JP5253033B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a cleanerless type image forming apparatus that collects a transfer residual toner on a photoreceptor at the time of image formation by a developing device, and more specifically, from a first toner charging member and a second toner charging member at the time of non-image formation. The present invention relates to control for discharging toner to a photoreceptor.

  2. Description of the Related Art A cleanerless type image forming apparatus that collects transfer residual toner on a photosensitive member during image formation with a developing device has been put into practical use. The cleanerless image forming apparatus contacts a first toner charging member to which a voltage having a polarity opposite to the normal charging polarity of the toner is applied on the downstream side of the transfer unit in the moving direction of the photoconductor, Align the charging polarity. Then, the second toner charging member applied with a voltage having the same polarity as the normal charging polarity of the toner is brought into contact with the downstream side of the first toner charging member so that the transfer residual toner can be reused in the developing device. Charge.

  In a cleanerless type image forming apparatus, transfer residual toner accumulates on the first toner charging member and the second toner charging member as image formation accumulates, and the normal charge-removing and charging functions gradually cannot be exhibited. . For this reason, at the time of non-image formation, control for discharging the transfer residual toner from the first toner charging member and the second toner charging member to the photoreceptor is executed.

  Japanese Patent Application Laid-Open No. 2005-228561 discloses control for discharging accumulated toner from a charging brush that contacts the photosensitive member by repeating reverse rotation and forward rotation of the photosensitive member during non-image formation. Also shown is control for vibrating the charging brush during non-image formation to discharge the accumulated toner to the photoreceptor.

  Patent Document 2 discloses a tandem intermediate transfer type image forming apparatus that uses first and second toner charging members to efficiently collect transfer residual toner to a developing device during image formation. Here, during non-image formation, a voltage different from that during image formation is applied to discharge the accumulated toner from the first and second toner charging members to the photosensitive member, and then from the photosensitive member to the intermediate transfer member. Transcription.

JP 2004-184934 A JP 2007-65475 A

  If the toner has an average charging performance, even if the toner is captured by the first and second toner charging members, the polarity of the voltage applied to the first and second toner charging members during the capturing is changed. It is charged and discharged again to the photoreceptor. Accordingly, the toner accumulated in the first and second toner charging members with the accumulation of image formation increases the proportion of toner that does not have normal charging performance.

  For this reason, if the toner discharged from the first and second toner charging members to the photosensitive member during non-image formation is collected and reused by the developing device, the reproducibility of the image density may be reduced immediately after the image formation is resumed. There is sex. In addition, toner that is too low in charging performance and cannot be collected by the developing device is rotated around the photoconductor to become fog toner, and the white image may become cloudy immediately after resuming image formation.

  Therefore, during non-image formation, the toner discharged from the first and second toner charging members to the photosensitive member is transferred onto the transfer medium (intermediate transfer belt, recording material conveyance belt, recording material) and collected to the developing device. It is desirable not to let it. The transfer means can apply a voltage higher than that during development in a state where the transfer medium is in contact with the discharged toner image, so that even a toner with low charging performance that cannot be recovered by the developing device can be recovered.

  However, in the control disclosed in Patent Document 2, since the toner is discharged simultaneously from the first and second toner charging members, the toner discharged from the first and second toner charging members is mixed on the photoreceptor. .

  For this reason, it is difficult to efficiently transfer to the intermediate transfer member using the charging means. As will be described later, the toner discharged from the first toner charging member is often charged to the normal charging polarity of the toner, while the toner discharged from the second toner charging member is the normal charging polarity of the toner. This is because many are charged with opposite polarity.

  The present invention efficiently transfers both the toner discharged from the first toner charging member and the toner discharged from the second toner charging member to the transfer medium, so that the toner whose charging performance is reduced is efficiently transferred. An object of the present invention is to provide an image forming apparatus that can be removed easily.

The image forming apparatus of the present invention includes a rotationally driven photoconductor, a charging unit that charges the photoconductor, an exposure unit that exposes the surface of the charged photoconductor to form an electrostatic image, and an electrostatic image toner There a developing means for forming a toner image formed surface of the photosensitive member is developed with toner, and transfer means for transferring the toner image on the photosensitive member to the intermediate transfer belt, attached to the intermediate transfer belt A cleaning unit that removes toner, and a downstream of the transfer unit and an upstream of the charging unit in the rotation direction of the photoconductor, and the transfer residual toner on the photoconductor is defined as a normal charging polarity of the toner. A first toner charging member that is charged to a reverse polarity; and a first toner charging member that is disposed downstream of the first toner charging member and upstream of the charging means in the rotational direction of the photosensitive member, and By material The transfer residual toner on the electrostatic been the photoreceptor possess a second toner charging member for charging the normal charge polarity of the same polarity as the toner, and at the time of image formation for forming a toner image by the developing unit, the photosensitive The transfer residual toner on the body is collected by the developing means. In the toner discharge mode in which the toner accumulated in the first toner charging member and the second toner charging member is discharged and transferred to the intermediate transfer belt by the transfer unit, the toner is not overlapped on the photoreceptor. Control means for controlling the timing at which toner is discharged from the first toner charging member and the second toner charging member; when transferring the toner discharged from the first toner charging member to an intermediate transfer belt; and And a switching unit that switches a bias applied to the transfer unit when the toner discharged from the second toner charging member is transferred to the intermediate transfer belt, and the control unit includes the first toner charging member. When the toner is discharged from the first toner charging member, the first toner charging member has a peak voltage having a polarity opposite to the normal charging polarity of the toner and a predetermined frequency component. When a voltage having the same voltage is applied from the DC power source and the toner is discharged from the second toner charging member, the second toner charging member has a peak voltage having the same polarity as the normal charging polarity of the toner and a predetermined voltage. It controls so that the voltage which has the frequency component of this may be applied from DC power supply .

  In the image forming apparatus of the present invention, the toner discharged from the first toner charging member and the toner discharged from the second toner charging member are carried at different positions on the photoreceptor. For this reason, by switching the bias and causing the transfer electric field formed between the transfer means and the photoconductor to act in the opposite direction, the toner at both positions discharged to the photoconductor is transferred to the transfer medium with high transfer efficiency. Can be transferred to.

  Therefore, both the toner discharged from the first toner charging member and the toner discharged from the second toner charging member are efficiently transferred onto the transfer medium, so that the toner whose charging performance is reduced can be efficiently transferred. Can be removed.

  Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings. As long as the toner is discharged from the second toner charging member to a position different from the position where the toner is discharged from the first toner charging member, the present invention replaces part or all of the configuration of the embodiment. Other embodiments replaced with a typical configuration can also be implemented.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

  In this embodiment, an embodiment in which the toner discharged to the photosensitive member is transferred to the intermediate transfer member will be described. However, the present invention is also implemented in an embodiment in which the toner discharged to the photosensitive member is transferred to the recording material conveyance member or the recording material. it can.

  In addition, about the general matter of the image forming apparatus shown by patent document 1, 2, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted. In addition, the reference symbols in parentheses shown in the configuration names used in the claims are examples for assisting understanding of the invention, and are not intended to limit the configuration to the corresponding members in the embodiments. Absent.

<Image forming means>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus according to the first embodiment, and FIG. 2 is an explanatory diagram of the configuration of the image forming unit.

  As shown in FIG. 1, the image forming apparatus 100 is a tandem full-color copying machine in which yellow, magenta, cyan, and black image forming portions Pa, Pb, Pc, and Pd are arranged along an intermediate transfer belt 16. Further, the image forming apparatus 100 employs a cleaner-less system of a simultaneous charging cleaning method and a contact charging method using a charging roller, and a fixed conductive brush material is used for the first and second toner charging members. It is an example.

  In the image forming portion Pa, a yellow toner image is formed on the photosensitive drum 11 a and is primarily transferred to the intermediate transfer belt 16. In the image forming unit Pb, a magenta toner image is formed on the photosensitive drum 11 b and is primarily transferred to the yellow toner image on the intermediate transfer belt 16. In the image forming portions Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 11c and 11d, respectively, and similarly, the toner images on the intermediate transfer belt 16 are overlapped with each other and sequentially primary transferred.

  The four-color toner images primarily transferred to the intermediate transfer belt 16 are transported to the secondary transfer portion T2, and are secondarily transferred collectively to the recording material fed to the secondary transfer portion T2 by the registration roller 33. The recording material on which the toner image is secondarily transferred at the secondary transfer portion T2 is separated from the intermediate transfer belt 16 by the separation device 18, and is heated and pressurized by the fixing device 21 to fix the toner image on the surface. , Discharged outside.

The intermediate transfer belt 16 is formed endlessly with a polyimide resin having a thickness of 75 μm, has a surface resistance efficiency of 1 × 10 ¹¹ to 10 ¹³ Ω / □, and a low volume efficiency of 1 × 10 ⁹ to 10 ¹⁰ Ω · cm. . The material may be PVDF, PET, PBT, EPDM, NBR, urethane rubber, silicon rubber, or the like. The intermediate transfer belt 16 is supported around a tension roller 31, a drive roller 32, and a backup roller 30, and is driven by the drive motor M1 to rotate in the direction of arrow R2 at a predetermined process speed.

  The secondary transfer roller 17 is pressed against the backup roller 30 via the intermediate transfer belt 16 to form a secondary transfer portion T <b> 2 between the intermediate transfer belt 16 and the secondary transfer roller 17. The backup roller 30 is formed of a metal cylinder and is connected to the ground potential.

  The power source D2 applies a positive constant voltage to the secondary transfer roller 17 to electrostatically move the toner image carried on the intermediate transfer belt 16 to the recording material.

  The belt cleaning device 19 removes the toner attached to the intermediate transfer belt 16 that has passed through the secondary transfer portion T2.

<Image forming unit>
The image forming portions Pa, Pb, Pc, and Pd are substantially the same except that the toner colors used in the attached developing devices 13a, 13b, 13c, and 13d are different from yellow, magenta, cyan, and black. Hereinafter, the image forming unit Pa will be described, and the other image forming units Pb, Pc, and Pd will be described by replacing “a” at the end of the reference numerals with “b”, “c”, and “d”.

  As shown in FIG. 2, the image forming unit Pa includes a charging roller 12a, an exposure device 23a, a developing device 13a, a primary transfer roller 14a, a toner charging brush 15a, and a toner auxiliary charging brush 24a around the photosensitive drum 11a. .

  The photosensitive drum 11a (photosensitive member) has an organic photoconductor layer (OPC) having a negative polarity on the outer peripheral surface of an aluminum cylinder having an outer diameter of 30 mm. The photosensitive layer may be composed of a photoconductor made of amorphous silicon, CdS, Se, or the like. The photosensitive drum 11a is distributed in driving force from the driving motor (M1: FIG. 1) and rotates in the direction of arrow R1 at a process speed of 140 mm / sec.

The charging roller 12a (charging member) is driven to rotate while being in pressure contact with the photosensitive drum 11a. The charging roller 12a is formed by forming an elastic layer of rubber material such as EPDM or NBR in which an ionic conductive agent or an electronic conductive material is dispersed around a metal central axis, and forming a release layer of a fluororesin material on the surface. It is. The resistance value (initial resistance at normal temperature and humidity) is adjusted to 1.0 × 10 ⁵ to 10 ⁷ Ω. However, the material may be rayon or nylon, and the shape may be a brush roller or blade type.

  The power source D12a applies an oscillating voltage obtained by superimposing a DC voltage and an AC voltage to the charging roller 12a to charge the surface of the photosensitive drum 11a to a uniform negative potential VD.

  The AC voltage of the charging voltage is a voltage that allows the surface of the photosensitive drum 11a to converge to a predetermined potential (the same potential as the DC voltage of the charging voltage).

  The exposure device 23a scans the scanning line image data obtained by developing the yellow separated color image with a rotating mirror, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 11a.

  The developing device 13a agitates a two-component developer in which toner is mixed with a magnetic carrier, and charges the toner to a negative polarity and the magnetic carrier to a positive polarity. The two-component developer is carried on the developing sleeve 42 (developer carrying member) rotating in the counter direction around the magnet 41 in a spiked state and supplied to the electrostatic image on the photosensitive drum 11a. The charge amount of the toner in the developing container is 25 to 35 μC / mg, and the content of the external additive mainly composed of oil-treated silica having an average particle diameter of 20 nm is set to 30% or less to increase the fluidity of the toner. I try not to pass too much.

  The power source D13a applies an oscillating voltage obtained by superimposing an AC voltage to a negative DC voltage to the developing sleeve 42, and supplies toner to the electrostatic image on the photosensitive drum 11a that has a relatively positive polarity relative to the developing sleeve 42. Then, the electrostatic image is reversely developed.

  The primary transfer roller 14 a is in pressure contact with the photosensitive drum 11 a via the intermediate transfer belt 16 having an outer diameter of 16 mm, and forms a primary transfer portion Ta of the toner image between the photosensitive drum 11 a and the intermediate transfer belt 16.

  The power supply D14a applies a positive direct current voltage to the primary transfer roller 14a to charge the negatively charged toner image carried on the photosensitive drum 11a to the intermediate transfer belt 16 passing through the primary transfer portion Ta. Let

<First and second toner charging members>
In recent years, image forming apparatuses have been miniaturized, but the overall image forming apparatus has only to be reduced in size by means of the respective image forming processes such as charging, exposure, development, transfer, fixing, and cleaning. There is a limit to downsizing. Further, the transfer residual toner on the photoconductor after the transfer is collected by the cleaning device and becomes waste toner, but it is preferable that this waste toner does not come out from the viewpoint of environmental protection.

  Therefore, a “cleanerless system” in which the cleaning device is removed, “development simultaneous cleaning” using the developing device is performed, and the transfer residual toner on the photoreceptor is collected and reused in the developing device has been put into practical use. . In the simultaneous development cleaning, the toner remaining on the photosensitive member that has passed through the transfer means is subjected to the fog removal voltage Vback (the potential difference between the DC voltage applied to the developer carrying member and the white image portion of the photosensitive member) during the subsequent development. ) To collect the developer carrier of the developing device.

  According to the simultaneous development cleaning, the transfer residual toner is collected by the developing device and reused, so that waste toner is eliminated and maintenance is less troublesome. By being cleanerless, there is a great advantage in terms of space, and the image forming apparatus can be greatly downsized.

  In the simultaneous development cleaning, in order to efficiently collect the residual toner in the developing device, the first and second toner charging members (charging brush, fur brush, Charging roller or the like) is disposed. A voltage having a polarity opposite to the normal charging polarity of the toner is applied to the first toner charging member, and a voltage having the same polarity as the normal charging polarity of the toner is applied to the second toner charging member. As a result, the transfer residual toner on the photosensitive member is neutralized when passing through the first toner charging member and then charged to the normal charging polarity when passing through the second toner charging member. This improves the recovery performance.

  As shown in FIG. 2, the image forming portion Pa employs a cleanerless system in which an independent cleaning device is not attached to the photosensitive drum 11a.

  In the primary transfer performed by the primary transfer roller 14a, the transfer residual toner remaining on the photosensitive drum 11a without being transferred to the intermediate transfer belt 16 passes through a toner auxiliary charging brush 24 which is an example of a first toner charging member. To do.

The toner auxiliary charging brush 24 is a stationary brush and uses conductive rayon fibers, which are conductive fibers. The fiber thickness is 6 denier, the pile length is 5 mm, and the fiber density is 100,000 / inch ^2. It is. As other conductive fiber materials, conductive nylon fibers and polyester fibers can be used. Desirably, the fiber has a thickness of 2 to 10 denier, a pile length of 3 to 8 mm, and a fiber density in the range of 50,000 / inch ² to 500,000 / inch ² . Further, the shape is not limited to the fixed system brush, but may be a brush material that reciprocates or a brush roller material that rotates.

  The power source D 24 a applies a DC voltage having a polarity opposite to the normal charging polarity of the toner to the toner auxiliary charging brush 24. As a result, the toner auxiliary charging brush 24 disperses the transfer residual toner on the surface of the photosensitive drum 11a and neutralizes (or weakly charges to the reverse polarity). Further, it also serves to eliminate potential unevenness on the photosensitive drum 11a due to the previous electrostatic image and prevent the occurrence of ghost images such as memory. Note that an oscillating voltage obtained by superimposing an AC voltage on a DC voltage may be applied to the toner auxiliary charging brush 24a.

  The transfer residual toner that has been neutralized and diffused through the toner auxiliary charging brush 24a then passes through a toner charging brush 15a, which is an example of a second toner charging member.

  The toner charging brush 15a is the same as the toner auxiliary charging brush 24a. However, it may be of a material and shape different from the toner auxiliary charging brush 24a, and may be a rotating charging roller, a roll brush or the like.

  The power source D15a applies a DC voltage having the same polarity as the normal charging polarity of the toner to the toner charging brush 15a. As a result, the transfer residual toner on the surface of the photosensitive drum 11a is charged with the same polarity as the toner in the developing device 13a by being injected with charges (electrons) of normal polarity in the process of passing through the contact portion with the toner charging brush 15a. .

<Discharge control>
In an image forming apparatus having first and second toner charging members to which voltages of different polarities are applied, the polarity of toner discharged from the first and second toner charging members is different, so that complicated discharge control is performed. Required. In other words, in the discharge control biased toward discharging the toner having the same polarity as that of the toner used at the time of image formation, when the toner having a polarity opposite to that used at the time of image formation is discharged, contamination of the charging means or downstream There is a problem of re-adhering to the second toner charging member on the side.

  Further, in the case of a full-color image forming apparatus, collecting all of the toner discharged from the first and second toner charging members by the developing device causes color mixing in the developing device, and the color associated with the accumulation of image formation. There is a problem with reproducibility.

  That is, the toner remaining on the photosensitive drum 11a without being transferred by the primary transfer portion Ta often does not have the normal charging polarity (negative polarity) of the toner, and the reversal toner (positive polarity) is dominant. For such a reversal toner, by applying a voltage of normal charging polarity (negative polarity) to the toner charging brush 15a, a certain level of discharge between the toner charging brush 15a and the toner charging brush 15a is generated. A charge having a charging polarity (negative polarity) is imparted. By such a charging process, the transfer residual toner charged to the same polarity as the normal toner passes through the charging roller 12a and is collected by the developing device 13a.

  However, when sufficient negative charge is not applied by discharge at the contact portion between the photosensitive drum 11a and the toner charging brush 15a, the positive reversal toner adheres to the negative toner charging brush 15a. This occurs when the positive polarity voltage applied to the primary transfer roller 14a is excessive, when the amount of residual toner is large, or when a large amount of reversal toner is generated in the developing device 13a in a low temperature and low humidity environment. Easy to do.

  If such a situation continues, reversal toner continues to accumulate on the toner charging brush 15a, and the charge imparting ability of the toner charging brush 15 gradually decreases, so that reversal toner and uncharged toner passing through the toner charging brush 15 Will increase. As a result, the untransferred toner that has passed through the toner charging brush 15 adheres and accumulates on the charging roller 12a to cause uneven charging, resulting in fogging and image defects due to uneven charging.

  Further, if a large amount of toner accumulates on the toner auxiliary charging brush 24a and the toner charging brush 15a, a large amount of toner may be discharged to the photosensitive drum 11a with a small trigger during image formation, and image smearing may occur.

  Thus, during non-image formation, conventionally, the toner is mechanically or electrically discharged from the toner auxiliary charging brush 24a and the toner charging brush 15a to the photosensitive drum 11a and collected by the developing device 13a.

  However, since the toner that adheres and accumulates on the toner charging brush 15 is often deteriorated toner or defective toner, there remains a problem that causes image quality degradation when the toner is collected and reused by the developing device 13a.

  Therefore, in the image forming apparatus 100, during non-image formation, the toner is discharged from the toner auxiliary charging brush 24a and the toner charging brush 15a to the photosensitive drum 11a so as not to overlap each other. Then, the toner discharged from the toner auxiliary charging brush 24a and the toner charging brush 15a is separately transferred to the intermediate transfer belt 16 by switching the bias applied to the primary transfer portion Ta and applying a reverse transfer electric field. And excluded from the image forming unit Pa. As a result, the toner is efficiently transferred from the photosensitive drum 11a to the intermediate transfer belt 16 to solve the above-described problems.

<Example 1>
3 is an explanatory diagram of the discharge control of the first embodiment, FIG. 4 is a time chart of the discharge control of the first embodiment, FIG. 5 is an explanatory diagram of the discharge control of the comparative example, and FIG. 6 is an effect of the discharge control of the first embodiment. It is explanatory drawing.

  The execution timing of the discharge control of the first embodiment is during non-image formation. That is, at the time of start-up rotation after turning on the power switch, at the time of JAM recovery after recovery of recording paper jam or communication failure, at the time of pre-rotation before the start of image formation on the first recording material, at the predetermined accumulation during continuous image formation For example, an enlarged space between sheets formed for each number of sheets.

  As shown in FIG. 3A, in the discharge control of the first embodiment, the toner accumulated from the toner auxiliary charging brush 24a and the toner charging brush 15a is discharged at different positions on the photosensitive drum 11a. . Thus, the toner discharged from the toner auxiliary charging brush 24a and the toner discharged from the toner charging brush 15a are avoided from being mixed and efficiently transferred to the intermediate transfer belt 16 and collected by the belt cleaning device 19.

  As shown in FIG. 3B, in the discharge control of the first embodiment, the primary transfer roller is used when transferring the toner discharged from the toner auxiliary charging brush 24a and when transferring the toner discharged from the toner charging brush 15a. The bias applied to 14a is switched and reversed. Thus, the discharged toner is efficiently transferred to the intermediate transfer belt 16, and the discharged toner is prevented from being collected again by the toner auxiliary charging brush 24a and the toner charging brush 15a.

  As shown in FIG. 4 with reference to FIG. 2, in the discharge control of the first embodiment, first, the accumulated toner is discharged from the toner auxiliary charging brush 24a to the photosensitive drum 11a.

  Since a positive voltage is applied to the toner auxiliary charging brush 24a at the time of image formation, the accumulated toner adhering and accumulating on the toner auxiliary charging brush 24a is generally charged to a negative polarity. In order to discharge the accumulated toner charged to the negative polarity from the toner auxiliary charging brush 24a to the photosensitive drum 11a, the control unit 110 controls the power source D24a to apply a positive rectangular wave voltage to the toner auxiliary charging brush 24a many times. Apply. When a DC voltage having a short cycle is repeatedly applied to the toner auxiliary charging brush 24a, the accumulated toner is discharged from the toner auxiliary charging brush 24a every time the positive voltage decreases.

Specifically, the following voltage conditions were used.
Applied voltage during image formation: 400V
Peak voltage during discharge: 400V
Bottom voltage during discharge: 150V
Square wave frequency: 10 Hz
Number of rotations of photosensitive drum during discharging period: 1.0 rotation

  By applying such a voltage pattern, the surface of the photosensitive drum 11a is charged to + 150V, and the deposited toner charged negatively is transferred from the toner auxiliary charging brush 24a to the photosensitive drum 11a and is electrically held. .

  As shown in FIG. 5A, the toner discharged from the toner auxiliary charging brush 24a passes through the toner charging brush 15a as the photosensitive drum 11a rotates.

  As shown in FIG. 5B, when the toner charging brush 15a is connected to the ground potential at this time, the positive polarity accumulated toner of the toner charging brush 15a is discharged from the toner auxiliary charging brush 24a. Will be drawn into the toner and mixed.

  As shown in FIG. 6A, therefore, in Example 1, a negative voltage is applied to the toner charging brush 15a until the toner discharged from the toner auxiliary charging brush 24a passes.

  As shown in FIG. 6B, the negative polarity toner in which the positive polarity accumulated toner of the toner charging brush 15a is discharged from the toner auxiliary charging brush 24a by applying a negative polarity voltage to the toner charging brush 15a. It becomes difficult to be drawn into.

  It should be noted here that by applying a negative voltage, the toner adhered and accumulated on the toner charging brush 15 is discharged to the photosensitive drum 11a. On the other hand, this problem is avoided by adjusting the magnitude of the applied voltage.

Specifically, the following voltage conditions were used.
Applied voltage during image formation: -800V
Applied voltage at discharge: -500V

  As shown in FIG. 4 with reference to FIG. 2, the control unit 110 applies a negative DC voltage to the charging roller 12a in the process in which the toner discharged from the toner auxiliary charging brush 24a passes through the charging roller 12a. . This prevents negative toner discharged from the toner auxiliary charging brush 24a from being electrically transferred to the charging roller 12a.

Specifically, the following voltage conditions were used.
Applied voltage during image formation: −700 VDC + 1600 VppAC
Applied voltage during discharge: -500 VDC

  During the discharge control, the control unit 110 stops the driving motor M13 that rotates the developing sleeve 42 so that the recovery of the deteriorated toner to the developing device 13a is minimized, and the developing sleeve 42 is stopped. The rotation of is stopped. Thereby, when the toner discharged from the toner auxiliary charging brush 24a passes through the developing device 13a, the deteriorated toner is not mixed into the developing device 13a.

  As shown in FIG. 3B, while the toner discharged from the toner auxiliary charging brush 24a passes through the primary transfer portion Ta, the control unit 110 causes the primary transfer roller 14a to have the same positive polarity as that during normal image formation. Apply DC voltage. As a result, the discharged toner that is negatively charged and carried on the photosensitive drum 11 a is transferred to the intermediate transfer belt 16, and is conveyed to the belt cleaning device (19: FIG. 1) and collected as the intermediate transfer belt 16 rotates. Is done.

Specifically, the following voltage conditions were used.
Applied voltage during image formation: + 500V
Applied voltage at discharge: + 500V.

  In the process in which the discharged toner passes through the secondary transfer portion T2 shown in FIG. 1, a negative DC voltage is applied to the secondary transfer roller 17 so that the discharged toner is not transferred to the secondary transfer roller 17. Yes.

  Next, after the toner discharged from the toner auxiliary charging brush 24a passes through the toner charging brush 15a, the control unit 110 discharges the accumulated toner from the toner charging brush 15a.

  Since a voltage having the same polarity (negative polarity) as the normal charging polarity of the toner is applied to the toner charging brush 15 at the time of image formation, the adhered and accumulated toner is charged with a polarity opposite to that of the toner in the developing device 13a. doing. The toner deposited and accumulated on the toner auxiliary charging brush 24a is discharged onto the photosensitive drum 11a by applying a rectangular wave having the same polarity as the applied voltage at the time of image formation many times, like the toner auxiliary charging brush 24a. The discharged toner is electrically held on the surface of the photosensitive drum 11a charged to −150 V by applying a rectangular wave.

Specifically, the following voltage conditions were used.
Applied voltage during image formation: -800V
Peak voltage during discharge: -500V
Bottom voltage during discharge: -150V
Square wave frequency: 10 Hz
Number of rotations of photosensitive drum during discharging period: 1.0 rotation.

  Further, since the toner discharged onto the photosensitive drum 11a does not contaminate the charging roller 12a, no voltage is applied to the charging roller 12a at the timing of contact with the toner discharged from the toner charging brush 15a. By not applying a DC voltage from the power source D15a, toner adhesion to the charging roller 12a is suppressed.

  Further, when the discharged toner passes through the developing device 13a, the drive motor M13 for rotating the developing sleeve 42 is stopped to prevent the deteriorated toner from being mixed into the developing device 13a. To do.

  Finally, when the toner discharged from the toner charging brush 15a passes through the primary transfer portion Ta, a DC voltage having a polarity opposite to that at the time of image formation is applied to the primary transfer roller 14a. Thus, the toner discharged from the toner charging brush 15a is efficiently transferred from the photosensitive drum 11a to the intermediate transfer belt 16.

Specifically, the following voltage conditions were used.
Applied voltage during image formation: + 500V
Applied voltage at discharge: -500V

  After that, the secondary transfer roller 17 is passed through the secondary transfer portion T2 to which a positive DC voltage is applied and is collected by the belt cleaning device 19, thereby completing the discharge control of the accumulated toner.

  As described above, in the first exemplary embodiment, the control of discharging the accumulated toner between the toner auxiliary charging brush 24a and the toner charging brush 15a to which voltages having different polarities are applied is executed at different positions on the photosensitive drum 11a. The toner discharged to the photosensitive drum 11a is efficiently transferred to the intermediate transfer belt 16 to prevent recovery to the developing device 13a. As a result, it is possible to realize the image forming apparatus 100 that has high productivity by suppressing downtime and suppresses deterioration in image quality when image formation is resumed.

<Example 2>
FIG. 7 is a time chart of the discharge control of the second embodiment, FIG. 8 is an explanatory view of the discharge control of the comparative example, and FIG. 9 is an explanatory view of the effect of the discharge control of the second embodiment.

  As shown in FIG. 7, the discharge control of the second embodiment is configured in the same manner as in the first embodiment except that the toner is discharged first from the toner charging brush 15 in the image forming apparatus 100 and is similarly controlled. . Therefore, the overlapping description is omitted, and differences from the first embodiment will be described.

  The discharge control according to the second exemplary embodiment is performed when the amount of toner adhered and deposited on the first and second toner charging members is large, for example, when image formation with a high printing rate continues or when the frequency of discharge control is low. It is valid.

  As shown in FIG. 8A, when the image formation with a high printing rate continues, or when the frequency of the discharge control is suppressed to the limit in order to increase the productivity, the downstream toner charging brush 15a has a considerable amount. Toner is deposited. When toner is discharged from the upstream toner auxiliary charging brush 24a in this state, the toner discharged to the photosensitive drum 11a passes through the toner charging brush 15a as shown in FIG. 8B. Will be drawn in. As described in the first embodiment, the toner charging brush 15a holds the negative polarity toner discharged from the toner auxiliary charging brush 24a even though the toner is discharged to different positions on the photosensitive drum 11a. Positive toner is mixed. As a result, in the primary transfer portion Ta in which a positive voltage is applied to the primary transfer roller 14a, positive toner remains on the photosensitive drum 11a and transfer efficiency is lowered.

  Therefore, in the discharge control of the second embodiment, the toner accumulated on the downstream toner charging brush 15a is first completely discharged onto the photosensitive drum 11a. As a result, when the toner discharged from the toner auxiliary charging brush 24a on the upstream side passes through the toner charging brush 15a, there is already no toner to be drawn into the toner charging brush 15a.

  As shown in FIG. 9A, in the discharge control of the second embodiment, first, the accumulated toner of the toner charging brush 15a disposed at the downstream position in the rotation direction of the photosensitive drum 11a is discharged to the photosensitive drum 11a. After the toner accumulated on the downstream toner charging brush 15a is completely discharged, the toner is discharged from the upstream toner auxiliary charging brush 24a. The discharge control of the toner charging brush 15a is terminated before the toner by the discharge control by the toner auxiliary charging brush 24a reaches the downstream toner charging brush 15a.

  As shown in FIG. 9B, when the toner discharged from the toner auxiliary charging brush 24a passes through the toner charging brush 15a, the toner attracting and accumulating on the toner charging brush 15a is prevented. Yes. Conversely, the phenomenon in which the toner discharged from the toner auxiliary charging brush 24a is taken into the toner deposited and deposited on the toner charging brush 15a is also prevented.

  For this reason, the mixture of the negative polarity toner and the positive polarity toner on the surface of the photosensitive drum 11a is reduced, and the primary transfer portion Ta can transfer to the intermediate transfer belt 16 with high transfer efficiency and collect the discharged toner.

  According to the discharge control of the second embodiment, an image that can cope with the case where the amount of toner adhered and accumulated on the auxiliary charging brush 24a is large, particularly when image formation with a particularly high printing rate continues, and the frequency of discharge control can be suppressed. A forming apparatus 100 is provided.

<Example 3>
In the first and second embodiments, the discharge control of the accumulated toner in the yellow image forming unit Pa has been described. Actually, the discharge control of the accumulated toner is performed by a plurality of image forming units (Pa, Pb, Pc, Pd: In parallel with FIG.

  In the third embodiment, the timing of starting and ending individual discharge control performed in parallel in a plurality of image forming units (Pa, Pb, Pc, Pd: FIG. 1) will be described. In addition, except for the difference in timing, the individual discharge control is configured in the same manner as in the first embodiment and is controlled in the same manner. Therefore, the overlapping description is omitted, and differences from the first embodiment will be described.

  In an image forming apparatus in which a plurality of (two or more colors) image forming units are attached to an intermediate transfer member or a recording material conveyance member, a toner image formed by an image forming unit positioned on the upstream side is an image positioned on the downstream side. It is retransferred to the photosensitive member of the forming part. For this reason, there is a possibility that the discharged toner that has been discharged to the photosensitive member located on the upstream side and transferred to the intermediate transfer member or the like is retransferred to the photosensitive member located on the downstream side and collected by the developing device. This may cause problems such as deterioration in transfer efficiency of discharged toner to an intermediate transfer member, color mixing in the developing device, and image contamination due to fog toner.

  Therefore, in the third embodiment, as shown in FIG. 1, the discharge control timing in the plurality of image forming portions Pa, Pb, Pc, and Pd is set so that the discharged toner having the opposite polarity is not transferred onto the intermediate transfer belt 16. doing. The image forming unit Pb is controlled so that the discharged toner is not transferred from the photosensitive drum 11b to the region of the intermediate transfer belt 16 to which the discharged toner is transferred from the photosensitive drum 11a. The image forming unit Pc is controlled so that the discharged toner is not transferred from the photosensitive drum 11c to the region of the intermediate transfer belt 16 to which the discharged toner is transferred from the photosensitive drums 11a and 11b. The image forming unit Pd is controlled so that the discharged toner is not transferred from the photosensitive drum 11d to the region of the intermediate transfer belt 16 to which the discharged toner has been transferred from the photosensitive drums 11a, 11b, and 11c. The discharged toner is sequentially transferred from the photosensitive drums 11a, 11b, 11c, and 11d to different positions on the intermediate transfer belt 16.

  The discharge control according to the third exemplary embodiment realizes the image forming apparatus 100 with higher productivity and the image forming apparatus 100 capable of maintaining the image quality at a high level through the accumulation of image formation.

It is explanatory drawing of a structure of the image forming apparatus of 1st Embodiment. It is explanatory drawing of a structure of an image formation part. It is explanatory drawing of the discharge control of Example 1. FIG. 3 is a time chart of discharge control according to the first embodiment. It is explanatory drawing of discharge control of a comparative example. It is explanatory drawing of the effect of the discharge control of Example 1. FIG. 6 is a time chart of discharge control according to the second embodiment. It is explanatory drawing of discharge control of a comparative example. It is explanatory drawing of the effect of the discharge control of Example 2. FIG.

Explanation of symbols

11a, 11b, 11c, 11d Photosensitive member (photosensitive drum)
12a, 12b, 12c, 12d Charging means (charging roller)
13a, 13b, 13c, 13d Developing means (developing device)
14a, 14b, 14c, 14d Transfer means (primary transfer roller)
15a, 15b, 15c, 15d Second toner charging member (toner charging brush)
16 Conveyor (intermediate transfer belt)
17 Secondary transfer roller 19 Belt cleaning device 21 Fixing devices 23a, 23b, 23c, 23d Exposure devices 24a, 24b, 24c, 24d First toner charging member (toner auxiliary charging brush)

Claims (1)

A rotationally driven photoreceptor;
Charging means for charging the photoreceptor;
Exposure means for exposing the surface of the charged photoreceptor to form an electrostatic image;
Developing means for developing a surface of the photoreceptor on which an electrostatic image is formed with toner to form a toner image;
Transfer means for transferring the toner image on the photoreceptor to an intermediate transfer belt ;
Cleaning means for removing toner adhering to the intermediate transfer belt;
A first charging roller disposed downstream of the transfer unit and upstream of the charging unit in the rotation direction of the photoconductor to charge the transfer residual toner on the photoconductor to a polarity opposite to the normal charging polarity of the toner. A toner charging member of
Transfer residual toner on the photoconductor that is disposed downstream of the first toner charging member and upstream of the charging means and charged by the first toner charging member in the rotation direction of the photoconductor was closed and the second toner charging member for charging the normal charge polarity of the same polarity as the toner, and
In the image forming apparatus for collecting the transfer residual toner on the photosensitive member by the developing unit at the time of image formation for forming a toner image by the developing unit,
In the toner discharge mode in which the toner accumulated in the first toner charging member and the second toner charging member is discharged and transferred to the intermediate transfer belt by the transfer unit, the first toner charging member and the second toner charging member are not overlapped with each other on the photoconductor. Control means for controlling the timing of discharging the toner from one toner charging member and the second toner charging member;
Bias applied to the transfer means when transferring the toner discharged from the first toner charging member to the intermediate transfer belt and when transferring the toner discharged from the second toner charging member to the intermediate transfer belt Switching means for switching between,
When the toner is discharged from the first toner charging member, the control means has a peak voltage having a polarity opposite to the normal charging polarity of the toner and a predetermined frequency component with respect to the first toner charging member. When a voltage having the same voltage is applied from the DC power source and the toner is discharged from the second toner charging member, the second toner charging member has a peak voltage having the same polarity as the normal charging polarity of the toner and a predetermined voltage. An image forming apparatus that controls to apply a voltage having a frequency component from a DC power source .

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