JPS60158467A - Two-color image forming device - Google Patents

Abstract

PURPOSE:To obtain a sharp 2-color image prevented from color-mixing by changing seconding electrostatic charging voltage or secondary development bias voltage in accordance with the surface potential of a photosensitive body used in both polarities. CONSTITUTION:The surface of a photosensitive body 1 is electrostatically charged, e.g., negatively by a primary corona discharger 2, potential is measured with a surface electrometer 6, and the surface of the body 1 is exposed to the light image of an original through a red filter 4, while variable bias voltage 9 is set to a prescribed value with a control circuit 7. Next, black development is executed with the first developing device 10 having bias 8 applied. Then, the body 1 is subjected to secondary positive charging with a secondary charging corona discharger 3, imagewise exposed again through a cyan filter, and developed to red with the second developing device 11 having bias of prescribed voltage applied from a bias 9. After the polarity of the toners are accorded with a polarity according device 12 for converting the toner polarity, the toner image is transferred to a paper, and the paper is separated with a separator 14. As a result, a sharp 2-color image freed of color mixing can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a two-color image forming apparatus using electrophotographic technology.

[Prior art and its problems]

The conventional two-color image forming process will be explained with reference to FIG. 1. First, a bipolar photoreceptor is uniformly and primarily charged with a predetermined polarity, for example, a negative polarity (a). Next, when the light image of the original OR, which is a two-color image having a black part B and a red part R on the white background part W, is exposed through a red filter, a first image corresponding to the black part B of the original OR appears on the photoreceptor. An electrostatic latent image is formed (b), and then a first development with black toner BT is performed to form a black image (c). After that, secondary charging with the opposite polarity to the primary charging is applied (d), and when the optical image of the original OR is exposed again through a cyan filter, a second electrostatic latent image corresponding to the red part R of the original OR is formed. is formed (e), and then a red image is formed when second development is performed using red toner RT (f).

A two-color image is obtained by transferring both the red and black images formed on the photoreceptor to a sheet of paper and further fixing the images.

However, in the above process, 'IA/! If environmental changes such as 2 degrees or dirt on the wire of the corona discharger for primary charging occur, the surface potential of the photoreceptor obtained after the primary charging will change, so the surface potential of the photoreceptor after the secondary charging will also change. Following this, not only the black image density but also the red image density fluctuates and becomes unstable.

For example, if the wire of the corona discharger for primary charging is dirty and the surface potential of the photoreceptor after primary charging is low [Figure 2 (a'
)), even after image exposure, the first electrostatic latent image is formed with the potential of the black area still low and the potential of the white area even lower (Figure 2 (b')). A black image is formed by development (Fig. 2 (CI). Next, perform secondary 41) electricity.

Not only the white background and red areas but also the black areas are highly charged with positive polarity (Fig. 2(d')).

When this state is exposed to light through a cyan filter, the red part remains at a high potential, but the white background part and even the black part have a potential higher than the phenomenon bias of the second phenomenon. Figure 2 (e')). If the second development is performed with the nose fixed in this state, not only the red part but also the white background part and the black part will be developed in red [Fig. 2 (f i )]
. Therefore, when both the red and black images described in 1. are transferred to paper and fixed, it becomes a two-color image that is very unsightly.

[Purpose of the invention]

In view of the above-mentioned conventional drawbacks, the present invention is capable of stably developing the second color even if the primary charging potential fluctuates or the potential of the first image area fluctuates, and provides a clear two-color image without color mixing. An object of the present invention is to provide a two-color image forming apparatus that can obtain a color image.

[Key points of the invention]

In order to achieve the above object, the present invention performs primary charging and secondary charging of opposite polarity to the primary charging on a bipolar photoreceptor, and charges a predetermined charge corresponding to each color of a two-color original. By performing the first exposure and the second exposure, a first latent image and a second latent image having mutually different polarities are formed, and the first latent image is visualized by first development, and the second and first images are visualized. In a two-color image forming apparatus that forms a 22-color image (elephant), the image is visualized by the second development.
The method is characterized in that the secondary (11 voltage) voltage and/or the bias for the second development are made variable in accordance with the surface potential of the bipolar photoreceptor.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a block diagram of a two-color image forming apparatus showing an embodiment of the present invention.

The photoreceptor 1 is rotatably provided in the direction of the arrow shown in the figure, and is, for example, a bipolar organic photoconductive photoreceptor.

Around the photoreceptor 1, there are a corona discharger 2 for primary charging, a corona discharger 31 for secondary charging, a surface electrometer 6°, and a first developing device 10.
．． Second developer 11. Polarity matcher 12, transfer device 132 separator 14. A cleaner 16° and a static elimination lamp 15 are arranged in sequence.

The variable bias 9 of the second developing device 11 is set to a predetermined magnitude by the action of the control circuit 7 in accordance with the detection result of the potential of the two-surface type position meter 6. The surface electrometer 6 may be any device that measures surface potential, such as a vibratory capacitance electrometer.

In the above configuration, first, the primary charging corona discharger 2 performs primary charging of a predetermined polarity, for example, negative polarity, and the potential is detected at the first surface mold position 6, and the control circuit is activated according to the detection result. While setting the variable bias 9 to a predetermined value by +l1IJ of 7, image exposure of the original (having a red part and a black part on a white background part) is performed through the red filter 4. Next, black development is performed in the first developing device 10 to which a bias 8 is applied. next.

A corona discharger 3 for secondary charging performs secondary charging with a positive polarity opposite to the primary charging, and this time image exposure is performed again through a cyan filter 5. Red color development is performed in the second developing device 11 to which a bias is applied. Next, a polarity matcher 12 converts the polarity of the toner.
After matching the polarity, the paper is transferred to the transfer device 13 (not shown).
Transcribed to.

The paper is separated from the photoreceptor 1 by the separator 14 and passed through a fixing section (not shown), thereby finally obtaining a two-color image on the paper. -Residual energy on force photoreceptor 1''2.

It is cleaned with a cleaner 16 and residual potential is erased with a static elimination lamp 15 in preparation for the ninth image formation.

FIG. 4 shows the relationship between the primary charging potential and the appropriate second bright image bias voltage set value in the above embodiment. As shown in the figure, the relationship between the primary charging potential and the appropriate second developing bias voltage is inversely proportional. In other words, when the primary charge potential is high, the second development bias is lowered, and when the primary charge potential is low, the second development bias is increased to stabilize the second development. I can do it. Therefore, color mixing due to adhesion of red toner to areas other than the red area during the second development does not occur, and a stable and clear two-color image can be obtained.

In addition, since the noise applied during the second development is variably set in this way, there is sufficient time from the surface pattern measurement to the bias control, and the potential can be measured in advance during the preliminary rotation like the potential control in one pass. There is no need to do so, and the 3-hour costume will not be produced.

In addition to the above-mentioned embodiments, the factor to be varied according to the surface potential of the surface and the photoconductor surface may be -secondary charging voltage, and it is also possible to vary both the secondary charging voltage and the 7't ia of the second development. It's okay.

Another method to which the present invention is applied is one in which a bipolar photoreceptor is used, and after latent images of positive and negative polarities are formed, development is performed sequentially.

〔Effect of the invention〕

As described in detail below, the two-color image forming apparatus of the present invention can stabilize the development of the second color even if the potential of the first image area changes due to fluctuations in the primary charging potential. Therefore, it is possible to form a clear two-color image without mixing two colors.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing changes in the surface potential of a photoreceptor in a conventional two-color image forming process, and FIG. 3 is a block diagram of a two-color image forming apparatus showing an embodiment of the present invention. FIG. 4 is a characteristic diagram showing the relationship between the primary charging potential and the second developing bias voltage in one embodiment of the present invention. 1... Photoreceptor, 2... Corona discharger for primary charging,
3...For secondary charging: +rI-)-discharger, 6.
...Surface electrometer, 9...Variable bias, 10...
・First developing device, 11... Second developing device, 13... Transfer device. 14... Separator, 15... Static elimination lamp. 16...Cleaner Fig. 1 Fig. 3 Fig. 4 Fig. 1; Saw 412 Electric 1 I L (

Claims (1)

[Scope of Claims] A bipolar photoreceptor is charged with a primary charge and a secondary charge with a polarity opposite to the primary charge is performed, and predetermined first and second exposures corresponding to each color of a two-color original are performed. By forming a first latent image and a second latent image of mutually different polarities, the first latent image is visualized by first development, and the second latent image is visualized by second development. . In a two-color image forming apparatus that forms a two-color image. A two-color image forming apparatus characterized in that the voltage for the secondary charging and/or the bias for the second development are made variable depending on the surface potential of the bipolar photoreceptor.