JPH0695529A - Image forming device - Google Patents

Abstract

PURPOSE:To surely clean up even materials that attach to a contact charging transfer device and are not dependent on a charge. CONSTITUTION:A cleaning member 20 is installed in such a manner as to be capable of being connected to and disconnected from the outside conductive layer 12b of a roller type contact charging transfer device 12 as indicated by the arrow in Figure, and the cleaning member 20 is made to abut to the surface of the conductive layer 12b of the transfer device 12 when a cleaning bias voltage of reversed polarity with respect to a transfer bias voltage is applied to the transfer device 12. Therefore, a charged developer attaching to the surface of the conductive layer 12b of the transfer device is returned to a photoreceptor drum 1 by the cleaning bias voltage and materials attaching to the surface which are not dependent on the charge, such as paper dust and a developer of non polarity, are surely removed by the sliding contact between the cleaning member 20 and the surface of the conductive layer 12b.

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 a copying machine or a printer such as an electrophotographic system or an electrostatic recording system,
More specifically, a contact charging type transfer means for contacting the back surface of the recording material to give an electric charge is used as a transfer means for transferring a visible image formed on an image carrier such as a photoconductor or a dielectric to the recording material. Image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, for example, in an electrophotographic image forming apparatus or an electrostatic recording type image forming apparatus, a visible image (toner image) formed on an image carrier such as a photoconductor or a dielectric is printed on paper. A transfer device (corona charger) that uses corona discharge is widely used as a transfer unit that transfers onto a recording material such as.

Such a corona transfer device is effective as a transfer means for applying a predetermined electric charge to the recording material in a non-contact state and transferring the toner image formed on the image carrier to the recording material. However, a considerably high voltage has to be applied to generate corona discharge, which requires a high-voltage power supply, and has a problem that ozone is generated due to corona discharge.

For this reason, in recent years, an image forming apparatus has been developed which uses a contact charging type transfer means which requires application of a relatively low voltage. This contact charging type transfer means is generally provided with a charging member such as a conductive roller or a conductive brush that comes into contact with the back surface of the recording material, and a relatively low transfer bias voltage is applied to the charging member to transfer the image onto the image carrier. The toner image formed on the recording medium is transferred to a recording material. As described above, the contact charging type transfer means is required to apply a low voltage, and thus has advantages such as a small power source, a light weight, a low cost, and a small amount of ozone generation.

FIG. 4 shows a primary charging device for uniformly charging an image carrier and a transfer device for transferring a visible image (toner image) formed on the image carrier onto a fed recording material. An example of an electrophotographic image forming apparatus using a contact charging type charging device and a transfer device is shown in FIG.

As shown in the figure, this image forming apparatus is provided with a photosensitive drum 1 as an image bearing member which is driven to rotate in the direction of the arrow in the figure, and the photosensitive drum 1 is uniformly charged around the photosensitive drum 1. Roller-type contact charging type primary charging device 2 for carrying out image formation, image exposure means 10 for forming an electrostatic latent image on the photosensitive drum 1 according to image information, and a static charging device formed on the photosensitive drum 1. A developing device 11 that develops the latent image into a visible image, a roller-type contact charging type transfer device 12 that transfers the visible image on the photosensitive drum 1 to the recording material 14 that has been fed, and a visible image transfer device. A cleaner 13 that removes the developer remaining on the photosensitive drum 1 after the transfer, a static eliminator (lamp) 15 that neutralizes and initializes the photosensitive drum 1 are sequentially arranged.

In this embodiment, the photosensitive drum 1 is composed of a conductive base layer 1b made of aluminum, iron or the like, and a photoconductive layer 1a made of, for example, an organic photoconductor adhered to the outer peripheral surface thereof.
Is a drum-type electrophotographic photosensitive member having as basic constituent layers, and is rotationally driven in the clockwise direction in the drawing at a predetermined peripheral speed around its supporting shaft 1d. The conductive base layer 1b is grounded.

Further, the contact charging type primary charging device 2 has a conductor roller 2c such as a metal roller as a core metal, a conductive layer 2b formed on the outer peripheral surface thereof, and a resistance layer 2a1 formed on the outer peripheral surface thereof. 2a2, both ends of the conductor roller 2c are rotatably supported by bearing members (not shown) and arranged parallel to the photoconductor drum 1, and are pressed in the direction of the photoconductor drum by pressing means such as springs (not shown). The outermost resistance layer 2a is biased to the outermost resistance layer 2a.
1 is pressed against the photoconductor drum 1 and is driven to rotate in accordance with the rotation of the photoconductor drum 1 in the direction indicated by the arrow. By applying a predetermined DC bias voltage from the power supply 3 to the conductor roller 2c through the electric contactor 3a, the peripheral surface of the photosensitive drum 1 is uniformly contact-charged to a predetermined polarity and potential.

The image forming operation of the image forming apparatus having the above-mentioned structure will be briefly described. After the photosensitive drum 1 is uniformly charged by the contact charging type primary charging device 2, an image of, for example, a laser scanner or slit exposing means is formed. Exposure means 10
The electrostatic latent image is formed by being exposed by the scanning light according to the image information from. This electrostatic latent image is developed by the developer carried in a thin layer on the developing sleeve 11a of the developing device 11 to form a visible image (toner image).

The visible image on the photosensitive drum 1 is transferred onto the recording material 14 fed by a sheet feeding mechanism (not shown) to the transfer area by the action of the contact charging type transfer device 12 in the transfer area.

The transfer device 12 of the present embodiment comprises a conductor roller 12a such as a metal roller as a core metal and a cylindrical conductive layer 12b formed on the outer peripheral surface of the conductor roller 12a.
Both ends of 2a are rotatably supported by bearing members (not shown) and arranged parallel to the photosensitive drum 1, and biased by a predetermined pressing force in the direction of the photosensitive drum by a pressing means such as a spring (not shown). , Outer conductive layer 12b
Is pressed against the photosensitive drum 1 and the recording material 14 is fed, the conductive layer 12b of the transfer device 12 contacts the back surface of the recording material 14 and is driven by the movement of the recording material 14 in the direction of the arrow shown in the figure. Rotate. At this time, by applying a predetermined transfer bias voltage from the power source 4 to the conductor roller 12a, an electric charge having a polarity opposite to that of the toner is directly applied to the recording material 14 from the back surface thereof and is formed on the photosensitive drum 1. The visible image is transferred onto the recording material 14.

Gears and the like may be attached to the contact charging type charging device 2 and the conductive rollers 2c and 12a of the transfer device 12, and they may be forcibly driven by a driving means such as a motor. Further, the contact charging type devices 2 and 12 are not limited to the roller type charging member and the transfer member, and may be, for example, a brush type or a blade type charging member or the transfer member.

After that, the recording material 14 is separated from the photosensitive drum 1 and sent to an image fixing means (not shown), the transferred image is fixed on the recording material, a desired print image is formed and discharged to the outside of the apparatus. .

On the other hand, the photosensitive drum 1 continues to rotate as it is, the developer and other adhered substances remaining on the surface thereof are cleaned by the cleaner 13, and the static eliminator 15 is further removed.
Then, the charge is removed and initialized to prepare for the next image formation.

[0015]

By the way, when the above-mentioned roller type contact charging type transfer device 12 is used,
Since the conductive layer 12b of the transfer device 12 is in contact with the photoconductor drum 1, a developer such as toner adheres to the surface of the conductive layer 12b when the recording material is not supplied, or due to some other reason. However, paper dust or the like will be attached when the paper is passed.
For this reason, when an image is formed after the developer or paper dust is attached, the resistance value varies on the surface of the conductive layer 12b of the transfer device 12, and thus a good transferred image, that is, an image cannot be obtained. there were.

Therefore, conventionally, as shown in the timing chart of FIG. 5, a cleaning bias voltage having a polarity opposite to that of the transfer bias voltage is applied to the transfer device 12 during the non-image forming period, so that the conductive layer 12b is exposed. By returning the developer or the like attached to the surface to the photosensitive drum 1, the surface of the conductive layer of the transfer device 12 is cleaned. However, in this cleaning method, paper dust, non-polar developer, and other adhering substances that adhere to the surface of the conductive layer of the transfer device 12 do not return to the photoconductor drum 1 and cannot be completely cleaned. There was a drawback.

Therefore, an object of the present invention is to apply a cleaning bias voltage to a contact charging type transfer device, and to rub the cleaning means against the surface of the transfer device to clean the transfer device, thereby making it dependent on the charge. An object of the present invention is to provide an image forming apparatus capable of surely cleaning even undesired deposits.

[0018]

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention develops an electrostatic latent image formed on an image carrier to form a visible image, and the visible image is contacted with the back surface of a recording material to be fed for transfer. In an image forming apparatus for transferring from the image carrier onto a recording material by a contact charging type transfer means for applying an electric charge, a means for applying a cleaning bias voltage having a polarity opposite to that at the time of transfer to the contact charging type transfer means. The image forming apparatus further comprises: a contacting / separating cleaning unit that contacts the contact charging type transfer unit to perform cleaning by sliding.

[0019]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic block diagram showing an embodiment of an image forming apparatus according to the present invention. In this embodiment also, the primary charging device for uniformly charging the image carrier shown in FIG. The transfer device for transferring the visible image (toner image) formed on the carrier to the fed recording material is applied to a contact charging type charging device and an electrophotographic image forming device using the transfer device. Since the present invention is applied, members, parts, elements and the like corresponding to those in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted unless necessary.

In the present embodiment, a cleaning member 20 such as a brush or a blade is installed on the outer conductive layer 12b of the roller-type contact charging type transfer device 12 so as to be able to come into contact with and separate from the outer conductive layer 12b as shown by an arrow in the drawing. When the transfer device 12 is cleaned during the non-image forming period, when the cleaning member 20 is applied with a cleaning bias voltage having a polarity opposite to that of the transfer bias voltage, the conductivity of the transfer device 12 is reduced. The charged developer or the like that is brought into contact with the surface of the layer 12b and adheres to the transfer device 12 is returned to the photosensitive drum 1 by the cleaning bias voltage, and the charge of paper dust or a non-polar developer or the like. The deposits that do not depend on the conductive layer 12 of the cleaning member 20.
b) The surface of the transfer device is surely removed by rubbing against the surface.

FIG. 2 is a timing chart showing a first example of the operation sequence of the image forming apparatus of this embodiment. This example shows a case where two sheets are continuously printed.

First, based on the print start signal, the rotation drive of the photosensitive drum 1 of the apparatus which has been in the standby state until then is started, and the pre-rotation period is started. In order to perform cleaning of the transfer device 12 in the pre-rotation period, a bias voltage for cleaning having a polarity opposite to that of the transfer is used for a predetermined time (usually about the time required for the transfer device 12 to rotate 1 to 2 times). Was applied to the transfer device 12, the developer such as toner attached to the surface of the transfer device 12 was returned to the photosensitive drum 1, and the transfer device 12 was cleaned.
After that, the first sheet of image is formed, and the formed image is transferred to the recording material by the transfer device 12, and the sheet interval (time from the completion of the first sheet of image formation to the start of the second sheet of image formation) 2), the cleaning of the transfer device 12 was performed in the same manner as described above, that is, the transfer device 12 was cleaned only by applying a cleaning bias voltage for a predetermined time. After that, the second image is formed, the formed image is transferred to the recording material by the transfer device 12, and then the transfer device 12 is cleaned in the post-rotation period of the photoconductor drum 1 as described above.

When the above operation is repeated, about 3
After forming about 10,000 images, the adhesion of paper powder, non-polar developer, etc. to the transfer device surface began to stand out,
If image formation is performed thereafter, a transfer failure may occur, and a good high-quality image may not be obtained.

On the other hand, the outer conductive layer 1 of the transfer device 12
The brush-like cleaning member 20 installed so as to be able to come into contact with and separate from the 2b is brought into contact with the surface of the conductive layer 12b of the transfer device 12 in synchronism with application of a cleaning bias voltage to the transfer device 12, When the operation sequence of this example that cleans the paper dust and the non-polar developer adhered to the surface of the conductive layer 12b is used, the transfer of the formed images after 30,000 sheets is satisfactory without causing the transfer failure. It was possible to obtain a high quality image. As is clear from the timing chart of FIG. 2, the cleaning member 20 is in contact with the transfer device 12 only during the time when the cleaning bias voltage is applied to the transfer device 12, and is removed from the transfer device at other times. It is separated.

In this embodiment, the resistance value of the conductive layer 12b of the transfer device 12 is 10 ⁷ to 10 ¹⁰ Ω.
Single-cell or continuous-cell EPDM,
SBR, BR, etc. processed into a roller diameter of 20 mm and a length of about 300 mm were used. The cleaning member 20 for cleaning the transfer device 12 may be brought into contact with the surface of the transfer device 12 only during the time when the cleaning bias voltage is applied as described above, but it is always contacted with the surface of the transfer device 12. However, no problem occurs.

Next, FIG. 3 shows a second example of the operation sequence of the image forming apparatus of this embodiment. In this example, the transfer device 1
2 is applied with a bias voltage for transfer, the surface area of the photoconductor drum 1 passing through this transfer area has a polarity opposite to that of the bias voltage for cleaning, and therefore has a predetermined polarity of the same polarity as during image formation. The charging is performed to a potential (preferably a potential lower than that during image formation) so that the developer attached to the surface of the transfer device 12 can be removed more reliably. Therefore, as shown in the timing chart of FIG. 3, the primary charging device 2 is turned on for the same time as the application time of the cleaning bias voltage from a time slightly before the time when the cleaning bias voltage is applied. Body drum 1
The surface of the photosensitive drum 1 is charged to a potential V _CL slightly lower than the potential V _D at the time of image formation, and when the transfer bias voltage is applied to the transfer device 12, this charged area of the photosensitive drum 1 just passes through the transfer area. It is something that is done.

As a result of using the operation sequence of this example, the life of the transfer device 12 was about 80,000 sheets in the first operation sequence shown in FIG. 2, but it became longer in the operation sequence of this example. It was possible to obtain a high-quality transferred image, that is, an image without any problem up to about 100,000 sheets.

Further, in order to improve the releasability of the developer and paper powder, the surface of the conductive layer 12b of the transfer device 12 is coated with polyurethane to a film thickness of about 10 μm, and the first operation of FIG. When images were formed in sequence, a good quality transferred image, that is, an image could be obtained even when the number of images formed exceeded 100,000.

In the above embodiment, the case where the present invention is applied to the electrophotographic image forming apparatus has been described.
The present invention is not limited to the image forming apparatus shown in the above embodiment, but the present invention can be applied to image forming apparatuses of various other configurations using the contact charging type transfer means, and similar effects can be obtained. Needless to say. Further, the configuration of the transfer unit, the cleaning unit for the transfer unit, the operation sequence of image formation, and the like are not limited to those in the above embodiment.

[0031]

As described above, according to the image forming apparatus of the present invention, when cleaning the contact charging type transfer means, the cleaning bias voltage is applied and the physical cleaning means is used as the transfer means. Since they are brought into contact with each other to perform the rubbing cleaning at the same time, not only the developer but also the adhering matter which does not depend on the electric charge such as the paper powder and the non-polar developer can be surely cleaned. Can be virtually completely cleaned,
There is a remarkable effect that the life of the transfer means is extended and a high quality transferred image, that is, an image can be obtained for a long period of time.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment in which the present invention is applied to an electrophotographic image forming apparatus including a contact charging type transfer device.

FIG. 2 is a timing chart for explaining a first example of an operation sequence of the image forming apparatus according to the present invention in FIG.

FIG. 3 is a timing chart for explaining a second example of the operation sequence of the image forming apparatus according to the present invention in FIG.

FIG. 4 is a schematic configuration diagram showing an example of an electrophotographic image forming apparatus provided with a conventional contact charging type transfer device.

5 is a timing chart for explaining an operation sequence of the image forming apparatus in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Contact charging type primary charging device 3, 4 Power source 10 Image exposure means 11 Developing device 12 Contact charging type transfer device 13 Cleaner 14 Recording material 15 Static eliminator 20 Cleaning member

Claims (4)

[Claims] 1. An electrostatic latent image formed on an image bearing member is developed to form a visible image, and the visible image is brought into contact with the back surface of a recording material to be fed to impart a transfer charge. In the image forming apparatus for transferring the image from the image carrier onto the recording material by the contact charging type transfer means, a means for applying a cleaning bias voltage having a polarity opposite to that at the time of transfer to the contact charging type transfer means, An image forming apparatus, comprising: a contacting / separating cleaning unit that contacts a contact charging type transfer unit to perform cleaning by sliding. 2. The image forming apparatus according to claim 1, wherein the cleaning unit is brought into contact with and separated from the transfer unit in synchronization with the application of the cleaning bias voltage. 3. The area of the image carrier that passes through the transfer area when the cleaning bias voltage is applied to the transfer means has a predetermined potential having a polarity opposite to that of the cleaning bias voltage. The image forming apparatus according to claim 1, wherein the image forming apparatus is charged. 4. The transfer means is composed of a roller type member, and a surface layer for enhancing releasability is formed on the surface of the roller type member. The image forming apparatus according to item 1.