JPS62218971A - Color electrophotographic recorder - Google Patents

Abstract

PURPOSE:To prevent a high original density part from the reduction of image density by setting up a developing bias voltage to be impressed during developing operation so that it is gradually reduced every development in accordance with the reduction of the potential of an electrostatic latent image formed on a photosensitive body. CONSTITUTION:An original platen 5 is moved from the left end side in the right direction, the electrostatic latent images of an original are successively formed on respective photosensitive drums 7c, 7y, 7m and the drums 7c, 7y, 7m complete respective development by three rotations, two rotations and one rotation respectively until the original platen 5 is completely carried up to the right end side. In this case, the absolute value of the developing bias voltage is gradually reduced in the order of the 1st, 2nd and 3rd development to keep the potential difference from that of the electrostatic latent image almost at a constant value. Even if the developing operation is continued up to the 3rd times, a developer temporarily adhering to the surface of the electrostatic latent image can be prevented from being peeled off by the developing bias voltage, so that the reduction of the image density in a high original density part can be suppressed and the image quality can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a color electrophotographic recording device, and particularly to a color electrophotographic recording device equipped with a plurality of photoreceptors.

(Prior Art) In recent years, various color electrophotographic recording apparatuses that are capable of performing color recording using developers of a plurality of different colors have been developed. Some color electrophotographic recording devices are equipped with separate photoreceptors for each color. In this case, devices are attached to each photoreceptor for each color to perform exposure, development, cleaning, etc., respectively.

These photoreceptors, etc., provided for each color are arranged in parallel along the paper feeding direction, and by sequentially transferring the developer of each color onto the recording paper, a predetermined color tone is created on the recording paper. The prepared statue is now recorded.

For example, if photoconductors for each color using yellow, magenta, and cyan developers are arranged in order from the paper feed side, first a yellow layer is transferred onto the recording paper, and then a yellow layer is transferred onto the recording paper. , a magenta layer is transferred, and a cyan layer is further transferred thereon in a layered manner.

Each photoreceptor for each color is always rotated at a constant speed, and after the photoreceptor is rotated a predetermined number of times and the electrostatic latent image formed on the photoreceptor is developed and visualized with a developer, it is recorded. Transfer to paper. When performing this development, a developing bias voltage is applied to the developing area in order to prevent background smearing.

Furthermore, after that, the photoreceptor is rotated a predetermined number of times to perform cleaning.

In this case, the number of rotations of the photoreceptors during the developing operation is different between the photoreceptors. Yellow mentioned above,
In an example using magenta and cyan developers, each photoconductor is rotated four times in total in one development and cleaning process, but the yellow photoconductor closest to the paper feed side undergoes one development rotation. After performing the cleaning operation for the remaining three rotations.

On the other hand, the magenta photoreceptor located in the center is 2
After the rotational developing operation is performed, the same two-rotational cleaning operation is performed. Roughly speaking, the cyan photoreceptor that is farthest from the paper feed side performs a cleaning operation in the remaining three rotations after one rotation of developing operation.

However, conventionally, development conditions such as the development bias voltage are always kept constant during multiple development operations, and in general image density areas, the electrostatic latent on the photoreceptor increases as the number of development increases. More developer will try to adhere to the image. However, in a high-density portion of the original, as the amount of developer attached increases, the charge from the electrostatic latent image is rapidly taken away, and the potential of the electrostatic latent image rapidly decreases.

As a result, the developer once attached to the electrostatic latent image in the plateau iI1 degree portion is separated again by the constant developing bias voltage, and the image density may be reduced instead.

That is, as shown in FIG. 3, one development (solid line), two
As the number of times of development increases, from two times development (broken line) to three times development (dotted chain line), the image density (vertical axis) decreases significantly in areas where the document density (horizontal axis) is high. A picture like this
A decrease in k density often poses a problem in terms of image quality.

(Objective) Therefore, it is an object of the present invention to provide a color electrophotographic recording apparatus that can satisfactorily prevent a decrease in image density in high document density portions even if development is performed multiple times.

(Structure) In order to achieve the above object, the present invention provides a color electrophotographic recording apparatus equipped with a plurality of photoreceptors, in which a developing bias voltage applied during a developing operation is applied to an electrostatic charge formed on the photoreceptor. As the potential of the latent image decreases, the potential is set to be temporarily reduced each time the development is performed, and as the number of development increases, the developer peeling function is weakened.

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

FIG. 1 shows a color copying machine to which the present invention is applied. In this copying machine, a recording paper 2 is fed from a paper feed unit 1 installed on the right side of the mouth surface in the order of three transfer stations M, Y, and C by a registration row 53, and at each transfer station M, Y, and C. Magenta, yellow, and cyan developers are sequentially transferred onto the recording paper 2, passed through the fixing device 4, and sent out from the left end side of the drawing.

That is, the transfer stations M, Y, and C are arranged in order from the paper feeding side (right side in the drawing) in the paper feeding direction. And each transfer station M
, Y, and C are an exposure section 6 disposed directly below the document table 5, and photoreceptor drums 7m, 7y, and 7 disposed directly below the exposure section 6 and using respective color developers.
c, and a developing/cleaning device ii attached to each of the photoreceptor drums 7m, 7y, and 7c! They are equipped with 8m, 8y, and 8c, respectively.

Of these, the exposure section 6 includes a document illumination device and the light reflected from the document to each photoreceptor drum 7m, 7M.

Exposure lens device a1 that forms an exposure image on 7C
1.

Further, each photosensitive drum 7m, 7y, 7c is always rotated at a constant speed during recording, and the main charger 12
After being charged, it is exposed by the exposure section 6 to form an electrostatic latent image. Next, each photoreceptor drum has a length of 7 m.
, 7y, and 7c are rotated a predetermined amount, each of the current transmission and leaning equipment ff18m.

sy and sc, the developer of each color is applied to each photoreceptor drum 7.
m, 7y, 7c and the electrostatic latent image is developed,
Be visualized. In this case, each of the photoreceptor drums 7m, 7m
The number of rotations of each developing operation in y and 7c is 3 times,
It is set to 2 times and 1 time.

Furthermore, a predetermined developing bias voltage is applied to each developing section of each photoreceptor drum 7m, 7y, and 7c during development. The developing bias voltage is set so that its absolute value is gradually reduced in the order of the first development, the second development, and the third development. In other words, as the electrostatic latent image potential decreases in the high density portion of the original, the developing bias voltage is reduced, and both during the first development, second development, and third development. The potential difference is kept almost constant.

Furthermore, immediately after this development operation is completed, images of each color are transferred onto the recording paper 2 by the transfer charges t13m, 13y, and 13c in a layered manner in the order of magenta, yellow, and cyan. .

After this transfer operation is performed, each photosensitive drum 7m, 7
The developer remaining on the photosensitive drums 7c, 8m, 8y, and 7c is removed by the developing and cleaning devices 8m, 8y, and 8C.
m, 7y, and 7c are cleaned and removed while being rotated for a predetermined period. In this case, each of the photosensitive drums 7m,
The cleaning operation rotation speeds 7y and 7c are set to 1 time, 2 times, and 3 times, respectively.

In the color copying machine having such a configuration, as the document table 5 moves from the left end side in FIG. Electrostatic latent images of the original are sequentially formed. Furthermore, the development of each photoreceptor drum 7c, 7y, and 7m is completed before the document mounting table 5 is completely fed to the right end side. At this time, the photosensitive drum 7c completes development after three rotations,
Further, the photoreceptor drum 7y completes development in two rotations, and roughly, the photoreceptor drum 7m completes development in one rotation.

During such a development operation, the absolute value of the development bias voltage is gradually reduced in the order of the first development, second development, and third development, and the potential difference with the electrostatic latent image potential becomes almost constant. Retained. For this reason, the developing operation is performed twice and three times.
Even if the developer is applied repeatedly, a situation in which the developer once attached to the electrostatic latent image is peeled off by the developing bias voltage can be avoided. That is, as shown in FIG. 2, the image & density (vertical axis) after each number of development operations is represented by almost the same curve as the original density (horizontal axis).

Immediately after this development is completed, transfer to the recording paper 2 is performed in the order of photoreceptor drums 7m, 7y, and 7C, and further,
Immediately after transfer, transfer the photoreceptor drum to 7m.

Cleaning of 7y and 7C is performed. At this time, cleaning is performed until the recording paper 2 is ejected, the photoreceptor drum 7m is cleaned with three rotations, the photoreceptor drum 7y is cleaned with two rotations, and the photoreceptor drum 7y is cleaned with two rotations.
In C, one rotation of cleaning is performed.

It goes without saying that the present invention can be applied not only to copying machines but also to other electrophotographic recording devices.

(Effects) As described above, the color electrophotographic recording device according to the present invention is designed to gradually reduce the developing bias voltage each time the development is performed, so as to prevent the peeling effect of the developer from occurring in the high-density portion of the original. This setting prevents a decrease in image density in high-density portions of the original, making it possible to stably obtain very high-quality images.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a color copying machine according to an embodiment of the present invention, FIG. 2 is a pictorial diagram showing the image density after each number of development steps, and FIG. 3 is a diagram showing the image density after each number of development steps in the conventional method. FIG. 7m, 7y, 7c...photosensitive drum, 8m, ay. 8C: Developing and cleaning device.

Claims (1)

[Claims] Multiple photoreceptors each using a different colored developer,
A color electrophotographic recording device in which a developing device is attached to each of the photoconductors, and the electrostatic latent images formed on each photoconductor are developed and visualized by the respective development devices while each photoconductor rotates for a predetermined period. In this case, the developing bias voltage applied during the developing operation is set so that its absolute value is gradually reduced each time the electrostatic latent image potential in the high density area decreases each time the development is performed. A color electrophotographic recording device characterized by: