JPH05188829A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image of high reliability while keeping down generation of stripes in an end edge of a transfer paper. CONSTITUTION:In the image forming device provided with an image carrier 1, electrostatic latent image forming means 3 and 4, a transfer device 8 utilizing a dielectric film to retain the transfer paper 18, a transfer corotron 10 to transfer a toner image formed on the image carrier 1 and a cleaning device 7 to clean the surface of the image carrier, a pre-cleaning corotron 6 to carry out negative discharging between the transfer corotron 10 and the cleaning device 7 is provided. Furthermore, the discharging is stopped by the transfer corotron 10 immediately after the transfer paper is passed by a wire for transfer corotron.

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 such as an electrophotographic copying machine, a facsimile, a printer, and the like.
The present invention relates to an image forming apparatus of a system in which a transfer paper is held on a dielectric film on a transfer drum and a toner image formed on an image carrier is transferred onto the transfer paper.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine, a facsimile or a printer, a transfer paper is held on a dielectric film on a transfer drum, and a toner image formed on an image carrier is transferred onto the transfer paper. There is a method. In this system, for example, when a latent image is formed on an image carrier having a negative charging characteristic and the toner is negatively charged to reversely develop the latent image, the polarity of the transfer corotron becomes positive. Is set. Then, the positive charges from the transfer corotron are injected into the transfer paper through the dielectric film, the positive charges are accumulated in the surface area of the rear end of the transfer paper, and the rear end of the transfer paper is separated from the image carrier. At that time, peeling discharge occurs, and the positive charge moves onto the image carrier having the negative charge, so that there is a problem that this portion becomes a streak and appears in the image in the next cycle.

In order to avoid this, JP-A-3-8788
As disclosed in Japanese Patent No. 4, there is a method of negatively charging before static elimination. This will be described with reference to FIG. 4. A charge corotron 52 is provided around the image carrier 51, a transfer drum 54 having a dielectric film 53 fixed on the outer periphery thereof, a transfer corotron 55, a discharger 56, a cleaning device 57, a pre-exposure lamp. 58 are provided. The figure shows a state in which the position of the image carrier 51, which is the trailing edge of the transfer paper, has reached the position of the discharger 56 when the transfer paper P has finished the transfer and has passed the transfer position. The image carrier 51 corresponding to the rear end of the transfer paper
A strong positive electric charge is charged in the area (1) due to the peeling discharge generated by the positive electric charge accumulated at the rear end of the transfer paper.

The discharger 56 is connected to an AC power source and a minus DC power source, and a slight positive charge on the image carrier 51 is removed by this AC current, so that the image carrier 51, which is the trailing edge of the transfer paper, is strong. The portion a, which is positively charged, is canceled by the negative DC current in addition to the AC current, and the surface b thereafter is almost completely neutralized. The surface potential of the image carrier 51 after being discharged by the discharger 56 is
Although it is partially deviated to a negative value, it is completely removed by the subsequent pre-exposure lamp 58.

[0005]

By the way, when an experiment was conducted on the relationship between the width of the transfer failure due to the off timing of the transfer corotron 55 and the contrast of the trailing edge line of the paper, the results shown in FIG. 3 were obtained. The off timing of the transfer corotron 55 is the distance L between the corotron wire and the rear end of the transfer paper when the transfer corotron is off, and the rear end of the paper when the AC current and the negative DC current of the discharger 56 are changed. Measuring muscle contrast.

However, in the above-mentioned conventional image forming apparatus, the transfer corotron 55 is located near the trailing edge of the transfer paper 8 mm.
Since the charging of the image carrier 51 has been stopped, the positive charging of the image carrier 51 sometimes reaches several kilovolts, and if an attempt is made to perform the negative charging enough to neutralize the charging by the discharger 56, a large current is generated as shown in FIG. Therefore, there is a problem in that it has to be washed away, which causes new problems such as leakage, poor cleaning, and deterioration of the image carrier. On the other hand,
It is known that this streak does not occur if the transfer corotron 55 is stopped sufficiently early even if it is not negatively charged before the charge removal. However, in this case, as shown in FIG. 3, a transfer defect occurs at the trailing edge of the image in a region where no streak is generated. The generation of muscles cannot be suppressed.

The present invention solves the above-mentioned problems. By making the discharge timing of the transfer corotron constant with respect to the transfer paper and suppressing the discharge current of the corotron before cleaning to a small value, the occurrence of the trailing edge streaks of the transfer paper is prevented. An object of the present invention is to provide an image forming apparatus capable of obtaining a highly reliable image while holding down the pressure.

[0008]

In order to achieve the above object, an image forming apparatus of the present invention uses an image carrier, an electrostatic latent image forming means, and a dielectric film for holding a transfer paper. A transfer device, a transfer corotron for transferring the toner image formed on the image carrier, and a cleaning device for cleaning the surface of the image carrier, the transfer corotron and the cleaning device. A pre-cleaning corotron that performs a negative discharge is provided between the transfer corotron and the transfer corotron is characterized in that the transfer paper stops the discharge immediately after passing through the transfer corotron wire. The pre-cleaning corotron may discharge only the portion corresponding to the rear end of the transfer sheet of the image carrier. Further, a paper detection unit capable of detecting the transfer paper on the transfer drum is provided in front of the transfer corotron in the transfer paper traveling direction, and the discharge stop timing of the transfer corotron is controlled based on the signal from the paper detection unit. Good.

[0009]

In the present invention, a dielectric film as a transfer paper holding member is wound around a transfer drum arranged in contact with the image carrier, and the transfer paper is electrostatically adsorbed and conveyed there by a transfer corotron. The toner image on the image carrier is transferred. The electric discharge of the transfer corotron is controlled by the TC driver, and the information necessary for the electric discharge such as the electric discharge time and the reference signal necessary for starting the electric discharge is sent to the TC driver from the CPU and the paper detection means, and the transfer process is completed. After that, the image carrier is given a negative charge by the pre-cleaning corotron arranged in front of the cleaning device. The discharge of the corotron before cleaning is the same as that of the transfer corotron.
Controlled by the CC driver, the PCC driver is sent with information necessary for discharging, such as a discharging time and a reference signal necessary for starting discharging, from the CPU and the sheet detecting means.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing an embodiment in which the image forming apparatus of the present invention is applied to a full-color electrophotographic apparatus. The present invention is not limited to such an electrophotographic apparatus, but a method of holding a transfer paper on a dielectric film on a transfer drum and transferring a toner image formed on an image carrier onto the transfer paper. The present invention can be applied to the image forming apparatus.

Around the image carrier 1 made of an organic photoconductor, a neutralization device 2 made of a red LED, a charging device 3 for uniformly negatively charging the image carrier 1, and an unnecessary portion to be statically charged. An exposure optical system 4 for forming a latent image, a developing device 5 for developing an electrostatic latent image into a visible image with toner, a transfer corotron 10 for transferring the toner image onto a transfer paper, and a potential on the image carrier 1 after transfer. A pre-cleaning corotron 6 for smoothing the irregularity of the image carrier, and a cleaning device 7 for scraping off the untransferred toner from the image carrier 1 are arranged.
The image forming process is repeated while rotating in the direction.

In the exposure optical system 4, the toner primary colors Y (yellow), C (cyan), M (magenta),
The K (black) image signal is converted into an optical signal, and a latent image corresponding to the original image is formed on the image carrier 1. For example, 1
When the latent image of the color is transferred to the transfer paper through the development, the image carrier 1 is charged by the charging device 3 again after the residual toner is removed by the cleaning device 7 and then discharged by the discharging device 2. An image signal of the second color is output from the optical system 4, and thereafter, latent images of the respective image signals are sequentially formed.

The developing device 5 has a black developing device 5K, a cyan developing device 5C, a magenta developing device 5M, and a yellow developing device 5Y, and each developing device is arranged around a rotary shaft. Then, for example, when a black toner image is formed, development is carried out by the black developing device 5B at the position shown in the drawing, and when a cyan toner image is formed, the developing device 5 is rotated so that the image carrier 1 is rotated. Cyan developing device 5 at the contact position
Place C.

The transfer drum 8 arranged in contact with the image carrier 1 has a metal plate connected to both ends of one support, and a dielectric film such as Mylar is wound around the disk. It has a drum shape by being attached. Transfer drum 8
Around the periphery of the transfer paper 18, the transfer paper 18 transferred from the transfer guide 19 is electrostatically adsorbed to the dielectric film, and the transfer paper 18 electrostatically adsorbed on the transfer drum 8 is neutralized and transferred. A peeling corotron 11 that assists peeling of the paper 18 is arranged, and the transfer drum 8 repeats the transfer process while rotating in the B direction. The transfer drum 8 rotates in synchronism with the image carrier 1. For example, the toner image developed in black is transferred onto the transfer paper 18 by the transfer corotron 10, and the transfer drum 8 rotates to sequentially transfer other colors. Is transcribed. When the transfer drum is rotated four times and the transfer of four colors is completed, the peeling corotron 11 removes the AC charge, and the transfer paper is separated by the peeling claw and sent to the fixing device.

The transfer corotron 10 and the pre-cleaning corotron 6 are connected to a transfer high-voltage power supply 12 and a discharge high-voltage power supply 14 for applying a high voltage to the respective corotrons. The transfer high-voltage power supply 12 is a positive DC power supply, and the discharge high-voltage power supply 14 is an AC power supply and a negative DC power supply. The transfer high-voltage power supply 12 and the discharge high-voltage power supply 14 are connected to a TC (transfer corotron) driver 13 and a PCC (pre-cleaning corotron) driver 15 that control the respective outputs. , 14 are controlled.

FIG. 2 shows the operation timings of the transfer corotron 10 and the pre-cleaning corotron 6. In the transfer corotron 10, the transfer paper 18 is the transfer corotron wire 10a.
The discharge is started at a position about 24 mm before the transfer, and the discharge is stopped when the trailing end of the transfer paper passes the transfer corotron wire 10a for about 3 mm. As a result, the positive charges concentrated on the trailing edge of the transfer paper can be suppressed to a small level.
The pre-cleaning corotron 6 starts discharging the AC component 600 msec after starting the copy cycle, ends the copy cycle, and stops the transfer corotron 22.
Discharge is continued after 00 msec until stopped. The minus DC component in the pre-cleaning corotron 6 is discharged in a region of ± 50 mm in the portion corresponding to the rear end of the transfer paper of the image carrier 1.

FIG. 3 shows the experimental results on the relationship between the transfer failure width due to the off timing of the transfer corotron 10 and the contrast of the trailing edge line of the paper. The off timing of the transfer corotron 10 is the color when the transfer corotron is turned off. The distance L between the tron wire and the trailing edge of the transfer sheet is set, and the contrast of the trailing edge of the sheet when the AC current and the minus DC current of the pre-cleaning corotron 6 are changed is measured. According to this, AC60 with dynamic current
.mu.A / DC-7 .mu.A is set, and the area of light positive deflection due to the AC current is corrected to the negative side of the area of strong positive deflection corresponding to the trailing edge of the transfer paper with the DC current component. When the pre-cleaning corotron 6 has this output and the discharge is stopped when the rear end of the transfer paper passes the transfer corotron wire by 2 to 3.5 mm through the transfer corotron 10, if the transfer failure width and the contrast of the rear end line of the paper are compared, Good results have been obtained.

In the above-described embodiment, all the image forming operations are performed with the signal from the transfer drum position detecting means 20 provided in the transfer drum 8 as a reference. But in this case
Due to the difference in the surface condition of the transfer paper transport roller, the type of the transfer paper, and the strength of the waist due to the water content, a slight deviation occurs in the position of the transfer paper 18 on the transfer drum 8 and In some cases, the transfer corotron 10 cannot be stopped at the correct position.

Therefore, as another embodiment of the present invention, the sheet detecting means 16 may be provided facing the position of the suction corotron 9. In this embodiment, the transfer paper 18 is adsorbed to the transfer drum 8 by the adsorbing corotron 9 and then passes in front of the paper detecting means 16. As a result, the paper detection means 16 detects the leading edge of the transfer paper 18 and sends the information to the TC driver 13 and the PCC driver 15. After each driver receives the signal from the paper detection means 16,
Discharge each corotron according to the determined procedure. As a result, even if the position of the transfer paper 18 is shifted, the trailing edge of the paper can be reliably removed, and a good image can be obtained.

[0020]

As is apparent from the above description, according to the present invention, the discharge timing of the transfer corotron is made constant with respect to the transfer paper, and the discharge current of the corotron before cleaning is suppressed to a small value, whereby the rear end of the transfer paper is streaked. It is possible to obtain a highly reliable image while suppressing the occurrence of

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment in which the image forming apparatus of the present invention is applied to a full-color electrophotographic apparatus. FIG. 1 is a configuration diagram showing an embodiment of the image forming apparatus of the present invention.

FIG. 2 is a diagram showing operation timings of a transfer corotron and a pre-cleaning corotron.

FIG. 3 is a diagram showing an experimental result regarding a relationship between a transfer failure width due to an off timing of a transfer corotron and a contrast of a trailing edge line of a sheet.

FIG. 4 is a diagram showing an example of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Elimination lamp, 3 ... Charging device, 4 ... Exposure optical system, 5 ... Developing device 6 ... Pre-cleaning corotron, 7 ... Cleaning device, 8 ... Transfer drum 10 ... Transfer corotron, 12, 14 ... High-voltage power supply, 13 ...
TC driver 15 ... PCC driver, 16 ... Paper detection means, 17 ...
CPU, 18 ... Transfer paper 20 ... Transfer drum position detection means

Claims (4)

[Claims] 1. An image carrier, an electrostatic latent image forming means, a transfer device using a dielectric film for holding a transfer paper,
In an image forming apparatus equipped with a transfer corotron for transferring a toner image formed on an image carrier and a cleaning device for cleaning the surface of the image carrier, a negative discharge is generated between the transfer corotron and the cleaning device. An image forming apparatus characterized by comprising a pre-cleaning corotron for carrying out the above, and the transfer corotron stops discharging immediately after the transfer paper passes through the transfer corotron wire. 2. The image forming apparatus according to claim 1, wherein the pre-cleaning corotron discharges only a portion corresponding to a rear end portion of the transfer sheet of the image carrier. 3. A paper detection means capable of detecting the transfer paper on the transfer drum is provided in front of the transfer paper traveling direction of the transfer corotron, and the discharge stop timing of the transfer corotron is controlled on the basis of a signal from the paper detection means. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 4. The image forming apparatus according to claim 3, wherein the discharge timing of the pre-cleaning corotron is controlled on the basis of a signal from the paper detecting means.