JPH09101646A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device for realizing the high image quality and the high speed output of a monochromatic image and the simplification of a fixing device in the color image forming device. SOLUTION: At the time of forming a color image, the toner images of respective colors formed on a photoreceptor belt 10 are successively transferred on a transfer body 16, and transfer material S is guided to a carrying route under the transfer body 16 on an opposite side to the photoreceptor belt 10, and the image is transferred by applying high voltage power supply output having a reverse polarity to toner by a second transfer means 22. At the time of forming the monochromatic image, the transfer material S is guided between the photoreceptor belt 10 and the transfer body 16, and a monochromatic toner image formed on the photoreceptor belt 10 is directly transferred on the transfer material S by applying the high voltage power supply output having the reverse polarity to the toner by a first transfer device 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a color copying machine, a color printer or a color facsimile equipped with an intermediate transfer member.

[0002]

2. Description of the Related Art As a typical one of conventional color image forming apparatuses, a photosensitive drum for forming a latent image and a transfer paper are held and a toner image on the photosensitive member is transferred. A method using a transfer drum and a method in which a plurality of toners are superposed on a photosensitive drum and transferred onto a transfer paper have been put into practical use.

In the method using the transfer drum, the transfer paper must be electrostatically or mechanically held on the transfer drum, so that it is difficult to use a small size paper such as a postcard or a thick paper as the transfer paper. It is not so-called paper-free. Further, the method of mechanically holding the front end of the transfer paper has a drawback that the image cannot be transferred onto the entire surface of the transfer paper. A method of superimposing a plurality of toner images on a photoconductor drum has also been proposed and put into practical use, but in this method, a latent image is formed by recharging and exposing the photoconductor on the previously transferred toner image. Since the developing process is performed a plurality of times, it is difficult to maintain good charging uniformity, and the image quality is inferior to that of the conventional transfer drum system.

Formed on the photoreceptor as a system which solves the above problems and achieves a paper-free property such that postcards and thick papers can be used as transfer papers and high quality images can be achieved. A method has been proposed in which toner images of respective colors are sequentially overlapped and transferred to the same position on an intermediate transfer member such as an endless belt, and the transferred images are transferred to a transfer paper to be fixed to obtain a full-color image. There is.

However, in this method, since the toner image on the photoconductor is transferred to the paper through the intermediate transfer body even when the monochrome image is formed, the transfer of the monochrome image to the paper is not performed efficiently, and as a result, the toner image is transferred. This has the disadvantage that the consumption amount increases, and the monochrome image forming speed is slow.

Therefore, in order to solve this point, Japanese Patent Laid-Open No. Hei 4
In Japanese Patent Laid-Open No. 1917776 and Japanese Patent Application Laid-Open No. 4-293062, a sheet is passed between an intermediate transfer body and a photoconductor, so that a toner image of the photoconductor is directly passed from the photoconductor without passing through the intermediate transfer body during monochrome image formation. A method of transferring onto paper has been proposed. Specifically, in Japanese Patent Laid-Open No. 4-191777,
By passing the paper between the intermediate transfer body and the photoconductor,
When a monochrome image is formed, the toner image on the photoconductor is directly transferred from the photoconductor to the paper without passing through the intermediate transfer body, and is passed between the intermediate transfer body and the photoconductor even when the color image is formed. In Japanese Patent Laid-Open No. 4-293062, a sheet is passed between an intermediate transfer body and a photoconductor only when a monochrome image is formed, and a toner image on the photoconductor is directly transferred from the photoconductor to the paper without passing through the intermediate transfer body. At the time of color image formation, the toner image is transferred from the intermediate transfer member to the paper through a separate conveyance path. At this time, the rotation direction of the photoconductor is reversed between the monochrome image and the color image, and the writing position is also changed. .

However, the above-mentioned Japanese Patent Laid-Open No. 19177/1992.
In the technology disclosed in No. 6, since the intermediate transfer member and the photoconductor are passed even during color image formation, the image forming surface is contradictory to the sheet conveyance between the monochrome image and the color image (front and back). However, the subsequent fixing device cannot be supported by a roll fixing device of a normal electrophotographic device (a fixing heat roller for fixing a toner image on one side and a pressure rubber roller for pressing on the other side), which is very expensive. There is a problem that it will become something. Further, Japanese Patent Laid-Open No. 4-29306
In the technique disclosed in No. 2, the toner image is transferred from the intermediate transfer member to the paper through another transport path during color image formation. However, the image forming surface is also different between the monochromatic image and the color image when the paper is transported. There is a contradictory (front and back) relationship, and two types of fixing devices are installed to deal with this, but there is a problem that the fixing function becomes expensive and complicated,
Moreover, since there is a mechanism for changing the writing position between the monochrome image and the color image on the photoconductor, there is also a problem that the apparatus main body becomes expensive and complicated.

In view of the above-mentioned problems of the prior art, the present invention provides a color image forming apparatus aiming at high image quality and high speed of a monochrome image in the color image forming apparatus, while simplifying the fixing device. With the goal.

[0009]

In order to achieve the above object, a color image forming apparatus according to a first aspect of the present invention repeatedly transfers a toner image formed on an image bearing member to an intermediate transfer member, In a color image forming apparatus that forms a composite toner image formed by superposing a plurality of toner images on an intermediate transfer body and transfers the composite toner image from the intermediate transfer body onto a sheet at a time to fix the image, a monochrome image is output. The paper is conveyed so as to pass between the image carrier and the intermediate transfer member, the toner image formed on the image carrier is directly transferred to the paper, and the intermediate image is output when a color image is output. After the synthetic toner image formed by superimposing a plurality of toner images is formed on the transfer body, the intermediate transfer body is reversely rotated to collectively transfer the synthetic toner image onto the sheet from the intermediate transfer body. Do

A color image forming apparatus according to a second aspect of the invention is characterized in that the intermediate transfer member is a belt transfer member, and the belt transfer member also serves as a sheet conveying unit for either monochrome or color image output. .

According to a third aspect of the present invention, in the color image forming apparatus, the intermediate transfer body is a belt transfer body, and a moving means for the belt transfer body is provided, and the belt transfer body is moved to output a monochrome image and a color image. It is characterized in that the paper transport path is switched.

According to a fourth aspect of the present invention, in the color image forming apparatus, the intermediate transfer body is a belt transfer body, and a moving means for the belt transfer body is provided, and in the color image output, the synthetic toner image on the intermediate transfer body. When the intermediate transfer body is rotated in the reverse direction after the formation of, the image carrier and the intermediate transfer body are displaced in a non-contact state.

According to a fifth aspect of the present invention, in the color image forming apparatus, the intermediate transfer body is a belt transfer body, and a moving means for the belt transfer body is provided, and the belt transfer body is moved to output a monochrome image and a color image. The contact condition between the image carrier and the intermediate transfer member in 1) is variable.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a schematic configuration of a color image forming apparatus to which the present invention is applied. The photoconductor belt 10, which is an image forming body, has a photosensitive layer deposited or coated on a flexible belt surface.
It is stretched between the two and is conveyed in the clockwise direction. Around the photosensitive belt 10, a charging unit 13, an exposing unit 14, developing units 15Y, 15M, 1
5C, 15Bk, the transfer member 16, the first via the transfer member 16
The transfer means 17 and the first cleaning means 18 are arranged in order.

The charging means 13 is provided to uniformly charge the photosensitive layer on the surface of the photoconductor belt 10 with a predetermined polarity, and is an existing charger such as a corona charger or a scorotron charger. For this, a scorotron charger is commonly used. The exposure unit 14 is composed of a semiconductor laser writing system unit, and exposes the surface of the photoreceptor belt 10 charged by the charger 13 to form an electrostatic latent image. The developing means 15Y to 15Bk are developers of different colors,
For example, it is composed of four developing devices that respectively store toners (developers) of yellow, magenta, cyan, and black. These developing means 15Y, 15M, 15C, 15
Bk includes a developing sleeve that keeps a predetermined gap from the photosensitive belt 10 and a stirring screw that stirs the toner of each color, and visualizes the electrostatic latent image on the photosensitive belt 10 on the toner image by a non-contact reversal developing method. It has a function. This non-contact development method does not hinder the movement of the photoconductor belt 10, and therefore a good toner image can be obtained. The developing method that can be used in the present invention is not limited to the non-contact developing method,
Contact development may be used. The transfer body 16 is in contact with the photosensitive belt 10 at the contact portion, and the toner image formed on the photosensitive belt 10 is transferred. The first transfer unit 17 transfers the toner image formed on the photoconductor belt 10 onto the transfer body 16 by a transfer device such as a transfer corona discharger. The first cleaning unit 18 has a cleaning blade 181, and remains after the toner image is transferred to the transfer body 16 by the first transfer unit 17 by contacting the surface of the photosensitive belt 10 with an appropriate pressing force. Remove toner, etc.

The transfer member 16 is a belt made of a flexible insulating film stretched between the rotating rollers 20 and 21, and is a flexible belt made of polyester which is excellent in transportability and transferability. desirable. Further, the transfer body 16 is
The first transfer means 17 is provided inside the transfer body 16 in contact with the photosensitive belt 10. In addition, the transfer body 16
Is conveyed in synchronism with the toner image formed on the photoconductor belt 10 at timing so that the toner images of a plurality of colors are superposed at the same position, and the conveying speed (linear velocity) is It is conveyed in the counterclockwise direction at the same speed as the conveying speed (linear velocity) of 10. A second transfer means 22 and a second cleaning means 24 are arranged around the transfer body 16.

The second cleaning means 24 has a cleaning blade 241 and removes the toner remaining on the transfer body 16 after the color toner image is transferred onto the transfer material. Further, the cleaning means 24 separates from the surface of the transfer body 16 during the image forming process and presses the surface of the transfer body 16 only during cleaning after the color toner image is transferred onto the transfer material to clean the transfer body 16.

A color image forming process by the color image forming apparatus having the above image forming process section will be described. First, when color image formation is selected by pressing a color image formation button on an operation panel or the like (not shown), a color image formation signal is input to control means (not shown), and the control means executes each operation based on the color image formation process. A color image is formed by controlling the image forming process unit as follows.

When the image signal of the first color output from the image reading device (not shown) is input to the exposing means 14, a semiconductor laser (not shown) in the exposing means 14 produces a laser beam. The polygon mirror 14 whose laser beam is rotationally driven by a drive motor (not shown)
It is rotationally scanned by 1 and passes through the fθ lens 142, the cylindrical lens 143, and the mirror 144, and is projected on the peripheral surface of the photoconductor belt 10 which is uniformly charged to a predetermined charge by the charger 13 to form a bright line.

On the other hand, in the sub-scanning direction, a belt index (not shown) corresponding to a specific position of the photosensitive belt 10 is detected or a print command signal is received, and this detection or command signal is used as a reference. Modulation of the semiconductor laser by the image signal is started to determine the main scanning line. When scanning is started, a laser beam is detected in the main scanning direction by an index sensor (not shown), the semiconductor laser is started to be modulated by the image signal of the first color based on this detection signal, and the modulated laser The beam scans over the surface of the photoreceptor belt 10. Therefore, a latent image corresponding to the first color is formed on the surface of the photosensitive belt 10 that is uniformly charged by the main scanning by the laser beam and the sub-scanning by the conveyance of the photosensitive belt.

This latent image is developed by developing means 15Y containing a yellow (Y) toner corresponding to the first color,
A Y toner image is formed on the surface of the photosensitive belt 10. After that, the Y toner image is held on the surface of the photoconductor belt 10 and conveyed to the contact portion where the photoconductor belt 10 and the transfer body 16 are in contact with each other, and the surface of the photoconductor belt 10 is transferred by the first transfer means 17. The upper Y toner image is transferred onto the transfer body 16. A high voltage power source having a polarity opposite to that of the toner is applied to the first transfer means 17 to transfer the toner.

The photosensitive belt 10 on which the Y toner image has been transferred to the transfer body 16 is further conveyed, and the residual Y toner is removed and cleaned by the first cleaning means 18 which is in contact with the surface of the photosensitive belt 10. To do. After the cleaning is completed, the photosensitive belt 10 is further conveyed and the process of forming the second color toner image is started. On the other hand, the transfer body 16 to which the Y toner image has been transferred is conveyed in the counterclockwise direction at the same linear velocity as the photoconductor belt 10, and after passing below the second cleaning means 24 separated from the surface of the transfer body 16. , The transfer process of the second color toner image is started.

That is, the photoreceptor belt 10 which has been cleaned after the Y toner image is transferred to the transfer body 16 is charged by the charger 1.
It is uniformly charged again by 3. Then, the image signal of the second color is input to the exposure device 14, and as in the case of the image signal of the first color described above, an image is written on the surface of the photosensitive belt 10 and an image of the second color is obtained. To form an electrostatic latent image of. Then, using this latent image as the second color, magenta (M)
Development is performed by the developing means 15M containing toner. M
The photoreceptor belt 10 on which the toner image is formed is further conveyed, and the M toner image is transferred onto the transfer body 16 by the first transfer device 17, as in the case of the Y toner image. At this time, the transfer member 16 is conveyed in synchronization with the photoconductor belt 10 so that the image position of the Y toner image already transferred and the M toner image formed on the photoconductor belt 10 coincide with each other, and the Y toner image is transferred. The M toner image is transferred to the transfer body 16 by the first transfer means 17 in the existing state.

Thereafter, the photosensitive belt 10 is cleaned by the first cleaning means 18, and the transfer body 16 is cleaned by the second cleaning means 18.
After passing under the cleaning unit 24, the third image formation is started. That is, similarly to the image formation of the second color, after the latent image is formed on the photoconductor belt 10 by the image signal of the third color, the developing means 15 for accommodating the cyan (C) toner.
A C toner image is formed by C, is transferred onto the transfer body 16, and a latent image is formed by the image signal of the fourth color. Then, the developing means 15Bk for accommodating black (Bk) toner is used to form the photoreceptor belt 10. A Bk toner image is formed on the surface of and the image is transferred onto the transfer body 16. That is, the color toner images formed on the photoconductor belt 10 are superimposed on the transfer body 16 to form a color toner image on the surface of the transfer body 16.

Thereafter, the transfer member 16 is stopped from being conveyed in the counterclockwise direction and is rotated in the reverse direction, that is, is conveyed in the clockwise direction, and a transfer process to a transfer material described later is started. In this case, the transfer body 1
The photosensitive belt 10 is conveyed in the reverse rotation (counterclockwise) direction at the same linear velocity as that of the transfer member 16 so as not to damage the color toner image superimposed on the image carrier 6. Further, as a measure for preventing color toner image loss, the photosensitive belt 10 and the transfer body 16 may be displaced in a non-contact state by the operation of the moving means of the transfer body 16 described later.

Each of these developing means 15Y, 15M, 15
A direct current or further alternating current bias is applied to C and 15Bk so that reversal development is performed in a non-contact manner on the photosensitive belt 10 whose base is grounded. Further, the driving of the developing unit not involved in the development is stopped to prevent the toner image formed on the photoconductor belt 10 from being damaged by cutting the bias or the like, and the unnecessary toner is not supplied to the latent image.

On the other hand, the transfer material S accommodated in the paper supply cassette 25 is supplied by the paper supply roller 26, and the separation claw 19 is set as shown in FIG. 2, whereby the transfer material S is guided to the lower conveying path, The sheet is further conveyed by the conveying roller 23, transferred by the timing roller 27 along the guide member 28 in time with the color toner image on the transfer body 16, and conveyed to the second transfer unit 22.

Then, the color toner image formed on the surface of the transfer member 16 is applied to the transfer material S conveyed as described above by the second transfer means 22 by applying a high voltage power source output having a polarity opposite to that of the toner. Transcribe. After that, the transfer material S is conveyed to the fixing means 29, sandwiched between the fixing heat roller 291 and the pressure rubber roller 292, the transferred toner is melted and fixed, and then discharged. Further, the transfer body 16 which has completed the transfer of the color toner image to the transfer material S is further conveyed in the clockwise direction to remove and clean the residual toner by the second cleaning means 24 which brings the cleaning blade 241 into a pressure contact state.
After cleaning, the cleaning blade 24
1 is separated from the transfer body 16, and a process for forming a new color image is started.

Next, a monochrome image forming process by the above-mentioned image forming apparatus will be described. It should be noted that although black monochrome image formation will be described as an example, the same applies to the formation of other color monochrome images.

First, when monochrome image formation is selected by pressing a monochrome image formation button on an operation panel or the like (not shown), a monochrome image formation signal is input to control means (not shown), and the control means performs the monochrome image formation process. Based on this, each image forming process unit is controlled as follows to form a monochrome image.

When a monochrome image signal output by an image reading device (not shown) is input to the exposing means 14, a laser beam is generated by a semiconductor laser (not shown) in the exposing means 14. The laser beam drives the driving motor ( A polygon mirror 14 driven to rotate by (not shown)
It is rotationally scanned by 1 and passes through the fθ lens 142, the cylindrical lens 143, and the mirror 144, and is projected on the peripheral surface of the photoconductor belt 10 which is uniformly charged to a predetermined charge by the charger 13 to form a bright line.

On the other hand, in the sub-scanning direction, a belt index (not shown) corresponding to a specific position of the photosensitive belt 10 is detected or a print command signal is received, and this detection or command signal is used as a reference. The modulation of the semiconductor laser by the image signal is started, and the main scanning line determines. When scanning is started, a laser beam is detected in the main scanning direction by an index sensor (not shown), the semiconductor laser is started to be modulated by the image signal of the first color based on this detection signal, and the modulated laser The beam scans over the surface of the photoreceptor belt 10. Therefore,
A latent image corresponding to a monochrome image is formed on the surface of the uniformly charged photoconductor belt 10 by the main scanning by the laser beam and the sub-scanning by the conveyance of the photoconductor belt.

In this case, a reversal development is carried out in a non-contact manner on the photosensitive belt 10 whose base is grounded by applying a DC or further AC bias only to the developing means 15Bk.
Incidentally, the developing means 15Y, 15M, 15 which do not participate in the phenomenon
The drive of C is stopped and the bias is cut so that unnecessary toner is not supplied to the latent image on the photosensitive belt 10.

On the other hand, the transfer material S accommodated in the paper feed cassette 25 is supplied by the paper feed roller 26, and the separation claw 19 is set as shown in FIG. 1, whereby the transfer material S is guided to the upper conveying path, Photosensitive belt 1 by timing roller 30
The Bk toner image on 0 is aligned with the timing, and the guide member 31 conveys the image along the transfer body 16 between the photoconductor belt 10 and the transfer body 16. Also at this time, the photoconductor belt 1
0 and the transfer body 16 are conveyed at the same linear velocity in the clockwise direction and the counterclockwise direction, respectively.

Then, the Bk toner image formed on the surface of the photoconductor belt 10 is applied to the transfer material S conveyed as described above by the first transfer device 17 by applying a high-voltage power source output having a polarity opposite to that of the toner. And transfer it. That is, the photosensitive belt 1
The Bk toner image formed on 0 is directly transferred from the photoconductor belt 10 to the transfer material S without the transfer body 16. In this case, the transfer body 16 acts only as a conveyor belt.

The transfer material S to which the Bk toner image has been transferred does not follow the direction of the photoconductor belt 10 that rapidly changes the direction (small diameter curvature) along the rotary roller 11 and does not change its direction. Separated from. This is the transfer body 1
6, the sheet is conveyed to the rear by way of the second cleaning means 24, and is conveyed to the fixing means 29 in the same manner as the color image,
The toner is melted and fixed, and then discharged. On the other hand, the transfer material S
After the transfer of the monochrome image to the photoconductor belt 10, the photoconductor belt 10 is further conveyed in the counterclockwise direction to remove and clean the residual toner by the cleaning blade 181 of the first cleaning means 18.

At this time, since a wide variety of transfer materials S pass between the transfer body 16 and the photoconductor belt 10 during monochrome image formation, the contact pressure between the transfer body 16 and the photoconductor belt 10 is relatively low. If it is not set, the conveyance quality of the transfer material itself such as jam may become a problem. The moving mechanism of the transfer body 16 described below is used when the transfer material S passes between the transfer body 16 and the photoconductor belt 10 during monochrome image formation.
Is moved to change the contact condition so that the transfer quality of the transfer material itself can be maintained.

The moving mechanism of the transfer member 16 is shown in FIG.
4 will be described. The rotary roller 21 of the transfer body 16 is provided with rotary shafts 211 at both ends thereof, and the bearing 32 is incorporated into the rotary shaft 211 to make the rotary operation of the rotary roller 21 smooth. The bearing 32 is fitted in a groove 33 formed in a side plate of the main body of the image forming apparatus (not shown), and is vertically swingable. Further, a compression spring 34 is incorporated in the groove 33 in order to constantly regulate the bearing 32 in one direction (lower side in this case).

In order to swing the rotary roller 21 in the vertical direction, cams 35 acting on the bearing 32 are provided at both ends of the rotary roller 21. The cam 35 is a cam rotation shaft 351.
The bearing 32 is displaced by rotating around the
6 is movable, and the contact condition between the transfer body 16 and the photosensitive belt 10 can be variably set. The drive source of the cam 35 may be a gear mechanism or the like provided on the image forming apparatus main body side, and rotation control may be performed by using an electromagnetic clutch or the like.
Further, the displacement amount of the transfer member 16 can be regulated by controlling the shape and rotation angle of the cam 34.

Next, a second embodiment of the present invention will be described with reference to FIGS. In this embodiment, the movable mechanism of the transfer member 16 is used to switch the paper transport path between monochrome and color image output.

In the apparatus of this embodiment, there is no separation claw, and when forming a monochrome image, the transfer member 16 is positioned as shown in FIG. 5, the transfer material S is conveyed by the paper feed roller 26, and the timing is set by the timing roller 30. In addition, the guide member 3
1 to convey along the upper portion of the transfer body 16. Subsequent operations are the same as the monochrome image formation in the first embodiment, and therefore the description is omitted. On the other hand, as shown in FIG. 6, when forming a color image, the movable mechanism raises and positions the lower surface of the transfer body 16 so that the lower surface of the belt of the transfer body 16 is above the conveyance path of the guide member 31. The timing of displacement is set immediately before the reverse rotation starts after the color toner images are superposed on the transfer body 16 in the color image forming process and the feeding operation of the transfer material S starts. As a result, the transfer material S is transferred to the paper feed roller 2
6, it guides to the color image conveyance guide 36 along the lower part of the belt of the transfer body 16 via the timing roller 30 and the guide member 31. Subsequent operations are the same as those in the color image formation in the first embodiment, and the description thereof will be omitted. Then, after the transfer by the second transfer means 22 is completed, the transfer body 16 is returned to the normal position.

[0042]

As described above, the color image forming apparatus according to the present invention is provided with a structure capable of forming a color image, but at the time of monochrome image formation, the toner image on the photoconductor is not passed through the intermediate transfer body. Since the image can be directly transferred from the photoconductor to the paper, the toner image on the photoconductor can be transferred at a high transfer rate, the image quality of the monochrome image can be improved, and as a result, the toner consumption amount at the time of forming the monochrome image can be reduced. Also, the image forming speed during monochrome image formation can be increased, and even during color image formation, the intermediate transfer body is rotated in the reverse direction after forming a synthetic toner image formed by superimposing a plurality of toner images on the intermediate transfer body. Then, the synthetic toner image is transferred from the intermediate transfer member onto the sheet of paper at once, so the photosensitive member rotation direction during the formation of the synthetic toner image on the intermediate transfer member is the same as the photosensitive member rotation direction during monochrome image formation. Can be
Moreover, since the image forming surface on the color image and the monochrome paper can be the same surface, the fixing device after the transfer process can be simplified,
There is an effect that a fixing device capable of fixing on both sides and two types of fixing devices are unnecessary.

In the color image forming apparatus according to the second aspect of the invention, although the monochrome image output and the color image output have separate sheet conveying paths, the belt transfer body also serves as a sheet conveying means. Therefore, in addition to the above common effects, parts such as a pair of transport rollers for transporting paper can be reduced,
There is an effect that the cost of the transportation means can be reduced.

In the color image forming apparatus of the third aspect, the belt transfer member moves to switch the paper conveying path between monochrome and color image output. Therefore, in addition to the common effects described above, the conveying path can be simplified and the apparatus can be used. There is an effect that the size can be reduced.

According to a fourth aspect of the present invention, in the color image forming apparatus, the movable member displaces the photosensitive member and the intermediate transfer member in a non-contact state, and the composite toner image on the intermediate transfer member is transferred to the photosensitive member without reverse rotation of the photosensitive member. Since there is no need to rub, there is an effect that in addition to the common effects described above, image loss can be prevented when the intermediate transfer member is rotated in the reverse direction.

In the color image forming apparatus according to the fifth aspect of the present invention, since the contact condition in monochrome and color image output can be variably set by moving the belt transfer member by the moving means of the belt transfer member, in addition to the above common effect, There is an effect that it is possible to meet the transfer contact conditions that satisfy both monochrome and color images.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of a color image forming apparatus according to the present invention and a monochrome image forming state in the present embodiment.

FIG. 2 is a diagram showing a color image forming state in the apparatus of FIG.

FIG. 3 is a diagram showing a movable mechanism of a transfer body.

FIG. 4 is a diagram showing an operating state of the mechanism of FIG.

FIG. 5 is a diagram showing a schematic configuration of a second embodiment of a color image forming apparatus according to the present invention and a monochrome image forming state in the present embodiment.

6 is a diagram showing a color image forming state in the apparatus of FIG.

[Explanation of symbols]

 10 Photosensitive Belt 11, 12 Rotating Roller 13 Charging Means 14 Exposure Means 141 Polygon Mirror 142 fθ Lens 143 Cylindrical Lens 144 Mirror 15Y, 15M, 15C, 15Bk Developing Means 16 Transfer Body 17 First Transfer Means 18 First Cleaning Means 181 Cleaning blade 19 Separation claws 20, 21 Rotating roller 211 Rotating shaft 22 Second transfer means 23 Conveying roller 24 Second cleaning means 241 Cleaning blade 25 Paper feeding cassette 26 Paper feeding roller 27 Timing roller 28 Guide member 29 Fixing means 291 Fixing heat roller 292 Pressure rubber roller 30 Timing roller 31 Guide member 32 Bearing 33 Groove 34 Compression spring 35 Cam 351 Cam rotation shaft 36 Color image transport guide S Transfer material

Claims (5)

[Claims] 1. A toner image formed on an image carrier is repeatedly transferred to an intermediate transfer member to form a synthetic toner image on the intermediate transfer member by superposing a plurality of toner images. In a color image forming apparatus that collectively transfers and fixes the above synthetic toner image onto a sheet from the body, when outputting a monochrome image, the sheet is conveyed so as to pass between the image carrier and the intermediate transfer body, The toner image formed on the image carrier is directly transferred to the paper, and at the time of color image output, after the synthetic toner image formed by superposing a plurality of toner images is formed on the intermediate transfer member, A color image forming apparatus characterized in that an intermediate transfer member is reversely rotated to collectively transfer a synthetic toner image onto a sheet from the intermediate transfer member. 2. The intermediate transfer member is a belt transfer member,
2. The color image forming apparatus according to claim 1, wherein the belt transfer member also serves as a sheet conveying unit for either monochrome or color image output. 3. The intermediate transfer member is a belt transfer member,
2. The color image forming apparatus according to claim 1, further comprising moving means for the belt transfer body, wherein the belt transfer body is moved to switch the sheet conveying path between monochrome and color image output. 4. The intermediate transfer member is a belt transfer member,
When the intermediate transfer body is rotated in the reverse direction after the composite toner image is formed on the intermediate transfer body in color image output, the image carrier and the intermediate transfer body are not moved. The color image forming apparatus according to claim 1, wherein the color image forming apparatus is displaced in a contact state. 5. The intermediate transfer member is a belt transfer member,
7. A movable member for the belt transfer member is provided, and the contact condition between the image carrier and the intermediate transfer member in monochrome and color image output is made variable by moving the belt transfer member. 1. Color image forming apparatus.