JPS6358465A - Two-color electrophotographic copying method - Google Patents

Abstract

PURPOSE:To reproduce sharp black color without requiring any complicated latent image-forming process by developing an electrostatic latent image in a state of applying development bias voltage as high as the surface potential of a first image part or higher than it. CONSTITUTION:A photosensitive body 1 is electrically charged by a charging corotron 3, exposed to light without using a color separation filter 2 to form an electrostatic latent image corresponding to the black image of the 2-color original, and subjected to a first development with a first developing device 4 using an electrically conductive black toner as a developer. Then, the photosensitive body 1 is charged by the corotron 3, subjected to second exposure through an A color separation filter 2 to form an electrostatic latent image corresponding to the black image part and the A color image part, developed with a second developing device 5 using an insulating A color toner as the developer, and the bias voltage as high as the surface potential of the black toner attached part or higher than it is applied from a bias voltage source 9, thus permitting the A color toner not to attach onto the black toner, and the black toner not to be recovered electrostatically to the side of the second developing device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a two-color electrophotographic copying method for copying a two-color image from a two-color original image.

[Conventional technology]

Conventionally, various processes have already been proposed as two-color electronic copying methods. For example, JP-A-53-115238
The method described in the publication uses a laminated photoconductor or a general photoconductor and a screen photoconductor, and colors A and B are printed on the photoconductor.
A process in which an electrostatic latent image consisting of + and -1O potentials corresponding to the color and background area is formed, and the A color area and B color area are developed using two color toners of different polarities from these electrostatic latent images. It has become.

However, since the photoreceptor used needs to be a special product, the photoreceptor becomes a sacrifice and lacks versatility. Furthermore, there is a problem in that the process of forming a latent image becomes considerably complicated, and the structure and control system of the copying apparatus also become complicated accordingly.

In addition, as another method, for example, JP-A-50-3424
There is one described in Publication No. 0. This is done by forming an electrostatic latent image of only one color image on a normal photoreceptor through a color separation filter, and then developing it with one color toner and then passing it through another color separation filter to form an electrostatic latent image of the other color. A two-color image is formed by forming an electrostatic latent image of only one color, which is further developed with the other color toner, and then transferred onto transfer paper to fix the two-color image.

[Problem that the invention seeks to solve]

In this way, the method using color separation filters can avoid complicating the device compared to the former method, and can also improve the degree of freedom in design. However, when one of the two colors is black, there is a problem that not only the black toner but also the other color toner is developed in the black image area, making it impossible to reproduce a clear black color.

The present invention was created in view of these problems, and an object of the present invention is to provide a two-color copying method that does not require a complicated latent image formation process and is capable of reproducing clear black color. .

[Means for solving problems]

In order to achieve the above object, the two-color electrophotographic copying method of the present invention develops an electrostatic latent image corresponding to one color portion of an original document formed on a photoconductor with a conductive toner of a first color. to form a first image, then form an electrostatic latent image corresponding to the two-color portion of the document on the photoreceptor, and further develop the electrostatic latent image to a surface potential higher than the surface potential of the first image portion. The insulating toner of the second color is attached to a portion of the photoconductor corresponding to the other color portion of the document by developing with the insulating toner of the second color while a bias voltage is applied. do.

[Effect]

The present invention will be described in detail using a specific example of forming black and A-color copies from a two-color original having black and A-color original images.

The charged photoreceptor is exposed to light reflected from the image of the two-color original, and an electrostatic latent image corresponding to the black image is formed.

This electrostatic latent image is then developed with black conductive toner. As a result, a black toner image of approximately -layer corresponding to the black color of the original is formed on the photoreceptor.

Next, the photoreceptor is charged again, and a second exposure is performed with original light passing through the complementary color filter of color A. As a result, an electrostatic latent image is formed on the photoreceptor, with the black portion and the A color portion serving as image portions. This electrostatic latent image is developed a second time with A color insulating toner. At this time, a bias voltage of approximately the same level as or higher than the surface potential of the black toner adhering portion is applied. Due to the presence of this bias voltage, there is still a potential difference sufficient for development in the A color area, but there is no potential difference contributing to development in the black toner adhered area. Therefore, the A color toner is never developed on the black toner.

In this way, a toner image of only black toner is formed on the photoconductor after the second development process in the part corresponding to the black part of the document, and a toner image of only A color toner is formed in the part corresponding to the A color part. A toner image is formed.

Through the steps described above, black and A-color copies are formed from a two-color original having black and A-color original images.

〔Example〕

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, features of the present invention will be specifically described based on examples with reference to the drawings.

FIG. 1 is an explanatory diagram showing the process of image formation according to the present invention, and FIG. 2 shows a copying apparatus used in the copying method according to the present invention. In the figure, W is the background corresponding to the black part of the original. Ao indicates the A color part.

In the figure, numeral 1 is a photoreceptor having photosensitivity at least in the A color gamut. First, after charging the photoreceptor 1 with the charging corotron 3 (Fig. 1 (al)), by exposing it to light without going through the color separation filter 2, it corresponds to the black part image of the two-color original (Fig. 1 (gl)). form an electrostatic latent image (Fig. 1)
), and this electrostatic latent image is developed once by the first developing device 4 using black conductive toner as a developer.

Through the above process, a black toner image of approximately -layer corresponding to the black color of the original is formed on the photoreceptor 1 (FIG. 1(C)).

After the first development, the photoreceptor 1 is transferred to the second developing device 5. Transfer device6. They are sequentially transported to the cleaning device 7. During the conveyance process in this -th cycle, these second developing devices 5. Transfer device6. Both cleaning devices 7 are moved away from the photoreceptor 1. With this operation, the black developing section is conveyed under the charging corotron 3 again without any change, and enters the second cycle.

The photoreceptor is charged a second time by the H corotron 3 (fd+ in Figure 1), and is further exposed to a second light through the color separation filter of color A (complementary color filter of color A) 2. An electrostatic latent image is formed having the black part and the A color part as image parts as shown in FIG.

The state of this latent image is shown in FIG. 3, where (i) shows the case where the black toner in the first development is a conductive toner, which corresponds to this embodiment. Further, (ii) is a case where the black toner in the first development is an insulating toner.

When the developed image is conductive toner, as shown in (i), the charged potential is much lower than that of the area without toner.On the other hand, the black toner in the first development is insulating toner. In this case, as shown in (ii), the first toner is charged to a level where there is almost no difference in potential between the two. In this embodiment, the first toner is charged to a level where there is almost no difference in potential between the two. To avoid adhesion of second developing toner to a developing section.

This electrostatic latent image is subsequently conveyed to the first developing device 4, but at this time, the first developing device 4 has moved the photoreceptor 1 to a position where it cannot be developed. By this operation, the electrostatic latent image is
It reaches the second developing device 5 portion without being developed by the developing device 4. During the first cycle, the second developing device 5 was moved to a position where it did not develop the photoreceptor 1, but during the second cycle, it returned to the position where it developed the photoreceptor 1. , the electrostatic latent image is developed a second time by this second developing device 5. The second developing device 5 uses insulating toner of color A as a developer, and the sleeve constituting the developer carrier of the second developing device 5 has a surface potential that is approximately the same as or higher than the surface potential of the black toner-attached portion. A bias voltage of the above level is applied from the bias voltage power supply 9.

To further explain with reference to FIG. 4, with this bias voltage, there is still a potential difference in the A color area that can be developed, but there is no potential difference in the black toner attached area that contributes to development. Therefore, the A color toner becomes the black toner. The black toner is not developed on top of the toner, and the black toner is not electrostatically collected on the second developing device 5 side.

On the other hand, in the non-image area, a reverse potential corresponding to the developing bias is generated. However, in this embodiment, the second
Since an insulating toner is used for development, it is easy to set the charging polarity in advance to the opposite polarity of the A color latent image polarity, that is, the same polarity as the potential generated in the non-image area. toner adhesion is avoided.

In this way, on the photoreceptor 1 which has undergone the second development process, a toner image of only black toner is formed in the part corresponding to the black part of the document as shown in FIG. A toner image of only A color toner is formed in a portion corresponding to .

This toner image is subsequently sent to a transfer device 6. 1st
In the second cycle, the transfer device 6, which has been separated from the photoreceptor 1, moves to a state close to the photoreceptor 1, and transfers the toner image onto the transfer paper 8.

After the transfer, the photoreceptor 1 is further cleaned by the cleaning device 7, and upon completion of this process,
The cycle of two-color copying is completed.

Note that the photoreceptor 1 used in this embodiment is selected to be one that is sensitive to the entire wavelength range or a part of the spectral characteristics of the color portion of the document. In addition, it is necessary to have good developability for charged toner, and an inorganic photoreceptor such as ZnO or a-5i or a photoreceptor is used. Further, the toner used in the first development has a volume resistivity of 10@Ωc11 or less and is electrically conductive, and is colored with a dye or a material of a desired color.

Since the toner used in the second development of this embodiment needs to be charged to one polarity before development, it has an insulating property with a volume resistivity of 10-4 Ωcm or more,
It is made of a material that is charged to a polarity different from that of the photoreceptor, and is colored in a desired color.

In addition, as a developing method for the toner used in the second development, magnetic brush development using a mag roll or touchdown development in which a conductive toner is made magnetic and trimmed into a thin layer on a sleeve can be used. Since the toner used is a conductive toner, the transfer device 6 can use a non-electrostatic transfer method such as an adhesive transfer method using St rubber or the like, or a static transfer method such as ordinary corotron transfer by insulating the transfer paper. An electrical transfer method is employed.

Next, an experimental example will be explained.

A ZnO photoreceptor having the spectral absorption characteristics shown in FIG. 5 is charged with one corona, and a document containing a black area and an edge is exposed to light to form an electrostatic latent image consisting of a background knee of 10V, an edge knee of 3QV, and a black area knee of 550V. was formed.

Subsequently, in case C, when the first development was carried out by one-component magnetic brush development using black toner for VHS manufactured by 3M, approximately one layer of toner adhered only to the black part of the latent image.

Next, the photoreceptor was corona charged, and then imagewise exposed for the second time through a red filter (roughtened gelatin filter #25 manufactured by Kodasoku) and an infrared cut filter.

Incidentally, FIG. 6 shows the spectral transmittance characteristics of this red filter.

By this process, the background part knee 10V,
Edge: -550V, black area (first developed image already attached): -220V electrostatic latent image was formed.

Next, the photoreceptor 1 was developed with a developing bias of 1220 μm applied to a one-component magnetic brush made of green insulating magnetic toner. As a result, the green insulating toner is developed in approximately one layer in the green latent image area, while the first layer is developed in the black latent image area.
No new development was performed except for the black toner that had already adhered during development, and the black toner was maintained in substantially the same state as the first developed image.

Furthermore, almost no toner adhesion was observed in the background area.

Furthermore, after adhesively transferring this developed image to a silicone sheet,
When the silicone sheet was brought into close contact with plain paper and pressed while applying heat from the plain paper side, a clear image consisting of black toner and green toner was formed on the plain paper.

〔Effect of the invention〕

As explained above, in the two-color electrophotographic copying method of the present invention, when the first developed image of conductive black toner is recharged, the charged potential becomes lower than that of the area where no toner is present. By using an insulating toner for the second development and applying a developing bias equal to the charging potential of the black toner developing area, it is possible to avoid developing the other color toner in the black toner developing area. Therefore, it is not necessary to use special specifications for the photoreceptor even for two-color copying, and the developing equipment in the copying apparatus can be simplified.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the process of image formation according to the present invention, FIG. 2 is a schematic diagram of a two-color copying apparatus for carrying out the method according to the present invention, and FIG. 3 is a diagram showing conductive and insulating toners. A graph showing the surface potential of an electrostatic latent image when using
Figure 5 shows the spectral absorption characteristics of the ZnO photoreceptor used in the example of the present invention, and Figure 6 shows the spectral transmission characteristics of the color separation filter. be. 1: Photoreceptor 2: Color separation filter 3: Charging corotron 4: First developer 5: Second developer 6
: Transfer device 7: Cleaning device 8: Transfer paper 9: Bias voltage power supply Patent applicant Fuji Xerox Co., Ltd. Agent
Masu Kobori (2 idiots) Fig. 1 (0) No.-f Electrical Dictionary +/- 5 yun +/- 5 aw w (C) B-Critique Knee- (lt&black To-size-) (f) No. = 5JLf Special B: ====:===:
=ko (9) Manuscript Figure 2 Figure 3 (12%93 TogeYkattotE1#I@tdU'WL
) Figure 4 10 Figure 5 Figure 6 Flea (mouth m)

Claims (1)

[Claims] 1. Develop the electrostatic latent image corresponding to one color portion of the document formed on the photoreceptor with a first color conductive toner to create a first image.
forming an image, then forming an electrostatic latent image corresponding to the two-color portion of the original on the photoreceptor, and applying a developing bias voltage higher than the surface potential of the first image portion to the electrostatic latent image; The two-color electronic device is characterized in that the insulating toner of the second color is attached to a portion of the photoreceptor corresponding to the other color portion of the document by developing the insulating toner of the second color in the state of Photocopying method.