JPH10307449A - Image forming device using potential division developing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain fringe development caused by the sweeping of fog by forming an electrostatic latent image which is not developed on a background part separated from an image part on the trailing edge side of the image part with respect to the rotating direction of a developing roll. SOLUTION: Image forming operation is performed by forming a latent image by an exposure means 10 after uniformly eletrifying a photoreceptor 1 by an electrifier 2. At such a time, an image signal 11 is recognized and the electrostatic latent image which is not developed is formed at a separate position on the trailing edge side of the latent image by a negative image pattern adding device 12. The latent image by potential division developing is developed with two kinds of toner by two developing machines 3 and 4. In a pretransfer electrifier 5, the electrifying polarity is adjusted because the electrifying polarities of two colors of toner with which the image is developed are different. Then, two colors of toner is transferred to transfer paper 6 by a transfer machine 7. Thereafter, the toner is melted and fixed on the paper 6 by a fixing machine 8. Then, the residual toner is recovered by a cleaner 9. Thus, the fringe development caused by the sweeping of the fog is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system, and more particularly to an image forming apparatus for forming two types of toner images on a photosensitive member by combining normal development and reversal development.

[0002]

2. Description of the Related Art As shown in JP-A-48-37148, after a photoreceptor is charged, the amount of exposure is changed between no exposure, weak exposure, and strong exposure according to the color information of an image during exposure. , The surface potential on the photoconductor is a high level area,
A three-level electrostatic image of a low-level area and an intermediate-level area therebetween is formed, a high-level area is regularly developed, and a low-level area is reversely developed to form two types of toner images on a photoconductor. There is a development method.

As a method for developing the electrostatic image, a two-component developer which is a mixture of a toner which is a colored particle and a carrier which is a magnetic particle is used. In the development, when developing the high-level region, a developing bias voltage between the surface potential of the high-level region and the surface potential of the intermediate-level region is applied to the developing roll of the developing device. When developing, the toner is developed into a high level area and a low level area by applying a developing bias voltage between the surface potential of the low level area and the surface potential of the intermediate level area to the developing roll of the developing device. Is done.

At this time, when an electrostatic latent image is formed on the photoreceptor, an electric field having an opposite polarity to the latent image (fringe) is formed around the latent image together with an electric field that emphasizes development at the end of the latent image. Development electric field). A phenomenon in which toner of opposite polarity adheres around the toner image due to the fringe development electric field (fringe development).
Occurs, and there is a problem that the image quality is significantly deteriorated.

[0005]

According to the results of experiments conducted by the present inventor, in the potential division development, there is a problem that fringe development occurs in an area which cannot be predicted from the location of the fringe development electric field around the latent image. I understood. As a result of a more detailed study, the above-mentioned fringe development was originally carried out when the developer was developed under the developing conditions in which the toner adhesion (fogging) to the area of the background potential (white image area) where the photoconductor potential is at an intermediate level is relatively large. It was found that this was caused by the fogging of fog caused by the rubbing force of the ears. An object of the present invention is to suppress the fringe development due to the above-mentioned sweeping of fog.

[0006]

The above object is achieved by forming an undeveloped electrostatic latent image on the background portion which is on the rear end side of the image portion in the direction of rotation of the developing roll and is distant from the image portion. It

[0007]

FIG. 1 is a side view of the overall structure of an image forming apparatus according to the present invention. 1 is a photoconductor, 2 is a charger, 3 is a developing machine 1, 4 is a developing machine 2, 5 is a pre-transfer charger, 6 is paper, 7 is a transfer machine, 8 is a fixing machine, 9 is a cleaner, 10 is exposure. Reference numeral 11 is an image signal, and 12 is an electrostatic latent image (hidden image pattern) addition device which is not developed. The image forming operation is
After uniformly charged on the photoreceptor 1 by the charger 2, a latent image is formed by the exposure unit 10. At this time, the image signal 11 is recognized, and the hidden image pattern adding device 12 forms an undeveloped electrostatic latent image at a distant position on the rear end side of the latent image. Thereafter, the latent images in the potential division development described later are developed by the two types of toners by the two developing machines 3 and 4. The pre-transfer charger 5 matches the charging polarities of the toners of the two colors to be developed, because they have different charging polarities. The two color toners are transferred onto the paper 6 by the transfer machine 7. After that, the fixing device 8 melts and fixes the toner on the sheet 6. Further, the residual toner is collected by the cleaner 9, and a series of processes is completed.

FIG. 2A is a diagram of the surface potential of the photosensitive member 1 after potential division development after exposure. By controlling the exposure amount and controlling the photoconductor expression potential 13 to three levels, the positively charged toner 14 is developed (normal development), that is, the positively charged toner potential 15 which is an unexposed portion, and the negatively charged toner. 16 forms a weakly exposed portion having a negatively charged toner potential 17 which is a strong exposure potential portion where development (reversal development) is performed and a white potential 19 which is a background portion where neither toner is developed.

In development, positively charged toner 1
4 is developed, a positively charged toner developing bias voltage Vc 18 is applied between the positively charged toner potential 15 and the white potential 19 to the developing roll of the developing device.
Is developed, the negatively charged toner potential 17 and the white potential 1
By applying the negatively charged toner developing bias voltage Vb20 to the developing roll of the developing device during the period 9, each toner is developed into a high level region and a low level region.

Next, the fringe will be described.

FIG. 2B is a diagram showing the electric field and the fringe corresponding to the surface potential of the photosensitive body after the exposure of FIG. 2A. Above the potential, the surface potential is the development bias voltage V
Binary development with c18 and Vb20 seems to cause no problem, but in reality, development is performed by an electric field obtained by differentiating the potential. Therefore, the enhancement of the electric field occurs at the edge of the surface potential. The positively charged toner 14 is developed by an electric field that is more negative than the development start electric field 22 of the positively charged toner developer, and the negatively charged toner 16 is developed by an electric field that is more positive than the development start electric field 23 of the negatively charged toner developer. You. Reverse electric field (fringe development electric field) generated in the background
Reaches a level higher than the level of the development start electric field of the developing machine, so that the reverse electric field generated in the background portion develops toner with different charge polarities (fringe development) around the image.

FIG. 3A is a diagram showing the force acting on the toner on the surface of the photosensitive member 1.

The toner adhering to the tips of the ears made of the developer is the product of the charge amount of the toner and the electric field force qEz as the electric field force.
As a result, development is performed from the developing roll 28 toward the photoconductor 1. In the illustrated example, the photoconductor 1 and the developing roll 28 rotate in the same direction. Generally, in order to improve the developing property, the peripheral speed of the surface of the developing roll 28 is higher than that of the surface of the photoconductor 1. Operate under fast conditions. At this time, a sliding force FR due to the ears of the developer acts on the toner due to a difference in peripheral speed between the photosensitive member 1 and the surface of the developing roll 28. In addition to qEz and FR, the toner has a force qEy due to an electric field Ey in a direction along the surface of the photoconductor 1 radially generated from the peripheral edge of the electrostatic latent image created by the electrostatic latent image on the photoconductor 1. work.

FIG. 3B is a diagram showing the force acting on the toner along the surface of the photosensitive member 1 on the leading end side and the trailing end side with respect to the rotation direction of the developing roller 28 of the electrostatic latent image. The directional relationship between FR and qEy is different between the leading end side and the trailing end side of the electrostatic latent image. On the leading end side of the electrostatic latent image, FR and Ey act in the same direction to remove the fringe-developed toner from the image edge portion, and on the trailing end side of the electrostatic latent image, FR and qEy act in opposite directions, resulting in fringe development. It works to store toner at the edge of the image.

FIG. 3C is a diagram showing a difference in the appearance of fringes between the leading end and the trailing end of the image with respect to the rotation direction, which is caused by the above-mentioned force acting on the toner on the surface of the photosensitive member 1. is there. Strong fringes appear on the rear end side of the image rather than on the front end side.

However, according to the experimental results of the present inventor, it has been found that there is a problem that fringe development occurs at a location which cannot be predicted even by the analysis of the force acting on the fringe-developed toner on the surface of the photoconductor 1. It was
FIG. 4A shows an example of fringe development that cannot be predicted by the above analysis. This fringe development was examined in more detail, and as a result, the photosensitive member 1 which was originally a background portion was developed.
In the case of the developing condition in which the toner adhesion (fogging) to the region of the white potential 19 of the intermediate level of FIG.
As shown in (1), it was found that the image pattern appeared on the trailing edge side of the image pattern with an open mouth. From this, the fringe generated at a place that cannot be predicted by the fringe appearance prediction method is caused by the fogging toner adhering to the white potential 19 weakly exposed portion, which is the unprinted portion, due to the rubbing force FR of the developer ears.
It can be said that it is swept up by and is generated. Hereinafter, a fringe generated at a location that cannot be predicted by the fringe appearance prediction method is called a sweep fringe.

A method for suppressing the above-described swept fringe will be described.

FIG. 4 (2) is a schematic diagram in which an undeveloped electrostatic latent image (hidden image) is formed in a portion of the present invention on the rear end side of the image portion, which is apart from the image portion.

FIG. 5 is a diagram showing the potential level of the hidden image.

The potential level of the hidden image is a potential level 26 between the positively charged toner developing bias potential 18 and the white potential 19 at the rear end side of the electrostatic latent image having the positively charged toner potential 15 and the negatively charged toner potential. On the rear end side of the electrostatic latent image 17, a hidden image is formed at a potential level 27 between the negatively charged toner developing bias potential 20 and the white potential 19.

This hidden image is not developed by either of the two toners having different charging polarities and does not affect the finally formed image. However, at the time of development, the hidden image generates a force qEy by the electric field in the direction along the surface of the photoconductor from the peripheral portion thereof to the outside, and the fog toner 24 swept away by the rubbing force of the developer ears.
Affect the path of travel.

The shape of the hidden image is such that the combined force of the force qEy generated by the electric field generated at the peripheral portion of the hidden image and the rubbing force FR generated by the ears of the developer causes the fog toner 24 to detour from the rear end of the image as a path 25. . As a result, the fogging toner 24 swept by the rubbing force of the ears of the developer is prevented from accumulating at the rear end of the image, and an effect of suppressing the occurrence of a sweeping fringe is produced. The shape of the hidden image is not limited to the shape shown in FIG.

[0023]

According to the present invention, fringe development due to fog sweeping can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an image forming apparatus that is an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the surface potential and the electric field of a photoreceptor after exposure.

FIG. 3 is a schematic diagram showing a force acting on a toner on the surface of a photoconductor and the appearance of fringes around a solid image.

FIG. 4 is a schematic diagram showing an example of a sweeping fringe and a hidden image.

FIG. 5 is a diagram showing a potential of a hidden image.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Charging device, 3 ... Developing machine 1, 4,
..Developing machines 2, 5 ... Pre-transfer charger, 6 ... paper, 7 ... transfer machine, 8 ... fixing machine, 9 ... cleaner, 10 ... exposure means, 11 ... ..Image signals, 12 ... Hidden image pattern adding device, 13 ... Photoconductor surface potential, 14 ... Positively charged toner, 1
5 ... Positively charged toner potential, 16 ... Negatively charged toner, 17 ...
-Negatively charged toner potential, 18 ... Positively charged toner developing bias potential, 19 ... White potential, 20 ... Negatively charged toner developing bias potential, 21 ... Photoconductor surface electric field, 22 ... Positive charging Development start electric field of toner developing machine, 23: Development start electric field of negatively charged toner developing machine, 24: Fog toner, 25: Fog toner traveling path, 26: Rear end side of positively charged toner potential , A hidden image potential formed on the trailing end side of the negatively charged toner potential, and a developing roll.

Claims (2)

[Claims] 1. A three-level electrostatic image having a developing roll and a photoconductor, charging the photoconductor, and exposing the photoconductor to a high-potential portion, a low-potential portion, and an intermediate potential portion. In an image forming apparatus that forms two types of toner images by performing normal development and reverse development using toners having different charging polarities, respectively, in the rear end side with respect to the developing roll rotation direction of the image section, An image forming apparatus, which forms an undeveloped electrostatic latent image on a distant background portion. 2. The image forming apparatus according to claim 1,
The direction of rotation of the developing roll of the electrostatic latent image of the negatively charged toner is at a potential level between the positively charged toner developing bias potential and the white potential on the rear end side with respect to the direction of rotation of the developing roll of the electrostatic latent image of the positively charged toner. In contrast, an image forming apparatus forms an undeveloped electrostatic latent image on the rear end side at a potential level between a negatively charged toner developing bias potential and a white potential.