JPH11224003A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device for satisfactorily transferring a toner image to recording material even in the case of using a high-resistance intermediate transfer body by uniformizing a charge on the intermediate transfer body. SOLUTION: As for the image forming device, the intermediate transfer body is provided with a dielectric layer, DC bias V1 and V2 are impressed on a conductive substrate which comes into contact with the intermediate transfer body, and also, a conductive member 115 for uniformizing the charge on the intermediate transfer body is arranged so that it may come into contact with the dielectric layer surface while facing the conductive substrate in the downstream position of intermediate transfer cleaning means 114 and 114a for cleaning the intermediate transfer body in the intermediate transfer body rotating direction, and a DC bias whose voltage is the same as those of the DC bias V1 and V2 is impressed on the conductive member 115.

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, a facsimile or the like, in which a charging means, an image exposing means, a developing means and an intermediate transfer body are arranged around an image forming body.
The present invention relates to an image forming apparatus for temporarily transferring a toner image formed on an image forming body to an intermediate transfer body and then transferring the toner image on the intermediate transfer body to a recording material.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus for a copying machine, a printer, a facsimile, etc., a charging means, an image exposing means, a developing means and an intermediate transfer body are arranged around an image forming body, and the image forming body is charged. A toner image is formed on the image forming body by performing charging by the means, forming a latent image on the image forming body by image exposure by the image exposing means, and developing the latent image by the developing means, and is formed on the image forming body. An image forming apparatus for temporarily transferring a toner image to an intermediate transfer member and then transferring the toner image carried on the intermediate transfer member to a recording material is disclosed in Japanese Patent Application Nos. 7-150293 and 8-4.
No. 6063 discloses this.

[0003]

When the intermediate transfer member is made of a low-resistance member, the resistance of the intermediate transfer member changes due to environmental changes and deterioration of the intermediate transfer member, even if the initial transferability is good.
There is a problem that the toner image on the image forming body is not transferred well. On the other hand, in the image forming apparatus using the above-described intermediate transfer body, if the intermediate transfer body is formed of a member having a high resistance, the intermediate transfer body has preferable transfer characteristics that are hardly affected by environmental characteristics and a transfer material. Since a discharge with the image forming body occurs due to the applied DC bias at the time, electric charges remain non-uniformly on the intermediate transfer body, causing transfer unevenness at the next transfer,
There is a problem that the toner image on the image forming body is not transferred well.

In general, regardless of whether a high-resistance roller-shaped member or a belt-shaped member is used as the intermediate transfer member, the amount of charge on the front and back of the intermediate transfer member may be different due to discharge at the time of transfer, or partially. As a result, the toner image on the image forming body is not transferred well.

The present invention solves the above-mentioned problems and makes the electric charge on the intermediate transfer member uniform so that the toner image on the recording material can be formed even on a high-resistance intermediate transfer member which is not easily affected by a change in resistance. It is an object of the present invention to provide an image forming apparatus capable of performing good transfer of an image.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to dispose a charging means, an image exposing means, a developing means and an intermediate transfer member around an image forming body, and to charge the image forming body by the charging means, Forming a latent image on the image forming body by image exposure of the exposing means and developing the latent image by the developing means to form a toner image on the image forming body, and forming the toner image on the image forming body In an image forming apparatus for temporarily transferring a toner image to the intermediate transfer body and then transferring the toner image carried on the intermediate transfer body to a recording material, the intermediate transfer body has a dielectric layer, A bias is applied to the conductive substrate that is in contact with the intermediate transfer body, and the intermediate transfer body cleaning unit that cleans the intermediate transfer body faces the conductive base at a position downstream of the intermediate transfer body in the rotation direction of the intermediate transfer body. Said The collector layer surface contact, placing the conductivity of the conductive member to equalize the charge of the intermediate transfer member,
An image forming apparatus is characterized in that a DC bias having the same voltage as the DC bias is applied to the conductive member.

[0007]

Embodiments of the present invention will be described below. The description of the present application does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope.

First Embodiment An image forming process and each mechanism of an image forming apparatus according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional configuration diagram of a color image forming apparatus showing a first embodiment of the image forming apparatus according to the present invention, and FIG. 2 is an enlarged view of the intermediate transfer member of FIG. An intermediate transfer roller composed of a roller-shaped member is used as the intermediate transfer member of the present embodiment.

According to FIG. 1 or FIG. 2, a photosensitive drum 10 as an image forming body is provided with a transparent conductive material around a cylindrical base formed of a transparent member such as optical glass or transparent acrylic resin. A photosensitive layer such as a layer, an a-Si layer or an organic photosensitive layer (OPC) is formed, and is rotated clockwise as indicated by an arrow in FIG. 1 with the conductive layer grounded.

According to the present invention, in the photoconductor layer of the photosensitive drum, which is the image forming point of the exposure beam for image exposure, an appropriate contrast is given to the light attenuation characteristic (photocarrier generation) of the photoconductor layer. It is sufficient that the exposure light amount has a wavelength that can be obtained. Therefore, the light transmittance of the light-transmitting substrate of the photosensitive drum in the present embodiment does not need to be 100%, but may be such that a certain amount of light is absorbed when the exposure beam is transmitted. Should just provide an appropriate contrast. Acrylic resin,
In particular, those obtained by polymerization using a methacrylic acid methyl ester monomer are preferably used because they are excellent in light transmission, strength, precision, surface properties, etc., but are used for other general optical members such as acrylic, fluorine, polyester, polycarbonate, Various translucent resins such as polyethylene terephthalate can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. As the light-transmitting conductive layer, indium tin oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, Au, Ag, N
A light-transmissive metal thin film made of i, Al, or the like is used. As a film forming method, a vacuum deposition method, an active reactive deposition method,
Various sputtering methods, various CVD methods, dip coating methods, spray coating methods, and the like are used. Various organic photosensitive layers (OPC) are used as the photoconductor layer.

A scorotron charger 11, which is a charging unit for each color, an exposure optical system 12, which is an image exposure unit for each color, and a developing unit 13, which is a developing unit for each color, form a set of yellow (Y) , Magenta (M), cyan (C)
4 for the image forming process of each color of black and black (K)
A set is provided and arranged in the order of Y, M, C, and K with respect to the rotation direction of the photosensitive drum 10 indicated by the arrow in FIG.

A scorotron charger 11, which is a charging means for each color, has a control grid maintained at a predetermined potential and a discharge electrode 11a composed of, for example, a saw-tooth electrode, and faces the photosensitive layer of the photosensitive drum 10. And installed
The charging operation (in the present embodiment, negative charging) is performed by corona discharge having the same polarity as that of the toner.
A uniform potential is given to 0. As the discharge electrode 11a, a wire electrode or a needle electrode may be used.

An exposure optical system 12 serving as an image exposure means for each color.
Indicates that the exposure position on the photosensitive drum 10 is different from that of the scorotron charger 11 for each color described above.
Photosensitive drum 1 so as to be located on the downstream side in the rotation direction of
0. Each exposure optical system 12
A linear exposure element in which a plurality of LEDs (light emitting diodes) as light emitting elements of image exposure light arranged in the main scanning direction in parallel with the drum axis are arranged, and a light converging light transmission as an imaging element. An exposure unit including a body (trade name: Selfoc lens array), which is attached to the holding member 20. The exposure optical system 12 for each color performs image exposure of the photosensitive layer of the photosensitive drum 10 from the back side in accordance with image data of each color read by a separate image reading device and stored in the memory, and electrostatically exposes the photosensitive layer on the photosensitive drum 10. Form a latent image. As the exposure element, in addition to an LED, an element in which a plurality of light emitting elements such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array can be used. The emission wavelength of the image exposure light emitting element is usually 7 that is highly transparent to Y, M, and C toners.
Although a wavelength in the range of 80 to 900 nm is used, in this embodiment, since the image is exposed from the back surface, a shorter wavelength of 400 to 780 nm, which does not have sufficient transparency to the color toner, may be used.

A developing unit 13 as a developing means for each color keeps a predetermined gap with respect to the peripheral surface of the photosensitive drum 10 and rotates in a forward direction with respect to the rotating direction of the photosensitive drum 10, for example, 0.5 to 1 mm in thickness. A developing sleeve 131 formed of a non-magnetic stainless steel or aluminum material having an outer diameter of 15 to 25 mm, and a developing casing 138. Inside the developing casing 138, yellow (Y) and magenta are provided, respectively. (M), one-component or two-component developer of cyan (C) and black (K). Each developing unit 1
Reference numeral 3 denotes a developing bias in which a DC voltage and an AC voltage are superimposed on the developing sleeve 131 and is kept in non-contact with the photosensitive drum 10 by a contact roller (not shown) with a predetermined gap, for example, 100 to 500 μm. When applied, non-contact reversal development is performed, and a toner image is formed on the photosensitive drum 10.

The fixing device 17 as a fixing means is composed of two roller-shaped fixing members, ie, a fixing roller 17a and a pressure roller 17b, and includes a fixing roller 17a and a pressure roller 17b.
The toner image on the recording paper P is fixed by applying heat and pressure at the nip T between the two.

Intermediate transfer roller 140 as an intermediate transfer member
For example, a silicone rubber having a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm as an elastic layer having a thickness of 1 to 5 mm is formed on the outer periphery of a metal roller 141 as a conductive base using a metal member such as an aluminum material or a stainless material. Provided with a thickness of 1 to
It is a soft roller provided with a dielectric layer 142 of, for example, a fluororesin tube or a fluororesin coat having a volume resistivity of 10 ¹² to 10 ¹⁶ Ω · cm at 10 μm.

An intermediate transfer member cleaning device 114, which is an intermediate transfer member cleaning means, is provided in contact with the photosensitive drum 10, and has an intermediate transfer member cleaning blade 114a whose leading end is always in contact with the intermediate transfer roller 140. The transfer residual toner on the intermediate transfer roller 140 is cleaned by the intermediate transfer body cleaning blade 114a.

The conductive brush 115, which is a conductive member, is connected to the intermediate transfer roller 14 of the intermediate transfer body cleaning device 114.
0, the intermediate transfer body cleaning device 11
4, is always in contact with the intermediate transfer roller 140, and makes the charge on the intermediate transfer roller 140 uniform by applying a bias voltage described later.

The transfer roller 150 is an intermediate transfer roller 140
And a metal roller 15 as a conductive substrate using a metal member such as an aluminum material or a stainless steel material.
A volume resistivity of 1 ⁶ to 10 μm and a volume resistivity of 10 ⁶ to 1
It is a hard roller provided with a resistance layer 152 of, for example, a silicon tube or a fluorine resin coat of 0 ¹² Ω · cm.

Next, the image forming process will be described.

The photosensitive drum 10 is rotated clockwise as indicated by an arrow in FIG. 1 by starting a photosensitive member driving motor (not shown) at the start of image recording, and at the same time, is exposed to light by the charging action of a yellow (Y) scorotron charger 11. Body drum 1
Application of a potential to 0 starts.

The latent image is reversely developed in a non-contact state by a Y developing unit 13, and a yellow (Y) toner image is formed on the photosensitive drum 10.

Next, a potential is applied to the photosensitive drum 10 from above the Y toner image by the charging action of a magenta (M) scorotron charger 11, and a second color signal, that is, an M color signal, is applied by an M exposure optical system 12. Image writing is performed by an electric signal corresponding to the image data, and the magenta (M) toner image is superimposed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13. It is formed.

According to the same process, the cyan (C) toner image corresponding to the third color signal is further superimposed by the cyan (C) scorotron charger 11, the exposure optical system 12 of C, and the developing device 13 of C. The black (K) toner image corresponding to the fourth color signal is sequentially superimposed thereon by a black (K) scorotron charger 11, a K exposure optical system 12, and a K developing device 13. A superposed color toner image of four colors of yellow (Y), magenta (M), cyan (C), and black (K) is formed on the peripheral surface within one rotation of the photosensitive drum 10. .

These Y, M, C and K exposure optical systems 12
Image writing on the photosensitive layer of the photosensitive drum 10 is performed from the inside of the drum through the above-described translucent substrate. Therefore, the writing of the images corresponding to the second, third and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. Can be formed.

The color toner image formed on the peripheral surface of the photosensitive drum 10 is once transferred onto the peripheral surface of the intermediate transfer roller 140.

The intermediate transfer roller 140 constitutes a first transfer position at a position where the intermediate transfer roller 140 is pressed against the peripheral surface of the photosensitive drum 10, and is driven in a counterclockwise direction so that the peripheral speed matches the drum. Is applied with a DC bias V1 of opposite polarity (positive polarity in the present embodiment), for example, 1000 to 2000 V, so that the toner image is transferred to the peripheral surface.

The toner image transferred onto the peripheral surface of the intermediate transfer roller 140 is then sent out by a transfer roller 150 serving as a transfer member from a paper feed cassette 15 serving as a recording material storage means by a feed roller 15a, and fed with a recording material. The recording paper P which is conveyed to the timing roller 15b and is fed in synchronization with the toner image of the intermediate transfer roller 140 by the driving of the timing roller 15b is pinched, and is transferred from the intermediate transfer roller 15 onto the recording paper P. You. That is, the transfer roller 150, which is a hard roller, is driven and rotated by forming a second transfer position having a nip at a position in contact with the peripheral surface of the intermediate transfer roller 140, which is a soft roller. A toner image on the intermediate transfer roller 140 is transferred onto the recording paper P by applying a DC bias V2 of 1500 to 3000 V higher than the applied DC bias V1. By setting the DC bias V2 to be higher, the transfer of the toner image from the intermediate transfer roller 140 to the recording paper P is performed favorably.

The recording paper P to which the toner image has been transferred is discharged by the discharge needle 91 and is separated from the peripheral surface of the intermediate transfer roller 140, and is fixed via the transport belt 16 to the fixing device 17.
Roller 17 which is a roller-shaped fixing member
A toner image is fixed by applying heat and pressure at a nip portion T between a and the pressure roller 17b. The recording paper P on which the toner image has been fixed is discharged to the outside of the apparatus by a discharge roller 18.

The toner remaining on the peripheral surface of the intermediate transfer roller 140 after the transfer is provided opposite the intermediate transfer roller 140 and has an intermediate transfer member cleaning blade 114a which is always in contact with the intermediate transfer roller 140. Intermediate transfer member cleaning device 114 as a cleaning unit
Cleaning.

The intermediate transfer roller 140 cleaned by the intermediate transfer member cleaning device 114 is disposed downstream of the intermediate transfer roller 140 in the rotation direction and close to the intermediate transfer member cleaning device 114.
The charge on the intermediate transfer roller 140 is made uniform by the conductive brush 115 which is always in contact with the toner, thereby improving the transfer of the next toner image. At this time, a DC bias voltage having the same value as the DC bias V1 applied to the intermediate transfer roller 140 is applied to the conductive brush 115. In other words, a DC bias having the same value is applied to the metal roller 141 as the conductive base of the intermediate transfer roller 140 and the conductive brush 115 with the dielectric layer 142 of the intermediate transfer roller 140 interposed therebetween.

Further, as shown in FIG.
For example, the frequency is 1 to 10 kHz, V _PP is 500 V
It is preferable to apply a bias voltage on which the AC bias AC1 of 2 kV is superimposed. If necessary, an AC bias AC1 may be superimposed on a different power supply from the DC bias V1 applied to the intermediate transfer roller 140, and a grounded bias voltage may be applied to the conductive brush 115. Since the DC bias V1 is used in transfer, 1000 to 2000 V of the opposite polarity (positive polarity in the present embodiment) to the toner is applied. DC bias V applied to metal roller 141
By applying a bias voltage having the same value as 1 to the conductive brush 115 having a resistance per 1 cm ² area of 10 ⁶ to 10 ¹⁰ Ω / cm ² , the volume resistivity of the intermediate transfer roller 140 becomes 1
The electric charge on the front and back surfaces of the dielectric layer 142, which has a high resistance of 0 ¹² to 10 ¹⁶ Ω · cm and is likely to be non-uniform, is made uniform to have the same potential. Thus, the transfer of the toner image from the photosensitive drum 10 to the intermediate transfer roller 140 is favorably performed. The bias voltage is the same as the bias voltage up to the surface of the intermediate transfer roller 140, so that it is less likely to be adversely affected by the change in resistance of the dielectric layer 142 due to environmental conditions or deterioration. In addition, the repetition of the discharge of the AC bias AC <b> 1 makes the electric charges more uniform and the same electric potential, so that the transfer of the toner image from the photosensitive drum 10 to the intermediate transfer roller 140 is performed favorably.

The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is transferred to a cleaning device 19 which is an image forming member cleaning means or a cleaning blade 19a made of a rubber material abutting the photosensitive drum 10. And is collected by a screw 19b in a waste toner container (not shown). The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is charged by the Y scorotron charger 11, and enters the next image forming cycle.

The transfer roller 150 is cleaned by the cleaning device 310 to remove stains due to toner adhesion and the like, and keeps the recording paper P clean.

As described above, the electric charge on the intermediate transfer body is made uniform, the resistance is hardly changed, and the transfer of the toner image from the intermediate transfer body to the recording material is performed well.

In particular, by using an AC bias superimposed on the conductive member, the charge on the intermediate transfer member can be made more uniform, and the transfer of the toner image from the intermediate transfer member to the recording material can be improved. Done in

Second Embodiment An image forming process and each mechanism of an image forming apparatus according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a sectional configuration view of a color image forming apparatus showing a second embodiment of the image forming apparatus according to the present invention, and FIG. 4 is an enlarged view of the intermediate transfer member of FIG. As the intermediate transfer member of the present embodiment, an intermediate transfer belt including a belt-shaped member is used. In the following description of the embodiment, the surface of the recording material on the side facing the image forming body in the transfer area is the front surface, and the surface of the other side of the recording material, that is, the surface of the recording material on the side facing the intermediate transfer body is the back surface. The image transferred to the front surface of the recording material is called a front image, and the image transferred to the back surface of the recording material is called a back image. Also, the image forming apparatus in the present embodiment will be described as an image forming apparatus using a two-sided image forming method, but the present invention is not limited to a two-sided image forming but uses a belt-shaped member as an intermediate transfer member. This applies to, for example, the image forming apparatus of the first embodiment in which the intermediate transfer roller is replaced with an intermediate transfer belt. The members having the same functions and configurations as those described in the first embodiment are denoted by the same reference numerals.

According to FIG. 3 or FIG. 4, the photosensitive drum 10, which is an image forming body, is provided with a transparent conductive material on the outer periphery of a cylindrical base formed of a transparent member such as optical glass or transparent acrylic resin. A photosensitive layer such as a layer, an a-Si layer or an organic photosensitive layer (OPC) is formed, and is rotated clockwise as indicated by an arrow in FIG. 1 with the conductive layer grounded.

According to the present invention, in the photoconductor layer of the photosensitive drum, which is the image forming point of the exposure beam for image exposure, an appropriate contrast is given to the light attenuation characteristics (photocarrier generation) of the photoconductor layer. It is sufficient that the exposure light amount has a wavelength that can be obtained. Therefore, the light transmittance of the light-transmitting substrate of the photosensitive drum in the present embodiment does not need to be 100%, but may be such that a certain amount of light is absorbed when the exposure beam is transmitted. Should just provide an appropriate contrast. Acrylic resin,
In particular, those obtained by polymerization using a methacrylic acid methyl ester monomer are preferably used because they are excellent in light transmission, strength, precision, surface properties, etc., but are used for other general optical members such as acrylic, fluorine, polyester, polycarbonate, Various translucent resins such as polyethylene terephthalate can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. As the light-transmitting conductive layer, indium tin oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, Au, Ag, N
A light-transmissive metal thin film made of i, Al, or the like is used. As a film forming method, a vacuum deposition method, an active reactive deposition method,
Various sputtering methods, various CVD methods, dip coating methods, spray coating methods, and the like are used. Various organic photosensitive layers (OPC) are used as the photoconductor layer.

A scorotron charger 11, which is a charging unit for each color, an exposure optical system 12, which is an image exposure unit for each color, and a developing unit 13, which is a developing unit for each color, form a set of yellow (Y) , Magenta (M), cyan (C)
4 for the image forming process of each color of black and black (K)
A set is provided and arranged in the order of Y, M, C, and K with respect to the rotation direction of the photosensitive drum 10 indicated by the arrow in FIG.

The scorotron charger 11, which is a charging means for each color, has a control grid maintained at a predetermined potential and a discharge electrode 11a composed of, for example, a sawtooth electrode, and faces the photosensitive layer of the photosensitive drum 10. And installed
The charging operation (in the present embodiment, negative charging) is performed by corona discharge having the same polarity as that of the toner.
A uniform potential is given to 0. As the discharge electrode 11a, a wire electrode or a needle electrode may be used.

Exposure optical system 12 as image exposure means for each color
Indicates that the exposure position on the photosensitive drum 10 is different from that of the scorotron charger 11 for each color described above.
Photosensitive drum 1 so as to be located on the downstream side in the rotation direction of
0. Each exposure optical system 12
A linear exposure element in which a plurality of LEDs (light emitting diodes) as light emitting elements of image exposure light arranged in the main scanning direction in parallel with the drum axis are arranged, and a light converging light transmission as an imaging element. An exposure unit including a body (trade name: Selfoc lens array), which is attached to the holding member 20. The holding member 20 has an exposure optical system 12 for each color.
In addition, a transfer simultaneous exposure unit 12d and a uniform exposure unit 12e are mounted, and housed integrally inside the light-transmitting base of the photosensitive drum 10. The exposure optical system 12 for each color performs image exposure of the photosensitive layer of the photosensitive drum 10 from the back side in accordance with image data of each color read by a separate image reading device and stored in the memory, and electrostatically exposes the photosensitive layer on the photosensitive drum 10. Form a latent image. As an exposure element, besides LED, FL (phosphor emission), EL (electroluminescence), PL
It is also possible to use a plurality of light-emitting elements such as (plasma discharge) arranged in an array. The emission wavelength of the image exposure light emitting element usually ranges from 780 to 900 nm, which is highly transparent to the Y, M, and C toners.
In this embodiment, since the image is exposed from the back surface, the wavelength may be shorter than 400 to 780 nm, which does not have sufficient transparency to the color toner.

The developing device 13 as a developing means for each color keeps a predetermined gap with respect to the peripheral surface of the photosensitive drum 10 and rotates in the forward direction with respect to the rotation direction of the photosensitive drum 10, for example, 0.5 to 1 mm in thickness. And a developing casing 131 formed of a cylindrical nonmagnetic stainless steel or aluminum material having an outer diameter of 15 to 25 mm, and a developing casing 138. Inside the developing casing 138, yellow (Y) and magenta ( M), cyan (C) and black (K) one-component or two-component developers. Each developing unit 13
Is maintained in a non-contact state with the photosensitive drum 10 with a predetermined gap, for example, 100 to 500 μm, by an abutting roller (not shown), and applies a developing bias in which a DC voltage and an AC voltage are superimposed on the developing sleeve 131. By doing
Non-contact reversal development is performed to form a toner image on the photosensitive drum 10.

Intermediate transfer belt 240 as an intermediate transfer member
For example, a high resistivity volume resistivity using engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, and nylon alloy is 10 ¹² to 10 ¹⁶ Ω · c.
The thickness 1 shown by the bold line in FIG.
This is an endless belt coated with a high-resistance fluororesin having a volume resistivity of the same resistance as that of the dielectric layer 242 of 10 to 10 μm and a resistance of 10 ¹² to 10 ¹⁶ Ω · cm. The intermediate transfer belt 240 is stretched in contact with a driving roller 14d, a ground roller 14j, a driven roller 14e, a guide roller 251 and a tension roller 14i which are roller members, and is rotated counterclockwise as indicated by an arrow in FIG. You. In accordance with the rotation direction of the intermediate transfer belt 240, the driven roller 14e, the ground roller 14j, the drive roller 14d, the tension roller 14i, and the guide roller 251 are provided in this order, and the driven roller 14e, the ground roller 14j, the drive roller 14d, and the guide roller 251 are provided.
Is fixedly rotated, movably supported by elastic force of a spring or the like (not shown), and tension roller 14i is rotated by stretching intermediate transfer belt 240. A drive roller 14d which is a roller member driven by a drive motor (not shown)
Is rotated to drive and rotate the intermediate transfer belt 240. The rotation of the intermediate transfer belt 240 causes the ground roller 14j, the driven roller 14e, the guide roller 251 and the tension roller 14i to be driven and rotated. The slack of the rotating intermediate transfer belt 240 is tightened by the tension roller 14i. The recording paper P is separated by curvature separation at a curvature portion KT at the end of the intermediate transfer belt 240 stretched around the driving roller 14d on the fixing device 17 side. The ground roller 14j is provided between a first transfer unit described later and the drive roller 14d. The guide roller 251 is formed of a conductive roller member using a metal member such as an aluminum material or a stainless steel material.

The transfer device 14c, which is a first transfer means, is a corona discharge device provided to face the photosensitive drum 10 with the intermediate transfer belt 240 interposed therebetween.
A transfer area 14b is formed between the photoconductor drum 10 and the photosensitive drum 10. A DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied to the transfer device 14c, and the toner image on the photosensitive drum 10 is transferred onto the intermediate transfer belt 240 or the surface of the recording paper P as a recording material. Transcribe.

The back transfer device 14g, which is the second transfer means, is preferably constituted by a corona discharger, and is a conductive ground roller 14 grounded with the intermediate transfer belt 240 interposed therebetween.
j, a DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied to transfer the toner image on the intermediate transfer belt 240 to the back surface of the recording paper P.

The paper charger 14k, which is a recording material charging means, is preferably constituted by a corona discharger, is provided opposite to the driven roller 14e which is grounded with the intermediate transfer belt 240 interposed, and has the same polarity as the toner (this embodiment). (In the embodiment, a negative polarity) is applied, and the recording paper P is charged and attracted to the intermediate transfer belt 240.

Paper separation AC static eliminator 1 as recording material separating means
Reference numeral 4h is preferably formed of a corona discharger, and is provided at an end of the intermediate transfer belt 240 on the side of the fixing device 17 so as to face the conductive drive roller 14d grounded with the intermediate transfer belt 240 interposed therebetween, as necessary. An AC voltage in which a DC voltage having the same polarity or opposite polarity to the toner is superimposed is applied, and the recording paper P conveyed by the intermediate transfer belt 240 is neutralized to separate the recording paper P from the intermediate transfer belt 240.

The transport section 160 is provided between the intermediate transfer belt 240 and the fixing device 17, and a spur 162 as a spur member is provided on the upper surface of the transport section 160. Spur 162
Scoops up the leading end of the recording paper P separated by the curvature of the curvature portion KT and the static elimination of the paper separating AC static eliminator 14h provided as necessary, and guides the recording paper P by guiding the back side of the recording paper P. The recording paper P is conveyed to the fixing device 17 while preventing the rear toner image of the recording paper P having the toner image on the rear surface from being disturbed, and keeping the entering direction to the fixing device 17 constant.

The fixing device 17 as a fixing means is composed of two roller-shaped fixing members, a fixing roller 17a and a pressure roller 17b.
The toner image on the recording paper P is fixed by applying heat and pressure at the nip T between the two.

The intermediate transfer member cleaning device 214, which is an intermediate transfer member cleaning means, has an intermediate transfer member cleaning blade 214a that can be brought into and out of contact with the intermediate transfer belt 240 at the tip using a support shaft 214b as a fulcrum. Then, the transfer residual toner on the intermediate transfer belt 240 is cleaned by the intermediate transfer body cleaning blade 214a.

Conductive brush 2 as a conductive member
Reference numeral 15 denotes an intermediate transfer member cleaning device 214 provided downstream of the intermediate transfer roller 140 in the rotation direction of the intermediate transfer roller 140 and close to the intermediate transfer member cleaning device 214, and synchronized with the contact and release of the intermediate transfer member cleaning blade 214a. The intermediate transfer belt 240 can be brought into contact with and released from contact with the intermediate transfer belt 240.
The above charge is made uniform.

Next, the image forming process will be described.

The photosensitive drum 10 is rotated clockwise as indicated by an arrow in FIG. 1 by starting a photosensitive member driving motor (not shown) at the start of image recording, and at the same time, is exposed to light by the charging action of a yellow (Y) scorotron charger 11. Body drum 1
Application of a potential to 0 starts.

After the photosensitive drum 10 is applied with a potential, the Y exposure optical system 12 starts image exposure (image writing) using a first color signal, that is, an electric signal corresponding to the Y image data, and exposes the photosensitive drum. An electrostatic latent image corresponding to the Y image of the document image is formed on the surface of the body drum 10.

The latent image is reversely developed by the Y developing device 13 in a non-contact state, and a yellow (Y) toner image is formed on the photosensitive drum 10.

Next, a potential is applied to the photosensitive drum 10 from above the Y toner image by the charging action of the magenta (M) scorotron charger 11, and the second color signal, that is, the M color signal, is applied by the M exposure optical system 12. Image writing is performed by an electric signal corresponding to the image data, and the magenta (M) toner image is superimposed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13. It is formed.

By the same process, the cyan (C) toner image corresponding to the third color signal is further superimposed by the cyan (C) scorotron charger 11, the exposure optical system 12 of C, and the developing device 13 of C. The black (K) toner image corresponding to the fourth color signal is sequentially superimposed thereon by a black (K) scorotron charger 11, a K exposure optical system 12, and a K developing device 13. A superposed color toner image of four colors of yellow (Y), magenta (M), cyan (C), and black (K) is formed on the peripheral surface within one rotation of the photosensitive drum 10. .

These Y, M, C and K exposure optical systems 12
Image writing on the photosensitive layer of the photosensitive drum 10 is performed from the inside of the drum through the above-described translucent substrate. Therefore, the writing of the images corresponding to the second, third and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. Can be formed.

In the transfer area 14b, the superimposed color toner image serving as the back surface image formed on the photosensitive drum 10 as the image forming body by the image forming process is formed.
The images are collectively transferred onto an intermediate transfer belt 240 as an intermediate transfer member by a transfer device 14c as a first transfer unit. At this time, uniform exposure may be performed by the simultaneous transfer exposure device 12d provided inside the photoconductor drum 10 so that good transfer is performed.

After the toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the photosensitive drum AC static eliminator 16, the toner is transferred to a cleaning device 19 which is an image forming body cleaning means, The toner is cleaned by a cleaning blade 19a made of a rubber material in contact with the toner, and collected by a screw 19b in a toner discharge container (not shown). Further, the peripheral surface of the photosensitive drum 10
For example, a uniform exposure device 12 before charging using a light emitting diode
The history of the photosensitive drum 10 in the previous image formation is eliminated by the exposure by e.

After the superimposed color toner image serving as the back surface image is formed on the intermediate transfer belt 240 as described above, the front surface image is continuously formed on the photosensitive drum 10 in the same manner as the above-described color image forming process. Is formed. At this time, the photosensitive drum 1
The image data is changed so that the front side image formed on 0 is a mirror image of the back side image formed on the photosensitive drum 10.

With the formation of a surface image on the photosensitive drum 10, recording paper P as a recording material is sent out from a paper feed cassette 15 as a recording material storage means by a feed roller 15a, and is used as a recording material feeding means. Timing roller 1
5b, and the timing roller 15b is driven to synchronize the color toner image of the front surface image carried on the photosensitive drum 10 with the color toner image of the rear surface image carried on the intermediate transfer belt 240. Transfer area 14
b. At this time, the fed recording paper P is charged to the same polarity as the toner by a paper charger 14k which is a recording material charging means provided on the front side of the recording paper P, and is attracted to the intermediate transfer belt 240 to transfer the recording area. 14b. By charging the paper with the same polarity as the toner, the toner image is prevented from being attracted to the toner image on the intermediate transfer belt 240 and the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed. The voltage is applied to the paper charger 14k as the recording material charging means only when the recording paper P is being fed, and the voltage applied to the paper charger 14k is cut off simultaneously with the passage of the recording paper P. You. In addition to the corona discharger, a paper charging brush or a paper charging roller capable of making contact with and releasing contact with the intermediate transfer belt 240 can be used as the paper charger 14k.

In the transfer area 14b, a first voltage to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied.
The surface image on the photosensitive drum 10 is collectively transferred onto the surface of the recording paper P by the transfer device 14c as a transfer means. At this time, the back surface image on the intermediate transfer belt 240 is present on the intermediate transfer belt 240 without being transferred to the recording paper P. At the time of transfer by the transfer device 14c, the photosensitive drum 10 is opposed to the transfer area 14b so that good transfer is performed.
A uniform exposure may be performed by a simultaneous transfer exposure device 12d using, for example, a light emitting diode provided inside the device.

The recording paper P on which the color toner image has been transferred to the front surface is conveyed to a back transfer device 14g as a second transfer means to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied. Then, the back surface image on the peripheral surface of the intermediate transfer belt 240 is collectively transferred to the back surface of the recording paper P by the back surface transfer device 14g.

The recording paper P on which the color toner images are formed on both sides is formed by a curvature of a curvature portion KT of the intermediate transfer belt 240 and a paper as a recording material separating means provided at an end of the intermediate transfer belt 240 as necessary. Due to the charge removing action of the separation AC charge remover 14h, the sheet is separated from the intermediate transfer belt 240, and is conveyed to a fixing device 17 as a fixing unit through a spur 162 provided in the conveying unit 160, where the fixing roller 17a and the pressure roller 17b are separated. The toner image on the recording paper P is fixed by applying heat and pressure in the nip portion T between them.
The recording paper P on which double-sided image recording has been performed is sent upside down, and is discharged by a discharge roller 18 to a tray outside the apparatus. Further, as shown by the dashed line in FIG.
A switching member (not shown) may be provided at the outlet of the apparatus, and the sheet may be discharged to a tray outside the apparatus without turning over.

The toner remaining on the peripheral surface of the intermediate transfer belt 240 after the transfer is provided to face the guide roller 251 to which a DC bias V3 of, for example, 1000 to 2000 V is applied, with the intermediate transfer belt 240 interposed therebetween. Support shaft 214
intermediate transfer member cleaning blade 214a capable of contacting and releasing contact with intermediate transfer belt 240 using b as a rotation fulcrum
The cleaning is performed by an intermediate transfer member cleaning device 214 which is an intermediate transfer member cleaning unit having

The intermediate transfer belt 240 cleaned by the intermediate transfer member cleaning device 214 is located downstream of the intermediate transfer belt 240 in the rotation direction.
0, is opposed to the conductive guide roller 251 to which the DC bias V3 of 1000 to 2000 V is applied, is disposed close to the intermediate transfer body cleaning device 214, and contacts the intermediate transfer body cleaning blade 214a. In addition, the electric charge on the intermediate transfer belt 240 is made uniform by the conductive brush 215 which can be brought into contact with and released from the intermediate transfer belt 240 in synchronization with the release of the contact, thereby improving the transfer of the next toner image. At this time, the conductive brush 215 includes
A DC bias voltage having the same value as the DC bias V3 applied to the intermediate transfer belt 240 is applied. That is,
The conductive guide roller 2 sandwiching the intermediate transfer belt 240
DC bias V3 of the same value is applied to 51 and conductive brush 215.

Further, as shown in FIG.
For example, the frequency is 1 to 10 kHz, V _PP is 500 V
It is preferable to apply a bias voltage on which an AC bias AC2 of 2 kV is superimposed. If necessary, an AC bias AC2 may be superimposed on a different power supply from the DC bias V3 applied to the intermediate transfer belt 240, and a grounded bias voltage may be applied to the conductive brush 215. In this case, since the charge of the intermediate transfer belt 240 is removed, the value of the DC bias is set to approximately 0 V (within ± 100 V). Guide roller 25
The resistance per 1 cm ² area of the bias voltage having the same value as the DC bias V3 applied to 1 is 10 ⁶ to 10 ¹⁰ Ω /
By applying to the conductive brush 215 of cm ² , the volume resistivity of the intermediate transfer belt 240 is as high as 10 ¹² to 10 ¹⁶ Ω · cm. Accordingly, discharge from the intermediate transfer belt 240 to the photosensitive drum 10 is prevented, and the transfer of the toner image from the photosensitive drum 10 to the intermediate transfer belt 240 is favorably performed. The bias voltage is the same as the bias voltage up to the surface of the intermediate transfer belt 240, so that it is less likely to be adversely affected by a change in resistance due to environmental conditions or deterioration. In addition, the repetition of the discharge of the AC bias AC2 makes the electric charge more uniform and the same potential, so that the transfer of the toner image from the photosensitive drum 10 to the intermediate transfer belt 240 is performed favorably. The intermediate transfer belt 240 in which the electric charge of the intermediate transfer belt 240 is made uniform by the conductive brush 215 receives corona discharge by the paper charger 14k, and the corona discharge current of the paper charger 14k is a weak current. The charge on the surface of the intermediate transfer belt 240 is made uniform without being affected by the discharge of the charger 14k, and the intermediate transfer belt 240 is conveyed to the transfer area 14b with the same potential.

The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the photosensitive drum AC static eliminator 19c, and then the residual toner is removed by the cleaning device 19 to remove the residual toner. The history of the photosensitive drum 10 in the previous image formation is canceled by the exposure unit 12e, and the next image forming cycle is started.

Since the superimposed color toner images are collectively transferred by using the above-described method, color misregistration of the color image on the intermediate transfer belt 240, scattering or rubbing of the toner, and the like are less likely to occur, and the image deterioration is small. Double-sided color image formation is performed.

Although the embodiment of the double-sided image forming apparatus has been described with reference to the color image forming apparatus, the present invention is not necessarily limited to this, and the present invention is not limited to this. The present invention is also applied to a double-sided image forming apparatus.

Further, in the image forming apparatus of the present invention, in addition to the double-sided image formation for forming an image on both sides of a recording material as described in the above embodiment, an image is formed on only one side of the recording material. It goes without saying that single-sided image formation can also be performed.

As described above, the electric charge on the intermediate transfer member is made uniform, the resistance is hardly changed, and the transfer of the toner image from the intermediate transfer member to the recording material is performed favorably. In particular, by superimposing the AC bias on the conductive member, the charge on the intermediate transfer body is made more uniform, and the transfer of the toner image from the intermediate transfer body to the recording material is performed more favorably. . Further, the electric charges on both sides of the belt-shaped intermediate transfer body are made uniform, and both sides have the same potential, so that the transfer of the toner image to the recording material is performed favorably.

[0075]

According to the first to third aspects of the present invention, since the charge on the intermediate transfer member is made uniform, the transfer of the toner image to the recording material is excellent even when a high-resistance intermediate transfer member is used. Done in

In particular, according to the second aspect of the present invention, the charge on the intermediate transfer body is made more uniform, and the transfer of the toner image from the intermediate transfer body to the recording material is performed more favorably.

According to the fourth aspect of the present invention, the electric charges on both sides of the belt-shaped intermediate transfer body are made uniform, and both sides have the same potential, so that the transfer of the toner image to the recording material is performed favorably.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged view of the intermediate transfer member of FIG.

FIG. 3 is a sectional configuration diagram of a color image forming apparatus showing a second embodiment of the image forming apparatus according to the present invention.

FIG. 4 is an enlarged view of the intermediate transfer member of FIG.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum 11 scorotron charger 12 exposure optical system 13 developing device 114, 214 intermediate transfer member cleaning device 114a, 214a intermediate transfer member cleaning blade 115, 215 conductive brush 140 intermediate transfer roller 141, 151 metal roller 142, 242 dielectric Body layer 240 Intermediate transfer belt 251 Guide roller AC1, AC2 AC bias V1, V2, V3 DC bias P Recording paper

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor ▲ Hama ▼ Shuta Tadashi 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation

Claims (4)

[Claims] A charging unit, an image exposing unit, a developing unit, and an intermediate transfer unit are arranged around the image forming body, and the image forming unit is charged by the charging unit, and the image formed by the image exposing unit is exposed to the image. Forming a latent image on a formed body and developing the latent image by the developing means to form a toner image on the image formed body; and temporarily transferring the toner image formed on the image formed body to the intermediate transfer body An image forming apparatus for transferring a toner image carried on the intermediate transfer member to a recording material after the transfer to the intermediate transfer member, wherein the intermediate transfer member has a dielectric layer, and a direct current bias is brought into contact with the intermediate transfer member. The intermediate transfer member cleaning means for cleaning the intermediate transfer member is applied to the conductive substrate, and is positioned downstream of the intermediate transfer member in the rotation direction of the intermediate transfer member. Contact, said An image forming apparatus, comprising: a conductive member that makes the charge of the intermediate transfer member uniform; and a DC bias having the same voltage as the DC bias is applied to the conductive member. 2. The image forming apparatus according to claim 1, wherein an AC bias is applied to the conductive member so as to overlap the DC bias. 3. The image forming apparatus according to claim 1, wherein the intermediate transfer member is a roller-shaped member. 4. The image forming apparatus according to claim 1, wherein the intermediate transfer member is a belt-shaped member.