JPS6165264A - Image exposing method of color electrophotography - Google Patents

Abstract

PURPOSE:To reproduce a low-density and a thin-line part without color mixing to a pure-color part on an image by using a filter for blue separation and a narrow-band vapor-deposited green filter. CONSTITUTION:A filter turret 2, lens assembly 3, and light shield plate 4 are provided on an optical axis 1, and the filter turret 2 consists of a green transmission filter 7 and a red transmission filter 8 and moves on a driving rail 9 while holding filter surfaces at right angles to the optical axis 1. The lens assembly 3 consists of a lens 3a which is used during red-green separation and a lens 3b which is used during blue separation, and a blue transmission type filter 10 is arranged at the pupil position of said lens 3b. The green transmission type has half-value width <=20 NM and is separated into two lenses, which are switched and used during exposure of each color to obtain a high MTF contrast bright image and a stable image.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image exposure method for color electrophotography, and more particularly, to a color exposure method for forming a latent image on a sensitive material in color electrophotography. This invention relates to a separated image exposure method.

(Prior Art and Problems to be Solved by the Invention) -C. As a color image recording method, there is a known method in which a monochromatic electrophotographic method is repeated a necessary number of times. With this method, color images can be obtained more easily and in a shorter time than with printing methods or color photography methods. However, the image quality is generally inferior to printing methods and color photography methods. The reason for this is that sufficient contrast between necessary and unnecessary colors cannot be obtained during the latent image formation stage, and color correction called masking, which is widely used in printing etc. It's because I can't do it.

The conventional color electrophotographic method will be explained below with reference to FIGS. 7 to 9. Figure 7 shows the conventional car for powder development;
．． Indicates l'r:.

As the photosensitive material, SE type or CdS is usually used, and in this case, the SE type will be explained. The jS material is first charged to -K using a charger, and then the color original is charged to the eighth
The image is exposed through a JTJ filter that separates the colors into 2 colors, and the colors 1 and 1!1. form. In FIG. 8, symbols A, C, and C indicate blue, green, and red color separation filters, respectively. Next, this latent color image is developed using a color separation film 7 (toner of a color complementary to that of Luther), and each of the toner images on the photosensitive material is transferred during the transfer process.
form. The above series of cycles is performed on H sheets of required colors (usually 1 toner (red) separated, C (cyan) toner, G (1:
Decomposition-M (magenta) toner, B (blue) decomposition-Y(
After transferring the required color onto the paper, the toner is fixed on the paper. C as a window material
When using dS, there are differences in the stage of latent image formation, but
The same can be said for the entire process.

There are two issues that arise in this case:

For example, considering the case where Fil 1Idj is 117 mm, the reflection characteristics of the process ink are shown in FIG. 9. In FIG. 9, the symbols 2, E, H, G, CH, and RI are cyan ink, yellow ink, magenta ink, and magenta ink, respectively.
The reflection characteristics of magenta ink, cyan ink and yellow ink, magenta ink x cyan ink, and yellow ink are shown. In this Figure 9, the reflection characteristics of each two are the necessary color (color to be developed) and unnecessary color (color to be developed) in each color separation.
(colors that must not be developed). During color separation, the three color filters shown in Figure 8 are used to expose the photosensitive material to light stars corresponding to the average reflectance of the original image in the transmission range of each filter. The post-exposure potential on the sensitive material is determined from the above steps for necessary and unnecessary colors, and the potential difference becomes the contrast.

In the developing step, a developing bias provided in the developing device is set between the necessary color potential and unnecessary color potential so that toner is developed for the necessary color and not for unnecessary colors. At this time, if the contrast on the photosensitive material is not sufficient,
The latitude of the development bias setting becomes narrower, and changes in development characteristics due to variable factors such as temperature and humidity tend to appear directly in the image n°.

Ru.

Now, according to Figures 8 and 9, the necessary color is cyan and the unnecessary color is red during photo-decomposition exposure.
The difference in average reflectance is large. but,
During green separation exposure and blue separation exposure, as shown in Figure 9, the unnecessary absorption of green and blue in the process ink is large, and
Due to the wide lfj overband of the filter during color separation (green exposure half value 5ONM, pre-exposure half value IQONM), the average reflectance difference between necessary colors and unnecessary colors is small and contrast does not appear sufficiently.

The above can be said about the solid part of the original picture,
Contrast is further reduced in the line image area. This is because in the case of a line image, due to the resolution of the lens, light from the surrounding non-image area wraps around the line image area, and the appearance of the light irradiated on the sensitive material is thicker than that of the solid area (and the required color is This is because the potential on the sensitive material is lower than that in the solid portion.

Therefore, in terms of image quality, problems occur such that color mixing occurs in the green and front parts of the original image, resulting in loss of vividness, and low-density solid areas and thin lines are not reproduced.

In order to deal with this, conventionally, according to the characteristics of the original picture,
An adjustment unit is provided to adjust the exposure amount, developing bias, etc., and the operator performs picture matching while performing certain adjustment procedures to achieve a somewhat satisfactory image quality. However, in such a way? Not only does it require a special adjustment mechanism, but it also requires a dedicated operator for adjustment.
It is difficult for customers to easily handle and obtain satisfactory image quality.

Another disadvantage is that it is difficult to maintain the stability of image quality because color correction is carried out in the entire adjustment section without sufficient contrast between necessary and unnecessary colors.

(Object of the Invention) “In view of the drawbacks of the prior art described above, the present invention enables high-contrast image exposure, that is, the ir1
Close to colored part; 9 colors are low'/+”: 1.!,!+3
However, it is an object of the present invention to provide an electrophotographic method capable of reproducing twisted fine line parts.

(Structure of the Invention) Invention H et al. il: -1'c;j phi (1) Color'1. 41. Used there for occasional printed matter. We investigated the color characteristics of process inks. At this time, the index of color separation efficiency was set to 4 as the h standard (which evaluates the influence of the color characteristics of the process ink on the contrast). Here, the color separation efficiency is given by the following formula.

Q (A) = -1,0G (R (λ)) [+- (λ)
; Necessary color density Du (λ) ; Unnecessary color density R (λ);
Process ink spectral reflectance Here, the necessary colors and unnecessary colors are cyan for red separation, yellows magenta, magenta for green separation, and cyan ×
When yellow and blue are separated, they are yellow, magenta x cyan. Figure 1 shows the illumination of four types of process inks.
The color separation efficiency shown in FIG.

In FIG. 1, the symbols null and o indicate blue, green, and red components; 1♀ efficiency, respectively.

The following two points can be drawn from this result.

■Depending on the color characteristics of the stamp material used as the original image, the 1 nt truss 1 or more is small when green and blue are separated.

(2) The wavelengths that give the maximum color separation efficiency (1q) of the various process inks used in printing are almost the same; at other wavelengths, the color separation efficiency drops dramatically.

From the above, it can be seen that in the color separation process, it is necessary to increase the contrast during green separation and blue separation, and an effective means for achieving this is to narrow the transmission band during color separation. . Furthermore, in order to reproduce the fine lines typical of phototype printing, the resolution performance of the lens must be improved when separating green and blue colors, which have low contrast.

Therefore, in the present invention, in the conventional color electrophotographic method shown in FIG. 7, a narrow band filter is used so that the transmission band is 2ONM or less at half maximum when separating blue and green, and in addition, when separating blue, a narrow band filter is used exclusively for blue separation. The structure uses a lens.

In this case, it is known that the lens resolution performance depends on the wavelength phase of the light that passes through the lens, and that the narrower the transmitted light wavelength band is, the better the lens resolution performance is.

In this way, by limiting the target light quality to narrow band monochromatic light when designing a lens, it is possible to eliminate the effects of chromatic aberration and realize a lens with high resolution performance.

Further, as a narrow band filter, a multilayer interference filter as shown in FIG. 2 can be used, and its half width and peak wavelength can be freely controlled in the visible range.

Therefore, it is also possible to adjust the peak wavelength to the wavelength (445 NM, 515 NM) that gives the maximum color separation efficiency shown in FIG.

(Example) FIG. 3 shows an example of the present invention. A filter turret 2, a lens assembly 3, and a round plate 4 are located on the optical axis l. The filter turret 2 consists of two filters, a green transmission filter 7 and a red transmission filter 8, and is movable on a drive rail 9 while keeping the filter surface perpendicular to the optical axis l.

The lens assembly 3 includes a lens 3a used for red/green separation and a lens 3b used for blue separation, and a blue transmission filter 10 is disposed at the pupil position of the lens 3b used for blue separation.

The assembly 3 can move on the drive rail 11 with the pupil plane kept perpendicular to the optical axis 1. In addition, the light shielding plate 4 is provided with an aperture 4a corresponding to the light flux from the lens (3a in the figure) located on the optical axis 1, and passes through the lens (3b in the figure) that is not on the optical axis. The luminous flux is cut. The lens assembly 3 and filter turret 2 configured as described above can be moved on the drive rail 11.9 by a drive motor (not shown), and the amount of movement is determined by a control signal manually input to the drive motor.

Hereinafter, the operation of the present invention will be explained in accordance with the fourth copying cycle for each color.
This will be explained using figures. Now, as an example, each color is different from each other.
Ikuru or play with you i, i, i! -.Outside green IW-.11 is assumed to be in the color separation order 'ζ. t:, 1\Red exposure song Ogo filter turret 2 A: Hirens Anno Senfuri 3 is returned to Ho J1 Bossinyon 1. Ru. At this time, a red passing filter 8 and a red/green color separation lens 3a are located on the optical axis. After the red separation exposure, the filter turret 2 and the auxiliary lens are moved in the forward direction (in the direction of arrow Ella in FIG. 3) by the driving motor, and the green transmission filter 7 is positioned on the optical axis 1. At this time, the lens antenna does not move. Next, after the green color separation exposure, the filter turret 2 and the lens assembly are simultaneously operated in the forward direction, and the blue color separation lens 3b is located on the optical axis IJ2 without the filter turret. After blue exposure, filter turret 2 and lens anno-f! The robot 3 is moved in the negative direction (direction b in the figure) and returns to the home position.

Next, the filter lens used in the above embodiment of the present invention will be explained. As filters, we used three filters, one for red transmission, one for blue transmission, and one for green color.
The transmissive and green transmissive filters are multilayer medical film filters. That transparency 1! The p-character is shown in Figure 5G.
< is.

Blue i3 type Center wavelength 445NM゛11 value [1≦
2ONM Bandpass filter Green transmission type Center wavelength 515NM Half value ≦2ONM Bandpass filter Red transmission type CIIT OFF Wavelength 59ONM Sharp cut filter Each filter can be manufactured by various optical parts manufacturers, and commercially available products such as Toshiba Kasei Industrial 'KL series filters have equivalent performance, and Japan Vacuum Optical, IF-3, and IF-W types can also be used.

At this time, as shown in FIG. 4, the center wavelengths of the blue-transmitting and green-transmitting filters are set to the wavelengths at which the color separation efficiency of the process inks for the 11 items to be printed as the document is maximized.

Next, as a lens, M T as shown in FIG.
F (Modulation Transfer F
A lens having a characteristic of In particular, since high lens M image performance is required during blue separation, the desired performance is obtained by using a lens exclusively for blue separation that takes into account only the light 1T in the blue separation filter described above. However, with this lens alone, the resolution performance during green and red separation will drop significantly, so another lens, such as a plate-making lens, is required to take green and red into consideration.・As a lens exclusively for blue separation, , MTF contrast is 1
A material having a resolution performance of 70% or more at 41 p/mn is used. It is possible to use an orthometal type aspherical lens designed based on a blue-only luminous flux.

In this way, by separating the lenses into two lenses and switching between them during exposure for each color, it is possible to obtain a corrected M T F , :+n(・last) during exposure for each color, as shown below. Ta.

The potential contrast on the photosensitive material obtained in the above embodiments of the present invention is compared with that in the conventional method and is shown in Table 1. At this time, the dark area potential was set to 900 V and the white area potential was set to 100 ■. are doing. Also, as a manuscript, process ink,
I use Color Nomasochi, which costs 11 yen.

Koryoku (ko, Psu, green 51i' 17 o'clock C 11koQ)
I, 5 (,'i, blue part) ・You can see that at 7 o'clock it was 1.21 times -7 n 1 → strike or up 1.7. In this way, the potential contrast on the photosensitive material has been greatly increased compared to the conventional one (1), so that the latitude amplitude during development can be measured, and the above-mentioned drawbacks of conventional image quality can be eliminated. .

(Effects of the invention) Compared to the conventional method, as described in 1-1, the potential contrast on In this case, color mixing in unnecessary parts is eliminated, a colorful image is obtained, and it is also easier to print a stable image. By making full use of the copy adjustment machine FIL, there is no need to perform picture matching, and the customer can obtain a copying machine that is easy to use.

[Brief explanation of drawings]

Figure 1 is a graph showing the color separation efficiency calculated from the color characteristics of process ink. Figure 2 is an example of a color separation filter that can be used in the present invention. Figure 3 is an outline of an embodiment of the present invention. Figure 4 is a sequence diagram showing the operation in the embodiment of the present invention; Figure 5 is a graph showing the spectral characteristics of the color separation filter used in the embodiment of the present invention; Figure 7 is a graph showing the lens resolution performance used in the example. Figure 7 is a process diagram of a conventional color electrophotography method. Figure 8 is an example of a color separation filter used in a conventional color electrophotography method. The graph shown in FIG. 9 is a graph showing the color characteristics of typical printing process inks. 1... Optical axis 2... Filter turret 3... Lens assembly Figure 1 Wavelength (NM) Figure 41 Figure 5 Liquid -A ( NM)

Claims (3)

[Claims] (1) An image exposure method for color electrophotography using a blue separation filter and a green separation filter which is a narrow band vapor deposited filter with a half width of 20 NM or less. (2) A color electrophotographic image exposure method according to claim 1, characterized in that at least two lenses are provided as color separation exposure lenses, and one of the lenses is used only for blue exposure. . (3) The resolution performance of the lens dedicated to blue exposure is MTF
The image exposure method for color electrophotography according to claim 2, characterized in that the contrast is 70% or more at 14 lp/mm.