JPH08305127A - Charger for image forming device - Google Patents

Abstract

PURPOSE: To achieve the uniform charge on the periphery of a photoreceptor by preventing toner and the like from sticking to a charging brush. CONSTITUTION: The device is provided with a shield member 21 which slides on the periphery of the photoreceptor 2 on the upstream side of the charge brush 11 in the direction of the rotation, thereby preventing toner and the like (T, D, etc.) stuck to the periphery of the photoreceptor 2 from coming into contact with the charge brush 11. Additionally, the shield member 21 is charged at the same polarity as that of the charge brush 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for an image forming apparatus having a charging brush capable of slidingly contacting a peripheral surface of a photoconductor rotating in one direction and charging the peripheral surface.

[0002]

2. Description of the Related Art FIG. 2 shows a schematic structure of an image forming apparatus incorporating a conventional charging device. In the figure, reference numeral 2 denotes a cylindrical photoconductor, which is rotationally driven in the clockwise direction (arrow R direction) in the figure. A photosensitive layer is formed on the peripheral surface of the photoconductor 2.

Reference numeral 10P denotes a charging device, which is a plate-shaped brush holder 12 extending in the axial direction of the photoconductor 2 (direction orthogonal to the drawing sheet), and is in sliding contact with the peripheral surface of the photoconductor 2 held by the holder 12. And a conductive charging brush 11 capable of charging the peripheral surface with a high voltage (for example, -5 kV) to the charging brush 11.
And a high-voltage power supply device (15) for applying

Specifically, as shown in FIG. 3, the charging brush 11 is held by the brush holder 12 so that the amount L of bite of the upstream portion 11a of the photosensitive member 2 and the tilt angle θ are, for example, 1 mm and 82 °. Has been done. The peripheral surface of the photoconductor 2 is uniformly charged (e.g., charging potential -530V) by discharging from the tip of the charging brush 11. In FIG. 2, 3 is an exposure device, 4 is a developing device,
Reference numeral 5 is a transfer device, and 6 is a fixing device.

When a printing operation is performed using the image forming apparatus, the peripheral surface of the photoconductor 2 is uniformly charged by the charging device 10P, and then the laser beam (B) based on the print data from the exposure device 3 is supplied. ) Irradiation forms an exposed portion (electrostatic latent image). The potential of the exposed portion is, for example, −50V,
The potential of the unexposed portion remains the charged potential.

Therefore, when the exposed portion moves to the developing position, the toner to which the developing bias potential (for example, -500V) is applied from the developing roller 4a of the developing device 4 is attracted by the electric field action to form a toner image. To be done. Since the absolute value of the potential of the unexposed portion is larger than the developing bias potential, toner is not adsorbed. The toner image is transferred onto the sheet P by the transfer device 5, and then fixed by the fixing device 6.

[0007]

By the way, in the above charging device 10P, when a printing operation or the like is performed for a long period of time, toner (T), paper dust (D) or the like (toners) adheres to the tip of the charging brush 11. Discharge failure occurs, and as a result, the photoconductor 2
In some cases, the peripheral surface of the sheet cannot be uniformly charged, and printing defects may occur. For example, black streaks may occur on the white background of the printing paper due to the charging brush 11, or uneven printing may occur.

In view of the above circumstances, an object of the present invention is to provide a charging device for an image forming apparatus capable of preventing toners from adhering to the charging brush and uniformly charging the peripheral surface of the photoconductor. Especially.

[0009]

According to a first aspect of the present invention, there is provided a charging device for an image forming apparatus, comprising a charging brush capable of slidingly contacting a peripheral surface of a photoreceptor rotating in one direction and charging the peripheral surface. It is characterized in that a shield member is provided which can slidably contact the peripheral surface portion of the photoconductor on the upstream side of the charging brush in the rotational direction and prevent the toners adhering to the peripheral surface of the photoconductor from contacting the charging brush. .

The invention of claim 2 is characterized in that the shield member is charged to the same polarity as the charging brush.

[0011]

According to the invention of claim 1 having the above-mentioned structure, when the photosensitive member is rotated in one direction, the toners attached to the peripheral surface of the photosensitive member are synchronously rotated, but they are separated from the peripheral surface of the photosensitive member by the shield member. Contact with the charging brush is prevented.
This prevents toners from adhering to the charging brush, and the peripheral surface of the photoconductor can be uniformly charged.

According to the second aspect of the present invention having the above-mentioned structure, even if the toner may pass between the shield member and the peripheral surface of the photoconductor as the photoconductor rotates, the toner is protected by the shield member. It is charged to the same polarity as the charging brush. Therefore, the toners do not repel and adhere to the charging brush, and the toners can be more reliably prevented from adhering to the charging brush.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. The charging device of the image forming apparatus is as shown in FIG.
Although the basic configuration is similar to that of the conventional example (FIGS. 2 and 3), a shield member 21 is provided, and toners (toner T, paper dust D, etc.) attached to the peripheral surface of the photoconductor 2 are charged by the charging brush. It is configured to prevent contact with 11.

The same components as those of the conventional example (FIGS. 2 and 3) are designated by the same reference numerals, and the description thereof will be simplified or omitted.

Toners (T, D, etc.) adhering to the peripheral surface of the photosensitive member 2 are slidably brought into contact with the peripheral surface portion of the photosensitive member 2 on the upstream side of the charging brush 11 in the rotational direction (R direction) of the shield member 21. A means for preventing contact with the charging brush 11, an insulator (for example, knit # 500) 24 and a fixture 25.
It is attached to the brush holder 12 via.

In this embodiment, the shield member 2
1 is formed to be conductive. That is, the photoconductor 2
Coated with a mixture of carbon on a plate-shaped urethane surface having a length approximately the same as the resistance of 10 ^-3 Ω.
It is formed so as to be less than or equal to cm. The shield member 21 has a bite amount L1 of 0.
It is attached to the brush holder 12 so as to have a thickness of 5 to 1 mm.

As a result, the shield member 21 tilts as shown by the solid line in FIG. 1 with the rotation of the photosensitive member 2 in one direction (R direction) and comes into contact with the upstream portion 11a of the charging brush 11, and the tip portion thereof. It is pressed against the peripheral surface of the photoconductor 2. Therefore, during the printing operation, the shield member 21
It is charged to the same polarity as the charging brush 11 (negative charging in this embodiment). When printing is stopped, in which the rotation of the photoconductor 2 is stopped, the photoconductor 2 is not in contact with the charging brush 11 and is insulated.

Next, the operation of this embodiment will be described. When the photoconductor 2 is rotated in one direction (R direction), the toners (T, D, etc.) attached to the peripheral surface of the photoconductor 2 are synchronously rotated, but are separated from the peripheral surface of the photoconductor 2 by the shield member 21. Therefore, the contact with the charging brush 11 is prevented. This prevents toner (T, D, etc.) from adhering to the charging brush 11 and uniformly charges the peripheral surface of the photoconductor 2.

At this time, even if toners (T, D, etc.) may pass between the shield member 21 and the peripheral surface of the photosensitive member 2, the toners (T, D, etc.) are shielded. 21 is charged to the same polarity as the charging brush 11 (negative charging). Therefore, the toners (T, D, etc.) do not repel and attach to the charging brush 11, and more reliably prevent the toners (T, D, etc.) from attaching to the charging brush 11. You can

According to this embodiment, however, since the shield member 21 is provided on the upstream side of the charging brush 11, the toners (T, D, etc.) adhering to the peripheral surface of the photoconductor 2 are transferred to the charging brush 11. It is possible to prevent contact. Therefore, the toner (T, D, etc.) can be prevented from adhering to the charging brush 11 and the peripheral surface of the photoconductor 2 can be uniformly charged.

Further, the shield member 21 is the charging brush 11.
Since it is charged to the same polarity as the
Etc.) passes between the shield member 21 and the charging brush 11, since the toners (T, D, etc.) are charged to the same polarity as the charging brush 11 by the shield member 21, Repulsive and does not adhere. Therefore, it is possible to more reliably prevent toner (T, D, etc.) from adhering to the charging brush 11.

The shield member 21 is attached to the brush holder 1
Since it is mounted on No. 2, the positioning with respect to the charging brush 11 can be accurately performed and the configuration can be simplified. Since the shield member 21 is electrically insulated from the brush holder 12, abnormal discharge or the like does not occur and the peripheral surface of the photoconductor 2 can be more surely charged uniformly.

Further, the shield member 21 is attached to the charging brush 1.
Since the brush 11 is charged with the same polarity as that of the brush 11, it is not necessary to use a dedicated power supply device or the like, and the configuration can be further simplified (downsized) and the cost can be reduced.

In the above embodiment, the shield member 21 was charged by contacting it with the charging brush 11, but it may be charged by using, for example, a dedicated power supply device.

[0025]

According to the first aspect of the invention, the shield member can prevent the toner attached to the peripheral surface of the photoconductor from coming into contact with the charging brush. Therefore, it is possible to prevent the toners from adhering to the charging brush and uniformly charge the peripheral surface of the photoconductor.

According to the second aspect of the present invention, even if the toners pass between the shield member and the peripheral surface of the photoconductor due to the rotation of the photoconductor, they are charged to the same polarity as the charging brush, and therefore repelled. However, the adhesion to the brush can be prevented more reliably.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an example of the present invention.

FIG. 2 is a diagram for explaining an overall configuration of an image forming apparatus incorporating a conventional charging device.

FIG. 3 is a diagram for explaining a conventional charging device.

[Explanation of symbols]

 2 Photoconductor 11 Charging brush 12 Brush holder 21 Shield member 24 Insulator

Claims (2)

[Claims] 1. A charging device of an image forming apparatus, comprising a charging brush capable of slidingly contacting a peripheral surface of a photoconductor rotating in one direction and charging the peripheral surface, wherein the photosensitive member on the upstream side in the rotation direction of the charging brush. 2. A charging device for an image forming apparatus, comprising: a shield member capable of preventing toners attached to the peripheral surface of the photoconductor from slidingly contacting the peripheral surface portion and contacting the charging brush. 2. The charging device for an image forming apparatus according to claim 1, wherein the shield member is charged with the same polarity as the charging brush.