JPS604960A - Two color image forming device - Google Patents

Abstract

PURPOSE:To prevent color mixing without lowering density of the second color and to form a sharp 2-color image by successively forming the first and the second toner images on an image bearing body, and then scraping down the second toner overlaid on the first image prior to the transfer of the first and the second toner images to a transfer material. CONSTITUTION:The surface of an electrophotographic sensitive body 1 is positively charged uniformly with an electrostatic charger 13, and the body 1 is exposed to the light emitted from a light source 29 reflected with an original 2 and passed through four mirrors, 8, 9, 10, 12 and a lens 11, and a red filter 3. An electrostatic latent image formed on the body 1 is developed with a negative black toner 4 in a developing device 14. Next on the contrary, the surface of the body 1 is negatively charged with a charger 13 and it is exposed to the light reflected from the original 2 passed through the four mirrors 8, 9, 10, 12, the lens 11, and a cyan filter 5 in synchronism with the black toner image. The electrostatic latent image formed on the body 1 is developed with a positive red toner in a developing device 16, and the parts of the red toner 6 overlaid on the black toner caused by the second red color development is scraped down.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a two-color image forming apparatus.

[Prior art]

A conventional two-color color process will be explained with reference to FIG.

First, the surface of the photoreceptor 1 is uniformly positively charged; a);
An optical image of the original 2 consisting of a white background part W, a red part R1, and a black part BK is exposed through a red filter 3 (ill.

The parts corresponding to the white background part W and the red part R lose charge due to optical attenuation, and an electrostatic latent image is formed with charges remaining only in the part corresponding to the black part BK. Develop C) to obtain a black toner image. Next, the surface of the photoreceptor 1 is subjected to secondary charging (positive polarity) (dl. At this time, the polarity of the black toner 4 is also converted to positive polarity).

Then, in synchronization with the black toner image.

The optical image of the original 2 is exposed again through the cyan filter 5 (e). Charges remain in the parts corresponding to the red part R and the black part BK, and if this is developed with the red toner 6 of negative polarity, (f
), a red toner image . Here, since the polarity of the red toner and the black toner are different, if the polarity is matched (g) and the toner image is transferred onto the transfer paper 7 (h), a two-color image of red and black is obtained.

[Problems with conventional technology]

In the conventional two-color color process, black toner and red toner are superimposed on the black part of the original, which inevitably causes color mixture, resulting in a reddish-black tone in the black part overall, and especially in the black part of the original. It has the disadvantage that the quality of one image is significantly degraded when the area is halftone.

In addition, the distance between the red developing device and the photoconductor is set larger than that of the black developing device so that the magnetic brush of the red developing device contacts the surface of the photoconductor more lightly than the magnetic brush of the black developing device.
There is a way to prevent the density of the second color from being mixed by reducing the density of the second color by making the magnetic flux density of the red developer smaller than the magnetic flux density of the black developer, but the density of the second color must be made extremely thin. In this case, the effect of preventing color mixture cannot be obtained, and in this way, the second
If the color is extremely lightened, the purpose of forming a two-color image will be completely lost.

[Purpose of the invention]

In view of the above conventional drawbacks, the present invention uses a simple mechanism to prevent color mixing without reducing the density of the second color.

An object of the present invention is to provide a two-color image forming apparatus capable of forming a clear two-color image.

[Key points of the invention]

And 1. In order to achieve the above-mentioned object.

In a two-color image forming apparatus that sequentially forms a first image and a second image on an image carrier using toners of different polarities and different colors, the first and second images are sequentially formed on the image carrier. After forming, and prior to transferring the first and second images to a transfer material,
The present invention is characterized in that a scraping means is provided for scraping off the toner that has been developed and superimposed on the first image.

[Example of implementing the invention]

An embodiment of the present invention will be described below with reference to FIGS. 2 to 4.

In FIG. 2, a photoreceptor 1 serving as an image carrier is a bipolar photoreceptor and is provided so as to be rotatable in five counterclockwise directions. At the outer periphery of the photoreceptor 1, there are a charger 13.degree. and a first developer 14.degree. Second
Developer 16. Color mixing prevention device 18, polarity matching charger 2
0. Transfer device 212 Separator 22. Static eliminator 23. Each device of the cleaner device 24 is provided.

The original exposure section is provided with a light source 29. Mirrors 8, 9, 10°12, lenses 11. Red filter 3. It consists of a cyan filter 5.

A black toner replenishing device 15 is provided in the first developing device 14 .

The second developing device 16 is provided with a red toner replenishing device 17, and each toner is replenished.

The color mixture prevention device 18 also includes a bias roll 27 as shown in FIG. A scraping member 28 for scraping off the toner adhering to the bias roll 27; a toner recycling device 1 for returning the scraped toner to the second developing device 16;
It consists of 9.

Next, a two-color image forming process will be explained.

First, as the photoreceptor 1 rotates counterclockwise.

The charger 13 applies a uniform positive charge to the surface of the photoreceptor 1 (
Figure 4A). Next, the original 2 (
The reflected light from the four mirrors 8, 9°, 10.12. Lens 11.
Then, the photoreceptor 1 is exposed to light through the red filter 3. The parts corresponding to the white background part W and the red part R lose their charge due to light attenuation.

An electrostatic latent image is formed on the photoreceptor 1 in such a way that charges remain only in the portion corresponding to the black portion BK (FIG. 4B).

This electrostatic latent image is transferred to a negative polarity black toner 4 by a first developing device 14.
(Fig. 4C). Next, the cloth electric device 20 for polarity adjustment. Transfer device 213 Separator 22° Static eliminator 23. Then, the photoreceptor 1 is charged by the charger 13 with the charging polarity reversed from the previous time.
The surface is uniformly negatively charged (FIG. 4D). continue,
In synchronization with the black toner image, the reflected light from the document 2, which is irradiated again by the light source 29, is reflected by four mirrors 8°9.
．． 10.12. Lens 11. The photoreceptor 1 is exposed to light through the cyan filter 5. Only the part corresponding to the white background part W loses charge due to optical attenuation, and the red part R and the black part B
An electrostatic latent image is formed on the photoreceptor 1 with negative charges remaining in the portion corresponding to K (FIG. 4E). This electrostatic latent image is developed with positive polarity red toner 6 in the second developing device 16 (Fig. 4) By performing red development, a red toner image is formed in the red area R corresponding area, and the black area BK corresponding area is developed. Now, the red toner will overlap on top of the black toner.

Color mixing prevention device 1 prevents red toner in this overlapping area.
8 (Figure 4G). In order to scrape off the red toner 6 on the black part toner 4 adhering to the electrostatic latent image part corresponding to the black part BH, a negative voltage having a polarity opposite to the charge of the red toner 6 is applied to the bias roll 27 in the color mixing prevention device 18. is applied, and as the bias roll 27 rotates counterclockwise, the red toner 6 is drawn onto the bias roll 27.

The red toner attracted and attached to the bias roll 27 is scraped off from the bias roll 27 by a scraping member 28 and returned to the second developing device 16 by a toner recycling device 19.

In this way, the red toner 6 in the overlapping portion of the black toner 4 and red toner 6 is scattered, so that only a black toner image is formed on the surface of the photoreceptor 1 corresponding to the black portion BK. .

After a toner image faithful to the original 2 is obtained by the color mixture prevention device 18, the black toner 4 and the red toner 6 are charged to the same polarity (negative polarity in this example) by the polarity matching charger 2o to match the polarities. (Figure 4 ■). Subsequently, the toner image on the photoreceptor 1 is transferred onto the transfer paper 7 fed from the paper feed cassette 25 by the transfer device 21, and separated by the separator 22 (FIG. 4I).

Further, the image is fixed by a fixing unit 26 to obtain a two-color image.

After the transfer, the surface of the photoreceptor 1 is subjected to static elimination and cleaning by a static eliminator 23 and a cleaner device 24 as necessary, in preparation for starting a new primary process.

Note that when the red toner 6 is scraped off by the color mixture prevention device 18, the electrostatic adsorption force between the black toner 4 that adheres first and the red toner 6 that is charged with the opposite polarity causes a bias. In order to prevent the black toner 4 from being pulled together onto the roll 27, the electrostatic adhesion force between the black toner 4 and the photoreceptor I must be increased by increasing the voltage of the -order positive charge (see FIG. 4A). Good. Furthermore, even if the black toner 4 enters the color mixture prevention device 18, the black toner 4 and the red toner 6
It is also possible to provide the color mixture prevention device 18 with a means for separating the two black toners 4 by utilizing the difference in charging polarity between the toners and discharging the two black toners 4 to the outside of the color mixture prevention device 18 and, if necessary, returning them to the first developing device 14. .

In this embodiment, the case where the bias roll 27 is rotated counterclockwise has been described.

The direction is not limited to this, and the direction may be clockwise.

Further, in this embodiment, the case where the toner is scraped off by the bias roll 27 has been described, but the toner may be scraped off by a magnetic brush device.

〔Effect of the invention〕

As described above in detail, the two-color image forming apparatus of the present invention prevents color mixing due to superimposition of colors with a simple mechanism, and also prevents a decrease in the density of the second color, resulting in a clear image that is faithful to the original. A two-color image can be formed.

[Brief explanation of the drawing]

Figure 1 is a process diagram showing the conventional two-color color process;
The figure is a block diagram of a two-color image forming apparatus showing an embodiment of the present invention, and FIG. 3 is an enlarged block diagram of the color mixture prevention device in FIG.
FIG. 4 is a process diagram of two-color image formation in the two-color image forming apparatus of the present invention. 1... Photoreceptor, 2... Original, 3... Red filter, 5... Cyan filter, 8.9.10.12
···mirror. 11... Lens, 13... Charger. 14...First developing device, 16...Second developing device, 1
8... Color mixing prevention device. 19... Toner recycling device. 20... Charger for polarity matching, 21... Transfer device,
22...Separator, 23...Static eliminator, 24...
cleaner device. 27... Bias roll, 28... Scraping member, 29... Light source patent applicant Casio Computer Co., Ltd. Same as above ID Co., Ltd. Representative patent attorney Yoshiyuki Osuga Figure 1 Figure 2 Figure 3 Figure 6 Figure 4-]-1 -ζ0(

Claims (4)

[Claims] (1) In a two-color image forming apparatus that sequentially forms a first image and a second image on an image carrier using toners of different polarities and different colors, the first and second images are formed on the image carrier. A scraping means is provided for scraping off the toner that has been developed and superimposed on the first image after being sequentially formed on the first image and before the first and second images are transferred to the transfer material. A two-color image forming device characterized by: (2) The two-color image forming apparatus according to claim 1, wherein the scraping means is a bias roll. (3) The two-color image forming apparatus according to claim 1, wherein the scraping means is a magnetic brush device. (4) The two-color image forming apparatus according to claim 1, wherein the scraping means includes means for collecting the scraped toner.