JPH05289473A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce various kinds of problems due to an electric discharge product generated by the discharge of a primary charger without causing problems of image unevenness, adhesion, etc., of developer to an image carrier always, even when an image forming process is repeated. CONSTITUTION:Between the start of an image forming sequence and the na discharge current value of the primary charger charging uniformly a photosensitive body drum is set to -400muA and succeedingly the total discharge current value of the first charger is changed to -800muA synchronizing with the start of the formation of the electrostatic latent image and further, the total discharge current value is changed to -400muA again synchronizing with the end of the formation of the electrostatic latent image. By repeating the process till the image formation of four colors is ended, a multi-color image is formed. Thus, the integrated value of the total discharge current of the first charger per one time of the image forming process is suppressed while performing excellent image formation by uniform and stable charge in an electrostatic latent image forming interval.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to electrophotographic, electrostatic recording, etc. image forming apparatus, including, but not limited to, multicolor electrophotographic copying machines, facsimiles and computers. The present invention relates to an image forming apparatus that can be suitably embodied in various color copying machines such as recording apparatuses and color printers that form an output unit such as. Of course, the image forming apparatus of the present invention is not limited to this as described above.

[0002]

2. Description of the Related Art Conventionally, various multicolor electrophotographic copying apparatuses have been proposed. FIG. 2 shows a schematic configuration of an example of a multicolor electrophotographic copying machine equipped with a developing device which is a typical so-called rotary developing device.

To briefly explain with reference to FIG. 2, a multicolor electrophotographic copying apparatus of this type has an image bearing member which is rotatably supported and rotates in the direction of an arrow shown in FIG.
And the image forming means is arranged on the outer periphery thereof.
This image forming means can be any means, but in this example,
A primary charger 2 for uniformly charging the photoconductor drum 1 and a color-separated light image or a light image corresponding thereto are irradiated to form an electrostatic latent image on the photoconductor drum 1, for example, laser beam exposure. An exposure unit 3 including a device and the like, and a rotary developing device 4 for converting the electrostatic latent image on the photosensitive drum 1 into a visible image are provided.

This rotary developing device 4 includes, for example, four developing devices 4Y and 4M which respectively store four color developers, that is, a yellow color developer, a magenta color developer, a cyan color developer and a black color developer. 4C, 4BK and these four developing devices 4
It is composed of a cylindrical body 4a that holds Y, 4M, 4C and 4BK and that is rotatably supported. The rotary developing device 4 conveys a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 1 by the rotation of the cylindrical body 4a, develops an electrostatic latent image on the photosensitive drum, and the cylindrical body 4a. Is 1
By rotating, so-called full-color development for four colors can be performed.

A visible image, that is, a toner image on the photosensitive drum 1 is transferred to a transfer material P carried by a transfer device 5 and conveyed. In this example, the transfer device 5 is a transfer drum that is rotatably supported. The transfer drum 5 has a structure in which a transfer material carrying sheet 5a such as a dielectric sheet is stretched over the opening of the outer peripheral surface of the cylinder.

Next, a process of forming a full-color image by the multicolor electrophotographic copying apparatus having the above-mentioned structure will be briefly described. First, the primary charging device 2 and the exposure means 3 are driven to form a blue color-separated electrostatic latent image on the outer peripheral surface of the photosensitive drum 1, and the electrostatic latent image is stored in the developing device 4Y. It is developed with a yellow developer. On the other hand, the transfer material P fed to the transfer drum 5 by a sheet feeding device (not shown) is gripped at its tip by the gripper 5c, and the transfer drum 5 is transferred.
And is conveyed to a transfer area where the toner image formed on the outer peripheral surface of the photosensitive drum 1 is transferred as the transfer drum 5 rotates. The toner image is transferred onto the transfer material P by the operation of the transfer charger 5b.

The above-mentioned image forming and transfer operations are performed by magenta,
Repeatedly for each color of cyan and black,
The operation of the transfer charger 5b is repeated until the transfer operation for the fourth color is completed. When the superimposed transfer of the four color visible images onto the transfer material P is completed, the transfer material P is transferred to the transfer drum 5.
The charge is removed by the inner charger 5d and the outer charger 5e, and then the gripper 5c is released and the separation claw 8 is operated to separate from the transfer drum 5, and the fixing device (heat roller fixing device) 6 through the conveying means. To be fixed and discharged outside the machine. On the other hand, the residual toner on the photosensitive drum 1 is removed by the cleaner 7, and the photosensitive drum 1 is discharged by the discharging lamp 9 so that the next image forming process can be performed.

[0008]

The multicolor electrophotographic copying machine having the above-mentioned structure operates extremely well. However, in order to maintain the photoconductor drum 1 at a desired potential even in a section other than the section in which the electrostatic latent image is formed, that is, from the feeding of the transfer material P to the discharging of the transfer material P, the primary charger 2 To operate. Therefore, O due to discharge of the primary charger 2
_3. Various problems due to discharge products such as NOx, that is, image unevenness due to product adhesion to discharge electrodes, deterioration of photoconductor drum due to discharge products, environmental pollution due to discharge products, and increase in power consumption It was increasing the problems such as. When the primary discharge current value of the primary charger 2 is set to be low in order to reduce such a problem, there is a problem that stable discharge is not performed and image unevenness occurs, and electrostatic latent image is generated. If the charging is not performed except in the image forming section (the primary charging device 2 is not operated), there is a problem that the developer adheres to the photosensitive drum from the developing device or the floating developer adheres. .. In particular, when a multicolor image is formed, the section in which one electrostatic latent image is not formed (the time when the primary charger 2 is not operated) included in one image forming step is considerably longer than that in the case of forming a single color image. However, there is a drawback that the above-mentioned problems appear more prominently.

Therefore, an object of the present invention is to prevent discharge of a primary charger without causing problems such as image unevenness and adhesion of a developer to an image carrier even when a multicolor image is formed. An object of the present invention is to provide an image forming apparatus in which various problems due to products are reduced.

It is another object of the present invention to be caused by discharge of the primary charger without causing problems such as image unevenness and adhesion of the developer to the image carrier even when the image forming process is repeated a number of times. An object of the present invention is to provide an image forming apparatus in which various problems caused by discharge products are reduced.

[0011]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention, in one aspect thereof, comprises uniformly charging an image carrier and then exposing the image carrier to an electrostatic latent image by exposing the electrostatic latent image to the electrostatic latent image. In an image forming apparatus that forms a visible image on the image carrier by developing the latent image, a corona charger is used as a charging unit that charges the image carrier, and an electrostatic latent image is formed on the image carrier. In at least a part or all of the section where the image carrier is not formed, the image carrier is discharged by using a discharge current value different from the discharge current value of the corona charger in the section where the electrostatic latent image is formed on the image carrier. An image forming apparatus that is electrically charged.

In another aspect, the present invention forms an electrostatic latent image by uniformly charging the image carrier and then exposing the image carrier in accordance with an image pattern. In an image forming apparatus that forms a visible image on the image carrier by developing a latent image, a corona charger having a grid electrode is used as a charging unit for charging the image carrier, and the image carrier is In at least a part of the section where the electrostatic latent image is not formed or the entire section, a discharge current value different from the discharge current value of the corona charger in the section where the electrostatic latent image is formed on the image carrier is used, An image type characterized in that the image carrier is charged by using a grid voltage value different from the voltage value applied to the grid electrode of the corona charger in a section where an electrostatic latent image is formed on the image carrier. It is a device.

[0013]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

Since the first embodiment of the present invention is applied to the multicolor electrophotographic copying apparatus shown in FIG. 2 described above, its configuration, operation and action are basically as described above.
Therefore, although these will not be described in detail, in the present embodiment, the photosensitive drum 1 is rotated in the direction of the arrow shown in the figure, and the surface of the photosensitive drum 1 is destaticized by the destaticizing lamp 9 and then the primary charging unit 2 deactivates it. Surface is -300 to -90
It was charged to 0V. Further, the surface potential of the photoconductor drum 1 was monitored by the potential sensor 10 and the proper photoconductor drum surface potential was calculated. A laser beam exposure device was used as the exposure means 3. Each developing device 4Y of the rotary developing device 4,
4M, 4C, and 4BK include toner of each color having a negative charge, and are applied to a developer carrier, such as a developing sleeve, which carries the toner and conveys the toner to a developing area which is in contact with or close to the photosensitive drum 1. Voltage (hereinafter, referred to as developing bias) and a developing electric field formed by the potential of the photoconductor drum 1 causes the toner to be reversed in the photoconductor drum 1 by reverse development.
It was attached to the electrostatic latent image formed above and visualized.

Further, in this embodiment, as shown in FIG. 5, a scorotron type charger is used as the primary charger 2, and the discharge amount of the charging line 24 discharged by the high voltage applied from the high voltage power source 20. The grid bias power supply 2
Control is performed by applying a predetermined control voltage from 1 to the grid line 26 to charge the surface of the photosensitive drum 1 to a desired potential.

In the multicolor electrophotographic copying apparatus having the above-described structure, in this embodiment, a section in which an electrostatic latent image is not formed on the photosensitive drum 1 (hereinafter referred to as an electrostatic latent image non-forming section), for example, a transfer material. During the period in which a preparatory step for image formation such as gripping P on the transfer drum 5 is performed, or after the image exposure of the first color is performed to form an electrostatic latent image, the image exposure of the second color is performed. The total corona discharge current value of the primary charger 2 is set to a value different from the total corona discharge current value in the electrostatic latent image forming section in the section until the electrostatic latent image is formed. Specifically, the total corona discharge current value in the electrostatic latent image forming section of the primary charger 2 is set to −800 μA,
The total corona discharge current value in the electrostatic latent image non-formation section is -4
It is set to 00 μA.

FIG. 1 shows an operation sequence corresponding to the positions of the photosensitive drum 1 and the transfer drum 5 in the first embodiment of the present invention. As will be understood with reference to FIG. 1, in this embodiment, the total corona discharge of the primary charger 2 is performed during the time from the start of the image forming sequence to the start of formation of the electrostatic latent image. The current value is set to −400 μA, and subsequently, the total discharge current value of the primary charger 2 is switched to −800 μA in synchronization with the start of the formation of the electrostatic latent image, and the formation of the electrostatic latent image is completed. In synchronism with the above, the total discharge current value switches to −400 μA again. Then, the above steps are repeated until the image formation of four colors is completed.

To explain in more detail, FIGS. 3 and 4 show the transition of the surface potential of the photosensitive drum 1 in this embodiment in association with the total discharge current value of the primary charger 2 and the image forming process. .. As shown in FIG. 3, in the electrostatic latent image forming section, the photoconductor drum 1 is neutralized by the static elimination lamp 9 until the surface potential becomes almost 0V, and then charged by the primary charger 2 to the surface potential of −600V. To be done. The developing bias voltage for forming the developing electric field was set to -450V. The difference between the charging potential of the photosensitive drum 1 of −600 V and the developing bias voltage of −450 V is 150 V, which is a fog-removing voltage, and the electric field formed by this potential difference always attracts the toner to the developing sleeve.
It is possible to obtain a good image without fogging in the white part of the image without adhering to the. On the other hand, since the portion of the photosensitive drum 1 corresponding to the image pattern is irradiated with the laser beam with the intensity corresponding to the image density, the potential of the portion exposed by this laser beam drops to a potential lower than the developing bias voltage. The toner adheres to the photosensitive drum 1 by the electric field formed by the developing bias voltage and the photosensitive drum surface potential of the exposed portion, and a toner image is formed. A portion where the surface potential of the photosensitive drum is lowered to -250 V by the above image exposure is shown by a dotted line in FIG.

Further, as shown in FIG. 4, in the electrostatic latent image non-formation section, the photosensitive drum 1 is neutralized by the static elimination lamp 9 until the surface potential becomes almost 0 V, and then charged by the primary charger 2. However, the total discharge current value of the primary charger 2 is −40 with respect to −800 μA in the electrostatic latent image forming section.
Since it is set as low as 0 μA, it is charged to a slightly lower potential. In this embodiment, the electrostatic latent image forming section is charged to -600V, whereas the electrostatic latent image non-forming section is charged to -500V. However, since the developing bias voltage is set to −450V, the difference between the charging potential of the photosensitive drum 1 and the developing bias voltage is 50V.
Therefore, the developing electric field is not formed, and the toner is not applied to the photosensitive drum 1.
It is never developed.

Next, the switching timing of the total discharge current value of the primary charger 2 will be described in more detail.
In this embodiment, the electrostatic latent image is formed only for the time required from the switching of the total discharge current value to the stabilization of the surface potential of the photosensitive drum 1, specifically 0.2 seconds. The total discharge current value is switched earlier for the section.

As described above, in this embodiment, the total discharge current value of the primary charger 2 is set to a lower value in the electrostatic latent image non-forming section than in the electrostatic latent image forming section.
In the electrostatic latent image forming section, the image forming process is performed while performing good image formation by uniform and stable charging in the electrostatic latent image forming section without causing a problem that toner is developed on the photosensitive drum. The integrated value of the total discharge current of the primary charger 2 per one time can be kept low. As a result, the amount of discharge products such as O ₃ and NOx generated by the discharge is significantly reduced, and it is possible to suppress the contamination of the discharge electrode and the deterioration of the photosensitive drum 1, especially when the image forming process is performed thousands of times. It is possible to prevent deterioration of image quality such as image unevenness that occurs when repeated, and as a result, it is possible to significantly extend the life of the discharge electrode and the photosensitive drum 1. Specifically, it is about 8000 times for the photoconductor drum and about 900 for the discharge electrode on average in the past.
While the replacement life was reached by repeating the image forming process 0 times, in the present embodiment, the replacement life could be greatly extended to about 20000 times the photosensitive drum and about 17,000 discharge electrodes on average, respectively.

Further, it is possible to reduce environmental pollution due to discharge products as a secondary effect, and it is also possible to reduce power consumption. As an example, FIG. 10 shows O ₃ of the ambient environment when the electrophotographic copying apparatus having the above-described configuration is continuously operated.
The density is shown for the case where the total discharge current amount of the primary charger 2 in the electrostatic latent image non-formation section is set to -800 μA, which is the same as the electrostatic latent image formation section, and when the density is switched to -400 μA in this embodiment. As can be understood from FIG. 10, by switching the total discharge current amount according to the present embodiment,
The O ₃ concentration can be reduced.

According to the present invention, as shown in FIG. 6, an image forming station is provided for each color developer, and each color is formed by a known image forming process on a photosensitive drum as an image carrier at each image forming station. Form a visible image for each
This visible image can also be suitably realized in a multicolor electrophotographic copying apparatus in which a visible image is sequentially transferred to a transfer material supplied from the outside and fixed in a batch to obtain a color image. Next, FIG.
A second embodiment in which the present invention is applied to the multicolor electrophotographic copying machine shown in FIG.

First, the structure and operation of the multicolor electrophotographic copying machine shown in FIG. 6 will be briefly described. This type of multicolor electrophotographic copying machine is provided with four image forming stations P _Y , P _M , P _C and P _BK which are first, second, third and fourth, and also carries and conveys a transfer material P. The transfer device 37, which is an endless transfer belt in this example, is stretched between a plurality of rollers in a known manner. The transfer belt 37 is driven in the direction shown by the arrow in the figure, carries the transfer material P fed through the paper feeding section, and is transferred to each of the image forming stations P _Y , P _M , P _C.
And sequentially to P _BK .

Image forming stations P _Y , P _M , P _C
And P _BK have substantially the same structure, and include photoconductor drums 31a, 31b, 31c, and 31d, which are image carriers that are normally driven to rotate in the direction of the arrow in the figure, and the outer periphery of each photoconductor drum. The image forming means is arranged in the section. These image forming means may be arbitrary means, but in this example, the primary charger 3 that uniformly charges the photosensitive drums 31a to 31d.
2a to 32d and a color-separated light image or a light image corresponding thereto are formed to form an electrostatic latent image on the photoconductor drums 31a to 31d. For example, exposure means 33a to 33d including a laser beam exposure device or the like. And the photosensitive drums 31a to 31d
Developing units 34a to 34d for converting the above electrostatic latent image into a visible image,
Transfer charger 35 for transferring the developed visible image to a transfer material
a to 35d and drum cleaners 36a to 36d for removing the toner remaining on the photosensitive drum are sequentially arranged in the drum rotating direction.

The developing device 31a contains yellow toner, and the developing device 31b contains magenta toner.
1c contains cyan toner, and the developing device 31d contains black toner.

In the multicolor electrophotographic copying apparatus having the above-mentioned structure, the photosensitive drums 31a to 3a of the respective image forming stations are provided.
The visible image formed on 1d, that is, the toner images of four colors are fed by a feed roller 38 or the like and sequentially transferred to a transfer material P carried on a transfer belt 37 running endlessly, A full-color image is formed on the transfer material P.

The image forming process by the multicolor electrophotographic copying apparatus having the above-mentioned structure is basically the same as that of the first embodiment, so that it will not be described in detail, but in this embodiment, the primary charger is also used. The total discharge current values of 32a to 32d are set to −800 μA in the electrostatic latent image forming section and −400 μA in the electrostatic latent image non-forming section, respectively.

FIG. 7 shows an operation sequence corresponding to the positions of the photosensitive drums 31a to 31d of the multicolor electrophotographic copying machine in this embodiment. As will be understood with reference to FIG. 7, also in this embodiment, during the time from the start of the image formation sequence to the start of the formation of the electrostatic latent images on the photoconductor drums 31a to 31d, respectively. , The total corona discharge current value of each of the primary chargers 32a to 32d is set to −400 μA.
The total discharge current value is switched to −800 μA again in synchronization with the start of formation of each electrostatic latent image 1a to 31d, and the total discharge current value is again synchronized with the end of formation of the electrostatic latent image. Switch to -400 μA.

By performing the image forming process of the present embodiment as described above, the image unevenness and the photosensitive drums 31a to 31d are also obtained in the present embodiment as in the first embodiment.
It was possible to reduce various problems due to the discharge product without causing problems such as toner adhesion to the above.

The present invention can be suitably implemented, for example, in a monochrome electrophotographic printer as shown in FIG. Next, a third embodiment in which the present invention is applied to the monochrome electrophotographic printer shown in FIG. 8 will be described.

First, the structure and operation of the monochrome electrophotographic printer of FIG. 8 will be briefly described. This type of black and white electrophotographic printer has a photosensitive drum 4 that rotates in the direction of the arrow in the figure.
1 and the image forming means is arranged on the outer periphery thereof. This image forming means may be any means, but in the present embodiment, the charge eliminating lamp 49, the primary charging device 42, the laser beam scanner 43 of the exposing device, the developing device 44, the transfer charging device 4 are used.
5, the cleaner 47 is sequentially arranged in the rotation direction of the photosensitive drum 41. Static elimination lamp 49, primary charger 42,
The toner image formed by reversal development on the photosensitive drum 41 by the operation of the laser beam scanner 43 and the developing device 44 is transferred by the transfer material P fed by the paper feed roller 46 or the like.
At the transfer portion where the photosensitive drum 41 and the photosensitive drum 41 contact each other, the transfer charger 4
By the operation of 5, the transfer is performed on the transfer material P.

FIG. 9 shows an operation sequence corresponding to the position of the photosensitive drum 41 of the electrophotographic printer in this embodiment. In this embodiment, the total discharge current value of the primary charger 42 is set to −750 μA in the electrostatic latent image forming section and −350 μA in the electrostatic latent image non-forming section. As will be understood with reference to FIG. 9, also in this embodiment, the primary charger 4 is provided during the time from the start of the image sequence to the start of the formation of the electrostatic latent image on the photosensitive drum 41.
The total corona discharge current value of No. 2 is set to −350 μA, and subsequently, the discharge current value is switched to −750 μA in synchronization with the start of the formation of the electrostatic latent image on the photoconductor drum 41, and further electrostatic discharge is performed. The total discharge current value switches to −350 μA again in synchronization with the formation of the latent image. Further, as is clear from the continuous printing sequence shown in FIG. 9, when an electrostatic latent image corresponding to continuous printing is formed on the photosensitive drum 41, an electrostatic latent image non-forming section corresponding to each printing is formed. , The discharge current value is −350 μA again.
Switch to.

By performing the image forming process of the present embodiment as described above, as in the first and second embodiments, in this embodiment as well, problems such as image unevenness and toner adhesion to the photosensitive drum are caused. It was possible to reduce various problems caused by the discharge product without causing

In each of the above embodiments, the case where the surface potential of the photosensitive drum is charged to −600 V in the electrostatic latent image forming section has been described, but the present invention is not limited to this, and the photosensitive member is not limited to this. Similar effects can be obtained even when the surface potential of the drum is charged to another different value, for example, -300 V to -900 V in the multicolor electrophotographic copying apparatus described in the above embodiment.

In the above embodiment, the total discharge current value of the primary charger is -800 μA in the electrostatic latent image forming section.
Or -750μA, -400μ in the area without electrostatic latent image formation
Although it is set to A or −350 μA, the present invention is not limited to this and any appropriate value can be adopted according to the configuration of the image forming apparatus according to the present invention.

The surface potential of the photosensitive drum after the primary charging, the surface potential after exposure to the laser beam, the developing bias voltage, etc. in each of the above-described embodiments are applied to both the electrostatic latent image forming section and the electrostatic latent image non-forming section. The values are not limited to the above values, and various values can be taken according to changes in the surrounding environment. Of course, the exposure is not limited to the laser beam exposure.

By the way, in each of the above embodiments, the discharge current value lower than that in the electrostatic latent image forming section is used in the electrostatic latent image non-forming section to reduce the total discharge current amount in the entire image forming process. By reducing the amount of discharge products generated, various problems as described above can be suppressed. Although the image forming apparatus of each of the above-described embodiments operates well, the problem gradually arises by repeating the image forming process many times.

FIG. 11 shows the relationship between the discharge current value of the primary charger and the surface potential of the photosensitive drum. In the image forming apparatus of each of the above-described embodiments, the discharge current value of the primary charger is set to −800 μA (−750 μA in the black and white image forming apparatus) in the electrostatic latent image forming section, and the photosensitive drum is set by the primary charger. It was charged to a surface potential of -600V. The developing bias voltage for forming the developing electric field is −
It is set to 450V and the charging potential of the photosensitive drum is -600.
The difference between V and the developing bias voltage of -450V, 150V, is a fog removing voltage, and the electric field formed by this potential difference always attracts the toner to the developing sleeve and does not adhere to the photosensitive drum.

In the electrostatic latent image non-forming section, the discharge current of the primary charger is set to -400 μA (-350 μA in the black and white image forming apparatus), so that the photosensitive drum is charged to a slightly lower potential. .. In the above embodiment, the electrostatic latent image forming section is charged to -600V, whereas the electrostatic latent image non-forming section is charged to -500V. However,
The developing bias voltage is set to -450V, and the difference between the charging potential of the photosensitive drum and the developing bias voltage is 50.
A developing electric field is not formed by V, and the toner is not developed on the photosensitive drum.

However, as the image forming process is repeated, the surface of the photosensitive drum is abraded by rubbing against a cleaner for removing the residual toner, and the like.
The film thickness decreases. This tendency is particularly remarkable when an organic photoconductor is used as the photoconductor drum. In the image forming apparatus of the above-described embodiment, the photoconductive layer of the photoconductor drum has a film thickness of 10,000 times. By repeating it, it is reduced to about ⅔, and by repeating it 20,000 times, it is reduced to about ⅓. As a result, as shown in FIG. 11, the chargeability of the photosensitive drum is remarkably reduced. For example, by repeating the image forming process 10,000 times, the total discharge current value of the primary charger is -400.
In the electrostatic latent image non-forming section where μA is set, the surface potential of the photosensitive drum drops to about −380 V, and as a result, a developing electric field is formed and toner adheres to the photosensitive drum. There is a possibility that it will occur. Further, the photosensitive drum becomes fatigued by repeating the image forming process, and the dark decay of the surface potential, that is, the attenuation amount of the surface potential from being charged by the primary charger to the developing area is increased. As a result, there arises a problem that the surface potential of the photosensitive drum in the developing area becomes lower than the above-mentioned potential.

Next, even if the image forming process is repeated a very large number of times, various problems due to the discharge products are alleviated without causing the problems such as the image unevenness and toner adhesion to the photosensitive drum. Still another embodiment of the present invention capable of performing will be described.

First, since the fourth embodiment of the present invention is applied to the above-described multicolor electrophotographic copying apparatus shown in FIG. 2, its structure, operation and action are basically as described above. .. Therefore, although these will not be described in detail, in the present embodiment, the photosensitive drum 1 is rotated in the direction of the arrow shown in the figure, and the surface of the photosensitive drum 1 is destaticized by the destaticizing lamp 9 and then the primary charging unit 2 deactivates it. Surface is -300
It was charged to ~ -900V. Further, the surface potential of the photoconductor drum 1 was monitored by the potential sensor 10 and the proper photoconductor drum surface potential was calculated. A laser beam exposure device was used as the exposure means 3. Each of the developing devices 4Y, 4M, 4C, and 4BK of the rotary developing device 4 contains toner of each color having a negative charge, and carries the toner to carry it to a developing area which is in contact with or close to the photosensitive drum 1. Toner is attached to the electrostatic latent image formed on the photosensitive drum 1 by reversal development by a developing electric field formed by a developing bias applied to a developer carrier, for example, a developing sleeve and the potential of the photosensitive drum 1. And visualized.

Further, also in this embodiment, a scorotron type charger as shown in FIG. 5 is used as the primary charger 2, and the discharge amount of the charging line 24 discharged by the high voltage applied from the high voltage power source 20. The grid bias power supply 21
Is controlled by applying a predetermined control voltage to the grid line 26 to charge the surface of the photosensitive drum 1 to a desired potential.

In the multicolor electrophotographic copying apparatus having the above-described structure, in this embodiment, a section where an electrostatic latent image is not formed on the photosensitive drum 1, that is, an electrostatic latent image non-formed section, for example, the transfer material P is used.
During the preparatory steps for image formation such as gripping the transfer drum 5 on the transfer drum 5, or after the first color image exposure is performed to form an electrostatic latent image, the second color image exposure is performed and The total corona discharge current value of the primary charger 2 is set to a value different from the total corona discharge current value in the electrostatic latent image forming section for the section until the formation of the electrostatic latent image. Specifically, the total corona discharge current value in the electrostatic latent image forming section of the primary charger 2 is set to −800 μA, and the total corona discharge current value in the electrostatic latent image non-forming section is set to −250 μA. ..

Moreover, in the present embodiment, with the switching of the total corona discharge current value of the primary charger 2 as described above,
The voltage applied to the grid line 26 of the primary charger 2 (hereinafter,
Switching of the grid bias voltage is also performed. That is, the grid bias voltage value of the primary charger 2 is set to a value different from the grid bias voltage value in the electrostatic latent image forming section in the electrostatic latent image non-forming section. Specifically, for example, when the grid bias voltage value in the electrostatic latent image forming section of the primary charger 2 is set to −550V, the grid bias voltage value in the electrostatic latent image non-forming section becomes −700V. It is set.

FIG. 12 shows an operation sequence corresponding to the positions of the photosensitive drum 1 and the transfer drum 5 in the fourth embodiment of the present invention. As will be understood with reference to FIG. 12, in this embodiment, the total corona discharge of the primary charger 2 during the time from the start of the image forming sequence to the start of formation of the electrostatic latent image. Current value is -250 μA
The grid bias voltage value is-
It is set to 700V. Then, in synchronization with the start of formation of the electrostatic latent image, the total discharge current value of the primary charger 2 is -800 μ.
A, the grid bias voltage value switches to −550V accordingly, and further, the total discharge current value switches to −250 μA again in synchronization with the end of the formation of the electrostatic latent image, and the grid bias accordingly. The voltage value also switches to -700V again. Then, the above steps are repeated until the image formation of four colors is completed.

13 and 14, the transition of the surface potential of the photosensitive drum 1 in this embodiment is shown in FIGS. 13 and 14 to show the total discharge current value of the primary charger 2, the grid bias voltage value and the image forming process. It corresponds and shows. Figure 1
As shown in FIG. 3, in the electrostatic latent image forming section, the photosensitive drum 1 is neutralized by the static elimination lamp 9 until the surface potential becomes almost 0 V, and then the total discharge current is −800 μA and the grid bias voltage is −550 V. It is charged to a surface potential of -600V by the primary charger 2 set to. The developing bias voltage for forming the developing electric field was set to -450V. The difference between the charging potential of the photosensitive drum 1 of −600 V and the developing bias voltage of −450 V is 150 V, which is a fog-removing voltage, and the electric field formed by this potential difference always attracts the toner to the developing sleeve.
It is possible to obtain a good image without fogging in the white part of the image without adhering to the. On the other hand, since the portion of the photosensitive drum 1 corresponding to the image pattern is irradiated with the laser beam with the intensity corresponding to the image density, the potential of the portion exposed by this laser beam drops to a potential lower than the developing bias voltage. The toner adheres to the photosensitive drum 1 by the electric field formed by the developing bias voltage and the photosensitive drum surface potential of the exposed portion, and a toner image is formed. A portion where the surface potential of the photosensitive drum is lowered to -250V by the above image exposure is shown by a dotted line in FIG.

Further, as shown in FIG. 14, in the electrostatic latent image non-forming section, the photosensitive drum 1 is discharged by the discharging lamp 9 until the surface potential becomes almost 0V, and then charged by the primary charger 2. However, the grid bias value is -5
When the voltage is still set to 50 V, the total discharge current value of the primary charger 2 is set to a small value of −250 μA with respect to −800 μA of the electrostatic latent image forming section, so that the battery is charged to a low potential. As indicated by a dotted line in FIG. 14, the electrostatic latent image forming section is charged to −600V, whereas the electrostatic latent image non-forming section is charged to −400V. Under this condition, the developing bias voltage is set to −450V, so that the difference between the charging potential of the photosensitive drum 1 and the developing bias voltage is 5V.
A developing electric field is formed by 0 V, and the toner is developed on the photosensitive drum 1.

Therefore, in this embodiment, the total discharge current value of the primary charger 2 is -800 μA in the electrostatic latent image non-forming section.
Along with the switching from −250 μA to −250 μA, the grid bias value of the primary charger 2 is switched to −700V. As a result, as shown by the solid line in FIG. 14, the surface potential of the photosensitive drum 1 is charged to approximately −600 V even in the electrostatic latent image non-forming section, and the toner does not adhere to the photosensitive drum 1.

[0051] Figure 19 a surface potential of the photosensitive drum 1 to the total discharge current value of the primary charger 2, respectively for the case of changing grid bias voltage value (V _G).
As is clear from FIG. 19, as the grid bias voltage value of the primary charger 2 is increased, the surface potential of the photosensitive drum 1 is also increased. That is, the decrease in the charging ability of the primary charger 2 with respect to the photosensitive drum 1 caused by setting the total discharge current value of the primary charger 2 low can be compensated by setting the grid bias voltage value high.

By the way, reducing the total discharge current value of the primary charger 2 lowers the uniformity of discharge, and increasing the grid bias voltage value equalizes the charging of the photosensitive drum 1 by the grid electrode. Although the effect is reduced, in the present embodiment, as described above, since the switching is performed only in the electrostatic latent image non-forming section, the image formation is not affected.

FIG. 18 shows the photosensitive drum 1 after the image forming process has been performed 20,000 times in the image forming apparatus of this embodiment.
The change of the surface potential of is shown. As shown in FIG. 11 described above, by repeating the image forming process, the photosensitive drum 1
In particular, in the present embodiment, the total discharge current value of the primary charger is −
Since it is set as low as 250 μA, it is more significantly affected, and the surface potential of the photosensitive drum 1 is reduced by about 80 V from the initial level. However, in this embodiment, since the grid bias voltage is switched in accordance with the switching of the total discharge current value, as a result, the surface potential of the photosensitive drum 1 becomes -520 V and the developing bias as shown in FIG. Since the voltage is set to −450V, the developing electric field is not formed yet due to the difference 80V between the charging potential of the photoconductor drum 1 and the developing bias voltage, and the toner is not developed on the photoconductor drum 1 and a good image is obtained. Can keep forming.

Further, in the image forming apparatus of this embodiment, the grid bias value of the primary charger is switched in the electrostatic latent image non-forming area, so that in the electrostatic latent image non-forming area in the first embodiment. The total discharge current value of 1 could be lowered to about -400 μA, but it can be lowered to -250 μA, and the effect can be further enhanced against the above-mentioned problems.

Next, the switching timing of the total discharge current value and the grid bias voltage value of the primary charger 2 will be described in more detail. In this embodiment, the photosensitive member is switched after the total discharge current value is switched. Drum 1
The total discharge current value and the grid bias voltage value are switched earlier in the electrostatic latent image forming section for a time required for the surface potential of the electrode to stabilize, specifically, for a time of 0.2 seconds. ..

As is clear from the above description, in this embodiment, the total discharge current value of the primary charger 2 is set to a value lower in the electrostatic latent image non-forming section than in the electrostatic latent image forming section, and In addition, by setting the grid bias voltage value to a high value, the toner is developed on the photosensitive drum in the electrostatic latent image non-forming section even after the image formation is repeated tens of thousands times, as in the initial state. In the electrostatic latent image forming section without causing a problem, good image formation by uniform and stable charging is performed, and the integrated value of the total discharge current of the primary charger 2 per image forming process is significantly reduced. I was able to suppress it. As a result, the amount of discharge products such as O ₃ and NOx generated by discharge is significantly reduced,
It is possible to suppress the contamination of the discharge electrode and the deterioration of the photosensitive drum 1, and it is possible to prevent the deterioration of the image quality such as the image unevenness which occurs particularly when the image forming process is repeated several thousand times. The service life of the discharge electrode and the photoconductor drum 1 could be greatly extended. Specifically, the replacement life was reached by repeating the image forming process about 8000 times for the photoconductor drum and about 9000 times for the discharge electrode, whereas in the present embodiment, the replacement life was averaged. Body drum about 25,000 times, discharge electrode about 2
The replacement life could be greatly extended to 0000 times.

Further, it is possible to reduce the pollution of the environment by the discharge products as a side effect, and it is also possible to reduce the power consumption. As an example, FIG. 17 shows O ₃ of the ambient environment when the electrophotographic copying apparatus having the above-described configuration is continuously operated.
When the density is set to −800 μA, which is the same as the electrostatic latent image forming section in the total discharge current amount of the primary charger 2 in the electrostatic latent image non-forming section, −400 μA in the embodiment and −25 in the embodiment.
The case of switching to 0 μA is shown below. As understood from FIG. 17, the O ₃ concentration can be further reduced by switching the total discharge current amount according to the present embodiment.

Next, a fifth embodiment of the present invention will be described in which the present invention is applied to the multicolor electrophotographic copying machine having a plurality of photosensitive drums shown in FIG. The structure, operation and action of the multicolor electrophotographic copying apparatus of this embodiment are basically the same as described above, and therefore their explanation is omitted unless necessary. Further, the image forming process is basically the same as that of the above-described fourth embodiment, and therefore will not be described in detail.

In this embodiment, the primary chargers 12a ...
The total discharge current value of 12d is set to −800 μA in the electrostatic latent image forming section and −250 μA in the electrostatic latent image non-forming section, and the grid bias voltage is also set to −550 V and −700 V, respectively. There is.

FIG. 15 shows an operation sequence corresponding to the positions of the photosensitive drums 31a to 31d of the multicolor electrophotographic copying machine in this embodiment. As will be understood with reference to FIG. 15, also in this embodiment, during the time from the start of the image formation sequence to the start of the formation of the electrostatic latent images on the photoconductor drums 31a to 31d, respectively. ,
The total corona discharge current value of each of the primary chargers 32a to 32d is -250 μA, and the grid bias voltage value is -700.
Is set to V, and then the photosensitive drums 31a to 31
The total discharge current value is switched to −800 μA and the grid bias voltage value is switched to −550 V again in synchronization with the start of formation of each electrostatic latent image of d, and further in synchronization with the end of formation of the electrostatic latent image. The total discharge current value switches to −250 μA and the grid bias voltage value switches to −700V again.

By performing the image forming process of the present embodiment as described above, the image unevenness and the photosensitive drums 31a to 31d are also obtained in the present embodiment as in the fourth embodiment.
It was possible to reduce various problems due to the discharge product without causing problems such as toner adhesion to the above.

Next, a sixth embodiment of the present invention in which the present invention is applied to the black and white electrophotographic printer shown in FIG. 8 will be described. The black-and-white electrophotographic printer of this embodiment is basically the same in its configuration, operation and action as described above.
Description of these is omitted unless necessary. Further, the image forming process is basically the same as that of the above-described fourth embodiment, and therefore will not be described in detail.

FIG. 16 shows an operation sequence corresponding to the position of the photosensitive drum 41 of the electrophotographic printer in this embodiment. In this embodiment, the total discharge current value and the grid bias voltage value of the primary charger 42 are −750 μA and −500 V in the electrostatic latent image forming section and −250 μA and −630 V in the electrostatic latent image non-forming section, respectively. It is set. As will be understood with reference to FIG. 16, also in the present embodiment, the total corona of the primary charger 42 during the time from the start of the image sequence to the start of the formation of the electrostatic latent image on the photosensitive drum 41. Discharge current value is -250μ
A, the grid bias voltage value is set to -630 V, and subsequently, the discharge current value is -750 μA and the grid bias voltage value is -500 V in synchronization with the start of the formation of the electrostatic latent image on the photosensitive drum 41. And the total discharge current value is again -2 in synchronization with the completion of the formation of the electrostatic latent image.
50 μA, and the grid bias voltage value switches to −630V. Further, as is clear from the continuous printing sequence shown in FIG. 16, when an electrostatic latent image corresponding to continuous printing is formed on the photosensitive drum 41, an electrostatic latent image non-forming section corresponding to each printing is formed. , The discharge current value switches to −250 μA and the grid bias voltage value switches to −630V.

By performing the image forming process of the present embodiment as described above, also in the present embodiment, various problems caused by the discharge products do not occur without causing problems such as image unevenness and toner adhesion to the photosensitive drum. I was able to reduce the points.

In each of the fourth to sixth embodiments, the surface potential of the photosensitive drum is set to -6 in the electrostatic latent image forming section.
Although the case of charging to 00 V has been described, the present invention is not limited to this, and the surface potential of the photosensitive drum may be another value, for example, the multicolor electrophotographic copying apparatus described in the above embodiment. At -300V to -900V
The same effect can be obtained when charged to the right.

Further, the surface potential of the photosensitive drum is measured,
Calculate the appropriate grid bias voltage value according to the measured value, or the total discharge current of the primary charger according to various parameters such as contrast potential, which is the difference between the light portion potential and the dark portion potential used when forming an image. By controlling the values and the grid bias value to appropriate values, a better effect can be obtained.

In the fourth to sixth embodiments, the total discharge current value of the primary charger is −800 μA in the electrostatic latent image forming section and −250 μA in the electrostatic latent image non-forming section.
However, the present invention is not limited to this, and any appropriate value can be adopted according to the configuration of the image forming apparatus according to the present invention.

The surface potential of the photosensitive drum after primary charging, the surface potential after laser beam exposure, the developing bias voltage, etc. in the fourth to sixth embodiments are the electrostatic latent image forming section,
Both of the electrostatic latent image non-forming sections are not limited to the above values, and can take various values according to changes in the surrounding environment. Of course, the exposure is not limited to the laser beam exposure.

Furthermore, the present invention is equally applicable to various copying machines such as electrophotographic systems and electrostatic recording systems other than multicolor electrophotographic copying machines, and image forming apparatuses such as printers.

[0070]

As is apparent from the above description, in the image forming apparatus according to the present invention, the electrostatic latent image is formed on the image bearing member in at least a part or the entire portion where the electrostatic latent image is not formed on the image bearing member. A discharge current value different from the discharge current value of the corona charger in the section where a latent image is formed, more specifically, a low discharge current value is used to charge the image carrier, so image unevenness and image bearing There is a remarkable effect that problems such as deterioration of the discharge electrode due to corona discharge products, deterioration of the image bearing member, and environmental pollution can be reduced without causing problems such as adhesion of the developer to the body. ..

Further, in the image forming apparatus according to the present invention, at least a part of the section where the electrostatic latent image is not formed on the image carrier or the entire section, corona charging is performed in the section where the electrostatic latent image is formed on the image carrier. Discharge current value different from the discharge current value of the charging device, more specifically, a low discharge current value is used, and the grid bias voltage value of the corona charger corresponding to it is different from the interval for forming the electrostatic latent image, More specifically, since the image carrier is charged by using a high voltage, deterioration of the discharge electrode due to corona discharge products does not occur without causing problems such as image unevenness and adhesion of the developer to the image carrier. There is a remarkable effect that problems such as deterioration of the image bearing member and pollution of the environment can be significantly reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an operation sequence corresponding to positions of a photosensitive drum and a transfer drum in a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic sectional view showing an example of a multicolor electrophotographic copying apparatus to which the present invention can be applied.

FIG. 3 is an explanatory diagram showing a transition of the surface potential in the electrostatic latent image forming section of the photosensitive drum in the first embodiment of the image forming apparatus according to the present invention.

FIG. 4 is an explanatory diagram showing a transition of the surface potential in the electrostatic latent image non-forming section of the photosensitive drum in the first embodiment of the image forming apparatus according to the present invention.

5 is an explanatory view showing a scorotron type charging means used in the multicolor electrophotographic copying machine of FIG. 2. FIG.

FIG. 6 is a schematic configuration diagram showing another example of a multicolor electrophotographic copying apparatus to which the present invention can be applied.

FIG. 7 is an explanatory diagram showing an operation sequence corresponding to the position of the photosensitive drum in the second embodiment of the image forming apparatus according to the present invention.

FIG. 8 is a schematic configuration diagram showing a third embodiment of an image forming apparatus to which the present invention can be applied.

FIG. 9 is an explanatory diagram showing an operation sequence corresponding to the position of the photosensitive drum in the third embodiment of the image forming apparatus according to the present invention.

10 shows the O ₃ concentration in the ambient environment when the multicolor electrophotographic copying apparatus of FIG. 2 is continuously operated and when the multicolor electrophotographic copying apparatus of FIG. 2 to which the present invention is applied is continuously operated. It is a figure.

FIG. 11 is a diagram showing the relationship between the discharge current value of the primary charger and the surface potential of the photosensitive drum in the image forming apparatus according to the present invention.

FIG. 12 is an explanatory diagram showing an operation sequence corresponding to the positions of the photosensitive drum and the transfer drum in the fourth embodiment of the image forming apparatus according to the present invention.

FIG. 13 is an explanatory diagram showing the transition of the surface potential in the electrostatic latent image forming section of the photosensitive drum in the fourth embodiment of the image forming apparatus according to the present invention.

FIG. 14 is an explanatory diagram showing a transition of a surface potential in an electrostatic latent image non-forming section of a photosensitive drum in a fourth embodiment of the image forming apparatus according to the present invention.

FIG. 15 is an explanatory diagram showing an operation sequence corresponding to the position of the photosensitive drum in the fifth embodiment of the image forming apparatus according to the present invention.

FIG. 16 is an explanatory diagram showing an operation sequence corresponding to the position of the photosensitive drum in the sixth embodiment of the image forming apparatus according to the present invention.

17 shows the O ₃ concentration in the ambient environment when the multicolor electrophotographic copying apparatus of FIG. 2 is continuously operated and when the multicolor electrophotographic copying apparatus of FIG. 2 to which the present invention is applied is continuously operated. It is a figure.

FIG. 18 is an explanatory diagram showing the transition of the surface potential in the electrostatic latent image forming section of the photoconductor drum after the end of 20,000 image forming steps in the fourth embodiment of the image forming apparatus according to the present invention.

FIG. 19 is a diagram showing the relationship between the discharge current value and the surface potential of the photosensitive drum when the grid bias voltage value of the primary charger in the image forming apparatus according to the present invention is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Primary charger 3 Exposure means 4 Rotational developing device 5 Transfer device 9 Elimination lamp 10 Potential sensor 31a to 31d Photoconductor drum 32a to 32d Primary charger 33a to 33d Exposure means 34a to 34d Developer 37 Transfer device 41 Photoreceptor Drum 42 Primary Charger 43 Laser Beam Scanner 44 Developer P Transfer Material

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G03G 15/06 101

Claims (8)

[Claims] 1. An electrostatic latent image is formed by exposing the image bearing member to light in a manner corresponding to an image pattern after uniformly charging the image bearing member, and developing the electrostatic latent image. In an image forming apparatus for forming a visible image on the image bearing member, a corona charger is used as a charging unit for charging the image bearing member, and at least a part of a section where an electrostatic latent image is not formed on the image bearing member. Alternatively, in all the sections, the image carrier is charged by using a discharge current value different from the discharge current value of the corona charger in the section where the electrostatic latent image is formed on the image carrier. Forming equipment. 2. In at least a part of or a whole section in which an electrostatic latent image is not formed on the image carrier,
The image forming apparatus according to claim 1, wherein a discharge current value lower than a discharge current value of the corona charger is used in a section where an electrostatic latent image is formed on the image carrier. 3. The image forming apparatus according to claim 1, further comprising a plurality of the image carriers. 4. The image forming apparatus according to claim 1, wherein a corona charger having a grid electrode is used as a charging unit that charges the image carrier. 5. An electrostatic latent image is formed by exposing the image bearing member to light in a manner corresponding to an image pattern after uniformly charging the image bearing member, and developing the electrostatic latent image. In an image forming apparatus for forming a visible image on the image carrier, a section in which a corona charger having a grid electrode is used as a charging means for charging the image carrier and an electrostatic latent image is not formed on the image carrier. In at least a part or all of the area, a discharge current value different from the discharge current value of the corona charger in the area where the electrostatic latent image is formed on the image carrier is used, and at the same time, the electrostatic latent image is formed on the image carrier. An image forming apparatus, wherein the image carrier is charged by using a grid voltage value different from a voltage value applied to a grid electrode of the corona charger in a section where an image is formed. 6. A grid electrode of the corona charger is applied to at least a part of an area where an electrostatic latent image is not formed on the image carrier or the entire area where an electrostatic latent image is formed on the image carrier. The image forming apparatus according to claim 5, wherein a grid voltage value higher than the voltage value to be used is used. 7. A discharge current value of the corona charger in a section in which an electrostatic latent image is formed on the image carrier in at least a part or a whole section in which an electrostatic latent image is not formed on the image carrier. Is used at the same time, a grid voltage value higher than the voltage value applied to the grid electrode of the corona charger is used while the electrostatic latent image is formed on the image carrier. Item 5
Image forming device. 8. The image forming apparatus according to claim 5, further comprising a plurality of the image carriers.