JP2012058594A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve local sensitivity reduction on an image holding body caused by an external additive of toner attached to the image holding body, and to prevent image defect due to a change in charging characteristics accompanying the local sensitivity reduction on the image holding body.SOLUTION: An image formation apparatus includes, as a sensitivity recovery device 7 for restoring partial sensitivity reduction of an image holding body 1 caused by attachment of an external additive of toner: an image holding body drive unit 8 for driving the image holding body 1 to idle-rotate for a plurality of times; a recovery electric field action unit 9 which is disposed upstream of a region where the image holding body 1 faces a plate-like cleaning member 5a of a cleaning device 5 in a rotation direction of the image holding body 1 and with which a recovery electric field generated by a recovery voltage having the same polarity as a DC voltage of a transfer device 4 and a recovery electric field generated by a reverse polarity recovery voltage having a polarity opposite to the recovery voltage act on different regions of the image holding body 1; and a static eliminator 10 which is disposed downstream of the region where the image holding body 1 faces the plate-like cleaning member 5a of the cleaning device 5 in the rotation direction of the image holding body 1 and eliminates a charge potential caused by the recovery electric field acting on the image holding body 1.

Description

  The present invention relates to an image forming apparatus.

Conventionally, as this type of image forming apparatus, for example, those described in Patent Documents 1 to 7 are already known.
In Patent Document 1, in order to suppress the wasteful developer adhesion to the photosensitive member as much as possible, after starting the operation of the charging device at the start of rotation of the photosensitive member, the operation of the developing device is started from the time when the operation of the charging device is started. After the time required to move to the developing position has elapsed, the rotation of the sleeve of the developing device is started, and the toner position is changed during the period in which the portion located at the developing position when the photosensitive member stops rotating passes the transfer position. In this technique, a voltage having the same polarity as the charging polarity is applied to the transfer roller.
In Patent Document 2, a voltage control means applies a transfer voltage over at least one turn of a latent image carrier before starting transfer to a recording material, and the latent image carrier is charged in advance before starting transfer to the recording material. This is a technique for suppressing density unevenness for each round of the latent image carrier without abruptly lowering the charged potential even when recharging after the transfer to the recording material is started.
Patent Document 3 has means for applying a bias having the opposite polarity to the transfer voltage of the transfer means and a bias having the same polarity so as to move the toner adhering to the transfer means to the image carrier. Is applied to the transfer unit at the start of the image forming operation and the other is applied to the transfer unit at the end of the image forming operation.
In Patent Document 4, in order to prevent generation of white streaks in halftone image printing, a humidity sensor is provided in the color printer apparatus, the humidity in the apparatus is measured, and the transfer in each transfer unit is determined by the humidity. This is a technique for setting the voltage application timing.
Patent Document 5 discloses that a constant current bias from the constant current power supply unit of the transfer high-voltage power supply to the transfer roller and a constant voltage bias having a polarity opposite to the constant current bias from the negative constant voltage power supply unit to the transfer roller before the image forming operation is started. Are alternately applied, and a voltage detection circuit detects a voltage generated when a constant current bias is applied. The control device is a technique for determining a voltage value to be applied to the transfer roller from the positive constant voltage power supply unit of the transfer high-voltage power supply during image formation based on the detection result.
In Patent Document 6, in order to cause a desired current to flow from the voltage application unit to the contact transfer member during transfer, a predetermined voltage is applied from the voltage application unit to the contact transfer member before starting the transfer operation, and the output current is controlled by the control unit. If the detected voltage value is detected to be larger than the desired voltage value by changing the applied voltage so that the desired output current is obtained, the leading edge of the transfer material in the conveyance direction is moved to the transfer nip portion. The first voltage is applied from the voltage applying means to the contact transfer member until the inner side of the transfer material in the conveyance direction rear end passes through the transfer nip portion, and the transfer material is moved a predetermined distance from the rear end of the transfer material in the conveyance direction. When the rear end side passes through the transfer nip portion after passing through the transfer nip portion, voltage application is performed so that a second voltage larger than the first voltage is applied from the voltage application means to the contact transfer member. Control means Is that technology.
Japanese Patent Application Laid-Open No. 2004-228561 performs transfer of a toner image with an optimal transfer bias, and in order to prevent a decrease in productivity in image formation, a transfer bias and transfer for optimally transferring a toner image during a multi-rotation process. In this technique, a relationship with current is obtained and the relationship is corrected during the image forming process.

Japanese Patent Laid-Open No. 06-083176 (Example, FIG. 1) Japanese Unexamined Patent Publication No. 2000-162889 (Embodiment of the Invention, FIG. 9) JP 2000-250327 A (Embodiment of the Invention, FIG. 1) JP 2002-196596 A (Embodiment of the Invention, FIG. 1) JP 2002-214938 A (Embodiment of the Invention, FIG. 1) JP 2002-296931 A (Embodiment of the Invention, FIG. 1) Japanese Patent Laying-Open No. 2004-252011 (Embodiment of the Invention, FIG. 5)

  The technical problem to be solved by the present invention is to improve the local sensitivity decrease on the image carrier due to the external additive of the toner adhering to the image carrier, and to reduce the local sensitivity on the image carrier. It is an object of the present invention to provide an image forming apparatus that prevents an image defect based on a change in charging characteristics accompanying the above.

  According to the first aspect of the present invention, there is provided an image carrier that holds and rotates a toner image, a latent image forming device that forms an electrostatic latent image on the image carrier, and a static image formed on the image carrier. A transfer electric field including a DC voltage having a predetermined polarity is applied between the image carrier and a developing device that visualizes the electrostatic latent image with toner, and the transfer electric field is applied to the image carrier. A transfer device that electrostatically transfers the formed toner image to a transfer medium; and a plate-like cleaning member that contacts the image carrier, and remains on the image carrier after the transfer by the transfer device. A cleaning device that cleans residual toner, a stop time determination device that determines whether or not a stop time after the image holding member has stopped exceeds a predetermined time, and the stop time determination device What is the image forming process under the condition that the stop time has exceeded a predetermined time? And a sensitivity recovery device that recovers a reduction in the sensitivity of a part of the image carrier caused by adhesion of external toner to the toner, and the sensitivity recovery device idles the image carrier multiple times. Provided on the upstream side in the rotation direction of the image carrier relative to the portion of the image carrier that is driven, and the opposed part of the image carrier and the plate-like cleaning member of the cleaning device, and by a recovery voltage having the same polarity as the DC voltage of the transfer device A recovery electric field action device in which a recovery electric field and a recovery electric field by a reverse polarity recovery voltage opposite in polarity to the recovery voltage act on different parts of the image carrier, and a plate-like cleaning member of the image carrier and the cleaning device; An image forming apparatus comprising: a neutralization device that is provided on the downstream side in the rotation direction of the image carrier from the opposite portion of the image carrier and removes a charging potential due to a recovery electric field that has acted on the image carrier.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a portion of the image holding member where the sensitivity is reduced due to the adhesion of the external additive of the toner is developed along the rotation direction of the image holding member. An image forming apparatus, wherein the image forming apparatus is an area extending from the apparatus to a cleaning apparatus and before and after the transfer area by the transfer apparatus.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the neutralization device of the sensitivity recovery device has a neutralization light source capable of irradiating the neutralizing light. It is.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the recovery field effect device of the sensitivity recovery device generates a recovery electric field by a recovery voltage having the same polarity as the DC voltage of the transfer electric field. It has a 1st recovery electric field generation device and the 2nd recovery electric field generation device which generates a recovery electric field by reverse polarity recovery voltage opposite in polarity to the recovery voltage of this 1st recovery electric field generation device An image forming apparatus.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect of the present invention, the image holding device is provided between the transfer device and the cleaning device along the rotation direction of the image holding member in the periphery of the image holding member. And a recovery electric field effect device of the sensitivity recovery device using the transfer device as the first recovery electric field generating device and recovering the same polarity as the DC voltage of the transfer electric field. A recovery electric field by voltage is applied, and a polarity adjusting device is used as the second recovery electric field generating device, and a recovery electric field by reverse polarity recovery voltage having a polarity opposite to that of the transfer device is applied. The image forming apparatus is characterized.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the latent image forming apparatus includes a charging device that charges the image holding member, and an electrostatic latent image written to the charged image holding member. The recovery electric field effect device of the sensitivity recovery device uses a transfer device as a first recovery electric field generating device to apply a recovery electric field by a recovery voltage having the same polarity as the DC voltage of the transfer electric field. In addition, the image forming apparatus is characterized in that the charging device is used as the second recovery electric field generating device to apply a recovery electric field by a reverse polarity recovery voltage having a reverse polarity to the recovery voltage by the transfer device. is there.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the fourth to sixth aspects, the transfer device includes a transfer electric field including a direct current voltage used in an image forming process, and the direct current voltage of the transfer electric field. The recovery electric field action device of the sensitivity recovery device is switched between a recovery electric field including a recovery voltage that is polar and has an absolute value larger than the direct current voltage. And a recovery electric field by a recovery voltage having the same polarity as the DC voltage of the transfer electric field used in the image forming process and having an absolute value larger than the DC voltage.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the fourth to sixth aspects, the transfer device includes a transfer electric field including a direct current voltage used in an image forming process, and the direct current voltage of the transfer electric field. The recovery electric field effect device of the sensitivity recovery device switches between a recovery electric field including one or a plurality of recovery voltages which are polar and have an absolute value larger than the direct current voltage. A transfer device is used as the device, and a recovery electric field by one or a plurality of recovery voltages having the same polarity as the DC voltage of the transfer electric field used in the image forming process and having an absolute value larger than the DC voltage is applied to the action time setting device. Thus, the image forming apparatus is characterized in that the larger the magnitude of the recovery electric field is, the shorter the action time of the recovery electric field is set.

According to the first aspect of the present invention, the local sensitivity decrease on the image carrier due to the external additive of the toner adhering to the image carrier is improved, and the local sensitivity decrease on the image carrier is accompanied. It is possible to prevent image defects based on a change in charging characteristics.
According to the second aspect of the present invention, it is possible to improve the local sensitivity decrease before and after the transfer area by the transfer device on the image carrier due to the external additive of the toner adhering to the image carrier. It is possible to prevent an image defect based on a change in charging characteristics accompanying a local sensitivity decrease.
According to the third aspect of the present invention, the sensitivity of a part of the image carrier due to the adhesion of the external additive to the toner is prevented while suppressing the deterioration of the image carrier as compared with the aspect without this configuration. can do.
According to the invention which concerns on Claim 4, the recovery electric field effect | action apparatus of a sensitivity recovery apparatus can produce | generate the recovery electric field from which polarity differs reliably.
According to the fifth aspect of the present invention, it is possible to easily generate recovery electric fields having different polarities when recovering the sensitivity of the image carrier using an existing transfer device and polarity adjusting device.
According to the sixth aspect of the present invention, it is possible to easily generate recovery electric fields having different polarities when recovering the sensitivity of the image carrier using an existing transfer device and charging device.
According to the seventh aspect of the present invention, compared to the aspect without this configuration, a stronger recovery electric field can be applied to the image carrier, and the sensitivity recovery processing of the image carrier is shortened accordingly. Can be implemented.
According to the eighth aspect of the present invention, compared to the aspect without this configuration, a strong recovery electric field can be applied to the image carrier in a short time, and the image carrier is degraded accordingly. It is possible to reduce the sensitivity and to perform the image carrier sensitivity recovery process in a short time.

1 is an explanatory diagram showing an outline of an embodiment of an image forming apparatus to which the present invention is applied. (A) is explanatory drawing which shows the example of a sensitivity recovery process by the typical aspect of embodiment of the image forming apparatus of FIG. 1, (b) is the sensitivity by another typical aspect of embodiment of the image forming apparatus of FIG. It is explanatory drawing which shows the example of a recovery process. 1 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to a first embodiment. 3 is an explanatory diagram illustrating a configuration example of an image forming unit for each color component used in Embodiment 1. FIG. 2 is an explanatory diagram schematically showing a control system of the image forming apparatus according to Embodiment 1. FIG. 3 is a flowchart showing a photoreceptor sensitivity recovery process used in the first embodiment. It is a flowchart which shows the process of the "white belt recovery sequence implementation" shown in FIG. (A) is explanatory drawing which shows typically the photoreceptor sensitivity recovery process by the image forming apparatus used in Embodiment 1, (b) is explanatory drawing which shows the effect | action accompanying a photoreceptor sensitivity recovery process. 6 is an explanatory diagram schematically showing an image forming apparatus and a control system thereof according to Embodiment 2. FIG. 10 is a flowchart showing a process of “execution of white band recovery sequence” during the photoreceptor sensitivity recovery process used in the second embodiment. FIG. 10 is an explanatory diagram schematically showing photoreceptor sensitivity recovery processing by the image forming apparatus according to Embodiment 3. 11 is a flowchart showing a process of “execution of white band recovery sequence” during the photoreceptor sensitivity recovery process used in the third embodiment. It is a graph which shows the relationship between the white belt recovery sequence execution time in Examples 1-3, and a white belt grade. FIG. 10 is an explanatory diagram illustrating a result of photoreceptor sensitivity recovery processing by the image forming apparatus according to the first and fourth embodiments. (A) is explanatory drawing which shows the surface potential change located in the back | inner side of a photoreceptor when changing the conditions which implement a white belt recovery sequence about the image forming apparatus which concerns on Example 4, (b) is (a). FIG. 10 is an explanatory diagram showing a change in surface potential located at the center of the photoconductor when the condition for executing the white band recovery sequence is changed in the image forming apparatus according to Example 4 as in FIG.

Outline of Embodiment First, an outline of an embodiment of an image forming apparatus to which the present invention is applied will be described with reference to FIG.
In FIG. 1, an image forming apparatus includes an image holding body 1 that rotates while holding a toner image, a latent image forming apparatus 2 that forms an electrostatic latent image on the image holding body 1, and the image holding body 1. A transfer electric field including a DC voltage having a predetermined polarity is applied between the image carrier 1 and the developing device 3 for visualizing the electrostatic latent image formed on the toner with the toner. The transfer device 4 for electrostatically transferring the toner image formed on the image carrier 1 to the transfer medium 12 and the plate-like cleaning member 5a in contact with the image carrier 1 are provided. A cleaning device 5 that cleans residual toner remaining on the image carrier 1 after transfer by the transfer device 4, and whether or not a stop time after the image carrier 1 has stopped exceeds a predetermined time. And the stop time discriminating device 6 for stopping the image carrier 1 in advance. A sensitivity recovery device 7 is provided that recovers a reduction in sensitivity of a part of the image carrier 1 caused by adhesion of the external additive of the toner as a process different from the image forming process under the condition that a predetermined time has elapsed. Yes.
In the present embodiment, the sensitivity recovery device 7 includes an image carrier driving device 8 that drives the image carrier 1 to rotate idly a plurality of times, and a plate-like cleaning member 5 a of the image carrier 1 and the cleaning device 5. And a recovery electric field by a recovery voltage having the same polarity as the DC voltage of the transfer device 4 and a recovery by a reverse polarity recovery voltage having a polarity opposite to the recovery voltage. A recovery electric field effect device 9 in which an electric field acts at different parts of the image carrier 1 and a rotation direction downstream of the image carrier 1 with respect to a facing portion between the image carrier 1 and the plate-like cleaning member 5 a of the cleaning device 5. And a static eliminator 10 that removes a charging potential caused by a recovery electric field that acts on the image carrier 1.

In such technical means, the image carrier 1 has a sensitivity due to the adhesion of the external additive Tg of the toner when a predetermined stop time has elapsed after the image carrier 1 is stopped. Any photosensitive material or dielectric material can be used as long as it has a function of lowering.
The latent image forming device 2 includes a wide range of devices that form an electrostatic latent image on the image carrier 1, but typically, a charging device 2a that charges the image carrier 1 and a charged image carrier. And a latent image writing device 2b for writing an electrostatic latent image by light or ions on the body 1.
Further, as the transfer device 4, in order to electrostatically transfer the toner image on the image carrier 1 to the transfer medium 12, a transfer member (discharge wire, which applies a transfer electric field including a DC voltage having a predetermined polarity) is used. Any material having a transfer roll) may be used.
Here, the transfer medium 12 is not limited to the recording material that is the final recording medium, but also includes an intermediate transfer member that is temporarily held before being transferred to the recording material.
Furthermore, the cleaning device 5 only needs to have at least a plate-like cleaning member 5a for scraping residual toner, and may include other cleaning members (for example, a brush or a roll-like rotary cleaning member 5b). .
Further, the stop time discriminating device 6 discriminates whether or not the image carrier 1 has stopped for a predetermined time or more. As the “predetermined time”, the toner external additive Tg is used. What is necessary is just to set the time when there is a concern that a part of the image holding body 1 in the stopped state is affected by the outside air and the sensitivity is lowered due to the adhesion.
As the sensitivity recovery device 7, the image carrier 1 is rotated idly a plurality of times by the image carrier driving device 8, and electrical vibration is applied by the recovery electric field effect device 9 to apply the toner external additive Tg. It is only necessary that the neutralizing device 10 is provided as a component that weakens the adhesive force and allows the external additive Tg of the toner to be scraped off by the plate-like cleaning member 5a, and further removes the charged potential due to electrical vibration.

Next, representative aspects or preferred aspects of the present embodiment will be described.
A typical aspect of the portion of the image carrier 1 where the sensitivity is lowered is a region from the developing device 3 to the cleaning device 5 along the rotation direction of the image carrier 1 and before and after sandwiching the transfer region by the transfer device 4. Areas.
For example, above the charging device 2 a as the latent image forming device 2 or above the developing device 3, air in which an air flow exists around the image carrier 1 even when the image carrier 1 is stopped around the image carrier 1. There is an aspect including a flow generating element (for example, the charging device 2a may adopt a configuration in which a uniform air flow is allowed to flow in the charging container so that the discharge oxide does not adhere to a discharge member such as a discharge wire). In such an embodiment, there is not much problem in a place where an air flow exists around the image carrier 1, but a developing device is provided along a place where the air flow does not exist as described above, for example, along the rotation direction of the image carrier 1. In the region from 3 to the cleaning device 5 and before and after the transfer region by the transfer device 4, if the image carrier 1 is stopped for a relatively long time, the external additive of the toner remaining on the image carrier 1 When the Tg is exposed to the stagnant outside air, a phenomenon occurs in which the external additive Tg of the toner tends to strongly adhere to the surface of the image carrier 1 by absorbing the moisture of the outside air.
Moreover, as a typical aspect of the static elimination apparatus 10 of the sensitivity recovery apparatus 7, what has the static elimination light source which can irradiate the light for static elimination is mentioned. The neutralization device 10 may use an AC electric field, but the optical neutralization method is more preferable from the viewpoint of suppressing the deterioration of the image carrier 1 to a small extent.

Further, as a typical mode of the recovery electric field effect device 9, a first recovery electric field generation device that generates a recovery electric field by a recovery voltage having the same polarity as the DC voltage of the transfer electric field, and a recovery of the first recovery electric field generation device The aspect which has the 2nd recovery electric field generation | occurrence | production apparatus which produces | generates the recovery electric field by the reverse polarity recovery voltage of reverse polarity to a voltage is mentioned. In this aspect, a first recovery electric field generation device and a second recovery electric field generation device are provided in order to generate recovery electric fields of respective polarities.
In such an embodiment, as a typical embodiment using an existing apparatus element, as shown in FIG. 2A, the transfer apparatus 4 is used as the first recovery electric field generating apparatus, and the DC voltage of the transfer electric field is the same. A recovery electric field by a polarity recovery voltage ((+) in this example) is applied, and a polarity adjusting device 11 is used as the second recovery electric field generating device, and the reverse polarity is opposite to the recovery voltage by the transfer device 4. A recovery electric field is applied by a recovery voltage ((−) in this example).
Therefore, the toner external additive Tg on the image carrier 1 is electrically vibrated by these recovery electric fields, so that the toner external additive Tg on the image carrier 1 is applied to the plate-like cleaning member 5a. The charge potential on the image carrier 1 is neutralized by the neutralization device 10.
Here, the polarity adjusting device 11 is provided between the transfer device 4 and the cleaning device 5 along the rotation direction of the image carrier 1 in the periphery of the image carrier 1, and remains on the image carrier 1. The toner has the same polarity.
For example, as the cleaning device 5, a cleaning voltage having a predetermined polarity is applied to the plate-like cleaning member 5 a and the rotary cleaning member 5 b added in addition to the plate-like cleaning member 5 a, and the residual toner on the image carrier 1 is statically removed. A method of electrically collecting may be employed. The polarity adjusting device 11 is configured to make the polarity of the residual toner uniform before being conveyed to the cleaning device 5 in order to enable such electrostatic recovery.
In particular, in the aspect using the transfer device 4 and the polarity adjusting device 11, the toner adhering to the image carrier 1 positioned immediately after passing through the development site by the development device 3 and before reaching the transfer site by the transfer device 4. This is preferable in that a recovery electric field having a different polarity can be immediately applied to the external additive Tg, and the sensitivity recovery processing time of the image carrier 1 can be shortened accordingly.

Moreover, as another typical aspect using the existing device element as the recovery electric field effect device 9, as shown in FIG. 2B, the transfer electric field is generated using the transfer device 4 as the first recovery electric field generating device. A recovery electric field with a recovery voltage (in this example, (+)) having the same polarity as that of the DC voltage is applied, and the charging device 2a is used as the second recovery electric field generating device and is opposite to the recovery voltage of the transfer device. Examples include those that apply a recovery electric field caused by a polarity reverse polarity recovery voltage (in this example, (−)).
Therefore, the toner external additive Tg on the image carrier 1 is electrically vibrated by these recovery electric fields, so that the toner external additive Tg on the image carrier 1 is applied to the plate-like cleaning member 5a. The charge potential on the image carrier 1 is neutralized by the neutralization device 10.

Moreover, as a preferable aspect of the recovery electric field effect | action apparatus 9 of the sensitivity recovery apparatus 7, there exist the following aspects.
That is, the transfer device 4 includes a transfer electric field including a DC voltage used in an image forming process, and a recovery electric field including a recovery voltage having the same polarity as the DC voltage of the transfer electric field and having an absolute value larger than the DC voltage. The recovery electric field action device 9 of the sensitivity recovery device 7 uses the transfer device 4 as the first recovery electric field generation device, and is the same as the DC voltage of the transfer electric field used in the image forming process. Some have a recovery electric field with a recovery voltage which is polar and has an absolute value larger than the DC voltage.
This mode is a mode in which the DC voltage of the transfer electric field and the recovery voltage of the recovery electric field are switched between levels for the transfer device 4 as the first recovery electric field generating device.
Furthermore, as a more preferable aspect of the recovery electric field effect device 9, there are the following aspects.
That is, the transfer device 4 has a transfer electric field including a DC voltage used in the image forming process, and one or a plurality of recovery voltages having the same polarity as the DC voltage of the transfer electric field and having an absolute value larger than the DC voltage. The recovery electric field action device 9 of the sensitivity recovery device 7 uses the transfer device 4 as the first recovery electric field generating device, and the transfer electric field used in the image forming process. Apply a recovery electric field by one or more recovery voltages that have the same polarity as the DC voltage and have an absolute value greater than the DC voltage. It is set to do.
In this embodiment, the level of the recovery voltage by the transfer device 4 can be switched to one or more than the transfer voltage, and the action time of the recovery electric field is changed and set according to the magnitude of the recovery voltage. This is preferable in that the deterioration associated with the charging process on the image carrier 1 is effectively suppressed.

Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.
Embodiment 1
<Overall configuration of image forming apparatus>
FIG. 3 is an explanatory diagram showing the overall configuration of the image forming apparatus according to the first embodiment to which the present invention is applied.
In FIG. 1, an image forming apparatus 20 includes an electrophotographic image forming engine 22 in an apparatus housing (not shown), and a paper supply device 23 is provided below the image forming engine 22. The paper supplied from the paper is guided to the image forming engine 22 through the paper conveyance path 24, and the image created by the image forming engine 22 is transferred to the paper S and then fixed by the fixing device 25. The sheet is discharged to a sheet discharge tray (not shown) provided on the side.
The paper transport path 24 guides the paper S supplied from the paper supply device 23 to the image forming engine 22 and transports it to the paper discharge receptacle through the fixing device 25. Transport members such as the transport roll 244 and the transport belt 245 are installed.

<Image creation engine>
In the present embodiment, as shown in FIGS. 3 and 4, the image forming engine 22 is configured to display an image of each color component (for example, yellow (Y), magenta (M), cyan (C), and black (K)). A plurality of image forming units 30 (specifically, 30a to 30d), and an image of toner as powder formed in the image forming unit 30 is passed through a belt-shaped intermediate transfer member 40. Then, the toner image is transferred to the sheet S, and the toner image is fixed to the sheet S by the fixing device 25.
In this example, each image forming unit 30 uses a photoconductor 31 as an image carrier, a charging device 32 for charging the photoconductor 31, and the photoconductor 31 charged by the charging device 32 with light. Development that develops the latent image written on the photosensitive member 31 with a corresponding color toner (negative polarity in this example), such as an exposure device 33 (specifically, 33a to 33d) such as a laser scanning device that writes the latent image. A device 34, a cleaning device 35 that cleans residual toner remaining on the photoconductor 31, and an upstream side in the rotation direction of the photoconductor 31 with respect to the opposing portion of the photoconductor 31 and the cleaning device 35. The pre-cleaning charging device 36 that aligns the polarity of the residual toner to the negative polarity, and the photosensitive member 31 is removed from the opposite side of the photosensitive member 31 and the cleaning device 35 in the rotational direction of the photosensitive member 31 and the charged potential of the photosensitive member 31 is removed. The static elimination device 37 is provided.

Here, to supplement each component, the charging device 32 has a charging container 320 that opens toward the photoconductor 31 and extends along the axial direction of the photoconductor 31, and discharges into the charging container 320. A wire 321 is provided, a grid electrode 322 for regulating the charging potential of the photosensitive member 31 is provided at the opening of the charging vessel 320 on the photosensitive member 31 side, and an air introduction port 323 is provided in a part of the charging vessel 320. Thus, an air flow is caused to flow along the longitudinal direction in the charging container 320 to prevent discharge products from adhering to the discharge wires 321 and the grid electrodes 322.
Further, the developing device 34 includes a developing container 340 that accommodates a two-component developer composed of toner of each color component and a carrier and opens toward the photosensitive member 31, and a portion facing the opening of the developing container 340 is developed. A developing roller 341 that holds and conveys the developer, and a pair of agitating and conveying members 342 and 343 that agitate and convey the developer to frictionally charge the toner is disposed on the back side of the developing roller 341 of the developing container 340; Further, a layer thickness regulating member 344 that regulates the thickness of the developer layer held on the developing roll 341 is provided around the developing roll 341. The toner used in this example is added with a charging auxiliary agent or other external additive, and the external additive peeled off from the toner on the photosensitive member 31 during the developing operation by the developing device 34 occurs. Is to get. In the figure, reference numeral 345 denotes a collecting roll for collecting the carrier and floating toner transferred onto the photosensitive member 31.
Further, the cleaning device 35 has a cleaning container 350 that opens to face the photoreceptor 31 and collects residual toner, and a cleaning blade made of an elastic material such as polyurethane rubber is provided at the upper edge of the opening of the cleaning container 350. 351 and a brush-shaped or roll-shaped rotary cleaning member 352 to which a predetermined cleaning voltage (positive bias in this example) is applied is provided upstream of the cleaning blade 351 in the rotation direction of the photosensitive member 31. Further, a sealing member 353 that contacts the photoreceptor 31 is provided at the lower opening edge of the cleaning container 350. In this example, a conveying member 354 extending along the axial direction of the photosensitive member 31 (for example, an aspect in which a spiral blade is provided around the rotating shaft member) is provided below the rotating cleaning member 352 of the cleaning container 350. Residual toner adhering to the rotary cleaning member 352 is scraped off by a flicker 355 as a scraping member, and is transported to the one end side of the cleaning container 350 by the transport member 354.
Further, as shown in FIGS. 4 and 5, the pre-cleaning charging device 36 is provided with a discharge wire 361 in the charging container 360, and a switching switch for switching the charging bias 362 (negative polarity bias in this example) to the discharge wire 361. It is applied via 363.
In addition, as the charge removal device 37, a charge removal lamp that removes charge by irradiating the surface of the photoreceptor 31 with light is used.

On the other hand, the belt-shaped intermediate transfer body 40 is stretched using a plurality of stretching rolls 41 to 45, and is circulated and rotated, for example, using the stretching roll 41 as a driving roll. The intermediate transfer body 40 has a primary transfer device 51 on the back surface of each image forming unit 30 facing the photoconductor 31. As shown in FIG. 5, the primary transfer device 51 has, for example, a primary transfer roll 510 as a transfer member. A transfer bias (positive bias in this example) 511 is connected to the primary transfer roll 510 with a switch 512. It is adapted to be applied via.
Further, a secondary transfer device 52 is provided at a portion corresponding to the paper transport path 24. In the secondary transfer device 52, for example, the secondary transfer roll 53 is disposed in contact with the surface of the intermediate transfer body 40, and the stretching roll 44 positioned on the back surface of the intermediate transfer body 40 facing the secondary transfer roll 53 is opposed to the secondary transfer roll 53. A roll (backup roll) 54 is used, and a secondary transfer bias is applied to one of the secondary transfer roll 53 and the counter roll 54 and the other is grounded.
Further, a cleaning device 55 is provided at a portion of the intermediate transfer body 40 that faces, for example, the stretching roll 41.

<Control system of image forming apparatus>
FIG. 5 shows a control system of the image forming apparatus in this embodiment.
In the figure, reference numeral 100 denotes a control device that controls the image forming apparatus. The control device 100 includes a drive motor 101 for the photosensitive member 31, a discharge wire 321 for the charging device 32, a grid electrode 322, an exposure device 33, and a developing device. A predetermined control signal is sent to a developing roll 341 of 34, a transfer roll 510 of the primary transfer device 51, a discharge wire 361 of the pre-cleaning charging device 36, a rotary cleaning member 352 of the cleaning device 35, and the like. Each component is controlled in accordance with a program, and an image based on each color toner image is formed by the image forming unit 30 for each color.
In particular, in this embodiment, when the photosensitive member 31 is stopped and the stop time is relatively long, as shown in FIG. 4, for example, in the area m before and after the transfer area M of the primary transfer device 51, Assuming that the external air stays in a state where no flow is generated and the outside air stays, the external additive of the toner adhering to the photosensitive body 31 absorbs the moisture of the external air, and the outer surface of the photosensitive body 31 becomes stronger. The case of adhering to the case occurs. When such a situation occurs, the sensitivity of the photoreceptor 31 is locally reduced in the area m before and after the transfer area M of the primary transfer device 51, and the photoreceptor is maintained in such a situation. For example, if a halftone toner image is formed on 31, white band-like image unevenness may occur in the halftone toner image formed corresponding to the portion of the photoreceptor 31 having a lowered sensitivity.
For this reason, in the present embodiment, the control device 100 executes the photosensitive member sensitivity recovery processing program shown in FIGS. 6 and 7 so as to perform the sensitivity recovery processing for recovering the sensitivity reduction of the photosensitive member 31. It has become. In this example, when the photoreceptor sensitivity recovery process is performed, the white band recovery sequence SW (switch) is set to ON beforehand.

<Photosensitive sensitivity recovery processing>
The photoreceptor sensitivity recovery process in the present embodiment is performed according to the program shown in FIGS.
First, the control device 100 checks whether or not the white band recovery sequence SW (switch) is set to ON. If the switch is set to ON, the control device 100 monitors the stop time Ts of the photoconductor 31 and monitors It is checked whether or not the stopped time Ts exceeds a predetermined threshold value Tth. If the stopped time Ts of the photoconductor 31 exceeds the threshold value Tth, a “white belt recovery sequence” is performed. On the other hand, if the stop time Ts of the photoconductor 31 is within the threshold value Tth, the “white belt recovery sequence” is not performed.
Next, a specific example of the “white belt recovery sequence” employed in this example is shown in FIG.
In the figure, first, the photosensitive member 31 is idly driven a plurality of times, and during the idling, the photosensitive member 31 is positively charged (+ charged) by the primary transfer device 51 and is also exposed by the charging device 36 before cleaning. The body 31 is negatively charged (-charged), cleaned by the cleaning blade 351, and further, the charged potential of the photoconductor 31 by the charge eliminating lamp as the charge eliminating device 37 is removed. The unit cycle described above is repeated until the white belt recovery sequence time elapses.
In this example, in the “white belt recovery sequence”, the rotary cleaning member 352 and the conveying member 354 of the cleaning device 35 are not driven.

In this 'white belt recovery sequence', as shown in FIG. 8A, A (positive charging) by the primary transfer device 51 and B (negative charging) by the pre-cleaning charging device 36 are performed. An electrical vibration is applied to the toner external additive Tg, whereby the adhesion force of the toner external additive Tg on the photoreceptor 31 is reduced. For this reason, as shown by C in FIG. 8A, the external additive Tg of the toner whose adhesion is weakened by the cleaning blade 351 of the cleaning device 35 is easily scraped off by the cleaning blade 351. Thereafter, as indicated by D in FIG. 8A, the charged potential of the photoconductor 31 is removed by the static eliminator 37 and refreshed.
When such processing is repeated, as shown in FIG. 8B, the adhesion force of the external additive Tg of the toner adhering to the photoconductor 31 gradually weakens and is gradually scraped off by the cleaning blade 351. To go. When the idle rotation of the photoconductor 31 reaches near the final time (n times), the external additive Tg of the toner adhering to the photoconductor 31 is almost scraped off by the cleaning blade 351. sensitivity U _L of desensitization part was formed before and after the transfer region M m (see FIG. 4) of the primary transfer unit 51 on the photoreceptor 31 to the sensitivity U substantially equal other portion not reduced sensitivity Recover. As a result, the locally reduced sensitivity portion on the photoconductor 31 is recovered. If the image forming program is executed at this stage, even if a halftone toner image is formed, the photoconductor 31 is formed. The white band due to the local sensitivity decrease does not occur, and a halftone toner image is provided as a good one without image defects.
Further, in the present embodiment, the local sensitivity reduction portion of the photoconductor 31 is likely to occur before and after the transfer region of the primary transfer device 51, but in this example, the primary transfer device 51 and the pre-cleaning charging device 36 are used. Since the positive and negative recovery electric fields are applied by using these, when the photosensitive member 31 is idly rotated, the positive and negative recovery electric fields can be immediately applied to the place where the external additive of the toner is likely to adhere. Accordingly, the processing time for the sensitivity recovery processing of the photoconductor 31 can be shortened, which is effective in reducing the processing time.

Embodiment 2
FIG. 9 shows the overall configuration of the image forming apparatus according to the second embodiment.
In the figure, the basic configuration of the image forming apparatus is substantially the same as that of the first embodiment, but unlike the first embodiment, the transfer bias 513 to the transfer roll 510 of the primary transfer apparatus 51 can be changed. In the image forming sequence, a predetermined transfer bias is applied, while in the 'white belt recovery sequence' of the photoreceptor sensitivity recovery process, a recovery bias having a higher bias level than the transfer bias of the image forming sequence is applied. It is a thing.
That is, in this example, the control device 100 executes the photosensitive member sensitivity recovery processing program of FIG. 6 as in the first embodiment, and as shown in FIG. Is driven idly several times, and during this idling, a sensitivity recovery current Ir larger than the transfer current It of the primary transfer device 51 (specifically, a value larger than the transfer bias is selected as the sensitivity recovery bias). The photosensitive drum 31 is positively charged (+ charged) by the primary transfer device 51, and the white band recovery sequence time is changed and set according to the sensitivity recovery current Ir. Specifically, when the sensitivity recovery current Ir larger than the transfer current It is selected compared to the white belt recovery sequence time t ₁ when the sensitivity recovery current Ir is set to be the same as the transfer current It, A time t ₂ shorter than the white belt recovery sequence time t ₁ may be set. If the sensitivity recovery current Ir is selected at a plurality of levels, the white band recovery sequence time may be set shorter as the sensitivity recovery current Ir increases.
Further, the photosensitive member 31 is negatively charged (-charged) by the pre-cleaning charging device 36, cleaned by the cleaning blade 351, and further, the charged potential of the photosensitive member 31 by the discharging lamp as the discharging device 37 is removed. The unit cycle described above is repeated until the white belt recovery sequence time elapses.
In the present embodiment, the sensitivity recovery current Ir by the primary transfer device 51 is selected to be larger than the transfer current It compared to the first embodiment, but compared to the first embodiment, the white band recovery sequence. Since the time is set to be short, the deterioration of the photoconductor 31 due to the sensitivity recovery process of the photoconductor 31 is suppressed, and the time required for the sensitivity recovery process of the photoconductor 31 is shortened compared to the case of the first embodiment. The

Embodiment 3
FIG. 11 is an explanatory diagram showing an image forming apparatus according to the third embodiment.
In the drawing, the sensitivity recovery process of the photoconductor 31 is performed using a charging device 32, a primary transfer device 51, a cleaning blade 351, and a charge removal device 37.
Specifically, in the 'white belt recovery sequence' of the sensitivity recovery process of the photoconductor 31, first, the photoconductor 31 is idly driven a plurality of times as shown in FIGS. 6 and 12, and during this idling, The charging device 32 is negatively charged (-charged), and the primary transfer device 51 is positively charged (+ charged), cleaned by a cleaning blade 351, and further as a charge removal device 37. The charged potential of the photosensitive member 31 by the static elimination lamp is removed. The unit cycle described above is repeated until the white belt recovery sequence time elapses.
In this example, in the “white belt recovery sequence”, the rotary cleaning member 352 and the conveying member 354 of the cleaning device 35 are not driven.
As described above, the “white belt recovery sequence” of the present example is, as shown in FIG.
By performing A (negative charging) by B and B (positive charging) by the primary transfer device 51, an electrical vibration is applied to the external additive Tg of the toner of the photoconductor 31. The adhesion force of the toner external additive Tg is reduced. For this reason, as shown by C in FIG. 11, the external additive Tg of the toner whose adhesion is weakened by the cleaning blade 351 of the cleaning device 35 is easily scraped off by the cleaning blade 351. Thereafter, as shown by D in FIG. 11, the charged potential of the photoconductor 31 is removed by the static eliminator 37 and refreshed.

Example 1
The image forming apparatus according to the first embodiment was used, and 30 μA similar to the transfer current was used as the sensitivity recovery current of the primary transfer apparatus 51.
Example 2
The image forming apparatus according to the second embodiment was used, and 40 μA larger than the transfer current was used as the sensitivity recovery current of the primary transfer apparatus 51.
Example 3
The image forming apparatus according to Embodiment 2 was used, and 50 μA larger than the transfer current was used as the sensitivity recovery current of the primary transfer apparatus 51.
Example 4
The image forming apparatus according to Embodiment 2 was used, and 55 μA (or 56 μA) larger than the transfer current was used as the sensitivity recovery current of the primary transfer apparatus 51.

-Change of white belt grade by white belt recovery sequence-
When Examples 1 to 3 were examined for changes in white band grade with respect to the execution time of the “white band recovery sequence”, the results shown in FIG. 13 were obtained. Here, the white belt grade is an evaluation of the presence or absence of a white belt visually with respect to a halftone toner image, and a standard that makes a white belt less noticeable when it becomes smaller than '3'. Selected.
According to the figure, in Examples 2 and 3, the white band grade reached 0 when 60 seconds passed from the start of the “white band recovery sequence”, whereas in Example 1, “white band recovery sequence”. The white belt grade reached 0 when 150 seconds had elapsed from the start of. It can be understood that the sensitivity of the photosensitive member is recovered early when a large value is selected as the sensitivity recovery current by the primary transfer device 51.

-Photosensitive sensitivity recovery level-
Regarding Example 1 and Example 4, when the change in the surface potential VL of the photoconductor after exposure with the light amount fixed was examined, the result shown in FIG. 14 was obtained.
According to the figure, in Example 1, when the “white belt recovery sequence” was performed for 120 seconds, VL changed from 295.5 V to 288.7 V, and the sensitivity of the photoconductor 31 was recovered. Is done.
On the other hand, in Example 4, when the “white belt recovery sequence” was performed for 30 seconds and 150 seconds, VL changed from 293.9 V to 288.3 V, and further to 281.5 V, which is compared with Example 1. It is understood that the degree of recovery of sensitivity of the photoconductor 31 is better.

-Photosensitivity change with the use of paper-
Regarding Example 4, when the sensitivity recovery process of the photoconductor is first performed, and then the change in sensitivity of the photoconductor when the image forming process is performed on a predetermined number of sheets is examined, FIG. a) The results shown in (b) were obtained.
Here, in FIG. 15A, the back side position is selected as the surface potential measurement portion of the photosensitive member after exposure in a state where the light amount is fixed, and the “white band recovery sequence” in Example 4 is subjected to primary transfer for 30 seconds. The case of positive charging (1st BTR 55 μA) by the apparatus (Example 4-1) and the case of positive charging (1st BTR 56 μA) by the 150-second primary transfer apparatus (Example 4-2) are performed. The case where the “band recovery sequence” is not performed is shown.
On the other hand, in FIG. 15B, the center position is selected as the surface potential measurement portion of the photoreceptor after exposure in a state where the light amount is fixed, and two cases (Example 4) as the “white band recovery sequence” in Example 4 are selected. -1,4-2) and a comparative example, a case where the “white belt recovery sequence” is not performed is shown.
According to these, in the case of Example 4-1, the VL of the initial photoconductor was 290.6 V, 294.1 V, whereas when the sensitivity recovery process of the photoconductor was first performed, 284.3 V, When the image forming process is performed on the paper after that, the VL gradually changes as the PV (paper number: Paper Volume) increases, and after stopping for 12 hours after the PV 500 sheets, the initial sensitivity is reached. Return.
Similarly, in the case of Example 4-2, the VL of the initial photoconductor was 289.5 V and 294.1 V, but when the sensitivity recovery process of the photoconductor was first performed, 276.9 V and 281. When the image forming process is performed on the sheet after that, the VL gradually changes as PV (the number of sheets: Paper Volume) increases. Return.
In the case of the comparative example, when the VL of the initial photoconductor is 294.6V and 299V, the VL gradually changes from the first VL as PV (paper number: Paper Volume) increases. Will be understood.

DESCRIPTION OF SYMBOLS 1 ... Image holding body, 2 ... Latent image forming device, 2a ... Charging device, 2b ... Latent image writing device, 3 ... Developing device, 4 ... Transfer device, 5 ... Cleaning device, 5a ... Plate-shaped cleaning member, 5b ... Rotating cleaning member, 6 ... stop time discriminating device, 7 ... sensitivity recovery device, 8 ... image carrier driving device, 9 ... recovery electric field effect device, 10 ... static elimination device, 11 ... polarity adjusting device, 12 ... transfer medium, Tg ... Toner external additive

Claims (8)

An image carrier that holds and rotates the toner image;
A latent image forming apparatus for forming an electrostatic latent image on the image carrier;
A developing device that visualizes the electrostatic latent image formed on the image carrier with toner;
A transfer device that applies a transfer electric field including a DC voltage having a predetermined polarity to the image carrier and electrostatically transfers the toner image formed on the image carrier to the transfer medium by the transfer electric field; ,
A cleaning device that has a plate-like cleaning member that contacts the image holding member, and that cleans residual toner remaining on the image holding member after transfer by the transfer device with the plate-like cleaning member;
A stop time discriminating device for discriminating whether or not the stop time after the image holding member has stopped exceeds a predetermined time;
As a process different from the image forming process under the condition that the stop time of the image carrier has passed a predetermined time by the stop time discriminating device, a part of the image carrier due to the adhesion of the external additive of the toner is obtained. With a sensitivity recovery device that recovers sensitivity reduction,
The sensitivity recovery device includes an image carrier driving device that drives the image carrier to rotate idly a plurality of times;
A recovery electric field provided by a recovery voltage having the same polarity as the direct-current voltage of the transfer device, provided on the upstream side of the rotation direction of the image carrier relative to a portion where the image carrier and the plate-like cleaning member of the cleaning device are opposed to each other, and the recovery voltage A recovery electric field effect device in which a recovery electric field by a reverse polarity recovery voltage of reverse polarity acts at a different part of the image carrier;
A static eliminator that is provided on the downstream side in the rotation direction of the image carrier relative to the facing portion between the image carrier and the plate-like cleaning member of the cleaning device, and removes a charging potential due to a recovery electric field acting on the image carrier. An image forming apparatus. The image forming apparatus according to claim 1.
The portion of the image carrier where the sensitivity is reduced due to the adhesion of the toner external additive is the region from the developing device to the cleaning device along the rotation direction of the image carrier, and before and after sandwiching the transfer region by the transfer device. An image forming apparatus characterized by being an area. The image forming apparatus according to claim 1 or 2,
An image forming apparatus comprising: a static elimination device of a sensitivity recovery device having a static elimination light source capable of irradiating with static elimination light. The image forming apparatus according to claim 1,
A recovery electric field effect device of the sensitivity recovery device includes a first recovery electric field generation device that generates a recovery electric field by a recovery voltage having the same polarity as the DC voltage of the transfer electric field,
An image forming apparatus comprising: a second recovery electric field generation device that generates a recovery electric field by a reverse polarity recovery voltage having a reverse polarity to the recovery voltage of the first recovery electric field generation device. The image forming apparatus according to claim 4.
A polarity adjusting device provided between the transfer device and the cleaning device along the rotation direction of the image carrier in the periphery of the image carrier, and for aligning the polarity of the toner remaining on the image carrier,
The recovery electric field effect device of the sensitivity recovery device uses a transfer device as a first recovery electric field generation device to apply a recovery electric field by a recovery voltage having the same polarity as the DC voltage of the transfer electric field, and to generate the second recovery electric field generation An image forming apparatus, wherein a polarity adjusting device is used as a device to apply a recovery electric field by a reverse polarity recovery voltage having a reverse polarity to the recovery voltage by the transfer device. The image forming apparatus according to claim 4.
The latent image forming apparatus includes a charging device that charges the image holding member, and a latent image writing device that writes an electrostatic latent image on the charged image holding member,
The recovery electric field effect device of the sensitivity recovery device uses a transfer device as a first recovery electric field generation device to apply a recovery electric field by a recovery voltage having the same polarity as the DC voltage of the transfer electric field, and to generate the second recovery electric field generation An image forming apparatus, wherein the charging device is used as a device to apply a recovery electric field by a reverse polarity recovery voltage opposite in polarity to a recovery voltage by the transfer device. The image forming apparatus according to claim 4, wherein:
The transfer device includes a transfer electric field including a DC voltage used in an image forming process,
The switching electric field is switched to act as a recovery electric field having the same polarity as the DC voltage of the transfer electric field and including a recovery voltage that is larger in absolute value than the DC voltage,
The recovery field effect device of the sensitivity recovery device uses a transfer device as a first recovery electric field generation device, and recovers in the same polarity as the DC voltage of the transfer electric field used in the image forming process and in an absolute value larger than the DC voltage. An image forming apparatus characterized by applying a recovery electric field by voltage. The image forming apparatus according to claim 4, wherein:
The transfer device includes a transfer electric field including a DC voltage used in an image forming process,
The switching electric field is switched between a recovery electric field including one or a plurality of recovery voltages having the same polarity as the DC voltage of the transfer electric field and having an absolute value larger than the DC voltage,
The recovery electric field effect device of the sensitivity recovery device uses a transfer device as a first recovery electric field generation device, and has the same polarity as the DC voltage of the transfer electric field used in the image forming process and an absolute value larger than the DC voltage. Alternatively, an image forming apparatus characterized in that a recovery electric field by a plurality of recovery voltages is applied, and an operation time setting unit is configured to shorten the operation time of the recovery electric field as the magnitude of the recovery electric field increases.

Images