JPH04319968A - Full-color copying device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to full-color copying control of originals containing black images.

0002

[Prior Art] In a conventional full-color copying device that forms a full-color image using yellow, magenta, and cyan color developers, the black image of a document is created using the three types of yellow, magenta, and cyan color developers. It is reproduced by strictly balancing the concentrations of

[0003] However, in reality, it is extremely difficult to reproduce black by controlling this density balance, and the black is reproduced as a reddish black or a bluish black with some hue. Ta. For this reason, black line drawings such as letters lacked sharpness compared to the original.

Furthermore, in order to improve the gradation, a process has been carried out in which, for example, the reflected light from the original is transmitted through a special slit-shaped screen and then incident on the photoreceptor; is reproduced as a series of dots. The clarity was reduced.

On the other hand, in a full-color copying apparatus equipped with a color developer tank containing color developer and a black developer tank containing black developer, for example, an image darker than a preset density in a document is extracted. By setting in advance a density level that can almost distinguish between a dark black line drawing such as black text and a color image area consisting of a lighter hue, The image was extracted by the high-density image extracting means and formed as a black copying device using a black developer. This black copy image was superimposed on the full color image formed by the color developer.

[0006]

[Problems to be Solved by the Invention] However, in the case where black line images are formed using the above yellow, magenta, and cyan color developers, it is difficult to completely reproduce black, and the clarity is lower than that of originals. The result was a duplicate image lacking in quality.

Furthermore, in a device equipped with a black developer tank containing a black developer, the toner image transferred to the intermediate transfer member is transferred last because the toner transfer efficiency deteriorates each time the images are overlapped. Black toner images such as letters lacked sharpness.

[0008]

[Means for Solving the Problems] The present invention has been made in order to solve the above-mentioned conventional drawbacks, and is provided with a developer tank containing yellow, magenta, and cyan color developers and a black developer. In a full-color copying device, when performing full-color copying of a document containing a black image, the black developer is first used to form a black image on the intermediate transfer body, and then color images are formed in the order of yellow, magenta, and cyan. It is characterized by comprising an image formation control means for superimposing the images.

[0009]

[Operation] According to the full-color copying apparatus described above, the black image is developed and transferred first, and then the color images are superimposed in the order of yellow, magenta, and cyan.
Black line drawings such as letters can be reproduced clearly without reducing the transfer efficiency.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a full-color copying apparatus according to the present invention.
An exposure optical system 2 is disposed below the document table 1. This exposure optical system 2 includes two light source lamps 2a and 2a' that irradiate light onto a document 3 placed on a document table 1, and reflects light from the document 3, for example, as shown by a dashed line. It includes a plurality of reflecting mirrors 2b that guide the light onto the belt-shaped photoreceptor 4, an imaging lens 2c disposed on the optical path, and a color separation filter 2d having color filters of three primary colors (red, green, and blue). ing. Furthermore, the photoreceptor 4
A special screen 5 for improving gradation is disposed in a position close to the gradation, and this special screen 5 is mounted so that it can be switched between an inserted position in the optical path and a removed position shown by the broken line in the figure. It is in a state. Further, below the exposure optical system 2, there are four developer tanks 6 to 9, the above-mentioned belt-shaped photoreceptor 4, and two paper feed cassettes 11 and 12 according to size.
and is provided. Furthermore, a belt-shaped intermediate transfer body 13, a conveyance belt 14, and a fixing device 15 are arranged in this order on the side of the photoreceptor 4 in the paper output direction.

The photoreceptor 4 has first and second rollers 16
・It is designed to be rotationally driven by 17. A charger 18 for charging the photoreceptor 4 is disposed around the outer periphery of the photoreceptor 4 near the first roller 16 on the side to which the reflected light from the exposure optical system 2 is irradiated. A cleaning device 19 for removing toner remaining on the photoreceptor 4 is disposed below the photoreceptor 4 in the vicinity of the charger 18 .

Further, the above-mentioned developing layers 6 to 9 are placed near the center above the photoreceptor 4 in a non-contact state with the photoreceptor 4.
The three color developer tanks 6 to 8 contain yellow, magenta, and cyan color developers, and the black developer tank 9 contains a developer containing a black pigment such as carbon black. agents are contained in each.

On the other hand, the intermediate transfer body 13 is rotationally driven by three rollers 21, 22, and 23. The second roller 17 side of the photoconductor 4 is pressed against one side of the intermediate transfer body 13, and a transfer charger 24 is also placed on the back side of the intermediate transfer body 13 in the area where the photoconductor 4 is pressed. , a transfer charger 25 and a separation charger 26 are arranged on the lower side of the intermediate transfer member 13, respectively.

The full-color copying machine is further provided with a control device 28 having a built-in microcomputer or the like as copy image formation control means, and the light source lamps 2a and 28 are controlled in accordance with instructions from the control device 28. 2
A lamp light amount control device (high-density image extraction means) that controls the voltage applied to a', a filter setting actuator (that positions any of the color filters in the color separation filter 2d, and a correction filter to be described later) on the optical path. A filter selection means) is provided.

Next, the operation of the full-color copying apparatus controlled by the above-mentioned control device will be explained. First, the black image of the original 3 placed on the original placing table 1 is processed. Scanning is performed while irradiating light from the light source lamps 2a and 2a' onto image areas such as black characters and lines on the original 3. Then, the uniformly charged photoreceptor 4 is irradiated and exposed by the charger 18. Next, a black developer tank 9 containing a developer in which the latent image formed on the photoreceptor 4 is black.
After being developed and visualized with the developer in the image forming apparatus, the image is transferred to the intermediate transfer member 13 by the transfer charger 24 .

Next, the original 3 placed on the original placing table 1
Scanning is performed three times while irradiating light from the light source lamps 2a and 2a'. As a result, the reflection mirror 2 from the original 3
The reflected light passing through b... is sequentially separated into red, green, and blue color components by the color separation filter 2b. Light for each color component for each scan is irradiated onto the photoreceptor 4, which is uniformly charged by the charger 18, and the photoreceptor 4 is exposed. As a result, electrostatic latent images for each color component corresponding to the image of the original document 3 are sequentially formed on the photoreceptor 4 . Note that during the scanning operation to obtain a latent image corresponding to blue light, the photoreceptor 4
Since the sensitivity to blue light is lower than that of other colors, the two light source lamps 2a and 2a' are turned on at the same time.

Each of the above electrostatic latent images is separated by a color separation filter 2d.
A color developing tank 6 containing developers of yellow, magenta, and cyan colors, which are complementary colors of each color filter in
.about.8, the toner image is developed and visualized with each developer to form a toner image. These toner images for each color component are sequentially transferred to the intermediate transfer body 13 by the transfer charger 24. In this way, a full-color toner image is formed by sequentially overlapping toner images for each color component. In this way, toner images of black, yellow, magenta, and cyan are superimposed on the intermediate transfer member 13 in this order.

Next, the toner image on the intermediate transfer member 13 is transferred to the transfer charger when the transfer paper 27 fed from one of the paper feed cassettes 11 and 12 is brought into close contact with the lower surface of the intermediate transfer member 13. 25, the image is transferred onto the transfer paper 27. Thereafter, the transfer paper 27 is separated from the intermediate transfer body 13 by the separation charger 26, and the conveyor belt 1
4, the transferred image is sent to the fixing device 15, where the transferred image is fixed on the transfer paper 27, and is formed as a full-color copy image.

As described above, in the above embodiment, a process of superimposing a full-color toner image on a black toner image is performed, which improves the sharpness of line drawings such as black characters in the full-color image. In other words, in a full-color toner image, by overlapping the black area formed by the balance of yellow, magenta, and cyan color developers on the black image, line drawings such as black characters as shown above become clearer. Reproduced.

[0020]

[Effects of the Invention] According to the full-color copying apparatus of the present invention,
Images such as black characters and lines on the original are more clearly reproduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a schematic configuration of a full-color copying apparatus according to the present invention.

[Explanation of symbols]

28 Control device

Claims (1)

[Claims] Claim 1: In a full-color copying apparatus equipped with a developer tank containing yellow, magenta, and cyan color developers and a black developer, when performing full-color copying of a document containing a black image, the black developer is first used. 1. A full-color copying apparatus comprising an image-forming control means for forming a black image on an intermediate transfer member using an agent, and then superimposing color images in the order of yellow, magenta, and cyan.