JPS61212865A - Developing device - Google Patents

Abstract

PURPOSE:To execute the time attenuation correction of each color latent image with a simple constitution and to obtain a picture having an excellent density by constituting a clearance between the developer carriers of plural developing units and a layer thickness regulating member so that the unit at the downstream side can be larger than that at the upstream side. CONSTITUTION:Plural developing units 3A and 3B of the same structure are disposed along a photosensitive body, and a magnet 24 and a developing sleeve 26 comprise a developing roll 22. A toner 30 is attracted on the surface of the sleeve 26 by the magnet 24, and is thinned to the prescribed thickness of a layer by a magnetic blade 32. In terms of clearance l between the sleeve 26 and the blade 32 with respect to the photosensitive body, the clearance of the developing unit at the downstream side is larger than that at the upstream side. Accordingly, when the clearance l is set larger, an appropriate density can be obtained even if the contrast potential of the photosensitive body is small, and its dark attenuation can be compensated with a far simple constitution.

Description

Detailed Description of the Invention Field of the Invention The present invention relates to a developing device having a plurality of developing units, and generally relates to a black and white electrophotographic copying device, a color electrophotographic copying device, or a computer output unit. It is effective as a developing device for color recording devices, etc., and is especially suitable for use in electrophotographic copying devices for two or more monochromatic colors, so-called multicolor, and even for full-color electrophotographic copying devices. This invention relates to a color developing device.

Recently, the demand for color copying has increased rapidly not only in specialized fields but also in general office fields, and there is a desire for improved quality of color copied images and low-cost copying devices.

One of the important problems to be solved in order to meet such demands is how to use the developing device that visualizes the electrostatic latent images of each color formed on the object to be developed, that is, the latent image carrier, in a color copying apparatus. There is a way to configure it.

In the past, various means have been proposed as developing devices for color electrophotographic copying devices, but the developing devices that are currently in widespread use include a plurality of developing devices each having a developer of each color along the surface of a latent image carrier. This is a side-by-side type developing device in which two developing units are arranged in parallel. In normal commercially available electrophotographic copying devices,
Since the latent image carrier is usually a cylindrical photosensitive drum, the developing units of the developing device are arranged close to the surface of the photosensitive drum and arranged in parallel along the circumferential direction of the photosensitive drum. .

A8 Problems that the company aims to solve According to such a side-by-side developing device, it is only necessary to sequentially arrange developing units having a plurality of different color developers around the photosensitive drum, which simplifies the structure. However, according to this type of developing device, multiple developing units are sequentially arranged around the photosensitive drum, so even though the latent image formation position of each color on the photosensitive drum is fixed, First, the development position by the development unit of each color is different, therefore the time until the latent image of each color is developed is different, the time decay of the latent image of each color is different, and the image density varies depending on the position of the development unit used for development. The problem was that it changed. Similarly, even in a developing device that has a plurality of developing units of the same color and has an increased developing capacity, there is a problem in that the image density changes depending on the developing unit used.

For this purpose, time decay correction of each color latent image, that is, time decay correction of the latent image depending on the developing unit used is required. Such correction work is not technically simple and complicates the overall structure and control 71u of the developing device and the copying device.

To explain further by citing an example, FIG. 2 is a schematic cross-sectional view of a color electrophotographic copying apparatus for obtaining two-color images of black and red to which a conventional multi-color developing device is applied.

A latent image carrier 1, which in this case is a photosensitive drum having an electrophotographic photosensitive layer formed on its surface, is arranged approximately at the center of the copying apparatus. The photosensitive drum 1 is rotatably and detachably attached to a rotation support shaft (not shown) having a rotation center O in a well-known manner, and rotates in the direction of the arrow, that is, clockwise in FIG. 2.

A primary charger 2 is located approximately directly above the photosensitive drum 1, a multicolor developing device 3 is located on the right side of the photosensitive drum 1 in FIG. 2, and a transfer discharger 8 and a photosensitive drum 1 are located approximately directly below the photosensitive drum 1. A cleaning device 9 is disposed on the left side in FIG. Further, an optical system 5 is disposed above the electrophotographic copying loader, and the original image is transferred onto the photosensitive drum 1 at an exposure section 4 located between the primary charger 2 and the multicolor developing device 3. configured to project. Optical system 5 can use any optical system. Further, between the exposure position 4 and the developing device 3, a blank exposure device 6 for erasing charges in unnecessary parts outside the image area and a potential sensor 7 for measuring the surface potential of the photosensitive drum 1 are provided. A light source 10 is provided between the secondary charger 2 and the cleaning device 9 for erasing residual charges on the photosensitive drum 1 if-.

As mentioned above, the color copying machine described here is black,
Since it is a color electrophotographic copying apparatus for obtaining a red two-color image, the multicolor developing device 3 includes developing units) 3A and 3B.
It has two developing units.

In the above configuration, the diameter of the photosensitive drum 1 is 120'm.
' m, and the terminal point of primary charger 2 is point A,
It is assumed that the development point of the first development unit) 3A is point B, the development point of the second development unit) 3B is 0 point, and the angle AOB=60° and the angle AOC=115°. In such a configuration, the surface peripheral speed of the photosensitive drum 1 is 250 mm/
When s e c, the surface potential at point A is +525v
Even if it is charged so that B
Approximately +400V and +30V at point and 0 point respectively
If the voltage drops to 0V and the same developing unit is used to develop under the same conditions, the density of the second developing unit will be lower than that of the first developing unit.

For example, when using a developing device that can obtain an appropriate image when the difference in surface potential between a dark place (black background) and a bright place (white background), that is, the contrast VC is 250 V, the above example explains. Then, the potential Vl in the bright place is about +5 due to the residual charge.
0V, and +150V (= V +
A bias potential of 100v) is applied. Therefore, at point B, the contrast is 1 to 250V, and a proper image can be obtained, but at point C, the contrast is 1 to 250V.
= 150 V, resulting in the inconvenience that an image with an appropriate density cannot be obtained.

Therefore, the main object of the present invention is to provide a developing device that can perform time decay correction for images of each color layer and obtain images of good density without requiring any special equipment. .

Another object of the present invention is to provide a multi-color developing device equipped with a plurality of developing units, which has a simple structure and can always produce high-quality color copies.

Measures to Solve the Problems] The above objects are completely achieved by the multicolor developing device according to the present invention. To summarize the present invention, the present invention provides a developing device in which a plurality of developing units are arranged along a latent image carrier to develop an electrostatic latent image on the surface of the latent image carrier. Comparing the gap between the developer layer thickness regulating member and the developing unit in any two developing units, the developing unit located on the downstream side is larger than the developing unit located on the first stream side in the rotational direction of the latent image carrier. This is a developing device characterized by the following.

As mentioned above, the uninvented developing device can be suitably used in a multi-color or full-color electrophotographic copying device, a color recording device for a computer output section, etc., but the developing device shown in FIG. The present apparatus will be described as being applied to a color electrophotographic copying apparatus for obtaining two-color black and red images.

Since the color copying apparatus described here is a color electrophotographic copying apparatus for obtaining two-color images of black and red as described above, the multicolor developing device 3 includes two developing units, ie, developing units 3A and 3B. However, the present invention is not limited to this configuration, and it is also possible to have three or more developing units.

To briefly explain the image forming process of the electrophotographic copying apparatus shown in FIG. 2, an electrostatic latent image is formed on the photosensitive drum 1 by the action of the charger 2 and the optical system 5 in a well-known manner. Next, the latent image on the photosensitive drum 1 is visualized as a toner image by a developing device 3. The toner image is transferred onto a transfer material P fed from a paper feeding device (not shown) in a transfer area where a transfer discharger 8 is arranged. The transfer material P carrying the toner image is then conveyed to a fixing device (not shown) and fixed thereon.

After the photosensitive drum 1 is subjected to the action of the cleaning device 9 and the light source 1O, the next image forming process is performed again.

Next, the developing units 3A and 3B will be explained. Each developing unit 3A, 3B has the same structure, and also uses a jumping developing method using component developers, for example, Japanese Patent Publication No. 58-3237.
This is a developing device using the method described in Publication No. 7. The developing units 3A and 3B have the structure shown in FIG. 1, for example. That is, the developing units 3A and 3B each have a developer supply container 20 with an open side. A container 20 is placed in the opening.
A developer carrier is arranged to carry the developer inside and convey it to the opening. In the wooden embodiment, the developer carrier is a developing roll 22, and includes, for example, a fixed magnet 24 and a developing sleeve 26 surrounding the magnet 24 and rotatably attached to the developing container 20. The developing sleeve 26 is made of a non-magnetic material such as aluminum or stainless steel, and rotates as shown by an arrow 28 in the figure. Further, the developing roll 22 does not have a developing sleeve 26,
It can also be configured with only the rotating magnet 24,
Furthermore, it is also possible to use a belt-like member instead of the developing sleeve 26.

Red or black toner 30 containing magnetite is stored in the developer container 20 . The black toner 30 is attracted to the surface of the developing sleeve 26 by the magnetic field of the magnet 24 fixed within the developing sleeve 26, and the black toner 30 is attracted to the surface of the developing sleeve 26.
The toner 30 is conveyed from the inside of the developer container to the outside of the developer container toward the photosensitive drum 1 by the rotation of the developer container, and the toner 30 is transferred to the developer container by a magnetic blade 32 provided at the opening of the developer container at a distance from the developer sleeve 26. The magnetic toner 30 is prevented from moving outside, and the magnetic toner 30, which has become a thin layer on the developing sleeve 26 and is charged to the opposite polarity to the electrostatic latent image, is transferred to the outside of the developing container. As understood from the above explanation,
The magnetic blade 32 is a developer thickness regulating member that regulates the thickness of the developer carried on the developing sleeve 26, and therefore, a roller-shaped regulating member can be used instead of the magnetic blade 32.

Figure 3 shows the gap between the developing sleeve 26 and the magnetic blade 32 to obtain the appropriate density, and the photopic potential and dark potential at each development position of the latent image formed on the photoreceptor 1''. It shows the difference from the given potential Vd, that is, the relationship with the contrast potential Vc.

As is clear from FIG. 3, by increasing the gap between the developing sleeve 26 and the magnetic blade 32, it is possible to obtain an appropriate density even if the contrast potential of the photoreceptor is small.

In the developing device of the present invention, as seen at point B in Fig. 2 = 2008L
By setting m to 0 point and setting Q to 300 gm, it is possible to obtain an image density that can compensate for the dark decay of the photoreceptor.

In addition, in the above embodiment, a japing development method using a one-component magnetic toner was shown as an example, but Japanese Patent Publication No. 58-32375
The present invention can also be applied to the developing method using non-magnetic toner described in the above publication, and the same effect can be expected by changing the distance between the carrier brush regulating member and the developing sleeve in the carrier brush developing method.

The multicolor developing device according to the present invention configured as above
The gap between the developer carrying member and the developer thickness regulating member of the developing unit arranged around the latent image carrying member is set at a position downstream of the developing unit located upstream in the rotational direction of the latent image carrying member. Just by configuring the developing unit to be large,
In other words, it is possible to compensate for the dark decay of the latent image carrier with an extremely simple configuration, and it is possible to obtain high-quality copies with images of approximately the same density.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a developing device showing one embodiment of the developing device according to the present invention. FIG. 2 is a schematic cross-sectional view of a color copying apparatus to which the developing device according to the present invention can be applied. FIG. 3 shows the difference between the gap between the developing sleeve and the magnetic blade to obtain the appropriate density, and the bright potential at each development position of the latent image formed on the photoreceptor and the dark potential Vd. That is, it is a graph showing the relationship with contrast potential Vc. 3: Multicolor developing device 3A, 3B: Developing units 26A, 26B: Developing roll Fig. 2

Claims (1)

[Claims] 1) In a developing device that develops an electrostatic latent image on the surface of the latent image carrier by arranging a plurality of developing units along the latent image carrier, the developer carrier of the developer unit and the developer layer thickness regulating member are A developing device characterized in that when comparing the gap between any two developing units, the developing unit located downstream is larger than the developing unit located upstream in the rotational direction of the latent image carrier. Device.