JPH09197841A - Image forming device - Google Patents

Abstract

(57) Abstract: A toner image formed on a photoconductor is transferred to a transfer paper by a transfer roller, and the transfer residual toner on the photoconductor after the transfer of the toner image is collected by a cleaning roller. In an image forming apparatus that redeposits toner on a photoconductor and collects the redeposited toner on a developing device, the toner on the photoconductor adheres to a transfer roller, which adheres to the transfer paper and stains the transfer paper. Prevent defects. A transfer roller 7 is loaded at a time other than a toner image transfer operation for transferring a toner image on a photoconductor 1 onto a transfer paper 16.
Are separated from the photoconductor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms an electrostatic latent image on a rotationally driven image carrier by means of latent image forming means,
The electrostatic latent image is visualized as a toner image by a developing device, the toner image on the image carrier is transferred to a recording medium by a transfer device, and transfer residual toner on the image carrier after the toner image transfer is removed. The present invention relates to an image forming apparatus that collects by a cleaning member and cleans the surface of the image carrier.

[0002]

2. Description of the Related Art In an image forming apparatus of the above type configured as a copying machine, a printer, a facsimile, or a complex machine thereof, an image carrier is repeatedly used, and therefore, the surface of the image carrier after the toner image is transferred. It is necessary to clean the surface of the image bearing member by removing and collecting the residual toner remaining on the image carrier by a cleaning member. Therefore, conventionally, various cleaning devices for cleaning the image carrier have been proposed and put into practical use, but the conventional cleaning device generally stores the toner collected from the image carrier in a waste toner tank or the like, It is configured to discard this.

By the way, in recent years, in an image forming apparatus of this type which employs an electrophotographic process, it is possible to further reduce the cost and further reduce the amount of toner to be discarded as part of measures against environmental problems. Is requested.

In view of the above point, if the transfer rate of the toner image from the image carrier to the recording medium is set to 100% to eliminate the residual toner after the transfer, the so-called cleanerless system can be adopted. it can. As a result, not only can the toner to be discarded be eliminated, but also the cleaning device can be omitted, and the image forming system can be simplified and the cost of the image forming device can be reduced. However, at present, it is difficult to make the transfer rate of the toner image 100%, and there is a problem from the viewpoint of reliability.

Therefore, as a next best measure, the transfer residual toner remaining on the surface of the image carrier after the toner image is transferred is adhered to the cleaning member to be recovered, and then the recovered toner is re-adhered to the image carrier. , A method of collecting with a developing device and reusing it has been proposed (for example, Japanese Patent Publication No.
-30274 publication). Transfer residual toner remaining on the image carrier after the toner image is transferred is temporarily collected by the cleaning member, and the collected toner is affected by the next electrostatic latent image formation on the image carrier. The toner re-adhered to the non-existing surface portion and further re-adhered to the surface of the image carrier is collected by the developing device. This eliminates the need for a dedicated means for transferring the collected toner to a waste toner tank or a developing device, thus reducing the cost of the image forming apparatus and reusing the toner. It can be lost.

By the way, in the image forming apparatus of the type described at the beginning, a transfer device for transferring a toner image on the image carrier to the recording medium by contacting the surface of the image carrier via the recording medium. It is well known in the art to use a contact type transfer device such as a roller or a transfer belt. In such a contact type transfer device, an image of a type in which residual toner after transfer is temporarily collected by a cleaning member, the recovered toner is reattached to the surface of the image carrier, and the reattached toner is recovered by the developing device. It can also be used in a forming device. However, if the contact type transfer device is adopted in this type of image forming apparatus, the following problems occur.

When the rear end of the image forming area on the image carrier passes through the developing device, the surface portion of the image carrier on which the toner image is not formed subsequently passes through the developing device. In this type of image forming device, the toner image is not formed. A relatively long area of the surface which is not formed passes through the developing device. At this time, it is generally unavoidable that the toner of the developing device is attached little by little, but adheres to the surface portion thereof.

The toner thus attached to the image carrier adheres to the transfer device which is in contact with the surface of the image carrier. At this time, in the image forming apparatus of this type, as described above, the surface portion of the image carrier in a relatively long range where the toner image is not formed passes through the developing device, so that the toner from the developing device is attached to the surface portion. Even if they adhere to each other in very small amounts, the total amount of the adhered toner becomes considerably large,
Therefore, a large amount of toner adheres to the transfer device. The large amount of toner thus attached to the transfer device is attached to the recording medium when the next recording medium is sent to the transfer portion between the image carrier and the transfer device. In this way, the recording medium is unavoidably contaminated with a relatively large amount of toner.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to collect transfer residual toner on a cleaning member, to re-adhere the recovered toner to the surface of an image carrier, and then to attach the re-adhered toner to a developing device. An object of the present invention is to provide an image forming apparatus that solves the above-mentioned peculiar problems in the image forming apparatus of the collecting type and can prevent the recording medium from being stained with toner.

[0010]

In order to achieve the above object, the present invention is directed to an image carrier which is driven to rotate, a latent image forming means for forming an electrostatic latent image on the carrier, and an electrostatic latent image forming means. A developing device that visualizes the latent image as a toner image, a transfer device that transfers the toner image on the image carrier to a recording medium, and a transfer residual toner on the image carrier after the toner image transfer is temporarily collected. And a cleaning member for reattaching the collected toner to the surface portion of the image bearing member that does not affect the formation of the next electrostatic latent image, and the toner reattached to the surface of the image bearing member. Is collected in a developing device, and the transfer device is
In an image forming apparatus including a contact type transfer device that contacts a surface of an image carrier via a recording medium and transfers the toner image on the image carrier to the recording medium, the toner image on the image carrier is recorded on the recording medium. Transfer device contacting / separating means for bringing the transfer device into contact with the surface of the image carrier via the recording medium during the transfer operation for transferring and separating the transfer device from the surface of the image carrier at times other than the transfer operation. An image forming apparatus characterized by having:

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings, and the above-mentioned conventional drawbacks will be more specifically clarified with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus according to the present invention. In the figure, a drum-shaped photoreceptor 1 which is an example of the configuration of an image carrier is rotationally driven in the clockwise direction in the figure by a drive device (not shown), and at the time of this rotation, a charging roller 2 which is an example of the charging device operates. As a result, the surface of the photoconductor 1 is uniformly charged with a predetermined polarity.
In this example, the charging roller 2 is connected to the voltage power source E ₁₀ , and uniformly charges the surface of the photoconductor 1 to a negative (negative) polarity while rotating in contact with the photoconductor 1. By the action of the charging roller 2, the surface of the photoconductor 1 is charged to, for example, -850V. As a charging device for uniformly charging the photoconductor 1,
It is also possible to use a charging device, such as a corona discharger, which is arranged apart from the photoconductor.

Next, in the exposure section 3, an exposure scanning device (not shown) performs optical writing scanning with, for example, the light-modulated laser beam 11, so that a predetermined electrostatic latent image is formed on the surface of the photoconductor 1. Is formed. Photoconductor 1
The surface potential of the upper part A irradiated with the laser beam 11, that is, the surface potential of the electrostatic latent image is, for example, about −150 V, and the surface potential of the part B not irradiated with the laser beam 11, that is, the background potential of the background portion of the electrostatic latent image is almost It is maintained at -850V. As described above, in this example, the charging roller 2 and the exposure scanning device form a latent image forming unit that forms an electrostatic latent image on the image carrier made of the photoconductor 1.

The developing device 4 includes a developing roller 5 which is an example of a developer carrying / conveying member arranged to face the photoconductor 1, and a pair of agitating paddles 10A and 10B, which form the main body of the developing device. Each of the developing casings 9 is provided inside and is rotatably supported by the casing 9.
A voltage of about -600 V, for example, is applied to the developing roller 5 by the voltage power source E ₁ . A voltage having the same polarity as the charging polarity of the photoconductor 1 is applied to the developing roller 5.

In the developing device 4 exemplified here, a two-component developer D having toner and carrier is used, and the developer D is housed in the developing casing 9. Then, as the stirring paddles 10A and 10B rotate, the toner is charged to a predetermined polarity by friction with the carrier, that is, the same polarity as the charging polarity of the photoconductor 1 in this example, that is, a negative polarity. As described above, in the image forming apparatus of this example, the charging polarity of the toner during development is negative. A developing device using a one-component developer having no carrier may be employed.

The developing roller 5 is driven to rotate counterclockwise in the drawing, and the developer carried on the peripheral surface of the developing roller 5 is conveyed in the rotating direction of the developing roller 5, and the roller 5 is rotated.
The developer regulating member 15 oppositely arranged with a predetermined gap therebetween is scraped. The developer whose conveyance amount is regulated by the developer regulating member 15 is conveyed toward the developing section 6 where the developing roller 5 and the photoconductor 1 face each other, and the toner in the developer is conveyed to the photoconductor by the developing section 6. 1 is electrostatically attracted to the electrostatic latent image on 1 and adheres to that portion. That is, the toner charged to the negative polarity, which is the same as the charging polarity of the photoconductor, adheres to the surface portion A of the photoconductor irradiated with the laser beam, and the electrostatic latent image is visualized as a toner image. As described above, the image forming apparatus of this embodiment employs the reversal development method (negative / positive development method).

A transfer roller 7, which is an example of a transfer device, is disposed below the photoconductor 1. The transfer roller 7 rotates in the forward direction with respect to the rotation direction of the photoconductor 1, and toward the transfer portion 8 between the transfer roller 7 and the photoconductor 1 facing the transfer roller 7, a recording medium made of a transfer paper 16 is formed. Are transferred in the direction of the arrow P, and the transfer roller 7 is pressed against the surface of the photoconductor 1 via the transfer paper 16 sent to the transfer unit 8, and at this time, the function of the transfer roller 7 causes the photoconductor to move. The toner image formed on the transfer sheet 1 is transferred onto the transfer paper 16. That is, the power source E _{3 is applied} to the transfer roller 7 so that
Positive (plus) polarity voltage opposite to the charge polarity of the above toner,
For example, a voltage of + 950V is applied, and at this time, the negative toner T on the photoconductor 1 is electrostatically attracted to the transfer paper 16 side and adheres to the transfer paper. In this way, the transfer roller 7 is a contact type transfer device that contacts the surface of the photoconductor 1 via the transfer paper 16 and transfers the toner image on the photoconductor 1 to the transfer paper 16.

The transfer paper 16 on which the toner image has been transferred is separated from the photoconductor 1 by a separating device (not shown) and is sent to a fixing device (not shown).
The toner image on 6 is fixed. In this way, the transfer paper 1
6 is ejected outside the image forming apparatus main body as copy paper.

As described above, the image forming apparatus of this embodiment has the image carrier composed of the photosensitive member 1 which is rotationally driven, the latent image forming means for forming an electrostatic latent image on the image carrier, and the latent image forming means. It has a developing device 4 for visualizing the electrostatic latent image as a toner image, and a transfer device constituted by a transfer roller 7 for transferring the toner image on the image carrier to a recording medium made of transfer paper 6. There is. Then, the transfer device comes into contact with the surface of the image carrier configured as the photoconductor 1 via the recording medium made of the transfer paper 16 to transfer the toner image on the image carrier to the recording medium. Of the transfer device.

The toner image on the photoconductor 1 is transferred to the transfer paper 16 at the transfer section 8. After the toner image is transferred, the photoconductor 1 is transferred.
The toner remaining on the photoconductor 1 without being transferred to the transfer paper 16 adheres to the surface of the. When the transfer residual toner T ₁ reaches the cleaning unit 14, it is temporarily collected on the surface of a cleaning roller 12 which is an example of a cleaning member.

The cleaning roller 12 has a core member 12a made of a rigid body, and a conductive or medium-resistance elastic body 12b fixed on the surface of the core member 12a. In the illustrated example, the core member 12a. Is made of a conductive metal having a round shaft shape, and the elastic body 12b is formed in a cylindrical shape concentric with the core member 12a. The cleaning roller 12 is housed in a cleaning case 17, and each end of the core member 12b is rotatably supported on the front and rear side walls of the cleaning case 17. Cleaning roller 12
Are located substantially parallel to the photoconductor 1 together with the developing roller 5, the charging roller 2, and the transfer roller 7.
The image forming apparatus of this example has a cleaning member including such a cleaning roller 12.

Here, in FIG. 1, most of the toner T of the toner image directed from the developing unit 6 to the transfer unit 8 is toner having a charging polarity at the time of development, that is, a negative polarity toner in this example. On the other hand, when the toner image is transferred, a voltage having a polarity opposite to the toner charging polarity at the time of development, which is a positive polarity in this example, is applied to the transfer roller 7, so that the toner remains on the photoconductor 1 after the toner image is transferred. The adhered toner, that is, the transfer residual toner T ₁ is a toner in which positive and negative toners are mixed. The transfer residual toner is transferred to the cleaning unit 14 in a state in which both positive and negative polarity toners are mixed.

The cleaning roller 12 of the present embodiment, when recovering the residual toner T ₁ of the the photosensitive member 1, a clockwise direction in FIG. 1, that is, the driving (not shown) in a counter direction with respect to the rotation direction of the photosensitive member 1 It is driven to rotate by the control means, and rotates while rubbing against the surface of the photoconductor 1. The cleaning roller 12 has its own surface portion elastically deformed by the photoreceptor 1.
A pressure contact is made with the photoreceptor 1, and a nip region N is formed at this pressure contact portion as shown in FIG. This nip area N becomes a cleaning area.

In the nip region N, the transfer residual toner T ₁ having both positive and negative polarities is a toner having the same polarity (negative polarity in this example) as the toner at the time of development while being in contact with the cleaning roller 12. It is frictionally charged. Transfer residual toner T ₁
However, the negative polarity, which is the charging polarity at the time of development, can be obtained.

Thus, the cleaning roller 1 of this example
2 is the transfer residual toner that is frictionally charged between the photosensitive member 1 and
It also performs the function of frictionally charging the toner so that the toner has a negative polarity, which is the original polarity. That is, the cleaning member including the cleaning roller 12 includes a toner whose transfer residual toner toward the cleaning roller 12 has a polarity opposite to the charging polarity of the toner at the time of development, and the toner has the charging polarity ( The toner is triboelectrically charged so that the toner can have the original polarity). The elastic body 12b of the cleaning roller 12 is composed of a charging series charging material capable of frictionally charging the toner to its original polarity, in this example, negative polarity.

[0026] Returning to FIG. 1, when recovering the residual toner T ₁ of the the photosensitive member 1 to the cleaning roller 12, the core member 12a of the cleaning roller 12, the charging of the toner is frictionally charged by the roller 12 A voltage having a polarity opposite to that of the polarity, in this example, a positive polarity voltage, for example, a voltage of +200 V is applied by the voltage power supply E ₄ . Therefore, the residual toner after the transfer of the toner image, which has passed through the transfer portion 8, that is, the residual transfer toner T ₁ is electrostatically attracted to the surface of the cleaning roller 12 to which the positive voltage is applied, and the residual toner of the roller 12 is transferred. It adheres to the surface and is temporarily collected by this roller. As a result, the surface of the photoconductor 1 is cleaned. In this manner, the cleaning roller 12 rotating in contact with the photoconductor 1 electrostatically attracts the transfer residual toner T ₁ on the photoconductor ₁ to the surface of the cleaning roller 12 with the photoconductor _1. The voltage as described above is applied so that an electric field to be obtained is formed.

As described above, the cleaning roller 12
The toner collected on the surface of the toner is indicated by reference numeral T _{2 in} FIGS. 1 and 2. In FIG. 3, the toner image on the photoconductor 1 is transferred to the transfer paper 16, and the transfer residual toner T ₁
FIG. 6 is a schematic view showing a state where is collected on the surface of the cleaning roller 12. The surface portion of the photoconductor 1 that has been cleaned by the cleaning roller 12 is subjected to static elimination action by a static elimination lamp 13 which is an example of a static elimination device, and the surface potential thereof is lowered to a reference value. The charge eliminating lamp 13 continues to be turned on during the image forming operation. The surface of the photoconductor that has been subjected to the static elimination is continuously charged by the charging roller 2 as shown in FIG. 3, and the above-described image forming operation is continued.

In this way, one sheet of toner image is formed on the photosensitive member 1 while the photosensitive member 1 is rotated several times, for example.
This is continuously transferred onto the transfer paper 16, and the circumferential area on the photoreceptor 1 where such a toner image is formed is the image forming area. In FIG. 3, this image forming area is designated by a reference numeral X, and the tip end thereof in the rotation direction of the photosensitive member is designated by a reference numeral Y. There is substantially no transfer residual toner in the portion of the image forming area X that has passed through the cleaning roller 12 and is in a cleaned state.

In FIG. 4, the rear end of the image forming area X in the direction of rotation of the photosensitive member is indicated by a symbol Z, and the rear end Z is shown.
When the charging roller 2 passes through the charging roller 2, the charging roller 2 is separated from the surface of the photoconductor 1 at this time (see FIG. 5). At the same time, the switch S ₁₀ shown in FIG. 1 is switched to turn off the voltage application to the charging roller 2.

When the trailing edge Z of the image forming area passes the developing roller 5 of the developing device 4 as shown in FIG. 5, the switch S ₁ shown in FIG. ₁ is switched, and the developing roller 5 is operated by the voltage source E ₂ . A positive polarity voltage opposite to the charging polarity of the toner, for example, a voltage of + 500V is applied to the developing roller 5 so that the toner does not adhere to the photoconductor 1. Subsequently, as shown in FIG. 6, when the trailing edge Z of the image forming area passes the transfer portion 8, at this time, the voltage application to the transfer roller 7 is stopped.

As described above, in the illustrated image forming apparatus, the transfer residual toner T ₁ on the photoconductor 1 after the transfer of the toner image onto the recording medium composed of the transfer paper 16 is contact-rotated with the photoconductor 1. The cleaning member including the cleaning roller 12 is temporarily collected. When the transfer residual toner on the photoconductor 1 is collected by the cleaning roller 12, the cleaning roller 12 is electrostatically transferred to the cleaning roller 12 at the time of development so that the cleaning roller 12 is electrostatically transferred to the cleaning roller 12. A voltage having a polarity opposite to the charging polarity of the toner (positive polarity in this example) is applied.

As described above, the cleaning roller 12 temporarily collects the transfer residual toner. Then, the collected toner T ₂ is collected on the surface portion of the photoconductor 1 which does not affect the formation of the next latent image. Reattach. That is, when the trailing edge Z of the image forming area after the toner image is transferred onto the transfer paper 16 passes through the cleaning roller 12 as shown in FIG. 7, the switch S ₂ shown in FIG. Reference numeral 12 is connected to a voltage power source E ₅ , and a voltage of, for example, −3000 V having the same negative polarity as the charging polarity of the toner frictionally charged by the cleaning roller 12 is applied to the core member 12 a of the cleaning roller 12. .
In this way, the toner on the cleaning roller 12 is provided between the cleaning roller 12 and the non-image forming area W (FIG. 7) on the surface of the photosensitive member on the rear side in the rotation direction of the photosensitive member 1 with respect to the rear end Z of the image forming area. An electric field is formed in the direction in which T ₂ is emitted toward the photoconductor 1.

Due to the electric field, as shown in FIG.
The toner T ₂ temporarily collected on the cleaning roller 12 is reattached to the non-image forming area W on the photoconductor 1 and returned. At this time, the cleaning roller 12 of this example is
It is rotationally driven in the forward direction with respect to the photoconductor 1. As shown in FIG. 9, the toner T ₃ redeposited on the photoconductor 1 passes under the charge removing roller 13 and the charging roller 2 separated from the photoconductor 1 by the subsequent rotation of the photoconductor 1, and as shown in FIG. The developing device 4 is reached as shown. At this time, the developing roller 5
As described above, since the positive polarity voltage opposite to the charging polarity of the toner at the time of development is applied to the negative polarity toner T ₃ redeposited on the photoconductor 1, Electrostatically moves to the side and is collected in the developer in the developing device.

As described above, the cleaning roller 12
Removes the toner T ₂ temporarily collected on the surface of the photoreceptor 1.
The toner T ₃ redeposited on the image carrier composed of the toner T ₃ and redeposited on the surface of the image carrier is electrostatically collected in the developing device 4. The toner collected in the developing device 4 is reused in the developing device 4. In this way,
It is possible to eliminate the waste toner, and it is not necessary to provide a toner conveying pipe for returning the toner collected by the cleaning roller 12 to the developing device 4.

The toner T ₂ collected on the cleaning roller 12 reattaches to the non-image forming area W in the vicinity of the rear end Z of the image forming area X on the photoconductor 1, so that the reattached toner T ₃ causes Not only the electrostatic latent image formed during the image forming operation but also the electrostatic latent image formed next is not affected. The collected toner is redeposited on the surface portion of the photoconductor 1 that does not affect the formation of the next latent image. It is also possible to re-adhere the toner from the cleaning roller 12 to the rear portion of the image forming area X.

As shown in FIG. 9, when the collected toner on the cleaning roller 12 is completely attached to the photosensitive member 1, the cleaning roller 12 is again charged with a toner having a polarity opposite to that of the toner during development. By applying a positive voltage and rotating the cleaning roller 12 in the counter direction with respect to the rotation direction of the photoconductor 1, even a very small amount of toner, which should not have originally adhered, adheres to the photoconductor. If so, it is preferable to control the cleaning roller 12 so as to collect the toner.

When the image forming operation is continued,
When the next image forming area X1 shown in FIG. 9 and FIG. 10 is continuously subjected to the static elimination action by the static elimination lamp 13, and the leading end Y1 of the photoconductor rotating direction moves to the position of the charging roller 2, the charging roller 2 is exposed to light. The next image forming area X1 is negatively charged by contacting the surface of the body 1, and an electrostatic latent image is formed on the next image forming area X1 in exactly the same manner as described above. At, a visible image is formed as a toner image. Then, as shown in FIG. 11, when the leading edge Y1 of the image forming area reaches the transfer portion 8, the leading edge of the next transfer paper 16 reaches the transfer portion 8 and the toner image formed in the next image forming area X1. Are transferred to the transfer paper 16. The transfer residual toner at this time is temporarily collected by the cleaning roller 12 as described above, and the above-described operation is repeated. In this way, the image forming operation is repeated a predetermined number of times.

In the state shown in FIG. 9, neither the electrostatic latent image nor the toner image has been formed in the next image forming area X1. To be exact, the area X1 shown in FIG. It can be said that the area is to be the next image forming area. 1 to 11, the toners T, T ₁ , T ₂ , T ₃ and T ₄ on the photoconductor 1 or the cleaning roller 12 are schematically enlarged.

As described above, the transfer residual toner on the image carrier is electrostatically transferred to the cleaning member by applying the bias voltage of the polarity opposite to the charging polarity of the toner at the time of development to the cleaning member. It is possible,
As a result, the transfer residual toner can be collected by the cleaning member. Further, after the collection, the polarity of the bias voltage applied to the cleaning member is switched, and the bias voltage having the same polarity as the charging polarity of the toner at the time of development is applied to the cleaning member, so that the toner collected on the cleaning member is carried as an image. It can be electrostatically transferred to the body. As a result, the collected toner can be reattached to the image carrier, and the reattached toner can be collected in the developing device.

By the way, in the illustrated image forming apparatus, as a transfer device, the toner image on the photoconductor 1 is transferred to the transfer paper 16 while rotating while contacting the surface of the photoconductor 1 via the transfer paper 16. The contact type transfer roller 7 is used. Here, if the transfer roller 7 is always in contact with the surface of the photoconductor 1 directly or via the transfer paper 16, the following problems occur as described above.

As shown in FIG. 5, when the trailing edge Z of the image forming area on the photosensitive member 1 passes through the portion of the developing device 4 facing the developing roller 5, the photosensitive member on the rear side of which the toner image is not formed is formed. The body surface portion S passes through the portion of the developing roller 5. At that time, in the image forming apparatus of the illustrated format,
Even when the trailing edge Z of the image forming area X after being cleaned by the cleaning roller 12 reaches the portion of the developing roller 5 again as shown in FIG. 10, a toner image is still formed behind the photoconductor rotating direction. The next image forming area X1 that has not been formed exists. Since each image is formed on the photoconductor 1 at such a timing, the toner image is not formed after the trailing edge Z of the image forming area first passes the developing roller 5 as shown in FIG. The photosensitive member surface portion S in a relatively long range passes through the portion of the developing roller 5. Compared to an image forming apparatus that does not return the toner collected by the cleaning member to the photoconductor,
The surface portion S of the photosensitive member on which the toner image is not formed passes over a long area of the developing roller 5. That is, the distance between one transfer sheet and the next transfer sheet (so-called distance between sheets) becomes long.

As described above, when the photosensitive member surface portion S on which the toner image is not formed passes through the portion of the developing roller 5, the toner of the developing device 4 should not adhere to the surface portion S. Therefore, in this example, when the photosensitive member surface portion S on which the toner image is not formed passes the developing roller 5, the polarity (positive polarity) opposite to the charging polarity of the toner accommodated in the developing device 4 is relative to the developing roller 5. A bias voltage is applied to draw the toner toward the developing roller 5 to prevent the toner from adhering to the surface portion S of the photoconductor. This surface portion S acts as a developer on the developing roller 5. By rubbing, the toner in the developer may be attached to the photoconductor due to a mechanical external force. Further, the toner of the developer D housed in the developing casing 9 is triboelectrically charged to a predetermined polarity, in this example, a negative polarity, but since the charging action is insufficient, it has a polarity opposite to the predetermined polarity. There is also a very small amount of positively charged toner. At this time, the positive bias voltage is applied to the developing roller 5 as described above, and the surface portion S of the photoconductor 1 passing through the developing roller 5 is not substantially charged. The toner charged on the developing roller 5 may electrostatically transfer to the surface portion S of the photoconductor and adhere to the portion S. This also occurs when a one-component developer is used in the developing device.

As described above, the toner attached to the surface portion S of the photosensitive member, which should not be attached to the toner, is transferred to the transfer roller 7.
If the transfer roller 7 is still in contact with the surface of the photoconductor 1 when it reaches a portion facing to, the toner adheres to the transfer roller 7. When the surface portion S of the uncharged photoconductor passes through the transfer roller 7, the transfer roller 7
Since no voltage is applied to the transfer roller 7, the positive polarity toner that has adhered to the photoconductor 1 does not electrostatically move to the transfer roller 7 and adhere, and at this time, the positive voltage is applied to the transfer roller 7. The same applies when the toner is kept applied, but the toner of the positive polarity of the photoconductor 1 receives a mechanical force from the transfer roller 7, so that the toner adheres to the surface of the transfer roller 7.

At this time, as described above, since the surface portion S on which the toner image is not formed passes the developing roller 5 over a considerably long range, the developing roller 5 is attached to the surface portion S.
Even if only a small amount of toner migrates from the toner and adheres, the total amount of the adhered toner becomes considerably large. Therefore, a large amount of toner adheres to the transfer roller 7. Therefore, the next transfer paper 16 onto which the toner image formed in the next image forming area X1 shown in FIG. 11 is transferred
When the paper passes the transfer portion 8, the transfer roller 7
The toner adhered to the toner adheres to the transfer paper 16 and the transfer paper 16 is contaminated with the toner.

In order to eliminate such a conventional defect, in the image forming apparatus of this embodiment, the transfer roller 7 is replaced by the photosensitive member 1.
A transfer device contacting / separating means for contacting / separating the surface of the transfer device is provided. It is possible to occupy a contact position where the transfer roller 7 contacts the photoconductor 1 via the transfer paper 16 and a separated position where the transfer roller 7 is separated from the photoconductor 1.

As described above, the transfer operation for transferring the toner image formed on the photosensitive member 1 onto the transfer paper 16, that is, FIG.
In the state of FIG. 6 to FIG. 6, the transfer roller 7 contacts the surface of the photoconductor 1 via the transfer paper 16. Therefore, the toner image on the photoconductor 1 can be transferred onto the transfer paper 16 without any trouble.

On the other hand, as shown in FIG. 6, when the trailing edge Z of the image forming area X reaches the transfer roller 7 and passes through it, at the same time, the transfer roller 7 is shown in FIGS. Thus, it is separated from the photoconductor 1. Then, when the front end Y1 of the photosensitive member rotating direction in the next image forming area X1 shown in FIG. 11 reaches a portion facing the transfer roller 7, the transfer roller 7 passes the next transfer paper 16 and the photosensitive member 1 The toner image on the photoconductor 1 is transferred onto the transfer paper 16 by coming into contact with the surface.

Since the transfer roller 7 is separated from the surface of the photosensitive member 1 in this way, when the photosensitive member surface portion S behind the rear end Z of the image forming area passes the portion of the developing roller 5 of the developing device 4, Even if toner is transferred from the developing roller 5 and adheres to the surface portion S, it does not adhere to the transfer roller 7. Therefore, it is possible to prevent a problem that the next transfer paper 16 is soiled with toner without any trouble.

As described above, the transfer device contact / separation means transfers the toner image on the photoconductor 1 which is an example of the image carrier to the recording medium made of the transfer paper 16 during the transfer operation. The transfer device including the transfer roller 7 is brought into contact with the surface of the image carrier, and the transfer device is separated from the surface of the image carrier at times other than the transfer operation.

FIG. 12 shows an example of such a transfer device contact / separation means. The contact / separation means exemplified here is the transfer roller 7.
It has a case 17 that rotatably supports, a compression spring 18 that pressurizes the case 17, a pressing lever 19, and a solenoid 20 that operates the pressing lever 19. The case 17 has a base end 1
7a is swingably supported by the image forming apparatus main body via a pin 21, and the compression spring 18 is mounted between the case 17 and the image forming apparatus main body. The lever 19 has an intermediate portion pivotally supported by the main body of the image forming apparatus via a pivot pin 22, and a plunger of a solenoid 20 is connected to one end of the lever 19.

During the transfer operation for transferring the toner image on the photosensitive member 1 onto the transfer paper 16, the transfer roller 7 has its case 17
The surface of the photoconductor 1 is abutted via the transfer paper 16 by the urging force of the compression spring 18 that pressurizes.

On the other hand, as shown in FIG. 6, when the leading edge Z of the image forming area passes through the portion of the transfer roller 7, a command from a controller (not shown) is input to the solenoid to operate the solenoid 20, As a result, the pressure lever 19
One end of the lever 19 is pulled in the direction of arrow Q by the solenoid 20, and the other end of the lever 19 presses the case 17 in the direction of arrow R. As a result, the transfer roller 7 is separated from the surface of the photoconductor 1.

Further, as shown in FIG. 11, a command is input from the control device to the solenoid 20 immediately before the next image forming area tip Y1 reaches the portion facing the transfer roller 7, whereby the solenoid 20 operates, The pressing action of the case 17 by the pressing lever 19 is released. In this way, the transfer roller 7 again presses against the surface of the photoconductor 1 via the next transfer paper 16 by the action of the compression spring 18, and executes the transfer operation of the toner image. In this way, the transfer roller 7
It can be brought into contact with or separated from the surface of the photoreceptor 1.

In the illustrated example, the transfer roller 7 is used as the contact type transfer device, but a contact type transfer device composed of a transfer belt wound around a plurality of rollers may be used.

The transfer residual toner T ₁ on the photosensitive member 1 which has passed through the transfer portion 8 shown in FIG. 1 is the toner having a polarity opposite to the charging polarity of the toner at the time of development as described above. (Abnormal polarity toner) is mixed, and in this example, the abnormal polarity toner is used as the cleaning roller 1.
By frictional charging with No. 2, it is arranged to have the same polarity as the charging polarity of the toner at the time of development. However, it is difficult to completely align the charging polarities of the transfer residual toners existing in the nip area N shown in FIG. 2, and in some cases, the toners having the charging polarities opposite to the charging polarities of the toners at the time of development, that is, There are also abnormal polarity toners. At the time of toner recovery, a voltage having a polarity opposite to the charge polarity of the toner at the time of development is applied to the cleaning roller 12 as described above, and the toner having the charge polarity at the time of development is electrostatically transferred to the cleaning roller 12. The roller 12
At this time, the toner having a polarity opposite to the charging polarity at the time of development (abnormal polarity toner) is also collected on the surface of the cleaning roller 12 by the mechanical scraping force received from the cleaning roller 12. It will stick. If such abnormal polarity toner is transferred to the photoconductor 1 during the operation of collecting the toner from the photoconductor 1, background stains on the image and stains on the charging roller 2 are likely to occur.

Therefore, in the image forming apparatus of the present embodiment, as shown in FIG. 2, when the transfer residual toner T ₁ is collected from the photosensitive member 1 to the cleaning roller 12, as described above,
In the contact area between the photoconductor 1 and the cleaning roller 12, that is, in the nip area N where they are in pressure contact with each other, the rotation direction of the cleaning roller 12 is controlled so that they move in opposite directions (counter direction), and The rotation of the cleaning roller 12 is controlled so that the transfer residual toner T ₁ on the photoconductor 1 is collected by the cleaning roller 12 with the rotation of the cleaning roller 12 less than one rotation. With the rotation of the cleaning roller 12 less than one rotation, the operation for collecting the transfer residual toner T ₁ on the photoconductor 1 is completed.

With this configuration, the cleaning roller 12
The toner T ₂ collected in the
It does not contact the photoreceptor 1 again. Moreover, it is possible to prevent the abnormal polarity toner collected on the cleaning roller 12 from being electrostatically transferred to the surface of the photoconductor 1 after cleaning during the toner collecting operation.

If the transfer residual toner T ₁ is collected, the cleaning roller 12 is rotated in a direction in which the cleaning roller 12 and the photoconductor 1 move in the same direction in the nip region N with the photoconductor 1, as shown by a chain line arrow b in FIG. If so, the collected toner T ₄ is present on the cleaning roller 12 on the downstream side in the rotation direction of the photoconductor 1, and if the toner T ₄ is an abnormal polarity toner that remains positively charged, cleaning is performed. Since the same positive voltage as that is applied to the roller 12 when the toner is collected, the toner T ₄ having the positive polarity is electrostatically attracted toward the photoconductor 1 and adheres to the surface of the photoconductor. . In this case, the cleaning failure of the photoconductor 1 occurs, and the toner adheres to the charging roller 2, so that the toner image formed subsequently has a background stain.

In order to eliminate such a problem, as described above, the cleaning roller 12 is rotated so that the cleaning roller 12 rotates in the counter direction with respect to the rotation direction of the photosensitive member 1, that is, in the direction of the solid arrow a in FIG. The direction is set.

At this time, if the cleaning roller 12 is rotated once or more to collect the transfer residual toner from the photosensitive member 1, the toner collected by the cleaning roller 12 has an abnormally positive polarity. When the toner is present, when the toner approaches the photoconductor 1 again or comes in contact with the photoconductor 1, the toner adheres to the photoconductor 1 and cleaning failure of the photoconductor 1 occurs. Therefore, in this example, the toner collecting operation from the photoconductor 1 to the cleaning roller 12 is completed while the cleaning roller 12 is rotationally driven for less than one rotation.

According to the above construction, the cleaning roller 1
It is possible to make it difficult to transfer the toner (abnormal polarity toner) having a polarity opposite to the charge polarity at the time of development, which is collected in No. 2, to the photoconductor 1.

The cleaning roller 12 for reattaching the collected toner on the cleaning roller 12 to the photosensitive member 1
May rotate in any direction. In this example, as described above, in the nip region N with the photoconductor 1, the cleaning roller 12 and the photoconductor 1 have the same direction (the direction of the chain line arrow b in FIG. 2). The rotation direction of the cleaning roller 12 is controlled so that the cleaning roller 12 rotates. Moreover, the rotation speed thereof is set higher than that at the time of toner recovery, and the photosensitive member 1 is rotated at a speed higher than the peripheral speed so that the toner can be reattached to the photosensitive member 1 efficiently in a short time.

The present invention is an image forming apparatus using not only a roller-shaped cleaning member but also an endless belt-shaped cleaning member, or an image formation using an endless belt-shaped member other than a drum-shaped image carrier. It can also be applied to devices. Further, the present invention can be applied to an image forming apparatus in which an intermediate transfer member is used as a recording medium, a toner image is transferred from the image carrier to the intermediate transfer member, and then the toner image is transferred to a transfer material. Further, according to the present invention, after the image bearing member is charged by the charging device, an electrostatic latent image is formed by a portion which is not irradiated with light at the time of image exposure on the surface of the image bearing member, and the latent image potential is charged to the opposite polarity. It can also be applied to a so-called positive / positive developing type image forming apparatus in which the generated toner is adhered to the electrostatic latent image to perform development.

[0064]

According to the image forming apparatus of the present invention, the toner image on the image carrier is transferred to the recording medium by the contact type transfer device, and the transfer residual toner at that time is collected by the cleaning member. Then, in the image forming apparatus in which the collected toner is reattached to the image carrier and the reattached toner is recovered to the developing device, the toner on the image carrier adheres to the contact type transfer device, thereby recording It is possible to effectively suppress the problem that the medium is soiled with the toner.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional explanatory view of an image forming apparatus according to an exemplary embodiment of the present invention, in which the toner on a photoconductor and a cleaning roller is schematically illustrated and enlarged.

FIG. 2 is an enlarged schematic illustration of a toner and a frictional contact portion between the photosensitive member and the cleaning roller, for explaining that the charging polarities of the toner are made uniform.

FIG. 3 is an explanatory diagram illustrating a relative positional relationship between a charging roller, a developing roller, a transfer roller, a cleaning roller, and a photoconductor, and illustrating a state in which residual toner remaining on the photoconductor is collected by the cleaning roller. Is.

FIG. 4 is an explanatory diagram similar to FIG. 3, showing a state in which a rear end of the image forming area reaches a portion facing a charging roller.

FIG. 5 is an explanatory diagram similar to FIG. 3, showing a state in which the rear end of the image forming area reaches a portion facing the developing roller.

FIG. 6 is an explanatory view similar to FIG. 3, showing a state when the rear end of the image forming area reaches a portion facing the transfer roller.

FIG. 7 is an explanatory diagram similar to FIG. 3, showing a state when the rear end of the image forming area reaches a portion facing the cleaning roller.

FIG. 8 is an explanatory diagram similar to FIG. 3, showing a state in which the collected toner on the cleaning roller is reattached to the photoconductor.

FIG. 9 is an explanatory view similar to FIG. 3, showing how redeposited toner on the photoconductor is conveyed toward the developing device.

FIG. 10 is an explanatory view similar to FIG. 3, showing how the redeposited toner on the photoconductor is collected by the developing device.

FIG. 11 is an explanatory view similar to FIG. 3, showing a state when the next image forming area reaches a portion facing the transfer roller.

FIG. 12 is a diagram showing an example of a transfer device contact / separation unit.

[Explanation of symbols]

4 Developing device T ₁ toner T ₂ toner

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masako Yoshii 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (1)

[Claims] 1. An image carrier that is driven to rotate, a latent image forming unit that forms an electrostatic latent image on the carrier, and a developing device that visualizes the electrostatic latent image as a toner image. A transfer device that transfers the toner image on the image carrier to the recording medium, and the transfer residual toner on the image carrier after the toner image transfer is temporarily collected, and then the collected toner is collected on the image carrier. A cleaning member for reattaching to a surface portion that does not affect the formation of the next electrostatic latent image, and the toner reattached to the surface of the image carrier is collected in a developing device, and the transfer device is used to record the recording medium. In an image forming apparatus including a contact-type transfer device that contacts a surface of an image carrier via a sheet to transfer the toner image on the image carrier to the recording medium, the toner image on the image carrier is transferred to the recording medium. During the transfer operation, the transfer device is imaged via the recording medium. It is brought into contact with the surface of the lifting body, the image forming apparatus at a time other than the time of the transfer operation, characterized in that it comprises a transfer device moving means to separate the transfer unit from the surface of the image bearing member.