JP2008129339A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem, of remarkably low productivity because of long control time required for a replacing mode in a cleaner-less image forming apparatus performing the replacing mode in which unnecessary toner in a developing means is discharged and replaced while an image is not being formed. <P>SOLUTION: When performing the replacing mode, toner left after transfer that is the discharged toner is highly electrified by an electrifying means, so that it is hardly collected by the developing means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus (hereinafter simply referred to as “image forming apparatus”) such as a copying machine, a facsimile machine, a printer, and a multifunction machine as a multi-function copying machine. In particular, the present invention relates to an image forming apparatus that discharges and removes unnecessary toner on an image carrier from a charging device, a developing device or the like provided in the image forming apparatus.

  In recent years, in order to reduce the size of image forming apparatuses, the image forming apparatus adopts a cleaner-less system that eliminates the cleaner of the image carrier, collects the transfer residual toner remaining on the image carrier by the developing means, and reuses it. There is a device.

  According to this method, since the transfer residual toner is collected by the developing means and used after the next step, waste toner can be eliminated, and troublesome maintenance can be reduced. Further, the cleaner-less has a great advantage in terms of space, and has an advantage that the image forming apparatus can be greatly reduced in size (for example, see Patent Document 1).

  In addition, in this cleanerless, in order to efficiently collect the residual toner by the developing unit, a charging brush, a fur brush, or the like as a charging auxiliary unit is provided downstream of the transfer unit and upstream of the charging unit in addition to the charging unit. There is a configuration in which it is arranged at a position and charged in an auxiliary manner. With this charging assisting means, an appropriate charge is imparted when the transfer residual toner passes through the charging assisting means, thereby improving the recoverability of the developing means.

  However, for example, when image formation with a low image ratio is continuously performed, or when the time until image formation is performed next (left time) is long, the toner in the developing unit may deteriorate. . If an image is formed with such deteriorated toner, it has been an obstacle to maintaining high image quality. To deal with such problems, the conventional method has performed toner replacement control such as periodically replacing the toner in the developing means.

  On the other hand, in the cleanerless system, when toner accumulates on the auxiliary charging brush as charging means, discharge control for discharging unnecessary toner is used.

The above control is performed at the time of non-image formation, and most of the toner discharged from the auxiliary charging brush is deteriorated toner, or in the case of a color image forming apparatus, it is retransfer toner of the previous color. The toner was not collected in the developing device. Conventionally, as a method not to collect, a method of stopping the rotation of the sleeve of the developing device and reducing the electric field formed by the photosensitive drum surface potential and the developing sleeve potential has been taken.
JP 2001-092330 A

  However, in the conventional configuration in which the developing bias is turned ON / OFF so that unnecessary toner is not collected by the developing device at the time of control for discharging unnecessary toner from the developing means and the auxiliary charging brush (charging means), a high voltage is started. Extra downtime is required.

  For this reason, the control time required for the discharge mode becomes longer, and the productivity is significantly reduced.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to suppress collection of unnecessary toner discharged by a developing unit in an image forming apparatus capable of discharging unnecessary toner from a developing unit, a charging unit, and the like, and to remove unnecessary toner in a short time. An object of the present invention is to provide an image forming apparatus that can be removed efficiently.

  In order to achieve the above object, a typical configuration of the image forming apparatus according to the present invention is such that the residual toner that has not been transferred by the transfer unit comes into contact with the charging unit before charging, and auxiliary charging is applied with voltage. An image forming apparatus having a discharging step of discharging toner from the auxiliary charging unit or the developing unit onto the image carrier at the time of non-image formation, and charging the toner discharged in the discharging step The recovery rate by the developing unit is lowered by charging the image forming unit or the auxiliary charging unit so that the charge amount is higher than that at the time of image formation, and the transfer unit can be removed from the image carrier. It is characterized by.

  In an image forming apparatus capable of discharging unnecessary toner from developing means, auxiliary charging means, etc., image formation capable of efficiently removing unnecessary toner in a short time by suppressing the discharged unnecessary toner from being collected by the developing means Equipment can be provided.

  Embodiments of the present invention will be described below.

  The embodiment described below is an example of a color image forming apparatus using a cleaner-less system of a simultaneous development cleaning system, using a charging roller as a contact charging unit, and a fixed charging brush as a charging auxiliary unit.

(1) Image Forming Apparatus FIG. 1 is a schematic diagram of an image forming apparatus according to the present embodiment.

  In FIG. 1, photoconductors 11a to 11d, which are image carriers, are rotatably arranged in the direction of the arrow. Around the photoconductor 11, along the rotation direction, there are charging rollers 12a to 12 as developing means, developing devices 13a to 13d, and primary transfer means 14a to 14d. Further, charging auxiliary means 15a to 15d are provided as charging means for charging the transfer residual toner after transfer. Further, the image forming apparatus includes an intermediate transfer belt 16 and a secondary transfer unit 17 as transfer units, and a toner image formed on the photoconductor 11 is transferred to a recording material by the secondary transfer unit 17 via the intermediate transfer belt 16.

  Further, a paper separating unit 18 and an intermediate transfer belt cleaning unit 19 as a cleaning unit are arranged. In this embodiment, the primary transfer unit 14, the intermediate transfer belt 16, and the secondary transfer unit 17 are collectively used as a transfer unit that transfers the toner image on the image carrier to a recording material. A paper feeding device 20 that feeds the recording medium P toward the secondary transfer unit 17 is disposed below the image forming apparatus, and is further downstream in the conveyance direction of the recording medium P separated by the separation device 18. A fixing device 21 and a paper discharge tray 22 are arranged.

  A laser exposure device 23 serving as a latent image forming unit is disposed obliquely above the photoconductor 11, and projects a laser beam modulated by image information onto the surface of the photoconductor 11, and electrostatically forms on the photoconductor 11. A latent image is formed.

  Here, the procedure of the image forming mode of this embodiment will be described.

  When the power is turned on, the photoconductor 11 and the charging unit 12 start to rotate at a predetermined rotation speed by a main motor (not shown). When the execution of the image forming operation is instructed, a DC voltage superimposed with an alternating voltage is applied to the charging roller 12 from a high voltage power source (not shown), and the surface of the photoconductor 11 is charged to a predetermined potential. The photosensitive drum 11 is formed by applying an organic photoreceptor (OPC), a photoconductor made of A-Si, CdS, Se, or the like to the outer peripheral surface of an aluminum cylinder.

  As the material constituting the charging means 12, ion conductive or electronic conductive materials such as EPDM and NBR, rayon, nylon and fluorine materials are used. The shape may be that of a brush roller or a charging roller, and a resistance value (initial resistance at normal temperature and humidity) of 1.0e + 5 to 1.0e + 7Ω is used.

  A laser beam modulated by image information is projected from the laser exposure device 23 onto the surface of the photoconductor 11, and an image latent image is formed on the surface of the photoconductor 11. When the formed image latent image comes to the position of the developing device 13 by the rotation of the photosensitive member 11, it contacts the developing roller of the developing device 13 and is developed with toner to be visualized, and the toner is formed on the photosensitive member 11. An image is formed. The charge amount of toner in each developing device is −25 to 35 μC / mg. Further, the content of 20 nm oil-treated silica is set to 30% or less so as not to increase the fluidity of the toner.

The toner image developed on the photosensitive member 11 is transferred onto the intermediate transfer member 16 by applying a bias having a polarity opposite to that of the toner to the primary transfer unit 14. The material of the intermediate transfer belt 16 is made of PI (polyimide resin), has a thickness of 5 μm, a surface resistance efficiency of 11 to 13 Ω / cm ² , and a volume low efficiency of 9 to 10 Ω · cm. The material may be PVDF, PET, PBT, EPDM, NBR, urethane rubber, silicone rubber, or the like. The intermediate transfer belt 16 is stretched by three rollers, a driving roller, a tension roller, and a secondary transfer counter roller, and is driven to rotate by a driving roller that is rotated by a motor.

  As described above, toner images similarly formed on the photoconductors 11 a to 11 d are sequentially transferred onto the intermediate transfer body 16, and then transferred onto the transfer paper P at once by the secondary transfer unit 17.

  On the other hand, the recording paper P is fed from the paper feeding device 20 at a timing when the toner image formed on the intermediate transfer member 16 comes to the position of the secondary transfer means 17, and the toner image on the intermediate transfer member 16 is recorded on the recording paper. Transferred to P. The recording paper P to which the toner image has been transferred is separated from the intermediate transfer body 16 by the separating device 18 and further conveyed to the fixing device 21, where the toner image on the recording paper P is subjected to a fixing process and placed on the paper discharge tray 22. Discharged. In the transfer process to the recording medium P, the toner remaining on the intermediate transfer body 16 without being transferred to the recording medium P is collected by the intermediate transfer belt cleaning means 19 by the rotation of the intermediate transfer body 16.

(2) Cleanerless system (normal image formation mode)
Next, the cleanerless system of the present embodiment will be described.

  In the transfer process performed by the primary transfer unit 14, the toner remaining without being transferred to the intermediate transfer member passes through the contact portion between the photoreceptor 11 and the charging auxiliary unit 15, and the toner is transferred to the charging auxiliary unit 15. A bias having the same polarity as the charging polarity is applied, and the same polarity as the toner is processed.

  The charging auxiliary means will be described in detail.

  As the fibers constituting the auxiliary charging means 15, for example, conductive rayon fibers with a stationary brush are used, and the fiber thickness is 6 denier, the pile length is 5 mm, and the fiber density is 100 KF. In addition, nylon fiber or polyester fiber may be used. The fiber thickness is preferably 2 to 10 denier, the pile length is 3 to 8 mm, and the fiber density is in the range of 50 to 500 KF. The shape may be a brush roller or a charging roller.

  The bias applied to the auxiliary charging means 15 is a DC voltage having the same polarity as that of the normal toner.

  The processing method of the auxiliary charging means 15 will be described in detail.

  Most of the toner that remains on the photoconductor 11 without being transferred often has almost no normal toner normal polarity (negatively charged here), and the reverse toner component (here positively charged polarity) is dominant. It is in a state. Therefore, in this embodiment, as a normal mode, the toner image is transferred to the intermediate transfer member by the primary transfer unit and then transferred to the reversal toner in order to efficiently collect the transfer residual toner remaining on the photosensitive member without being transferred. On the other hand, a negative charge having the same polarity as that of the regular toner is applied. That is, when the reversal toner passes through the contact portion between the photosensitive member 11 and the auxiliary charging means 15, a bias having the same polarity as that of the normal toner is applied to the auxiliary charging means to generate a discharge exceeding a certain level. In this way, negative charge having the same polarity as that of the regular toner is applied to the reversal toner. Actually, −900 V is applied to the charging auxiliary means 15, and charge is imparted to the reversal toner as shown in FIG. 4, and the charge amount is about −112 μC / mg. However, when the toner charge is -112 μC / mg, the recovery efficiency of the developing means 13 is very poor as shown in FIG. However, in actuality, when passing through the charging unit 12, DC-700 V and AC 1800 Vpp are biased to the charging unit 12 so that the toner charge is controlled to be −50 μC / mg (not shown). At this time, DC-550 V and AC 1500 Vpp are biased to the developing means 12, and the distance D between the photosensitive drum 11 and the developing means 13 is 400 μm.

  As a result of the above processing, as shown in FIGS. 5 and 6, the relationship of “mirror force <force of the toner receives from the electric field from the developing means (development recovery force)” is established, and most of the transfer on the photoreceptor is performed. The remaining toner is collected by the developing device by the developing bias. That is, as shown in FIG. 7, the result of high development recovery efficiency is obtained. FIG. 7 shows the collection efficiency of the developing unit when the toner charge reaching the developing unit 13 is changed by the setting of the charging unit 12 and the auxiliary charging unit 15. In this embodiment, when the development recovery efficiency is as high as 100%, the relationship of “mirror power <development recovery power” is established. On the contrary, when the development recovery efficiency is as low as 40%, the relationship of “mirror power> development recovery power” is established.

  As described above, a cleaning system that cleans the surface of the photoconductor is established by collecting the transfer residual toner remaining on the photoconductor 11 in the developing unit 13 (or collecting it in the charging auxiliary unit 14 as described later). .

(3) Toner Replacement Mode of Developing Device Next, a toner replacement mode (toner removal mode) for replacing deteriorated toner in the developing device, which is the gist of the present invention, will be described.

  For example, when image formation with a low image ratio is continuously performed, the toner in the development assisting unit 13 is not often deteriorated because the toner is hardly replaced.

  Of the toner images formed on the photoreceptor, the deteriorated toner is deformed or the coating of the toner external additive is different from the usual, so the transfer efficiency is low and the high image quality is stably maintained. It was difficult.

  Therefore, in this embodiment, when the image formation of a certain image ratio or less is continuously performed, the toner replacement control in the developing device is performed as described below to solve the above problem. In this embodiment, the control timing is performed at a predetermined timing during non-image formation, such as post-rotation after image formation, a sheet interval during image formation, or a pre-rotation at the next image formation.

  FIG. 2 shows a sequence of toner replacement control in this embodiment.

  FIG. 3 shows an image diagram at the time of control.

  First, in order to replace the deteriorated toner in the developing device during non-image formation, a pulsed electrostatic latent image is formed by the exposure means as shown in FIG. When the electrostatic latent image for toner replacement reaches the developing portion, the toner is developed on the photosensitive drum 11 by the developing means 13. The developed toner is transferred to the intermediate transfer member 16 by the transfer unit 14 and collected by the cleaning unit 19 for the intermediate transfer member. Further, the transfer residual toner remaining on the photosensitive drum 11 by the transfer unit 14 has a charge center in the vicinity of zero. In this embodiment, the exposure unit and the development unit function as a transfer unit that transfers unnecessary toner in the development unit onto the drum.

  Therefore, in this embodiment, the charging condition of the auxiliary charging brush 15 is different from the charging condition at the time of normal image formation so that the transfer residual toner is not collected by the developing device. Specifically, charging is performed by the charging unit so that the toner charge amount of the transfer residual toner is larger than that during normal image formation so that the transfer residual toner is not collected when passing through the developing device. Then, the transfer residual toner that has passed through the developing means is transferred to the intermediate transfer member at the transfer portion of the transfer means, and is collected by the cleaning means 19 of the intermediate transfer member. In this embodiment, since the transfer bias electric field is set to be larger than the developing bias electric field, the force received from the electric field from the transfer means overcomes the reflection force and is removed from the drum.

  That is, when the transfer residual toner passes through the auxiliary charging brush 15, a DC-1000 V bias is applied to the auxiliary charging brush 15, and charge control is performed so that the toner charge after the auxiliary charging brush becomes −120 (μC / mg). Is done. That is, an electric charge is applied so that the untransferred toner increases the mirror power with the photosensitive drum 11. The photosensitive drum 11 is simultaneously charged to −400 V by the auxiliary charging brush 15. Next, the charged transfer residual toner passes through the charging unit 12. At this time, DC-400V and AC0Vpp are applied as the bias applied to the charging unit 12 unlike the normal image forming mode. As a result, the charge of the transfer residual toner reaches the contact portion between the photosensitive drum 11 and the developing means 13 at −120 μC / mg without changing before and after passing through the charging means 12, so that “mirror power> development recovery power”. Since the above relationship is established, recovery to development is minimized. At this time, the developing means 12 is biased with DC-250V and AC1500Vpp.

  In the toner charge measuring method described above, an image is formed on the photosensitive drum 11 in the normal mode, and the main body power supply is stopped immediately after the toner image is formed on the photosensitive drum 11 from the developing means 13. Thereafter, 0.0140 g of toner on the photosensitive drum 11 is sampled and measured with a Q meter. The Q meter used this time is 617 PROGRAMMABLE-ELECTROMETER made by Toyo Technica.

  Here, the force acting on the toner on the photosensitive member in the developing nip formed between the developing unit and the photosensitive drum 11 will be described in detail. FIGS. 5 and 6 show image views acting on the toner on the photosensitive drum 11.

  First, the van der Waals force and the liquid bridging force, which are the mechanical adhesion force of the toner on the photosensitive member 11 to the surface of the photosensitive member 11, are scattered by the magnetic spikes (brushes) of the contact developing means. Almost lose.

Next, the reflection force F _1, which is an electrostatic adhesion force with the surface of the photosensitive member, is proportional to the square of the charge Q of the toner.
F ₁ = A * Q ² * A is a constant And the Coulomb force F _2, which is the electrostatic recovery force of the toner on the photoconductor 11 by the developing means 13, is
F ₂ = QE
It is represented by Also here
Q: Toner charge after being controlled by the charge control means E: Expressed as the surface potential of the photosensitive member 11 and the electric field strength of the developing means, the surface potential of the photosensitive drum is Vd, the DC voltage applied to the developing means is Vdc, the surface of the photosensitive drum And the distance between the developing means (in this embodiment, the distance between the photosensitive drum and the developing sleeve) is D,
E = | Vd−Vdc | / D
It becomes. Therefore, from the above, F ₁ > F ₂ > 0 (1)
When the above relationship is satisfied, the relationship “mirror power> development recovery force” is established, and the recovery efficiency to the developing means can be suppressed.

  In the configuration of this embodiment, the relationship between “mirror power and development recovery power” is actually obtained through experiments. The result is shown in FIG. From this result, when the charge of the toner is Q / M <−70 μC / mg, a result satisfying Expression (1) is obtained. The reason why the absolute value in the figure does not become 40% or less is that the toner on the drum is scraped off by the carrier on the developing sleeve because the rotating direction of the developing sleeve of the developing means 13 is counter to the photosensitive drum 11. It is.

  By executing the replacement mode (removal mode) according to the above method, the toner replacement control of the developing unit is performed, and recovery of the deteriorated transfer residual toner by the developing unit is prevented, and the intermediate transfer member 16 is efficiently obtained. The toner is transferred and recovered to the intermediate transfer member cleaning means 19. The transfer bias applied to the transfer unit 14 may be set higher than that for normal image formation to increase the transfer efficiency for toner that is not collected by the developing unit.

  The charging conditions of the charging means in the toner discharge mode (removal mode) of this embodiment may be set as follows. For example, the amount of toner per unit area (toner recovery rate) recovered by the developing device in the next step, out of the transfer residual toner after forming a solid image of 100% image density and transferring the solid image by the transfer means taking measurement. Then, the bias applied to the charging unit is adjusted so that the recovery rate is lower in the toner discharge mode than in the normal image formation mode.

  A method for measuring the transfer residual toner recovery rate of this embodiment will be described.

First, the toner recovery rate is defined as follows.
Toner recovery rate = (transfer residual toner amount per unit area after solid image transfer residual toner is recovered (passed) by developing means) / (transfer residual toner amount per unit area after transfer of solid image) ... (Formula 1)
In this embodiment, the toner recovery rate during normal image formation is measured as follows. That is, after forming a solid image with a density of 100% and transferring it by the transfer means, the drum is stopped, the amount of residual toner on the solid image on the drum is measured several times, and the residual transfer per unit area is measured. The average value of the toner amount is measured to obtain the numerator of Formula 1. Similarly, after forming and transferring a solid image, the average value of the toner amount per unit area of the solid image forming region after the zero-density image is superimposed on the region where the solid image was created is measured. And the denominator of Equation 1.

  The toner recovery rate in the toner removal mode is measured as follows.

  That is, after forming a solid image with a density of 100% and transferring it by the transfer means, the drum is stopped, the amount of residual toner on the solid image on the drum is measured several times, and the residual transfer per unit area is measured. The average value of the toner amount is measured to obtain the numerator of Formula 1. Also, during execution of the toner replacement mode (removal mode) from the developing device during non-image formation, after the transfer, the drum is stopped and the amount of residual toner on the solid image on the drum is measured several times. The average value of the residual toner amount per unit area is measured to obtain the numerator of Formula 1.

  Similarly, when the toner replacement mode is executed from the developing device during non-image formation, the amount of toner per unit area remaining on the drum after the toner discharge area passes through the developing means after transfer is transferred. The average value is measured and used as the denominator of Equation 1.

  In the normal image forming mode, the toner recovery rate is 95% to 100% as shown in FIG. 7, and in the discharge mode, the toner recovery rate is preferably 60% or less. More preferably, the toner recovery rate is 40% or less.

  In this embodiment, the collection efficiency is controlled by appropriately adjusting the bias applied to the charging unit 12 and the auxiliary charging unit 15.

  As described above, according to the present exemplary embodiment, an image forming apparatus that achieves stable high image quality and shortens the control time for achieving the high image quality is provided. That is, as in the prior art, in the method of stopping the rotation of the developing sleeve and suppressing the applied bias applied to the developing device so that the transfer residual toner is not collected by the developing device, the control time becomes long as follows. That is, after passing through the area where the transfer residual toner remains, an extra time (because charging high voltage setting change + development sleeve rotation start + high pressure start is sequentially performed so that the photosensitive drum is set to a predetermined potential) is required. On the other hand, in this embodiment, the extra time can be eliminated.

  In the present exemplary embodiment, the case where the toner replacement mode (removal mode) is executed is described as a case where image formation below a certain fixed image ratio is continuously performed. However, the present invention is not limited to this. When the above is performed, the above mode may be executed.

  The schematic diagram of the image forming apparatus of the present embodiment is the same as that of the first embodiment (FIG. 1).

  For example, when the time until the next image formation (leaving time) is long, the toner in the developing unit 13 deteriorates due to the length of the leaving time.

  Therefore, in the present embodiment, the same control as in the first embodiment is performed, so that the toner in the developing unit 13 can be replaced efficiently, maintaining a stable high image quality, and reducing the control time for achieving it. An image forming apparatus is provided.

  The schematic diagram of the image forming apparatus of the present embodiment is the same as that of the first embodiment (FIG. 1).

  For example, when image formation with a high image ratio is continuously performed, a large amount of untransferred toner may temporarily accumulate in the auxiliary charging brush 15. As described above, when the toner accumulated in the auxiliary charging means 15 through a certain amount of durability exceeds a certain amount, the current flowing through the auxiliary charging brush 15 decreases and image contamination occurs. Therefore, the toner discharge control from the auxiliary charging member 15 is controlled. Necessary.

  Conventionally, the method of discharging the toner accumulated in the auxiliary charging means 15 includes an electrostatic discharging method such as a rectangular DC bias on the auxiliary charging member, and a mechanical discharging method using vibration when the photosensitive member 11 is driven. both are fine.

  In the normal image forming mode, a charge assisting member applies a bias having the same polarity as the toner to control the charge of the transfer residual toner. At this time, a small part of the transfer residual toner temporarily accumulates in the auxiliary charging means 15. The accumulated toner charge is a toner whose charge could not be controlled and has a toner charge of almost zero. Since the negative DC bias is applied to the auxiliary charging member 15 during the normal image forming mode, the toner accumulated in the auxiliary charging member 15 is mainly toner having a positive charge. Next, a method for discharging the toner collected in the auxiliary charging means 15 will be described. When the toner accumulated from the auxiliary charging member 15 is discharged, it is sufficient to have a positive potential rather than a photosensitive drum potential.

  Therefore, in this embodiment, DC-1300V and AC0Vpp are applied to the charging means 12 as a transfer means for transferring the toner from the auxiliary charging means 15, and the surface potential on the photosensitive drum 11 is set to -500V. When the position of the photosensitive drum 11 charged by the charging unit 12 reaches the auxiliary charging unit 15, the potential of the auxiliary charging unit 15 is set to zero, so that the toner accumulated in the auxiliary charging unit 15 is electrically photosensitive. It is discharged onto the drum 11.

  Further, the toner discharged from the auxiliary charging unit may not be collected in the developing unit 13 in some cases. This is because there are cases where deteriorated toner or foreign matter is mixed in the toner accumulated in the auxiliary charging brush, or in the case of a color image forming apparatus, the previous color toner is accumulated.

  Therefore, in this embodiment, when control for discharging toner from the auxiliary charging means is executed, a DC bias is applied so that DC discharge occurs between the charging means 12 and the photoconductor 11, and this discharge causes the same as in Embodiments 1 and 2. The toner charge is controlled to increase the mirror power. A certain amount of AC bias may be superimposed. The toner discharge control from the auxiliary charging member can be performed by shortening the control time.

  The toner discharged from the auxiliary charging member 15 is supplied to the charging unit 12.

  Next, when the discharged toner passes through the charging unit 12, DC-1300 V is applied to the charging unit 12, so that the discharged toner is charged to −125 μC / mg. This control timing is performed in the post-rotation after image formation, the interval between sheets during image formation, or the pre-rotation in the next image formation. Further, in order to shorten the control time, the toner discharge control is performed in parallel with other control for forming the toner image on the photosensitive drum 11 from the developing unit 13.

  The toner discharge sequence of this embodiment is shown in FIG.

  FIG. 9 shows an image of toner ejection in this embodiment.

  The charged toner is not recovered to the developing means 13 but is transferred to the intermediate transfer belt 16 by the transfer means 14 and recovered by the cleaning means 19 for the intermediate transfer member due to the relationship between “mirror power and development recovery power”. Is done.

  Here, the bias applied to the transfer means is a bias larger than that during normal image formation, and 600 V is applied in this embodiment.

  As described above, in the present embodiment, toner discharge control from the auxiliary charging brush 15 is performed simultaneously with other control for forming a toner image from the developing unit 13, thereby improving productivity, CRG life, and durability. An image forming apparatus that achieves high image quality is provided.

  That is, conventionally, when the toner discharged from the auxiliary charging brush passes through the developing means 13, a method has been adopted in which the developing electric field formed during normal image formation is weakened and the rotation of the developing sleeve is stopped. According to the conventional method, the toner discharge control from the inside of the developing device cannot be performed by setting the developing sleeve rotation stop and the weak developing electric field while the toner discharged from the auxiliary member passes through the developing region. However, in this embodiment, even when the toner discharged from the auxiliary member passes through the developing region, the developing sleeve is rotated, and the control of discharging the toner from the developing device can be executed.

Schematic of the image forming apparatus shown in the first to third embodiments Sequence at the time of toner replacement control shown in Examples 1 and 2 Image diagram at the time of toner replacement control shown in the first and second embodiments Toner charge change by toner charge control means shown in Examples 1 to 3 The force acting on the toner on the photosensitive drum shown in Examples 1 to 3 Relationship between forces acting on toner on the photosensitive drum shown in the first to third embodiments Toner charge change by toner control means shown in Examples 1 to 3 Sequence of toner discharge control from auxiliary brush shown in the third embodiment Explanation of toner discharge control from the auxiliary brush in the third embodiment

Explanation of symbols

11 Photoconductor (Drum)
DESCRIPTION OF SYMBOLS 12 Charging means 13 Developing means 14 Primary transfer means 15 Charging auxiliary means 16 Intermediate transfer belt 17 Secondary transfer means 18 Fixing means 19 Cleaning means for intermediate transfer member 23 Laser exposure means

Claims (4)

An image carrier for carrying a toner image;
Charging means for charging the surface of the image carrier;
Latent image forming means for forming an electrostatic latent image on the surface of the charged image carrier;
Developing means for developing the latent image formed on the image carrier with toner, and collecting transfer residual toner remaining on the image carrier without being transferred in a previous image forming step;
Transfer means for transferring a toner image formed on the image carrier to a recording material;
A residual toner that has not been transferred by the transfer unit and an auxiliary charging unit that is in contact before charging by the charging unit and to which a voltage is applied;
In an image forming apparatus having a discharging step of discharging toner from the auxiliary charging unit or the developing unit onto the image carrier during non-image formation,
A bias different from that at the time of image formation is applied to the toner discharged in the discharge step so that a charge larger than the amount of charge applied to the transfer residual toner at the time of image formation is applied. An image forming apparatus characterized in that the recovery rate by the developing means is reduced by applying to the means, and the transfer means can be removed from the image carrier.   In the discharging step, the mirror force of the image carrier and the residual toner is greater than the force received by the residual toner from the electric field formed between the developing means and the image carrier. The image forming apparatus according to claim 1, wherein the transfer residual toner is charged by the charging unit or the auxiliary charging unit.   3. The image forming apparatus according to claim 1, wherein a voltage applied to the transfer unit during the removal mode is larger than a voltage applied during normal image formation.   The transfer unit includes an intermediate transfer member that receives a toner image formed on the image carrier from the image carrier, and a cleaning unit that cleans the surface of the intermediate transfer member, and the removal unit 4. The image forming apparatus according to claim 1, wherein in the mode, the toner electrostatically removed from the image carrier is collected by the cleaning unit.

Images