JPH0264665A - Two color image forming device - Google Patents

Abstract

PURPOSE:To obtain a two-color image forming device of high speed, low cost, and small size with a simple constitution by utilizing developer of two colors, which have opposing electrifying polarity to each other, and switch controlling the image exposing levels to a photosensitive body in the three stages of non- exposure, strong exposure, and weak exposure. CONSTITUTION:The surface of the photosensitive body 3 is uniformly electrified by an electrifying device 4, and this electrified part receives a light image exposure with its level controlled by a signal generating device 5 by switching to the three stages of non-exposure, strong exposure, weak exposure, and an electrostatic latent image is formed on the surface of the photosensitive body 3. In this case, developer of two colors, which have the opposing electrifying polarity to each other are provided inside a same developing device 6, one color is developed on the non-exposure part, the other color is developed on the strong exposure part, and the weak exposure part is not developed by either developer. Thus, a high speed, low cost, and a small sized two-color image forming device with a simple constitution can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming apparatus using electrophotographic technology,
In particular, it relates to electrophotographic processes for obtaining two-color images.

[Prior Art] Conventionally, a toner image is formed on an image carrier such as a photoconductor,
Image forming apparatuses that utilize so-called electrophotographic technology, which repeats the printing process by cleaning the surface of the image carrier after being transferred and fixed to recording paper, have recently been put into practical use, and have recently become capable of producing multicolor images. 2. Description of the Related Art Devices (hereinafter referred to as multicolor image forming devices) are beginning to become widespread.

Such a multicolor image forming apparatus repeats a printing process on a sheet of recording paper a number of times corresponding to the number of color types, and a developing device used in the printing process prints the multicolor image in a number corresponding to the number of color types. It is usually provided within the forming device. Specifically, in the case of a two-color image forming apparatus, the printing process is repeated twice for -sheets of recording paper, and two developing devices are provided within the two-color image forming apparatus.

[Problem to be Solved by the Invention 1] However, in the case of the multicolor image forming apparatus described above, since the printing process is repeated many times on a sheet of recording paper, only -
The problem is that it takes several tens of seconds to several minutes to print a sheet. In addition, the running costs for printing are: recording paper cost, electricity cost, printing process cost x number of times the printing process is repeated,
Consists of the sum of Among these, the printing process type has the highest unit cost, so multicolor image forming apparatuses that repeat the printing process many times also have the problem of high running costs.

Furthermore, since the multicolor image forming apparatus is always equipped with a number of developing devices corresponding to the number of colors, (1) the main body of the multicolor image forming apparatus is very large.

(2) The price of the multicolor image forming apparatus becomes higher than in (1).

It also had the following problems.

The present invention is intended to solve these problems, and its purpose is to provide a two-color image forming apparatus that has an extremely simple configuration, is fast, inexpensive, and compact.

[Means for Solving the Problems] A two-color image forming apparatus of the present invention is an image forming apparatus using electrophotographic technology, in which two-color developers having different charging polarities are provided in the same developing device. , the image exposure level on the photoreceptor is switched and controlled in three stages: non-exposure, forced light, and weak exposure, one color of the developer is used to develop the non-exposed area, and the other color is used to develop the image on the forced light. The method is characterized in that a two-color image is obtained in one printing process by controlling the voltage applied to the developing device so that the weakly exposed portions are not developed with any of the developer.

[Function] According to the present invention, the two color developers are charged with mutually different polarities. That is, they are charged positively or negatively. The charged developer has a potential difference (hereinafter, Vs −Vs
Development is selectively carried out in accordance with the magnitude and direction of the developing potential difference (denoted as Δ■ and development potential difference Δ■), and specifically, as follows.

(t) When V, >Vs, the sign of Δ■ is positive, and a positively charged developer appears.

(2) When VB <V, the sign of Δ■ is negative, and the negatively charged developer is developed.

(3) In the case of V, = V, △■ = 0, and there is no potential difference, so there is no development.Based on the above explanation, the image exposure level to the photoreceptor is switched to three levels, and the level is switched to three levels. The relationship between the surface potential (3) of the photoreceptor in the image exposure area and the voltage V applied to the developing device, which is set to a certain value, is expressed by (1), (2) and (
If control is performed so that 3) applies to each of them, it is possible to obtain a two-color image in one printing process.

[Embodiment 1] FIG. 1 is a sectional view for explaining the process of a two-color image forming apparatus according to the present invention. A drum-shaped photoreceptor 3, which is formed by laminating a photoconductive layer 2 on a conductive substrate l made of aluminum or the like, is rotated in the direction of arrow Y, and the surface of the photoreceptor 3 is first uniformly charged by a charger 4. be done. This charged portion receives an optical image exposure whose level is switched in three levels by the optical signal generator 5, and an electrostatic latent image is formed on the surface of the photoreceptor 3. This electrostatic latent image is visualized by a developer when it passes through a developing device 6 that forms a magnetic brush. The developer image thus formed is aligned to one of the polarities (negative in the figure) by the charge polarity controller 7, and has a polarity opposite to that of the charge polarity controller 7 (positive in the figure). The image is transferred from a transfer paper stacker (not shown) onto a transfer paper 11 fed to a transfer position in synchronization with the developer image on the photoreceptor l by the transfer device 8 to which a voltage of .

After the transfer, the transfer paper 11 is sent to a device 12 comprising a photoreceptor 3, and is ejected to a paper ejection tray (not shown). Approximately 30 to 40% of the untransferred developer remains on the surface of the photoreceptor 30 after the transfer has been completed as described above, and this residual developer is removed by the cleaning device 9. In the two-color printing method of the present invention, the photoreceptor 3 that has been cleaned is subjected to static electricity removal by a static elimination lamp lO to a certain level, and is prepared for the next image forming process by continuously repeating a series of 0 or more steps. It is an image forming apparatus. Here, the material of the photoconductive layer 2 is OPC・α-5i-ZnO-3e
-CdS, etc., and the optical signal generator 5 can be a laser, LED, LCS, etc. or,
The image exposure level switching means of the optical signal generating device 5 includes:
No matter which method is used, such as switching the output of the light source, adjusting the image exposure size, switching the lighting time of the light source, or using a filter, it will not affect the image forming process of the two-color image forming apparatus in the present invention.

FIG. 2 is a diagram showing the potential relationship between the distribution of an electrostatic latent image and how the developer is developed in the two-color image forming apparatus according to the present invention. Each symbol will be explained here.

A--Unexposed area, the surface potential of which is Voff.

B - Indicates a strongly exposed area, the surface potential of which is V.

n 2 ・C - Indicates a weakly exposed area, its surface potential is ■0n+a V8 - Indicates the voltage applied to the developing device, its value is Von+
be equivalent to.

If each item is set as described above and the sign of each item is negative, then A
In the non-exposed area of B, the sign of the development potential difference ΔV is positive, and the positively charged developer is developed, and in the strongly exposed area of B, the sign of the development potential difference ΔV is positive.
The sign of V is negative, the negatively charged developer is developed,
Further, in the weakly exposed area C, the development potential difference Δ■=0, and since there is no potential difference, no developer is developed.

FIG. 3 is a diagram showing the relationship between the development potential difference of the developer used in the two-color image forming apparatus of the present invention and the optical reflection density of the resulting image. The optical reflection density depends on the magnitude of the development potential difference ΔV, and when the development potential difference ΔV exceeds a certain value, the optical reflection density is saturated. Here, when the sign of the development potential difference △V is positive, the developer is positively charged, and when the sign of the development potential difference is negative, the developer is of a different color from the positively charged developer and is negatively charged. The developer is used for development.

[Effects of the Invention] As described above, the two-color image forming apparatus of the present invention has the following effects:
A two-color image can be formed in a single printing process, and only one developing device is required for the two-color image forming apparatus, so the two-color image formation device has an extremely simple configuration, and is fast, inexpensive, and compact. The device can be realized.

Furthermore, the running cost is low and it is user-friendly in all respects.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining the process of the two-color image forming apparatus according to the present invention. FIG. 2 is a diagram showing the potential relationship between the distribution of an electrostatic latent image and the manner in which developer is developed in the two-color image forming apparatus according to the present invention. FIG. 3 is a diagram showing the relationship between the development potential difference Δ■ of the developer used in the two-color image forming apparatus of the present invention and the optical reflection density of the obtained image. Figure 1

Claims (1)

[Claims] In an image forming apparatus using electrophotographic technology, two color developers with different charging polarities are provided in the same developing device, and the image exposure level on the photoreceptor is set to three levels: non-exposure, strong exposure, and weak exposure. One color of the developer develops the non-exposed area, the other developer develops the strongly exposed area, and none of the developers develops the weakly exposed area. A two-color image forming apparatus, characterized in that a two-color image is obtained in one printing process by controlling the voltage applied to the developing device so as to prevent the development from occurring.