JPH1010804A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a transfer material electrifying means from being soiled due to filming toner left on an image carrying means and a toner bank left on the image carrying means when a cleaning means is released by enabling the means to be moved between a transfer material electrifying position abutted on a transfer material and a non-electrifying position away from the transfer material. SOLUTION: At the electrifying position, a paper electrifying brush 150 being the transfer material electrifying means abuts on a toner image receiving body 14a and a recording paper P and a bias voltage E1 is impressed when the paper is passed. At the non-electrifying position, the brush 150 is released from the body 14a and is away from the paper P and preferably the bias voltage E1 is impressed when the paper is not passed. Then, the brush 150 is moved between the electrifying position and the non-electrifying position synchronously with such an action that the paper P is passed through a brush member 151 part. Besides, when the blade member 141 of a cleaning device for a toner image receiving body 140 is released, the brush 150 is set at the non-electrifying position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine in which a charging means, an image exposing means and a developing means are arranged around an image carrier to transfer and fix a toner image formed on the image carrier onto a transfer material. And an electrophotographic image forming apparatus such as a printer, a facsimile and the like.

[0002]

2. Description of the Related Art Conventionally, in double-sided copying, an image on one side formed on an image carrier is transferred and fixed on a transfer material, and this is temporarily stored in a two-sided reversing paper feeder, and the image bearing is again performed. A method has been adopted in which a transfer material is fed from a double-sided reversing sheet feeder in synchronization with an image formed on the body, and an image on the other surface is transferred and fixed onto the transfer material.

In this double-sided copying apparatus, as described above, the transfer of the transfer material, such as feeding to the two-sided reversing paper feeder and passing through the fixing device twice, is performed, so that the reliability of transfer of the transfer material is low. And so on. In contrast, JP-B-49-37538 and JP-B-54-28740.
And JP-A-1-44457 and JP-A-4-21
Japanese Patent Application Laid-Open No. 4576/1994 proposes a method in which a toner image is formed on both surfaces of a transfer material and then fixed once.
JP-A-44457 and JP-A-4-214576 disclose that a plurality of sets of image forming means including an image carrier, a charging means, an image exposing means, a developing means and the like are arranged in parallel on a toner image receiving body. Has been proposed.

[0004]

However, Japanese Patent Application Laid-Open Nos. Hei 1-44457 and Hei 4-214576 mentioned above.
In the double-sided color image formation proposed in Japanese Patent Application Laid-Open Publication No. H08-27, the transferability of the transfer material is improved, but the color toner images are superimposed one by one on the toner image receiver, so that color misregistration, toner scattering and rubbing, etc. Image degradation easily occurs.

On the other hand, as shown in FIG. 9, the present inventors temporarily transfer the toner image formed on the image carrier (first image carrier) 910 to a toner image receiver (second image carrier). )
The toner image formed on the image carrier 910a and the toner image formed on the image carrier 910a are again transferred to a recording paper (transfer material). We are studying a double-sided image forming method for transferring to both sides of P.

At this time, cleaning means 940 for the toner image receiver is provided opposite to the toner image receiver 914a, and the transfer residual toner on the toner image receiver 914a is cleaned by the cleaning means 940. Transfer material charging means (paper charging brush) 9 for charging the recording paper P and adsorbing the toner on the toner image receiving member 914a and transporting the recording paper P over the toner image receiving member 9
50, the brush member 951 at the leading end of the paper charging brush 950 is contaminated with toner, the charging current is reduced, the adhesion to the toner image receiver 914a due to the charging of the recording paper P is deteriorated, and the transportability is deteriorated. Problem arises.

In particular, when the blade 941 of the cleaning means 940 is released from the toner image receiving member 914a,
The toner accumulation on the toner image receiving member 914a stains the paper charging brush, deteriorating the adhesion of the recording paper P to the toner image receiving member 914a, and deteriorating the transportability.

The present invention has been made to solve the above-mentioned problems, and a transfer material such as a filming toner remaining on the second image bearing means or a toner pool remaining on the second image bearing means when the cleaning means is released. An object of the present invention is to provide an image forming apparatus in which a charging unit is prevented from being stained.

[0009]

An object of the present invention is to provide a first image carrying means for carrying a toner image formed by a toner image forming means, and a transfer of the toner image carried by the first image carrying means. A second image holding means for holding the transferred toner image on the surface, a first transfer means for transferring the toner image carried on the first image holding means to a surface of a transfer material, An image forming apparatus comprising: a second transfer unit configured to transfer a toner image carried by a second image carrying unit to a back surface of the transfer material; and a fixing unit configured to fix the toner images transferred to both surfaces of the transfer material. In the apparatus, a transfer material charging means for charging the transfer material entering the second image bearing means and adsorbing the transfer material on the second image bearing means is charged to contact the transfer material and charge the transfer material. And a non-charging position separated from the transfer material. It is achieved by an image forming apparatus characterized by being movable (the first invention).

The above object is also achieved by a first image carrying means for carrying a toner image formed by a toner image forming means,
A second image carrier for transferring the toner image carried on the first image carrier, and carrying the transferred toner image on the surface; and a toner image carried on the first image carrier. Transfer means for transferring a toner image carried by the second image carrying means to the back surface of the transfer material, and first and second transfer means for transferring the toner image carried by the second image carrying means to the back surface of the transfer material. Transfer device charging means for charging the transfer material entering the second image bearing means and adsorbing the transfer material onto the second image bearing means in the image forming apparatus having a fixing means for fixing the toner image transferred to the second image bearing means. And a bias voltage having the same polarity as that of the toner on the second image carrying means is applied to the transfer material charging means when passing through the transfer material, and The second image bearing even when the transfer material is not passing It is achieved by an image forming apparatus and applying the toner of the same polarity of the bias voltage of stages above the transfer material charging means (second invention).

[0011]

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. In the following description of the embodiment, when transferring a color toner image to a transfer material, an image to be transferred to a surface of the transfer material on the side facing the image carrier in the transfer area is a surface image or the other of the transfer material. The image transferred to the surface on the side of is referred to as a back surface image.

Embodiment 1 An image forming process and each mechanism of an embodiment of an image forming apparatus using a first example of prevention of contamination of transfer material charging means of the present invention will be described with reference to FIGS. . FIG.
FIG. 2 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of the image forming apparatus of the present invention, FIG. 2 is a diagram showing a state of forming toner images on both sides, and FIG. FIG. 3 is a diagram showing the contact timing with the image receiving body, and FIG.
3A is a diagram showing the contact timing of the transfer material charging unit, FIG. 3B is a diagram showing the release state of the transfer material charging unit, and FIG. 4 is a first diagram of the transfer material charging unit. FIG. 4 is a diagram showing an example of the above and its contact and release mechanism.

The photosensitive drum 10 serving as an image carrier has, for example, a cylindrical base formed of a transparent member such as optical glass or transparent acrylic resin provided inside, and a transparent conductive layer,
A photosensitive layer such as an a-Si layer or an organic photosensitive layer (OPC) is formed on the outer periphery of the substrate, and is rotated clockwise as shown by an arrow in FIG. 1 in a grounded state.

Scorotron charger 11 as charging means
Is used in an image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K), and is exposed in a direction orthogonal to a moving direction of the photosensitive drum 10 as an image carrier. It is installed facing the body drum 10,
A control grid maintained at a predetermined potential with respect to the above-described photoconductor layer of the photoconductor drum 10 and a discharge electrode 11 a
For example, a charging action (minus charging in the present embodiment) is performed by corona discharge having the same polarity as the toner using a sawtooth electrode, and a uniform potential is applied to the photosensitive drum 10. Other wire electrodes can be used as the discharge electrode 11a.

The exposure unit 12 as an image exposure means for each color moves an exposure position on the photosensitive drum 10 between a discharge electrode 11a of the scorotron charger 11 and a development position of the development device 13 by a developing sleeve 131. Is provided on the upstream side in the rotation direction of the photosensitive drum 10 with respect to the photosensitive drum 10.

The exposure unit 12 is a linear exposure element 12a in which a plurality of LEDs (light emitting diodes) as image exposure light emitting elements arranged in the main scanning direction in parallel with the axis of the photosensitive drum 10 are arranged in an array. And a SELFOC lens 12b as an equal-magnification imaging element are configured as an exposure unit attached to a holder (not shown). The exposure unit 12 for each color is attached to the holding member 20. In addition to the exposure unit 12 for each color, the uniform exposure unit 12c and the simultaneous transfer exposure unit 12d are attached to the holding member 20 to form the base of the photosensitive drum 10. Housed inside. Image data of each color read by a separate image reading device and stored in the memory is sequentially read from the memory and input to the exposure unit 12 for each color as an electric signal.

As the exposure element, an element in which a plurality of light-emitting elements such as FL (phosphor light emission), EL (electroluminescence), PL (plasma discharge), and LED (light-emitting diode) are arranged in an array is used. The light-emitting wavelength of the light-emitting element used in this embodiment may be shorter than the wavelength at which the color toner does not have sufficient transparency because the image exposure is performed from the back surface. Usually, a toner having a high transmittance of 680 nm to 900 nm for Y, M and C toners is used.

The developing device 1 provided on the rotating photosensitive drum 10 in accordance with the color sequence in which an image is formed.
3, in the present embodiment, the Y and M developing units 13 are on the left side of the photosensitive drum 10 and the C and K developing units 13 are photosensitive on the photosensitive drum 10 indicated by arrows in FIG. The Y and M scorotron chargers 11 are disposed below the developing casing 138 of the Y and M developing units 13, and the developing casing 1 of the C and K developing units 13 is disposed on the right side of the body drum 10.
The C and K scorotron chargers 11 are arranged above 38.

A developing device 13 as a developing means for each color contains a one-component or two-component developer of yellow (Y), magenta (M), cyan (C) and black (K), respectively. At a developing position, the photosensitive drum 10 rotates in the same direction as the rotation direction of the photosensitive drum 10 while maintaining a predetermined gap from the peripheral surface of the body drum 10, for example, a thickness of 0.5 mm to 1 m.
m, cylindrical developing sleeve 131 made of non-magnetic stainless steel or aluminum material having an outer diameter of 15 mm to 25 mm
It has.

The developing unit 13 is urged by an abutting roller (not shown) to a gap of a predetermined value from the photosensitive drum 10, for example, 300 μm.
In the developing operation of the developing unit 13 for each color, a developing bias to which a DC voltage or an AC voltage AC is applied is applied to the developing sleeve 131, and a developing bias is applied to the developing sleeve 131. Jumping development with a component or two-component developer is performed, and a DC bias of the same polarity as the toner (minus polarity in the present embodiment) is applied to the negatively charged photosensitive drum 10 that grounds the transparent conductive layer. Thus, non-contact reversal development for attaching toner to the exposed portion is performed. At this time, the precision of the development interval needs to be about 20 μm or less in order to prevent image unevenness.

The developing unit 13 for each color applies a developing bias voltage to the electrostatic latent image on the photosensitive drum 10 formed by the charging by the scorotron charger 11 and the image exposure by the exposure unit 12. (In the present embodiment, the photosensitive drum is negatively charged,
Reversal development is carried out with a negative polarity toner).

As a document image, an image read by an image sensor of an image reading apparatus separate from the apparatus or an image edited by a computer is temporarily stored as image data for each of Y, M, C and K colors. And stored.

The start of image recording causes the photosensitive drum drive motor (not shown) to start, so that the photosensitive drum 10 is rotated clockwise as shown by the arrow in FIG. 1, and at the same time, yellow (Y) is developed on the left side of the photosensitive drum 10. Developing casing 1 of container 13
The application of a potential to the photoconductor drum 10 is started by the charging action of the Y scorotron charger 11 arranged below 38.

After a potential is applied to the photosensitive drum 10, the Y exposure unit 12 starts exposure with a first color signal, that is, an electric signal corresponding to Y image data, and the rotation of the drum scans the surface to expose the photosensitive drum 10. An electrostatic latent image corresponding to the Y image of the original image is formed on the layer.

The latent image is reversal-developed by the Y developing device 13 in a state where the developer on the developing sleeve is not in contact with the developer, and a yellow (Y) toner image is formed in accordance with the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 is placed on the yellow (Y) toner image, and further on the left side of the photosensitive drum 10 and above the yellow (Y), a magenta (M) developing device 1 is provided.
An electric signal corresponding to the second color signal of the M exposure unit 12, that is, the M image data, is applied by the charging action of the magenta (M) scorotron charger 11 disposed below the third developing casing 138. Is performed, and magenta (M) is formed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13.
Are sequentially superimposed and formed.

By the same process, the developing casing 13 of the developing unit 13 for cyan (C) is located on the right side of the photosensitive drum 10.
The cyan (C) toner image corresponding to the third color signal is further obtained by the cyan (C) scorotron charger 11, the exposure unit 12 of C, and the developing unit 13 of C, which are arranged above the photoconductor 8 The black (K) scorotron charger 11, the exposure unit 12, and the developing device 13 are arranged on the right side of the drum 10 and below the developing casing 138 of the black (K) developing device 13 at the lower part of the fourth color by the fourth unit. A black (K) toner image corresponding to the signal is sequentially superposed, and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10 (toner image forming means).

Exposure unit 1 for Y, M, C and K
Exposure of the organic photosensitive layer of the photosensitive drum 10 by 2 is performed from the inside of the drum through the transparent substrate described above. 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 the same exposure as the image corresponding to the first color signal is performed. It is possible to form an electrostatic latent image.

By the above-described image forming process, a superimposed color toner image serving as a back image is formed on the photosensitive drum 10 (first image carrying means) as an image carrier. The transfer roller 14c to which a DC voltage having the opposite polarity (positive polarity in the present embodiment) is applied to the superposed color toner image in the transfer area 14b by the driving roller 14d and the driven roller 1
4e, and is collectively transferred onto a toner image receiving member 14a (second image carrying means) provided in proximity to or in contact with the photosensitive drum 10. 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 image carrier AC static eliminator 16 and then enters the cleaning device 19 or the photoconductive drum 10.
Cleaning blade 19a made of rubber material in contact with
In order to eliminate the history of the photoreceptor up to the previous print, the peripheral surface of the photoreceptor is removed by, for example, exposure by a uniform exposure unit 12c before charging using a light emitting diode, and the charge at the previous print is removed. Is removed and the next color image formation of the front surface image is performed.

The back side image formed on the toner image receiving body 14a is synchronized with the transfer area 14b, and the surface image of the superimposed color toner image is transferred to the photosensitive drum in the same manner as in the above-described color image forming process. 10 is formed. 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 formation on the image carrier.

The recording paper P, which is a transfer material, is sent out by a feed roller 15a from a paper feed cassette 15, which is a transfer material storage means, and is conveyed to a timing roller 15b.

The recording paper P is driven by a timing roller 15b to form a color toner image of a front image carried on the photosensitive drum 10 and a color toner image of a back image carried on the toner image receiver 14a. The paper is fed to the transfer area 14b in synchronization.

At this time, the paper charging brush 150 as a transfer material charging means can be brought into contact with and released from the toner image receiving member 14a with the support shaft 152 as a rotation fulcrum.
The recording paper P as the transfer material is charged to the same polarity as the toner by the paper charging brush 150 provided with the brush member 151 which is brought into the contact state with the recording paper P in the contact state with the toner image 4a. The transfer area 14b is absorbed by the body 14a.
Is sent to

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 toner image receiving member 14a or the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed. . Simultaneously with the passage of the recording paper P, the paper charging brush 150 is separated from the toner image receiving body 14a, and the contact is released.

A surface image on the peripheral surface of the photosensitive drum 10 is collectively recorded on a recording paper by a transfer unit 14c as a first transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied. It is transferred to the upper surface side (front side) of P. At this time, the back surface image on the peripheral surface of the toner image receiver 14a is not transferred to the recording paper P but exists on the toner image receiver 14a. Next, a backside image on the peripheral surface of the toner image receiving body 14a is collectively recorded by a backside transfer unit 14g as a second transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. The image is transferred to the lower surface (back surface) of the paper P. At the time of transfer by the transfer device 14c, uniform exposure is performed by a simultaneous transfer exposure device 12d using, for example, a light emitting diode, provided inside the photosensitive drum 10 so as to perform good transfer so as to face the transfer device 14c. Is performed. Alternatively, a bias roller can be used as the first transfer unit.

Since the toner images of the respective colors overlap each other, it is preferable that the toners in the upper layer and the lower layer of the toner layer are charged to the same polarity with the same charge amount in order to enable batch transfer. Therefore, in a double-sided image formation in which the polarity of the color toner image formed on the toner image receiving member 14a is inverted by corona charging or the polarity of the color toner image formed on the image carrier 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 image carrier, and the color toner images of the same polarity formed by superimposing are collectively transferred to the toner image receiver 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 image carrier, and the color toner images of the same polarity formed by superimposition are collectively transferred to the recording paper P without changing the polarity. It is preferable because it contributes to improvement of the property.

From the above, in the color image formation, the first transfer means is operated to form a color toner image on the surface of the transfer material by using the above-described front and back surface image forming method. 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 means is preferably employed.

The toner image receiver 14a has a thickness of 0.5 mm
A 2.0 mm endless rubber belt, a semiconductive substrate of silicon rubber or urethane rubber having a resistance of 10 ⁸ Ω · cm to 10 ¹² Ω · cm, and a toner filming prevention layer outside the rubber substrate. It has a two-layer structure in which a fluorine coating having a thickness of 5 μm to 50 μm is performed. This layer also preferably has a similar semiconductivity. Instead of the rubber belt substrate, semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate, or the like having a thickness of 0.1 mm to 0.5 mm can also be used.

The recording paper P on which the color toner images are formed on both sides is discharged by a paper separation AC discharger 14h for separating the transfer material, separated from the toner image receiver 14a, and a heater is provided inside both rollers. The sheet is conveyed to a fixing device 17 as a fixing unit including two rollers.
By applying heat and pressure between the fixing roller 17a and the pressure roller 17b, the toner adhered to the front and back of the recording paper P is fixed, and the recording paper P on which double-sided image recording has been performed is sent by the paper discharge roller 18. And discharged to a tray outside the apparatus.

The toner remaining on the peripheral surface of the toner image receiving member 14a after the transfer is provided to a toner image receiving member cleaning device 140 as a cleaning means as described later, and the toner image receiving member is rotated around a support shaft 142 as a rotation fulcrum. Body 14a
The cleaning is performed by a blade member 141 which can be brought into contact with and released from the blade. The toner remaining on the peripheral surface of the photoconductor drum 10 after the transfer is subjected to static elimination by the image carrier AC static eliminator 16, and then enters a cleaning device 19 or is made of a rubber material that abuts on the photoconductor drum 10. The toner is scraped into the cleaning device 19 by the cleaning blade 19a, and is collected by a screw 19b into a waste toner container (not shown). The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is uniformly charged by the Y scorotron charger 11, and enters the next image forming cycle.

By using the above-described method, since the superimposed color toner images are transferred collectively, color shift of the color image on the toner image receiving member, scattering or rubbing of the toner, and the like are less likely to occur, and image deterioration is small. A double-sided color image is formed.

In the above-described image forming apparatus, it is a matter of course that only one side is copied by the first image bearing means or the second image bearing means.

In the above-described double-sided image forming process, as shown in FIG.
The driven roller 14e of the toner image receiver 14a
A toner image receiver cleaning device 140 as a cleaning unit is provided in opposition to the cleaning device.

The recording paper P is carried on the photosensitive drum 10 in a state where the blade member 141 provided in the toner image receiver cleaning device 140 and rotatable around the support shaft 142 is separated from the toner image receiver 14a. The color toner image of the front side image and the color toner image of the back side image carried on the toner image receiver 14a are synchronized with each other, and are transferred by a timing roller (not shown) on a transfer unit 14c as a first transfer unit. Immediately before the recording paper P, which is fed to the transfer area 14b and is to be conveyed onto the toner image receiver 14a, overlaps with the color toner image of the back side image carried on the toner image receiver 14a, the transfer material A paper charging brush 150 as charging means is rotated in contact with the toner image receiving member 14a about a support shaft 152 as a rotation center, and the paper charging brush 15
The leading end of the No. 0 brush member 151 is set to a charging position where the leading end of the recording paper P is abutted.

At the charging position, the paper charging brush 150 is applied with the bias voltage E1 simultaneously with the contact. While the paper charging brush 150 is in contact with the toner, the toner has the same polarity (in the present embodiment, minus polarity) of −500 VDC or more.
A bias voltage E1 of -2 kVDC is applied.

The paper charging brush 150 is rotated just before or at the same time as the trailing edge of the recording paper P, and is released from the contact with the toner image receiving body 14a, and as shown in FIG. It is moved to the separated non-charging position.

At this time, at the non-charging position, the bias voltage E1 is applied to the paper charging brush 150 not only when the recording paper P is being fed but also when the recording paper P is separated. Voltage, for example, -500, which is about the same as at the time of contact
It is preferable that the bias voltage E1 of VDC to −2 kVDC is applied to the brush member 151 of the paper charging brush 150. AC component (500Hz-1
0kHz, 100V _PP ~1000V _PP) by superimposing further possible to prevent the toner from adhering to the paper charging brush 150.

Paper charging brush 15 as transfer material charging means
0 is separated from the toner image receiver 14a.
By preventing the toner from adhering to the toner image receiving member 14a and applying a voltage having the same polarity as the toner to the paper charging brush 150, the toner on the toner image receiving member 14a is moved from the toner image receiving member 14a to the paper charging brush. The movement to 150 is suppressed, and toner contamination of the paper charging brush 150 is prevented. In particular, the toner image receiver cleaning device 140
When the toner pool at the time of releasing the blade member 141 passes through the paper charging brush 150, the paper charging brush 150
Image receiving member 1 of paper charging brush 150 so that
It is necessary to release the contact with 4a.

As described above, when the recording paper P passes, the paper charging brush 150 is brought into contact with the toner image receiving member 14a, and the charging position where the paper charging brush 150 comes into contact with the recording paper P and the bias voltage E1 is applied is recorded. When the paper P is not passing, the paper charging brush 150
Is released from the toner image receiver 14a, and the recording paper P
Movement to and from the non-charging position to which the bias voltage E1 is preferably applied is performed in synchronization with the passage of the recording paper P by the brush member 151 of the paper charging brush 150 as the transfer material charging means. . When the blade member 141 of the toner image receiver cleaning device 140 is released, it is preferable that the paper charging brush 150 be at least in the non-charging position.

Paper charging brush 15 as transfer material charging means
FIG. 4 shows a mechanism for abutting and releasing zero. Paper charging brush 15
Numeral 0 is constituted by a brush member 151 and a holder 153, and is rotated about the support shaft 152 as a rotation fulcrum. The spring 154 locked to the holder 153 causes the holder 153 to be attracted in the direction of the toner image receiver 14a to a position where the stopper 155 abuts, and is brought into contact with the toner image receiver 14a, so that the brush member 151 is recorded. It comes into contact with paper P.

At the non-charging position when the recording paper P does not pass,
The solenoid SD1 is synchronized with the conveyance timing of the recording paper P.
Is activated, the lever 156 of the solenoid SD1 locked by the holder 153 is sucked, and the paper charging brush 15
0 is rotated in the direction indicated by the arrow in FIG. 4, the recording paper P is released from the toner image receiver 14 a to which the recording paper P is conveyed, and is separated from the recording paper P.

The moving distance of the leading end of the brush member 151 of the paper charging brush 150 from the toner image receiver 14a at the time of separation is preferably 1 mm or more and 10 mm or less as the closest distance. If it is 1 mm or less, the toner pool on the toner image receiving member 14a may contact the tip of the brush member 151, and if it is 10 mm or more, the brush member 151 contacts the periphery, which is not preferable.

Another example of the transfer material charging means will be described with reference to FIGS. FIG. 5 is a view showing a second example of the transfer material charging means and a contact and release mechanism thereof. FIG. 6 is a view showing a third example of the transfer material charging means. FIG. 6B is a cross-sectional view of a transfer material charging unit of a third example, and FIG.
FIG. 9 is a perspective view of a transfer material charging unit in the example of FIG.

As shown in FIG. 5, a second example uses a paper charging roller 250 as the transfer material charging means. The mechanism for contacting and releasing the toner image receiving member 14a has been described with reference to FIG. A mechanism similar to the above-described one is used, and depending on the charging position and the separation due to the contact with the recording paper P as a transfer material according to the contact state or the released state of the paper charging roller 250 with the toner image receiving member 14a. The non-charging position is the same as that described in FIG. 4, and is used in the same process as that described in the image forming apparatus.

Paper charging roller 25 as transfer material charging means
Reference numeral 0 denotes a roller member 251 and a holder 253. The roller member 251 includes a shaft 251b and a conductive rubber roller 251a provided on the outer periphery of the shaft 251b.
1a is rotatably mounted.

The paper charging roller 250 is rotated about the support shaft 252 as a rotation fulcrum. At the charging position when the recording paper P passes, one end is fixed to the apparatus main body and the other end is locked to the holder 253. The spring 254 pulls the holder 253 in the direction of the toner image receiver 14a to a position where the stopper 255 abuts, and is brought into contact with the toner image receiver 14a.
The rubber roller 251a contacts the recording paper P.

At the charging position, the paper charging roller 250 is applied with the bias voltage E1 at the same time as the contact. While the paper charging roller 250 is in contact with the toner, the toner has the same polarity (in the present embodiment, minus polarity) of −500 VDC to
A bias voltage E1 of −2 kVDC is applied to the roller member 251.

The paper charging roller 250 is released from contact with the toner image receiver 14a immediately before or at the same time as the trailing edge of the recording paper P, and is moved to a non-charging position separated from the recording paper P.

At the non-charging position when the recording paper P does not pass,
The solenoid SD2 is synchronized with the conveyance timing of the recording paper P.
Is activated, the lever 256 of the solenoid SD2 locked by the holder 253 is sucked, and the paper charging roller 25
0 is rotated in the direction indicated by the arrow in FIG. 5, the recording paper P is released from the toner image receiver 14 a to which the recording paper P is conveyed, and is separated from the recording paper P.

At this time, at the non-charging position, the bias voltage E1 is applied to the paper charging roller 250 not only when the recording paper P is being fed but also when the recording paper P is separated from the toner. Voltage, for example, -500, which is about the same as at the time of contact
It is preferable that a bias voltage E1 of VDC to −2 kVDC is applied to the roller member 251 of the paper charging roller 250.

The moving distance of the rubber roller 251a of the paper charging roller 250 from the toner image receiving member 14a at the time of separation is preferably 1 mm or more and 10 mm or less as the closest distance. 1m
m or less, there is a possibility that the toner pool on the toner image receiving member 14a may come into contact with the rubber roller 251a.
The above is not preferable because the roller member 251 comes into contact with the surroundings.

Paper charging roller 25 as transfer material charging means
0 is separated from the toner image receiver 14a.
By preventing the toner from adhering to the toner image receiving member 14a and applying a voltage having the same polarity as the toner to the paper charging roller 250, the toner on the toner image receiving member 14a is moved from the toner image receiving member 14a to the paper charging roller 250a. The flying to the paper charging roller 250 is repelled, and toner contamination of the paper charging roller 250 is prevented. In particular, as described above, when the toner pool at the time of releasing the blade member 141 of the toner image receiver cleaning device 140 passes through the paper charging roller 250, the paper charging roller 250, particularly the rubber roller 251a, is cleaned so that the paper is not stained. It is necessary to release the contact of the charging roller 250.

As described above, when the recording paper P passes, the paper charging roller 250 is brought into contact with the toner image receiving member 14a, and the recording position is brought into contact with the recording paper P and the bias voltage E1 is applied thereto. When the paper P does not pass, the paper charging roller 250
Is released from the toner image receiver 14a, and the recording paper P
Movement to and from the non-charging position to which the bias voltage E1 is preferably applied is performed in synchronization with the passage of the recording paper P by the roller member 251 of the paper charging roller 250 as a transfer material charging unit. . When the blade member 141 of the toner image receiver cleaning device 140 is released, it is preferable that the paper charging roller 250 be at least in the non-charging position.

As shown in FIG. 6, a non-contact type corona discharger 350 can be used as the transfer material charging means.

The corona discharger 350 includes a shield member 351
And a wire electrode 351 a as a corona discharge electrode. A holder 353 is provided at a side end of the shield member 351, and a support shaft 35 provided on the holder 353 is provided.
6A, the corona discharger 350 can be moved from the charging position in FIG. 6A to a non-charging position rotated in the direction shown by the solid line arrow by a rotating means (not shown).

The corona discharger 350 performs corona discharge simultaneously with the entry of the recording paper P at the charging position, and the recording paper P
The corona discharge is stopped simultaneously with the passage of, and it is rotationally moved to the non-charging position. By being moved to the non-charging position, toner contamination is prevented.

Reference numeral 355 denotes recording paper P to the corona discharger 350
The bridge 355 is provided with a wire 355a made of, for example, a nylon thread.

The bridge 355 can be opened in the direction indicated by the dotted line with one end of the shield member as a fulcrum, and can be cleaned by opening the bridge 355 at the non-charging position.

In the above-described embodiment, the transfer material charging means has been described as being in contact with and separated from the second image bearing means. Good.

Embodiment 2 A second example of prevention of contamination of the transfer material charging means will be described with reference to FIG.
This will be described with reference to FIG. 8, FIG. 1 and FIG. FIG. 7 is a diagram illustrating a charging process of the transfer material charging unit, and FIG. 8 is a diagram illustrating a timing chart of a bias voltage.

In this embodiment, the same image forming process and mechanism as those described with reference to FIGS. 1 and 2 of Embodiment 1 are used, but in this embodiment, the transfer material charging means in the embodiment is used. Instead of the rotatable paper charging brush 150, a fixed paper charging brush 450 is used to prevent contamination. Members having the same functions and structures as described in the first embodiment are denoted by the same reference numerals.

Paper charging brush 45 as transfer material charging means
0 is fixed in contact with or close to the toner image receiver 14a, and when the recording paper P enters the toner image receiver 14a together with the leading end of the back side image, the recording paper P is on the toner image receiver 14a immediately before entering. To maximize the repulsion with the toner and to prevent the paper charging brush 450 from being stained, the toner on the paper charging brush 450 is transferred to the toner image receiving member 14a.
In FIG. 8C, for example, -1 kV of the same polarity (minus polarity in the present embodiment) as the toner is applied to the paper charging brush 450 by the bias voltage E2.
The highest voltage of DC to -3 kVDC is applied. In addition, for example, 500 Hz to 10
kHz, it is preferable to superimpose an AC voltage of 100V _PP ~1000V _PP.

When a voltage value lower than -1 kVDC is applied, the paper charging brush 450 is easily stained. When a voltage value higher than -3 kVDC is applied, discharge occurs, and the paper charging brush 450 is discharged.
And the toner image receiver 14a. Further, by superimposing an AC voltage, the effect of preventing toner adhesion is promoted.

The recording paper P is aligned with the leading end of the back side image and enters the toner image receiving member 14a. When the recording paper P passes through the transfer material in contact with the brush member 451 of the paper charging brush 450, the recording paper P A bias voltage E2 having the same polarity as that of the toner (minus polarity in the present embodiment), for example, −500 VDC to −2 kVDC shown in FIG. 8A is applied. Driven roller 14e and driving roller (not shown)
Is grounded. The driven roller 14e, which is grounded, and the application of the negative bias voltage E1 having the same polarity as the toner applied to the paper charger 150, cause the toner image receiver 14
The recording paper P charged to the negative polarity by the positive charging induced by the a is adsorbed on the toner image receiver 14a and conveyed.

When a voltage value lower than -500 VDC is applied, the adhesion of the recording paper P to the toner image receiving member 14a is deteriorated. When a voltage value higher than -2 kVDC is applied, charge is injected during charging of the paper and the toner image receiving member 14a is charged. The tendency of the toner image to be disturbed becomes remarkable.

When the recording paper P passes through the non-transferring material after passing through the brush member 451 of the paper charging brush 450, the paper charging brush 450 is applied to the paper charging brush 450 by the bias voltage E2 to have the same polarity as toner (minus polarity in this embodiment). FIG. 8 (b)
For example, a voltage of -100 VDC to -500 VDC is applied to prevent the toner from adhering to the paper charging brush 450 by repulsion with the toner on the toner image receiver 14a, and the toner adhering to the paper charging brush 450 Image receiver 14
a. The paper charging brush 450 may be in a floating state. In addition, in order to improve the cleaning property of the paper charging brush 450, for example, 500 Hz to 10 kHz, 100 V _{PP to} 1000
It is preferable to superimpose an AC voltage of V _PP .

When a voltage value lower than -100 VDC is applied, the repulsion of the toner due to the applied voltage is weak, and the tendency of the toner to adhere to the paper charging brush 450 becomes remarkable. Also, -500
If a voltage value higher than VDC is applied, the toner image receiving body 14a is damaged due to long-term use. The superimposition of the AC voltage promotes the effect of preventing toner adhesion.

As another bias voltage application method, the transfer material charging means is grounded, and the driven roller 14
The same charging effect can be obtained by controlling the application of the same voltage as that of the toner e with a polarity opposite to that of the toner.

Also in this embodiment, when the blade member 141 of the toner image receiver cleaning device 140 is released, it is preferable that the paper charging brush 450 is at least in the non-charging position. Further, similarly to the above-described embodiment, a paper charging roller can be used as the transfer material charging unit.

Although the present invention has been described using a color image forming apparatus, it is a matter of course that the present invention can be applied to a monochrome image forming apparatus. Further, it is needless to say that the control timing is appropriately changed according to the image forming size and the size of the transfer material.

The present invention is not limited to this method but also includes a modification for forming a double-sided image.
Japanese Patent Application Laid-Open Nos. 63-180969 and 63-2, in which after inverting the polarity of the toner corresponding to the backside image shown in JP-A-28740, the toner is simultaneously transferred to both sides of the transfer material.
In the tandem method of JP-A-98255 and JP-A-1-44457, changing the process conditions and image data processing conditions between the front surface and the back surface as described above is used, and the image density and color tone are adjusted. And a double-sided image can be formed.

[0084]

According to the first or second aspect of the present invention, the toner adhered to the second image bearing means does not adhere to the transfer material charging means, so that toner contamination of the transfer material charging means is prevented, and the transfer material Good adhesion to the image carrying means 2 is maintained, and good transfer of the transfer material is performed.

According to the third aspect, the toner adhered to the second image bearing means is repelled by the bias voltage having the same polarity as the toner applied to the transfer material charging means, and does not fly to the transfer material charging means. In addition, toner contamination of the transfer material charging means is prevented.

According to the fourth aspect, the transfer material charging means is the second type.
Is not directly in contact with the image carrying means, and toner contamination of the transfer material charging means by toner adhered to the second image carrying means is prevented.

According to the fifth aspect, the toner accumulation on the second image bearing means when the cleaning means of the second image bearing means is released does not come into direct contact with the transfer material charging means, and the toner of the transfer material charging means is not contacted. Dirt is prevented.

According to the sixth aspect, the toner adhered to the second image bearing means is repelled by the bias voltage having the same polarity as the toner applied to the transfer material charging means and does not adhere to the transfer material charging means. In addition, toner contamination of the transfer material charging means is prevented, good adhesion between the transfer material and the second image bearing means is maintained, and good transfer of the transfer material is performed.

According to the present invention, in particular, when the cleaning means of the second image bearing means is released, the toner pool on the second image bearing means is biased to the same polarity as the toner applied to the transfer material charging means. The transfer material charging means is prevented from being stained with toner without being repelled by the voltage and adhering to the transfer material charging means.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a state where toner images are formed on both surfaces.

FIG. 3 is a diagram illustrating a contact timing of a transfer material charging unit to a toner image receiver.

FIG. 4 is a diagram illustrating a first example of a transfer material charging unit and a contact and release mechanism thereof.

FIG. 5 is a diagram illustrating a second example of a transfer material charging unit and a contact and release mechanism thereof.

FIG. 6 is a diagram illustrating a third example of a transfer material charging unit.

FIG. 7 is a diagram illustrating a charging process of a transfer material charging unit.

FIG. 8 is a diagram showing a timing chart of a bias voltage.

FIG. 9 is a diagram showing a conventional problem.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum 11 scorotron charger 12 exposure unit 13 developing device 14a toner image receiver 14c transfer device 14g backside transfer device 17 fixing device 140 toner image receiver cleaning device 150,450 paper charging brush 151,451 brush member 250 paper charging Roller 251 Roller member 350 Corona discharger E1, E2 Bias voltage P Recording paper

Claims (7)

[Claims] A first image carrying means for carrying the toner image formed by the toner image forming means; and a toner image carried by the first image carrying means is transferred. A second image carrying means carried on the surface; a first transferring means for transferring the toner image carried on the first image carrying means onto the surface of the transfer material; and a carrying means carried on the second image carrying means. An image forming apparatus comprising: a second transfer unit configured to transfer the toner image transferred to the back surface of the transfer material; and a fixing unit configured to fix the toner image transferred to both surfaces of the transfer material. A transfer material charging unit for charging the transfer material entering the holding unit and adsorbing the transfer material on the second image holding unit;
An image forming apparatus, wherein the image forming apparatus is movable to a charging position at which the transfer material is charged by contacting the transfer material, and a non-charging position separated from the transfer material. 2. The image forming apparatus according to claim 1, wherein a moving distance between the charging position and the non-charging position of the transfer material charging unit is 1 mm to 10 mm. 3. The image forming apparatus according to claim 1, wherein a bias voltage having the same polarity as that of the toner on the second image bearing unit is applied to the transfer material charging unit at the non-charging position. apparatus. 4. The apparatus according to claim 1, wherein the movement between the charging position and the non-charging position is synchronized with the passage of the transfer material through the transfer material charging unit. Image forming apparatus. 5. A cleaning means having a blade member which can be brought into contact with and released from the second image bearing means and which cleans the second image bearing means is provided opposite to the second image bearing means. 5. The image forming apparatus according to claim 1, wherein at least the transfer material charging unit is at a non-charging position when the blade member is released. 6. A first image carrying means for carrying a toner image formed by a toner image forming means, and a toner image carried by the first image carrying means is transferred, and the transferred toner image is A second image carrying means carried on the surface; a first transferring means for transferring the toner image carried on the first image carrying means onto a surface of the transfer material; and a carrying means carried on the second image carrying means. An image forming apparatus comprising: a second transfer unit configured to transfer the toner image transferred to the back surface of the transfer material; and a fixing unit configured to fix the toner image transferred to both surfaces of the transfer material. A transfer material charging means for charging the transfer material entering the support means and adsorbing the transfer material on the second image holding means; provided near or in contact with the second image bearing means; A bias voltage having the same polarity as that of the toner And a bias voltage having the same polarity as that of the toner on the second image bearing means is applied to the transfer material charging means even when the transfer material is not passing. Image forming apparatus. 7. A cleaning device having a blade member which can be brought into contact with and released from the second image bearing means and which cleans the second image bearing means is provided opposite to the second image bearing means. 7. The image forming apparatus according to claim 6, wherein when the blade member is released, a bias voltage having at least the same polarity as that of the toner on the second image bearing unit is applied to the transfer material charging unit.