JPH0532749B2 - - Google Patents

Description

[Detailed description of the invention]

In the present invention, developers of three primary colors, magenta (hereinafter referred to as M color), yellow (hereinafter referred to as Y color), and cyan color (hereinafter referred to as C color), are sequentially applied one by one onto electrostatic recording paper. The present invention relates to a developing method in an electrostatic recording system, in which a multicolor image is formed by subtractive color mixing. The object is to provide a developing method that enables ideal multicolor image formation by mixing three primary colors. First, subtractive color mixing using three primary colors will be briefly explained. FIG. 1 is an explanatory diagram of subtractive color mixture of three primary colors, and FIG. 2 is an explanatory diagram showing the relationship between wavelength and spectral reflectance of the three primary colors. Humans perceive hues such as red and blue because they perceive hues that correspond to the wavelength components of the light that enters their eyes. Now suppose that an image is formed using a coloring material such as a toner of hue M color 1 shown in Figure 1, and then an image of the same density is formed on top of that image using a coloring material of hue Y color 2. do. In this case, the image of M color 1 is 400 to 500 nm and 600 to 600 nm of the incident white color.
Light in the 700nm wavelength range is reflected, but 500-600n
Light in the m wavelength range is absorbed and not reflected. On the other hand, Y
Color 2 reflects light in the wavelength range of 500 to 700 nm,
Absorbs light in the wavelength range of 400 to 500 nm. Therefore, only light in the wavelength range of 600 to 700 nm is reflected from the overlapping portion of the M color 1 image and the Y color 2 image and enters the eye. Since the color corresponding to the wavelength region of 600 to 700 nm is red, the overlapping portion of M color 1 and Y color 2 is perceived as red 4. Similarly, if you overlap Y color 2 and C color 3, you get green 5, if you overlap C color 3 and M color 1, you get blue 6, and if you stack M color 1, Y color 2, and C color 3, you get black 7. . Therefore, it is possible to form images of seven different hues by combining the primary colors and color mixtures of the above-mentioned coloring materials. Next, the process of image formation using the electrostatic recording method will be briefly explained. FIG. 3 is an explanatory diagram of the image forming process of a general electrostatic recording method, in which a shows the stages of electrostatic latent image formation, b shows development, and c shows the fixing stages. There are two types of electrostatic recording paper, which is a recording medium, a two-phase type and a three-layer type, and the two-layer type will be explained as an example. The two-layer electrostatic recording paper 8 (hereinafter referred to as recording paper) has an insulating layer 8a on the surface of a paper base, and the paper base is impregnated with a conductive substance to form a conductive layer 8b. ing. As shown in FIG. 3a, when a multi-needle electrode 9 is brought into contact with the surface of the insulating layer 8a and a voltage is applied between it and the conductive layer 8b, charges are generated in the insulating layer 8a. Generally, the multi-needle electrodes 9 are insulated from each other and arranged in a line in the width direction of the recording paper 8. An electrostatic latent image is formed on the insulating layer 8a of the recording paper 8 by selectively applying a pulse voltage to the multi-needle electrode 9 according to image recording information while moving the recording paper 8 in the direction of the arrow X. The charge constituting the electrostatic latent image can be either positive or negative depending on the polarity of the applied voltage, but it is generally said that generating a negative charge is more reliable because it causes fewer so-called missing spots. The charges forming the electrostatic latent image will be explained below as negative charges. The recording paper 8 having the electrostatic latent image formed on its surface is developed by a developing device 10 as shown in FIG. 3b. There are two types of development methods: wet and dry, but in both cases, development is performed by bringing toner 10a, which is colored particles charged to the opposite polarity to the electrostatic latent image, into contact with the electrostatic latent image and causing it to be electrically adsorbed. be exposed. Since the toner that has been developed is vulnerable to mechanical shock, it is heated in the fixing device 11, which includes a heater, as shown in FIG. 8, the image forming process for one hue is completed. In the case of multicolor development, the above image forming process is repeated for the number of hues. In this case, during the development, the charge of the electrostatic latent image and the toner 10
If the charges on a are equal in polarity and equal in amount, and both charges are neutralized during development, there will be no residual charge on the image surface formed at the end of the image forming process for one hue, and subsequent There is no problem with the image formation process for other hues, but the amount of charge on the electrostatic latent image is actually larger, and in the above development, the charge on the electrostatic latent image is not completely neutralized and some residual charge remains. do. Therefore, if this amount of residual charge is large, when the second toner 10a is developed, the second toner 10a will be present even in the first image formation area where the second electrostatic latent image does not exist. are electrostatically attracted, resulting in color mixing. Therefore, for example, in the case of image formation using the hue of M color 1 in the first process and the hue of Y color 2 in the second process, ideally three colors are formed: M color 1, Y color 2, and red 4 by color mixture. However, all M color 1 is mixed with Y color 2 and becomes red 4, making it impossible to obtain an image of M color 1. The present invention was made in view of the above circumstances,
The present invention provides a developing method that uses toners 10a of three primary colors to prevent color mixing different from image information, that is, so-called fog, and to obtain images of seven different hues. The factors that cause residual charges to occur on images after development will be explained below. The reason for this is that the amount of charge on both the recording paper 8 and the developer varies widely depending on the environmental conditions even if they are charged under constant conditions. This means that even if the charges of the electrostatic latent image and the developer are adjusted to maintain a balance under a certain environment, the above balance may no longer be maintained due to changes in the environment. In the recording paper 8, the base paper is porous and easily absorbs moisture, so the volume resistivity of the insulating layer 8a that makes up the recording paper 8 varies depending on environmental conditions such as humidity, temperature, and atmospheric pressure.
It varies widely from 10 ¹⁰ to 10 ¹⁷ Ωcm. Insulating layer 8
Since a has a function similar to that of a dielectric in a type of capacitor, the amount of charged charge also fluctuates by about 60% in response to the above-mentioned change in volume resistivity. On the other hand, in the case of three primary color developers, static charges are generally applied to the developer due to friction, etc.
The amount of charge changes due to changes over time and the flow process caused by pumps, etc., and increases and decreases by about 40%. As described above, since the charge amount of both the recording paper 3 and the developer changes widely, the above phenomenon, which is relatively not a problem in monochrome recording using one type of toner, becomes a major problem related to fog in multicolor recording. Become. The present invention focuses on the fact that the charging characteristics of the three primary color developers and the minimum voltage that starts electrostatic adsorption to the electrostatic latent image are different, and multicolor development is performed by the development order according to the above-mentioned physical properties of the developer. As a result, a 7-color image without fogging and in accordance with the image information is obtained. First, let us consider the fog caused by the next developer on the image forming area. When the surface potential due to the electrostatic latent image charge on the recording paper 8 is constant, the surface potential of the image area due to the residual charge on the image area after electrostatically adsorbing each developer of M color 1, Y color 2, and C color. Assuming that the order of potential magnitude is C color 3 < M color 1 < Y color 2, the smaller the absolute value of the surface potential due to the residual charge in the image area, the more the next developer will be electrostatically attracted to that area. Hateful. Therefore, if we focus only on the residual charge in the image area, the fog will be minimized if the developer is developed in the order of C color 3, M color 1, and Y color 2. Next, the potential of the electrostatic latent image at which each developer starts adhering to the electrostatic latent image will be considered. Now, if the order of the above-mentioned adsorption start electrostatic latent image potential values for each developer is C color 3 < M color 1 < Y color 2, then the higher the adsorption start electrostatic latent image potential of the developer, the harder it is to adsorb. Assuming that the amount of residual charge after development is constant, the developer is difficult to be adsorbed by the residual charge on the image forming surface that has already been formed, so the developer will be applied in the order of C color 3, M color 1, and Y color 2. It is more advantageous in terms of fog prevention when the color is developed in the order of the hues of Y color 2, M color 1, and C color 3 at least. Focusing on the fact that there are differences in the amount of residual charge after development and the electrostatic latent image potential at the start of adsorption of the developer depending on the developer, we conducted an experiment to find that when developing in the order of C color 3, M color 1, and Y color 2. The most excellent 7-hue image was obtained compared to the case where the images were developed in the same order. Table 1 shows the development order of the developer and the obtained color tone according to the experiment.

[Table] In the table, the ○ mark indicates a case where the theoretical hue was obtained, the △ mark indicates a case where the hue was slightly different from the theoretical hue, and the × mark indicates a case where the theoretical hue was completely different. As described above, in item 5, the theoretical seven hues are obtained only when the development order is C color 3, M color 1, and Y color 2. An example of the various conditions for the above experimental example is described below. The voltage applied to the recording paper 8 is 600V, the surface potential of the electrostatic latent image generated by the above applied voltage is 40 to 100V,
When the potential of the three primary color developers is 8 to 15V, the surface potential of the image surface due to the residual charge of each developer immediately after development is 15V for C color 3, 23V for M color 1, and 23V for Y color 2.
It was 32V. Note that there is a method to remove the residual charge on the image forming surface using a static eliminator such as a corona discharge, but it is extremely difficult to reduce it to zero, and the static eliminator may even induce charging, so it is not a stable effect. I can't. As described above, according to the multicolor development method according to the present invention, an image with seven hues according to the image information can be obtained without removing the residual charge after development, so that the practical effect is extremely large.

[Brief explanation of the drawing]

Figure 1 is an illustration of subtractive color mixing of 3 primary colors, Figure 2 is 3
An explanatory diagram showing the relationship between primary color wavelength and spectral reflectance,
FIG. 3 is an explanatory diagram of an image forming process using a general electrostatic recording method. 8... Electrostatic recording paper, 10... Developing device, 10a...
...Toner, 11...Fuser.

Claims (1)

[Claims] 1. In an electrostatic recording method in which an electrostatic recording paper that forms an electrostatic latent image is used as a recording material and is developed multiple times with one type of developer of at least magenta, yellow, and cyan, the development is performed using the developer. The electrostatic latent image potential at the start of adsorption and the surface potential of the image due to the residual charge immediately after development are carried out in the order of cyan, magenta, and yellow, from the lowest absolute value to the highest absolute value of the surface potential of the image. Multicolor development method in recording system.