JP2003015389A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the soiling of an electrifying roll from occurring again due to excessive development caused by faulty electrification associated with the uneven soiling of the electrifying roll even in the case of performing the cleaning cycle of the electrifying roll under a condition that a developing device is at a developing position oppositely to an image carrier when an image is not formed. SOLUTION: This image forming device is provided with a control means for controlling electrification voltage and developing bias voltage so that latent image potential may be equal to or above zero and smaller than the latent image potential at image forming time in a state where both a potential difference between electrification potential and developing bias potential and a potential difference between the developing bias potential and the latent image potential are still kept the respective potential differences at the image forming time in the case of performing the cleaning cycle of the electrifying roll.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus typified by a printer, a copying machine, a facsimile, a multi-function machine, etc., which uses an electrophotographic system, and more particularly, to a charging roll which is not charged during image formation. The present invention relates to an improvement of an image forming apparatus that executes a charging roll cleaning cycle of cleaning with a cleaning member.

[0002]

2. Description of the Related Art In an image forming apparatus of this type, as shown in FIG.
As illustrated in FIG. 2, as a charging unit that charges the image carrier 110 such as a photoconductor on which an electrostatic latent image is formed due to a potential difference, to a predetermined charging potential, the image carrier is used for the purpose of preventing generation of ozone. There is a tendency to use a contact-type charging roll 120 that charges in a state of being in contact with the body.

On the other hand, such a charging roll 120
In the case of using, the adhering substances (external additives externally added to the developer (toner), developer, paper dust, etc.) adhering to the image bearing member 110 remove the adhering substances on the image bearing member 110. May not be completely removed by the cleaning device 160, and a part (mainly an external additive) of the adhered matter may reach the contact position with the charging roll 120 and adhere to the surface of the charging roll.
As a result, the charging roll 120 may be contaminated. In FIG. 5, reference numeral 130 indicates the image carrier 11.
A latent image forming device for forming an electrostatic latent image having a predetermined latent image potential at 0, 140 conveys the electrostatic latent image on the image carrier 110 by a developer carrier 145 to which a developing bias voltage is applied. Developing device for developing a toner image by developing with a developed developer,
Reference numeral 150 denotes a primary transfer device for transferring the toner image on the image carrier 110 to the recording medium P or the intermediate transfer member 200 under the condition that a transfer voltage is applied, and 170 denotes a surface potential of the image carrier 110 of 0 (zero). ) A static eliminator that eliminates static electricity to V.

When the charging roll is soiled in this way, a charging failure occurs in which the image carrier cannot be charged to a predetermined charging potential, which leads to deterioration of image quality. . In particular, when a halftone image is formed on the entire surface of the image carrier after the same image is continuously formed, the adhered matter that adheres to other non-image areas than the image area corresponding to the same image on the image bearing member. As a result, the portion of the charging roll corresponding to the non-image area is contaminated with the adhering substances, and as a result, uneven charging of the image carrier (insufficient charging) occurs due to partial contamination of the charging roll. ) Occurs and finally appears as a density difference of the image (that is, the density of the image area corresponding to the part other than the same image in the whole halftone image decreases, while the image density corresponds to the same image part). The density of the image area is relatively high).

Therefore, in order to prevent such contamination of the charging roll, in general, a charging voltage having a polarity opposite to that at the time of image formation is applied to the charging roll 120 to electrostatically image the deposit on the charging roll. A cleaning means for returning to the side of the carrier 110 to remove it is adopted (for example, Japanese Patent Laid-Open No. 181351), or an elastic blade for cleaning is brought into contact with the charging roll 120 to mechanically remove the deposit on the charging roll. A cleaning means for selectively removing is employed (for example, Japanese Patent Laid-Open Nos. 6-342237 and 10-123).
No. 800). In the former electrostatic cleaning means, the adhering material on the charging roll 110 is pressed and adheres to the surface of the charging roll 110 when passing through the image carrying body 110, and electrostatically adheres to the image carrying body 110 side. The latter mechanical cleaning means 180 is advantageous because it is difficult to be transferred and may not be removed.

[0006]

However, in the conventional image forming apparatus employing the cleaning means 180 for the charging roll 110, the charging roll 120 is used.
However, the cleaning means 180 may not be able to sufficiently remove the stains on the entire surface, resulting in uneven stains on the charging roll 120, which causes the following problems.

That is, in particular, in the image forming apparatus which executes the cleaning cycle for cleaning the charging roll 120 by the cleaning means 180 under the condition where the developing device 140 faces the image carrier 110 and is in the developing position, the charging roll is used. Due to the stain unevenness of 120, the image carrier corresponding to the dirty portion of the charging roll is not properly charged, and in the worst case, it is hardly charged. As a result, the following new charging roll stains occur. Will trigger.

That is, as illustrated in FIG. 6, in the cleaning cycle, first, the image carrier 1 is hardly charged by the charging roll 120 having the uneven stain.
10 defective charging areas (in the worst case, the static eliminator 170
(The area where the surface potential of the image carrier is OV while the charge is removed)
Occurs. The defective charging area is the developing device 1.
After passing through 40, the potential difference (V _NG ) between the developing bias potential V _DB and the charging failure potential V _E becomes _smaller than the potential difference (V _DEVE ) between the developing bias potential V _DB and the latent image potential V _L during image formation. Because of the large relationship, the developer (toner), which is larger than the development amount at the time of image formation, excessively adheres to the poorly charged area of the image carrier 110. V _CLN in the figure indicates the potential difference between the charging potential V _H and the developing bias potential V _DB .

As a result, the developer excessively attached to the image carrier 110 is transferred to the recording medium P or the intermediate transfer member 200 even when the transfer voltage for image formation is applied to the primary transfer device 150. As a result, a large amount of residual toner remains on the image carrier 110. As described above, the toner (including the external additive) that remains in a larger amount than when the image is formed may not be sufficiently removed by the cleaning device 160 of the image carrier 110, resulting in poor cleaning. The toner and the external additive that have passed through are eventually attached to the charging roll 120.

Further, the occurrence of such stain unevenness of the charging roll 110 and the occurrence of new stain of the charging roll due to the stain unevenness are more remarkable when the spherical toner is used as the developer instead of the pulverized toner. Tends to be. This is because the spherical toner may slip through the elastic blade of the cleaning device 160 of the image carrier 110, and the toner itself adheres to the charging roll 120 and becomes dirty.

The present invention has been made in view of the above circumstances, and an object of the present invention is to charge a developing device in a state in which the developing device faces the image carrier at the developing position during non-image formation. Provided is an image forming apparatus capable of reducing the occurrence of new charging roll stains due to excessive development that occurs due to defective charging due to uneven stains on a charging roll even when a roll cleaning cycle is executed. Especially.

[0012]

An image forming apparatus of the present invention (first invention) capable of achieving the above object is an image carrier on which an electrostatic latent image is formed due to a potential difference, and this image carrier. A charging roll that is charged with a charging voltage to a predetermined charging potential, and a latent image formation that forms an electrostatic latent image having a predetermined latent image potential on the image carrier charged by the charging roll. An apparatus and an electrostatic latent image on the image carrier formed by the electrostatic latent image forming apparatus are developed by a developer carried by a developer carrier to which a developing bias voltage is applied, and toner is developed. A developing device for forming an image, and a primary transfer device for transferring a toner image on the image bearing member developed and formed by the developing device to a recording medium or an intermediate transfer member by applying a transfer voltage,
A charging roll cleaning member that removes adhering matter that adheres to the charging roll by contacting the surface of the charging roll, and an image carrier cleaning device that removes adhering matter that adheres to the image carrier, and a non-image At the time of formation, under the condition that the developing device faces the image carrier at the developing position,
In an image forming apparatus that executes a charging roll cleaning cycle for cleaning the charging roll with the charging roll cleaning member, at the time of the charging roll cleaning cycle, the potential difference between the charging potential and the developing bias potential and the developing bias potential and the latent image potential are detected. The charging voltage and the charging voltage are set so that the latent image potentials are 0 V (volts) or more and smaller than the latent image potentials during image formation while keeping the potential differences at the respective potential differences during image formation. It is characterized in that a control means for controlling the developing bias voltage is provided.

According to the image forming apparatus of the first aspect of the invention, at the time of the charging roll cleaning cycle, the control means causes the latent image potential to be 0 V or more and smaller than the latent image potential at the time of image formation. The charging voltage and the developing bias voltage are controlled so that the potential difference between the charging potential and the developing bias potential and the potential difference between the developing bias potential and the latent image potential at that time are almost the same as the respective potential differences during image formation. It remains held. As a result, even if a charging failure occurs due to uneven stain on the charging roll, the potential difference between the developing bias potential and 0 V is maintained at the same level as the potential difference between the developing bias potential and the latent image potential during image formation. Therefore, the amount of development for the poorly charged portion (the portion of the image carrier having a surface potential of 0 V or close to that due to poor charging) is almost the same level as the amount of development at the time of image formation. As a result, the developer attached to the poorly charged portion is
Since it is not an abnormally large amount, it can be sufficiently removed by the image carrier cleaning device, and the developer (including only the external additive) hardly reaches the charging roll side. The latent image potential at the time of image formation means the maximum potential. Further, it is desirable to perform the above control so that the latent image potential becomes 0 V as much as possible.

In the image forming apparatus of the first invention,
When the toner image on the image carrier is transferred to the intermediate transfer body, the control means may be configured to apply a transfer voltage at the time of image formation to the primary transfer device during the charging roll cleaning cycle.

In this case, even if the developer attached to the poorly charged portion is not sufficiently removed by the cleaning device for the image carrier, the developer is primarily transferred to the intermediate transfer member by the primary transfer device. As a result, the developer can be prevented from reaching the charging roll side. At this time, the developer transferred to the intermediate transfer body is usually removed by an intermediate transfer body cleaning device that removes the adhered matter that adheres to the intermediate transfer body. It may be configured so as to be secondarily transferred to and removed from a recording medium such as a recording paper, an OHP sheet, and a thick paper.

Even when the toner image on the image carrier is transferred to the recording medium, the control means applies the transfer voltage at the time of image formation to the primary transfer device during the charging roll cleaning cycle. It is also possible to configure. In this case, the recording medium may be supplied to the primary transfer position to transfer the toner image on the image carrier to the recording medium.

On the other hand, the image forming apparatus of the present invention (the second invention) which can achieve the above object, the image carrier on which an electrostatic latent image is formed due to the potential difference, and the image carrier are used for charging. A charging roll to which a voltage is applied and which is charged to a predetermined charging potential,
A latent image forming device for forming an electrostatic latent image having a predetermined latent image potential on the image carrier charged by the charging roll, and the image carrier formed by the electrostatic latent image forming device. Developing device for developing the electrostatic latent image of No. 3 into a toner image by the developer carried by the developer carrying member to which a developing bias voltage is applied, and the image carrying member developed and formed by this developing device. A primary transfer device that applies a transfer voltage to transfer the above toner image to an intermediate transfer member; a charging roll cleaning member that removes adhered matter that adheres to the charging roll by contacting the surface of the charging roll; An intermediate transfer member cleaning device for removing deposits adhering to the intermediate transfer member, and at the time of non-image formation, the developing device faces the image carrier and is in a developing position, and the charging roll is Charging roll cleaner In an image forming apparatus that executes a charging roll cleaning cycle of cleaning with a charging member, a control unit that applies a voltage larger than a transfer voltage during image formation to the primary transfer device during the charging roll cleaning cycle is provided. It is a feature.

According to the image forming apparatus of the second aspect, at the time of the charging roll cleaning cycle, the controller applies a voltage higher than the transfer voltage at the time of image formation to the primary transfer device. As a result, even if charging failure occurs due to uneven charging of the charging roll, the developer excessively attached to the charging failure portion has a stronger transfer electric field than that during image formation by the primary transfer device. Is almost transferred to the intermediate transfer body by the intermediate transfer body. As a result, the amount of the developer remaining on the image carrier after the primary transfer becomes almost equal to or less than that at the time of image formation, and thus the developer (including only the external additive) is sufficiently supplied to the image carrier cleaning device. Is almost completely removed and almost never reaches the charging roll side.

At this time, the developer transferred to the intermediate transfer body may be usually removed by the above-mentioned intermediate transfer body cleaning device, but if necessary, further recording such as recording paper from the intermediate transfer body may be performed. It may be configured to be secondarily transferred to the medium and removed. Further, in this case, the transfer voltage applied to the primary transfer device can be appropriately set, but it is preferable to set the transfer voltage to about 1.1 to 1.5 times the transfer voltage at the time of image formation.

As the charging roll cleaning member in the first and second image forming apparatuses, it is preferable that the charging roll cleaning member is a brush body and the resistance value of the brush portion is 1 × 10 ¹⁰ Ω · cm or less. The brush body may be a fixed type brush fixedly installed (fixed brush), or
It may be a rotary brush (rotary brush) that is rotatably installed. However, in the case of a rotating brush, it is preferable that the rotating brush is installed so as to rotate with a peripheral speed difference from that of the charging roll.

When such a charging roller cleaning member having a brush body is used, it is possible to greatly reduce the scratches and abrasions on the surface of the charging roller which are likely to occur when an elastic blade is applied, and the insulating property is also improved. It is possible to prevent abnormal discharge between the brush body and the charging roll due to charge-up that occurs when the brush body is applied. This makes it possible to perform good cleaning of the charging roll without inducing extra defects. When an elastic blade is used as the charging roll cleaning member, the resistance value of the elastic blade is 1 × 10 ^10.
It is preferable to set it to be Ω · cm or less.

Further, the developer in the first and second image forming apparatuses has a shape factor SF of the toner particles expressed by the following equation.
An average value of 135 or less, more preferably 130 or less can be used. SF = (M ² / A) × (π / 4) × 100, where M is the absolute maximum value of the toner particle size, and A is the projected area of the toner particle.

Even when there is a possibility that the spherical toner is used to promote the contamination of the charging roll as described above, the charging is performed by the control by the control means during the cleaning cycle of the charging roll. The occurrence of new stains on the charging roll due to uneven stains on the roll is reduced.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a schematic diagram showing an image forming apparatus according to a first embodiment of the present invention.

This image forming apparatus has four image forming units 1 for forming toner images of yellow (Y), magenta (M), cyan (C), and black (K) based on image information.
Individually formed in 0Y, 10M, 10C, 10K,
After the primary transfer is performed so as to be sequentially superposed on the intermediate transfer belt 20 as the intermediate transfer body, the secondary transfer is collectively performed on the recording paper P as the recording medium supplied from the paper feeding device 30, and finally the fixing device 40 performs recording. The color printer is capable of forming a full-color image on the recording paper P by fixing the toner image on the paper P. In the figure, the solid line with arrows indicates the rotation direction of each rotating component, and the alternate long and short dash line indicates the transport path of the recording paper P.

Image forming units 10Y, 10M, 10
In C and 10K, image information input from an externally connected device, a document reading device, or the like is subjected to image processing to separately form a toner image into which the above color components are separated by an electrophotographic process. As shown in FIG. 2, each of the image forming units 10 includes a photosensitive drum 11 as an image carrier, a charging roll 12 for contacting and charging the surface of the photosensitive drum 11, and a photosensitive drum 11. An exposure device 13 as a latent image forming device that forms an electrostatic latent image by exposing a charged surface to light beams (dotted arrows) corresponding to image signals of respective color components, and an electrostatic latent image on the photosensitive drum 11. Of a predetermined color (toner) supplied by the developing roll 14a
Developing device 14 for developing into a toner image, a transfer roll type primary transfer device 15 for transferring the toner image on the photosensitive drum 11 to the intermediate transfer belt 20, and toner remaining on the photosensitive drum 11 after the primary transfer. Similarly, a drum cleaning device 16 for removing adhered matters such as a cleaning blade 16a and the like, and a destaticizing device 17 for destaticizing the surface of the photosensitive drum 11 to 0V are similarly provided.

The photosensitive drum 11 has an organic photosensitive layer formed on the surface of a grounded drum-shaped conductive support. The charging roll 12 has a roll structure in which an elastic layer made of solid rubber of epichlorohydrin or the like is formed on a metal shaft for power supply, and the elastic layer is coated with fluorine. Charging power source 12 for applying a charging voltage having a polarity opposite to the charging polarity
b is connected. The charging roll 12 is configured to charge the surface (organic photosensitive layer) of the photosensitive drum 11 to a predetermined charging potential (surface potential) V _H. Exposure device 13
Is a semiconductor laser on the surface of the charged photosensitive drum 11,
Beam light is emitted from a light source such as a light emitting diode to form an electrostatic latent image having a predetermined latent image potential V _L.

The developing device 14 is a two-component developing device which uses a two-component developing agent composed of toner and carrier, uses negatively charged toner which is negatively charged, and has a spherical spherical toner with good transfer efficiency. Are using. Also,
In the developing device 14, a developing power source 14b for applying a predetermined developing bias voltage V _DB is connected to the developing roll 14a, and the developing roll 14a holds a two-component developer and closely faces the photosensitive drum 11. It is designed to be transported to the developing area. Further, the developing device 14 is always placed in a state in which the developing roll 14a is fixed at the developing position facing the photosensitive drum 11. The primary transfer device 15 includes a transfer roll 15a in which an elastic layer such as urethane foam rubber is formed on a conductive roll core material, and a transfer voltage in which a transfer voltage having a polarity opposite to the charging polarity of toner is applied to the transfer roll 15a. It is composed of a power supply 15b.

The intermediate transfer belt 20 includes a drive roll 21,
The tension roll 22 and a backup roll 23 that constitutes a part of the secondary transfer device are stretched around the photosensitive drum 11 of each image forming unit 10 so as to pass through the primary transfer position of the photosensitive drum 11 and are driven. The roll 21 rotates in the direction of the arrow. The intermediate transfer bell 20 is made of a synthetic resin such as polyimide or polyamide containing a conductive agent such as carbon black, and is molded into an endless belt having a thickness of about 0.1 mm. used.

Around the intermediate transfer belt 20, a secondary transfer roll 25 that rotates while pressing the intermediate transfer belt 20 against a backup roll 23, toner remaining on the intermediate transfer belt 20 after the secondary transfer, and the like. A belt cleaning device 26 that removes the adhered substances with a cleaning blade 26a and the like, and a position detection sensor 27 that detects a reference position mark formed on the intermediate transfer belt 20 are provided. As the secondary transfer roll 25, a roll adjusted to have a low volume resistivity of 10 Ω · cm or less is used in a grounded state. In the figure, reference numeral 24 denotes a power supply roll that supplies a secondary transfer voltage having the same polarity as the charging polarity of the toner to the backup roll, and 28 removes adhering substances such as toner adhering to the secondary transfer roll 25 with a cleaning blade or the like. A transfer roll cleaner.

The paper feeding device 30 includes a paper feeding tray 31 for accommodating and stacking a large number of recording papers P, and the paper feeding tray 3.
A delivery device 32 for delivering the recording paper P one by one from 1,
A plurality of paper transport roll pairs 33 for transporting the recording paper P delivered by the delivery device 32 toward the secondary transfer position.
And a sheet feed guide, and a registration roll 34 that stops the recording sheet P once and feeds it to a secondary transfer position at a predetermined timing. Reference numeral 29 in the figure
Is a paper conveyance guide member. The fixing device 40 is provided with a heating roll 41 having a heating source 42 and a pressure roll 43 that rotates in pressure contact with the heating roll 41, and the pressure contact portion between the heating roll 41 and the pressure roll 43 ( The fixing process is performed by introducing and passing the recording paper P after transfer to the nip portion).

Then, in this color printer,
A brush body 18 is provided as a charging roll cleaning member that comes into contact with the charging roll 12 and removes adhered substances such as toner and external additives that adhere to the roll. The brush body 18 is formed by arranging a large number of conductive brush bristles on an elongated substrate along the axial direction of the charging roll 12, and the charging roll 12 is attached to the charging roll 12 by a retract means (not shown) such as an eccentric cam mechanism. It is installed so that it can be connected to and separated from it. As the brush bristles, brush bristles made of conductive PET, nylon, polyester or the like having a resistance value of 1 × 10 ¹⁰ Ω · cm or less (thickness 40 denier / 12 F, length 3.5 m)
m) is used. Further, the brush bristles were planted on a base cloth so as to have a density of 4000 brushes / cm ² , and were mounted on the substrate.

Further, at the time of non-printing (for example, after a predetermined number of printing operations are performed, after the printing operation is finished, before the printing operation is started, etc.), the brush body 18 is brought into contact with the charging roll 12. By doing so, the cleaning cycle of the charging roll for cleaning the charging roll 12 is executed for a predetermined time.

During this cleaning cycle, in addition to the developing device 14 facing the developing position, the charging roll 12, the primary transfer device 15, and the drum cleaner 1 are provided.
6, the static eliminator 17 and the like are also in operation. In addition, the intermediate transfer belt 20, the secondary transfer roll 25, the belt cleaner 26, and the like are placed in an operating state. In this embodiment, the charging roll cleaning cycle is set to be executed every time the printing operation for 10,000 sheets is accumulated. From the viewpoint of more reliably cleaning the charging roll 12, it is preferable to set the charging roll cleaning cycle to be executed every time the printing operation of 2500 sheets is accumulated.

FIG. 3 is a block diagram showing the configuration of a control system for controlling the charging roll 12 during the cleaning cycle. Reference numeral 50 in the figure denotes a main control unit composed of a microcomputer or the like, which comprehensively controls each operation in the cleaning cycle. The main controller 50 includes a position detection sensor 2 for the intermediate transfer belt 20.
7 is connected, and the detection signal input from the sensor 27 is used as a reference timing signal for each drive system. Further, the main control unit 50 includes a control unit 51 for controlling the drive of the retracting means of the charging roll 12, a control unit 52 for adjusting the charging voltage in the charging power source 12b, and a developing bias voltage in the developing power source 14b. A control unit 52 for adjusting and a control unit 53 for adjusting the primary transfer voltage in the primary transfer power supply 15b are connected.

During the cleaning cycle of the charging roll 12, the main control section 50 executes a predetermined control operation as will be described later according to a control program for the charging roll cleaning cycle stored in the storage section of the main control section 50. It has become. Incidentally, in this embodiment, the latent image potential V _{L is set} to be approximately 0 V under a certain condition (in other words, the potential difference between the developing bias voltage and 0 V and the potential difference between the developing bias voltage and the charging potential). Is about the same as the potential difference (V _DEVE ) between the developing bias voltage and the latent image potential and the potential difference between the developing bias voltage and the charging potential (V _CLN ) at the time of image formation).
The charging voltage and the developing bias voltage described above are controlled (FIG. 4).

In this color printer, a two-component developer composed of non-magnetic spherical toner and magnetic carrier was used as the developer. As the toner, particles having a shape factor SF of 135 or less were used. The shape factor SF at this time is determined by an optical microscope (manufactured by Nikon: Micro Photo FX
A magnified photograph of the toner particles obtained in A) was subjected to image analysis by an image analyzer (NURECO: Luzex3) and calculated by the above-mentioned formula, and this was taken as an average value when similarly calculated for 100 toner particles. It is what I asked for.

Further, this toner has the above-mentioned four colors (Y, M,
Each of the toners C and K) was prepared by an emulsion polymerization method, and the volume average particle size and the particle size distribution were almost the same. The volume average particle diameter was 3 to 7 μm when measured with a Coal counter (manufactured by Coulter), and the particle size distribution index (GSD) was 1.23. Further, this toner contains silica having an average particle size of 10 to 150 nm,
An appropriate amount of inorganic fine particles such as titania was externally added as an external additive. On the other hand, as the carrier, ferrite beads having an average particle diameter of 35 μm were used.

Next, the operation of this color printer will be described.

First, when a print start signal for a full-color image is issued, the following print operation is executed.

First, the reference position signal is received from the position detection sensor 27.
When a predetermined time has elapsed since the issue was obtained, the image forming unit 10
Rotate in the direction of the arrow in Y, 10M, 10C, and 10K
The surface of the photosensitive drum 11 to be driven is charged by the charging roll 12.
Predetermined charging potential V_HAfter being charged to each exposure device 13
And the predetermined latent image potential V _L
To form an electrostatic latent image. Then, each photosensitive
The electrostatic latent image on the ram 11 is colored in a predetermined color by each developing device 14.
Is developed with the developer (toner) of
The four color toner images are individually formed on the drum 11.
It

The photosensitive drum 11 of each image forming unit 10
The four-color toner images formed above are primary-transferred in such a state that they are successively superposed on the intermediate transfer belt 20 that rotates and moves in the arrow direction at the primary transfer position facing the primary transfer device 15. In this primary transfer, the toner image is electrostatically intermediated by a transfer electric field formed between the transfer roll 15a and the photosensitive drum 11 by a primary transfer voltage applied from the transfer power supply 15b to the primary transfer roll 15a. This is performed by shifting to the transfer belt 20 side. After the primary transfer, the photosensitive drum 11 is cleaned by removing untransferred toner and the like by the drum cleaner 17, and then discharged to 0 V by the static eliminator 18.
Is discharged to.

On the other hand, after the recording paper P is sent out from the paper feed tray 31 of the paper feed device 30 through the paper feed path in accordance with the toner image forming operation, the intermediate transfer is performed by the registration roll 34 at the secondary transfer timing. The sheet is fed to the secondary transfer position between the belt 20 and the secondary transfer roll 25. As a result, the four-color multi-toner images primarily transferred to the intermediate transfer belt 20 are secondarily transferred to the recording paper P all together. In this secondary transfer, the toner image is electrostatically recorded on the recording paper by the transfer electric field formed between the secondary transfer roll 26 and the secondary transfer voltage applied to the backup roll 23 via the power feeding roll 24. This is done by shifting to the P side. The intermediate transfer belt 20 after the secondary transfer is cleaned by removing untransferred toner and the like by the belt cleaner 26. In addition, the secondary transfer roll 25 after the secondary transfer is
The transfer roll cleaner 28 removes adhering substances such as toner and cleans them.

Next, the recording paper P after the secondary transfer is peeled from the intermediate transfer belt 20 and then sent to the fixing device 30, where it passes through the nip portion between the heating roll 41 and the pressure roll 43 and is heated and pressed. Then, the toner image is fixed on the recording paper P. As described above, a full-color image is formed on one side of the recording paper P.

Then, at the time of the cleaning cycle of the charging roll 12, the following cleaning operation is executed.

First, in this embodiment, by the control operation of the main controller 50, the brush member 18 which is the cleaning member of the charging roll 12 is brought into contact with the charging roll 12, and the charging voltage is applied as described later. And the development bias voltage is adjusted. Then, the printer basically forms the electrostatic latent image by the exposure device 13 and the recording paper P.
The operation is performed under the same conditions as those at the time of printing (at the time of image formation), except that the above is not supplied. That is, the image forming units 10 and the intermediate transfer belt 20 operate.

As shown in FIG. 4, the main control unit 50 sets the charging potential V _H to −720 V at the time of printing for the purpose of setting the maximum latent image potential V _L (= 720 V) at the time of printing to almost 0 V. The charging voltage applied from the charging power source 12b is changed via the control unit 52 so that the developing bias potential V _DB changes from −600 V during printing to “−300 V”. The control unit 53 controls the developing bias voltage applied from the developing power source 14b.
Change through. Regarding the primary transfer voltage,
It is controlled so that the same transfer voltage as at the time of printing is applied from the transfer power supply 15b.

As a result, the charging roll 12 basically charges the surface of the photosensitive drum 11 from which electric charge has been removed, and at the same time, the brush member 18 as a cleaning member removes and cleans the deposits.

At this time, the cleaning member is the brush body 18.
Therefore, the surface of the charging roll 12 is hardly scratched or worn by the contact of the brush body 18.
Further, the resistance of the brush portion of the brush body 18 is 1 × 10 ¹⁰
Since it has a semi-conductivity or a conductivity of Ω · cm or less, there is no possibility of abnormal discharge occurring between the charging roll 12 and the charging roll 12.

Further, if an external additive of spherical toner or the spherical toner itself adheres to a part of the charging roll 12, and a defective charging portion occurs on the photosensitive drum 11 due to uneven stain of the roll. Even as a result of the adjustment of the charging voltage and the developing bias voltage as described above,
As shown in FIG. 4, the cleaning cycle time of the developing bias the developing bias voltage V _DB voltage V _DB 'and the potential difference between 0V (V ₁₎ is at the time of printing and the latent image potential V _L
And a potential difference (V ₂ ) between the developing bias voltage V _DB ′ and the charging potential V _H ′ during the cleaning cycle is approximately the same as the potential difference V _DEVE between the developing bias voltage V _DB and the charging potential V _DB. The potential difference with _H becomes approximately the same as V _CLN .

For this reason, even if the defectively charged portion of the photosensitive drum 11 passes through the developing device 14 to be developed, the developing bias voltage V _DB ′ at the defectively charged portion.
Since the potential difference (V ₁ ) between 0 V and 0 V is almost the same as the potential difference V _DEVE at the time of printing, the amount of the developer (toner) adhering to the _poorly charged portion is almost the same as that at the time of normal printing. Become.

The toner (including its external additives) on the photosensitive drum 11 attached to the poorly charged portion is first
Since the same transfer voltage as that at the time of printing is applied to the primary transfer roll 15a, it is primarily transferred to the intermediate transfer belt 20. At this time, in principle, the toner transferred to the intermediate transfer belt 20 is removed by the belt cleaner 26. Further, at this time, the toner on the photosensitive drum 11, which is left without being primarily transferred to the intermediate transfer belt 20 side, is thereafter removed by the drum cleaner 16. Here, when the secondary transfer roll 25 is always in pressure contact with the intermediate transfer belt 20, the toner transferred onto the intermediate transfer belt 20 contacts the secondary transfer roll 25 before reaching the belt cleaner 26. Will pass through. However, when such toner passes through the secondary transfer roll 25,
From the viewpoint of avoiding adhesion to the secondary transfer roller, it is desirable to apply a voltage having a polarity opposite to the normal secondary transfer voltage to the secondary transfer roll 25 during this cleaning cycle.

The toner on the photosensitive drum 11 thus attached to the poorly charged portion is transferred to the intermediate transfer belt 20 at the primary transfer position and removed, and then removed by the drum cleaner 16. Therefore, the toner on the photosensitive drum 11 is removed. The toner is almost removed, and as a result, the toner does not reach the charging roll 12. Therefore, during this charging roll cleaning cycle, the charging roll 12
Even if there is uneven stain on the surface and a defective charging portion is generated, it is possible to prevent the toner attached to the defective charging portion from newly adhering to the charging roll 12. That is, the occurrence of new stains on the charging roll 12 due to uneven stains on the charging roll 12 is reduced.

In the first embodiment, the case where the main controller 50 controls the primary transfer roll 15a to apply the same transfer voltage as during printing during the charging roll cleaning cycle has been described. The transfer roll 15a may be so controlled that no transfer voltage is applied to it. In this case, the toner on the photosensitive drum 11 attached to the poorly charged portion may be physically transferred and attached to the intermediate transfer belt 20 contacting the photosensitive drum 11, but most of the toner is on the drum. It will be removed by the cleaning cleaner 16.

In addition to this, the main controller 50 may be configured to control so as to apply a transfer voltage larger than that during printing. In this case, the toner on the photosensitive drum 11 attached to the poorly charged portion may be the toner on the intermediate transfer belt 2.
The amount of toner that should be removed by the drum cleaner 16 can be reduced, and the amount of toner that reaches the charging roll 12 can be eliminated altogether.

Further, in the first embodiment, during the charging roll cleaning cycle, the main controller 50 causes the developing bias voltage V _DB ′ and the charging potential V _H during the cleaning cycle to be increased.
The potential difference (V ₂ ) with respect to ‘is controlled so as to be approximately the same as the potential difference V _CLN (about 120 V) between the developing bias voltage V _DB and the charging potential V _H during printing. The configuration may be such that V ₂ ) is controlled within a range of ± 50 V with respect to the potential difference V _CLN during printing. In this case, if the potential difference (V ₂ ) is made larger than +50 V with respect to the potential difference V _CLN at the time of printing, the carrier will be developed in the non-image forming portion (background portion) on the photosensitive drum 11. . On the contrary, if the potential difference (V ₂ ) is smaller than −50 V with respect to the potential difference V _CLN at the time of printing, the toner on the non-image forming portion on the photosensitive drum 11 adheres and is fogged.

[Second Embodiment] In the second embodiment, in the color printer according to the first embodiment (FIGS. 1 to 3), the main controller 50 causes the charging roll cleaning cycle as described above to be performed. Instead of adjusting the working voltage and the developing bias voltage, the control unit 54 controls the primary transfer roll 15a to apply a transfer voltage larger than the transfer voltage at the time of printing. . Other configurations are the same as those in the first embodiment.

In the second embodiment, the primary transfer roll 1
A transfer voltage of about 1.1 times the transfer voltage during printing was applied to 5a. The transfer voltage at this time is preferably set to 1.5 times or less the transfer voltage at the time of printing. If the transfer voltage is set to a value higher than this, there is a possibility that the charging memory due to the transfer voltage may remain on the photosensitive drum 11, which is not appropriate.

In the printer thus constructed, when the charging roll cleaning cycle is reached, the charging voltage and the developing bias voltage which are the same as those at the time of printing are applied to the charging roll 12 and the developing roll 14a, and A cleaning cycle similar to that of the first embodiment is executed except that a transfer voltage higher than the transfer voltage at the time of printing is applied to the transfer roll 15a.

As a result, if the external additive of spherical toner or the spherical toner itself adheres to a part of the charging roll 12, and the charging failure occurs on the photosensitive drum 11 due to uneven stain of the roll. In this case, a larger amount of toner (amount of toner that is additionally attached to the potential difference between the latent image potential _VL at the time of printing and the surface potential of the poorly charged portion at the time of printing) is attached to the poorly charged portion. However, at the primary transfer position, such toner is mostly transferred to the intermediate transfer belt 20 side by the transfer electric field stronger than that at the time of printing and removed. The toner transferred to the intermediate transfer belt 20 is, as described in the first embodiment, the cleaner 28 of the secondary transfer roll 26 and the belt cleaner 26.
Removed by. At this time, the toner remaining on the photosensitive drum 11 without being transferred to the intermediate transfer belt 20 side is thereafter removed by the drum cleaner 16.

As described above, the toner on the photosensitive drum 11 adhered in large amounts to the poorly charged portion is transferred to the intermediate transfer belt 20 at the primary transfer position and is almost removed, and is also removed by the drum cleaner 16 if necessary. Therefore, the toner is almost completely removed from the photosensitive drum 11, and as a result, the toner does not reach the charging roll 12. Therefore, during this charging roll cleaning cycle, even if the charging roll 12 is unevenly stained and a defective charging portion is generated, the toner attached to the defective charging portion is newly attached to the charging roll 12. It will be avoided.

[Other Embodiments] In the first and second embodiments, the image forming apparatus adopting the intermediate transfer system using the intermediate transfer belt 20 is exemplified, but the present invention does not adopt the intermediate transfer system. Can be similarly applied to.

[0063]

As described above, according to the image forming apparatus of the present invention, by providing each of the above-mentioned control means, the developing device is charged while the developing device faces the image carrier at the developing position. Even when the roll cleaning cycle is executed, it is possible to reduce the occurrence of new charging roll stains due to excessive development caused by defective charging due to uneven stains on the charging roll.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an image forming apparatus according to a first embodiment (2).

FIG. 2 is an enlarged view of a main part showing a configuration of an image forming unit in the image forming apparatus in FIG.

FIG. 3 is a block diagram showing a configuration of a control system related to a charging roll cleaning cycle.

FIG. 4 is an explanatory diagram showing each potential state during printing and during a charging roll cleaning cycle.

FIG. 5 is a conceptual diagram showing a main part of a conventional image forming apparatus.

FIG. 6 is an explanatory diagram showing each potential state during a charging roll cleaning cycle and image formation in a conventional image forming apparatus.

[Explanation of symbols]

11 ... Photosensitive drum (image carrier), 12 ... Charging roll, 1
4 ... Developing device, 14a ... Developing roll (developer carrying member),
15 ... Primary transfer device, 18 ... Brush body (charging roll cleaning member), 20 ... Intermediate transfer belt (intermediate transfer body), 50 ... Main control part (control means), P ... Recording paper (recording medium).

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) G03G 21/00 370 G03G 21/00 370 F term (reference) 2H005 AA15 EA10 2H027 DA02 DA45 EA01 EA03 EA05 ED03 ED09 ED24 EE02 2H073 AA09 BA02 BA22 BA23 BA43 CA03 2H200 FA02 GA16 GA23 GA33 GA34 GA45 GA47 GB12 GB22 GB25 HA02 HA28 HA29 HB12 HB22 JA02 JC03 JC07 JC12 JC15 LB02 LB03 LB08 LB12 LB35 LB36 LB37 MA10 MA14 MA03

Claims (5)

[Claims] 1. An image bearing member on which an electrostatic latent image is formed due to a potential difference, a charging roll for charging the image bearing member to a predetermined charging potential by applying a charging voltage, and the charging roll. Latent image forming device that forms an electrostatic latent image having a predetermined latent image potential on the charged image carrier, and an electrostatic latent image formed on the image carrier by the electrostatic latent image forming device. A developing device that develops an image into a toner image by developing the developer carried by a developer carrying body to which a developing bias voltage is applied, and a toner image on the image carrying body developed and formed by the developing device. A primary transfer device for transferring a transfer voltage to a recording medium or an intermediate transfer member, a charging roll cleaning member for contacting and removing adhered matter adhering to the charging roll from the surface of the charging roll, and the image Remove the deposits on the carrier A charging roll cleaning cycle that includes an image carrier cleaning device and cleans the charging roll with the charging roll cleaning member while the developing device faces the image carrier and is in the developing position during non-image formation. In the image forming apparatus that executes the above, during the charging roll cleaning cycle, both the potential difference between the charging potential and the developing bias potential and the potential difference between the developing bias potential and the latent image potential are held at the respective potential differences during image formation, An image forming apparatus provided with a control means for controlling the charging voltage and the developing bias voltage so that the latent image potential is 0 V or more and smaller than the latent image potential during image formation. . 2. When transferring a toner image on the image carrier to an intermediate transfer member, the control means applies a transfer voltage at the time of image formation to the primary transfer device at the time of executing the charging roll cleaning cycle. The image forming apparatus according to claim 1. 3. An image bearing member on which an electrostatic latent image is formed due to a potential difference, a charging roll for charging the image bearing member to a predetermined charging potential by applying a charging voltage, and the charging roll. Latent image forming device that forms an electrostatic latent image having a predetermined latent image potential on the charged image carrier, and an electrostatic latent image formed on the image carrier by the electrostatic latent image forming device. A developing device that develops an image into a toner image by developing the developer carried by a developer carrying body to which a developing bias voltage is applied, and a toner image on the image carrying body developed and formed by the developing device. To the intermediate transfer body by applying a transfer voltage to the intermediate transfer body, a charging roll cleaning member for removing the adhered matter adhering to the charging roll by contacting the surface of the charging roll, and the intermediate transfer body. An intermediate transfer member cleaner that removes adhered substances And a charging roll cleaning cycle in which the charging roll is cleaned by the charging roll cleaning member while the developing device faces the image carrier at the developing position during non-image formation. In the image forming apparatus, a control unit that applies a voltage higher than a transfer voltage during image formation to the primary transfer device during the charging roll cleaning cycle is provided. 4. The charging roll cleaning member is a brush body, and the resistance value of the brush portion is 1 × 10.
The image forming apparatus according to claim 1, wherein the image forming apparatus has a resistance of ¹⁰ Ω · cm or less. 5. The shape factor SF {= (M ² / A) × (π / 4) × 100 of the toner particles of the developer, where M is the absolute maximum particle size of the toner and A is the toner. The image forming apparatus according to claim 1, wherein the average value of the projected area of the particles] is 135 or less.