JPH07234591A - Electrophotographic device - Google Patents

Abstract

(57) [Summary] [Structure] The pre-transfer charging means 13 is interlocked with the bias voltage of the transfer means 7 for transferring the toner image 6 onto the transfer medium 8 so that the charge of the residual toner does not become reverse polarity in the transfer process. Change the bias voltage. [Effect] It is possible to prevent occurrence of an afterimage due to residual toner in an electrophotographic apparatus using a bias cleaning method and obtain a good image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus, and more particularly to a pre-transfer charging means for charging a toner image to a toner image before transferring the toner image to a transfer medium, and a cleaning for electrostatically removing residual toner. The present invention relates to an electrophotographic apparatus using the apparatus.

[0002]

2. Description of the Related Art In an electrophotographic method, a toner image is formed on a recording body which is a photoconductor, and the toner image thus formed is transferred onto a transfer medium such as paper and recorded. However, usually, the transfer efficiency of the toner image on the recording medium to the transfer medium is 70 to 90% and 100% is not completely transferred. Therefore, the residual toner on the recording medium is removed by a cleaner. Conventionally, as one of the cleaners, for example, JP-A-62
As disclosed in Japanese Patent Laid-Open No. 168191, a so-called bias cleaning method is used in which a voltage is applied to a conductive brush to electrostatically adhere and remove residual toner. Further, if a large amount of residual toner cannot be completely removed by a cleaner, as shown in JP-A-55-17111, a toner image is transferred onto a transfer medium by a pre-transfer charging means in order to improve transfer efficiency. Previously, a method of charging the toner image has been taken. In this bias cleaning method, a voltage is applied to a conductive brush to electrostatically attach the residual toner, so that the residual toner having a charging polarity opposite to the normal polarity is cleaned. Without being left, the residual image is transferred to a transfer medium later and transferred to cause a problem that the print quality of the original recorded image is deteriorated.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for obtaining an excellent image by preventing the occurrence of an afterimage due to residual toner in an electrophotographic apparatus using a bias cleaning system.

[0004]

In order to achieve the above object, the present invention prevents the occurrence of an afterimage by preventing the charges of the residual toner from having opposite polarities in the transfer process.

[0005]

In the present invention, since the residual toner on the recording medium can be completely cleaned by the electrophotographic apparatus using the bias cleaning system, a good image without any afterimage can be obtained.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention.
In the figure, a recording body 1 made of an organic photoreceptor rotating clockwise.
Is uniformly negatively charged by the charger 2. Next, the laser beam 3 modulated by the image information is irradiated to form a negative electrostatic latent image. The electrostatic latent image is reversely developed by the negatively charged toner 5 of the developing device 4. The toner image 6 formed on the recording body 1 is electrostatically transferred onto a transfer medium 8 which is a recording paper by a transfer means 7 including a roller having a metal shaft to which a positive voltage is applied and a conductive elastic rubber covered. The residual charge on the surface of the recording body 1 is erased by the eraser 9. The toner image on the transfer medium 8 is thermally fixed by the fixing device 12. The residual toner 10 after the transfer is removed by the cleaner 11. The cleaner 11 is a conductive brush roller 110,
Recovery roller 111, third bias voltage applying means 11
2, fourth bias voltage applying means 113, blade 11
4, the residual toner 10 is attracted to the brush roller 110 to which a positive voltage having a polarity opposite to that of the toner 5 is applied by the third bias voltage applying means 112, and a higher positive voltage is applied by the fourth bias voltage applying means 113. Is transferred to the recovery roller 111 to which is applied, and is scraped off by the blade 114 and recovered at the bottom of the cleaner 11. When the amount of the residual toner 10 is large, the residual toner 10 is not completely removed by the cleaner 11 and remains after passing through the cleaner 11 and appears as a residual image in a later recorded image to deteriorate the image quality. In order to reduce the amount of the residual toner 10, it is necessary to improve the transfer efficiency when the toner image 6 is electrostatically transferred to the transfer medium 8 by the transfer unit 7. Therefore, before the toner image 6 is transferred onto the transfer medium 8, the pre-transfer charging unit 13
The toner image 6 is charged with the negative electric charge as in the toner 5. In the electrophotographic apparatus having such a configuration, for example, when the transfer efficiency is lowered in an environment of high temperature and high humidity, the positive second bias voltage of the second bias voltage applying means 71 of the transfer means 7 is increased. Excessive positive charge is applied to the residual toner 10 through the transfer medium 8, and a part of the residual toner 10 is positively charged, which is opposite to the negative charge that was present before the transfer. Since a positive voltage is applied to the brush roller 110, the positively charged toner of the residual toner 10 is not attracted to the brush roller 110 and causes cleaning failure to cause an afterimage. In order to prevent this, in the present invention, the first bias voltage applied to the pre-transfer charging means 13 by the first bias voltage applying means 131 is changed in conjunction with the second bias voltage. That is, when the second bias voltage is increased, the first bias voltage is also increased to increase the negative charge amount of the toner image 6 and prevent the charge polarity of the residual toner 10 from reversing to the positive polarity in the transfer process. By doing so, the residual toner 10 is completely removed by the cleaner 11, and the afterimage can be prevented from occurring.

FIG. 2 shows a second embodiment of the present invention. The main point that is different from the first embodiment is that the recording body 1 receives the toner image 6 by transfer from another toner image forming body made of a photoconductor instead of the photoconductor, and transfers the toner image 6 to the transfer medium 8. It is an intermediate transfer body. Figure 2
Shows an example of a printer that forms a full-color image. The first developing device 41 has a yellow toner, the second developing device 42 has a magenta toner, the third developing device 43 has a cyan toner, and the third developing device 43 has a black toner. It has four developing machines, four developing machines 44. The belt-shaped toner image forming body 14, which is an organic photoconductor, rotates counterclockwise and is uniformly negatively charged by the charger 2. Next, the laser beam 3 modulated by the image information is irradiated from the optical system 31 to form a negative electrostatic latent image. This electrostatic latent image is reversely developed by the first developing device 41 having a negatively charged yellow toner. The formed yellow toner image is electrostatically transferred to the recording body 1 which is an intermediate transfer body. The residual yellow toner on the toner image forming body 14 is removed by the blade cleaner 15, and the residual charge is erased by the eraser 9. This toner imaging process is repeated for each toner,
A full-color toner image 6 is formed on the recording body 1 by transferring the colors one by one onto the recording body 1 in an overlapping manner. Next, the toner image 6 is negatively charged by the pre-transfer charging unit 13, and then transferred to the transfer medium 8 housed in the paper cassette 81 by the transfer unit 7. The toner image on the transfer medium 8 is thermally fixed by the fixing device 12. The residual toner 10 after transfer is removed by a cleaner 11 similar to that used in the first embodiment. When the transfer medium 8 is sandwiched between the cleaner 11 and the recording medium 1 in order to keep the transfer efficiency high with respect to changes in environmental conditions and types of recording paper, the transfer medium 8 passes through the transfer medium 8 within about 10 mm at the leading end. The current It flowing between the transfer means 7 and the recording body 1 is measured, and the control means 72 changes the second bias voltage of the second bias voltage applying means 71 based on the measured value to increase the transfer efficiency. Adjust so that For example, when the humidity is high, the current It increases and the transfer efficiency generally decreases. Therefore, in this case, the second bias voltage is increased according to the value of the current It. However, when the second bias voltage is increased, a part of the residual toner 10 is positively charged. Therefore, the first bias voltage of the pre-transfer charging unit 13 is increased to prevent the residual toner 10 from being positively charged. To prevent.

In this embodiment, the case where a toner image is formed by reversal development has been described, but it is obvious that the same applies to the case of regular development.

[0009]

According to the present invention, since the residual toner on the recording medium can be completely cleaned by the electrophotographic apparatus using the bias cleaning method, a good image without an afterimage can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a printer showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a printer showing a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Recording medium, 6 ... Toner image, 7 ... Transfer means, 8 ... Transfer medium, 10 ... Residual toner, 11 ... Cleaner, 13 ... Pre-transfer charging means, 71 ... Second bias voltage applying means, 11
0 ... Brush roller, 131 ... First bias voltage applying means.

Claims (4)

[Claims] 1. A cleaning device that electrostatically transfers a toner image on a recording medium onto a transfer medium by a transfer means, and then electrostatically adsorbs and collects residual toner adhering to the surface of the recording medium. And a pre-transfer charging unit that charges the toner image to the same polarity as the charging polarity of the toner image before transferring the toner image to the transfer medium. A first bias voltage applying unit for applying a bias voltage; and a second bias voltage applying unit for applying a second bias voltage to the transfer unit, wherein the second bias voltage and the first bias are provided. An electrophotographic apparatus, wherein the electrophotographic apparatus is characterized in that the first bias voltage is increased / decreased in response to an increase / decrease in the second bias voltage by interlocking with the voltage. 2. The electrophotographic apparatus according to claim 1, wherein the second bias voltage is changed according to environmental conditions. 3. The electrophotographic apparatus according to claim 1, wherein the second bias voltage is changed by measuring a current flowing between the second bias voltage applying unit and the recording medium through the transfer medium. 4. The electrophotographic apparatus according to claim 1, wherein the recording body is an intermediate transfer body that receives the toner image by transfer from another toner image holding body and transfers the toner image onto a transfer medium.