JPH0815946A - Color image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize a high-quality color output device with low running cost. [Structure] For the transfer from the image carrier to the intermediate transfer belt, it is ideal that the electric field acts only on the transfer nip. That is,
The gap between the image carrier and the intermediate transfer belt is adjusted by the diameter of both rollers (ratio of the roller diameter and the image carrier diameter is 0.6 or less) to prevent the toner from flying in the gap. This produces a very high quality color image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a facsimile,
The present invention relates to a printer, and more particularly to a color image device.

[0002]

2. Description of the Related Art In recent years, documents have been created and edited using color displays in offices by enhancing the equipment centering on personal computers. However, an output device that prints a created sentence on paper is mainly a monochrome machine. The reason for this is that the existing color output device has major problems in terms of performance and price. The electrophotographic color output device can also print on plain paper.
It has excellent advantages such as excellent halftone reproduction and high printing speed, but since the device is complicated, maintenance is expensive,
The cost is 10 to 50 times higher than that of a black-and-white output device, so that it is not popular enough.

An electrophotographic color output device optically or electrically color-separates an original image, forms a latent image corresponding to each color of yellow, magenta, and cyan, and then charges powder particles (corresponding to each color). The process of visualizing with toner is the same as in a black and white machine. What is most different from the black-and-white machine is the step of superposing each of these colors on the transfer material.

FIG. 2 shows a schematic configuration of a conventional color output device disclosed in JP-A-6-19331 and JP-A-6-19332. In FIG. 2, reference numeral 50 is a photosensitive drum, 51 is an exposing means, 52 is a developing device provided with a group of rotatable developing devices of yellow (Y), magenta (M), cyan (C), and black (BK), 54 is a corona discharger, 56
Is a transfer drum and is made of a dielectric or resistor film. 58 is a cleaning means, 60 is a conveyor belt, and 62
Is a fixing device, and 64 is a paper feed roller. Next, the operation will be described. A color original is read by an image scanner (not shown) to obtain yellow, magenta, cyan, and black information.
These pieces of information are temporarily stored in the memory. To form a color image, color signals are sequentially sent to the illustrated apparatus. First, the exposure unit 51 forms a yellow latent image on the photosensitive drum 50. The latent image formation is similar to that of a normal monochrome output device. The developing device 52 rotates to press the yellow (Y) developing device against the photosensitive drum 50 to visualize the latent image with yellow toner. The image receiving paper is supplied onto the transfer drum 56 by the paper feed roller 64 in synchronization with the image formation and is attracted by the electrostatic force. The yellow image on the photosensitive drum 50 is transferred onto the image receiving paper by the transfer charger 57. The photosensitive drum 50 after the transfer is cleaned by the cleaning device 58.
The transfer residual toner is removed by, and the toner is charged by the corona discharger 54, and the next latent image is formed. When all the images of the yellow signal are transferred onto the image receiving paper, the magenta (M) image formation is performed similarly to the case of yellow. Following the magenta image formation, cyan and black image formation are sequentially performed. The image receiving paper on the transfer drum 56 is yellow,
Images of magenta, cyan, and black are sequentially superimposed, and at the same time when the formation of the black image is completed, the image receiving paper is peeled off from the transfer drum 56, passes through the transfer belt 60, and reaches the fixing device 62.
It is fixed to obtain an image.

[0005]

In the color image forming method described above, the image receiving paper is wound around the transfer drum to form three color images and a black image. For this reason, since the image receiving paper is adsorbed to the transfer drum and is separated from the transfer drum, the image receiving paper path becomes complicated and causes paper jam. In particular, adsorption and peeling using electrostatic force depend on the usage environment and the physical properties of the image receiving paper, and thus lack stability and impair reliability. The above method has an advantage that the deterioration of the image can be minimized because the image is directly transferred from the photosensitive drum to the image receiving paper, but the holding of the image receiving paper is complicated and the maintenance cycle is increased and the cost is increased. , Color output devices are not popular. It is believed that the image will be dramatically popularized by simplifying the path of the image receiving paper and maintaining high image quality.

[0006]

In order to solve the above problems, the present invention provides a color image forming method and a color image forming apparatus having the following features.

An image carrier that rotates at least, a charging unit that charges the image carrier, a developing unit that has a developer of a different color, and a cleaning unit that removes the toner remaining on the image carrier. And a plurality of movable image forming unit groups arranged in a ring shape capable of forming toner images of different colors on the image carrier, and a plurality of color toner images formed by the image forming unit group. An endless rotatable intermediate transfer belt made of a resistor for transferring and holding the intermediate transfer belt and a pressing roller for pressing the intermediate transfer belt against the image carrier, and a diameter of the pressing roller with respect to a diameter of the image carrier. A color image forming apparatus having a ratio of 0.6 or less.

[0008]

In order to simplify the image receiving paper passage of the color image forming apparatus, the images corresponding to the respective colors are temporarily held on the intermediate transfer belt and then collectively transferred to the image receiving paper. By this method, it is possible to realize an image receiving sheet conveyance path equivalent to that of the conventional black and white image forming apparatus, reduce the frequency of occurrence of image receiving sheet jams, and improve maintainability.

In the method using the intermediate transfer belt, the transfer of the toner image from the image carrier to the intermediate transfer belt and the transfer from the intermediate transfer belt to the image receiving paper are performed twice. Therefore, image disturbance such as toner scattering in one transfer must be suppressed as much as possible. When the toner image is transferred from the image carrier, it is desirable that the electric field is applied only when the transferred body comes into contact with the image carrier. However, the roller that presses the image carrier and the intermediate transfer belt against the image carrier contacts with a nip of a certain width, and the electric field also acts on the void around the nip, so the toner on the image carrier does not leave a void. It flies through and becomes an image disorder. Therefore, good toner image transfer is achieved by minimizing the electric field that acts on this void.

[0010]

【Example】

(Embodiment 1) FIG. 1 is a schematic view of the configuration of a color image forming apparatus according to the first embodiment of the present invention. In FIG. 1, reference numeral 10 denotes an image forming unit, which has four colors of yellow, magenta, cyan, and black, each of which is provided with an image carrier 12 (φ30 mm), a charging roller 14, a developing device 16, and a cleaning blade 17. The image forming unit 10 includes an image carrier 12 and a developing device 1.
It is composed of two blocks, that is, a developing unit combining 6 and a toner collecting unit combining the charging roller 14 and the cleaning blade 17. The unit group of four colors can be rotated around the center of movement rotation of the unit group by the unit rotating device 18. When the image forming unit group is moved counterclockwise, the developing unit is at the top at the image forming position, and
The toner collecting unit is located at the bottom. Reference numeral 20 denotes an exposing unit, which allows one unit in the image forming unit 10 to be exposed through a substantially parallel slit between the developing unit and the toner collecting unit of the image forming unit 10 and a reflecting mirror 21 near the center of rotation. Are arranged as follows. The reflection mirror 21 is fixed without rotating as the image forming unit 10 rotates. 1
An intermediate transfer belt 9 has a diameter of 120 mm so that it can hold at least one A4 size image. The intermediate transfer belt 19 is used by kneading a conductive filler in an insulating resin and forming a film with an extruder. In this embodiment, a polycarbonate resin (for example,
A film obtained by adding 5 parts of conductive carbon (for example, Ketjen Black) to 95 parts of Mitsubishi Gas Chemical's Iupilon Z300) was used. The film thickness is about 350
μm. An antioxidant, a dispersion aid, a release member and the like may be mixed in the resin. The resistance of this film was about 10 ⁷ to 10 ⁸ Ω · cm. The surface roughness is 10
The point average roughness was about 8 to 10 μm. It is desirable to control the surface roughness to be equal to or smaller than a value close to the particle size of the toner used. This is to consider cleaning the toner from the intermediate transfer belt. Electric resistance is 10 ⁵ to 10
A range of ¹¹ Ω · cm is effective. When it is less than 10 ⁵ Ω · cm, electric discharge occurs to the image carrier and a conductive roller that transfers an image to an image receiving paper described later. On the other hand, when it exceeds 10 ¹¹ Ω · cm, there arises inconveniences such as an increase in the resin ratio of the conductive portion forming the intermediate transfer belt 19, an increase in applied voltage, and a large environmental change. The intermediate transfer belt 19 is not limited to the configuration described above, and may be, for example, an insulating base material coated with a conductive layer. In this case, polyethylene terephthalate (PET), polyimide, polyamide, polyurethane or the like is used as the insulating substrate. As described above, the conductive layer is provided by dispersing a conductive filler in an insulating resin and spraying or dipping. The intermediate transfer belt 19 is stretched around a pressing roller 24, a stretching roller 26, and a driving roller 27. The pressing roller 24 has a foam sponge provided on a metal shaft of Φ10 mm, and has a hardness of 30 ° or less on the JIS A scale. The conductive foam sponge layer is made by dispersing a conductive filler such as carbon in a rubber material such as polyurethane or EPDM or containing an ionic conductive material. The metal shaft of the pressing roller 24 is grounded.

The diameter of the pressing roller 24 is the intermediate transfer belt 1
The image quality is most affected when the toner image is transferred from the image carrier 12 onto the image carrier 9. In this embodiment, the diameter of the image carrier 12 is 30
The pressure roller 24 has a diameter of 30 mm to 1 mm.
Intermediate transfer belt 19 with 5mm pitch change up to 5mm
The disorder of the image above was observed. The results are summarized in Table 1.

[0012]

[Table 1]

When the ratio of the diameter of the pressing roller 24 divided by the diameter of the image carrier 12 exceeds 0.63, the intermediate transfer belt 19
Toner scatters around the upper transferred characters and deteriorates the image quality.

In the intermediate transfer belt, the pressing roller 24 is moved by the contacting / separating device 25 so as to be separated from the image carrier 12 of the image forming unit 10 while the image forming unit 10 is moving for color exchange, or, The intermediate transfer belt 19 is placed at a position where there is no toner image to prevent image damage due to replacement of the image forming unit 10. A transfer roller 28 is a backup roller for pressing the image receiving paper 37 against the intermediate transfer belt 19 to transfer the toner image when the toner image on the intermediate transfer belt 19 is transferred to the image receiving paper 37. The transfer roller 28 is formed by foaming a conductive material such as lithium salt in polyurethane rubber on a metal shaft of φ10 mm. The outer diameter is φ19 mm, the hardness is 30 ° or less on the JIS A scale, and the resistance is about 10 ⁹ Ω · cm, which is larger than the specific resistance value of the intermediate transfer belt 19. Now, the intermediate transfer belt 1
Since the diameter of 9 is 120 mm, when the A4 size image is transferred onto the intermediate transfer belt 19 and further used as the image receiving paper 37, the transfer from the image carrier 12 to the intermediate transfer belt 19 and the intermediate transfer belt 19 are performed. Transfer to the image receiving paper 37 is performed at the same time. Even if the width of the intermediate transfer belt 19 is wider than the width of the image receiving paper 37, if the specific resistance value of the intermediate transfer belt 19 and the specific resistance value of the transfer roller 28 are as described above, the intermediate transfer belt 19 transfers to the transfer roller 28. An appropriate voltage is applied to the intermediate transfer belt 19 without causing a current leak, and the toner image is satisfactorily transferred from the image carrier 12. The transfer roller 28 applies a voltage having the same polarity as the toner from the transfer power supply 30 while the toner image is being transferred from the image carrier onto the intermediate transfer belt 19. When transferring to the image receiving paper 37, a voltage having a polarity opposite to that of the toner is applied from the transfer power supply 30. Alternatively, it may be separated from the intermediate transfer belt 19 when it is not mechanically transferred to the image receiving paper. Reference numeral 26 denotes a tension roller, which has a diameter of 10 mm and is made of a metal roller. Reference numeral 27 denotes a drive roller for rotating the intermediate transfer belt 19, which is made of a metal roller and has a diameter of 16 mm and is grounded.
Reference numeral 31 denotes an electrode for applying a voltage to the intermediate transfer belt 19, and in the present embodiment, a stainless rod of Φ10 is used and is driven to rotate as the intermediate transfer belt 19 rotates. The power supply position to the intermediate transfer belt 19 is located on the downstream side of the contact position between the image carrier 12 and the intermediate transfer belt 19, at which the intermediate transfer belt 19 rotates, that is, at a position past the transfer nip. Since the intermediate transfer belt 19 is composed of the resistor as described above, when the transfer is performed from the downstream side, the voltage on the upstream side of the transfer nip becomes low and the forward jump phenomenon can be avoided. When the intermediate transfer belt 19 is moving due to color exchange of the image forming unit 10 or the like, the intermediate transfer belt 19 moves along with it. 32 is the intermediate transfer belt 19
It is an intermediate transfer power source for applying to. It is possible to apply the same and opposite polarities of the toner. 34 is the intermediate transfer belt 19
Is a cleaning device for removing the toner remaining on the surface after the transfer from the sheet to the image receiving paper 37 is completed. In the cleaning device 34, a roller provided with a conductive foam sponge on a metal shaft is brought into contact with the intermediate transfer belt 19 and a voltage having a polarity opposite to the charging polarity of the toner is applied to the intermediate transfer belt 1.
9 is equipped with a roller for removing the toner. The toner adhering to the surface of the roller is scraped off by a scraper and collected in a toner reservoir in the cleaning device 34. However, in the sequence, the reverse polarity voltage is applied after the transfer of the toner image on the intermediate transfer belt 19 to the image receiving paper 7 is completed. In the meantime, a voltage having the same polarity as the toner is applied to the roller so that the toner is not collected. 38
Is a paper feed roller that conveys the image receiving paper 37 one by one from the cassette tray by the paper feed roller. Manual feed roller 40
Is a roller for feeding the paper that is not set in the cassette. A timing roller 42 is a roller that is in contact with the metal roller 43 and sends out the fed image receiving paper 37 to the transfer portion according to the image signal. A scraper for removing paper dust is attached to the metal roller 40. A fixing device 46 fixes the toner image on the image receiving paper 37 that has been transferred. After the fixing process, the image receiving paper 37 is ejected outside the machine. The image carrier 12 of each unit is 33 mm
It rotates at a speed of / s. The appropriate speed difference between the image carrier 12 and the intermediate transfer belt 19 is about 1 to 5%. The transfer roller 28 and the intermediate transfer belt 19 also rotate at almost the same speed difference.

The intermediate transfer belt 19, the pressing roller 24, the stretching roller 26, the driving roller 27, the electrode 31, and the cleaning device 34 are integrated into a unit. The width of the pressing roller 24 side is made smaller than the length stretched by both the stretching roller 26 and the driving roller 27 as shown in FIG. 1, and the manual feed roller 40 shown in the dotted line on the right side in FIG. ,
Timing roller 42, metal roller 43, transfer roller 2
8. When the fixing device 46 is attached to the opening / closing lid of the color image forming apparatus and put together, the above-described unit can be easily pulled out to the transfer roller 28 side. When this unit is pulled out to the side of the opening / closing lid (front side of the apparatus) and when it is pulled out in the axial direction of the image carrier 12, it is easy to design a positioning mechanism and an avoidance mechanism for preventing damage to devices such as the image carrier 12, and at the same time. Maintainability is greatly improved.

The operation will be described with reference to FIG. The process of printing a color image will be described. When printing a color image, images are formed in the order of yellow (Y), magenta (M), cyan (C), and black (BK). First, when a yellow image signal is sent, the image forming unit 10 rotates, and the yellow image forming unit 10 moves to the intermediate transfer belt 1.
Rotate until it contacts 9 in horizontal position. The intermediate transfer belt 19 comes into contact with the image carrier 12 in synchronization with the movement of the yellow image forming unit 10 to the image forming position. Exposure device 2
From 0, laser light corresponding to the yellow image signal is emitted, and the image is visualized through the steps of charging, latent image formation, and development as in a normal black-and-white printer. In this embodiment, the image carrier 12 is negatively charged, and the toner is also negatively charged. This yellow toner image is generated by the intermediate transfer power source 3
2 is transferred onto the intermediate transfer belt 19 to which a voltage is applied via the electrode 31. The applied voltage at this time is +500
It was V. The toner remaining on the image carrier 12 is removed by the cleaning blade 17 and is again subjected to the visualization process. When the image formation of one screen is completed, the intermediate transfer belt 19 temporarily stops at the position where the portion not holding the toner image comes into contact with the image carrier 12. The position to stop on the intermediate transfer belt 19 is about 80 mm between the leading end and the rear end when the A4 size image is fed vertically, and the distance from the charging position of the image forming unit 10 to the transfer position is considered. To set. During the series of operations for transferring the toner image to the intermediate transfer belt 19, the voltage of the same polarity as the toner is applied to the roller of the cleaning device 34, and the toner image on the intermediate transfer belt 19 is collected by the cleaning device 34. There is no such thing. When the intermediate transfer belt 19 stops, the group of image forming units 10 rotates and moves to the position where the next magenta image forming unit 10 can contact the intermediate transfer belt 19. When the rotational movement of the unit is completed, a magenta toner image is formed on the image carrier 12 through the same process as the yellow image formation, and the position of the magenta toner image is aligned with the front end of the yellow image of the intermediate transfer belt 19, and the intermediate transfer is performed. Belt 19
Starts rotating again, and about + from the intermediate transfer belt power supply 30
A voltage of 600 V is applied, and the magenta toner image is transferred onto the yellow toner image on the intermediate transfer belt 19. Since a voltage of + 600V, which is about 100V higher than that at the time of yellow transfer, is applied to the intermediate transfer belt 19,
The yellow toner previously transferred to the image carrier 12 of the magenta image forming unit 10 does not reversely transfer. Similarly,
A voltage of +700 V for a cyan image and a voltage of +800 V for a black image are applied to the intermediate transfer belt 19 to form an image in which four colors are overlapped on the belt. The transfer roller 28 remains in contact with the intermediate transfer belt 19 during the formation of the four color toner images.
Approximately -1000V of the same polarity as toner by the transfer power supply 30
Is applied, the toner image on the intermediate transfer belt 19 is not transferred to the transfer roller 28. When the black image of the fourth color starts to be formed on the intermediate transfer belt 19, the image receiving paper 37 is fed from the paper feed roller 38 or the manual paper feed roller 40 at the timing of the image front end, and the timing roller 42 and the metal roller. After adjusting the timing between 43, it is supplied between the transfer roller 28 and the intermediate transfer belt 19. The transfer roller 28 aligns the position with the leading edge of the image and switches the polarity of the applied voltage to +1000 V, and transfers the toner images of the four colors superimposed on the intermediate transfer belt 19 onto the image receiving paper 37. When the rear end of the four-color image is transferred from the image carrier 12 of the black image forming unit 10 to the intermediate transfer belt 19, the voltage of the intermediate transfer power supply 32 switches from + 800V to -1000V with the polarity, and at least the intermediate level. -1000V having the same polarity as the toner is applied for one rotation of the intermediate transfer belt 19 after the transfer power source 32 is switched, and the toner remaining on the intermediate transfer belt 19 without being transferred to the image receiving paper 37 is transferred to the image carrier 12. Return it electrically. At the same time, a voltage is applied to the roller of the cleaning device 34 because it has a positive polarity which is the opposite polarity to the charging polarity of the toner,
The toner remaining on the intermediate transfer belt 19 is cleaned at least while the intermediate transfer belt 19 makes one round. After the operation is completed, the intermediate transfer belt 19 is again brought into contact with the yellow image forming unit 10 by the separating / contacting device 25, and a new image is formed.

The transfer voltage is the state of the image receiving paper 37, for example,
It may be set low in a high temperature and high humidity environment and high in a low temperature and low humidity environment to obtain optimum transfer. This is because the resistance fluctuation of the resistance layer of the transfer roller 28 is absorbed. Similarly, when the toner image is transferred from the image carrier 12 of the image forming unit 10 to the intermediate transfer belt 19, the applied voltage of the intermediate transfer power supply 32 may be adjusted according to the environment. After the transfer process to the image receiving paper 37 is completed, the image receiving paper 37 passes between the heat rollers of the fixing device 46, and the toner image is fixed and discharged to the outside of the machine.

As described above, when the ratio of the diameter of the image carrier 12 divided by the diameter of the pressing roller 24 is set to 0.6 or less, the toner is scattered during the transfer from the image carrier 12 to the intermediate transfer belt 19. A good image can be obtained. The color image thus obtained was good without toner scattering.

(Embodiment 2) The configuration and operation are almost the same as those of FIG. 1 shown in the first embodiment. Just the intermediate transfer belt 19
The diameter was 200 mm. This is to secure the length between the pressing roller 4 and the transfer roller 28 for one A4 size image. To secure one image of another size, the peripheral length of the intermediate transfer belt 19 may be adjusted. If the circumference of the intermediate transfer belt 19 is increased in this way, the image carrier 1
The polarity of the transfer roller 28 can be switched at the same time when the transfer from 2 to the intermediate transfer belt 19 is completed. That is, assuming that the polarity of the toner is negative as in the example of FIG. 1, a positive voltage is applied when transferring to the intermediate transfer belt 19. At this time, a negative voltage is applied to the transfer roller 28 and the roller of the cleaning device 34 that are in contact with the intermediate transfer belt 19 to prevent toner adhesion. When the transfer of the rear end portion of the image from the image carrier 12 to the intermediate transfer belt 19 is completed, this time, the negative of the same polarity as the toner is applied to the intermediate transfer belt 19, and the opposite positive is applied to the transfer roller 28. In addition, a voltage having a polarity opposite to that of the toner is applied to the roller of the cleaning device 34 in view of the timing of passage of the trailing edge of the image on the intermediate transfer belt 19. The image receiving paper 37 fed at the timing of the leading edge of the image portion described above is efficiently transferred by applying an electric force to attract the toner from the back and a repulsive force from the surface to the toner from the intermediate transfer belt 19. In the present invention, since four color toners are superposed on the intermediate transfer belt 19, the toner layer thickness is large, and the method of the present invention is effective in improving transfer efficiency. Further, a cleaning device 34 dedicated to cleaning the toner remaining on the intermediate transfer belt 19 is also used.
Since it is electrostatically performed twice on the roller and the image carrier 12 provided in the above, it can be performed efficiently and reliably.

[0020]

As described above, according to the present invention, each image carrier rotates at least, charging means for charging the image carrier, and developing means having a developer of a different color.
A plurality of movable image forming unit groups arranged in a ring shape, each of which is capable of forming a toner image of a different color on the image carrier, and a cleaning unit for removing toner remaining on the image carrier, An endless rotatable intermediate transfer belt made of a resistor for transferring and holding toner images of a plurality of colors formed by the image forming unit group, and a pressing roller for pressing the intermediate transfer belt against the image carrier, A color image forming apparatus characterized in that the ratio of the diameter of the pressing roller to the diameter of the image carrier is 0.6 or less, and a stable high-quality color image having a simple apparatus configuration and high maintainability can be obtained. it can.

In the transfer from the image carrier to the intermediate transfer belt, it is ideal that the electric field acts only on the transfer nip. That is, the gap between the image carrier and the intermediate transfer belt is adjusted by the diameters of both rollers to prevent the toner from flying in the gap. This produces a very high quality color image.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional color output device.

[Explanation of symbols]

 10 image forming unit 12 image carrier 14 charging roller 16 developing device 17 cleaning blade 19 intermediate transfer belt 20 exposure means 24 pressing roller 28 transfer roller 30 transfer power supply 32 intermediate transfer power supply 34 cleaning device 37 image receiving paper 38 paper feed roller

Claims (1)

[Claims] 1. An image carrier that rotates at least, a charging unit that charges the image carrier, a developing unit that has developers of different colors, and a toner that remains on the image carrier. A plurality of movable image forming unit groups arranged in a ring shape, each of which is capable of forming a toner image of a different color on the image bearing member, and a plurality of color images formed by the image forming unit group. An endless rotatable intermediate transfer belt made of a resistor for transferring and holding a toner image, and a pressing roller for pressing the intermediate transfer belt against the image carrier are provided. A color image forming apparatus having a diameter ratio of 0.6 or less.