JPH0792811A - Developing device and image forming device provided with the same - Google Patents

Abstract

PURPOSE:To provide a developing device which is a simple structure and carries out development satisfactorily without causing omission of the rear end of an image and a decrease in image density, and an image forming device provided with the developing device. CONSTITUTION:The developing device is equipped with a magnet roller 16 which is provided opposite to a photosensitive drum 1, disposes a plurality of magnetic poles 17-22 in its circumferential direction, and forms a developer magnetic-brush, and a non-magnetic sleeve 23 which is fitted over the periphery of the magnet roller 16, slides the developer magnetic-brush against the photosensitive drum 1 by its rotation, and has an outside diameter of 30mm or more. Out of the magnetic poles 17-22 of the magnet roller 16, the magnetic pole which is positioned opposite to the photosensitive drum 1 serves as the main magnetic pole 17 and its width is 6 mm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a developing device provided in an electrophotographic apparatus for supplying a two-component developer consisting of toner and carrier, and an image forming apparatus equipped with this developing apparatus.

[0002]

2. Description of the Related Art Generally, a developing device of this type includes a magnet roller having four to five or more ferrite magnets, and a non-magnetic sleeve rotatably attached to the magnet roller. The developing roller is composed of

A magnetic brush of developer is formed on the sleeve of the developing roller by a magnetic force, and the sleeve is rotated to slide the magnetic brush of the developer onto the latent image on the photosensitive member. It is designed to come into contact with each other for development.

The developing method using the magnetic brush has relatively good image quality and is one of the most widely used developing methods.

By the way, in the developing method using the magnetic brush of the two-component developer, an appropriate speed ratio between the magnetic brush and the photoconductor is set mainly in order to secure the image density and reduce the fog in the non-image area. There is a need.

Usually, it is 1.5 with respect to the rotational speed of the photoconductor.
It is necessary to rotate the sleeve of the developing roller at a speed of about 2.5 times.

Therefore, if the rotation speed of the photoconductor is increased to improve the copying speed, the developing roller must be further increased in speed, and the rotation speed becomes too high for a developing roller having a small diameter, resulting in toner scattering. Problems such as occur.

For this reason, it is necessary to design the developing roller with an appropriate diameter. For example, in an electrophotographic apparatus having a copying speed of 30 or more sheets of A4 size paper per minute, a developing roller having a diameter of 30 mm or more is required. It was

In order to carry the developer satisfactorily with such a developing roller having a diameter of 30 mm or more, it is necessary to optimize the magnetic force, width, angle and the like of the ferrite magnet of each pole. Also in the main magnetic pole, which is the region, a magnetic body having an appropriate magnetic force and a width of 10 mm or more is usually used.

However, as described above, when the main magnetic pole having the width dimension of 10 mm or more is used, the spike width of the magnetic brush becomes wide, and particularly in the reversal development, the magnetic brush is formed at the trailing edge of the image. Since the toner hits the non-image portion having the same polarity as the toner and a high potential, the toner comes into sliding contact with the latent image portion, which hinders the development and causes the trailing edge of the image to be chipped.

Therefore, in order to solve this problem, in the prior art, the peripheral speed ratio between the photoconductor and the developing roller is reduced, or the developer layer thickness is reduced, or the photoconductor and the developing roller are reduced. Measures such as widening the distance from the roller were taken.

[0012]

However, in any of the above-mentioned methods, there is a problem that the image density is lowered, and it is difficult to set proper conditions.

In view of the above, the present invention has a simple structure, but a developing device and an image forming apparatus equipped with the developing device, which can develop favorably without causing trailing edge chipping of an image or reducing the image density. The purpose is to provide.

[0014]

In order to solve the above-mentioned problems, the present invention is directed to an image bearing member carrying an electrostatic latent image, and a plurality of magnetic poles are provided in the circumferential direction to form a developer. A magnetic brush forming means for forming a magnetic brush, and a magnetic brush of the developer, which is attached to the outer peripheral portion of the magnetic brush forming means and is rotated, is brought into sliding contact with the image carrier to form the electrostatic latent image. And a non-magnetic rotating body having an outer diameter of 30 mm or more, wherein a magnetic pole facing the image carrier among a plurality of magnetic poles of the magnetic brush forming means is a main magnetic pole. The width of the main pole is 6 mm or less. Further, an image carrier for carrying an image, an image forming means for forming an electrostatic latent image on the image carrier, and a plurality of magnetic poles provided facing the image carrier are arranged in the circumferential direction. A magnetic brush forming means for forming a magnetic brush of the developer, and the magnetic brush of the developer is attached to the outer peripheral portion of the magnetic brush forming means and is rotated to bring the magnetic brush of the developer into sliding contact with the image bearing member. An image developing device, comprising a non-magnetic rotating body having an outer diameter of 30 mm or more, and a magnetic pole facing a plurality of magnetic poles of the magnetic brush forming means is a main magnetic pole. The width of the main pole is 6 mm or less.

[0015]

By setting the outer diameter of the rotor attached to the outer peripheral portion of the magnetic brush forming means to 30 mm or more and the width of the main magnetic pole to 6 mm or less, the sharpness of the magnetic brush is sharpened. To This prevents the magnetic brush from hitting the high-potential non-image portion having the same polarity as the developer at the trailing edge of the image and slidingly contacting only the latent image portion, thereby preventing occurrence of the trailing edge chipping of the image.

[0016]

The present invention will be described below with reference to an embodiment shown in the drawings.

FIG. 2 shows the internal construction of the electrophotographic apparatus. In the figure, reference numeral 1 is a photosensitive drum as an image bearing member which is rotatable in the direction of the arrow.

A charging charger 2 for uniformly charging the surface of the photosensitive drum 1 along the rotation direction of the peripheral portion of the photosensitive drum 1, and an exposure system 1 as an image forming means.
A developing device 4 for developing the latent image formed by 2; a transfer charger 5 for transferring the image on the photosensitive drum 1 onto a sheet; a peeling charger 6 for peeling the image-transferred sheet from the photosensitive drum 1; A cleaning device 7 for removing the toner remaining on the photosensitive drum 1 is provided.

Reference numeral 8 in the drawing denotes a paper transport path for transporting paper, and a paper feed roller 9 for feeding the paper, a registration roller 10 for aligning the paper, the transfer and peeling described above in the paper transport path 8. Chargers 5 and 6 and a conveyor belt 11 that conveys a sheet are provided.

However, during image formation, the surface of the photosensitive drum 1 is uniformly charged by the charging charger 2.
The charged surface of the photosensitive drum 1 is exposed to form an electrostatic latent image. This electrostatic latent image is sent to the developing device 4 by the rotation of the photosensitive drum 1, and the developer is supplied by the magnetic brush described later to be visualized.

On the other hand, at this time, a sheet is fed from a sheet feeding section (not shown) by the rotation of the sheet feeding roller 9, the sheet is aligned by the registration roller 10, and then the photosensitive drum 1 and the transfer charger are aligned. It is sent between -5 and. Here, the visible image on the photoconductor drum 1 is transferred to the sheet by the action of the transfer charger 5, and after this transfer, it is peeled from the photoconductor drum 1 by the action of the peeling charger 6. After the peeling, the toner remaining on the photosensitive drum 1 is removed by the cleaning device 7 and cleaned. After this cleaning, the photosensitive drum 1 is charged again, and the above process is repeated.

By the way, the developing device 4 includes the developing container 13
The developing container 13 contains a two-component developer t composed of a toner and a carrier. further,
In the developing container 13, a developing roller 14 is rotatably provided so as to face the photosensitive drum 1, and a carrying auger 15 for carrying the developer t is rotatably provided. Has been done.

The developing roller 14 is, as shown in FIG. 1, a magnet roller 1 which constitutes a magnetic brush forming means.
6 and a plurality of magnetic poles 17 to 22 arranged in the magnet roller 16 in the circumferential direction. Of the plurality of magnetic poles 17 to 22, the magnetic pole 17 facing the photosensitive drum 1 is the main magnetic pole (hereinafter, magnetic pole 1).
7 is called the main pole). A sleeve 2 as a non-magnetic rotating body is rotatably provided on the outer periphery of the magnet roller 16 described above.
3 is worn.

The outer dimension of the sleeve 23 of the developing roller 14 is 30 mm, and the main pole 17 of the developing roller 14 is
Has a width h of 6 mm or less.

At the time of development, the non-magnetic sleeve 23 of the developing roller 14 is rotated and a magnetic brush 25 as shown in FIG. 3 is formed between the plurality of magnetic poles 17 to 22. The magnetic brush 25 is brought into sliding contact with the electrostatic latent image on the photosensitive drum 11 by the rotation of the non-magnetic sleeve 23 to develop the image.

By the way, in reverse development using negatively chargeable toner and carrier as a developer, the copying speed is set to 30 sheets per minute (A4), and the extreme width is 10 mm in order to prove the effect of the present invention on the developing device side. , 8 mm, 6 mm, or 38 mm diameter consisting of 5 pole ferrite magnet with 4 mm main pole
Image development evaluation was performed using the developing roller of FIG.
It was as shown in.

That is, the image density has an extreme width of 10 mm and 8
mm, 6mm, or even 4mm of the main pole,
Although the width is constant, the width of the trailing edge of the image is 6 mm
If it is above, the level rises sharply, and the trailing edge chipping level by visual observation sharply deteriorates. However, the pole width of the main pole is 6
If it is less than or equal to mm, the width of occurrence of the trailing edge chipping of the image is small,
Further, the trailing edge chipping level by visual observation becomes a good level.

FIG. 5 shows a magnetic brush 32 using a conventional main magnetic pole 31 having a width of 10 mm. The magnetic brush 32 has the main magnetic pole 17 having a width of 6 mm shown in FIG. The width is wider than that of the magnetic brush 25 when used, and at the time of development, the rear end of the image hits a non-image portion having the same polarity as the toner and a high potential, and development is hindered and the rear end of the image is chipped.

As described above, in the present invention, in the two-component magnetic brush developing system in which the developing roller 14 has a diameter of 30 mm or more, the main pole width is set to 6 mm or less.
The spikes of the magnetic brush can be sharpened, and even in the case of reversal development, the magnetic brush 25 does not hit the non-image portion of high potential having the same polarity as the toner at the trailing edge of the image, and is directly slid on the latent image portion. Contact and develop.

Therefore, the development is not hindered, and the rear edge of the image can be prevented from being chipped.

[0031]

As described above, according to the present invention, the outer size of the rotor is set to 30 mm or more, and the width of the main pole is set to 6 mm.
From the following, it is possible to sharpen the spikes of the magnetic brush of the developer, while maintaining the image quality such as image density,
The effect that the trailing edge chipping of the image can be remarkably improved is obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a magnetic pole of a developing roller which is an embodiment of the present invention.

FIG. 2 is an internal configuration diagram of an electronic copying machine including the developing roller of FIG.

FIG. 3 is an explanatory diagram showing a magnetic brush formed by the developing roller of FIG.

FIG. 4 is a graph showing changes in image density, trailing edge application width, and trailing edge application level when the main pole width of the developing roller of FIG. 1 is changed.

FIG. 5 is an explanatory view showing a magnetic brush formed by a conventional developing roller.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (image carrier), 12 ... Exposure system (image forming means), 16 ... Magnet roller (magnetic brush forming means), 17 to 22 ... Magnetic pole, 23 ... Sleeve (rotating body),
25 ... Magnetic brush.

Claims (2)

[Claims] 1. A magnetic brush forming means which is provided so as to face an image bearing member carrying an electrostatic latent image, and which has a plurality of magnetic poles arranged in a circumferential direction to form a magnetic brush of a developer, and a magnetic brush. The electrostatic latent image is developed by being attached to the outer peripheral portion of the forming means and being rotated so that a magnetic brush of the developer is brought into sliding contact with the image carrier to develop the electrostatic latent image. A non-magnetic rotating body, which has a width of 6 mm, and the main magnetic pole is a magnetic pole facing the image carrier among a plurality of magnetic poles of the magnetic brush forming means.
A developing device characterized by being set to mm or less. 2. An image forming unit for forming an electrostatic latent image on an image carrier, and a plurality of magnetic poles provided facing the image carrier in the circumferential direction to form a magnetic brush of developer. And a magnetic brush forming unit that is attached to the outer peripheral portion of the magnetic brush forming unit and rotates to bring the magnetic brush of the developer into sliding contact with the image carrier to develop the electrostatic latent image. And a non-magnetic rotating body having an outer diameter of 30 mm or more, wherein a magnetic pole facing the image carrier among the plurality of magnetic poles of the magnetic brush forming means is a main magnetic pole, and a width dimension of the main magnetic pole. 6
An image forming apparatus having a size of less than or equal to mm.