JPH09325663A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently from front and back images onto an image carrier and to transfer them to the front and back of a transfer material at the same time by allowing image formation on a toner-image receiving body to precede image formation on the photosensitive drum used for transfer to the front of the transfer material, by synchronization with the reading of an original document. SOLUTION: In a transfer area 14b, superimposed color-toner images as a back image on the photoreceptor drum 10 are transferred all at once onto the toner-image receiving body 14a, provided close to the photoreceptor drum 10, by means of a transfer unit 14c to which a voltage having the opposite polarity of toner is applied. In synchronization, in the transfer area 14b, with the back image formed on the toner-image receiving body 14a, the front image as superimposed color-toner images is formed onto the photoreceptor drum 10. Thus, because, the superimposed color-toner images are transferred all at once, color slippage of the toner images on the toner-image receiving body 14a, toner scatter and rub, etc., hardly occur, and satisfactory both-sided color- image-formation with less image-deterioration is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine which arranges a charging means, an image exposing means and a developing means around an image carrier to transfer and fix a toner image formed on the image carrier onto a transfer material. The present invention relates to an electrophotographic image forming apparatus such as a printer, a FAX, or 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 No. 4576 discloses a method in which a toner image is formed on both surfaces of a transfer material and then fixing is performed once.

[0004]

As described above, the image forming apparatus for forming a double-sided image by using the above-mentioned double-sided reversal sheet feeding apparatus, as is well known, has a long transporting distance of the transfer material, and therefore is often used for copying. It takes a long processing time, and the transfer material is heated twice for fixing the image, so that the paper quality is damaged.

Therefore, the present inventor previously provided two image carrying means and two transfer means to transfer the toner images to both surfaces of the transfer material and simultaneously fix the transfer material having the toner images on both surfaces. We have conducted research on a device that can perform double-sided copying and realized an image forming device that can significantly increase the processing speed.

Further, according to the present invention, regardless of the reading order of the front and back sides of an original, the front and back images can be efficiently formed on a predetermined image carrying means in the shortest time and simultaneously transferred to the front and back sides of a transfer material. It is an object of the present invention to provide an image forming apparatus capable of efficiently copying a plurality of sheets of the same original.

[0007]

SUMMARY OF THE INVENTION The above-mentioned object is to combine 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 together. Second image carrying means for carrying the transferred toner image on the surface again, and first transfer carrying the toner image carried on the first image carrying means on the surface of the transfer material. Means, a second transfer means for transferring the toner image carried by the second image carrying means to the back surface of the transfer material, and a first transfer means carrying the toner image on the first image carrying means. The toner image formed on the transfer material is transferred to the surface of the transfer material, and the toner image carried on the second image carrying means is transferred to the back surface of the transfer material by the second transfer means. And fixing means for fixing the toner images transferred on both sides of the In the image forming apparatus, a document reading unit, housed in the image memory reads a document corresponding to the front and back surfaces, the output than either or the image memory synchronized with the original reading, the second
The image forming apparatus is characterized in that the image formation on the image carrying means is performed prior to the image formation on the first image carrying means for transferring the image onto the surface of the transfer material.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Two embodiments of an image forming apparatus to which the present invention is applied will be described. The present invention is not limited to the embodiments described below. The description in this section does not limit the technical scope of the claims and the meaning of terms. 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. Each of the embodiments described below is an embodiment of a color image forming apparatus that forms a color image, but the present invention is also applied to a monochrome image forming apparatus.

The image forming process and each mechanism of the first embodiment of the color image forming apparatus of the present invention will be described with reference to FIG. FIG. 1 is a sectional configuration diagram of a first embodiment of a color image forming apparatus of the present invention.

The photosensitive drum 10, which is an image bearing member, is provided with a cylindrical substrate formed of 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 rotated clockwise with the transparent conductive layer being grounded, as shown by the arrow in FIG.

In the present embodiment, it is sufficient that the photoconductive layer of the photosensitive drum has an exposure light amount capable of giving 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). An exposure unit 12 for each color and a uniform exposure device 1 are attached to a cylindrical holding member 20.
2c and a transfer simultaneous exposure device 12d are attached and housed inside the substrate of the photoconductor drum 10. It is read by an image reading device provided separately or on the upper surface of the device, which will be described later.
The image data of each color 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, there is a linear element in which a plurality of light emitting elements such as FL (fluorescent substance emission), EL (electroluminescence), PL (plasma discharge), LED (light emitting diode) are arranged in an array. Used. The emission wavelength of the light emitting element used in this embodiment is usually Y,
The range of 680 to 900 nm, which has high transparency of M and C toners, is preferable. However, since the image exposure is performed from the back side, a wavelength shorter than the above wavelength or a wavelength which does not have sufficient transparency for color toners may be used. .

In the present embodiment, the developing device provided in accordance with the color order in which images are formed and the rotating photosensitive drum is arranged in the rotational direction of the photosensitive drum 10 in the present embodiment. 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. 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 formed on the photoconductor drum 10 formed by the charging by the scorotron charger 11 and the image exposure by the exposure unit 12 described above. The toner having the same polarity as the charging polarity in a non-contact state by the non-contact developing method according to (the photosensitive drum in this embodiment is negatively charged,
Reversal development is carried out with a negative polarity toner).

At the start of image recording, the photoconductor driving motor (not shown) is started to rotate the photoconductor drum 10 in the clockwise direction indicated by the arrow in FIG. 1, and at the same time, the left side of the photoconductor drum 10 develops yellow (Y). Developer casing 13 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 the photoconductor drum 8.

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.

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.

Next, regarding the image forming process and each mechanism of the second embodiment of the color image forming apparatus of the present invention,
This will be described with reference to FIG. FIG. 2 is a sectional configuration diagram of the second embodiment of the color image forming apparatus of the present invention. 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.
2 is rotated in the direction shown by the dotted arrow a in FIG. 2 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 clockwise in the state of being grounded as shown by the arrow in FIG.

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.
An image that has been uniformly charged to the peripheral surface by the unit 1 and then electrically read by an exposure unit 121 as an image exposing unit by an image reading device provided separately or on the upper surface of the device and electrically processed. Image exposure is performed based on the 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. 2 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 image 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. 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 driving roller 14d in the direction shown by the dotted arrow b in FIG. 2 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 about the axis of 4d in the direction shown by the dotted arrow a in FIG. 2 and is 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.

The image data for each color of the document input to the color image forming apparatus of each of the above-described embodiments is, for example, the image reading apparatus 50A or 50B provided separately from the apparatus main body shown in FIG. Read by

In the case of the above-mentioned image reading apparatus 50A, the originals D are stacked in page order from the lower side with the front side facing downward, and the operation of the carry-out belt 51A and the separating roller 52 directs the lowermost original D to the conveying path 53. Be shipped.

The discharged document D is retracted to the position shown by the broken line by removing the guide plate G biased to the position shown by the solid line, and is placed on the transparent platen glass 55 via the conveyor belt 54. After being fed, it is temporarily stopped at the document reading position with the back side facing downward.

The rear surface image of the document D on the platen glass 55 is a first mirror unit 56 including an illumination lamp and a first mirror which form a scanning optical system, and a second V-shaped second mirror unit.
A second mirror unit 57 including a mirror and a third mirror
Of the first mirror unit 56 at the speed V and the speed V / 2 in the same direction by the second mirror unit.
Is read by the moving exposure of the camera, and an image is formed on the image sensor CCD by the projection lens L. The back surface image formed on the image pickup device CCD is shown in FIG.
As shown in (a), the image is temporarily stored in the image memory (I), and in the color image forming apparatus of the first embodiment, each of the exposure units 12 is used, while the color image forming of the second embodiment is performed. For the apparatus, the exposure unit 121
Are output as electric signals to the photoconductor drum 10 respectively.
The latent image is formed on the toner image, and the toner image formed after the development is transferred by the transfer device 14c, and the back surface image is formed on the toner image receiving body 14a.

When the image reading device 50A finishes reading the back side image, the document D is turned upside down through the reversing paper feeding path 58 by the temporary reverse rotation of the conveying belt 54, and again passes through the conveying path 53 and the conveying belt 54. The sheet is fed onto the platen glass 55 via the sheet and is temporarily stopped at the document reading position with the front side facing downward.

The surface image of the original D on the platen glass 55 is read by the scanning optical system, is temporarily stored in the image memory (II) as image data for each color, and is electrically supplied to the exposure unit 12 or 121. The image is output as a signal to form the surface image on the photosensitive drum 10 described above.

The back side image formed on the toner image receiving body 14a and the front side image formed on the photosensitive drum 10 are the front and back sides of the first recording sheet P fed from the sheet feeding cassette 15. And the first copy cycle is completed. The recording paper P holding the front-side toner image and the back-side toner image is fixed by the fixing device 17, and the front and back sides are reversed so that the front side faces downward and the recording paper P is discharged onto a tray outside the apparatus.

When copying the second and subsequent sheets, the image of the original D is not read, and the back side image is output by outputting the image data from the image memory (I) as shown by the broken line in FIG. 4 (a). In addition, the image memory (I
A front side image is formed by outputting the image data from I), and the front side image and the back side image are transferred to the front and back sides of the second and subsequent recording sheets P fed from the sheet feeding cassette 15, respectively. Done. The recording paper P holding the front toner image and the rear toner image is fixed by the fixing device 17, and is stacked in a page order on the recording paper discharged first with the front side down.

On the other hand, in the image reading apparatus 50A, the originals D for which the image reading has been completed are stacked in order from the lower side in the page order with the front side facing downward on the tray 60 via the discharge rollers 59 by the operation of the conveying belt 54. Is ejected.

On the other hand, in the case of the image reading apparatus 50B, the originals D are stacked in page order from the upper side with the front side facing upward, and the uppermost original D is directed to the conveying path 53 by the operation of the carry-out roller 51B and the separating roller 52. Be carried out.

The carried-out original D is fed onto the platen glass 55 through the same process as in the case of the image reading apparatus 50A described above, and is temporarily stopped at the original reading position with the front side facing down, The image is read by the scanning optical system and temporarily stored in the image memory (I) as image data for each color as shown in FIG.

When the reading of the front side image is completed, the document D
The platen glass 55 is again passed through the reverse paper feed path 58 by the same process as in the case of the image reading apparatus 50A described above.
The paper is fed on top and paused at the document reading position with the back side facing down.

The back side image of the original D on the platen glass 55 is read by the scanning optical system, is temporarily stored in the image memory (II) as image data for each color, and is electrically supplied to the exposure unit 12 or 121. The back surface image output as a signal and formed on the photoconductor drum 10 is transferred by the transfer device 14C, and the back surface image is formed on the toner image receiving body 14a.

Next, the image data of the front surface image is output from the image memory (I) to form the front surface image on the photosensitive drum 10, and the paper is fed from the paper feeding cassette 15 1
The front and back images are transferred to the front and back of the first recording sheet P, and the first copy is completed. The recording paper P holding the toner images on the front and back sides is fixed by the fixing device 17,
The paper is ejected onto the tray outside the device with the front and back reversed and the front side facing down.

When copying the second and subsequent sheets of the same original, the image is not read and the image data from each of the image memories (I) and (II) is output as indicated by the broken line in FIG. 4B. As a result, front and back images are formed in the order of the back surface image and then the front surface image. The recording paper P that holds the toner images on the front and back sides is fixed, and is sequentially ejected outside the apparatus, and is stacked on the previously ejected recording paper in page order.

Further, in the image reading apparatus 50B, the originals D for which the image reading has been completed are reversed via the paper ejection rollers 62 and are ejected so as to be stacked in page order from the bottom side with the front side facing downward.

In each of the image reading apparatuses 50A and 50B, the image data stored in the image memories (I) and (II) are erased by the start of image reading of a new document, and Prepare to store image data.

[0084]

The present invention has been made paying attention to that the time required for recording an image on the image carrier requires a longer time than the time required for storing it in the image memory when reading an original image. According to the present invention, even if the image reading of a double-sided original is started by giving priority to which of the front and back sides, the front and back sides of the transfer material can be formed by forming the toner images on the front and back sides within the shortest time. In contrast, it is possible to perform simultaneous transfer (Claims 1, 2 and 3), and it is also possible to efficiently perform a plurality of copies of the same original document subsequently (Claim 4). A double-sided image forming apparatus that is excellent in terms of quality is provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a sectional configuration diagram of an image forming apparatus according to a second embodiment.

FIG. 3 is a sectional configuration diagram of the image reading apparatus.

FIG. 4 is a flowchart showing an image forming process.

[Explanation of symbols]

 10 Photoconductor drum 11 Scorotron charger 12,121 Exposure unit 13 Developer 14a Toner image receiver 14c, 14g Transfer device 15 Paper cassette 17 Fixing device 19 Cleaning device 50A, 50B Image reading device 54 Conveyor belt 55 Platen glass 56 No. 1 mirror unit 57 2nd mirror unit 58 reverse paper feed path D (double-sided) original

 ─────────────────────────────────────────────────── ─── 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 bearing means for bearing a toner image formed by a toner image forming means, and a toner image carried on the first image bearing means are collectively transferred and transferred. Second image carrying means for carrying the toner image again on the surface; first transfer means for transferring the toner image carried by the first image carrying means onto the surface of a transfer material; and the second image Second transfer means for transferring the toner image carried by the carrying means onto the back surface of the transfer material; and the toner image carried by the first image carrying means by the first transfer means for the transfer material. Of the toner image transferred to the front surface of the transfer material, and the toner image carried by the second image carrying means by the second transfer means to the back surface of the transfer material, and the toner image transferred to both surfaces of the transfer material. In an image forming apparatus having a fixing unit for fixing A document corresponding to the front side and the back side is read by the document reading means and stored in the image memory, and the image formation on the second image carrying means is performed by a transfer material in synchronization with the document reading or by the output from the image memory. The image forming apparatus is characterized in that the image formation is performed prior to the image formation on the first image bearing unit for transferring the image onto the surface of the image formation unit. 2. When first reading the front side, the image is stored in an image memory, the image is formed on the second image carrier in synchronization with the reading of the back side, and then the first image is output by the output from the image memory. The image forming apparatus according to claim 1, wherein an image is formed on the image carrier. 3. When first reading the back side, the image formation on the second image carrier is performed in synchronization with the reading, and the image formation on the first image carrier is performed in synchronization with the reading on the front side. The image forming apparatus according to claim 1, wherein: 4. The image forming apparatus according to claim 1, wherein the output from the image memory is repeated.