JPH09258518A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hardly cause color smear, the scattering and rubbing of toner, etc., in a color image on a toner image receiving body and to reduce the deterioration of an image by batch-transferring superimposed color toner images. SOLUTION: A transfer belt 41 is provided to face a photoreceptor drum 10 and the superimposed color toner images are formed on the periphery of the drum 10 by a scorotron electrifier 11, an exposure unit 12 and a developing unit 13. The superimposed color toner images being rear surface images are formed on the drum 10. The superimposed color toner images of the rear surface images on the drum 10 are transferred temporarily onto the intermediate transfer belt 41 by a transfer roller 42, and then are batch-transferred to the toner image receiving body 14a by a transfer unit 14c to which a voltage having a polarity opposite to that of the toner is applied in a transfer area 14b. Surface images of the color toner images are formed on the drum 10 and transferred to the intermediate transfer belt 41, again. A recording paper P is attracted to the toner image receiving body 14 and fed to the transfer area 14b to prevent the irregularities of the image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a copying machine, a printer, a fax machine, etc., in which a charging means, an image exposing means and a developing means are arranged around the image carrier to form a toner image on the image carrier. The present invention relates to an electrophotographic color image forming apparatus that forms a color image by superimposing images on each other.

[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 Laid-Open No. 4445/1992 proposes a method in which after fixing both surfaces of a transfer material, fixing is carried out once.
No. 7, JP-A-4-214576, etc., an image forming unit including an image carrier, a charging unit, an image exposing unit, a developing unit and the like is arranged in parallel on a plurality of sets of toner image receiving bodies to form a color image. Methods have been proposed for making double-sided copies.

[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.

An object of the present invention is to solve the above problems and to provide a double-sided color image forming apparatus with less image deterioration.

[0006]

The first object is to carry a color toner image formed by superposing toner images by repeating charging, image exposure and reversal development on an image carrier.
Image carrying means, the color toner images carried by the first image carrying means are collectively transferred, the second image carrying means for carrying again the transferred toner images on the surface, and the first image carrying means.
First transfer means for transferring the color toner image carried by the image carrying means on one surface of the transfer material, and the color toner image carried by the second image carrying means on the other side of the transfer material. Second transfer means for transferring to the surface of the transfer material, the first transfer means, and then the second transfer means to transfer the color toner image to both surfaces of the transfer material, And a fixing unit for fixing the color toner image.

[0007]

Embodiments of the present invention will be described below. Note that the description in this column 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 a first embodiment of a color image forming apparatus of the present invention will be described with reference to FIGS. FIG. 1 is a sectional configuration diagram of a first embodiment of a color image forming apparatus of the present invention, FIG. 2 is a side sectional view of the image carrier of FIG. 1, and FIG. 3 is a first embodiment. FIG. 3 is a diagram showing a toner image formation state on both sides relating to the above.

The photosensitive drum 10, which is an image bearing member, is provided with a cylindrical substrate formed of, for example, a transparent member such as glass or transparent acrylic resin inside, and a transparent conductive layer a-
A photosensitive layer such as a Si layer or an organic photosensitive layer (OPC) is formed on the outer periphery of the substrate.

The photosensitive drum 10 is sandwiched by a front flange 10a and a rear flange 10b, and the front flange 10a is bearing-supported by a guide pin 10P1 provided on a cover 103 attached to a front side plate 101 of the apparatus main body.
The rear flange 10b is fitted onto a plurality of guide rollers 10R attached to the rear side plate 102 of the main body of the apparatus to hold the photosensitive drum 10. A gear 10G provided on the outer periphery of the rear flange 10b is meshed with a driving gear G1, and the power of the gear 10G rotates the photosensitive drum 10 in a clockwise direction indicated by an arrow in FIG. 1 with the transparent conductive layer being grounded. It

In the present embodiment, it is sufficient that the photoconductive layer of the photosensitive drum has an exposure light amount that can provide an appropriate contrast. Therefore, the light transmittance of the transparent substrate of the photosensitive drum in the present embodiment does not need to be 100%, and may have a characteristic that some light is absorbed when the exposure beam is transmitted. As the material of the translucent substrate, an acrylic resin, particularly one polymerized using methyl methacrylate monomer, has transparency, strength, accuracy,
Acrylic, fluorine used for other general optical members, etc.
Various translucent resins such as polyester, polycarbonate, and polyethylene terephthalate can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. The light-transmitting conductive layer is made of indium-tin-oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, or a light-transparent metal thin film made of Au, Ag, Ni, Al, or the like. As a film forming method, a vacuum evaporation method, an active reaction evaporation method, various sputtering methods, various CVD methods, a dip coating method, a spray coating method, and the like are used. As the photoconductor layer, an amorphous silicon (a-Si) alloy photosensitive layer, an amorphous selenium alloy photosensitive layer, or various organic photosensitive layers (OPC) can be used.

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 charging operation is performed by a control grid maintained at a predetermined potential with respect to the above-described organic photoconductor layer of the photoconductor drum 10 and a corona discharge having the same polarity as the toner using, for example, a sawtooth electrode as the discharge electrode 11a (this embodiment). , 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 exposing means for each color is arranged such that the exposure position on the photosensitive drum 10 is between the discharge electrode 11a of the scorotron charger 11 and the developing position of the developing device 13 and a developing sleeve 131. With respect to the photoconductor drum, the photoconductor drum is arranged on the upstream side in the rotation direction.

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). Exposure for each color is performed on a cylindrical holding member 20 fixed with guide pins 10P2 provided on the rear plate 102 of the apparatus main body and guide pins 10P1 provided on the cover 103 attached to the front plate 101 as guides. Unit 12, uniform exposure device 1
2c and a transfer simultaneous exposure device 12d are attached and housed inside the substrate of the photoconductor drum 10. 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, other linear elements in which a plurality of light emitting elements such as FL (fluorescent substance emission), EL (electroluminescence), PL (plasma discharge), and LED (light emitting diode) are arranged in an array form are used. Used. The emission wavelength of the light emitting element used in this embodiment is usually Y,
A range of 680 to 900 nm, which has a high transmittance of the M and C toners, is preferable, but a shorter wavelength which does not have sufficient transparency for the color toner since image exposure is performed from the back surface may be used.

In the present embodiment, the color sequence for image formation and the developing device provided on the rotated photosensitive drum in the color sequence are arranged in the rotational direction of the photosensitive drum 10 indicated by the arrow in FIG. On the other hand, the Y and M developing devices 13 are arranged on the left side of the photoconductor drum 10, and the C and K developing devices 13 are arranged on the right side of the photoconductor drum 10. The Y and M scorotron chargers 11 are arranged below, and the C and K scorotron chargers 11 are arranged above the developing casing 138 of the C and K developing units 13.

The developing device 13, which is a developing means for each color, contains one-component or two-component developers of yellow (Y), magenta (M), cyan (C) and black (K), respectively, and is exposed to light. Rotating in the same direction as the rotation direction of the photoconductor drum 10 at the developing position while maintaining a predetermined gap with respect to the peripheral surface of the body drum 10, for example, 0.5 mm to 1 m in thickness
The developing sleeve 131 is made of cylindrical non-magnetic stainless steel or aluminum and has an outer diameter of 15 to 25 mm.

The developing device 13 is provided with an abutting roller (not shown) and a gap of a predetermined value from the photosensitive drum 10, for example, 100 μm.
.About.1000 .mu.m and kept in a non-contact state, and when developing by the developing device 13 for each color, the developing sleeve 131
A developing bias to which a DC voltage or an AC voltage AC is further applied is applied to the photosensitive drum, a jumping development is performed with a one-component or two-component developer contained in the developing device, and a negatively charged photosensitive member grounds the transparent conductive layer. The same polarity as the toner for the drum 10 (minus polarity in this embodiment)
Is applied, and non-contact reversal development is performed in which toner is adhered to an exposed portion.

The developing device 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).

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 as an original image. And stored.

A gear 10 provided on the rear flange 10b of the photoconductor drum 10 is driven through a drive gear G1 by starting a photoconductor drive motor (not shown) when image recording is started.
G is rotated to rotate the photosensitive drum 10 in the clockwise direction indicated by the arrow in FIG. 1, and at the same time, Y disposed below the developing casing 138 of the yellow (Y) developing device 13 to the left of the photosensitive drum 10. The application of a potential to the photosensitive drum 10 is started by the charging action of the scorotron charger 11 described above.

After a potential is applied to the photosensitive drum 10, exposure is started by a first color signal, that is, an electric signal corresponding to the Y image data in the Y exposure unit 12, and the surface of the photosensitive drum 10 is exposed by rotational scanning of the drum. 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 magenta (M) developing unit 1 on the yellow (Y) toner image and further on the left of the photosensitive drum 10 and above the yellow (Y).
3 is provided with a potential by the charging action of the magenta (M) scorotron charger 11 disposed below the developing casing 138, and an electric signal corresponding to the second color signal of the M exposure unit 12, that is, the image data of M. Exposure is performed by non-contact reversal development by the developing device 13 of M, and magenta (M) is formed on the yellow (Y) toner image.
Toner images are sequentially superposed and formed.

By the same process, the developing casing 13 of the cyan (C) developing device 13 is provided 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. In order to stabilize the temperature inside the photosensitive drum 10 and prevent the temperature from rising due to the heat generated by each exposure optical system 12, a material having good thermal conductivity is used for the holding member 20, and a heater 201 is used when the temperature is low. When the temperature is high, it can be suppressed to a level without any trouble by taking measures such as radiating heat to the outside through the heat pipe 202.

By the above image forming process, a superposed color toner image to be a back side image is formed on the photosensitive drum 10 (first image carrying means) as an image bearing member, and the back side image on the photosensitive drum 10 is formed. In the transfer area 14b, the superimposed color toner image is stretched between the driving roller 14d and the driven roller 14e by the transfer device 14c to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied. Toner image receiving body 14a (second image carrying means) provided close to or in contact with the drum 10.
It is transcribed all at once. 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 photosensitive 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 photosensitive drum 10.
Cleaning blade 19a made of a rubber material abutting against
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 and the transfer area 14b are synchronized with each other, and the front side image of the superimposed color toner image is formed on the photosensitive drum in the same manner as in the above-mentioned color image forming process. Formed on 10. 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.

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, fed by a feed roller 15b, and conveyed to a timing roller 15c.

The recording paper P is driven by the timing roller 15c to form a color toner image of a front surface image carried on the photosensitive drum 10 and a color toner image of a rear surface image carried on the toner image receiver 14a. Are fed to the transfer area 14b in synchronization with the above. At this time, the recording paper P is charged to the same polarity as the toner by the paper charger 14f, adsorbed to the toner image receiving body 14a, and fed to the transfer area 14b. By charging the paper with the same polarity as that of the toner, it is possible to prevent the toner image on the toner image receiving body and the toner image on the image carrier from being attracted to each other, thereby preventing the toner image from being disturbed.

The surface image on the peripheral surface of the photosensitive drum 10 is collectively recorded on the recording paper P by the transfer device 14c to which a voltage of the opposite polarity (plus polarity in this embodiment) to the toner is applied.
(First transfer means). 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,
Polarity opposite to toner (positive polarity in this embodiment)
The transfer of the back surface image on the peripheral surface of the toner image receiving body 14a to the lower surface side of the recording paper P is collectively performed by the back surface transfer device 14g to which the above voltage is applied (second transfer means). At the time of transfer by the transfer device 14c, the transfer device 14c
Uniform exposure is performed by a transfer simultaneous exposure device 12d, which is provided inside the photosensitive drum 10 so as to face the above, and uses, for example, a light emitting diode.

Since the toner images of the respective colors are overlapped with each other, it is preferable that the upper layer toner and the lower layer toner are charged with the same charge amount and the same polarity 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 superimposition 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.

As described 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 0.5-2.
An endless rubber belt of 0 mm, a semiconductive substrate of silicon rubber or urethane rubber having a resistance value of 10 ⁸ to 10 ¹² Ω · cm, and a thickness of 5 μm to 50 μm as a toner filming prevention layer outside the rubber substrate. And a two-layer structure with fluorine coating. This layer also preferably has a similar semiconductivity. 0.1-thick instead of rubber belt base
0.5mm semiconductive polyester or polystyrene,
Polyethylene, polyethylene terephthalate and the like 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 receiver 14a after the transfer is removed from the toner image receiver cleaning device 14i.
Cleaning. The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is transferred to the image carrier AC static eliminator 1.
After being discharged by 6, the cleaning device 19 is scraped into the cleaning device 19 by the cleaning blade 19a made of a rubber material which is in contact with the photosensitive drum 10, and is collected by a screw 19b in a toner discharge container (not shown). To be done. The photoconductor 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 the above method, the superimposed color toner images are collectively transferred, so that color deviation of the color image on the toner image receiver, toner scatter and rubbing hardly occur, and good double-sided color with little image deterioration. An image is formed.

Embodiment 2 The image forming process and each mechanism of the second embodiment of the color image forming apparatus of the present invention will be described with reference to FIGS. 4 and 5. FIG. 4 is a cross-sectional configuration diagram of a second embodiment of the color image forming apparatus of the present invention, and FIG. 5 is a diagram showing a toner image forming state on both surfaces according to the second embodiment. Members having the same functions and structures as those in the first embodiment are designated by the same reference numerals.

The toner image receiving body 14a stretched between the driving roller 14d and the driven roller 14e is the driving roller 14d.
4 is rotated in the direction indicated by the dotted arrow a in FIG. 4 and the following image formation is performed in a state of being separated from the photosensitive drum 10.

The photosensitive drum 10, which is an image carrier, has a cylindrical substrate provided inside and a photosensitive layer such as a conductive layer, an a-Si layer or an organic photosensitive layer (OPC) formed on the outer periphery of the substrate. Yes, it is rotated in the clockwise direction indicated by the arrow in FIG. 4 in the grounded state.

The photosensitive drum 10 as the image bearing member is driven and rotated, and in order to eliminate the history of the photosensitive drum 10 up to the pre-printing, the uniform exposure device 1 as the discharging means before charging.
21a, for example, a light-emitting diode is used to uniformly expose the peripheral surface of the photoconductor to remove the charge from the previous printing.

Scorotron charger 11 as charging means
Performs a charging action (in this embodiment, negative charging) on the above-described organic photoconductor layer of the photoconductor drum 10 by the control grid held at a predetermined potential and the corona discharge by the discharge electrode 11a. A uniform electric potential is applied to.

The photosensitive drum 10 is a scorotron charger 1.
After being uniformly charged to the peripheral surface by 1, an exposure unit 121 as an image exposure unit performs image exposure based on an image signal, and a latent image is formed on the photosensitive drum 10.

An exposure unit 121 as an image exposing means is a semiconductor laser as a light emitting element (not shown), and a rotary polygon mirror 12 for rotationally scanning a laser beam emitted from the semiconductor laser.
1b, an fθ lens 121c, a reflection mirror 121d, and the like, and a laser beam emitted from a semiconductor laser (not shown) is rotationally scanned by the rotary polygon mirror 121b, and rotates via the fθ lens 121c, the reflection mirror 121d, and the like. Image exposure is performed based on an image signal in the main scanning direction of the drum 10, and a latent image is formed on the photoconductor drum 10.

The peripheral portion of the photosensitive drum 10 is a developing means in which a developer composed of toner such as yellow (Y), magenta (M), cyan (C), black (K) and a carrier is filled. The developing device 13 for each color is provided, and first, development of the first color (for example, yellow) is performed by the developing sleeve 131.

The developing device 13 uses a non-contact developing method by applying a developing bias voltage to the electrostatic latent image formed on the photosensitive drum 10 formed by the charging by the scorotron charger 11 and the image exposure by the exposure unit 121. In a non-contact state, development is performed by reversal development with toner having the same polarity as the charging polarity (in this embodiment, the photosensitive drum is negatively charged, toner having a negative polarity).

The developing device 13 is provided with an abutting roller (not shown) and the photosensitive drum 10 and a predetermined value, for example, 100 μm to 10
The developing sleeve 13 is maintained in a non-contact state with a gap of 00 μm, and during the developing operation by the developing device 13, a developing bias in which a direct current or an alternating current is applied to the developing sleeve 131 is applied, and the one-component or two-component developing accommodated in the developing device is applied. A jumper development with an agent is performed, and a DC bias having the same polarity (negative polarity in this embodiment) as that of the toner is applied to the negatively charged photosensitive drum 10 that grounds the transparent conductive layer to apply toner to the exposed portion. The non-contact reversal development is performed to attach the.

After the development of the first color is completed, the image process of the second color (for example, magenta) is started, and the photoconductor drum 10 is again processed.
Are uniformly charged by the scorotron charger 11, and a latent image based on the image data of the second color is formed by the exposure unit 121. At this time, the charge removal by the uniform exposure means 121a performed in the image forming process for the first color is not performed. Two
Development with the magenta developer of the color is the development sleeve 13
1 is performed. The development is performed by non-contact reversal development by applying an AC bias and a DC bias in a superimposed manner between the developing sleeve 131 and the photosensitive drum 10.

For the third color (cyan) and the fourth color (black), the same image forming process as for the second color is performed, and four color toner images are superposed and developed on the photosensitive drum 10 (toner image). Forming means).

By the above image forming process, a superposed color toner image to be a back side image is formed on the photosensitive drum 10 (first image carrying means) as an image carrying body.
The toner image receiving body 14a is rotated about the axis of the driving roller 14d in the direction shown by the dotted arrow b in FIG. 4, and is brought into contact with the photosensitive drum 10. At the fifth rotation of the photoconductor drum 10, the superimposed color toner image of the back side image on the photoconductor drum 10 is applied with a voltage having a polarity opposite to that of the toner (a positive polarity in this embodiment) in the transfer area 14b. The transfer device 14c collectively transfers the toner image on the toner image receiver 14a (second image carrier) provided in contact with the photosensitive drum 10. 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.

After the superposed color toner images of the back side images on the photosensitive drum 10 are collectively transferred onto the toner image receiving body 14a, the toner image receiving body 14a is again centered on the axis of the driving roller 14d as shown in FIG. Is rotated in the direction indicated by the dotted arrow a, and is separated from the photoconductor drum 10.

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 goes to the cleaning device 19 or the photoconductor drum 10.
Cleaning blade 19a made of a rubber material abutting against
In order to eliminate the history of the photoconductor until the previous printing, the peripheral surface of the photoconductor is erased by the exposure by the uniform exposure device 121a before the charging using a light emitting diode, for example, and the charge at the time of the previous printing is performed. Are removed and color image formation of the next surface image is subsequently performed.

In the same manner as the color image forming process described above, the surface image of the superimposed color toner image is formed on the photosensitive drum 10.

Next, the front surface image formed on the photosensitive drum 10 and the back surface image formed on the toner image receiving body 14a are synchronized with each other in the transfer area 14b so that the toner image receiving body is formed. 14a is rotated about the axis of the drive roller 14d in the direction indicated by the dotted arrow b in FIG. 4, and is brought into contact with the photosensitive drum 10.

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

The recording paper P is driven by the timing roller 15c, and the color toner image of the front surface image carried on the photosensitive drum 10 and the color toner image of the back surface image carried on the toner image receiving body 14a are recorded. Are synchronized and fed to the transfer area 14b. At this time, the recording paper P is charged to the same polarity as the toner by the paper charger 14f, adsorbed to the toner image receiving body 14a, and fed to the transfer area 14b. By charging the paper with the same polarity as that of the toner, it is possible to prevent the toner image on the toner image receiving body and the toner image on the image carrier from being attracted to each other, thereby preventing the toner image from being disturbed.

The surface image on the peripheral surface of the photosensitive drum 10 is collectively recorded on the recording paper P by the transfer device 14c to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied.
(First transfer means). 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,
Polarity opposite to toner (positive polarity in this embodiment)
The transfer of the back surface image on the peripheral surface of the toner image receiving body 14a to the lower surface side of the recording paper P is collectively performed by the back surface transfer device 14g to which the above voltage is applied (second transfer means).

Since the toner images of the respective colors are overlapped with each other, it is preferable that the upper layer toner and the lower layer toner are charged with the same charge amount and the same polarity 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.

Repeated reversal development on the image carrier, the color toner images of the same polarity formed by superposition are collectively transferred to the toner image receiving body 14a without changing the polarity, and then the recording paper without changing the polarity. The batch transfer to P is preferable because it contributes to the improvement of transferability in the back side 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 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-mentioned front and back image forming methods, and then, A double-sided image forming method in which the second transfer unit is operated to form a color toner image on the back surface of the transfer material is preferably adopted.

The toner image receiver 14a has a thickness of 0.5-2.
An endless rubber belt of 0 mm, a semiconductive substrate of silicon rubber or urethane rubber having a resistance value of 10 ⁸ to 10 ¹² Ω · cm, and a thickness of 5 μm to 50 μm as a toner filming prevention layer outside the rubber substrate. And a two-layer structure with fluorine coating. This layer also preferably has a similar semiconductivity. 0.1-thick instead of rubber belt base
0.5mm semiconductive polyester or polystyrene,
Polyethylene, polyethylene terephthalate and the like can also be used.

The recording paper P on which the color toner images are formed on both sides is discharged by the paper separation AC discharger 14h for separating the transfer material, separated from the toner image receiving body 14a, and both rollers have heaters. The sheet is conveyed to a fixing device 17 as a fixing unit composed of 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 image receiver 14a is again driven by the drive roller 1.
It is rotated in the direction shown by the dotted arrow a in FIG. 4 about the axis of 4d and separated from the photosensitive drum 10. The toner remaining on the peripheral surface of the toner image receiving body 14a after the transfer is cleaned by the blade of the toner image receiving body cleaning device 14i which is brought into contact with the toner image receiving body 14a. Also,
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 the cleaning device 19 or a cleaning blade made of a rubber material contacting the photoconductor drum 10. 19a is scraped off into the cleaning device 19 and screw 19b
Is collected in an unillustrated waste toner container. The photoconductor drum 10 from which the residual toner has been removed by the cleaning device 19 is uniformly charged by the scorotron charger 11 and enters the next image forming cycle.

Since the superimposed color toner images are collectively transferred by the above-described method, color deviation of the color image on the toner image receiver, toner scattering and rubbing are less likely to occur, and good double-sided color with little image deterioration. An image is formed.

Embodiment 3 The image forming process and each mechanism of the third embodiment of the color image forming apparatus of the present invention will be described with reference to FIG. FIG. 6 is a sectional configuration diagram of a third embodiment of the color image forming apparatus of the invention. In this embodiment, the color toner image on the image carrier is formed by the same image forming process as in the first embodiment, and the color toner image on the image carrier is transferred to the toner image receiver or the intermediate image transfer member via the intermediate transfer member. The toner image is transferred to the transfer material, and therefore the arrangement of the toner image receiving body and the feeding direction of the transfer material are opposite to those in the first embodiment. Members having the same functions and structures as those in the first embodiment are designated by the same reference numerals.

A transfer belt 41 as an intermediate transfer member is provided so as to face the photosensitive drum 10 as an image carrier,
A first roller 42 as a transfer roller for pressing the intermediate transfer belt 41 against the photosensitive drum 10, a second roller 43 for pressing the intermediate transfer belt 41 against the toner image receiving body 14a in the transfer area 14b, and a backup roller 44, Stretched between. Reference numeral 45 is an intermediate transfer belt cleaning device.

In the same manner as described in the first embodiment, the scorotron charger 1 as the charging means for each color.
1. An overlapping color toner image is formed on the peripheral surface of the photosensitive drum 10 within one rotation of the photosensitive drum 10 by the exposure unit 12 as the image exposing unit and the developing device 13 as the developing unit (toner image formation). means).

The toner image forming means forms a superposed color toner image as a back side image on the photoconductor drum 10 as an image carrier, and the superposed color toner image of the back side image on the photoconductor drum 10 is transferred to the transfer roller. After being temporarily transferred to the intermediate transfer belt 41 (first image carrier) by 42, in the transfer area 14b, a transfer device 14c to which a voltage having a polarity opposite to the toner (positive polarity in the present embodiment) is applied, Drive roller 14d and driven roller 14e
The image is collectively transferred onto the toner image receiving body 14a (second image carrying means) which is stretched between and provided close to or in contact with the photosensitive drum 10.

Again, the surface image of the superimposed color toner image is formed on the photosensitive drum 10 by the toner image forming means and transferred to the intermediate transfer belt 41. 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.

A recording paper P as a transfer material is formed on the photosensitive drum 10, and once transferred to the intermediate transfer belt 41, the color toner image of the surface image carried on the intermediate transfer belt 41 and the toner image receiver. 14a is synchronized with the color toner image of the back side image carried on the transfer area 14a.
sent to b. At this time, the recording paper P is the paper charger 14f.
Is charged to the same polarity as the toner by the toner, and the toner image receiving body 1
It is adsorbed by 4a and fed to the transfer area 14b. By charging the paper with the same polarity as that of the toner, it is possible to prevent the toner image on the toner image receiving body and the toner image on the image carrier from being attracted to each other, thereby preventing the toner image from being disturbed.

The surface image on the peripheral surface of the intermediate transfer belt 41 is collectively transferred onto the upper surface side of the recording paper P by the transfer device 14c to which a voltage having a polarity opposite to the toner (plus polarity in this embodiment) is applied. (First transfer means). On this occasion,
The rear surface image on the peripheral surface of the toner image receiving body 14a is not transferred to the recording paper P and exists on the toner image receiving body 14a. Next, the back surface image on the peripheral surface of the toner image receiving body 14a is collectively transferred to the lower surface side of the recording paper P by the back surface transfer device 14g to which a voltage having a polarity opposite to the toner (plus polarity in this embodiment) is applied. (Second transfer means).

The toner image receiver 14a has a thickness of 0.5-2.
An endless rubber belt of 0 mm, a semiconductive substrate of silicon rubber or urethane rubber having a resistance value of 10 ⁸ to 10 ¹² Ω · cm, and a thickness of 5 μm to 50 μm as a toner filming prevention layer outside the rubber substrate. And a two-layer structure with fluorine coating. This layer also preferably has a similar semiconductivity. 0.1-thick instead of rubber belt base
0.5mm semiconductive polyester or polystyrene,
Polyethylene, polyethylene terephthalate and the like can also be used.

The recording paper P on which the color toner images are formed on both sides is neutralized by the paper separation AC neutralizer 14h for separating the transfer material and separated from the toner image receiver 14a, and both rollers have heaters inside. The toner is conveyed to a fixing device 17 as a fixing unit composed of two rollers, and heat and pressure are applied to fix the adhered toner on the front and back of the recording paper P to perform double-sided image recording. Will be ejected to the tray.

Toner image receiver 1 after transfer in this embodiment
The toner remaining on the peripheral surface of 4a is the toner image receiving body 14a.
Cleaning device for toner image receptor 1
It is cleaned by a 4i blade.

Since the superimposed color toner images are transferred in a batch by the above method, color deviation of the color image on the toner image receiver, toner scattering and rubbing are less likely to occur, and good double-sided color with little image deterioration. An image is formed.

In the above first to third embodiments, it is needless to say that the first image forming means makes a copy on only one side.

[0079]

According to the first or fourth aspect of the present invention, since the superimposed color toner images are collectively transferred, color deviation of the color image on the toner image receiving body, toner scattering and rubbing hardly occur, and image deterioration occurs. A good double-sided color image formation is achieved.

According to the second aspect, the image carrier is downsized, and the color image forming apparatus is downsized.

According to the third aspect, it is easy to dispose the charging means, the image exposing means, the developing means and the like arranged around the image carrier.

[Brief description of drawings]

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

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

FIG. 3 is a diagram illustrating a toner image formation state on both surfaces according to the first embodiment.

FIG. 4 is a cross-sectional configuration diagram of a second embodiment of a color image forming apparatus of the present invention.

FIG. 5 is a diagram showing a toner image formation state on both surfaces according to the second embodiment.

FIG. 6 is a cross-sectional configuration diagram of a third embodiment of a color image forming apparatus of the present invention.

[Explanation of reference numerals] 10 photoconductor drum 11 scorotron charger 12,121 exposure unit 13 developing device 14a toner image receiver 14c transfer device 14g back surface transfer device 17 fixing device 41 intermediate transfer belt P recording paper

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masakazu Fukuchi 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica stock company (72) Inventor Akiyo Matsubara 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica stock company (72) Inventor Tadayoshi Ikeda 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Stock Company

Claims (4)

[Claims] 1. A first image carrier for carrying a color toner image formed by superposing toner images by repeating charging, image exposure and reversal development on the image carrier, and the first image carrier. A color toner image carried by the means, and a second image carrying means for carrying the transferred toner image again on the surface; and a color toner image carried by the first image carrying means. A first transfer means for transferring the color toner image carried on the one surface of the transfer material to the other surface of the transfer material, and a second transfer means for transferring the color toner image carried by the second image carrying means on the other surface of the transfer material. And a fixing unit for fixing the transferred color toner image after the color toner images are transferred to both surfaces of the transfer material by operating the first transfer unit and then operating the second transfer unit. A color image forming apparatus characterized by the above. 2. The color toner image according to claim 1, wherein charging, image exposure, and development are repeated on the image carrier to form a color toner image by one rotation of the image carrier. Image forming apparatus. 3. The color image forming apparatus according to claim 2, wherein the color toner images are superposed and formed by one rotation, and then transferred to the second image carrying means through an intermediate transfer member. . 4. The color toner according to claim 1, wherein the image bearing member is repeatedly charged, image-exposed, and developed, and the color toner images are superimposed and formed by multiple rotations of the image bearing member. Image forming apparatus.