JPS607789B2 - color electrophotography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color electrophotographic method, and more particularly to a color electrophotographic method that enables optimal color correction by arbitrarily setting the amount of masking.

Conventionally, in color electrophotography, appropriate color matching has been performed by modifying the spectral sensitivity characteristics of the photoreceptor and the characteristics of the color separation filter, or by changing the exposure time of each color.

These techniques differ in principle from the masking techniques applied to printing methods, silver halide color photography, etc., and are nothing more than techniques that try to improve the overall balance of the image as much as possible, and essentially match the hue. That's not what I'm trying to do. or,
It is practically difficult to apply the masking techniques such as the above-mentioned printing method to color electrophotography as it is because it requires advanced technology and costs.

In general, printing methods, silver halide color photography methods, and color electrophotography methods employ subtractive color methods as color reproduction methods.
Cyan, magenta, and yellow are used as the primary colors, but as is well known, the spectral sensitivity characteristics of pigments that exhibit these hues are not ideal, and there is approximately 39% yellow component in magenta color and magenta component in cyan color. Approximately 33% is contaminated. In order to reproduce colors faithful to the original image, it is necessary to remove the color components mixed in with each of the above colors.
As mentioned above, in color electrophotography, it is technically difficult to investigate the masking method as it is. was balancing. However, this method is not a technical solution because color reproduction is inherently poor and the hues cannot be matched sufficiently. As mentioned above, it is not possible to obtain sufficient color reproduction with conventional color electrophotography, so as a method to obtain reproduced images that are faithful to the original image, electrostatic color correction is performed at the stage of latent image formation. A method of doing this, for example, Samurai Sekisho 48-102627, has been proposed.

This method is similar to the above-mentioned masking technique, and it goes without saying that it is a better color reproduction method. The present invention is based on such a method of electrostatically correcting color, but it is an object of the present invention to provide a color electrophotographic method that can obtain more faithful reproduced images than the methods that have already been proposed. This is the purpose.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given below with reference to the drawings, but before discussing the present invention, the previously proposed color image reproduction method that performs electrostatic color correction will be described first.

Figure 1 shows an example of Tokoseki Sho 48-102627, which shows the image forming process when a two-layer photoreceptor, commonly called electrofax paper (hereinafter abbreviated as EF paper), is used as the photoreceptor. It shows.

To briefly explain the process from the beginning, first, a positive primary charge is applied to the chargeable area of the EF paper using, for example, corona discharge, then a reverse charge is applied at the same time as correction exposure using a color correction filter, and then a single color of development toner is applied. Spectral exposure is performed using a color filter having a complementary color relationship with the color filter, and finally development is performed using the above toner to complete one cycle process. Among the series of steps, the above-mentioned element of the invention is intended to provide a feature in the negative band and to obtain a masking effect.In other words, in the second step of reverse charging, the corona charger eliminates the charge dissipation in the chargeable region. The existing area is charged to the extent that it almost reaches a saturation potential, and color correction is performed using the potential difference between the bright and dark areas at that time.

By developing the color-corrected static exposure latent image, as mentioned above, about 39% of the yellow component mixed into magenta is removed.
%, and about 33% of magenta mixed in with cyan.

However, this potential difference increases the amount of masking by exactly 33% to reduce the ideal amount of masking, for example, magenta that overlaps with cyan.
is very difficult to set.

In other words, setting the reverse charge to a saturation potential in the above process is an extremely insufficient charging state compared to the capacity of the corona charger, lacks stability, and also causes unevenness of the photoreceptor and the atmosphere. Fluctuations in humidity, etc., make adjustment and control of the corona charger and photoreceptor difficult, and the potential difference becomes extremely unstable, resulting in uneven charging. Further, referring to FIG. 2, the drawbacks of the above invention will be explained in detail as follows.

FIG. 2 shows potential curves up to the second step of reverse charging and corrective exposure when the charging levels of the primary positive charging in FIG. 1 are set respectively.

The surface potential at each point is determined by the corona house characteristics, corona voltage, charging characteristics of the photoreceptor, and co. The respective charging voltages match each other at the opposite charging potential saturation point P, which is determined by the charging speed and the like. Therefore, the optimal value of the masking amount and the optimal value of the reverse charging time are set somewhere between the primary charging end potential point S and the reverse charging potential saturation point P. However, at this point M When reverse charging is stopped at , the amount of masking is about 25% calculated from the potential at point M, and the optimum value is 33% as mentioned above, so this value is not the optimum value.

In the above invention, the only way to control the amount of masking is to set the charging capacity or reverse charging time of the corona charger.In other words, the amount of masking is determined by the charging capacity of the reverse charger, the relative speed to the photoreceptor, Therefore, the above-mentioned invention has the disadvantage of being difficult to control, tends to cause charging unevenness, and reproduces a color-corrected reproduced image. There is also a high possibility that it will become incomplete and unstable.

In addition, as another proposal, Hakama Kaisho 48-1026
As described in Example 27, a three-layer photoreceptor in which a transparent insulator, a photoconductive layer, and a conductor are laminated in this order is used as a photoreceptor, and as a first step, primary charging and corrected image exposure are performed simultaneously. There is an image forming method that consists of a series of steps in which the second step is irradiation with uniform light, the third step is reverse charging and positive image exposure, and the fourth step is irradiation with uniform light over the entire surface, but this method completely eliminates masking. Even if it were possible, it would not be possible to obtain sufficient density for other colors.

To explain according to Table 1, in Example 1, the capacitance ratio of the photoreceptor plus the transparent insulator to the transparent insulator is 1 without masking.
:4, Example 2 has the same capacitance ratio with masking, Example 3 has the same capacitance ratio of 7:10 with masking, and the transparent insulator surface potential corresponding to each color and its potential ratio are calculated by applying the Q=CV formula and shown in the respective columns.As can be seen from this table, in the case of Example 1 without masking, it is natural that a potential remains in the cyan part. Even when the masking effect according to the above-mentioned invention of 2 is exhibited, the cyan component disappears, but B(
The surface potential corresponding to the blue) and BL (black) areas decreases, and as a whole, cyan is emphasized in the B (blue) area and magenta is lost in the BL (black) area, making it impossible to obtain optimal masking. .

Example 1: No masking 1:4 Example 2: With masking 1:4 Example 3: With masking 7:・〇Table 1 Also, the electrical capacitance ratio of the photoreceptor and transparent insulator is B (blue)
Even if the reproduction ratio of BL and BL (black) is set to 7:10 as in Example 3 of Table 1, the overall surface potential decreases, resulting in insufficient density.

The above shows that even though the ratio of the amount of magenta mixed in the cyan component and the ratio of the amount of yellow mixed in the magenta component are different, it is basically impossible to perform optimal masking for both under the same conditions. This is because it is occurring.

The present invention eliminates the above-mentioned drawbacks and provides a method that can perform color correction on any photoreceptor and determine the optimal amount of masking without causing a decrease in surface potential. Accordingly, the optimum masking amount can be controlled more stably and reliably without having to perform extensive control. In order to achieve the above effects, the present invention first uniformly charges the chargeable surface with a primary charge, corrects the original image, and simultaneously irradiates it with uniform white light (hereinafter referred to as bias light) with variable illuminance. The first step is configured.

If the present invention having such a configuration is implemented, the potential distribution will be as shown in Table 2 based on the principle described later.

Example 4: With masking 1:4 Table 2 The present invention will be explained below with reference to the drawings.

FIG. 3 is a conceptual diagram showing the configuration of the present invention, in which an arbitrary three-layer photoreceptor 1 is first charged in a chargeable area on its surface in a first step, and an original image is transferred to a correction filter 2. At the same time, a light source 3 emits uniform white light whose illuminance can be varied by a power source 6 and a variable resistor 7.

In this case, the process may be divided into two steps: the first step, charging, bias light irradiation, and corrected image exposure. Then, in a second step, the original image 5 is subjected to spectral exposure by the spectral exposure filter 4 and at the same time is reversely charged, and in the third step, the entire surface is uniformly irradiated by the light source 8.

Incidentally, according to the prior art, AC static elimination may be performed instead of reverse charging in the second step.

With this configuration, that is, by irradiating the bias light in addition to the corrective exposure in the first step, it is possible to arbitrarily change the masking amount in the section DD in FIG. 41.

This means that, for example, the magenta component in cyan can be optimally masked by appropriately changing the bias light, and it also means that it can be done stably and reliably.

That is, in the first step, by appropriately controlling the illuminance of the bias light according to the corona charging characteristics, etc., it is possible to finally extract the magenta component of cyan and eliminate the adhesion of toner during magenta development.

It will be easier to understand that charging and simultaneous bias light irradiation are effective in determining such an optimum value by considering the schematic charge distribution diagram in FIG.

- FIG. 5 1 shows the case where bias light is not irradiated, and FIG. 2 shows the case where bias light is irradiated, and schematically shows the state of charge distribution on or within the photoreceptor in each step. 4. FIGS. 1 and 2 are potential displacement diagrams of each step corresponding to FIGS. 1 and 2, respectively.

In both Figures 4 and 5, A and A' are the respective first steps, A is the primary charging + correction (image) exposure step,
A' indicates the primary charging and correction (image) exposure + bias light irradiation process, B and B' indicate the opposite charging and sufficient light exposure process, C and C' indicate the entire surface irradiation process, L indicates the bright area, and D indicates the dark area. Show.

When developing with negatively charged magenta toner after the above steps, it is necessary to use red for the filter in the first steps A and A' and to use green for the filter in the second steps B and B'.

Figure 5 1 A, C, C and 2 indicate the original color: yellow, magenta,
Given the primary colors cyan, red, green, blue, white, and black, this indicates the photoreceptor areas corresponding to (blue, black), (cyan, green), (magenta, red), and (yellow, white), respectively. The same applies to A', 口', ', ', and ko' in FIG. 2. Since the magenta toner is negatively charged, it adheres to areas C and C' in the figure and is developed, but a considerable amount must also adhere to areas A and A' in the figure.

The amount of masking determines the amount of toner adhering to the chargeable area of the portion A, and is determined by the amount of charge in the chargeable area.

On the other hand, when comparing Fig. 4 and Fig. 5, the difference between 1 and 2 in both figures is that the D-D section in Fig. 4 1 is variable;
The reason is that part ○1D in Figure 2 is fixed.
In other words, it is possible to arbitrarily vary the charge distribution in the photoreceptor regions in sections A' and A in FIG. 5, which correspond to sections DD in FIGS. 1 and 2 in FIG. 4, respectively.

In other words, the gist of the present invention is that in the step 2 of FIGS. 4 and 5 showing the present invention, by irradiating the chargeable region of A' in FIG. 5 with bias light in the first step A'. , 4th
This means that the potential of the section DD in FIG. 1 can be changed upward or downward, and the optimal point for the amount of masking can be set arbitrarily.

In this way, the present invention can set the optimal masking point by simply performing the bias light irradiation process at the same time as the first charging process.Furthermore, as another effect of the above-mentioned configuration, masking can be achieved by simply changing the illuminance of the bias light. Since the amount can be varied, the control system can be static and the reproduced image can be extremely stable.

[Brief explanation of the drawing]

Figure 1 is a potential change diagram of the conventional method in which color correction is performed at the latent image formation stage, Figure 2 is a potential change diagram when the primary charging voltage is changed in the first two steps of Figure 1, and Figure 3 is a diagram of the original method. Conceptual diagrams of the invention, FIGS. 4, 1 and 2, and FIGS. 5, 1 and 2 are a potential change diagram and a charge distribution diagram, respectively, showing a comparison between the presence and absence of bias light irradiation,
FIG. 2...Filter for corrective exposure, 3...
Bias light source, 4...Filter for spectral exposure, 8...Light source for full-surface irradiation. Figure 1 Figure 2 Figure 3 Figure 5 Figure 4

Claims (1)

[Claims] 1 uniformly primary charging the surface of a photoreceptor that can be charged to both positive and negative polarities, irradiating uniform white light that can be arbitrarily changed, and correcting and exposing the original image at the same time as or after the primary charging, Next, the original image is subjected to spectral exposure, and at the same time, secondary charging with a polarity opposite to the primary charging or AC neutralization is performed, and then the entire surface is irradiated with uniform white light to form an electrostatic latent image. Color electrophotography.