JPS6011352B2 - 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 for reproducing the colors of a color original as faithfully as possible to obtain an excellent color copy image.

An electrophotographic photoreceptor has a photoconductive layer formed on a conductive support, and the conductive support may be a metal such as an aluminum plate or aluminum foil, or a paper or plastic sheet that has been subjected to conductive treatment. The photoconductive layer is made of an inorganic or organic photoconductive substance such as selenium, a mixture of zinc oxide (or titanium oxide, etc.) and a resin, or poly-N-pynylcarbazole. It is well known that this is a method of obtaining a duplicate image (copy) using a photoreceptor as described above, through the steps of charging a photoconductive layer, exposing the image to light, and developing it.
In color electrophotography, a photoreceptor as described above is used, and the above steps are repeated at least twice, each time exposing to light through a different colored filter and developing with a different colored developer (toner). As is well known, in the commonly used color electrophotographic method, the above steps are repeated three times.

To summarize and explain this, the original drawing of multicolor (color) is
The colors are separated by blue, green, and red filters, and electrostatic latent images corresponding to the respective filters are formed on the photoconductive layer of the photoreceptor. Toners of complementary colors, that is, yellow, magenta, and The three-color images obtained by developing with cyan toner are aligned and the colors are superimposed to obtain a color copy image corresponding to the color original. However, none of the above steps are carried out according to theory, and the spectral characteristics of the color separation filter, the sensitivity of the photoreceptor, the developer, the lens, and the mirror are far from ideal.

Among them, it is not possible to obtain an ideal developer. This is because, as shown in Figure 1, the spectral reflectance of each yellow, magenta, and cyan developer is based on the green light (light with a wavelength of 500 to 60 nm) that should be reflected by the cyan developer. ) and red light to be absorbed (600-7
It reflects a considerable amount of light (light from the 0-board side). The magenta developer absorbs a significant amount of blue light (400-50 degrees of light) that should be reflected and reflects a significant amount of green light that should be absorbed. Due to these characteristics, accurate color reproduction cannot be obtained from the color original. Among the three developer colors of yellow, magenta, and cyan, yellow shows the closest value to the theoretical value, and cyan shows the farthest value.

Therefore, in order to reproduce a color original using three colors, it is necessary to use cyan as the base color and weaken the other colors. The present invention
It was developed to achieve this purpose by charging two photoconductors with different polarities, and irradiating one photoconductor with a color-separated image of the original color image. After irradiating two photoreceptors with a light image having color components to be color-corrected, the two photoreceptors each having an electrostatic latent image are aligned and brought into contact, and the color correction is performed on one photoreceptor. The method is characterized in that it includes a step of forming a latent image. The color electrophotographic method of the present invention will be specifically explained with reference to the drawings.

In FIG. 2a, 1G is an N-type electrophotographic photoreceptor having a photoconductive layer made of, for example, polyvinylcarbazole on a conductive support, and 2 is a photoconductive layer made of, for example, selenium on a conductive support. It is a P-type electrophotographic photoreceptor having layers, each of which is negatively and positively charged.

After giving a negative charge to the photoconductive layer of the photoreceptor 1 by a negative corona discharge, image exposure is performed using tungsten white light through a color original 3 using a green filter 4, as shown in FIG. 2b. A color-separated electrostatic latent image is formed on the photoconductive layer. The state of charging is qualitatively indicated by the number of negative signs. Some negative charge remains in the cyan and green areas as well. On the other hand, using the photoreceptor 2, after applying a positive charge to the photoconductive layer by positive corona discharge, image exposure is performed with tungsten white light through the color original image 3 using the red filter 5, and color separation is performed. A static exposure latent image is formed on the photoconductive layer. The state of charging is qualitatively indicated by the number of positive signs. When the surfaces of the photoconductive layers of the photoreceptors 1 and 2, on which negative and positive static latent images have been formed respectively as described above, are aligned and brought into contact as shown in FIG. 2d, the photoreceptor The negative charge on the body 1 is neutralized by the positive charge on the photoreceptor 2, and the charged state of the photoreceptor 1, that is, the distribution state of the charges becomes as shown in FIG. 2e.

The photoreceptor 1 is brought into contact with the transfer paper 6 and pressure is applied (see FIG. 2 f) to transfer the static latent image on the photoreceptor 1 to the transfer paper 6.
When this transferred electrostatic latent image is developed with a positively charged magenta developer (magenta dusk toner), a magenta image is formed on the surface of the transfer paper 6, as shown in FIG. 2g. Ru. Next, as shown in FIGS. 3a to 3g, the steps described in FIGS. 2a to 2f are repeated, except that a blue filter is used for photoreceptor 1 and a green filter is used for photoreceptor 2. The same process forms a negative electrostatic image on the transfer paper, which is developed with a positively charged yellow developer (yellow toner). In this case, the transfer paper is
Transfer paper on which a magenta image has already been formed is used. To explain this, a blue filter 7 is applied to the N-type photoreceptor 1 and the P-type photoreceptor 2 shown in FIG. 3A through the color original image 3, as shown in FIGS.
Imagewise exposure is performed using the green filter 4 and a color-separated static latent image is formed on each photoconductive layer of the photoreceptors 1 and 2. The state of charging is qualitatively indicated by the number of negative and positive signs. When the surfaces of the photoconductive layers of photoreceptors 1 and 2 are aligned and brought into contact as shown in FIG. 3d, photoreceptor 1 having a charged state as shown in FIG. 3e is obtained. A transfer paper 6 having a magenta image is brought into contact with this photoreceptor 1 (see FIG. 3 f), and the transferred static latent image is developed with a yellow developer (yellow toner) having a positive charge. , as shown in FIG. 3g, the transfer paper 6
A yellow image is formed in addition to a magenta image on the surface. Next, as shown in FIGS. 4a and 4b, after applying a negative charge to the light guide layer of the N-type photoreceptor 1, image exposure is performed using the red filter 5 through the color original image 3,
A color-separated electrostatic latent image is formed on the photoconductive layer, and this electrostatic latent image is transferred to transfer paper 6 on which magenta and yellow images are formed, as shown in FIG. When the resulting static exposure latent image is developed with a positively charged cyan developer (cyan toner), a cyan image is formed in addition to magenta and yellow images, as shown in Figure 4d. , it is possible to obtain a color copy image that is relatively faithful to the color of the color original.

By the method of the present invention as explained above, a reproduced image whose color is faithful to the color of the original drawing can be obtained because:
As shown in FIGS. 2 to 4, two photoreceptors 1
and 2 are charged with different polarities, that is, negative and positive, and photoconductor 1 is irradiated with a color separated image of the color original image, and photoconductor 2 is irradiated with a light image having color components whose color is to be corrected. After that, the photoreceptors 1 and 2 having negative and positive electrostatic latent images are aligned and brought into contact, and the photoreceptors 1 and 2 are brought into contact with each other.
After forming a color-corrected static latent image, this electrostatic latent image was transferred to a transfer paper, and the process of developing was repeated twice, and in the third time, a red filter was used. By forming a negative latent image on the photoreceptor 1, transferring it and developing it, the green and red colors of the original image can be relatively faithfully reproduced, as shown in FIG. 4d. Further, the yellow, magenta and cyan colors of the color original image are faithfully reproduced by yellow, magenta and cyan toners, respectively.

In this case, less magenta toner adheres to the area corresponding to the blue-purple color of the original image compared to cyan toner, so a strong cyan blue-purple color is reproduced. It must be acknowledged that there is a drawback in that a strong magenta red color is reproduced because less yellow toner adheres compared to color toners.Examples of the present invention are shown below.

A layer of an organic photoconductive material containing 1 mole of 214,7-trinitro-9-fluorene per monomer unit of poly-N-vinylcarbazole was formed on an aluminum drum to a thickness of 12 µm to form a photoreceptor. Photoreceptor 2 was prepared by depositing a layer of Se--Te in a weight ratio of 97:3 to a thickness of 50 um on an aluminum drum by vapor deposition.

First, a magenta image is formed.

Using a charger on the photoreceptor I, 17. Corona discharge of blood V provided a negative charge to charge the photoconductive layer. Its surface potential was -900V. Green separation filter (
Kodak Ratten Filter No. 58) using
Exposure was carried out through a color original. The exposure amount in this case was such that the surface potential of the photoreceptor area (photoconductive layer) corresponding to the white part of the color original became about -350 V, and in this case, it was 150 lux·sec. On the other hand, the photoreceptor 2 was charged by corona discharge of 14.0 kV so that the surface potential of the photoconductive layer was 1300 V. Red correction filter (Kodak Ratten Filter N
o. 25) and was exposed through a color original. The exposure amount in this case was such that the surface potential of the photoreceptor area corresponding to the white portion of the color original became OV, and in this case, it was about 130 lux·sec. When photoreceptors 1 and 2, which have been exposed respectively, are aligned and brought into contact, a modified static haze image for forming a magenta color image is formed on photoreceptor 1, and this static latent image is transferred. It was transferred to paper by applying pressure.

Transfer paper has a dielectric layer made of resin on the surface of base paper.
A conductive agent is coated on the back side. The transfer paper with the electrostatic latent image was developed using a liquid developer containing positively charged magenta toner to obtain a color-corrected magenta image, and then thoroughly dried in a dryer. . On the other hand, photoreceptors 1 and 2 are quenched by a quenching lamp and used for the next step. In the above, the surface potential of each region of the photoconductive layer after photoreceptors 1 and 2 were exposed using a green filter and a red filter, respectively, the surface potential of photoreceptor 1 after correction and after transfer, and the surface potential formed on transfer paper. The density of the magenta color image obtained is shown in Table 1 below.

Table 1 Next, a yellow image is formed.

After photoconductors 1 and 2 were charged in the same manner as in the previous magenta image formation, photoconductor 1 was charged using a blue separation filter (Kodak Wratten Filter No. 47B). , exposure was carried out through a color original. The exposure amount in this case is such that the surface potential of the photoreceptor area (photoconductive layer) corresponding to the white part of the color original becomes -350V;
It was a look second. On the other hand, the photoreceptor 2 is equipped with a green filter (Kodak Ratten Filter No. 58).
), exposure was carried out through a color original. The amount of light in this case was such that the surface potential of the photoreceptor area corresponding to the white part of the color original was OV', and in this case, it was 80 lux·sec. The photoreceptors 1 and 2, each exposed as described above, are brought into contact in the same manner as before,
A modified electrostatic latent image for forming a yellow image is formed on the photoconductor 1, and this electrostatic latent image is transferred to the transfer paper on which the previous magenta color image was formed, and contains a positively charged yellow toner. A color-corrected magenta+yellow copy image was obtained, which was dried in the same manner as before.

In the above, the surface potential of each region of the photoconductive layer after exposing photoreceptors 1 and 2 to light using a blue filter and a green filter, respectively, the surface potential of photoreceptor 1 after correction and after transfer, and the surface potential of photoreceptor 1 after exposure to light using a blue filter and a green filter, respectively, and the surface potential on transfer paper. The density of the yellow image formed is shown in Table 2 below.

Table 2 Next, a cyan image is formed.

Since there is no need for color correction to form a cyan image, the photoreceptor 2 is not used. After the photoreceptor 1 was charged in the same manner as before, it was exposed to light using a red separation filter (Kodak Wratten Filter No. 25) in the same manner as before. The exposure amount in this case was also such that the surface potential of the photoreceptor area corresponding to the white portion of the color original was -250 V, and in this case, it was 70 lux·sec. The static exposure latent image formed on the photoreceptor 1 by exposure as described above is transferred to a transfer paper on which a magenta and yellow image is formed, and a liquid developer containing positively charged cyan toner is used to It was developed and dried as before to obtain a color copy image formed by yellow, magenta and cyan toners.This color copy image is a relatively faithful reproduction of the colors of the color original. In the above, the surface potential of each region of the photoconductive layer after photoconductor 1 was exposed to light using a red filter, the surface potential of photoconductor 1 after transfer, and the density of the cyan image formed on the transfer paper. is shown in Table 3 below.Table 3

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the spectral reflectance of yellow, magenta, and cyan light, and FIGS. 2 to 4 are illustrative diagrams for explaining the method of the present invention, including color originals, filters, The cross sections of the photoreceptor and transfer paper are shown enlarged in the thickness direction. 1, 2... Photoreceptor, 3... Color original drawing, 4, 5, 7
...Filter, 6...Transfer paper. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 The photoconductive layer of an electrophotographic photoreceptor having a photoconductive layer on a conductive support is negatively or positively charged, and the electrostatic charge formed on the photoconductive layer by exposing it to light through a color original using a filter. In color electrophotography, the process of transferring a latent image to a transfer paper and developing it with a developer having a polarity opposite to that of the electrostatic latent image is repeated at least twice, using two photoreceptors, Each photoreceptor is charged with a different polarity, and one photoreceptor is irradiated with a color separated image of the original color image, and the other photoreceptor is irradiated with a light image having the color components whose color is to be corrected. and then aligning and bringing the two photoreceptors each having an electrostatic latent image into contact with each other to form a color-corrected electrostatic latent image on one photoreceptor. Electrophotography.