JPH11237780A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device, capable of a color image formation using an intermediate transfer body, which is the same in high speediness, productivity, and operability to a conventional monochromatic image forming device. SOLUTION: The image forming device is equipped with a color developing unit 8 in which color developing devices, yellow, magenta, and cyan, are integrally composed, a cartridge 31 in which a photoreceptor 2, a black developing device 16, an electrifier, and a cleaner 24 are integrally composed, and the intermediate transfer body. The device forms a toner image on the photoreceptor 2 or the intermediate transfer body, inserts recording paper in a contact part between the photoreceptor 2 and intermediate transfer body, and transfers the toner image to the recording paper. The color developing unit 8, in which the color developing devices for yellow, magenta, and cyan are integrally composed, and the cartridge 31, in which the photoreceptor, black developing device 16, electrifier, and cleaner 24 are integrally held, are so composed as to be detachable, thereby realizing monochromatic image formation by a simple structure, at a high speed, at high productivity, and by simple operability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a color printer,
The present invention relates to an image forming apparatus that can be applied to a color copying machine, a color facsimile, and the like, and particularly to an image forming apparatus that forms a color image by superposing multicolor toner images using an electrophotographic method.

[0002]

2. Description of the Related Art Generally, in order to form a color image by an electrophotographic method, a color image is formed by superimposing yellow, magenta, cyan, and black toner images on a transfer material or an intermediate transfer member. Has been taken. As a method for forming these color images, there are generally a transfer drum method, an intermediate transfer member method, a continuous superimposition method, and the like. The transfer drum method is a method in which toner images of each color are sequentially formed on one photoconductor, and each time a toner image of each color is formed on the photoconductor, the transfer material wound around the transfer drum is rotated and repeated. In this method, the toner images of the respective colors sequentially formed thereon are transferred in a state of being opposed to the photoconductor. The intermediate transfer member system uses an intermediate transfer member instead of a transfer drum, temporarily superimposes a toner image on the surface of the intermediate transfer member, and collectively transfers the formed full-color toner image onto a transfer material. is there. The continuous superposition method is a method in which a plurality of image forming units are arranged side by side, and the transfer material conveyed by a belt or the like passes through the position of each image forming unit, and the toner images of each color are sequentially transferred and superimposed.

As an example of a conventional image forming apparatus using the above-mentioned transfer drum system, there is a color image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 1-252982. FIG. 5 is a cross-sectional view showing the outline of the overall configuration of this conventional color image forming apparatus. The configuration and operation will be briefly described below. In FIG. 5, a charger 102, a developing unit 103, and a transfer drum 1 are provided inside a color image forming apparatus so as to face a photoreceptor 101.
04 and a cleaner 105 are provided. Developing unit 10
3 is a Y developing device 10 for forming a yellow toner image.
6. M developing device 10 for forming a magenta toner image
7. C developing device 10 for forming cyan toner image
8 and a Bk developing unit 109 for forming a black toner image. The developing unit 103 is configured such that the developing units of the respective colors are rotated and the developing units of the respective colors are sequentially arranged so as to face the photoreceptor 101, so that the respective colors can be developed on the photoreceptor 101. Note that a developer replenishing device 11 for replenishing toner as a developer from the outside of the apparatus is provided in each color developing device.
8 is connected, and the toner corresponding to each color developing device is supplied from each hopper of the developer supply device 118.

[0004] Toner density is detected by an optical detection means for detecting the toner density at the developing position, and toner supply to the developing device is performed in accordance with the toner density value detected at another position rotated 90 ° from the developing position. Will be At the time of continuous formation of a single-color toner image, when the toner density decreases, the entire developing unit 103 rotates, and the developing device having the reduced toner density is moved to the toner supply position to supply toner. Developer supply device 11
The toner sent from the hopper 8 is conveyed through a pipe (not shown) and supplied to the developing device. The toner conveyed in the pipe passes through the hollow rotation center shaft of the developing unit 103 and is conveyed to a toner supply hole (not shown) provided in a part of the center shaft. Supplied inside the vessel. The toner supplied to each developing device is reciprocated in the axial direction by rotating a screw (not shown) provided in each developing device.

Next, an image forming operation of the conventional color image forming apparatus having the above-described configuration will be described. As shown in FIG. 5, during the image forming operation, the transfer drum 104 and the photoreceptor 101 arranged opposite to each other are configured to rotate at a constant speed in the direction of the arrow. In the color image forming apparatus shown in FIG.
01 rotates in the direction of the arrow, and its surface is uniformly charged by the charger 102. Then, the photoconductor 10
The first surface is irradiated with a laser beam 110 modulated with a signal for forming a first color yellow image, so that a latent image is formed. This latent image is first developed in the yellow Y developing device 106 facing the photoreceptor 101 to form a yellow toner image. By the time the yellow toner image formed on the photoreceptor 101 comes to a position facing the transfer drum 104, the paper feed unit 1 is already on the outer periphery of the transfer drum 104.
One recording sheet as a transfer material sent from 11 is wound with its leading end caught by a claw 112. When the recording sheet is placed at a predetermined position, the timing is set so that the yellow toner image on the photoconductor 101 faces the toner sheet, and the movement of the photoconductor 101 forms a toner image on the recording sheet.

After the yellow toner image formed on the photoreceptor 101 is transferred to the recording paper by the charging action of the transfer charger 113, the surface of the photoreceptor 101 is cleaned by the cleaner 105, and the next color image is formed. Preparation for formation is made. Subsequently, magenta, cyan, and black toner images are similarly formed. At that time, the developing unit 103 arranges each developing device in a position facing the photoconductor 101 in accordance with each color, and makes each color developable. The diameter of the transfer drum 104 is long enough that the longest recording paper is wound and that the timing of replacement of the developing device between images of each color is sufficient. The irradiation timing of the laser beam 110 for forming an image of each color is such that the toner image formed on the photoconductor 101 and the toner image already transferred on the recording paper on the transfer drum 104 coincide with each other and face each other. It is set as follows. As described above, the four color toner images are transferred to the transfer drum 104.
A color image is formed on the recording paper by being transferred onto the upper recording paper. After the toner images of all colors have been transferred to the recording paper, the recording paper is separated from the transfer drum 1 by the peeling claws 114.
04. The recording paper peeled off from the transfer drum 104 is transported to the fixing device 116 via the transport unit 115, where the toner image formed on the recording paper is fixed, and the recording paper is discharged out of the apparatus.

[0007]

In the field of image formation, not only color image formation but also monochrome image formation has the same high speed, productivity, and simple operability as a conventional monochrome image forming apparatus. There is a demand for realizing a color image forming apparatus. In order to satisfy the demand, it has been considered to use a transfer drum system or an intermediate transfer body system which can minimize the size of the apparatus as much as possible and has a simple configuration. However, in the conventional transfer drum method and the intermediate transfer member method, even when making a monochrome copy, the time required for rotating the transfer drum and the intermediate transfer member is required, so that the monochrome image output is conventionally performed. There is a problem that the operation becomes extremely slow as compared with the monochrome image forming apparatus. Further, simply increasing the rotation speed of the transfer drum and the intermediate transfer member causes various problems such as image deterioration, noise, and vibration. For this reason, in a color image forming apparatus using a transfer drum system or an intermediate transfer body system, high image quality and high performance have been achieved.
There has been a demand for an apparatus capable of forming a monochrome image at high speed. Further, it is difficult for conventional color image forming apparatuses to replace consumable parts such as photoconductors, chargers, cleaners, and developing units, and toner replenishment with the same simplicity as conventional monochrome image forming apparatuses. And a very cumbersome device.

The image forming apparatus of the present invention integrally holds a color developing unit in which yellow, magenta, and cyan developing units are integrally formed, and a photosensitive member, a black developing unit, a charging unit, and a cleaner. By using a cartridge configuration, in an apparatus using an electrophotographic system that forms a full-color image, monochrome image formation with a simple configuration can be realized with excellent high speed, high productivity, and simple operability. It is an object to provide an image forming apparatus.

[0009]

In order to achieve the above object, an image forming apparatus according to the present invention has a substantially cylindrical shape, and a photosensitive member which rotates around a rotation axis of the cylinder; A charging unit for uniformly charging the surface of the photoconductor, an exposure unit for exposing the surface of the photoconductor downstream of the charging unit in a rotation direction of the photoconductor, and a rotation unit for the photoconductor. A color developing unit that is arranged on the downstream side of the exposure unit in the moving direction to face the photoconductor, and has a color development unit for forming a yellow, magenta, and cyan color toner image on the surface of the photoconductor; Black developing means for forming a black toner image on the surface of the photoconductor downstream of the color developing unit in the rotation direction of the photoconductor; and the black developing device in the rotation direction of the photoconductor. An intermediate transfer member disposed downstream of the stage to face the photoconductor, sequentially receiving each toner image formed on the photoconductor, and forming a color toner image on the surface; Cleaning means for cleaning the surface of the photoreceptor on the downstream side of the intermediate transfer member in the rotation direction. Therefore, the image forming apparatus of the present invention can form a full-color image, and can realize monochrome image formation with high speed, high productivity, and simple operability with a simple configuration.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment showing a preferred embodiment of the image forming apparatus of the present invention will be described below with reference to FIGS. << First Embodiment >> FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. As shown in FIG. 1, a photoconductor 2, a corona charger 4, a laser exposure device 6, a color developing unit 8, a black developing device 16, a fixing device 30, and the like are provided in the image forming apparatus main body 1 of the first embodiment. Is provided. The photoreceptor 2 is formed in a cylindrical shape from a conductive material such as aluminum, and is formed by providing a photoconductive layer such as an organic optical semiconductor on the surface of the cylinder. The photoreceptor 2 has a diameter of 40 mm and is configured to be rotatable in the direction of arrow a in FIG. The corona charger 4 has a function of uniformly and negatively charging the photoconductor 2 by a scorotron method.
The laser exposure device 6 that exposes the photoconductor 2 includes a semiconductor laser (not shown), a polygon mirror 6a, a reflection mirror 6b,
It is constituted by a lens 6c and the like, and scans and exposes a pixel laser signal light 6d corresponding to a time-series electric pixel signal of image information in the generatrix direction of the cylindrical photosensitive member 2.

The color developing unit 8 has yellow, magenta, and cyan color developing units 12Y, 12M, and 12C, which are integrally formed in a substantially cylindrical shape. Each of the color developing units 12Y, 12M, and 12C is a toner 10Y of each color of yellow, magenta, and cyan of negative charge.
10M and 10C are stored respectively. Yellow, magenta, and cyan toners 10Y, 10M, and 10C
Is formed by dispersing a pigment in polyester resin of each color. Each color developing unit 12 of the color developing unit 8
Y, 12M, and 12C include toners 10Y, 10Y of respective colors.
Developing rollers 14Y, 14 carrying M, 10C on the surface
M, 14C. Developing rollers 14Y, 14M,
14C is formed with a rubber elastic body having a rubber hardness of 15 to 40 degrees or a rubber elastic body layer of sponge-like urethane or silicone having the same hardness on the surface. . The image forming apparatus according to the first embodiment includes:
A so-called non-magnetic one-component contact development system is used in which the developing rollers 14Y, 14M, and 14C are pressed against the photoconductor 2 to develop an electrostatic latent image formed on the surface of the photoconductor 2.

The color developing unit 8 includes three color developing units 12Y, 12M, and 12 for yellow, magenta, and cyan.
C is integrally formed, and is configured to be rotatable by the motor 13 in the direction of arrow b around the fulcrum shaft 8a. The color developing unit 8 supports each of the color developing units 12Y, 12M, and 12C so as to be able to reciprocate in both directions of arrows c1 and c2 by urging means 15 such as an electromagnetic plunger. ,
14C is configured to be detachable from the photoconductor 2.
For example, when forming a yellow image, the color developing unit 8 rotates the yellow developing roller 14 </ b> Y to a position facing the photoconductor 2. Next, the entire color developing unit 8 is urged in the direction of arrow c1 by the urging means 15 such as a plunger, so that the developing roller 14Y comes into pressure contact with the photosensitive member 2. In a state where the developing roller 14 </ b> Y and the photoconductor 2 are in press contact, the yellow toner 10 </ b> Y develops the electrostatic latent image on the surface of the photoconductor 2. Further, when forming a magenta or cyan image, the developing rollers 14M and 14C of the respective colors are pressed against the photosensitive member 2 and developed in the same manner as in the yellow case.

The black developing device 16 includes a developing roller 18 having a rubber elastic body on the surface thereof for carrying the black toner 10Bk. At the time of color development, the developing roller 18 of the black developing device 16 is separated from the photoconductor 2, but at the time of black development, it is configured to be in pressure contact with the photoconductor 2 by an urging means 19 such as an electromagnetic plunger. I have. The black developing device 16 has arrow e1 and arrow e.
The developing roller 18 is configured to be reciprocally movable in both directions.
The black developing roller 18 has on its surface a rubber elastic body having a rubber hardness of 15 to 40 degrees or a rubber elastic body layer of sponge-like urethane or silicone having the same hardness. . The black developing roller 18 of the first embodiment is brought into pressure contact with the photosensitive
A so-called non-magnetic one-component contact development system for developing an electrostatic latent image formed on the surface of the device is used.

A transfer drum 20 arranged to face the photoconductor 2 captures a toner image formed on the photoconductor 2 and secondary-transfers the toner image onto a recording sheet 22 as a transfer material. belongs to. The transfer drum 20 has a semiconductive layer 20b such as a polycarbonate resin, a fluororesin, or a fluorine-coated urethane rubber formed on a surface of a conductive metal base material 20a formed in a substantially cylindrical shape with a conductive metal material such as aluminum. Have been. The semiconductive layer 20b has a thickness of 2 to 8 mm, and has a cylindrical shape with a diameter of 120 mm. After the toner image is transferred to the transfer drum 20, the toner remaining on the surface of the photoconductor 2 is cleaned by the cleaner 24. The cleaner 24 includes a rubber cleaning blade 26 and a screw 28 that transports the scraped toner to a waste toner case (not shown) provided on the back of the apparatus.

As shown in FIG. 1, a cleaner 32 for cleaning the toner remaining on the surface of the transfer drum 20 and a charger 34 for reversing the polarity of the toner on the surface of the transfer drum 20 are provided around the transfer drum 20. The position sensor 42 is disposed inside the transfer drum 20 and detects a cue position of the transfer drum 20. The cleaner 32 includes a rubber cleaning blade 36 for cleaning and removing toner remaining on the surface of the transfer drum 20;
A waste toner case 38 for storing the scraped toner. The cleaner 32 rotates about the fulcrum 40 so that the toner image on the transfer drum 20 is not scraped off during the period of forming a color toner image on the transfer drum 20, and the cleaning blade 36 is moved from the transfer drum 20 to the cleaning blade 36.
Has a separating mechanism (not shown) for separating the components. Also,
During the period when the image forming operation of the image forming apparatus main body 1 is stopped, the cleaning blade 36 is set to be constantly pressed against the transfer drum 20.

The fixing device 30 has a function of fixing the toner image transferred to the recording paper 22 as a permanent image on the recording paper 22 when the recording paper 22 passes through a contact position between the heating roller 54 and the pressure roller 56. Having. The heat insulating plate 57 provided between the fixing device 30 and the laser exposure device 6 insulates the space between the fixing device 30 and the laser exposure device 6 to prevent the temperature of the laser exposure device 6 from rising. A pair of paper discharge rollers 58 is provided downstream (in the paper discharge direction) of the fixing device 30, and the recording paper 22 that has passed through the fixing device 30 by the rotation of the paper discharge rollers 58 is discharged onto a paper discharge tray 60. Is done.

FIG. 2 is a sectional view showing a state where the color developing unit 8 and the cartridge 31 are replaced in the image forming apparatus of the first embodiment. As shown in FIG. 2, by opening the top door 1a of the housing of the image forming apparatus main body 1 with the hinge shaft 1b as a fulcrum, the color developing unit 8 can be put in and out from the outside of the image forming apparatus main body 1. . Therefore, in the image forming apparatus of the first embodiment,
Magenta and cyan color developing units 12Y and 12
A color developing unit 8 in which M and 12C are integrally formed.
Can be easily replaced by opening the top door 1a. In FIG. 2, the photosensitive member 2, the charger 4, the black developing device 16, and the cleaner 24 are configured in a cartridge type, and are integrally formed as a cartridge 31. The cartridge 31 is detachably held from the image forming apparatus main body 1 similarly to the color developing unit 8 described above. Therefore, when the black toner 10Bk stored in the black developing device 16 is consumed, the cartridge 31 can be removed and the black developing device 16 can be easily replaced. The developing roller 18 of the black developing device 16 is separated from the photoconductor 2 at the time of color development, but the developing roller 18 is pressed against the photoconductor 2 by urging means (not shown) such as a plunger at the time of black development. doing.

As shown in FIG. 2, the front alligator 1c of the main body 1 of the image forming apparatus is hinged to the housing of the main body 1 of the image forming apparatus at a hinge shaft 1d. is there. The front alligator 1c includes a fixing device 30, a transfer drum 20, a front paper guide 48a,
48b and the like are attached, and when the front alligator 1c is moved forward, these structures also fall down at the same time. As a result, the front portion of the image forming apparatus main body 1 is largely opened, and the cartridge 31 and the transfer drum 20 can be detached from the front portion. Further, when a paper jam occurs, the recording paper 22 having the paper jam can be easily removed by opening the front alligator 1c.

[Single-Color Continuous Image Forming Step] Next, a single-color continuous image forming step using only the black toner 10Bk by the image forming apparatus of the first embodiment configured as described above will be described. First, when the power of the image forming apparatus main body 1 is turned on, the image forming apparatus main body 1 enters an initialization mode, and confirms the presence / absence of the transfer drum 20, the cartridge 31, and the color developing unit 8; Performs an operation to check for presence. In the initialization mode, the image forming apparatus according to the first embodiment can be configured to detect the remaining amount of the toner 10 stored in each of the developing units 12Y, 12M, 12C, and 16; When the amount is small, it is possible to display that no toner is present.

After confirming whether or not each part is abnormal, the fixing device 3
0 starts heating. When the fixing device 30 reaches a prescribed condition, the image forming apparatus main body 1 enters a ready state for image formation. When the image formation starts, the polygon mirror 6a of the laser exposure device 6 starts rotating. Polygon mirror 6a
After the rotation speed of the developer reaches a predetermined condition, the black developing device 1
6, the process of forming a black toner image is started. First, a drive source (not shown) of the image forming apparatus main body 1 starts operating, and the photoconductor 2, the transfer drum 20, and the like start rotating. A charging voltage is applied to the corona charger 4 0.1 seconds after the drive source starts operating, and the corona charger 4 starts a charging operation. At this time, the urging of the color developing unit 8 to the photoreceptor 2 remains released, and the black developing device 16 is urged in the direction of arrow e1. After the black developing roller 18 starts rotating in the direction indicated by the arrow f by connecting the driving source and the power of the image forming apparatus main body 1, the developing roller 18 comes into pressure contact with the photosensitive member 2. At this time, the cleaning blade 36 pressed against the transfer drum 20
The state pressed by the transfer drum 20 is maintained. Next, the recording paper 22 is fed from the paper feeding unit 45 to the registration rollers 46.
And the recording paper 22 is stopped until the paper feed timing in a state where the leading end of the recording paper 22 is held between the registration rollers 46.

In synchronization with an image forming timing signal from the image forming apparatus main body 1, a laser beam 6d is irradiated from the laser exposure device 6 to the photosensitive member 2 in accordance with a black image signal. As a result, an electrostatic latent image corresponding to the black image signal is formed on the surface of the photoconductor 2. The image formation timing signal does not necessarily need to use the detection signal of the leading end position of the image by the position sensor 42 provided on the transfer drum 20, and uses a signal created based on the timing at which the recording paper is supplied to the registration rollers 46. You may use it. At the black developing position, a black electrostatic latent image is formed on the surface of the developing roller 18, and the black toner 10 </ b> Bk is carried on the electrostatic latent image and is sequentially developed and visualized. As a result, a black toner image is formed on the surface of the photoconductor 2. The black toner image formed on the photoconductor 2 is transferred to a recording sheet 22 inserted at a position where the photoconductor 2 and the transfer drum 20 are in contact with each other. Registration roller 46
Performs a rotation operation such that the recording paper 22 is inserted into the contact position between the photoconductor 2 and the transfer drum 20 at the timing when the toner image moves to the position where it contacts the transfer drum 20. By the rotation operation of the registration roller 46,
The recording paper 22 is transported to a contact position between the photoconductor 2 and the transfer drum 20.

The black toner image formed on the surface of the photoconductor 2 is directly transferred (directly transferred) to a recording sheet 22 inserted between the photoconductor 2 and the transfer drum 20. At this time, the conductive base material 20a of the transfer drum 20 has +
A DC voltage of 1.0 kV is applied. The timing of applying a voltage to the conductive substrate 20a of the transfer drum 20 is also based on a timing signal for image formation. The recording paper 22 to which the toner image has been transferred is conveyed to the fixing device 30, and the toner image on the recording paper 22 is fixed. The recording paper 22 on which the toner image has been fixed is discharged onto a discharge tray 60 from a pair of discharge rollers 58. The recording paper 22 is the upper surface of the recording paper 22 from which the image forming surface has been discharged, and is discharged in a so-called face-up state.

After the toner image is transferred onto the recording paper 22, the photosensitive member 2 is prepared for the next image forming step.
The toner remaining on the surface is scraped off by the cleaning blade 26. The toner scraped from the surface of the photoconductor 2 is conveyed to the waste toner case by the screw 28. The cleaned photoconductor 2 is charged again, exposed, and developed to form a next image. In the case of the above-described single-color continuous image forming process, the transfer drum 20 does not function as an intermediate transfer member, but functions to satisfy electric field conditions and mechanical pressing conditions for transfer from the back of the recording paper 22. It functions as a so-called transfer roller. Therefore, after the transfer from the photoconductor 2 to the recording paper 22, the amount of toner attached to the surface of the transfer drum 20 is extremely small. If the toner has adhered to the transfer drum 20, the toner is scraped off by the cleaning blade 36 pressed against the transfer drum 20, and sent to the next image forming step. Thus, the cleaning blade 36 is pressed against the transfer drum 20, and the same operation is continued until the formation of a single-color continuous image is completed. The interval between the recording papers 22 when a single-color continuous image is formed is the same as that of a normal black and white image forming apparatus, and the interval between the recording papers 22 may be 20 to 50 mm. For this reason, the image forming apparatus of the first embodiment does not need to form an image in accordance with the cycle of the intermediate transfer body unlike a conventional color image forming apparatus using an intermediate transfer body. An image can be formed at exactly the same speed as the above, and the productivity can be satisfied.

The color developing unit 8 is not required in the image forming process using only the black single color using the image forming apparatus of the first embodiment. 1 can be implemented even when the color developing unit 8 is not mounted.
In the image forming apparatus of the first embodiment, even when a single color image is formed using yellow, magenta, or cyan color toner, the developing device that presses and contacts the photoconductor 2 is formed by using a developing device of a specific color. An image can be formed by a process similar to the forming process.

[Full Color Image Forming Step] Next, a full color image forming step by the image forming apparatus of the first embodiment will be described. As in the case of the above-described image formation of only a single color, when image formation is started in the image forming apparatus main body 1, the polygon mirror 6a of the laser exposure device 6 starts rotating. After the rotation speed of the polygon mirror 6a reaches a predetermined condition,
The image forming process using yellow toner using the yellow developing device 12Y is started. First, a drive source (not shown) of the image forming apparatus main body 1 starts operating, and the photoconductor 2, the transfer drum 20, and the like start rotating. A charging voltage is applied to the corona charger 4 0.1 seconds after the drive source starts operating, and the corona charger 4 starts a charging operation. The color developing unit 8 has already been moved to a position where the yellow developing roller 14Y faces the photoconductor 2 in the initialize mode. At this time, the urging of the black developing device 16 to the photoconductor 2 remains released. When the color developing unit 8 is urged in the direction of arrow c1, the yellow developing roller 14Y is connected to the driving source of the image forming apparatus main body 1 and the power, and the developing roller 14Y starts rotating in the direction of arrow d. After the developing roller 14Y starts rotating, the developing roller 14Y comes into pressure contact with the photoconductor 2.

At this time, the cleaning blade 36 pressed against the transfer drum 20 is separated from the transfer drum 20. When the cleaning blade 36 is separated from the transfer drum 20, the toner adhering to the tip of the cleaning blade 36 is generated in the generatrix direction on the surface of the transfer drum 20 as streaky toner residue. In the image forming apparatus of the first embodiment, the timing at which the cleaning blade 36 is separated from the transfer drum 20 is set so as not to transfer the toner image to the portion where the residual toner is generated. In addition, in synchronization with the timing at which the portion where the residual toner is generated is sent to the contact position between the photoconductor 2 and the transfer drum 20, the conductive base material 20 a of the transfer drum 20 −1.0 to −1.0.
A DC voltage of −2.0 kV may be applied to transfer the remaining toner on the surface of the transfer drum 20 to the photoconductor 2, and the photoconductor 2 may be cleaned by the cleaner 24.

When the recording paper 22 is supplied from the paper feeding unit 45 to the registration roller 46, the recording paper 22 stops until the paper feeding timing with the leading end held between the registration rollers 46. A position sensor 42 for detecting the front end position of the image on the transfer drum 20 detects the front end position of the image, and a laser beam 6d matched with the yellow image signal from the laser exposure device 6 is applied to the photoconductor 2 in synchronization with this detection signal. Irradiated. An electrostatic latent image corresponding to the image signal is formed on the surface of the photoconductor 2. At the color developing position, the electrostatic latent image on the surface of the photoreceptor 2 is sequentially developed by the yellow toner 10Y carried on the surface of the developing roller 14Y, visualized, and developed into a yellow toner image on the surface of the photoreceptor 2. Is formed. The yellow toner image formed on the surface of the photoconductor 2 is transferred to the transfer drum 20.
At the contact position with the transfer drum 20. The yellow image forming operation is continued by performing the above operation for one A4 screen, and ends after the end of the image is transferred to the transfer drum 20.

After the yellow toner image has been transferred to the transfer drum 20, the photoreceptor 2 is cleaned with toner remaining on the surface of the photoreceptor 2 in preparation for forming the next magenta toner image. It is scraped off by 26. The toner scraped from the surface of the photoconductor 2 is conveyed to a waste toner case by the screw 28. The cleaned photoconductor 2 is charged again, exposed, and developed to form a magenta toner image. In the image forming step, the corona charger 4 moves the photoconductor 2 to -45.
The photosensitive member 2 is charged to 0 V, and the exposure potential of the photosensitive member 2 after laser exposure is -50 V. A DC voltage of -250 V is applied to the developing roller 14Y from a high-voltage power supply. In order to transfer the toner from the photoconductor 2 to the transfer drum 20, a DC voltage of +1.0 kV is applied to the conductive base material 20a of the transfer drum 20 in synchronization with the detection signal of the position sensor 42 of the transfer drum 20. Applied.

As described above, when the yellow image formation is completed, a magenta toner image is formed next. First, the urging of the color developing unit 8 in the direction of arrow c1 is released,
The yellow developing roller 14Y is separated from the photoconductor 2. At this time, the transmission of the driving force to the developing roller 14Y is released. Next, the color developing unit 8 is rotated 120 degrees in the direction of arrow b so that the magenta developing roller 14M moves to a position facing the photoconductor 2. When the developing roller 14M is arranged at a position facing the photoconductor 2, the color developing unit 8 is urged in the direction of the arrow c1. At this time, the magenta developing roller 14M is connected to the driving source of the image forming apparatus main body 1 and the power, and after the developing roller 14M starts rotating in the direction of arrow d, the developing roller 14M is pressed against the photosensitive member 2. This switching operation is performed within a time period in which the area other than the range of the A4 image on the surface of the transfer drum 20 is in contact with the photoconductor 2. During this time, the photoconductor 2, the transfer drum 20, and the like are kept rotating, and the corona charger 4 also continues the charging operation on the surface of the photoconductor 2. Thereafter, the position sensor 42 detects the position of the leading end of the image on the transfer drum 20, and the laser exposure device 6 irradiates the photosensitive member 2 with laser light 6 d in synchronization with the magenta image signal in synchronization with the detection signal. As a result,
An electrostatic latent image corresponding to an image signal is formed on the surface of the photoconductor 2.

At the color developing position, the electrostatic latent image on the surface of the photosensitive member 2 is sequentially developed by the magenta toner 10M carried on the surface of the developing roller 14M, visualized, and developed on the surface of the photosensitive member 2. Is formed. The magenta toner image formed on the surface of the photoreceptor 2 is transferred to the transfer drum 2 at a contact position with the transfer drum 20.
0 is sequentially transferred. The magenta image forming operation is continued by performing the above operation for one A4 screen, and ends after the image end is transferred to the transfer drum 20. In this manner, magenta image formation is performed in the same manner as yellow image formation,
On the surface of the transfer drum 20, a toner image in which two colors of yellow and magenta are overlapped is formed. Subsequently, cyan image formation is also performed in the same manner as the yellow and magenta image formation, and yellow, magenta,
, And a toner image in which three colors of cyan and cyan are superimposed. After the yellow, magenta, and cyan images are formed, finally, a black image is formed. At the time of forming a black image, all the urging of the color developing unit 8 to the photoconductor 2 (the urging in the direction of arrow c1) is released, and the black developing device 16 is instead applied to the photoconductor 2 in the direction of arrow e1. Be inspired. At this time, the black developing roller 18 has started to rotate in the direction indicated by the arrow f by being connected to the drive source of the image forming apparatus main body 1 and the motive power.
Is pressed into contact. The black image forming process is performed in the same manner as the above-described color image forming process such as yellow except that the black developing roller 18 is pressed against the photoconductor 2.

As in the above-described image forming process, image formation of yellow, magenta, cyan, and black is sequentially repeated to form a full-color toner image in which four colors are superimposed on the surface of the transfer drum 20. After the four color toner images are formed on the transfer drum 20, based on the detection signal of the leading end position of the image from the position sensor 42 of the transfer drum 20,
The recording paper 22 is conveyed to the contact position between the photoconductor 2 and the transfer drum 20, and is inserted. The recording paper 22 is conveyed to the contact position between the photoconductor 2 and the transfer drum 20 by the rotation of the registration roller 46 in synchronization with the timing at which the head position of the image passes through the contact position between the photoconductor 2 and the transfer drum 20. You. The four color toner images formed on the surface of the transfer drum 20 are collectively and secondarily transferred onto a recording paper 22 inserted between the photoconductor 2 and the transfer drum 20. At this time, the charging potential on the surface of the photoconductor 2 is uniformly -50 V, and a DC voltage of -1.0 kV is applied to the conductive substrate 20a of the transfer drum 20. The timing of applying a voltage to the conductive substrate 20 a of the transfer drum 20 is set based on a detection signal of the position sensor 42. The recording paper 22 to which the toner image has been transferred is conveyed to the fixing device 30 and the recording paper 22
The upper toner image is fixed. The recording paper 22 on which the toner image has been fixed is discharged from a paper discharge roller 58 onto a paper discharge tray 60. The recording paper 22 is located on the lower surface of the discharged recording paper 22 with its image forming surface, and is discharged in a so-called face-down state.

As described above, a full-color image is formed by using the yellow, magenta, cyan, and black toners by the image forming apparatus of the first embodiment. Is formed, only the necessary color image forming process is performed, and the toner image formed on the surface of the transfer drum 20 is secondarily transferred to the recording paper 22 in a lump, so that the required color image is formed. Formation is possible.
For example, when forming an image in red and black, an image forming process for yellow, magenta, and black is performed, and the three-color superimposed toner image formed on the surface of the transfer drum 20 is collectively formed on the recording paper 22 as a secondary image. By transferring, an image in red and black can be obtained.
Further, in the case of forming an image of only a single color, the toner image on the photoconductor 2 is temporarily transferred to the transfer drum 20 and then secondary-transferred onto the recording paper 22 by the above-described image forming method. At this time, the recording paper 22 can be discharged onto the discharge tray 60 in a so-called face-down state in which an image is formed on the lower surface of the recording paper 22. As described above, in the image forming apparatus according to the first embodiment, the face-up state and the face-down state of the recording paper 22 can be simply configured without adding a special mechanism for switching the transport path of the recording paper 22. State has been switched. In the first embodiment, the recording paper 22 is
The paper is discharged onto the same paper discharge tray 60 in the face-down state and the face-up state. Therefore, even when an image is formed by mixing face-down and face-up variously, the discharge of the recording paper 22 can be confirmed on only one discharge tray 60, and the image forming apparatus of the first embodiment can be confirmed. Has the advantage that the discharge confirmation operation can be performed very easily.

[Image formation on both sides of recording paper]
The image formation on both sides of the recording paper 22 using the image forming apparatus of the embodiment will be described. The image forming apparatus according to the first embodiment of the present invention includes a transfer drum 20 on a recording sheet 22.
A color or monochromatic image is formed on a transfer surface (hereinafter, abbreviated as a paper back surface) facing the image forming apparatus, and a monochromatic image is formed on a transfer surface (hereinafter, abbreviated as a paper surface) of the recording paper 22 facing the photoreceptor 2. It is possible. In the case where images are formed on both sides of the recording sheet 22 in the image forming apparatus of the first embodiment, the recording sheet 2 is formed like the conventional image forming apparatus.
It is not necessary to repeat the transfer / fixing process two or more times by drawing the inside of the apparatus 2 and repeating the transfer / fixing process twice or more. The fixing can be performed simultaneously on both sides by passing through the fixing device 30.

Hereinafter, a process of forming a two-sided image in which four full-color images are formed on one transfer surface of the recording paper 22 and a black image is formed on the other transfer surface of the recording paper 22 will be described. Similar to the above-described four-color image forming process, the yellow, magenta, cyan, and black image forming processes are sequentially repeated to form a full-color toner image in which the four colors are superimposed on the transfer drum 20. This full-color toner image is a toner image transferred to the back of the sheet. After the black toner image, which is the last step in the four-color image forming process, is transferred onto the surface of the transfer drum 20, the charger is synchronized with the timing at which the toner image passes through the charger 34. A high voltage is applied to 34 to invert the charging polarity of the toner particles of the four colors on the surface of the transfer drum 20 to plus. Charger 34 at this time
Is charged by a high voltage power supply (not shown).
A DC voltage of 6.0 kV is applied. At this time, ±
A 2.0 kV AC voltage may be superimposed on the DC voltage. As described above, by superimposing the AC voltage on the DC voltage, there is an effect that the charging polarity of the toner particles forming the toner image can be efficiently inverted. For the four color toner images of which the charging polarities are inverted on the transfer drum 20, the position of the leading end of the image is detected by the position sensor 42 of the transfer drum 20. With reference to the detection signal of the position sensor 42, the timing at which the head position of the image passes through the contact position between the photoconductor 2 and the transfer drum 20 and the recording paper 2
The registration roller 46 rotates so that the timing at which the sheet 2 passes through the contact position is synchronized, and the recording paper 22 is conveyed and inserted into the contact position between the photoconductor 2 and the transfer drum 20.

Further, based on the detection signal of the leading end position of the image from the position sensor 42, the leading position of the image is
A black toner image formed on the surface of the paper is formed on the surface of the photoreceptor 2 so as to synchronize with the timing when the recording paper 22 passes through the contact position with the transfer drum 20 and the timing when the recording paper 22 passes through the contact position. The black toner image is formed on the surface of the photoconductor 2 by performing the same image forming process as the above-described black monochromatic image forming process.
The four-color toner image on the surface of the transfer drum 20 and the black toner image on the surface of the photoconductor 2 are combined with the photoconductor 2 and the transfer drum 20.
And are collectively transferred to both sides of the recording paper 22 inserted between them. At this time, the conductive substrate 20a of the transfer drum 20
Is applied with a DC voltage of +1.0 kV. The timing of applying a voltage to the conductive substrate 20 a of the transfer drum 20 is also performed based on the detection signal of the position sensor 42. The recording paper 22 on which the toner images have been transferred to both sides is conveyed to the fixing device 30, and the toner images on both sides of the recording paper 22 are fixed. Then, the recording paper 22 on which the toner image is fixed is
Is discharged from the paper discharge roller 58 onto the paper discharge tray 60.
On the image forming surface, which is the transfer surface of the recording paper 22, a black toner image is formed on the upper surface of the discharged recording paper 22, and four full-color toner images are formed on the lower surface.

As described above, according to the image forming apparatus of the first embodiment, it is possible to form a black monochromatic toner image on the surface of the recording paper 22 and to print four yellow, magenta, cyan, and black toner images on the back of the paper. A color toner image can be formed. In the above-described first embodiment, a case has been described in which a black monochromatic toner image is formed on the surface of a sheet and a full-color toner image is formed on the back of the sheet. It is possible to form a single-color toner image using a color toner on the surface, and form a two-color or three-color superposed color image or a single-color toner image on the back surface of the sheet by the above-described image forming method.

As described above, in the image forming apparatus according to the first embodiment of the present invention, the recording paper is routed inside the apparatus as in the conventional image forming apparatus, and the transfer and fixing steps are repeated two or more times. That is, it is possible to form an image on both sides of the recording sheet 22 without adding a special structure for a conveyance path of the recording sheet 22 for double-sided recording.
The image forming apparatus of the first embodiment has a very simple structure and a simple conveyance path for the recording paper 22.
The risk of paper jams and the like can be minimized. In the image forming apparatus of the first embodiment, the color image forming surface is discharged face-down, but the discharge path may be changed to discharge face-up. In addition, by providing switching means to switch between face down and face up,
In image formation on both sides of a recording sheet, a color image can be formed on either side.

In the image forming apparatus of the first embodiment, a laser beam 6d radiated from the laser exposure device 6 to the photosensitive member 2
Must be an inverted signal between the paper front and the paper back. In general, image data sent to an image forming apparatus is an image signal corresponding to a document. Therefore, in the image forming apparatus according to the first embodiment, the image signal transmitted to the image forming apparatus is transmitted from the image signal to the front side and the back side of the sheet. An image signal generation circuit board (not shown) capable of generating two types of image signals is provided. In the image forming apparatus of the first embodiment, since the color developing unit 8 is disposed upstream of the black developing device 16 in the rotation direction of the photoconductor 2, even if the black toner 10Bk spills from the black developing device 16. , Each of the color developing units 12Y, 12Y of the color developing unit 8 without being mixed in the color developing unit 8.
The color of the toner in 2M and 12C does not change.
As a result, according to the image forming apparatus of the first embodiment, stable image formation can always be realized without deteriorating the color reproducibility of the image.

The image forming apparatus of the first embodiment can realize full-color image formation while maintaining the same operability, high speed, and productivity as the conventional monochrome image forming apparatus, and can realize monochrome image formation. Images can also be formed. Therefore, giving priority to forming a monochrome image using the black toner 10Bk, the black toner 1
In consideration of the consumption of 0Bk, the cartridge 31 having a cartridge structure integrally holding the black developing device 16, the photoconductor 2, the corona charger 4, and the cleaner 24 is integrally replaced and discarded as a consumable part of the image forming apparatus. Can be configured. In the image forming apparatus of the first embodiment, the color developing unit 8 is formed integrally with the yellow, magenta, and cyan developing units 12Y, 12M, and 12C. It is not necessary to replace only the depleted developing unit every time, and by replacing the color developing unit 8, a color image can always be stably formed. Further, in the image forming apparatus of the first embodiment, since the developing units 12Y, 12M, and 12C for the respective colors can be configured by using the common frame of the resin molded product, the color developing unit 8 can be manufactured inexpensively and simply. Can be manufactured.

In the image forming apparatus of the first embodiment,
Although the color developing unit 8 has a mechanism for separating and contacting the photoconductor 2, such a separating mechanism may not be provided.
This is because the rotation direction (the direction of the arrow b) for switching the color of the color developing unit 8 is the same as the rotation direction (the direction of the arrow a) of the photoconductor 2 (the tangential direction of rotation at the contact portion is the same). Each developing roller 14Y, 1
Even if the color developing unit 8 is rotated in the direction of the arrow b while the 4M and 14C are kept in contact with the photoreceptor 2 and color switching is performed, the developing rollers 14Y, 14M, 1
This is because there is little damage to the photoconductor 2 and 4C. In the image forming apparatus according to the first embodiment, yellow,
Magenta and cyan color developing units 12Y, 12M, 12
C and the black developing device 16 use a non-magnetic one-component contact developing method.
4Y, 14M, 14C, and 18 cannot be developed unless the photosensitive member 2 is brought into contact. For this reason, the image forming apparatus of the first embodiment has a separation / contact mechanism, but the image forming apparatus of the present invention does not necessarily need to use the non-magnetic one-component contact developing method. If adopted,
As a matter of course, a mechanism for separating the developing roller from the photosensitive member 2 is not required.

In the image forming apparatus of the first embodiment, yellow, magenta, and cyan developing units 12Y, 12M, and 12C in the substantially cylindrical color developing unit 8 are used.
Is divided into three equal parts by a container having a central angle of 120 degrees. For example, only yellow has a container having a central angle of 180 degrees, and magenta and cyan have a central angle of 90 degrees. By using a container having corners, it is possible to increase the yellow toner capacity. As described above, the image forming apparatus according to the first embodiment includes:
The toner capacity distribution in the substantially cylindrical color developing unit 8 can be freely selected according to the output image. However, as a matter of course, it is necessary to similarly select the rotation angle of the color developing unit 8 at the time of color switching according to the toner capacity distribution.

In the image forming apparatus of the first embodiment,
Since the color developing unit 8 has a substantially cylindrical shape, the color developing device 12 facing the photoconductor 2 can be switched in a very small space. As a result, although the corona charger 4, the cleaner 24, the color developing unit 8, and the black developing unit 16 are arranged to face each other around the photoreceptor 2, the diameter of the image forming apparatus of the first embodiment is small. It is possible to use the photosensitive member 2 having a relatively small diameter of 40 mm.
In the image forming apparatus of the first embodiment, since the color developing unit 8 and the transfer drum 20 are arranged at substantially symmetric positions with respect to the photoconductor 2, the image forming apparatus main body 1 is well balanced.
Can be configured. Further, by opening the front alligator 1c, the transport system of the recording paper 22 is opened, and the replacement of the cartridge 31, the transfer drum 20, the removal of the jammed recording paper 22, and the like are performed in the same manner as the conventional monochrome image forming apparatus. Can be easily performed by user maintenance.

[Fixing Step] Next, the fixing step in the image forming apparatus according to the first embodiment of the present invention will be described in detail with reference to FIG. FIG. 3 is an explanatory diagram illustrating the operation of the fixing device 30 in the image forming apparatus according to the first embodiment. In FIG. 3, the fixing device 30 includes a heating roller 54 having a heating source 62 therein, and a pressure roller 56 having an elastic characteristic on its surface. The heating roller 54 has a diameter of 30 mm.
A cylindrical roller having a thickness of about 1 to 3 mm, a surface of a metal substrate 54a formed of a metal material such as aluminum or iron in a cylindrical shape, a fluororesin, a heat resistant material such as a fluorine tube, and A high release layer 54b having a high release characteristic in which the recording paper or the like easily peels off from the surface is formed. The heating roller 54 is heated from the inner surface of the metal base 54 a by a heating source 62, and the surface of the heating roller 54 is in contact with a temperature sensor 64 that detects the surface temperature of the heating roller 54. The temperature sensor 64 outputs a temperature signal corresponding to the surface temperature of the heating roller 54 to the control circuit 66,
Numeral 6 controls the heating source 62 so as to keep the surface temperature of the heating roller 54 constant. The pressure roller 56 has an elastic layer 56b having elasticity and heat resistance such as silicone rubber adhered to an outer peripheral surface of a shaft core 56a formed of a metal material such as aluminum or iron. On the surface of the elastic layer 56b, there is provided a high release layer 56c having heat resistance of a fluororesin, a fluorine tube or the like and high release characteristics in which the recording paper or the like is easily peeled off from the surface. Is a 30 mm cylindrical body. The pressure roller 56 is in contact with the heated surface of the heating roller 54, and the high release layer 56 c on the surface of the pressure roller 56 is heated. Around the pressure roller 56, a cleaning roller 68 formed of a metal such as aluminum for cleaning the surface of the pressure roller 56 into a cylindrical shape, and a high heat-resistant oil such as silicone oil, fluorine oil or the like inside. Impregnated,
An oil application roller 70 having a porous fluorine layer on its surface is provided. The oil application roller 70 cleans foreign substances such as toner adhered to the surface of the pressure roller 56 and performs oil application in order to enhance the release characteristics of the surface of the pressure roller 56 so that the toner is easily peeled off. .

In the image forming apparatus of the first embodiment, the recording paper 22 is inserted into the fixing device 30 such that the surface of the recording paper 22 contacts the heating roller 54 and the back surface of the recording paper contacts the pressing roller 56. Is done. The heat energy required for fixing a single-color toner image formed on the surface of the sheet is directly supplied to the heating roller 54 from a heating source 62 inside the heating roller 54. Therefore, the monochrome toner image is fixed on the surface of the sheet. The surface temperature of the heating roller 54 is controlled by the control circuit 6 so that toner offset or the like hardly occurs.
6 to 180 ° C. While the recording paper 22 passes through the fixing device 30, a slight temperature fluctuation occurs in the heating roller 54, but the toner image on the paper surface can be reliably fixed without any problem. Further, even if image formation is performed continuously, since the heat energy supply source of the heating roller 54 is provided inside the heating roller 54, it is easy to control the surface temperature of the heating roller 54 within a specified range. It is possible.

When fixing the toner image formed on the back surface of the sheet, the pressure roller 56 needs to be heated. The heat energy to the pressure roller 56 is transmitted from the surface of the heating roller 54 to the pressure roller 56. Heating roller 54
While the recording paper 22 is passing between the recording paper 22 and the pressure roller 56, the surface temperature of the pressure roller 56 does not rise, and conversely, the recording paper 22 takes heat energy. Therefore, when the recording paper 22 passes between the heating roller 54 and the pressure roller 56, the surface temperature of the pressure roller 56 decreases. Therefore, the control circuit 66 sets the surface temperature of the heating roller 54 to 200 ° C. so that the surface temperature of the pressure roller 56 becomes 180 ° C., which is a fixing temperature at which a toner image can be fixed and toner offset is unlikely to occur. Is controlled. While the recording paper 22 passes through the fixing device 30, some temperature fluctuation occurs, but the toner image on the surface of the paper can be reliably fixed without any problem.

Further, when four color images are continuously formed, while the recording paper 22 is passing through the contact portion between the heating roller 54 and the pressure roller 56, the heating roller 54
, And heat is hardly supplied to the pressure roller 56. However, compared to the case of forming a single color toner image on the paper surface,
To form a four-color image, the transfer drum 2
After the transfer of the toner image to the surface of the recording paper 22, the toner image is secondarily transferred to the back surface of the recording paper 22, so that a paper passing interval time corresponding to one rotation of the transfer drum 20 is generated. It is possible to raise the temperature to a specified temperature. In any case, when an image is formed once on the transfer drum 20 and then secondary-transferred to the recording paper 22, it depends on the number of colors of the toner to be superimposed. The paper passing interval time becomes longer. For this reason, in the image forming apparatus of the first embodiment, it is possible to secure sufficient time for increasing the surface temperature of the pressure roller 56. When image formation is performed continuously as described above, the image forming apparatus of the present invention may set the surface temperature of the heating roller 54 to be slightly higher. Further, the image forming apparatus of the present invention includes a pressing roller 56.
When a temperature sensor for detecting the surface temperature of the sheet is provided and the toner image on the back side of the sheet is fixed, the heating source 62 inside the heating roller 54 is controlled so that the temperature of the pressure roller 56 becomes the specified temperature of 180 ° C. It may be performed.

It is generally known that the fixation of a color image is achieved by sufficiently heating and melting the toner on the recording paper 22 to mix toner particles of each color, thereby improving color development. However, in a state where the toner is melted, the cohesive force in the toner layer is reduced, and the recording paper 22
When the toner leaves the fixing roller such as the heating roller 54 or the pressure roller 56, the toner tends to be easily offset. Further, when the toner layer is offset, the toner tends to adhere to the surface of the fixing roller, and the recording paper 22 may adhere to the fixing roller and not peel off. The fixing device 30 in the image forming apparatus according to the first embodiment of the present invention has a high release resistance such as a fluororesin tube having high heat resistance and high release characteristics on the surface of the pressure roller 56 for fixing a color image. The layer 56c is formed, and oil is applied to the surface of the pressure roller 56 by an oil application roller 70 to improve the release characteristics of the surface of the pressure roller 56. For this reason, in the fixing device 30 in the image forming apparatus of the first embodiment, the occurrence of the toner offset state is very small. In the fixing device 30 of the image forming apparatus of the first embodiment, the surface of the pressure roller 56 is fixed on the surface of the oil application roller 70 so that the toner does not clog the holes of the porous fluorine layer. A cleaning roller 68 for cleaning the offset toner is provided.

When a color image is formed by the image forming apparatus of the first embodiment, a soft pressure roller 56 having an elastic layer 56b is opposed to a transfer surface (back surface of the paper) of the recording paper 22 which contacts the toner. On the other hand, a hard heating roller 54 having no elasticity is arranged facing a surface (paper surface) not in contact with the toner. At the contact portion between the heating roller 54 and the pressure roller 56, a soft pressure roller 56
Is deformed. Considering the separation between the recording sheet 22 and the pressure roller 56 when the recording sheet 22 is discharged from the contact portion of these fixing rollers, the pressure roller 56 and the recording sheet 22 accompanying the melting of the toner on the back surface of the sheet are considered. Is greater than the adhesive force of each. As a result, the toner surface on the back of the paper is not roughened,
The recording paper 22 is surely separated from the surface of the fixing roller without lowering the transparency (glossiness) of the toner. In the image forming apparatus of the first embodiment, the surface of the pressure roller 56 is heated by the heating roller 54 that comes into contact with the surface of the pressure roller 56. This is because when heated from the inner surface of the pressure roller 56, the surface of the high release layer 56c is heated to 180 ° C. through the elastic layer 56b having extremely poor thermal conductivity on the surface of the pressure roller 56.
It is necessary to heat to the vicinity. For this reason, the pressure roller 5
When heating 6 from its inner surface, it is necessary to heat the inner surface of the elastic layer 56b to 240 to 250 ° C. or higher, and the elastic layer 56b becomes close to the temperature at which the rubber elastic body deteriorates at high temperature.
As a result, there is a problem that the rubber elasticity of the elastic layer 56b is rapidly deteriorated and durability is deteriorated. In order to solve this problem, the image forming apparatus according to the first embodiment includes a pressure roller 56
The heating roller 5 is brought into contact with the surface of the pressure roller 56 for heating.
4

In the image forming apparatus of the present invention,
It is also possible to change the set temperature of the surface of the heating roller 54 according to the type of the transfer surface on the paper surface and the back surface of the paper and the type of toner used for the image formed on the transfer surface.
In general, even when toner of each color is manufactured using the same resin material such as polyester, the fixing condition of the toner slightly varies depending on the kind of the pigment such as the pigment, the charge control agent and the like, and the mixing amount. Therefore, by setting the set temperature of the surface of the heating roller 54 to an optimum temperature in accordance with the toner to be used, it is possible to realize a fixing condition which is more excellent in the fixing property and can suppress the offset state of the toner. it can. In this case, the set temperature of the surface of the heating roller 54 is selected so that the surface temperature of the pressure roller 56 matches the fixing condition of the toner used. As described above, if the set temperature of the surface of the heating roller 54 is changed according to the transfer surface of the recording paper 22 inserted into the fixing device 30, the type of toner to be used, and the like, the problem of more stable offset and defective fixing can be obtained. Is less likely to occur in the fixing device 30.

<< Second Embodiment >> A second embodiment of the image forming apparatus of the present invention will be described below with reference to FIG. FIG. 4 is a sectional view showing a schematic configuration of an image forming apparatus according to a second embodiment of the present invention. In FIG. 4, components having the same functions and configurations as those in the first embodiment are denoted by the same reference numerals. Second
The image forming apparatus according to the third embodiment has the same configuration as that of the first embodiment except for the color developing unit 8 and the transfer drum 20 in the image forming apparatus according to the first embodiment. This will be described in detail. In FIG. 4, the color developing unit 80 has color developing units 82Y, 82M, and 82C for the respective colors of yellow, magenta, and cyan, each of which is integrally formed in a cartridge type. The color developing units 82Y, 82M, and 82C have yellow, magenta, and cyan toners 10Y, 10M,
10C is stored. Each color toner 10Y, 10
M and 10C are negatively charged toners in which pigments of each color are dispersed in a polyester resin. Color developing device 8 for each color
2Y, 82M and 82C are the toners 10Y and 10Y, respectively.
M, 10C on the surface of the developing rollers 14Y, 14
M, 14C.

The color developing unit 80 in which the three color developing units 82Y, 82M, and 82C of yellow, magenta, and cyan are integrally formed, has an arrow g centered on a fulcrum shaft 80b.
It is configured to be able to reciprocate in a swinging manner in the direction. Each of the color developing units 82Y, 82M, and 82C is supported by a color developing unit 80 in a reciprocating manner in an arrow h1 direction and an arrow h2 direction by an urging means (not shown) such as a plunger. Developing roller 14
Is switched so as to be able to be separated from and connected to the photoconductor 2. In the image forming apparatus of the second embodiment configured as described above, for example, when forming a yellow image, the developing unit 80 rotates so that the yellow developing roller 14Y is disposed at a position facing the photosensitive member 2. Moving. Next, the color developing unit 8
The entirety of 0 is urged in the direction of arrow h1 by urging means such as a plunger, so that the developing roller 14Y comes into pressure contact with the photosensitive member 2. In this state, the yellow toner 10Y
As a result, the electrostatic latent image on the surface of the photoreceptor 2 can be developed. The image forming apparatus according to the second embodiment includes three color toners 10Y, 10M, and 10C of yellow, magenta, and cyan.
The color toner box 86 in which the image is stored can be mounted on the upper part of the color developing unit 80. When the color toner box 86 is attached, only the consumed toner can be replenished in the color toner box 86 without replacing the color developing unit 80. Further, the developing device of the second embodiment can freely select the capacity of yellow, magenta, and cyan toners in the color developing unit 80 without changing the appearance of the color developing unit 80 at all. That is, by changing the positions of the wall surfaces 80c and 80d in the color developing unit 80, the capacity distribution of the toner capacity of each color can be changed according to the purpose of use.

The transfer belt 86 disposed so as to face the color developing unit 80 via the photosensitive member 2 captures the toner image formed on the surface of the photosensitive member 2 and transfers the toner image onto the recording paper 22. The next transfer is performed. The transfer belt 86 is made of a semiconductive material such as a polycarbonate resin, a fluororesin, a urethane rubber having a fluorine coating, has a thickness of 0.1 to 2 mm, and has an endless belt shape having a diameter of 120 mm. is there. A drive pulley 88a for driving the transfer belt 86, a driven pulley 88b, and a tension pulley 88c for applying tension to the transfer belt 86 are provided inside the transfer belt 86. The transfer belt 86 is held and driven by the driving pulley 88a, the driven pulley 88b, and the tension pulley 88c. When the toner image is transferred from the photoconductor 2 to the transfer belt 86, and when the toner image is secondarily transferred from the transfer belt 86 to the recording paper 22, the driving pulley 8 is used to generate an electric field for transfer.
A DC voltage is applied to 8a. Drive pulley 88a
Is a roller formed of a conductive metal having a diameter of 40 mm and at least a surface of which an aluminum metal is adhered. The driven pulley 88b and the tension pulley 88c are each a roller having a diameter of 40 mm and formed of a conductive metal made of aluminum. The driven pulley 88b and the tension pulley 88c
It is also possible to connect to the same potential as a, to ground, or to connect a desired power supply. As shown in FIG. 4, around the transfer belt 86, a charger 34 for inverting the charge polarity of the toner on the surface of the transfer belt 86 using a driven pulley 88b as an opposite electrode, and a cue position of the transfer belt 86 are detected. A position sensor 42 is provided.

In the image forming apparatus of the second embodiment, the surface of the transfer belt 86 is cleaned by using a reverse transfer to the photosensitive member 2 using a charge of toner without using a special cleaner. I have. A high voltage is applied to the charging wire of the charger 34 in synchronization with the timing at which the toner remaining on the surface of the transfer belt 86 passes through the charger 34 to make the polarity of the toner remaining on the surface of the transfer belt 86 positive. I do. At this time, a DC voltage of +6.0 kV is applied to the charging wire of the charger 34 by a high-voltage power supply.
Thereafter, in synchronization with the timing at which the residual toner passes through the contact portion between the photosensitive member 2 and the transfer belt 86, the driving pulley 8
A DC voltage of +1.0 kV is applied to 8a. As a result, the toner remaining on the surface of the transfer belt 86 is reversely transferred to the photoconductor 2, and the toner reversely transferred to the surface of the photoconductor 2 is cleaned by the cleaner 24. In addition, the charger 3
4, a positive voltage was applied to adjust the charge polarity of the toner to be positive. However, the charge polarity of the toner is not necessarily required to be positive. Conversely, the charge polarity is the same as the initial charge polarity of the toner. Is also good. However, in this case, it is important that the voltage applied to the drive pulley 88a at the time of the reverse transfer to the photoconductor 2 is also inverted in polarity.

[0054]

As described above, the image forming apparatus of the present invention comprises a color developing unit in which yellow, magenta and cyan developing units are integrally formed, a photosensitive member, a black developing unit and a charging unit. The cartridge that integrally holds the cleaner is configured to be detachable, so that monochrome image formation with a simple configuration can be realized with high speed, high productivity, and simple operability. INDUSTRIAL APPLICABILITY The image forming apparatus of the present invention can realize monochrome image formation having the same high speed and operability as a conventional monochrome image forming apparatus, while being an image forming apparatus capable of realizing full-color image formation. Further, according to the image forming apparatus of the present invention, the color developing unit integrally forms a color developing device for accommodating yellow, magenta, and cyan toners, and is configured to be easily replaceable. It is possible to easily supply toner and replace consumable parts. Further, according to the image forming apparatus of the present invention, since the color developing unit is arranged on the upstream side of the black developing device in the rotation direction of the photoconductor, the color developing device is stable without any contamination by the black toner. Color image can be formed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a state in which a front alligator of the image forming apparatus according to the first embodiment is opened.

FIG. 3 is a schematic sectional view illustrating a configuration of a fixing device of the image forming apparatus according to the first exemplary embodiment.

FIG. 4 is a sectional view illustrating a schematic configuration of an image forming apparatus according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating an overall configuration of a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus main body 2 Photoconductor 4 Corona charger 6 Laser exposure device 8 Color developing unit 16 Black developing device 20 Transfer drum 24 Cleaner 30 Fixing device 31 Cartridge

Claims (16)

[Claims] 1. A rotating photoconductor, a charging unit for uniformly charging the surface of the photoconductor, and exposing the surface of the photoconductor downstream of the charging unit in a rotation direction of the photoconductor. Exposure means for disposing the photoreceptor downstream of the exposure means in the direction of rotation of the photoreceptor so as to face the photoreceptor and forming yellow, magenta and cyan color toner images on the surface of the photoreceptor A color developing unit having a color developing unit, a black developing unit for forming a black toner image on the surface of the photoconductor downstream of the color developing unit in a rotation direction of the photoconductor, It is arranged downstream of the black developing means in the rotation direction and opposed to the photoconductor, sequentially receives each toner image formed on the photoconductor, and forms a color toner image on the surface. Intermediate transfer member, and an image forming apparatus characterized by comprising a cleaning means for cleaning the surface of the photosensitive member at a downstream side of the intermediate transfer body in the rotating direction of the photosensitive member for. 2. The image forming apparatus according to claim 1, wherein the photosensitive member, the charging unit, the black developing unit, and the cleaning unit are integrally configured as a cartridge. 3. The image forming apparatus according to claim 1, further comprising a separation / contact unit for switching the black developing unit to a contact state and a separation state with respect to the photosensitive member. 4. The image forming apparatus according to claim 1, wherein the color developing unit is configured such that each of yellow, magenta, and cyan color developing units is configured as a cartridge. 5. A color switching unit according to claim 1, further comprising a color switching unit configured to rotationally drive the color developing unit and to switch between yellow, magenta, and cyan color developing units so as to face the photosensitive member. Image forming device. 6. A color switching unit that rotationally drives a color developing unit and switches each of yellow, magenta, and cyan color developing units to face a photosensitive member.
3. The image forming apparatus according to claim 1, further comprising: a unit that separates and separates each of the yellow, magenta, and cyan color developing units from the photosensitive member after the color switching unit drives the color developing unit.
An image forming apparatus according to claim 1. 7. The color developing unit has a substantially cylindrical shape, and by rotating the color developing unit, each of yellow, magenta, and cyan color developing means is arranged to face the photoconductor. 3. The image forming apparatus according to claim 1, further comprising a color switching unit for switching. 8. The color developing unit has a substantially cylindrical shape, and yellow, magenta, and cyan color developing means are arranged to face the photoconductor by rotational driving and reciprocating driving of the color developing unit. 3. The image forming apparatus according to claim 1, further comprising a color switching unit configured to switch each color developing unit to perform a separating operation from the photosensitive member. 9. A color switching means for switching the yellow, magenta, and cyan color developing means to face the photosensitive member by reciprocatingly rotating the color developing unit around a fulcrum. The image forming apparatus according to claim 1, further comprising: 10. The color developing unit arranges yellow, magenta, and cyan color developing means in opposition to the photoreceptor by reciprocating rotation operation and reciprocating linear operation, and moves the color developing means to the photoreceptor. The image forming apparatus according to claim 1, further comprising a color switching unit configured to perform a separation operation. 11. The image forming apparatus according to claim 1, further comprising means for changing the capacity of the toner stored in each of the yellow, magenta, and cyan color developing means of the integrated color developing unit to a desired capacity distribution. An image forming apparatus according to claim 1. 12. The image forming apparatus according to claim 1, further comprising a color toner replenishing unit that stores toner to be supplied to each of yellow, magenta, and cyan color developing units of the color developing unit. 13. A transfer means for inserting a transfer material into a contact position between a photoreceptor and an intermediate transfer body and transferring a color toner image formed on a surface of the intermediate transfer body to the transfer material. The image forming apparatus according to claim 1, wherein: 14. The image forming apparatus according to claim 1, wherein the color developing unit and the intermediate transfer member are disposed at substantially symmetric positions with respect to the photosensitive member. 15. The image forming apparatus according to claim 1, wherein the intermediate transfer member is an intermediate transfer drum having a substantially cylindrical shape. 16. The image forming apparatus according to claim 1, further comprising an opening unit that opens a housing by separating a position where the photosensitive member and the intermediate transfer member are in contact with each other.