JP2000315021A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure conventional throughput in the case of image formation on a transfer material which is equal to or smaller in width than a transfer material subjected to the previous image formation and to minimize a throughput decrease, by limiting a cleaning operation for a secondary transfer means to image formation on a transfer material which is larger in width than the transfer material subjected to the previous image formation. SOLUTION: In the case the widthwise size of a transfer material to be subjected to image formation is larger than that of a transfer material subjected to the previous image formation, a secondary transfer belt 3 is brought into contact with an intermediate transfer drum 2 and is pressurized before the image formation. Then, by the application of a cleaning bias of a negative polarity to the secondary transfer belt 3, negative polarity toner stuck to the secondary transfer belt 3 during secondary transfer in the image formation on the previous transfer material is transferred to the intermediate transfer drum 2, thereby cleaning the secondary transfer belt 3. In the case the widthwise size of the transfer material is equal to or smaller than that of the transfer material subjected to the previous image formation, an image forming process starts without a cleaning process.

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 of an electrophotographic type or the like, and more particularly to a method in which a visible image formed on a photosensitive member as a first image carrier is temporarily converted into an intermediate image as a second image carrier. The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and the like, in which an image is primarily transferred onto a transfer member and then secondary transferred onto a transfer material to obtain an image on the transfer material.

[0002]

2. Description of the Related Art Conventionally, a full-color image forming apparatus using an intermediate transfer member has been known. This image forming apparatus is capable of forming a multicolor image stably without being affected by a transfer material such as paper when the primary transfer process is repeated for each color, and winding the transfer material around a transfer drum. Since there is no need, the transfer path of the transfer material can be configured in a straight line, so that there is an advantage that various types of transfer materials such as thin paper, thick paper, and envelopes can be used.

A full-color image forming apparatus using an intermediate transfer member includes a photosensitive member as a first image carrier, an intermediate transfer member as a second image carrier, primary charging means, exposure means, a developing device,
It is composed of a secondary transfer unit and a fixing device.

To form an image, first, the surface of the photoreceptor is uniformly charged by a primary charging member. Next, an image pattern is exposed on the surface of the photoreceptor by an exposure unit such as a laser, and a potential difference is generated between an exposed portion and an unexposed portion of the photoreceptor surface to form an electrostatic latent image on the photoreceptor surface. When this electrostatic latent image is developed using a developing device, the charged toner adheres to the exposed portion, and the latent image is visualized as a toner image.

In the primary transfer section where the photosensitive member and the intermediate transfer member are opposed to each other, a voltage (primary transfer bias: T1) having a polarity opposite to that of the toner (primary transfer bias: T1) is applied to the intermediate transfer member at a constant value. The transferred toner image is primarily transferred to the intermediate transfer member. In the case of a full-color image, this process is repeated for toners of a plurality of colors to form an image in which a plurality of colors are superimposed on the surface of the intermediate transfer member.

A transfer belt is used as a secondary transfer member, and this is brought into contact with an intermediate transfer member to form a secondary transfer nip. Next, the transfer material is sent to the secondary transfer nip,
By applying a voltage (secondary transfer bias: T2) having a polarity opposite to that of the toner to the secondary transfer member, the single-color or multiple-color images formed on the intermediate transfer member are collectively transferred onto a transfer material such as paper. Next transfer. Then, the transfer material on which the secondary transfer has been performed is sent to a fixing device, and the toner is fixed on the transfer material using heat and pressure, so that a print image can be obtained on the transfer material.

[0007]

By the way, in the secondary transfer step, for example, A4 length paper or B4 paper is passed through the secondary transfer section to an A3-compatible printer, that is, as shown in FIG. When the transfer material P having a width smaller than the maximum paper-passable width is passed, if toner is covered on the intermediate transfer drum 2, outside the width of the transfer material P,
Since the intermediate transfer drum 2 and the secondary transfer belt 3 are in direct contact with each other, a secondary transfer bias is applied as shown in FIG. 11, and the fog toner of the intermediate transfer drum 2 adheres to the secondary transfer belt 3. I will. In such a state, FIG.
As shown in (2), when a wide sheet such as A3 is passed as the transfer material P, the toner adhered to the secondary transfer belt 3 adheres to the back surface of the transfer material P, and the amount of adhered toner is large. Then, as shown in FIG. 13, dirt S appears along both ends in the width direction of the back surface of the transfer material P.

In order to remove dirt such as toner in the non-sheet passing areas at both ends in the width direction of the secondary transfer belt 3,
A cleaning bias is applied to the secondary transfer belt outside the paper passing area. However, conventionally, there have been the following problems.

In the continuous printing shown in FIG. 14, the area other than the paper passing area in the moving direction of the secondary transfer belt 3, that is, the paper interval D between the transfer material P and the next transfer material P is the secondary transfer. If the length is shorter than the circumference of the belt 3, even if a cleaning bias is used between sheets, it is not possible to remove the contaminated toner for one rotation of the transfer belt 3.

Therefore, after the image is formed, the cleaning for one round of the secondary transfer belt may be performed at all times. However, the productivity (through-top) of the print is reduced, and the photosensitive drum, the intermediate transfer drum, the secondary transfer The number of rotations of the belt or the like may increase, which may lead to a reduction in the life of these members.

An object of the present invention is to minimize a decrease in throughput, and even when a transfer material wider than a transfer material on which a previous image has been formed is passed through a secondary transfer unit, It is an object of the present invention to provide an image forming apparatus capable of always obtaining a good image on a transfer material without causing back contamination of the transfer material.

[0012]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
The toner image primarily transferred from the first image bearing member on which the toner image is formed to the second image bearing member is brought into contact with the second image bearing member by a detachable and rotatable secondary transfer means. ,
In an image forming apparatus, a secondary transfer bias is applied to a secondary transfer unit from a secondary transfer power source to perform secondary transfer on a transfer material inserted between the second image carrier and the secondary transfer unit. The length in the width direction perpendicular to the transfer direction of the transfer material,
When the transfer material on which the image is formed is larger than the transfer material on which the previous image is formed, the secondary transfer unit is brought into contact with the second image carrier before performing the image formation. A cleaning bias is applied to the secondary transfer means.

According to the present invention, a bias having the same polarity as the secondary transfer bias can be applied as the cleaning bias, a bias having a different polarity can be applied, and a bias having the same polarity and a different polarity can be applied. Polarity biases can be applied in this order or the reverse order. Preferably, the application of the cleaning bias includes:
This is performed while the secondary transfer unit rotates at least once. The secondary transfer power supply can be used as a power supply for the cleaning bias having the same polarity. The secondary transfer unit may be an endlessly rotating transfer belt that carries the transfer material and transports the transfer material to the secondary transfer unit.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention. This example was applied to a full-color laser printer using a negative process.

This image forming apparatus includes a photosensitive drum 1 which is a drum-shaped electrophotographic photosensitive member as a first image carrier,
The photosensitive drum 1 rotates in the direction of the arrow, and a primary charger 7 that uniformly charges the surface of the photosensitive drum 1 to a negative polarity around the photosensitive drum 1 in the rotating direction.
Laser exposure device 1 for exposing the surface of the device to form an electrostatic latent image
3. A fixed developing device 8 and a rotary developing device 9 for applying toner to the electrostatic latent image for development, an intermediate transfer drum 2 as a drum-shaped intermediate transfer member as a second image carrier, and A drum cleaner 6 is provided. A secondary transfer belt 3 is provided on the side of the intermediate transfer drum 2 opposite to the photosensitive drum 1.
Is disposed, and a pre-transfer charger 12 is disposed upstream thereof. A fixing device 20 is disposed downstream of the secondary transfer belt 3 in the transfer material transport direction.

To form an image, the photosensitive drum 1 is rotated, and the surface of the photosensitive drum 1 is
Thus, when the image pattern is exposed by the laser exposure device 13, the potential (VL) of the exposed portion is attenuated to -150V with respect to the potential (VD) of the unexposed portion of -550V. Thus, an electrostatic latent image is formed on the surface of the photosensitive drum 1.

Next, the electrostatic latent image on the photosensitive drum 1 is developed by the developing device 8 or the developing device 9. When a developing bias of -350 V is applied to the developing sleeve of the developing device, the negative toner carried on the developing sleeve adheres to the exposed portion VL where the surface potential of the photosensitive drum 1 is low, and the latent image is developed.
The latent image is visualized as a toner image.

The intermediate transfer drum 2 has a cylindrical conductive support (core bar) provided with at least an elastic layer made of rubber, elastomer or resin, and at least one coating layer thereon. . The intermediate transfer drum 2 also serves as a primary transfer unit of the toner image on the photosensitive drum 1, and rotates at a substantially constant speed in a direction facing the photosensitive drum 1 in the same direction.

A primary transfer power source 2 is attached to a core of the intermediate transfer drum 2.
When +300 V is applied as the primary transfer bias (T1) from 1 to 1, the toner image on the photosensitive drum 1 is
In the primary transfer nip portion where the photosensitive drum 1 and the intermediate transfer drum 2 face each other, the potential VL portion of the photosensitive drum 1 (potential: -150
V) and the intermediate transfer drum 2 (potential: +300 V) is transferred onto the intermediate transfer belt 2 by a potential difference of 450 V (primary transfer).

The above-described steps of charging, exposure, development and transfer are repeated for the four colors of yellow (Y), magenta (M), cyan (C) and black (K), so that A color image is formed by superimposing and transferring the four color toner images.

The secondary transfer belt 3 also serves as a secondary transfer means, and one end of the secondary transfer belt 3 is installed on the intermediate transfer drum 2 by a swinging cam mechanism so as to be able to freely come and go. The secondary transfer belt 3 is
The secondary transfer portion is formed by contacting with the intermediate transfer drum 2, and is rotated at substantially constant speed by a driving source (not shown) in a direction in which the portion facing the intermediate transfer drum 2 moves in the same direction.

The four color toner images on the intermediate transfer drum 2 are
Transfer Material P Conveyed to Secondary Transfer Section of Intermediate Transfer Drum 2
Then, a secondary transfer bias is applied to the secondary transfer belt 3 to collectively transfer (secondary transfer). The transfer material P onto which the four color toner images have been transferred is sent to the fixing device 20, where the toner is mixed with the toner by heating and pressurizing. An image is obtained.

Next, the secondary transfer step in this embodiment will be described in detail. FIG. 4 shows a timing chart of a sequence in the case where the size of the transfer material for forming an image in the width direction is larger than that of the transfer material for forming the previous image. For example, B
This is a case where an image is formed on A3 paper after an image is formed on four papers.

As shown in FIG. 4, after the image formation on the previous transfer material is completed, the print signal for image formation on the next transfer material is turned ON, and before the image formation is started in FIG. When the swing cam 31 is rotated to a pressing position for the secondary transfer belt 3 by a driving source (not shown), one end of the secondary transfer belt 3 is pushed up, and is pressed against the intermediate transfer drum 2. Then, a secondary transfer bias is applied at about +1000 V as a cleaning bias from a secondary transfer power source 30 connected to the secondary transfer belt 3, and in this state, the secondary transfer belt 3 is idled one or more rounds. By the application of the secondary transfer bias, the positive toner adhered to the secondary transfer belt 3 during the secondary transfer in the image formation of the previous transfer material is transferred to the intermediate transfer drum 2, and the secondary transfer belt 3 is cleaned. You.

Next, as shown in FIG. 3, the swing cam 31 is rotated to the separated position, and the secondary transfer belt 3 is separated from the intermediate transfer drum 2 again. During this time, charging, exposure, and development on the photosensitive drum 1 and primary transfer on the intermediate transfer drum 2 are performed. Then, the secondary transfer belt 3 is pressed against the intermediate transfer drum 2 by the swing cam 31 to be transferred to the secondary transfer unit. The transfer material P is passed. The secondary transfer bias (T2) is applied to the secondary transfer belt 3 by +1 kV depending on the type of transfer material and environmental conditions.
When a voltage of about 2 kV is applied, the toner image on the intermediate transfer belt 2 is transferred to the transfer material P. When the secondary transfer is completed, the secondary transfer belt 3 is separated from the intermediate transfer drum 2 again by the swing cam 31.

According to this, since the secondary transfer belt 3 is not stained with the toner, it is possible to obtain a print image without back stain.

If the size of the transfer material for forming an image in the width direction is the same as or smaller than the transfer material for the previous image formation, the toner on the transfer material from the intermediate transfer belt 3 during the secondary transfer of the image formation is used. Since there is no dirt due to the adhesion, the sequence shown in the timing chart of FIG. 5 is performed.

As shown in FIG. 5, when the image formation on the previous transfer material is completed and the print signal for image formation on the next transfer material is turned on, the charging, exposure, and
After each step of the development and the primary transfer to the intermediate transfer drum 2, the swing cam 31 is rotated to the pressing position to press the secondary transfer belt 3 against the intermediate transfer drum 2, and to transfer the transfer material to the secondary transfer portion. Pass P. A secondary transfer bias (T2) of +1 kV to 2 kV is applied from the transfer power source 30 depending on the type of transfer material and environmental conditions, and the toner image on the intermediate transfer drum 2 is transferred onto the transfer material P. Next, the secondary transfer belt 3 is separated from the intermediate transfer drum 2 again by the swing cam 31.

In this case, since the image forming process starts without performing the cleaning process, the first print time can be maintained at the same level as in the related art.

In the above embodiment, the secondary transfer bias is applied as the cleaning bias. However, a bias power supply having the same polarity as that of the secondary transfer power supply 30 may be provided exclusively for cleaning to apply the cleaning bias. Good.

As described above, according to the present embodiment, a decrease in throughput can be minimized, and even when a transfer material wider than the previous transfer material is passed through the secondary transfer portion. , Without the back transfer of the wide transfer material
A good image can always be obtained on the transfer material.

Embodiment 2 In this embodiment, an example in which a cleaning bias having a polarity opposite to that of the secondary transfer bias is applied to clean the secondary transfer belt will be described.

The ordinary image forming process is the same as that of the first embodiment, and a description thereof will be omitted. In this embodiment, as shown in FIG. 6, a cleaning bias power supply 32 is switchably connected to the secondary transfer belt 3 in addition to the secondary transfer power supply 30. The cleaning power supply 32 outputs a positive secondary transfer bias and a negative bias having a polarity opposite to that of the secondary transfer bias.

If the size of the transfer material for forming an image in the width direction is larger than that of the transfer material for the previous image formation, the sequence shown in the timing chart of FIG. 7 is performed. This is the case where A3 paper is printed after printing B4 paper.

As in the first embodiment, after the image formation on the previous transfer material is completed, a print signal for image formation on the next transfer material is set to O.
N, before the image formation is started, the swing cam 31
Is rotated to the pressing position on the secondary transfer belt 31,
The secondary transfer belt 3 is brought into contact with the intermediate transfer drum 2 and pressurized. Then, about -1000 V having a polarity opposite to that of the secondary transfer bias is applied to the secondary transfer belt 3 as a cleaning bias from the cleaning power supply 32, and in this state, the secondary transfer belt 3 idles one or more rounds. By applying the cleaning bias of the negative polarity, the toner of the negative polarity attached to the secondary transfer belt 3 at the time of the secondary transfer in the image formation of the previous transfer material is transferred to the intermediate transfer drum 2, and the secondary transfer belt 3 is cleaned. Is done.

Thereafter, as in the first embodiment, the swing cam 31
To separate the secondary transfer belt 3 from the intermediate transfer drum 2 again. During this time, charging, exposure, development,
Then, the primary transfer to the intermediate transfer drum 2 is performed, and then the secondary transfer belt 3 is pressed against the intermediate transfer drum 2 by the swing cam 31 to pass the transfer material P through the secondary transfer portion, and the secondary transfer belt 3, a secondary transfer bias (T2) is applied at +1 kV to 2 kV depending on the type of transfer material and environmental conditions, and the toner image on the intermediate transfer belt 2 is transferred onto the transfer material P. When the secondary transfer is completed, The secondary transfer belt 3 is separated from the intermediate transfer drum 2 by the swing cam 31 again.

Since the secondary transfer belt 3 is not stained with toner, a printed image without back stain can be obtained.

When the width of the transfer material for forming an image is the same as or smaller than that of the previous transfer material for forming an image, the sequence of the timing chart of FIG. 8 is performed, which is substantially the same as the timing chart of FIG. Is the same.

According to this embodiment, the decrease in throughput can be minimized. Even when a transfer material wider than the previous transfer material is passed through the secondary transfer portion, the transfer material having a wider width can be used. , And a good image can always be obtained on the transfer material.

Embodiment 3 In this embodiment, an example will be described in which the secondary transfer belt is cleaned with a cleaning bias having the same polarity and opposite polarity as the secondary transfer bias. A secondary transfer bias was used as a cleaning bias having the same polarity.

As in Embodiment 2, the secondary transfer belt 3 has
A positive secondary transfer power supply 30 and a negative cleaning power supply 32 are switchably connected. When the width of the transfer material for forming an image is the same as or smaller than the transfer material for the previous image formation, the sequence of the timing chart of FIG.

If the size of the transfer material for forming an image in the width direction is larger than that of the transfer material for the previous image formation, the sequence shown in the timing chart of FIG. 9 is performed. This is the case where printing is performed on A3 paper after printing on B4 paper.

After the image formation on the previous transfer material is completed, the print signal for image formation on the next transfer material is turned on,
Before image formation is started, the swing cam 31 is rotated to a pressing position on the secondary transfer belt 31 so that the secondary transfer belt 3
To the intermediate transfer drum 2. And the secondary transfer power supply 3
From 0, the secondary transfer belt 3 is rotated by one revolution while a secondary transfer bias of about +1000 V is applied as a cleaning bias to transfer the positive toner adhered to the secondary transfer belt 3 to the intermediate transfer drum 2. I do. Next, a cleaning bias is applied from the cleaning power source 32 to about -1000.
In a state where V is applied, the secondary transfer belt 3 is idled one or more times to transfer the negative toner adhered to the secondary transfer belt 3 to the intermediate transfer drum 2.

Thereafter, the swing cam 31 is operated as before.
To separate the secondary transfer belt 3 from the intermediate transfer drum 2 again. During this time, charging, exposure, development,
Then, the primary transfer to the intermediate transfer drum 2 is performed, and then the secondary transfer belt 3 is pressed against the intermediate transfer drum 2 by the swing cam 31 to pass the transfer material P through the secondary transfer portion, and the secondary transfer belt 3, a secondary transfer bias (T2) is applied at +1 kV to 2 kV depending on the type of transfer material and environmental conditions, and the toner image on the intermediate transfer belt 2 is transferred onto the transfer material P. When the secondary transfer is completed, The secondary transfer belt 3 is separated from the intermediate transfer drum 2 by the swing cam 31 again.

According to the present embodiment, the secondary transfer belt 3 is
Since both the positive polarity toner and the negative polarity toner are removed, it is possible to more reliably prevent the back stain on the printed image.

[0047]

As described above, according to the present invention,
When the width of the transfer material on which an image is to be formed is orthogonal to the transport direction of the transfer material on which the previous image was formed, the secondary transfer means is applied to the intermediate transfer member before forming the image on the transfer material. Contact, apply a cleaning bias to the secondary transfer means,
Since the dirt due to the toner of the secondary transfer means is cleaned, even if a transfer material wider than the previous transfer material is passed through the secondary transfer portion, the transfer material is not stained on the back side and is always applied to the transfer material. Good images can be obtained. Also, since the cleaning operation of the secondary transfer means is limited to the case where an image is formed on a transfer material wider than the transfer material on which the previous image was formed, a transfer material having the same width or a transfer on which the previous image was formed is performed. When an image is formed on a transfer material having a width smaller than that of the material, the throughput is almost the same as the conventional one, and it is possible to minimize the decrease in the throughput.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram illustrating a state where a secondary transfer belt is in contact with an intermediate transfer drum of the image forming apparatus of FIG. 1;

FIG. 3 is an explanatory diagram illustrating a state in which a secondary transfer belt is separated from an intermediate transfer drum.

FIG. 4 is a timing chart showing a sequence of a secondary transfer step including a cleaning step in the embodiment of FIG. 1;

FIG. 5 is a timing chart showing a sequence of a secondary transfer step without a cleaning step in the embodiment of FIG. 1;

FIG. 6 is an explanatory view showing a state in which a cleaning power source is provided in addition to the secondary transfer power source for the secondary transfer belt according to another embodiment of the present invention.

FIG. 7 is a timing chart showing a sequence of a secondary transfer step including a cleaning step in the embodiment of FIG.

FIG. 8 is a timing chart showing a sequence of a secondary transfer step without a cleaning step in the embodiment of FIG. 6;

FIG. 9 is a timing chart showing a sequence of a secondary transfer step including a cleaning step in still another embodiment of the present invention.

FIG. 10 is a perspective view showing a state in which a transfer material having a width smaller than the maximum possible paper width is passed through a secondary transfer portion where an intermediate transfer drum and a secondary transfer belt are in contact.

11 is a perspective view showing that the fogging toner of the intermediate transfer drum adheres to the secondary transfer belt when the paper passes in FIG.

FIG. 12 is a perspective view showing a state where a wide transfer material is passed through the dirty secondary transfer belt of FIG. 11;

FIG. 13 is a plan view showing the back surface of the transfer material on which back contamination has occurred in the paper passing of FIG. 12;

FIG. 14 is a perspective view illustrating a sheet interval of a transfer material on a secondary transfer belt during continuous printing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Intermediate transfer drum 3 Secondary transfer belt 30 Secondary transfer power supply 31 Swing cam 32 Cleaning power supply P Transfer material

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshinori Ito 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H032 AA05 BA02 BA05 BA08 BA09 BA12 BA18 BA26 BA30 CA02 CA12 CA13

Claims (7)

[Claims] A first image carrier on which a toner image is formed is transferred from the first image carrier to a second image carrier;
The secondary transfer means, which is freely detachable and rotatable, is brought into contact with the image bearing member, and a secondary transfer bias is applied to the secondary transfer means from a secondary transfer power source, so that the secondary transfer member is in contact with the second image bearing member. In an image forming apparatus that performs secondary transfer on a transfer material inserted between the transfer material and a next transfer unit, a length of a width direction orthogonal to a conveying direction of the transfer material is set before the transfer material performing the image formation. When larger than the transfer material on which the image was formed, before performing the image formation,
An image forming apparatus, wherein the secondary transfer unit is brought into contact with the second image carrier, and a cleaning bias is applied to the secondary transfer unit. 2. The cleaning bias according to claim 1, wherein a bias having the same polarity as the secondary transfer bias is applied.
Image forming apparatus. 3. A bias having a polarity different from that of the secondary transfer bias is applied as the cleaning bias.
Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein a bias having the same polarity as that of the secondary transfer bias and a bias having a different polarity are applied as the cleaning bias in this order or a reverse order. 5. The image forming apparatus according to claim 1, wherein the application of the cleaning bias is performed during at least one rotation of the secondary transfer unit. 6. The power supply for a cleaning bias of the same polarity, wherein the secondary transfer power supply is used as a power supply for the cleaning bias of the same polarity.
Image forming apparatus. 7. The image forming apparatus according to claim 1, wherein the secondary transfer unit is an endlessly rotating transfer belt that carries the transfer material and conveys the transfer material to the secondary transfer unit. apparatus.