JPH09244423A - Color electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make component parts inexpensive and to prevent irregularities in an image and misprinting by providing a discharging device with a discharging means moving mechanism which brings an electrode into contact with the back surface of a recording medium to impress DC high voltage and retreats it so as not to be brought into contact with an intermediate transfer body at the time of forming a color image. SOLUTION: A discharging system in this device is a system where discharging is performed by using a metallic brush 2 for the electrode of the discharging device 1 constituting a discharging means and directly bringing it into contact with the back surface of the recording medium. By integrating the electrode with a moving mechanism for a transfer roller 6, the electrode is retreated at the time of forming the color image, so that there is no fear that a toner image is disturbed. In this example, the moving mechanism for the device 1 is integrated with that for the transfer device 6 so as to be used in common, but it is good to provide them separately. By making the device 1 a contact type one, the number of circuits of a power source used for the device 1 is reduced and output specification is decreased. Then, misprinting caused by winding round the intermediate transfer body is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic apparatus using an intermediate transfer member, and more particularly to a charge removing means after a color image has been transferred onto a recording medium.

[0002]

2. Description of the Related Art Conventionally, color electrophotographic apparatuses are
A color image is formed by using four color toners of three primary colors of yellow, magenta, cyan and black.
In forming a color image, a latent image for each color is formed on a photoconductor based on color-coded print data, the latent image is developed by developing means having toner for each color, and is superimposed on an intermediate transfer body. . The toner images superposed on the intermediate transfer member are transferred at once to a recording medium by transfer means (see Japanese Patent Application Laid-Open No. 2-183288) which can be separated from and contacted with each other, and then heat-fixed by the fixing means to obtain a final color image. Is formed. The transfer from the intermediate transfer body to the recording medium is performed by superposing the toner images of four colors, and then contacting the transfer means with the intermediate transfer body with the recording medium sandwiched therebetween to apply a DC high voltage. The transfer voltage variably controls the voltage value to be applied according to the detection result of the environment detection means for detecting the environmental state of the color electrophotographic apparatus and the type of the recording medium that is set. After the transfer, the electric attraction between the intermediate transfer body and the recording medium is erased, and the charge is removed so that the recording medium is easily separated from the intermediate transfer body.
The conventional static elimination method is performed by placing a charger having an extremely thin metal wire at a predetermined distance from the surface of the intermediate transfer member and applying AC high voltage. In such an AC neutralization system, corona discharge from a charger metal wire neutralizes the charge on the back surface of the recording medium charged during transfer, and erases the potential difference from the surface of the intermediate transfer body.

As an apparatus equipped with another static elimination mechanism
Some are disclosed in Japanese Patent Publication No. 2-55266.

[0004]

In the AC charge eliminating system as described above, since the electrode of the charge eliminating means does not directly contact the intermediate transfer member, the toner image on the intermediate transfer member is not disturbed and the image is not disturbed. It can be said that this method is superior in terms of quality. However, since this method is non-contact, it is necessary to generate corona discharge in order to apply a charge to the intermediate transfer member. To generate corona discharge, A of 4-5kV
C High voltage power supply is required. Furthermore, it is necessary to superimpose a DC component for correcting the offset component on the AC high voltage power source. As described above, the conventional AC static elimination method has a problem that the high-voltage power source used for the static elimination means becomes expensive. Further, if the metal wire of the charger becomes dirty, there is a problem that sufficient corona discharge cannot be performed, and the recording medium winds around the intermediate transfer member, resulting in misprinting. Since the metal wire is extremely thin, it is difficult to handle even if it is cleaned, and it is not suitable for user maintenance.

Next, the conventional color electrophotographic apparatus has a problem that misprinting is likely to occur under certain conditions (environment, type of recording medium). This problem is that since the static elimination voltage is a fixed value, a potential difference remains between the back surface of the recording medium and the surface of the intermediate transfer body under a certain condition, and the recording medium easily winds around the intermediate transfer body. From this, it can be seen that even in static elimination, it is necessary to apply an optimum static elimination voltage depending on the environment and the type of recording medium.

[0006] The present invention provides a charge eliminating method for the charge eliminating means of a color electrophotographic apparatus, the components of which are inexpensive, and is free from image distortion and misprinting, resulting in higher quality image output than ever before. The purpose is to achieve high reliability.

[0007]

To reduce the cost of the high-voltage power supply, which is the above-mentioned problem, a DC static elimination method in which electrodes are directly contacted from the back surface of the recording medium to apply a DC high voltage is effective. A metal brush or a conductive roller may be used as the electrode. In this method, the electrodes are brought into direct contact with each other, and therefore it is necessary to provide a mechanism for moving the static eliminator for retracting the electrodes when creating a color image. The movable mechanism has a proven record in the transfer means and can be constructed in the same manner, or the movable means can be shared by providing the transfer means and the charge eliminating means on the same structural component.

Next, in order to eliminate misprinting due to winding around the intermediate transfer member and to improve the reliability of the color electrophotographic apparatus, the detection result and recording by the apparatus environment detecting means for detecting the environmental state of the color electrophotographic apparatus are recorded. It is effective to variably control the voltage applied from the charge eliminating unit based on the setting contents of the medium setting unit.

In the DC static elimination method, since the electrodes are in direct contact with the back surface of the recording medium, it is not necessary to generate corona discharge. Therefore, the voltage may be about 1 kV, which is slightly higher than the surface potential of the intermediate transfer member, and the cost of the high-voltage power supply used for the charge eliminating means can be reduced. Since the static elimination means movable mechanism keeps the electrodes of the static elimination means retracted when creating a color image,
It serves to provide the same image quality as before without disturbing the toner image. It should be noted that the movable mechanism has a track record in the transfer area and can be easily realized with a similar structure. Further, by variably controlling the voltage applied from the charge eliminating unit depending on the environment and the type of the recording medium, it is possible to always provide an optimum charge eliminating voltage and reliably erase the potential difference between the back surface of the recording medium and the surface of the intermediate transfer member. . As a result, the recording medium is surely peeled off from the intermediate transfer member, and misprinting does not occur in the apparatus under any conditions (environment, type of recording medium), which improves the reliability of the color electrophotographic apparatus.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

First, the outline of the color electrophotographic apparatus will be described with reference to the schematic view of FIG. Organic photoconductive material (OP
The photosensitive belt 11 coated with C) is rotationally driven in the direction of the arrow in the figure during image formation. The belt cleaner 25 cleans the toner remaining on the photosensitive belt after the completion of toner image formation for each color. The charger 15 charges the electric charges necessary to form an electrostatic latent image on the surface of the photosensitive belt. The laser beam 22 exposes the surface of the charged photosensitive belt to form an electrostatic latent image. Developing device 12 (Y, M, C, K)
Develops the electrostatic latent image formed on the surface of the photosensitive belt with each developer in the order of first yellow, second magenta, third cyan, and fourth black. By the way, there are two types of developing devices, one using a one-component developer and the other using a two-component developer. In this embodiment, an example using a two-component developer will be described, but the present invention does not depend on the developing method. The intermediate transfer body 8 is rotated by contact with the photosensitive belt 11, and the toner images formed on the surface of the photosensitive belt 11 on the intermediate transfer body 8 are transferred to yellow, magenta, cyan, and A color image is formed by transferring in the order of black (first transfer) and superposing toner images of respective colors. The transfer device 6 transfers the toner image formed on the intermediate transfer member 8 to
By applying a potential having a polarity opposite to that of the potential of the surface of the intermediate transfer body 8 from the back side of the recording medium 24, it is transferred onto the recording medium 24 (second transfer). The static eliminator 1 erases the potential difference generated between the surface of the intermediate transfer body 8 and the back surface of the recording medium 24 so that the intermediate transfer body 8 and the recording medium 24 are easily separated. Fixing device 2
3 fuses the toner image transferred onto the recording medium 24 by heat. The intermediate transfer member cleaner 13 cleans the toner remaining on the intermediate transfer member 8 after the toner image is transferred onto the recording medium 24.

Next, the structure of the high voltage power source of the entire color electrophotographic apparatus according to the present invention will be described with reference to FIG. This apparatus uses an intermediate transfer body as a reference for the entire power source that constitutes a process, and carries out so-called transfer of toner by generating a potential difference with respect to the intermediate transfer body.
First, the belt bias (CBV) 18 is the photosensitive belt 1
The potential difference between 1 and the intermediate transfer member 8 is set. The belt surface charging power supply (CHV) 17 is a belt bias (CB).
V) 18 further charges the surface of the photosensitive belt 11 having a negative potential difference from the intermediate transfer member 8 to the negative side. The developing bias 16 sets a potential for developing the electrostatic latent image formed on the belt surface by the laser light. The electrostatic latent image is visualized by the negatively charged toner of the developing device 15 to form a toner image. The formed toner image is the photosensitive belt 11
When it comes to the contact point with the intermediate transfer member 8 due to the rotation of, there is a potential difference set by the belt bias (CBV) 18, and the image is transferred to the intermediate transfer member 8. Transfer power supply (THV) 7
Applies a positive potential to the toner image transferred to the intermediate transfer member 8 to transfer the toner image onto the recording medium 24. After the toner image is transferred to the recording medium 24, the charge is removed so that the recording medium 24 does not remain adsorbed on the intermediate transfer body 8. A detailed description of the charge removal will be given later.
Next, the intermediate transfer member cleaning power source (FCBV) 19
Sets a potential for removing the toner remaining on the intermediate transfer member 8. The high voltage power supply constituting the above color electrophotography is turned on / off according to the process by the control means 21, and the voltage value of the high voltage power supply is variably controlled depending on the environment or the environment and the type of the recording medium 24. Is going. As an environment detecting method, a current flowing when a voltage is applied from a transfer power source (THV) like the apparatus environment detecting means 20 is detected, and it is judged from the resistance value of the semiconductor material used for the intermediate transfer member. There are ways.

In the color electrophotographic apparatus as described above, a problem in the conventional static eliminating system will be described with reference to FIGS. FIG. 5 is a diagram showing a configuration of a conventional transfer and charge eliminating portion. First, the transfer mechanism will be described. In the transfer, the voltage is applied by the transfer roller which constitutes the transfer device 6, and cannot always be in contact with the color image in order to form the color image. Therefore, the transfer roller is movable, and the transfer means pressing spring 4 and the transfer means drive cam 5 for controlling the transfer roller are provided. In operation, as shown in FIG. 6, when the cam rotates, the transfer means operating lever 30 integrated with the transfer roller is pushed and the transfer roller is separated from the intermediate transfer body. Next, the static elimination method will be described. As for static elimination, as shown in FIG. 4, the potential difference between the back surface of the recording medium and the surface of the intermediate transfer body caused by the transfer is applied from the direction of the arrow to erase the potential difference between the back surface of the recording medium and the surface of the intermediate transfer body. However, it is performed for the purpose of facilitating the separation of the recording medium from the intermediate transfer member. The conventional static elimination is an AC static elimination method, and is performed by applying an AC high voltage of about 5 kV from an AC high voltage power source (ACV) 28 to a static elimination charger 26 having an extremely thin metal wire 27 stretched as shown in FIG. The charge eliminating charger is arranged at a predetermined distance from the intermediate transfer member, and is a so-called non-contact type charge eliminating system. Therefore, it is necessary to apply a voltage as high as 5 kV to generate corona discharge. As shown in Fig. 7, the characteristic of AC high voltage is that the corona discharge starts at about 3kV and the potential becomes 0 at about 4.2kV, and becomes more negative than that. Due to such characteristics, AC is actually set to 5 kV at which the corona discharge is stable, and the direct current superposed power source (DCV) 29 is used for correction as shown in FIG. For this reason, the conventional method has a problem in that the power source used for static elimination becomes expensive. Furthermore, in the conventional method, the voltage setting of the static eliminator was fixed under all environmental conditions in which the color electrophotographic apparatus was used, so under certain conditions the balance was unbalanced and the recording medium wrapped around the intermediate transfer member, causing misprinting. There is also the problem of becoming.

In order to solve the above problems, the present invention employs a structure using the static eliminating means shown in FIG.

The static elimination method of the present invention is a method for eliminating static electricity by directly contacting the back surface of the recording medium with the metal brush 2 used as the electrode of the static eliminator 1 which constitutes the static elimination means. By integrating with the moving mechanism of the transfer roller, the electrodes are retracted when a color image is formed, so there is no concern of disturbing the toner image. In the example of FIG. 1, the movable mechanism of the static eliminator is integrated and shared with that of the transfer device, but may be provided separately. By making the static eliminator contact type in this way,
The number of circuits of the power supply used for the static eliminator can be simplified and the output specifications can be reduced, and the cost of the power supply can be reduced. In addition, by variably controlling the applied voltage depending on the environment and the type of recording medium, it is possible to always set the optimum conditions, reduce misprint due to winding around the intermediate transfer member, and improve the reliability of the color electrophotographic apparatus. It is possible to improve.

[0016]

According to the present invention, it is possible to perform contact-type static elimination by using a static eliminator having a movable mechanism. By adopting the contact method, the high-voltage power supply used for the static eliminator can be converted into DC, and the specifications of the output voltage can be significantly reduced, so that the cost of the high-voltage power supply can be reduced. Further, the movable mechanism has a proven record in transfer, and can be easily realized with a similar structure. Since the electrodes of the static eliminator are retracted by the movable mechanism when the color image is formed, the toner image formed on the intermediate transfer member is not disturbed and the image quality similar to the conventional one can be maintained.

Further, by variably controlling the voltage applied from the static eliminator depending on the environment and the type of recording medium, misprint due to winding around the intermediate transfer member can be reduced under all conditions in which the color electrophotographic apparatus can be used. There is an effect that the reliability of the color electrophotographic apparatus can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a static eliminator according to the present invention.

FIG. 2 is a diagram showing a high-voltage power supply configuration of the entire color electrophotographic apparatus in the present invention.

FIG. 3 is a schematic diagram illustrating the structure of a color electrophotographic apparatus.

FIG. 4 is a schematic diagram illustrating an electrical state between a recording medium and an intermediate transfer body.

FIG. 5 is a diagram showing a configuration of a conventional static eliminator.

FIG. 6 is a diagram for explaining the operation of FIG. 5, part A (movable mechanism).

FIG. 7 is a diagram showing characteristics of AC high voltage.

[Explanation of symbols]

1 ... Static eliminator, 2 ... Metal brush, 3 ... DC power source for static elimination (J
HV), 4 ... Transfer device pressing spring, 5 ... Transfer device driving cam, 6 ... Transfer roller (transfer device), 7 ... Transfer power supply (TH
V), 8 ... Intermediate transfer member, 9 ... Paper guide, 10 ... Conveying roller, 11 ... Photosensitive belt, 12 ... Developing device, 13 ... Intermediate transfer member cleaner, 14 ... Collection roller, 15 ... Charging device, 16
… Development bias (DBV), 17… Belt surface charging power supply
(CHV), 18 ... Belt bias (CBV), 19 ... Intermediate transfer member cleaning power source (FCBV), 20 ... Device environment detection means, 21 ... Control means, 22 ... Laser light, 23 ... Fixer, 24 ... Recording medium , 25 ... Belt cleaner, 26 ... Charge removal charger, 27 ... Metal wire, 28 ... AC high-voltage power supply (ACV), 29 ... Direct current superimposing power supply (DCV), 30 ... Transfer device operating lever, 31 ... Toner.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isamu Terashima 1-1-1, Higashitaga-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Electric Appliances Division Taga Headquarters (72) Inventor Masashi Yamamoto Omika, Hitachi-shi, Ibaraki 7-1-1, Machi, Hitachi Co., Ltd. Hitachi Research Laboratory

Claims (5)

[Claims] 1. A photoreceptor for irradiating a laser beam on the basis of color-coded print data to form a latent image, and a plurality of latent images for each color formed on the photoreceptor are developed with toner for each color. A developing device, an intermediate transfer member for transferring the toner images of the respective colors and overlapping them to form a color image, a transfer device for transferring the color image formed on the intermediate transfer member onto a recording medium, and the recording device. A color electrophotographic apparatus having a fixing device for fixing a color image on a medium, wherein the transfer device is provided with a transfer device moving mechanism that keeps the transfer device from contacting with the intermediate transfer member during color image formation. A static eliminator that erases an electric attraction force between the intermediate transfer body and the recording medium in order to peel the recording medium from the intermediate transfer body after the image is transferred onto the recording medium. Record electrodes With contacting the back surface of the body to apply a DC high voltage, the color electrophotographic apparatus during color image formation characterized by comprising a charge removing means movable mechanism to be retracted so as not to contact the intermediate transfer member. 2. A color electrophotographic apparatus according to claim 1, wherein said charge eliminating means and said transfer means are arranged on the same structural component, and a movable mechanism portion is shared. 3. The color electrophotographic apparatus according to claim 1, further comprising an apparatus environment detecting means for detecting an environmental state of the apparatus, and the static eliminating means uses an applied voltage as a detection result of the apparatus environment detecting means. A color electrophotographic device characterized by variable control based on the above. 4. The color electrophotographic apparatus according to claim 1, further comprising recording medium setting means for setting the type of recording medium, and said charge eliminating means varies the voltage to be applied depending on the type of the recording medium to which it is set. A color electrophotographic device characterized by being controlled. 5. The color electrophotographic apparatus according to claim 1, further comprising an apparatus environment detecting means for detecting an environmental state of the apparatus and a recording medium setting means for setting a type of a recording medium, and the static eliminating means comprises: A color electrophotographic apparatus characterized in that the applied voltage is variably controlled according to the detection result of the apparatus environment detecting means and the type of recording medium.