JP2002296867A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a high-quality image in a state where an unnecessary member is not actuated at normal processing speed whether color image formation or black monochromatic image formation is selected in a color image forming device. SOLUTION: A processing part for color 100A for forming a color toner image on the peripheral surface of a transfer belt 14a provided to be stretched and a processing part for monochrome 100B for forming a black toner image thereon are installed in parallel, and respective transfer rollers 14c1 and 14c2 provided in the respective processing parts are put in a state where they hold the belt 14a in between and freely contact with/separate from photoreceptors in the respective processing parts. Then, the device is constituted so that the color image or the black monochromatic image may be selectively formed by the image formation by either processing part and the movement of the transfer roller based on information whether the image obtained by reading the image is color or monochrome.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic color image forming apparatus capable of arbitrarily selecting and forming a black monochrome image or a multicolor image.

[0002]

2. Description of the Related Art Recently, an electrophotographic color image forming apparatus capable of recording a color image as a clear image with a well-balanced color tone on a transfer material has been widely used for office use.

In many of the color image forming apparatuses, a color image is formed by superimposing yellow (Y), magenta (M), cyan (C) and black (K) color images. For this reason, it is also used as a monochrome image forming apparatus for forming a monochrome image by operating only a process for forming a black image.

[0004]

However, in such a color image forming apparatus, in the case of monochrome image formation, various image forming equipment such as an image carrier of each color other than black, a developing means, etc. are unnecessary. It is said that it is worn out and degrades quickly because it runs idle. As a countermeasure, measures are taken to suspend the operation of each device that is not necessary.In this case, however, a large change in the load on the drive system causes a change in the process speed of monochrome image formation, and therefore, a stabilization for the stabilization of the process. There has been a problem that it takes a long time to wait and it is not possible to quickly switch the image forming process.

As a result of solving the above problems, the present invention is directed to a color image forming apparatus capable of rapidly changing the image forming process corresponding to each color or monochrome image and forming an image with stable high quality. It is intended to be provided.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide a process unit for forming a black (K) single color toner image,
K, a color process unit for forming a color toner image in four colors, wherein a black monochromatic image or a color image is formed by selective transfer from each process unit to a transfer material. This is achieved by the forming apparatus (the invention of claim 1).

It is another object of the present invention to provide a monochrome processing unit for forming a black (K) monochromatic toner image, and at least Y, M, and
C, a color processing unit for forming a color toner image in three colors, and a black single-color image or a color image is formed by transfer from a monochrome process unit to a transfer material and selective transfer from the color process unit. This is achieved by a color image forming apparatus (the invention of claim 6).

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A color image forming apparatus according to the present invention is a color process unit 100A for forming a color toner image by superimposing toner images of respective colors and a monochrome process for forming only a black (K) toner image. A process unit 100B is also provided, and one of the process units operates according to color information or operation input of an image obtained by reading a document image, and a color or monochrome image is selected and formed.

The present invention is also directed to a color image forming apparatus capable of forming an image on either one side or both sides of a transfer material, and each example of a double-sided image forming apparatus will be described below. . However, the present invention is not limited to this.

The color processing section 100A comprises an image bearing means and yellow (Y), magenta (M), cyan (C) and black (K) developing means disposed on the peripheral surface thereof. On the other hand, the monochrome process section 100B includes an image carrier and black (K) developing means disposed on the peripheral surface thereof. In the image forming apparatus shown in FIG. 1 as an image carrier, a photosensitive belt 10A (1) and a photosensitive drum 10
B (1), the intermediate transfer belts 14A and 14B together with the photosensitive drums 10A (2) and 10B (2) in the image forming apparatus shown in FIG. 2, and the photosensitive drum 10A (3) in the image forming apparatus shown in FIG. ) And 10B (3) are used.

In FIG. 1, reference numeral 10A (1) denotes a photoreceptor belt serving as an image carrying means for the processing section 100A, 11 denotes a scorotron charger which serves as a charging means for each color, and 12 denotes an exposure optical system which serves as an image exposing means for each color. , 13 are developing devices as developing means for each color, 14a is an intermediate transfer member, 14c1 and 14c
Reference numeral c2 denotes a primary transfer roller as a first transfer unit, 14g denotes a secondary transfer unit as a second transfer unit, 15c denotes a timing roller as a transfer material supply unit, and 30 denotes a fixing device as a fixing unit.

In the process section 100A, a photoreceptor belt 10A (1), which is an image carrying means, is provided, for example, on the outer periphery of an endless flexible base, a conductive layer, an a-Si layer or an organic photosensitive layer (OPC). And the like, and is rotated clockwise as indicated by an arrow in FIG.

A scorotron charger 11 serving as a charging unit for each color, an exposure optical system 12 serving as an image exposing unit for each color, and a developing unit 13 serving as a developing unit for each color constitute one set of these units, and are designated as yellow (Y). , Magenta (M), cyan (C)
4 for the image forming process of each color of black and black (K)
A set is provided and arranged in the order of Y, M, C, and K with respect to the rotation direction of the photosensitive drum 10 indicated by the arrow in FIG.

A scorotron charger 11, which is a charging means for each color, is mounted to face the photoreceptor belt 10A (1) in a direction orthogonal to the moving direction of the photoreceptor belt 10A (1). 10A (1) has a control grid maintained at a predetermined potential with respect to the above-mentioned photosensitive layer and a discharge electrode formed of, for example, a sawtooth electrode, and is charged by corona discharge having the same polarity as the toner (the present embodiment). Is negatively charged), and the photoreceptor belt 10A
A uniform potential is applied to (1). As a discharge electrode,
Other wire electrodes can also be used.

Reference numeral 12 denotes an exposure optical system as an image writing means for performing K, C, M, and Y image exposure based on image data.
A (1) or a scanning optical system that performs scanning in parallel with the rotation axis of the photosensitive drum 10B (1). Uniformly charged photoreceptor belt 10A (1) or photoreceptor drum 10B (1)
A latent image is formed thereon by performing image exposure using the exposure optical system 12.

A developing device 13 as a developing means for each color includes
A predetermined gap is maintained with respect to the peripheral surface of the photoreceptor belt 10A (1), and the photoreceptor belt 10A (1) rotates in the forward direction with respect to the rotation direction, for example, a thickness of 0.5 to 1 mm and an outer diameter of 15 to 25 mm
Having a developing sleeve formed of a non-magnetic stainless steel or aluminum material having a cylindrical shape, and one or two-component developer of yellow (Y), magenta (M), cyan (C) and black (K) inside Is housed. Each of the developing units 13 is driven by an abutting roller (not shown) to drive the photosensitive belt 10A.
A non-contact is maintained with a predetermined gap, for example, 100 to 1000 μm, from (1), and a DC voltage and an AC voltage having the same polarity as the toner (in this embodiment, a negative polarity) are superimposed on the developing sleeve 131. By applying the developed bias, non-contact reversal development is performed, and a color toner image is formed on the photoreceptor belt 10A (1).

On the other hand, in the processing section 100B for forming a monochrome image, the photosensitive drum 1 serving as an image bearing means is used.
Reference numeral 0B (1) denotes an organic photosensitive layer (OPC) having photoconductivity formed on the outer periphery of a cylindrical substrate, and is rotated clockwise as indicated by an arrow in FIG.

A scorotron charger 11, a scanning optical system 12K and a developing device 13K for containing black (K) toner are arranged on the peripheral surface of the photosensitive drum 10B. ) Is formed.

The transfer belt 14a as an intermediate transfer member has a volume resistivity of 10 ¹⁰ to 10 ¹⁵ Ω · cm and a surface resistivity of 10 10
It is an endless belt of ¹⁰ to 10 ¹⁵ Ω / □, for example, a conductive material dispersed in an engineering plastic such as a modified polyimide, a thermosetting polyimide, an ethylene tetrafluoroethylene copolymer, a polyvinylidene fluoride, a nylon alloy, and the like. This is a two-layer seamless belt in which a 1 to 1.0 mm semiconductive film substrate is coated with a fluorine coating having a thickness of 5 to 50 μm, preferably as a toner filming preventing layer. In addition, as the base of the transfer belt 14a, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber or urethane rubber can be used. The transfer belt 14a is stretched around a drive roller 14d, a driven roller 14e, a tension roller 14k, and a backup roller 14j. During image formation, the drive roller 14d is rotated by a drive motor (not shown). At the transfer position for each color, the primary transfer roller 14c1 or 14c
2, the transfer belt 14a is pressed against the photoreceptor belt 10A (1) or the photoreceptor drum 10B (1), and the transfer belt 14a is rotated in the direction indicated by the arrow in the figure.

Primary transfer roller 14 as first transfer means
c1 and 14c2 are provided opposite to the photoreceptor belt 10A (1) or the photoreceptor drum 10B (1) with the transfer belt 14a interposed therebetween.
A transfer area 14b is formed between the photosensitive drum 10A (1A) and the photosensitive drum 10B (1). Primary transfer rollers 14c1 and 1
A DC voltage having the opposite polarity (positive polarity in this embodiment) to the toner is applied to 4c2, and a transfer electric field is formed in the transfer area 14b, so that the photoreceptor belt 10A (1)
Alternatively, the toner image on the photosensitive drum 10B (1) is transferred onto the transfer belt 14a or onto the surface of the recording paper P as a transfer material.

A secondary transfer unit 14g as a second transfer unit
Is provided opposite to a conductive backup roller 14j that is grounded with the transfer belt 14a interposed therebetween. A DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied to the toner. Image on recording paper P
Transfer to the back of

Timing roller 1 as transfer material supply means
5c transfers the recording paper P as a transfer material in synchronization with the toner image of the front surface image on the photosensitive belt 10A (1) or the photosensitive drum 10B (1) or the toner image of the back surface image on the transfer belt 14a. Feed to area 14b.

A fixing device 30 serving as a fixing unit includes a first fixing roller 310 having a heater therein and a second fixing roller 3 having a heater therein.
20 and two fixing members in the form of rollers, and heat and pressure are applied between the first fixing roller 310 and the second fixing roller 320 to fix the toner image on the recording paper P.

In the image forming apparatus shown in FIG. 2, a process section 100A for forming a color image is of a tandem type, and Y, M, C and K formed on the peripheral surface of each photosensitive drum 10A (2). Of the toner image of the intermediate transfer belt 14A
The toner image is sequentially transferred to the peripheral surface and is once carried as a color toner image by superposition. Similarly, in the process section 100B for forming a monochrome image, the photosensitive drum 10B
The K toner image formed on the peripheral surface of (2) is transferred to the peripheral surface of the intermediate transfer belt 14B and is once carried as a black toner image.

Further, the process section 100A of the image forming apparatus shown in FIG. 3 includes a transparent conductive layer formed on the outer periphery of a cylindrical base on which the photosensitive member 10A (3) is formed of a transparent member such as optical glass or transparent acrylic resin. A photosensitive layer such as an a-Si layer or an organic photosensitive layer (OPC) is formed.

In FIG. 3, the exposure unit 12, which is an image exposing means for each color, has an exposure position on the photosensitive drum 10A (3) which is different from the scorotron charger 11 for each color. Is arranged inside the photosensitive drum 10A (3) so as to be located on the downstream side in the rotation direction of the photosensitive drum 10A. The exposure unit 12 includes L as light emitting elements arranged in the main scanning direction in parallel with the axis of the photosensitive drum 10A (3).
It comprises a linear light-emitting element in which a plurality of EDs (light-emitting diodes) are arranged in an array, and a holder (not shown) to which a selfoc lens as an equal-magnification imaging element is attached. Image data of each color read by a separate image reading device and stored in the memory is sequentially read from the memory and input to the exposure unit 12 for each color as an electric signal.

The process section 100 in the present image forming apparatus
A and 100B also use the same process as in the image forming apparatus shown in FIG.
A color toner image is formed on the peripheral surface of (3), and a black (K) single color toner image is formed and carried on the peripheral surface of the photosensitive drum 10B (3).

The transfer belt 14a used in each of the above-described image forming apparatuses is provided between the driven roller 14e and the backup roller 14j, as shown by a two-dot chain line in FIG. The transfer roller 14c1 or 14c2 is moved up and down to move toward and away from the photosensitive member and the intermediate transfer member to form respective transfer areas 14b. And release is performed.

The function will be described below with reference to FIG. 4 which is a main part view of the image forming apparatus shown in FIG.

Each transfer roller 14c1 or 14c2 is mounted on a support member 40 having a U-shape together with a separator 14f provided in parallel with the transfer roller 14c1 or 14c2. Accordingly, it is moved up and down along the guide member 42. When the support member 40 is at the upper position, the transfer roller 14c1 or 14c2 is urged by the elastic member 43 so that the transfer belt 14a is
A (1) or the photosensitive drum 10B (1)
When the support member 40 is at the lower position, each transfer roller 14c1 or 14c2, the photosensitive belt 10A (1), or the photosensitive drum 10B resists the urging of the elastic member 43.
In the case of (1), the sheet is further separated from the transfer belt 14a and retracted downward.

Next, the process of forming images on both front and back sides is shown in FIG.
A description will be given by using the image forming apparatus shown in FIG.

In an image reading apparatus separate from the present apparatus, image data of a document image read by an image pickup element or image data of an image edited by a computer is Y (yellow), M (magenta), (Cyan) and K (black) are temporarily stored and stored in the memory as image signals for respective colors. When the original image is determined to be color by reading, the control unit is operated by the color mode program stored in the memory according to the identification signal.
The input to the control system on the 00A side causes the process section 100A to preliminarily operate and start warming up. At the same time, the eccentric cam 41A rotates to the rotation angle shown in FIG. When the transfer belt 14a is moved in contact with (1), the color transfer area 14 is moved.
b is formed. On the other hand, the transfer roller 14c2 on the process section 100B side is kept at a position separated from both the photosensitive drum 10B (1) and the transfer belt 14a.

The photosensitive belt 10A (1) is rotated clockwise as indicated by an arrow in FIG. 1 by starting a photosensitive member drive motor (not shown) at the start of image recording, and at the same time, the yellow (Y) scorotron charger 11 is charged. By the action, the application of the potential to the photoreceptor belt 10A (1) is started.

After the photoreceptor belt 10A (1) is applied with a potential, exposure by the first color signal, ie, an electric signal corresponding to the Y image data is started in the Y exposure optical system 12, and the photoreceptor belt 10A (1) is exposed. An electrostatic latent image corresponding to the Y image of the back surface image of the document is formed on the photosensitive layer on the front surface by the rotational scanning of 1).

The latent image is reversal-developed in a non-contact state by the Y developing unit 13 to form a yellow (Y) toner image in accordance with the rotation of the photosensitive belt 10A (1).

Next, the photosensitive belt 10A (1) is applied with a potential from above the yellow (Y) toner image by the charging action of the magenta (M) scorotron charger 11, and the second exposure optical system of the M exposure optical system. Exposure with an electrical signal corresponding to the color signal of M, ie, M image data, is performed, and the M developing device 1
The magenta (M) toner image is superimposed on the yellow (Y) toner image by the non-contact reversal development by No. 3.

By the same process, the cyan (C) toner image corresponding to the third color signal is further superimposed by the cyan (C) scorotron charger 11, the exposure optical system 12 of C and the developing device 13 of C. The black (K) toner image corresponding to the fourth color signal is sequentially superimposed thereon by a black (K) scorotron charger 11, an exposure optical system 12 for K, and a developing device 13 for K. A color toner image is formed on the peripheral surface within one rotation of the photoreceptor belt 10A (1).

By the above-described image forming process, a superimposed color toner image serving as a back side image is formed on the photoreceptor belt 10A (1) as the image carrying means, and the back side image on the photoreceptor belt 10A (1) is superposed. In the transfer area 14b of the combined color toner image, a DC voltage having the opposite polarity (positive polarity in the present embodiment) to the toner is applied 1
The next transfer unit 14c1 collectively transfers the images onto the intermediate transfer body 14a.

The toner remaining on the peripheral surface of the photoreceptor belt 10A (1) after the transfer reaches the cleaning device 19, and is cleaned by a cleaning blade 19a made of a rubber material in contact with the photoreceptor belt 10A (1). Subsequently, color image formation of the next surface image is performed.

After the superimposed color toner image serving as the back side image is formed on the intermediate transfer body 14a as described above, the back side image on the intermediate transfer body 14a and the transfer area 1
4b, the superimposed color toner image serving as the surface image is formed on the photoreceptor belt 10A (1) in the same manner as in the above-described color image forming process.
The surface image formed at this time is a photoconductive belt 10
On A (1), it is necessary to change the image data so that the back image is a mirror image of the back image.

A 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 15a.
, And are fed by the feed roller 15b and conveyed to the timing roller 15c.

The recording paper P is transferred to the photosensitive belt 10A by driving a timing roller 15c as a transfer material supply means.
(1) The color toner image of the front surface image formed thereon and the color toner image of the rear surface image carried on the intermediate transfer body 14a are synchronized and fed to the transfer area 14b.

When the recording paper P is fed to the transfer area 14b,
The recording paper P is charged to the same polarity as the toner by a paper charger 14i as a transfer material charging means capable of coming into contact with and releasing from the intermediate transfer body 14a, and is adsorbed by the intermediate transfer body 14a to the transfer area 14b. Will be fed. By charging the paper with the same polarity as that of the toner, the toner is prevented from being attracted to the toner image on the intermediate transfer member 14a and the toner image on the photoreceptor belt 10A (1), thereby preventing the toner image from being disturbed. In addition, as the transfer material charging unit, a conductive roller that can be brought into contact with and released from the intermediate transfer member 14a, a corona discharger that does not contact the intermediate transfer member 14a, or the like can be used.

In the transfer area 14b, a first voltage to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied.
The surface image on the peripheral surface of the photosensitive drum 10 is collectively transferred onto the surface (upper surface) of the recording paper P by the primary transfer device 14c1 as a transfer unit. At this time, the back surface image on the peripheral surface of the intermediate transfer member 14a is not transferred to the recording paper P but exists on the intermediate transfer member 14a.

Next, the recording paper P on which the color toner image has been transferred onto the surface thereof is used as a second transfer means to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied.
The sheet is conveyed to the next transfer device 14g, and the back surface image on the peripheral surface of the intermediate transfer member 14a is collectively transferred to the back surface (lower surface) of the recording paper P by the secondary transfer device 14g.

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. Therefore, the color toner image formed on the intermediate transfer member 14a is inverted in polarity by corona charging, and the color toner image formed on the photoreceptor belt 10A (1) is inverted in polarity by corona charging. In such a case, the toner in the lower layer is not sufficiently charged to the same polarity, so that the transfer becomes poor.

The reversal development is repeated on the photoreceptor belt 10A (1), and the color toner images of the same polarity formed by superimposition are collectively transferred to the intermediate transfer member 14a without changing the polarity, and then the polarity is not changed. Transfer to the recording paper P at once is preferable because it contributes to the improvement of the transferability of the backside image formation. Also for surface image formation, reversal development is repeatedly performed on the photoreceptor belt 10A (1), 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 the improvement of transferability of image formation.

As described above, in the color image formation, the first transfer means and the second transfer means are separately provided, and the first transfer means is operated to form a color toner image on the surface of the transfer material. Next, 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 unit is preferably adopted.

The recording paper P, which is a transfer material having a color toner image formed on both sides, is neutralized by a paper separation AC static eliminator 14h for separating the transfer material, separated from the intermediate transfer member 14a, and separated by both upper and lower rollers. The sheet is conveyed to a fixing device 30 as a fixing unit composed of two fixing rollers having a heating unit (heater) therein. By applying heat and pressure to the recording paper P between the first fixing roller 310 on the upper side and the second fixing roller 320 on the lower side, the toner adhered to the front and back of the recording paper P is fixed, and the two-sided image recording is performed. The discharged recording paper P is fed by a paper discharge roller 18 and discharged to a tray outside the apparatus.

The toner remaining on the peripheral surface of the intermediate transfer member 14a after the transfer is provided to an intermediate transfer member cleaning device 190 which is a cleaning means for the intermediate transfer member.
The blade 4a is cleaned by a blade capable of abutting and releasing. The photoreceptor belt 10A (1) after the transfer
The toner remaining on the peripheral surface of the photosensitive member 10 is subjected to static elimination by the image forming body AC static eliminator 16 and then reaches the cleaning device 19, where the cleaning device 19 is formed by the cleaning blade 19a made of a rubber material in contact with the photosensitive belt 10A (1). 19, and is collected by a screw 19b in a waste toner container (not shown). The photoreceptor belt 10A (1) from which the residual toner has been removed by the cleaning device 19 is uniformly charged by the Y scorotron charger 11 after the peripheral surface of the photoreceptor is neutralized, and enters the next image forming cycle. .

When it is determined that the original image is black (K) monochrome, the control unit uses the identification signal to input the original image to the control system of the process unit 100B by the monochrome mode program stored in the memory. As a result, the process unit 100B performs a preliminary operation to start warming up, and at the same time, the eccentric cam 41B
(B), the transfer roller 14c2 is brought into contact with the photosensitive drum 10B (1) and the transfer belt 14a is rotated.
, A monochrome transfer area 14b is formed. On the other hand, the transfer roller 14c1 on the process unit 100A side is maintained at a position separated from both the photoreceptor belt 10A (1) and the transfer belt 14a, and the process unit 100B forms a monochrome image on the front and back of the recording paper P.

By the same function, in the image forming apparatus shown in FIG. 2, the color image is transferred to the transfer belt 14A by the black (K)
3 is transferred to the transfer belt 14B, and in the image forming apparatus shown in FIG.
A (3) shows a black (K) monochrome image on the photosensitive drum 10.
After being formed on B (3), they are transferred to both front and back surfaces of the recording paper P.

When a color image and a monochrome image are mixed in an original, during the image forming operation of one process unit 100, the other process unit 100 receives color information of a subsequently input image. If the warm-up is started by preliminarily operating the image forming apparatus 100, the image forming operation is immediately performed by the other process unit 100 by switching the transfer roller 14C after image transfer from one process unit 100 from 14c1 to 14c2 or from 14c2 to 14c1. Can start,
Subsequently, it is possible to perform monochrome image formation from color image formation or color image formation from monochrome image formation.

Further, when the size of the formed toner image is small and has a size relationship capable of carrying two toner images on the peripheral surface of the intermediate transfer member 14a, both process units 10
0 is set to the active state, and the timing of forming both toner images is appropriately controlled, so that the monochrome toner image and the color toner image are transferred side by side on the intermediate transfer member 14a to form a continuous monochrome image. And a two-sided image of a color image can be formed on recording paper.

The color image forming apparatus described above includes Y, M,
A color process unit for forming a color toner image by superimposing toner images of C, K and four colors and a monochrome process unit for forming only a black (K) toner image are provided side by side. One of the process units is selectively operated to form a color or monochrome image. In addition, a color toner image is formed by superposing at least three color toner images of Y, M, C. And a monochrome process unit for forming only a black (K) toner image, the color process unit is selectively operated, and the monochrome process unit is provided. By constantly operating, it is also possible to select and form a color or monochrome image.

[0056]

According to the present invention, regardless of whether a color or black and white image is selected according to claim 1 or claim 6,
Unnecessary image forming members are in a halt state so that an image of stable image quality is always formed at a constant printing speed, and the switching between the color and monochrome image forming processes is performed promptly according to claims 2 and 3. Further, the switching of the image forming process can be realized with a very simple structure, and the switching speed can be further increased in accordance with the size of the transfer material. As a result, the image forming member is not unnecessarily fatigued or worn and deteriorated, and the color and black monochrome images are recorded as high quality images by switching the image forming process. A color image forming apparatus has been provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus of the present invention including a belt-shaped photoconductor.

FIG. 2 is a cross-sectional configuration diagram of a color image forming apparatus of the present invention using a tandem system.

FIG. 3 is a cross-sectional configuration diagram of a color image forming apparatus of the present invention including a drum-shaped photoconductor.

FIG. 4 is a main part view showing a switching mechanism of an image forming process.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor belt (drum) 11 scorotron charger 12 exposure optical system (unit) 13 developing device 14a transfer belt, intermediate transfer member 14b transfer area 14c (primary) transfer roller 14g (secondary) transfer device 15 paper cassette 15c Timing roller 19, 190 Cleaning device 30 Fixing device 40 Support member 41 Eccentric cam 42 Guide member 43 Elastic member 100A (color) Process unit 100B (monochrome) Process unit P Recording paper

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G03G 21/00 384 G03G 21/00 372 F term (Reference) 2H027 DA01 DA32 DB02 DE02 DE09 EB04 ED01 ED04 ED24 EE04 EE05 EF09 FA28 FB02 FB05 FB19 ZA07 2H030 AA01 AA06 AB02 AD05 AD07 AD08 AD12 AD17 BB02 BB23 BB42 BB46 BB53 BB56

Claims (6)

[Claims] 1. A process section for forming a black (K) single color toner image, and a color process section for forming a color toner image in four colors of Y, M, C, K, and A color image forming apparatus for forming a black monochrome image or a color image by selective transfer from each process unit. 2. The color image forming apparatus according to claim 1, wherein a preliminary operation of the process unit is started prior to use according to print information indicating whether the image is a monochrome image or a color image. 3. The preparatory operation of one of the process units is performed while the other of the process units is in operation.
Or the color image forming apparatus according to 2. 4. The method according to claim 1, wherein the change between the black monochrome image and the color image is performed by moving an intermediate transfer member.
The color image forming apparatus according to claim 1. 5. The image forming apparatus according to claim 1, wherein at the time of changing the image between the black monochrome image and the color image, image formation and transfer are performed in parallel in accordance with each transfer sheet passing therethrough. Item 7. The color image forming apparatus according to Item 1. 6. A monochrome processing unit for forming a black (K) single color toner image, and a color processing unit for forming at least three color toner images of Y, M, C and three colors, A color image forming apparatus for forming a black monochrome image or a color image by transfer from a monochrome process unit and selective transfer from a color process unit.