JP2001051519A - Image forming device and color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously form an image in a state where an intermediate transfer body is cleaned by imparting charge having a reverse polarity to residual toner on the intermediate transfer body by an electrifying roller when a toner image is transferred to both surfaces or the back surface of the transfer material and applying bias voltage having the reverse polarity to the electrifying roller when the toner image is transferred only to the front surface of the transfer material so as to perform consecutive printing. SOLUTION: At the time of double-sided image forming and one-sided (back surface) image forming, the bias voltage obtained by superposing DC voltage on AC voltage and having the reverse polarity to developing toner is applied to the electrifying roller 141 so as to positively electrify the residual toner on the intermediate transfer body 14a. Then, the residual toner is restored to a photoreceptor drum 10 side by a primary transfer device 14c to which the DC current having positive polarity is applied at a transfer area 14b. In the midst of one-sided (front surface) image forming that the consecutive printing is performed, the bias voltage having the reverse polarity to the residual toner is applied to the roller 141 so as to stick the residual toner in a negatively electrified state to the peripheral surface of the roller 141.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transferring a toner image formed on an image forming body to a transfer material by a toner image forming means.
More specifically, the present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile which obtains an image by fixing. The present invention relates to an image forming apparatus for obtaining a double-sided or single-sided image, and a color image forming apparatus for transferring a toner image onto a transfer material via an intermediate transfer body after forming a plurality of toner images on the image forming body by superimposition.

[0002]

2. Description of the Related Art In a conventional double-sided image forming apparatus, an image on one side formed on an image bearing means is transferred and fixed on a transfer material, and the transfer material is temporarily stored in a double-sided reversing feeding device.
Next, the transfer material is fed from the double-sided inversion feeding device in synchronization with the image on the other surface formed on the image bearing means,
A method of transferring and fixing an image on the other surface of a transfer material has been adopted.

In this double-sided image forming apparatus, the transfer material is conveyed such that the transfer material is once stored in a two-sided reversal feeding device and then fed again, so that the transfer distance of the transfer material is increased, and the double-sided image forming device is formed. However, there is a problem that it takes a lot of processing time. In addition, since the transfer material which has once passed through the fixing means and is easily curled is fed again, the reliability of transfer of the transfer material is low, which causes a jam or wrinkles of the transfer material.

On the other hand, JP-B-49-37538, JP-B-54-28740, and JP-A-1-444.
No. 57 and Japanese Unexamined Patent Publication No. 4-214576,
An image forming apparatus and an image forming method have been proposed in which a toner image formed by an image carrier is transferred to both surfaces of a transfer material using an intermediate transfer member, and a double-sided image is obtained by one-time fixing.

Also, a color image forming apparatus in which a plurality of toner images are superimposed and formed on an image forming body, particularly a color image in which a color toner image is superposed and formed during one rotation of the image forming body In the forming apparatus, yellow (Y), magenta (M), cyan (C),
Four sets of charging means, image exposing means, and developing means for forming each black (K) toner image are to be arranged, but a long circumferential length is required for arranging the image forming means on the periphery of the image forming body. It is necessary to have. Further, when the color toner image formed by superimposing on the image forming body is to be directly transferred onto the transfer material, the image forming means cannot be provided in the tangential range of the image forming body corresponding to the transfer path of the transfer material. However, the space is greatly restricted. Therefore, the color toner image formed on the image forming body is temporarily transferred to the intermediate transfer body,
A compact color image forming apparatus has been proposed in which a color toner image transferred on an intermediate transfer member is transferred to a transfer material, and a space at a peripheral portion of the image forming member is effectively used.

[0006]

(1) In an image forming apparatus in which a toner image formed on an image forming member is formed on both sides of a transfer material via an intermediate transfer member, an image forming member is generally used. A cleaning unit is provided for removing the residual toner, and a cleaning unit is provided on the intermediate transfer member so as to come into contact with and separate from the intermediate transfer member for removing the adhered toner. When the cleaning unit that comes into contact with or separates from the intermediate transfer member performs contact or separation, the operation causes drive unevenness in the operation of the intermediate transfer member and the image forming body, and this causes image unevenness.

According to the present invention, in such an image forming apparatus, when only one portion of waste toner is collected by the cleaning means and an image is formed on one side or both sides of a transfer material, image unevenness does not occur in any case. It is a first object of the present invention to provide an image forming apparatus capable of continuously forming an image while an intermediate transfer member is cleaned.

(2) In a color image forming apparatus in which a plurality of toner images are superimposedly formed on an image forming body and then transferred onto a transfer material via an intermediate transfer body, image forming is generally performed. Cleaning means for removing residual toner on the body is provided, and cleaning means for removing adhered toner is also provided on the intermediate transfer member. As a cleaning means for removing the toner adhered to the intermediate transfer member, cleaning using a blade is difficult because the intermediate transfer member is an elastic member. It will be difficult.

Another object of the present invention is to provide a color image forming apparatus capable of continuously forming an image while the intermediate transfer member is cleaned while only one waste toner is collected by the cleaning means. This is the purpose of 2.

[0010]

A first object of the present invention is to provide an image forming apparatus for forming a toner image on both surfaces of a transfer material via an intermediate transfer member from a toner image formed on the image forming member.
A charging roller is provided upstream of the transfer material of the intermediate transfer body, and when the image forming body side of the transfer material is used as a front surface, and when a toner image is transferred to both surfaces or a back surface of the transfer material, the charging roller is used to transfer the toner image onto the intermediate transfer body. When the remaining toner is applied with a charge of the opposite polarity and returned to the image forming body, and the toner image is transferred only to the surface of the transfer material to perform continuous printing, a bias voltage of the opposite polarity is applied to the charging roller. An image forming apparatus for moving the residual toner on the intermediate transfer member to the charging roller side, and transferring the toner image formed on the image forming member via the intermediate transfer member. In an image forming apparatus that forms a toner image on both surfaces of a transfer material, a charging roller is provided upstream of the transfer material of the intermediate transfer body, and when the image forming body side of the transfer material is a surface, the toner image is formed only on the surface of the transfer material. Transfer and print continuously At this time, a bias having a polarity opposite to that of the remaining toner is applied to the charging roller to move the remaining toner on the intermediate transfer body to the charging roller side, and after the end of the continuous printing, the polarity of the charging roller is changed. This is achieved by an image forming apparatus (invention of claim 3), wherein the remaining toner is returned to the intermediate transfer member again, and further returned to the image forming member.

A second object of the present invention is to provide a color image forming apparatus for transferring a toner image onto a transfer material via an intermediate transfer member after forming a plurality of toner images on the image forming member in a superimposed manner. The image forming apparatus further includes a recharging unit that performs charging of a polarity opposite to that of the roller-shaped toner image that comes into contact with the transfer body, and moves residual toner on the intermediate transfer body from the intermediate transfer body to the image forming body. This is attained by a color image forming apparatus characterized by performing collection (the invention of claim 7).

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claims 1 and 3 of the present invention relates to an image forming apparatus for forming a toner image on both sides of a transfer material via an intermediate transfer member by using a toner image formed on the image forming body. (Embodiment 1)
The invention according to claim 7 of the present invention relates to a color image forming apparatus that transfers a toner image onto a transfer material via an intermediate transfer member after forming a plurality of toner images on an image forming member in a superimposed manner. Therefore, the present invention will be described by (Embodiment 2).

(Embodiment 1) Prior to the description of the present invention, a color double-sided image forming apparatus will be described with reference to an embodiment of the image forming apparatus of the present invention. However, the present invention is not limited to the embodiments described below. The description in this section does not limit the technical scope of the claims and the meaning of terms. Further, in the following description of the embodiment, when transferring the color toner image to the transfer material, the surface of the transfer material on the side facing the image carrying means in the transfer area, the surface on the other side of the transfer material, The surface facing the intermediate transfer member is called a back surface, an image transferred to the front surface of the transfer material is called a front image, and an image transferred to the back surface of the transfer material is called a back image.

An image forming process and each mechanism of an embodiment of the image forming apparatus of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a color double-sided image forming apparatus according to a first embodiment of the present invention, FIG. 2 is a side cross-sectional view of an image forming unit of FIG. 1, and FIG. 3 is a toner image according to the embodiment. FIG. 3 is a diagram illustrating a formation state and supply of a transfer material.

In FIG. 1, reference numeral 10 denotes a photosensitive drum as an image forming means, 11 denotes a scorotron charger which is a charging means for each color, 12 denotes an exposure unit which is an image exposing means for each color, and 13 denotes a developing unit for each color. A developing device, 14a an intermediate transfer member, 14c a primary transfer device as a first transfer device,
14g is a secondary transfer unit as a second transfer unit, 15c is a timing roller as a transfer material supply unit, and 30 is a fixing device as a fixing unit.

The photosensitive drum 10, which is an image forming means, has a transparent conductive layer, a, on the outer periphery of a cylindrical substrate formed of, for example, a transparent member of optical glass or transparent acrylic resin.
-A photosensitive layer such as an Si layer or an organic photosensitive layer (OPC) is formed, and is rotated clockwise as indicated by an arrow in FIG.

As shown in FIG. 2, the photosensitive drum 10 has flange members 10a and 10a at both ends for engaging and fixing it.
b is rotatably supported by bearings 110a and 110b fitted into flange members 10a and 10b at both ends with respect to a drum shaft 110 erected and fixed to the apparatus main body, and is rotatably supported. Is driven at a constant speed in a predetermined direction by being driven by meshing with a drive gear on the apparatus body side.

A scorotron charger 11, which is a charging unit for each color, an exposure unit 12, which is an image exposure unit for each color, and a developing unit 13, which is a developing unit for each color, constitute one set of these units, and include yellow (Y), Four photoconductor drums 1 are provided for image forming processes of magenta (M), cyan (C), and black (K), and are indicated by arrows in FIG.
With respect to the 0 rotation direction, they are arranged in the order of Y, M, C, and K.

A scorotron charger 11, which is a charging means for each color, is mounted so as to face the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10, and the photosensitive layer of the photosensitive drum 10 described above. Has a control grid maintained at a predetermined potential and a discharge electrode 11a made of, for example, a sawtooth electrode, and performs a charging action (minus charging in the present embodiment) by corona discharge having the same polarity as the toner. A uniform potential is applied to the photosensitive drum 10. Other wire electrodes can be used as the discharge electrode 11a.

Exposure unit 1 as image exposure means for each color
2 is arranged inside the photoconductor drum 10 such that the exposure position on the photoconductor drum 10 is located on the downstream side in the rotation direction of the photoconductor drum 10 with respect to the scorotron charger 11 for each color. The exposure unit 12 includes the photosensitive drum 1
A linear light-emitting element 12a in which a plurality of LEDs (light-emitting diodes) as light-emitting elements arranged in the main scanning direction in parallel to the 0 axis, and a selfoc lens 12b as an equal-magnification imaging element; And a holder (not shown) to which is attached. In addition to the exposure unit 12 for each color, a uniform exposure unit 12c and a simultaneous transfer exposure unit 12d are attached to the holding member 20, and are housed integrally inside the base body of the photosensitive drum 10. The image data of each color read by a separate image reading device and stored in the memory is sequentially read from the memory, and the exposure unit 12 for each color is read.
Are respectively input as electric signals. As the light emitting device, a device in which a plurality of light emitting devices such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used. The emission wavelength of the light-emitting element used in this embodiment is preferably in the range of 680 to 900 nm, which is generally high in transmittance for the Y, M, and C toners. The wavelength may be shorter than this, since the color toner does not have sufficient transparency since the image exposure is carried out in the step (1).

The developing device 13 as a developing means for each color includes
For example, a cylindrical non-magnetic stainless steel having a thickness of 0.5 to 1 mm and an outer diameter of 15 to 25 mm, which 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 It has a developing sleeve 131 formed of an aluminum material and a developing casing 138, and contains therein a one-component or two-component developer of yellow (Y), magenta (M), cyan (C) and black (K). ing. Each of the developing devices 13 is provided with a predetermined gap, for example, 100 to 1000 μm, from the photosensitive drum 10 by an abutting roller (not shown).
m, and is kept in a non-contact state.
A non-contact reversal development is performed by applying a developing bias in which a DC voltage and an AC voltage having the same polarity as the toner (in this embodiment, a negative polarity) are superimposed, and a toner image is formed on the photosensitive drum 10. Form.

The developer used here is a spherical toner having a volume average particle diameter of 1 to 20 μm, preferably 4 to 10 μm, since the transfer of the toner can be effectively controlled by an oscillating electric field. Average particle size is 10
A two-component developer comprising a carrier having a size of from 60 to 60 μm, preferably from 20 to 50 μm is preferably used. When a toner having a volume average particle diameter of 10 μm or less is used, the resolving power is remarkably improved, and a clear high-quality image with faithful reproduction of the density difference is obtained, and the volume average particle diameter is 20 μm. Above, the image quality is reduced. When the volume average particle diameter of the toner is 4 μm or less, the cohesive force is large and triboelectricity is likely to be insufficient. When the volume average particle diameter is 1 μm or less, the toner is liable to be scattered, which is not preferable.

The intermediate transfer member 14a has a volume resistivity of 10 ⁸ to 1
It is an endless belt of 0 ¹² Ω · cm, for example, having a thickness of 0.5 in which conductive material is dispersed in silicon rubber or urethane rubber.
Outside the anti-conductive rubber belt substrate having a thickness of 5 to 50 μm, preferably as a toner filming prevention layer
This is a seamless belt having a two-layer structure and a fluorine coating of m. In addition to the above, a conductive material is dispersed in an engineering plastic such as a modified polyimide, a thermosetting polyimide, an ethylene tetrafluoroethylene copolymer, a polyvinylidene fluoride, or a nylon alloy. A 0 mm semiconductive film can also be used. An intermediate transfer member 14a, which is a toner image receiver, has a driving roller 14d and a driven roller 14d.
e, 14j and the tension roller 14k are stretched in contact with each other, and are rotated counterclockwise as indicated by arrows in FIG.

A primary transfer device 14c as a first transfer means
Is provided to face the photosensitive drum 10 with the intermediate transfer member 14a interposed therebetween, and forms a transfer area 14b between the intermediate transfer member 14a and the photosensitive drum 10. The primary transfer unit 14c has a polarity opposite to that of the toner (positive polarity in this embodiment).
Is applied to form a transfer electric field in the transfer area 14b, thereby transferring the toner image on the photoconductor drum 10 onto the intermediate transfer body 14a or onto the surface of the recording paper P as a transfer material.

A secondary transfer unit 14g as a second transfer unit
Is provided so as to face a conductive driving roller 14d that is grounded with the intermediate transfer member 14a interposed therebetween, and a DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied to the intermediate transfer member 14a. Is transferred to the back surface of the recording paper P.

Timing roller 1 as transfer material supply means
5c feeds the recording paper P as a transfer material to the transfer area 14b in synchronization with the color toner image of the front surface image on the photosensitive drum 10 or the color toner image of the back surface image on the intermediate transfer body 14a.

The fixing device 30 serving as a fixing means includes a first fixing roller 310 having a heater therein and a second fixing roller 3 having a heater therein.
20 and two fixing members in the form of rollers, and heat and pressure are applied between the first fixing roller 310 and the second fixing roller 320 to fix the toner image on the recording paper P.

Next, the image forming process will be described.

In an image reading apparatus separate from the present apparatus, image data of a document image read by an image sensor or image data of an image edited by a computer is Y (yellow), M (magenta), (Cyan) and K (black) are temporarily stored and stored in the memory as image signals for respective colors.

The gear G provided on the rear flange 10b of the photosensitive drum 10 is rotated through a driving gear (not shown) by the start of a photosensitive member driving motor (not shown) at the start of image recording, and the photosensitive drum 10 Is rotated clockwise as indicated by the arrow in FIG. 1, and at the same time, the application of a potential to the photosensitive drum 10 is started by the charging action of the scorotron charger 11 for yellow (Y).

After the photosensitive drum 10 is applied with a potential, the first color signal, that is, Y
Exposure by an electric signal corresponding to the image data is started, and an electrostatic latent image corresponding to the Y image of the original image is formed on the photosensitive layer on the surface of the photosensitive drum 10 by rotational scanning.

The latent image is reversal-developed in a non-contact state by the Y developing unit 13 to form a yellow (Y) toner image in accordance with the rotation of the photosensitive drum 10.

Next, a potential is applied to the photosensitive drum 10 from the yellow (Y) toner image by the charging action of the magenta (M) scorotron charger 11, and the second color signal of the M exposure unit 12 is applied. That is, exposure is performed by an electric signal corresponding to M image data, and the M developing device 13
Yellow (Y) by non-contact reversal development
A toner image of magenta (M) is formed on the toner image of FIG.

In a similar process, a cyan (C) toner image corresponding to the third color signal is further formed by the cyan (C) scorotron charger 11, the exposure unit 12 of C and the developing unit 13 of C. Further, a black (K) toner image corresponding to the fourth color signal is sequentially superimposed and formed thereon by a black (K) scorotron charger 11, an exposure unit 12 of K, and a developing unit 13 of K. As a result, a color toner image is formed on the peripheral surface of the photosensitive drum 10 within one rotation.

Exposure unit 1 for Y, M, C and K
Exposure of the photosensitive layer of the photosensitive drum 10 by 2 is performed from the inside of the photosensitive drum 10 through the aforementioned transparent substrate. Therefore, the exposure 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. It is possible to form an electrostatic latent image.

By the above-described image forming process, a superimposed color toner image serving as a backside image is formed on the photosensitive drum 10 serving as an image bearing means, and the superimposed color toner image of the backside image on the photosensitive drum 10 is transferred. Area 14b
In the above, the primary transfer device 14c to which a DC voltage having the opposite polarity (positive polarity in the present embodiment) to the toner is applied is collectively transferred onto the intermediate transfer member 14a. At this time, for example, uniform exposure is performed by the simultaneous transfer exposure device 12d using a light emitting diode so that good transfer is performed.

The toner remaining on the peripheral surface of the photoconductive drum 10 after the transfer is subjected to static elimination by the photoconductive drum AC static eliminator 16 and then reaches the cleaning device 19 where the toner is transferred to the photosensitive drum 1.
Cleaning blade 19 made of rubber material in contact with zero
In order to eliminate the history of the photoreceptor up to the previous printing, the peripheral surface of the photoreceptor is neutralized by, for example, exposure by a uniform exposure unit 12c before charging using a light emitting diode, and the previous printing is performed. After the charge is removed, the next color image is formed.

After the superimposed color toner image serving as the back side image is formed on the intermediate transfer body 14a as described above, the back side image on the intermediate transfer body 14a and the transfer area 1
4b, the superimposed color toner image serving as the surface image is formed on the photosensitive drum 10 in the same manner as in the above-described color image forming process. It is necessary to change the image data so that the front side image formed at this time is a mirror image of the back side image on the photosensitive drum 10.

A recording paper P, which is a transfer material, is fed from a paper feed cassette 15 which is a transfer material storage means to a feed roller 15a.
, And are fed by the feed roller 15b and conveyed to the timing roller 15c.

The recording paper P is driven by a timing roller 15c, which is a transfer material supply unit, to drive the color toner image of the front surface image formed on the photosensitive drum 10 and the back surface image of the intermediate transfer member 14a. The sheet is fed to the transfer area 14b in synchronization with the color toner image. FIG. 3 shows the toner image formation state of the back side image carried on the intermediate transfer body 14a and the front side image formed on the photosensitive drum 10 and the recording paper P supplied in synchronization therewith.

When the recording paper P is fed to the transfer area 14b,
The recording paper P is charged to the same polarity as the toner by a paper charger 14f as a transfer material charging means capable of coming into contact with and releasing from the intermediate transfer body 14a, and is attracted to the intermediate transfer body 14a to the transfer area 14b. Will be fed. By charging the paper with the same polarity as the toner, it is possible to prevent the toner image on the intermediate transfer member 14a and the toner image on the photosensitive drum 10 from being attracted to each other.
Prevents toner image disturbance. In addition, as the transfer material charging unit, a conductive roller that can be brought into contact with and released from the intermediate transfer member 14a, a corona discharger that does not contact the intermediate transfer member 14a, or the like can be used.

In the transfer area 14b, a first voltage to which a voltage having a polarity opposite to that of the toner (positive in this embodiment) is applied.
The surface image on the peripheral surface of the photosensitive drum 10 is collectively transferred onto the surface (upper surface) of the recording paper P by the primary transfer device 14c as the transfer means. At this time, the back surface image on the peripheral surface of the intermediate transfer member 14a is not transferred to the recording paper P but exists on the intermediate transfer member 14a.

Next, the recording paper P on which the color toner image has been transferred to the surface thereof is used 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.
The sheet is conveyed to the next transfer device 14g, and the back surface image on the peripheral surface of the intermediate transfer member 14a is collectively transferred to the back surface (lower surface) of the recording paper P by the secondary transfer device 14g.

Since the toner images of the respective colors overlap each other, it is preferable that the toner in the upper layer and the toner in the lower layer of the toner layer are charged to the same polarity with the same charge amount in order to enable batch transfer. Accordingly, in a double-sided image formation in which the polarity of the color toner image formed on the intermediate transfer member 14a is inverted by corona charging or the polarity of the color toner image formed on the photosensitive drum 10 is inverted by corona charging, the lower layer is formed. The toner is not sufficiently charged to the same polarity, so that the transfer becomes unfavorable.

The reversal development is repeated on the photosensitive drum 10, and the color toner images of the same polarity formed by superimposition are collectively transferred to the intermediate transfer member 14a without changing the polarity, and then the recording paper is changed without changing the polarity. The batch transfer to P is preferable because it contributes to the improvement of the transferability of the backside image formation. Also for the surface image formation, reversal development is repeatedly performed on the photoreceptor drum 10, and the color toner images of the same polarity formed by superposition are collectively transferred to the recording paper P without changing the polarity. It is preferable because it contributes to the improvement of transferability.

From the above, in the color image formation, the first transfer means and the second transfer means are separately provided, and the first transfer means is operated to form a color toner image on the surface of the transfer material. Next, a two-sided image forming method of forming a color toner image on the back surface of the transfer material by operating the second transfer unit is preferably adopted.

The recording paper P, which is a transfer material having a color toner image formed on both sides, is neutralized by a paper separating AC static eliminator 14h for separating the transfer material, separated from the intermediate transfer member 14a, and removed from both upper and lower rollers. The sheet is conveyed to a fixing device 30 as a fixing unit composed of two fixing rollers having a heating unit (heater) therein. By applying heat and pressure to the recording paper P between the first fixing roller 310 on the upper side and the second fixing roller 320 on the lower side, the toner adhered to the front and back of the recording paper P is fixed, and the two-sided image recording is performed. The discharged recording paper P is fed by a paper discharge roller 18 and discharged to a tray outside the apparatus.

The toner remaining on the peripheral surface of the intermediate transfer body 14a after the transfer is cleaned by an intermediate transfer body cleaning device 140 which is a cleaning means of the intermediate transfer body using a charging roller for recharging, which will be described in detail later. You. Further, the toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer and the toner moved from the intermediate transfer member 14a to the photosensitive drum 10 according to the present invention are discharged by the image forming member AC discharger 16 and then cleaned. The cleaning device 19 reaches the device 19 and is scraped into the cleaning device 19 by a cleaning blade 19a made of a rubber material, which is in contact with the photosensitive drum 10, and collected by a screw 19b into a not-shown waste toner container. The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is exposed to the uniform exposure device 12c.
After the peripheral surface of the photoconductor is neutralized by the exposure by Y,
, Is uniformly charged by the scorotron charger 11 and enters the next image forming cycle.

FIG. 4 is a sectional view of an intermediate transfer member cleaning device 140 according to the present invention. The intermediate transfer member cleaning device 140 is provided with a charging roller 141 that can be brought into contact with and separated from the intermediate transfer member 14a. In a contact state, the charging roller 141 rotates on a driven roller 14j that is grounded behind. The intermediate transfer member 14a contacts the intermediate transfer member 14a with a pressing force of 500 to 1500 gf. At the contact position, the charging roller 141 is configured to rotate at the same peripheral speed as the belt. By driving the charging roller 141 to rotate at the same speed as the belt speed of the intermediate transfer member 14a, it is possible to prevent belt speed unevenness that occurs when the charging roller 141 comes into contact with the belt, thereby preventing image shrinkage. Has an effect.

The charging roller 141 is functionally composed of three layers. That is, a core 141a serving as a conductive rotating shaft to which a different bias voltage is applied depending on the situation as described below, and a functional member provided on the core 141a via a sliding electrode (not shown) at the center. A conductive elastic layer 141b made of EPDM and urethane rubber in which conductive carbon powder is dispersed and ensuring contact with the intermediate transfer member 14a is provided. The medium resistance layer 141c is provided thereon. The medium resistance layer 141c has a semiconducting characteristic of about 10 ⁸ Ωcm, and has a function of suppressing an electric current by a voltage drop in the layer against an excessive current and preventing a charging failure due to a power supply voltage drop and a dielectric breakdown of the intermediate transfer member 14a. Have. The protective layer 141d serving as a surface layer prevents accumulation of dirt on the roller surface due to adhesion of a developer, paper powder, or the like, and is made of a resin material such as nylon.

When the intermediate transfer member 14a rotates, the charging roller 141 abuts on the belt at the abutting position except when the toner image on the back surface passes, and a bias voltage is applied. Is different between the double-sided image formation and the single-sided (front) image formation as follows.

(1) Double-sided image formation During double-sided image formation and single-sided (backside) image formation, a DC voltage (positive in the present embodiment) and an AC voltage having a polarity opposite to that of the developing toner are superimposed on the charging roller 141. The residual toner on the intermediate transfer member 14a is positively charged by applying the bias voltage, and the residual toner is transferred to the photosensitive drum 10 by the primary transfer device 14c to which a positive DC voltage is applied in the transfer area 14b. And return. In the process of transferring the toner image on the back surface to the intermediate transfer member 14a by the primary transfer device 14c, the transfer of the residual toner on the intermediate transfer member 14a to the photosensitive drum 10 is performed simultaneously with this transfer. The residual toner transferred to the photosensitive drum 10 is cleaned by the cleaning device 19 together with the transfer residual toner.

The bias voltage applied to the charging roller 141 is a bias voltage obtained by superimposing a positive DC voltage component of 800 V to 3 kV and an AC component of 2.5 to 5.0 kV _PP at 1 to 2 kHz. And the charged amount of the developed toner was −10 to −20 μC / g,
The charge amount of the residual toner having a positive polarity of 30 μC / g is transferred to the photosensitive drum 10 by the primary transfer device 14c satisfactorily.

(2) When Forming a Single-Side (Front) Image The transfer of the residual toner on the intermediate transfer member 14a to the photosensitive drum 10 described above is performed only while no recording paper exists in the transfer area 14b. When forming a two-sided image, the interval between one recording sheet to be conveyed and the next recording sheet is the recording sheet 1
Since the intermittent sheet feeding is performed with an interval equal to or longer than the number of sheets, the transfer of the remaining toner to the photosensitive drum 10 is performed favorably during this period. The space between the papers is narrow, and it is difficult to transfer the remaining toner to the photosensitive drum 10 during this time. Therefore, in the present invention, during the formation of a single-sided (front) image on which continuous printing is performed, a bias voltage having a polarity opposite to that of the residual toner (positive in the present embodiment), for example, a positive bias voltage of 200 to 1000 V is applied to the charging roller 141. By applying the voltage, the remaining toner in the negative charge state is attached to the peripheral surface of the charging roller 141. When the continuous printing is completed, the bias voltage applied to the charging roller 141 is switched to the application of a bias voltage in which DC and AC are superimposed in the same manner as that applied during double-sided image formation, and
1 is recharged to a positive polarity and transferred to the intermediate transfer member 14a, and the same positive bias voltage as that used when transferring the toner image is applied to the primary transfer device 14c to expose the remaining toner. The transfer to the body drum 10 is performed.

During both-side image formation and one side (front side)
The embodiment in which the AC component is superimposed when the bias voltage is applied to the charging roller 141 during image formation has been described. However, the AC component applied here imparts a uniform charge to the residual toner, and the This has an effect that the transfer of the residual toner from the photosensitive drum 10 to the photosensitive drum 10 is performed favorably.

FIG. 4A shows a cross-sectional configuration of the intermediate transfer member cleaning device 140. FIG. 4A shows a state in which the charging roller 141 is pressed against the intermediate transfer member 14a, and FIG. The embodiment shown here is configured such that the entire cleaning device moves toward and away from the intermediate transfer member 14a with the rotation of the cam 142 with respect to the fixed frame 140A fixed to the image forming apparatus main body.

The charging roller 141 is mounted in a housing 143 having the intermediate transfer member 14a side opened.
43 can be moved left and right with respect to the moving frame 145 via a compression spring 144 in the figure. When the cam 142 rotates clockwise in FIG.
The moving frame 145 in contact with the fixed frame 1
The charging roller 141 moves to the left on the drawing on the surface 40A, and is in contact with the intermediate transfer member 14a. As the cam 142 continues to rotate, the compression spring 144 is further compressed, and the contact pressure between the charging roller 141 and the intermediate transfer member 14a increases. The cam 142 has a driving source and a camshaft 142.
A torque limiter (not shown) is provided between the charging roller 141 and the intermediate transfer member 14a. When the torque reaches a preset torque value, the cam 142 stops rotating, and a predetermined 500 to 1500 gf It comes into contact with the pressing force between them.

Here, the speed at which the cleaning device is moved in the contact direction by the rotation of the cam 142 is V (c
m / sec) and the moving speed of the intermediate transfer member 14a is V _B (c
When the m / sec), it is desirable, the moving speed of the cleaning apparatus set to be within the above range is _{(V B / 10) <V} <V B. When (V _B / 10) ≧ V, the pressing force of the charging roller 141 in the initial stage of contact with the belt is insufficient, and a cleaning failure portion occurs in a relatively long range. Is required. When V ≧ V _B , there is a shock when the charging roller 141 comes into contact with the belt and when the contact is released, and the belt speed of the intermediate transfer body 14a becomes uneven,
The formed image will expand and contract.

FIG. 5 shows the roller width W _{A of the} charging roller 141.
And the roller width W of the developing sleeve 131 which is a developing roller.
And _B, an illustration of the relationship between the belt width W _C of the intermediate transfer member 14a, it is desirable that a relationship of _{W B <W A <W C} . W _B ≧ W _A it and becomes the toner remaining untransferred on the belt of the intermediate transfer member 14a is remaining accumulated residual toner stored is to reduce the image quality attached to move on the recording sheet. If W _A ≧ W _C , the remaining toner adhered to the charging roller 141 is accumulated without being transferred to the belt of the intermediate transfer member 14a, and the accumulated residual toner moves to the belt and adheres to the back surface of the recording paper. This degrades the quality.

(Embodiment 2) Prior to the description of the present invention, an embodiment of the color image forming apparatus of the present invention will be described. The present invention is not limited to the embodiments described below. The description in this section does not limit the technical scope of the claims and the meaning of terms. In the present embodiment, members having the same functions as those in the first embodiment are denoted by the same reference numerals.

An image forming process and each mechanism of the embodiment of the color image forming apparatus of the present invention will be described with reference to FIG. In FIG. 6, a photosensitive drum 1 as an image forming means
Reference numeral 0 denotes a case where a photosensitive layer such as a transparent conductive layer, an a-Si layer, or an organic photosensitive layer (OPC) is formed on the outer periphery of a cylindrical substrate formed of, for example, a transparent member made of optical glass or transparent acrylic resin. And rotated counterclockwise as indicated by the arrow in FIG.

The photosensitive drum 10 has the same configuration as that shown in FIG. 2 described above, and the flange members 10a and 10b at both ends to be engaged and fixed are connected to the drum shaft 110 which is erected and fixed to the apparatus main body. Flange members 10 at both ends
bearings 110a, 110 fitted in a and 10b
b, and is rotatably supported. The gear G integrated with the flange member 10b is driven in mesh with a driving gear on the apparatus main body side to rotate at a constant speed in a predetermined direction.

The scorotron charger 11, which is a charging unit for each color, the exposure unit 12, which is an image exposure unit for each color, and the developing unit 13, which is a developing unit for each color, form a set of these units, Four photoconductor drums 1 are provided for image forming processes of magenta (M), cyan (C), and black (K), and are indicated by arrows in FIG.
With respect to the 0 rotation direction, they are arranged in the order of Y, M, C, and K.

The scorotron charger 11, which is a charging unit for each color, is mounted to face the photosensitive drum 10 in a direction perpendicular to the moving direction of the photosensitive drum 10. Has a control grid maintained at a predetermined potential and a discharge electrode 11a made of, for example, a sawtooth electrode, and performs a charging action (minus charging in the present embodiment) by corona discharge having the same polarity as the toner. A uniform potential is applied to the photosensitive drum 10. Other wire electrodes can be used as the discharge electrode 11a.

Exposure unit 1 as image exposure means for each color
2 is arranged inside the photoconductor drum 10 such that the exposure position on the photoconductor drum 10 is located on the downstream side in the rotation direction of the photoconductor drum 10 with respect to the scorotron charger 11 for each color. The exposure unit 12 includes the photosensitive drum 1
A linear light-emitting element 12a in which a plurality of LEDs (light-emitting diodes) as light-emitting elements arranged in the main scanning direction in parallel to the 0 axis, and a selfoc lens 12b as an equal-magnification imaging element; And a holder (not shown) to which is attached. In addition to the exposure unit 12 for each color, a uniform exposure unit 12c and a simultaneous transfer exposure unit 12d are attached to the holding member 20, and are housed integrally inside the base body of the photosensitive drum 10. The image data of each color read by a separate image reading device and stored in the memory is sequentially read from the memory, and the exposure unit 12 for each color is read.
Are respectively input as electric signals. As the light emitting device, a device in which a plurality of light emitting devices such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used. The emission wavelength of the light-emitting element used in this embodiment is preferably in the range of 680 to 900 nm, which is generally high in transmittance for the Y, M, and C toners. The wavelength may be shorter than this, since the color toner does not have sufficient transparency since the image exposure is carried out in the step (1).

The developing device 13 as a developing means for each color includes
For example, a cylindrical non-magnetic stainless steel having a thickness of 0.5 to 1 mm and an outer diameter of 15 to 25 mm, which 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 It has a developing sleeve 131 formed of an aluminum material and a developing casing 138, and contains therein a one-component or two-component developer of yellow (Y), magenta (M), cyan (C) and black (K). ing. Each of the developing devices 13 is provided with a predetermined gap, for example, 100 to 1000 μm, from the photosensitive drum 10 by an abutting roller (not shown).
m, and is kept in a non-contact state.
A non-contact reversal development is performed by applying a developing bias in which a DC voltage and an AC voltage having the same polarity as the toner (in this embodiment, a negative polarity) are superimposed, and a toner image is formed on the photosensitive drum 10. Form.

The developer used here is a spherical toner having a volume average particle diameter of 1 to 20 μm, preferably 4 to 10 μm, since the transfer of the toner can be effectively controlled by an oscillating electric field. Average particle size is 10
A two-component developer comprising a carrier having a size of from 60 to 60 μm, preferably from 20 to 50 μm is preferably used. When a toner having a volume average particle diameter of 10 μm or less is used, the resolving power is remarkably improved, and a clear high-quality image with faithful reproduction of the density difference is obtained, and the volume average particle diameter is 20 μm. Above, the image quality is reduced. When the volume average particle diameter of the toner is 4 μm or less, the cohesive force is large and triboelectricity is likely to be insufficient. When the volume average particle diameter is 1 μm or less, the toner is liable to be scattered, which is not preferable.

At the start of image recording, the photosensitive drum 10 is rotated counterclockwise by the start of the photosensitive member drive motor, and at the same time, the application of potential to the photosensitive drum 10 is started by the charging action of the scorotron charger 11 (Y). Is done.

After a potential is applied to the photosensitive drum 10, exposure by an electric signal corresponding to a first color signal, that is, an image signal of yellow (Y) is started in the exposure optical system 12 (Y), and the photosensitive drum 10 is started. An electrostatic latent image corresponding to the yellow (Y) image of the original image is formed on the photosensitive layer on the surface by the rotational scanning.

The yellow (Y) latent image is developed by the developing unit 13 (Y).
As a result, the developer on the developing sleeve is reversely developed in a non-contact state, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 is yellow (Y)
A potential is further applied to the toner image by the charging action of the scorotron charger 11 (M), and the exposure optical system 12 (M)
Is exposed by an electric signal corresponding to the second color signal, i.e., the magenta (M) image signal, and the non-contact reversal development by the developing unit 13 (M) is performed on the yellow (Y) toner image. The magenta (M) toner images are sequentially superimposed and formed.

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

In the image formation, a black (K) scorotron charger 11 (K) and a black (K) exposure optical system 12 are used as a black (K) toner image forming means.
The (K) and black (K) developing units 13 (K) are arranged at the most downstream in the rotation direction of the photosensitive drum 10.

The exposure of the organic photosensitive layer of the photosensitive drum 10 by each of the exposure optical systems 12 is performed by the photosensitive drum 10.
From the inside through a substrate that is transparent to the above-mentioned exposure wavelength. Therefore, the exposure 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. It is possible to form an electrostatic latent image. In the developing operation of each developing device 13, a developing bias to which a direct current or a further alternating current is applied is applied to the developing sleeve 131, and jumping development is performed by a one-component or two-component developer contained in the developing device 13. ,
Non-contact reversal development is performed on the photosensitive drum 10 that grounds the translucent conductive layer.

The color toner image of four colors of Y, M, C and K formed on the peripheral surface of the photosensitive drum 10 is transferred to the uppermost layer of black (K) by a pre-transfer charger 11A as pre-transfer charging means. After the toner is recharged, the toner is transferred onto the peripheral surface of the intermediate transfer belt 14 provided as an intermediate transfer member.

The intermediate transfer belt 14 as an intermediate transfer member has a volume resistivity of 10 ⁸ to 10 ¹⁶ Ω · cm, preferably 10 ⁹ to 10 ⁹ Ω · cm.
An endless belt of 10 ¹² Ω · cm, for example, a conductive material dispersed in engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, and the like. It is a seamless belt having a two-layer structure in which a 0.05 mm semiconductive film substrate is coated with a fluorine coating having a thickness of 5 to 50 μm, preferably as a toner filming preventing layer. In addition, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber, urethane rubber, or the like can be used as the base of the belt. The intermediate transfer belt 14 is stretched between a guide roller 14A, a transfer roller 14B serving as a transfer unit, an entrance roller 14C, a backup roller 14D, and a tension roller 14E.
By the power transmitted to D, the photosensitive drum 10 is circulated and conveyed clockwise in synchronization with the peripheral speed of the photosensitive drum 10.

The intermediate transfer belt 14 forms a transfer area (primary transfer area) of the toner image on the belt surface by bringing the belt surface between the guide roller 14A and the transfer roller 14B into contact with the peripheral surface of the photosensitive drum 10. On the other hand, the belt surface on the outer periphery of the entrance roller 14C is in contact with a roller transfer unit 18 as a transfer member, and a transfer area (secondary transfer area) for transferring a toner image to a transfer material is formed at the contact point.

The color toner image adhered to the peripheral surface of the photosensitive drum 10 is first applied to the intermediate transfer belt 14 by applying a bias voltage having the opposite polarity to the toner to the transfer roller 14B at the contact point between the intermediate transfer belt 14 and the intermediate transfer belt. 14 is transferred to the peripheral surface side. That is, the color toner image on the photosensitive drum 10 is transported to the transfer area without scattering the toner by the guide of the grounded guide roller 14A.
By applying a bias voltage of 1 to 3 kV to B, the image is efficiently transferred to the intermediate transfer belt 14 side (primary transfer). At this time, exposure is performed by a simultaneous transfer exposure device 12d, which is a simultaneous transfer exposure means, so that good transfer is performed.

On the other hand, the transfer paper P as a transfer material is carried out from a paper feed cassette (not shown) by the operation of the paper feed roller 17 and fed to the timing roller 15c, and the color toner image on the intermediate transfer belt 14 is transferred. The sheet is fed to a transfer area (secondary transfer area) of a roller transfer unit 18 which is a transfer member in synchronization with the conveyance of the sheet.

The roller transfer unit 18 is rotated in a counterclockwise direction in synchronization with the peripheral speed of the intermediate transfer belt 14, and the fed transfer paper P is transferred to the entrance roller 14C which is in a ground contact state with the roller transfer unit 18. In a secondary transfer area formed by a nip portion between the transfer papers, the color toner image is brought into close contact with the color toner image on the intermediate transfer belt 14 and a bias voltage having a polarity opposite to that of the toner of 1 to 2 kV is applied to the roller transfer unit 18 so that the color toner image is transferred. It is transferred onto P (secondary transfer).

The transfer paper P to which the color toner image has been transferred is neutralized by the brush neutralizer 18A, is conveyed to the fixing device 30 via the conveying plate, and has the heat roller 310 and the pressure roller 3
The toner is heated by being pinched and conveyed between the fixing roller 20 and the toner. The toner is fused and fixed, and then discharged to the outside of the apparatus via a discharge roller.

A blade provided with a cleaning device 19 as a cleaning means is constantly pressed against the photosensitive drum 10 so that the remaining adhered toner is removed and the peripheral surface is always kept clean. I have.

Conventionally, the intermediate transfer belt 14 is provided with the same cleaning means as the cleaning device 19 for cleaning the photosensitive drum 10 to clean the intermediate transfer belt 14. The present invention provides a recharging roller 200 that performs charging of a polarity opposite to that of the toner image abutting on the intermediate transfer belt 14 without providing such a cleaning unit, and removes transfer residual toner on the intermediate transfer belt 14 from the intermediate transfer belt 14. The toner is moved to the photoconductor drum 10 and the transfer residual toner is collected by the cleaning device 19.

FIG. 7 is a sectional view of the recharging roller 200 portion. The recharging roller 200 abuts on the intermediate transfer belt 14 moving on the grounded backup roller 14D behind with a pressing force of 300 to 2000 gf, and rotates following the movement of the intermediate transfer belt 14. Recharging roller 2
00 is functionally composed of three layers. In other words, a core metal 200a serving as a conductive rotating shaft to which a bias voltage for superimposing an AC component on a DC component and recharging the transfer residual toner is applied through a sliding electrode (not shown) at the center. A conductive elastic layer 200b, which is functionally provided on the metal core 200a and is made of EPDM and urethane rubber in which conductive carbon powder is dispersed, and which ensures contact with the intermediate transfer belt 14 is provided. The medium resistance layer 200c is provided thereon. The medium resistance layer 200c has a semiconductive property of about 10 ⁸ Ωcm, and has a function of suppressing an electric current by a voltage drop in the layer with respect to an excessive current, and preventing charging failure due to a power supply voltage drop and insulation breakdown of the intermediate transfer belt 14. Have. The protective layer 200d serving as a surface layer prevents accumulation of dirt on the roller surface due to adhesion of a developer or paper powder, and is made of a resin material such as nylon.

The recharging roller 200 having such a configuration keeps the contact state while the intermediate transfer belt 14 is rotating, and recharges the transfer residual toner by applying a bias voltage.
It is necessary to change the pre-transfer charging and transfer conditions including the bias voltage conditions to be applied between monochrome image formation and color image formation in order to perform good cleaning and image formation. .

(1) At the time of monochrome image formation At the time of monochrome image formation, a scorotron charger 11 (K) applies a potential to the photosensitive surface to the photosensitive drum 10 rotating in the counterclockwise direction. 12
A latent image is formed by (K), and a black (K) toner image is formed by the developing unit 13 (K). Photoconductor drum 1
The monochrome toner image formed on the top 0 moves to the primary transfer area by disabling the pre-transfer charger 11A since there is no need to make the potentials of the toner images formed one upon the other superposed like a color image. .

In the primary transfer area, the transfer roller 14B
Is applied with a bias voltage of 1-2 kV having a polarity opposite to that of the toner (positive in the present embodiment), and the monochrome toner image on the photosensitive drum 10 is efficiently transferred to the intermediate transfer belt 14 side.

The monochrome toner image on the intermediate transfer belt 14 is applied with a positive bias voltage of 2 to 4 kV to the roller transfer unit 18 in the secondary transfer area, and the monochrome toner image is efficiently transferred onto the recording paper P. .

The transfer residual toner of the monochrome image on the intermediate transfer belt 14 after the transfer in the secondary transfer unit is
By passing through the recharging roller 200 to which the bias voltage has been applied, the polarity is changed from negative to positive. The bias voltage applied to the recharging roller 200 is 5
0.5V with a positive DC component of 00V and 1-2kV _PP
The operation is performed in a form in which an AC component of 2.0 kHz is superimposed, and the charge amount of the developing toner is −10 to −20 μC / g, and becomes a charge amount of +15 to +30 μC / g by recharging. The recharged monochrome transfer residual toner is efficiently transferred to the photosensitive drum 10 by the transfer roller 14B to which a positive bias voltage of 1-2 kV is applied.

(2) At the time of forming a color image The color toner image of four colors of Y, M, C and K formed on the peripheral surface of the photosensitive drum 10 is based on the charging condition of the Y, M and C toner images. Since the charging condition of the K toner image forming the uppermost layer is different, the pre-transfer charger 11A is used in order to make the transfer conditions of the Y, M, C and K toner images at the time of transfer uniform.
Recharging is performed. The charge amount of the developed toner is -1
The color toner image on the photoreceptor drum 10 has a primary charge of 0 to −20 μC / g, and has a primary charge of −15 to −30 μC / g due to the pre-transfer charging. Move to transfer area.

In the primary transfer area, the transfer roller 14B
A positive bias voltage of 0.5 kV to 1.5 kV lower than that at the time of monochrome image formation is applied, and the color toner image on the photosensitive drum 10 is efficiently transferred to the intermediate transfer belt 14 side.

For the color toner image on the intermediate transfer belt 14, a bias voltage of 1.5 to 3.5 kV lower than that for monochrome image formation is applied to the roller transfer unit 18 in the secondary transfer area, and the color toner image is recorded on the recording paper. It is efficiently transferred onto P.

After the transfer in the secondary transfer area, the transfer residual toner of the color image on the intermediate transfer belt 14 passes through the recharging roller 200 to which the bias voltage is applied, so that the charge amount is smaller than that of the monochrome image. Is a transfer residual toner having a large positive polarity. Recharging roller 2
The bias voltage applied to 00 is a positive DC component of 700 V, whose absolute value is higher than that at the time of monochrome image formation, and 1-2.
It is performed in a form in which an AC component of 0.5 to 2.0 kHz is superimposed at kV _PP , and the charging amount is set to +20 to +40 μC / g whose absolute value is larger than that at the time of monochrome image formation by recharging. As a result, in the primary transfer area, 0.5-1.
The transfer residual toner of the color image is efficiently transferred to the photosensitive drum 10 by the transfer roller 14B to which the positive bias voltage of 5 kV is applied.

As described above, by performing control differently between monochrome image formation and color image formation, a good image can be obtained on the recording paper P, and the transfer residue on the intermediate transfer belt 14 can be obtained. The toner also efficiently transfers to the photosensitive drum 10 and is cleaned.

The optimum bias conditions for the transfer roller 14B, the roller transfer unit 18, and the recharging roller 200, including the operation / non-operation of the pre-transfer charger 11A during the formation of a monochrome image and the formation of a color image, are described below. In accordance with whether the image to be printed is a monochrome image or a color image, the corresponding bias condition is called up to form an image, so that a good image is always obtained regardless of the image. Print images are obtained continuously.

[0096]

According to the first to sixth aspects of the present invention, there is provided an image forming apparatus for forming a toner image on both surfaces of a transfer material via an intermediate transfer member from a toner image formed on the image forming body.
There has been provided an image forming apparatus capable of always obtaining good one-sided image prints or two-sided image prints without providing a conventionally required cleaning means for the intermediate transfer member.

According to the seventh and eighth aspects of the present invention, a color image forming apparatus for forming a plurality of toner images on an image forming body in a superimposed manner, and then transferring the toner image onto a transfer material via an intermediate transfer body. With respect to the above, a color image forming apparatus capable of always obtaining good monochrome image prints or color image prints without providing a cleaning means for an intermediate transfer body which has been conventionally required has been provided.

[Brief description of the drawings]

FIG. 1 is a sectional configuration diagram of a double-sided image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a side sectional view of the image forming body of FIG. 1;

FIG. 3 is a diagram illustrating a toner image forming state and supply of a transfer material.

FIG. 4 is a cross-sectional configuration diagram of an intermediate transfer body cleaning device.

FIG. 5 is an explanatory diagram showing a relationship among a charging roller width, a developing roller width, and an intermediate transfer belt width.

FIG. 6 is a sectional configuration diagram of a color image forming apparatus according to a second embodiment of the present invention.

FIG. 7 is a sectional view of a recharging roller portion.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum 11 scorotron charger 11A pre-transfer charger 12 exposure unit 13 developing device 14 intermediate transfer belt 14a intermediate transfer member 14c primary transfer device 14g secondary transfer device 14B transfer roller 18 roller transfer device 19 cleaning device 140 intermediate transfer Body cleaning device 141 Charging roller 200 Recharging roller

Continued on the front page (72) Inventor Yotaro Sato 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Corporation F-term (reference) 2H028 BA03 BA06 BA16 BB04 2H032 AA02 AA05 AA15 BA01 BA05 BA09 BA23 BA26 BA30 CA02 CA12 CA13 CA15

Claims (8)

[Claims] 1. An image forming apparatus for forming a toner image on both surfaces of a transfer material via an intermediate transfer member from a toner image formed on the image forming member, wherein a charging roller is provided upstream of the transfer material of the intermediate transfer member. When the image forming body side of the transfer material is the surface,
When transferring the toner image to both sides or the back side of the transfer material,
When the charge roller applies a charge of the opposite polarity to the residual toner on the intermediate transfer member and returns to the image forming member, and when the toner image is transferred only on the surface of the transfer material and continuous printing is performed, the charge roller is used. An image forming apparatus, wherein a bias voltage having a reverse polarity is applied to move residual toner on an intermediate transfer member to the charging roller side. 2. The method according to claim 1, wherein when the toner image is transferred to both surfaces of the transfer material, the charging of the remaining toner by the charging roller is performed by applying a bias in which an AC voltage and a DC voltage are superimposed. The image forming apparatus according to claim 1. 3. An image forming apparatus for forming a toner image on both sides of a transfer material via an intermediate transfer member from a toner image formed on the image forming member, wherein a charging roller is provided upstream of the transfer material of the intermediate transfer member. When the image forming body side of the transfer material is the surface,
When performing continuous printing by transferring the toner image only to the surface of the transfer material, a bias having a polarity opposite to that of the remaining toner is applied to the charging roller to move the remaining toner on the intermediate transfer body to the charging roller side, An image forming apparatus, wherein after the continuous printing is completed, the polarity of the charging roller is changed, the remaining toner is returned to the intermediate transfer body again, and further returned to the image forming body. 4. The image forming apparatus according to claim 1, wherein the charging roller is driven and rotated at the same speed at a contact portion when the charging roller contacts the intermediate transfer member. . 5. The relation of W _B <W _A <W _{C is provided} , where the width of the charging roller is W _A , the width of the developing roller is W _B , and the width of the belt of the intermediate transfer member is W _C. The method according to any one of claims 1 to 4, wherein
Item 10. The image forming apparatus according to item 1. 6. The charging roller has a contact / release mechanism, wherein the speed at which the charging roller contacts and releases the intermediate transfer member is V (cm / sec), and the linear speed of the intermediate transfer member is V _B.
(Cm / sec) to the time _{(V B / 10) <V} < any one of claims 1 to 5, characterized in that a relationship of V _B
Item 10. The image forming apparatus according to item 1. 7. A color image forming apparatus for transferring a toner image onto a transfer material via an intermediate transfer body after forming a plurality of toner images on the image formation body by superimposition, and abutting on the intermediate transfer body. The image forming apparatus further includes a recharging unit that performs charging of a polarity opposite to that of the roller-shaped toner image, and moves transfer residual toner on the intermediate transfer body from the intermediate transfer body to the image forming body.
A color image forming apparatus that performs collection. 8. The method according to claim 7, wherein the pre-transfer charging is performed at the time of forming a color image, and the charge amount of the toner is set to be higher at the time of forming a color image than at the time of forming a monochrome image.
3. The color image forming apparatus according to 1.