JP2006259198A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which has improved performance of collecting residual toner by a developing device without staining a charging device. <P>SOLUTION: The image forming apparatus has a photoreceptor drum 2 which carries an electrostatic latent image. Further, the charging device 3, a control member 7 for electric charges after charging, a developing unit 4, a transfer device 5, and a control member 6 for electric charges before charging are arranged around the photoreceptor drum 2 one after another in the rotating direction thereof. The control member 6 for electric charges before charging makes the polarity of residual toner uniform and collects part of the residual toner, and to the control member 6, a bias having the same polarity with developing toner is applied. The control member 7 for electric charges after charging reduces the charging quantity of the residual toner and to the control member 7, a bias which is small enough not to disorder the surface potential of the photoreceptor drum 2 is applied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms an image by electrophotography. More specifically, the present invention relates to an image forming apparatus in which a developer remaining on an image carrier after transfer (hereinafter referred to as “residual toner”) is collected by a developing device and reused as a developer.

  Conventionally, in an electrophotographic image forming apparatus, for the purpose of reducing waste toner and downsizing of the apparatus, a method in which development and cleaning are performed together in a developing device (hereinafter referred to as “development simultaneous cleaning method”). ) Have been put into practical use (for example, Patent Document 1). In this simultaneous development type image forming apparatus, residual toner on the image carrier is collected by the developing device.

  In the image forming apparatus of this simultaneous development cleaning system, it is important to adjust the charge amount of the residual toner. That is, the residual toner includes many toners having a transfer history and reverse polarity toner such as fog toner. Then, when the residual toner having the opposite polarity or the residual toner having a low charge amount is sent to the charging unit as it is, the charging device collects the residual toner. As a result, the charging device is contaminated. In particular, in the case of a contact charging device such as a roller type, the charging device is easily contaminated.

In view of this, in the image forming apparatus of the simultaneous development cleaning system, a charge control member is provided in order to adjust the adhesion amount and the charge amount of the residual toner. This charge control member is located between the transfer unit and the charging unit during the image forming process, and applies a predetermined bias to uniformize the charge (polarity) of the residual toner that has not been transferred at the transfer unit. Yes. That is, the reverse polarity toner contained in the residual toner is shifted to the normal polarity to avoid collection by the charging device.
Japanese Patent No. 3113803

  However, the conventional image forming apparatus described above has the following problems. In other words, the application of charge to the residual toner is performed not only by the charge control member but also by a charging device. That is, as the image carrier is charged, the residual toner is also charged. Therefore, the charge amount of the residual toner after passing through the charging device is increased to the normal polarity side. The charge amount depends on the bias applied to the charging member. Therefore, the charge amount of the residual toner is considerably high at the outlet of the charging unit. Therefore, the mirror image force between the residual toner and the image carrier is increased, and there is a possibility that it cannot be collected by the developing device. When the unrecovered residual toner is retransferred, the image is defective.

  In order to suppress the charge amount of the residual toner after passing through the charging device, it is conceivable to lower the bias applied to the charging device. However, when the bias applied to the charging device is lowered, the surface potential of the image carrier does not become a desired value. For this reason, there are restrictions on reducing the bias applied to the charging device. It is also conceivable to lower the bias applied to the charge control member. However, if the bias applied to the charge control member is lowered, the charging device is contaminated with toner. Therefore, it is necessary to increase the charge amount of the residual toner as much as possible before entering the charging device.

  In other words, the charging device is contaminated if the charge amount of the residual toner before passing through the charging device is too low. For this reason, the bias applied to the charge control member needs to be set higher than a certain level. However, if the charge amount of the residual toner is too high, it becomes difficult to collect it by the developing device after passing through the charging device. That is, the problem of contamination of the charging device and the problem of recoverability of the developing device are in a trade-off relationship and cannot be compatible.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide an image forming apparatus that improves the recoverability of residual toner by the developing device without contaminating the charging device.

  An image forming apparatus designed to solve this problem includes an image carrier that carries a toner image, a charging member that charges the surface of the image carrier to a predetermined level, and a function and an image that apply toner to the image carrier. An image forming apparatus having a developing member having a function of collecting toner on the carrier, and located downstream of the charging member and upstream of the developing member, and a charge amount of toner on the image carrier It has the charge control member which controls this.

  The image forming apparatus of the present invention is an image forming apparatus of a simultaneous development cleaning system in which a developing member can simultaneously apply toner on an image carrier and collect toner on the image carrier. A charge control member for controlling the charge amount of the toner on the image carrier is disposed between the charging member and the developing member. By this charge control member, the charge amount of the residual toner that is increased by the charging member is reduced. Accordingly, the mirror image force between the residual toner and the image carrier is weakened, and recovery by the developing member is facilitated.

In addition, the bias value applied to the charge control member satisfies the following condition (1) and condition (2).
| V _MAX −Vo | <| V _th | (1)
| V _MIN −Vo | <| V _th | (2)
In conditions (1) and (2), V _MAX is the maximum value of the bias applied to the charge control member, V _MIN is the minimum value of the bias applied to the charge control member, and Vo is the image carrier after passing through the charging member. The surface potential of the body, V _th means the discharge start voltage of the charge control member. By satisfying these conditions, discharge of the charge control member can be suppressed. Therefore, the charge amount of the residual toner can be controlled without disturbing the surface potential of the image carrier after passing through the charging member.

  Further, it is better that the charge control member is positioned upstream of the exposure position. By arranging in this way, disturbance of the electrostatic latent image due to the charge control of the charge control member can be suppressed, and a higher quality image can be obtained.

  The image forming apparatus of the present invention further includes a second charge control member that is located upstream of the charging member and downstream of the transfer position, and that imparts a charge to the surface of the image carrier, and the second charge control. It is better that a bias having the same polarity as that of the charging member is applied to the member. That is, before charging by the charging member, the residual toner having the opposite polarity present on the image carrier is shifted to the normal polarity by the second charge control member. In addition, the application of charge by the second charge control member serves as preliminary charging, and the amount of charge of the residual toner before entering the charging member can be increased. Therefore, the collection of residual toner by the charging member can be suppressed, and contamination of the charging member can be avoided.

  According to the present invention, the charge amount of the residual toner is controlled by the charge control member after passing through the charging device. That is, the charge amount of the residual toner is reduced. Therefore, the toner can be easily collected by the developing device. Further, the charge amount of the residual toner is increased by the second charge control member before passing through the charging device. Therefore, toner collection by the charging device can be avoided. Therefore, an image forming apparatus is realized in which the recoverability of residual toner by the developing device is improved without contaminating the charging device.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a tandem type color printer.

  The image forming apparatus of this embodiment is a tandem full-color printer, and has four image forming units arranged in parallel as shown in FIG. Specifically, the color printer 100 according to this embodiment includes four color image forming units 1K, 1C, 1M, and 1Y. In addition, an intermediate transfer belt 8, a secondary transfer roller 9, a cleaning blade 10 and the like are provided. Each image forming unit forms an image of each color on the intermediate transfer belt 8. Each image forming unit corresponds to each color of black (K) for the image forming unit 1K, cyan (C) for the image forming unit 1C, magenta (M) for the image forming unit 1M, and yellow (Y) for the image forming unit 1Y. ing. The arrangement of the image forming units is not limited to the above order.

  Further, the image forming unit 1K has a photosensitive drum 2 carrying an electrostatic latent image as shown in FIG. The photosensitive drum 2 rotates at a constant speed in the direction of the arrow in FIG. Further, around the photosensitive drum 2, a charging device 3, a post-charging charge control member 7, a developing device 4, a transfer device 5, and a pre-charging charge control member 6 are sequentially arranged along the rotation direction. An exposure unit for forming a latent image is provided between the post-charging charge control member 7 and the developing device 4. The other image forming units have the same configuration.

  The charging device 3 uniformly charges the surface of the photosensitive drum 2. As the charging device 3, in addition to a non-contact type corona charging device that is charged by corona discharge, a contact type charging device that charges a conductive contact charging member in contact with the surface of the photosensitive drum 2 can be applied. . There are various types of contact-type charging devices such as a roller type, a blade type, a brush type, and a sheet type.

  In this embodiment, a DC voltage of −1100 V is applied to the charging device 3. At this time, the surface potential of the photosensitive drum 2 immediately after passing through the charging device 3 is set to −500V. In this embodiment, a DC voltage is supplied to the charging device 3, but the present invention is not limited to this. That is, the applied bias may be any as long as the surface potential of the photosensitive drum 2 can be set to a predetermined value. For example, an oscillating voltage obtained by superimposing an AC voltage on a DC voltage may be used. Further, a pulse voltage, a rectangular wave voltage, or other waveform voltage may be used. Further, the surface potential of the photosensitive drum 2 is not limited to the minus side, and may be the plus side.

  The developing device 4 has a function of collecting toner in addition to a function of applying toner onto the latent image. That is, the residual toner on the photosensitive drum is collected for the white background portion of the electrostatic latent image, and the toner in the toner tank is applied to the other portions. The developing device 4 may be a contact type or a non-contact type. Further, the developing method may be a two-component developing method including toner and a carrier, or a one-component developing method not including a carrier. In this embodiment, a negatively charged toner is used. However, a positively charged toner may be used as long as the toner image can be developed.

  The charge control members (pre-charge charge control member 6, post-charge charge control member 7) are for adjusting the charge amount of the residual toner and the adhesion amount. As the charge control member, the same member as the charging device can be applied. For example, as shown in FIG. 3, the roller-shaped member 7 may be fixedly arranged. Further, as shown in FIG. 4, the roller-shaped member 7 may be rotated. In that case, it is better if the rotation direction and rotation speed can be adjusted. Moreover, as shown in FIG. 5, the sheet-like member 7 may be sufficient. As a material of the sheet member, a member that does not easily adhere to the surface of the toner is preferable from the viewpoint of preventing contamination with toner. For example, a conductive fluororesin sheet can be applied. Further, since the charge is applied by frictional charging, it is desirable that the charging direction of the toner is the same as the charging direction. Further, as shown in FIG. 6, a pressing member 71 may be provided. That is, the sheet-like member 7 may be pressed against the surface of the photosensitive drum 2 by applying pressure from the back side of the sheet-like member 7 via the pressing member 71.

  As other charge control members, there are various members such as a blade-type member 7 as shown in FIG. 7 and a brush-type member 7 as shown in FIG. In the case of the brush type, of course, the brush roll may be rotated or fixed.

  Specifically, the pre-charging charge control member 6 is for uniformizing the polarity of the residual toner and collecting a part of the residual toner. A bias having the same polarity as the developing toner (in this embodiment, a negative AC bias) is applied to the pre-charging charge control member 6. The applied bias may be a DC voltage in addition to the AC voltage. Also, a rectangular wave voltage obtained by switching a DC voltage, a pulse voltage, or other waveform voltage may be used. Moreover, it may be simply grounded. Further, the charge control member 6 before charging imparts a charge not only to the residual toner but also to the surface of the photosensitive drum 2, and thus has a function as a preliminary charge before the main charge by the charging device 4.

The post-charging charge control member 7 is for reducing the charge amount of the residual toner. A bias (DC-500 V in this embodiment) is applied to the post-charging charge control member 7 so as not to disturb the surface potential of the photosensitive drum 2. In other words, the post-charging charge control member 7 needs to prevent discharge from the photosensitive drum 2. Therefore, the applied bias is set to a value that satisfies the following conditions (A) and (B).
| V _MAX −Vo | <| V _th | (A)
| V _MIN −Vo | <| V _th | (B)
In the above conditions, V _MAX is the maximum value of the bias applied to the charge control member 7 after charging, V _MIN is the minimum value of the bias applied to the charge control member 7 after charging, and Vo is the photoreceptor after passing through the charging device 3. The surface potential of the drum 2 and _Vth mean the discharge start voltage of the post-charging charge control member 7, respectively. The applied bias may be an oscillating voltage obtained by superimposing an AC voltage on a DC voltage in addition to the DC voltage. Also, a rectangular wave voltage obtained by switching a DC voltage, a pulse voltage, or other waveform voltage may be used. Moreover, it may be simply grounded.

  In order to prevent contamination due to toner collection, it is preferable to apply a bias having the same polarity as the toner.

  Next, an operation when an image is formed by the color printer 100 of this embodiment will be described. First, the surface of the photosensitive drum 2 is charged to a predetermined potential by the negative bias of the charging device 3. Next, a latent image of the first page is formed at the exposure unit. Any exposure means may be used as long as it can form an electrostatic latent image. For example, laser exposure is applicable.

  Although the post-charge charge control member 7 passes before the exposure portion, the bias applied to the post-charge charge control member 7 does not disturb the surface potential of the photosensitive drum 2 and thus does not affect the exposure. . Further, since the post-charging charge control unit 7 is positioned before the exposure unit, there is no influence on the electrostatic latent image.

  Next, development with a negative toner is performed by the developing device 4, and a first-page toner image is formed on the photosensitive drum 2. Next, the toner image of the first page is transferred onto the intermediate transfer belt 8 by the transfer device 5. That is, the toner on the photosensitive drum 2 is transferred to the intermediate transfer belt 8 by the positive polarity bias of the transfer device 5. At this time, a part of the toner remains on the photosensitive drum 2 without being transferred and becomes residual toner. Further, a part of the residual toner is shifted to positive polarity.

  Next, the charge polarity of the positive residual toner is shifted to the negative polarity by the pre-charging charge control member 6. Further, the surface of the photosensitive drum 2 is also charged to a negative polarity. Thereby, the charge amount of the residual toner is increased, and the adhesion of the residual toner to the charging device 3 is suppressed. Thereafter, the surface of the photosensitive drum 2 is charged again by the charging device 3. At this time, the residual toner is also charged at the same time, and the charge amount of the residual toner is further increased.

  Next, the charge amount of the residual toner is reduced by the post-charging charge control member 7. As a result, the mirror image force between the residual toner and the photosensitive drum 2 is weakened, and recovery by the developing device 4 is facilitated. Note that the bias applied to the charge control member 7 after charging is such that the surface potential of the photosensitive drum 2 is not disturbed, so there is no influence on exposure. Next, an electrostatic latent image of the second page is formed at the exposure unit. Next, development and recovery of residual toner are performed simultaneously in the developing device 4. That is, of the residual toner, the toner existing on the white background is collected by the developing device 4, and the toner existing on the other part is transferred as a toner image again.

  Such an operation is repeated for each image forming unit, and the toner images of the respective colors are superimposed on the intermediate transfer belt 8. A color image is formed on the intermediate transfer belt 8 by superimposing the four color toner images. This color image is transferred onto the recording paper by the secondary transfer roller 9. Then, the recording paper is output to the discharge tray via the fixing device.

  Next, measurement results of the charge amount of the residual toner after charging the photosensitive drum by the charging device and before and after passing through the charge control member will be described. In this experiment, a roller type (see FIG. 3) charge control member and a sheet type (see FIG. 6) charge control member are used as subjects.

FIG. 9 shows a measurement result when the bias _{B C} applied to the charge control member is set to the same potential as the surface potential V ₀ of the photosensitive drum. This experiment shows that the absolute value of the charge amount after passing through the charge control member has decreased regardless of the charge amount before passing through the charge control member. In addition, it can be seen that the roller type and the sheet type decreased.

FIG. 10 shows the charge after passing through the charge control member when the charge amount before passing through the charge control member is fixed (charge amount: −50 μC / g) and a predetermined DC bias is applied to the charge control member. The measurement result of the amount of decrease is shown. As a result of this experiment, if the difference between the applied bias V _C and the surface potential V ₀ of the photosensitive drum is smaller than the discharge start voltage V _th (± 500 V in this embodiment), the charge control member is used regardless of the magnitude of the difference. It can be seen that the amount of charge after passing through decreased. In addition, it can be seen that the roller type and the sheet type decreased.

  That is, it can be seen from this experiment that the charge amount of the residual toner can be reduced by the post-charging charge control member 7. Although the surface potential on the photosensitive drum was measured within the range of this experiment, the surface potential of the photosensitive drum was not disturbed before and after passing through the charge control member.

  As described in detail above, the color printer 100 of the present embodiment is an image forming apparatus of the simultaneous development cleaning system, and the post-charging charge control member 7 is provided between the charging device 3 and the developing device 4. Thereby, the charge amount of the residual toner after passing through the charging device 3 can be reduced. Accordingly, the mirror image force between the residual toner and the photosensitive drum 2 is weakened, and the recovery by the developing device 4 is facilitated.

  In addition, a pre-charging charge control member 6 is provided between the transfer device 5 and the charging device 3. Thereby, the charge amount of the residual toner before passing through the charging device 3 can be increased. Therefore, the collection of residual toner by the charging device 3 can be reduced, and contamination of the charging device 3 is suppressed. Therefore, an image forming apparatus is realized in which the recovery performance of the residual toner by the developing device is improved without contaminating the charging device.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the color printer according to the embodiment employs a so-called simultaneous development cleaning system in which toner can be applied and collected by a developing device, but is not limited thereto. That is, the type having a cleaner is also applicable.

  The image forming apparatus is applicable to any printer, copier, scanner, FAX, or the like that forms an image by electrophotography. Further, it may be one that forms a color image or one that is dedicated to a monochrome image. Further, a tandem method or a four-cycle method may be used.

1 is a schematic diagram illustrating a configuration of a color printer according to an embodiment. 1 is a schematic diagram illustrating a configuration of an image forming unit according to an embodiment. It is a figure (the 1: roller shape) which shows the example of composition of a charge amount control member. It is a figure (the 2: roller shape) which shows the example of composition of a charge amount control member. It is a figure (the 3: sheet shape) which shows the example of composition of a charge amount control member. It is a figure (the 4: sheet shape) which shows the structural example of a charge amount control member. It is a figure (the 5: brush shape) which shows the structural example of a charge amount control member. It is a figure (the 6: blade shape) which shows the example of composition of a charge control member. It is a graph which shows the charge amount after passing through the charge control member after charging. It is a graph which shows the change of the charge amount after passing the charge control member after charge.

Explanation of symbols

1K Image forming unit 2 Photosensitive drum (image carrier)
3 Charging device (charging member)
4 Development device (developing member)
5 Transfer device 6 Charge control member before charging (second charge control member)
7 Charge control member after charging (charge control member)
8 Intermediate transfer belt 100 Color printer (image forming device)

Claims (4)

An image carrier that carries a toner image, a charging member that charges the surface of the image carrier to a predetermined level, a function that applies toner to the image carrier, and a function that collects toner on the image carrier An image forming apparatus having a developing member
An image forming apparatus comprising: a charge control member that is located downstream of the charging member and upstream of the developing member and that controls a charge amount of toner on the image carrier. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the bias value applied to the charge control member satisfies the following condition (1) and condition (2):
| V _MAX −Vo | <| V _th | (1)
| V _MIN −Vo | <| V _th | (2)
V _MAX : Maximum value of bias applied to the charge control member V _MIN : Minimum value of bias applied to the charge control member Vo: Surface potential of the image carrier after passing through the charging member V _th : Charge control member Discharge start voltage The image forming apparatus according to claim 1, wherein:
The image forming apparatus, wherein the charge control member is located upstream of an exposure position. The image forming apparatus according to any one of claims 1 to 3,
A second charge control member that is located upstream of the charging member and downstream of the transfer position and imparts a charge to the surface of the image carrier;
An image forming apparatus, wherein a bias having the same polarity as that of the charging member is applied to the second charge control member.

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