JPH07140807A - Image forming device - Google Patents

Abstract

PURPOSE:To simplify control operation and constitution and to reduce production cost by applying transfer voltage by which charge on the surface of an image carrier can be removed on a transfer means as soon as a toner image is transferred to a recording material. CONSTITUTION:Toner triboelectrified to have a negative polarity (or positive polarity) in a developing tank 28 is fed to a developing area 30 by a developing roller 28, and an electrostatic latent image is developed with the toner. The transfer bias voltage of the positive polarity(or negative polarity) is applied a on a transfer roller 20 from a bias circuit 24, thereby forming transfer electric field toward a photoreceptor drum 12 from the transfer roller 20. When the recording material 32 is supplied to the drum 12, the toner image formed on the surface of the drum 12 is attracted by the transfer electric field and transferred to the recording material 32 and the charge remaining on the surface of the drum 12 is removed at the same time. The recording material 32 to which the toner image is transferred is carried to a fixing device 34, and ejected to the outside after the toner image is fixed on the recording material 32.

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,
In particular, for example, it is applied to an electrostatic recording device, a copying machine, a printer or the like in which a transfer electric field is formed from the back surface of the recording material to transfer the toner image formed on the surface of the image carrier to the recording material. Forming apparatus

[0002]

2. Description of the Related Art An example of a conventional image forming apparatus of this type is disclosed in Japanese Patent Laid-Open No. 64-7086. In the image forming operation according to this conventional technique, first, the surface of the image carrier is uniformly charged by the conductive charging member to which the superimposed voltage of the DC voltage and the AC voltage is applied, and then the surface of the image carrier is exposed by the exposing unit. A light image is irradiated on the surface, and an electrostatic latent image is formed on that portion. Then, after the electrostatic latent image is toner-developed by the developing device, the toner image is transferred to the recording material by the transfer roller. A DC voltage equal to or lower than the charging start voltage of the image carrier is applied to the transfer roller. The toner remaining on the surface of the image carrier after the transfer is removed by a cleaning device, and the electric charge remaining on the surface of the image carrier is removed by the conductive charging member to which only an AC voltage is applied.

[0003]

In the prior art, a superposed voltage of a DC voltage and an AC voltage is applied to the conductive charging member when the image carrier is charged, and an AC voltage is applied when the residual charge is removed. Since only the conductive charging member is applied to the conductive charging member, a voltage switching means or the like is required. Therefore,
There is a problem that the control operation and configuration are complicated and the cost is high.

Therefore, a main object of the present invention is to provide a simple and inexpensive image forming apparatus.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to an image carrier, a charging unit for charging the image carrier to a predetermined potential, and an exposing unit for exposing the charged image carrier to form an electrostatic latent image. An image forming apparatus including: a developing unit that adheres toner to the electrostatic latent image to form a toner image; and a transfer unit that forms a transfer electric field from the back surface of the recording material to transfer the toner image to the recording material. The image forming apparatus is characterized in that a transfer voltage capable of removing a charge on the surface of the image carrier is applied to the transfer means at the same time when the toner image is transferred to the recording material.

[0006]

A transfer voltage equal to or higher than the charging start voltage of the image carrier is applied to the transfer means to transfer the toner image formed on the surface of the image carrier to the recording material, and at the same time, the charge remaining on the surface of the image carrier is removed. .

[0007]

According to the present invention, since the charge remaining on the surface of the image carrier is removed by using the transfer means, it is not necessary to provide the charging member with the charge removing function as in the conventional case. Therefore, the control operation and configuration can be simplified, and the manufacturing cost can be reduced. The above-mentioned object of the present invention,
Other objects, features and advantages will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0008]

EXAMPLE An image forming apparatus 10 of this example shown in FIG.
Is applied to an electrostatic recording device, a copying machine, a printer, or the like that employs a reversal development method, and includes a photosensitive drum 12 as an image carrier. Around the photosensitive drum 12, the charging device 1 is arranged in the order of its rotation direction (arrow direction).
4, an exposing unit 16, a developing device 18, a transfer roller 20, a cleaning device 22 and the like are arranged, and a bias circuit 24 is provided in the charging device 14, the developing device 18 and the transfer roller 20.
Are connected.

The charging device 14 has a negative polarity (or a positive polarity).
This is for uniformly charging the surface of the photosensitive drum 12 to the negative polarity (or the positive polarity) by the DC corona discharge. Photoconductor drum 1 charged by the charging device 14
When the light image is irradiated onto the surface of No. 2 by the exposure unit 16,
An electrostatic latent image is formed on the surface of the photoconductor drum 12 according to its photoconductive property.

The developing device 18 includes a developing tank 26 and a developing tank.
26 for transporting the toner into the photosensitive drum 12
Including the image roller 28 and the like, the negative polarity (or
The toner that has been triboelectrically charged to the positive polarity is transferred to the developing roller 28.
Then, the electrostatic latent image is transferred to the developing area 30 and developed with toner.
Be done. The transfer roller 20 is, for example, urethane foam rubber or the like.
Of the conductive elastic body of the
Then, they are pressure-welded with an appropriate pressure (for example, a total pressure of 1 kg).
In this example, the ion transmission made of urethane foam rubber is used.
Conductive type with volume resistivity of 10 ⁶Ωcm roller is transfer roller 20
Used as. In addition, the transfer roller 20 has a bias rotation.
Transfer bias voltage from path 24 of positive polarity (or negative polarity)
(600 V) is applied, whereby the transfer roller 2
A transfer electric field is formed from 0 toward the photosensitive drum 12.
It From the right side in FIG.
When 2 is supplied, it is formed on the surface of the photosensitive drum 12.
The transferred toner image is attracted to the transfer electric field and transferred onto the recording material 32.
Be done. Then, the recording material 32 on which the toner image is transferred is fixed.
After being transported to the device 34 and the toner image is fixed,
Is discharged.

The cleaning device 22 includes a blade 36 made of rubber or the like, and the blade 36 scrapes off toner, paper dust, and the like remaining on the surface of the photosensitive drum 12. Although a series of operations is completed in this way, it is necessary to remove the surface charge of the photoconductor drum 12 in preparation for the next operation. Therefore, in this embodiment, a sufficient transfer efficiency is obtained, and a transfer bias voltage that makes the surface potential of the photosensitive drum 12 approximately 0 V is applied to the transfer roller 20.
Applied to. Here, as shown in FIG. 2, when the transfer bias voltage is set between approximately 500 V and 1200 V, transfer efficiency of 85% or more can be obtained, and as shown in FIG. About 500V-800V
It has been confirmed by an experiment that the surface potential of the photoconductor drum 12 can be suppressed within the allowable range (0 ± α) when it is set during the period. Therefore, the transfer bias voltage is set to 5
If it is set between 00V and 800V (desirably 600V), both transfer efficiency and charge removal efficiency can be satisfied.

According to this embodiment, by appropriately setting the transfer bias voltage, it is possible to transfer the toner image onto the recording material 32 and at the same time remove the electric charges remaining on the surface of the photosensitive drum 12. As described above, it is not necessary to provide the charging device 14 with a static eliminating function, and it is not necessary to separately provide a static eliminating device. Therefore, the control operation and configuration can be simplified, and the manufacturing cost can be reduced.

Before cleaning, the photosensitive drum 12
Since the static electricity is removed, the electrostatic adhesion of the residual toner can be weakened, and the cleaning efficiency of the cleaning device 22 can be improved. As the transfer means, in addition to the transfer roller 20 of the above-described embodiment, as shown in FIG. 4, a transfer roller 42 having a conductive brush 38 formed on its surface,
A transfer brush 46 including the conductive brush 44 as shown in FIG. 5, a transfer film 50 including the conductive film 48 as shown in FIG. 6, or a transfer charger 52 utilizing corona discharge as shown in FIG. May be used.
However, in the transfer charger 52 that uses corona discharge, corona discharge products such as ozone are generated and the photoconductor 12
Therefore, it is desirable to use a contact type transfer means using a roller, a brush, a film or the like, since it may have a bad influence on.

Further, in the above-mentioned embodiment, the case of using the corona discharge as the charging device 14 is shown, but instead of this, for example, the roller 54 made of a conductive elastic body as shown in FIG. 8 is used. The contact type charging device 56 including the above may be used. Further, in the above-described embodiments, the case where the photoconductor drum 12 is used as the image carrier is shown, but instead of this, for example, a photoconductor belt or a photoconductor plate may be used.

Further, the present invention can be applied to a backside exposure developing system in which the backside of the image carrier is exposed.

[Brief description of drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention.

FIG. 2 is a graph showing the relationship between transfer bias voltage and transfer efficiency.

FIG. 3 is a graph showing the relationship between transfer bias voltage and surface potential.

FIG. 4 is an illustrative view showing a state in which a transfer roller having a conductive brush formed on its surface is used as a transfer unit.

FIG. 5 is an illustrative view showing a state in which a transfer brush is used as a transfer unit.

FIG. 6 is an illustrative view showing a state where a transfer film is used as a transfer means.

FIG. 7 is an illustrative view showing a state where a transfer charger is used as a transfer means.

FIG. 8 is an illustrative view showing a state in which a roller type charging device is used in the embodiment of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image forming device 12 ... Photosensitive drum 14 ... Charging device 16 ... Exposure means 18 ... Developing device 20 ... Transfer roller 22 ... Cleaning device

Claims (1)

[Claims] 1. An image carrier, charging means for charging the image carrier to a predetermined potential, exposing means for exposing the charged image carrier to form an electrostatic latent image, and the electrostatic latent image. An image forming apparatus comprising: a developing unit that adheres toner to an image to form a toner image; and a transfer unit that forms a transfer electric field from the back surface of a recording material to transfer the toner image to the recording material. The image forming apparatus is characterized in that a transfer voltage capable of removing electric charges on the surface of the image carrier is applied to the transfer means at the same time when the image is transferred to the recording material.