JPS6075844A - Color electrophotographic method - Google Patents

Abstract

PURPOSE:To obtain an image having various densities which are continuously gradational at the same hue by repeating plural times of electrification and exposing and electrifying again uniformly a photosensitive body prior to development. CONSTITUTION:A photosensitive body 1 which is uniformly electrified by the 1st corona electrifier 2 is exposed imagewise by the 1st exposing light source 3 having increased exposure, by which an electrostatic latent image is formed and further the photosensitive surface thereof is uniformly electrified by the 2nd constant current type corona electrifier 4. The uniformly electrified photosensitive surface is exposed with the same image by the 2nd exposing light source 5 in succession to the above-mentioned electrification and is further uniformly electrified by the 3rd constant current type electrifier 6. The image having excellent various densities which are continuously gradational is thus obtd. at the same hue.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to image 18! Regarding color electrophotography, in which an electrostatic latent image formed on a photoconductor by exposure is developed using multicolor toner, especially for original images with a wide contrast range,
This invention relates to color electrophotography that provides excellent gradation reproducibility.

Conventional and advanced technology The brightness decay characteristics of conventional color electrophotographic photosensitive materials (hereinafter simply referred to as photosensitive materials) are similar to those for monochrome use, and the relationship between original image density and photosensitive material potential is linear as shown in Figure 1. Therefore, the relationship between the original image density (DIN) and the copy density (DOUT) also has a narrow dynamic range as shown in FIG.

For this reason, in color electrophotography, when inputting gradations of the same hue, hue discrepancies may occur between low and high density areas.
For original paintings with a wide contrast range like photographs,
Poor gradation occurred in low and high density areas.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a color electrophotographic method that eliminates the above-mentioned drawbacks and can provide images with excellent gradation writing performance and no hue shift even for original images with a wide contrast range.

The constitution of the invention, that is, the object of the present invention is to provide a color electronic device characterized in that charging and exposure are repeated multiple times by gradually increasing or decreasing the amount of light by 6% from the first time, and uniformly charging is performed again before development. Achieved through photography.

Example Hereinafter, the method of the present invention will be explained using the drawings.

FIG. 6 is a schematic diagram of a color electrophotographic copying machine used in an embodiment of the present invention.

In FIG. 6, a first corona charging device r-2 is located close to the surface of the drum-shaped photoreceptor 1 and uniformly charges the surface of the photoreceptor, and the exposure amount is set to 60% ( A first exposure light source 3 whose density is increased by 0.5) and a second constant current type corona charging device 4 which uniformly charges the photoreceptor again.
, second exposure light #5 having normal exposure h\, and a sixth constant current type corona charging device 6 for uniformly charging the photosensitive surface again are provided.

In addition, the first method for multicoloring. Second. Sixth developing device7.
8. 9, and a transfer band device 10 that performs pre-transfer processing.
, a transfer drum 11 and a cleaner device 12 are provided along the photosensitive surface.

Further, a fixing roll 14 is provided in contact with the transfer drum 11 to fix the transfer paper 16 under pressure.

An embodiment of the color electrophotographic method of the present invention will be explained along the copying process using the copying machine configured as described above.

Photoreceptor 1 uniformly charged by first corona charging device 2
is subjected to image exposure by the first exposure light source B with increased exposure amount to form an electrostatic latent image, and further, the photosensitive surface is uniformly charged by the second commercially available corona charging device 4. This uniform (i'f') photosensitive surface is then exposed to the second exposure light source 5.
The same image is exposed by the 6th constant current type band ?
is uniformly charged by device B.

In the sixth charging device 6, the charging potential is lowered than the previous two times, for example, from about 900 V to 100 to ff16DOVa.
Charging is carried out at a certain degree.

By carrying out the above steps, the relationship between the original image density (DIN) and the potential of the photosensitive material in terms of brightness decay characteristics becomes as shown in FIG.

In other words, the bright attenuation characteristic (shown by curve A in the figure) created by the first charging and exposure process with increased exposure (i. (Illustrated; same as Figure 1), the high-density area image of the original image is emphasized and extracted.Therefore, this first band is overlaid with the exposure process, and the second charging and exposure process using the normal exposure amount is performed. By performing this process, the brightness attenuation characteristic (indicated by ff$0 in the figure) is improved, and an image with a wider density range is extracted.

Furthermore, by performing a sixth charging step in which the band'[11t potential is lowered, the linearity of the bright attenuation characteristic (a-line C) created by the second band's exposure step is corrected, In particular, images in the low density region are emphasized, and a bright attenuation characteristic (curve D in the figure) with a dynamic range expanded to about 1.0 is finally obtained.

After the static latent image obtained over time in such a process is developed in, for example, yellow by the first developing device 7, the charge is neutralized in the transfer charging device 1o and transferred to the photoreceptor 1] - The image is transferred to the transfer paper 16 that is conveyed between the rams 11.

The transfer paper 13 on which the image has been transferred is fixed under pressure by the fixing roll 14, and then wound around the transfer drum 11 for one rotation in preparation for the next transfer, and then returned to the original transfer start position and held there. That is, the transfer trim 11 is provided to hold the transfer paper 16 onto which the first color image has been transferred, and to allow images of the second and subsequent colors to be superimposed and transferred.

On the other hand, when the residual toner on the photoreceptor 1 is removed by the cleaner device 12, an electrostatic latent image of the same image is formed in the same manner as the previous time. This latent image is then developed in magenta, for example, by the second developing device 8 to form a second color image, which is superimposed on the first color image and transferred and fixed. Similarly, in the next step, the image of the sixth color is developed by the third developing device 9, and when the overlapping transfer and fixing are completed, the transfer paper 16 is then conveyed outside the machine and the C copying is completed.

In the above embodiment, the constant current charging device 4 is used for the second and subsequent charging.
, 6, the potential difference between the latent image area and the non-latent image area formed on the photosensitive material is made relatively large as shown in FIG. The dynamic range is expanded.

Furthermore, although the charging and exposure processes are performed twice in this embodiment, they may be performed more times.

That is, the present invention changes the exposure peak as a means of matching the acuity range of the original image with a wide contrast range to the highest sensitivity region of Sensitivity I (portion with a large slope in bright decay characteristics). Therefore, it is possible to perform this charging and exposing process several times over a wide range of situations. This improves reproducibility.

In the above embodiment, the number of exposed portions is gradually reduced, but the number of exposed portions may be gradually increased.

Moreover, although pressure fixing is used in the above embodiment, various other conventionally known fixing methods can be used, but it is necessary to consider the Uji method, which does not affect the transfer process that is repeatedly performed.

Effects of the Invention As described above, according to the present invention, in order to improve the f1 printing of an original image having a wide contrast range, the exposure area is changed for each density region. By superimposing 4J images, the dynamic range is expanded, and an image with excellent continuous tone shading can be obtained in the same hue. Further, by performing the above steps for each hue, a clear image without embellishment or color shift can be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the original density and the sensitive potential in the bright decay characteristics of electrophotographic paulownia material, Figure 2 is a diagram showing the relationship between the original density and the copy density, and Figure 6 is the book. FIG. 4 is a schematic diagram of a color photocopy 4 used in an embodiment of the invention, and is a diagram illustrating the brightness attenuation characteristic formed by the invention. 1... Photoreceptor 2, 4, 6... Corona charging device 6.
5... Exposure light source 7,8.9... Developing device 10...
・Transfer charging device 11...Transfer 1/9 ram 12...
・Cleaner device 16...Transfer paper 14...Fixing roll

Claims (2)

[Claims] (1) In color electrophotography, which involves the processes of charging, exposure, development, transfer, and fixing, and develops an electrostatic latent image formed on a photoreceptor by imagewise exposure, the amount of exposure is controlled from the initial stage. A color electrophotographic method characterized by repeatedly performing charging and exposure multiple times with gradual increases or decreases, and uniformly charging again before development. (2) The color electrophotographic method according to claim 1, wherein constant current type corona charging is performed for the second and subsequent charging.