JPS58100141A - Color electrophotography - Google Patents

Abstract

PURPOSE:To obtain a good quality image, by selecting a mode of a business copy consisting of black characters and lines and a picturesque copy mode through independent control of developing bias of each color. CONSTITUTION:In making business copies consisting of black characters and black lines, development gamma characteristics of each color of Y, M, and C are controlled so as to adjust an amt. of each toner to be attached to a photoreceptor, to the following ratio: M:C:Y=1:0.7-1.0:0.5-1.0. In gamma characteristics most suitable for reproducing tones of a picturesque original, cyan, magenta, and yellow are expressed with a single color of each toner, and red, green, and blue, etc., are expressed by mixing 2 colors, and turbidity of the color due to color mixing by changing development gamma characteristics of each Y, M, and C, for example, the color mixing of the M toner in green reproduction, etc. can be prevented by changing development starting voltage VK to 300V for Y, and 400V for M as compared with 200V for C.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention separates a document into three colors to create eight types of latent images, develops them with a developer containing yellow, magenta, and cyan toner, and superimposes them on the same transfer paper. This invention relates to an electrophotographic method for obtaining color images by transferring images.

In this type of color electrophotography, original faj! Equipped with 8 color filters of blue, green, and red that can be switched to 9 colors, 8 types of latent images are formed on the photoreceptor by color separation by these filters, and the images are formed by the light transmitted through the blue filter. The latent image formed by the light transmitted through the green filter is a developer containing yellow toner, the latent image formed by the light transmitted through the red filter is a developer containing magenta toner, and the latent image formed by the light transmitted through the red filter is a developer containing cyan toner. The toner images of each color are superimposed and transferred onto the same transfer paper, and then fixed, thereby creating a color copy similar to the original in Step 9.

As the above color separation filter, for example, the blue filter is a bandpass filter B manufactured by Fuji Photo Film Co., Ltd.
PB45 is used for the green filter, the same company's band pass filter BP153 is used for the red filter, and the same company's sharp cut filter SC60 is used for the red filter. The characteristic curves of these filters are shown in FIG. In the figure, the horizontal axis shows the wavelength in nm, and the vertical axis shows the spectral transmittance in chi. As the color separation filter, it is also possible to use a filter equivalent to the above, such as a Wratten filter manufactured by Kodak.

The color tone reproduction of an image on a copy varies depending on the ratio of the amount of yellow, magenta, and cyan (hereinafter abbreviated as Y, M, and C) color toners attached to the transfer paper. FIG. 2 shows general reflectance characteristic curves of Y, M, and C toners used in this type of color electrophotography.

By the way, in color electrophotographic copying machines, there are many black characters (including black line drawings, etc.), and between color reproduction and character reproduction, it is more important for business copying, which is more important for character reproduction, and color photographs, paintings, etc. It is desirable to be able to arbitrarily select and obtain image quality of both types of pictorial copying with emphasis on color tone reproduction of the original.

As a method of selecting between the above-mentioned functional-oriented business copy and pictorial copy by adjusting the contrast of the copy,
A screen with countless parallel opaque straight lines drawn on a transparent film is provided close to the photoreceptor drum in the exposure path, and in the painterly mode, the contrast of the F-copy is adjusted by adjusting the distance between the screen and the drum. In the business mode, a method is known in which the screen is moved out of the optical path when the mode selection switch is operated, so that the light beam is not modulated.

An object of the present invention is to provide a method other than the contrast adjustment described above, that is, a color electrophotographic method that can selectively obtain business copies and pictorial copies from the viewpoint of color reproducibility.

Hereinafter, the present invention will be explained in detail based on examples thereof.

It is difficult to reproduce a wide variety of colors with the combination of filters and toners with the characteristics shown in Figures 1 and 2 on the front floor.
In particular, the balance between color reproduction of black characters and color reproduction of green, purple, red, cyan, magenta, and yellow is a problem.

The optimum development r characteristics for each color of Y and MSC for reproducing black lines are that the amount of toner adhering to the photoconductor is M: 'c: y = l: 0.7 to t, regardless of the surface potential of the latent image. ,o:
It is better to set o, s to 1.0.

This is shown in Figure 8.
The 〇γ characteristic, which shows that it is necessary to keep the development start voltage (vK) of the characteristic at the same value (Fi 200V in the case of the example in Fig. 3) and the toner adhesion amount ratio as above, is as follows. When set to , it is possible to obtain business copies with good reproducibility of black characters, black lines, etc.

Next, we will consider the γ characteristic that is optimal for color tone reproduction of pictorial originals. When reproducing the colors cyan, magenta 1, yellow, red, green, and violet, it is basically necessary to reproduce the colors using two colors or a single color. Cyan, magenta, and yellow are each a single color toner of that color, red is a mixture of M and Y, green is C,
! : When Y is combined with purple, it becomes an ideal color when the color is produced by mixing C and M.

However, when a filter with the characteristics shown in Figure 1 is used, the mixture is not ideal; for example, when reproducing green, only C and Y are needed; However, the colors are mixed, resulting in a dark green. Similarly, in the case of cyan reproduction, M toner is mixed with other colors besides cyan, resulting in a dark cyan color.

In order to solve this problem, the development γ characteristics of M%, M%, and C may be changed. For example, as shown in FIG.
By shifting V', Mi to 400 V, it is possible to prevent color mixing of Mj) toner in green reproduction, and as a result, a painterly copy with good tone reproducibility can be obtained.

It is extremely difficult to achieve both γ characteristics such as those illustrated in FIGS. 3 and 4 above under one condition, and no practical measure has yet been considered. It is possible to change the aperture of the exposure system and control it using the latent potential, but the sensitivity of the photoreceptor changes greatly due to fatigue, drum dirt, temperature and humidity, and it is difficult to find the optimal conditions. It's hard to compare.

In the present invention, by selectively switching the developing bias pressure of the M and Y developing units between the business copy mode and the pictorial copy mode, the development γ of each color of YlM and C is achieved.
The characteristics were changed as illustrated in FIGS. 3 and 4. This allows the user to select between business copy and pictorial copy at will with a simple operation of switching the mode selection switch, making it possible to obtain high-quality images of each.

[Brief explanation of the drawing]

Figure 1 shows an example of the characteristic curve of a color separation filter used in color electrophotography, and Figure 2 shows an example of the spectral reflectance characteristic curve of eight colors of toner used in color electrophotography. FIG. 8 is a diagram showing an example of a development γ characteristic curve of each color that is optimal for black line reproduction, and FIG. 4 is a diagram showing an example of a development γ characteristic curve of each color that is optimal for painterly tone reproduction.・', 1. 2) Figure 1 Wavelength (nm) Figure 2 Wavelength (nm) Figure 3 (Surface frost level ■ Figure 4 (1d) Cloth surface electron Lγ M)

Claims (1)

[Claims] (1) Separate the original into 8 colors to create 8 types of latent images, develop each with a developer containing yellow, magenta, and cyan toner, and transfer them onto the same transfer paper to obtain a color image. In electrophotography, the selection between a business copy mode centered on black characters and black lines and a pictorial copy mode is achieved by independently controlling and setting the developing bias of the developing means for each color. Features color electrophotography. (Bottle) When the pictorial copy mode is selected, the developing bias of each developing means is independently controlled so as to maximize the magenta developing bias during each developing bias. color electrophotography.