JPH1195492A - Double-sided color image forming device and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-sided color image forming device capable of forming a double-sided image good in hue. SOLUTION: A color toner image is formed on a first image carrying means 10 by repeating electrification, exposure and development, and successively superposing the toner images of different colors; and the formed color toner image is transferred to a second image carrying means 14a. Next, a color toner image is formed on the means 10 differently from the superposing order of the toner image obtained when the previous color toner image is formed. This color toner image is transferred to the first surface of a transfer material P, and also the color toner image transferred to the means 14a is transferred to the second surface of the material P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a color toner image by superposing toner images of different colors on an image bearing means, and transferring and fixing the color toner image to a transfer material to form a color image. The present invention relates to an electrophotographic color image forming apparatus and method such as a copying machine, a printer, and a facsimile, and more particularly to a two-sided color image forming apparatus and method for forming a color toner image on both surfaces of a transfer material.

[0002]

2. Description of the Related Art Conventionally, in double-sided image formation, a toner image formed on an image bearing means is transferred to one surface of a transfer material.
After fixing and temporarily storing the transfer material in the two-sided reversing feeder,
The transfer material is fed from the double-sided reversing feeding device again in synchronization with the toner image formed on the image bearing means, and the toner image on the image bearing means is transferred and fixed to the other surface of the transfer material. The method of forming an image on both sides is adopted.

In this double-sided image forming apparatus, as described above, the transfer of the transfer material is performed such as feeding to the two-sided reversing feeder and passing through the fixing device twice, so that the reliability of transfer of the transfer material is low.
This causes the transfer material to jam or wrinkle. A color image has a larger toner adhesion amount on a transfer material than a normal monochrome image (a solid image such as a photograph instead of a character or a line. It is not one color but four colors). For this reason, the curl after fixing is larger in color, and jams and wrinkles are more remarkably generated.

[0004]

For this reason, the applicant of the present invention has disclosed in Japanese Patent Application No. 8-70322 or the like an image carrying means (first image carrying means).
The toner image formed on the image bearing means is transferred to the front surface of the transfer material, and the toner image formed on the image bearing means is temporarily transferred to the toner image receiving member (second image bearing means). And an image is formed on both sides of the transfer material by fixing the toner image transferred on both sides of the transfer material at one time. With this apparatus, the reliability of transfer material transfer is improved, and the occurrence of jams, wrinkles, and the like of the transfer material can be suppressed.

When a color image is formed in the double-sided image formation proposed in Japanese Patent Application No. 8-70322 or the like, toner images of different colors are sequentially superimposed by repeating charging, exposure and development. And a method of forming a color toner image on the first image carrying means (KNC process). Therefore, if a color image is to be formed by the double-sided image formation according to the above-mentioned proposal, the image formation on the surface of the transfer material is completed by a single transfer from the image carrying means to the transfer material. In the image formation on the back surface of the image forming apparatus, two transfers are performed from the image carrying means to the toner image receiving member and from the toner image receiving member to the transfer material. Therefore, the order in which the color toner images are stacked differs between the upper and lower surfaces of the transfer material. Therefore, the color image formed on both sides of the transfer material is
The color is different between the front and back sides.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a double-sided color image forming apparatus and a double-sided color image forming method capable of forming a double-sided image having a uniform color.

[0007]

The above object can be attained by the following constitution.

(1) It has a first image holding means for holding a toner image and a plurality of developing units having different colors of toner to be accommodated. The charging, exposure and development are repeated to form a first image holding means on the first image holding means. A color toner image forming means for sequentially superimposing toner images of different colors to form a color toner image;
A second image carrying means on which the color toner image formed on the image carrying means is transferred and carrying the transferred color toner image on a surface; and a color toner image formed on the first image carrying means, A first transfer unit that transfers the image onto the first surface of the transfer material or the color toner image that is transferred onto the second image support unit; and a second transfer surface that is opposite to the first surface of the transfer material. A second transfer unit, a fixing unit for fixing the color toner image transferred to the transfer material, and forming a color toner image to be transferred onto the second surface of the transfer material on the first image carrier. When the color toner image to be transferred onto the first surface of the transfer material is formed on the first image carrier, the order in which the color toner image forming means superimposes the toner images of different colors is changed. Control means for controlling the color toner image forming means; Sided color image forming apparatus, comprising.

(2) Image processing conditions are changed between when a color toner image is transferred to the second surface of the transfer material and when a color toner image is transferred to the first surface of the transfer material. (2) The double-sided color image forming apparatus according to (2).

(3) Charging conditions and exposure conditions for forming a color toner image to be transferred to the second surface of the transfer material and for forming a color toner image to be transferred to the first surface of the transfer material The two-sided color image forming apparatus according to (1) or (2), wherein any one of development conditions is changed.

(4) a first color toner image forming step of forming a color toner image on a first image carrying means by successively superimposing toner images of different colors by repeating charging, exposing and developing; A step of transferring the color toner image formed in the color toner image forming step onto the second image carrying means, and an order in which charging, exposure and development are repeated to superpose the toner images in the first color toner image forming step. A second color toner image forming step of forming a color toner image on the first image carrying means by superimposing toner images in different orders, and a color toner image formed in the second color toner image forming step. Transferring the color toner image formed in the first color toner image forming step and transferred onto the second image carrying means to the second surface of the transfer material, Process and the first and second surfaces of the transfer material
Fixing the color toner image transferred on the surface onto a transfer material.

[0012]

Embodiments of the present invention will be described below. In the following description, in the transfer area 14b, the surface of the transfer material on the side facing the photoreceptor drum 10 as the first image holding means is the front surface (first surface), and the other surface of the transfer material is the back surface (first surface). The image transferred to the front surface of the transfer material is called a front surface image, and the image transferred to the back surface of the transfer material is called a back surface image.

First, an image forming process and each mechanism according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a cross-sectional configuration diagram of a two-sided color image forming apparatus, FIG. 2 is a diagram illustrating a state of forming a toner image and supply of a transfer material, and FIG. 3 is a diagram illustrating a stacked state of color toner images formed on the transfer material. It is a figure which shows typically.

Photosensitive drum 10 as first image bearing means
Is obtained by forming a photosensitive layer such as an a-Si layer or an organic photosensitive layer (OPC) on a cylindrical substrate (outer periphery) formed of a metal such as aluminum. The photoreceptor drum 10 rotates in a direction indicated by an arrow (clockwise) in FIG. 1 by a power from a driving source (not shown) with the base being grounded.

In this embodiment, the color toner image forming means comprises a charging means, an exposing means, a plurality of developing means (containing different colors of toner), and further comprises a charge removing means and a cleaning means. These are arranged around the photosensitive drum 10.

Uniform exposure unit 120 serving as a charge removing unit before charging.
Reference numeral a denotes a means for eliminating the history of the photosensitive drum 10 up to the previous image formation. For example, uniform exposure by a light emitting diode is performed, the peripheral surface of the photosensitive body is neutralized, and the charging history at the time of the previous image formation. Is removed.

Scorotron charger 11 as charging means
Has a control grid 115 maintained at a predetermined potential and a corona discharge electrode 111 composed of, for example, a saw-tooth electrode (may be a wire electrode), and is exposed in a direction orthogonal to the rotation direction of the photosensitive drum 10. The photoconductive layer of the body drum 10 is opposed to and is mounted close to the photoconductive layer. The scorotron charger 11 includes a control grid 115 and a corona discharge electrode 1.
A charging action (minus charging in the present embodiment) is performed by corona discharge having the same polarity as the toner 11, and a uniform potential is applied to the photosensitive drum 10.

The exposure unit 120 as an exposure means includes:
A semiconductor laser (not shown) serving as a light emitting element, and a rotary polygon mirror 12 for rotating and scanning a laser beam emitted from the semiconductor laser
0b, fθ lens 120c, reflection mirror 120d, and the like. The exposure unit 120 rotationally scans the laser beam emitted from the semiconductor laser by the rotary polygon mirror 120b, passes through the fθ lens 120c, the reflecting mirror 120d, and the like, and scans the main scanning direction on the rotating photosensitive drum 10 (in FIG. 1, Image exposure based on the image signal is performed in the direction perpendicular to the paper surface to form a latent image on the photosensitive drum 10.

The developing means has yellow (Y),
Four developing devices 13Y, 13M, 13 containing a two-component developer (may be a one-component developer) including magenta (M), cyan (C), and black (K) toners and a carrier.
C and 13K, which are arranged around the photosensitive drum 10. The developing units 13Y, 13M,
13C and 13K have the same configuration except that the colors of the toners to be stored are different. Therefore, the following description of the configuration of the developing device will be omitted without adding Y, M, C and K.

The developing device 13 has, for example, a thickness of 0.5 mm
A developing sleeve 131 which is a developer carrier made of a non-magnetic stainless steel or aluminum material having a cylindrical shape of 1 mm and an outer diameter of 15 to 25 mm is provided. Developing sleeve 13
1 includes a fixed magnet (not shown) in which N and S magnetic poles are alternately arranged, is stirred and mixed by a stirring screw (no sign), and is conveyed and supplied from a stirring unit by a supply roller (no sign). The two-component developer is supplied to the developing section. At this time, the layer thickness of the two-component developer on the peripheral surface of the developing sleeve 131 is made of a magnetic material having a circular cross section of a magnetic material having a diameter of 3 to 10 mm and is uniformly pressed against the peripheral surface of the developing sleeve 131 with a predetermined load. It is regulated by a thin layer forming rod (not shown) as a thin layer forming member. The two-component developer that has passed through the developing section has one end of the long side of the belt shape
Is removed from the developing sleeve 131 by a scraper (not shown) made of a plate-like elastic member such as SUS or urethane rubber provided in pressure contact in parallel with, and is conveyed to a stirring unit by a supply roller to achieve a predetermined toner density. So that
The mixture is stirred and mixed by a stirring screw.

In the developing section, the developing sleeve 131 is kept out of contact with the photosensitive drum 10 by a contact roller (not shown) with a gap of a predetermined value, for example, 100 μm to 1000 μm. When a DC voltage having the same polarity as toner (in this embodiment, a negative polarity) or a superimposed voltage of DC and AC is applied to the developing sleeve 131 as a developing bias, the photosensitive drum is exposed to light. Non-contact reversal development is performed on the latent image portion of the body drum 10 where the image has been exposed.

The cleaning device 19, which is a cleaning means, cleans the toner remaining on the photosensitive drum 10 after the color toner image on the photosensitive drum 10 is transferred by the first transfer means described in detail later. is there. In the present embodiment, cleaning is performed by bringing a cleaning blade 19a made of a rubber material into sliding contact with the photosensitive drum 10. The cleaning blade 19a is provided so as to be capable of coming into contact with and separating from the photosensitive drum 10. As will be described in detail later, after the color toner image formed on the photosensitive drum 10 is transferred, the cleaning blade 19a is 10 is located at a distance from the photosensitive drum 10 during the formation of the color toner image.

Therefore, the color toner image forming means uniformly charges the photosensitive drum 10 by the scorotron charger 11, forms a latent image by the exposure unit 120, and
The toner image is formed on the photoreceptor drum 10 by performing the development (visualization) by 3. Then, the toner image formation is repeated a plurality of times, that is, the photosensitive drum 10 is rotated a plurality of times, and the developing devices 13Y, 13M, 13
A color toner image is formed on the photosensitive drum 10 by forming a toner image by using any one of the developing devices C and 13K and superimposing toner images of different colors sequentially.

Toner image receiver 1 as second image bearing means
Reference numeral 4a denotes a transfer material P which carries a color toner image and
Is a means for carrying. The toner image receiving member 14a is an endless rubber belt, and is stretched by a driving roller 14d driven by driving means (not shown), a driven roller 14e, and a tension roller 14j. The toner image receiver 14a is integrated with a driven roller 14e and a tension roller 14j to form a drive roller 14d.
As described later in detail, when the color toner image formed on the photoconductor drum 10 is transferred, the photoconductor drum 10 comes into contact with the photoconductor drum 10 and the color toner is rotated. During image formation, the photosensitive drum 10
In a position away from

The toner image receiving member 14a is an endless rubber belt having a thickness of 0.5 to 2.0 mm, and is a semiconductive material of silicon rubber or urethane rubber having a resistance of 10 ⁸ to 10 ¹⁵ Ω · cm. It has a two-layer structure in which a fluorine coating having a thickness of 5 μm to 50 μm is applied as a toner filming prevention layer on the outside of a rubber substrate and a rubber substrate. This layer also preferably has a similar semiconductivity. Instead of the rubber belt substrate, semiconductive polyimide or modified polyimide, polyester, polystyrene, polyethylene, polyethylene terephthalate, or the like having a thickness of 0.1 to 0.5 mm can also be used.

The paper charger 14f, which is a transfer material charging means,
This is a means which is constituted by a corona discharger and applies a charge of the same polarity as the toner to a transfer material (recording paper) P which is separately conveyed, thereby bringing the toner image receiving body 14a and the recording paper P into close contact with each other.
By charging the toner with the same polarity as the toner, the toner image is prevented from being attracted to the toner image on the toner image receiving member 14a or the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed.

The primary transfer unit 14c, which is the first transfer means,
A color toner image (reverse image) formed on the photosensitive drum 10 is constituted by a corona discharger,
a, and transfers the color toner image (surface image) formed on the photosensitive drum 10 to the toner image receiver 14.
This is a means for transferring the image to the surface of the recording paper P conveyed by a. In the present embodiment, a voltage having a polarity opposite to that of the toner (positive polarity) is applied to the primary transfer device 14c from a power supply (not shown). Note that the primary transfer device 14c is
The photosensitive drum 10 is integrated with the toner image receiver 14a.
May be provided so as to be able to come and go.

A secondary transfer unit 14g, preferably a corona discharger, which is a second transfer unit, is used to convert the color toner image (back side image) transferred onto the toner image receiving body 14a by the primary transfer unit 14c to a toner image. This is a unit for transferring the image to the back surface of the recording paper P conveyed by the image receiving body 14a. In the present embodiment, a voltage having a polarity opposite to that of the toner (positive polarity) is applied to the secondary transfer unit 14g from a power supply (not shown).

Since the toner images of the respective colors overlap with each other, it is preferable that the toner in the upper layer and the toner in the lower layer of the toner layer are charged to the same polarity with the same charge amount in order to enable batch transfer. From this, the toner image receiver 14
In the double-sided image formation in which the polarity of the color toner image formed on the photosensitive drum 10 is inverted by corona charging, or the polarity of the color toner image formed on the photosensitive drum 10 is inverted by corona charging, the toner of the lower layer has sufficient polarity. Since it is not charged, the transfer becomes poor, which is not preferable.

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

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

Paper separation AC neutralizer 1 as transfer material separating means
Reference numeral 4h denotes a means for removing electricity to separate the recording paper P from the toner image receiver 14a.
Since the separation of the recording paper P is facilitated by reducing the diameter of the drive roller 14d that stretches the recording paper P, this can be omitted.

The fixing device 17 serving as a fixing unit is provided with a recording paper P
Is a means for fixing the color toner image transferred to both surfaces of the recording paper P. For this purpose, in the present embodiment, a fixing roller 17a and a pressure roller 17b are used, and a heater (no reference numeral) is built in each of the rollers 17a and 17b.

Next, a process of forming a double-sided color image by the double-sided color image forming apparatus will be described. The formation of a two-sided color image is first started from the formation of a back side image.

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

A drive source (not shown) is started by the start of image recording, and rotates the photosensitive drum 10 clockwise as indicated by an arrow in FIG. Prior to the formation of the color toner image of the back surface image, uniform exposure is performed on the photosensitive drum 10 by the uniform exposure device 120a to remove the charge during the previous image formation.

Then, a potential is applied to the photosensitive drum 10 by the charging action of the scorotron charger 11. After the photosensitive drum 10 is applied with a potential, the exposure unit 12 starts scanning exposure by an electrical signal corresponding to black (K) image data on the back surface, and the back surface is placed on the photosensitive drum 10 by rotational scanning of the drum. An electrostatic latent image corresponding to the K image is formed. This latent image is reversely developed in a non-contact state by a K developing unit 13K, and a black (K) toner image is formed on the photosensitive drum 10.

Next, the photosensitive drum 10 is moved, and the toner image receiving member 1 which is separated from the photosensitive drum 10 is moved.
The rotation is continued without contacting the cleaning blade 4a and the cleaning blade 19a, and the process proceeds to the second rotation. At this time, the uniform exposure device 120
No uniform exposure by a is performed.

In the second rotation in the image formation on the back surface of the photosensitive drum 10, a potential is applied to the black (K) toner image already formed by the charging action of the scorotron charger 11. Exposure using an electric signal corresponding to the image data of C on the back side is performed, and the cyan (C) toner image is superimposed on the black (K) toner image by non-contact reversal development by the C developing device 13C. Formed.

By the same process, the photosensitive drum 10
In the third rotation, the magenta (M) toner image corresponding to the M image data on the back surface is further formed on the K and C toner images by the scorotron charger 11, the exposure unit 12, and the M developing device 13M. Is done. Similarly, in the fourth rotation of the photosensitive drum 10, a yellow (Y) toner image corresponding to the Y image data on the back surface is formed by the scorotron charger 11, the exposure unit 12, and the Y developing device 13Y.
It is formed on the K, C and M toner images. Therefore, the K, C, M, and Y toner images are sequentially superimposed on the photosensitive drum 10 in order from the bottom to form a color toner image on the back surface (first color toner image forming step). .

When a color toner image is formed on the photosensitive drum 10, the toner image receiver 14a is driven by a driving roller 14d.
1 is rotated in the direction indicated by the dotted arrow a in FIG. Then, at the fifth rotation of the photosensitive drum 10, a primary transfer unit in which a superimposed color toner image of the back surface image formed on the photosensitive drum 10 is applied with a voltage having a polarity opposite to that of the toner in the transfer area 14 b. By 14c, they are collectively transferred onto the toner image receiver 14a. Accordingly, the color toner image on the back surface formed by superimposing the K, C, M, and Y toner images on the photosensitive drum 10 from below is sequentially transferred to the primary transfer device 14c.
Is a color toner image superimposed on the toner image receiver 14a in the order of Y, M, C, and K toner images from below.

After the superimposed color toner image of the back surface image of the photosensitive drum 10 is transferred to the toner image receiving member 14a, the toner image receiving member 14a
It is rotated about the axis 4d in the direction of the dotted arrow a in FIG.

On the other hand, the toner remaining on the peripheral surface of the photoreceptor drum 10 after the transfer is subjected to static elimination by the photoreceptor drum AC static eliminator 16 and then enters the cleaning device 19 or at a position where it comes into contact with the photoreceptor drum 10. The cleaning is performed by the moved cleaning blade 19a. When the toner remaining on the photosensitive drum 10 is removed by the cleaning blade 19a, the cleaning blade 19
“a” moves to a position separated from the photosensitive drum 10. On the other hand, the photosensitive drum 10 that has been cleaned is subjected to exposure by the uniform exposure device 120a before charging to remove electricity from the peripheral surface of the photosensitive drum, and subsequently, the next surface image is formed.
It is necessary to change the image data so that the formed front surface image is a mirror image of the back surface image formed on the photosensitive drum 10.

The surface image is formed by the scorotron charger 1
1 is supplied with a potential by the charging action of
As a result, exposure is performed with an electric signal corresponding to the Y image data on the surface, and a yellow (Y) toner image is formed on the photoconductor drum 10 by non-contact reversal development by the Y developing device 13Y.

Next, the photosensitive drum 10 is moved, and the toner image receiving member 1 which has been separated from the photosensitive drum 10 is moved.
The rotation continues without contacting the cleaning blade 4a and the cleaning blade 19a, and the second rotation is performed at the time of forming the front image (the seventh rotation is counted from the formation of the back image, but hereinafter, the number is counted from the formation of the front image). Move on to At this time, the uniform exposure device 12
No uniform exposure with 0a is performed.

In the second rotation of the photosensitive drum 10, a potential is applied from above the already formed yellow (Y) toner image by the charging action of the scorotron charger 11, and the exposure unit 12 removes the surface M. Exposure is performed by an electric signal corresponding to the image data, and a magenta (M) toner image is formed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13M. .

By the same process, the photosensitive drum 10
In the third rotation, the cyan (C) toner image corresponding to the image data of C on the surface is further formed by Y and M by the scorotron charger 11, the exposure unit 12, and the developing device 13C of C.
Is formed on the toner image. Similarly, in the fourth rotation of the photosensitive drum 10, the black (K) toner image corresponding to the image data of K on the surface is formed by the scorotron charger 11, the exposure unit 12, and the developing device 13K of K to Y, M. And C toner images. Therefore, on the photosensitive drum 10 at the time of forming the front surface image, the color order is different from that at the time of forming the back surface image, that is, the order of the Y, M, C, and K toner images from the bottom. A color toner image on the surface is formed by superimposing sequentially in the reverse color order (second color toner image forming step).

On the other hand, the recording paper P, which is a transfer material, is fed from a paper feed cassette 15 which is a transfer material storage means to a feed roller 1.
The sheet is sent out by 5a, fed by a feed roller 15b, and conveyed to a timing roller 15c. The fed recording paper P is driven by a timing roller 15c, as shown in FIG. 2, to form a color toner image of a surface image carried on the photosensitive drum 10 and a toner image receiver 14a.
The sheet is fed to the transfer area 14b in synchronization with the color toner image of the backside image carried thereon. At this time, the recording paper P is charged to the same polarity as the toner by the paper charger 14f, is attracted to the toner image receiver 14a, and is fed to the transfer area 14b. At this time, the toner image receiver 14a is rotated about the axis of the drive roller 14d in the direction indicated by the dotted arrow a in FIG.

The surface of the photosensitive drum 10 on the peripheral surface of the photosensitive drum 10 is rotated by the primary transfer unit 14c to which a voltage having a polarity opposite to that of the toner is applied in the transfer area 14b at the fifth rotation when the photosensitive drum 10 forms a surface image. Recording paper P collectively
Is transferred to the surface of Accordingly, the color toner image on the surface formed by superimposing the Y, M, C, and K toner images on the photosensitive drum 10 in order from the bottom is formed by the primary transfer device 14c.
As shown in FIG. 3, the color toner image is superimposed on the recording paper P in the order of K, C, M, and Y from below. When the front image is transferred, the back 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, the toner image receiver 14a moves further with the rotation of the drive roller 14d, and is moved on the peripheral surface of the toner image receiver 14a by a secondary transfer unit 14g to which a voltage having a polarity opposite to that of the toner is applied. The back side images are collectively transferred to the back side of the recording paper P. Accordingly, the color toner image on the back surface, which is superimposed on the toner image receiving member 14a in the order of the Y, M, C, and K toner images from below, is transferred on the recording paper P by the transfer by the secondary transfer device 14g. As shown in FIG. 3, a color toner image is obtained by superimposing K, C, M, and Y toner images from below (assuming the recording paper P side is the bottom).

The recording paper P on which the color toner images are formed on both sides in this manner is discharged by the paper separation AC discharger 14h, separated from the toner image receiver 14a, and conveyed to the fixing device 17. And a fixing roller 17a;
By applying heat and pressure to the pressure roller 17b, the color toner images adhered to the front and back surfaces of the recording paper P are fixed. The fixed recording paper P is sent by a paper discharge roller 18 and discharged to a tray outside the apparatus.

On the other hand, the toner remaining on the peripheral surface of the toner image receiver 14a after the transfer is cleaned by the toner image receiver cleaning device 14i. Further, the toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is the photosensitive drum A
After being subjected to static elimination by the C static eliminator 16, it is scraped into the cleaning device 19 by the cleaning blade 19a, and is collected by the screw 19b in a waste toner container (not shown).

As described above, in this embodiment, the recording paper P
The color toner image transferred to the back surface of the photosensitive drum 10
On the photosensitive drum 10 when forming the toner image on the photosensitive drum 10 and when forming the color toner image transferred on the surface of the recording paper P.
Since the order in which the toner images of different colors are superimposed by the color toner image forming means is changed, it is possible to form a two-sided image with a uniform tint. In particular, since the black toner, which greatly affects the color, is formed on the recording paper P as the lowermost layer on both the front and back surfaces, the color can be easily adjusted. Further, in the present embodiment, the order of superimposing the back surface and the order of superposing the front surface are reversed, so that the same color can be prepared on both surfaces by the same image processing, and the image processing circuit can be simplified. Can be achieved.

In the above-described double-sided image formation, the image formation on the back surface is performed by the toner image from the photosensitive drum 10 as compared with the image formation on the front surface which requires only one transfer from the photosensitive drum 10 to the front surface of the recording paper P. Since the transfer is performed twice from the image receiving member 14a and the toner image receiving member 14a to the back surface of the recording paper P, the image density of the back surface image is reduced. This is due to the fact that the transfer rate is not 100% at the time of transfer and the amount of toner adhered decreases.

In order to solve this problem, in the present embodiment, the image forming conditions at the time of forming the image on the back surface are as follows.
The image forming conditions at the time of image formation on the front surface are changed to be different. That is, when the same image is formed when forming the color toner image transferred to the back surface than when forming the color toner image transferred to the front surface, the amount of toner adhering to the photosensitive drum 10 is reduced. Do more. As a result, during the image formation on the back side, the decrease in the amount of adhered toner can be compensated for by one-time transfer compared with the image formation on the front side, and a double-sided image with a uniform image density is formed. The image forming conditions are charging, exposure, and development process conditions (charging condition, exposure condition, and development condition, respectively). More specifically, in order to change the process conditions for charging,
When forming an image on the back side, compared to when forming an image on the front side,
The absolute value of the charging potential by the scorotron charger 11 is set to be high. For this purpose, the absolute value of the potential applied to the control grid 115 or the corona discharge electrode 111
The absolute value of the voltage or the current applied to is increased.

In order to change the exposure process conditions,
When forming an image on the back side, compared to when forming an image on the front side,
In forming the same image, the exposure amount is changed so that the absolute value of the latent image potential formed on the photoconductor drum 10 by the exposure unit 12 becomes low. For this purpose, the exposure intensity is increased by changing the current or voltage applied to the semiconductor laser, or the pulse width is increased.

In order to change the development process conditions,
When forming an image on the back side, compared to when forming an image on the front side,
When developing the same latent image, the developing conditions are changed so that the toner adhesion amount is increased. To this end, the rotation speed of the developing sleeve 131 is increased (in short, the amount of toner adhesion depends on the rotation speed ratio (movement speed ratio) between the photosensitive drum 10 and the development sleeve 131; Increase), or increase the absolute value of the bias voltage applied to the developing sleeve 131, or increase the AC component voltage value or current value of the bias voltage applied to the developing sleeve 131.

By changing at least one of these conditions between the time of forming the front image and the time of forming the back image, the time of forming the color toner image to be transferred to the back surface is better than that of forming the color toner image on the back surface. When the same image is formed, the amount of toner adhering to the photosensitive drum 10 can be increased more than when a color toner image is formed. 1
The decrease in the amount of adhered toner can be compensated for by performing the transfer many times, and a double-sided image with a uniform image density is formed.

In general, when copying (image forming) an image of a document in a color image forming apparatus, as shown in FIG. 4 showing an example of a digital image processing system for color reproduction, a sensor such as a scanner is used. The image of the document is read (S1), and the read r, g, b image information is
After shading correction (S2)
3) Matrix operation (S4), density conversion (S4)
5) Obtain C, M, Y signals. And masking
Apply inking / UCR (under color removal) processing (S6)
The signals of C ′, M ′, Y ′, and K ′ are obtained, and are subjected to γ correction using a γ correction curve (S7) and multi-value processing (S8) to be used as color signals by a printer P1 which is a color image forming apparatus. Supplied. When an image is formed using a signal from a computer or the like, the signal is directly input to S5 or S6. As described above, in the color image forming apparatus, it is necessary to perform various kinds of image processing in order to form an optimum color image by the image forming apparatus.

In the double-sided color image forming apparatus of the present embodiment, it is preferable to change the image processing conditions between when forming a front color image and when forming a back color image. That is, as in the present embodiment, since the image formation on the back surface is performed twice, the halftone tends to be broken (gamma is increased) and the characters are thickened. Therefore, in the present embodiment, the image processing conditions are changed between when forming the color toner image transferred to the back surface of the recording paper P and when forming the color toner image transferred to the front surface of the recording paper P. Is preferred. More specifically, the γ correction (S7), which is one of the image processing, is performed at the time of forming the color image on the front surface, and the low γ correction (the corrected γ correction curve is performed at the time of forming the color image on the back surface). Used.
That is, the γ correction curve is made different between when forming an image on the front surface and when forming an image on the back surface, and fine print processing (MTF filter is strengthened. Is preferably performed.

[0061]

As described in detail above, according to the present invention,
It is possible to provide a double-sided color image forming apparatus and a double-sided color image forming method for forming a double-sided image with a good color.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a two-sided color image forming apparatus.

FIG. 2 is a diagram illustrating a toner image forming state and supply of a transfer material.

FIG. 3 is a diagram schematically illustrating a stacked state of color toner images formed on a transfer material.

FIG. 4 is a diagram illustrating an example of a digital image processing system for color reproduction.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum (first image holding unit) 11 scorotron charger 120 exposure unit 13 developing unit 14a toner image receiver (second image holding unit) 14c primary transfer unit (first transfer unit) 14g secondary transfer unit ( (Second transfer unit) 17 Fixing device P Recording paper (transfer material)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Haneda Konica Corporation 2970 Ishikawacho, Hachioji-shi, Tokyo

Claims (4)

[Claims] A first image holding means for holding a toner image; and a plurality of developing units having different colors of toner to be accommodated. The charging, exposure and development are repeated to provide different images on the first image holding means. A color toner image forming means for sequentially superimposing color toner images to form a color toner image; and a color toner image formed on the first image holding means is transferred, and the transferred color toner image is held on the surface. Second
Image carrying means, first transfer means for transferring the color toner image formed on the first image carrying means to the first surface of the second image carrying means or the transfer material, and transfer to the second image carrying means Second transfer means for transferring the transferred color toner image to a second surface opposite to the first surface of the transfer material; fixing means for fixing the color toner image transferred to the transfer material; The color toner image transferred to the two surfaces is
Different color toner images are formed by the color toner image forming means when forming the image on the image carrier and when forming the color toner image transferred on the first surface of the transfer material on the first image carrier. And a control unit for controlling the color toner image forming unit so as to change the order of superimposing the color toner images. 2. An image processing condition is changed between when a color toner image to be transferred to the second surface of the transfer material is formed and when a color toner image to be transferred to the first surface of the transfer material is formed. The double-sided color image forming apparatus according to claim 1, wherein: 3. A method for forming a color toner image to be transferred onto a second surface of a transfer material and a method for forming a color toner image to be transferred onto a first surface of a transfer material, comprising: The two-sided color image forming apparatus according to claim 1, wherein one of development conditions is changed. 4. A first color toner image forming step of forming a color toner image on a first image carrying means by successively superimposing toner images of different colors by repeating charging, exposure and development, and What is the step of transferring the color toner image formed in the toner image forming step onto the second image carrying means, and the order of repeating charging, exposing and developing to superpose the toner images in the first color toner image forming step A second color toner image forming step of forming a color toner image on the first image carrying means by superimposing the toner images in different orders, and a color toner image formed in the second color toner image forming step. Transferring the first color toner image to the first surface of the transfer material;
A step of transferring the color toner image transferred on the image carrying means to the second surface of the transfer material; and fixing the color toner image transferred on the first and second surfaces of the transfer material to the transfer material. And a step of forming a double-sided color image.