JPH08240948A - Electrophotographic device - Google Patents

Abstract

PURPOSE: To reduce the deviation in printing position or image blurring caused by the speed difference between the circumferential speed of a photoreceptor and the carrying speed of a paper sheet by making toner having different polarity on a photoreceptor have the same polarity as that of the photoreceptor with a pretransfer electrifier. CONSTITUTION: A high-potential part executes normal development with positively charged color toner having the polarity opposite to that of the photoreceptor 1 by a first developing device 4. Then, a low-potential part executes reversal development with negatively charged black toner having the same polarity as that of the photoreceptor 1 by a second developing device 5. After the development, the positively charged color toner and the negatively charged black toner which have the different polarity on the photoreceptor 1 are irradiated with a negative corona discharge by the pretransfer electrifier 6, to be negatively electrified, that is, obtain the same polarity as the photoreceptor 1. Then, a paper sheet 15 is irradiated with a positive corona discharge by a transfer device 7 and electrified to the polarity opposite to the toner, that is the photoreceptor 1, to transfer the toner to the paper 15. At this time, the photoreceptor 1 and the paper 15 have the different polarity, to generate electrostatic attracting force and the deviation in the printing position or the image blurring caused by the speed difference between the photoreceptor 1 and the paper 15 can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus capable of two-color printing, and more specifically, to a printing position shift or an image blurring caused by a speed difference between a peripheral speed of a photosensitive member and a sheet conveying speed. The present invention relates to an electrophotographic device for reducing the number.

[0002]

2. Description of the Related Art A so-called tri-level method as shown in, for example, U.S. Pat. No. 4,078,929 is one of the methods for realizing two-color printing by using toners charged with positive and negative polarities different from each other. It has been known. In this system, a high-potential portion VH that is not irradiated with laser light, an intermediate potential portion VM that is irradiated with a laser light amount PM that is about half the exposure amount of the photosensitive member, and a half-exposure amount of 3 to 4 are provided on a uniformly charged photosensitive member. A three-step potential of the low-potential portion VL irradiated with the laser light amount PH of about twice is formed. Next, the first developing device normally develops the toner charged to the high potential portion VH with the opposite polarity to the photoreceptor, and the second developing device reversely develops the toner charged to the low potential portion VL with the same polarity as the photoreceptor. The intermediate potential portion VM becomes a background portion (blank sheet portion) without toner development. At this time, the bias voltage VBH between the high potential portion VH and the intermediate potential portion VM is applied to the first developing device which carries out the regular development, and the second developing device which carries out the reversal development.
A bias voltage VBL between the low potential portion VL and the intermediate potential portion VM is applied to the developing device. After development, the toners having different polarities on the photoconductor are made to have the same polarity by the pre-transfer charging device and transferred onto the paper at once, and then heated and pressed by the fixing device to fix the toner on the paper.

[0003]

In the tri-level method, one optical system can realize one pass and two colors, so that the printing position is accurate. However, even if the printing position on the photoconductor is accurate, if the speed difference between the paper conveyance speed for transferring the toner on the photoconductor and the peripheral speed of the photoconductor, the image on the photoconductor can be faithfully transferred. The printing on the paper is misaligned.
In addition, due to speed fluctuations that occur at the time of starting the paper, blurring occurs in printing, and the line becomes thick only in that portion in the feeding direction. Therefore, if the resolution is increased, even a blur of several tens of μm may cause a significant decrease in print quality.

An object of the present invention is to reduce the deviation of the printing position or the blurring of the image caused by the speed difference between the peripheral speed of the photoconductor and the conveying speed of the paper.

[0005]

SUMMARY OF THE INVENTION The above object is to provide a developing device and a photoconductor that form a three-step potential on a uniformly charged photoconductor by a laser beam and normally develop a toner having a polarity opposite to that of the photoconductor. In an electrophotographic device that is composed of a developing device that reverse-develos toner of the same polarity and a pre-transfer charging device that aligns toner of different polarities on the photoconductor to the same polarity before transferring the toner to the paper, pre-transfer charging This is achieved by aligning the toners of different polarities on the photoconductor to the same polarity side as the photoconductor by the device.

[0006]

In the electrophotographic apparatus configured as described above, since the charging polarity of the photoconductor and the charging polarity of the paper by the transfer device are different polarities, the photoconductor and the paper are electrostatically attracted at the transfer portion. To do. As a result, since the photoconductor and the paper move at the same speed while the paper sticks to the photoconductor, even if there is a speed difference between the photoconductor and the paper, the printing position shifts at the transfer point or the image blurs. Can be reduced.

Further, in the case of continuous paper, since the speed of the photosensitive member and that of the paper are made to be the same at the transfer portion, the speed difference between the photosensitive member and the paper is accumulated, the load is applied to the paper conveying portion, and the conveying holes at both ends of the continuous paper are formed. May cause holes or tractor jams. In order to prevent this, the transfer device is turned off when the perforation reaches the transfer point, so that the electrostatic attraction force between the photoconductor and the paper is eliminated and the accumulated load on the paper transport unit can be eliminated.

Further, in the pre-transfer charging device used for reversing the polarity of the toner, the function of reversing the polarity of the toner contaminated with the toner is significantly deteriorated due to the toner scattering occurring when the polarity of the toner is reversed. Therefore, by reversing the polarity of the color toner that consumes less, the contamination of the pre-transfer charging device with the toner can be reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing the outline of an embodiment of the present invention. The photoconductor 1 is arranged so as to be rotatable at a constant speed in the direction of the arrow, and around it, the charging device 2, the optical device 3, the first developing device 4, the second developing device 5, the pre-transfer charging device 6, and the transfer device. The device 7 and the cleaning device 8 are arranged. Further, the charging device 2, the pre-transfer charging device 6, the high voltage power source 9 for the charging device for applying a high voltage to the corotron wire of the transfer device 7 to generate corona discharge, the high voltage power source 10 for the pre-transfer charging device, the transfer device High-voltage power supply 1 for bias that applies a bias voltage to the high-voltage power supply 11, the first developing device 4, and the second developing device 5.
2 and 13 are installed. Further, a control device 14 for turning on / off the high voltage power supply 11 for the transfer device according to the paper length data is installed. In addition, the paper 15 is placed in the direction of the arrow on the tractor 1.
It is transported by 6.

Next, the printing process according to the present invention will be described. Here, the photosensitive member 1 will be described by taking a negative charging type as an example. The photoconductor 1 is uniformly charged by the charging device 2, and is irradiated with the laser beam from the optical device 3 so that the high potential portion VH (-900V) and the intermediate potential portion VM (-500).
V) and the low potential portion VL (-100V) are formed. Here, the charging potential of the photoconductor 1 by the charging device 2 is charged several tens of V higher in consideration of the dark decay characteristic of the photoconductor and the moving time between the charging device 2 and the first developing device 4. Next, high potential part VH
In the above, the first developing device 4 normally develops a positively charged color toner having a polarity opposite to that of the photoconductor 1. At this time, the bias voltage VBH (-600V) is applied to the developing roll of the first developing device 4, and the toner is not developed on the intermediate potential portion VM and the low potential portion VL. Next, the low potential portion VL reversely develops the negatively charged black toner having the same polarity as the photoconductor 1 by the second developing device 5. At this time, the bias voltage VBL (-400V) is applied to the developing roll of the second developing device 5, and the toner is not developed on the intermediate potential portion VM and the high potential portion VH. After the development, the positively charged color toner and the negatively charged black toner having different polarities on the photoconductor 1 are irradiated with the negative corona by the pre-transfer charging device 6,
The negative charge having the same polarity as that of the photoconductor 1 is arranged. Next, the paper 15 is irradiated with a positive corona by the transfer device 7, and is positively charged with a polarity opposite to that of the toner, that is, a polarity opposite to that of the photoconductor 1.
Transfer the toner to the paper. At this time, the photoconductor 1 and the paper 15
Has a reverse polarity and an electrostatic attraction force is generated, so that the shift of the printing position or the blurring of the image caused by the speed difference between the photoconductor 1 and the paper 15 can be reduced. Further, the transfer device 7 turns off the high voltage power supply 11 for the transfer device when the perforation reaches the transfer point according to the paper length data, and eliminates the electrostatic attraction force between the photoconductor 1 and the paper 15, and the photoconductor 1 and the paper 15. The load on the paper transport unit accumulated due to the speed difference with 15 is eliminated. The optimum off time of the high voltage power supply 11 for the transfer device is 10 to 30 ms.

[0011]

As described above, according to the present invention, it is possible to reduce the deviation of the printing position or the blurring of the image caused by the speed difference between the peripheral speed of the photoconductor and the conveyance speed of the paper, and to realize high print quality. it can.

[Brief description of drawings]

FIG. 1 is a schematic view of an electrophotographic apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a light decay curve of a photoconductor and a potential distribution on the photoconductor.

[Explanation of symbols]

1 ... Photosensitive member, 2 ... Charging device, 3 ... Optical system, 4 ... First
Developing device, 5 ... second developing device, 6 ... pre-transfer charging device,
7 ... Transfer device, 15 ... Paper

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisaka Kato 1060 Takeda, Hitachinaka City, Ibaraki Prefecture Hitachi Koki Co., Ltd.

Claims (3)

[Claims] 1. A developing device for forming a three-stage potential on a uniformly charged photoconductor by a laser beam to normally develop a toner having a polarity opposite to that of the photoconductor, and a developing device for reversing the toner having the same polarity as that of the photoconductor. In the electrophotographic apparatus including a developing device that performs the transfer and a pre-transfer charging device that aligns toners of different polarities on the photoconductor to the same polarity before transferring the toner to the paper, the pre-transfer charging device varies the photo conductor. An electrophotographic device characterized in that polar toner is aligned on the same polarity side as the photoconductor. 2. The electrophotographic apparatus according to claim 1, wherein the transfer device installed downstream of the pre-transfer charging device is turned off when the perforation of the continuous paper reaches the transfer point. 3. The electrophotographic apparatus according to claim 1, wherein the toner having a polarity opposite to that of the photoconductor is colored and the toner having the same polarity as the photoconductor is black.