JPH112968A - Transfer device in electrophotographic image forming apparatus - Google Patents

Abstract

(57) Abstract: The application of an electrostatic transfer bias for transferring a color toner image to recording paper does not interfere with a potential gradient for transferring a toner image from a photosensitive belt to an intermediate transfer drum. To realize good transfer. SOLUTION: In a transfer device for forming a color toner image on a peripheral surface of an intermediate transfer drum 2 by transferring a toner image from a photoreceptor belt 1 and transferring the color toner image to a recording medium, a transfer device of the recording medium is used. The bias is set based on the potential of the intermediate transfer drum 2, and the potential gradient between the photosensitive belt 1 and the intermediate transfer drum 2 and between the intermediate transfer drum 2 and the transfer means 3 of the recording medium is set. Can be operated independently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus based on electrophotographic recording, such as various color copying machines and laser printers, and more particularly to an apparatus for transferring an image to a recording medium such as a sheet via an intermediate transfer drum. And a transfer device.

[0002]

2. Description of the Related Art In various electrophotographic image forming apparatuses such as a copying machine and a laser printer, an electrostatic latent image is formed on a photosensitive member by an exposure device, and then the electrostatic latent image is formed as a toner image by a developing device. Then, a process of transferring the toner image to a recording medium such as paper, and further heating and melting the toner by a fixing device to fix the toner image on the recording medium is repeated.

A conventional general transfer device in such an image forming apparatus includes a rotating drum or a traveling belt as a photosensitive member, and forms a toner image on the peripheral surface of the drum and the surface of the belt. The recording medium is directly transferred to the recording medium by passing the recording medium while forming a nip portion with respect to a drum or a belt.

On the other hand, instead of such a transfer method, for example, a toner image is transferred to an intermediate transfer member of a rotary drum type, and then a transfer processing image on the surface of the intermediate transfer member is transferred to a recording medium, and the image is transferred to a fixing process. A delivery method has already been proposed. With a rotating drum-type intermediate transfer body, the outer diameter is large, and the transfer by stable rotation can be performed by utilizing the function as a flywheel, so that image formation can be optimized. In particular, development in the field of high-speed color image formation is expected.

FIG. 2 is a circuit diagram of a conventional example showing a potential setting by applying a voltage to each component in a transfer device including a rotary intermediate transfer member.

In FIG. 2, an intermediate transfer drum 2 rotates while forming a nip by bringing the peripheral surface into contact with the toner image forming area of the photosensitive belt 1 traveling in the direction of the arrow.
And the transfer belt 3 is arranged so as to be able to run in the direction of the arrow in contact with the intermediate transfer drum 2.

A charger 4 is disposed at a position facing the photoreceptor belt 1, and the photoreceptor belt 1 is uniformly charged to a negative polarity by the charger 4, and the photoreceptor belt 1 passes through the charger 4. On the other hand, an electrostatic latent image is formed by exposing with a laser beam. Then, a developing device 5 is arranged downstream of the electrostatic latent image forming area, and the electrostatic latent image is developed and visualized as a toner image.

In the case of a color image forming apparatus, as is well known, the developing units 5 for black, yellow, magenta, and cyan are arranged as four units, and each of these developing units develops an electrostatic latent image. Therefore, the photosensitive belt 1 is repeatedly passed four times. In the illustrated example, one developing unit 5 is shown, but this corresponds to a unit including the developing units of black, yellow, magenta, and cyan.

By setting the intermediate transfer drum 2 to a positive potential, the intermediate transfer drum 2 has a higher potential than the photosensitive belt 1, whereby the negative toner image on the photosensitive belt 1 is placed on the intermediate transfer drum 2. It is electrostatically transferred.

A transfer charger 6 is disposed at a position facing the transfer belt 3 and corresponding to a nip portion with the intermediate transfer drum 2. The transfer charger 6 includes:
A transfer electric field is applied to the back of the recording medium by corona discharge,
The negatively charged toner image on the intermediate transfer drum 2 is electrostatically transferred onto a recording medium. Then, the recording medium after the transfer of the toner image is supplied to a fixing device (not shown), where the transferred toner image is heated and melted and fixed, and output.

In this conventional example, as described above, the photosensitive belt 1 is set to the ground potential. Based on this, the charger 4 for charging the photosensitive belt 1 to the negative polarity is used.
An intermediate transfer drum 2 for transferring a toner image from the photoreceptor belt 1 and transferring the toner image onto a recording medium, and a transfer for electrostatically transferring a negative toner image from the intermediate transfer drum 2 to the transfer belt 3 For each of the chargers 6, a high voltage required for the transfer operation is applied as a bias.
That is, in the illustrated circuit, a bias power supply 4a connected to the charger 4, a bias power supply 2a connected to the intermediate transfer drum 2, and a transfer charging power supply 6a connected to the transfer charger 6 are provided, respectively. Potential difference between the intermediate transfer drum 2 and the intermediate transfer drum 2
And a recording medium traveling on the transfer belt 3.

In such a transfer device, the bias voltage applied by the charger 4 to the photosensitive belt 1 at the ground potential is about -500 V. The potential of the exposed portion due to the irradiation of the laser beam based on the image signal is reduced to about -100 V with respect to the potential of the photoreceptor belt 1, thereby forming an electrostatic latent image. Then, a negative toner image is carried on the photoreceptor belt 1 by the developing device 5.

The intermediate transfer drum 2 has a bias power supply 2
By applying a positive bias, a transfer electric field is applied by applying a positive bias, thereby electrostatically transferring the negative toner image on the photosensitive belt 1 to the surface of the intermediate transfer drum 2. The toner image on the intermediate transfer drum 2 is maintained at a negative polarity, and a bias from a transfer charging power source 6a causes the transfer charger 6 to transfer a positive charge to the intermediate transfer drum by corona discharge. A transfer electric field is applied to the back surface of the recording medium passing through the nip between the drum 2 and the transfer belt 3. Therefore,
The toner image on the intermediate transfer drum 2 is electrostatically transferred onto a recording medium, whereby the transfer process is completed.

[0014]

As described above, in the transfer apparatus in which the intermediate transfer drum 2 is interposed, the potential difference between the photosensitive belt 1 and the intermediate transfer drum 2 and the potential difference between the intermediate transfer drum 2 and the recording medium are set. The toner images are respectively transferred by the potential gradient between them.

Different transfer biases are applied to the intermediate transfer drum 2 when the toner image is transferred to and from the photosensitive belt 1 and when the toner image is transferred to and from the recording medium. , 6a. In the case of forming a color image, the toner image is transferred from the photosensitive belt 1 to the intermediate transfer drum 2 for each of black, yellow, magenta, and cyan. A transfer bias to the recording medium is applied simultaneously with the transfer from the belt 1 to the intermediate transfer drum 2.

The application of such a transfer bias causes a transfer failure when transferring a toner image from the photosensitive belt 1 to the intermediate transfer drum 2.

That is, when an electrostatic transfer bias of the transfer charger 6 is applied to the recording medium, a current flows into the intermediate transfer drum 2 so that the bias of the intermediate transfer drum 2 based on the ground potential is temporarily set. Will fluctuate. Such a change in the bias of the intermediate transfer drum 2 causes a change in the potential gradient between the photosensitive belt 1 and the intermediate transfer drum 2, and as a result, the photosensitive belt 1 moves from the photosensitive belt 1 to the intermediate transfer drum 2. The transfer of the toner image becomes defective.

Although the intermediate transfer drum 2 and the transfer charger 6 are each independently biased with reference to the ground potential, the bias of the transfer charger 6 is configured with the ground potential. Therefore, when the transfer condition between the photosensitive belt 1 and the intermediate transfer drum 2 is changed, the bias condition between the intermediate transfer drum 2 and the transfer charger 6 is changed.

That is, even when the bias potential of the intermediate transfer drum 2 is changed, the transfer charger 6 remains unchanged with respect to the ground potential. Therefore, although the bias potential between the intermediate transfer drum 2 and the photosensitive belt 1 can be set to a predetermined value, the bias potential between the intermediate transfer drum 2 and the recording paper on the transfer belt 3 changes. If the setting of the bias of the intermediate transfer drum 2 is changed with respect to the photosensitive belt 1 at the ground potential in this way, the relationship of the bias setting between the intermediate transfer drum 2 and the transfer charger 6 is broken. Would.

When the transfer bias of the transfer charger 6 is changed so as to be optimal according to the type and thickness of the sheet, the space between the sheet on the transfer belt 3 and the intermediate transfer drum 2 is appropriately adjusted. However, a preset bias relationship between the intermediate transfer drum 2 and the photosensitive belt 1 is broken.

As described above, when the bias of the intermediate transfer drum 2 and the bias of the transfer charger 6 are separately changed, the bias between the photosensitive belt 1 and the paper on the transfer belt 3 is changed. The interference causes fluctuations, resulting in poor transfer of the toner image on the intermediate transfer drum 2 and on the paper.

A problem to be solved in the present invention is that the bias between the photoreceptor belt and the intermediate transfer drum and between the intermediate transfer drum and the paper can be set independently without interfering with the set bias, thereby achieving good transfer. It is to realize.

[0023]

According to the present invention, there is provided an endless photoreceptor belt for carrying a plurality of color toner images by sequentially forming a plurality of electrostatic latent images and then developing each of the plurality of electrostatic latent images.
A rotary intermediate transfer drum that rotates in synchronization with the photosensitive belt and transfers a toner image from the photosensitive belt, and a transfer unit that transfers a color toner image on the peripheral surface of the intermediate transfer drum to a recording medium. A transfer device, wherein the setting of each potential gradient between the photosensitive belt and the intermediate transfer drum and between the intermediate transfer drum and the transfer means of the recording medium can be independently operated.

With such a configuration, for example, when a sheet is used as a recording medium, even when the potential gradient between the intermediate transfer drum and the transfer means of the recording medium is changed according to the conditions such as the paper quality and thickness, There is no temporary variation in the potential gradient between the photoreceptor belt and the intermediate transfer drum.

[0025]

According to the present invention, an endless photoreceptor belt for carrying a plurality of color toner images by sequentially forming a plurality of electrostatic latent images and then developing each of the plurality of electrostatic latent images. A rotary intermediate transfer drum that contacts the photosensitive belt and rotates synchronously to transfer a toner image from the photosensitive belt; and a transfer unit that transfers a color toner image on the peripheral surface of the intermediate transfer drum to a recording medium. And a transfer device comprising:
The setting of each potential gradient between the photoreceptor belt and the intermediate transfer drum and between the intermediate transfer drum and the transfer means of the recording medium can be independently operated, and the transfer of the intermediate transfer drum and the recording medium is performed. Even when the potential gradient between the photosensitive drum and the intermediate transfer drum is changed, the potential gradient between the photosensitive belt and the intermediate transfer drum is not changed.

According to a second aspect of the present invention, in the configuration of the first aspect, the bias of the transfer means of the recording medium is set with reference to the potential of the intermediate transfer drum, and the bias of the intermediate transfer drum is adjusted with respect to the photosensitive belt. The potential is set as a reference, and even if the setting of the potential gradient between the photoreceptor belt and the intermediate transfer drum is changed, the potential gradient between the intermediate transfer drum and the transfer means of the recording medium is changed accordingly. The transfer bias from the photoreceptor belt to the intermediate transfer drum and the transfer bias from the intermediate transfer drum to the transfer means of the recording medium are prevented from interfering with each other.

According to a third aspect of the present invention, the photosensitive belt is set to an arbitrary potential, and the intermediate transfer drum is biased to have a polarity opposite to the charging polarity of the toner image of each color based on the potential of the photosensitive belt. It is included in a closed circuit that applies an electrostatic transfer bias by a power supply, and the transfer to the recording medium is performed by a bias power supply that biases the charge polarity of the color toner image on the intermediate transfer drum to the opposite polarity with respect to the potential of the intermediate transfer drum. This is a circuit configuration included in a closed circuit for applying an electrotransfer bias. For example, if the photoconductor belt is set to the ground potential, it has the effect of increasing the degree of freedom in circuit design.

Hereinafter, embodiments of the present invention will be described. FIG. 1 is a circuit diagram showing a potential setting by applying a voltage to each component of the transfer device according to the embodiment of the present invention. Note that the same members in the example shown in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

The endless photoreceptor belt 1 is a conventional one having a photoconductor layer formed on the surface of a conductor layer, and the intermediate transfer drum 2 is made of a hollow tube made of aluminum and coated with polycarbonate. This is coated to form a dielectric layer. Although FIG. 1 shows one developing unit 4 as one unit, as described in the section of the related art, the developing units for the four colors of black, yellow, magenta, and cyan run on the photosensitive belt 1. In which a plurality of types of electrostatic latent images for different colors are sequentially formed on the photoreceptor belt 1, toner is transferred from a developing unit corresponding to these colors to the photoreceptor belt 1. The toner image is formed on the belt 1 to form a toner image.

The circuit configuration of the transfer device according to the present invention is different from that of the prior art shown in FIG. 2 in that the transfer charging power supply 6a has a circuit configuration with reference to the ground potential of the photosensitive belt 1, whereas the intermediate transfer drum 2 has a circuit configuration. The only difference is that the potential is used as a reference. In FIG. 1, what is in contact with the peripheral surface of the intermediate transfer drum 2 is a cleaning device 7 for removing residual toner after transfer to a recording medium.

With such a circuit configuration, one closed circuit between the photosensitive belt 1 and the intermediate transfer drum 2 to which an electrostatic transfer bias from the bias power supply 2a is applied with reference to the ground potential; Intermediate transfer drum 2 and transfer belt 3
A combination with another closed circuit to which an electrostatic transfer bias is applied by the transfer charging power supply 6a corresponding to the bias power supply 4a is provided between the recording medium and the upper recording medium. Therefore, the intermediate transfer drum 2 of the toner image from the photosensitive belt 1
The potential gradient for transferring the toner image to the recording medium is uniquely determined by the application of the bias voltage from the bias power supply 2 a with respect to the ground potential, and the toner image is transferred from the intermediate transfer drum 2 to the recording medium on the transfer belt 3. The potential gradient for transfer is similarly determined uniquely by the transfer charging power supply 6a based on the potential of the intermediate transfer drum 2 by the bias power supply 2a.

As described above, the setting of the potential gradient between the photosensitive belt 1 and the intermediate transfer drum 2 and the setting of the intermediate transfer drum 2
The setting of the potential gradient between the transfer belt 3 and the recording medium on the transfer belt 3 is performed in closed loops of independent loops. Therefore, as described above, the setting of the potential gradient for the transfer from the intermediate transfer drum 2 to the recording medium does not interfere with the potential gradient between the photosensitive belt 1 and the intermediate transfer drum 2. . Therefore, no defective transfer of the toner image from the photoreceptor belt 1 to the intermediate transfer drum 2 occurs, and a good reproduced image can be obtained.

On the other hand, in the prior art, since each of the bias power supply 2a and the transfer charging power supply 6a is based on the ground potential, for example, when the bias by the bias power supply 2a is changed, the transfer charging It is necessary to change the bias of the power supply 6a. On the other hand, in the circuit configuration shown in FIG. 1, the potential gradient between the photosensitive belt 1 and the intermediate transfer drum 2 and the intermediate transfer drum 2
The potential gradient between the transfer belt 3 and the recording medium on the transfer belt 3 is determined by a bias power supply 2a and a transfer charging power supply 6a, respectively. Therefore, even if the bias power supply 2a is changed, there is no need to operate the transfer charging power supply 6a at all, and control becomes easy.

[0034]

According to the first aspect of the present invention, even when the potential gradient between the intermediate transfer drum and the transfer means of the recording medium is changed, the potential gradient between the photosensitive belt and the intermediate transfer drum does not change. In addition, the transfer of the toner image between the photoreceptor belt and the intermediate transfer drum is performed favorably, and the image is not lost or disturbed during the transfer of the toner image.

According to the second aspect of the present invention, the transfer bias from the photosensitive belt to the intermediate transfer drum and the transfer bias from the intermediate transfer drum to the transfer means of the recording medium are prevented from interfering with each other. An image can be formed without affecting the image quality even if the setting is changed by the dependence characteristic.

According to the third aspect of the invention, for example, if the photosensitive belt is set to the ground potential, the degree of freedom in circuit design is increased, so that it is possible to commercialize the conventional product simply by changing the design.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a potential setting by applying a voltage to each component of a transfer device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional example showing potential setting by voltage application to each component in a transfer device including a rotary intermediate transfer member.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoreceptor belt 2 intermediate transfer drum 2 a bias power supply 3 transfer belt 4 charger 4 a bias power supply 5 developing device 6 transfer charger 6 a transfer charging power supply (bias power supply) 7 cleaning device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshinori Ejima 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.・ Es

Claims (3)

[Claims] An endless photoreceptor belt for carrying a plurality of color toner images by developing each of the plurality of electrostatic latent images after the electrostatic latent images are formed; and contacting the photoreceptor belt for synchronization. A transfer device comprising: a rotary intermediate transfer drum that rotates and transfers a toner image from a photoreceptor belt; and a transfer unit that transfers a color toner image on a peripheral surface of the intermediate transfer drum to a recording medium. A transfer device for an electrophotographic image forming apparatus, wherein setting of a potential gradient between a body belt and an intermediate transfer drum and between an intermediate transfer drum and a transfer means of a recording medium can be independently operated. . 2. The method according to claim 1, wherein the bias of the transfer means other than the recording area is set with reference to the potential of the intermediate transfer drum, and the bias of the intermediate transfer drum is set with reference to the potential of the photosensitive belt. Item 2. A transfer device in the electrophotographic image forming apparatus according to Item 1. 3. The photoreceptor belt is set at an arbitrary potential, and the electrostatic transfer bias is applied to the intermediate transfer drum by a bias power supply biasing the polarity of the toner image of each color to the opposite polarity with respect to the potential of the photoreceptor belt. The transfer to the recording medium is included in a closed circuit that applies an electrostatic transfer bias by a bias power source that biases the charge polarity of the color toner image on the intermediate transfer drum to a polarity opposite to that of the intermediate transfer drum. 3. The transfer device according to claim 1, wherein the transfer device has a circuit configuration included in the circuit.