JPH10274890A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which is capable of transferring a toner image to a transfer paper and then, uniformly discharging an intermediate transfer belt, so as to be prepared for the transfer of the toner image from the next photoreceptor drum. SOLUTION: The image forming device is provided with a control part 900 for switching discharging conditions by a belt discharger charger, in accordance with the surface potential of the intermediate transfer belt after the toner image is transferred to the transfer paper. For instance, a DC voltage applied to the belt discharger charger from a discharging power source 804 is switched according to the number of the transfer times of the toner image from the photoreceptor drum to the intermediate transfer belt.

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 such as a copying machine, a printer and a facsimile, and more particularly to an image forming apparatus using an intermediate transfer member.

[0002]

2. Description of the Related Art Conventionally, as this type of image forming apparatus,
An intermediate transfer member for carrying a toner image transferred from an image carrier, and a primary transfer charge applying means for applying a charge for transferring the toner image from the image carrier to the intermediate transfer member to the intermediate transfer member; Means for applying a charge for transferring a toner image from the intermediate transfer member to a transfer material to the transfer material or the transfer material carrier, and the intermediate transfer member transferring the toner image to the transfer material There is known an image forming apparatus provided with an intermediate transfer member static eliminator for neutralizing the surface of a sheet. In this image forming apparatus, the surface of the intermediate transfer member after the transfer of the toner image to the transfer material is neutralized by the intermediate transfer member static elimination means, so that the surface potential of the intermediate transfer member is uniformed, and the intermediate transfer member is transferred from the next image carrier. Prepare for primary transfer to body.

[0003]

However, in the above-described conventional image forming apparatus, even if the intermediate transfer member is discharged by the intermediate transfer member discharging means, the surface potential of the intermediate transfer member is not at a predetermined potential, In some cases, potential unevenness remained. Such a charge elimination defect has an adverse effect on the next transfer step from the image carrier to the intermediate transfer member.

The inventors of the present invention have investigated the cause of the defective static elimination of the intermediate transfer member. As a result, it was found that the surface potential of the intermediate transfer member before the static elimination by the intermediate transfer member static elimination means greatly fluctuated. It turned out to be the main cause of the failure.

In particular, primary transfer is performed a plurality of times so that toner images of respective colors formed on an image carrier are superimposed on the intermediate transfer body, and the superimposed toner images on the intermediate transfer body are collectively transferred to a transfer material. When the image forming apparatus is configured to perform
The surface potential of the intermediate transfer member before the charge is removed by the intermediate transfer member discharging means varies greatly depending on the number of toner images superimposed on the intermediate transfer member, that is, the number of times of primary transfer to the intermediate transfer member.

The present invention has been made in view of the above problems, and has as its object to transfer a toner image onto a transfer material,
It is an object of the present invention to provide an image forming apparatus capable of uniformly discharging an intermediate transfer member and preparing for transfer of a toner image from a next image carrier.

[0007]

To achieve the above object, the present invention is directed to an intermediate transfer member for carrying a toner image transferred from an image carrier, and an intermediate transfer member for transferring the toner image from the image carrier. Primary transfer charge applying means for applying a charge for transferring a toner image to the intermediate transfer member, and transferring the charge for transferring a toner image from the intermediate transfer member to a transfer material to the transfer material or transfer material carrier An image forming apparatus comprising: a secondary transfer charge applying means for applying the toner to the transfer member; and an intermediate transfer member removing means for removing charge from the surface of the intermediate transfer member after transferring the toner image to the transfer material. Control means for switching the charge elimination condition by the intermediate transfer member charge elimination means in accordance with the above.

In the image forming apparatus according to the first aspect, the charge elimination conditions of the intermediate transfer member are switched according to the surface potential of the intermediate transfer member, and when the surface potential of the intermediate transfer member is high, the charge of the intermediate transfer member is removed. On the contrary, when the surface potential of the intermediate transfer member is low, the charge elimination ability is lowered. By switching the charge elimination conditions in this way, even if the surface potential of the intermediate transfer member before charge elimination varies, the charge of the intermediate transfer member is uniformly removed.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the toner image formed on the image carrier is transferred onto the intermediate transfer member by superimposing the toner image a plurality of times. The image forming apparatus is characterized in that the neutralization conditions by the intermediate transfer body neutralization unit are switched according to the number of times of image transfer.

In the image forming apparatus according to the present invention, the condition for removing the charge by the intermediate transfer member discharging means is switched in accordance with the number of times of transfer of the toner image from the image carrier to the intermediate transfer member. The surface potential of the intermediate transfer member is increased because the surface potential of the intermediate transfer member is increased, and conversely, when the number of transfers is small, the surface potential of the intermediate transfer member is decreased and the charge removal capability is reduced. By switching the charge elimination conditions in this way, even if the surface potential of the intermediate transfer member before charge elimination varies due to a difference in the number of times of transfer to the intermediate transfer member, the charge of the intermediate transfer member is uniformly removed.

According to a third aspect of the present invention, in the image forming apparatus of the first aspect, whether or not the surface of the intermediate transfer body faces the secondary transfer charge applying means during a charge applying operation is determined.
It is characterized in that the neutralization condition by the intermediate transfer body neutralization means is switched.

In the image forming apparatus according to the third aspect, the condition for removing the charge by the intermediate transfer body discharging means is switched depending on whether or not the surface of the intermediate transfer body faces the secondary transfer charge providing means during the charge providing operation. When facing the secondary transfer charge applying means during the charge applying operation, the surface potential of the intermediate transfer body is high, so that the charge removing capability of the intermediate transfer body charge eliminating means is increased, and conversely, the secondary transfer during the charge applying operation is performed. When not facing the charge applying means, the surface potential of the intermediate transfer member is low, so that the charge removal ability is reduced. By switching the charge elimination conditions in this way, even if the surface potential of the intermediate transfer member before charge elimination varies depending on whether the intermediate transfer member has opposed the secondary transfer charge applying means during the charge application operation, the intermediate transfer member can be used. The transfer member is evenly discharged.

According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the transfer of the intermediate transfer member when the transfer from the intermediate transfer member to the transfer material is performed in accordance with the type of the transfer material. A moving speed control means for switching a speed is provided, and a charge elimination condition of the intermediate transfer body charge elimination means is switched according to a moving speed of the intermediate transfer body.

In the image forming apparatus according to the fourth aspect, the moving speed of the intermediate transfer member when performing the transfer from the intermediate transfer member to the transfer material is switched according to the type of the transfer material, and the transfer speed from the intermediate transfer member to the transfer material is changed. This allows stable transfer of
For example, when the transfer material is thick, the movement speed of the intermediate transfer body is switched to a lower speed. Then, the neutralization condition of the intermediate transfer body discharging means is switched according to the moving speed of the intermediate transfer body. When the moving speed of the intermediate transfer body is high, it is difficult to remove the charge. When the moving speed of the transfer member is low, static elimination is performed at a low price, so that the charge elimination capability of the intermediate transfer member static elimination means is reduced. By switching the charge elimination conditions in this way, even if the surface potential of the intermediate transfer member before charge elimination varies due to the difference in the moving speed of the intermediate transfer member, the charge of the intermediate transfer member is uniformly removed.

According to a fifth aspect of the present invention, in the image forming apparatus of the first, second, third or fourth aspect, the intermediate transfer body static eliminator includes a corona neutralizer to which a voltage having a DC component and an AC component is applied. Preferably, the static elimination condition is a magnitude of a DC component applied to the corona static eliminator.

In the image forming apparatus according to the present invention, the magnitude of the DC component, which is easier to control than the AC component, of the voltage applied to the corona neutralizer used as the intermediate transfer body static elimination means is changed, so that the intermediate transfer is performed. Switches the static elimination conditions for the body.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic color copying machine (hereinafter, referred to as "color copying machine") as an image forming apparatus will be described. FIG. 1 is a schematic configuration diagram of an image forming unit that is a main part of the color copying machine according to the present embodiment. The color copying machine includes, in addition to the image forming unit shown in FIG. 1, a color image reading unit (hereinafter, referred to as a color scanner) (not shown), a paper feeding unit, a control unit, and the like.

The color scanner converts color image information of a document into, for example, Red, Green, Blue (hereinafter, referred to as Red, Green, Blue).
(R, G, B, respectively)) and read out for each color separation light to convert it into an electrical image signal. Then, based on the R, G, and B color separation image signal intensity levels obtained by the color scanner, a color conversion process is performed by an image processing unit (not shown), and Black (hereinafter, referred to as “Bk”), Cyan
(Hereinafter referred to as "C"), Magenta (hereinafter referred to as "C").
"M"), Yellow (hereinafter "Y")
Is obtained.

The image forming section shown in FIG. 1 includes a photosensitive drum 100 as an image carrier and a charger 2 as a charging unit.
00, a photoconductor cleaning device 300 including a cleaning blade and a fur brush, a writing optical unit (not shown) as an exposure unit, a revolver development unit 400 as a development unit, an intermediate transfer unit 500, a paper transfer unit 600, and a fixing roller pair 701. It is composed of the used fixing unit and the like.

The photosensitive drum 100 rotates in the counterclockwise direction indicated by an arrow. Around the photosensitive drum 100, a charger 200, a photosensitive member cleaning device 300, and a revolver developing unit 4 are provided.
00, an intermediate transfer belt 501 as an intermediate transfer member of the intermediate transfer unit 500, and the like are disposed.

The writing optical unit converts the color image data from the color scanner into an optical signal, and writes the optical signal corresponding to the image of the original on the surface of the photosensitive drum 100 uniformly charged by the charger 200. Is performed to form an electrostatic latent image on the photosensitive drum 100. This writing optical unit can be composed of, for example, a semiconductor laser as a light source, a laser emission drive control unit, a polygon mirror and its rotation motor, an f / θ lens, a reflection mirror, and the like.

The revolver developing unit 400
Are a Bk developing device 401 using Bk toner, a C developing device 402 using C toner, and an M developing device 40 using M toner.
3, a Y developing unit 404 using Y toner, a developing revolver driving unit for rotating the entire unit counterclockwise, and the like. Each developing device installed in the revolver developing unit 400 includes a developing sleeve as a developer carrier that rotates by contacting the ears of the developer with the surface of the photosensitive drum 100 to develop an electrostatic latent image; It is composed of a developer paddle that rotates to pump up and agitate the developer, a developing roller driving unit that rotates the developing roller clockwise as indicated by an arrow, and the like.

In the present embodiment, the toner in each developing device is negatively charged by stirring with the ferrite carrier.
A negative DC voltage V is applied to each developing sleeve by a developing bias power source (not shown) as a developing bias applying unit.
A developing bias voltage in which an AC voltage Vac (AC component) is superimposed on dc (DC component) is applied, and the developing sleeve is biased to a predetermined potential with respect to the metal base layer of the photosensitive drum 100.

In a stand-by state of the main body of the color copying machine, the revolver developing unit 400 is stopped at a home position where the Bk developing device 401 is located at the developing position. Starts reading Bk color image data, and optically writes with a laser beam based on the color image data.
The formation of the electrostatic latent image starts (hereinafter, the electrostatic latent image based on the Bk image data is referred to as “Bk electrostatic latent image”, and the same applies to C, M, and Y). Before the front end of the electrostatic latent image reaches the Bk development position to enable development from the front end of the Bk electrostatic latent image, B
The rotation of the k developing sleeve is started, and the Bk electrostatic latent image is developed with the Bk toner. After that, the developing operation of the Bk electrostatic latent image area is continued, but when the rear end of the Bk electrostatic latent image passes the Bk developing position, the developing unit of the next color is promptly moved to the developing position. The revolver developing unit 400 rotates.
This is completed at least before the leading end of the electrostatic latent image based on the next image data arrives.

The intermediate transfer unit 500 includes an intermediate transfer belt 5 as an intermediate transfer member stretched over a plurality of rollers.
01 or the like. Around the intermediate transfer belt 501, a pre-transfer charger (hereinafter, referred to as “PTC”) 502 as a pre-transfer charging unit, and a paper transfer unit 6
00 secondary transfer belts 601 and 2 as transfer material carriers
Secondary transfer bias roller 6 as secondary transfer charge applying means
05, a belt discharging charger 503 as an intermediate transfer body discharging unit, a belt cleaning blade 504 as an intermediate transfer body cleaning unit, a lubricant applying brush 505 as a lubricant applying unit, and the like are arranged to face each other.

The intermediate transfer belt 501 includes a primary transfer bias roller 507 as a primary transfer charge applying means, a belt driving roller 508, a belt tension roller 509,
Next transfer facing roller 510, cleaning facing roller, and belt neutralizing roller 512 as a neutralizing unit before primary transfer
It is stretched over. Each roller is formed of a conductive material,
Each roller other than the primary transfer bias roller 507 is grounded. The primary transfer bias roller 507 is supplied with a transfer bias controlled by a primary transfer power source 801 controlled by a constant current or a constant voltage to a predetermined magnitude of current or voltage in accordance with the number of superimposed toner images. Have been. Further, the intermediate transfer belt 501 is driven in a direction indicated by an arrow by a belt drive roller 508 that is rotationally driven by a drive motor (not shown).

As shown in the sectional view of FIG. 2, the intermediate transfer belt 501 has a surface layer 501a and an intermediate layer 501.
b, a belt material having a multilayer structure composed of a base layer 501c. The outer peripheral surface side contacting the photosensitive drum 100 is the surface layer 501a, and the inner peripheral surface side is the base layer 501c. Further, an adhesive layer 501d for bonding the two layers is interposed between the intermediate layer 501b and the base layer 501c.

In a transfer section for transferring the toner image on the photosensitive drum 100 to the intermediate transfer belt 501 (hereinafter, referred to as “primary transfer section”), the primary transfer bias roller 507 and the belt discharging roller 512 use the intermediate transfer belt 501. Is stretched so as to be pressed against the photosensitive drum 100 side, so that a nip portion having a predetermined width is formed between the photosensitive drum 100 and the intermediate transfer belt 501. Further, a grounded belt neutralization brush 513 as a primary transfer unit neutralization means is brought into contact with the inner peripheral surface of the intermediate transfer belt 501 in the nip portion.

As shown in FIG. 3, the nip width Wn of the primary transfer portion and the distance L from the downstream end of the nip portion in the belt moving direction to the contact position of the belt neutralizing brush 513 are shown.
Is set so that predetermined transfer conditions can be obtained.

The PTC 502 is an intermediate transfer belt 501 transferred from the photosensitive drum 100 in the primary transfer section.
Before transferring the above toner image to transfer paper as transfer material,
The toner image is charged uniformly.

As the belt neutralization charger 503, a discharger to which only an AC voltage or an AC + DC voltage is applied is used. Further, the belt cleaning blade 504 is brought into contact with the intermediate transfer belt 501 in a portion wrapped around the cleaning opposing roller 511 by a counter method, and is brought into contact with the intermediate transfer belt 501 by a separation mechanism (not shown). It is possible to switch the distance from the camera.

The above-described belt static elimination charger 503 and belt cleaning blade 504 are turned on / off as follows.
FF control is performed. For example, in the case of forming one full-color image, after the completion of the secondary transfer, at least until the intermediate transfer belt 501 makes one rotation, the belt neutralization charger 503 is used.
Is turned on to bring the belt cleaning blade 504 into contact. In the case of forming a full-color image repeat, after completion of the secondary transfer, the belt neutralization charger 503 is turned on and the belt cleaning blade 504 is applied until the leading end of the next toner image reaches the neutralization position and the cleaning position, respectively. Contact When one monocolor image is formed, after the primary transfer is completed, at least until the intermediate transfer belt 501 makes one rotation, the belt neutralization charger 503 is turned on, and the belt cleaning blade 504 is brought into contact. Further, in the case of forming a repeat of a monocolor image, after the primary transfer is completed, the belt discharging charger 503 is turned on until the leading end of the next toner image reaches the discharging position and the cleaning position, and the belt cleaning blade 504 is turned on. Abut.

The lubricant applying brush 505 is for polishing zinc stearate 506 as a lubricant formed in a plate shape and applying the polished fine particles to the intermediate transfer belt 501. The lubricant application brush 505 is also configured to be able to contact and separate from the intermediate transfer belt 501, and is controlled so as to contact the intermediate transfer belt 501 at a predetermined timing.

The paper transfer unit 600 includes a secondary transfer belt 60 stretched around three support rollers 602 to 604.
1 and the support roller 6 of the intermediate transfer belt 501.
02, 603 is the secondary transfer facing roller 51
It can be pressed against 0. Three support rollers 6
One of 02 to 604 is a driving roller that is rotationally driven by a driving unit (not shown), and drives the secondary transfer belt 601 in the direction of the arrow in the drawing. The secondary transfer bias roller 605 is disposed so as to sandwich the intermediate transfer belt 501, the transfer paper and the secondary transfer belt 601 between the secondary transfer bias roller 510 and the secondary transfer opposing roller 510. A transfer bias of a predetermined current is applied by a power supply 802. Also, the secondary transfer belt 60
The separation roller (not shown) that drives the support roller 602 and the secondary transfer bias roller 605 so that the primary and secondary transfer bias rollers 605 can take a position where the primary and secondary transfer bias rollers 605 press against the secondary transfer opposing roller 510 and a position where the primary transfer roller 605 separates. A contact mechanism is provided. The secondary transfer belt 60 at the separated position
1 is indicated by a two-dot chain line in FIG. (Hereinafter, margin)

A portion of the secondary transfer belt 601 wrapped around the support roller 603 on the side opposite to the fixing roller is provided with a transfer paper charge 606 as a transfer material charge eliminator and a belt charge eliminator as a transfer material carrier charge eliminator. 60
7 are facing each other. A cleaning blade 608 as a transfer material carrier cleaning unit is in contact with a portion of the secondary transfer belt 601 that is wound around the lower support roller 604 in the drawing.

The transfer paper discharging charger 606 discharges the electric charge held on the transfer paper so that the transfer paper can be separated from the secondary transfer belt 601 by the strength of the transfer paper itself. It is. The belt static eliminator 607 includes a secondary transfer bias roller 605.
The charge remaining on the secondary transfer belt 601 is removed. In addition, the cleaning blade 6
Reference numeral 08 denotes a device that removes and adheres to the surface of the secondary transfer belt 601 for cleaning.

In the above-described color copying machine, when the image forming cycle is started, first, the photosensitive drum 100 is rotated by a drive motor (not shown) in a counterclockwise direction indicated by an arrow, and the intermediate transfer belt 501 is rotated clockwise by an arrow. It is rotated by a driving roller. With the rotation of the intermediate transfer belt 501, Bk toner image formation, C toner image formation, M toner image formation, and Y toner image formation are performed, and finally Bk, C,
A toner image is formed on the intermediate transfer belt 501 in the order of M and Y.

The formation of the Bk toner image is performed as follows. The charger 200 uniformly charges the photosensitive drum 100 with a negative charge to approximately a predetermined potential by corona discharge.
Then, raster exposure is performed by the writing optical unit based on the Bk color image signal. When this raster image is exposed, the exposed portion of the photosensitive drum 100 that is initially uniformly charged loses charge proportional to the amount of exposure light,
A Bk electrostatic latent image is formed. When the negatively charged Bk toner on the Bk developing roller comes into contact with the Bk electrostatic latent image, the toner does not adhere to the portion of the photosensitive drum 100 where the charge remains, and the portion without the charge, that is, the exposure Bk toner is adsorbed on the portion where the toner image is removed, and the Bk toner similar to the electrostatic latent image is used.
A toner image is formed. Then, the Bk toner image formed on the photosensitive drum 100 is transferred to the surface of the intermediate transfer belt 501 that is driven at a constant speed in a state of contact with the photosensitive drum 100. Hereinafter, the transfer of the toner image from the photosensitive drum 100 to the intermediate transfer belt 501 is referred to as “belt transfer”.

A small amount of untransferred residual toner remaining on the surface of the photoconductor drum 100 after the belt transfer is cleaned by the photoconductor cleaning device 300 in preparation for reuse of the photoconductor drum 100.

On the photosensitive drum 100 side, the process proceeds to the C image forming process after the Bk image forming process. At a predetermined timing, reading of C image data by a color scanner is started. A latent image is formed. Then, after the rear end of the previous Bk electrostatic latent image has passed and before the front end of the C electrostatic latent image has reached, the rotating operation of the revolver developing unit is performed, and the C developing device 402 is moved to the developing position. And the C electrostatic latent image is developed with C toner. Thereafter, the development of the C electrostatic latent image area is continued. When the rear end of the C electrostatic latent image passes, the revolver developing unit rotates as in the case of the Bk developing device 401, and the next operation is performed. Is moved to the developing position. This is also completed before the leading end of the next M electrostatic latent image reaches the developing position. Note that, for the M and Y image forming steps, the respective color image data reading,
The operations of forming and developing the electrostatic latent image are the same as those of the above-described processes of BK and C, and the description is omitted.

The Bk, C, M, and Y toner images sequentially formed on the photosensitive drum 100 are transferred onto the intermediate transfer belt 501 while being sequentially aligned on the same surface. As a result, a toner image in which a maximum of four colors are superimposed is formed on the intermediate transfer belt 501. This intermediate transfer belt 50
The superimposed toner image on 1 is uniformly charged by the PTC 502, and then is collectively transferred to transfer paper in the next secondary transfer step.

At the time when the above-described image forming operation is started, the transfer paper is fed from a paper feed unit such as a transfer paper cassette (not shown) or a manual feed tray and stands by at a nip of a pair of registration rollers (not shown). Then, the secondary transfer facing roller 51
When the leading edge of the toner image on the intermediate transfer belt 501 approaches the secondary transfer portion where the nip is formed by the 0 and secondary transfer bias rollers, the registration is performed such that the leading edge of the transfer paper coincides with the leading edge of the toner image. The roller pair is driven, and registration of the transfer sheet with the toner image is performed. Then, the transfer paper is superimposed on the toner image on the intermediate transfer belt 501 and passes through the secondary transfer portion. At this time, the transfer bias formed on the intermediate transfer belt 501 by the transfer bias formed by the transfer bias applied to the secondary transfer bias roller.
The color superimposed toner image is collectively transferred onto the transfer paper. And
The transfer paper is discharged when passing through a portion facing the transfer paper discharging charger 606 disposed downstream of the secondary transfer portion in the secondary transfer belt moving direction, and the intermediate transfer belt 501 is removed.
From the fixing roller pair 701. Then, the toner image is fused and fixed at the nip portion of the fixing roller pair 701, sent out of the apparatus main body by a discharge roller pair (not shown), and stacked face up on a copy tray (not shown) to obtain a full-color copy.

On the other hand, the toner remaining on the surface of the intermediate transfer belt 501 after the transfer of the toner image onto the transfer paper is cleaned by a belt cleaning blade 504 pressed against the intermediate transfer belt 501 by a contact / separation mechanism (not shown).

Here, in the case of a repeat copy, the operation of the color scanner and the image formation on the photosensitive drum 100 follow the image formation process of the fourth sheet (Y) of the first sheet.
At a predetermined timing, the process proceeds to the image forming process for the first color (Bk) of the second sheet. Further, the intermediate transfer belt 501 transfers the second sheet of Bk toner to the area of the surface cleaned by the belt cleaning blade 504 following the batch transfer step of the first sheet of four-color superimposed toner image onto transfer paper. The image is transferred to the belt. Thereafter, the operation is the same as that of the first sheet.

The above is the copy mode for obtaining a four-color full-color copy. However, in the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Become. In the case of the single-color copy mode, only the developing device of the predetermined color of the revolver developing unit 400 is in the developing operation state and the belt cleaning blade 504 is pressed against the intermediate transfer belt 501 until the predetermined number of sheets is completed. The copy operation is performed continuously with the state as it is.

Next, the intermediate transfer belt 5 after the secondary transfer
The control of the belt static elimination charger 503 for neutralizing 01 will be described. FIG. 4 shows the belt static elimination charger 50.
Control unit 900 as control means for controlling the static elimination condition of No. 3
FIG. 3 is a block diagram of a control system configured by the above-described steps. 4, a control unit 900 includes a CPU 901, a ROM 902, an R
An AM 903, an I / O interface 904, and the like.
04, belt drive roller 508 of the intermediate transfer belt 501
Motor 508a connected to the intermediate transfer belt 50
A mark sensor 905 and the like for detecting a rotational position detection mark (not shown) provided on the inner peripheral surface of the device 1 are connected.

As the power supply 804 for removing static electricity, a voltage having a DC component and an AC component is applied to the belt static elimination charger 50.
3 that can be applied. In order to switch the static elimination condition by the belt static elimination charger 503, at least one of the magnitudes of the DC component and the AC component of the applied voltage may be changed. However, in the present embodiment, from the viewpoint of easy control, The control unit 900 switches the magnitude of the DC component.

The ON / OFF timing of the charge removing power supply 804 for applying a voltage to the belt charge removing charger 503 detects a rotational position detecting mark (not shown) provided on the inner peripheral surface of the intermediate transfer belt 501. This is set based on the output signal of the mark sensor 508 to be executed.

FIG. 5 shows the change in the surface potential of the intermediate transfer belt 501 and the change of the belt neutralization charger 503 when the full-color copying operation for superimposing the four color toner images on the intermediate transfer belt 501 is performed twice consecutively. ON / OFF
6 is a time chart illustrating an example of a timing. The upper line in the drawing shows the surface potential of the intermediate transfer belt 501 measured by the potential sensor at the position where the PTC in FIG. 1 is opposed. The surface potential of the portion where the primary transfer of the second, third, and fourth colors is performed. This figure 5
As can be seen from the drawings, each time the primary transfer is performed, a positive charge is applied from the back surface of the intermediate transfer belt 501 from the primary transfer bias roller 507, and the surface potential of the intermediate transfer belt 501 on the photosensitive drum side becomes negative. It is getting bigger. In particular, when the intermediate transfer belt 501 having a relatively high resistance is used as in this embodiment, the charge once applied is likely to be retained on the intermediate transfer belt 501, and the above-mentioned increase in the surface potential is remarkable. As described above, the surface potential of the intermediate transfer belt 501 increases in the negative polarity direction each time the primary transfer is performed, and thus depends on the number of times of the primary transfer, that is, the number of times of superimposing the toner images on the intermediate transfer belt 501. As a result, the surface potential of the intermediate transfer belt 501 varies.

Therefore, in this embodiment, the control unit 90
When 0, the neutralization condition of the belt neutralization charger 503 is switched according to the surface potential of the intermediate transfer belt 501 so that the static electricity can be uniformly eliminated. Specifically, according to the number of superimpositions of the toner image on the intermediate transfer belt 501,
The control is performed so as to switch the magnitude of the DC component of the output voltage of the power supply 803 for static elimination. When the number of times of superimposition of the toner image is large, the DC component is increased to increase the static elimination ability to eliminate the static electricity. When the number of times of superposition of the toner images is small, the DC component is reduced to reduce the charge elimination ability so that the intermediate transfer belt 501 is not charged to the opposite polarity.

When thick paper is used as the transfer paper, the belt drive roller 50
8 to control the intermediate transfer belt 50
The moving speed of No. 1 is switched to almost half that of plain paper. When the moving speed of the intermediate transfer belt 501 is reduced as described above, the charge is easily removed by the belt charge 503. Therefore, in the present embodiment, when the moving speed of the intermediate transfer belt 501 is reduced by executing the thick paper mode,
By setting the DC component of the applied voltage to be smaller than that of plain paper, the charge removal ability is reduced so that the intermediate transfer belt 501 is not charged to the opposite polarity, and the charge is removed.

As described above, according to the present embodiment, even if the surface potential of the intermediate transfer belt 501 before the neutralization of the belt varies due to the difference in the number of times of transfer to the intermediate transfer belt 501, the belt neutralization charger is changed according to the number of transfers. 503
Since the magnitude of the voltage (DC component) applied to the intermediate transfer belt 501 is switched, the intermediate transfer belt 501 can be uniformly discharged. Further, the intermediate transfer belt 50 is executed by executing the thick paper mode.
Even if the surface potential of the intermediate transfer belt 501 before static elimination varies due to the difference in the moving speed, as in the case where the moving speed of the intermediate transfer belt 1 is switched, the intermediate transfer belt 501 can be uniformly neutralized. In this way, the intermediate transfer belt 501 can be uniformly discharged, and can be prepared for the next transfer of the toner image from the photosensitive drum 100.

In the above embodiment, the surface potential of the intermediate transfer belt 501 may vary depending on whether or not the intermediate transfer belt 501 faces the secondary transfer charge applying means during the charge applying operation. In such a case, the magnitude of the voltage (DC component) applied to the belt neutralization charger 503 is switched depending on whether or not the intermediate transfer belt 501 faces the operating secondary transfer charge applying unit. Is preferably uniformly removed.

In particular, without using the relatively high-resistance secondary transfer belt 601 of FIG. 1, a medium-resistance secondary transfer bias roller to which a positive bias voltage is applied and a secondary transfer opposing roller. In the case where the transfer paper is directly held, the absolute value of the surface potential of the image portion on the intermediate transfer belt 510, that is, the portion facing the secondary transfer bias roller to which a predetermined transfer bias is applied is determined by the non-image portion. And the surface potential tends to vary. In this case, depending on whether the image portion faces the secondary transfer bias roller to which the transfer bias is applied or the other non-image portion,
The magnitude of the voltage (DC component) applied to the belt static elimination charger 503 is switched. For example, when the image portion facing the secondary transfer bias roller to which the transfer bias is applied is to be neutralized, the magnitude of the DC voltage applied to the belt neutralization charger 503 is switched so as to be smaller than that of the non-image portion. This switching timing can be performed based on the output signal of the mark sensor 905.

[0055]

EXAMPLES Next, more specific examples of the color copying machine according to the above embodiment will be described. As the intermediate transfer belt 501, an intermediate transfer belt having a thickness of 0.15 mm, a width of 368 mm and an inner peripheral length of 565 mm was used, and the moving speed of the intermediate transfer belt 501 was set to 200 mm / sec.

The surface layer 5 of the intermediate transfer belt 501
01a is formed of an insulating layer having a thickness of about 1 μm, and the intermediate layer 501b is formed of an insulating layer made of PVDF (polyvinylidene fluoride) having a thickness of about 75 μm (volume resistivity: about 10 ¹³ Ωc).
m), and the base layer 501c is made of PVDF (polyvinylidene fluoride) and titanium oxide to a thickness of 75 μm.
m resistance layer (volume resistivity: 10 ⁸ to 10 ¹¹ Ωcm
). When such a volume resistivity of the entire intermediate transfer belt formed of a material was measured, ¹⁰⁷ to
It was ¹² Ωcm. Each of the above volume resistivities is JIS K6
911 using the measuring method described in 911.
For 10 seconds. The surface resistivity of the surface of the intermediate transfer belt 501 on the side of the surface layer 501a is measured by using a resistance measuring device “Hiresta I” manufactured by Yuka Electronics.
P "was 10 ⁷ to 10 ¹² Ω / □. This surface resistivity uses the above-mentioned resistance measuring instrument,
It can also be measured by the surface resistance measurement method described in JIS K 6911.

Further, a nickel-plated metal roller was used as the primary transfer bias roller 507, a metal roller was used as the belt discharging roller 512, and a metal roller or a conductive resin roller was used as the other rollers. The primary transfer bias roller 507 has, for example, 1.0 kV for the first color toner image, 1.3 to 1.4 kV for the second color toner image, and 1.3 kV for the third color toner image. A DC transfer bias of an appropriate magnitude was applied, such as 1.6 to 1.8 kV for the fourth color toner image and 1.9 to 2.2 kV for the fourth color toner image.

The nip width Wn of the primary transfer portion is 1
The distance L from the downstream end of the nip portion in the belt moving direction to the contact position of the belt neutralization brush 513 was set to 7 mm (see FIG. 3). As the belt neutralizing brush 513, a conductive brush having carbon-containing resin fibers implanted was used.

As the PTC 502, a charger with a grid electrode was used. The PTC power supply 803 supplies the PTC 502 to the intermediate transfer belt 50.
A DC bias voltage having the same polarity as the charging polarity of the toner image on No. 1 was applied. More specifically, a constant current controlled DC voltage of -500 μA is applied to the main wire 502a of the PTC 502, and 0 to -3 is applied to the grid electrode 502b.
A DC voltage set within the range of kV was applied.

The DC component of the voltage applied to the belt static elimination charger 503 was set as shown in Table 1 below. The peak-to-peak voltage of the AC component was set to 6 kVp-p, and the frequency was set to 500 Hz. (Hereinafter, margin)

[Table 1]

The secondary transfer bias roller 605
A roller having a surface layer made of conductive sponge or conductive rubber and a core layer made of metal or conductive resin was used, and a transfer bias controlled at a constant current of 10 to 20 μA was applied to this roller. The secondary transfer belt 601 is made of PVDF (polyvinylidene fluoride) with a thickness of 100 μm and a volume resistivity of 10 μm.
A belt material of ¹³ Ωcm was used.

Further, the transfer sheet static elimination charger 606 can be operated by an AC power source alone or an AC +
A discharger to which a DC voltage was applied was used, and a discharger to which only an AC voltage or an AC + DC voltage was applied by a power supply (not shown) was used as the belt static elimination charger 607. Further, the cleaning blade 608 is supported by the support roller 6.
A portion of the secondary transfer belt 601 that was wrapped around 04 was contacted by a counter method. (Hereinafter, margin)

In the above embodiment, an example in which the photosensitive drum 100 is used as the image carrier has been described. However, the present invention can be applied to an image carrier having another shape. For example, the present invention can also be applied to a photosensitive belt that is stretched between two rollers and moves endlessly.

In the above embodiment, the example in which the intermediate transfer belt 501 is used as the intermediate transfer body has been described. However, the present invention can be applied to an apparatus using an intermediate transfer body having another shape. The intermediate transfer belt 50
1, electrical characteristics (volume resistivity, surface resistivity, etc.), thickness,
The structure (single-layer, two-layer,...), Material, material, and the like can be appropriately selected and adopted depending on image forming conditions and the like.

In the above-described embodiment, an example has been described in which a charge elimination brush is used as the primary transfer portion charge eliminating means in the nip portion of the primary transfer portion. , A roller using a member having another shape such as a roller. Further, the position where the charge is removed by the charge removing means is not limited to the position shown in the above embodiment, but may be one position upstream of the primary transfer bias roller 507 in the direction of movement of the intermediate transfer belt.
What is necessary is just to be in the nip part of a next transfer part. Further, the position of static elimination in the nip portion of the primary transfer portion is not limited to one location, and static elimination may be performed at a plurality of locations. Further, in the present embodiment, the charge removing brush is grounded, but a bias having a polarity opposite to the polarity of the transfer charge may be applied in a range that does not affect the transfer charge required for transfer in the nip portion. .

In the above embodiment, an example in which the primary transfer bias roller is used as the primary transfer charge applying means has been described. However, the present invention is directed to an apparatus employing a primary transfer charge applying means having another shape. Can also be applied. Also,
1 such as the above-described neutralizing brush in the moving direction of the intermediate transfer belt;
The primary transfer charge may be applied within the nip of the primary transfer portion as far as the downstream side of the charge removal position by the secondary transfer non-charge removing means.

In the above embodiment, the values of the voltage and current of the primary transfer bias applied to the primary transfer charge applying means such as the primary transfer bias roller 507 are not limited to the above examples. , Can be set to a suitable value according to various image forming conditions.

In the above embodiment, an example was described in which the belt static elimination roller 512 was used as the pre-primary transfer static elimination means. In the present invention, instead of this roller, a member having another shape such as a blade or a brush was used. It can also be applied to things.

In the above embodiment, an example was described in which a secondary transfer bias roller was used as the secondary transfer charge applying means. However, the present invention uses a member of another shape such as a blade or a brush instead of this roller. It can also be applied to what was there.

In the above embodiment, the secondary transfer belt 60 is used as a transfer material carrier for supporting the transfer material in the secondary transfer section.
However, the present invention can be applied to a belt using a member having another shape such as a drum instead of the belt.

In the above embodiment, the photosensitive drum 1
Although the case where the developing device adopting the reversal development method using the two-component developer and having the charging potential of 00 is negative has been described, the present invention is limited to the charging potential of the photosensitive drum 100. In addition, the present invention can be similarly applied to a developer using a one-component developer or a developer employing a regular development method.

[0072]

According to the first, second, third, fourth or fifth aspect of the present invention, even if the surface potential of the intermediate transfer member before static elimination varies, the intermediate transfer member is uniformly discharged, and the next image is removed. There is an effect that it is possible to prepare for the transfer of the toner image from the carrier.

In particular, according to the second aspect of the present invention, even if the surface potential of the intermediate transfer member before static elimination varies due to the difference in the number of times of transfer to the intermediate transfer member, the intermediate transfer member is uniformly discharged. This is effective in preparing for the transfer of the toner image from the image carrier.

In particular, according to the third aspect of the present invention, the surface potential of the intermediate transfer member before static elimination varies depending on whether or not the intermediate transfer member faces the secondary transfer charge applying means during the charge applying operation. Even in this case, there is an effect that the intermediate transfer body can be uniformly discharged to prepare for the transfer of the toner image from the next image carrier.

In particular, according to the fourth aspect of the present invention, even if the surface potential of the intermediate transfer member before static elimination varies due to the difference in the moving speed of the intermediate transfer member, the intermediate transfer member is uniformly discharged, and the next charge is removed. There is an effect that it is possible to prepare for the transfer of the toner image from the image carrier.

In particular, according to the fifth aspect of the present invention, the control of the neutralization of the intermediate transfer member is performed by switching the DC component which is easily controlled among the voltages applied to the corona discharger used as the intermediate transfer member neutralization means. There is an effect that it can be easily performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a color copying machine according to an embodiment.

FIG. 2 is a sectional view of an intermediate transfer belt used in the color copying machine.

FIG. 3 is an enlarged view of a primary transfer unit of the color copying machine.

FIG. 4 is a block diagram of control of a belt static elimination charger in the color copying machine.

FIG. 5 is a time chart showing changes in the surface potential of the intermediate transfer belt and ON / OFF timings of the belt static eliminator;

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 photoconductor drum 500 intermediate transfer unit 501 intermediate transfer belt 502 pre-transfer charger (PTC) 503 belt static eliminator 504 belt cleaning blade 507 primary transfer bias roller 508 belt drive roller 508a drive motor 509 belt tension roller 510 secondary transfer opposing roller 511 Cleaning opposing roller 512 Belt neutralizing roller 513 Belt neutralizing brush 601 Secondary transfer belt 605 Secondary transfer bias roller 801 Primary transfer power supply 802 Secondary transfer power supply 803 Power supply for PTC 804 Power supply for static elimination 900 Control unit 905 Mark sensor

Continued on the front page (72) Inventor Mitsuru Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Katsuya Kawagoe 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Hiroshi Ono 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Toshiaki Motobashi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd.

Claims (5)

[Claims] An intermediate transfer member for carrying a toner image transferred from an image carrier, and a primary transfer member for applying a charge to the intermediate transfer member for transferring a toner image from the image carrier to the intermediate transfer member. Transfer charge applying means, secondary transfer charge applying means for applying a charge for transferring a toner image from the intermediate transfer member to a transfer material to the transfer material or the transfer material carrier, and transferring the toner image to the transfer material An image forming apparatus comprising: an intermediate transfer body discharging unit that discharges the surface of the intermediate transfer body; and a control unit that switches a charge elimination condition by the intermediate transfer body discharging unit in accordance with a surface potential of the intermediate transfer body. An image forming apparatus characterized in that: 2. The image forming apparatus according to claim 1, wherein the toner image formed on the image carrier is transferred onto the intermediate transfer member by superimposing the toner image a plurality of times. An image forming apparatus, wherein the neutralization condition by the intermediate transfer body static elimination means is switched according to the condition. 3. The image forming apparatus according to claim 1, wherein the condition of the charge removal by the intermediate transfer body discharging means depends on whether or not the surface of the intermediate transfer body faces the secondary transfer charge providing means during a charge providing operation. An image forming apparatus, wherein 4. The image forming apparatus according to claim 1, wherein the moving speed of the intermediate transfer body is changed when the transfer from the intermediate transfer body to the transfer material is performed in accordance with the type of the transfer material. An image forming apparatus, comprising: a control unit, wherein a charge elimination condition of the intermediate transfer member charge elimination unit is switched according to a moving speed of the intermediate transfer member. 5. The image forming apparatus according to claim 1, wherein the intermediate transfer body static elimination means uses a corona eliminator to which a voltage having a DC component and an AC component is applied. Is the magnitude of a DC component applied to the corona discharger.