JPH07248709A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent an electrifying roller from being soiled with the retained toner and simultaneously to prolong the service lifes of a photoreceptor and a cleaning blade, when the photoreceptor is stopped for a long period by preventing a stripe toner image from being formed in an area where a cleaning member reaches a cleaning position up to the stoppage of the photoreceptor in its nonimage area. CONSTITUTION:When a copy button is depressed and an image is started to be formed, the voltage of -1400V is applied to the electrifying roller 11 before irradiation for an image exposure 12 is started (an image region) and uniform electrification(-700V) is started on the surface of the photoreceptor 10 and the stripe toner image is formed on the surface of the photoreceptor 10 in the nonimage region before entering the image region by a developing device 13. After the stripe toner image is formed, the irradiation for the image exposure 12 is attained to form an electrostatic charge image corresponding to the image. After the irradiation of the image exposure 12 is completed, the cleaning member 18 comes into contact with the electrifying roller 11 rotated with the movement of the surface of the photoreceptor 10, to clean the surface of the electrifying roller 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer, and more particularly to an apparatus for charging a photosensitive member by bringing a photosensitive member into contact with a charging member to which a predetermined voltage is applied. .

[0002]

2. Description of the Related Art In a conventional device of this type, a predetermined voltage is applied to a roller-shaped semi-conductive member that comes into contact with the surface of the photoconductor and rotates in synchronization with the movement of the surface of the photoconductor, thereby uniformly applying the predetermined voltage. After the electrostatic latent image formed by irradiating the charged photoreceptor surface with image exposure is developed into a toner image by the developing device, the toner image is transferred to the transfer material by the transfer device and the toner remaining on the photoreceptor surface is removed. An image forming apparatus that uses a plate-shaped elastic body that is in contact with the surface of a photoconductor to remove the image is in practical use.

In the following, the roller-shaped semiconductive member will be called a charging roller, and this type of charging method will be called roller charging.

[0004]

However, the above-mentioned conventional technique has the following drawbacks.

In the roller charging type charging device,
Since the charging roller is in contact with the surface of the photoconductor, if foreign matter such as toner adheres to the surface of the charging roller, uniform charging cannot be performed.

On the other hand, after the toner image formed on the surface of the photoconductor is transferred to a transfer material by a transfer device, the toner remaining on the surface of the photoconductor is removed by a plate-like elastic body which is in contact with the surface of the photoconductor. In such an image forming apparatus, a configuration in which a belt-shaped toner image having a predetermined width is formed by a developing device in a non-image area after the start of the movement of the photoconductor surface and before the end of the photoconductor surface is widely used. .

Hereinafter, the plate-shaped elastic member that contacts the surface of the photosensitive member will be referred to as a cleaning blade.

The purpose of forming a band-shaped toner image in the non-image area is to always hold a small amount of toner between the cleaning blade and the surface of the photosensitive member.

When the toner is completely removed between the cleaning blade and the surface of the photoconductor, the frictional resistance between the cleaning blade and the surface of the photoconductor becomes too large, so that the abrasion of the cleaning blade and the surface of the photoconductor is accelerated. Will end up. That is, if the image formation is performed only for an image in which the amount of toner remaining on the surface of the photoconductor after the transfer of the toner image is extremely small, such as an image in which the ratio of black portions in the image is very small, the life of the photoconductor and the cleaning blade is reduced Becomes shorter.

In the image forming apparatus for removing the residual toner on the surface of the photosensitive member by using the cleaning blade, forming a belt-shaped toner image in the non-image area is effective for ensuring the durability of the photosensitive member and the cleaning blade. . In the prior art, in order to always hold a small amount of toner between the cleaning blade and the surface of the photosensitive member, a structure in which a belt-shaped toner image is formed in a non-image area after the image forming area passes is mainly used. It was

In the case where the roller charging type charging device and the structure for forming a belt-shaped toner image in the non-image area are combined, the following serious drawbacks occur.

As in an image in which the ratio of black portions in the image is very large, the amount of toner remaining on the surface of the photoconductor after the transfer of the toner image is extremely large. When an image is formed, an excessive amount of toner is retained between the cleaning blade and the surface of the photoconductor. If left in this state for a long time, the excessive amount of toner adheres to the surface of the photoconductor due to the pressure of the cleaning blade.

Therefore, at the time of the first image formation after being left for a long time, the adhered toner is conveyed to the charging roller portion through the cleaning blade along with the movement of the surface of the photoreceptor, and a part of the adhered toner is charged on the charging roller. Will adhere to the surface of. Therefore, in the subsequent image formation, the surface of the photoconductor cannot be uniformly charged, and the toner image formed on the surface of the photoconductor has uneven density. When the corona discharger is used instead of the charging roller, the wire electrode of the discharger is hardly soiled by the adhered toner.

In order to solve such a drawback, a structure has been proposed in which a member for cleaning the surface of the charging roller is brought into contact with the charging roller. In this structure, the surface of the photosensitive member corresponding to the image area is being charged. However, when the cleaning member is brought into contact with the charging roller, the rotation speed of the charging roller becomes uneven, and as a result, uniform charging cannot be performed.

[0015]

According to the present invention, in an image forming apparatus in which a roller charging system and a blade cleaning system are combined, the non-exposure before the irradiation of the image exposure is started after the movement of the surface of the photoconductor is started. A belt-shaped toner image is formed on the surface of the photoconductor corresponding to the image area, and it is a non-image area of the photoconductor after the irradiation of the image exposure is completed and an area which reaches the cleaning position of the cleaning member before the photoconductor stops. By not forming the belt-shaped toner image, the surface of the photoconductor can be uniformly charged regardless of the state of the image to be formed and the state of being left at the same time, and at the same time, the life of the photoconductor and the cleaning blade can be extended to the maximum.

[0016]

【Example】

[Embodiment 1] FIG. 2 is a sectional view showing the main part of an image forming apparatus according to the present invention. A charging roller 11 in which a cylindrical photoconductor 10 is wrapped around a metal cored bar with a semiconductive elastic material in a cylindrical shape.
By touching and applying a predetermined voltage to the core bar.
The surface of the photoconductor 10 rotating in the direction of is uniformly charged.

The electrostatic latent image formed by irradiating the uniformly exposed surface of the photoreceptor 10 with the image exposure 12 is developed into a toner image by the developing device 13, and the toner image is synchronized by the transfer device 14 with the movement of the toner image. Then, it is transferred to the transfer material 15 that is conveyed. The transfer material 15 on which the toner image is transferred is output to the outside of the device after the toner image is fixed by a fixing device (not shown).
On the other hand, a part of the toner image left on the surface of the photoconductor 10 after the transfer is carried to the cleaning device 16 by the photoconductor 10 rotating as waste toner. The cleaning device 16 is provided with a cleaning blade 17 made of a plate-shaped elastic body so as to come into contact with the photoconductor 10 at a predetermined pressure, and removes waste toner on the surface of the photoconductor 10.

The uniform charging potential on the surface of the photoconductor 10 is -700.
At V, the image exposure 12 irradiates the image white area to the bright area and the image black area to the dark area. To the developing sleeve of the developing device 13, a developing bias in which a DC voltage is superimposed on an AC voltage is applied. A DC voltage of −700 V is applied to the non-image area other than the portion where the belt-shaped toner image is formed, and −2 for the portion where the belt-shaped toner image is formed and the image area.
A DC voltage of 00V is applied. Toner polarity is positive.

The cleaning member on / off device 19 is configured to bring the cleaning member 18 made of felt or the like into contact with or separate from the charging roller 10.

FIG. 1 is a characteristic of the present invention, that is, image formation,
7 shows a timing chart for forming a belt-shaped toner image, cleaning the charging roller, and the like. The horizontal axis of the timing chart of FIG. 1 represents the relative position corresponding to the position of the image formed on the photoconductor 10, and includes the charging roller 11, the image exposure 1
2. The timing shift due to the difference in the arrangement position of the developing device 13 and the like is not included.

As shown in FIG. 1A, when the copying button is pressed and the apparatus starts image formation, the photoconductor 10 starts to rotate. As shown in FIG. 1B, a voltage of −1400 V is applied to the charging roller 11 before the irradiation of the image exposure 12 is started (image area), and the photoreceptor 1
0 surface uniform charging (-700 V) is started. Then, as shown in FIG. 1C, a belt-shaped toner image is formed by the developing device 13 on the surface of the photoconductor 10 in the non-image area before entering the image area. As shown in FIG. 1D, image exposure 12 is irradiated after a belt-shaped toner image is formed, and an electrostatic latent image corresponding to the image is formed. As shown in (e) of FIG. 1, after the irradiation of the image exposure 12 is completed, the cleaning member 18 contacts the charging roller 11 that rotates as the surface of the photoconductor 10 moves, and cleans the surface of the charging roller 11. . If the charging roller is cleaned in an area before the image forming area of the photoconductor, the first copy time becomes long, so it is preferable to clean the charging roller in an area after the image forming area. Further, if the charging roller is cleaned while the voltage is being applied to the charging roller, it cannot be satisfactorily performed due to the electrostatic force between the charging roller and the adhered toner. Therefore, it is preferable to clean the charging roller after turning off the voltage applied to the charging roller.

According to this embodiment, even when an image is formed in which the amount of toner remaining on the surface of the photosensitive member after the transfer of the toner image is extremely small, the belt-shaped toner image formed before the irradiation of the image exposure is cleaned by the cleaning blade. The life of the cleaning blade and the photosensitive member carried between the surface of the photosensitive member and the photosensitive member is not shortened.

According to the present embodiment, even when an image having a remarkably large amount of toner remaining on the surface of the photoconductor after the transfer of the toner image is formed, the toner is left between the cleaning blade and the surface of the photoconductor after the irradiation of the image. Since there is a time for the photoconductor to rotate without being transported, the amount of toner retained between the cleaning blade and the photoconductor will be an appropriate amount, and the toner will be charged even during the first image formation after being left for a long time. The roller does not become soiled with toner and cause poor charging.

According to this embodiment, since the cleaning member of the charging roller contacts the charging roller after the electrostatic latent image is formed,
The uneven rotation of the charging roller does not cause a defect in the image.

The width of the belt-shaped toner image is from 0.3 mm to 10 mm.
mm is desirable.

[0026]

As described above, according to the present invention, in the image forming apparatus in which the roller charging method and the blade cleaning method are combined, before the irradiation of the image exposure is started after the movement of the surface of the photoconductor is started. A belt-shaped toner image of a predetermined width is formed on the surface of the photoconductor corresponding to the non-image area by the developing device, and the non-image area of the photoconductor after the irradiation of the image exposure is completed and before the photoconductor stops. By not forming the belt-shaped toner image in the area reaching the cleaning position of the cleaning member, the surface of the photoconductor can always be uniformly charged regardless of the state of the image to be formed and the state of being left, and at the same time, the photoconductor and the cleaning blade The life can be maximized.

[Brief description of drawings]

FIG. 1 is a timing chart of an image forming operation that best represents the features of the present invention.

FIG. 2 is a cross-sectional view of main parts of the image forming apparatus according to the first exemplary embodiment.

[Explanation of symbols]

 10 Photoconductor 11 Charging Roller 12 Image Exposure 13 Developing Device 14 Transfer Device 15 Transfer Material 16 Cleaning Device 17 Cleaning Blade 18 Cleaning Member 19 Cleaning Member On / Off Device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuka Abe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (1)

[Claims] 1. An electrostatic latent image formed by applying a predetermined voltage to a charging member, which is in contact with the surface of a photosensitive member, and irradiating the uniformly charged surface of the photosensitive member with image exposure is converted into a toner image by a developing device. In the image forming apparatus, after the development, the toner image is transferred to the transfer material by the transfer device and then the toner remaining on the surface of the photoconductor is removed by the cleaning member in contact with the surface of the photoconductor.
A belt-shaped toner image is formed on the surface of the photoconductor corresponding to the non-image area before the irradiation of the image exposure is started after the movement of the surface of the photoconductor is started. An image forming apparatus, wherein the belt-shaped toner image is not formed in an area which reaches a cleaning position of the cleaning member in the image area and before the photoreceptor stops.