 1 and the developing bias applied to the developing roller 29 at the developing nip portion. The electrostatic latent image is developed by flying on the surface of the drum 1. When the external additive attaching step is executed, the external additive is preferentially moved to the surface of the photosensitive drum 1 by applying a bias according to the polarities of the external additive and toner base particles to the developing roller 29.

  The present invention is not limited to the tandem type color printer shown in FIG. 1 or the monochrome printer as shown in FIG. 8, but a digital or analog type monochrome copying machine, a rotary developing type color printer and color copying machine, or a facsimile. The present invention can be applied to various image forming apparatuses including a developing device that causes toner to fly in a non-contact manner on an image carrier. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

  The two-component developer was put into the developing devices 3a and 3 shown in FIGS. 3 and 9, and mounted on the test machines (unused) of the first and second embodiments as shown in FIGS. When the external additive attaching step and the toner discharging step are sequentially executed (Inventions 1 to 7), when neither the external additive attaching step and the toner discharging step are executed (Comparative Example 1), the external additive When only the adhesion process is executed (Comparative Example 2) and only the toner discharge process is executed (Comparative Example 3), a halftone image with a printing rate of 25% is printed immediately after setup, and a streak image and image density unevenness are printed. The occurrence was visually observed.

  As the photosensitive drum, an OPC drum having a diameter of 30 mm with an OPC (organic photosensitive layer) formed on the outer peripheral surface was used, and the drum peripheral speed was set to 130 mm / second. The charging device was a contact charging method using a charging roller, and the charging bias was 1300V. The diameter of the developing roller was 16 mm, the rotational speed was 250 rpm, the diameter of the magnetic roller was 16 mm, the rotational speed was 280 rpm, and the distance between the drum and the developing roller (DS distance) was 110 μm.

  In addition, voltage application conditions to the developing roller during normal printing were Vslv (DC) = 150 V, Vslv (AC) Vpp of 1400 V, frequency of 3.6 kHz, and Duty = 30%. Further, Vmag (DC) = 450 V, Vmag (AC) Vpp of 650 V, frequency of 3.6 kHz, and Duty = 70% were applied to the magnetic roller in reverse phase. Further, a two-component developer composed of a positively charged toner having an average particle diameter of 6.8 μm and a coated ferrite carrier having an average particle diameter of 35 μm was used, and the mixing ratio (T / C) of the toner to the carrier was set to 10% by weight.

  The test results are shown in Tables 1 and 2 together with the bias application conditions and execution time in each step. As for the development methods in Tables 1 and 2, the method using only the development roller as shown in FIG. 9 is “two components”, and the method using the magnetic roller and the development roller as shown in FIG. 3 is “TD”. (Touch-down method) In addition, the voltage application conditions to the developing roller and the magnetic roller in the toner discharge process were the same as in normal printing.

  The evaluation of the streak image is ◎ when there are no streaks on the image or on the drum surface, ○ when there are no streaks on the image and there are less than 10 streaks on the drum surface, there are no streaks on the image, The case where there were 10 or more streaks on the drum surface was indicated by Δ, and the case where there was a streak on the image was indicated by ×, and Δ was judged to have no practical problem since no streak was observed on the image. In the evaluation of the image density unevenness, the case where there is no density unevenness in the image is indicated by ◯, and the case where there is density unevenness is indicated by x.

  As is clear from Table 1, in the present invention 1 to 5 in which both the external additive attaching step and the toner discharging step are performed in the two-component developing type developing device 3 shown in FIG. The external additive layer formed on the surface reduces the frictional resistance between the photosensitive drum and the cleaning blade and improves the cleaning performance, so that the generation of streak images can be effectively suppressed. Further, since the external additives are reduced and the charged up deteriorated toner is forcibly consumed, it is possible to prevent the occurrence of density unevenness in the halftone image.

  In particular, in the present inventions 4 and 5 in which the Vsl (DC) applied to the developing roller during the execution of the external additive attaching step is set to 50 V, which is lower than that during normal printing, the book set to 150 V, which is the same as during normal printing. In comparison with the first to third aspects, the generation of streak images is suppressed, and the Vpp of Vsl (AC) applied to the developing roller during execution of the external additive attaching step is set to 1450 V, which is larger than that during normal printing (1400 V). In the fifth aspect of the present invention, no streaking was observed on the image or the drum surface.

  Further, in the present inventions 6 and 7 in which both the external additive attaching step and the toner discharging step are executed in the touch-down developing type developing device 3 shown in FIG. Vsl (DC) applied to the developing roller can be set to 50 V, which is lower than that during normal printing, or Vpp of Vsl (AC) applied to the developing roller can be set lower than that during normal printing. It was confirmed that the generation of streaks is further suppressed by setting the voltage to 1450 V which is large.

  On the other hand, as is clear from Table 2, in Comparative Example 1 in which both the external additive attaching step and the toner discharging step were not executed, the external additive layer was not formed on the edge portion of the cleaning blade, so printing Occasionally, the toner remaining on the surface of the photosensitive drum could not be uniformly cleaned, and streaks were generated in the image. Further, in Comparative Example 2 in which only the external additive attaching step was executed and the toner discharging step was not executed, the deteriorated toner remaining on the developing roller by the execution of the external additive attaching step was used for development, and the halftone image Density unevenness occurred.

  Further, in Comparative Example 3 in which only the toner discharge process is executed, the toner discharged onto the surface of the photosensitive drum is supplied to the edge portion of the cleaning blade at a time, and therefore, the adhesion of the external additive to the edge portion varies. . As a result, the external additive layer was not uniformly formed on the edge portion of the cleaning blade, and streaks were generated in the image as in Comparative Example 1.

  From the above results, according to the present invention, by performing both the external additive attaching step and the toner discharging step at the time of setting up the image forming apparatus, it is possible to effectively generate streak images and image density unevenness immediately after the image forming apparatus is set up. It was confirmed that it can be suppressed. Although the two-component developing method and the touch-down method using the two-component developer have been described here, the same effect is confirmed even when the one-component developer is used in the developing device shown in FIG. .

  The present invention can be used for an image forming apparatus in which a developing device including a toner carrier that is disposed in a non-contact manner and opposed to an image carrier is mounted. By utilizing the present invention, it is possible to effectively suppress the generation of streak images due to the turning and vibration noise of the cleaning blade immediately after the setup of the image forming apparatus and the cleaning failure, and the toner with little external additive remaining on the toner carrier. It is possible to provide an image forming apparatus that can be forcibly consumed to suppress occurrence of uneven image density.

1, 1a to 1d Photosensitive drum (image carrier)
2, 2a to 2d charger (charging means)
3, 3a to 3d Developing device 5, 5a to 5d Cleaning device 7 Fixing unit 27 Magnetic roller (developer carrier)
29 Development roller (toner carrier)
31 Cleaning blade 41 Bias control circuit (voltage application means)
42 Development bias power supply (voltage application means)
90 control unit 100 color printer 101 monochrome printer P, Pa to Pd image forming unit T toner base particle G external additive

Claims (4)

An image carrier having a photosensitive layer formed on the surface;
Charging means for uniformly charging the surface of the image carrier;
Exposure means for exposing the surface of the image carrier charged by the charging means to form an electrostatic latent image;
A developing device having a toner carrier that is disposed in contact with the image carrier in a non-contact manner and carries toner including toner base particles and an external additive;
A cleaning blade pressed against the surface of the image carrier at a predetermined pressure;
Voltage application means for applying a bias comprising a direct current component and an alternating current component to the toner carrier to attach toner to the electrostatic latent image on the image carrier;
In an image forming apparatus comprising:
When setting up the image forming apparatus, the charging unit is used to uniformly charge the surface of the image carrier, and the voltage applying unit is used to bias the external additive on the image carrier. By applying to the toner carrier, an external additive is attached to the edge portion of the cleaning blade, and then the image carrier is pre-rotated for a predetermined time in a state where the application of bias to the toner carrier is stopped. In the toner discharge step, an external additive attaching step and a toner discharge step forcibly discharging the toner remaining on the toner carrier to the image carrier side following the external additive attachment step are performed . An image forming apparatus, wherein a discharge length of the toner discharge pattern in the circumferential direction of the image carrier is equal to or greater than an outer circumference of the toner carrier .   2. The image forming apparatus according to claim 1, wherein a DC component of a bias applied to the toner carrier during execution of the external additive attaching step is made smaller than a DC component of a bias applied during image formation.   The peak-to-peak value of the alternating current component of the bias applied to the toner carrier during execution of the external additive attaching step is made larger than the peak-to-peak value of the alternating current component of the bias applied during image formation. The image forming apparatus according to claim 2. The developing device includes a developer carrier that is disposed opposite to the toner carrier and supplies toner to the toner carrier using a magnetic brush formed on a surface thereof, and the voltage application unit includes the developer carrier. A bias consisting of a DC component and an AC component can be applied to the body,
4. The bias DC component applied to the developer carrying member during the external additive attaching step is set to the same voltage as the bias DC component applied during image formation. The image forming apparatus described.

Images